956 10 13078 https://digitalcollections.lakeheadu.ca/files/original/cc298447724a6f0310d974e4a09aacc8.jpg c46a8f230c57a15daa493a7b2e0847fe https://digitalcollections.lakeheadu.ca/files/original/fd7ff56cff5a59328389d1ae4d1b99ca.jpg 6794a35135231ff1a615ab17d910bd3b https://digitalcollections.lakeheadu.ca/files/original/b3a76303c8c6e269f0ae57e80e64ebdc.jpg fbd0ab118a82e91cce8a33b9857b2d56 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay Finnish Canadian Historical Society Collection Subject The topic of the resource Finnish-Canadians Life in Thunder Bay Description An account of the resource Photographs collected by the Thunder Bay Finnish Canadian Historical Society from a wide range of collectors, documenting Finnish immigration to and life in Thunder Bay. Creator An entity primarily responsible for making the resource Thunder Bay Finnish Canadian Historical Society Publisher An entity responsible for making the resource available Lakehead University Library Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Funeral procession in honour of Viljo Rosval and John Voutilainen Subject The topic of the resource Organizations Labour and Labour Unions Description An account of the resource Funeral procession in honour of Viljo Rosval and John Voutilainen, Port Arthur, Spring 1930. 3 copies. Date A point or period of time associated with an event in the lifecycle of the resource 1930 Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource JPG Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context MG8_D12Gi31 MG8_D12Gi31a MG8_D12Gi31b Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay Canada - Ontario - Port Arthur https://digitalcollections.lakeheadu.ca/files/original/5d187e4a6972d16b137d2af8c2102e43.jpg 7bdd038b72fe3e5c6ef04b6d7bb43fcb Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay Finnish Canadian Historical Society Collection Subject The topic of the resource Finnish-Canadians Life in Thunder Bay Description An account of the resource Photographs collected by the Thunder Bay Finnish Canadian Historical Society from a wide range of collectors, documenting Finnish immigration to and life in Thunder Bay. Creator An entity primarily responsible for making the resource Thunder Bay Finnish Canadian Historical Society Publisher An entity responsible for making the resource available Lakehead University Library Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Funeral procession in honour of Viljo Rosval and John Voutilainen Subject The topic of the resource Organizations Labour and Labour Unions Description An account of the resource Funeral procession in honour of Viljo Rosval and John Voutilainen, Port Arthur, Spring 1930. Date A point or period of time associated with an event in the lifecycle of the resource 1930 Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource JPG Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context MG8_D12Gi32 Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay Canada - Ontario - Port Arthur https://digitalcollections.lakeheadu.ca/files/original/2aab51c56098bfbeb5d103006911347e.pdf 7bb1f734a9dc806cd2045142ff376e0f PDF Text Text ONTARIO, CANADA �Thunder Bay, Ont. 108,048 (1970) Population 156 sq. miles *Square Miles * ( includes waterlots). January 1, 1970, Thunder Bay emerged as a bright new city, the sixth largest in Ontario. This historic event occurred through the merging of The City of Fort William The City of Port Arthur The Township of Neebing The Township of McIntyre Co-operatively pro·duced by: THUNDER BAY CHAMBER OF COMMERCE THUNDER BAY CONVENTION BUREAU INDUSTRIAL COMMISSION OF THE CITY OF THUNDER BAY INC. For More Information Write: P.O. BOX 2000 THUNDER BAY, 'F' ONTARIO June 23, 1969, the name Thunder Bay was chosen by plebiscite. Simultaneously an election of a Mayor and 12 Aldermen took place and the following govern the City of Thunder Bay, made up of four wards, Fort William, McIntyre, Neebing and Port Arthur: Mayor Saul Laskin Aldermen Don Aedy W. M. Assef H. L. G. Badanai, Jr. H. J. Cook, Jr. Mickey Hennessy C. M. Johnston, M.D. T. J. Jones Edgar Laprade D. J. Lenardon George Lovelady W. M. Morgan Grace Remus The Council of Thunder Bay, to remain in office until Dec. 31, 1972, became operative in the latter months of 1969 smoothing out administrative and legal problems of uniting four separate units on Jan. 1, 1970. Previously elected officials of the amalgamated communities continued in office until Dec. 31, 1969, when all assets and liabilities of the Corporation were officially turned over to the new city. As far back as the early 1900's, individuals had advocated the amalgamation of the two cities commonly known The Lakehead. Now as one unit, the historical background of the communities will be retained with their designation as Wards of the city. Thunder Bay will continue to be regarded as the capital city and administrative headquarters of the District of Thunder Bay. The City of Thunder Bay is located at the western Canadian end of Lake Superior on the north shore of Thunder Bay. Canada's newest city is 861 road miles northwest of Toronto, 424 miles east of Winnipeg and 348 miles north of Minneapolis. Third largest Canadian port in total tonnage handled, Thunder Bay is the western terminus of the Great Lakes and St. Lawrence deep waterway. Thunder Bay is a transportation centre of mid-Canada and is served by Trans-Continental Railways, three scheduled airlines, intercontinental bus service, the Trans-Canada Highway and the St. Lawrence Seaway. The vast district of Thunder Bay, of which the city of Thunder Bay is the hub, covers 52,471 square miles extending from White River on the east to English River on the west and bounded on the north by the Albany River and Lake Superior on the south. The city rests on a delta of the Kaministiquia River, 18 miles downstream from Kakabeka Falls and extends northeastward upon a series of natural terraces. From the terraces, the shoreline, Mount McKay, Thunder Bay and the giant elevators unfold a panoramic view reminiscent of the renowed Bays of Naples and famous fiords of Norway. Thunder Cape, a part -o f Sibley Penninsula, resembles the unique natural shape of a sleeping giant Nanabijou of Indian lore. The "Giant" guards Thunder Bay 18 miles off shore and rises 1100 feet and stretches 6½ miles long. From the mainland it gives the impression of a mighty Indian warrior resting on the water, hence the popular designation - The Land of the Sleeping Giant. 3 �HISTORICAL Prior to the spreading French exploration through the Great Lakes Basin from New France, the Ojibway Indians inhabited the shores of Thunder Bay and the inland lakes. Even today, descendants of the Ojibway tribes live on reservations at the foot of Mount McKay and Squaw Bay. The District of Thunder Bay is steeped in Indian tradition. "Kaministiquia", the present name of the river flowing through Thunder Bay is Indian and has been interpreted in two ways 'the long winding river' and 'the river with three mouths.' The famous French explorers, Radisson and Groseilliers, are credited with the early explorations of the north shore of Lake Superior, around 1659. There is mention, also, of trading concessions being extended to a leading fur trader of those days, Sieur Dupuy, who explored the watershed of Lake Nipigon, 60 miles east of Thunder Bay. Missionaries and traders continued to spread westward along Lake Superior shore. The first recorded trading post established, on the site of the present city, was in 1679 when Daniel Greysolon Sieur du Lhut (founder of Duluth, Minnesota) built a trading post and fort on the south bank of the river near its mouth and called it "FORT CAMINISTIGOYAN". It flourished for a number of years. With other interests taking the attention of French officials at the time, the fort gradually had little use. The only recorded use made in subsequent years was a visit in 1688 by Jacques De Noyon, a trader from Trois Rivieres, who was searching for a route to China. In 1717 a Canadian officer of the time, Robertel De La Noue, was sent to rebuild the trading post, but found it advisable to make a fresh start. He built a new fort on the north bank opposite the old fort and called it "FORT CAMINISTIGOYAN". This sec• ond trading post was operated until 1758, the end of the French regime in Canada. La Verendrye wintered in the Fort in 1731. His explorations for a western route led him away from the established Kaministiquia River, Dog Lake route, to the unknown Grand PortagePigeon River Canoe Highway. A station and post were established at the mouth of the Pigeon River in the area now a part of the State of Minnesota. It attained considerable importance. In 1798 Roderick McKenzie, of the North West Company, moved northward from Grand Portage and examined and reported the ruins of old FORT KAMINISTIQUIA. Its location is now marked by granite monument at the foot of McTavish Street. The famous FRENCH VOYAGEURS and TRADERS continued to arrive in their large heavily - laden canoes, bringing much needed supplies to the settlements, then returning to Montreal with bountiful cargoes of furs. The North West Company and the Hudson's Bay Gompany inhabited the District amidst great rivalry. In 1802 the Fort was acquired by the North West Company and called the "NEW FORT". In the summer of 1807 at the annual meeting of the Partners and by a resolution of the Wintering Associates, the name of the Fort was changed to "FORT WILLIAM", after William McGillivray, Governor of the North West Company, who was also a member of the Quebec Legislative Council and a prominent Montreal merchant. The struggle for control of the fur trade on the North American continent is the most intriguing and fascinating part of our history. Between 1816 and 1821 the two fur companies carried on war-like activities against each other with the Fort being occupied by each at various times. Finally, the two companies united in 1821. The Hudson's Bay Post at Point de Meuron, a few miles up river, was abandoned soon after 1872. Meantime, three to four miles to the north, a small settlement was growing which in 1857 became known as "THE STATION". This military staging area later was to become the City of Port Arthur. It was from this point in 1870 that the first Red River Expedition ventured to We st e r n Canada. On July 10, 1868, a small party of prospectors, headed by Thomas MacFarlane, Montreal mining engineer, working out of "The Station" discovered the area's silver mines. Silver Islet Mines was one of the discoveries which had a most famous history. By the autumn of 1869, a 25 mile military road was under construction west of the "Station". In the following year Colonel Sir Garnet Wolseley (later Lord Wolseley) leading troops from eastern Canada, disembarked from the scenic anchorage. Enchanted with the natural beauty of "The Station", Wolseley renamed the post "PRINCE ARTHUR'S LANDING" in honour of Prince Arthur, son of Queen Victoria, who was then in Canada. In 1884, the villagers changed the name to "PORT ARTHUR" and had the town incorporated. The year previous William Van Horne, C.P.R. General Manager, changed the name from the Station to Port Arthur. 4 5 �It was about this time, the infant Canadian Government, formed in 1867, started to think of expanding the country westward . A young civil engineer, Simon J. Dawson was appointed to make a survey of a possible wagon and water route to the Red River Colony now Winnipeg, still under the control of the paternalistic rule of the Hudson's Bay Co. After considering alternate routes, Dawson finally recommended a wagon road to Lake Shebandowan, then over the old canoe water route to the west shore of the Lake of the Woods and onward over a wagon road to the Red River Settlement . Today the road is commemorated w ith the name "THE DAWSON TRAIL" starting at the harbour in Port Arthur Ward and traversing Hwy. 17A-11A, then Hwy. 17-11 (TransCanada to Hwy. 11 and Shebandowan Village , on the lake of the same name . Fort William was also growing into a large community and great impetus to growth was supplied when the Canadian Pacific Railway Company was started in 1875, and commenced building a railroad westwardly. Fort Will iam became an incorporated town in 1892 and later in 1907 a city with John McKellar as first Mayor. Unfortunately, the progress of the community made it necessary to dismantle old "FORT WILLIAM" in 1881, to make way for the steam railway. The Ontario Government has announced a $16 million capital project to restore the old fort on the Kaministiquia River. With the advent of a new mode of transportation, a flood of settlers arrived, some to stay and the remainder to continue west to a new lan-d. The first Mayor of Port Arthur in 1884 was Thomas Marks. Port Arthur attained city status in 1906. As the century closed, the present day educational complex was started when schools were built in both cities between 1871 and 1894. Newspapers were first printed in 1877. The two cities were in the vanguard of communities of the era experimenting with electricity. Port Arthur is counted among the first cities in North America to establish an electric street railway system around 1888, operated by a steam dynamo. This railway line was extended into Fort William in 1892. Distribution of electricity is still under municipal control. Municipally-owned telephone systems were inaugurated in 1902 and remain a city-owned utility. Fort William lost its city hall by fire in 1903, but it was rebuilt in 1905 and lasted until replaced by the modern edifice in 1966. Port Arthur's town hall also suffered the ravages of fire. Electric power went hand in hand with the growing industry of the cities. The first steam plant in Fort William was installed in 1898. In 1901 Port Arthur built the first hydro plant on the Current River. Kakabeka Falls (the Niagara of the North) 18 miles up river from the cities was harnessed for power in 1907-08 by the Kam Power Co. This gave a powerful surge to the power hungry industries in the cities and brought new industry. Records indicate 15 industries had established by 1903 and 71 by 1913. These included Port Arthur Shipbuilding & Dry Dock Co.; Canadian Car Co. Ltd.; Ogilvie Flour Mill; N. M. Paterson & Son, Grain and Shipping; and numerous grain elevators, lumbering and logging companies. The need for water supplies for industry and citizens led both cities to install underground systems. Port Arthur pumped water from Lake Superior. Later Fort William designed a unique sytem to bring water by gravity from Loch Lomond, 300 feet above the city, south of Mount McKay. These systems are in use today with tremendous supplies available for the future. By 1920 the paper industry was born with the advent of Great Lakes Paper Co. Ltd. and the Fort William Paper Co. ( later the Abitibi Paper Co. Ltd.) Grain elevators and rail trackage continued to grow durin~ this period to the present number of 23 elevators. In 1947 street cars disappeared from the streets to be replaced by rubber-tired trackles trolleys and gas buses. The cities turned to dial telephones in 1949. In 1951 the large Fort William Gardens ooened to provide an answer to the problem of satisfying the many avid hockey and sports fans and players. Natural Gas came to the cities in 1958, and in 1962 the first thermal electric power station in Northwestern Ontario was opened on the Mission River to generate 100,000 kilowatts. The first Kraft Mill in the cities came in 1966 with the addition of a $31,000,000 plant to the facilities of Great Lakes Paper. An advanced design automatic iron pellet handling plant was opened in 1968 on the Mission River to receive units trains containing 15,000 tons of pellets from mines in the area. Lakehead University, opened as a college in the late 40's and soon outgrew temporary facilities in downtown Port Arthur, and a large campus was secured on the western limits of the city. From a small beginning, attractive modern buildings have sprung up which now include a Teachers College, academic facilities, engineering and science laboratories, athletic building and playing fields, dormitories etc. In excess of $25 million has been invested in the present facilities of Lakehead University harbouring almost 4,500 students. The Confederation College of Applied Arts & Technology was the next step in building area educational facilities. Over $7½ million was invested in permanent teaching facilities . In 1967 a start was made on the construction of Lakehead Expressway extending 19 miles from east of the city to circle the populated areas and join Trans-Canada Highway outlets east and west and Hwy. 61 to the south. Approximately $25 million was required to complete the five year construction program. Planning for urban renewal of the core areas of both main business centres commenced in 1966. The Port Arthur Ward plan has been accepted and Stage One of a $15 million redevelopment scheme commenced in the spri n~ of 1971 . 7 6 �LAKEHEAD HARBOUR Best views of Thunder Bay and the harbour are from Hillcrest Park and the first ledge of Mount McKay. Both may be reached by road, except the latter in winter. However, the best impression of the massive size of the giant grain elevators, marching around the shore, must be from the water side of the harbour. Thunder Bay stretches 35 miles from north to south. Through the bay opening can be seen Isle Royale, Mich., a United States Federal Park 38 miles from the harbour shore. rock breakwater, one mile from shore protects the docks stretching acros~ the harbour front. The Thunder Bay Harbour, supervised by a five-man Harbour Commission, covers 27 miles of shore installations. In front of Port Arthur Ward, various industries and elevators are martialed around the shore. In Fort William Ward, the three river openings offer secure dockage for elevators, a modern iron ore storage and shipping plant, bulk oil depots etc. The main channel of the Kaministiquia River extends six miles upstream to a turning basin. Depth of water in the harbour varies from 20 to 27 feet with major installations running to Seaway depth. A shipyard at the northern end of the harbour is equipped to handle the largest seaway ships in dry dock. Grain elevators extending into the deep water, permit ships to glide right to dockside to take on their loads of grain. The ~ecord grain loading in one ship is in excess of 1,000,000 bushels. The heaviest shipping year saw 500,000,000 bushels arriving from the west being cleaned, processed, inspected: certified by government inspectors and shipped overseas. At the top end of the famous Kaministiquia River channel, a paper mill ships rolled newsprint in great quantities from dockside to port destinations in the U.S.A. A 8 Keefer Lakehead Terminal was opened in 1962 and provides a massive general cargo shed and an overseas cargo shed. Ocean freighters and fast lake boats can simultaneously be loaded and unloaded. The terminal is classed as one of the most modern in the world with an investment in facilities exceeding $15,000,000. In 1969 a $3,500,000 expansion of cargo sheds and dockage area was completed. It is also one of the fastest tran_sit terminals, with highly mobile ~quIpment handling material unloading around the clock. Over 700,000 tons of general cargo, steel, vehicles etc. are transferred to and from Canadian and overseas vessels. Excellent waterfront acreage is available for industrial development near the Terminal an~ on the islands formed by the three rivers in Fort William Ward. Lumber mills also cluster near the harbour for direct shipment of products and retention of logs near the water. A yacht club is established on the Mission River and a Marina is being developed on the waterfront in Port Arthur Ward. In all, four pulp and paper mills operate on the shore of Thunder Bay Harbour. In addition, a flour mill, malt plant, wheat starch plant, petroleum products plant, tar-processing plant, chemical plants, etc. all operate near the deep water of the harbour. Iron ore (pellets), potash and coal, loaded in many cases directly into vessels are shipped in large tonnages. A modern mechanized belting system on the Mission River operates all year to stockpile iron ore pellets for transfer in the shipping season. Coal from the Western Provinces is transferred from unit rail trains to ships for transfer to steel mills and hydro plants in the East. 1970 was a record shipping year for the Thunder Bay port. 20,779,767 tons were handled in 1,488 ships. Included was 13,299,851 tons of grain; 5,357,056 iron ore and 587,685 of general cargo. Kakabeka Falls CLIMATE From June 1 to Oct. 31, the climate of Thunder Bay is pleasant and mild; humid days being exceedingly rare. Summer is delightfully clear and balmy with light winds off the great expanses of Thunder Bay and Lake Superior. Each year hundreds of hay fever sufferers come to Thunder Bay where they enjoy complete relief. Normal summer mean temperature (July, July, August) is 60.9 degrees above zero. Normal winter mean temperature ( Dec. Jan. Feb.) is 10.2 degrees above zero. The highest recorded temperature 104 degrees occured July 1936 and the lowest, 42 de~rees below zero, January 1951. Fall days provide a kaleidoscope oi colour as the leaves change. Poplar and birch supply vivid contrast with the fir and spruce. This is "THE SEASON OF THE FLAMING LEAVES" and oc- Giant Lake Freighter curs normally the last two weeks of September into October. Winters are fresh and crisp with limited periods of below zero temperatures. Snow-falls average 90.2 inches annually in Thunder Bay but further away from the Lake Superior, substantial snowfalls provide excellent skiing, tobogganing and snowmobiling. Lake shipping continues from April 1 to December 19 most seasons. Thunder Bay citizens are healthy and robust living in clear fresh air, with modern health facilities and a great relaxing, year round vacationland close by. 9 �INDUSTRIAL GROWTH A ~umber of new plants and expansion of plants occurred in recent years including Larson Woodland Research Ltd., B. & B. Stone Ltd. (reinforced concrete bridging beams), Coastal Steel Construction Ltd., Northwestern Structural Steel Limited Brayshaw S t e e I Ltd., Northland Machinery Supply Co. Ltd., West Coast Wire Works Ltd., Great Lakes Steel Ltd., Superior Brick & Tile Ltd., Lakehead ~battor Limited, Unitized Manufa~turmg Ltd: ( prefab buildings). . Kee~mg par with commercial and industrial progress was the installation of . new arenas, shopping plazas, mannas and retirement homes. INDUSTRIAL PARKS Lakehead University Library EDUCATIONAL FACILITIES Thunder Bay is endowed with excellent educational facilities including: 60 primary schools; 10 secondary schools; 1 sheltered workshop fof ret_arde~ adults; business college; 1 unIversIty; 1 teachers' college; 1 college applied arts and technology. Also located here are an adult retraining school, providing training for adults changing vocations, a retarded children's nursery school and a school for retarded children. Lakehead University recently completed a $25,000,000 building and expansion program with almost 4,500 students enrolled in a campus eventually to harbour 8,000. The Confederation College of Applied Arts & Technology, established in late 1967, currently has 650 full time students and 600 night students. A campus building program totailing $7,500,000 was completed in 1971 near Lakehead University. ' Primary and secondary schools are operated by a Board of Education and Separate School_ Board, elected every two years. Jointly, they supervise 10 2,100 employees who care for over 32,000 students. Student graduates from Thunder Bay halls of learning totalled 2 680 in 1970 including 1,904 from' high schools, 151 from Teachers College, 560 from Lakehead University and 65 from business schools. Three public libraries are strategically located. throughout Thunder Bay t<:>get~er with a well equipped Univer~Ity Library and College Library. There Is also a regional library with a moblie book service. Night school classes are provided during the school season for those wishing to upgrade their education and knowledge. Lakehead University and Confederation College of Applied Arts_ & Technology also provides ser~Ices of night classes on many subJ~cts. Artistic courses, pottery making and many hobby arts are also taught. Extensive evening use is made of sports equipment and facilities in various school gyms for gymnastics, volley-ball, weight-lifting, wrestling, etc. A new Athletic Building at the University is the largest and bestequipped sports palace in the area. Beaverha/1 Industrial Park Fort Will!am Ward has excellent lots, serviced and available for sale at reasonable cost. Intercity Industrial Park, Port Arthur ~ard, . is being developed into an indu_stnal park complex of 160 acres, serviced, and located in the Intercity area. Keefer Lake head Terminal Industrial Park, extensive acreage in the central ~arbour area adjacent to the terminal Is cu_rre_ntly under development. Mission Island Industrial Park 15~. acres on waterfront in Fort W1ll1am Ward, near Hydro Station and accessible to river and lake dockage. Ba/moral Industrial Park - serviced lots, streets, occupied by light industry and commercial enterprise. INDUSTRIAL INCENTIVE GRANTS Thunder Bay has been designated by the Federal Government as an industry development incentive growth area and eligible to participate in payment of financial grants to industry constructing facilities in the city. Grants range up to $12,000,000 in cash ~o new secondary industry constructing and equipping a plant to manufacture a new product line in the area. The Northern Ontario Development Corportation offers financial and planning consulting service and forgiven loans up to $500,000. CHURCHES, HOMES, HOSPITALS Most of Thunder Bay's 87 churches of all denominations are conveniently located in residential areas. Three of the six hospitals are modern general treatment institutes, the remaining three include a psychiatric hospital, a tuberculosis sanatorium convalescent home and a hospital for the aged. Four well organized public senior citizen homes provide company, care and recreation for their residents. A home for the blind is operated a!'"ld maintained by the National Council for the Blind. 11 �ENTERTAINMENT AND SPORTS Lakehead Symphony Orchestra gives numerous concerts during the year and a Junior Symphony assures future expansion of the experienced symphony. Three popular Pipe Bands are in great demand. Numerous high schools have student bands, baton twirlers, and cheerleaders. Cambrian Players stage popular plays by local actors and actresses. The Navy and Army Bands supply martial music for special occasions. Fort William Male Choir has won world renown on tours to Europe. They are in great demand in the cities. The Annual Lakehead Exhibition, the third largest in Ontario, extends for nine days in the summer. Numerous hotels, motels and nightclubs provide live entertainment by local and out-of-town artists. Rowing Clubs use the Kam River for contests and practice runs. YM-YWCA Clubs in Thunder Bay maintain indoor pools and gyms for the healthy training of young people. In the summer, five filtered, out-door pools are busy spots. Two motor hotels have year-round indoor pools for guests. Four theatres in downtown sections show the latest movies. An outdoor movie operates in the Northwest section during the summer. One lawn bowling green operates in the summer and seven indoor bowling alleys operate year round. Five curling rinks are crowded from early fall to late spring by the rock enthusiasts. During the summer five golf courses cater to the outdoor swingers. Three tennis courts attract many teenagers and others. Boulevard Lake and Chippewa Park supply swimmers with sandy beaches, clean water and playgrounds for oldsters and youngsters. 12 Car racing, both in summer on dirt tracks and on Lake Superior ice in the winter is a thrilling sport. Over 100 outdoor hockey rinks are provided to train youngsters from Pee-Wee to Junior. Four artificial ice covered rinks cater to senior hockey championship games. Tubing parties are popular in winter. This is a modernization of old time tobogganing or sleighing group parties. Surplus rubber inner tubes, from huge forest vehicles are fully inflated to make a comfortable vehicle on which a couple or group slide down a step long, snowy hill. It is believed this is the only such commercial fun scheme in Canada. Four Ski Hills of championship category provide thrills for thousands of local and visiting skiers. They are within 10 miles of downtown city hotels. Modern up-hill equipment gives quick ascent. The hills are under careful constant grooming. A fifth ski area is under development. Three AM Radio and 1 FM Radio Station plus a local TV station and 3 U.S. channel cable TV provides world sport, entertainment and news coverage. Three additional channels are provided for local educational programming. A number of Finnish Saunas are a delight to citizens and visitors alike. g J. ~- //·. j \\' 0 13 �LOCAL POINTS OF INTEREST Almost 100,000 travellers annually visit the two Tourist Information Reception Centres in the downtown business sections of Thunder Bay. Administered by the Thunder Bay Chamber of Commerce. Competent and courteous staffs are prepared to answer inquiries concerning attractions of the area, tours, points of interest etc. One reception centre is located in Paterson Park, the other, the Pagoda, a unique and historical building is located near the waterfront. Both information centres are opened annually from May to October. Known for its rugged scenic beauty, Thunder Bay is situated in a river valley with terraced hills on one side and the picturesque Nor-Westers mountain range on the other. BOULEVARD LAKE - Situated in the north eastern section of the city, this beautiful lake is surrounded by a lovely drive through a woodland setting. Natural attractions include expansive beaches, swimming under the watchful eye of lifeguards, boating and picnicking. Nearby is Centennial Park where you may tour a complete bush camp complex ( circa 1910) furnished with authentic equipment. People of all ages enjoy the Muskeg Express train ride and a model farm for children stocked with domestic animals. Close by, beside Current River, is Trowbridge Tent & Trailer Park. CHIPPEWA PARK - In the South end is a picturesque setting within the shadow of the mighty Mountain McKay. Chippewa Park provides pleasure spots and entertainment with every facility to serve the family. This natural playground has a small animal zoo, supervised swimming, swings and slides, amusement rides, a tent and trailer camp and housekeeping cabins. CENTENNIAL BOTANICAL GARDENS located near Chapples Park, this vast glass three part enclosure displays 14 a year round world wide variety of plant life. The main conservatory displays subtropical plants and the two wings specialize in desert flora and seasonal flower shows. MOUNT McKAY - One of the finest panoramic views of Thunder Bay may be seen from the first ledge of Mount McKay accessible by car or bus. Mount McKay towers 1600 feet above sea level. IRON ORE AND PELLET HANDLING FACILITIES handle over five million tons of iron ore and pellets a year which are shipped from the famous Steep Rock Lake, Atikokan, and from Bruce Mines near Red Lake. Appriximately 100,000 tons of potash from Saskatchewan is trans-shipped annually. Paterson Park Mount McKay Thunder Bay Airport EXCITING CHAIRLIFT RIDES Thunder Bay has two thrilling chairlift rides - One up to the first ledge of Mount McKay and the other to the top of Mount Baldy. TOURS - Both bus tours and harbour cruises can be easily arranged. Directions for departure locations and times may be obtained from the tourist bureaus. THUNDER BAY HISTORICAL MUSEUM The public Library, 216 South Brodie Street. KAKABEKA FALLS - "Niagara of the North" - 128 feet in depth - a sight to behold - all camping facilities are available such as over night tenting, trailer park, picnic grounds, and a fine supervised swimming area for all ages. Located just 18 miles from the heart of Thunder Bay. THE INTERNATIONAL FRIENDSHIP GARDEN - Nine different ethnic and social groups contributed delightful floral designs to entice people of all ages to relax in a picturesque setting beside a reflective pond encircled by an ornamental pathway. Great Lakes Paper Mill Centennial Park Bush Camp Sleeping Giant �TRANSPORTATION Thunder Bay citizens have reasonably-priced public transit, extending across both cities by mainline trolley buses and branch line gas or diesel buses. In 1970, 5,035,887 passengers used this convenient street side service. Equipment includes 20 electric trolley buses, 20 gas buses and 16 diesel buses. Twenty three taxi companies operate fleets of cars throughout the City. Air Canada schedules three flights daily east and one west. North Central Airlines schedules a return flight daily to and from Chicago via Duluth, Minnesota. Transair schedules two flights daily to Toronto, two flights daily to Winnipeg via Dryden and Kenora. Superior Airways Ltd. and On-Air supply charter air service to all parts of the continent. Thunder Bay International Airport equipped to service modern jet aircraft, h a n d I e d 188,540 passengers on scheduled airlines in 1970. Air cargo handled was 3,710,026 lbs. Canadian Pacific Railway provides daily east and west mainline passenger service by the CANADIAN, as well as fast merchandise and piggyback freight. Canadian National Railway supplies branch line passenger service to Winnipeg and mainline points. Both railroads handle tremendous quantities of bulk materials including grain, lumber, potash, paper pulpwood and coal. The CNR operates unitized trains carrying iron ore and pellets from Atikokan and Bruce Lake, to the Thunder Bay Harbour, as well as potash and coal from the prairies. Greyhound Bus Lines supply daily transcontinental passenger service. Grey Goose Bus Lines offer passenger service to Winnipeg and Northeastern Ontario points. Trans-Canada Highway threads its way from coast to coast through Thunder Bay. A new EXPRESSWAY beginning 10 miles east of the city circles the north and west section for 19 miles to join Hwy. 17-11 (Trans-Canada) West, and continues on to Hwy. 61 on the south, leading to Duluth, Minnesota. With excellent highway connections, Thunder Bay is the base for 11 major highway transport companies and five moving van and storage companies. Water routes bring to Thunder Bay overseas ships of many nations. Most often seen are British, German and Norwegian vessels. Canada Steamships Lines Ltd. ships are the most frequently seen Canadian ships. They operate six fast package freighters shuttling cargoes from eastern Canada and returning with products of the Northwest. Tug service is provided by two companies operating in the Lakehead Harbour. POPULATION FORECAST GOVERNMENT CENSUS The last population count of the four n:,unicipalities prior to their amalgamation on January 1, 1970 was: City of Fort William 49 860 City of Port Arthur . 48 989 Municip_ality of Neebing 3:592 Township of McIntyre .. 4,565 TOTAL 107,006 1 A population forecast by the Ontario Water Resources Commission based on natural growth, predicted. ' 1973 1978 1988 2000 - 118,100 129,300 151 , 100 201,800 Ethnic Groups British ........ .. ... .... ..... .... ..... ..... . 42.8% 6.2 German 3.7 Italian 8.6 Polish 4.9 Scandinavian 6.4 Ukrainian .... ...... ................. ...... _ 10.3 Other .... .............................. .. 17.1 French Religions 57.8% Protestant ......... . Roman Catholic . ... . ..... .. . 32.8 St. Joseph' s General Hospital 16 17 �ABITIBI PAPER CO. LTD. - Operates three mills two newsprint mills and a mill producing coated papers for books, catalogues, magazines, for Time - Macleans, etc. CANAD IAN CAR A division of Hawker Siddeley Canada Ltd. - engineering and manufacturing of woodlands logging equipment, highway transport trailers, subway cars, transit coaches, cargo containers and aircraft components. COASTAL STEEL CONSTRUCTION LTD. Fabricator and erector of structural steel. DORAN'S NORTHERN ONT AR I 0 BREWERIES LTD. Oldest manufacturing industry in Thunder Bay. Formed in 1876 as Diamond Brewing Company produces beer and ale. DOW CHEMICAL OF CANADA LTD. - Supplies chemicals for paper mills. GREAT LAKES PAPER COMPANY Produces large quantities of newsprint mostly for export to the USA. A $31 million Kraft mill supplies domestic and foreign markets. This company's wood supply is trucked and railed from abundant forest properties as distant as 250 miles from the plant, and consumes almost ¾ million cords of wood annually. Shipments of finished products approached 500,000 tons in 1970. GREAT LAKES STEEL PRODUCTS LTD . Suppliers, fabricators and erectors of structural steel. GREAT WEST TIMBER LTD. Operates a large saw mill, planing plant and kiln, producing up to 40 million board feet of lumber annually. NORTHERN ENGINEERING & SUPPLY CO. LTD. - Manufacturers of woodlands equipment, suppliers of wholesale plumbing, electrical and heating supplies. Complete machine and welding metal shops. Forest Harvesting Equi pment NORTHERN WOO D PRESERVERS LTD. Has its own extensive forest operation to supply two modern saw mills that produce 45 million board feet of railway ties, construction lumber and timbers annually. In addition, poles, piles, ties, and lumber are pressure treated with locally produced preservatives, and tar products. NORTHLAND MACHINERY SUPPLY CO. LTD. Designs, fabricates and installs complete dust control systems. Manufacturers of grain cleaning machines. Sheet metal contractors. Distributors of industrial welding supplies. PORT ARTHUR SHIPBUILDING CO. LTD. - Shipbuilders, ship repairs, 750 ft. dry dock - general and industrial engineering - structural steel bridges -iron and brass foundry castings to 25 tons millwork, plastic division, and pulp and paper machinery division. Pasco Shops SUPERIOR BRICK & TILE CO. LTD. Manufacture brick and clay products. TEE-KAY APPAREL LTD. Major manufacturer of teen clothing. WEST COAST WIRE WORKS LTD. Produces four drinier wire mesh for area paper mills. WESTERN IRON AND METAL CO. LTD. 60 year old iron and steel scrap and wrecking contractor. Operates largest triple compression baling press in Canada. Supplies new and used structural steel. LAKEHEAD INSULATION AND PLASTICS LTD. Produces special pipe insulation and fibre glass plastic, large diameter pipe for the paper mills and others. WOODS BAG & CANVAS CO. LTD. - Produces a wide variety of sporting goods, including tents, trailers, sleeping bags, etc. LARSON WOODLAND RESEARCH LTD. Produces heavy forest harvesting machinery. NEWPORT METAL INDUSTRIES LTD. Produce air flow and pollution control equipment. Giant Paper Making Machine 18 19 �MINING The vast mineral wealth of Northwestern Ontario has hardly been scratched. Most if not all this valuable material will channel through Thunder Bay to various processors. It is conceivable that at some future date, secondary industries will be located near the Lakehead to process the concentrated material into a solid state. Iron ore shipments have recently diminished with the installation of concentrating plants which upgrade the raw ore to pellets of high grade iron. Steep Rock Iron Mines and Caland Iron Ores, Atikokan, have installed palletizing plants and currently are making substantial shipments. The Griffith Mine at Bruce Lake. 350 miles west of the Lakehead, ships iron pellets through Thunder Bay Harbour to Steel Company of Canada Ltd., Hamilton, Ontario. Over 5,000,000 tons of pellets was shipped from these mines in 1970. International Nickel currently is constructing a large concentrator at its mine located at Lake Shebandowan, 50 miles west of Thunder Bay, to produce concentrated powder for shipment to the Sudbury smelter. Great Lakes Nickel Co. and other companies nearby, are exploring and developing a mountain mass of nickel- copper, 40 miles south of Thunder Bay near the U.S. border. Over 140,000,000 tons of low grade ore have been reportedly outlined. An ore to smelter complex worth $100 million dollars is currently being considered. Silver has been known to inhabit the Precambrian Shield around Thunder Bay for 100 years, since Silver Islet Mine was discovered and worked. Today, with the price of silver at its highest, a number of silver mines are being re-examined. Further north, as many as 150-200 miles from Thunder Bay, huge deposits of rich iron ore have been uncovered and moth-balled for the time being while operating pits closer to market are being developed. In the Sturgeon Lake area, Mattabi Mines is building a $36 million mining complex and nearby Falconbridge Mines is exploring additional interestin~ base metal ground. South Bay Mines is investing $6 million in a base metal mining complex at Confederation Lake. Mayburn Mines near Kenora has started production. The future is bri~ht for expansion of activities in the field of mining in Thunder Bay area. THUNDER BAY Formerly ( Fort William - Port Arthur) STATISTICAL INFORMATION Population: Metropolitan Thunder Bay 108,048 Formerly Twin Cities of Fort William and Port Arthur which amalgamated Jan. 1, 1970. Population: 108,048. Altitude: Harbour, 601 feet above sea level. Mount McKay, 1600 feet. Area: 156 square miles ( including water lots). Commercial Buildings: 1,175. Streets: 399.1 miles. Sidewalks: 165 miles. Watermains: 276.7 miles. Sewers: 230 miles; 218.8 sanitary, 43.2 storm. Churches: 87, all denominations. Financial Institutions: 40 bank, trust, and loan offices. Vehicle Registration: 1969, 47,965. Households: 28,691, (1970). Average Income: $6,085. Per Capita Income: $2,740. Hospitals: 6. Newspapers: 2 dailies, 2 weeklies. Libraries: 5. Families: 22,646. Police: City, 2 stations, 143 personnel, 21 cars. RCMP, Ontario Provincial Police. Harbour Police Units. Railways. CPR, CNR. Airlines: Air Canada, North Central .. Superior, Transair and On-air. Schools: 60 primary, 10 secondary, 1 business college, 1 university, 1 teachers' college, 1 community college. Medical: 11 clinics. Telephones: 56,033, ( Dec. 1970). Annual Precipitation: 27.62 inches. Averaqe Temperature: 60.9°, summer. 10.2°, winter. High Temperature: 104°, July 1936. Low Temperature: -42°, Jan. 1951. Elevators: 24; Capacity, 104,347,210 bushels. Theatres: 4 plus 1 outdoor, summer. Fire Departments: 5 stations, 160 personnel. Curling Rinks: 5. Golf Courses: 5. Tennis Courts: 3. Swimming Pools: 4 indoor, heated; 5 outdoor, 3 hotel; (2 indoor, 1 outdoor). Hockey Rinks: 4 artificial, 100 natural. Ski Hills: 5 ski areas; 3 chair lifts. Radio-TV: 3 AM radio, 1 FM radio, 1 TV (CBC) local, 3 U.S. channel cable TV. 1 community channel. Saunas: 3. Hotels - Motels: 55 with 1,936 rooms, daily accommodations for 4,218. Water Pumping Capacity: 31,500,000 gal. daily present consumption 13,768, 120 gal. daily. . Sewage Disposal: 7,500,000 gal. daily. Transportation: City Transit 20 electric trolly buses, 20 gas buses, 16 diesel buses, 5,035,887 passengers in 1970. Hydro: In excess of 130,000 KVA in Thunder Bay. Natural Gas: 12,305,000 M .C.F ., 270 miles of pipeline within city. Building Permits (1970): $18,524,954. PRIMARY INDUSTRIES: -· 4 mills produce 813,237 tons of paper products annually. -· 60 million board feet of lumber processed yearly. 1,925 tons of fresh fish processed yearly. 5 million tons of iron-ore transshipped annually. SECONDARY INDUSTRIES: Brick and tile, castings, chemicals, brewing, dust control systems, aircraft, rail and highway equipment, plastics, shipbuilding, prefab homes, recreation equipment. 21 20 �" MIKADO 22 II A Lakehead Choral Group production. �� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay, brochure Subject The topic of the resource Business and Industry Description An account of the resource Brochure promoting Thunder Bay, produced by the Thunder Bay Chamber of Commerce, Thunder Bay Convention Bureau, and Industrial Commission of the City of Thunder Bay. Likely 1970 or shortly after. Creator An entity primarily responsible for making the resource Thunder Bay Chamber of Commerce Thunder Bay Convention Bureau City of Thunder Bay Date A point or period of time associated with an event in the lifecycle of the resource 1970 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Type The nature or genre of the resource Text Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay https://digitalcollections.lakeheadu.ca/files/original/fae2d4572b976a053dcb9b2bcdd77492.pdf 83c152759ec72773556331769ebf20eb PDF Text Text THE CITY OF U~<!&~ ONTARIO · VEVELOPMENT BUREAU OF THE CITY OF THUNVER BAY, 19 3 Atr;thu.1t S:tlte.e;t,, THUNVER BAY, P, ONTARIO. 807-344-2341 AN INVITATIQ TO EXPLORE THUNVER BAY \ ThundeJt Bay be.eagte. .:the. 6.:th la.Jz.gu.:t wy in 0,n.:taJuo and .:the. 15.:th levtgu.:t in Canada. on Ja.n,tfevty 1, 1970 .:t.Jvwugh .:the. amalgamation 06 .:the. 6otLmeJt C.lliu 06 Foll..:t W ~ and Poll..:t Atr;thwz. and .:the. Mun.lc..lpaliilu 06 Nee.bing and Mein.:tyJte.. I.:t ).,,6 ai.6 o one. o 6 .:the. levtg u.:t e,.,[;t.,[u, evte.a.w)-1> e., in Canada. having 151.1 1.>quevte. milu oft 99,977 a.Mu, aeeommodating a popui.ation 06 108,000 p~OM. Vevt.loMly known in .:the. pM.:t M .:the. Twin C.lliu oft Canadian Lake.he.ad, .:the. poll..:t ).,,6 .:the. eonne.e.:t.lng unk be..:twe.e.n e.M.:t and wu.:t :tfta.de., wa,teJt and !tail. In e.xeu-6 06 20,000,000 .:toM 06 va.Jt.le.d eevtgo annually :tlta.Mli .:the. poll..:t inelud.lng gJta.ln, eoa.l, ,iJl,on oJte., mineJtai.6, papeJt, ge.ne.Jtal eevtg o , e;t,e, . ThundeJt Bay ).,,6 .:the. -6 Vtviee. ee.n:tlte. 6oJt a. vM.:t na,tu.1ta.l JtU ou.Jtee. and Jte.Me.atio na.l evte.a e.neompMJ.>ing 1I 4 mill.lo n -6 quevte. milu o 6 laku and 6oJtu.:t-6. The. a.w_v.luu u.ndeJtWa.y in me.n.:t PJtogJtam indiea,tu will inelude. 1.>e.eonda.Jty a.l 6a ~u . 6oliowing pa.gu au.tune. Jome. 06 .:the. de.ve.lopme.n.:t .:the. Thu.ndeJt Bay evte.a. On.:taJuo '-6 Vuign 6oJt Ve.ve.lop.:the. Cliy ).,,6 a pft.lme. .:tevtge..:t 6oJt 6u..:twz.e. gJtow.:th, wh.leh and pJt,tme, indM:tlty, J.>Vtviee. indM:tlty and Jte.Me.ation- You Me. invlied .:to eommu.niea.:te. wlih .:the. Ve.ve.lopme.n.:t Bwz.e.au 06 .:the. Cliy 06 Thu.nde1t Bay i6 1.>e.e.k,i,ng a.dd.lliona.l inooJtmation. 06 eou.Me., e.veJty.:th.lng ).,,6 ke.p.:t on a CONFIVENTIAL bM.l-6. SineeJte.ly, GWM/ap G. W. Mc.Fadden, V,iJr,e.e.:toJt. �The City of Thunder Bay was chosen a "Prime Centre of Industrial Opportunity" when the Ontario Government unveiled the results of a comprehensive study of Northwestern Ontario under the program "Design for Development" Phase II. Industrial growth is to be strenuously encouraged but "Quality of Life" is to be retained. It is contended life in Northwestern Ontario now has many fine qualiti es not found elsewhere. This relates to low pollution, easy access to recreation and relaxed, healthy living. The Design for Development Report recommends substantial Federal and Provincial Government incentives for the establishment of new industry over and above the current government incentive plans. It suggests Thunder Bay is a choice spot for establishment of a smelter, refinery or primary metal industry. Greater end use of forest products is encouraged. The primary goal for increased employment in the next 20 years should be a minimum of 18,000 and an optimum of 54,000 new jobs. Implementation of the first phase of the development program should commence early in 1972. PLANNING FOR THE FUTURE Thunder Bay, in addition to participating in the Design for Development Program, has been studiously looking to the future in its own planning. An Official Plan for Thunder Bay has been unveiled, to direct proper growth of the City and its suburbs over the next 20 years. A Transportation Study has been completed outlining a forecast of how traffic can be channelled in the City up to 1990. A Regional Water Supply and Pollution Control Study was completed in 1969 by the Ontario Water Resources Commission to guarantee full use of water facilities in the city, yet control adverse pollution of waterways. This study required indepth review of past experience and the expected growth to the year 2000. A Survey of Internal Transit Facilities is currently underway as well as a survey to determine expansion possibilities of the City-owned Telephone system, one of the few and most profitable in Canada. A Thunder Bay Urban Renewal Project was announced in October 1970 to rebuild the core business section of Port Arthur Ward. Over $15 million dollars of private c~pital will be invested in the Development and $4 million by governments. The initial rebuilding will commence in the fall of 1971 with the expansion totalling $3 million of the T. Eaton ComP,any store and the $1~ million Sayvette Store. Included in this program is the installation of a connecting climate-controlled mall of all buildings. �AND --- R E S OURC E S Historically, silver is the basic mim~ral found in Thunder Bay area. However, technology has radically changed this and now iron ore is King, followed closely by nickel, copper, zinc, etc. IRON ORE Atikokans 120 miles west is the base operation for Steep Rock Iron Mines, Inland Steel and Caland Ore. Steep Rock Iron Mines ships raw ore and pellets. Bruce Lake, 315 miles west is the site of Steel Company of Canada iron ore operations. Stelco ships only pellets. The others ship both pellets and raw ore. Most pellet shipments are processed through Valley Camp Coal Ltd., modern belt loading facilities on the Mission River, Thunder Bay. The storage capacity exceeds 1½ million tons. Some pellets and all raw ore is also shipped over a CNR ore trestle. FUTURE RESERVES -- IRON Anaconda Iron Company Limited uncovered and developed a massive iron . ore body and mothballed it for the future. The open pit mine is located 40 miles north of Nakina. Steep Rock and Algoma own a large iron ore body in the Lake St. Joseph area which very shortly will have to be opened up by a massive operation including installation of railroad . services and lifting of hugh quantities of overburden. NICKEL International Nickel Company is completing a $32 million mine site and concentrator at Lake Shebandowan, 50 miles west of Thunder Bay and will likely go on stream early in 1972. Concentrates will be shipped to Sudbury. Great Lakes Nickel Ltd. is arranging finances preliminary to building a $100 million plus mine, smelting and refining complex, 38 miles south of Thunder Bay to process up to 140,000,000 tons of nickel, copper, zinc, platinum and pladium ore. URANIUM Large areas near Dryden were staked in a uranium rush late in 1967. Claims are currently being examined. �*2* COPPER AND OTHER BASE METALS Mattabi Mines Limited has expended $36 million plus other expenditures to construct a mill and concentrator to extract 12½ million tons of base metal ore from its property at Sturgeon Lake, 185 miles west of Thunder Bay. The mill went on stream in the fall of 1971. South Bay Mines, Utchi Lake, southeast of Red Lake went into production in the sumer of 1971 at 500 tons daily. Construction cost to get the mill into operation exceeded $5 million. COAL SHIPMENTS Substantial shipments of Alberta, B. C. and Saskatchewan coal are forecast if test shipments arranged in 1970 through the Port of Thunder Bay prove economically successful. Stelco is interested in coking coal and Ontario Hydro for the thermal plants in Southern Ontario. Up to 5 million tons may be required. FORESTRY Eleven paper mills in Northwestern Ontario are assured of continuous wood supplies from the substantial forest cover. Great Lakes Paper, for example, consume 800,000 cunits annually in the largest paper and Kraft mill east of the Rockies. • New technology in wood harvesting has maintained extraction costs in a rising cost market. Machines are used extensively. New roads, new transportation systems in the future will undoubtedly open up unknown riches i~ the area. �l!!!!!!!!f E. ! ~! S T AT I S T I C AL DAT A (Obtained from FinanciaT Post Survey of Mai•kets 1970) 1970 Current Growth Rate Per Decade Population (000) (April 1, 1970) %Of Canadian Total %Change Since 1961 - 1970 Market - Above National Average Retail Sales - 1969 (Millions$) %Canadian Total (Retail) Per Capita (Retail Sales) Income - Above National Average Personal Disposable Income - 1969 %Of Canadian Total (POI) Per Capita (PDI) Building Pennits, Value (000) MANUFACTURING INDUSTRIES No. of Plants Employees Salaries - Wages ($000) Cost of Materials ($000) Value of Shipments ($000) Value Added ($000) CENSUS INFORMATION Population, Male Population, Female Total Population 1969 1968 1967 13% 12% 14% 7% 13% 108.0 105.8 98.6 97.9 95.2 0.50 o.~8 o. 51 0.48 0.48 +10.2 +8.95 +8. 18 +2.50 +5.1 15% 16% 18% 26% 24% $i58.3M $149. lM $134. 9M $133.6M $120.SM 0.58 0.59 0.56 0.60 0.60 $1,420 $1 , 375 $1 2 385 $12290 $12480 11% 11 % 15% 13% 1if% $294 .1M $163.6M $222.7M $205.6M $17a.OR 0.53 o.58 0.5~ 0.56 0.57 $2 510 $2 27S $2 130 $1 2 910 $2 740 $28:427 {$22:047}$1s:121 s22:8oa $21,759 1967 98 6,878 $41,581 $95,900 $193,736 $90,816 1964 1962 1961 1966 99 100 71T 714 5,083 7,102 5,743 5,431 39,635 28,622 26,113 28, 131 100,434 64,768 61,188 56,477 196,446 141,113 125,353 116,021 87,211 70,234 59,657 52,946 1966 58,958 47,590 106,548 1961 46,359 44,131 90,490 1961 38,749 5,607 3,333 7,815 4,475 3,975 9,336 % of Total AVERAGE WEEKLY EARNINGS 1962 1964 1966 1967 1968 1969 THUNDER BAY $81.04 86.20 97 .71 102.36 105.68 117. 02 CANADA $80.54 86.51 96.30 102.79 109.88 117 .63 RETAIL TRADE 1966 CENSUS Total Sales ($000) No. of Stores Year End Inventory ($000) No. of Employees Payroll: Total ($000) $130,295.1 642 15,705.0 4,383 13,271.6 RACIAL ORIGIN British French Gennan Italian Polish Scandinavian Ukranian 1965 42.8% 6.2 3.7 8.1 4.9 4.4 10.3 �HYDRO - E L E CT R I C - - - - - - - 1· - - - - ..... General Rates -- Industrial Colllllercial (Monthly) Loads from O -- 5,000 Kilowatts Demand Charge First 50 kilowatts of billing demand per month - nil Balance at $1.60 per kilowatt of billing demand per month Energy Charge 4.0¢ per kilowatt-hour for the first 1 . 6¢ II • II II II II next 1 • 3¢ U II II II II II 0 • 5¢ II II II II II 11 50 kilowatt-hours per month 200 9 t 750 2 t 240 t 000 ti II It II II II II II H II 11 Balance of monthly consumption at 0.3¢ per kilowatt hour. II • Loads over 5 2000 kilowatts Demand Charge $2.50 per kilowatt for all kilowatts of billing demand per month Energy Charge , All consumption be billed at 0.3¢ per kilowatt-hour. NOTE: The general rate is based upon service at utilization voltage. Where the customer provides transformation facilities the authorized allowance of .25¢ per kilowatt of billing demand per month for stepdown from sub-transmission voltage and .15¢ per kilowatt billing demand per month for stepdown from distribution voltage will apply. Residential Service (Monthly) 1 4.0¢ per kilowatt-hour for the first 50 kilowatt-hours per month 1 . 4¢ 0.9¢ II II II II 11 11 11 11 II " next 200 II II II II all additional monthly consumption. All rates are net and subject to a late payment charge of 5% if not paid on or before due date. �WH A T ---- A !Q.!l T l!!!l!!~~ R WE A T H E R ? --------The Mid-Canada Development Corridor Foundation Inc. is working to dispel the myth that Canada's North is uncomfortable and unproductive. Some day soon it is anticipated a new and exciting era will open up the north with new growth centres and greater populations of people enjoying a new and clean environment. Thunder Bay is on the extreme southern edge of the contemplated development corridor on the Northwestern shore of Lake Superior, the largest lake in the world. The lake, 601 feet above sea level, controls the winds passing over it and tempers the climate of the City both winter and sunwner. It could be named a "built-in air conditioner". WEATHER RECORDS Records have been kept since 1879 and indicate temperatures average over a period 1921 - 1950 as follows: -- (Degrees) Annual Average January Average April Average July Average October Average Extreme Maximum Extreme Minimum 36.8 7.6 35.4 63.4 42.6 (Ottawa Average 41.6) (Montreal Average 15.4) (Toronto Average 43.8) (London Average 69.6) (Calgary Average 42.1) 104 -42 Killing frost -- last in spring average June 4, first in fall average September 7. Average annual total precipitation -- 27.62 inches Average annual total snowfall -- 68.8 inches (Montreal average -- 100.8) Sunshine records show an average of 2174 hours per year making Thunder Bay one of the brightest and sunniest cities in Canada. • Average yearly wind is 8.4 M.P.H. The prevailing winds in winter are west and northwest and in surrmer easterly winds edge westerly for the prevailing direction. Humidity is extremely low at all times of the year and the area is a delightful refuge for sufferers of Hay Fever. Thunder Bay is located in the centre of Canada as the hub city of what is commonly known as Northwestern Ontario. Actually, this is a misdirection as geographically it is in the southwestern portion of the Province of Ontario -- Latitude 48.23 N. Longitude 89.16 W. The City is in the Eastern Standard Time Zone, but reverts to Eastern Daylight Saving Time during the same period as other major cities. �!! QR T !!IE.li !l!!lAE.lQ D E V E L O P ME N T CO E.f..:. P E R F O R MA N C E ----------~ The Northern Ontario Development Corporation, a Crown Corporation of the Province of Ontario, maintains a head office at 134 S. May Street, Thunder Bay, F, Ontario. A subsidiary office is in Tinmins, Ont. The purpose of the Corporation is to assist in the develop~ ment of secondary industry in Northern Ontario extending from the Manitoba border to the Quebec border and approximately north of Hwy. 17. The City of Thunder Bay is eligible for full qualifications for its business interests. FORMULA FOR CALCULATING LOANS: For Canadian companies qualifying for Perfonnance Loans, NODC can assist with cash grants of up to 50% of capital costs of building and equipment up to a maximum Perfonnance Loan of $500,000. For companies other than those of Canadian registry, the formula is as follows: 33 1/3% 25% of the first $250,000 of building and equipment cost. of the balance of building and equipment cost up to a maximum loan of $500,000. 1. Loans are progressively forgiven over a five-year period at 10% per year. Final forgiveness is in the 6th year. No interest or charges are involved. 2. Maximum $500,000 additional loan at regular interest rates can bearranged under certain circumstances for both categories of Canadian and foreign companies. 3. The loans are income tax exempt. Businesses establishing in Thunder Bay are eligible for either the Federal Incentive Program and Grants or the Northern Ontario Development Corporation Perfonnance Loans, but not both. In practice it is desirable to approach the Federal Department of Regional Economic Expansion for financial assistance. Should this assistance be inadequate or refused, an approach can then be made to the Northern Ontario Development Corporation for their assessment of the application. For further infonnation on the Northern Ontario Development Corporation Perfonnance Loans, contact the head office ~t 134 S. May Street, Thunder Bay, F, Ontario or: I I DEVELOPMENT BUREAU OF THE CITY OF THUNDER BAY, 193 ARTHUR STREET, THUNDER BAY,P, Ontario. 807-344-2341. �I NC E NT I V E --------i- 10 September 19, 1967, the Ontario Government announced a new incentive plan -- "Equalization of Industrial Opportunity", directed primarily to improve secondary industry in underdeveloped areas of the Province. All industry in Northwestern Ontario is eligible to participate in the program. In June, 1971, the Ontario Equalization of Industrial Opportunity changed certain terms of grants to industry. Canadian companies are now eligible to receive 50% of the cost of construction and equipping new plants. The old fonnula of 33 1/3% and 25% continues for foreign-owned companies. ELIGIBILITY {l) Secondary manufacturing companies establishing new facilities or making approved additions to existing facilities. The grants will also be available to companies building a new plant. If 75% of the machinery installed is new, then the grant will also apply on the machinery. Companies buying, . renting or leasing a building and installing machinery can apply for a loan on the machinery only, if such machinery is 75% new. (2) Warehouses and other concerns of a closely related nature to secondary industry, which can contribute substantially to the local economy. (3) Tourist developments that will effectively raise the occupancy levels in local tourist establishments. NOT ELIGIBLE {1) Primary industries such as mining, logging, fishing and agriculture. (2) Service industries. (3) Companies transferring operations from other areas of the Province into an incentive area only to become eligible for the grant. (4) Those companies not organized on a businesslike basis and lacking management ability and proper financing. (5) Companies receiving financial assistance under any other government program such as Federal Incentives, ARDA, etc. CALCULATION OF GRANTS For Canadian companies 50% of the full cost of construction and equipping of plant up to a total Performance Loan of $500,000. �* 2* FOR FOREIGN-OWNED COMPANIES 33 1/3% of the first $250,000 of the approved capital cost of new buildings and equipment. 25% of the balance of the approved cost of these facilities. The maximum grant will be limited to $500,000. ADMINISTRATION OF GRANTS Grants are administered by the Northern Ontario Development Corporation, 134 South May Street, Thunder Bay, F, Ontario, and will be made available to qualifying finns in the fonn of interest-free loans for a period of six years. Each year 10% of the loan will be forgiven through the 5th year. At the end of the 6th year, provided the company has stayed in the locality and perfonned satisfactorily, the balance of the loan is forgiven. CONSULTANTS Expert consultants are provided to assess applicants for loans. This service is free. Advice is also supplied by consultants on business matters, finances, etc., to any company. The Northern Ontario Development Corporation may also provide Conventional loans to deserving firms, ineligible for Perfonnance Loans, or unable to secure adequate financing through nonnal banking channels. Speculative enquiries to Northern Ontario Development Corp~ oration consultants for "Performance Loans" are not encouraged as it is most difficult to assess a project without complete and factual information. It is desirable to have a fully documented outline of the projected installation, financial background and future planning, available for examination by the NODC consultants. All inter.views are strictly CONFIDENTIAL. �THE CITY OF UJm;JgafZfUJP ONTARIO DEVELOPMENT BUREAU OF THE CITY OF THUNDER BAY, 193 Arthur Street, THUNDER BAY, P, ONTARIO. 807-344-2341 B.I§.10.[Ab_ DEVELOPME_ttT I NC E NT I V E S ACT --- Bill C-202 creating the Regional Development Incentives Act was first read May 26, 1969, and became law July 1, 1969. HEREWITH ARE SOME EXTRACTS FROM THE ACT: DESIGNATION OF SPECIAL AREAS The Governor and Council after consultation with the government of any province may by order designate as a special area for the period set out in the order, any area in that province that is detennined to require by reason of the exceptional inadequacy of opportunities for productive employment of the people of that area or of the region of which that area is a part, special measures to facilitate economic expansion and social adjustment. (All NWO below the 51st parallel has now been designated.) CO-OPERATION WITH PROVINCES In fonnulating and carrying out these plans, the Minister shall make provision for appropriate co-operation with the provinces in which special areas are located and for the participation of persons, voluntary groups, agencies and bodies in those special areas, and the Minister in co-operation with any province may fonnulate a plan of economic expansion of social adjustment in a special area and with the approval of the Governor in Council and subject to the regulations, enter into an agreement with that province for the joint carrying out of such a plan. DEVELOPMENT INCENTIVES Upon application therefore to the Minister by an applicant (company) proposing to establish a new facility or to expand or modernize the existing facilities in a designated region, the Minister may authorize a provision to the applicant subject to this Act and upon such tenns and conditions as prescribed by the regulations of: �l!!Q!!iT.B.! DEVELOPMENT INCENTIVE f.hA!i All of Northwestern Ontario, including the City of Thunder Bay, has been designated as a "Growth Area 11 and industry will qualify for substantial ~ash grants. I NDU S T R I AL ---------- I N C E NT I V E PROGRAMS This plan is administered by the Department of Regional Economic Expansion. Here is how it looks: 1. PRIMARY DEVELOPMENT INCENTIVE GRANT $ 2. For establishment, expansion or modernization of plants producing an established product line. Minimum Capital Cost -- $30,000 for Expansion or Modernization -- $60,000 for a new plant Maximum Grant -- $6,000,000 SECONDARY DEVELOPMENT INCENTIVE GRANT Not to Exceed 20% 5,000 per Employee Maximum Grant Up to 25% and up to $5,000 per employee for construction and equipping new plant or expansion of an existing plant to introduce a new product line. Cost -- $30,000 for modernization or expansion $60,000 for a new plant $12,000,000 or $30,000 per employee. a. New or used machinery purchased to equip plant will qualify for grant. b. No contractural arrangements can be made ;prior to signing grant agreement. c. The Secondary Development Incentive shall not exceed half of the capital employed in the operation. d. The plan is aimed primarily to assist secondary industry. Numerous other conditions are stitched into the plan to ensure good business practices are maintained. Further infonnation can be obtained by contacting the Department of Regional Economic Expansion, 66 Slater Street, Ottawa, Ontario, KlA OM4 or by direct contact with the: \ DEVELOPMENT BUREAU OF THE CITY OF THUNDER BAY, 193 ARTHUR STREET, THUNDER BAY, P, ONTARIO. PHONE: AREA CODE 807-344-2341. �*2* (a) A primary development incentive by way of financial assistance to the applicant for the establishment, expansion, or modernization of the facility and, (b) In the case of a proposal to establish a new facility or to expand an existing facility to enable the manufacturing or processing of a product not previously manufactured or processed in the operation, a secondary development incentive by way of additional financial assistance to the applicant for the establishment of the new facility, or the expansion of the existing facility for that purpose. MAXIMUM AMOUNTS 1. The amount of a erimary development incentive shall be based on the approved capital costs of establishing, expanding or modernizing the facility in respect of which the primary development incentive is authorized and shall not exceed: a. b. 20% of those approved capital costs or $6,000,000 whichever is the lesser amount. 2. The amount of a secondary development incentive shall be based on the approved capital costs of establishing or expanding the facility in respect of which the secondary development incentive is authorized and on the number of jobs created directly in the operation and shall not exceed: a. b. 5% of those approved capital costs plus $5,000 for each job determined by the Minister to have been created directly in the operation. 3. A secondary development incentive in respect of any facility shall not exceed an amount that when added to the amount of the primary development incentive authorized, in respect of that facility would result in a combined development incentive that exceeds: a. $30,000 for each job determined by the Minister to have been created directly in the operation. $12 million or Half of the capital to be employed in the operation which ever is the least amount. b. c. DETERMINATION OF AMOUNTS OF INCENTIVES Subject to this act, the Minister may authorize the provision of development incentive in the maximum amount provided for by this Act or in any lesser amount, and in detennining whether to authorize the provision of a development incentive in the maximum amount so provided for, or in any lesser amount, the Minister shall take into con~ sideration the following factors:- �*3* a. The extent of the contribution that the establishment, expansion or modernization of the facility would make to economic expansion and social adjustment in the des . lgnated region. b. The probable cost of provincial, municipal or other public authorities of providing service or utilities required for in connection with the facility. c. The amount or present value of any federal, provincial or municipal assistance given or to be given other than under this Act in respect of the establishment, expansion or modernization of the facility. d. The probable cost of preventing or eliminating any significant air, water or other pollution that could result from the establishment, expansion or modernization of the facility. e. In the case of any proposal to establish or expand a facility constituting the necessary components of a processing operation whether the resources to be exploited would be adequate or on a sustained-yield basis to support the facility together with the existing facilities that utilize the same resources and f. Such other factors relating to the economic and social benefits and costs of the facility as the Minister considers relevant. INELIGIBLE FACILITIES No development incentive may be authorized under this Act for the establishment, expansion or modernization of any facility if in the opinion of the Minister: a. It is probable that the facility would be established, expanded or modernized without the provision of such an incentive or b. The establishment, expansion or modernization of the facility would not make a significant contribution to economic expansion and social adjustment within the designated region. c. No development incentive may be authorized under this Act for the establishment, expansion or modernization of any facility the capital costs of which would not in the opinion of the Minister exceed such minimum amount as is prescribed by the regulations. LIMITING PROVISIONS In calculating the amount of any development incentive for the establishment, expansion or modernization of any facility, there may be included in the approved capital costs of establishing, expanding or �*4* LIMITING PROVISIONS (Cont'd) modernizing the facility, any capital expenditures made by the applicant to provincial, municipal or other public authorities for the provision of services or utilities required for or in connection with the facility if the Minister is of the opinion that the expenditures were reasonably and responsibly made, but no such expenditure shall be so included in excess of 20% of the total amount of the approved capital cost of establishing, expanding or modernizing the facility after deducting from those approved capital costs all federal, provincial and municipal grants or other financial assistance made or to be made in connection herewith or for which the applicant would ordinarily have been eligible by reason of the establishment, expansion or modernization of the facility. In calculating the amount of any secondary development incentive for the expansion of any facility there may be included in the capital to be employed in the operation only such part of that capital as is to be employed in connection with the manufacturing or processing of a product not previously manufactured or processed in the operation. No development incentive may be authorized under this Act for the establishment, expansion or modernization of a facility for which a contractual comnitment was made whether or not the conwnitment remains in force before a. b. The first day of July 1969 or The day on which an application for the development incentive is received by the Minister, whichever is the later date. Where an application for a development incentive is received by the Minister before the first day of January, 1970 in respect of a facility for which a contractual commitment was made on or after the first day of July 1969 provision of the development incentive may be authorized and the development incentive may be paid in accordance with this Act as if the contractual co111Tiitment has not been so made. No development incentive may be provided under the Act. a. For the establishment of a facility that is not brought into commercial production until after the 31st day of December 1976 or b. In the case of the expansion or modernization of a facility ff the expanded or modernized facility is not brought into commercial production until after the 31st day of December 1976. No development incentive may be authorized for the modernization of any facility in respect of which a development incentive has previously been authorized under this Act. �*5* PAYMENT OF INCENTIVES 1 When the Minister is satisffed that facility for the establishment of which a primary development incentive only has been authorized, has been brought into conmercial production or in the case of a facility for the expansion or modernizatio~ of whith a primary of which a primary development incentive only has bee~ authorized, the expanded or modernized facility has been brought into ·conwnercial production, the Minister shall pay to the applicant, an amount on account of the primary development incentive not exceeding 80% of t~e amount estimated by the Minister to be the amount of the incentive and the remainder of the incentive shall be paid in such amounts and within such period not longer than 30 months from the day the facility or th~ expanded or modernized facility was brought i_nto commercial production as are prescribed by the regulations. COMBINED DEVELOPMENT INCENTIVE When the Minister is satisfied that a facility for the establishment of which a primary development incentive and a secondary development incentive have been authorized, has been .brought into co11111ercial production or in the case of a facility for the expansion of which a primary development incentive and a secondary development have been authorized, the expanded facility has been brought 1ntQ conmercial production, the Minister shall pay to the applicant an amount on account of a combined developnent incentive not exceeding a. 80% of the amount estimated .by the Minister to be the amount of the combined development incentive or b. $24,000 for each job that the Minister estimates will be created directly in the operation, whichever is the lesser amount and the remainder of the combined incentive shall be paid in such amounts and within such a period not longer than 42 months from the day facility or the expanded facility was brought into comnercial production. TAX PROVISIONS An amount payable to an applicant on account of a development incentive under this Act is exempt of income tax. GENERAL LIMITATIONS Where in the opinion of the Minister, a development incentive could be provided under this Act, in respect of an undertaking, an agreement providing for a guarantee (loan and interest) may be entered into only if in the opinion of the Minister the approved capital costs of the undertaking would exceed �*6* GENERAL LIMITATIONS (Cont'd) a. $75,000 for each job that the Minister estimates would be created directly in the undertaking or b. $30,000,000. NOTE: In Bill C-173, an Act re-organizing various departments of the government there is an interesting section relating to the Department of Regional Economic Expansion and its relationship to co-operation with the Provincial Governments. One section reads as follows: The Minister may provide for the payment to a province of contributions in respect of the costs of the programs and projects to which the agreement relates and are to be undertaken by the government of the province or any agency thereof or any of those programs or projects and 11 a. May provide that Canada and a province may procure the incorporation of one or more agencies or other bodies to be jointly controlled by Canada and the Province for the purpose of undertaking or implementing programs or projects to which the agreement relates or any part of such programs or projects." �THE CITY OF U~ef!J1UJP ONTARIO DEVELOPMENT BUREAU OF THE CITY OF THUNDER BAY, 193 Arthur Street, THUNDER BAY, P, Ontario. 807-344-2341 .EI.Q.IR~h A!!i>_ l!!fI!ill!fi PROVINCIAL TO lNQ~iTR! This outlin~ deals with major government incentives available to manufacturers. It is intended as a guide only, and appropriate authorities should be referred to for detailed infonnatfon and confirmation. Federal Incentives to be dealt with -(1) (IRDIA) Industrial Research and Development Incentives Act (2) Income Tax Allowances (3) (IRAP) Industrial Research Assistance Program (4) (PAIT) Program for the Advancement of Industrial Technology (5) Federal Sales Tax -- Exemption/ Reduction (6) Customs Incentives (7) Tariff Relief -- Manufacturers (8) Dies and Moulds (9) Duty Drawbacks (10) Defence Production {a) (DIR) Defence Industrial Research {b) Defence Development Sharing Program (11) National Design Program (12) {BEAM) Building, Equipment, Accessories and Materials .Q.!!!~R 1.Q. l!!f I!!!l! I f.!:. A!! (1) EQUALIZATION OF INDUSTRIAL OPPORTUNITY The Development Bureau of the City of Thunder Bay is prepared to assist any finn seeking participation in any of these incentive plans. �* 2* (IRDIA) INDUSTRIAL RESEARCH AND DEVELOPMENT INCENTIVES ACT Initiated March 1967. Taxable Canadian Corporations may apply for cash grants or credits against federal income tax equal to 25% of -(a) All capital expenditures (other than for land) incurred in the past fiscal year on research and development carried out ·1n Canada; and (b) The increase in current expenditures in Canada for scientific research and development over the average of such expenditures in the preceding 5 years. Grants made under the Act are not subject to Federal income tax and are in addition to the normal 100% deduction of all expenditures for scientific research under the Income Tax Act. For details write: IRDIA Department of Industry Ottawa 4, Ontario INCOME TAX ALLOWANCES Under Section 72 of the Federal Income Tax Act a corporation may deduct from its income all expenditures of a current nature made in Canada for scientific research and all expenditures of a capital nature (for the acquisition of property other than land) for scientific research, in the year in which they were incurred. In some cases, expenditures to develop, test and evaluate a prototype are considered as scientific research expenditures. (IRAP} INDUSTRIAL RESEARCH ASSISTANCE PROGRAM Program was initiated in 1962 by National Research Council. Assistance is in the fonn of grants on a 50-50 basis with industry, primarily for applied research and development up to, but not including, pre-engineering preparation for production. Financial assistance is concentrated mainly of relatively long tenn research through the establishment of new industrial research teams or the expansion of existing research groups. Conmercial security of industrial projects is,maintained and all title and rights to research results are retained by industry. For details, contact Secretary, NRC Comnittee on Industrial Research Assistance National Research Council Ottawa, Ontario �* 3* {PAIT) PROGRAM FOR THE ADVANCEMENT OF INDUSTRIAL TECHNOLOGY Direct financial assistance, administered by the Department of Industry, to stimulate sound industrial growth through the application of· science and technology and upgrade technology and innovation in industry activity by underwriting specific development projects which involve a significant advance and if successful, offer good prospects for coRlllercial exploitation. Under the program, for Canadian companies undertaking development projects, the Department can share up to 50% of the cost of special equipment and prototypes. When the projects have been successfully put into colTlllercial use, the company will be required to repay the Department's contribution with interest, on an arranged basis. If the project is not commercially successful, the Department's contribution need not be repaid. For details contact PAIT Program Office Department of Industry Ottawa, Ontario FEDERAL SALES TAX EXEMPTION/REDUCTION Effective March 30, 1966, the following are exempt from federal sales tax when for use by manufacturers or producers directly in the manufacture or production of goods. (a) Dies, jigs, fixtures and moulds Patterns for dies, jigs, fixtures and moulds (c) Tools for use in or attachment to production machinery that a_re for working materials by turning, milling, grinding, polishing, drilling, punching, boring, shaping, shearing, pressing or planing. (b) Effective June 2, 1967 the federal sales tax was removed on machinery and apparatus sold to or imported by manufacture or production of goods. CUSTOM INCENTIVES Canadian customs legislation contains a number of concessions favourable to domestic manufacturing activity - including (a) Tariff Relief With the intention of encouraging processing operations in Canada, certain items may be imported duty free if used in the manufacture of merchandise in Canada. The Minister of Finance can also authorize certain reductions in duty on a temporary basis. �*4 ~ (b) Dies, Moulds Authority may be obtained to import into Canada on a temporary basis for a maximum of 12 months, plant equipment such as dies, moulds, patterns, and related jigs and fixtures, paying·duty in Canada, subject to a minimum $25.00 per entry. (c) Duty Drawbacks The customs Tariff includes several drawback items which permit the return of duty to the importer when materials, machinery or equipment are applied to specified uses. In addition, drawback provisions also apply in the case of goods imported for further processing in Canada and reexported. In such circumstances, a 99% duty drawback is nonnally available. DEFENCE PRODUCTION (a) (DIR) DEFENCE INDUSTRIAL RESEARCH Research projects are aided by the Defence Research Board to ensure no such worthwhile projects are abandoned through lack of funds. (b) DEFENCE DEVELOPMENT SMARING PROGRAM Encourages developments which have commercial defence export potential and is administered by the Department of Industry. NATIONAL DESIGN PROGRAM products. The object is to promote the improvement of design of Canadian This is achieved by clinics and selection of well-designed products on which awards are made. Also in co-operation with industry encouragement is given in the fonn of scholarships and exhibitions to designing new products by professionals. (BEAM) BUILDING EQUIPMENT, ACCESSORIES AND MATERIALS Fonnulated by the Department of Industry, the program, in conjunction with the building equipment industry encourages increased productivity, efficiency, exchange of information, the adoption of modular co-ordination in the manufacture of building material, and the adoption of universal building codes. Further infonnation The Director Materials Branch Department of Industry Ottawa, Ontario �• M I D - C A NA D A D E V E L O P ME N T f. o .B.ftlQQft -C -O -N -C -E.-P -T The first Conference to investigate the feasibility of developing another coast-to-coast strip of land in Canada's Mid-North took place at Lakehead University, Thunder Bay, August 18 - 22, 1969. This first step is a long-tenn plan of development to open up vast, inhabitable but untapped, potentially rich natural resources. Problems are being attacked in a systematic manner and long-held ideas that extracting the northern natural resources economica)ly was impossible are being rapidly discarded. One hundred twenty-five industrialists, economists, and academics discussed and argued the pros and cons of the initial concept at this week-long conference. Since then, members assigned to special Task Forces have spent 60,000 man-hours travelling 1,000,000 man-miles travelling and examining the 4,000 mile arc stretching from coast to coast and 200 500 miles wide, and known as the "boreal forest" of Canada. Officials have also visited Scandinavia and the Soviet Union gathering information for further research. A final Report of the Conference and travels is now prepared and in the hands of the Federal and Provincial Governments. No ready-made answers are forthcoming but step by step . progress is being made. The plan is long ter111 -- aiming at the need in the year 2000 for more space to settle an ever increasing population demanding job opportunities and the necessities of life. THUNDER BAY, being the only city in the entire corridor, stands to gain substantially from the initiation of this pioneering effort. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource An Invitation To Explore Thunder Bay Subject The topic of the resource Business and Industry Description An account of the resource Information package about Thunder Bay, to promote the new city for business and development. Created by the Development Bureau of the City of Thunder Bay, likely 1970. Creator An entity primarily responsible for making the resource City of Thunder Bay Date A point or period of time associated with an event in the lifecycle of the resource 1970 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Type The nature or genre of the resource Text Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay https://digitalcollections.lakeheadu.ca/files/original/17967a5471c388ac8165c4ea7dab0dd8.pdf d5b577d19281c16f6266aad8e4c17755 PDF Text Text BAY --GREATEST GRAIN PORT ---- --- - 11! THE WORLD - -- --- The statistics outlined on the attached sheets are a condensation of the almost, overwhelming data, required to describe the movement of grain out of Canad~ via the Seaport of Thunder Bay. The iize of ships, particularly bulk carriers, used on the Great Lakes is only_ deter-mined by the size of the canal locks at Welland and St. Lawrence River. · New ships on the Upper Great Lakes using only the Sault Ste. Mar.ie Locks ·will be 1000 feet long and wi 11 carry iron ore to_U. S.. furnaces in Chi c~go ~nd area . . Canada has set her sights on producing and exporting a billion bushels of assorted grains. This ·will be approximately a 25% increase over current production. When it is visualized this is a bulk-food product, the aim is st~ggering in its potential. 50,00"0,000 tons of grain moving overseas to -hungry people will not only have a great impact on the h~alth of all countries, but, will require massive mobilization of finances, scheduling and control of v·ehicles such as_ rail cars, ships, ·storage fac•i 1i ti es," etc. Thunder Bay's facilities are not presently overtaxed. Current put~through 'is being handled on a 5½-day week. basis, one · shift. lhcreasing the shifts even to two per day, 7 days a week will still not tax the working capacity. The greatest delay factor remains with obtaining sufficient rail cars to transport the grain upwards of 1000 miles from the Prairies to the Terminal Elevators, and the availability of sufficient ships, at the right time. (cont'd) �. ,/ .... 2 Canada is also exploring the possibility of keeping the Great Lakes and Seaway open for longer periods during the winter. The 1971 Shipping Season was extended to January 3, 1972, when the last ship left. I Ice conditions are not heavy at this time as the deeper build-up has not occurred. Perhaps in the · immediate future, the season can be extended to the end -of January -- making 10·-month shipping possible. Bubblers at docks, huge icebreaking ships and control of Canal gates are a necessity. Grain is the major commodity transported out of Thunder Bay, but the Port also currently handles massive bulk quantities of iron ore and pellets, potash, coal and oil. In addition, Keefer Terminal, the western end of the Seaway ·handles many shiploads • of general cargo moving east and west for Canadian and overseas destinations. Approximately 300,000 square feet of covered warehousing is provided· for transfer of goods by rail, truck or water. Thunder Bay, the Po~t City, in the .exact geographic centre of Canada -- and the continent --- has a population of 111,000 and services a land area of 255,000 square miles in Northwestern · Ontario, a vertiable empire of unspoiled recreati6nal and undeveloped natural resource potential. PREPARED BY: DEVELOPMENT BUREAU OF THE CITY OF THUNDER BAY �GRA-I -N TOTAL 1971 SHIPPING S T AT I S T I C S ---------- 540,725,000 Bushels ********** ********** EMPLOYEES - ELEVATORS 1971 ********** ********** 1500-1600 ********** ********** 65 Hopper cars in unit train carries 186,260 bushels wheat Thunder Bay Quebec City in two days. 10,000,000 bushels carried by unit train in 1972 ********** ********** ********** One of two highest seaports in World at 601 feet, sharing honour with Duluth-Superior. ********** ********** ********** 1970 - 1971 CROP YEAR -- AUGUST 1 - AUGUST 1 SHrPMENTS FROM COUNTRY ELEVATORS -- 815.9 Million Bushels Barley Flax Rapeseed Wheat Oats Rye 222 Mill ion 29 Mi 11 ion 49 Million -- 460 Million 44 Mill ion 1O Mi 11 ion Bushels Bushels Bushels Bushels Bushels Bushels MOVED TO THUNDER BAY -- 477 Million Bushels (58.5%) MOVED TO PACIFIC COAST -.:. 429 Million Bushels (30.6%) MOVED TO CHURCHILL -- 21 .2 Million Bushels ( 2.6%) MOVED TO OTHER -- 67 Mil 1ion Bushels ( 8.3%) ********** ********** ********** 9,000 Grain cars a week at 125 cars per train requires -- 70 full trains and 70 empties ********** ********** ********** �G'RAIN STATISTICS (CONT'D) 24 TERMINAL ELEVATORS 7 On Kaministiquia River 17 On Lakefront RATED CAPACITY -- 105,376,400 Bushels Saskatchewan Pool #7 has 9 Million Bushels Capa~ity UNLOADING CAPACITY -- 8 hours 1421 cars SHIPPING CAPACITY -- 8 hours 10,134,000 bushels ********** ********** ********** 1970 - 1971 CROP YEAR -- AUGUST l - AUGUST 1. VESSEL SHIPMENTS FROM: THUNDER BAY~- 498.5 Million Bushels DIRECT OVERSEAS (SALTIES) Inc. above 42.5 Million Bushels SHIPMENTS FROM: PACIFIC COAST 269.6 Million Bushels CHURCHILL 23.4 Million Bushels DOMESTIC USE 217 Million Bushels ********** ********** ********** A farm yield of 51,000 acres requir~d to produce a million bushels cargo - 5 trains totalling 566 cars required to transport this· grain .- 1 lake freighter 730 feet long 75 feet wide will take a million bushels ********** ********** ********** ********** ********** COST OF ALL WATER TRANSPORT 9¢ - 12¢ Bushel COST OF ALL RAIL TRANSPORT 20¢ Bushel ********** �GRAIN STATISTICS (CONT'D) ASSESSMENT OF ELEVATORS -- Approximately $20 Million CITY TAXES PAID ON ASSESSMENT -- Approximately $2 - $3 Million WAGES PAID TERMINAL ELEVATORS -- Approximately $10 Million WAGES PAID RAILWAY EMPLOYEES -- Approximately $6 Million WAGES PAID IN SERVICE INDUSTRIES -- Approximately $4 - $5 Million • ********** ********** ********** THUNDER BAY HARBOUR -- RECORD SHIPPING YEARS 1966 1967 1968 1969 1970 ** 1971 -- 19,503,923 Tons -- 15,629,208 -- 13,201 ,770 13,604,854 20,779,767 II II II II -- 22,164,923 II (RECORD) ** INCLUDES: 15,461,077 Tons -- Grain 4,814,190 Tons 598,277 Tons Iron Ore General Cargo 211,210 Tons-~ Newsprint 1403 Vessels required to move cargo 1971 SHIPPING SEA?ON -- April 10, 1971 - January 3, 1972 TOTAL SHIPPING -- 54Q,725,000 Bushels ********** ********** .********** � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay: Greatest Grain Port In The World Subject The topic of the resource Business and Industry Description An account of the resource Information package on grain shipment out of the Port of Thunder Bay. Prepared by the Development Bureau, City of Thunder Bay, likely 1972. Creator An entity primarily responsible for making the resource City of Thunder Bay Date A point or period of time associated with an event in the lifecycle of the resource 1972 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Type The nature or genre of the resource Text https://digitalcollections.lakeheadu.ca/files/original/724806812bf3d046c67dfa019bfcb246.pdf 8ff18baf3e0b5cd5f1c62cb64fddac52 PDF Text Text �Thunder Bay, Ontario, Canada THE CANADIAN LAKEHEAD The City of Thunder Bay originated, January 1, 1970, and became the eighth largest city in the Province of Ontario with a CMA population of 111,492, residing in 155 square miles of city area. The City of Thunder Bay was formed by the merging of the two larger Cities of Port Arthur and Fort William and parts of the surrounding Townships of Neebing and McIntyre. All the mechanical adjustments of intregating the communities were quickly resolved. The Ontario Design for Development of Northwestern Ontario names the City of Thunder Bay as a "Primate Centre" for development, and this is being forcefully carried out, but the City has not forgotten its historic beginning. Back in the fur trading era of 1678, it was a trans-shipping point of furs and trading goods. The famous Voyageurs used Fort Kaministiquia at Fort William as a strategic turnaround. Later, with the opening of the lakes to sailing and motorized vessels, bulk goods commenced flowing across the land, until today, Thunder Bay, or the Lakehead as the area is known, is the 3rd largest seaport in Canada. Grain as well as natural resources including iron, coal, potash and paper, contribute greatly to the 20,000,000 tonnage flowing in and out of the huge, protected harbour on the top step of the St. Lawrence - Great Lakes Seaway, almost 2,000 miles from the sea. Being in almost the exact geographic centre of a continent, Thunder Bay is the connecting link in Canada for east and west trade, Water, rail, road and air services converge at this point to provide unequalled transport to any place on the continent, or in the world. Thunder Bay is the distribution capital of a vast area of Northwestern Ontario, rich in natural resources, including forestry products, minerals and tourist facilities. From these natural resources has grown an industrial complex comprised of pulp and paper companies, mines, and in addition a large flourishing tourist establishment serving an increasing number of world-wide visitors. Secondary industry has grown around these primary industries to produce harvesting equipment for the forests and mines. Service industries supply facilities for shipping, transportation and the accommodation trade, etc. There are currently 108 secondary industries flourishing in Thunder Bay and numerous service industries as well. The City has been chosen as the focal point - the centre of the projected development of the Mid-Canada Development Corridor Concept. This plan visualizes development in future years of a 200-mile wide corridor across Canada, north of the present developed areas. Thunder Bay is the only city in the corridor. Thunder Bay is blessed with an unpolluted environment, with modern living accommodation and a growing educational complex. The city boasts unparalleled entertainment and relaxed recreational opportunities. Thousands of lakes are nearby in almost virgin territory. Huge Lake Superior, the largest fresh water lake in the world, not only provides abundant water for consumption, but carries the largest ships on the Great Lakes. In addition, it tempers the climate of the city in all seasons. Government in Canada is notably stable and the Province of Ontario has the most progressive economy in Canada. The City of Thunder Bay enjoys a solid, imaginative, elected Council governing a growth area with vast potential. INDUSTRY INCENTIVE GRANTS Thunder Bay has been chosen a growth centre and secondary industry, particularly, is entitled to share in cash grants up to $12,000,000 offered by the Federal Department of Regional Economic Expansion. In addition, the Province of Ontario cooperates in supplementing Federal assistance where feasible, by offering cash grants up to $500,000 under what is known as "Performance Loans''. The Northern Ontario Development Corpo- ration, through an office in Thunder Bay, administers grants for the Northwestern Ontario area. It will assist industry with all forms of financing, advice, including ''bridge financing" up to $500,000 at current interest, where applicable. Enquiries under the Federal or Ontario Incentive Grant systems can be directed to the Development Bureau of the City of Thunder Bay, 193 Arthur Street, Postal Station P, Thunder Bay, Ontario. �GEOGRAPHICAL LOCATION Situated on the north shore of Lake Superior, THUNDER BAY is in the exact centre of Canada, at the western terminus of the St. Lawrence - Great Lakes Deep Waterway, and a transportation point astride national rail, road, air and water routes. Toronto (water) . ... 903 road 865 Miles Montreal (water) . . 1212 road 1039 Miles Chicago (water) .. .. 686 road 692 Miles road 335 Miles Minneapolis ........ .. road 450 Miles Winnipeg ......... ... .. Sault Ste. Marie (water) .. .. .. .... .. 273 road 445 Miles Altitude - Harbour-601 ft. above sea level. MUNICIPAL SERVICES Police - 2 stations, 143 personnel, 22 radio equipped cars, rescue equipment, boats Provincial Police - District Headquarters, full staff, vehicle equipped, radio controlled area Harbour Police - Staff - launch Railway Police - CNR-CPR Staff Fire Protection - 6 stations, 143 personnel Sewage Disposal - 2 primary plants, 7,500,000 gallons daily Streets - 410 miles; Provincial Highways 36 miles; Sidewalks - 165 miles; Watermains 290 miles; Sewers - 220 miles sanitary, 46 miles storm. Water Unlimited supply of pure, clean water available through City Utilities. Pumping capacity 31,500,000 gallons daily Zoning By-Law - Official Planning Act; Urban Renewal underway POPULATION Thunder Bay (CMA 1971) ............ Thunder Bay District Market Area Forecasts (City) 1973 .. ... .. ... .. .. .. 1978 ................ 1988 ................ 2000 .. ..... ... ... .. . '{. I • 111,492 148,993 118,100 129,300 151,000 201,800 TRANSPORTATION Road 11 Highway Transport Companies 5 National Moving Van and Storage 2 Motor Bus Companies Air - Served by Thunder Bay Airport: - Air Canada - North Central - ON-Air - Superior Airways Ltd. - Trans Air Rail - Canadian National Railway - Canadian Pacific Railway Water Keefer Lakehead Terminal - Valley Camp Coal & Ore Dock - C.N.R. Ore Dock City Transit - 20 Electric Buses 17 Gas Buses - 20 Diesel Buses - 5,368,407 passengers in 1970 PROFESSIONAL SERVICES Accountants 16; Architects & Engineers 5; Contractors - General 62; Dentists 41; Engineers 19; Lawyers 52; Optometrists 6; Physicians & Surgeons 116; Surveyors 4; Veterinary Surgeons 4. EDUCATIONAL FACILITIES Lakehead University with a modern building complex situated on a 300-acre campus offers degrees and diplomas in Arts and Sciences, Forestry, Engineering and Business Administration, to 3,000 full time and 3,000 part time students. Confederation College of Applied Arts and Technology situated on a new 130-acre campus educates 3,500 full and part time students to attain proficiency in two and three year diploma courses. Adult retraining provides upgrading in modern industrial techniques. UTILITIES NATURAL GAS Electric Power - lowest cost, high voltage hydro available from Ontario Hydro Electric Commission, 1 distributed by Thunder Bay Hydro Electric ' Commission. Natural Gas - Distributed by Twin City Gas Co. Ltd. direct from Trans Canada Pipeline running through area. Cost is very low due to proximity of western source. Annual volume 12,305,000 MCF. �COMMUNITY LIVING CONDITIONS MARKET Hospitals - 7 Churches - 104 Financial Institutions - 47 Households - 28,691 Libraries 5 Newspapers - 2 dailies, 2 weekly Medical Clinics - 11 Telephones - 58,711 Theatres - 4 plus 1 outdoor Golf Courses - 5 Curling Rinks - 4 Tennis Courts - 3 Ski Areas - 6 Swimming Pools - 4 indoor heated, 5 outdoor, 2 hotel indoor, 1 health pool-gym Hockey Rinks - 5 artificial ice, covered, 100 natu ra I ice Radio & TV - 3 AM Radio, 1 FM Radio, 1 TV (CBC) local, 3 U.S., 3 Educational chan. cable TV Hotels - Motels - 64 with 1916 rooms, daily accommodation 4178 guests Population growth rate per decade 11% Income above National average 17% Market above National average 14% Average Income $6,246 Retail Sales - City $162.5 million Retail Sales - Dist. Area $304.1 million INDUSTRIAL LAND 119 acres private serviced land 1390 acres private unserviced land 160 acres city owned serviced land 716 acres city owned unserviced land 2385 acres total Serviced land with water, sewer, and utilities is priced at $40 front footage, up Unserviced land priced at $10 front footage, up or can be leased There are 7 industrial parks under active development at present. MUNICIPAL TAXES Industrial - Commercial Fort William Ward Public School 133.13 mills Fort William Ward Separate School 133.00 mills Port Arthur Ward Public School 111.92 mills Port Arthur Ward Separate School 115.23 mills McIntyre Ward Public School 106.62 mills McIntyre Ward Separate School 99.22 mills Neebing Ward Public School 93.13 mills Neebing Ward Separate School 89.21 mills NOTE: Differing tax rates and assessment methods will continue until assessment on basis of market value becomes effective. Basis of current industrial assessment - Land - 50 % per acre value Building - 30 - 35 % replacement Average industrial real estate tax 25c per square foot. CURRENT INDUSTRIAL PRODUCTION . Some of the local manufactured products: railway and subway cars trailers dust control systems newsprint stainless steel equipment kraft stock fibre and plastic bags starch sodium hypochlorite gluten steel door frames prefab homes ~ aircraft components lumber grey iron castings poles liquid alu. sulphate railway ties glazed fine papers tar products fourdrinier wire sleeping bags conveying buckets trailer tents boilers caustic chlorine barley malt camper trailers fish processing logging skidders lockers brick and tile chlorine fibreglas pipe beer -- ale teen clothing forest harvesters ENTERTAINMENT AND SPORTS Lakehead Symphony and Jr. Symphony 3 Pipe Bands, 1 City Band, numerous school bands Cambrian Players amateur theatricals Famous 40 member Male Choir Sports car racing - summer and winter Annual Exhibition Jr. and Sr. Hockey - peewees and midgets Fastball - Baseball Service Clubs - 10 Fraternal Organizations - 42 Night-Clubs - Hotels & Motels - 10 TEMPERATURES June 1 - October 31 the climate is pleasant and mild; humid days are exceedingly rare. The area is a haven for hay fever sufferers. Normal summer mean temp. (June-July-Aug.) 60.9 degrees above. Normal winter mean temp. (Dec.-Jan.-Feb.) 10.2 degrees above. Highest recorded temp. 104 degrees above, lowest 42 degrees below. Average annual snowfall 75 in. Average annual rainfall 27 in. �CITY OF THUNDER BAY (FORMERLY PORT ARTHUR-FORT WILLIAM) ONTARIO, CANADA '/4 0 LEGEND D D D COMMERCIAL AREAS ~ 10-15 YEAR URBAN RENEWAL ESTABLISHED HEAVY -LIGHT INDUSTRY INDUSTRIAL PARKS AND AVAILABLE INDUSTRIAL AREA �� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay: Centre of a Continent Subject The topic of the resource Business and Industry Description An account of the resource Brochure encouraging industry to locate in Thunder Bay. No creator attribution; probably 1970. Date A point or period of time associated with an event in the lifecycle of the resource 1970 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Type The nature or genre of the resource Text Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay https://digitalcollections.lakeheadu.ca/files/original/18fd51ee65642289cfb33fc14030102e.pdf 71db64055c86846756ee627afe76f091 PDF Text Text 70th Annual Meeting Institute on Lake Superior Geology Houghton, Michigan May 15-18, 2024 Proceedings Volume 70 Part 1 - Program and Abstracts �70th Annual Meeting Institute on Lake Superior Geology Houghton, Michigan May 15-18, 2024 Sponsored by: A. E. Seaman Mineral Museum Great Lakes Research Center Department of Geological and Mining Engineering and Sciences Michigan Technological University Meeting Co-Chairs Theodore J. Bornhorst, Erika C. Vye, Patrice Cobin, and James DeGraff Proceedings Volume 70 Part 1: Program and Abstracts Edited by Theodore J. Bornhorst and Erika C. Vye Cover Photo: The only known color photograph of in situ colorless calcite crystals with inclusions of native copper. Vug is about 15 cm across and 30 cm deep; located at the top of the Knowlton basalt lava flow at the 4 th level, 850 ft stope, of the Caledonia Mine, Michigan. Photo taken in 1994 soon after the vug was blasted open. Native copper in the calcite crystals has not been visibly altered despite being about 1 billion years old. Photograph by Theodore J. Bornhorst i �70th Institute on Lake Superior Geology Volume 70 consists of: Part 1: Program and Abstracts Part 2: Field Trip Guidebook Trip 1: Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Trip 2: Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan Trip 3: Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty Trip 4: Keweenaw Fault System Geometry and Kinematics: Clues to Its Nature and Origin Trip 5: Geology and History of a Native Copper Mine: Adventure Mine, Ontonagon County, Michigan Trip 6: Southern Complex Granitoids, Gneisses, and Migmatites: New Data, Discoveries, and Perspectives Trip 7: Landslides on the Ontonagon River at Military Hill Reference to material in Part 2 should follow the example below: Authors, 2024, Field Trip title, 70th Institute on Lake Superior Geology, Abstracts and Proceedings, v. 70, Part 2, Field Trip Guidebook, p. xx-xx. Proceedings Volume 70, Part 1: Program and Abstracts and Part 2: Field Trip Guidebook are published by the 70th Institute on Lake Superior Geology and distributed by the Institute Secretary: Peter Hollings Department of Geology Lakehead University Thunder Bay, ON P7B 5E1 CANADA peter.hollings@lakeheadu.ca Some figures in this volume were submitted by authors in color but are printed black and white. Full color imagery will appear in the digital version of the volume when it is available on-line at: http://www.lakesuperiorgeology.org ISSN 1042-99 ii �Part 1: Program and Abstracts Table of Contents Institutes on Lake Superior Geology, 1955-2024 ............................................................. iv Sam Goldich and the Goldich Medal ............................................................................... vii Goldich Medal Guidelines ................................................................................................ ix Goldich Medalists ............................................................................................................. xi 2024 Goldich Medal Recipient ......................................................................................... xi Goldich Medal Committee ............................................................................................... xi Citation for 2024 Goldich Medal Recipient..................................................................... xii Honoring the Pioneers of Lake Superior Geology……………………………………….xiv Citation for 2024 Pioneer of Lake Superior Geology Recipient………………………...xv In Memoriam……………………………………………………………………………xix Eisenbrey Student Travel Awards ................................................................................... xx Joe Mancuso Student Research Award ........................................................................... xxi Doug Duskin Student Paper Awards and 2024 Student Paper Awards Committee ...... xxii Board of Directors and 2024 ILSG Meeting Volunteers .............................................. xxiii 2024 ILSG Meeting Volunteers and Session Chairs…………………………………..xxiv Field Trip Leaders and Guidebook Authors .................................................................. xxv Banquet Speaker Robert M Hazen ................................................................................ xxvi Report of the Chair of the 69th Annual Meeting ........................................................ xxvii Sponsors ........................................................................................................................ xxxi Technical Program ....................................................................................................... xxxii Abstracts ........................................................................................................................ xliii iii �Institutes on Lake Superior Geology, 1955-2024 # Date Place Chairs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Houghton, Michigan Duluth, Minnesota Ishpeming, Michigan St. Paul, Minnesota Sault Ste. Marie, Michigan East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Michigan St. Paul, Minnesota Thunder Bay, Ontario C.E. Dutton A.K. Snelgrove B.T. Sandefur R.W. Marsden G.M. Schwartz & C. Craddock E.N. Cameron E.G. Pye A.K. Snelgrove H. Lepp A.T. Broderick P.K. Sims & R.K. Hogberg R.W. White W.J. Hinze A.B. Dickas G.L. LaBerge M.W. Bartley & E. Mercy D.M. Davidson J. Kalliokoski M.E. Ostrom P.E. Giblin J.D. Hughes M. Walton M.M. Kehlenbeck iv �# 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Date 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Place Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Cable, Wisconsin Sudbury, Ontario Minneapolis, Minnesota Marquette, Michigan Thunder Bay, Ontario Madison, Wisconsin Kenora, Ontario Iron Mountain, Michigan Duluth, Minnesota Nipigon, Ontario Sault Ste. Marie, Ontario Lutsen, Minnesota Marquette, Michigan Ely, Minnesota International Falls, Minnesota 57 58 59 60 61 62 63 64 65 66 67 68 69 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 Ashland, Wisconsin Thunder Bay, Ontario Houghton, Michigan Hibbing, Minnesota Dryden, Ontario Duluth, Minnesota Wawa, Ontario Iron Mountain, Michigan Terrace Bay, Ontario Meeting cancelled Virtual meeting Sudbury, Ontario Eau Claire, Wisconsin v Chairs G. Mursky D.M. Davidson P.E. Myers W.C. Cambray D.L. Southwick T.J. Bornhorst G.L. LaBerge C.E. Blackburn J.K. Greenberg E.D. Frey & R.P. Sage J. S. Klasner J.C. Green M.M. Kehlenbeck P.E. Myers A.B. Dickas D.L. Southwick T.J. Bornhorst M.C. Smyk L.G. Woodruff R.P. Sage & W. Meyer J.D. Miller & M.A. Jirsa T.J. Bornhorst & R.S. Regis S.A. Kissin & P. Fralick M.G. Mudrey & Jr., B.A. Brown P. Hinz & R.C. Beard L. Woodruff & W.F. Cannon S. Hauck & M. Severson M. Smyk & P. Hollings A. Wilson & R. Sage L. Woodruff & J. Miller T.J. Bornhorst & J. Klasner J. Miller, G. Hudak, D. Peterson M. Jirsa, P. Hollings & T. Boerboom, P. Hinz & M.Smyk T. Fitz P. Hollings T.J. Bornhorst & A. Blaske J. Miller & M. Jirsa R. Cundari & P. Hinz J. Miller, C. Schardt & D. Peterson A. Pace, A. Wilson & T.J. Bornhorst L. Woodruff, W. Cannon & E.K. Stewart P. Hollings & M.C. Smyk Cancelled by the COVID-19 pandemic M. Jirsa, M. Smyk & P. Hollings R.M. Easton & W. Bleeker R. Lodge, E.K. Stewart, & C. Ames �# 70 Date Place 2024 Houghton, Michigan Chairs T.J. Bornhorst, E. Vye, P. Cobin, & J. DeGraff vi �Sam Goldich and the Goldich Medal Sam Goldich received an A.B. from the University of Minnesota in 1929, a M.A. from Syracuse University in 1930, and a Ph.D. from the University of Minnesota in 1936. During World War II Sam worked for the U.S. Geological Survey in mineral exploration. In 1948, Sam returned to the University of Minnesota, and became Professor and Director of the Rock Analysis Laboratory the following year. He rejoined the U.S. Geological Survey in 1959 and was appointed as the first Branch Chief of the Branch of Isotope Geology. Sam returned to academia in 1964 when he went to Pennsylvania State University. He left PSU in 1965 and moved to the State University of New York at Stony Brook, where he stayed for 3 years. Restless yet again, he moved to Northern Illinois University in 1968 where he was a professor until his retirement in 1977. Sam’s final move was to Denver where he became an emeritus at the Colorado School of Mines. Sam died in 2000, less than a month before his 92nd birthday. In the late 1970s, Geological Society of America Special Paper 182, which included seminal geochronological studies by Sam Goldich and coworkers on the Archean rocks of the Minnesota River Valley, was nearing completion. At this time various ILSG regulars began discussing the possibility of recognizing Sam for his pioneering work on the resolution of age relationships and thus the geology of Precambrian rocks in the Lake Superior region. Three members, R.W. Ojakangas, J.O. Kalliokoski, and G.B. Morey, presented the idea to the ILSG Board of Directors in 1978. The Board approved the creation of an award, provided funding could be obtained. It was suggested that collecting one or two dollars at registration for a dedicated account would provide resources for striking the medal. A general request was made to the ILSG membership for donations and Sam himself offered a challenge grant to match the contributions. In total, $4,000 was collected and thus began the work of creating the Goldich Medal. The initial Goldich Award was presented to Sam by G.B. Morey in 1979 and consisted of a large paper proclamation. For the actual medal, G.B. Morey consulted with the foundry on production details, while Dick Ojakangas and Jorma Kalliokoski worked on the design of the award, suggesting that it be given for “outstanding contributions to the geology of the Lake Superior region.” Simultaneously, a committee of J.O. Kalliokoski, W.F. Cannon, M.M Kehlenbeck, G.B. Morey, and G. Mursky developed the Award Guidelines that were approved by the ILSG Board. By 1981 all the elements of the Goldich Award had come together, and the second recipient, Carl E. Dutton, Jr., received the Goldich Medal for 50 years of significant contributions to the understanding of the geology of the Lake Superior region. Since the beginning, the Awards Committee has consisted of individuals representing industry, government and academia, with each member of the Committee serving for three years. The medal is now awarded every year at the annual ILSG meeting. Reference: Morey, G.B. and Hanson, G.N. (editors). 1980. Selected studies of Archean gneisses and Lower Proterozoic rocks, southern Canadian Shield. Geological Society of America, Special Paper 182, 175 p. Prepared by various Goldich Medal Awardees, 2007 vii �INSTITUTE ON LAKE SUPERIOR GEOLOGY GOLDICH MEDAL viii �Goldich Medal Guidelines (Adopted by the Board of Directors, 1981; amended 1999) Preamble The Institute on Lake Superior Geology was born in 1955, as documented by the fact that the 27th annual meeting was held in 1981. The Institute’s continuing objectives are to deal with those aspects of geology that are related geographically to Lake Superior; to encourage the discussion of subjects and sponsoring field trips that will bring together geologists from academia, government surveys, and industry; and to maintain an informal but highly effective mode of operation. During the course of its existence, the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the ILSG by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the understanding of Lake Superior geology and mineral deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Subsequent medalists and this year’s recipient are listed in the table below. Award Guidelines 1) The medal shall be awarded annually by the ILSG Board of Directors to a geologist whose name is associated with a substantial interest in, and contribution to, the geology of the Lake Superior region. 2) The Board of Directors shall appoint the Goldich Medal Committee. The initial appointment will be of three members, one to serve for three years, one for two years, and one for one year. The member with the briefest incumbency shall be chair of the Nominating Committee. After the first year, the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In his/her third year this member shall be the chair. The Committee membership should reflect the main fields of interest and geographic distribution of ILSG membership. The out-going, senior member of the Board of Directors shall act as liaison between the Board and the Committee for a period of one year. 3) By the end of November, the Goldich Medal Committee shall make its recommendation to the Chair of the Board of Directors, who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, inform the medalist, and have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. ix �Nominating Procedures 1) The deadline for nominations is November 1. Nominations shall be taken at any time by the Goldich Medal Committee. Committee members may themselves nominate candidates; however, Board members may not solicit for or support individual nominees. 2) Nominations must be in writing and supported by appropriate documentation such as letters of recommendation, lists of publications, curriculum vita’s, and evidence of contributions to Lake Superior geology and to the Institute. 3) Nominations are not restricted to Institute attendees but are open to anyone who has worked on and contributed to the understanding of Lake Superior geology. Selection Guidelines 1) Nominees are to be evaluated on the basis of their contributions to Lake Superior geology (sensu lato) including: a) importance of relevant publications; b) promotion of discovery and utilization of natural resources; c) contributions to understanding of the natural history and environment of the region; d) generation of new ideas and concepts; and e) contributions to the training and education of geoscientists and the public. 2) Nominees are to be evaluated on their contributions to the Institute as demonstrated by attendance at Institute meetings, presentation of talks and posters, and service on Institute boards, committees, and field trips. 3) The relative weights given to each of the foregoing criteria must remain flexible and at the discretion of the Committee members. 4) There are several points to be considered by the Goldich Medal Committee: a) An attempt should be made to maintain a balance of medal recipients from each of the three estates—industry, academia, and government. b) It must be noted that industry geoscientists are at a disadvantage in that much of their work in not published. 5) Lake Superior has two sides, one the U.S., and the other Canada. This is undoubtedly one of the Institute’s great strengths and should be nurtured by equitable recognition of excellence in both countries. x �Goldich Medalists 1979 Samuel S. Goldich 1998 Zell Peterman 2016 Mark A. Jirsa 1980 not awarded 1999 Tsu-Ming Han 2017 Philip Fralick 1981 Carl E. Dutton, Jr 2000 John C. Green 1982 Ralph W. Marsden 2001 John S. Klasner 2018 Val W. Chandler 2019 Mark Severson 1983 Burton Boyum 2002 Ernest K. Lehmann 2020 not awarded 1984 Richard W. Ojakangas 2003 Klaus J. Schulz 2021 Alan MacTavish 1985 Paul K. Sims 2004 Paul Weiblen 2022 Terrence J. Boerboom 1986 G.B. Morey 2005 Mark Smyk 2023 Peter Hollings 1987 Henry H. Halls 2006 Michael G. Mudrey 2024 Suzanne W. Nicholson 1988 Walter S. White 2007 Joseph Mancuso 1989 Jorma Kalliokoski 2008 Theodore J. Bornhorst 1990 Kenneth C. Card 2009 L. Gordon Medaris, Jr 1991 William Hinze 2010 William D. Addison & 1992 William F. Cannon Gregory R. Brumpton 1993 Donald W. Davis 2011 Dean M. Rossell 1994 Cedric Iverson 2012 James D. Miller 1995 Gene La Berge 2013 Tom Waggoner 1996 David L. Southwick 1997 Ronald P. Sage 2014 Laurel Woodruff 2015 Rodney J. Ikola 2024 GOLDICH MEDAL RECIPIENT Suzanne W. Nicholson Goldich Medal Committee Serving through the meeting year shown in parentheses. Dorothy Campbell (2019-2024) Ontario Geological Survey, Government Member (Committee Chair) Dean Peterson (2022-2025) Big Rock Exploration, Industry Member Marcia Bjornerud (2023-2026) Lakehead University, Academic Member xi �Citation for the 2024 Goldich Medal Recipient Suzanne W. Nicholson It is a pleasure and honor to present the 2024 Goldich Medal to our close friend and colleague, Suzanne Nicholson, recently retired from a long and fruitful career at the U.S. Geological Survey. Suzanne began working for the USGS as a student field assistant in 1978, and then, after completing a master’s degree at the University of Massachusetts, was hired as a full-time employee in 1981. Suzanne’s interest in the geology of the Lake Superior region began with her dissertation work with Paul Weiblen at the University of Minnesota on felsic magmatism in the Portage Lake Volcanics in Michigan, part of the Mesoproterozoic Midcontinent Rift System (MRS). This study included detailed mapping and sampling (typically big samples that had to be carried long distances) followed by major and trace element whole rock analysis and determination of a suite of radiogenic isotopes (Sr, Nd, Pb). Using modern petrologic methods, her research documented the presence of two distinct felsic magma types, one derived by partial melting of felsic basement and the other related to rift basalts through partial melting and/or fractional crystallization. Suzanne also was one of the first to provide comprehensive radiogenic isotope analyses of host basalts, documenting their distinctive isotopic character and that of their mantle sources. Her 1990 seminal publication (Nicholson, S.W., and Shirey, S.B., 1990, Midcontinent Rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin: Journal of Geophysical Research, v. 95, p. 10,85110,868) described the unique geochemical character of rift magmatism around the Lake Superior region. Her on-going interest in MRS geochemistry culminated in the 1997 paper that established a rift-wide correlation of MRS basalts (Nicholson, S.W., Schulz, K.J., Shirey, S.B., and Green, J.B., 1997, Rift-wide correlation of 1.1 Ga Midcontinent Rift System basalts: multiple mantle sources during rift development: Canadian Journal of Earth Sciences, v. 34, p. 504-520), providing a foundation for future interpretations of MRS-related volcanic rock geochemistry. Suzanne was also a leader in advancing an understanding of the spatial-temporal evolution of MRS metallogeny (Nicholson, S.W., Cannon, W.F., and Schulz, K.J., 1992, Metallogeny of the Midcontinent Rift System of North America: Precambrian Research, v. 58, p. 355-386), further refined in a 2020 paper (Woodruff, L.G., Schulz, K.J., Nicholson, S.W., and Dicken, C.L., 2020, Mineral deposits of the Mesoproterozoic Midcontinent Rift system in the Lake Superior region A space and time classification: Ore Geology Reviews, 103716). Along with colleagues from the USGS, Suzanne helped produce a series of 1:100,000-scale geologic maps for the MRS and adjacent rocks from the Keweenaw Peninsula, extending through Michigan into northern Wisconsin to the Minnesota state line. These maps summarized legacy mapping and, along with new fieldwork, resulted in interpretations and correlations that xii �are the current standard for understanding the distribution and origin of the MRS volcanic and intrusive rocks of that area. Suzanne also initiated and continues to lead an on-going cooperative government/academia effort to compile and digitize existing MRS geology, geochemistry, isotope data, and age dates that will promote and direct future research of the region. Throughout her career, Suzanne was a careful and meticulous researcher who held her own results to a very high standard for accuracy, completeness, and thoroughly documented interpretations. Through the years, Suzanne has been a strong supporter of the Institute on Lake Superior Geology. She was a first or co-author on 17 abstracts presented at ILSG meetings from 1990 through 2019, a co-leader for two ILSG field trips, and co-editor for the 1996 Proceedings, Part 1- Program and Abstracts volume. Suzanne also was always willing and able to help with anything needed at ILSG meetings (a common trait among ILSG participants), such as acting as a session chair or serving on the student paper committee. In 2015, Suzanne moved into increasingly responsible managerial positions within the USGS, which curtailed her direct involvement with research in the Lake Superior region. In 2020, she received the U.S. Department of Interior's second highest honorary award—the Meritorious Service Award— in recognition of her scientific leadership and noteworthy contributions to the USGS Mineral Resources Program. Suzanne retired from her position as Associate Program Coordinator for the USGS Mineral Resources Program in 2021 but was retained for 2 years as an annuitant to keep the Program on budgetary track during a time of transition. Her qualities as a scientist transferred to her administrative duties, demonstrating the same dedication and skills she brought to her research. Now that Suzanne’s service to the Program has ended, we look forward to her return to MRSrelated research as a USGS Emeritus scientist. Throughout her managerial tenure, Suzanne never lost her attachment to the Lake Superior region and was able to promote and maintain funding for ongoing regional project work for her USGS colleagues. This support resulted in many new and exciting discoveries, such as tracing the extent and nature of the Sudbury ejecta layer across Michigan and Wisconsin, and tackling legacy seismic data to help understand the tectonicmagmatic evolution of the MRS. Through her thoughtful discussions, critical reviews, cheerful field assistance, and friendship for the past 40-some years, Suzanne helped enrich the lives and careers of many people, including those of her fellow USGS MRS aficionados. We remain a convivial group and all of us look back fondly on the times we spent together in the field. Who could forget death marches across Isle Royale, or raccoons swiping rhyolite samples in the Porcupine Mountains, or six long weeks at the Hurley Holiday Inn, among our many other adventures? So now, the three of us, all former recipients of the Goldich Medal, are joined by Suzanne in that honor. In recognition of her decades of accomplishments and dedication to the geology of the Lake Superior region and to the Institute on Lake Superior Geology, it is our pleasure to present the 2024 Goldich Medal to its second female recipient, Suzanne Nicholson. Citation by: Laurel G. Woodruff, USGS, Goldich Medal Winner, 2014 Klaus J. Schulz, USGS, retired, Goldich Medal Winner, 2003 William F. Cannon, USGS, Emeritus, Goldich Medal Winner, 1992 xiii �Honoring the Pioneers of Lake Superior Geology (Adopted by the Board of Directors, 2016) Preamble At the suggestion of Gene LaBerge, the 2016 executive board agreed to implement a program to recognize historic pioneers in the understanding of geology in the Lake Superior region. Beginning with the 2017 annual meeting, nominations will be accepted from the membership for geologists whose work was conducted primarily before the inception of the Institute in 1955. Biographical sketches of those pioneers will be presented at future annual meetings so that all may appreciate the value of their contributions. Selection of nominees will be decided in part by the organizing committee of each year's annual meeting, in consultation with the Board, to ensure equitable geographic representation in the selection process. Award Guidelines 1) Nominations from the membership will be submitted via the Institute web site and forwarded to the Chair of the next Annual Meeting. The nominations will be no more than half a page in length and will summarize the contribution of the nominee. 2) The Organizing Committee will select one or two individuals to be highlighted at the next Annual meeting and submit those names to the Board for approval. 3) The nominator will be requested to prepare a brief presentation to be given during the next annual meeting with a summary to be included in the Proceedings volume. 4) Unsuccessful nominations will be kept by the Secretary for two years and forwarded to the next meeting Chair; these nominations may be resubmitted at a later date. The Board will review this award every five years. Pioneers of Lake Superior Geology 2017 Douglass Houghton (1809-1845) 2018-20 not presented 2021 Newton Horace Winchell (1839-1914) 2022 Thomas Leslie Tanton (1890-1971) 2023 Thomas Benton Brooks (1836-1900) 2024 Roland Duer Irving (1847-1888) xiv �2024 Citation for the Roland Duer Irving Pioneer of Lake Superior Geology It is my great honor to nominate and promote Roland Duer Irving (1847-1888) as the 2024 Pioneer of Lake Superior Geology. I suspect that many ILSG members are unfamiliar with Dr. Irving and his many truly pioneering contributions to our understanding of various aspects of Lake Superior geology. Were it not for his premature death at the age of 41, I have no doubt that his continued work on the Precambrian geology of the Lake Superior region would have ranked him as one of the greatest Lake Superior geologists of his time. As it stands, his nearly two decades of mapping, petrography, and geochemical studies and mentoring of students at the University of Wisconsin provided a firm and rational foundation for our further understanding of Lake Superior geology. Roland Duer Irving Roland Duer Irving was born in New York City on April 29th, 1847 (1847 – 1888) as grand-nephew to the classic American novelist-essayist Washington Irving and the New York State Supreme Court Justice, John Duer. John Wesley Powell (2nd USGS Director 1881-1894) noted in his memoriam of Dr. Irving (Powell, 1891) that in his youth, “Roland was subject to frequent and alarming attacks of illness, also to a weakness of sight, which proved to be his greatest obstacle through life” and as such “his early education was at home, his sisters and his father being his instructor”. Ultimately, he enrolled at Columbia College School of Mines in 1863, and with the continued help of his sisters, he graduated in 1868 with a degree in mining engineering. During and after his time at Columbia, he worked for coal mines and smelters in Pennsylvania and New Jersey. In 1870, he was offered a mining and metallurgy chair position at the University of Wisconsin. Irving’s arrival at the University of Wisconsin in 1870 marked the emergence of the “Wisconsin School of Precambrian Geology” (Dott, 2001). He quickly gained prominence within the university as a faculty leader and outside the university as a research investigator (Curti and Carstenson, 1949). Soon after his arrival, the Wisconsin Geological Survey was established by the legislature in 1873 with Irving, T.C. Chamberlain, and Moses Strong serving assistant geologists. By 1876, Chamberlin took the reins as chief geologist of the survey, a position he would hold until its legislative termination in 1879. In 1880, Clarence King, first director of the US Geological Survey, recruited both Chamberlin and Irving to join the USGS in an effort to develop a geologic map of the entire United States. In 1881, Chamberlin was appointed director of the Glacial Division of the USGS. In 1882, Irving was appointed to head the USGS’s Lake Superior Precambrian Division, all the while continuing as head of the Department of Mineralogy and Geology at the University of Wisconsin. xv �During Roland Irving’s teaching and research time with the University of Wisconsin, the Wisconsin Geological Survey and the USGS, he came to mentor and collaborate with several notable geologists who would make their own mark on Lake Superior geology (Dott, 2001). Charles Van Hise arrived at UW as a geology student under Irving’s supervision in 1874. He completed his BS in 1879, his MS in 1882, and his PhD in 1892 (1st PhD at UW). With the passing of Dr. Irving in 1888, Van Hise became not only the principal geologist for the USGS’s Lake Superior Division, but also the head of Wisconsin’s geology department. Another notable student of Roland Irving’s at Wisconsin was Florence Bascom. She conducted a petrographic study of the Mellen Complex under the supervision of Irving and Van Hise and received the second ever MS degree in geology from UW in 1887. She later earned her doctorate degree from Johns Hopkins in 1893, the first woman in the US to be awarded a PhD in geology. Irving’s work with the Wisconsin Geological Survey (1873-1879) involved many aspects of Wisconsin geology. In Volume 1 (actually published last in 1883), which was intended to be a general summary of the geology, natural history and economic geology of the state for the general education of the public, Irving contributed chapters on the minerals, rock types, and iron ores of the state. In Volume 2 (1877), Irving reported on the Precambrian, Paleozoic, and Quaternary geology of central Wisconsin. His descriptions of the general structure and lithologic attributes of the Baraboo Quartzite and its unconformable relationship with adjacent “Silurian” (Paleozoic) rocks is particularly noteworthy. Volume 3 (1880), which focussed on the geology of Northern Wisconsin, included Irving’s summary report on the general geology of the Lake Superior region (Part 1) and a more detailed report on the geology of the eastern Lake Superior District (Part III). This work, which was based on field studies conducted between 1875 and 1878, formed the basis of his subsequent USGS work detailing the overall geology and structure of the Keweenawan System in the Lake Superior region. It is noteworthy that the renown petrographer, Raphel Pumpelly, contributed a chapter on the petrography of Keweenawan rocks (Part II) collected by Irving and others. Irving relied heavily on petrographic examination of field samples in his subsequent USGS work. In the final volume (#4, 1882) devoted to the geology, paleontology, natural history, and glacial geology of the southern half of the state Irving’s contribution focussed on the field and petrographic attributes of crystalline rocks of the Wisconsin River valley. He recruited his MS student, Charles Van Hise, to carry out most of the petrographic descriptions. Joining the US Geological Survey in 1880 as head of the Lake Superior Precambrian Division, Irving took advantage of being able to explore beyond the confines of Wisconsin and immediately embarked on his long-standing desire to produce a “resume of the results obtained in the Lake Superior country by other geologists up to the present” (Geology of Wisconsin, Volume III (1880) Part 1, p. 3). Building on his own studies of the Keweenawan System in northern Wisconsin, he reviewed and, where appropriate, integrated all former geologic studies in the Lake Superior dating back to the Michigan surveys of Douglass Houghton (1831-1844), the surveys of Upper Canada starting with Logan (1846), and the work of Joseph Norwood in northeastern Minnesota as part of the D.D. Owen US Survey (1847-1852). Between July 1880 and March 1882, Irving conducted reconnaissance mapping, along with a crew of five assistant geologists, in several poorly understood areas throughout the Lake Superior basin. xvi �In 1880, the Minnesota Geological Survey, headed by N.H. Winchell, was in its 9th year of existence, but had only just begun to map the Precambrian geology of the state. As such, Irving decided to spend much of his mapping efforts on the north shore of Lake Superior between Duluth and Nipigon Bay to ascertain how it correlated with the south shore. This occurred at a time when many frontier states were developing their own geologic surveys with the expressed purpose of excluding the federal survey. The USGS already had a strong foothold in Michigan and after the ending of the Wisconsin survey in 1879, developed a strong presence there as well. Suffice it to say that Irving’s work in Minnesota was not well received or valued by the Winchell’s Minnesota Survey. Notwithstanding Winchell objections, Irving’s publication of USGS Monograph 5 - The Copperbearing Rocks of Lake Superior (Irving, 1883) proved to be a remarkably complete and accurate picture of the geology and structure of Keweenawan System (Figure 1). The many important observations and interpretations about Keweenawan geology put forth by Irving include: • formalizing the lithostratigraphy of the Keweenawan System • • defining the synclinal structure of the lavas in the Lake Superior area recognizing that eruptive rocks consist of basic, intermediate, and felsic types • noting no obvious relation of volcanic type to stratigraphic position • interpreting that basic lavas were erupted subaerially from fissures, not ash-generating volcanoes • recognizing that amygdaloidal zones capping basalts are themselves volcanic (not sedimentary) • accurately estimating the thickness of the North Shore Volcanics to be about 18,000’ • interpreting gabbroic and granitic rocks to be intrusive into the volcanic rocks (thus younger) and likely formed in staging chambers that fed surface eruptions Following on the publication of Monograph 5, Irving continued to apply his geologic and petrographic expertise to studies of other Precambrian systems (greenstones, quartzites, and iron formations) in collaboration with students and USGS colleagues. When Roland Irving unexpectedly died (from “paralysis”, perhaps a stroke) on May 30, 1888, he was engaged with Van Hise on another USGS monograph (#19) on the Gogebic Iron Range, which was published posthumously (Irvine and Van Hise, 1892). This monograph launched Charles Van Hise on a career path to becoming an internationally recognized expert on Lake Superior iron formations. While Van Hise will ultimately be recognized as pioneer of Lake Superior geology, it is fitting that we first acknowledge the remarkable accomplishments of his advisor and mentor, Roland Duer Irving. One can only imagine the professional stature he would have attained were he not struck down at the peak of his creativity and expertise. xvii �Figure 1: Plate 1 of USGS Monograph 5 by R.D. Irving, 1883 References Curti, M., and Carstenson, V., 1949, The University of Wisconsin, A History, 1848-1925 (v. 1). Madison, Wisconsin, University of Wisconsin Press, 739 p. Dott, Robert H., Jr., 2001, The remarkable legacy of the Wisconsin School of Precambrian Geology. Geoscience Wisconsin, v. 18, p. 27-40. Irving, R.D., 1883, The Copper-bearing Rocks of Lake Superior. USGS Monograph 5, 464p. Irving, R.D., and Van Hise, C.R., 1892, Penokee Iron-Bearing Series of Michigan and Wisconsin. USGS Monograph 19, 534p. Powell, J.W., 1891, Roland Duer Irving. Eleventh Annual report of the Director of the United States Geological Survey, Part 1- Geology: 1889-1890 p. 38-42. Citation by: James Miller University of Minnesota-Duluth xviii �In Memoriam Louis Mattson Obituary 12/31/2023 Louis A. Mattson, 89, of Pengilly, MN. passed away December 31, 2023, in Grand Rapids, MN. He was a long-time member of the Institute on Lake Superior Geology. The son of commercial fishermen, Lou was the last surviving member of the Mattson Tobin Harbor Fishery on Michigan’s Isle Royale. The fishery on Isle Royale, and family homesteads settled in the 1890’s at Larsmont, and the French River on Minnesota’s North Shore were part of Lou’s DNA. If you knew Lou, you knew about the family legacy on Lake Superior. The landscape of northern Minnesota inspired Lou to pursue a BS in Geology from the University of Minnesota Duluth and an MS in Geology from the University of Minnesota and the Colorado School of Mines. This education would lead to a 30-year career highlighted by travel around the world while working for M.A. Hanna’s Minerals Research Laboratory in Nashwauk. Lou’s sharp mind did not rest in retirement. He extensively researched family genealogy culminating in connections with relatives in Larsmo, Finland, enhanced his boat collection at the home he and Peggy built on Swan Lake, supported the Isle Royale Friends and Family Association (IRFFA). xix �Eisenbrey Student Travel Awards The 1986 Board of Directors established the ILSG Student Travel Awards to support student participation at the annual meeting of the Institute. The name “Eisenbrey” was added to the award in 1998 to honor Edward H. Eisenbrey (1926-1985) and utilize substantial contributions made to the 1996 Institute meeting in his name. “Ned” Eisenbrey is credited with discovery of significant volcanogenic massive sulfide deposits in Wisconsin, but his scope was much broader - he has been described as having unique talents as an ore finder, geologist, and teacher. These awards are intended to help defray some of the direct travel costs of attending Institute meetings, and include a waiver of registration fees, but exclude expenses for meals, lodging, and field trip registration. The number of awards and value are determined by the annual Chair in consultation with the Secretary and Treasurer. Recipients will be announced at the end of the annual meeting. The following general criteria will be considered by the annual Chair, who is responsible for the selection: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the annual meeting of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away from the meeting location. 5) Each travel award request shall be made in writing to the annual Chair, and should explain need, student and author status, and other significant details. Successful applicants will receive their awards during the meeting. xx �Joe Mancuso Student Research Awards The 2005 Board of Directors established the ILSG Student Research Fund with $10,000 US from the Institute’s general fund to encourage student research on the geology of the Lake Superior region. A minimum of two awards of $500 US each for research expenses (but not travel expenses) will be made each year. Students are expected to present their research orally or during a poster session at an ILSG meeting. The award winners will also be automatically eligible for the Eisenbrey Travel Awards. To allow the fund to grow, the Fund will receive one-half of any additional proceeds from each annual meeting, after all other commitments and expenses are covered. • The ILSG Board of Directors will be responsible for selecting a minimum of two awards each year. The ILSG Treasurer will issue the awards. • The ILSG Student Research Fund is available for undergraduate or graduate students working on geology in the Lake Superior region. • The applications are due to the ILSG Secretary by August 31st of each year. Awards will be made by October 1st of each year. • Names of the award recipients will be announced at the next annual meeting and posted on the ILSG website. • Details of the application process can be found on the ILSG web site. • The proposal will need to be signed by the researcher’s supervisor. The 2012 Board of Directors approved modification of the fund’s name, adding “Mancuso” to reflect the many contributions of Joseph Mancuso to the organization and sizeable donations made in his name. “Doc Joe,” as he was known by his students, taught geology for 36 years at Bowling Green State University, Ohio. He advised many graduate students in field-oriented research, and frequently brought them to Institute meetings. Joe was the 2007 Goldich Medalist. In fall 2023, the ILSG Board of Directors selected two students to be granted research funding of $500 each from the Joe Mancuso Student Research Fund. The awardees were: Adrian Perez Avila Lakehead University Braxton Murphy Michigan Technological University Department of Geological and Mining Engineering and Sciences TOPIC: Characterization of the host rocks to mineralization in the Shebandowan greenstone belt in the vicinity of the Moss Lake deposit, NW Ontario TOPIC: Determine the relative paleostress state and tectonic conditions that resulted in formation and movement of faults making up the Keweenaw fault system near Houghton, Michigan, USA. Zsuzsanna P. Allerton University of Minnesota- Twinn Cities TOPIC: Investigate the timing and genesis of massive and semi-massive hematite ore bodies located in the Neoarchean (~2.7 Ga) Lake Vermilion/Soudan Underground Mine State Park (SSP) Farhan Ahmed Bhuiyan University of Minnesota- Duluth TOPIC: Evaluating post-depositional mineral reactions in the 1.71 – 1.47 Ga Freedom Formation, Baraboo, WI xxi �Doug Duskin Student Paper Awards Each year, the Institute selects the best of student presentations and honors the presenters with a monetary award. Funding for the award is generated from registrations of the annual meeting, and from generous donations to the fund in honor of Doug Duskin—an exploration geologist and longtime friend of the Institute. The 2012 ILSG Board of Directors approved adding Doug’s name to the award to acknowledge his contributions and distribute those donations in a manner that would have pleased him. The Duskin Student Paper Committee is appointed by the Meeting Chair. Criteria for best student paper—last modified by the Board in 2001—follow: 1) The contribution must be demonstrably the work of the student. 2) The student must present the contribution in-person. 3) The Student Paper Committee shall decide how many awards to grant, and whether or not to give separate awards for poster vs. oral presentations. 4) In cases of multiple student authors, the award will be made to the senior author, or the award will be shared equally by all authors of the contribution. 5) The total amount of the awards is left to the discretion of the meeting Chair in conjunction with the Secretary, but typically is in the amount of about $500 US (increase approved by Board, 10/01). 6) The Secretary maintains, and will supply to the Committee, a form for the numerical ranking of presentations. This form was created and modified by Student Paper Committees over several years in an effort to reduce the difficulties that may arise from selection by raters of diverse background. The use of the form is not required but is left to the discretion of the Committee. 7) The names of award recipients shall be included as part of the annual Chair’s report that appears in the next volume of the Institute. Student papers will be noted on the Program. 2024 Student Paper Awards Committee Stacy Saari – Minnesota Department of Natural Resources (Committee Chair) Paula Leier-Englehardt – HydroGeo Solutions LLC, Wisconsin Dan Hirvi – Consulting Geologist, Michigan Allison Severson – Minnesota Geological Survey xxii �Board of Directors Theodore J. Bornhorst, Chair (2024-2027) — Michigan Technological University Carysn Ames (2023-2026) — Wisconsin Geological and Natural History Survey Mike Easton (2022-2025) — Ontario Geological Survey Mark Smyk (2019-2024) — Lakehead University Peter Hollings Secretary (2019-2024) — Lakehead University Mark A. Jirsa Treasurer (2022-2025) — Minnesota Geological Survey Board member through the close of the meeting year shown in parentheses. xxiii �2024 ILSG Meeting Michigan Tech Volunteers Great Lakes Research Center Daniel J. Lizzadro-McPherson Student Volunteers: Affiliated with Michigan Tech Jhuleyssy Liesseth Sánchez Aguilar Gabriel Ahrendt Katherine Langfield Marie, Lansbery Braxton Murphy Abe Stone 2024 ILSG Meeting Session Chairs Allan Blaske, GEI Consultants Amy Radakovich Block, Minnesota Geological Survey Patty Cobin, A. E. Seaman Mineral Museum, Michigan Tech Mary Louise Hill, Lakehead University Allan MacTavish, AGC GeoConsulting Ashley Quigley, Michigan Geological Survey Bernie Saini-Eidukat, North Dakota State University Mark Smyk, Lakehead University xxiv �Field Trip Leaders and Guidebook Authors Field trips have been the mainstay of the ILSG since its inception 70 years ago. We give special thanks to the field trip leaders and guidebook authors who volunteered their time and talent in carrying that tradition forward. Trip 1: Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Ted Bornhorst (Michigan Tech) Trip 2: Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan Tom Wright (Quincy Mine Hoist Association) Jim DeGraff and Ted Bornhorst (Michigan Tech) Trip 3: Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty Erika Vye, Charlie Kerfoot (Michigan Tech) Stephanie Swart (Michigan Department of Environmental Quality) Dione Price and Evelyn Ravindran (Keweenaw Bay Indian Community) Trip 4: Keweenaw Fault Geometry and Kinematics: Clues to Its Nature and Origin Jim DeGraff, Katherine Langfield, and Dan Lizzadro-McPherson (Michigan Tech) Trip 5: Adventure Mine, Ontonagon County, Michigan: Geology and History of a Native Copper Mine Matt Portfleet (Adventure Mining Company) Ted Bornhorst (Michigan Tech) Trip 6: Southern Complex Granitoids, Gneisses and Migmatites: New Data, Discoveries, and Perspectives Chad Deering (Michigan Tech) Trip 7: Landslides in the Glacial Lake Ontonagon Sediments Stan Vitton and Mohammad Sadeghi (Michigan Technological University) xxv �Mineral Informatics: A New Frontier in Understanding Earth Robert M. Hazen Banquet Speaker Senior Staff Scientist, Earth and Planets Laboratory Carnegie Institution for Science, Washington, DC 20015 Email: rhazen@carnegiescience.edu The story of Earth is a 4.5-billion-year saga of dramatic transformations, driven by physical, chemical, and biological processes. The co-evolution of life and rocks unfolded in an irreversible sequence of evolutionary stages. Each stage re-sculpted our planet’s surface, while introducing new planetary processes and phenomena. This grand and intertwined tale of Earth’s living and non-living spheres is coming into ever-sharper focus, thanks to advances in “mineral informatics” - a field that employs large and growing mineral data resources to tell the deep-time stories of our evolving planet. Minerals are remarkably information rich, holding dozens of trace and minor elements, scores of stable isotopes, solid and fluid inclusions, chemical zoning, twinning, exsolution, countless defects, and a host of optical, magnetic, electrical, and other properties. Every mineral specimen is a time capsule waiting to be opened—waiting to tell its story. This lecture will explore some of the advanced data analytical and visualization methods that are shining new light on the old field of mineralogy, while revealing in ever greater clarity the co-evolution of the geosphere and biosphere. A network diagram of all known minerals colored by the way the minerals form. For example, red indicates high-temperature igneous minerals, while green indicates minerals formed by life. xxvi �REPORT OF THE 69th ANNUAL MEETING OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Robert Lodge (University of Wisconsin-Eau Claire), Esther Stewart, and Carsyn Ames (Wisconsin Geologic and Natural History Survey) hosted the 69th Annual Institute on Lake Superior Geology on April 23 – 26, 2023 at the Lismore Hotel and Conference Center in Eau Claire, Wisconsin. The meeting consisted of two days of technical sessions with pre- and posttechnical session field trips. First, we would like to thank the meeting sponsors for their generous support, either through direct funding or in-kind support, namely: Talon Metals, American Institute of Professional Geologists, Geological Society of Minnesota, Crystal Cave, and Visit Eau Claire. We also thank the Individual Contributors to the Student Travel Scholarship fund: Val Chandler, Jim DeGraff, Thomas Erickson, Tom Fitz, Dave Good, Bob Mahin, Gordon Medaris Jr., Jim Miller, Steven Pinta, Tod Roush, and Gerry White. The 2023 meeting was the first conference held in the US since the 2018 Iron Mountain meeting, the first in Wisconsin since the 2011 Ashland meeting, and the first meeting in Eau Claire since 1991. Total meeting registration was 126, including 19 students. Attendance from both Canadian and United States was excellent despite other conferences in the Lake Superior region in April and May (GAC-MAC, Sudbury; Northcentral GSA, Grand Rapids). The technical program was nevertheless excellent with a good array of topics from Archean and Paleoproterozoic geology, to Midcontinent Rift geology and mineralization, to Quaternary Geology, Geoscience Education and Geoheritage. In addition, a student-industry networking lunch was held at the Riverview Room in the Eau Claire Public Library and an evening social was held at Reboot Social. Proceedings Volume 69 was published in two parts. Part 1 – Program and Abstracts, compiled and edited by Carsyn Ames (WGNHS) contains 54 published abstracts for 34 oral and 19 poster presentations. Students presented 8 oral and 10 poster presentations. Part 2 – Field Trip Guidebooks, was compiled and edited by Robert Lodge (UWEC). It contains descriptions of two pre-meeting and two post-meeting field trips. Hard copies of the Abstract Volume and Field Trip Guidebooks for trip participants were printed by University Printing at the University of Wisconsin-Eau Claire. Both volumes are available for download from the Institute on Lake Superior Geology website. The 69th ILSG marked only the third time in the Institute’s long history that its annual meeting was held in Eau Claire, the last time being in 1991. Plans for another Wisconsin-based ILSG meeting had been discussed for a while. With recent work in the Paleoproterozoic geology and mineralization in the Penokean orogen in northwestern Wisconsin and the central location of Eau Claire, it seemed appropriate to host the meeting there. Eau Claire sits on the boundary between Precambrian Shield, Paleozoic Platform, and the terminus of the continental ice sheet and allowed organizers to host four field trips examining billions of years of geologic history. Two field trips focused on the Precambrian geology of the Penokean orogen exposed in the Chippewa and Eau Claire River Valleys. While the preconference field trip got to see historic flooding on the Chippewa River (there are not many days when a bunch of Precambrian geologists are xxvii �looking at the river rather than the rocks), waters receded for the post-conference field trip. Field stops on this trip were originally (in some cases, exclusively) described in previous ILSG meetings (Eau Claire, 1980; 1991) but benefitted from new research and analyses and new viewpoints on the tectonics and metallogeny of the region. One fieldtrip visited classic exposures Paleozoic stratigraphy around the Eau Claire and Menominee regions and enjoyed lunch in an ancient meteorite impact structure. One field trip visited Quaternary geology and fluvial geomorphology of the Chippewa River valley. All the field trips, and the meeting itself, were blessed with good weather. Total field trip participation was 116 (excluding leaders and volunteer drivers). A list of field trips is provided below: Pre-meeting field trips (and leaders) on Tuesday, April 23. 1) Precambrian Geology of the Chippewa River valley: A Transect through the Marshfield Terrane (Robert Lodge, Bob Hooper, UW-Eau Claire) 2) Wisconsin’s Paleozoic stratigraphy and tour of Crystal Cave (Carsyn Ames, Esther Stewart, Bill Batten, Eric Stewart, Ian Orland, WGNHS) Post-meeting field trips (and leaders) on Friday, April 26. 3) Precambrian Geology of the Eau Claire River valley: Re-discovering the Eau Claire Volcanic Complex (Robert Lodge, Evan Weber, Bob Hooper, UW-Eau Claire) 4) Quaternary Geology and Geomorphology of the Eau Claire Region (Doug Faulker, UW-Eau Claire; Elmo Rawling, WGNHS; Phil Larson, Minnesota State University, Mankato) Many registrants attended the welcoming reception on Tuesday evening. Furthermore, the vast majority of registrants and invited guests attended the annual ILSG banquet on Wednesday night. Although a Homer Award overview presentation was given, no “recipients” were identified during the 2023 annual meeting, or in the previous 4 years! As always, a highlight of the post-banquet activities was presentation of the 2023 Goldich Medal. This year’s very deserving recipient was Dr. Pete Hollings. The Goldich Medal citation was presented by Mark Smyk, his colleague for many years. Mark described Pete’s many contributions to the ILSG, to the greater understanding of Archean and Proterozoic geology of the Lake Superior region, and his commitment to students. Pete is indeed a worthy recipient of this prestigious award. The 69th ILSG continued the post-banquet guest speaker tradition. Curt Meine, a conservation biologist, historian, and writer from the Aldo Leopold Foundation and Center for Humans and Nature, gave a presentation entitled Imagining “Conservation Geology”: Lessons from the Driftless Area. His talk provided an insightful viewpoint of how geology and landscapes integrate with history and culture in the Driftless Area of central Wisconsin. In 2023, the student paper committee remarked on the high quality of student research across all participants and had a difficult time of selecting the best among the excellent oral and poster presentations. The committee awarded four prizes for the best oral and poster presentations by xxviii �both undergraduate and graduate students. The best graduate oral presentation was awarded to Justin Jonsson and his talk on “Petrogenesis of the mineralized horizons in the Offset and Creek zones, Lac des Iles Complex, N. Ontario”. The best undergraduate oral presentation was awarded to Blaize Briggs for his talk on “Quetico-Wabigoon Subprovince Boundary in the Superior Province north of Thunder Bay, Ontario, Canada”. The best graduate poster presentation was awarded to Fransisca Nunez Ferreira for her poster on “Morphometry and formation process of eskers developed under the Chippewa Lobe of the Laurentide Ice Sheet”. The best undergraduate poster presentation was awarded to Lillian Glodowski for her poster on “Characterizing volcanic host stratigraphy and syn-volcanic intrusions at the Lynne Zn-Pb-Cu deposit, Oneida Co., Wisconsin”. Eisenbrey Student Travel Grants were given to twelve students: Zsuzsanna Allerton, Ryan Barkley, Blaize Briggs, Tianna Groeneveld, Justin Jonsson, Daniel Lizzardo-McPherson, Francisca Nunez Ferreira, Jordan Peterzon, Sam Ghantous, Madeline Taylor, BJ Itai, and Katherine Langfield. The Institute’s Board of Directors met on Thursday, April 25, 2023, and a brief overview of the meeting notes is provided below: 1. Accepted report of the Chairs for the 68th ILSG, as published in the Proceedings volume, and minutes of last Board meeting, May, 2022 (Hollings) 2. Received, discussed, and accepted 2022-2023 ILSG Financial Summary (Jirsa). 3. Received, discussed, and accepted 2022-2023 report of the Secretary (Hollings). 4. Approved Carsyn Ames as on-going ILSG Board member 5. Discussed and approved Amy Radakovich Block as Assistant Treasurer in a non-voting role (end of term 2026). 6. Discussed and approved replacing Steve Kissin as the “member from academia” on Goldich Committee (end of term 2023) with Marcia Bjornerud 7. Approved Houghton as the site for the 70th annual ILSG meeting. The meeting will be hosted by Ted Bornhorst. 8. Discussed the role of the Michigan Tech archives as the host of hard copies of the publications of the Institute. A formal agreement has been signed with the Archives who will request financial support as needed rather than the previous model of providing a donation of $1 per attendee. 9. A number of future meeting locations were discussed. Peter Hinz has offered Kenora as a future site and Mark Jirsa is keen to host the Mountain Iron meeting that was cancelled due to the pandemic. Bernie Saini-Eidukat to be approached to see if he is still interested in organizing a meeting in St Cloud. 10. The cost of insurance was again discussed and it was agreed that the Board of Directors insurance should be maintained and that the costs would be included in the cost of each meeting. Given the high costs quoted for field trip insurance the Board to investigate field trip insurance options. Hollings to approach GAC. Amy to approach GSA and Carsyn to approach a risk advisor. The Board discussed embedding a Liability waiver in the registration process. 11. The Board discussed embedding a photo release in the meeting and/or field trip registration process such that anyone registering for the field trip is aware they are agreeing to be photographed and have their image used in ILSG publications/website etc. It was agreed that the Institute does not want to turn anyone away from the meeting/trips simply because xxix �they do not want to be photographed, and the result is that before any photos are uploaded to the website, someone on the Board (or a future social media position) will need to go through the photos and make sure that no one who has NOT signed a photo release is shown in a shot where they are identifiable. The 69th ILSG meeting was a great success, and we wish to thank all the people who contributed to that success, field trip leaders and drivers, UWEC student volunteers, and businesses and organizations in downtown Eau Claire that hosted and entertained visitors. Patty Cobin and Ted Bornhorst (A.E. Seaman Mineral Museum, Michigan Technological University) handled the premeeting registration and supplied the poster boards. Thanks also go to the staff at Lismore Hotel and Conference Center who helped the meeting and banquet run smoothly and providing lunches and snacks during the technical sessions. Thanks to Eau Claire Public Library for hosting our student-industry luncheon, Reboot Social for hosting our post-meeting evening social, Eau Claire Cheese and Deli for field trip lunches, and Eau Claire Student Transit for bus transportation for fieldtrips. Robert Lodge (UWEC), Carsyn Ames (WGNHS), and Esther Stewart (WGHNS) Co-Chairs, 69th Institute on Lake Superior Geology xxx �Donations to Support Student Participation at the Annual Meeting of the Institute on Lake Superior Geology A SPECIAL THANK YOU TO OUR INDIVIDUAL CONTRIBUTORS Roger Anderson Aaron Hirsch Wouter Bleeker Allan MacTavish Terry Boerboom Bob Mahin Ted Bornhorst Gordon Medaris Jr. Alex Brown Jim Miller Michael Carr Rick Sandri Val Chandler Isabel Serrano Kate Clover Mark Severson Abraham Drost Jim Small Thomas Erickson Gerry White Annia Fayon Graham Wilson Mary Louise Hill xxxi �TECHNICAL PROGRAM xxxii �Wednesday May 15, 2024 All field trips begin and end at the Michigan Tech Memorial Union Building Parking tickets are given between 7 am to 4 pm weekdays. Between ticketing hours all vehicles need a parking pass; these will be available from trip leaders. Pre-meeting Field Trips May 15, 2024 8:00 am - 5:00 pm PRE-MEETING FIELD TRIPS Trip 1: Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Ted Bornhorst (Michigan Tech University) Trip 2: Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan Tom Wright (Quincy Mine Hoist Association), Jim DeGraff, Katherine Langfield, and Ted Bornhorst (Michigan Tech) Trip 3: Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty Erika Vye and Charlie Kerfoot (Michigan Tech) Stephanie Swart (Michigan Department of Environmental Quality) Dione Price and Evelyn Ravindran (Keweenaw Bay Indian Community) Wednesday evening May 15, 2024 4:00 pm - 8:00 pm Registration (2nd floor, Michigan Tech Memorial Union) 6:30 pm - 8:30 pm Poster Setup and Viewing (2nd floor, Michigan Tech Memorial Union) 6:30 pm - 8:30 pm Welcoming Reception (2nd floor, Michigan Tech Memorial Union) xxxiii �* Denotes a student eligible for Best Student Paper Award. To be eligible students must have graduated no more than one month before the ILSG meeting, be first author, and present the paper at the meeting + Denotes author that will present the paper if different than the first author. Thursday - May 16, 2024 All vehicles need a parking pass between 7am to 4pm weekdays; these will be available from registration 7:15 am - noon Registration (2nd floor, Michigan Tech Memorial Union) 8:15 am OPENING REMARKS (2nd floor, Michigan Tech Memorial Union) Ted Bornhorst, Erika Vye, Patty Cobin, and Jim DeGraff Co-Chairs, 2024 ILSG TECHNICAL SESSION I – ORAL PRESENTATIONS Session Chair: Mark Smyk 8:20 Jim MILLER Roland Duer Irving - Pioneer of Lake Superior geology 8:35 Graham WILSON, Charles BUTT, Robert GARRETT and Heather ROBINSON R.W. Boyle’s History of Geochemistry and Cosmochemistry 8:55 James DeGRAFF, Nolan GAMET, Katherine LANGFIELD, Daniel LIZZADROMcPHERSON, Sophie MUELLER, and Colin TYRRELL Transpressional Nature of the Keweenaw Fault System, Lake Superior Region, and Its Relationship to Grenville Orogenesis 9:15 Alex BROWN Re-interpretation of hydrothermal alteration, mineralization and host-rock oxidation to form the Keweenaw native copper lodes, northern Michigan 9:35 Esther STEWART, Michael TAPPA, Ann BAUER, Anthony PRAVE, and Latisha BRENGMAN Geochemical fingerprints from the late Mesoproterozoic epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA 9:55 END OF TECHNICAL SESSION I 9:55-10:10 COFFEE BREAK xxxiv �TECHNICAL SESSION II – ORAL PRESENTATIONS Session Chair: Ashley Quigley 10:10 Sarah GORDEE, Madison RIAN, Stacy SAARI, and Matthew CARTER Description and application of the Consolidated Minerals Database to support geological investigations: an example from the Cuyuna Range, central Minnesota 10:30 Stacy SAARI, Sarah GORDEE, Madison RIAN, and Matt CARTER Compiled historical drillhole and geochemical data from the Cuyuna Range, Minnesota, provides powerful new insights for geological and mineral potential investigations. 10:50 Bob MAHIN, Ashley QUIGLEY, John YELLICH, John ESCH, and Nolan GAMET Critical Mineral Systems in the Upper Peninsula of Michigan, A Cooperative Effort Between the USGS and the Michigan Geological Survey 11:10 Paul BEDROSIAN, Dana PETERSON, and Bennett HOOGENBOOM Geophysical imaging of the Paleoproterozoic Animikie basin in Minnesota 11:30 Dan HOLLIS Use of Ambient Noise Tomography for Mineral Exploration in the Lake Superior Region 11:50 END OF TECHNICAL SESSION II 11:50-1:10 LUNCH BREAK and ILSG BOARD OF DIRECTORS MEETING - lunches not provided to conference attendees- TECHNICAL SESSION III- ORAL PRESENTATIONS Session Chair: Mary Louise Hill 1:10 *Demily THIBODEAU-BELLO, Mary Louise HILL, Andrew CONLY, An evaluation of structural and mineralogical controls on gold mineralization on the GoldRich property in the Abbie Lake area, Wawa, Ontario 1:30 Dean PETERSON and Alex STEINER The geology and ore deposit model of the high-grade Emily Manganese Deposit, Cuyuna Range, Minnesota: Results from the 2023 drilling program 1:50 *Gabriel AHRENDT and Aleksey SMIRNOV Rock magnetic investigation of the Vulcan Iron Formation: Unveiling Paleoproterozoic Paleoenvironments 2:10 *Zsuzsanna ALLERTON, George HUDAK, Christian TEYSSIER, Annia FAYON, Martin DANIŠIK, Liam COURTNEY-DAVIES, and Phillip LARSON Geochronology and geochemistry of hematite ore in northeastern Minnesota xxxv �2:30 Joyashish THAKURTA and Beau HAAG Sulfur-isotope ratios in Paleoproterozoic Michigamme Formation at the Lake Superior Region: Implications on basin evolution and ambient seawater composition in the Greater Animikie Basin 2:50 *Jordan PETERZON, Noah PHILLIPS, Pete HOLLINGS, and Lionnel DJON Deformation conditions, micromechanics, and fault zone development in mafic protoliths at the Lac des Iles mine, northwestern Ontario 3:10 END OF TECHNICAL SESSION III 3:10-3:30 COFFEE BREAK TECHNICAL SESSION IV – POSTER PRESENTATIONS Session Chair: Allan Blaske and Patty Cobin 3:30-5:00 AUTHORS PRESENT AT THEIR POSTERS 5:00 END OF TECHNICAL SESSION IV Thursday evening May 15, 2024 6:00 pm RECEPTION AND CASH BAR (2nd floor, Michigan Tech Memorial Union) 7:00 pm ANNUAL BANQUET (2nd floor, Michigan Tech Memorial Union) 2024 Goldich Medal Recipient: Suzanne W. Nicholson Banquet Speaker: Robert M. Hazen, Carnegie Institution for Science “Mineral Informatics: A New Frontier in Understanding Earth” xxxvi �Friday - May 17, 2024 All vehicles need a parking pass available from co-chairs 8:15 INTRODUCTORY REMARKS AND UPDATES (2nd floor, Michigan Tech Memorial Union) Ted Bornhorst, Erika Vye, Patty Cobin, and Jim DeGraff Co-Chairs, 2024 ILSG TECHNICAL SESSION V – ORAL PRESENTATIONS Session Chair: Bernie Saini-Eidukat 8:20 *Farhan Ahmed BHUIYAN, Latisha BRENGMAN, and Esther STEWART Assessing depositional and post-depositional mineral associations in the <1.71 Ga Freedom Formation, Baraboo, WI, USA. 8:40 Jack MALONE, Ryan CLARK, Amira HARRIS-BOMMARITO, and David MALONE Baraboo Interval Quartzites in Iowa: Reassessing the Origin and Provenance of the Washington County Quartzite, SE Iowa 9:00 Gordon MEDARIS, Chloe BONAMICI, Phil BROWN, Laurel GOODWIN, Brian JICHA, Brad SINGER, Michael SPICUZZA and John VALLEY, The Evolution of Baraboo Interval Sedimentary Rocks: Deposition at 1.63 Ga and Metamorphism at 1.47 Ga 9:20 Amy Radakovich BLOCK, George HUDAK, and Kate SOUDERS Insights into the southwestern Superior Province: New igneous geochronology and geochemistry in northwestern Minnesota, USA 9:40 Ryan CLARK, David PEATE, Allison KUSICK, Kenny HORKLEY, and Chris MACFARLANE Baddeleyite age reveals timing of the Northeast Iowa Intrusive Complex (NEIIC) 10:00 END OF TECHNICAL SESSION V 10:00-10:20 COFFEE BREAK TECHNICAL SESSION VI – POSTER PRESENTATIONS Session Chair: Allan Blaske and Patty Cobin 10:20-11:40 AUTHORS PRESENT AT THEIR POSTERS 11:40 END OF TECHNICAL SESSION VI 11:40-1:00 LUNCH BREAK xxxvii �TECHNICAL SESSION VII – ORAL PRESENTATIONS Session Chair: Allan MacTavish 1:00 Jim MILLER and John GREEN Two decades of teaching the geologic heritage of Minnesota’s North Shore at the North House Folk School, Grand Marais 1:20 Erika VYE, Daniel LIZZADRO-MCPHERSON, and James JUIP The Keweenaw Geoheritage Summer Internship Experience 1:40 Eric NOWARIAK, S, Allison SEVERSON, and Amy Radakovich BLOCK Lithostratigraphy and Geochronology of the Lower Northeast Sequence of the North Shore Volcanic Group, Cook County, MN, USA 2:00 Pete HOLLINGS and Mark SMYK New Insights into the Geology and Geochemistry of the Osler Group and Related Rocks, Midcontinent Rift System, Northern Lake Superior, Ontario 2:20 David GOOD MCR Synthesis 1. Characterizing the MCR mantle plume 2:40 END OF TECHNICAL SESSION VII 2:40-3:00 COFFEE BREAK and TAKE DOWN POSTERS TECHNICAL SESSION VIII – ORAL PRESENTATIONS Session Chair: Amy Radakovich Block 3:00 Bill ROSE and James DeGRAFF Lidar Topography: Bright opportunity for reading Keweenaw Landscapes 3:20 Wouter BLEEKER, Natasha WODICKA, Sandra KAMO, Michael HAMILTON, Quinn EMON, and Jennifer SMITH The Lake Superior area “event layer”: Testing the connection with the Sudbury impact 3:40 Tien GRAUCH, S. HELLER, Laurel WOODRUFF, and Esther STEWART Revisiting geophysical interpretations of the Midcontinent Rift below Lake Superior— Insights from GLIMPCE seismic-reflection line C 4:00 Aaron HIRSCH Recent developments on the use of the Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic method to determine depth to bedrock in Minnesota 4:20 END OF TECHNICAL SESSION VIII xxxviii �4:20 Presentation of Student Awards Best Student Paper Awards – Stacy Saari Student Travel/Participation Awards – Ted Bornhorst 4:40 Concluding Remarks and Field Trips Ted Bornhorst, Erika Vye, Patty Cobin, and Jim DeGraff Co-Chairs, 2024 ILSG END OF TECHNICAL SESSIONS OF THE 70th ANNUAL MEETING Friday Evening May 17, 2024 7 pm ATDC Building across the parking lot from the A.E. Seaman Mineral Museum 2024 Edith D. and E. Wm. Heinrich Lecture “Mineral Evolution: A Case Study of a New Natural Law" by Robert M. Hazen Sponsored by the Edith D. and E. Wm. Heinrich Mineralogical Research Foundation and the A. E. Seaman Mineral Museum Saturday May 18, 2024 Field trips begin and end at the Michigan Tech Memorial Union Parking pass not needed on weekend. 8:00 am – 5:00 pm POST-MEETING FIELD TRIPS Trip 4: Keweenaw Fault Geometry and Kinematics: Clues to Its Nature and Origin Jim DeGraff, Katherine Langfield, and Dan Lizzadro-McPherson (Michigan Tech) Trip 5: Adventure Mine, Ontonagon County, Michigan: Geology and History of a Native Copper Mine Matt Portfleet (Adventure Mining Company), Ted Bornhorst (Michigan Tech) Trip 6: Southern Complex Granitoids, Gneisses and Migmatites: New Data, Discoveries, and Perspectives Chad Deering (Michigan Tech) Trip 7: Landslides in the Glacial Lake Ontonagon Sediments Stan Vitton (Michigan Tech) xxxix �POSTER PRESENTATIONS * Denotes a student eligible for Best Student Paper Award. To be eligible students must have graduated no more than one month before the ILSG meeting, be first author, and present the paper at the meeting + Denotes author that will present the paper if different than the first author. Numbered Posters and Abstracts are in sequential order Poster Number 1. withdrawn 2. Sheree HINZ GeologyOntario: a powerful search tool for Ontario explorationists Therese PETTIGREW, Robert CUNDARI, Rebecca PRICE, and Manuel DUGUET Identification of Fertile Parent Granitoid Units in the Superior Province of Ontario withdrawn 3. Mia MORSON and + Shannon ZUREVINSKI Quartz trace element chemistry: Exploring the link between a fertile parental granite and a mineralized pegmatite 4. *Kevin MEXIA, Pete HOLLINGS Geochemistry of Midcontinent Rift-related intrusive rocks of the Sunday Lake intrusion 5. Justin JONSSON, Paul MALEGUS, Sophie CHURCHLEY, and Rebecca PRICE Characterizing the geochemistry and nickel-copper-platinum group elements potential of mafic and ultramafic intrusions in northwestern Ontario withdrawn 6. *Andrea Paola CORREDOR BRAVO, Pete HOLLINGS, Matthew BRZOZOWSKI, and Geoff HEGGIE Magmatic and hydrothermal evolution of the Mesoproterozoic Current ultramafic PGECu-Ni deposit within the Thunder Bay North Intrusive Complex: insights from trace elements, Nd, Sr, O, and H isotopes 7. Max LAXER and + David GOOD Building a 3D model for Cu/Pd inflection points throughout the Marathon PGE-Cu Deposit 8. *Vlad SHESHNEV, Pete HOLLINGS, Noah PHILLIPS, Ryan WESTON, Matt DELLER, and Dana CAMPBELL Geochemistry and Petrology of the Eagle’s Nest Intrusion, McFaulds Lake Greenstone Belt, Northern Ontario xl �9. *Yiruo XU and Robert HOLDER Cooling of an Archean metamorphic terrane: garnet diffusion study of the Quetico Subprovince, Canada 10. *Clare BEAUDRY, Madelyn HESS, Cristian PEREIRA, and Bernhardt SAINI-EIDUKAT Petrology and geochemistry of Precambrian basement rocks in Walsh County, North Dakota 11. *Cristian PEREIRA, Timothy NESHEIM, Jeffrey D. VERVOORT, and Bernhardt SAINI-EIDUKAT Major element geochemistry and first zircon U-Pb age dates of Precambrian basement rocks in eastern North Dakota 12. Jamey JONES, Bill CANNON, Ben DRENTH, and Paul O’SULLIVAN Geologic and tectonic implications of detrital zircon U-Pb ages from the Dickinson Group in the western Upper Peninsula of Michigan, USA 13. Bill CANNON, A. SOUDERS, Ben DRENTH, and Robert AYUSO The Sacred Heart Orogeny in Michigan: Latest Archean Granites and the Great Lakes Tectonic Zone 14. A. SOUDERS, W. CANNON, B. DRENTH, R. SALERNO, J. THOMPSON, and P. SYLVESTER New LA-ICP-MS U-Pb geochronology of Archean rocks, central Upper Peninsula, Michigan, USA: a step toward refining the final assembly of the Superior craton 15. *Zsuzsanna ALLERTON, Annia FAYON, George HUDAK, Christian TEYSSIER, Liam COURTNEY-DAVIES, and Martin DANIŠIK Geochronology campaign in northeastern Minnesota 16. Ross SALERNO, Bill CANNON, Amanda SOUDERS, Jay THOMPSON Understanding the evolution of the upper Midwest Archean gneiss dome corridor using apatite, titanite, and monazite LA-ICP-MS U-Pb geochronology and microstructural analyses 17. *Trent EDIGER and Marcia BJØRNERUD Glimpses of a Paleoproterozoic landscape: Analysis of exhumed topography on Archean basement rocks northwest of Marquette, Michigan 18. Rebecca STOKES, Bill CANNON, and Ross SALERNO Characteristics of graphitization across a metamorphic gradient in the Michigamme Formation of the Marquette Trough and Baraga Basin, MI 19. Tom BUCHHOLZ, Alexander FALSTER, and Wm. SIMMONS Preliminary mineralogy of a pegmatite in the pyroxene syenites of the Stettin Complex, Wausau Complex, Marathon County, Wisconsin xli �20. *Katherine LANGFIELD, Nolan GAMET, James DeGRAFF Cross-sectional Geometry of the Keweenaw Fault System between Hancock and Mohawk, Upper Peninsula of Michigan 21. *Braxton MURPHY, Katherine LANGFIELD, and James DeGRAFF Geometry, Slip Kinematics, and Deformation along the Hancock Fault in the Quincy Mine Workings, Upper Peninsula of Michigan 22. *Kenz CARLTON, Basil TIKOFF, and Esther STEWART The Honey Creek Structure, Sauk County, Wisconsin: Asymmetric Faulting Associated with Seismic-Induced Fluid Escape 23. *Alex LAWRENCE, Adam VANDERKIN, and Robert LODGE Volcanic and Hydrothermal Reconstruction of the Paleoproterozoic Butler Zn-Cu occurrence, Clark County, Wisconsin 24. *Lyndsie VICKERS, and Robert LODGE Petrology and Geochemistry of Felsic Magmatism in the Paleoproterzoic Eau Claire Volcanic Complex, Northcentral Wisconsin 25. *Dan SHAKKED, Lucas ROBARGE, and Robert LODGE Analysis of deformation-related structures in the Eau Claire Volcanic Complex, Wisconsin 26. *Gwendolyn MARTIN and Marcia BJØRNERUD Investigating the origin of pervasive breccias in the Paleoproterozoic Saunders Formation in northern Wisconsin 27. Aaron HIRSCH, Emma SCHNEIDER Lithostratigraphic discrimination of Quaternary core in Minnesota using magnetic susceptibility 28. Bill ROSE and Erika VYE Michigan Coastal Path: A Social Commitment to Geoeducation 29. Bill ROSE and Erika VYE Jacobsville geoheritage is globally celebrated and locally loved 30. *Alice MARTIN, Zsuzsanna ALLERTON, Emma JOHNSON, Annia FAYON, Jim ESSIG, Sarah GUY-LEVAR,George HUDAK The Soudan Geology Trail Project: Let’s talk about rocks in northeastern Minnesota A tribute to Jean Peterman Kemp Zimmer and Jeanne Seaman Farnum by the A.E. Seaman Mineral Museum: Trailblazers for Women in Geology xlii �ABSTRACTS xliii ��Rock magnetic investigation of the Vulcan Iron Formation: Unveiling Paleoproterozoic Paleoenvironments AHRENDT, Gabriel1 and SMIRNOV, Aleksey1,2 1 Department of Geological Mining and Engineering Sciences, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931 2 Department of Physics, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931 The Paleoproterozoic (~1.88 Ga) Vulcan Iron Formation, located in the Southwestern Upper Peninsula of Michigan, is a significant Superior-type Banded Iron Formation, comprising four main members. The lower, Traders Member is characterized by banded ferruginous-siliciclastic layers with distinct alternating layers of ferric iron. The middle, Brier Member is a fissile slate with varying concentrations of magnetite from low to locally enriched. The upper, Curry Member, is an oolitic iron formation enriched with specular hematite and lacking noticeable banding. In some locations, the Curry Member is overlain by the ferric slate referred to as the Loretto Member. We conducted comprehensive rock magnetic investigations of three lower formation members, using thermal demagnetization of natural remanent magnetization, magnetic hysteresis and first-order reversal curve measurements, and thermomagnetic analyses. Our findings suggest that the members may be genetically distinct, reflecting shifts in depositional regimes that dramatically affected their texture and mineralogy. The Traders Member, characterized by abundant small paramagnetic grains, likely formed during a period of rapid subsidence and soluble transport of ferrous iron into a euxinic basin, followed by alternating periods of CO2 fixing and sulphide-oxidizing cyanobacteria. The subsequent transition to a shallow, foreshortened basin as the Pembine-Wasau terrane accreted led to the increased silica saturation and local concentration of superparamagnetic ferrous iron mud, forming the Brier slate. A further evolution due to the flooding of a shallow sea inducing high turbidity and increased oxygenation in the water column, resulted in the formation of the Curry Member, marked by a mix of magnetically hard minerals, including specular hematite. We speculate that, subsequently, a decrease in sea level, associated with the basin’s contraction, created conditions conducive to high silica input from continental margins and a change in the biotic regime which reduced the formation of granules and led to the creation of the Lorretto slate member. 1 �Geochronology campaign in northeastern Minnesota ALLERTON, Zsuzsanna1, FAYON, Annia1, HUDAK, George1, TEYSSIER, Christian1, COURTNEY-DAVIES, Liam2, and DANIŠIK, Martin3 1 Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA Geological Sciences, University of Colorado, Thermochronology Research and Instrumentation Lab, Boulder, CO 80309-0399, USA 3 School of Earth and Planetary Sciences Department, John de Laeter Centre, Curtin University, Perth, WA 6845. Australia 2 Northeastern Minnesota is known from volcanic rocks along the north shore of Lake Superior and the intrusive suit of the Duluth Igneous Complex (DC) to its west with associated Ni-Cu-PGE mineralization (Leu, 2015; Miller, 2002). These lithologic units are part of the ~1100 Ma Midcontinent Rift System (MRS). During the rifting event, the hot (~1000°C) DC was emplaced into the “cold” Neoarchean (~2700 Ma) monzo-granitic Giants Range Batholith (GRB) footwall, resulting in contact metamorphism, sulfide mineralization (Benko et al., 2015), and hydrothermal activity. The focus of this project is to constrain the hydrothermal effect of DC emplacement and other regional events by tracking isotopic, chemical, and textural changes in accessory minerals zircon and apatite along a transect from the DC/GRB contact westward into the Archean basement. Samples in this study are collected from the GRB and the Purvis Lake tonalite. Six of the GRB samples were analyzed for U-Pb dating of in-situ apatite, and twelve GRB samples and one Purvis Lake tonalite sample were disaggregated to isolate individual zircon grains to acquire UPb radiometric dates (Figure 1). U-Pb data were obtained by Laser Ablation-Inductively Coupled Figure 1: Simplified geologic map of Minnesota's arrowhead region showing the study area (yellow inset). Samples are numbered within lithological units of the Giants Range Batholith (GRB) and Purvis Lake tonalite. Maps are modified from Griffin and Morey (1969) and Peterson and Jirsa (1999). 2 �Plasma Mass Spectrometry (LA-ICP-MS) at laboratories of University of Santa Barbara (in-situ apatite) and University of Colorado, Boulder (zircon separates). Results show bimodal dates signifying crystallization age and the timing of hydrothermal alteration. In-situ apatite U-Pb yields 2594.3 ± 30.8 Ma ages at ~ 2 km from the contact, and the rest of the apatite U-Pb dates suggest Pb-loss as a function of hydrothermal alteration from ~1067.24 ± 7.64 Ma to ~1084.89 ± 9.23 Ma within ~1 km of the contact. Zircons separated from twelve samples yield U-Pb crystallization ages ranging from ~2640 to 2700 Ma, and lower intercepts ranging from ~700 to 1200 Ma with uncertainties of ~4-200 Ma. The average lower intercept is ~1150 Ma, and we interpret these ages to record hydrothermal activity-induced Pbloss. Crystallization age and error increase, and the timing of hydrothermally driven Pb-loss becomes more elusive with distance from the contact. The tonalite ~20 km from the DC/GRB contact yields a crystallization age of 2708 ± 25 Ma and displays Pb-loss at 1140 ± 116 Ma. The large uncertainty associated with Pb-loss might be suggestive of multiple hydrothermal events. These data are consistent with hematite (U-Th)/He dates of the massive hematite ore bodies of Soudan Iron Mine, ~40 km (map distance) from the DC/GRB contact, that record hydrothermal alteration at ~ 1100 Ma (see Allerton at al., 2024 “Geochemistry and geochronology of hematite ore in northeastern Minnesota”, ILSG 2024). References Benko, Z., Mogessie, A., Molnar, F., Severson, M., Hauck, S., & Raic, S., 2015. Partial melting processes and Cu-Ni-PGE mineralization in the footwall of the South Kawishiwi Intrusion at the Spruce Road Deposit, Duluth Complex, Minnesota. Economic Geology and the Bulletin of the Society of Economic Geologists, 110(5), 1269-1293. Leu, A., 2016. Geology and Petrology of the Wilder Lake Intrusion, Duluth Complex, Northeastern Minnesota [thesis]. Miller, J., & Minnesota Geological Survey, 2002. Geology and mineral potential of the Duluth complex and related rocks of northeastern Minnesota. Report of investigations (Minnesota Geological Survey; 58). Saint Paul: University of Minnesota, Minnesota Geological Survey. Peterson, D. M., and Jirsa, M.A., 1999. Bedrock geologic map and mineral exploration data, western Vermilion district, St. Louis and Lake Counties, northeastern Minnesota: MGS Miscellaneous Map M-98, scale 1:48,000. Griffin, W. L. and Morey, G. B., 1969. Geology of the Isaac Lake Quadrangle, St. Louis County, Minnesota. Published in Cooperation with the Minnesota Department of Iron Range Resources and Rehabilitation. Minnesota Geological Survey 5 P-8 Special Publication Series. University of Minnesota. 3 �Geochronology and geochemistry of hematite ore in northeastern Minnesota ALLERTON, Zsuzsanna1, HUDAK, George1, TEYSSIER, Christian1, FAYON, Annia1, DANIŠIK, Martin2, COURTNEY-DAVIES, Liam3, and LARSON, Phillip4 1 Earth & Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA School of Earth and Planetary Sciences, John de Laeter Centre, Curtin University, Perth, WA 6845, Australia 3 Geological Sciences, University of Colorado Boulder, Thermochronology Research and Instrumentation Lab, Boulder, CO 80309-0399, USA 4 Earth and Environmental Sciences, University of Minnesota, Duluth, MN 55812, USA 2 The Neoarchean Lake Vermilion-Soudan Underground Mine State Park is known for its Algoma-type banded iron formation (BIF). The BIF encloses lens-shape high-grade (63-65% Fe) iron ore locally. The well-established view is that massive to semi-massive hematite ore bodies are the product of hydrothermal alteration of BIF, during which process hydrothermal fluids leached silica, resulting in volume reduction (production of vug spaces) and Fe-replacement (Gruner 1930; Klinger, 1960; Thompson, 2015). Studies have postulated that ore mineralization was syn- or post-depositional with BIF (Gruner, 1926; Thompson, 2015), but the absolute timing of hematite ore had not been established until now. Figure 1: The diagram illustrates hematite mineralization consistent with the timing of Yavapai and Mazatzal orogenies based on U-Pb ages, and Midcontinent Rift System signatures overprint mineralization ages with (U-Th)/He analysis. Presented is a novel technique based on coupled U-Pb and (U-Th)/He hematite radiometric dating (Courtney-Davies et al., 2022) to determine the formation age and thermal history recorded by hematite. Initial electron probe microanalyses (EPMA) allowed for hematite characterization (microcrystalline and microplaty) that helped locating inclusion-free mineral surfaces for radiometric age dating. U-Pb Laser AblationInductively Coupled-Plasma Mass Spectrometry results suggest Paleoproterozoic mineralization at 1740.4±72.5 Ma and 1640.8±47.2 Ma and (UTh)/He ages clustered at 1093.1±16.4 Ma, the latter indicating a hydrothermal overprint of the original mineralization event (Figure 1). We propose a regional scale model that describes the hydrothermal alteration of Archean BIF at ~1700-1600 Ma with the formation of hematite ore including the growth of microcrystalline then microplaty textures, followed 4 �by a thermal overprint at ~1100 Ma associated with the development of the Midcontinent Rift System (Figure 2). Figure 2: Schematic diagrams display S-N cross-section starting with A) pre-D2, showing Gafvert Lake sequence (GL) unconformably above the Soudan Member (SM) that is stratigraphically above the Lower Member (LM) of Ely Formation. B) D2 regional transpression resulting in right lateral shear zones within SM, constrained to 2685-2674 Ma from dating of regional metamorphic fabrics (Lodge et al., 2013). C) Orogenic magmatism—depicted by a mafic dike (MD) at 1700-1600 Ma—generates hydrothermal fluids, and shear zones are utilized for fluid flow and facilitate a 2-stage hematite ore mineralization (microcrystalline and microplaty). D) The Midcontinent Rift System at ~1100 Ma results in hydrothermal overprint of original mineralization recorded in hematite (U-Th)/He ages. Whole-rock — including major, trace and rare earth elements—lithogeochemical analysis has been performed on four iron formation and ore samples, and results are currently being processed. Klinger (1969) proposed a volume-to-volume replacement mineralization, while Thomson (2015) calculated 39% volume loss by silica leaching and 9% Fe mass gain with Fe replacement. Additionally, isocon analysis (Grant, 2005) is underway to better understand the relationship between mobile and immobile elements during ore mineralization and the paragenesis of hematite. References Courtney-Davies, L., et al., 2022. Hematite geochronology reveals a tectonic trigger for iron ore mineralization during Nuna breakup: Geology, v. 50, p. 1318-1323, doi: 10.1130/G50374.1. Grant, J.A., 2005, Isocon analysis: A brief review of the method and applications: Physics and Chemistry of the Earth, Parts A/B/C, v. 30, p. 997–1004, doi: 10.1016/j.pce.2004.11.003. Gruner, J. W., 1926. Hydrothermal alteration of iron ores of the Lake Superior type—a modified theory: Economic Geology, v. 32, p.121-130. Gruner, J.W., 1930. Hydrothermal oxidation and leaching experiments; their bearing on the origin of Lake Superior hematite-iron ores: Economic Geology, v. 25, p. 697-719. Klinger, F.L., 1960. Geology and ore deposits of the Soudan mine, St. Louis County, Minnesota [thesis]. Lodge, R.W.D., et al., 2013. New U-Pb geochronology from Timiskaming-type assemblages in the Shebandowan and Vermilion greenstone belts, Wawa subprovince, Superior Craton: implications for the Neoarchean development of the southwestern Superior Province, Precambrian Research, v. 235, p. 264-277. Schulz, K. J., 1982. The magmatic evolution of the Vermilion greenstone belt of Minnesota: Tectonophysics, v. 190, p. 233-268. Thompson, A., 2015. A hydrothermal model for metasomatism of Neoarchean Algoma-Type banded iron formation to massive hematite ore at the Soudan Mine, NE Minnesota [thesis]. 5 �Petrology and geochemistry of Precambrian basement rocks in Walsh County, North Dakota BEAUDRY, Clare1, HESS, Madelyn1, PEREIRA, Cristian1, and SAINI-EIDUKAT, Bernhardt1,2 1 Department of Earth, Environmental and Geospatial Sciences, 2Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA In 1977, thirty-two cores were drilled in eastern North Dakota and western Minnesota along the Red River, for the purpose of evaluating uranium potential (Figure 1). The project was funded by the Department of Energy and overseen by Bendix Corporation. A technical report (Moore, 1978), a M.S. thesis that focused on the weathered horizon at the top of the Precambrian bedrock (Kelley, 1980), and several ILSG abstracts were published. For this study, three cores from Walsh County, North Dakota were sampled at the North Dakota Geological Survey Drill Core Library (Grand Forks, ND). Samples were taken from RRVD #17, RRVD #18, and RRVD #19A to focus the study to Walsh County, ND. Figure 2 shows the lithology of the three cores and outlines sample locations. Figure 2: Stratigraphic column of RRVD drill core Precambrian layers. Black Xs indicate sample locations. Numbers to the left correspond to the XRF analysis in Table 1. Data taken from Moore (1979) and optical observations. Figure 1: Location map of Eastern North Dakota and Western Minnesota. Era of Precambrian Bedrock is outlined. Red River Valley Drill Cores are outlined. Petrography and whole rock geochemical analyses (Table 1) were carried out on Precambrian layers. Precambrian sediments are buried under younger layers in Eastern North Dakota, the sampled areas are underlain by Archean gneiss, (Klasner and King, 1986). RRVD #17 was characterized as quartz monzonite with heavier alterations of biotite and feldspar farther up in the core. The alterations may be due to stronger weathering agents on the paleoweathered horizon. RRVD #18 was characterized as a granodiorite with uniform foliation and mineral percentages throughout the drill core. RRVD #19A was characterized as a gneissic granite with 6 �higher foliation as the sample increases in depth. The top of the cores is bleached, likely an effect of paleoweathering processes. Analyses were plotted on AFM and TAS diagrams (Figure 3). Table 1: RRVD #17-785, 2: RRVD #18-645.5, 3: RRVD #18-655.5, 4: RRVD #19A-1284.5, 5: #19A1291, 6: #19A-1296.5. Chemical data from NDSU XRF analysis. wt% 1 2 SiO2 59.1 69.2 TiO2 0.58 Al2O3 Fe2O3 MnO 3 4 5 6 71 68.2 73.5 73.6 0.39 0.32 0.31 0.21 0.22 23.6 14.7 13.8 20.4 13.5 13.1 6.77 0.07 3.55 0.05 3.06 0.04 3.53 0.03 2.54 0.03 2.57 0.03 MgO 2.25 1.19 1.04 0.87 0.44 0.44 CaO 3.44 3.83 3.44 N.D. 3.12 2.8 Na2O 5.32 5.23 5.51 N.D. 4.82 4.32 K2O 1.84 1.46 1.32 6.4 1.36 2.47 P2O5 0.20 0.15 0.13 0.07 0.09 0.07 Total 103.1 99.75 99.66 99.81 99.61 99.62 Figure 3: Classification diagrams for measured samples. REFERENCES: Kelley, L.I., 1980, Kaolinitic weathering zone on Precambrian basement rocks, Red River Valley, eastern North Dakota and northwestern Minnesota. M.S. Thesis, University of North Dakota. 85 pp. Klasner, J.S. and E. R. King. 1986. Precambrian basement geology of North and South Dakota. Canadian Journal of Earth Sciences. 23(8): 1083-1102. https://doi.org/10.1139/e86-109 Moore, W. L., 1978, A preliminary report on the geology of the Red River Valley Drilling Project, eastern North Dakota and northwestern Minnesota: Bendix Field Engineering Company Subcontract H77-059-E, 292p. https://www.osti.gov/biblio/6538603 doi:10.2172/6538603. 7 �Geophysical imaging of the Paleoproterozoic Animikie basin in Minnesota BEDROSIAN, Paul A., PETERSON, Dana E. and HOOGENBOOM, Bennett E. U.S. Geological Survey, Bldg 20, MS 964, Denver Federal Center, Denver, CO 80225 The 1.88-1.83 Ga Penokean orogen is preserved as a discontinuous fold belt stretching nearly 1500 km from central Minnesota to eastern Ontario. In Minnesota, the supracrustal sequence occupies a NW-facing salient broadly divided into a southern fold-and-thrust belt and a northern tectonic foredeep. The former consists of volcanic and sedimentary rocks in several structural panels while the latter - the ‘main bowl’ Animikie basin (AB) - consists of thick sedimentary sequences and is one of the least deformed remnants of this former continentalmargin. Metasedimentary rocks of the AB include chemical sedimentary rocks (e.g., iron formation of the Mesabi iron range) and turbidites of the Virginia and Thomson Formations. The latter are an important source of sulfur for Ni-Cu mineralization within the intruding Duluth Complex and satellite intrusions. The USGS has been collecting geophysical data in the AB and surrounding areas, including airborne electromagnetic, broadband and nodal seismic, and magnetotelluric data. These data and resulting models reveal the main bowl AB to be more complex than suggested from surface geological mapping. High-electrical conductivity is mapped throughout the basin, including along its northern edge where it is linked to the gently dipping bedded-pyrrhotite-unit and along the steeply dipping SW edge of the Duluth Complex, where it may reflect a hornfels zone formed during contact metamorphism. At the basin scale, a discontinuous bowl-shaped high conductivity zone extends to ~5 km depth. This intra-basin conductor shows some relation to deformation boundaries, such as a demarcation between rocks exhibiting folding and cleavage and those that do not. Some deep (>5 km) geophysical variations are likely related to structural variations within the Archean basement or within thrust panels inferred to project some distance beneath the basin. Where exposed, strong conductors within some of the adjacent thrust belts suggest a correlation with metamorphic grade. Elevated conductivity can, in most cases, be related to a combination of metallic sulfides and graphite. A 9-20 km deep, steeply dipping conductive band is also imaged internal to the Duluth Complex and adjacent to modeled high-density bodies interpreted as magmatic feeder zones. We interpret this conductor as a remnant of AB metasediments preserved within the complex and speculate that the AB played an important control on magma emplacement. 8 �Assessing depositional and post-depositional mineral associations in the <1.71 Ga Freedom Formation, Baraboo, WI, USA. BHUIYAN, Farhan Ahmed 1, BRENGMAN, Latisha 1, and STEWART, Esther 2 1 University of Minnesota Duluth, Earth & Environmental Sciences Department, University of Minnesota Duluth, 1114 Kirby Drive, Heller Hall 229, Duluth, MN 55812. 2 Wisconsin Geological and Natural History Survey, University of Wisconsin-Madison Division of Extension, 3817 Mineral Point Rd, Madison, WI 53705. Some geochemical proxy records suggest that the period following Earth’s initial rise in atmospheric oxygen ~2.4 billion years ago was marked by low, fluctuating oxygen levels (Lyons et al., 2014; 2021). Such conditions would likely have made the ocean’s photic zone inhospitable to multicellular life forms that require oxygen (e.g. Krause et al., 2022). Interpreting the trajectory of Earth’s oxygenation is complicated due to uncertainties in the diagenetic effects on redox proxy records and limited preservation, especially across the late Paleoproterozoic and early Mesoproterozoic (e.g. Slotznick et al., 2022). To fill in critical knowledge gaps in surface redox conditions and geochemical characteristics of Mid-Proterozoic depositional environments, we investigated the Freedom Formation, a <1.71 Ga and >1.47 Ga iron-rich chemical sedimentary unit preserved in historic drill cores near Baraboo, WI, USA (Stewart et al., 2021). Our goal is to decipher primary redox information that links back to the depositing fluid. To accomplish this goal, and separate primary depositional signatures from post-depositional overprinting, we integrate core observations, mineral, petrographic, and geochemical datasets. The Freedom Formation includes a lower unit composed of thin-bedded, interlaminated, fine-grained clastic and chemical sediments and an upper unit composed of dolomite. We document a coarsening upward sequence in the lower Freedom Formation, accompanied by mineralogical changes in three drill cores (H122, H22, and H23). Two of the cores (H122 and H22) show a transition in mineralogy from a base assembly of chamosite, quartz, and magnetite to a Mn-carbonate and hematite-dominant assembly towards the top of the sections. This mineralogical transition is accompanied by an increase in the proportion of sand-sized material, a decrease in mud-sized material, and a noticeable transition to carbonate. Veining and disrupted beds occur throughout all the cores. Whole rock geochemical samples targeting carbonate-rich beds across the lower Freedom Formation indicate a decline in clastic contamination up section, marked by falling Al2O3 concentrations and reduced Zr/Hf ratios. Positive shale normalized Eu/Eu*SN anomalies indicate a role for hydrothermal fluids in precipitation of the authigenic mineral phases. Throughout the lower units, anoxic conditions are dominant, indicated by positive shale-normalized cerium (Ce/Ce*SN) anomalies. Interpreting the observed mineralogical transition in drill cores and the geochemical dataset requires detailed, systematic petrographic observation to distinguish the relative order of events and develop a paragenetic sequence. We identify texturally early minerals based on criteria outlined in LaBerge (1964) and separate those from post-depositional phases to interpret the history of the unit. To classify as a texturally-early phase, minerals must meet the following criteria: 1) be very fine-grained (where no grain size reduction can be attributed to metamorphism); 2) form even and consistent grain size distributions throughout the sample; 3) form the main component of granules or mud-sized particles in fine-grained layers characterized by a granular or particulate textural pattern; and 4) be associated with sedimentary features like 9 �bedding. From this work, we identified quartz and chamosite as the texturally earliest phases in the lowermost Freedom Formation. Towards the top of the lower Freedom Formation, carbonate phases were most commonly identified as texturally earliest. Additionally, the following key observations were made: (1) if quartz is not present, chamosite is the texturally earliest phase; (2) if chamosite is not present, then carbonate is the texturally earliest phase; (3) nano-scale hematite exists at boundaries of chamosite, quartz, carbonate, and stilpnomelane crystals, and within veinlets; (4) euhedral magnetite cross-cuts all other phases, and is often associated directly with chamosite; and (5) large hematite sometimes crosscuts small magnetite, or forms oxidized rims on euhedral magnetite crystals; (6) multiple generations of quartz and oxides exist; and (7) at least two types of carbonate are present (Fe- and Mn-rich and poor). Combining core and mineral datasets, we note that because multiple generations of oxides are present Figure 1: Reflected light photomicrograph of slide no: H122 538 (Fig. 1), post-formational fluid FF (50X) documenting oxidized hematite rims on magnetite flow may directly connect to crystals. observed redox changes in oxide phases. The most critical of these post-depositional observations is the oxidation of magnetite rims (Fig. 1). Overall, across all the cores, independent of redox changes observed in oxide phases, we note a transition in texturally early phases from reduced fine-grained, Fe2+- containing minerals to Mn-Carbonate. This mineralogical transition is marked by anoxic geochemical signatures and possibly indicates minor variations in oxygen conditions during the formation of the mineral phases preserved in the Freedom Formation. References: Krause, A. J., W. Mills, B. J., Merdith, A. S., Lenton, T. M., & Poulton, S. W. (2022). Extreme variability in atmospheric oxygen levels in the late Precambrian. Science Advances. https://doi.org/abm8191 LaBerge, G. L. (1964). Development of magnetite in iron formations of the Lake Superior region. Economic Geology, 59(7), 1313–1342. Lyons, T. W., Diamond, C. W., Planavsky, N. J., Reinhard, C. T., & Li, C. (2021). Oxygenation, life, and the planetary system during Earth’s middle history: An overview. Astrobiology, 21(8), 906–923. Lyons, T. W., Reinhard, C. T., & Planavsky, N. J. (2014). The rise of oxygen in Earth’s early ocean and atmosphere. Nature, 506(7488), 307–315. Slotznick, S. P., Johnson, J. E., Rasmussen, B., Raub, T. D., Webb, S. M., Zi, J. W., Kirschvink, J. L., & Fischer, W. W. (2022). Reexamination of 2.5-Ga “whiff” of oxygen interval points to anoxic ocean before GOE. Science Advances, 8(1), eabj7190. Stewart, E. K., Brengman, L. A., & Stewart, E. D. (2021). Revised Provenance, Depositional Environment, and Maximum Depositional Age for the Baraboo (< ca. 1714 Ma) and Dake (< ca. 1630 Ma) Quartzites, Baraboo Hills, Wisconsin. The Journal of Geology, 129(1), 1–31. 10 �The Lake Superior area “event layer”: Testing the connection with the Sudbury impact BLEEKER, Wouter1, WODICKA, Natasha1, KAMO, Sandra2, HAMILTON, Michael2, EMON, Quinn1, and SMITH, Jennifer1 1 Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8; wouter.bleeker@canada.ca Jack Satterly Geochronology Lab., University of Toronto, 22 Ursula Franklin St., Toronto, ON M5S 3B1 2 Following the initial publication of Addison et al. (2005) [1], there has been growing recognition of a major “event layer” near the top of the Gunflint Formation in the Thunder Bay area [e.g. 2,3,4], and at equivalent stratigraphic levels in the Marquette Range Supergroup of Michigan and Wisconsin [5,6]. Despite some initial hesitation [7,8], a consensus quickly emerged that this event layer represents the local manifestations, in the Lake Superior area, of the 1850 Ma Sudbury impact event that, ~600 km to the east, formed a multiring impact crater centered on the Sudbury area (see [9,10] for a recent review). The deformed and partially preserved remnants of this crater are known as the “Sudbury Structure” and, with a reconstructed final crater diameter of ~300 km, it represents the largest terrestrial impact crater known in the geological record [9]. As such, it would have had far-reaching effects extending out to several crater diameters from “ground zero”, in addition to a global fall-out layer of impact material (cf. the global K-Pg ejecta layer). A curious question, raised in Bleeker & Kamo (2022) [10], is why then this event layer is not more widely recognized in Canada, in places where ca. 1850 Ma basinal stratigraphy is reasonably well preserved (e.g., Mistassini Basin, Fox River Belt, Belcher Islands, Labrador Trough etc.)? Some of these localities are not much farther away from a “ground zero” near Sudbury. This has prompted us to undertake further tests of the putative link between the Lake Superior area event layer and the Sudbury impact structure. Our first test is to more precisely date, by CA-ID-TIMS, felsic ash layers in the lowermost Rove Formation, i.e. the first well-defined and well-preserved tuff layers overlying the event layer. Currently our results suggest the oldest of these tuff layers is ca. 1842 Ma, thus tightening the permissible time interval for the event layer to 1856-1842 Ma [cf. 1,2]. Our second test (in progress) is to attempt a precise CA-ID-TIMS zircon date of the ca. 1850 Ma Peavy Pond Granodiorite (which currently has a SHRIMP age with ±11 Myr uncertainty, see [11]). This granodiorite is known to intrude the lower Michigamme Slates, Baraga Group, in Michigan (W. Cannon, pers. comm. 2023), thus constraining a minimum age for the event layer. Our third and potentially most definitive test is to identify “tracers” in the event layer of the Lake Superior area that can be uniquely tied to target rocks of the Sudbury area. One such tracer would be 2460 Ma zircons from the Copper Cliff Rhyolite and its subvolcanic intrusions (Creighton and Murray granites) that are unique to the area and represent the final felsic rift volcanism/magmatism of the lowermost Huronian Supergroup [12,9,10]. For this test we processed a large bulk sample (~7.5 kg) of the event layer, with its diagnostic grey accretionary lapilli, from the HWY 588 locality west of Thunder Bay. Zircons were separated and mounted for SHRIMP U-Pb analysis at the Geological Survey of Canada, Ottawa. Eighty three zircon grains were spot dated, of which 71 returned high-quality results (Figure 1). Figure 1: U-Pb concordia plot for spot dates by SHRIMP on 71 zircon grains from the Gunflint event layer, HWY 588 roadside outcrop. 11 �The age distribution shows several well-defined clusters with 2(3) of the dated zircons defining a small but discrete subpopulation at ca. 2460 Ma. One of these zircons shows possible shock features (PDFs, planar deformation features; see Figure 1 inset) identified during picking. Although this particular grain is likely ca. 2460 Ma in origin, its result shows considerable discordance and should thus be treated with caution. Nevertheless, we think the 2460 Ma subpopulation uniquely ties fall-out material in the event layer, including rare shocked quartz grains [e.g. 2], to the Sudbury crater and its target rocks. In addition to the conclusive result of the 2460 Ma zircons, the data also identify a distinct ca. 2310-2320 Ma subpopulation of zircon grains that are known to first show up (in a regional stratigraphic sense) in the Gordon Lake Formation of the upper Huronian Supergroup. These zircon grains could have been delivered to the Thunder Bay area either as 1) ejecta from the Sudbury impact event, or perhaps more likely 2) as reworked detrital zircons from widespread felsic ash material that was deposited across the wider Superior craton at 23102320 Ma. Finding shock features in these grains would favour the first scenario, whereas a total absence of shock features would favour the second scenario. To further constrain the impact event, we also subsampled the large sample from the HWY 588 event layer into 6 small slabs with varying abundances of 1–3 cm accretionary lapilli (i.e. from ~5 to ~95 vol% lapilli) and analyzed these for major and trace elements, and for low-level PGE abundances. Results show a negative correlation between siderophile elements such as Ir (also Ru, Ni, Cr etc.) and lapilli abundance, indicating that the lapilli consist largely of diluting material and are not the optimum target for identifying the nature of the impactor [e.g. 13]. The highest Ir content of 0.3–0.4 ppb, i.e. ~1–2 orders of magnitude above average crustal values, actually occurs in laminated, dark, fine sand- to silt-size sediments that overlie the lapilli-rich horizon fall-out material (~0.5–1.0 m above). Future work will entail more detailed sampling of this overlying stratigraphy to identify the Ir peak and define the detailed mineralogy and Ir deportment in this material. Incidentally, values of 0.3–0.5 ppb Ir are also the maximum recorded values in the upper Onaping Formation filling the Sudbury crater and overlying its melt sheet [14]. From our initial results it appears that a maximum of impactor material condensed relatively late and was least diluted in fine grained fall-out material near the top of the event layer, well above the accretionary lapilli. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Addison, W.D., Brumpton, G.R., Vallini, D.A., McNaughton, N.J., Davis, D.W., Kissin, S.A., Fralick, P.W., and Hammond, A.L., 2005. Geology, vol. 33(3), p. 193–196. Addison, W.D., Brumpton, G.R., Davis, D.W., Fralick, P.W., and Kissin, S.A., 2010. GSA Special Paper 465, p. 245–268. Jirsa, M.A., Fralick, P.W., Weiblen, P.W., and Anderson, J.L.B., 2011. GSA Field Guide 24, p. 147–169. Huber, M.S., McDonald, I., and Koeberl, C., 2014. Meteoritics & Planetary Science, vol. 49(10), p. 1749–1768. Pufahl, P.K., Hiatt, E.E., Stanley, C.R., Morrow, J.R., Nelson, G.J., and Edwards, C.T., 2007. Geology, vol. 35(9), p. 827–830. Cannon, W.F., Schulz, K.J., Horton Jr, J.W., and Kring, D.A., 2010. GSA Bulletin, vol. 122(1–2), p. 50–75. Kissin, S.A., and Fralick, P.W., 1997. Journal of the Royal Astronomical Society of Canada, vol. 91(5), p. 216. Kissin, S.A., Okamoto, M., Addison, W.D., and Brumpton, G.R., 2000. 46th Annual Meeting of the Institute on Lake Superior Geology, vol. 46, part 1, p. 31–32. Bleeker, W., and Kamo, S., 2022a. 68th Annual Meeting of the Institute on Lake Superior Geology, vol. 68, part 1, p. 5–6. Bleeker, W., and Kamo, S., 2022b. 68th Annual Meeting of the Institute on Lake Superior Geology, vol. 68, part part 2, Field Trip Guidebook, p. 4–57. Ayuso, R.A., Schulz, K.J., Cannon, W.F., Woodruff, L.G., Vazquez, J.A., Foley, N.K., and Jackson, J., 2018. 64th Annual Meeting of Institute on Lake Superior Geology, vol. 64, part 1, p. 7–8. Bleeker, W., Kamo, S.L., Ames, D.E., and Davis, D., 2015. Geological Survey of Canada Open File 7856, p. 151–166. Mougel, B., Moynier, F., Göpel, C., and Koeberl, C., 2017. Earth and Planetary Science Letters, vol. 460, p. 105–111. Mungall, J.E., Ames, D.E., and Hanley, J.J., 2004. Nature, vol. 429(6991), p. 546–548. 12 �Insights into the southwestern Superior Province: New igneous geochronology and geochemistry in northwestern Minnesota, USA BLOCK, Amy Radakovich1, HUDAK, George J.2, SOUDERS, A. Kate3 1 Minnesota Geological Survey, 2609 Territorial Road, St. Paul, MN 55114 University of Minnesota –- Twin Cities, 116 Church Street SE, Minneapolis, MN 55455 3 U.S. Geological Survey, Denver, CO 80225 2 The U.S. Geological Survey Earth Mapping Resources Initiative (Earth MRI) program recently funded acquisition of new airborne geophysical (Allen Langhans and Drenth, 2023), geochronologic, and geochemical data in a part of the Superior Province in northwest Minnesota that is prospective for numerous Archean critical-mineral-producing systems. The study area comprises three subprovinces of the Archean Superior Province (Fig. 1). Previous work in the area (Jirsa et al., 2012; Jirsa et al., 1999) has been severely limited by an absence of outcrop, sparse drill hole data, and the existence of only one geochronologic age. These new ages and geochemical analyses, obtained through the Earth MRI program, represent the first highresolution geologic data in the Neoarchean subprovinces of the southwestern Superior Province. Seven new U-Pb zircon LA-ICP-MS magmatic ages (Souders, in review) establish the timing of intrusive activity in the southwestern extent of both the Wawa and Wabigoon subprovinces. A biotite-hornblende tonalite in the Red Lake Falls pluton (207Pb/206Pb weighted mean age of 2701 ± 4 Ma, 2s), a biotite tonalite in the Snake River batholith (207Pb/206Pb weighted mean age of 2738 ± 12 Ma, 2s), and a diorite in the Grygla pluton (207Pb/206Pb weighted mean age of 2771 Ma ± 8 Ma, 2s) define three distinct Neoarchean episodes of intermediate intrusive activity near the present-day southern margin of the Wabigoon subprovince. A preliminary magmatic age from a small hornblende monzodiorite stock in the Wabigoon indicates ca. 2727 intermediatemafic intrusive activity. In the Wawa subprovince, a 207Pb/206Pb weighted mean age of 2702 ± 6.5 Ma age (2s) from the Fertile pluton biotite granodiorite indicates Neoarchean intermediate intrusive activity at the northern margin of the Wawa subprovince coincident with similar activity in the Wabigoon. A small mafic body that intrudes a mafic volcanic sequence in the Wawa yields a preliminary age of ca. 2690 Ma. Finally, a combined 207Pb/206Pb weighted mean age from two closely spaced anorthosite samples confirms a Neoarchean (2737 ± 4.5 Ma, 2s) age for the Mentor Anorthosite Intrusive Complex (MAIC). High-precision CA-TIMS U-Pb zircon analyses provide age constraints on supracrustal rocks in both subprovinces. Two trachyandesite lapilli tuff samples from the Wabigoon subprovince yield 207 Pb/206Pb weighted mean ages of ca. 2730 Ma and ca. 2733 Ma (Block et al., in prep. b), >25 Ma older than the few other volcanic ages from the Wabigoon in Minnesota. Two feldspathic wackes in the Wawa subprovince are still being processed for ages. Newly dated intermediate intrusions are LREE enriched and have arc-like trace element patterns. Discrimination diagrams indicate that these intrusions are generally I-type, calc-alkaline, volcanic arc-granites. Samples from the MAIC exhibit complex REE patterns, and their interpretation is less straightforward. The newly dated intermediate volcanic samples from the Wabigoon are also calc-alkaline and exhibit arc-like signatures. In combination with ~130 additional geochemical analyses and detailed petrography, results presented here provide significant insight into the tectonic evolution of the southwestern Superior Province and invite comparison with well-studied rock packages in the Wabigoon and Abitibi provinces in Canada. 13 �Figure 1. Bedrock geology map of northwestern MN, USA. Units within the project area (Block et al., in prep. a) are shown in the legend. Units outside the map area are from Jirsa et al. (2012). Newly obtained LA-ICPMS U-Pb ages are shown as yellow stars, and newly obtained TIMS U-Pb ages are shown as green stars. References Allen Langhans, A.D., and Drenth, B.J., 2023, Airborne magnetic and radiometric survey, northwestern Minnesota, 2021: U.S. Geological Survey data release, https://doi.org/10.5066/P97D2JJE. Block, Amy Radakovich, Drenth, Benjamin J., Souders, A. Kate, Hudak III, George J, Hirsch, Aaron C., and Saari, Stacy M., in prep. A, Geologic map of the Mentor Igneous Complex Focus Area, Northwest Minnesota: Minnesota Geological Survey, Miscellaneous Map Series M-200, scale: 1:100,000. Block, Amy Radakovich, Hudak III, George J, Souders, A. Kate, Drenth, Benjamin J., Schmitz, M., Hirsch, Aaron C., and Saari, Stacy M., in prep. b, Preliminary investigation of the geologic history and critical mineral potential of the Mentor Igneous Complex Focus Area, Northwest Minnesota: Minnesota Geological Survey, Report of Investigations 74. Jirsa, M. A., Boerboom, T. J., Chandler, V. W., 2012, Geologic Map of Minnesota, Precambrian Geology: Minnesota Geological Survey, Map S-22, 1:500,000. Jirsa, M. A., Chandler, V. W., and Runkel, A. C., 1999, Bedrock geologic map of northwestern Minnesota: Minnesota Geological Survey, Miscellaneous Map Series M-92, 1:200,000. Souders A.K., in review. U-Pb geochronology of the Mentor Anorthosite Intrusive Complex (MAIC) and regional plutonic units: U.S. Geological Survey data release, https://doi.org/10.5066/P9WMD477. 14 �Magmatic and hydrothermal evolution of the Mesoproterozoic Current ultramafic PGE-CuNi deposit within the Thunder Bay North Intrusive Complex: insights from trace elements, Nd, Sr, O, and H isotopes CORREDOR BRAVO, Andrea Paola1, HOLLINGS, Pete1, BRZOZOWSKI, Matthew1, and HEGGIE, Geoff2 1 Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1 Canada Clean Air Metals, 1004 Alloy Drive, Thunder Bay, ON P7B 6A5 Canada 2 The Mesoproterozoic PGE-Cu-Ni enriched Current intrusion, part of the Thunder Bay North Intrusive Complex, is located 50 km northeast of Thunder Bay, Ontario. The northwest-trending intrusion is a 3.4 km long conduit-type that intruded the rocks of the Quetico Basin during the early stages of the Midcontinent Rift System (MRS; Woodruff et al, 2020). The intrusion has four mineralized zones; the Current and Bridge Zone in the northwest are characterized by shallow and thin features; in the middle lies the BeaverCloud Zone, characterized by its substantial thickness, while the southeast is the deepest 437Southeast Anomaly (SEA) Zone (Kuntz et al., 2022). The intrusion exhibits a primitive mantle- Figure 1. Schematic model of the Current intrusion and the Quetico country rock. normalized pattern resembling ocean island Illustration compiled in Leapfrog using data basalt, characterized by LREE enrichment and provided by Clean Air Metals Inc. small positive anomalies in Nb, La, and Ce, consistent with minimal continental crust contamination. The La/Smn values in the Current intrusion samples, ranging from 1.8 to 2.6, align with previous studies, indicating a basaltic magma derived from an enriched mantle plume. The enriched nature of the magma in the Current intrusion is consistent with other mineralized and unmineralized intrusions associated with the MRS (Escape, Seagull, Lone Island intrusion, and Nipigon Embayment; Heggie, 2005; Hollings et al., 2007b; Caglioti, 2023; Yahia, 2023). The intrusion has slightly lower Sri (0.7021 to 0.7043) and εNd (-1.18 to -4.02) values compared to typical the mantle source at 1100 Ma. Therefore, it is suggested that the plume-derived magma interacted with an enriched subcontinental lithospheric mantle, which may have contributed to the slightly negative εNd values of the intrusion.The stable isotope analysis data from the Current intrusion indicates an interaction between magmatic mantle-derived fluids (δ2H from −40 to −80‰, δ18O from 5.5 to 7.0‰), meteoric fluids (δ2H <-80‰, δ18O <5.5‰), and devolatilization/ dehydration fluids of the Quetico country rocks (δ18O >7‰). Three distinct domains within the intrusion were identified based on alteration intensity and micro-textural observations and each showing varying secondary mineral assemblages Domain A consists of antigorite, tremolite, clinochlore, epidote, pyrite, cubanite, millerite, secondary pyrrhotite ± chamosite ± sericite, and ± secondary magnetite, Domain B consists of 15 �lizardite-chrysotile, tremolite, clinochlore, epidote, pyrite, cubanite, millerite ± sericite, and ± secondary magnetite Domain C consists of talc and carbonates. Domain A and B have characteristics of interaction with meteoric, mantle, and/or subcontinental lithospheric mantle -derived fluids, whereas Domain C is associated with fluids from devolatilization of the country rock and is overprinted on Domains A and B. The alteration processes in the different domains Figure 2. δ18O and δ2H values of bulk rock in the four involved two distinct fluid types at mineralized zones of the Current intrusion (Current, varying temperatures, Domain A likely Bridge, Beaver-Cloud, and 437-SEA) and the involved higher temperatures (>300°C) surrounding country rock of the Quetico basin. and fluids rich in H2O. In contrast, domain B was altered by fluids at lower temperatures (<300°C). Later CO2-bearing fluids of Domain C overprinted earlier alteration at temperatures below 50°C. The alteration of the intrusion also resulted in significant volume reduction of primary sulfides and oxides that have been replaced by secondary minerals, such as chalcopyrite and pyrrhotite were replaced by secondary magnetite and pyrite and primary magnetite was replaced by pyrite and chamosite. References Caglioti, C. (2023). PGE–Cu–Ni sulfide mineralization of the Mesoproterozoic Escape intrusion, northwestern Ontario (MSc). Lakehead University, Thunder Bay, Ontario. https://knowledgecommons.lakeheadu.ca/handle/2453/5195 Heggie, G. (2005). Whole rock geochemistry, mineral chemistry, petrology, and Pt, Pd mineralization of the Seagull Intrusion, Northwestern Ontario. Lakehead University, Thunder Bay, Ontario. https://knowledgecommons.lakeheadu.ca/handle/2453/689 Hollings, P., Richardson, A., Creaser, R. A., and Franklin, J. M. (2007b). Radiogenic isotope characteristics of the Mesoproterozoic intrusive rocks of the Nipigon Embayment, northwestern Ontario. Canadian Journal of Earth Sciences, 44(8), 1111-1129. https://doi.org/10.1139/e06-128 Kuntz, G., Wissent, B., Boyk, K., Harkonen, H., Jones, L., Muir, W., Buss, B., and Peacock, B. (2022). NI 43- 101 Technical report and preliminary economic assessment for the Thunder Bay North Project, Thunder Bay, Ontario Woodruff, L. G., Schulz, K. J., Nicholson, S. W., and Dicken, C. L. (2020). Mineral deposits of the Mesoproterozoic Midcontinent Rift system in the Lake Superior region–a space and time classification. Ore Geology Reviews, 126, 103716 Yahia, K. (2023). Geochemistry, petrography, geochronology, and radiogenic isotopes of the weakly mineralized intrusions in Thunder Bay North Igneous Complex (MSc). Lakehead University, Thunder Bay, Ontario. https://knowledgecommons.lakeheadu.ca/handle/2453/5283 16 �Re-interpretation of hydrothermal alteration, mineralization and host-rock oxidation to form the Keweenaw native copper lodes, northern Michigan BROWN, Alex C. 13250 rue Acadie, Pierrefonds, Quebec, Canada, H9A 1K9, acbrown@polymtl.ca The sandstone/conglomerate-hosted portions of the native copper ores of northern Michigan (e.g., the Calumet and Hecla Conglomerate ores) occur mostly in deeply reddish sediments. In the immediate vicinity of native copper ores, the reddish sediments appear to have been hydrothermally bleached to salmon-red colors (Butler and Burbank, 1929; Cornwall, 1956; White, 1968; Weege and Pollock, 1972). This communication notes that fine-grained salmoncolored clastic sediments may host fine-grained disseminations of native copper enclosed by salmon-red aureoles, not unlike grey reduction halos commonly found in red sandstones (Figs. 1, 2). If the interpreted origin and preservation of reduction halos in red sandstones is applied to the native copper-hosting aureoles in the Calumet and Hecla Conglomerate, the deep reddening of the conglomerates hosting native copper of the Keweenaw Peninsula may be interpreted as a post-ore event. Redbed sandstones commonly show centimeter-scale reduction spots and blotches, e.g., rift-hosted Carboniferous clastic sediments of eastern Canada (Poll and Sutherland, 1976), the Permian fluvial Abo Formation of New Mexico (Bensing et al., 2005), and the Jacobsville sandstones of northern Michigan. Petrographic and chemical analyses of reduction spots in the Abo Formation indicate that those reduction spots have never been reddened – ferrous clastic grains within the reduction spots are still ferrous while similar grains in the enclosing red sandstone are oxidized (Bensing et al., 2005). Interpretation: wood trash in the cores of reduction spots maintained elliptical reducing conditions in the immediate vicinity of wood trash (i.e., within the grey halos), while oxidizing post-sedimentary water reddened all other portions of the clastic sediments. Figure 1. Carboniferous redbeds of Dorchester Cape, New Brunswick, Canada, showing abundant centimetric-scale reduction spots with dark-greyish cores centered on fossilized organic matter. Figure 2. Close view of greyish reduction spots in redbeds of Figure 1 (tip of hammer for scale). Cores of reduction spots contain fossil wood debris and base-metal sulfides e.g., chalcocite, partially oxidized to malachite). 17 �Native copper in the Calumet and Hecla Conglomerate occurs as interstitial fillings in conglomerates and as fine-grained disseminations in finer sandy sediments. Curiously, very finegrained disseminations of native copper in fine-grained sediments are observed to be surrounded by elliptical salmon-red sediment (Fig. 3). A possible, chemically justified interpretation: native copper was deposited with salmon-red alteration, mostly within highly permeable conglomeratic portions of the sandstone-conglomerates and also as very fine-grains in associated sandy sediments. Subsequently, all sandstone-conglomerates were thoroughly oxidized to their classic deep-red color during post-ore circulations of oxygenated ground water, except in the finergrained sediments where local salmon-red alteration was preserved against reddening by reduction-inducing fine grains of native copper. Post-ore deep-red oxidation of copper in the fine-grained sediment was inhibited by the poor permeability of this fine-grained sediment to late deep-reddening groundwaters, but also by the reducing property of metallic copper. Figure 3. Cut and epoxy-ed sample of Calumet and Hecla Conglomerate native copper ore. Upper half: Deep red, coarse conglomeratic sediment with coarse-grained native copper. Lower half: Fine-grained clastic sediment containing fine-grained native copper enclosed by “bleached” salmon-red alteration halos. Bleached halos and core native copper are equated here to reduction spots with fossil wood debris common in redbed sandstones (see text for explanation). References Bensing, J.P., Mozley, P.S., and Dunbar, N.W., 2005. Importance of clay in iron transport and sediment reddening: evidence from reduction features of the Abo Formation, New Mexico, U.S.A. Sedimentary Research, 75: 562–571. Butler, B.S. and Burbank, W.S., 1929. The copper deposits of Michigan. US Geol. Surv. Prof. Paper 144, 238 p. Cornwall, H.R., 1956. A summary of ideas on the origin of native copper deposits. Economic Geology, 51: 615–631. Weege, R.J. and Pollock, J.P., 1972. The geology of two new mines in the native copper district of Michigan. Economic Geology, 67: 622–633. White, W.S., 1968. The native-copper deposits of northern Michigan, in Ridge, J.D., ed., Ore Deposits of the United States, 1933–1967 (Graton-Sales Volume 1), American Inst. Min. Metall. & Petrol. Eng., 303–326. 18 �Preliminary mineralogy of a pegmatite in the pyroxene syenites of the Stettin Complex, Wausau Complex, Marathon County, Wisconsin Buchholz, Thomas 1, Falster, Alexander 2, and Simmons, Wm 2 1 1140 12th Street North, Wisconsin Rapids, Wisconsin 54494 MP Research Group, Maine Mineral and Gem Museum, PO Box 500, 99 Main Street, Bethel, Maine 04217, USA 2 2 The Stettin Complex is the oldest (1565 +3-5 Ma, Van Wyck 1994) and most alkalic of the four intrusions that comprise the Wausau Syenite Complex, and is composed of various syenite phases. Recently an opportunity arose to examine the mineralogy of a pegmatite located in the pyroxene syenites of the Stettin Complex. Upper portions of the roughly horizontal pegmatite are below tilled soils but in-situ, are weathered, and fragments are coated with Fe-oxides and clays. Excavations over the last several years has exposed somewhat fresher material at depth and allowed better study. The pegmatite is zoned, but numerous included syenite screens complicate evaluation. Pegmatite-host syenite contacts are often sharp with no notable contact zones, suggesting relatively minor temperature contrast between the two phases, but thin 2-3 cm reaction zones are also common, with minor coarsening of feldspar and arfvedsonite compared to host syenite, small miaroles, scattered patches of abundant, tiny pink zircons and yet unidentified minerals, and in the freshest material, fluorite. The upper weathered portions of the dike, probably corresponding to border and intermediate zones, consist of anorthoclase (often showing “moonstone” visual effects; the recovery of these feldspars is the objective of those working the dike), highly altered former pyroxenes(?) with-sparse remnant hedenbergite, arfvedsonite, quartz, abundant clear pink to orange zircons and other accessory phases, including small miarolitic cavities. Per Medaris & Koellner (2010), pyroxenes in the Stettin complex range from Fe-rich diopside, to hedenbergite and aegirine. In this pegmatite pyroxenes appear to have been affected by late-stage oxidizing fluids, altering Fe2+-rich pyroxenes to Fe3+ rich smectite-group clays ± Fe-oxyhydroxides with sparse remnants of hedenbergite, while aegirine is absent from the dike. Ca released by pyroxene alteration may have contributed to the formation of various late-stage Ca-rich species. Deeper interior zones are mostly anorthoclase with arfvedsonite and other accessory minerals, with contact zones (or lack thereof) repeated around included syenite fragments. Graphic quartz-anorthoclase intergrowths “graphic syenite” are locally common, as are small miarolitic cavities. Several small-volume pegmatite units are: rare irregular patches of granular albite +- larger anorthoclase crystals, with abundant pyrochlore(?) crystals and possibly other species; and enigmatic thin 2-5 cm thick irregular veins or pods, mainly quartz, albite and anorthoclase: these are confined to the pegmatite and do not enter the host syenite, and includes sparse arfvedsonite, abundant cassiterite grains (≈2-4 μm), fergusonite, metamict zircons (some showing Hf-enrichment), sparse microlite (Ta-dominant pyrochlore group), sparse tantalite-(Mn) (Ta-Mn dominant columbite-group species), tiny grains of barite, and other yet-unidentified species. These anomalous pods or veins may be derived from highly fractionated late-stage differentiates. Perhaps high F activity supported unusual enrichment of HFSE in latecrystallizing melt. . 19 �Other accessory mineralogy of the main dike includes: Aeschynite-(Ce): Elongated, dark greyblack crystals in anorthoclase. Synchysite/Parisite: Small red to pinkish hexagonal crystals. High Ca contents suggest they are either synchysite or parisite. Bavenite(?): Small white bladed crystals included in clear quartz crystals; tentative ID based on their morphology and presence of Ca, Si and O (EDS). Calcite: White crusts and masses in vugs from lower portions of the excavation. Chevkinite-group(?): Dark grains with white borders; often heavily altered to soft, chalky, fine-grained niobian Ti-oxides with minor Th, Ca, LREE ± Si and Al. Columbite-group: Sparse columbite-(Fe) noted as inclusions in a porous fergusonite-(Y) grain. Fayalite: Uncommon gray radiating acicular crystals and glassy brown grains associated with arfvedsonite. Fergusonite-(Y): Small yellowish to reddish-brown tapering crystals in anorthoclase, arfvedsonite and miaroles. Ferro-anthophyllite: Uncommon, patches of white acicular crystals in smectite-rich altered pyroxenes. Fluorapatite: Sparse crystals in vugs with arfvedsonite. Fluorite: Late in vugs and isolated grains, likely often removed by weathering. Graphite: Sparse Thin hexagonal platy crystals, typically showing thin hexagonal overgrowths. Ilmenite: Common; thin black metallic plates with a pyrophanite component in anorthoclase and miaroles. Kainosite-(Y)(?): One off-white crystal in pegmatite, appears to be a Ca-Y-LREE silicate, may be kainosite-(Y). Magnetite: Common as irregular masses, rarely as well-formed octahedral crystals. Molybdenite: Sparse as thin soft hexagonal plates. Monazite-(Ce): Uncommon, small brick-red crystals in feldspar and in vugs. Niocalite(?): Yellow to pale yellow-brown elongated crystals in anorthoclase. Very sparse. Some compositions strongly suggest niocalite, others are yet-unidentified species. Pyrochlore: Rare: yellow-brown octahedral crystals. Quartz: Common, generally as a later-stage mineral. Siderite: now absent, but goethite pseudomorphs after probable siderite are common in small vugs. Thorite: Rare; red to red-black grains associated with fergusonite-(Y). Titanite: Uncommon, as brown to redbrown grains. Zircon: Abundant in upper intermediate zone, less so in coarse interior zones. As work continues, it is likely that additional phases will be identified, as there are a number of unknowns awaiting further work, and much material awaits cleaning and study. Thanks are due to Austin Gausmann, Bill Schoenfuss, and Trent and Shana Rebeck for access to the pegmatite. REFERENCES: Medaris, L. Gordon Jr., Koellner, Susan E., 2010. Ferromagnesian minerals in the Stettin Syenite Complex, Marathon County, Wisconsin: compositions and contrasts with the Wolf River Batholith (abstract): Institute on Lake Superior Geology Proceedings, 56th Annual Meeting, International Falls, MN, v. 56, part 1, p. 42-43. Van Wyck, N. 1994. The Wolf River A-type magmatic event in Wisconsin: U/Pb and Sm/Nd constraints on timing and petrogenesis (abstract): Institute on Lake Superior Geology, 40th Annual Meeting, Part 1, Program and Abstracts, p. 81-82. 20 �The Sacred Heart Orogeny in Michigan: Latest Archean Granites and the Great Lakes Tectonic Zone CANNON, W. F.1, SOUDERS, A. K2, DRENTH, Benjamin J.2, AYUSO, Robert A.1 1 U.S. Geological Survey, Reston, VA 20192, 2U.S. Geological Survey, Denver, CO 80225 The Sacred Heart Orogeny, as defined in Minnesota (Schmitz, et al., 2018), is the terminal Archean contractional and magmatic event during which the Minnesota River Valley Subprovince (MRVS) was sutured to the southern edge of the Superior craton along the Great Lakes Tectonic Zone (GLTZ), accompanied by voluminous granitic magmatism. The ages of those granites are tightly clustered from 2.58-2.6 Ga. In Michigan’s Upper Peninsula voluminous granites of the Southern Complex, the eastern extension of the MRVS, have ages very similar to those in Minnesota and were emplaced near and within the GLTZ during suturing. The granitic phase of the Bell Creek Gneiss (Cannon and Simmons, 1973), a coarse-grained, K-spar megacrystic granite, is well dated (Petryk, 2019; Barth, 2023). The average of ten dates is 2.56 Ga. An additional age from SHRIMP analyses (Ayuso, presented here) is 2584+5.3/-2.79 Ma, fully consistent with previous determinations. We have recently recognized and dated a batholithic-scale intrusion of medium-grained, massive, K-rich granite, informally the New Swanzy granite, that borders the granitic phase of the Bell Creek Gneiss to the east and is adjacent to and interacted with the GLTZ during suturing. A regionally extensive negative gravity anomaly south and southeast of the exposed granite suggests that the batholith is substantially larger than its exposed portion (see map below). Both granites intruded an older gneiss complex with ages ranging from 2.6-2.9 Ga. The Bell Creek granite has an internal foliation defined by alignment of K-spar megacrysts broadly conformable with trends of adjacent gneisses, and contains no angular xenoliths. In contrast, the New Swanzy granite, although compositionally uniform as judged in outcrop, has numerous pegmatitic segregations and dikes. It has sharp cross-cutting contacts with older gneisses and contains many xenoliths. These characteristics and several instances of dikes of New Swanzy-like granites cutting the Bell Creek, suggests that the New Swanzy granite post-dates the Bell Creek Gneiss, at least slightly, and has an intrusive contact with it. The New Swanzy granite has a complex interaction with sheared rocks of the GLTZ. The GLTZ is a 2.5 km-wide, SW-dipping zone of dextral shear-thrusting where rocks of the MRVS were thrust northward over the Superior craton (Sims, 1991). The age of suturing was suggested to be about 2.69 Ga. Close to the GLTZ, the New Swanzy granite has a shear foliation parallel to the GLTZ. Within the GLTZ areas of granite are enveloped in intensely sheared rocks whose protolith is uncertain. Many dikes and stringers of granite cut mylonitic foliation. These show varying intensity of deformation, but all were emplaced after the most intense shearing. An undeformed granite dike was intruded across shear foliation at 2559±19.5 Ma (U-Pb apatite). We consider this to set a minimum age for deformation in the GLTZ in this region. Thus, the New Swanzy seems best interpreted as a syntectonic granite emplaced adjacent to the active suture late in development of the GLTZ The data summarized here indicate the latest Archean tectonic and intrusive events in northern Michigan and Minnesota are correlative. Thus, we deem it appropriate to extend the Minnesota-derived term “Sacred Heart Orogeny” to the culminating phase of development of the Southern Complex in Michigan. Because rocks of the Southern Complex are exposed in direct contact with the GLTZ, they present a unique opportunity to study the interaction of intrusion and suturing of the MRVS to the Wawa-Abitibi terrane. 21 �A-Massive New Swanzy granite cutting country rock gneiss. B- GLTZ mylonite cut by granitic stringers with varying degrees of deformation. C- undeformed 2.56 Ga granite dike cutting foliation of GLTZ. References Barth, E. G., 2023, Age and chemistry of the Bell Creek Batholith: Michigan Technological University, M.S. Thesis https://doi.org/10.37099/mtu.dc.etdr/1589 Cannon, W.F., and Simmons, G C., 1973, Geology of part of the Southern Complex, Marquette District, Michigan: Journal of Research of the U.S. Geological Survey, v.1, n.2, p. 165-173. Petryk, B. 2019, The origin of an Archean batholith in Michigan’s Upper Peninsula: Michigan Technological University, M.S. Thesis. https://doi.org/10.37099/mtu.dc.etdr/932 Sims, P.K, 1991, Great Lakes Tectonic Zone in Marquette Area, Michigan-implications for Archean tectonics in north-central United States: U.S. Geological Survey Bulletin 1904-E, 17 p. Schmitz, M.D., Southwick, D.L., Bickford, M.E., Mueller, P.A., and Samson, S.D., 2018, Neoarchean and Paleoproterozoic events in the Minnesota River Valley subprovince, with implications for southern Superior craton evolution and correlation: Precambrian Research, v.316, p. 206-226. 22 �The Honey Creek Structure, Sauk County, Wisconsin: Asymmetric Faulting Associated with Seismic-Induced Fluid Escape Kenz CARLTON1, Basil TIKOFF1, & Esther K. STEWART2 1 2 University of Wisconsin–Madison, Department of Geoscience, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Wisconsin Geological and Natural History Survey, UW-Madison Division of Extension, Madison, Wisconsin 53705, USA The Honey Creek structure occurs in the Balfanz quarry in Sauk County, Wisconsin. It is south of the Baraboo syncline and in the vicinity of the Denzer syncline. The Honey Creek structure is dominantly a N dipping fault (striking ~250 and dipping ~30 using right hand rule) that deforms the Ordovician Oneota Formation and underlying Cambrian Jordan Formation. The hanging wall contains units that are stratigraphically younger than those immediately adjacent across the fault; this geometry requires that the Honey Creek structure contains a normal fault. The footwall side of the fault was deformed, such that the beds were rotated to a nearly vertical orientation and occasionally overturned next to the fault. The folding in the footwall is consistent with drag on a reverse fault, which is opposite to the direction of inferred stratigraphic offset. Soft sediment deformation, interpreted as sand injection emanating from the Jordan Formation, is prevalent alongside the fault on the footwall side, although a sand lens crosscuts the fault in one place. A smaller-scale structure is located less than 30 m S of the Honey Creek structure. This feature has a similar strike and dip, normal sense of offset, and folding of the footwall. It differs from the Honey Creek structure insofar as there is brecciation but no sand injection along the fault. Finally, there appears to be a recumbent fold located less than 40 m S from the main Honey Creek structure, with a vergence away from the Honey Creek structure. We interpret this recumbent fold to have formed in the same deformational event. We consider two possible interpretations for this structure, both of which invoke significant ground shaking. First, the deformation could result from intracratonic seismicity. The timing of deformation (Early Ordovician) is broadly consistent with that of the Taconic orogeny, although the orientation of the fault is at a high angle to the inferred regional shortening direction (EW). Its location, directly south of the Baraboo syncline, could be consistent with reactivation of a Proterozoic fault. Second, the deformation could result from a distant (<200 km) meteor impact. The timing of deformation is consistent with a swarm of meteorites that occurred at the same time in the upper Midwest, and resulted in a number of craters (e.g., Decorah, Elm Creek, etc.). This interpretation is consistent with regional soft-sediment deformation in the Oneota Formation. 23 �Baddeleyite age reveals timing of the Northeast Iowa Intrusive Complex (NEIIC) CLARK, Ryan1, PEATE, David2, KUSICK, Allison2,3, HORKLEY, Kenny4, and MACFARLANE, Chris5 1 Iowa Geological Survey, University of Iowa, 300 Trowbridge Hall, Iowa City, IA, 52242, USA University of Iowa, Department of Earth & Environmental Sciences, 115 Trowbridge Hall, Iowa City, IA, 52242, USA 3 University of Wisconsin-Milwaukee, Department of Geosciences, 3209 N. Maryland Avenue, Milwaukee, WI, 53211, USA 4 University of Iowa, Materials Analysis, Testing and Fabrication Facility, 205 N. Madison Street, Iowa City, IA, 52242, USA 5 University of New Brunswick, Department of Earth Sciences, 2 Bailey Drive, Fredericton, New Brunswick, Canada 2 Recent geophysical surveys over portions of the entirely concealed Northeast Iowa Intrusive Complex (NEIIC) have provided a clearer picture of the region’s Precambrian basement geology (Drenth et al., 2015 and 2020). High amplitude magnetic and gravity anomalies remain the focus of further research into their mineral resource potential, due in part to the likelihood that the NEIIC is related to the ~1,100 Ma Midcontinent Rift System (MRS). A core drilled into the northeast-trending Osborne Anomaly in Clayton County, Iowa provides the only samples in the vicinity of the NEIIC. The Osborne core encountered 722 feet (220 m) of mafic-ultramafic rocks that has been previously described as olivine-plagioclase cumulate. Recent screening using a portable X-ray fluorescence (pXRF) spectrometer revealed elevated concentrations of zirconium (Figure 1) as well as aluminum and potassium in several discrete zones of late stage melt (Clark et al., 2019). Datable minerals in the form of zirconolite and baddeleyite have been identified in samples from these zones. Obtaining a reliable age from the Osborne core has been paramount to making the argument that the NEIIC is Keweenawan and thus possibly related to other magmatic intrusive terranes in the Lake Superior Region. A recent study (Drenth et al, 2020) obtained an age of ~1,170 Ma from LA-ICP-MS analyses of apatite crystals from the Osborne core. However, accurate U-Pb ages on apatites are often limited by the need for a precise correction for the common Pb component. Here, we present new U-Pb ages on baddeleyite crystals from a depth of 2,416.3 feet (736.5 m) that were analyzed by LA-ICP-MS at the University of New Brunswick. The U-Pb crystallization age of 1,148 ± 14 Ma (weighted average of six concordant baddeleyite analyses) stands as the first reliable date to come from the NEIIC region. This age is comparable with other intrusions outboard of the MRS, such as the Corson Diabase in eastern South Dakota (1,149 ± 7 Ma), the Great Abitibi dike (1,141 ± 2 Ma), and the Inspiration diabase (1,159 ± 33 Ma) (McCormick et al., 2017 and references therein), and indicate a wider regional magmatic event that pre-dated initiation of the MRS by ~50 Ma. The general age of these intrusions has been interpreted as early stage magmatism related to the onset of the MRS. The latest geophysical survey over the majority of the southern portion of the NEIIC shows that the Osborne Anomaly is cut by NEIIC intrusions (Drenth et al., 2020), thus providing a maximum emplacement age of ~1,150 Ma. 24 �Figure 1. Graph of Zr concentration by depth from two separate rounds of pXRF analyses illustrates two distinct zones of Zr-enrichment. Inset backscattered electron image shows an elongated zirconolite crystal (gray) with inter-grown baddeyelite crystal (white) from a sample at 2,614.3 feet depth. References Clark, R.J., Anderson, R.R., and Peate, D.W., 2019. The northeast Iowa intrusive complex: a magmatic conundrum related to the Midcontinent Rift System. Geological Society of America Abstracts with Programs, v. 51, no. 2. Drenth, B.J., Anderson, R.R., Schulz, K.J., Feinberg, J.M., Chandler, V.M., and Cannon, W.F., 2015. What lies beneath: geophysical mapping of a concealed Precambrian intrusive complex along the Iowa-Minnesota border. Canadian Journal of Earth Science, v. 52: 279-293. Drenth, B.J., Souders, A.K., Schulz, K.J., Feinberg, J.M., Anderson, R.R., Chandler, V.M., Cannon, W.F., and Clark, R.J., 2020. Evidence for a concealed Midcontinent Rift-related northeast Iowa intrusive complex. Precambrian Research, v. 347. McCormick, K.A., Chamberlain, K.R., and Paterson, C.J., 2018. U-Pb baddeleyite crystallization age for a Corson diabase intrusion: possible Midcontinent Rift magmatism in eastern South Dakota. Canadian Journal of Earth Science, v. 55: 111-117. 25 �Transpressional Nature of the Keweenaw Fault System, Lake Superior Region, and Its Relationship to Grenville Orogenesis DeGRAFF, James 1, GAMET, Nolan 2, LANGFIELD, Katherine 1, LIZZADROMcPHERSON, Daniel 1, MUELLER, Sophie 3, and TYRRELL, Colin 4 1 Michigan Technological University, Houghton, MI 49931 Michigan Geological Survey, Marquette, MI 49855 3 Nevada Gold Mines, Elko, NV 89801 4 Self-empoyed, Mass City, MI 49948 2 The Keweenaw fault system (KFS) is a connected set of faults that extends along the southern margin of the Midcontinent Rift System from northwest Wisconsin to near Keweenaw Point in Michigan. A component of reverse slip has thrust Portage Lake Volcanics (PLV, 1.1 Ga) southeastward over younger, mostly flat-lying Jacobsville Sandstone (JS) on some faults in the system (Fig. 1). This motion enhanced a regional northwesterly tilt to PLV strata, produced counter-regional tilt near major fault segments, and locally tilted footwall JS strata to vertical and overturned attitudes (1, 2). Regionally, the KFS azimuth changes by 65° from 35° near Houghton to 100° at Big Bay, as does the strike of PLV layers. Locally, the Keweenaw fault on published maps changes azimuth by up to 85° at unusual bends, some of which have been attributed to offsets on transverse faults. These changes in fault azimuth are important clues to the geometry of faults making up the KFS and to their individual and collective slip behavior. If opposing rock masses across the KFS are relatively rigid, a reasonable assumption, the fault system cannot be pure dip slip everywhere along its curved path, which inference also applies to its component faults. Mapping along the KFS since 2017 reveals that the sinuous, mostly single fault trace on published maps oversimplifies important structural relationships. In any part of the system, three directional fault sets are recognized: (1) a dominant set that defines the KFS trend and locally separates steeper dipping PLV layers to the northwest from shallower dipping PLV layers to the southeast; (2) splay faults angled 15-30° clockwise from set 1; and (3) connector faults angled 3575° counterclockwise from set 1 that join footwall splays to the main fault trend (Fig. 1). The three fault sets maintain these angular relationships as the curved KFS changes direction from near Houghton to the tip of the peninsula. Interconnections between faults define fault-bounded blocks with long dimensions roughly parallel to the local KFS trend. The fault-bounded blocks and footwall splay faults defining their southeastern and southern edges are arrayed in a left-stepping pattern along the KFS, suggesting a component of right-lateral strike slip. Analysis of fault-slip data, i.e. slickenlines and slip-sense indicators, from the fault population along the KFS indicates that the system’s slip characteristics change between Houghton and the tip of the Keweenaw Peninsula. Near Houghton where the KFS trends northeasterly, the ratio of strike slip to dip slip is about 1:1 and is bimodal, whereas the ratio is more than 2:1 and is unimodal near Bête Grise Bay where the KFS trends easterly. Geologic relationships across some faults are consistent with their northwest and north sides sliding to the right and upward relative to opposing sides. Inversion of fault-slip data indicates that a strike-slip regime existed near Keweenaw Point with an azimuth of maximum shortening of about 100°, which favors a component of right-lateral slip on the KFS. Folding within and adjacent to the fault-bounded blocks exhibits two styles. Multiple folds subparallel to shorter northeast and east ends of fault-bounded blocks (i.e. NE- to N-trending axes) formed by shortening across such boundaries. In contrast, single folds subparallel to longer sides of the blocks in footwall JS strata (i.e. NE- to ESE-trending axes) formed by drape 26 �of JS strata over steeply dipping, mostly strike-slip faults with little to no shortening across them. Based on this evidence, we infer that oblique slip on the KFS becomes mostly right-lateral strike slip near Keweenaw Point and that crustal shortening is along a line roughly perpendicular to the Grenville front about 550 kilometers to the east-southeast (Fig. 1). Acknowledgements: Funding was provided by the USGS EDMAP program, matched by MTU’s Department of Geology and Mining Engineering and Sciences, and supplemented by grants from the Michigan Space Grant Consortium, Keweenaw Community Forest Company, and the ILSG. We thank the Michigan Geological Survey for its sponsorship and G. Hubbell, I. Gannon, G. Hemmila, G. Ahrendt, J. Hawes, B. Murphy, B. Heusdens, and D. Breen for fieldwork assistance. Figure 1: Keweenaw fault system (black lines) north of Portage Lake, Michigan. Five largest fault-bounded blocks numbered 1 – 5. Black arrows show inferred maximum shortening direction. Inset map modified from Northwestern University maps online (https://www.earth.northwestern.edu/spree/Maps.html). References 1. Cannon, W.F. and Nicholson, S.W., 2001, Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan: United States Geological Survey, Map I-2696, Scale = 1:100,000. 2. DeGraff, J.M. and Carter, B.T., 2022, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulletin, v. 135, no. 1/2, p. 449–466. 27 �Glimpses of a Paleoproterozoic landscape: Analysis of exhumed topography on Archean basement rocks northwest of Marquette, Michigan EDIGER, Trent and BJØRNERUD, Marcia Geosciences Department, Lawrence University, Appleton Wisconsin 54911 Background and purpose: Northwest of Marquette, MI, between the Yellow Dog River on the north, and Silver Lake and the Little Garlic River on the south, the modern land surface lies close to the nonconformity between an Archean granite-greenstone complex (the ~2.7 Ga Compeau Creek Gneiss and Mona Schist) and Paleoproterozoic metasedimentary rocks (the ~1.85 Ga Michigamme Formation). High areas are underlain by Archean rocks, while lower ones are underlain by the Michigamme Fm., suggesting that Michigamme sediments accumulated on an ancient land surface of hills and valleys with up to 70 m of relief. Although the Archean and Proterozoic rocks are locally in fault contact, good exposures of the nonconformity, together with systematic fining of grain size in the Michigamme with distance from Archean highs, support the interpretation that much of this area is an ancient exhumed landscape. Further evidence for a regional Paleoproterozoic landscape with significant relief comes from observations that the Sudbury ejecta layer in the region occurs at a wide range of stratigraphic heights above the base of the Michigamme Formation, and locally directly on Archean rocks (Cannon et al., 2010). The modern topography of this region is also qualitatively different - more rugged – than that seen on Archean rocks exposed only 25 km to the south, along the Black River east of Republic, even though the two areas share the same glacial history. In the study area, we suspect that the primary effect of glacial erosion was to remove the soft Michigamme Fm. from high spots, reexposing the sub-Michigamme surface. In the southern area, either the Michigamme Formation was never deposited or the pre-glacial landscape had been already been eroded to a level below the nonconformity. We believe, therefore, that the study area preserves a low-fidelity version of a Paleoproterozoic landscape and can provide insight into patterns of erosion and weathering at a time before land plants and modern atmospheric conditions. On an Earth with no vegetation and little to no soil, eroded sediments would have had a shorter residence time on landscapes and in river systems. Bedrock rivers would have been more common than they are today, and the primary mechanisms of landscape evolution would have been corrosion (chemical weathering) in a CO 2rich atmosphere, corrasion (abrasion of bedrock by entrained sediment), and cavitation (pitting of bedrock surfaces by bubble implosion in turbulent waters). Faults, joints, and other bedrock features would have been the primary influences on river channel location and potholes would have played an important role in channel development (Wohl, 1998). The goal of the study was to develop quantitative metrics to characterize the exhumed ancient landscape and contrast these with modern topography in areas with similar bedrock in order to gain a better understanding of geomorphologic processes in Paleoproterozoic time. Methods: The boundaries of the 165 km2 study area -- the extent of the exposed Archean nonconformity surface -- were drawn based on the provisional geologic map by Klasner et al. (1979) in combination with field observations and visual assessment of the topography. The rocks in the southern comparison area along the Black River are not a granite-greenstone complex like those in the study area, but they do include a mix of felsic and mafic lithologies (Archean gneisses and Paleoproterozoic dikes; Cannon, 1975) and thus serve as a reasonable analog. In order to understand the role of climate in generating relief in granite-greenstone complexes, we also analyzed the topography of two other granite-greenstone terranes: the Pilbara craton in the desert of northwestern Australia (ca. 3.5-3.2 Ga) and the Umburanas complex in the rainforest of Bahia 28 �Province, Brazil (ca. 3.4-3.1 Ga). In both areas, the bedrock lies close to the surface and the regions have been tectonically stable since at least Mesoproterozoic time. Digital Elevation Models (DEMs) for the study site and comparison site came from LiDAR data collected by the USGS 3D Elevation Program and were accessed via OpenTopography’s data map. DEMs for the Bahia province in Brazil and the Pilbara craton in Australia were generated by the Shuttle Radio Topography Mission and accessed through USGS EarthExplorer, and Geoscience Australia’s data map, respectively. When necessary, DEMs were merged into a single feature layer in Esri ArcGIS Pro 3.2.0 and clipped to the areas of interest. Roughness visualizations were calculated by determining the difference between the highest and lowest elevation cell in each 3x3 rectangular pixel neighborhood (Wilson et al. 2007). In ArcGIS Pro, focal statistics (statistical operations on each pixel based on specified neighboring pixels), were used to generate maximum and minimum elevation rasters. These intermediary rasters were then used to quantify roughness and create visualizations using the raster calculator tool. Results: By several measures, the topography of the study area is significantly more rugged than that of both the Black River comparison site and the Pilbara Craton. The roughest 90 m2 parcel in the study area has 73 m of relief compared with 27 m for the Black River and 46 m for the Pilbara. The study site also has a greater percent of land area in the highest roughness classes (>16 m of relief within 90 m2 parcels). The Black River area and Pilbara craton are surprisingly similar in the distribution of elevations, despite representing very different erosional conditions (glacial scouring and desert exposure, respectively). However, along the Black River, lithology seems to have little control on topography while in the Pilbara craton, contacts between Archean batholiths and volcanogenic sediments are the roughest areas. The Umbaranas site is much rougher than the other three, with up to 392 m of local relief where greenstones are exposed, possibly reflecting the wide range of volcanic and sedimentary lithologies in the Umburanas complex (Barbosa & Sabaté, 2002). In the study site NW of Marquette, topographic roughness is concentrated along linear zones – presumably erosion-enhanced faults or fractures in the Archean bedrock. These straight paleochannels differ from the meandering shapes typical of alluvial (sediment-dominated) river systems. Moreover, some of these channels have scalloped edges, a possible record of their evolution through linkage of bedrock potholes (Wohl, 1998). In summary, the topography of the study area differs not only from that of the nearby Black River site, which shared the same recent glacial history, but also from both the desert and rainforest sites. We suggest, therefore, that the region northwest of Marquette represents a Paleoproterozoic bedrock landscape that may have developed under warm, wet conditions in the absence of vegetation, a combination that does not occur on Earth today. References cited Barbosa, J., & Sabaté, P., 2002. Geological features and Paleoproterozoic collision of four crustal segments, Sao Francisco craton, Anais Da Academia Brasileira de Ciências, 74, 343–359. Cannon, W.F., Schulz, K., Horton, J., & Kring, D., 2010. The Sudbury ejecta layer in the Paleoproterozoic iron ranges of northern Michigan, USA. GSA Bulletin, 122, 50-75. Klasner, J., Cannon, W.F., & Brock, M., 1979. Bedrock geologic map of Baraga, Dead River and Clark Creek basins, Marquette County Michigan, USGS Open File Report 79-1305. Cannon, W.F., 1975. Bedrock geologic map of the Republic Quadrangle, Marquette County, Michigan. USGS Miscellaneous Investigations Series Map I-862. Wohl, E. 1998. Bedrock channel morphology. Rivers Over Rock. AGU Monograph 107, 133-149. Wilson, M., OConnell, B., Brown, C., Guinan, J., & Grehan, A, 2007. Multiscale terrain analysis of multibeam bathymetry data. Marine Geodesy, 30, 3–35. 29 �MCR Synthesis 1. Characterizing the MCR mantle plume GOOD, David Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada The Midcontinent Rift (Keweenawan Large Igneous Province) contains the most diverse assemblage of mafic rock types for any LIP on earth with 9 distinct basalt groups and more than 15 major Ni-Cu-PGE occurrences or deposits. The main objective of the MCR synthesis is to build a coherent model to explain the vast array of observations, geochemical data and interpretations presented by numerous researchers over the past four decades. The project is subdivided into 4 related objectives: 1) Recognition of the key geochemical features of global rift/LIP settings that we should see in the MCR; 2) Build a classification scheme for all basalts, gabbros and ultramafic rocks using high-precision incompatible trace elements; 3) Apply analytical tools and modelling to unravel petrogenesis of recognized groupings; and 4) Represent the results in a model for the MCR that highlights spatial and temporal relationships in the rift. This project was inspired by several key events over the past decade, each of which indicate the project is feasible at this time. Proof of concept tests for objectives 2, 3 and 4 were presented in 2023 indicating a high degree of confidence for the success of this 4-to-5-year project. A few researchers have identified various stratigraphic units in the MCR to have originated by partial melting in the mantle plume and used their inherent isotopic or trace element compositions to model melt-crustal interaction and the petrogenesis of various intrusions that host Cu-Ni-PGE deposits. These plume-related basalt units include the lower Siemens Creek and Kallander Creek basalt in Michigan and the lower Osler and Mamainse Point basalt in Ontario. But these units each present slightly different trace element characteristics, so the question arises as to what criteria are useful for distinguishing mantle plume magmas from those generated in the upper mantle or at different depths within the plume. The main criteria for identifying plume magmas are based on ocean island basalt-like trace element characteristics. In this study, two MCR plume basalt types are identified (Groups 1 and 5) using the combination of λ1-λ2 REE coefficients, TiO2/Yb, and Gd/Yb diagrams. The differences between groups 1 and 5 are best explained by partial melting at different depths, based on differences between majorite (>~300 km) and pyrope garnet fractionation, respectively. Group 1 includes basalts from the Lower Osler and lower Kallander creek groups and the highly fractionated Devon volcanic unit. Group 5 includes basalts from the lower series A and B units at Mamainse Point, Central Osler Volcanic Group and the lower Siemens Creek basalt located at the Skinny, Bluff and Bond Falls sites in Michigan. A well-understood and fundamental characteristic of highly incompatible trace element ratios is their use to correlate basalt and intrusive rocks. These typically unique trace element signatures can be used in a manner like finger printing. However, in all cases, care must be taken, particularly for TiO2, to evaluate clinopyroxene or spinel fractionation, as is the case for basalt and intrusions in Group 1. Based on these comparisons, the Bovine, Current Lake, Disraeli, Haystack, Hele, Kitto, Riverdale Sill, Seagull, Shillabeer, and Thunder Intrusions belong to Group 1, whereas the McIntyre, Jackfish, and Logan sills belong to Group 5. 30 �Description and application of the Consolidated Minerals Database to support geological investigations: an example from the Cuyuna Range, central Minnesota GORDEE, Sarah 1, RIAN, Madison 1, SAARI, Stacy 1, and CARTER, Matthew1 1 Minnesota Department of Natural Resources, Division of Lands and Minerals, 1525 3rd Ave E, Hibbing, MN 55746 Over the past ~50 years, the Minnesota Department of Natural Resources (DNR) Lands and Minerals Division has amassed numerous collections of mineral exploration-related documents, amounting to well over 10,000 hardcopy materials containing geoscience and related land data. Curating these collections has proven to be challenging given the sheer volume of documents from multitudinous sources, necessitating a concerted solution to manage these materials. The Consolidated Minerals Database (CMD) is under development by the DNR to support the initiative to bring the agency’s collections of historical and contemporary documents into digital format and to make them readily available for public use. It is a database of unique collections containing cross-referenced documents with linkages to other internal and external databases, including the Hibbing Drill Core Library (DCL) database, and a web map, where geospatially linked documents can be retrieved from specific localities or regions. The various collections comprising the CMD are designated by project, company, or other relevant shared interest(s). Documents are individually entered into a particular collection and assigned a unique numerical identifier, which is used to cross-reference to different databases. Metadata (e.g., title, date, source) are recorded in a series of entries, and attributes of the document (e.g., scope, subject, content, methods, materials, discipline) are classified in a series of dropdown menus, enabling users to search and find documents meeting specific criteria relating to documents’ contents and origin. In the current initiative, the DNR utilizes the CMD intake application to produce digital records of documents from the Cuyuna Range in central Minnesota, where exploration and mining for iron and manganese ores was active throughout much of the early-middle 20th century. The objective is to curate mineral exploration documents and compile geological data from these records in a large database. A synthesis of these data will help to better understand the geological architecture and extent of historical exploration in the region, and the compiled datasets will help to evaluate the potential for additional iron, manganese, and other resources. Historical documents from the Cuyuna mining district are stored in the Hibbing Lands and Minerals office. Dozens of different exploration companies drilled at least 12,000 boreholes and created thousands of documents spanning multiple decades of mineral exploration and mining in this district. Relevant documents in this collection range from 1905 to the 1970s, and include geological maps, surface maps with drillhole collars and associated metadata, mine maps (surface, subsurface, infrastructure), tables with geochemical data, drillhole profiles with tabular geochemical data, geological information and interpretations, geological cross-sections, field notes, and notes and correspondences regarding property ownership, exploration results and resource estimates. Because of the number of companies involved and diversity in the presentation of data it is necessary to address certain challenges before curation into CMD. Documents are first sorted by company and locality in the Public Land Survey System, which allows for the identification and removal of duplicate maps and other documents shared 31 �among and across different companies. Once sorted, all relevant documents with clear datasets and sufficient metadata to identify the source and locality are curated into the CMD. Following curation, plan-view maps are converted to picture format and brought into ArcGIS, where they are spatially located using georeferencing methods. This method helps to resolve problematic drillhole locations, and to identify less obvious duplicate documents and datasets, including drillholes that were renamed over time as operators changed hands. Drillhole collar locations can then be added to a database of known drillholes in the region, and integrated and compared to cores from the DCL database. Once correctly positioned, individual geospatial datasets, such as geological logs, and geochemical and geophysical data, are extracted from each document. Extracting and compiling geologic data such as geologic logs and assays into tabular format has been a challenging endeavor. These data were hand-written or typed using a typewriter, and utilizing optical character recognition technology to extract text is not straightforward. However, transcribing the data by hand is a cumbersome and protracted process, and potentially introduces errors that must be checked for quality assurance. With the advance of artificial intelligence (AI) and machine learning, it is now possible to train an AI model to extract data into tables. Training the AI data extraction model is an efficient process. First, pages (10 minimum) containing example data listed in an internally consistent format are imported; then table(s) are delineated using the associated headers, labels, and rows per each page. Once the model is trained, numerous documents or pages of the same format are uploaded and the data are auto-extracted, and the output reflects the model’s specified number of tables, columns, and rows. Before the outputted data are extracted, they are enhanced within the model workflow to account for spelling errors, incorrect symbols, etc., so that it is unnecessary to resolve errors individually by hand. Once a model is trained for a specific table format, thousands of pages of tabular data can be extracted into a tabular database en masse in a matter of minutes. Using MircoMine modeling software, the tabulated data are visualized in a 3D model, where any remaining tabulation errors are identified and corrected. This process is ongoing, as many still-uncurated documents remain in the Cuyuna collection. To date, nearly 2,000 documents totalling over 20,000 pages have been scanned, georeferenced and lodged in the CMD, and the drillhole database contains over 4,000 individual drillholes with assay data totaling over 60,000 lines. Incompleteness notwithstanding, the current database is a growing and ever-refining, data compilation from thousands of geological investigations. Together, the newly compiled data are sufficiently expansive to make new observations and interpretations pertaining to the geology and distribution and style of iron and manganese resources, as well as the potential for other base and precious metal resources, in the Cuyuna Range. 32 �Revisiting geophysical interpretations of the Midcontinent Rift below Lake Superior— Insights from GLIMPCE seismic-reflection line C GRAUCH, V.J.S.1, HELLER, S.J.2, WOODRUFF, Laurel G.3, and STEWART, Esther K.4 1 U.S. Geological Survey, MS 973, Federal Center, Denver, CO 80225 U.S. Geological Survey, MS 939, Federal Center, Denver, CO 80225 3 U.S. Geological Survey, 2280 Woodale Drive, St. Paul, MN 55112 4 Wisconsin Geological & Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 2 The 1.1 Ga Midcontinent Rift System (MRS) has been investigated in the Lake Superior region for more than a century, driven by mineral exploration, academic study, and, for a brief time, oil and gas exploration. Limited outcrops on land and the extent of MRS rocks under the lake have motivated many workers to use geophysical methods to investigate the nature and extent of the rift. The most influential geophysical data for modern paradigms has come from seismic-reflection profiles collected by the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) in the late 1980s. Notably, many previous workers have used interpretations of GLIMPCE line C (Fig. 1, inset) to demonstrate the architecture of the MRS in western Lake Superior. A recurring theme from the previous work is that syn-extensional basalt flows accumulated in half-grabens bounded by normal growth faults, which then reactivated as reverse faults in response to later compression (e.g., Cannon et al., 1989; Hinze et al., 1992; Dickas and Mudrey, 1997; Stein et al., 2015). We are revisiting GLIMPCE line C by constructing a detailed velocity model for conversion of the seismic data measured in two-way travel time to a section plotted versus depth (Grauch et al., 2023). This approach allows for digital verification of the modeled velocities and more accurate depiction of thicknesses and dips of units to tie to geology onshore. We have constructed an analogous gravity model along line C that provides independent evaluation of our velocity model using velocity-density relations developed from analysis of region-wide rock property compilations (Grauch, 2023). Preliminary results from the velocity modeling, depth conversion, and ties to onshore geology have led to a significantly different view of Line C as primarily a sag basin rather than a half-graben, showing both syn- and post-magmatic subsidence (Fig. 1; Grauch et al., 2023). Narrow intervals of high velocities, which indicate a composition of gabbro (Grauch, 2023), emanate upwards along both sides of the sag basin from an inferred mantle bulge. The intervals are associated with strong linear reflections that truncate sub-horizontal layers in the sag basin and may obscure any minor faulting that occurred before or after intrusion. Cross-cutting mafic intrusions provide an alternate explanation for the termination of layers that was previously thought to indicate major faulting. This new view of line C implies that basin subsidence was the dominant process in the development of rift stage troughs rather than major half-graben structures. Other important interpretations include the following. • Portage Lake Volcanics show syn-magmatic basin subsidence • The Lower Oronto Group section shows post-magmatic basin subsidence • Onlap of Upper Oronto Group onto tilted Porcupine Volcanics suggest the deformation pre-dated deposition of Oronto Group sediments 33 �• Rocks of the lower northeast sequence of the North Shore Group may connect to rocks of similar age from the south shore that lie underneath the sag basin. Figure 1. Interpreted depth section for GLIMPCE Line C. No vertical exaggeration. NSVG, North Shore Volcanic Group. PLV, Portage Lake Volcanics. The new rendition of the Line C seismic data also raises several questions. • How do the sedimentary sections correlate from north to south? • What caused the truncation of volcanic layers at the volcanic-sedimentary contact in the middle of the seismic section and was reverse faulting involved? • What is the tectonic process that drove the syn-magmatic subsidence? • Where does the reverse Keweenaw fault extend into the section from the south shore and what was its influence? These and other questions can be addressed through the construction of velocity models and depth conversions of other seismic lines in the lake. Future insights will benefit from a three-dimensional view that these additional seismic lines will provide. Cannon, W.F., Green, A.C., Hutchinson, D.R., Lee, M.W., Milkereit, B., Behrendt, J.C., Halls, H.C., Green, J.C., Dickas, A.B., Morey, G.B., Sutcliffe, R.H., and Spencer, C., 1989, The North American Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling: Tectonics, v. 8, p. 305-332., https://doi.org/10.1029/TC008i002p00305 . Dickas, A.B., and Mudrey, M.G., Jr., 1997, Segmented structure of the Middle Proterozoic Midcontinent System, North America, in R.J. Ojakangas, A.B. Dickas, and J.C. Green (eds.), Middle Proterozoic to Cambrian Rifting, Central North America: Geological Society of America Special Paper 312, 37-46., https://doi.org/10.1130/08137-2312-4.37 . Grauch, V.J.S., 2023, Compressional wave seismic velocity, bulk density, and their empirical relations for geophysical modeling of the Midcontinent Rift System in the Lake Superior region: U.S. Geological Survey Scientific Investigations Report 2023-5061, 60 p., https://doi.org/10.3133/sir20235061. Grauch, V.J.S., Heller, Sam J., Stewart, Esther K., and Woodruff, Laurel G. 2023. Exploring the geology of the Midcontinent Rift under western Lake Superior using a preliminary velocity model of seismic line GLIMPCE C, in Ames, C. (ed.), 69th Annual Institute on Lake Superior Geology Proceedings—Part 1, Program and Abstracts, p. 37-38. Hinze, W. J., Allen, D. J., Fox, A. J., Sunwood, D., Woelk, T., and Green, A. G., 1992, Geophysical investigations and crustal structure of the North American Midcontinent Rift system: Tectonophysics, v. 213, p. 17-32. Stein, C.A., Kley, J., Stein, S., Hindle, D., and Keller, G.R., 2015, North America’s Midcontinent Rift: When rift met LIP: Geosphere, v. 11, p. 1607-1616. 34 �GeologyOntario: a powerful search tool for Ontario explorationists HINZ, Sheree1 Ontario Geological Survey, 435 James Street South, Thunder Bay, ON, P7E 6S7 Canada W ith dr aw n In March of 2023, the Ministry of Mines released a new online platform to search and query Ontario Geological Survey data. The Ontario Geological Survey maintains and provides public access to a wealth of geological information including maps, publications, assessment files, mineral inventory points, miscellaneous data releases, geophysical data, abandoned mine site information, and more. Though this information has been available online for many years, the previous iteration of GeologyOntario had significant constraints, including a lack of spatial search abilities, and users experienced challenges in finding relevant information. The new GeologyOntario consists of separate text (Figure 1) and spatial search (Figures 2 and 3) tools which provides ample opportunities to discover information. Geological information is often dependent on spatial data, and the new spatial search tool runs on a powerful Esri-based system, allowing clients to build queries to focus on the types of data relevant to their interests, within the geographical areas they are working. The new GeologyOntario Search Hub is located at https://geology-ontario-en-mndm.hub.arcgis.com/. Figure 1. GeologyOntario text search page (https://www.geologyontario.mines.gov.on.ca/). 35 �aw n dr W ith Figure 2. GeologyOntario spatial search page showing regional geology, mineral inventory, and the results of a search for mineral inventory points listing lithium as a primary commodity in the area of the Separation Rapids pluton(https://mndm.maps.arcgis.com/apps/webappviewer/index.html?id=66ee0efe4d3c4816963737dbdb 890708). Figure 3. GeologyOntario spatial search page with regional geology, mineral inventory, assessment files, Resident Geologist Program (RGP) site visits, and exploration activity layers active. 36 �Recent developments on the use of the Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic method to determine depth to bedrock in Minnesota HIRSCH, Aaron C.1 1 Minnesota Geological Survey, University of Minnesota, 2609 Territorial Road, St. Paul MN 55114 Bedrock depth is an important dataset for water resource management, hydrological studies, mineral exploration, and general well planning. In Minnesota, bedrock depth is highly variable; thin to nonexistent in the northeast, up to 250m+ in areas to the west, and irregular elsewhere. In areas where bedrock depth is not known from existing water, exploration, or scientific drilling, various geophysical techniques can be used. One of these methods is the Horizontal-to-Vertical Spectral Ratio (HVSR) (Nogoshi and Igarashi, 1971; Nakamura, 1989) which utilizes horizontal ambient noise surface wave frequencies that are excited and amplified dependent on the depth to the basement bedrock below a less dense and seismically slower velocity upper layer (i.e. unconsolidated glacial sediments). The HVSR method has been utilized in Minnesota to estimate the depth to bedrock since the late 2000’s (Chandler and Lively, 2014) and has become a standard measurement in the MN County Geological Atlas program (e.g. Bauer et al., 2023; Mayer et al., 2023). The initial HVSR dataset used 1647 passive seismic measurements with 303 locations with a known bedrock depth, also known as control points, to develop parameters to accurately estimate the depth to bedrock across Minnesota (Chandler and Lively, 2016). The Minnesota Geological Survey has now collected a total of over 6000 HVSR measurements and 480 control points resulting in a new assessment from the larger and more geographically and geologically widespread dataset. Analyses has included a new quantitative data quality ranking using international HVSR guidelines (SESAME, 2004) and new control parameters have been investigated. The shape of the HVSR curve is now being captured in a passive seismic database due to its relationship with bedrock depth topography, bedrock weathering, and the underlying velocity structure. Ongoing evaluation of this database will help refine the HVSR depth to bedrock estimation and more accurately identify potential bedrock valleys while future work will include measuring densities and ultrasonic velocities of Quaternary cores to constrain the control point parameters more accurately. References Bauer, E. J., Cicha, J., Radakovich Block, A., Jirsa, M. A., Hirsch, A. C., Meyer, G. N., Scott, S. B., Lively, R. S.. (2023). C-55, Geologic Atlas of Otter Tail County, Minnesota. Minnesota Geological Survey. Retrieved from the University of Minnesota Digital Conservancy, https://hdl.handle.net/11299/256920. Chandler, V. W., Lively, R. S., 2016, Utility of the horizontal-to-vertical spectral ratio passive seismic method for estimating thickness of Quaternary sediments in Minnesota and adjacent parts of Wisconsin, Interpretation, Vol. 4, No. 3, p. SH71-SH90. http://dx.doi.org/10.1190/INT-20150212.1. Chandler, V.W., and Lively, R.S., 2014. OFR14-01, Evaluation of the horizontal-to-vertical spectral ratio (HVSR) passive seismic method for estimating the thickness of Quaternary deposits in Minnesota and adjacent parts of Wisconsin. Minnesota Geological Survey. Retrieved from the University of Minnesota Digital Conservancy, https://hdl.handle.net/11299/162792. Mayer, J. A., Bradley, M. C., Retzler, A. J., Severson, A. R., Jirsa, M. A., Chandler, V.W., Conrad, D. R., Gowan, A. S., Radakovich Block, A., and Hamilton, J. D., 2023. C-58, Geologic Atlas of Lincoln 37 �County, Minnesota. Minnesota Geological Survey. Retrieved from the University of Minnesota Digital Conservancy, https://hdl.handle.net/11299/260212. Nakamura, Y., 1989, A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface: Quarterly Report Railway Technical Research Institute, 25–30. Nogoshi, M., and Igarashi, T., 1971. On the amplitude characteristics of microtremor (part 2) (in Japanese with English abstract): Journal of the Seismological Society of Japan, 24, 26–40. SESAME, 2004. Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations. Measurements, processing, and interpretation: WP12 European commission — Research general directorate project no. EVG1-CT-2000-0026 SESAME, report D23.12, 62, http://www.gripweb.org/gripweb/sites/default/files/HV_User_Guidelines.pdf. 38 �Lithostratigraphic discrimination of Quaternary core in Minnesota using magnetic susceptibility HIRSCH, Aaron C.1, SCHNEIDER, Emma, L.1 1 Minnesota Geological Survey, University of Minnesota, 2609 Territorial Road, St. Paul MN 55114 Most of Minnesota is covered by Quaternary sediments deposited during multiple glaciation events. This Quaternary stratigraphy is highly complex due to multiple glacial events in which ice lobes emanated from differing locations north of Minnesota and deposited sediment (diamict, till) of variable thicknesses (up to 250m), provenance, and morphology across the state (Johnson et al., 2016). The Minnesota Geological Survey uses grain counts, color, sedimentary structures, and composition to establish Quaternary lithostratigraphic units that distinguish these deposits by lithology, stratigraphy, and geomorphology. Nine lithostratigraphic regions were identified using cuttings, outcrops, and rotary sonic core (Johnson et al., 2016). Magnetic susceptibility measurements were taken at 1-2 meter intervals from many of these rotary sonic cores during core analysis by applying a magnetic field to the core and recording the magnetic response. This study was conducted to determine if magnetic susceptibility measurements from cores can aid unit correlation across Minnesota regions as part of a USGS funded data preservation project. Over 11,000 measurements were recorded in a newly established Quaternary magnetic susceptibility database with over 7,000 measurements assigned to a lithostratigraphic formation and unit interpretation. Magnetic susceptibility logs were generated for each measured core and statistics calculated for each unit. Analysis of this database has identified lithostratigraphic units with distinctive magnetic susceptibility ranges as compared to nearby and similarly aged units. Due to these results, this newly established database functions as another tool for lithostratigraphic identification of Quaternary sediments and local and regional correlations. References Johnson, Mark D., Adams, Roberta S., Gowan, Angela S., Harris, Kenneth L., Hobbs, Howard C., Jennings, Carrie E., Knaeble, Alan R., Lusardi, Barbara A., and Meyer, Gary N., 2016. RI-68 Quaternary Lithostratigraphic Units of Minnesota. Minnesota Geological Survey. Retrieved from the University of Minnesota Digital Conservancy, https://hdl.handle.net/11299/177675 39 �New Insights into the Geology and Geochemistry of the Osler Group and Related Rocks, Midcontinent Rift System, Northern Lake Superior, Ontario HOLLINGS, Pete and SMYK, Mark Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1 Canada Ongoing geological reconnaissance and lithogeochemical sampling were undertaken on parts of the Black Bay Peninsula, St. Ignace Island and neighbouring islands in 2022 and 2023. New field and geochemical data have helped to both distinguish lithostratigraphic units and suggest common magmatic histories in developing a model for the Midcontinent Rift System (MRS)related Osler Volcanic Group and related intrusive rocks. The Osler Group (1108-1105 Ma), a ~3 km-thick succession of predominantly basaltic flows and clastic sedimentary rocks on the north shore of Lake Superior, represents some of the earliest MRS magmatism. Previous studies have largely focused on the paleomagnetism (e.g. SwansonHysell et al., 2019; Halls, 1974) and geochemistry (e.g. Hollings et al., 2007; Keays and Lightfoot, 2015) of the flood basalts in developing a stratigraphic sequence. However, only basic mapping and some initial studies had been conducted on felsic extrusive and intrusive rocks (e.g. St. Ignace Island Complex, Hollings et al., 2023, Smyk et al., 2006; geochronology, SwansonHysell et al., 2019 and references therein). Sampling efforts were most recently focused on these felsic rocks in order to determine their geochemical affinity and to suggest how they, and related mafic igneous rocks, may fit in with the provisional tectono-magmatic model for the Osler Group. Felsic rocks include the Agate Point rhyolite flows (1105.15 Ma); thin felsic fragmental units; aphanitic felsite; and massive, subvolcanic(?), quartz-feldspar-phyric rocks (aka “quartz-feldspar porphyry”/QFP). These red, brown or gray rocks occur predominantly on St. Ignace Island (including in the core of the St. Ignace Island Complex (SIC)) and on smaller islands, south to Agate Point. Rhyolites tend to be LREE-enriched (La/Smn= 5.20-5.47), have higher total REE than the QFPs and more pronounced negative Ti anomalies. The majority of QFPs, including those in the core of the SIC, tend to display a coherent, tightly grouped REE trend, characterized by moderate LREE enrichment (La/Smn= 2.34-4.71, averaging 3.50), relatively flat HREE patterns and pronounced negative Nb anomalies. This similarity in the REE distribution of both extrusive and subvolcanic felsic rocks suggests that they may share a common magmatic and fractionation history. In contrast, the basaltic flows into which felsic rocks have been emplaced have flatter REE distribution patterns (La/Smn= 1.61-3.51) than those of the felsic rocks, with less-pronounced negative Ti anomalies. Mafic and felsic flows situated above an unconformity/conglomerate at Bullers Bay, St. Ignace Island, display pronounced negative Nb anomalies whereas those below do not. This suggests that the lower flows are part of the more primitive Lower Formation of the Osler Group, while the flows above the unconformity resemble those of the more crustally contaminated Central Formation (cf. Keays and Lightfoot 2015; Hollings et al. 2007) as delineated on nearby Simpson Island. 40 �Gabbroic rocks occur at the margin of the SIC, in the Moss Lake Intrusion and as numerous diabase sills and dykes with various orientations which intrude the supracrustal rocks. SIC and Moss Lake gabbro samples display similar REE patterns, characterized by moderate LREE enrichment (La/Smn= 2.59-3.23), moderate negative Ti anomalies and pronounced negative Nb anomalies. By comparison, smaller, diabasic dykes and sills have relatively flat REE distribution and less-pronounced negative Ti anomalies. Prominent, regional-scale mafic dykes (i.e. McEachan, Shesheeb, Paps) display lower total REE and lack negative Sm anomalies. Hollings et al. (2023) suggested that the rocks of the SIC likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate felsic end members which then ascended to shallower levels in the crust. The SIC QFPs are geochemically similar to both the massive, subvolcanic(?) QFPs elsewhere on St. Ignace Island and nearby islands, as well as to the rhyolites at Agate Point, suggesting a similar origin for all of these felsic rocks. REFERENCES Halls, H., 1974, A paleomagnetic reversal in the Osler Volcanic Group, northern Lake Superior: Canadian Journal of Earth Sciences, v. 11, p. 1200–1207, doi:10.1139/e74-113. Hollings, P., Fralick, P. and Cousens, B. 2007. Early history of the Midcontinent Rift inferred from geochemistry and sedimentology of the Mesoproterozoic Osler Group, northwestern Ontario. Canadian Journal of Earth Sciences, 44, 389–412, https://doi.org/10.1139/e06-084. Hollings, P., Hanley, J., Smyk, M., Heaman, L., Cousens, B., and Zajacz, Z. 2023. The ~ 1.1 Ga St. Ignace Island Complex, Northern Ontario, Canada: Evidence for Magma Mixing and Crustal Melting in the Generation of Midcontinent Rift-Related Bimodal Magmas and Implications for Regional Metallogeny, Journal of Petrology, Volume 64, Issue 6, June 2023, egad032, https://doi.org/10.1093/petrology/egad032. Keays, R.R. and Lightfoot, P.C. 2015. Geochemical stratigraphy of the Keweenawan Midcontinent Rift volcanic rocks with regional implications for the genesis of associated Ni, Cu, Co, and platinum group element sulfide mineralization. Economic Geology, 110, 1235– 1267, https://doi.org/10.2113/econgeo.110.5.1235. Smyk, M.C., Hollings, P.N. and Heaman, L. 2006. Preliminary investigations of the petrology, geochemistry and geochronology of the St. Ignace Island Complex, Midcontinent Rift, northern Lake Superior, Ontario; 52nd Institute on Lake Superior Geology, Annual Meeting, Sault Ste. Marie, Ontario, May, 2006, Proceedings Volume 52, Part 1, p.61-62. Swanson-Hysell, N.L., Ramezani, J., Fairchild, L.M., and Rose, I.R. 2019. Failed rifting and fast drifting: Midcontinent Rift development, Laurentia’s rapid motion and the driver of Grenvillian orogenesis; GSA Bulletin 131 (5-6), 913-940. 41 �Use of Ambient Noise Tomography for Mineral Exploration in the Lake Superior Region HOLLIS, Dan1 1 Sisprobe SAS, 831 Pacific Street, #1A, Morro Bay, California, 93442 USA Abstract Ambient noise tomography (ANT) is a relatively new passive seismic tool used in mineral exploration. The method has been successfully used in the Lake Superior region in mapping subsurface structure and rock properties. This presentation will provide a brief introduction to the ANT method and review recent ANT work done in the Lake Superior region. Introduction Exploration for mineral resources uses a variety of geophysical methods to detect and delineate mineral deposits and systems in order to optimize core drilling programs: gravity, magnetics, active-source reflection seismic and electromagnetics methods to name a few. Ambient noise tomography is a relatively new seismic geophysical tool that has seen increasing use in the past couple of years for mineral resource exploration. ANT uses natural earth vibrations and human-generated seismic vibrations to image subsurface structure and map physical properties of the subsurface. Four ANT surveys for mineral resources in the Lake Superior region have been completed: three surveys within the Coldwell Complex near the town of Marathon, Ontario, and one in the Duluth Complex in northeastern Minnesota. Ambient Noise Tomography Method The Earth is constantly vibrating. For the ANT exploration method, useful vibrations, sometimes referred to as “ambient seismic noise”, are generated by hydrosphere-lithosphere interaction such as the oceanic microseism caused by swell (a similar microseism is caused by swell in Lake Superior and the other Great Lakes), and anthropogenic sources such as vehicular traffic, industrial sites, railroads, and other human activity. An ANT survey uses continuous passive seismic data collected with an array of nodal seismometers (“nodes”) and uses surface waves to image the subsurface. The data recording duration is usually between 1 to 4 weeks. Surface waves are dispersive with different frequencies propagating at different velocities related to the seismic velocities of subsurface lithology. Frequency-velocity dispersion curves are picked for all receiver pairs. These dispersion curves serve as input for a tomographic process resulting in an array of frequency-velocity points for each cell in a grid. All cells within the grid are inverted to produce depth-velocity profiles and the result is a 3D shear wave velocity (Vs) cube where velocity is the seismic velocity of the lithology and subsurface structure interpreted from the velocity model. Case Studies Coldwell Complex, Marathon Area, Ontario The first Marathon ANT survey was collected in October 2017 in the Marathon area over a VMS target. This first survey was intended as a noise test using 31one-component (vertical) 10 Hz nodes. The purpose of the noise test was to characterize the spectral power, temporal variation and azimuthal distribution of the local ambient noise. The collected data was also used to cross-correlate all receiver pairs to assess the signal-to-noise ratio of surface waves in the virtual source gathers and processed to produce a crude 3D velocity model which showed agreement with available core hole data. The positive results of the noise test led to the go-ahead for an expanded survey over the target. 42 �An 8.6 km2 expanded ANT survey over the Marathon target was collected in November-December 2017 using 91 one-component (vertical) 10 Hz nodes. The resulting 3D velocity volume had usable imaging down to 1500 meters and imaged the gabbro intrusion slab target. Details about the noise test and expanded ANT survey and its interpretation can be found in Hollis et al. In July-August 2018, the Sally ANT survey was conducted over an exploration target several kilometers to the northwest of the Marathon surveys. The Sally survey was collected using 196 three-component 5 Hz nodes. This survey demonstrated the effectiveness of using three-component data to produce a more accurate velocity model. Details of the Sally survey can be found in Lavoué et al. With the good results of the expanded Marathon survey, funding was obtained through the European Union Horizon 2020 program to conduct larger, higher resolution survey again over the Marathon target in order to test the limits of the ANT method and to test other potential ANT analyses and passive seismic methods. This survey was acquired in September-October 2018 using 983 one-component (vertical) 10 Hz nodes. This third Marathon ANT survey generated several publications on its results some of which are listed in the Reference section. Duluth Complex, Northeast Minnesota In September 2023, a 32 km2 survey was collected over a helium exploration target in Lake County, Minnesota. This survey used 183 three-component seismic nodes. Logging of a post-survey confirmation well has helium shows between 533 – 671 meters which agrees with the interpreted reservoir depth range from the ANT 3D data (Pulsar Helium). Conclusion Past work in the Lake Superior region has shown the ambient noise tomography is an effective tool for mineral exploration in the area. References Dales, P., L. Pinzon-Ricon, F. Brenguier, P. Boué, N. Arndt, J. McBride, F. Lavoué, C. J. Bean, S. Beaupretre, R. Fayjaloun, et al. (2020). Virtual Sources of Body Waves from Noise Correlations in a Mineral Exploration Context, Seismological Research Letters XX, 1–9, doi: 10.1785/0220200023. Hollis D., McBride J., Good D., Arndt N., et al (2019). Ambient noise surface wave tomography at the Marathon PGM-Cu deposit, Ontario, Canada, CSEG Recorder, June 2019. Lavoué A., Nicholas Arndt, John McBride, Aurélien Mordret, Florent Brenguier, Pierre Boué, Roméo Courbis, Sophie Beauprêtre, Charles Beard, Dan Hollis, and Richard Lynch, (2020), Ambient noise Rayleigh and Love wave tomography beneath the Sally Palladium-Copper Deposit (Ontario, Canada), SEG Technical Program Expanded Abstracts : 2075-2079. Pulsar Helium, https://files.elfsightcdn.com/eafe4a4d-3436-495d-b748-5bdce62d911d/2f2bca29-47e64d88-851e-d97bbca643b5/Pulsar_corp_deck_20Mar24x_FINAL-compressed.pdf. Accessed 3/29/2024. Sharma H., Molnar S., Hollis D. and McBride J. (2018). Application of ambient-noise analysis and velocity modeling in mineral exploration. SEG Technical Program, Expanded Abstracts, 3072–3076. Teodor, Daniela & Beard, Charles & Pinzon-Rincon, Laura & Mordret, Aurelien & Lavoué, François & Beaupretre, Sophie & Boué, Pierre & Brenguier, Florent. (2021). High-frequency ambient noise surface wave tomography at the Marathon PGE-Cu deposit (Ontario, Canada). 10.5194/egusphere-egu21-13152. 43 �Geologic and tectonic implications of detrital zircon U-Pb ages from the Dickinson Group in the western Upper Peninsula of Michigan, USA JONES, James V.1, CANNON, William F.2, DRENTH, Benjamin J.3 and O’SULLIVAN, Paul4 1 U.S. Geological Survey, Anchorage, AK 99508, USA jvjones@usgs.gov U.S. Geological Survey, Reston, VA 20192, USA 3 U.S. Geological Survey, Denver, CO 80225, USA 4 GeoSep Services LLC, Moscow, ID 83843, USA 2 In the Lake Superior region of the northern United States and southern Canada, Paleoproterozoic metasedimentary successions record the breakup of southern Superia (in present coordinates) that began ca. 2.3 Ga and the eventual transition to long-lived accretionary orogenesis along the southern Laurentia margin ca. 1.90–1.85 Ga. These successions are difficult to correlate for reasons that include contrasts in thickness and facies at multiple scales, similarities in depositional environment through hundreds of millions of years of sedimentation, and polyphase tectonism that variably produced intense deformational and metamorphic overprints. Detrital zircon U-Pb geochronology is useful for correlating siliciclastic strata that are widespread throughout the successions and for identifying provenance patterns in space and time. We present new data for samples collected from ca. 2.3–1.8 Ga strata across the western Upper Peninsula of Michigan and northern Wisconsin that provide a baseline for regional geologic mapping and correlations with similar strata regionally to globally. Our findings provide new insights into stratigraphic relationships of the ca. 2.1 Ga Dickinson Group and require revision of the depositional history, tectonic evolution, and regional significance of the succession. The Dickinson Group is a distinctive succession of metasedimentary and metavolcanic rocks exposed only in the Felch trough area of the western Upper Peninsula. The strata are bounded by the Randville Dolomite of the Chocolay Group to the north and Archean banded gneiss to the south. These bounding contacts are mostly interpreted to be structural. The lowermost unit of the Dickinson Group is the East Branch Arkose, a coarse cobble to boulder conglomerate that contains rounded clasts of granite and quartzite in a matrix of feldspathic to lithic wacke. The conglomerate is moderately sorted and generally matrix-supported. At a few localities, the East Branch appears in unconformable contact with coarse-grained granite, interpreted as one of the ca. 2.6 Ga batholiths that are common in the southern Superior Province. At these basal localities, cobbles are strongly flattened and the entire unit contains a well-developed foliation defined by the flattened cobbles and aligned biotite in the sedimentary matrix. The East Branch Arkose is overlain by the Solberg Schist, the lower part of which contains fine-grained mafic schist and amphibolite together with discontinuous calc-silicate horizons up to 15 cm thick. Compositional layering in the Solberg is isoclinally folded with a consistent foliation defined by fine-grained chlorite and amphibole. The middle Solberg contains a ~100-ft-thick bed of iron-formation called the Skunk Creek Member that includes biotitehornblende schist and thinly bedded metachert with magnetite layers (James, 1958). The upper Solberg is made up of interlayered biotite quartzite, massive gray quartz-mica schist, and staurolite-biotite schist. The Solberg Schist is overlain by the Six-Mile Lake Amphibolite, which is made up of fine- to medium-grained amphibolite with a strong tectonic foliation defined by hornblende. As originally mapped, the Dickinson Group defines a subvertical, south-facing homocline and was previously thought to be Archean based on an inferred gradational contact between the Six-Mile Lake Amphibolite and the Archean banded gneiss (James, 1958; James et 44 �al., 1961). However, detrital zircon data published by Craddock et al. (2013) showed that the East Branch arkose was deposited ca. 2.1 Ga or later, thus implying a Paleoproterozoic age for the entire succession. Our detrital zircon U-Pb data from the East Branch Arkose match previously published data from Craddock et al. (2013) and are dominated by ca. 2.6 Ga grains interpreted to reflect local granitic sources that are also observed as cobbles. Rare, but statistically significant ca. 2.1 Ga populations, confirm the Paleoproterozoic maximum depositional age. Mafic Solberg Schist that overlies the arkose does not contain abundant zircon, although some small grains that were recovered show a mix of ages ranging from ca. 3.1 to 2.6 Ga and a small ca. 2.1 Ga population. Detrital zircon age spectra from upper Solberg exposures are distinctly different, though. Samples of biotite quartzite and staurolite schist both contain prominent ca. 1.86–1.84 Ga age populations together with more minor ca 2.5 and 2.3 Ga age populations. The upper Solberg age spectra closely match samples of the Michigamme Formation from throughout the surrounding region, suggesting that the upper siliciclastic component of the Solberg schist should, instead, be mapped as Baraga Group. This revised interpretation raises the possibility that the mafic volcanic rocks and iron formation of the lower and middle Solberg Schist could also correlate with the lower Baraga and(or) Menominee Groups, though additional data are required to test these possibilities. Furthermore, it raises questions about the age of the Six-Mile Lake Amphibolite, the uppermost unit of James’ (1958) Dickinson Group. We suggest that the Six-Mile Lake may be Archean as previously inferred by James (1958), in which case its concealed contact with the upper Solberg or Michigamme Formation would be tectonic rather than depositional. We are presently working to test this revised hypothesis through new geochronology and 40Ar/39Ar thermochronology across the contact. The actual depositional age of the East Branch Arkose remains uncertain, as it can be younger than the ca. 2.1 Ga detrital zircon age populations that it contains. This age population overlaps with the ca. 2.1 Ga porphyritic red granite that crops out among the western exposures of Dickinson Group strata, though cross-cutting relationships between the Dickinson and porphyritic red granite are not observed. A ca. 2.1 Ga depositional age for the arkose would require rapid unroofing of the coeval granite in a manner not presently observed elsewhere in the region. In summary, prior interpretations of a continuous ca. 2.1–2.0 Ga Dickinson Group succession in the western Upper Peninsula of Michigan are not consistent with new detrital zircon ages from siliciclastic strata previously mapped as the upper Solberg Schist. These units correlate with the Michigamme Formation instead and raise new questions about the age, setting, and tectonic evolution of multiple Archean and Paleoproterozoic units in the region. References cited Craddock, J.P., Rainbird, R.H., Davis, W.J., Davidson, C., Vervoort, J.D., Konstantinou, A., Boerboom, T., Vorhies, S., Kerber, L., and Lundquist, B., 2013, Detrital zircon geochronology and provenance of the Paleoproterozoic Huron (~2.4-2.2 Ga) and Animikie (~2.2-1.8 Ga) basins, southern Superior Province: Journal of Geology, v. 121, p. 623–644, https://doi.org/10.1086/673265. Drenth, B.J., Cannon, W.F., Schulz, K.J., and Ayuso, R.A., 2021, Geophysical insights into Paleoproterozoic tectonics of the Superior Province, central Upper Peninsula, Michigan, USA: Precambrian Research, v. 359, https://doi.org/10.1016/j.precamres.2021.106205. James, H.L., 1958, Stratigraphy of pre-Keweenawan rocks in parts of northern Michigan: U.S. Geological Survey Professional Paper 314-C, 44 p. James, H.L., Clark, L.D., Lamey, C.A., and Pettijohn, F.J., 1961, Geology of central Dickinson County, Michigan: U.S. Geological Survey Professional Paper 310, 176 p. 45 �Characterizing the geochemistry and nickel-copper-platinum group elements potential of mafic and ultramafic intrusions in northwestern Ontario JONSSON, Justin1, MALEGUS, Paul1, CHURCHLEY, Sophie1, PRICE, Rebecca1 1 aw n Resident Geologist Program, Ontario Geological Survey, Ministry of Mines, Suite B002, 435 James Street South, Thunder Bay, ON P7E 6S7 Canada Globally, magmatic sulphide deposits host significant resources of nickel, copper, cobalt and platinum group elements (PGE). These deposits occur as concentrations of sulphide minerals hosted within mafic to ultramafic intrusive rocks and are widespread across Ontario, occurring in every Precambrian geologic terrane. Ontario is home to 10 operating mines in magmatic sulphide deposits: 9 within the Paleoproterozoic Sudbury Igneous Complex and one within the Neoarchean Lac des Iles Complex. W ith dr In 1999, Operation Treasure Hunt was initiated by the Ontario Government to stimulate mineral exploration by acquiring new airborne geophysical data, surficial and bedrock geochemical data, and development of new methods. In 2003, following completion of the Operation Treasure Hunt project, the Ontario Geological Survey published a report (Vaillancourt et al. 2003) that assessed 109 mafic to ultramafic intrusions across Ontario. The purpose of this part of Operation Treasure Hunt was to characterize and publish data for intrusions known to be prospective for PGE-dominated magmatic sulphide mineralization. Many of the intrusions studied during Operation Treasure Hunt were host to significant known mineralization, including current and past-producing mines, and several of these intrusions are the focus of ongoing mineral exploration. Despite the work by Vaillancourt et al. (2003), there are hundreds of mafic to ultramafic intrusions in Ontario that have not been systematically assessed for magmatic sulphide mineralization potential. Many of these intrusions have favourable characteristics for potentially containing magmatic sulphide deposits, including geophysical anomalies (e.g., magnetic, conductivity), overburden geochemical anomalies and known sulphide mineralization. In 2023, the Resident Geologist Program of the Ontario Geological Survey initiated a project to systematically characterize geochemistry of a subset of mafic-ultramafic intrusions in northwestern Ontario that largely have not been subject to significant historical evaluation by academic researchers, government surveys, or mineral exploration companies. Evaluating the geochemistry of mafic to ultramafic intrusions can provide insight into the magma history, tectonic setting and potential for economic metal endowment. Factors that may influence metal endowment, that can be determined from the examination of geochemical data, include determining magma source characteristics, the timing of sulphur saturation and the degree of interaction of the magma(s) with their country rocks. Careful evaluation of physical characteristics and whole-rock geochemistry can inform future mineral exploration and/or the development of models for the emplacement of mafic to ultramafic intrusions and any hosted mineralization. 46 �W ith dr aw n Initial sample collection and analytical work took place during 2023. Areas of interest are shown in Figure 1, and include the Red Lake, Onaman–Tashota, and Heaven Lake greenstone belts. In this display, we provide examples of preliminary results and interpretations from areas targeted in the first year of field work, including the Trout Bay intrusion (Red Lake greenstone belt), Westwood intrusion (northeast of the Lumby Lake greenstone belt), and the Big Ghee Lake intrusion (south of the Shebandowan greenstone belt). Figure 38.1. Simplified bedrock geology map of a portion of northwestern Ontario, showing project target areas: Red Lake greenstone belt (outlined in blue); Heaven Lake greenstone belt (outlined in black); and Onaman–Tashota greenstone belt (outlined in white). Regional geology modified from Ontario Geological Survey (2011). References Ontario Geological Survey 2011. 1:250 000 scale bedrock geology of Ontario; Ontario Geological Survey, Miscellaneous Release—Data 126 – Revision 1. Vaillancourt, C., Sproule, R.A., MacDonald, C.A. and Lesher, C.M. 2003. Investigation of mafic-ultramafic intrusions in Ontario and implications for platinum group element mineralization: Operation Treasure Hunt; Ontario Geological Survey, Open File Report 6102, 335p. 47 �Cross-sectional Geometry of the Keweenaw Fault System between Hancock and Mohawk, Upper Peninsula of Michigan LANGFIELD, Katherine1, GAMET, Nolan2, DeGRAFF, James1 1 Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI, USA 2 Michigan Geological Survey, Marquette, MI, USA The Keweenaw fault system (KFS) is a major compressional feature along the Keweenaw Peninsula near the southern edge of the Midcontinent Rift System (MRS). The MRS formed in the Mesoproterozoic when a major extensional event split the ancient North American continent across the Upper Midwest, yielding large volumes of basaltic lava such as the Portage Lake Volcanics (1.1 Ga, PLV). The PLV strata were thrust southeastward over the Jacobsville Sandstone (JS) along the KFS during post-rift compression by the Grenville Orogeny (1), and some have postulated an earlier origin by normal faulting during rifting (2,3). A recent interpretation based partly on cross-section modeling is that faults making up the KFS are parts of a detached thrust system that formed during the Grenville Orogeny (4). Faults of the KFS have been interpreted to have dip slip – recent reverse slip and possibly earlier normal slip. Since 2017, bedrock mapping and analysis of fault-slip indicators have revealed a significant component of right-lateral strike slip on the KFS, which at its northeast end is inferred to have twice the magnitude of north-side-up reverse slip (5). The collective oblique motion across the KFS is accommodated on fault segments with three distinct orientations that overlap and intersect: (1) major segments parallel to the KFS trend, (2) splay faults striking clockwise to major segments by less than 35°, and (3) shorter connector faults striking counterclockwise to major segments and splays by up to 75° (Fig. 1). The ratio of dip slip to strike slip should vary among faults with such a range of orientations, as should the style of deformation in their hanging walls and footwalls. To help understand these relationships, cross-sections were constructed across various fault components of the KFS using recent mapping data, heritage data from published maps, and drill hole data. Cross-section work employed the dip-domain-bisector method and principles of detached thrust systems and conservation of volume. The new cross-sections attempt to model the subsurface geometry of the segmented KFS and to build on previous work in the area (4). Important unknowns are the JS thickness in the footwall and how JS strata deform adjacent to major faults. A minimum JS thickness of 800 meters was assumed, based on Mayflower drill hole #41 that crosses the Keweenaw fault at 476 meters below sea level (Fig. 2). Ductile deformation of a poorly indurated, mud-prone section near the base of JS was the method used to accommodate flexural slip in the overlying section, but other mechanisms remain to be investigated. A common feature of cross-sections transverse to the KFS trend is a thrust sheet with shallowly dipping PLV strata between a major fault segment and a splay fault. The cross-sections are adding to our understanding of deformation within the KFS and to the tectonic forces that created it. Acknowledgements This project was funded by the USGS EDMAP program (Award G21AC10681), Department of Geological and Mining Engineering and Science of Michigan Tech, ILSG Student Research Fund, Michigan Space Grant Consortium, and sponsored by the Michigan Geological Survey. We thank Tom 48 �Wright for access to Quincy Mine; Ian Gannon, Breeanne Heusdens, Jack Hawes, Braxton Murphy, and Dillon Breen for field assistance; and Dan Lizzadro-McPherson for ArcGIS assistance. References 1. Cannon, W.F., 1994, Closing of the Midcontinent rift ‒ A far-field effect of Grenvillian compression: Geology, v. 22, p.155-158. 2. Cannon, W.F., Green, A.G., Hutchinson, D.R. and nine others, 1989, The North American Midcontinent Rift beneath Lake Superior from GLIMPCE seismic reflection profiling: Tectonics, v. 8, p. 305-332. 3. Hinze, W.J., Braile, L.W., and Chandler, V.W., 1990, A geophysical profile of the southern margin of the Midcontinent Rift System in western Lake Superior: Tectonics, v. 9, no. 2, p. 303-310. 4. DeGraff, J.M. and Carter, B.T., 2022, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulletin, v. 135, no. 1/2, p. 449–466. 5. Lizzadro-McPherson., D.J., 2023, Structural Analysis and Slip Kinematics of the Keweenaw Fault System between Bête Grise Bay and Gratiot Lake, Keweenaw County, Michigan: Michigan Technological University M.S. thesis, 140 p. Figure 1: Updated bedrock geologic map and legend of study area, with fault segments labelled: KF – Keweenaw Fault, HFHancock Fault, AGF – Allouez Gap Fault Figure 2: Crosssection showing Keweenaw (KF) and Hancock Faults (HF) at Douglass-Houghton Falls. Main units: JS – Jacobsville Sandstone, PLV - Portage Lake Volcanics 49 �Volcanic and Hydrothermal Reconstruction of the Paleoproterozoic Butler Zn-Cu occurrence, Clark County, Wisconsin LAWRENCE, Alex1, VANDERKIN, Adam1, and LODGE, Robert, W.D.1 1 Department of Geology, University of Wisconsin-Eau Claire, Eau Claire, WI 54701 USA The Butler Zn-Cu occurrence is located in western Clark County, northcentral Wisconsin, and is an example of a volcanogenic massive sulfide (VMS) deposit. These VMS deposits are mined globally for numerous metals including Zn, Cu, Pb, Ag, and Au, and are formed at or near the seafloor in extensional submarine volcanic environments through the discharge of hot, metalrich hydrothermal fluids (e.g. Franklin et al., 2005). The Butler occurrence is hosted in the Paleoproterozoic Eau Claire Volcanic Complex (1.8-1.9 Ga) within the Marshfield terrane of the Penokean Orogen (Shultz and Cannon, 2007; DeMatties, 2022). Historically, the interpreted setting for Penokean volcanism within the Marshfield terrane was a “continental’ setting with younger magmas emplaced within older Archean crust. New data from the Eau Claire Volcanic Complex suggests the absence of Archean crust during Penokean volcanism (Weber et al., 2023). The goal of this project is to interpret the volcanic and hydrothermal setting of the Butler Zn-Cu deposit and test whether the lithostratigraphic and petrochemical associations fit an oceanic or continental model. Extensional environments that form VMS deposits can exist in both oceanic and continental settings. This imparts unique lithostratigraphic (Franklin et al. 2005) and petrochemical (Piercey, 2011) characteristics on the host stratigraphy and alteration styles. The lithostratigraphy of continental-associated VMS tends to be more felsic in nature with a higher abundance of siliciclastic rocks relative to oceanic-settings. Mafic rocks are much more abundant in ocean environments whereas are rare and largely intrusive in continental settings. Chemically, felsic rocks in continental settings are HFSE- and REE-enriched while mafic rocks are typically alkalic- to MORB-affinities commonly found in continental rift settings. Approximately 2700 linear feet of drill core from the Butler occurrence were re-logged and sampled for petrographic and geochemical characterization of the host volcanic and hydrothermally-altered rocks. Petrography divided the host strata into three main units: 1) felsic volcanic rocks, 2) amphibolite, and 3) metapelite. The felsic volcanic rocks are fine-grained, foliated quartzofeldspathic schists (Figure 1A) that have layered volcaniclastic textures and local stretched and flattened lapilli fragments. The amphibolite units (Figure 1B) are fine- to mediumgrained, homogenous, and largely unaltered suggesting an intrusive origin that post-dates the main VMS-forming event. The metapelite units (Figure 1C) are made up of a micaceous matrix composed of muscovite, chlorite, and biotite. The metapelite units are characterized by large porphyroblasts of garnet, staurolite, and/or cordierite. Hydrothermally-altered rocks that host sulfide mineralization are metamorphosed to biotite±chlorite±talc schists and calc-silicate mineral assemblages. The sulfide mineralization is primarily pyrite with variable amounts of chalcopyrite, and sphalerite. Massive sulfides (Figure 1D) are weakly banded with chloritic gangue while semi-massive vein-type mineralization is found throughout altered rocks. The relative abundance of the felsic and amphibolite units coupled with an intrusive origin for amphibolite, suggests a bimodal-felsic type VMS, described in the paper Volcanogenic Massive Sulfide Deposits that is typical of continental magmatism (Franklin et al., 2005). Mafic units are interpreted to be island arc to MORB-type based on Ti vs. V discrimination plots. Felsic volcanic rocks have an FII-type affinity on Zr/Y vs. Y discrimination diagrams and have within plate affinities on Nb vs. Y discrimination diagrams. Geochemical abundances of the host rocks support a continental petrochemical association. 50 �Figure 1. Photographs of core samples from the Butler deposit featuring the host rocks of the VMS. White scale bar equals about 1 cm. (A) Foliated felsic volcanic rock that is the main host rock of the Butler formation. (B) Amphibolite unit, image displays how homogenous the matrix is. (C) Metapelite unit, tan staurolite porphyroblasts along with large purple to grey cordierite porphyroblasts found throughout the matrix. (D) Massive sulfide unit containing pyrite and chalcopyrite. References DeMatties, T.A., 2022. Exploration-resource assessment of productive felsic volcanic centers in the Paleoproterozoic Penokean volcanic belt of northern Wisconsin, Michigan and East-central Minnesota, USA: Ore Geology Reviews, v. 141: 104489. Franklin, J. M., Gibson, H. L., Jonasson, I. R., and Galley, A. G., 2005, Volcanogenic massive sulfide deposits, in Hedenquist, J. F. H., Goldfarb, R. J., and Richards, J. P., eds., Economic Geology, 100th Anniversary Volume, p. 523-560. Piercey, S. J., 2011, The setting, style, and role of magmatism in the formation of volcanogenic massive sulfide deposits: Mineralium Deposita, v. 46, p. 449-471. Schulz, K.J., and Cannon, W.F., 2007. The Penokean orogeny in the Lake Superior region: Precambrian Research, v. 157: 4-25. Weber, E.M., Lodge, R.W.D., Marsh, J.H. (2023). U/Pb geochronology and zircon petrochronology of Paleoproterozoic magmas from the Marshfield terrane, Penokean Orogen, Wisconsin. Institute on Lake Superior Geology Proceedings, 69th Annual Meeting, Eau Claire, Wisconsin, Part 1Program and Abstracts, p. 97-98. 51 �Building a 3D model for Cu/Pd inflection points throughout the Marathon PGE-Cu Deposit LAXER Max1, GOOD David1 1 Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada The Marathon PGE-Cu deposit is hosted in the North American Midcontinent rift system, a failed continental rift (Good et al., 2015). Magmatic activity in the area created an optimal environment for the formation of economically significant sulphides (Smith et al., 2022) bearing copper (Cu), and platinum group elements (PGE) at the Marathon deposit. The deposit lies in the Two Duck Lake Gabbro, a subophitic, coarse-grained intrusion located at the eastern margin of the Coldwell Complex. This study explores how Cu/Pd varies in 3D space at the deposit scale and aims to use it as a vectoring tool to guide exploration. The ratio of Cu/Pd is a useful marker of the enrichment of Pd relative to the mantle. Low Pd relative to Cu indicates previous Pd depletion due to the early formation of sulphides in the intruding magma that formed the deposit, whereas a relatively higher Pd concentration implies Pd enrichment (Barnes et al., 1993). The 3D model helps to visualize the positions of the abrupt shifts (inflection points) in Cu/Pd ratio throughout the Marathon deposit. Identifying and modelling Cu/Pd inflection points facilitated the search for trends in mineralization. To create the model, a data filtration process was employed to define wide mineralization intervals containing at least 80 ppm Cu and 0.15 ppm Pd. Zones of continuous mineralization of at least 16 m in length were identified. To identify inflection points the difference in Cu/Pd ratio was evaluated at 10 m intervals. The mineralized zones were searched for points that surpassed the thresholds found to constitute trend reversals in Cu/Pd (ΔCu/Pd >5000 or <-5000). Approximately 1150 inflection points have been identified in 404 drillholes from a dataset of 997 drillholes and 61960 assays. Figure 1. Graphs showing the trends of concentration Cu and Pd in ppm, the ratio of Cu/Pd, and the 10 m difference calculations used to identify inflection points, down drill hole M-20-541 (depth in m) at the Marathon PGE-Cu deposit. The dashed lines indicate filtration cut-offs for Cu (80 ppm) and Pd (0.15 ppm) and the inflection point thresholds in the Cu/Pd graph (at -5000 and 5000). 52 �Three zones of interest were identified within the model of the deposit with distinct trends in the occurrence Cu/Pd ratio inflection points (Fig. 2). Area 1 included zones of high grade Pd mineralization occurring independently of any high-grade copper or any inflection points. In Area 2 the arrangement of inflection points suggests a boundary which aligns with the paleosurface at the contact between the Footwall and the Main Zone. A fault runs through Area 3 (Good et al., 2015), along which there are no Cu/Pd inflection points, indicating that there may be a link between faulting and the consistency of Cu/Pd ratio. The most prominent pattern observed in the 3D model of the inflection points was that Cu/Pd correlates better with lithological changes than with shifts in Cu and Pd grade. Area 1 Area 2 Area 3 Figure 2. Views of the Leapfrog model of the Marathon deposit, including all Cu and Pd assays and all inflection points. Showing plan views of the whole deposit, Areas 1 and 3 and a cross-section of Area 2. References Barnes, S.-J., Couture, J., Sawyer, E., & Bouchaib, C., 1993. Nickel-copper occurrences in the BelleterreAngliers Belt of the Pontiac subprovince and the use of Cu-PD ratios in interpreting platinumgroup element distributions. Economic Geology, 88(6), 1402–1418. Good, D. J., Epstein, R., McLean, K., Linnen, R. L., & Samson, I. M., 2015. Evolution of the main zone at the marathon Cu-PGE sulfide deposit, Midcontinent Rift, Canada: Spatial relationships in a magma conduit setting. Economic Geology, 110(4), 983–1008. Smith, J. M., Ripley, E. M., Li, C., Shirey, S. B., & Benson, E. K. (2022). Magmatic origin for the massive sulfide ores in the sedimentary country rocks of mafic–ultramafic intrusions in the midcontinent rift system. Mineralium Deposita, 57(7), 1189–1210. 53 �Critical Mineral Systems in the Upper Peninsula of Michigan, A Cooperative Effort Between the USGS and the Michigan Geological Survey MAHIN, Robert2, QUIGLEY, Ashley2 YELLICH, John1, ESCH, John1, and GAMET, Nolan2, 1 Michigan Geological Survey, Western Michigan University, Kalamazoo MI 49008-5241 2 Michigan Geological Survey, Western Michigan University, Gwinn MI 49841 In 2018, the U.S. Geologic Survey (USGS) released a list of critical minerals defined as “non-fuel mineral or mineral material essential to the economic or national security of the U.S., and which has a supply chain vulnerable to disruption” and updated it in 2022 to a total of 50 critical minerals (Burton, 2022). Since 2021, President Biden has made the domestic supply of critical minerals a national priority. With federal funding, the USGS Earth Mapping Resource Initiative (EMRI) is collaborating with State geological surveys on geologic mapping and critical mineral assessments, as well as inventorying and characterizing mine wastes. The USGS has identified broad focus areas within the United States to target critical minerals (Hammarstrom and others, 2023). These focus areas are based on known mineral occurrences and favorable geologic settings. The Precambrian of the Upper Peninsula (UP) figures in 17 mineral systems. The Michigan Geological Survey (MGS) has narrowed the list to nine systems in the UP to focus our future work (Table 1). With the support of the USGS, forthcoming mapping and geochemical reconnaissance programs by the MGS over the next few years will assess these systems. Name of focus area Midcontinent Rift magmatic sulfide Ni-Cu-PGE Manganese (Mn) in ironformations Graphite in black shales Mineral system Deposit type(s) Critical minerals in Critical minerals the deposit types Identified Mafic magmatic Nickel-copper-PGE sulfide Co, Ni, PGE, Te Nickel, Co, PGE Marine chemocline Iron-manganese Co, Mn Manganese Metamorphic Graphite (carbonaceous sed) Humboldt Granite Porphyry Sn (granite-related) Porphyry/skarn Humboldt Granite Magmatic REE Southern Complex pegmatites Porphyry Sn (granite-related) Pegmatite LCT Mesoproterozoic Phosphate Marine chemocline Peavey Pond Complex IOA-IOCG Western Upper Peninsula, IOCG IOA-IOCG Peralkaline syenite/granite/rhyolite/ alaskite/pegmatites Graphite Be, Nb, Sc, Sn, Ta, W Be, Fl, Hf, Nb, REE, Ta, Te, V, Zr Be, Ce, Li, Nb, Sc, Ta, Sn Co, REE Phosphate Iron oxide apatite; Iron oxide copper Co, REE gold Iron oxide apatite; Iron oxide copper Co, REE gold Trace Trace Trace Phosphate Unknown Unknown Table 1: USGS-MGS Critical Mineral Focus Areas for the UP (modified from Hammarstrom and others, 2023) The existence of some critical minerals is well-established in the UP, such as magmatic sulfide Ni-Cu-Pt-Pd-Co. Others, such as graphite, manganese, and phosphate have been documented in small occurrences or as accessory minerals in larger deposits (Cannon and Klasner, 1976: Hwang and others, 1986; James and others, 1968; Peterman and others, 1987, 54 �Mancuso, 1975). Evidence for critical minerals such as rare-earth elements, beryllium, and fluorspar in pegmatites, granites, and iron-oxide-copper-gold/oxide apatite deposits (IOCG/IOA) is sparse. A limited number of studies of UP pegmatites and the Humboldt granite have identified trace REE, Be, and Ta minerals (e.g. Buchholz and others, 2014; Johnson and others, 2015; Moss, 1975, Schulz and others, 1988). Mineralization directly tied to IOCG/IOA has not been identified, although the tectonic history and metal endowment suggests the UP is a permissive, if not prospective region for them. The USGS has also mounted a mine waste characterization program intended to identify potentially recoverable critical minerals in historical mine stockpiles, waste piles and tailings and prioritized by size, potential mineral resources. As part of the effort, the MGS has identified over 80 mine sites in the UP within EMRI critical mineral focus areas that have published references to possible critical mineral content. Future assessments will involve representative sampling of mine waste features and geochemical evaluations. References Buchholz, T. W., Simmons, W. B., and Falster, A.U., 2014: Accessory mineralogy of the Black River Pegmatite and Humboldt granite, Marquette County, Michigan. In Fortieth Rochester Mineralogical Symposium: Contributed Papers in Specimen Mineralogy, Part 1, Rocks & Min., 89:4, 370-374. Burton, J., 2022. U.S. Geological Survey Releases 2022 List of Critical Minerals: https://www.usgs.gov/news/national-news-release/us-geological-survey-releases-2022-list-criticalminerals. Cannon, W.F. & Klasner, J.S., 1976. Phosphorite and other apatite-bearing sedimentary rocks in the Precambrian of Northern Michigan: US Geological Survey Circular, 746, 6 p. Hammarstrom, J.M., Woodruff, L.G., and Dicken, C.L., 2023, Critical mineral deposits of the United States: U.S. Geological Survey data release, https://doi.org/10.5066/P9K1HBNT Hwang, J. Y., Carlson, D. H., Johnson, A. M., and Van Alstine, J., 1986. Preliminary investigation of graphite resources in Michigan, in Process Mineralogy VI: Applications to Precious Mineral Deposits, Industrial Minerals, Coal, Liberation, Mineral Processing, Agglomeration, Metallurgical Products and Refractories, with Special Emphasis on Cathodoluminescence Microscopy, (Ed. by, Hagni, R. D.), p. 315- 327. James, H.L., Dutton, C.E., Pettijohn, F.J. and Wier, K.L., 1968. Geology and ore deposits of the Iron River-Crystal Falls District, Iron County, Michigan: U.S. Geological Survey Professional Paper 570, 127 p. Johnson, Christopher M. and Van Daalen, Christopher M., 2015. Mineralogy and geochemistry of Late Archean and Paleoproterozoic granites and pegmatites in the Northern Penokean terrane of Marquette and Dickinson Counties, Michigan. University of New Orleans Theses and Dissertations. 2088. Mancuso, J.J., 1975. Carbonate-apatite in Precambrian cherty iron formation, Baraga County, Michigan. Economic Geology, 70, p. 583-586. Moss, Michael J., 1975. Some pegmatites near Gwinn, Michigan. Master's Thesis 2451, Western Michigan University. Peterman, J.F., Johnson, A.M. and Van Alstine, J., 1987. Geological and geophysical investigation of graphite resources in Upper Michigan, in Institute on Lake Superior Geology, 33rd Annual Meeting, Proceedings and Abstracts, p. 53-54. Schulz, K.J., P.K. Sims, Z.E. Peterman. 1988. A post-tectonic rare-metal-rich granite in the southern complex, Upper Peninsula, Michigan. in Institute on Lake Superior Geology, 34th Annual Meeting, Proceedings and Abstracts, p. 34. 55 �Baraboo Interval Quartzites in Iowa: Reassessing the Origin and Provenance of the Washington County Quartzite, SE Iowa MALONE, Jack1, CLARK, Ryan1, HARRIS-BOMMARITO, Amira2, and MALONE, David2 1 Iowa Geological Survey, 300 Trowbridge Hall, University of Iowa, Iowa City, IA 52242 Geography-Geology, Felmley Hall of Science, Illinois State University, Normal, Illinois 61790 2 The Washington County Quartzite (WCQ) in southeastern Iowa is the southernmost occurrence of the Baraboo Interval quartzites in the midcontinent region (Figure 1). Two drill holes encountered poorly sorted quartzite and phyllite at a depth greater than 2,300 feet, likely deposited in a braided fluvial or deltaic environment near the Laurentian continental margin on the Columbia supercontinent. One hundred new LA-ICPMS detrital zircon ages from the WCQ show a prominent 1.78 Ga age peak, representing local Yavapai-aged basement, a secondary peak at 1.8-1.9 Ga representing a distal Penokean source, and minor <2.5 Ga peak derived from distal sources in the Superior Province. Multidimensional scaling of other Baraboo Interval quartzites and potential sources show that the WCQ is indistinguishable from the lower interval of the Baraboo quartzite (Figure 2). Cumulative and stacked probability plots also reflect principal source areas locally derived by erosion of underlying Yavapai-aged crust and distally derived Penokean and older sources from the Pembine-Wausau Terrane or southern Superior Province. The WCQ likely serves as the down slope equivalent during initial Baraboo deposition. Figure 1. Geological map of Precambrian basement rocks in the northern midcontinent (modified from Medaris et al., 2021). Baraboo Interval Inliers are B = Barron, F = Flambeau, M = McCaslin, T = Thunder Mountain, R = Rib Mountain, and N = Necedah. SLTZ = Spirit Lake Tectonic Zone, ECMP = East-Central Minnesota Batholith, GLTZ= Great Lakes Tectonic Zone, and NFZ = Niagara Fault Zone. 56 �Figure 2. Three-dimensional multi-dimensional scaling plot of Baraboo Interval strata in the northern midcontinent. Included data compiled from Malone et al. (2022), Van Wyck and Norman (2004), Stewart et al. (2018), Stewart et al. (2021), and Medaris et al. (2021). The red circle is the WCQ from this study. The yellow cluster includes samples from the lower members of the Baraboo Quartzite in the Baraboo Hills that are dominated by Yavapai-age zircons. The blue cluster includes the middle members of the Baraboo Quartzite in the Baraboo hills, other quartzites north of the SLTZ, and Necedah reflects a complex sedimentary provenance that includes proximal and distally derived zircons from the Penokean Province, Superior Province, and Trans-Hudson belt. The purple cluster includes the Waterloo Quartzite and the upper members of the Baraboo Quartzite in the Baraboo Hills that are dominated by southerly derived Mazatzal-age zircons. References Malone, D.H., Craddock, J.P., Holm, D., Krieger, A., and Baumann, S.J., 2022. Continent‐scale sediment dispersal for the Proterozoic Baraboo Interval quartzites in the Laurentian midcontinent. Terra Nova, 34(6): 503-511. Medaris, L.G., Jr., Singer, B.S., Jicha, B.R., Malone, D.H., Schwartz, J.J., Stewart, E.K., Van Lankvelt, A., Williams, M.L., and Reiners, P.W., 2021. Early Mesoproterozoic evolution of midcontinental Laurentia: Defining the geon 14 Baraboo orogeny. Geoscience Frontiers, 12: 101174. Stewart, E.K., Brengman, L.A., and Stewart, E.D., 2021. Revised Provenance, Depositional Environment, and Maximum Depositional Age for the Baraboo (<ca. 1714 Ma) and Dake (<ca. 1630 Ma) Quartzites, Baraboo Hills, Wisconsin. Journal of Geology, 129: 1-31 . Stewart, E.D., Stewart, E.K., Walker, A., and Zambito, J.J., IV., 2018. Revisiting the Paleoproterozoic Baraboo interval in southern Wisconsin: Evidence for syn-depositional tectonism along the south-central margin of Laurentia. Precambrian Research, 314: 221-239. Van Wyck, N., and Norman, M., 2004. Detrital zircon ages from early Proterozoic quartzites, Wisconsin, support rapid weathering and deposition of mature quartz arenites. Journal of Geology, 112: 305-315. 57 �The Soudan Geology Trail Project: Let’s talk about rocks in northeastern Minnesota MARTIN, Alice1, ALLERTON, Zsuzsanna1, JOHNSON, Emma1, FAYON, Annia1, ESSIG, Jim2, GUY-LEVAR, Sarah2, HUDAK, G. H. 1 1 Earth and Environmental Science Department, University of Minnesota, 150 John Tate Hall, 116 Church St. SE, Minneapolis, MN 55455, USA 2 Minnesota Department of Natural Resources, 1302 McKinley Park Rd, Soudan, MN 55782, USA As part of a larger research endeavor within the Archean terrane of northern MN, we are developing educational outreach content created to engage the public with portions of the important geology of the region. Rocks exposed in the Lake Vermilion-Soudan Underground Mine State Park, located near Tower, MN, record glimpses of environmental and tectonic conditions from 2.7 billion years ago to the present, including mysteries of the early Earth, complexities of modern history, and possibilities of the future. The planned content will be designed to follow outcrops located along a paved trail that runs through the park (Figure 1). Figure 1: This figure shows recently exposed units along the proposed trail (bold line in center of the figure). Starting at the banded iron formation (A), the trail leads north then east (clockwise) to the next units (B) consisting of pillow basalts and basaltic lava flows, followed by felsic tuff (C) and lastly a large, exposed outcrop along the paved road is chlorite schist with intertwined with banded iron formation (D). 58 �The chosen outcrops consist of well-preserved greenschist-facies metamorphosed igneous, sedimentary, and sheared rocks. Selected rock units along the trail include Neoarchean basaltic lava flows, pillow basalts, felsic tuff, gabbro, oxide-facies banded iron formation, and chloriteand sericite-dominant schists. These rock units represent an ancient submarine volcanic and hydrothermal environment that was subsequently regionally deformed (Hudak et al., 2016). The work being done will be included in educational materials designed to communicate the scientific content in digestible ways. Plain language writing, paired with visuals, modern analogues and analogies will present the information in a variety of ways with the intention of supporting a range of learning styles. The materials will be available in physical forms (on paper and/or trail signs) and with QR codes which will link to additional online content. Visual illustrations will be designed in collaboration with a Minnesota high school student. Combining educational material with the hands-on outdoor experience of visiting the trail and highlighted outcrops aims to facilitate cognitive development and understanding of the long history and importance of the regional geology. This initiative is a collaboration among park officials Jim Essig (Park Manager) and Sarah Guy-Levar (Interpretive Supervisor) from the MN Department of Natural Resources, the University of Minnesota Department of Earth and Environmental Sciences, and local and state educators. References Hudak, G.J., Peterson, D.M., Radakovich, A., Pignotta, G., Schwierske, K., and Students from the 2010-2013 Precambrian Research Center Geology Field Camp, 2016, Bedrock geologic map of Lake Vermilion/Soudan Underground Mine State Park – Report to the Minnesota Department of Natural Resources: Natural Resources Research Institute, University of Minnesota Duluth, Technical Report NRRI/TR-2016/20, 23 p. 59 �Investigating the origin of pervasive breccias in the Paleoproterozoic Saunders Formation in northern Wisconsin MARTIN, Gwendolyn and BJØRNERUD, Marcia Department of Geosciences, Lawrence University, 711 E Boldt Way, Appleton WI 54911 The Paleoproterozoic Saunders Formation is an enigmatic unit with limited exposure along the Brule River, which forms the border between northern Wisconsin and the Upper Peninsula of Michigan. The unit occurs just north of the Niagara Fault zone, the Penokean-age (ca. 1.88 Ga) tectonic suture between the Superior Craton and the Wisconsin Magmatic Terranes (Schulz & Cannon, 2007). Variously described as a “massive dolomite” (Allen 1910), a “silicified dolomite” (Sims, 1992), and a “silica rock” (Cannon, 1986), the Saunders Fm. is thought to be part of the lower Chocolay Group, correlative with the Randville, Bad River, and Kona Dolomites, and possibly also the quartzites underlying these units (Sturgeon River, Sunday, and Mesnard Fms.). Each of these carbonate formations is overlain by a major unconformity, at ca. 2.1 Ga., representing at least 100 million years of erosion. Every published description of the Saunders Fm. mentions that it tends to be brecciated, yet the nature of these breccias has not been explored in detail. Dutton & Linebaugh (1967) suggested that the Saunders Fm. represents a condensed section of basal Chocolay quartzite and dolomite, related to the formation of the regional unconformity. James et al. (1968) similarly hypothesized that “silcretes” within the Saunders had formed by Proterozoic weathering but also pointed out that none of the other Chocolay Group carbonate units displays evidence of such deep weathering. They speculated, therefore, that the Saunders breccias could have had a tectonic origin but did not pursue that hypothesis further. The purpose of this study was to characterize and interpret Saunders breccias in outcrops at Brule River Cliffs State Natural Area in Wisconsin. At this site, outcrops of the Saunders Formation are of two types: 1) beige to orange-colored dolostone with a ‘gritty’ but otherwise massive (unveined, unlaminated) texture; and 2) dramatically fragmented dolostone with extensive ‘stockwork” quartz veins that constitute most of the rock mass. Immediately southwest of the Natural Area boundary, large boulders of dolomite-matrix breccias with angular chert fragments are common. Although these are not in situ, we suspect they come from the Saunders Fm., and were transported ca. 12 km by glacial ice. If so, these chert breccias represent a third, distinct textural type within the Saunders. The gritty dolomite, which is typically unveined, has a distinctive diamictic, granular texture, with scattered mm-sized, rounded grains set in a much finer matrix. In thin section, the matrix also appears granular, unlike the crystalline texture typical of most carbonate rocks. Similar gritty/ granular dolomites have been observed along a major upper crustal fault zone in Namibia. Rowe et al. (2012) interpreted these unusual textures as records of decarbonation and fluidized granular flow caused by rapid frictional heating during seismic slip in rocks that had been at ambient crustal temperatures of around 200°C. (Carbonate rocks typically devolatilize, rather than melt, during seismic slip, so pseudotachylyte is rare along faults cutting through dolostone). The absence of talc or other calc-silicate metamorphic minerals in the Saunders Formation points to subgreenschist temperatures in an upper crustal setting comparable to the Namibian case. The veined breccias have an ‘exploded’ look, with quartz veins in multiple orientations that appear to have increased the volume of the rock mass more than 100%. The isolated fragments of host dolostone have narrow, slab-like shapes that suggest fragmentation occurred partly along bedding planes. In thin section, most of the veins have a coarse, blocky texture with no preferred orientation of crystals. Fluid inclusions arrays are common, particularly in the interiors of the crystals. Some of the vein quartz shows slight undulose extinction. The chert breccia boulders 60 �found southwest (in the down-ice direction) of the Saunders outcrops have the texture of cataclasites. The angular fragments of chert within these breccias appear to represent thin silicified stromatolitic layers that were fractured and dismembered. We interpret these three textural types of the Saunders Fm. as distinct areas within a major Penokean-age fault zone. The chert breccias may represent the outer part of the fault zone, dominated by non-seismic cataclasis. The gritty dolomite, bearing evidence of co-seismic heating, would have been closer to the fault core, together with the heavily veined dolostone, whose ‘exploded’ nature points to extreme dilational strain and forceful fluid influx with little cataclasis or grinding. The large amounts of vein material relative to the host rock, as well the blocky texture of the veins, are consistent with the introduction of large volumes of overpressured, silicasupersaturated fluids into the shallow crust during the propagation of a fault rupture upward from depth. Such fluid influx can happen when co-seismic slip breaks the barrier between deep crustal, low-permeability rocks in which fluids are at lithostatic pressures and overlying high-permeability rocks with fluids at hydrostatic pressure (Cox and Munroe, 2016). Silica-rich fluids traveling upwards from below this barrier would be far from chemical equilibrium in the shallow crust, and they would rapidly precipitate their dissolved silica, easily overcoming kinetic quartz growth limits that exist under equilibrium conditions (Williams and Fagereng, 2022). This interpretation of the Saunders breccias is supported by oxygen isotope analyses of seven vein quartz samples, all of which yielded 18O values between 15.94 to 17.46 VSMOW. Although brecciated textures described in previous studies of the Saunders formation may be related to deep weathering and the post-Saunders unconformity, the breccias exposed in the Brule River Cliffs Natural Area are clearly tectonic -- and probably coseismic -- in origin. The Saunders Formation thus provides further evidence for great earthquakes at various crustal depths along major fault zones during the Penokean orogeny (Larson & Bjørnerud, 2017; Taylor & Bjørnerud, 2023). References cited Allen, R., 1910. The Iron River iron-bearing district. Mich. Geol. Biol. Survey Pub. 3, Ser. 2, 151 p. Cannon, W., 1986. Bedrock geologic map of the Iron River 1º x 2º quadrangle. USGS Map I-1360-B. Cox, S. & Munroe, S., 2016. Breccia formation by particle fluidization in fault zones. Am. J. Science, 316, 241-278. Dutton, C. & Linebaugh, R., 1967. Map of Precambrian geology of Menominee district, USGS Map I-466. James, H., et al., 1968. Geology & ore deposits of Iron River-Crystal Falls District. USGS Prof. Paper 570. Larson, M. & Bjørnerud, M., 2017. Seismic slip, mylonitization and fluid flow along the Penokean TwelveFoot Falls shear zone, Marinette County, NE Wisconsin. Proc. Inst. Lake Superior Geol., 63, 56-57. Rowe, C., Fagereng, Å., Miller, J. & Mapani, B., 2012. Signature of coseismic decarbonation in dolomitic fault rocks of the Naukluft Thrust, Namibia. Earth & Planetary Science Letters, 333, 200-210. Schulz, K. & Cannon, W., 2007. Penokean orogeny in the Lake Superior Region. Precam. Res. 157, 4-25. Sims, P.K., 1992. Geologic map of Precambrian rocks, southern Lake Superior region, USGS Map I-2185 Taylor, M., and Bjørnerud, M., 2023. Deciphering the metamorphic and deformational history of the Hardwood Gneiss, Felch District, Michigan. Proc. Inst. Lake Superior Geol., 69, 89-90. Williams, R. and Fagereng, Å., 2022. The role of quartz in the seismic cycle. Rev. Geophysics, 60, 2021RG000768. 61 �The Evolution of Baraboo Interval Sedimentary Rocks: Deposition at 1.63 Ga and Metamorphism at 1.47 Ga MEDARIS, Gordon Jr., BONAMICI, Chloe, BROWN, Phil, GOODWIN, Laurel, JICHA, Brian, SINGER, Brad, SPICUZZA, Michael, VALLEY, John Department of Geoscience. University of Wisconsin–Madison, Madison, Wisconsin 53706 Supermature siliciclastic sedimentary rocks of the Baraboo Interval (Dott, 1983) were deposited in the southern Lake Superior region following the 1.65-1.63 Ga Mazatzal orogeny and subsequently experienced 1.47 Ga fluid-rock interactions related to the trans-Laurentian Pinware-Baraboo-Picuris orogeny (Daniel et al., 2022). Metamorphic fluid-rock interactions include dehydration and metasomatic varieties, the latter having been promoted by regional-scale advective flow of brines along permeable channels in the various Baraboo Interval occurrences. In the Baraboo Range, south-central Wisconsin, the supermature sedimentary rocks are composed of five oxides, viz. SiO2, Al2O3, Fe2O3, TiO2, and H2O, with CaO, Na2O, and K2O having been largely removed during weathering of the igneous basement. During metamorphism, the original sedimentary mineral assemblage of kaolinite + quartz + hematite + rutile was transformed to one of pyrophyllite + quartz + hematite + rutile through the dehydration reaction, Al2Si2O5(OH)4 (kln) + 2SiO2 (qtz) = Al2Si4O10(OH)2 (prl) + H2O (fluid) Note that in shale, which consisted mostly of kaolinite, the appearance of pyrophyllite is accompanied by diaspore, as expressed by the dehydration reaction, 2Al2Si2O5(OH)4 (kln) = Al2Si4O10(OH)2 (prl) + 2AlO(OH) (dsp) + 2H2O (fluid) Figure 1. Schematic cross-section of the Baraboo Range, indicating the various metasomatic mineral assemblages; the numbers specify 40Ar/39Ar plateau ages for muscovite. Folding and metamorphism in the Baraboo Range were accompanied by advective flow of brines and potassium metasomatism along the base of the quartzite and in the overlying slate (Fig. 1). At the base of the quartzite, kaolinite was replaced by muscovite in paleosol, kaolinite was replaced by pyrophyllite and accompanied by precipitation of muscovite in metapelite (pipestone), and thin diaspore hydrothermal veins (bordered by muscovite) intruded quartzite 62 �above the metapelite. Slate that overlies the quartzite consists of muscovite, chlorite, quartz, hematite, and rutile and contains 4.7% to 6.4% K2O, due to potassium metasomatism, compared to 3.5% K2O in average shale. The paleosol at the base of the quartzite in Baxter Hollow (Fig. 1), which is 796 cm thick, experienced a total flux of 0.46 mol cm-2 K2O during metasomatism. Five additional Proterozoic paleosols in the southern Lake Superior region, ranging in thickness from 300 cm to 950 cm, also experienced potassium metasomatism, with K2O fluxes between 0.22 and 0.73 mol cm-2, respectively; for all six paleosols taken together, K2Oflux = 0.00066  thicknesscm + 0.06, for which R2 = 0.82. SiO2 was mobilized high in the quartzite section at the base of the metasiltstone and metapelite horizon in the south limb of the syncline, where quartz was precipitated in several bedding-parallel slickenfiber layers, 3 mm to 8 mm thick (Fig. 1). Individual slickenfibers are cylindrical, having a:b:c fabric ratios of 8:1:1, in which the a-dimension is up to 4 mm in length. Slickenfibers plunge down-dip approximately perpendicular to the fold axis of the syncline, and slickenfiber steps record top-to-the-south shear. SiO2 was also mobilized above the metasiltstone/metapelite horizon, where quartz was precipitated in bedding-parallel quartzite breccia zones up to 100 m thick (Fig. 1). The breccia zones consist of angular red quartzite fragments cemented by a stockwork of white quartz veins that consist predominantly of coarse-grained quartz and small amounts of specular hematite and locally, coarse-grained muscovite. Euhedral quartz crystals occur in late-stage vugs, some of which are partly to completely filled by kaolinite. Values of 18O (-2‰ to +31‰ VSMOW, SIMS) in euhedral quartz correlate with complex patterns of growth zoning and healed fractures (SEM-CL) to reveal multiple fluid events, including high-T (~300 oC) and low-T (50-100 oC) exchange with hydrothermal and meteoric fluids (Schranz et al., 2017). The pyrophyllite + diaspore mineral assemblage in metapelite constrains the temperature of Baraboo recrystallization to between 315 oC and 360 oC at a pressure of 2.0 kbar. An isochor for fluid inclusions in quartz in a folded quartz vein in metapelite, combined with phase equilibrium considerations, yields T-P conditions between 320 oC, 2.7 kbar, and 385 oC, 4.0 kbar, corresponding to a thermal gradient of ~30 oC/km. Expressed another way, the thermal gradient for metamorphism of the Baraboo quartzite was ~1700 oC/GPa, which places Baraboo metamorphism in the high T/P type of metamorphism (775 oC/GPa < T/P < 2000 oC/GPa), as defined by Brown and Johnson (2019). 40 Ar/39Ar plateau ages for muscovite in paleosol (1467 ± 11 Ma), hydrothermal veins (1478 ± 12 Ma), quartzite breccia (1472 ± 3 Ma), and four samples of slate (between 1493 ± 3 and 1473 ± 3 Ma) demonstrate that recrystallization and K-metasomatism in the Baraboo Range were contemporaneous with emplacement of the 1476-1470 Ma Wolf River A-type ferroan granitic batholith in Wisconsin. Such metamorphism and magmatism in Wisconsin represent the local expression of the continental-scale geon 14 Pinware-Baraboo-Picuris orogeny, which is characterized by high T/P metamorphism and A-type ferroan granitic batholiths. References Brown, M. and Johnson, T., 2019. Metamorphism and the evolution of subduction on Earth. Am. Mineral., 104: 1065-1082; Dott, R.H. Jr., 1983. The Proterozoic red quartzite enigma in the north-central U.S. – resolved by plate collision? Geol. Soc. Am. Mem., 160: 129-141; Daniel, C.G., et al., 2023. Linking the Pinware, Baraboo, and Picuris orogens: Recognition of a trans-Laurentian ca. 1520-1340 Ma orogenic belt. Geol Soc. Am. Mem., 220: 175-190; Schranz, L., et al., 2017, Stable oxygen isotopes, fluid inclusions, and microstructures in Baraboo Quartzite breccia. Proc. ILSG, v. 63/1: 83-84. 63 �Geochemistry of Midcontinent Rift-related intrusive rocks of the Sunday Lake intrusion MEXIA, Kevin1 and HOLLINGS, Pete1 1 Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, On P7B 1J4, Canada. The Sunday Lake intrusion is located 25 km north of Thunder Bay, Ontario and hosts Ni-CuPGE mineralization. It has an age of 1109.0±1.3 (Bleeker et al., 2020), and is related to the ~1115 to 1106 Ma magmatic event of the Midcontinent Rift System (MRS; Heaman et al. 2007). The intrusion is emplaced in Archean rocks of the Quetico Basin along the Crock Fault (Flank, 2017). It is not exposed at surface but was first identified from airborne magnetic surveys. In 2008, platinum and palladium mineralization was discovered by HTX Minerals Corp. In 2017 Impala Canada Ltd. Partnered on a joint venture with more than 30 holes drilled to date. The intrusion is funnel-shaped with a width of up to 1.5 kilometers and is 3 kilometers in length. It varies from 350 meters to 1000 meters in thickness. The intrusion consists of maficultramafic layers divided into three series: the Upper Gabbro Series, the Lower Gabbro Series, and the Ultramafic Series (Flank, 2017). Reef-style mineralization present in the lower zones of the intrusion consists of disseminated to blebby chalcopyrite-pyrrhotite-pyrite bearing olivine melagabbro (Fig. 1; Miller, 2020). One hole intersected the basal zones of the intrusion with more than 20 meters of mineralization at 2.11 g/t Pt, 0.95 g/t Pd, 0.16g/t Au, 0.26% Cu, and 0.11% Ni (Flank, 2017). The objectives of this project are to characterize the paragenesis of the Sunday Lake intrusion and the Ni-Cu-PGE mineralization, investigate the effects of crustal contamination on mineralization within the Sunday Lake Intrusion, and to place the Sunday Lake intrusion within the evolution of the MRS. This project utilizes two representative drill holes from which a total of 71 samples were collected. A total of thirty polished thin sections were generated for petrographic studies. Rocks were classified based on relative proportions of olivine, clinopyroxene, and plagioclase with modal rock names such as melagabbro, olivine melagabbro, and wehrlites. Fifty-five samples were analyzed for major and trace elements. Spider diagrams show different compositions within the layered intrusion, with primitive samples having trends consistent with a plume-like composition (Fig. 2A) while others suggest interaction with and contamination by host rocks (Fig. 2B). Variation in the behavior of trace elements suggest contamination, assimilation, and fractional crystallization processes were involved in the magmatic evolution of the intrusion. Sixteen samples have been sent for Sm-Nd and Rb-Sr isotope studies. The results of this study will be used to assess the source of mineralization and extent of contamination of the Sunday Lake Intrusion. 64 �A SL23KM41 Cpy Po B 5 mm Gangue Figure 1. Photomicrograph in reflected natural light (PPL) of a gabbroic sample containing pyrrhotite and chalcopyrite. Polished thin section scanned using a Zeiss microscope. References Figure 2. Primitive mantle normalized REE spider diagram of two samples. A: Sample showing a plume-like trend. B: Sample suggesting an interaction with the host rock. Normalising values from Sun and McDonough (1989). 9 Bleeker, W., et al. "The Midcontinent Rift and its mineral systems: Overview and temporal constraints of Ni-Cu-PGE mineralized intrusions." Targeted Geoscience Initiative 5 (2020): 7-35. Flank, S. (2017). The Petrography, Geochemistry and Stratigraphy of the Sunday Lake Intrusion, Jacques Township, Ontario. School of graduate studies. Heaman, L. M., Easton, R. M., Hart, T. R., MacDonald, C. A., Hollings, P., & Smyk, M. (2007). Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario. Canadian Journal of Earth Sciences, 44(8), 1055-1086. Miller, J.D., Green, J.C., and Severson, M.J. (2002). Terminology, nomenclature, and classification of Keweenawan igneous rocks of northeastern Minnesota. In Miller, J.D. Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.E., and Wahl, T.E., Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota. Minnesota Geological Survey Report of Investigations 58, p. 5-20. Miller, J.D. (2020). Report on the Petrography, Geochemistry, and Lithostratigraphy of DDH SL10-026 from the Southern Sunday Lake Intrusion. JDM GeoConsulting. Sun, S. S., & McDonough, W. F. (1989). Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society, London, Special Publications, 42(1), 313-345. Wold, R.J., Hinze, W.J. (1982). Geology and tectonics of the Lake Superior basin. Geol. Soc. Am. Mem. 156, 280. 65 �TWO DECADES OF TEACHING THE GEOLOGIC HERITAGE OF MINNESOTA’S NORTH SHORE AT THE NORTH HOUSE FOLK SCHOOL, GRAND MARAIS MILLER, Jim1 and GREEN, John2 1 2 Department of Earth and Environmental Science, UMD – retired; current residence: Shuniah, ON Department of Earth and Environmental Science, UMD – retired; current residence: Duluth, MN Since 1997, the North House Folk School, located in Grand Marais, Minnesota, has been promoting lifelong learning in the traditional arts and crafts and in knowledge about our northern culture and environment - present and past. Starting with a dozen courses at its inception, North House currently offers over 350 classes per year to over 3,000 students. From 2004 to 2010, John Green lent his expertise to North House by offering weekend lectures and field courses each year on basic geology and the geology of the North Shore and the Gunflint Trail. As a bonus, he also compiled lists of the native plants seen on these field excursions. In 2013, Jim Miller revived the course and has come to offer 2-3 courses per year that explore the Midcontinent Rift geology of the North Shore (What’s This Rock series) and the diverse geology at the end of the Gunflint Trail (Geology up the Trail series). By 2022, three different North Shore classes are offered (two per year, rotating in May and August) that explore different segments of the shore: What’s this Rock? – Grand Portage to Grand Marais, What’s this Rock Too? - Grand Marais to Tettegouche State Park, and What’s this Rock 3? - Tettegouche to Two Harbors (Fig. 1). From 2014 to 2019, a mid-October weekend field trip at the head of the Gunflint Trail was run out of the Gunflint. We hope to reinstate this course this fall or next, but will run it out of Grand Marais. Due to the Covid pandemic, no in-person field courses were permitted during 2020 and most of 2021 (one WTR course was run in October 2021, but participants drove their own vehicles). North House opted to host on-line webinars during the winter of 2021-22. Jim presented three webinar series. In January 2021, three lectures were offered on North Shore geology which was virtually attended by 104 students. During March 2022, three lectures were presented on the geology of Minnesota State Parks and Waysides with 83 people logged in. Then, in January 2023, a two-lecture webinar on the geology of the Gunflint Trail was viewed by 50 people. With the lifting of all Covid restrictions in the winter of 2022-23, North House reverted to only offering in-person classes. As currently taught, the three weekend WTR courses start with an introductory meeting on Friday evening on the North House campus in Grand Marais to discuss trip logistics and provide a geologic overview. Saturday is devoted entirely to a field trip that visits various classic geological exposures along the North Shore. Travel has typically involved carpooling with personal vehicles, but starting in August, 2023, the field trips have used a mini-bus. This or a 15passenger van will be the preferred method of transport going forward. In the evening, participants have the option to gather for informal discussions or a special lecture on various topics, especially at wood-fired pizza party held either Friday or Saturday evenings at the North 66 �House campus. The weekend concludes with a half-day field trip on Sunday morning, after which the group gathers either on a cobbled beach on Lake Superior to practice their newfound rock identification skills. Each field course is limited to about 15 registrants. A total of over 400 students have attended the field courses we have taught at North House over the past 20 years. Participants have ranged in age from 10 to 80 and come from all over the US and Canada, though most are from Minnesota, especially the Twin Cities. Their backgrounds range from those who have never heard of plate tectonics, to those who have had a few geology courses in their past. The common denominator among all participants is that they can all be characterized as being “rock curious”. Figure 1: Geology of northeastern Minnesota showing the general locations of geology field courses currently taught at North House Folk School - three “What’s this Rock?” courses and a Gunflint Trail (GFT) course. 67 �Quartz trace element chemistry: Exploring the link between a fertile parental granite and a mineralized pegmatite MORSON, Mia, and ZUREVINSKI, Shannon Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1 Canada Recent studies have proposed the use of pegmatitic quartz trace element chemistry as an indicator to lithium mineralization of potential economic pegmatite deposits (Müller et al., 2021). Using Laser Ablation- Inductively Coupled Mass Spectrometry (LA-ICP MS), the trace elements are determined in situ within a single quartz grain. Trace elements such as Al, Ge, Ti, P, B, and Fe3+, can substitute for Si4+ at very low concentrations, and the elements H, Li, Na, K, Fe2+ can enter the quartz crystal lattice via interstitial lattice positions (Götze et al., 2004). In this study, quartz from the 2685 Ma fertile Ghost Lake granitic batholith (GLB) and related Mavis Lake pegmatites group (Dryden, Ontario) were used to compare trends in quartz trace element concentrations within a single system (Figure 1). The focus of this study was to test the applicability of using quartz to (1) help identify fertile parental granitoid plutons and (2) help decipher any internal fractionation trends in mineralized pegmatites. If trace element concentrations in quartz from the granitic parent show any relationship to the mineralized pegmatites, this would prove beneficial in other exploration programs where potentially enriched Li pegmatites have not yet been identified. It could allow for an early assessment of an S-type granitoid and show indication of a potential nearby mineralized pegmatite, essentially the technique could be deemed a ‘fertility indicator’. Furthermore, if the quartz trace element compositions in the pegmatite zones show enrichment trends similar to the proposed model of Černý (1991), the technique would prove powerful in defining potential areas for further investigation (i.e. following the trend of enrichment). Figure 1: Study sample location through the zones of fractionation and enrichment, from the Ghost Lake Batholith to the Mavis Pegmatites (modified from Breaks and Selway, 1991). The results show correlations with increasing Li, Al, and Ge, and decreasing Ti from the GLB fertile parent granite to mineralized Mavis Lake pegmatites (Figure 2). The quartz trace elements can be used to form a simple fractionation model, similar to the pegmatite fractionation model of Černý (1991) to show elemental enrichments in a fertile LCT pegmatite system upon evolution (Figure 3). In summary, the quartz chemistry indicates fractionation and enrichment 68 �trends can be identified across the pegmatite zones. It is still unclear whether or not the technique could be applied to granites in order to assess fertility, as more work is required to understand the key differences in the quartz chemistry between a barren granite and a fertile parent granite. Figure 2: Trends in quartz trace element concentration in the GLB granites, intermediate beryl columbite zone, and mineralized Mavis Lake pegmatites. (a) Al vs Li bivariate plot. (b) Ti vs Ge bivariate plot. Figure 3: Fractionation model showing quartz trace element trends within the GLB-Mavis Lake system (modified from Černý, 1991). Breaks F.W., Selway, J.B., Tindle, A.G., 2005. Fertile peraluminous granites and related rare-element pegmatites, Superior Province of Ontario. Rare-Eelement Geochemistry and Mineral Deposits: Geological Association of Canada (GAC) Short Coarse Notes 17: 87-125. Černý, P., 1991. Rare-element granitic pegmatites. Part 1: Anatomy and internal evolution of pegmatite deposits. Part 2: Regional to global environments and petrogenesis. Geoscience Canada 18:49– 81. Götze, J., Plötze, M., Graupner, T., Hallbauer, D.K., Bray, C. J., 2004. Trace element incorporation into quartz: A combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography. Geochimica et Cosmochimica Acta, 68(18): 3741–3759. Müller A., Keyser W., Simmons W. B., Webber K., Wise M., Beurlen H., Garate-Olave I., Roda-Robles E., Galliski M. A., 2021. Quartz chemistry of granitic pegmatites; implications for classification, genesis and exploration. Chemical Geology, 584:1-17. 69 �Geometry, Slip Kinematics, and Deformation along the Hancock Fault in the Quincy Mine Workings, Upper Peninsula of Michigan MURPHY, Braxton, LANGFIELD, Katherine, DeGRAFF, James Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI, USA 49931 The Hancock fault is one of several major compressional features along the southern edge of the Midcontinent Rift System. It forms part of the Keweenaw fault system (KFS) whose connected segments follow the spine of Michigan’s Keweenaw Peninsula. The Hancock fault is a splay in the hanging wall of the KFS that intersects the main Keweenaw fault zone at an acute angle to define a thrust slice (Fig. 1). It extends along an azimuth of 55° for 17 kilometers from a point west of Houghton to its intersection with the main Keweenaw fault zone between Calumet and Lake Linden. Volcanic and sedimentary layers of the Portage Lake Volcanics (PLV, 1.1 Ga) are shown on bedrock geology maps with left-lateral offset across the Hancock fault (1, 2). Figure 1: Hancock (HF) and Keweenaw (KF) faults shown on USGS bedrock geology maps (1, 2). Major layers: pb-Bohemia conglomerate, psc-Scales Creek flow, pkKearsarge flow, pgGreenstone flow, chc-Copper Harbor conglomerate (base). Like other faults of the KFS, the Hancock fault has a major component of reverse slip that occurred during compression related to the Grenville Orogeny (3). Recent mapping and fault-slip measurements on the population of faults associated with the KFS reveal that the fault system has a right-lateral component of strike slip. This raises the question of whether the leftlateral offset of units across the Hancock fault in map view can be reconciled with net reverse and right-lateral slip along the KFS. The work reported here builds on previously reported work on the Hancock fault in the Quincy Mine workings to address this and other questions about its geometry, slip kinematics, and deformation (4). An adit in east Hancock provides access to the 7th level of the historic Quincy Mine, whose workings run along and across the Hancock fault at four locations (Figs. 1 and 2). The current phase of the project focused on acquiring data from the fault southwest of the adit, which data 70 �were combined with data previously collected from the adit toward the northeast. Fault-slip measurements were made on all accessible fault surfaces and consisted of fault attitude, slickenline rake, and slip sense where possible. The Hancock fault’s strike and dip were measured at well-exposed locations, and the thickness of its gouge and breccia were measured where possible. Orientations were measured using the FieldMove Clino app as well as a Brunton compass. Stereonet and FaultKin freeware were used to plot and analyze the orientation data. Figure 2: Geology along the Hancock fault in the Quincy adit and connected mine workings. The project is ongoing but some results have emerged. The Hancock fault cuts upward across stratigraphy in the direction of thrusting at angles between 4° and 18°, similar to cut-off angles for the Keweenaw fault (5). The low cut-off angles of both faults, which have significant reverse slip, are consistent with the properties of a detached thrust system. Both faults also have components of strike slip as indicated by the population of nearby faults, but right-lateral slip is slightly dominant over left-lateral slip. This implies that the significant left-lateral offset of PLV layers seen in map view is the result of mostly reverse slip on the Hancock fault as it cuts slightly clockwise to strike of the layers. Acknowledgements Funding for this work was provided by the ILSG Student Research Fund and is gratefully acknowledged. References 1. Cornwall, H.R. and Wright, J.C., 1956a, Geologic Map of the Hancock Quadrangle, Michigan: U.S. Geological Survey, Mineral Investigations Field Studies Map MF-46, scale 1:24,000. 2. Cornwall, H.R. and Wright, J.C., 1956b, Geologic Map of the Laurium Quadrangle, Michigan: U.S. Geological Survey, Mineral Investigations Field Studies Map MF-47, scale 1:24,000. 3. Cannon, W.F., 1994, Closing of the Midcontinent Rift: a far-field effect of Grenvillian compression: Geology, v. 22, pp. 155-158. 4. Langfield, K.M., DeGraff, J.M., and Gamet, N.G., 2023, Slip kinematics of the Keweenaw and Hancock faults within the Midcontinent Rift System, Upper Peninsula of Michigan: Inst. on Lake Superior Geology, 69th An. Meeting, Eau Claire, WI, Part 1 – Program and Abstracts, v. 69, p. 50-51. 5. DeGraff, J.M. and Carter, B.T., 2023, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulletin, v. 135, no. 1/2, p. 449–466. 71 �Lithostratigraphy and Geochronology of the Lower Northeast Sequence of the North Shore Volcanic Group, Cook County, MN, USA NOWARIAK, Eric S., SEVERSON, Allison R., BLOCK, Amy Radakovich Minnesota Geological Survey, Department of Earth and Environmental Sciences, University of Minnesota-Twin Cities, MN, USA The Lower northeast sequence (LNE) of the North Shore Volcanic Group (NSVG) in northeastern Minnesota represents some of the earliest known sedimentary and volcanic rocks of the Midcontinent Rift System (MRS) including the Puckwunge Formation (PF), Grand Portage Lavas (GPL), Esther Lake Lavas (ELL), and the Hovland Lavas (HL) (Miller and others, 2002). New 1:24,000 field mapping in northern Cook County, paired with U/Pb TIMS zircon geochronology have established an updated lithostratigraphic sequence of the LNE and understanding of its relationships with surrounding intrusive rocks, providing new insights on magmatic evolution and spreading rates during the Plateau Stage of MRS magmatism. The LNE is a shallow to moderately south dipping bimodal volcanic sequence that youngs southward and is segregated from the overlying Upper northeast sequence by the cross-cutting Brule-Hovland Gabbro, a complex of texturally and mineralogically varied gabbroic and diabasic intrusions (Fig. 1). To the north, the LNE is bounded predominantly by cross-cutting Early Stage Duluth Complex granophyric intrusions and locally by underlying Paleoproterozoic metasedimentary sequences. The arenitic sandstones and conglomerates of the PF, which forms the base of the LNE, lie unconformably on top of Paleoproterozoic bedrock and forms the base of the LNE on to which the NSVG rocks were erupted. GPL volcanics were erupted disconformably atop the PF, and consist of geochemically primitive basalts, as compared to overlying LNE volcanics (Mattis, 1972). Basal units of the GPL are defined by pillowed and fragmental olivine basalts, transitioning to thick flows of massive to sparsely amygdaloidal basalts with rubbly tops. The boundary between the GPL and the overlying ELL is marked by a distinct change from olivine tholeiite basalts to thick, pilotaxitic flows of amygdaloidal, oxide-rich ferroandesites and andesitic basalts which exhibit steeper REE 72 Figure 1. Schematic Stratigraphic Section of the LNE showing locations of geochronologic samples. See text for details. �profiles than GPL basalts. U/Pb zircon geochronologic analysis of a thin rhyolite flow interlayered with the massive andesitic basalts near the base of the ELL returned an age of ca. 1105.4 Ma (Fig. 1). Bimodal volcanics of the HL sequence above the ELL are typified by feldspar-phyric to glomeroporphyritic flows of basalt, basaltic andesite, trachyandesite, and rhyolites. Plagioclase phenocrysts within the mafic and intermediate lithologies are fractured, locally resorbed, contain inclusions of olivine and clinopyroxene, and have compositions estimated to be more calcic than the groundmass feldspars. Mafic and intermediate lithologies are locally pillowed, though most flows do not show evidence of subaqueous eruption. Rhyolites constitute a large volume of the upper half of the HL sequence. These rhyolites exhibit abundant autobreccia textures, flow foliation, pumice fragments, and phenocrysts of feldspar and quartz. Microscopically, HL rhyolites are texturally diverse, containing microlites, perlitic structures, fiamme, and spherules interpreted to be a product of volatile-rich lavas and pyroclastic flows. U/Pb zircon analyses of upper HL rhyolites returned ages of ca. 1105.69 Ma and 1106.0 Ma (Fig. 1). Basalt flows intercalated with the rhyolite units are thick, structured flows with basal breccias, columnar jointed massive flow centers, and amygdaloidal flow tops. Subvolcanic, plagioclase ultraphyric diabase dikes and sills of Burnell’s (1976) Brule Lake Porphyry (BLP) are abundant throughout the HL. The BLP contains 20-70% plagioclase phenocrysts hosted within a compositionally varied matrix, and although they have not been dated, a synvolcanic interpretation has been applied to these intrusions based on their local amygdaloidal nature and textural similarities to the HL. New ages from rhyolites in the basal portion of the ELL and upper portion of the HL at ca. 1106 Ma suggest these lavas are volcanic expressions of the coeval Early Stage Duluth Complex Cucumber Lake and Misquah Hills granophyres exposed to the north of the LNE (Vervoort and others, 2007). The Early Stage granophyres are interpreted to be a product of assimilation of continental crust (Vervoort and others, 2007). Such a change in magma composition is reflected in the lithologic and geochemical character of the ELL and HL as compared to the underlying GPL. The overlap in ages presented here suggests rapid eruption rates at ca. 1106 Ma, which indicate the entire ELL and HL sequence erupted within ~1 Ma. Phenocryst-rich volcanic and hypabyssal rocks throughout the HL and BLP may have been derived from anorthositic cumulates that formed in the roof of a mid-crustal staging chamber during a period of slow rift spreading, and subsequently remobilized during magma recharge and venting events at 1106 Ma. References Burnell, J.R., Jr., 1976, Petrology and structural relations of the Brule Lake intrusions, Cook County, Minnesota: Minneapolis, University of Minnesota, M.S. thesis, 105 p., 1 pl. Mattis, A. F., 1972. The Petrology and Sedimentation of the Basal Keweenawan Sandstones of the North and South Shores of Lake Superior. University of Minnesota – Duluth, M.S. thesis. Miller, James D., Jr.; Green, J.C.; Severson, M.J.; Chandler, V.W.; Hauck, S.A.; Peterson, D.M.; Wahl, T.E., 2002. RI-58 Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota. Minnesota Geological Survey. Vervoort, J. D., Wirth, K., Kennedy, B., Sandland, T., & Harpp, K. S., 2007. The magmatic evolution of the Midcontinent rift: New geochronologic and geochemical evidence from felsic magmatism. Precambrian Research, 157(1-4), 235-268. 73 �Major element geochemistry and first zircon U-Pb age dates of Precambrian basement rocks in eastern North Dakota PEREIRA, Cristian1, NESHEIM, Timothy2, VERVOORT, Jeffrey D. 3, and SAINIEIDUKAT, Bernhardt1,4 1 Department of Earth, Environmental and Geospatial Sciences, North Dakota State University, Fargo, ND 58102, USA 2 North Dakota Geological Survey, 2835 Campus Rd., Grand Forks, ND 58202 USA School of the Environment: Earth Sciences, Washington State University, Pullman, WA 99164 USA 3 4 Dept of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA We are re-examining cores of the 1977 Red River Valley Drilling Project (Moore, 1978). Other previous work includes study of the paleoweathered horizon on the Precambrian bedrock (Kelley, 1980), Klasner and King (1986), Sims et al. (1991) and various ILSG abstracts. We sampled the Precambrian portions of three of these cores (RRVD #5, #8, #11) from eastern North Dakota, and a core cut by Kennecott Exploration Company in 2010 (10NDV001; Nesheim, 2013) (Fig. 1; Table 1). Samples were analyzed at Washington State University (WSU) for U-Pb zircon age dates. Kelley (1980) reported major element analyses and new analyses were carried out at WSU and North Dakota State University using XRF (Table 2). Figure 1. Precambrian geology map of North Dakota after Nesheim (2012) and Sims et al. (1991), with location map and core locations (stars) for this study Table 1. Summary of samples, lithology, and zircon age dates Core / depth Lat / Long lithology Zircon age (MSWD) RRVD 5 46.225514 Fine to medium grained 2715.0 +/- 18.1 Ma (3.4) 379 ft (115.5 m) -96.932504 quartz monzonite RRVD 8A 46.897502 Fine to medium grained 2782.7±9.3 Ma (0.72) 600 ft (182.9 m) -97.370662 chlorite gneiss RRVD 11 47.614926 Medium grained biotite 2 populations: younger 693 ft (211.2 m) -97.291738 granitoid 2671±23.2 Ma (3.0) 10NDV001 48.61706 Medium grained 2694.5±13.6 Ma (1.19) 837 ft (255.1 m) -97.316902 magnetite-rich granitic gneiss 74 �Table 2. Whole rock major element analyses wt.% 1 2 3 4 SiO2 74.00 68.91 64.30 65.80 TiO2 0.16 0.18 0.13 0.42 Al2O3 13.7 10.43 17.40 15.20 Fe2O3 1.36 2.04 4.67 FeO 1.65 MnO 0.01 0.31 0.02 0.10 MgO 0.04 0.44 0.71 0.00 CaO 1.49 4.60 0.91 1.65 Na2O 4.60 0.87 8.16 6.00 K2O 4.22 6.82 5.96 5.90 P2O5 0.09 0.03 0.06 0.05 SO3 0.04 LOI 5.44 sum 99.67 99.72 99.68 99.79 1: RRVD 5-383.5''; 2: RRVD 8A-602'; 3: RRVD 11-695'; 4: 10NDV001-836' Figure 2. U-Pb concordia diagrams for zircons from the Precambrian core samples with weighted mean 207 Pb/206Pb ages. Error ellipses represent 2SE uncertainties. Open ellipses with thick grey lines depict outlier U-Pb zircon analyses removed from final age determinations. The analyzed rocks contain 64-74 wt.% SiO2, with RRVD 11-695' showing high total alkalis (Na2O+K2O = 14.12 wt. %). All show Neoarchean zircon ages (2.7 –2.8 Ga) with the granitoids showing slightly younger ages than the gneisses (Table 1; Fig. 2). Sample RRVD 11-693 appears to be a 2 component rock with two zircon populations. These chemical results and measured ages are consistent with those measured in other areas of the Superior Craton (cf. Li et al., 2020). REFERENCES: Kelley, L.I., 1980, Kaolinitic weathering zone on Precambrian basement rocks, Red River Valley, eastern North Dakota and northwestern Minnesota. M.S. Thesis, University of North Dakota. 85 pp. Klasner, J.S. and E. R. King. 1986a. Precambrian basement geology of North and South Dakota. Canadian Journal of Earth Sciences. 23(8): 1083-1102. https://doi.org/10.1139/e86-109 Li, D., Hollings, P., Chen, H., Sun, X., Tan, C., and Zurevinski, S., 2020, Zircon U–Pb and Lu–Hf systematics of the major terranes of the Western Superior Craton, Canada: Mantle-crust interaction and mechanism(s) of craton formation, Gondwana Research, v. 78, p. 261-277. Moore, W. L., 1978, A preliminary report on the geology of the Red River Valley Drilling Project, eastern North Dakota and northwestern Minnesota: Bendix Field Engineering Company Subcontract H77-059-E, 292p. https://www.osti.gov/biblio/6538603 doi:10.2172/6538603 Nesheim, T., 2012, Review of Radiometric Ages from North Dakota’s Precambrian Basement. North Dakota Geological Survey Geologic Investigations No. 160. Nesheim, T., 2013, Recent Diamond Exploration in Eastern North Dakota. NDGS GeoNews, p. 5-7. Sims, P.K., Peterman, Z.E., Hildenbrand, T.G., and Mahan, S., 1991, Precambrian Basement Map of the Trans-Hudson Orogen and adjacent terranes, northern Great Plains, U.S.A.: USGS Miscellaneous Investigations Series Map, I-2214. 75 �The geology and ore deposit model of the high-grade Emily Manganese Deposit, Cuyuna Range, Minnesota: Results from the 2023 drilling program PETERSON, Dean1, and STEINER, Alex1 1 Big Rock Exploration, 2505 West Superior Street, Duluth, MN 55806. The Emily deposit is the highest-grade manganese resource in the USA. The deposit is located along the western margin of the Paleoproterozoic Animikie Basin (Southwick and Morey, 1991) and is hosted by the Emily Iron Formation, a shallow water Superior type iron formation. Recent work by Big Rock Exploration on a drilling program for Electric Metals has identified coherent zones of high-grade mineralization (30 to ≥40 wt.% Mn) over a 1.25-kilometer strike length. An ore deposit model has been developed that incorporates the deposition of primary thin-bedded manganese-iron carbonates (Fig. 1) and later conversion into massive manganese oxide through early folding (Fig. 2) and prolonged periods of weathering, oxidation, and erosion. Figure 1. Model of the primary depositional setting of the Paleoproterozoic Superior-type iron formations of the western Animikie basin. Figure 2. Schematic model for the formation of the Emily District thrust-front folds as related to the Penokean fold & thrust belt of the Cuyuna North and South iron ranges. 76 �Historic exploration and drilling in the 1940’s and 1950’s by Pickands Mather and US Steel identified iron and manganese-bearing mineralization within the Emily Iron Formation (Strond, 1959). US Steel developed but did not implement a preliminary mine plan for mining of the Emily Deposit. Following approximately 50 years of inactivity, Cooperative Mineral Resources (subsidiary of Crow Wing Power) pursued a pilot mining operation using pressurized water that ultimately proved unsuccessful. As a follow up investigation into the outcomes of the pilot mining, a small-scale drill program was completed in 2010-2012. An Emily deposit drilling program was designed and executed by Big Rock Exploration, LLC, in 2022-2023. A total of 29 drill holes were completed to extend mineralization and refine the previous resource estimates. A total of 13,107 feet of drilling was completed for this program. Data collected for this project includes lithological, structural, geotechnical, and geochemical data from drill cores as well as geophysical data from selected drill holes. Through interpretation of legacy, recent and new drilling data, Big Rock Exploration has redefined the stratigraphy of the Emily Iron Formation and developed an ore deposit model for the high-grade manganese oxides of the Emily deposit (Fig. 3). This ore deposit model and associated geological model have been used to support an updated and expanded mineral resource estimate for the Emily Deposit, to be completed by Forte Dynamics. Figure 3. Integrated stratigraphy, permeability, texture, and Mn-grade diagram for the Emily deposit. REFERENCES Southwick, D.L. and Morey, G.B., 1991, Tectonic imbrication and foredeep development in the Penokean orogen, east-central Minnesota; an interpretation based on regional geophysics and results of test drilling, U.S. Geological Survey Bulletin 1904-C, pp. C1–C17. Strong, R., 1959, Report on Geological Investigation of the Cuyuna District, Minnesota, 1949-1959, US Steel Internal Report, 318 pages. 77 �Deformation conditions, micromechanics, and fault zone development in mafic protoliths at the Lac des Iles mine, northwestern Ontario PETERZON, Jordan1, PHILLIPS, Noah1, HOLLINGS, Pete1, and DJON, Lionnel2 1 Department of Geology, Lakehead University, 955 Oliver Road Thunder Bay, ON P7B 5E1, Canada Impala Canada, 69 Yonge Street, Suite 700 Toronto, ON M5E 1K3, Canada 2 Faults and their associated damage zones are important geologic structures that serve as permeable pathways through the upper crust; however, the effect of host lithology on fault core development and damage zone structure remains poorly constrained. The development of fault cores and damage zones is typically controlled by the strength and composition of the protolith, conditions of deformation, and fluid chemistry (Caine et al., 1996). Fault zones are characterized by a variably developed fault core composed of unconsolidated gouge or silicified breccias, outward into a highly fractured damage zone and then a relatively unaltered protolith. Trapped mineralization may be offset or remobilized by later faulting. Faults may act as conduits or barriers for fluid flow depending on the proportion of fault core to damage zone (i.e., the fault zone architecture; Caine et al., 1996; Faulkner et al., 2010). Permeability is typically enhanced in damage zones due to the high density of fractures and is diminished in fault cores due to the presence of clay-rich fault gouges. This study examines deformation conditions and fluid-rock interaction of fault zones within the Lac des Iles Complex. The Lac des Iles Complex is a series of mafic-ultramafic intrusive bodies occurring within the Marmion terrane of the Superior Province (Figure 1). The complex has been dated at 2689 ± 1.0 Ma and was emplaced into a ~3.01 to ~2.68 Ga granitegreenstone terrane (Djon et al., 2018). Extensive Ni-Cu-PGE mineralization has been offset by two late reverse faults in the high-grade zones (>4 g/t Pd) called the Camp Lake fault and the Offset fault. A depletion in Pd is observed within the damage zone of each fault, approximately 145 – 180 meters from the actual fault. This depletion is likely due to late fluid flow within the damage zones. Fault cores in tonalite mainly are composed of breccias with calcite to quartz-rich matrix, while fault cores in gabbro are composed of chlorite-rich gouges (Figure 2). Fracture densities in felsic protoliths have a higher fracture density than mafic protoliths suggesting that fluid flow would be more effective in felsic protoliths which may have contributed to depleted mineralization. This implies that host rock lithology strongly affects fault zone structure, including alteration assemblages, fracture densities, and permeabilities. We hypothesize that the development of a frictionally weak, chlorite-rich fault core impeded the development of a more fracture-dense damage zone in the gabbros. Electron microprobe analyses on chlorite grains reveal three generations of chlorite growth have occurred: pre-faulting at ~350°C, syn-faulting at ~150 – 200°C, and post-faulting at ~150°C (Figure 3). Elemental gains and losses from unaltered protolith to fault core were examined to understand the interactions between alteration and fault zones. Within fault cores and damage zones, there is an observable gain in Mg and Fe in mafic protoliths, due to the precipitation of new chlorite within the fault zone. In mafic protoliths, fluid-rock interactions play an important role in the development of fault core and damage zone structures. 78 �Figure 2 Variations in drill core with proximity to faulting. Figure 1 Local geology of the Lac des Iles Intrusion with faults of study. Modified from Djon et al., (2018). Figure 3 Results of chlorite thermometry from electron microprobe analyses. References Caine, J.S., Evans, J.P., and Forster, C. B., 1996. Fault zone architecture and permeability structure. Geology, 24 (11): 1025-1028. Djon, M.L., Peck, D.C., Olivo, G.R., Miller, J.D., and Joy, B., 2008. Contrasting Style of Pd-rich Magmatic Sulfide Mineralization in the Lac des Iles Intrusive Complex, Ontario, Canada. Economic Geology, 113 (3): 741-767. Faulkner, D.R., Jackson, C.A.L., Lunn, R.J., Schlische, R.W., Shipton, Z.K., Wibberley, C.A.J., and Withjack, M.O., 2010. A review of recent developments concerning the structure, and fluid flow properties of fault zones. Journal of Structural Geology, 32 (11): 1557-1575. 79 �Identification of Fertile Parent Granitoid Units in the Superior Province of Ontario PETTIGREW, Therese1, CUNDARI, Robert1, PRICE, Rebecca2, and DUGUET, Manuel3 1 Ontario Geological Survey, 435 James St. South, Thunder Bay, ON P7E 6S7 Ontario Geological Survey, 227 Howey St, Red Lake, ON P0V 2M0 3 Ontario Geological Survey, 933 Ramsey Lake Rd, Sudbury, ON P3E 6B5 Canada aw n 2 Peraluminous granites are widely distributed throughout the Superior Province of Ontario, most notably within and adjacent to the metasedimentary rocks of the English River and Quetico subprovinces from which they were derived by partial melting. There has been a significant amount of work that proposes a direct genetic relationship between peraluminous, S-type granitoids (i.e., fertile parent granites) and rare-element pegmatites of the lithium-cesiumtantalum (LCT) group across the world (see for instance Černý, 1989, 1991; Wise, Müller and Simmons, 2022, and references therein). W ith dr A fertile granite is the parental granite to rare-element pegmatite intrusions. Many granitic melts have the capability to generate fertile granite plutons that will, in turn, produce even more fractionated melts enriched in incompatible elements. In the case of the LCT group pegmatites, the residual melt may percolate into the surrounding host rock and crystallize rare-element pegmatites (Breaks, Selway and Tindle, 2003). Identifying fertile parent granites is an important step in the exploration for rare-element pegmatites as it greatly reduces the search area on a regional scale (Breaks and Tindle, 1997). A significant amount of work was performed by the Ontario Geological Survey (OGS) in the late 1990s and early 2000s to improve our understanding of rare-element pegmatites and their parent granitoid units in the Superior Province, with a focus on northwestern Ontario (e.g., Breaks, Selway and Tindle, 2003). In 2022, ten areas of the Superior Province in Ontario were identified for study as part of the fertile granite project (Figure 1). Locations for sampling were selected to complement the existing granitoid geochemical databases acquired by the OGS, as well as to provide coverage in areas previously not investigated for the presence of fertile granitoid rocks and associated LCT group pegmatites. The 2022 field season was intended as a preliminary investigation of the selected areas. A total of 100 samples were collected (Figure 1) and analyzed for major, trace element and rare earth element geochemistry at the Geoscience Laboratories (Sudbury) to identify potential fertile parent granite bodies. Due to several staffing changes during the spring and summer of 2023, focus on the project was delayed and did not resume until the winter of 2023-24. Further work in support of the fertile granite project will include preliminary evaluation of the geochemical data set generated during the summer of 2022, compilation of geochemical data from previous studies and planning for additional sampling during the 2024 field season. The primary deliverable of the project will be an MRD compiling previously released whole-rock geochemical data related to fertile granites. This compilation will be supplemented with the new whole-rock geochemical data acquired during this study. Additionally, several articles will be generated and released during the course of the project in both the Resident Geologist Program Recommendations for Exploration (released annually in January) and the Report of Activities (published annually in the spring). 80 �aw n dr W ith Figure 1. Locations of fertile granite project target areas (outlined in black) and sample locations (green dots) collected in 2022. Regional geology from Ontario Geological Survey (2011, see publication for a detailed geological legend). Subprovince boundaries are based on Stott (2011) and are outlined in blue (from Cundari, 2022). References Breaks, F.W., Selway, J.B. and Tindle, A.G., 2003. Fertile peraluminous granites and related rare-element mineralization in pegmatites, Superior Province, northwest and northeast Ontario: Operation Treasure Hunt; Ontario Geological Survey, Open File Report 6099, 179 p. Breaks, F.W. and Tindle, A.G., 1997. Rare-element exploration potential of the Separation Lake area: An emerging target for Bikita-type mineralization in the Superior Province of northwest Ontario; in Summary of Field Work and Other Activities, 1997, Ontario Geological Survey, Miscellaneous Paper 168, p. 72-88. Černý, P., 1989. Exploration strategy and methods for pegmatite deposits of tantalum; in Lanthanides, tantalum and niobium, Springer-Verlag, New York, p. 274-302. ——— 1991. Rare-element granitic pegmatites. Part 1: Anatomy and internal evolution of pegmatite deposits. Part 2: Regional to global environments and petrogenesis; Geoscience Canada, v.18, p. 4981. Cundari, R.M., 2022. Identification of Fertile Parent Granitoid Units in the Superior Province of Ontario: Project Description; in Summary of Field Work and Other Activities, 2022, Ontario Geological Survey, Open File Report 6390, p. 30-1 to 30-5. Ontario Geological Survey, 2011. 1:250 000 scale bedrock of Ontario; Ontario Geological Survey, Miscellaneous Release—Data 126 – Revision 1. Stott, G.M., 2011. A revised terrane subdivision of the Superior Province in Ontario; Ontario Geological Survey, Miscellaneous Release—Data 278. Wise, M.A., Müller, A. and Simmons, W.B., 2022. A proposed new mineralogical classification system for granitic pegmatites; The Canadian Mineralogist, v.60, p. 229-248. 81 �Lidar Topography: Bright opportunity for Reading Keweenaw Landscapes ROSE, Bill1 and DeGRAFF, James1 1Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 USA A GeoAtlas for Keweenaw, Houghton, and Baraga counties will soon be publicly accessible as an exciting new tool for understanding landscapes through lidar surveys and convenient geospatial display tools. In this presentation, we discuss hypotheses that emerged from a “first look” at this remarkable data which reveals greater detail than standard topographic maps. The purpose of this discussion is to stimulate robust investigation to build new geological awareness of geomorphology. The work may be a useful element for geoeducation because of the improved resolution. 82 �Figure 1: Lidar topography may reveal in situ differentiation within thick lavas of the Portage Lake Volcanics. Here, lidar data from the Keweenaw GeoAtlas is used with field mapping data from Cornwall (1951) and Longo (1984). These thick lavas reveal cooling of about 1000 years where the interior texture of the basalt is pegmatoidal, contrasting with ophitic textures near the bottom and top of the flow where solidification was faster. Arrows show the same crossections on lidar and geologic maps. Figure 2: Geology at Traverse Island in Keweenaw Bay. Left -aerial image from Google Earth with offshore tracing of Jacobsville Sandstone strata (yellow) and fractures (red). Onshore features are from Denning (1949). Right – onshore tracing of sandstone strata from 2-m resolution Lidar data. White outline is a caprock of “quartzite” with a possible channel form at its western edge. References Cornwall, H.R., 1951, Differentiation in Magmas of the Keweenawan Series, J Geol, v. 59, pp. 151-172. Denning, R.M., 1949, The Petrology of the Jacobsville Sandstone, Lake Superior: Michigan College of Mining and Technology [MTU], M.S. thesis, 71 p. Longo, A.A., 1984, A correlation for a middle Keweenawan flood basalt: the Greenstone flow, Isle Royale and Keweenaw Peninsula, Michigan, M.S. thesis, Michigan Technological University, Houghton, MI, 198 pp. 83 �Michigan Coastal Path: A Social Commitment to Geoeducation ROSE, Bill1 and VYE, Erika2 1 Geological and Mining Engineering & Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 USA 2 Great Lakes Research Center, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 USA The geology of the Midcontinent Rift is beautifully exposed for researchers, teachers, students, and geotourists in the Keweenaw Peninsula and Isle Royale (http://carnegiekeweenaw.org/social-post/keweenaw-shorelines-bill-rose). Michigan holds title to the surrounding bottomlands of the Great Lakes under the Public Trust Doctrine in addition to a public trust interest in the shorelands up to the ordinary high water mark (OHWM). Michigan confronts the challenge of discerning the boundaries between public trust interests and private property rights at the shore (Norton et al, 2013). In 1968, the Michigan Legislature adopted an elevation-based approach for discerning the ordinary high water mark (OHWM). In 2005, the Michigan Supreme Court reaffirmed that Michigan's public trust interest extends up to the OHWM, but it left unresolved questions of exactly how the two methods of marking ordinary high water relate to one another, and precisely how far up the shore the state has authority to regulate private shoreline development extends. (Norton et al, 2011). Here we describe the definitions of high water lines for geologic discussion. How may both landowner and hiker amicably agree on the high water mark when we meet along the shore? Figure 1: Shoreline exposures reveal the rock details clearly - veins of calcite (near the Copper Harbor Light) and native copper (Washington Island). 84 �Figure 2: Shoreline of Copper Harbor Conglomerate on Manitou Island. The zonation and succession of shorelines may be seen and used to define the high water mark. References Norton, R. K., Meadows, G.A., and Meadows, L.A. (2013). The deceptively complicated “elevation ordinary high-water mark” and the problem with using it on a Laurentian Great Lakes shore. Journal of Great Lakes Research, Volume 39, Issue 4, pp 527-535. Norton, R.K. & Meadows, G.A. (2014). Land and water governance on the shores of the Laurentian Great Lakes. Water International 39:6, pages 901-920. 85 �Jacobsville Geoheritage is Globally Celebrated and Locally Loved ROSE, Bill1 and VYE, Erika2 1 Geological and Mining Engineering & Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 USA 2 Great Lakes Research Center, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 USA The Jacobsville Sandstone is a well-known red bed sandstone of Neoproterozoic age from Upper Michigan, USA (Cannon and Nicholson, 2001) and is part of the Keweenaw Supergroup related to the Midcontinent Rift System. The rift formed ~1100 Ma and is a ~3000 km long feature in North America, centered on the Lake Superior area. The Jacobsville is the youngest of the area’s Precambrian rocks and was deposited during the Rigolet Phase of the Grenvillian Orogeny (1010-980 Ma) (Hodgin et al 2022). Cliff exposures show crossbedding and channels interpreted as fluvial deposits. Jacobsville Sandstone was a fashionable building stone in much of Eastern North America. From 1885 to 1920, it was used in hundreds of prominent buildings including the famous Astoria Hotel in New York City (Eckert, 2000). It was mined from several quarry sites near Jacobsville, Michigan. The location is part of a significant geoheritage location where native copper has also been mined, valued, and utilized for thousands of years. The development of copper mining drove extensive immigration of Europeans to Upper Michigan. The Jacobsville quarries offered an alternative to underground employment in the booming mining industry of the Keweenaw. Since quarrying has ceased, Jacobsville quarries have been overgrown and are often overlooked. Highlighting the significance of these places and increasing access offers an opportunity to teach locals and visitors about Earth's history and natural/cultural resources. It connects people to a significant element of Keweenaw geoheritage often eclipsed by the history of copper mining. In recent years we have been building awareness of the geohistory and geoheritage of Jacobsville quarrying. This awareness is building educational outreach focused on this remarkable rock formation which features in many local towns. The International Union of Geological Sciences (IUGS) and UNESCO’s International Geoscience Programme (IGP) have announced that the Jacobsville Sandstone - a rock formation named for Jacobsville, Michigan - is now one of only 15 Global Heritage Stone Resources (GHSR) in the world and the first in the United States (Rose et al, 2017). Global Heritage Stone Resources (GHSR) are scientific designations created and managed by the Heritage Stone Subcommission – HSS (IUGS/IAEG) to enhance the geological knowledge, use, and conservation of natural stones of historical importance worldwide. Highlights of recent Jacobsville geoheritage efforts include boat tours that explore the rock exposures in spectacular cliff views and Michigan historic signage in Houghton and other towns. References WF Cannon and SW Nicholson, 2001, Geologic Map of the Keweenaw and Adjacent Area Michigan: U.S. Geological Survey Map I-2696, scale = 1:100,000. WI Rose, EC Vye, CA Stein, DH Malone, JP Craddock and S Stein (2017) Jacobsville Sandstone: A candidate for nomination for Global Heritage Stone Resource, Michigan, USA. Episodes 40 (3), 213-219 86 �K.B. Eckert, (2000). The Sandstone Architecture of the Lake Superior Region. Wayne State University Press, Detroit, USA, 344 p. EB Hodgin, NL Swanson-Hysell, JM DeGraff, ARC Kylander-Clark, MD Schmitz, AC Turner, Y Zhang, DA Stolper (2022). Final inversion of the Midcontinent Rift during the Rigolet Phase of the Grenvillian Orogeny. Geology 2022; 50 (5): 547–551 Fig 1: Red Jacket firehouse in Calumet (built in 1898–99) – National Register of Historic Places. Use through Creative Commons by Andrew Jameson. Fig 2: One of many cliff exposures of the Neoproterozoic Jacobsville Sandstone, here about 1 km N of the town of Jacobsville, 19 km SE of Houghton, in Michigan’s Keweenaw Peninsula. Cliff exposures are found in dozens of locations within Keweenaw Bay. Photo by Steve Brimm. Fig 3: Jacobsville Quarry near Portage Entry, in operation, about 1895 (MTU Neg 03965, Michigan Technological University Archives and Copper Country Historical Collections, Houghton, Michigan Michigan Technological University Archives). 87 �Compiled historical drillhole and geochemical data from the Cuyuna Range, Minnesota, provides powerful new insights for geological and mineral potential investigations. SAARI, Stacy1, GORDEE, Sarah1, RIAN, Madison1, and CARTER, Matt1 1 Minnesota Department of Natural Resources, Lands and Minerals, 1525 Third Ave. East, Hibbing, MN 55746 The Minnesota Department of Natural Resources (DNR) staff of Lands and Minerals (LAM) compiled a large tabular dataset of drill hole locations, geological logs, and geochemical data from the Cuyuna Iron Range of central Minnesota as part of the federally funded Earth Mapping Resources Initiative (Earth MRI). These data will help to determine where potential resources of iron and manganese, as well as other critical minerals, may exist in the underlying bedrock. Iron in the Cuyuna Range was discovered in 1903 by Cuyler Adams and was actively mined until 1984. Prior to the end of WW1, there were 37 active mines on the Cuyuna Range. The lack of outcrop hindered the geological understanding and definition of the resources, and over 12,000 exploration holes were drilled over this period (Morey et al., 1977). Some of the historical explorers and mining operators in this area included: Orelands Mining Company, Evergreen Mining, Pittsburg-Pacific, Pickands-Mather, Oliver Iron Mining (division of US Steel), Inland Steel, Rogers-Brown Company, and Zontelli Brothers (Sutherland, 2016). Since the end of active mining in this district, the DNR LAM office in Hibbing has accumulated thousands of mining and mineral exploration documents from various companies. Current estimates suggest that the Cuyuna Range is among the top three largest manganese occurrences in the United States, justifying continued interest in its resource potential (Strong, 1959; Beltrame et al., 1981; Kilgore and Thomas, 1982; Cannon et al., 2017). From the 1940s to 1960s, the US Bureau of Mines (USBM) assembled, coded, and entered location and geochemical data for about 40% of the 12,833 drill holes available from the USBM Minnesota Mineral Development Atlas. USBM used criteria such as depth of overburden, past mining activity, availability of manganese data, and the availability of the sample material to determine which data to prioritize. All data were entered from public land survey (PLS) sections if there were fewer than 80 drillholes. For PLS sections exceeding 80 drillholes, then only 5 drillholes were entered for each quarter-quarter. This compilation resulted in data for 5,045 drillholes across the entire Cuyuna Range (Morey et al., 1977). Further, in the early 1990s, the Minnesota Geological Survey (MGS) created several databases to compile the assays and geologic logs from the USBMs dataset. Their database contains around 12,000 holes which have limited assay data and generalized geologic logs. Many of these drillhole sites were also entered in the Minnesota Well Index. As part of the Earth MRI project the MGS transferred thousands of maps and drill logs to the DNR. Compiling and managing 10,000s of documents and drill hole locations is a complicated and enormous undertaking, however, the use of geospatial software (i.e., ArcGIS), artificial intelligence and machine learning, and MicroMine 3D modelling software has accelerated the process. Without these technological resources, it would be difficult and time consuming to track 88 �duplication among the various exploration documents as well as the rebranding of drillhole names by successive explorers. The DNR merged the USBM and MGS databases and used the MicroMine software to help identify and resolve missing intervals, overlapping intervals, missing or incorrect azimuth and inclination, drillholes without analytical data, missing total depth, values beyond the end of the drillhole, and coincident drillhole collars. It would be nearly impossible to uncover these errors by hand. DNR staff curated and compiled a collection of US Steel data from the 1950s that was not included in its entirety in either the MGS or USBM compilations. These and other historic exploration data added drill logs and assays for hundreds of holes to the DNR’s drillhole compilation, mainly from the Emily area. Intervals that were assayed from these holes were often missing geological information, likely because the alteration and mineralization made interpretation difficult for the earliest explorers. Any missing collar elevations were obtained from 2012 1-m Lidar, knowing that inaccuracies may exist from previously mined areas or existing stockpiles post-exploration. DNR staff consolidated lithology types by limiting modifiers related to alteration or mineralization and extracted all assay data to create a working 3D model of the Emily district. Not only will future users have access to this model, but they will also be able to easily search by key words, sort based on geochemical results, and view the geographical location of the data. The data compilation is the first of a three-phase project which will be followed by ground and airborne geophysics and later supported by petrographical, lithochemical and geochronological analyses. Subsequent geologic mapping, mineral potential evaluation, and a geological interpretation for the rest of the Cuyuna district will complete this project. The project will culminate in an Earth MRI data release and report in 2026. REFERENCES: Beltrame, R.J., Holtzman, R.C., and Wahl, T.E., 1981, Manganese resources of the Cuyuna Range, eastcentral Minnesota: Saint Paul, Minn., Minnesota Geological Survey Report of Investigations 24, 22 p. Cannon, W.F., Kimball, B.E., and Corathers, L.A., 2017, Manganese, in chap. L of Schulz, K.J., DeYoung, J.H., Jr., Seal, R.R., II, and Bradley, D.C., eds., Critical mineral resources of the United States—Economic and environmental geology and prospects for future supply: USGS Professional Paper 1802, p. L1–L28. Jirsa, M. A., Boerboom, T. J., Chandler, V. W., 2012, Geologic Map of Minnesota, Precambrian Geology, Minnesota Geological Survey Map S-22, 1:500,000. Kilgore, C.C., and Thomas, P.R., 1982, Manganese availability - Domestic: U.S. Bureau of Mines Information Circular 8889, 14 p. Morey, G.B., Broberg, J., Beltrame, R.J., and Holtzman, R.C., 1977, Manganese-Bearing Ores of the Cuyuna Iron Range, East-Central Minnesota, MGS Report of Investigation for Grant U.S.D.I., Bureau of Mines G0264002, 185 p. Strong, R., 1959, Report on Geological Investigation of the Cuyuna District, Minnesota, 1949-1959, U.S. Steel - Oliver Iron Mining Division, 301 p., 6 plates. Sutherland, Frederick E., 2016, The Cuyuna Range: Legacy of a 20th Century Industrial Community. Ph.D. thesis, Michigan Technological University, 271 p. 89 �Understanding the evolution of the upper Midwest Archean gneiss dome corridor using apatite, titanite, and monazite LA-ICP-MS U-Pb geochronology and microstructural analyses SALERNO, Ross1, CANNON, William1, SOUDERS, Amanda2, and THOMPSON, Jay2 1 U.S. Geological Survey, Reston, VA 20192, 2U.S. Geological Survey, Denver, CO 80225 The origin of the Archean gneiss dome corridor stretching across Minnesota, Wisconsin, and northern Michigan is an important question for understanding the Paleoproterozoic tectonic evolution of the upper Midwest. The formation of these gneiss domes was originally attributed to orogenic collapse during the Penokean orogeny (1.86-1.83 Ga) (Schneider et al., 2004). More but more recent work, however, indicates their exhumation may be more closely linked to a suite of younger structures and metamorphism which are broadly concurrent with the Yavapai event between 1.78-1.75 Ga (e.g., Tinkham and Marshak, 2004; Schulz and Cannon, 2007). In this study, we leverage new LA-ICP-MS U-Pb geochronology and microstructural observations using EBSD (electron backscatter diffraction) to shed light on the timing of metamorphism and deformation related to the exhumation of these domes to understand the broader tectonic framework in which they formed. We investigate a suite of metamorphosed and deformed rocks collected from both inside and adjacent to these gneiss domes in northern Michigan (Figure 1). We show that these rocks have metamorphic U-Pb ages ranging from Neoarchean to Mesoproterozoic, reflecting the prolonged tectonic history of the southern margin of Laurentia (Figure 2). In the Paleoarchean Watersmeet gneiss, titanite grains have U-Pb intercept ages of 2550±46 (2σ, n=36) Ma, concurrent with the Sacred Heart orogeny. The U-Pb concordia ages of apatite in the Watersmeet gneiss at 1869±32 (2σ, n=27) Ma, and monazite U-Pb ages in the Hardwood gneiss at 1826±21 (2σ, n=36) Ma, reflect metamorphism of these rocks during the Penokean orogeny. Several samples have apatite U-Pb concorida ages that indicate heating continued for tens of millions of years after the end of the Penokean orogeny at about 1830 Ma: at 1815±32 Ma (2σ, n=17) in the Republic trough, at 1803±29 Ma (2σ, n=49) in the Hardwood gneiss, and at 1796±29 (2σ, n=51)Ma in the Michigamme Formation directly adjacent to the Watersmeet dome. Our dataset documents the influence of post-Penokean orogenic events on the rocks of the gneiss dome corridor in northern Michigan. In the Neoarchean Carney Lake gneiss, migmatitic rocks have titanite U-Pb ages of 1752±71 Ma (2σ, n=53), indicating reactivation during the Yavapai orogeny. In the Solberg schist, in the Felch trough, titanite grains have recrystallized into aggregates of subgrains, likely formed during deformation. These titanite grains have U-Pb ages of 1713±32 Ma (2σ, n=82), which we interpret to reflect the timing of deformation-induced recrystallization. The U-Pb ages of apatite in the Solberg schist are markedly younger at 1588±28 Ma (2σ, n=46) and align with the timing of the Mazatzal orogeny. Together, these new U-Pb data add to a growing body of evidence that the present architecture of the gneiss dome corridor in the upper Midwest is at least in part due to post-Penokean orogenic events. 90 �Figure 1. Generalized geologic map of the study area (modified from Tinkham and Marshack, 2004) showing the locations of sample sites with yellow stars. Black dots show the position of towns W: Watersmeet, R: Republic, H: Hardwood, and M: Marquette. Figure 2. The LA-ICP-MS U-Pb ages of apatite, titanite, and monazite for the samples in this study. The vertical bars represent the timing of major orogenic events along the southern margin of the Superior craton and Laurentia. References Schneider. S., Holm. D., O’Boyle. C., Hamilton. M., Jercinovic. M., 2004, Paleoproterozoic development of a gneiss dome corridor in the southern Lake Superior region, USA: GSA Special Paper 380, 339357. Schulz. K., Cannon. W., 2007, The Penokean orogeny in the Lake Superior Region: Precambrian Research, 157, 4-5. Tinkham. D., Marshak. S., 2004, Precambrian dome and keel structure in the Penokean orogenic belt of northern Michigan, USA: GSA Special Paper 380, 321-338. 91 �Analysis of deformation-related structures in the Eau Claire Volcanic Complex, Wisconsin SHAKKED, Daniel, L.1, ROBARGE, Lucas, C.1 and LODGE, Robert W.D. 1 1 Department of Geology and Environmental Sciences, University of Wisconsin-Eau Claire, Eau Claire, WI 54701, USA This study is focused on the Penokean-aged (1.8-1.9 Ga) deformation fabrics and microstructures in the Big Falls region of the Eau Claire Volcanic Complex (ECVC), Northwestern Wisconsin. Varying intensities of deformation and metamorphism within the Penokean Orogeny are extensive and well documented, particularly in the External Domain in the northern parts of the orogen. However, the southernmost regions are more poorly studied because outcrops are present as rare erosional outliers in river channels. Structural interpretation, and by association terrane boundaries, have largely been inferred from geophysical data. This project focused on describing the structural and metamorphic fabric development at two field areas: one studying the origin of the gneissic banding within the amphibolitic banded gneiss (Figure 1A), while the other being a study on the genesis of the migmatitic fabrics (Figure 1B). The goal of this research is to petrographically and geochemically interpret the deformation mechanisms of the ECVC and improve its tectonic context to the rest of the Penokean orogeny. There are two main volcanic terranes within the Penokean Orogeny and are sutured together by the Eau Pleine Shear Zone. The Pembine-Wausau terrane is characterized as a juvenile arc-system formed through subduction and was accreted onto the southern edge of the Superior Craton. This was followed by the accretion of the Marshfield Terrane; an Archean microcontinent overprinted by Paleoproterozoic magmatism. Historical interpretations of the ECVC suggested these rocks were deposited on the Marshfield Terrane, but recent geochemical and petrochronological studies show a mantle-derived, oceanic affinity (Lodge et al, 2023; Weber et al., 2023). Therefore, revisiting and reinterpreting the tectonic context of the ECVC to the Marshfield Terrane is warranted. The previous interpretation of the bedrock at Big Falls County Park suggests gneissic banding was inherited from igneous layering from a layered mafic intrusion (Cummings, 1984). This study describes field and petrographic observations that indicate intense ductile fabric development during shearing such as asymmetric inclusions, pressure shadows, and feldspar grain-boundary migration within the gneiss (Figure 1A, 1C). Comparison of these textures with other sheared amphibolites and amphibolitic gneisses support the interpretation that banding is, at least in part, caused by intense shearing (e.g. Bozkurt et al., 1997). Geochemical analysis of the Big Falls Region shows a hydrated, mantle-derived signature closely related to an E-MORB oceanic-arc system, indicating that these magmas are not derived from an Archean, continental fragment (Weber et al. 2023). Structural analysis of these rocks shows extensive fabric shearing and deformation, supporting the theory that these rocks are structurally emplaced. Petrographic and outcrop analysis of the tonalite intrusion and “lensoidal amphibolite” in the Little Falls region indicates the gneissic fabrics and banding are migmatites. Two possible theories for the genesis of the migmatites are suggested: anataxis of the amphibolite and granulite facies metamorphism (Ashworth 2011) or melt injection from the tonalite intrusion during the Penokean deformation. Previous interpretations of the Little Falls region indicated three episodes of metamorphism (Cummings 1984). Evidence of a weak foliation and recrystallization in the tonalite intrusion (Figure 1D) containing xenoliths of banded amphibolite gneiss suggests at least two metamorphic events. However, its relationship to the thermal event that formed the migmatites is uncertain. 92 �A B C D Figure 1: A: Outcrop photo of amphibolitic bands and sheared garnet-hornblende porphyroblasts in banded gneiss, Big Falls County Park, Wisconsin. B: Outcrop photo of migmatite at Little Falls County Park, Wisconsin. The neosome consists of quartz, plagioclase, and feldspars while the paleosome consists of hornblende, biotite, and chlorite in the picture. C: Photomicrograph (XPL, 10x) of strained feldspar crystal with grain boundary migration, and an amphibole band being deflected via shearing above the feldspar grain. D: Photomicrograph (XPL, 10x) of the tonalite intrusion at Little Falls which contains quartz, plagioclase, biotite, hornblende, and chlorite. References Ashworth, J.R., 2011, Migmatites. New York, NY, Springer, 371 pp. Bozkurt, E., and Park, R.G., 1997, Microstructures of deformed grains in the augen gneisses of southern Menderes Massif (western Turkey) and their tectonic significance: Geologische Rundschau: Zeitschrift für allgemeine Geologie, v. 86, p. 103–119. Cummings, M.L., 1984, The Eau Claire River complex: A metamorphosed Precambrian mafic intrusion in western Wisconsin: Geological Society of America bulletin, v. 95, p. 75. Lodge, R.W.D., Weber, E.M., and Hooper, R.L., 2023, Precambrian Geology of the Eau Claire River Valley: Re-discovering the Eau Claire Volcanic Complex, in Lodge, R.W.D. ed., Institute on Lake Superior Geology Proceedings, 69th Annual Meeting, Eau Claire, Wisconsin, Part 2 – Field Trip Guidebooks, p.47-70. Schulz, K.J., and Cannon, W.F., 2007, The Penokean orogeny in the Lake Superior region: Precambrian research, v. 157, p. 4–25. Weber, E.M., Lodge, R.W.D., and Marsh, J.H., 2023, U/Pb geochronology and zircon petrochronology of Paleoproterozoic magmas from the Marshfield terrane, Institute on Lake Superior Geology Proceedings, 69th Annual Meeting, Eau Claire, Wisconsin, Part 1-Program and Abstracts, p. 9798. 93 �Geochemistry and Petrology of the Eagle’s Nest Intrusion, McFaulds Lake Greenstone Belt, Northern Ontario SHESHNEV, Vlad1, HOLLINGS, Peter1, PHILLIPS, Noah1, WESTON, Ryan2, DELLER, Matt2, CAMPBELL, Dana2 1 Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON, P7B 5E1, Canada Wyloo Metals, 1-1127 Premier Way, Thunder Bay, ON, P7B 0A3, Canada 2 The Eagle’s Nest intrusion hosts economically significant orthomagmatic Ni-Cu-(PGE) mineralization located in the McFaulds Lake greenstone belt within the northern regions of the Archean Superior province, approximately 500km northeast of Thunder Bay, Ontario. The Eagle’s Nest intrusion is part of the 2734 Ma ultramafic-dominated Koper Lake subsuite of the larger Ring of Fire intrusive suite (Metsaranta et al., 2015; Houlé et al., 2020). The mineralized ore body of the Eagle’s Nest intrusion is zoned, with massive sulfide mineralization at its northwestern extent that gradationally becomes semi-massive, net-textured and disseminated to the southeast (Zucceralli et al., 2022). Mineralization consists of 11.1 million tonnes of proven and probable mineral reserves containing 1.68% Ni, 0.87% Cu, 0.89g/t Pt, 3.09g/t Pd and 0.18g/t Au (Burgess et al., 2012). The intrusion was emplaced along a sub-horizontal conduit, forming a blade-shaped dike (Barnes and Mungall, 2018). Mineralization is consistent with gravitational sulfide segregation at the basal, northwestern contact of the intrusion. Subsequent deformation rotated the intrusion into its present day, subvertical orientation, with a width of ~500m, thickness of ~150m and vertical extent >1600m. Parental magma composition of the Eagle’s Nest intrusion has been determined on a number of occasions but with contrasting outcomes. A low MgO komatiitic magma composition with ~22% MgO and ~12% total FeO was proposed by Mungall et al. (2010). In contrast, Zuccarelli et al. (2022) reported olivine compositions of Fo82-86 consistent with picritic parental magmas containing moderate MgO (10-20%) and high total FeO (>12%). The contrasting results means that parental magma composition of the Eagle’s Nest intrusion needs to be further constrained. The objectives of this study are to petrographically and geochemically characterize the (1) unmineralized portions of the Eagle’s Nest intrusion and (2) associated offshoot dikes in the vicinity, and (3) constrain the parental magma characteristics by using geochemical, petrographic, mineral chemistry, and radiogenic isotope techniques. A total of 136 samples were collected for this study. Forty-four samples came from offshoot dikes consisting of fine- to medium-grained mafic to ultramafic units. Eighty-seven samples were collected from within the intrusion comprising peridotite (Fig. 1), gabbro, and chilled margin samples. Lastly, five samples were collected from the host wall-rock of the intrusion which consists of tonalite. One-hundred and twenty-one samples were analyzed for major and trace elements using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), respectively. An initial batch of 30 thin sections was prepared consisting of 15 offshoot dikes, eight contacts, and seven peridotite samples. Twenty samples from the intrusion were selected for Sm-Nd isotopes. To constrain the parental magma composition, three approaches will be considered: (1) examination of preserved chilled margins along the length of the chonolith, (2) examination of chilled margins preserved in the magmatic breccia matrix within the stratigraphic hanging-wall 94 �of the intrusion, and (3) mineral chemistry of fresh olivine preserved within the peridotite horizons of the intrusion. The parental magma composition obtained from these three methods will be further compared to ensure consistency between the methods. The intrusion’s magmatic history will be constrained using the obtained Sm-Nd isotope data, which will provide further insights into the mantle source and contamination history of the melts that formed the Eagle’s Nest intrusion. Figure 1. Photomicrograph in crossed-polarized light (XPL) of a peridotite sample containing serpentinized cumulus olivine and poikilitic orthopyroxene with fresh olivine within the oikocryst. References Barnes, S.J. and Mungall, J.E. 2018 Blade-shaped dikes and nickel sulfide deposits: A model for the emplacement of ore-bearing small intrusions: Economic Geology, v. 113, p. 789 – 798. Burgess, H., Gowans, R., Jacobs, C., Murahwi, C. and Damjanović, B. 2012. Noront Resources Ltd.—NI 43–101 technical report feasibility study—McFaulds Lake Property, Eagle’s Nest Project, James Bay Lowlands, Ontario, Canada: Micon International Ltd., 197p. Houlé, M.G., Lesher, C.M., Metsaranta, R.T., Sappin, A.-A., Carson, H.J.E., Schetselaar, E.M., McNicoll, V., and Laudadio, A., 2020. Magmatic architecture of the Esker intrusive complex in the Ring of Fire intrusive suite, McFaulds Lake greenstone belt, Superior Province, Ontario: Implications for the genesis of Cr and Ni-Cu-(PGE) mineralization in an inflationary dyke-chonolith-sill complex: Geological Survey of Canada, Open File 8722, p. 141–163. Metsaranta, R.T., Houlé, M.G., McNicoll, V.J., and Kamo, S.L., 2015. Revised geological framework for the McFaulds Lake greenstone belt, Ontario: Geological Survey of Canada, Open File 7856, p. 61–73. Mungall, J.E., Harvey, J.D., Balch, S.J., Azar, B., Atkinson, J., and Hamilton, M.A., 2010, Eagle’s Nest: A magmatic Ni-sulfide deposit in the James Bay lowlands, Ontario, Canada: Society of Economic Geologists Special Publication, v. 15, p. 539–557. Zuccarelli, N., Lesher, C.M., Houlé, M.G., Weston, R. and Barnes, S.J. 2022. The diversity of nettextured sulfides in Magmatic Sulfide Deposits: Insights from the Eagle’s Nest Ni-Cu-(PGE) Deposit, McFaulds Lake greenstone belt, Superior Province, Canada: Economic Geology, v. 117 (8), p. 1731 – 1759. 95 �New LA-ICP-MS U-Pb geochronology of Archean rocks, central Upper Peninsula, Michigan, USA: a step toward refining the final assembly of the Superior craton SOUDERS, A.K.1, CANNON, W.F.2, DRENTH, B.J.1, SALERNO, R.A.2, THOMPSON, J.M.1, SYLVESTER, P.J.3 1 U.S. Geological Survey, Denver, CO 80225 USA (asouders@usgs.gov) U.S. Geological Survey, Reston, VA 20192 USA 3 Texas Tech University, Lubbock, TX 79409 USA 2 The central Upper Peninsula, Michigan consists of two contrasting Archean terranes of the Superior Province: the granite-greenstone terrane of the Wawa-Abitibi Subprovince in the north (Northern Complex) and the gneisses of the Minnesota River Valley Subprovince (MRVS) in the south (Southern Complex). The two terranes are separated by the Great Lakes Tectonic Zone (GLTZ). The suturing of the MRVS to the southern margin of the Superior Province and development of the GLTZ, long interpreted to have occurred at about 2.69 Ga, has more recently been suggested to be related to the ca. 2.58 - 2.6 Ga Sacred Heart Orogeny (Schmitz et al. 2018; Cannon et al. 2024, this volume), a proposal that we are still evaluating. In this study we present new LA-ICP-MS U-Pb geochronology for Archean crystalline rocks from both the Northern Complex and Southern Complex, across the GLTZ. This age characterization is essential to define/refine the regional geochronologic framework of ‘basement’ rocks in the central Upper Peninsula. This is essential to understand subsequent geologic processes. Heavy mineral separates were produced using Electro Pulse Dissagregation (EPD) followed by heavy liquid separation at Zirchron (AZ, USA). Individual zircon grains were hand-picked and mounted in 25 mm epoxy resin mounts and polished to a 1 µm finish. All samples were imaged via cathodoluminescence in the Denver Microbeam Lab (USGS) using the JEOL 5800 LV SEM. LA-ICP-MS analyses were made using a Nu AttoM sector field ICP-MS coupled to a NWR 193 ArF excimer laser system in the Mineral Isotope Laser Laboratory (MILL) at Texas Tech University. Typical laser ablation conditions during all analytical runs were a fluence of 3 J/cm2, 8 Hz, and 240 laser pulses using a 15 µm laser spot. Data was reduced using Iolite v.4 (Paton et al. 2011) and final age calculations were made using IsoplotR (Vermeesch, 2018). We are presently working on zircon LA-MC-ICP-MS Hf isotope analyses to characterize the source components of Archean crystalline rocks from the Northern Complex and Southern Complex. Zircon grains from nine rocks in the Southern Complex and six rocks in the Northern Complex were targeted for LA-ICP-MS U-Pb analysis. Examples of samples analyzed from Southern Complex granitic gneisses are shown in Figure 1. For all samples, the age spectrum of concordant grains is complicated with multiple inherited populations within a single sample. This observation is like that presented by Ayuso et al. (2018) for the ca. 2700 Ma Carney Lake gneiss and ca. 2750 Ma Hardwood gneiss, south of our current study area. Examples of crystalline samples analyzed from the Northern Complex are shown in Figure 2. A single age population for zircon grains analyzed with little to no evidence of Early or Middle Archean inheritance is common for Northern Complex basement samples. These data support the fundamental difference between the primitive volcanic/plutonic terrane of the Northern Complex and an older Archean continental crustal component in the Southern Complex. 96 �Figure 1. Examples of a subset of Archean granitic rocks sampled from the Southern Complex, MI Figure 2. Examples of a subset of Archean granitic rocks sampled from the Northern Complex, MI References Ayuso, R.A, Schulz, K.J., Cannon, W.F., Woodruff, L.G., Vazquez, J.A., Foley, N.K., Jackson J. (2018) New U-Pb Zircon Ages for Rocks from the Granite-Gneiss Terrane in Northern Michigan: Evidence for Events at ~3750, 2750, and 1850 Ma. ILSG, Proceedings 64th Annual Meeting. Cannon, W.F., Souders, A.K., Drenth, B.J., Ayuso, R.A. (2024) The Sacred Hearth Orogeny in Michigan: Latest Archean Granites and the Great Lakes Tectonic Zone. ILSG, Proceedings 70th Annual Meeting. Paton, C., Hellstrom, J., Paul, B.,Woodhead, J. and Hergt, J. (2011) Iolite: Freeware for the visualisation and processing of mass spectrometric data. JAAS. doi:10.1039/c1ja10172b. Schmitz, M.D., Southwick, D.L., Bickford, M.E., Mueller, P.A., Samson, S.D. (2018) Neoarchean and Paleoproterozoic events in the Minnesota River Valley subprovince, with implications for southern Superior craton evolution and correlation. Precambrian Research, v.316, p. 206-226. Vermeesch, P. (2018) IsoplotR: a free and open toolbox for geochronology. Geoscience Frontiers. doi: 10.1016/j.gsf.2018.04.001. 97 �Geochemical fingerprints from the late Mesoproterozoic epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA STEWART, Esther K.1,2, TAPPA, Michael1, BAUER, Ann1, PRAVE, Anthony3, and BRENGMAN, Latisha4 1 Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA Wisconsin Geological and Natural History Survey, UW-Madison Division of Extension, Madison, Wisconsin 53705, USA 3 School of Earth and Environmental Sciences, University of St. Andrews KY16 9TS, Scotland/UK 4 Department of Earth and Environmental Sciences, University of Minnesota-Duluth, Duluth, Minnesota 55812, USA 2 The Oronto Group (Copper Harbor Conglomerate, Nonesuch Formation, and Freda Formation) of the southern Lake Superior Region preserves an exceptional record of late Mesoproterozoic environments and associated microfossils (e.g., Cumming et al., 2013; Fedorchuk et al., 2016; Strother and Wellman, 2021). A lacustrine rift basin is often cited as the most plausible depositional setting for the ca. 1080 Ma Nonesuch Formation because of its association with alluvial deposits of the underlying Copper Harbor Conglomerate and overlying Freda Formation and because of its location within interior Laurentia (Elmore et al., 1989; Slotznick et al., 2023). Our recent sedimentologic and stratigraphic evidence demonstrates deposition of the lower Oronto Group within a tide- and wave-influenced estuary (Stewart et al., 2023, see also Hieshima and Pratt, 1991; Jones et al., 2020). New geochemical results from Nonesuch Formation carbonates (Figure 1), including strontium (Sr), carbon (C), and oxygen (O) isotope compositions, rare earth element - yttrium (REY) patterns, and trace element ratios complement and add new dimension to this environmental interpretation. Strontium isotope compositions refine the Precambrian marine 87Sr/86Sr curve (Chen et al., 2021), with the Nonesuch recording relatively radiogenic compositions at ca. 1080 Ma between previously reported values of 0.706600 at ca. 1109 Ma and 0.705965 at ca. 1058 Ma. Most shale-normalized REY patterns from Nonesuch Formation carbonates are characterized by positive lanthanum anomalies and elevated yttrium: holmium (Y/Ho) ratios. Many of the same samples are also enriched in heavy REE, while others record light REE enrichment. These patterns indicate Nonesuch Formation carbonates precipitated from brackish water, consistent with REY patterns observed in modern estuaries (Lawrence and Kamber, 2006). One sample has a flat shale-normalized REY distribution and likely precipitated within part of the estuary dominated by fluvial input. The combined geochemical evidence suggests Nonesuch Formation carbonates were minimally altered by diagenesis, and diagenetic alteration was dependent on sedimentary facies. While C and O isotopes are uncorrelated, initial Sr isotope compositions correlate positively with O isotopes, and C isotopes group by sedimentary facies. Minor diagenetic alteration thus resulted in less radiogenic Sr isotope compositions and did not impact C isotope compositions, which instead reflect facies-dependent incorporation of remineralized, isotopically light organic carbon during deposition or early diagenesis. Although ƩREY correlates with initial Sr isotope composition, there is no covariation between initial Sr isotope composition and lanthanide anomalies or Y/Ho ratios. This implies that carbonates likely precipitated in shallow pore waters where ƩREY was modified by contribution from surrounding detrital material, and REY profiles were determined by original pore water chemistry in connection with the overlying water body. 98 �Figure 1. Example of carbonate sampled for geochemistry from the Nonesuch Formation. (a) core scan showing fine-grained siliciclastic sediment (dark gray) and carbonate (light cray). Note molar tooth crack cross-cutting laminae. Core is 1 inch (2.54 cm) wide. (b) photomicrograph showing carbonate spar (light color) infilling molar tooth crack. Plain polars, scale bar is 1000 µm. Modified from Stewart et al. (2023). Chen, X., Zhou, Y., Shields, G.A., 2022. Progress towards an improved Precambrian seawater 87Sr/86Sr curve. Earth-Science Reviews 224, 103869. Cumming, V.M., Poulton, S.W., Rooney, A.D., Selby, D., 2013. Anoxia in the terrestrial environment during the late Mesoproterozoic. Geology 41(5), 583-586. Elmore, R.D., Milavec, G.J., Imbus, S.W., Engel, M.H., 1989. The Precambrian Nonesuch Formation of the North American mid-continent rift, sedimentology and organic geochemical aspects of lacustrine deposition. Precambrian Research 43(3), 191-213. Fedorchuk, N.D., Dornbos, S.Q., Corsetti, F.A., Isbell, J.L., Petryshyn, V.A., Bowles, J.A., Wilmeth, D.T., 2016. Early non-marine life: evaluating the biogenicity of Mesoproterozoic fluvial-lacustrine stromatolites. Precambrian Research 275, 105-118. Hieshima, G., Pratt, L., 1991. Sulfur/carbon ratios and extractable organic matter of the middle Proterozoic Nonesuch Formation, North American Midcontinent rift. Precambrian research 54(1), 65-79. Jones, S., Prave, A., Raub, T., Cloutier, J., Stüeken, E., Rose, C., Linnekogel, S., Nazarov, K., 2020. A marine origin for the late Mesoproterozoic Copper Harbor and Nonesuch Formations of the Midcontinent Rift of Laurentia. Precambrian Research 336, 105510. Slotznick, S.P., Swanson-Hysell, N.L., Zhang, Y., Clayton, K.E., Wellman, C.H., Tosca, N.J., Strother, P.K., 2024. Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life. Bulletin 136(3-4), 1628-1650. Stewart, E.K., Bauer, A.M., Prave, A.R., 2023. End-Mesoproterozoic (ca. 1.08 Ga) epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA. Geological Society of America Bulletin. Strother, P.K., Wellman, C.H., 2021. The Nonesuch Formation Lagerstätte: a rare window into freshwater life one billion years ago. Journal of the Geological Society 178(2). 99 �Characteristics of graphitization across a metamorphic gradient in the Michigamme Formation of the Marquette Trough and Baraga Basin, MI STOKES, Rebecca1, CANNON, William1, SALERNO, Ross1 1 U.S. Geological Survey, Geology, Energy and Minerals Science Center, Reston, VA 20192 Graphitization of carbonaceous material (CM) occurs by the progressive aromatization of carbon, expulsion of heteroatoms, and three-dimensional stacking of graphene layers — a process that alters the structure, isotopic, and trace element chemistry of the residual CM. Graphitization is generally considered thermally driven and has been extensively studied in the context of predictable changes in crystallinity as measured by Raman spectroscopy or X-ray diffraction, ultimately yielding the development of several graphite geothermometers (Henry et al., 2019). More broadly, crystalline graphite is an industrial mineral used in lithium-ion batteries and critical for the energy transition away from fossil fuels. The efficacy of graphite in the anode of batteries is directly related to its physicochemical properties which are a function of its geologic origin. The variably metamorphosed and deformed black shales and slates of the Michigamme Formation provide a natural laboratory to revisit our understanding of the graphitization process and the associated changes in structure and chemistry of CM in the context of technological applications. The Michigamme Formation is a Paleoproterozoic metasedimentary and metavolcanic sequence that is widespread in the Upper Peninsula of Michigan. The lower part of the formation is finer-grained black shale and siltstone, typically with a prominent slaty cleavage. In the Marquette Trough and Baraga Basin, the focus areas of our study, this fine-grained sequence has been mapped and formally designated the Lower Slate Member of the Michigamme Formation. Highly carbonaceous units are ubiquitous near the middle of this member and vary from ~70 meters on average along the Marquette Trough to 150 meters or more in the Baraga Basin. Along the Marquette Trough, the outcrop trace of the Lower Slate transects a regional metamorphic gradient from chlorite to staurolite grade whereas the metamorphic grade in the Baraga Basin is uniformly low, within the chlorite zone. In the Marquette Trough, the graphitic beds sampled for this study are along the north limb of this complex syncline, mostly dip steeply southward, and have a well-developed slaty cleavage that is axial planar to the larger structure of the trough. Deformational features diminish to the north and the northernmost of our samples, in the Baraga Basin, are from nearly flat lying beds with no penetrative structural features. An important and widely accepted distinction of the Michigamme Formation is that the development of the penetrative regional cleavage predates the final metamorphic event. Thus, graphitization of the CM occurred under both stressed (tectonic) and static conditions. A suite of thirteen core samples from the Upper Peninsula Geological Repository and three outcrop samples, all from carbonaceous sections of the Michigamme Formation, were selected for detailed evaluation (Figure 1). In all samples, CM occurs as disseminated and elongated fine-grained (<20 µm) particles that tend to be concentrated in bands parallel to the metamorphic fabric defined by phyllosilicates and quartz. Analysis of total carbon on decarbonated samples yielded values ranging from 1 to 24 wt.% C, with an average value of 7 100 �wt.%. Carbon isotopic analysis from decarbonated samples yielded a general trend towards heavier δ13C values with increasing metamorphic grade, ranging from -32.05‰ (Sample 4) to 21.85‰ (Sample 13). Raman spectroscopic analysis of CM yielded a similar trend with metamorphic grade across the sample suite. The R2 ratio, which is one parameter used to evaluate metamorphic grade, decreases from 0.64 in Sample 15 to 0.35 in Sample 8. These R2 values correspond to a temperature range from ~325°C to ~500°C using the empirical geothermometer from Aoya et al. (2010). Notably, Samples 11 and 13 from the garnet zone are significant outliers in both the Raman and C isotope datasets. Combining these results with additional data from scanning electron microscope imaging, X-ray diffraction mineralogical analysis, and laser ablation ICP-MS analysis of CM concentrates will yield a more detailed look at the evolution of CM with metamorphism and deformation. These results will help refine our understanding of the geologic processes that lead to economic graphite deposits and fine-tune graphite deposit models with an application focus. Figure 1. Geologic map and metamorphic isograds (red lines) of the field area in the Upper Peninsula region of Michigan. Map is generalized from Cannon and Ottke (1999). Core samples are noted with white dots, and blue dots for outcrop samples. References Aoya, M., Kouketsu, Y., Endo, S., Shimizu, H., Mizukami, T., Nakamura, D., Wallis, S., 2010. Extending the applicability of the Raman carbonaceous material geothermometer using data from contact metamorphic rocks. Journal of Metamorphic Geology, 28: 895–914. Cannon, W. F., and Ottke, D., 1999. Preliminary digital geologic map of the Penokean (early Proterozoic) continental margin in northern Michigan and Wisconsin: U.S. Geological Survey Open-File Report 99-547. Henry, D. G., Jarvis, I., Gillmore, G., & Stephenson, M. (2019). Raman spectroscopy as a tool to determine the thermal maturity of organic matter: Application to sedimentary, metamorphic and structural geology. Earth-Science Reviews, 198: 102936. 101 �Sulfur-isotope ratios in Paleoproterozoic Michigamme Formation at the Lake Superior Region: Implications on basin evolution and ambient seawater composition in the Greater Animikie Basin THAKURTA, Joyashish 1, and HAAG, Beau 2 1 Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Hermantown, MN 55811, USA 2 Niblack Project LLC, 136 River Street, Elko, Nevada 89801, USA A considerable variation in δ34S-ratios of sulfide minerals has been found in a sulfide-mineralrich succession of slate, metasiltstone, and metagreywacke in the Paleoproterozoic Michigamme Formation located within the Baraga Basin at the eastern edges of the Greater Animikie Basin in the Lake Superior Region (Ojakangas, Morey, and Southwick, 2001). Sulfide minerals such as pyrite, chalcopyrite and pyrrhotite display δ34S-values ranging between 2 and 40‰ (V-CDT) and appear to systematically vary with respect to the stratigraphic intervals (Figure 1). This variability is gradational and devoid of any anomalous spike. It is predominantly a function of stratigraphic location and it shows no relationship with the type of sulfide mineral or the textural mode of occurrence. This observation rejects the possibility that the δ34S values were influenced by selective infiltration of externally derived sulfur-rich fluids along the stratigraphic layers of the Michigamme Formation. It also overrules the possibility that the observed δ34S values were caused by low-grade metamorphism and recrystallization of the sedimentary rocks of the Michigamme Formation. The values are consistent with primary δ34S ratios in sulfide minerals which were precipitated from intergranular fluids within a sequence of clastic sediments in a basin shortly after deposition. Consequently, the measured δ34S ratios in the stratigraphic horizons represent Sisotopic signatures inherited from the S-reservoir in the ambient basin, as well as changes introduced by basin-evolution and diagenesis of the siliciclastic sediments in a marine foreland depositional environment along the eastern portion of the Greater Animikie Basin. While the observed general trend of gradual increase in δ34S-values in the lower and upper members of the sequence can be explained by a systematic chronological trend in the global seawater composition (Paiste et al., 2020), a significant rise and fall in δ34S-values in the Lower Slate and Upper Greywacke Members can be attributed to a limited-term separation of the Baraga Basin from an open-ocean circulation to an isolated basin environment in response to structural adjustments caused by the formation of a fold and thrust belt along the southern shore line of the foreland basin during the waning stages of the Penokean Orogeny (Schulz and Cannon, 2007). In this period of isolation, the sulfur-isotope composition was primarily controlled by intrabasinal bacterial fractionation leading to a significant rise in the δ34S values up to 40‰ in the observed sediments. Upon subsequent erosional removal of the thrust sequence, and associated structural readjustments, the connection of the Baraga Basin to an open ocean was restored and the δ34S-values in the new sedimentary rocks mimic values that are consistent with deposition in a larger open ocean setting. 102 �Figure 1: Observed variation in δ34S-ratios. Stratigraphy adapted from Rossell and Coombes (2005) References: Ojakangas, R.W., Morey, G.B. and Southwick, D.L., 2001. Paleoproterozoic basin development and sedimentation in the Lake Superior region, North America. Sedimentary Geology 141-142: 319-341. Paiste, K., Lepland, A., Zerkle, A.L., Kirsimae, K, Kreitsmann, T, Mand, K., Romashin, A.E., Rychanchik, D.V. and Prave, A.R., 2020. Identifying global vs. basinal controls on Paleoproterozoic organic carbon and sulfur isotope records. Earth-Science Reviews 207: 01320. Rossell, D. and Coombes, S., 2005. The Geology of the Eagle Nickel-Copper Deposit Michigan, USA. Report for Kennecott Exploration, dated April 29, 2005, 35 p. Schulz, K.J. and Cannon, W.F., 2007, The Penokean orogeny in the Lake Superior region: Precambrian Research, 157: 4-25. 103 �An evaluation of structural and mineralogical controls on gold mineralization on the GoldRich property in the Abbie Lake area, Wawa, Ontario THIBODEAU-BELLO, Demily, HILL, Mary Louise, CONLY, Andrew Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1 Canada The GoldRich property in the Abbie Lake area is an active gold prospect in the Michipicoten greenstone belt, within the Wawa subprovince of the Archean Superior province of the Canadian shield. The property is located 30 km northeast of Wesdome’s Eagle River mine and 10 km northeast of Wesdome’s Mishi property in northern Ontario. The Main Shear trench on the GoldRich property is an area of regional metamorphism dominated by ductile deformation hosting orogenic gold. The Main Shear trench hosts mylonites of felsic and intermediate composition with varying strain intensities; all lithologies strike east-west. The mylonite of intermediate composition is characterized by having en-echelon quartz veins perpendicular to the foliation. Gold occurrences have been found in zones of high strain, in both felsic and intermediate mylonite lithologies. This HBSc thesis project relies on detailed trench mapping, microstructural and petrographic analyses, and geochemical methods to discover how gold is hosted on this property. Understanding the controls on gold mineralization will guide future exploration. Gold mineralization in the Main Shear trench is related to deformation. Based on geochemical and petrographic analysis there is no correlation observed between alteration mineralogy and gold mineralization. Microstructural analysis revealed pervasive subgrain-rotation quartz recrystallization in both mylonitic lithologies indicating that the Main Shear trench has undergone deformation at the upper greenschist to lower amphibolite facies regional metamorphic conditions. Gold is associated with deformation, microstructurally related to recrystallized quartz grain boundaries, boudinaged veins, and shear bands. Based on these results, it is recommended that further exploration on this property should be focused on locating zones of similar structure and strain intensity, including areas of boudinage, regardless of lithology, to continue building the gold prospect. 104 �Petrology and Geochemistry of Felsic Magmatism in the Paleoproterzoic Eau Claire Volcanic Complex, Northcentral Wisconsin VICKERS, Lyndsie A. 1, LODGE, Robert W.D.1 1 Department of Geology and Environmental Sciences, University of Wisconsin-Eau Claire, Eau Claire, WI 54701 USA The 1.8-1.9 Ga Eau Claire Volcanic Complex (ECVC) (Figure 1) is the type locality for Penokean-age magmatism formed on an Archean crustal block (~2.6-3.0 Ga) called the Marshfield Terrane during the Penokean Orogen (Sims et al., 1989; Schulz & Cannon, 2007) and has influenced historic tectonic models and terrane-boundary maps. The other volcanic terrane within the Penokean Orogen, the Pembine-Wausau terrane (PWT), is interpreted to have formed with minimal influence of older crust and hosts about 150 million tonnes of volcanogenic massive sulfide (VMS) ores. The ‘continental’ setting of the Marshfield Terrane assumes a different metallogenetic system than the ‘oceanic’ setting of PWT and may be less prospective for the same VMS mineralization. However, recent U/Pb isotopic and other geochemical data (Lodge et al., 2023; Weber et al, 2023) indicates parts of the ECVC were mantle-derived and not contaminated by older Archean crust and challenges this ‘continental’ model. The ECVC is challenging to study because of a lack of mineral exploration (and drilling) coupled with rare outcrop exposure due to glacial/fluvial sediment and Paleozoic rock cover. This project studies remote, inaccessible outcrops along the Eau Claire River to refine the tectonic model and terrane boundaries of the southern Penokean Orogen. Samples obtained from mapping were petrographically characterized and analyzed for major and trace element geochemistry. Thirteen samples were analyzed for major and trace elements via WD-XRF and compiled with other geochemical datasets from the region. Trace element geochemical data are used to determine magmatic and tectonic settings of these rocks and improve regional tectonic models for the ECVC. Felsic magmatism in the region consists of fine-grained quartz-muscovite schists (Figure 1A) and banded quartzofeldspathic gneisses interpreted to be felsic volcanism and mediumgrained massive granodiorite (Figure 1B). Fine-grained quartz-muscovite schist are characterized by approximately 5% quartz porphyroclasts that are 1-3mm in size. The matrix is very finegrained quartz, feldspar, and muscovite that can have variable amounts of chlorite. Banded quartzofeldspathic gneisses have fine grained biotite and amphibole in quartz and feldspar-rich matrix that may define volcaniclastic textures at the outcrop-scale. Medium-grained, massive granodiorite is 15% biotite/hornblende and is characterized by weak to minimal foliation. These granodiorites are interpreted to be intruding felsic volcanic rocks, amphibolites, and metasedimentary units (Figure 1C). At one outcrop, the contact region is exposed revealing the formation of a megabreccia matrix, incorporating gneiss fragments that can reach up to 1 meter in size. These gneissic metasedimentary rocks are fine-grained with alternating bands of light and dark layers, ranging from straight to intensely folded. Samples from the ECVC on Zr/Ti vs. Nb/Y classification diagrams reveal a bimodal magmatic suite which is commonly associated with extensional tectonic settings. Felsic volcanic and intrusive rocks on Nb vs. Y discrimination plots suggest that felsic magmatism was likely formed in syn-collisional or volcanic arc settings. Rhyolite fertility discrimination diagrams (Zr/Y vs. Y) show that both felsic volcanic and intrusive suites from the ECVC are FII-type rhyolites, typical of upper-crustal melting in rift zones. Therefore, the ECVC region may be prospective for VMS mineralization and the tectonic setting should be further evaluated. 105 �Figure 1. Bedrock geologic map of the Eau Claire River region in northcentral Wisconsin showing extent of Precambrian bedrock. Map from Mudrey & Brown (1982). (A) Poorly exposed quartz-phyric micaceous schist near Rock Dam, WI interpreted as a metarhyolite. (B) Weathered surface of granodiorite intrusion along bank of Eau Claire River, (C) Contact region between granodiorite and dark gneiss or metasedimentary rocks. References Lodge, RWD, Weber, EM, Hooper, RL (2023), Precambrian Geology of the Eau Claire River Valley: Re-discovering the Eau Claire Volcanic Complex. in Lodge, RWD (Ed.), Institute on Lake Superior Geology Proceedings, 69th Annual Meeting, Eau Claire, Wisconsin, Part 2 – Field Trip Guidebooks. v.69, part 2, p.47-70. Mudrey, M.G., Jr., Brown, B. A., Greenberg, J. K. "Bedrock Geologic Map of Wisconsin." Wisconsin Geological and Natural History Survey, 1982. Schulz, K.J., and Cannon, W.F., 2007, The Penokean orogeny in the Lake Superior region: Precambrian Research, v. 157, p. 4–25. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectonostratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean orogen: Canadian Journal of Earth Sciences, v. 26, p. 2145-2158. Weber, EM, Lodge, RWD, Marsh, JH (2023). U/Pb geochronology and zircon petrochronology of Paleoproterozoic magmas from the Marshfield terrane, Penokean Orogen, Wisconsin. Institute on Lake Superior Geology Proceedings, 69th Annual Meeting, Eau Claire, Wisconsin, Part 1-Program and Abstracts, p. 97-98. 106 �The Keweenaw Geoheritage Summer Internship Experience VYE, Erika1, LIZZADRO-MCPHERSON, Daniel2, and JUIP, James2 1 Great Lakes Research Center, Michigan Technological University, 1400 Townsend Drive, Houghton, MI, 49931 2 Geospatial Research Facility, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 Earth science education benefits from holistic interpretation of geologic features, processes, and landscapes through multiple ways of knowing (Deloria & Wildcat, 2001; Morton & Gawboy, 2003; Ricci & Riggs, 2019; Semken, 2005). Geoheritage is an evolving field that emphasizes the importance of the varied personal values people have for geologic features and explores the wide-ranging relationships we have with landscapes; as such it is an excellent place-based education tool to explore connections to our underpinning geology (Semken et al, 2017; Tormey, 2019). In this project setting, the Keweenaw region of Michigan’s Upper Peninsula on Lake Superior, we demonstrate a regional, place-based approach to help deepen participant understanding of the billion-year-old geologic processes at the heart of the Midcontinent Rift system. These processes created both the Lake Superior basin and the largest known native copper deposit on Earth in a region further defined as the ancestral and contemporary homelands and waters of the Keweenaw Bay Indian Community (KBIC) on Lake Superior. The Keweenaw Geoheritage Summer Internship Experience was created in partnership with the Keweenaw Bay Indian Community's Natural Resources Department (KBIC NRD) and Tribal Historic Preservation Office (THPO), and Michigan Tech’s Great Lakes Research Center (GLRC) and Geospatial Research Facility (GRF). The experience was created to support intergenerational and multicultural learning about the Keweenaw landscape, its stories, and geology. Tribal and non-tribal high school student interns, community partners, and knowledge holders spent time together reading the landscape and sharing reflections on our varied relationships with land and water. Week 1 entailed a 5-day field experience visiting valued sites of the Keweenaw Bay Indian Community that also teach us how geology impacts land, life, and culture in our place asking “what gifts does geology offer us? what are the relationships with land and water in this place?”. During the field experience, youth interns collected and documented local knowledge by engaging in multi-sensory and multimedia documentation strategies to record their experiences (photos, audio recordings, drawing, 360 virtual reality images, etc.). Sacred Anishinaabe knowledge was not sought or shared in these experiences. Data collected during the field experience was then used as the foundation for a 5-day geospatial workshop following the field experience. The goal of the workshop was for youth interns to design, create, and publish ARC GIS StoryMaps depicting their personal reflections of the diverse relationships with local landscape and understanding of its formation. ARC GIS StoryMaps is a story-authoring, web-based application that enables sharing of maps in the context of narrative text and other multimedia content. Workshop participants worked with the data they collected during the field experience in combination with supporting data layers and 107 �maps specifically created for the experience. Interns were mentored by the geospatial research team who helped students develop digital storytelling skills, inspired brainstorming sessions for topics to explore in the maps, and facilitated peer-review of StoryMap content prior to publication. Upon completion, students presented their work at a community open house; all StoryMaps created have been peer-reviewed by all project partners and are now published. The StoryMaps reflect a deepened understanding of relationships between geology, mining, and current environmental justice issues within our community. In the context of the Keweenaw, the European copper mining boom is most prominently interpreted in our place; students also reflected on the long history of mining, ways of mining, changing narratives, and missing human stories seen and experienced when visiting our landscape. Of note, respect, gratitude, and deepened relationships with land and water featured in all StoryMaps. Students shared reflections on reciprocity and their responsibility to help steward their place. Figure 1: Left - students deepen their understanding of mining impacts to Buffalo Reef and our local communities; Right: students brainstorm story arcs for the foundation of their StoryMap References [1] Deloria, V. and Wildcat, D. R. (2001). Power and place: Indian education in America. Fulcrum Publishing: Golden, Colorado. [2] Morton, R. and Gawboy, C. (2003). Talking Rocks: Geology and 10,000 Years of Native American Tradition in the Lake Superior Region. University of Minnesota Press. [3] Ricci, J. and Riggs, E.M. (2019). Making a Connection to Field Geoscience for Native American Youth through Culture, Nature and Community. Journal of Geoscience Education, special theme issues on Diversity in the Geosciences, DOI:10.1080/10899995.2019.1616273. [4] Semken, S. (2005). Sense of place and place-based introductory geoscience teaching for American Indian and Alaska Native undergraduates. Journal of Geoscience Education, 53 (2), 149-157. [5] Semken, S., Geraghty Ward, E., Moosavi, S. and Chinn, P.W.U (2017). Place-Based Education in Geoscience: Theory, Research, Practice, and Assessment. Journal of Geoscience Education, 65:4, 542562, DOI: 10.5408/17-276.1. [6] Tormey, D. (2019). New approaches to communication and education through geoheritage. International Journal of Geoheritage and Parks, 7 (4), 192-198, ISSN 2577-4441, https://doi.org/10.1016/j.ijgeop.2020.01.001. 108 �R.W. Boyle’s History of Geochemistry and Cosmochemistry WILSON, Graham C.1, BUTT, Charles R.M.2, GARRETT, Robert G.3 and ROBINSON, Heather A.4 1 Turnstone Geological Services Limited. P.O. Box 1000, Campbellford, ON K0L 1L0 Canada, CSIRO Minerals Resources, Kensington, Western Australia; 3 Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8 Canada, 4 25 Chester Crescent, Ottawa. ON K2J 2J6 Canada 2 Robert W. Boyle (1920-2003) was a well-respected geochemist with a long career at the Geological Survey of Canada. He is perhaps best remembered for geological and geochemical studies of gold, silver and other commodities, and for his association with mining camps, such as Yellowknife, N.W.T. and Keno Hill, Yukon. Retiring in 1985, Boyle devoted much of his final two decades to trips to far-flung libraries, gathering information exotic and/or obscure, and penning a major 3-volume review of the evolution of human knowledge of the nature and use of metals and other materials, and of diverse fields within geochemistry, cosmochemistry and biogeochemistry. The result, with copious help in compilation, was almost 2,000 pages of discussion (90% of it typed, fortunately!), backed by a formidable bibliography of almost 3,000 references. It was essentially complete at the time of his death, but altogether lacking in illustration. In time, his G.S.C. colleague Bob Garrett made some editorial notes, and then, in 2011, Charles Butt assessed the manuscript and made a detailed scientific and editorial review, heavy in marginalia. However, the work evidently arrived too late for the glory days of Survey and Society printing budgets, and it sat upon the shelf. In 2015, Ryan Noble, of the Association of Applied Geochemists, broadcast the existence of the manuscript, which attracted Wilson, who undertook to advance the work of the earlier editors, with encouragement from Boyle’s daughter, biochemist Heather Robinson. Volume 1 of the trilogy is set for publication in 2024 (Boyle, 2024). It covers the vast span of human time from the inception of mining and agriculture to the fall of Rome in the West (476 A.D.), and so ventures onto ground traditionally left to aspects of the Classics, Ancient History and Archaeology. Despite the western time frame, it is a worldwide review, covering, besides Europe and the Middle East, India and China and the Americas, every part of the globe where Boyle found relevant knowledge to impart. The intended volumes 2 and 3 explore, respectively, history through the critical 19th century, and then the 20th century (and so to the present). Volume 1 traverses the long development of early thought on the nature of matter. In addition to the various, often conflicting strains of philosophy, there is an equal treatment of the harnessing of materials (Stone, Bronze and Iron ages), and the early stages of the broad swathe of Earth sciences, mining and metallurgy. Early practical ideas on “Earth, air, fire and water” are discussed, e.g., geochemistry and mineralogy, cosmochemistry (meteorites), and early ideas on the hydrosphere and atmosphere. How was the raw manuscript processed? In brief, Wilson: a) ported Boyle’s references into a database, the easier to split up the long bibliography by chapter, rendering each section and volume a stand-alone story; b) utilised his MINLIB bibliography to update Boyle’s references, which for Volume 1 had ended in 1987; c) split up the seminal chapter 3, which provides reviews for some 29 metals and commodity groups (e.g., Au, Ag, Cu; Fe; Sn, Pb; industrial minerals, gemstones and organics); d) added a third layer of editing and consistency checks; and e) 109 �ultimately added 132 individual or composite illustrations in 93 numbered figures, including two original versions of the periodic table. Some of the additions (mostly to post-1987 research) are inserted in the text, others are collected in endnotes to each section. Some of the additions may be skating on thin ice (in which case, it is Wilson who falls through), a problem that one suspects would not have unduly worried the author of the original text. Boyle himself travelled widely across Canada, and the world. In terms of the Lake Superior region, Volume 1 has multiple references to the native copper and native silver of the Mesoproterozoic Midcontinent Rift (Fig. 1; see, e.g., Bornhorst and Barron, 2013; Wilson, 2023). One of two additional text boxes is devoted to native copper, while the other concerns the wider literature on the chemical elements, including some of the most accessible, popular titles. An explicit reference is made to native elements, of which Boyle was fond (e.g., Zn, Pb), including the obvious starting point of Au, Ag and Cu, and listing some 30 elements (many of them very rare in their unalloyed forms). Figure 1. Samples from famous occurrences of native metals in the Lake Superior region. Left: A spectacular, 4,264-kilogram mass of native copper, the exterior coloured by secondary Cu salts (Calumet, Keweenaw peninsula, Michigan). Right: native silver revealed in sawn and polished faces of calcite-veined fractured diabase from the Silver Islet mine in northwestern Ontario, a rich but short-lived venture on the east side of the Sibley peninsula, east of Thunder Bay, in Lake Superior. References Bornhorst, T.J. and Barron, R.J. (2013) Geologic overview of the Keweenaw peninsula, Michigan. Institute on Lake Superior Geology, v. 59, part 2: 1-42, Houghton, MI. Boyle, R.W. (2024) A History of Geochemistry and Cosmochemistry. Prehistory to the end of the Classical Period. Cambridge Scholars Publishing, Newcastle upon Tyne, England (Wilson, G.C., Butt, C.R.M., Garrett, R.G. and Robinson, H.A., editors), circa 600pp., in press. Wilson, W.E. (editor) (2023) Michigan Copper Country II. Mineralogical Record, v. 54 no.1: 196pp. 110 �Cooling of an Archean metamorphic terrane: garnet diffusion study of the Quetico Subprovince, Canada XU, Yiruo1 and HOLDER, Robert1 1 Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109 United States Archean metamorphic terranes are traditionally suggested to have cooled significantly slower than their Phanerozoic counterparts. Many have argued that the contrast in metamorphic timescale reflects changes in Earth’s tectonic regime. However, diffusion chronometry-based cooling rate data on Precambrian rocks are very limited. We present a case study of metamorphic timescales on the Neoarchean Quetico metasedimentary belt of the Superior Province, which has been hypothesized to represent a fore-arc accretionary prism. We combine conventional thermobarometry and phase-equilibrium modeling to constrain the peak temperature and pressure and estimate metamorphic cooling rates from major element diffusion in garnet. We then compare cooling rates across the Quetico Subprovince and with those from Phanerozoic metamorphic terranes of similar conditions. The results will contribute to the diffusion chronometry data available on Precambrian orogens for assessing any fundamental change in global tectonics. 111 � https://digitalcollections.lakeheadu.ca/files/original/462b1934e715e86830529c08f5039d63.pdf d45ee759251a8ad2fecc3255f6c3c6ab PDF Text Text 70th Annual Meeting Institute on Lake Superior Geology Houghton, Michigan May 15-18, 2024 Proceedings Volume 70 Part 2 - Field Trip Guidebook �70th Annual Meeting Institute on Lake Superior Geology Houghton, Michigan May 15-18, 2024 Sponsored by: A. E. Seaman Mineral Museum Great Lakes Research Center Department of Geological and Mining Engineering and Sciences Michigan Technological University Meeting Co-Chairs Theodore J. Bornhorst, Erika Vye, Patrice Cobin, and James DeGraff Proceedings Volume 70 Part 2: Field Trip Guidebook Compiled by Patrice F. Cobin and Theodore J. Bornhorst Cover Photo: The only known color photograph of in situ colorless calcite crystals with inclusions of native copper. Vug is about 15 cm across and 30 cm deep; located at the top of the Knowlton basalt lava flow at the 4th level, 850 ft stope, of the Caledonia Mine, Michigan. Photo taken in 1994 soon after the vug was blasted open. Native copper in the calcite crystals has not been visibly altered despite being about 1 billion years old. Photograph by Theodore J. Bornhorst i ��70th Institute on Lake Superior Geology Volume 70 consists of: Part 1: Program and Abstracts Part 2: Field Trip Guidebook Trip 1: Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Trip 2: Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan Trip 3: Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty Trip 4: Keweenaw Fault System Geometry and Kinematics: Clues to Its Nature and Origin Trip 5: Geology and History of a Native Copper Mine: Adventure Mine, Ontonagon County, Michigan Trip 6: Southern Complex Granitoids, Gneisses, and Migmatites: New Data, Discoveries, and Perspectives Trip 7: Landslides on the Ontonagon River at Military Hill Reference to material in Part 2 should follow the example below: Authors, 2024, field trip title, 70th Institute on Lake Superior Geology, Abstracts and Proceedings, v. 70, Part 2, Field Trip Guidebook, p. xx-xx. Proceedings Volume 70, Part 1: Program and Abstracts and Part 2: Field Trip Guidebook are published by the 70th Institute on Lake Superior Geology and distributed by the Institute Secretary: Peter Hollings Department of Geology Lakehead University Thunder Bay, ON P7B 5E1 CANADA peter.hollings@lakeheadu.ca Some figures in this volume were submitted by authors in color but are printed grayscale to conserve printing costs. Full color imagery will appear in the digital version of the volume when it is available on-line at: http://www.lakesuperiorgeology.org ISSN 1042-99 ii ��Part 2: Field Trip Guidebook Table of Contents Trip 1: Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan………………………...1 Trip 2: Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan……………………………………………………….55 Trip 3: Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty…………………………………………………………………….79 Trip 4: Keweenaw Fault System Geometry and Kinematics: Clues to Its Nature and Origin………………………………………………………………………………..97 Trip 5: Geology and History of a Native Copper Mine: Adventure Mine, Ontonagon County, Michigan.…………………………………………………………137 Trip 6: Southern Complex Granitoids, Gneisses, and Migmatites: New Data, Discoveries, and Perspectives…………………………………..………….157 Trip 7: Landslides on the Ontonagon River at Military Hill…………………………………..173 iii ��Field Trip 1 Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Theodore J. Bornhorst A.E. Seaman Mineral Museum, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 Introduction The geology of the far western Upper Peninsula of Michigan consists of three temporally distinct episodes. During the Mesoproterozoic, about 1.1 Ga, up to 30 km of Keweenaw Supergroup volcanics and clastic sediments filled an intracratonic rift, the Midcontinent Rift (MCR) (Figures 1 and 2) (Cannon et al., 1989). After about 500 million years of erosion, the MCR rocks were buried by Phanerozoic sedimentary rocks from about 500 Ma to 175 Ma (Catacosinos et al., 2001). There are no exposures of rocks in the interval between 175 Ma to about 2.5 Ma (Velbel, 2009). Pleistocene continental glaciations, beginning about 2 million years ago, removed the Phanerozoic rocks from the Keweenaw Peninsula leaving only a few Phanerozoic outliers. About 10,000 years ago glaciers retreated from the Lake Superior basin and left behind a variety of unconsolidated clastic sediments. The geologic evolution of the far western Upper Peninsula is illustrated in Figure 3. Figure 1: Generalized geologic map of the Midcontinent Rift showing Grenville tectonic zone with interpretative cross-section in Figure 2. Modified from Bornhorst and Barron (2013). 1 �Figure 2: Generalized bedrock map showing the exposed rocks of the Midcontinent Rift around Lake Superior, the native copper occurrences, and the bedrock of the Upper Peninsula of Michigan modified from Bornhorst and Barron (2013). Interpretative cross section from Cannon et al. (1989). 2 �Figure 3: Cartoon NW to SE cross sections from Minnesota (left) to the Upper Peninsula (right) illustrating the progressive geologic evolution. Modified from Bornhorst and Lankton (2009). In the strictest sense, the geographic area of the Keweenaw Peninsula proper extends from L’Anse northwest to Lake Superior perpendicular to strike of the strata, however, the term Keweenaw Peninsula has also been applied to the area containing MCR rocks farther to the south from L’Anse to the White Pine area (Figure 4 and 5). The geologic descriptions in this field trip guide are mostly restricted to the Keweenaw Peninsula proper. The descriptions provided here were modified from a combination of Bornhorst and Barron (2011, 2013), Bornhorst and Lankton (2009), Bornhorst and Rose (1994) and Bornhorst et al. (1983). These sources are mostly used here without specific citation or quotation. 3 �Figure 4: Bedrock geologic may of the western Upper Peninsula of Michigan showing area of the Keweenaw Peninsula native copper district (from Bornhorst and Barron, 2013). Figure 5: Stratigraphic column the Keweenaw Peninsula, Michigan. 4 �Midcontinent Rift Strata The Keweenaw Peninsula is located on the southern margin of the Lake Superior segment of the MCR (Figures 1and 2). The rock units that are associated with the MCR have been termed the Keweenawan Supergroup (Figure 5). These rocks were deposited about 1.1 Ga (Heaman et al., 2007; Davis and Paces, 1990; Cannon et al., 1989). The MCR beneath Lake Superior is filled with up to about 30 km of volcanic rocks (Figures 2 and 3) (Hinze et al., 1990; Cannon et al., 1989). The MCR geology of the Keweenaw Peninsula can be divided into northwest-dipping, rift-filling volcanic and clastic sedimentary rocks under the central highlands and northwest flank of the Keweenaw Peninsula (Figure 4) and flat to low-dipping, rift-flanking clastic sedimentary rocks located on the southeast side. The Keweenaw Fault separates the rift-filling and rift-flanking strata. The rift-filling strata are subdivided into volcanic-dominated and clastic sedimentary rockdominated lithologies. (Figure 5). Portage Lake Volcanics The Portage Lake Volcanics of the Keweenaw Peninsula (Figures 4 and 5) are a 2,500 to 5,200 m thick formation dominantly composed of subaerial basalt lava flows with less than 1 % by volume intermediate to felsic volcanic and subvolcanic rocks which are located stratigraphically near the base of the exposed formation. Interflow reddish-colored conglomerate and sandstone layers are less than 5 % by volume and are stratigraphically scattered throughout the Portage Lake Volcanics although greater in abundance towards the top of the formation (Butler and Burbank, 1929; White, 1968). The base of the formation is truncated by the Keweenaw Fault. The lavas flowed from fissure vents that tended to be located near the axis of the rift zone which produced a layered succession of flood basalts comparable to the rift zones of East Africa and Iceland (e.g., Nicholson et al., 1997 and reference therein). Much of the Portage Lake Volcanics erupted over 2 to 3 million years from 1,096.2+/-1.8 (Copper City flow, Figure 6) to 1,094.0+/-1.5 (Greenstone flow, Figure 6) (Paces and Miller, 1993; Davis and Paces, 1990). There are more than 200 individual basaltic lava flows in the exposed Portage Lake Volcanics which are typically aphyric, Mg-rich, high-Al olivine tholeiites (Paces, 1988). The most abundant type of basalt flows are olivine tholeiites, followed by primitive olivine tholeiites and quartz tholeiites. Iron-rich olivine tholeiites are generally lesser in abundance (Table 1). The thicker lava flows are compositionally stratified due to magmatic differentiation after eruption. Magmatic differentiation after eruption is especially significant in the Greenstone flow, which is the thickest individual flow in the formation (Cornwall, 1951a and b; Broderick, 1935; Broderick and Hohl, 1935). The composition of the basalts of the Portage Lake Volcanics is cyclical with minor and major cycles superimposed on an overall trend. The basalt magmas were derived by partial melting of sub-continental upper mantle with an overall compositional trend towards younger more primitive basalt compositions as a result of less crustal contamination (Paces, 1988; Paces and Bell, 1989). The repeated magmatism at the rift axis and progressive crustal thinning provided pathways for magma with less extended contact with crustal rocks. The youngest rocks of the Portage Lake Volcanics in the Keweenaw Peninsula have compositions similar to MORB suggesting the MCR nearly formed an ocean basin. The major geochemical cycles are due to fractional crystallization 5 �and replenishment in large magma chambers near the crust/mantle interface whereas the minor cycles are due to closed system fractional crystallization in small magma chambers within the crust (Paces, 1988). The Portage Lake Volcanics were likely derived by partial melting of enriched plume-related mantle (Nicholson et al., 1997; Nicholson and Shirey, 1990; Paces and Bell, 1989). All observed basalt lava flows in the Portage Lake Volcanics were erupted subaerially and consist of a massive (vesicle-free) interior capped by a vesicular and/or brecciated flow top. There is one thin hyaloclastic unit in the upper part of the formation (Johnson, 1985). Subaerial eruption resulted in degassing of volatiles, notably SO2 (Cornwall, 1951c). The lava flows range in thickness from 1 to 450 m with most of them between 10 to 20 m thick (Paces, 1988; White, 1960). Most of the lava flows cannot be traced along strike with confidence although a few such as the Scales Creek, Kearsarge, and Greenstone flows have well documented lateral continuity (Figure 6). The Greenstone flow has been correlated down dip across the Lake Superior syncline to Isle Royale (Longo, 1982; Huber, 1975). Table 1: Average representative geochemical data for least altered lavas of the Portage Lake Volcanics (from Paces, 1988). Tholeiites were grouped by Ni content. Primitive olivine tholeiite Intermediate olivine tholeiite Iron-rich olivine and quartz tholeiites Olivine tholeiite Olivine tholeiite 400-300 300250 250200 200-100 100-15 n=5 n=9 n=14 n=8 SiO₂ 47.82 47.34 48.03 Al₂O₃ 15.89 15.27 FeOt 9.77 MgO Andesite Dacite Rhyolite n=6 n=1 n=1 n=1 48.55 49.94 56.39 68.44 77.89 15.32 15.12 13.28 13.78 15.17 12.77 11.82 12.32 12.86 14.91 9.87 4.46 1.11 12.44 11.69 9.85 9.06 7.78 5.52 1.14 0.17 CaO 10.58 10.24 10.16 9.65 6.64 5.10 1.40 0.04 Na₂O 2.04 2.10 2.25 2.31 2.91 3.94 4.74 3.67 K₂O 0.19 0.22 0.33 0.42 1.43 2.27 3.86 4.28 TiO₂ 0.98 1.13 1.35 1.60 2.34 1.83 0.51 0.08 P₂O₅ 0.16 0.19 0.22 0.25 0.36 1.00 0.19 0.01 MnO 0.14 0.16 0.16 0.18 0.24 0.30 0.08 0.01 Ni 326 279 231 172 54 10 7 5 Cu 37 51 73 86 126 5 13 61 Zr 78 85 101 126 212 430 573 145 Ni (ppm) Wt.% PPM FeOt=total Fe as FeO 6 �The uppermost 5 to 20% of the tops of most individual lava flows are vesicular with between 5 and 50% vesicles (White, 1968). The tops of 21 % of the flows are brecciated with clasts of vesicular basalt. The vesicles in most lava flows within the Portage Lake Volcanics are largely filled with secondary minerals, except for the stratigraphically uppermost lava flows; the filled vesicles are amygdules. Thus, local terminology is to call lava flows with vesicle-only tops, amygdaloids and those with brecciated tops fragmental amygdaloids. There are minor amounts of andesite, dacite, and rhyolite lava flows and subvolcanic plutons that interfinger with and cross-cut the basalts of the Portage Lake Volcanics (Table 1). Most of these occur in the stratigraphically lowermost portion of the Portage Lake Volcanics. A few dikes of intermediate composition and a diorite stock at Mt. Bohemia intrude into the exposed Portage Lake Volcanics. The rhyolitic volcanic setting is analogous to the shield-type central volcanoes of Iceland (Nicholson, 1991). Interflow clastic sedimentary rocks layers of the Portage Lake Volcanics are recognized as informal members since they are important stratigraphic markers in an otherwise monotonous succession of basalt lava flows. Many of them are given informal names (Figure 6). A few of them can be traced along strike for large distances, up to 90 km. These interflow sedimentary rock layers consist of redcolored conglomerates with lesser amounts of interbedded sandstone and occasional significant amounts of siltstone and shale. These informal members range in thickness from a few cm up to about 40 m (Merk and Jirsa, 1982; White, 1968; Butler and Burbank, 1927). The typical conglomerate is characterized by sub-rounded to angular pebbles in a sandy matrix. Clast size varies from granules to boulders and clast lithologies are predominantly felsic, although there is considerable variation within and between specific beds reflecting diversity in source terrane. Within the interflow Calumet and Hecla conglomerate, Kalliokoski and Welch (1985) interpreted a subunit as a caliche soil profile. The interflow clastic sedimentary beds were deposited during intervals of volcanic quiescence, as terrestrial alluvial fans in an arid to sub-arid climate. Deposition was on top of the shallow-dipping to flat-lying lava flows by streams flowing from the topographic high on the margins of the MCR toward the center of the rift basin (now under Lake Superior) (White, 1968). Copper Harbor Conglomerate The Copper Harbor Conglomerate is the oldest formation of rift-filling clastic sedimentary rocks and conformably overlies and interfingers with the top of the Portage Lake Volcanics (Figures 4 and 5). It consists of red-brown clastic sedimentary rocks with a maximum exposed thickness 2,000 m. Conglomerates and sandstones are the dominant lithologies in the Copper Harbor Conglomerate. The formation fines distally and up section, reflecting a waning sediment supply due to progressive erosion of the source area (Elmore, 1984). The poorly-sorted clasts in the conglomerates range in size from granules to boulders that are subrounded to rounded and are mostly volcanic in origin and have a ratio of mafic-to-intermediate + silicic composition of about 2:1 (Daniels, 1982). The conglomerates include clast-supported and matrix- supported varieties; some of the latter are diamictites. The conglomerates are interpreted as high-energy channel deposits on coalescing alluvial fans (Elmore, 1984). The diamictites are debris flow in origin. Sandstone interbeds are more common in the upper 2/3 of the formation. Sandstones are predominantly red-brown, subangular-to- 7 �angular lithic graywackes with volcanic lithic fragments. The sandstones exhibit current-ripples, trough-cross beds, current and parting lineations, and reduction spots. Abundant calcite cement in select conglomerate and coarse sandstone layers was probably deposited as vadose carbonate or caliche (Kalliokoski, 1986). Thin red-colored siltstone and shale interbeds have desiccation cracks and are interpreted as periodic drying of the surface. In the Copper Harbor area, there are also laminated cryptoalgal carbonate beds and ooid lenses. These are laterally-linked contorted layers in shale-siltstone that are draped over cobbles and are found as poorly developed mats in coarse sandstone (Elmore, 1983). The laminated carbonate beds are algal stromatolites (genus Colleria). Figure 6: Generalized stratigraphy of the Portage Lake Volcanics in a strike parallel (longitudinal) section. Modified from Stoiber and Davidson (1959). Figure 4 shows location of Greenland-Mass subdistrict (Michigan, Caledonia, Mass, Adventure Mines). For decades The Copper Harbor Conglomerate CHC and overlying Nonesuch Formation (Figure 5) have been interpreted by many geologists as non-marine. Elmore (1984) interpreted the environment as a prograding coalescing non-marine alluvial fan complex with proximal-to-distal braided stream and sheet flood facies on the alluvial fans to distal sand flats and flood plain facies (Elmore, 1984). However, a number of sedimentological features could be interpreted as either non-marine or marine and thus, non-marine interpretations often relied on other evidence (Jones et al., 2020). In the stromatolite interval, Jones et al. (2020) cite bimodal (herring-bone) transport 8 �directions indicated by ripple marks that are mud draped and reactivated as evidence of a shallow marine environment. Hummocky cross stratification suggests waves on a marine shelf generated by storms (Jones et al., 2020). Periodic to rhythmic sedimentological features are indicative of “cyclical periodicity” of tidal deposition on a marine shoreline and are among evidence cited by Jones et al. (2020). Jones et al. (2020) conclude that the Copper Harbor Conglomerate and overlying Nonesuch Formation were deposited in a “braided fluvial-evaporitic shoreline-marine embayment” rather than fluvial-non-marine lacustrine setting. Geochemical evidence provided by Stüeken et al. (2020) also supports a marine estuary. The climate was probably arid with flashy seasonal streams. The highlands to the southeast from which the Copper Harbor Conglomerate was derived are now buried under the Jacobsville Sandstone. The Copper Harbor Conglomerate in the Keweenaw Peninsula includes a succession of subaerially deposited lava flows. Lane (1911) used the name, Lake Shore Traps, for this informal member (Figure 5). This member is well exposed near the tip of the Keweenaw Peninsula where the unit is composed of 31 lava flows and one interflow conglomerate with a maximum thickness of about 600 m (Paces and Bornhorst, 1985). The composition of the Lake Shore Traps is different than the underlying Portage Lake Volcanics reflecting the change from active rift-filling magmatism to passive subsidence with rift-filling clastic sedimentation and little to no magmatism except for the Lake Shore Traps. These subaerial lava flows range from Fe-rich olivine tholeiitic basalt at the base to Fe-rich olivine-bearing tholeiitic basaltic andesites and tholeiitic andesites and are likely a shield volcano. Geochemical data are best explained by a combination of fractional crystallization, parental magma replenishment, and wall rock assimilation (Paces and Bornhorst, 1985). Davis and Paces (1990) report a U-Pb age on zircon of 1087.2 +/- 1.6 Ma for the Lake Shore Traps. Nonesuch Formation The Nonesuch Formation conformably overlies and locally interfingers with the Copper Harbor Conglomerate (Figures 4 and 5). It consists of dominantly black-to-gray-to-green to redgray siltstone and shale with a maximum thickness 240 m. Bornhorst and Williams (2013) provide a stratigraphic column of the entire Nonesuch Formation just south of the Porcupine Mountains State Park from exploration drilling. Exposures of the Nonesuch Formation in the Keweenaw Peninsula proper are limited with the best exposure at the Hancock campground and boat launch on M-203 (Stop 14). There are excellent exposures of the Nonesuch Formation along the Big Iron and Presque Isle rivers in the White Pine area (Woodruff et al., 2013). In areas with thicker stratigraphic section, siltstone and shale are the dominant lithologies with lesser very-fine sandstone and minor carbonate laminates. While gray (reduced) color characterizes most of this formation, the stratigraphic upper beds have more red-brown colors (Bornhorst and Williams, 2013). Well-laminated to massive black to dark-gray siltstone and shale are the dominant lithologies near the base of the Nonesuch Formation. The base of the Nonesuch Formation hosted economic quantities of chalcocite and native copper at the now closed White Pine Mine (Mauk et al., 1992) and chalcocite at the Copperwood project (Bornhorst and Williams, 2013; Williams and Bornhorst, 2023). A thin carbonate laminate yielded a Pb-Pb isochron age of 1,081 ± 9 Ma (Ohr,1993). The environmental setting of the Nonesuch is described above under the Copper Harbor Conglomerate. 9 �Freda Sandstone In the Keweenaw Peninsula the Freda Sandstone is the youngest rift-filling clastic sedimentary rock formations (Figures 4 and 5). The contact between the lower most Freda Sandstone and Nonesuch Formation is gradational (Bornhorst and Williams, 2013). The exposed thickness is greater than 3,700 m, with the top of the formation submerged beneath Lake Superior. The Freda Sandstone is generally poorly exposed except along the Lake Superior shoreline. This field guide provides an optional stop 13 at the McLain State Park where exposures of the Freda are visible during times of low levels of Lake Superior. Angular and tabular specimens are obtainable at the beach from outcrops just offshore. The last MCR magmatism was Bear Lake, an intrusive-extrusive dome of alkaline trachyandesite was emplaced near the middle of the exposed Freda Sandstone (Kulakov et al., 2018). Red-brown fine to very-fine sandstone, siltstone, and mudstone are the dominant lithologies in the Freda Sandstone. Fining-upward sequences occur on the scale of a few meters. The Freda Sandstone was deposited in an environment characterized by shallow meandering streams (Daniels, 1982). Based on regional correlations the Freda was likely deposited between 1,080 to 1,060 Ma. Jacobsville Sandstone The Jacobsville Sandstone was deposited in a rift-flanking basin (Figure 3D) and is outside the scope of this field guide. Its stratigraphic relationship with other formations is not determined. It occurs in a contiguous geographic region bound on the northwest side by the Keweenaw Fault and on the southeast by an unconformable contact with Paleoproterozoic and Archean basement rocks (Figure 4). The Jacobsville Sandstone is estimated to be more than 2,900 m thick and the top is not exposed (Kalliokoski, 1982). Red to red-brown sandstone is the dominant lithology with lesser amounts of red-brown conglomerate, siltstone, and shale. The sandstone varies from subarkose to quartz sublithic arenite although there are some beds of arkose and quartz arenite (Kalliokoski, 1982). The Jacobsville Sandstone was deposited in an environment characterized by shallow meandering streams (Kalliokoski, 1988). Faults, Folds, Fractures The last episode of the Midcontinent Rift was characterized by post-rift compressional inversion that facilitated hydrothermal formation of native copper deposits (Woodruff et al., 2020; Bornhorst, 1997). This compression transformed original normal faults into reverse faults, reactivated other extensional rift-related faults/fractures, and produced new compression-only faults/fractures and folds. Rather than being an inverted rift-related normal fault, the Keweenaw fault was likely a detached thrust (DeGraff and Carter, 2023). Cannon et al. (1993) have determined that compression occurred at about 1,060+/-20 Ma. The probable cause of this event was continental collision along the Grenville front (Figure 1) beginning as early as 1.08 Ga (Cannon, 1994; Cannon and Hinze, 1992; Hoffman, 1989). Final inversion of the MCR by compression during Grenville orogeny occurred between 1,010-980 Ma (Hodgin et al., 2022). 10 �The Mesoproterozoic Midcontinent Rift-filling strata of the Keweenaw Peninsula dip moderately toward the center of the rift with the angle of dip increasing toward Keweenaw fault where the stratigraphic base is truncated (Figure 7). The dip of the strata is interpreted as a combination of syn-depositional downwarpage and structural tilting in response to reverse faulting caused by regional continental compression (Woodruff et al., 2020; Cannon, 1994). There are many faults/fractures in the Mesoproterozoic rocks of the Keweenaw Peninsula. Some of these were exclusively formed during extension of the Midcontinent Rift when grabenbounding normal faulting was prominent along the margin (Figure 3). However, most faults/fractures were likely either reactivated by or directly produced by the regional compressional event. The Keweenaw Fault strikes and dips more or less parallel to the bedding of the truncated Portage Lake Volcanics (Figure 7) and is not necessarily one fault, as it is a zone with branches up to 0.8 km from the main fault (Butler and Burbank, 1929). It is a detached thrust fault related to regional compression. Although the Keweenaw Fault would make an ideal conduit for movement of hydrothermal fluids, there are no native copper deposits along it similar to other ore-bearing districts where the main faults are not well mineralized. However, the rocks within and adjacent to the fault are altered by late-stage hydrothermal fluids. Figure 7: Simplified geologic map showing the location of the major deposits within the Keweenaw Peninsula native copper district, Michigan. Table 2 provides the names and production for the numbered deposits. The areas shown on the map are the mined out down-dip portion projected to the surface. All of the native copper mines are hosted by the Portage Lake Volcanics. Modified from Bornhorst and Barron (2011). 11 �Table 2: Production from 1845 to 1968 of refined copper from native copper deposits (after Weege and Pollock, 1971). Million lbs Produced Refined Copper Location Number see Figure 7 Calumet & Hecla Conglomerate 4,229 7 Kearsarge Flow Top 2,263 3 Baltic Flow Top 1,845 12 Pewabic Flow Top 1,077 9 Osceola Flow Top 578 8 Isle Royale Flow Top 341 10 Atlantic Ashbed 143 11 Allouez Conglomerate 73 6 Houghton Conglomerate 38 4 Kingston Conglomerate 20 Greenland-Mass Subdistrict 72 5 See Figure 3 Other Flow Top and Conglomerate Deposits 137 Cliff Fissure 38 1 Central Fissure 53 2 Other Fissure Deposits 123 Name of Deposit District Total 11,030 Several faults occur oblique to the strike of bedding. In the Eagle River area, fault-controlled native copper veins are common in association with high-angle faults whose displacement is from 0 to 200 m, (Figure 7; see also Figure 19; Butler and Burbank, 1929). The Allouez Gap fault (Figure 7) bisects the largest lava flow top hosted native copper deposit in the district (see Figure 16) and was likely a significant conduit for native copper mineralizing hydrothermal fluids (Bornhorst, 1997). Correspondence between the thickness of the Kearsarge lava flow and the Allouez Gap fault suggests this fault was active during deposition of the Portage Lake Volcanics. It is interpreted as having been reactivated during regional compression. Faults were the principal pathway for the upward movement and focusing of ore fluids into the stratabound lava flow tops in the Baltic and Isle Royale deposits as well as those in the Greenland-Mass subdistrict (Broderick, 1931). Faulting occurred before, during, and after deposition of native copper and its associated alteration minerals based on fault brecciated and recemented alteration minerals. There is a close relationship between faulting/fracturing produced by or reactivated by compression and native copper deposits. The compressional structures acted as pathways for mineralizing hydrothermal fluids (Bornhorst 1997). 12 �Broad open synclines and anticlines, with wavelengths of around 10 km and various orientations, are superimposed on the regional dip. Faults with displacement and mineralized tension breaks are common near the crests of anticlines (Butler and Burbank, 1929). These post-depositional folds are likely related to the late regional compression (White, 1968). Keweenaw Peninsula Native Copper District Active copper mining occurred from 1845 to 1968 in the Keweenaw Peninsula native copper district. The estimated pre-mining geologic resource for the district is ~20 billion lbs of copper (Bornhorst and Barron, 2011). Small quantities of native silver are temporally and spatially associated with the native copper. The major ore producing horizons are located in a 45 km-long belt in the Keweenaw Peninsula (Figures 4 and 7) and in a subdistrict to the southwest. Native copper and silver were the only economic metallic minerals and were co-precipitated with a suite of nonmetallic alteration minerals (Figure 8). Sulfide minerals, such as chalcocite, are uncommon in native copper deposits and when present only occur in trace amounts. Sulfide minerals occur in latestage veins (Figure 8). Several chalcocite deposits of unknown connection to the native copper deposits are hosted by the stratigraphically older Portage Lake Volcanics; the largest of these contains roughly 230 million lbs of copper (Woodruff et al., 2020; Maki and Bornhorst, 1999); these will not be discussed here. Native Copper Ore Bodies Ore bodies in the Keweenaw Peninsula are tabular, stratabound concentrations of native copper hosted by the Portage Lake Volcanics where there is sufficient original porosity including brecciated and amygdaloidal flow tops (58.5% of production) and interflow conglomerate beds (39.5% of production). Secondary porosity occurs along fractures/faults which host veins (about 2% of production). Since the deposits represent important stratigraphic horizons, the host rocks were given informal member names (Butler and Burbank, 1929). Several mines with different names often worked the same deposit/ lithostratigraphic unit. About 85% of the total district production came from four deposits: Calumet and Hecla Conglomerate, top of the Kearsarge lava flow, top of the Baltic lava flow, and the top of the Pewabic lava flow (Table 2). The most common host rocks for native copper deposits are brecciated flow tops (fragmental amygdaloid) as their original porosity was typically much greater than vesicular (amygdaloidal) flow tops (White, 1968). The stratabound flow top deposits are “sandwiched” between a footwall consisting of barren massive basalt of the same flow as the mineralized flow top and hanging wall interior of the succeeding lava flow. Native copper is often more abundant near the top and bottom of the brecciated/fragmental amygdaloid interval of the flow top, however, in rich ore shoots, the entire brecciated/fragmental amygdaloid flow top contains significant amounts of copper. As brecciated/fragmental amygdaloidal transitions downward into massive basalt, it becomes deficient in native copper. In some cases, ore shoots are located in tongues of brecciated flow tops within massive basalt (Weege and Schillinger, 1962). The lateral and vertical distribution of brecciated/fragmental amygdaloid within the top of a lava flow is irregular and hence, so is the grade of copper. In general, mined stope heights are from 3 to 5 m. Ore shoots are elongated, but 13 �also occur in a wide variety of shapes, with widths of 30 to 150 m and down dip lengths from 50 m to 600 m (White, 1968). The strike length for major ore bodies ranges from 1.5 to 11 km with down dip mineralization extending from 1.5 to 2.6 km on the incline below the surface (Butler and Burbank, 1929; White, 1968). Although interflow conglomerate beds make up only a small volume of the Portage Lake Volcanics, about 40 % of the district production of refined copper were hosted by them. These deposits were tabular and stratabound, just like the flow top deposits. They are “sandwiched” between a footwall consisting of the top of the underlying lava flow and hanging wall of barren massive basalt interior in the overlying lava flow. The porosity of underlying brecciated/fragmental amygdaloid lava flow top is often greatly decreased by silt and sand filling the primary open space between fragments of the flow top hence, the originally porous flow top underlying a conglomerate bed acts more like an aquiclude in the paleohydrologic hydrothermal system. Native copper tends to be concentrated along specific stratigraphic bands within the conglomerate that are 0.5 to 5 m thick (Weege et al., 1972). The Calumet and Hecla Conglomerate was by far the largest single native copper deposit in the district producing 4.2 billion lbs. as compared to the next largest deposit, the Kearsarge flow top which produced 2.3 billion lbs. from a fragmental amygdaloid (Figure 7 and Table 2). The Calumet and Hecla Conglomerate was mined along a strike length of 4.9 km, and down-dip 2.8 km. The productive area corresponds to a thickening of the conglomerate from less than 1 m up to 6 m (Butler and Burbank, 1929; Weege et al., 1972). Ore grades decrease with depth where the width of the conglomerate is greater; essentially the same amount of copper is distributed throughout a greater volume. (Butler and Burbank, 1929). The highest grades correspond to beds where there is relatively little fine interstitial material in the clastic sedimentary host rock or where interstitial spaces are filled with coarse sand or small pebbles (Weege et al., 1972). Thus, localization of native copper ore is dependent on sedimentary environmental factors. The first mines in the district were developed on tabular steeply dipping deposits that cross-cut bedding at high angles. However, overall, the vein deposits are of slight economic importance in the district. The veins have widths of up to 3 m or more (Butler and Burbank, 1929). Veins are not single tabular bodies, but rather a series of parallel anastomosing filled open spaces. While brecciation within vein deposits is common, gouge is not present (Butler and Burbank, 1929). The lava flow tops and conglomerates adjacent to the vein are mineralized. The distribution of native copper in veins is more erratic than in either lava flow top or conglomerate deposits. The richest ore veins tend to be spatially associated with the intersections of the vein and well-oxidized lava flow tops (Butler and Burbank, 1929). Native copper occurs as both finely disseminated and as masses weighing many tons. The grade of native copper in the veins has the nugget-effect making determination of grade difficult. Several small vein deposits are localized just beneath the thickest basalt flow in the district, the Greenstone flow. For these veins the hydrothermal fluids moved up along the cross fractures until blocked by the very thick impermeable massive interior of the Greenstone Flow. There are veins spatially and genetically associated with the stratabound lava flow top or conglomerate deposits; these veins occur along faults that intersect major deposits such as the Baltic 14 �and Isle Royale faults (Broderick, 1931). This suggests that ore fluids moved upward along faults and outward into the permeable flow tops. The intersection of subsidiary faults with locally thick permeable horizons is a key factor in concentrating ore such as the Kearsage deposit (see Figure 16). White (1968) suggested that for the movement of ore fluids to occur, permeability due to fracturing was more important than primary permeability. Faults and small fractures cutting massive interior of lava flows were also likely important for upward transport of ore fluids. Overlapping of successive lava flows and minor unconformities suggests that simple up-dip movement of ore fluids was not likely without a network of fractures (Bornhorst, 1997). Hydrothermal Minerals The rocks within the Keweenaw Peninsula native copper district were pervasively altered by lowtemperature, low-pressure hydrothermal/burial metamorphic fluids. Alteration was most intensely associated with the native copper deposits although to some degree secondary hydrothermal minerals occur in all rocks of the Portage Lake Volcanics. Areas in the Keweenaw Peninsula more distal to the area of major native copper deposits rocks were less altered at lower temperature. The intensity and degree of alteration also varies as a function of position within lava flows; the massive interiors of lava flows are much less altered whereas the lava flow tops are relatively more altered. Lava flows in close proximity to cross cutting features tend to be more altered. The minerals occur as amygdule and vein fillings, and as whole rock replacements. Within the Portage Lake Volcanics, some original igneous minerals are present in the massive interiors of some flows, but secondary minerals exist in the massive interiors of all flows regardless of their thickness. While the thicker massive interiors of lava flows contain secondary minerals, their original igneous geochemical composition is often only slightly or essentially not modified by secondary hydrothermal processes. There are more than 50 different secondary alteration minerals in the Keweenaw Peninsula; most of them are related to hydrothermal processes and some are related to supergene processes. Only about 20 alteration minerals are major to less common minerals (Figure 8). Native copper with small quantities of native silver represents over 99% of the metallic minerals in the mined ore bodies of the district. Most of the native copper carries a small amount of arsenic in solid solution (typically less than 0.2 % arsenic of total copper + silver + arsenic; Broderick, 1929). Copper-nickel arsenides occur in veins that are paragenetically late (Moore, 1971; Stoiber and Davidson, 1959; Butler and Burbank, 1929). There is a district wide temporal (paragenetic) and spatial variation in the assemblage of alteration minerals which was first well described by Butler and Burbank (1929) and later summarized by White (1968). Recently Bodden et al. (2022) have refined the paragenetic and spatial variation of the hydrothermal minerals (excluding igneous and supergene related minerals) (Figure 8). The hydrothermal alteration minerals can be subdivided into main-stage which paragenetically overlap with the precipitation of native copper (Figure 8). While district-wide there is a well-defined mineral paragenesis, individual deposits may not exactly follow the district-wide timing of precipitation (compare Figure 8 to Stop 5). The main-stage is interpreted by Bodden et al. (2022) as formed during a continuous hydrothermal event. 15 �Figure 8: Paragenesis and relative abundance of secondary hydrothermal alteration minerals in the Keweenaw Peninsula native copper district. After Bodden et al. (2022). The late-stage minerals are widespread but volumetrically minor. They commonly occur in small veins/fractures which cross-cut the main stage minerals or as coatings on main-stage vug filling minerals. Late-stage alteration minerals are notably more abundant near the Keweenaw fault. The suite of late-stage minerals are distinguishable by the occurrence of sulfur-bearing minerals, sulfides and sulfates, and by an assemblage of lower temperature minerals in areas where they overprint an assemblage of main-stage minerals formed at higher temperatures. The timing of the late-stage hydrothermal event is uncertain. There could have been no time break or a major time break between the main-stage and late-stage hydrothermal events. Bodden et al. (2022) suggested that the main-stage and late-stage hydrothermal events are practically continuous with each other. Main-stage alteration minerals are spatially zoned perpendicular to stratigraphic strike as demonstrated for the Calumet area of the district (Figure 9). Epidote and the appearance of quartz are spatially associated with major native copper deposits (Stoiber and Davidson, 1959). A detailed study by Stoiber and Davidson (1959) of the Kearsarge deposit shows that native copper is much more irregularly distributed than secondary mineral zones, but there is a general correlation with the abundance of native copper associated with the variation of quartz and microcline (Stop 5). The alteration mineral zones of the Portage Lake Volcanics are similar to the North Shore Volcanic Group of Minnesota (Schmidt and Robinson, 1997). Bodden et al. (2022) mapped the occurrence of 16 �Figure 9: Distribution of prominent secondary hydrothermal alteration minerals in the Portage Lake Volcanics in a cross-section in vicinity of Calumet at the center of the major deposits of the Keweenaw Peninsula native copper district modified from Bornhorst and Rose (1994). Figure 10: Main-stage hybrid metamorphogenic hydrothermal mineral zones of the Keweenaw Peninsula (modified from Bodden et al., 2022) 17 �alteration minerals of the Keweenaw Peninsula into those zones used for the North Shore Volcanic Group (Figure 10; Schmidt and Robinson, 1997). These zones can be equated to the temperatures of mineral formation (Bodden et al., 2022). The spatial zoning of alteration minerals is consistent with a thermal high associated with the major native copper deposits (compare Figure 4 and 10). The mineral zones dip more gently towards Lake Superior than the strata, implying that the strata were at least somewhat tilted prior to main-stage hydrothermal alteration (Livnat, 1983; Broderick, 1929). Native copper mineralization is younger than the Copper Harbor Conglomerate, which hosts rare veins of calcite and native copper (see Stop 7). White (1968) interpreted the age of native copper mineralization as after the deposition of parts or all of the Freda Sandstone. The Bear Lake igneous body within the Freda Sandstone is native copper mineralized. Minor amounts of native copper occur within the lower beds of the Jacobsville Sandstone near Rice Lake (Calumet and Hecla unpublished drill core log). Based on field relations, hydrothermal alteration is younger than deposition of rift-filling strata and at least some of the rift-flanking Jacobsville Sandstone. The absolute age of hydrothermal alteration is between 1060 and 1050 Ma (+/- ~ 20 Ma) (Bornhorst et al., 1988). This age is consistent with the approximate age of 1060+/-20 Ma for regional continental compression that caused thrust faulting along the Keweenaw Fault (Cannon et al., 1993). Thus, the age of main-stage hydrothermal alteration is about 1060 to 1050 Ma contemporaneous with regional continental compression and some 30 million years after eruption of the Portage Lake Volcanics. Genesis of the Main-Stage Native Copper Deposits This section is summarized from Bornhorst and Mathur (2017) and Bodden et al. (2022) and illustrated in Figure 11. Native copper occurs throughout the MCR in Wisconsin, Minnesota, and Ontario (Figure 2). It formed during a regional hydrothermal event from about 1060 to 1050 Ma (Bornhorst et al., 1988). The regional Cu-bearing hydrothermal fluids are best explained as generated during burial metamorphism of rift-filling basalts with temperatures reaching a thermal maximum approximately 30 million years after the end (~1085 Ma) of widespread rift magmatism. The suite of main-stage hydrothermal minerals precipitated, except native copper, (Figure 7 and 8) is similar to those found elsewhere rocks have undergone very low to low grade burial metamorphism at less than about 300OC. The coincidence of regional continental compression with a burial thermal maximum (Woodruff et al., 1995) provided an integrated paleohydrologic system through reactivated and new faults and fractures. This allowed the upward movement of hydrothermal fluids to focus in sites of future copper deposits at the very time of greatest fluid availability (Bornhorst 1997). During generation of the regional burial metamorphogenic hydrothermal ore fluids, copper was leached at depth from the rift-filling basalt strata (Bornhorst and Mathur, 2017, 2018). More than sufficient amount of copper was available to have been leached from the buried rift-filling basalts. 18 �Figure 11: Cartoon cross sections showing conceptual genetic model of the native copper deposits of the Keweenaw Peninsula formed at about 1070 to 1040 million years ago. Modified from Bodden et al. (2022). A. Marine incursions and seawater penetration during deposition of volcanic and sedimentary rocks in MCR. B. Area prior to burial metamorphism with sulfur depleted evolved seawater providing salinity for ore-forming fluids. C. Burial metamorphism with generation of burial metamorphic hydrothermal fluids. Mixing the burial metamorphic fluids with evolved seawater produces copperbearing hybrid metamorphogenic ore-forming hydrothermal fluids. D. Precipitation of main-stage minerals as a result of mixing of the ore-forming fluids with meteoric water, decreasing temperature, and water-rock reactions. 19 �The rift-filling volcanic rocks were low in sulfur when they erupted and the little available sulfur was degassed prior to solidification (Bodden et al., 2022; Bornhorst and Mathur, 2017). These lowsulfur rift-filling volcanic rocks were buried into the source zone where burial metamorphogenic hydrothermal fluids were generated (Figure 3 and 11C). Since the very low sulfur rift-filling basalts in the source zone were the same as those in the fluid pathways to the zone of precipitation, the fluids remained sulfur poor. Since the native copper ore host rocks were again the same rift-filling very low sulfur volcanic rocks, the burial metamorphogenic hydrothermal fluids remained depleted in sulfur. The lack of sulfur resulted in the precipitation of native copper rather than copper sulfides. While the metamorphogenic hydrothermal fluids lacked sulfur, several studies (Kelly, 2022; Kelly, 2020; Püschner, 2001; Brown, 2006; Livnat, 1983; Jolly, 1974) have suggested that the main-stage hydrothermal fluids had at least moderate degree of salinity. The possible sources of salinity were evaluated by Bornhorst and Mathur (2017), Bornhorst (2021), and Bodden et al. (2022). Viable sources of salinity for the hydrothermal fluids need to also satisfy the constraint of very low sulfur. Bornhorst (2021) hypothesized that evolved formation water derived from sulfur depleted seawater could have been the source of salinity. As seawater penetrates midocean ridge basalts it is heated, reacts with the host basalt, and as a result of precipitation of minerals it becomes depleted in sulfur. If the sulfur content of the Mesoproterozoic seawater was low in sulfur, as proposed by Blattlet et al. (2022), then less depletion of sulfur would have been needed. During deposition of the youngest Portage Lake Volcanics and overlying Copper Harbor and Nonesuch formations there were probable incursions of an arm of the sea into the rift for a significant amount of time. This could have resulted in seawater deeply penetrating into the underlying rift-filling volcanic rocks (Figure 11A; Bornhorst, 2021). During burial, the riftfilling volcanic and clastic sedimentary rocks and contained seawater was progressively heated and thereby evolved to be depleted in sulfur (Figure 11B). Continued heating during burial resulted in burial metamorphic hydrothermal fluids which then thoroughly mixed with the evolved seawater to form a hybrid metamorphogenic-dominated ore-forming fluid (Figure 11C; Bodden et al., 2022). These main-stage ore-forming hydrothermal fluids moved upwards from the source zone through the same very sulfur poor strata as in the source rocks (Figure 11D). As they moved upwards they cooled, interacted with host rocks, and in the relatively shallow zone of precipitation they variably mixed with sulfur-poor, low salinity, reduced meteoric water (Figure 11D; Bodden et. al, 2022). These processes resulted in precipitation of native copper and main-stage hydrothermal minerals. Higher temperature main-stage mineral assemblages are spatially associated with the area of native copper deposits where the thermal anomaly was greatest because of focused hydrothermal fluids (Figure 10). The possible depth of the zone of precipitation is poorly estimated with a best guess at this time of 10 to 15 km (Kelly et al., 2022; Kelly, 2020). Within the native copper district, the suite of main-stage minerals, including native copper, is followed by late-stage minerals precipitated at lower temperatures than the main-stage hydrothermal fluids coincident with the native copper district. 20 �Late-Stage Hydrothermal Minerals The suite of late-stage minerals is widespread and similar throughout the Keweenaw Peninsula. The late-stage suite is readily distinguished in the main area of the native copper district since late-stage minerals are lower temperature (100 to 150OC) than the main-stage minerals in district itself. However, outside of the native copper district where main-stage minerals are expected to be formed at lower temperature, the main-stage and late stage are indistinguishable. Bodden et al. (2022) suggested that late-stage fluids are a variable mixture of hybrid metamorphogenic hydrothermal fluids, meteoric water, and shallow seawater, the latter being a source of sulfur in the late-stage fluids. Phanerozoic The Keweenaw Peninsula was subjected to a 500-million-year period of erosion, from about 1 Ga to 0.5 Ga (500 Ma) and multiple kilometers of rock were eroded exposing the native copper deposits at the surface (Figure 3). Downward percolating groundwaters supergene altered native copper and produced a suite of including cuprite, tenorite, malachite, and chrysocolla (Bornhorst and Robinson, 2004). The rocks of the Keweenaw Peninsula were subsequently buried by Paleozoic sedimentary rocks associated with the Michigan basin beginning about 500 Ma (Figure 3) and ending Precambrian supergene alteration. Over the past two million years, the Keweenaw Peninsula was subjected to several continental glacial periods which removed all of the overlying Paleozoic sedimentary rocks with the exception of Paleozoic outliers slightly south of the Keweenaw Peninsula (Figure 3). The last glacial episode exposed the native copper deposits at roughly the same erosional level as at 500 Ma or the end of the Precambrian (Bornhorst and Robinson, 2004). The continental glaciers sculpted the bedrock of the Keweenaw Peninsula and when the last glacier retreated about 10,000 years ago, it left behind a variety of unconsolidated glacial-related sediments that included entrained boulders of native copper. The glaciers carved out the topographic low the Lake Superior basin corresponding to the less competent clastic sedimentary rocks under the center of the MCR. After the glaciers retreated, very large volumes of water filled this topographic low and initially all but the highest land elevations were submerged under a large glacial lake. The glacial lake levels successively dropped over time to the current level of Lake Superior (Farrand 1960). As the lake levels receded humans populated the area. 21 �Figure 12: Geologic map of the far western part of the Upper Peninsula of Michigan showing field trip stops. Objectives of Field Trip This field trip is designed to provide an overview of the Mesoproterozoic Midcontinent Rift-filling strata and native copper deposits of the Keweenaw Peninsula (Figure 12). There are four rift-filling formations: Portage Lake Volcanics, Copper Harbor Conglomerate, Nonesuch Formation, and Freda Sandstone. The Nonesuch and Freda formations are poorly exposed in the Keweenaw Peninsula thus, only two optional stops are included in this field guide. The Jacobsville Sandstone is a rift-flanking formation and is outside the scope of this field trip. The rift-filling strata are overlain by unconsolidated Pleistocene glacial sediments. There is one glacial related stop. IMPORTANT NOTE TO ALL READERS: Many of the field trip stop descriptions and significant parts of the introductory geologic overview have been previously published especially in other Institute on Lake Superior guidebooks e.g., Bornhorst and Barron (2013) and the extensive guides by Bornhorst and Rose (1994) and Bornhorst et al. (1883). The stop descriptions in this field guide, as compared to previously published guides range from exact wording to significantly modified wording without specific citation. Two of the stops in this field guide, Stops 2 and 8, were not visited by previous field guides involving Bornhorst. These stop descriptions are new. 22 �Stop 1: Subaerial basalt lava flow cross-section at South Range Quarry Latitude: 47.07750N; Longitude: -88.64240W Directions: Drive west through downtown Houghton on US-41 to south M26. Drive about 4.5 miles to unmarked road on west side of M-26 just before church on south side of unmarked road. Proceed on road to tree line. Walk NE uphill to quarry. THIS STOP IS ON PRIVATE PROPERTY. PLEASE GET PERMISSION TO ENTER PROPERTY. Volcanic textures and structures typical of moderate-to-thick subaerial lava flows within the Portage Lake Volcanics are well exposed in this old quarry (Figure 13). As one traverses up the hill to the quarry along the rubbly path there is a low-profile exposure of a 4 m thick interflow conglomerate bed which is also exposed laterally along the SE slope face of this knob. The conglomerate layer is stratigraphically the National Sandstone member and is approximately near the middle of the exposed Portage Lake Volcanics stratigraphic section (Figure 6). The conglomerate is overlain by an 18 m thick lava flow (A). Figure 13: Geologic cross section of the South Range Quarry (modified from White, 1971). Laterally continuous interflow sedimentary beds provide critical stratigraphic markers within the Portage Lake Volcanics, an otherwise monotonous volcanic pile with many laterally discontinuous lava flows. The sedimentary unit exposed below the quarry has been correlated with the National Sandstone, a marker bed in the Mass-Rockland area (Figure 6). At South Range Quarry, the National Sandstone is a massively bedded, pebble-cobble framework conglomerate, composed of silicic with subordinate mafic volcanic clasts that are subangular to subrounded, within a matrix of poorly-sorted medium-to-coarse sand of similar composition. The Portage Lake Volcanics basalts in this part of the stratigraphic section are mainly olivine tholeiites and erupted as subaerial lava sheets. The principal lava flow exposed in the quarry walls illustrates many of the volcanological features of Portage Lake Volcanics lava flows. The top and bottom of the South Range Quarry lava flow (B) are exposed. Flow B was deposited directly on top of Flow A and consists of aphanitic chilled basalt. The base of Flow B occurs where amygdules disappear abruptly in the top of the underlying flow. 23 �The upper surface of the main flow (B) was brecciated slightly by movement of lava after the formation of an upper crust. The flow top breccia (locally termed fragmental amygdaloid) is laterally discontinuous. The fragmental amygdaloid rapidly grades downward to an unbrecciated, highly amygdaloidal (vesicular) flow top. Note the variation in vesicle size and shape downward in the flow. There are numerous layers of flattened amygdules (vesicles) in the flow top with their orientation parallel to the top and bottom of the flow (B). The orientation of these layers may represent laminar flow planes within the flow top. The section was tilted after emplacement. Slow cooling of the lava flow caused solidification toward the flow interior at a rate which allowed development of subophitic to ophitic textures (ophitic texture denoted by large oikocrysts of clinopyroxene enclosing a felted framework of An-rich plagioclase and intergranular olivine). The resulting massive, non-vesicular flow interior constitutes about two-thirds of the flow (B). Before final solidification, small amounts of volatile-rich, differentiated residual liquid were likely injected into thin discontinuous layers and lenses (tabular openings produced during cooling). Most of these pegmatoid layers are subparallel to the bottom and top surfaces of the flow. A typical pegmatoid zone consists of a 5 to 10 cm border zone at the top and bottom which is composed of a medium-to-coarse grained aggregate of Ab-rich plagioclase, prisms of Fe-rich clinopyroxene and abundant Fe-Ti oxides, as well as accessory minerals such as apatite and zircon (Cornwall, 1951c). The cores of the pegmatoid zones are 5 cm to 1.2 m thick consisting of a green vesicular basaltic rock. Zircons extracted from pegmatoids within thick Portage Lake Volcanics basalt flows have yielded high-precision U-Pb dates (e.g., Davis and Paces, 1990). There are thin tabular layers and flattened amygdules (vesicles) in the top of the flow and in the massive interior of the flow (B) that are composed of a brown and sometimes green fine-grained material that have been described interpreted by White (1971) as detrital material. Alternatively, this green-to-red cherty rock, could be simply alteration minerals (quartz, prehnite, epidote, and pumpellyite) filling fractures and nearly complete pseudomorphic replacement of basalt. Numerous pegmatoid layers are exposed in the quarry walls, as well as in the glacially-polished surfaces above and to the north of the quarry. The effects of regional hydrothermal alteration can be observed within the vesicular flow top and pegmatoid zones. Vesicles are filled with a variety of secondary minerals including quartz, epidote (olive green), prehnite (waxy light green), calcite, pumpellyite (pale bluish green), chlorite (dark green to black) and traces of native copper (pinkish color). Pseudomorphic replacement of basalt by fine-grained secondary minerals is most intense where permeability was highest. The massive interior of the flow is only a little visibly altered, however plagioclase is altered to albite and pyroxene is altered to chlorite. In the vicinity of selected fractures there can be intense epidote or prehnite alteration. The massive interior was a relatively impermeable horizon in the paleohydrothermal system. Fracturing during late compression integrated the system and provided limited pathways for upward movement of ore fluids. 24 �Stop 2: Subaerial basalt lava flow, eastbound US-41 Houghton Latitude: 47.12144N; Longitude: -88.56474W Directions: Drive west through downtown Houghton and loop around (Yooper Loop) to head east for 0.8 miles along US-41 or Montezuma Avenue (one-way two-lane highway). Stay left (north side) as though going back through downtown and turn into unmarked gravel lot just before large outcrops on left (north). Use sidewalk to walk to outcrop. BE CAREFUL OF TRAFFIC. The rock cut at the southeast end of downtown Houghton provides an excellent example of the characteristics of Portage Lake Volcanics subaerial basalt lava flows (Figure 14). There is a sidewalk providing access to the Stop 2 south-facing road cut. While there is also a sidewalk on the other side of the road crossing the road is discouraged. These other outcrops can be accessed by parking uphill from them on the other side of the road. There are also north-facing exposures of this same stratigraphic interval on west bound US-41 (Shelden Avenue) east of the Houghton U.S. Post Office. The exposures at Stop 2 are located stratigraphically above the Scales Creek flow and below the Kearsarge flow, slightly closer to the Scales Creek flow (Figure 6). The lava flows of the exposure and vicinity strike approximately N30oE and dip toward the center of the rift (Lake Superior) at about 55o northwest (White, 1956). Figure 14: Geologic cross section of road cut eastbound US-41, southeast end of downtown Houghton. There are parts of two lava flows exposed at Stop 2 (Figure 14). The base of the stratigraphically lower of these two lava flows (A) is not exposed on the east end of the Stop 2 exposures. It is also not exposed on the other side of the road. The top of Flow A is well exposed and is overlain by massive basalt of Flow B. The contact itself is denoted by an abrupt change from underlying highly altered greenish, slightly brecciated amygdaloidal basalt of Flow A (about 0.5 m thick) that is overlain by massive dark grey to black basalt of Flow B. This greenish zone of the top of Flow A is underlain by about 3.5 m of amygdaloidal basalt with slightly fragmental (brecciated) basalt, also Flow A. The slightly fragmental basalt is gradational downward (east) towards the center of Flow A where the abundance of amygdules (filled vesicles) is sufficient to call the rock amygdaloidal basalt. Amygdaloidal basalt lacking fragments is about 4 m thick. There is an arbitrary boundary where the 25 �abundance of amygdules is too low to call the rock amygdaloidal, although it contains some amygdules. The abundance of amygdules progressively decreases towards the center of Flow A, the porous and permeable top of Flow A is about 8 m thick. Flow A is greater than 14 m thick as its base is not exposed. Notably, flattened amygdules (vesicles) occur along planar layers in the flow A top with their orientation roughly parallel to the top of the flow. Larger flattened amygdules are about 2 by 2 by 1 cm and between them, appearing to connect larger amygdules, are much smaller amygdules 1 to 2 mm thick. The orientation of these layers may represent laminar flow planes within the flow top. Layers of flattened amygdules are also numerous at Stop 1. Flow A is overlain by Flow B and the top of Flow B is not exposed at Stop 2. However, its top is poorly exposed on the other (south) side of the road. Flow B is about 30 m thick. There is a pegmatoid layer in the massive basalt interior of Flow B (Figure 14). Flow B is thicker than the average flow. The pegmatoid is distinguished as notably amygdaloidal. Pegmatoids are discussed further at Stop 1. The effects of regional hydrothermal alteration can be observed within the top of Flow A and the pegmatoid layer in Flow B. The massive basalt interior of Flow A and B are much less altered than the flow top. However, the primary magmatic plagioclase in the massive basalt has been replaced by albite and the primary mafic minerals are replaced by chlorite, pumpellyite, and iron oxides. The intensely altered basalt at the very top of Flow A is largely replaced by hydrothermal alteration minerals including epidote, prehnite, pumpellyite, quartz, chlorite, calcite, and trace native copper. Amygdules are frequently filled with colorless to white quartz. a mixture of prehnite pumpellyite and quartz, a mixture of pumpellyite, a mixture of quartz with lesser calcite, only quartz, and only pink inclusions of native copper in milky or colorless quartz. There is visible native copper in some amygdules. The massive interior of the flow is much less altered than the flow top and represents a relatively impermeable horizon in the paleohydrothermal system. In contrast, the flow top was a pathway for movement of hydrothermal fluids. 26 �Stop 3: Overview at Bumbletown Hill Latitude: 47.290100N; Longitude: -88.417250W Directions: From Portage Lift Bridge follow US-41 towards Copper Harbor and proceed through Calumet towards Allouez for about 15.5 miles to Bumbletown Road. Turn left (west) and proceed one mile up to the top of Bumbletown Hill via Cedar Street. Walk around outside of communication tower fence to get excellent views as described below. Figure 15: Geologic sketch map of Bumbletown Hill modified from White (1971). From the overlook on a clear day, Isle Royale may be seen 80 km to the northwest and the Huron Mountains may be seen beyond Keweenaw Bay, 60 km to the southeast. From the top of Bumbletown Hill the land slopes very gradually to the northwest toward Lake Superior. This slope is similar throughout much of the northwestern side of the Keweenaw Peninsula. The area is underlain mainly by conglomerates and sandstones of the Copper Harbor Conglomerate dipping at about 20 to 30 degrees NW. The southeastern flank of the Keweenaw Peninsula has a steeper slope at the skyline, following approximately the line of the Keweenaw fault. The low-lying plain between the fault and Keweenaw Bay is underlain by flat-lying Jacobsville Sandstone. Next to the Keweenaw fault beds of the Jacobsville Sandstone can be steeply dipping. Looking northeast along the strike of the Portage Lake Volcanics, one can see the cuesta form of the ridge underlain by the Greenstone flow. At Bumbletown Hill, the Greenstone flow is only 75 m thick (Figure 15), but the flow thickens abruptly to more than 400 m near this end of the cuesta ridge. The Greenstone flow dips northward at about 25o toward the center of the Lake Superior. It can be traced along much of the Keweenaw Peninsula (Figure 6) and has been stratigraphically and 27 �geochemically correlated with a similar unit on Isle Royale, 90 km away, on the opposite side of the rift. Thus, the areal extent of this great flow exceeds 5,000 km2, and its volume is on the order of 800 to 1,500 km3 (Longo, 1983; White, 1960). The Greenstone Flow is an enormous lava flow. It is possible that rather than having been a lava flow the Greenstone Flow was a lava lake. Regardless, the Greenstone Flow perhaps is the greatest single continuous outpouring of lava on Earth. Very slow solidification of this great mass of magma allowed extensive in-situ magmatic differentiation (Cornwall (1951a, 1951b). Magmatic differentiation resulted in a massive, ophitic (lath-shaped plagioclase surrounded by large irregular masses of clinopyroxene) base of the flow; an overlying zone of intercalated subophitic and pegmatoidal layers; an upper ophitic zone; and a finegrained, vesicular flow top. The lower ophitic zone experienced rates of undercooling low enough to allow growth of clinopyroxene oikocrysts up to 5 cm in diameter. The geochemical composition of the Greenstone Flow magma is more evolved than typical olivine tholeiites; which constitute the greatest volume of the Portage Lake Volcanics. Primitive olivine tholeiite and quartz tholeiite occur between the Greenstone Flow and the top of the Portage Lake Volcanics. Generally, magmas of the Portage Lake Volcanics become more primitive and less crustal contamination with time during the development of the Midcontinent Rift (Paces, 1988). At Bumbletown Hill, the Greenstone Flow is only 75 m thick and is composed of a thick amygdaloidal flow top with some exposures of fine-grained columnar basalt. To the left of the cuesta ridge the rocks consist of the top of the Portage Lake Volcanics and the bottom of the Copper Harbor Conglomerate. To the right of the ridge, the more distant hills are formed by lava flows near the base of the Portage Lake Volcanics. Bumbletown Hill is located on the southwest side of Allouez Gap, a NW- to SE-trending valley (see Figure 7). The valley follows the Allouez Gap fault, a zone of faults and fractures, along which the Portage Lake Volcanics and Keweenaw fault, are offset. At this gap, the strike of the Portage Lake Volcanics swings from about N35oE to N50oE (Figure 7). Almost every permeable horizon near the Allouez Gap fault contains above average amounts of native copper; nowhere else in the district are there so many mineralized beds (Figure 7). About 60% of the district production can be linked to the fault as a primary pathway for ore fluids. The fault bisects the Kearsarge deposit (see Figure 16), which was the second largest copper producer in the native copper district. There was a readily visible line of poor rock piles, a little more than 1,500 m southeast of Bumbletown Hill, from the many mines which were producing native copper from the Kearsarge deposit. Many of these piles are now gone as they have been crushed for aggregate. The line is still visible in the fall when leaves are not on the trees. About 1,200 m N65oE of the hilltop, the Houghton conglomerate and the stratigraphically lower Iroquois flow produced 33 million pounds of copper. East of Bumbletown Hill but no longer visible is the Kingston Mine, one of the most recent native copper mines to open and last to close. It was discovered by exploration near the Allouez Gap fault. It only produced 20 million pounds of copper from 1963 to 1968. 28 �Stop 4: Interflow Conglomerate at Bumbletown Hill Latitude: 47.287136N; Longitude: -88.415365W Directions: From top of Bumbletown Hill turn around and head downhill 0.5 miles to pull over on left just before dirt road. Specimens of Allouez Conglomerate are scattered about the southeast flank of base of Bumbletown Hill. The remnants of Allouez Conglomerate poor rock piles are private property (Figure 15). Near this pullover there is the opportunity to collect specimens of the Allouez Conglomerate. The Allouez Conglomerate is one of a small number of interflow clastic sedimentary horizons within the Portage Lake Volcanics and is visible on the lower slopes southeast of Bumbletown Hill. Conglomerate layers within the Portage Lake Volcanics are important stratigraphic marker horizons (Figure 6). Correlation of basaltic lava flows along strike would be difficult without clastic sedimentary marker beds deposited during periodic waning of volcanism. The Allouez Conglomerate can be traced more than 120 km along strike from Mass to Delaware (Figure 6). The Allouez conglomerate is just below the Greenstone flow. At Bumbletown Hill the Allouez Conglomerate was mined for native copper (Figure 15) albeit it only yielded about 75 million lbs of refined copper (Table 2). Elsewhere the Allouez Conglomerate has yielded additional native copper. The Allouez Conglomerate consists of mostly red-colored conglomerate with lesser amounts of sandstone and siltstone. The largest clasts at this locality are about 65 cm in diameter and the median size is about 8 cm. A pebble count of boulders more than 20 cm across by White (1971) gave the following results: 16% basalt, mostly amygdaloidal; 36% quartz porphyritic rhyolite; 11%, feldspar porphyritic rhyolite; and 37% felsic granophyre. The Houghton Conglomerate is almost entirely clasts of quartz porphyry as is the Kingston Conglomerate. There are conglomerates within the lower Portage Lake Volcanics near the tip of the Keweenaw Peninsula whose clasts are clearly sourced from an extrusive dome of rhyolite. This could be the explanation for the uniformity of clasts in the Houghton and Kingston Conglomerates. In contrast, the heterogeneity of the Allouez Conglomerate clasts suggests a less restricted source area (White, 1971). Evidence of native copper mineralization can be seen in some rocks of the Allouez Conglomerate at nearby this stop. Occasionally, one can find a specimen with native copper filling the void space between clasts and grains. Calcite and chlorite are the dominant pore-filling secondary minerals visible on this rock pile. Thin black veinlets cutting the Allouez conglomerate consist of calcite with chalcocite “dust.” Chalcocite is a product of late- stage hydrothermal fluids. Supergene alteration resulting from the downward percolation of groundwater is not common at depth in most the native copper deposits. Supergene alteration products are likely common when native copper ore bodies are at or very near the surface. At this stop, supergene alteration minerals are common including chrysocolla, malachite, and cuprite. The depth of occurrence is unknown although given the widespread distribution in rocks of the poor rock piles it seems likely at least some supergene alteration occurred at depth as documented elsewhere. The occurrence of supergene alteration minerals at depth in the native copper mines was used by Bornhorst and Robinson (2004) to hypothesize that at least some supergene alteration was Precambrian in age. 29 �Stop 5: Seneca Mine Rock Pile Latitude: 47.311915N; Longitude: -88.365818W Directions: At the intersection of Bumbletown Road and US-41, turn left (northeast). Drive about 2.9 miles almost through Mohawk to 1st Street when you will turn left (northwest). Proceed on 1st Street/Seneca Location Road 0.3 miles to gated road. Walk to rock piles. THIS STOP IS ON PRIVATE PROPERTY. PLEASE GET PERMISSION TO ENTER PROPERTY. The Kearsarge lode was worked by the Seneca Mine, one of multiple mines which produced native copper from the top of the Kearsarge lava flow over a strike length of more than 12 km and downdip as much as 2,500 m (Figure 16). About 1,026 million kg of refined copper were produced at an average grade of 1.05% Cu, making the Kearsarge deposit the largest flow top hosted deposit and the second largest producer in the district behind the Calumet & Hecla Conglomerate mines (Table 2). Production of copper from the Kearsarge lode began in 1887 and stopped in 1967. The Kearsarge lava flow has been recognized for a distance of about 55 km along strike and dips between 35 and 40o NW (Figures 6 and 16). It lies directly above the Wolverine Sandstone (Figure 6). The amygdaloidal and/or brecciated top of the Kearsarge flow ranges from near zero up to 10 m in thickness. The productive top has an average thickness of around 2 m and consists of brecciated basalt (individual fragments of amygdaloidal basalt are generally less than 15 cm in greatest dimension). The brecciated basalt grades downward into amygdaloidal basalt with amygdules concentrated in layers. Further downward, the top grades into a zone of fewer and larger amygdules, and then into massive basalt in the interior of the flow. Just below the brecciated and/or amygdaloidal top of the flow, there is distinct plagioclase porphyritic basalt. The abundance and size of the plagioclase phenocrysts in this zone are variable, but they can make up a large percentage and phenocrysts are up to 2.5 cm in length. This zone is probably the result in situ floating of plagioclase during surface crystallization of the flow. The phenocrysts likely formed in a shallow magma chamber. Specimens with abundant plagioclase phenocrysts are common on this rock pile. The basalt of the Kearsarge flow is well oxidized. Albitized and pumpellyitized basalt consists of pseudomorphically replaced plagioclase set in a fine-grained to cryptocrystalline groundmass. Original igneous minerals were replaced in areas where alteration was intense. Olivine is almost invariably completely replaced while other igneous minerals are replaced by alteration minerals to varying degrees. The amygdule and interfragment spaces are filled with (in order of most to least abundant): calcite, epidote, K-feldspar, quartz, and lesser amounts of chlorite, prehnite, pumpellyite, laumontite, and sericite. Native copper is closely associated in time and space with the secondary amygdule minerals (Stoiber and Davidson, 1959). Paragenetically, chlorite; epidote; microcline; and prehnite are early-formed minerals, and the latest-formed minerals are quartz; native copper; calcite; and chlorite (Figure 17). A zonal stratabound arrangement of amygdule minerals in the Kearsarge deposit is seen in the Ahmeek Shaft No. 3 (Figure 18). The zoning may be explained by deposition of secondary minerals from a hydrothermal solution moving along a permeable channel. Chlorite and microcline would have been deposited first, along the outer limits of the solution channel; 30 �followed by quartz and epidote in the center of the channel; and finally, deposition of calcite in the remaining openings. This is consistent with the paragenetic relationships seen in individual samples from the rock pile. No strict correlation exists between the stratabound zoning and the grade of native-copper mineralization (Stoiber and Davidson, 1959). The amygdule minerals and grade of copper mineralization vary with depth. Within the upper limit of quartz (Figure 16), the quartz content is typically about 15 % of open space fillings although it is considerably less than 10% at shallower depths. The lower limit of microcline may also mark the limit of significant copper mineralization. The amount of native copper present is much more irregular than variation of the mineral zones. Figure 16: Thickness of the Kearsarge lava flow showing the productive area to be the thickest in the top diagram modified from Butler and Burbank (1929). The Kearsarge flow top ore body is bisected by the Allouez Gap fault. Bottom diagram shows strike parallel down-dip projection to vertical showing distribution of higher-grade native copper ore and occurrence of important alteration minerals modified from Stoiber and Davidson (1959). Abundance of quartz in amygdules is greater than 10 % on the downdip side of the line (lower) and K-feldspar is absent on the down-dip side lower line shown. The Kearsarge flow dips about 35 to 40o NW. Mine names and shaft numbers are noted. 31 �Figure 17: Paragenesis of secondary hydrothermal alteration minerals in the Kearsarge deposit at the Wolverine No. 2 Mine. Figure 18: Cross section of the top of the Kearsarge lava flow (amygdaloid) deposit showing the distribution of secondary hydrothermal amygdule-filling alteration minerals at the Ahmeek Mine, 35th level, 400 to 500 ft south of the shaft. Modified from Stoiber and Davidson (1959). Data from the back and walls are projected to a horizontal plane. There is a barren laumontite-quartz-calcite zone not shown here. 32 �The Allouez Gap Fault bisects the thickest segment of the Kearsarge Flow along its 55 km strike length (Figure 16). Higher grades and production occur northeast of the fault where fractures with orientations that parallel the fault are more abundant. Within the Allouez Gap Fault zone, early epidote and quartz were brecciated and recemented by calcite, quartz, and native copper. After another episode of brecciation, the fault zone was recemented again with calcite; quartz; and lesser laumontite (Butler and Burbank, 1929). The latter may be late-stage. Movement along the fault occurred before, during, and after deposition of native copper. The fault apparently was a conduit for transport of ore fluids to the permeable flow top. The coincidence of this fault with the relatively thick flow top resulted in the second largest deposit in the district. The Seneca Mine is an excellent locality to study the character of a representative basaltic flow top hosted native copper deposit. Specimens of massive basalt, massive basalt with abundant plagioclase phenocrysts, and amygdaloidal basalt can be found on this rock pile. Masses of native copper are readily collectable especially when using a metal detector. Open-space filling minerals (amydgules and between breccia fragments) that occur in the lode can be found on the rock pile. Stoiber and Davidson (unpublished data) made a quantitative analysis of open-space filling minerals for the Seneca Mine rock pile and found open-space filling minerals consisted of: calcite, 57%; red feldspar 8% (microcline); pink feldspar (adularia) 15%; epidote, 17%; prehnite, trace; pumpellyite, trace and quartz, trace. Many specimens contain multiple minerals and illustrate paragenetic relationships. Stop 6: Eagle River Falls Latitude: 47°24'44.9N; Longitude: - 88°17'47.3W Directions: Return to US-41 from Seneca Mine and turn left (northeast) continuing 7.2 miles to junction of US-41 and M-26. Turn left (north) on M-26 towards Eagle River and proceed 2.3 miles across bridge and immediately right after the bridge into the parking lot. The waterfalls of Eagle River are near the contact between the top of the Portage Lake Volcanics and the base of the Copper Harbor Conglomerate (Figure 5). The contact dips about 30o NNW. The beds strike roughly parallel to the shoreline of Lake Superior; the orientation of the Keweenaw Peninsula changes from NE in vicinity of Houghton to ENE at Eagle River to E-W near the tip of the peninsula. The tholeiitic basalt subaerial lava flows just below the contact are pahoehoe type with a ropy upper surface. The orientation of the ropes indicates that the flow erupted from a vent to the north geographically under Lake Superior. That the ropy flow top is preserved suggests that little erosion occurred between deposition of the last of the lava flows of the Portage Lake Volcanics and the Copper Harbor Conglomerate. The Copper Harbor Conglomerate consists of red-brown rhyolite-pebble conglomerate but includes many sandstones and even some shale beds. Under the bridge, one can get a good view of the lithology of the lower part of the Copper Harbor Conglomerate. The environmental setting of the Copper Harbor Conglomerate is discussed further at Stop 8. This contact marks an abrupt change in the geologic evolution of the Midcontinent rift. Below this contact the dominant strata is a very thick succession of subaerial basalt lava flows erupted from fissure vents under Lake Superior that filled the progressively extended and down dropped rift basin 33 �during active Midcontinent rifting. Below this contact the Portage Lake Volcanics consists of more than 200 individual lava flows with a cumulative exposed thickness of about 5,000 m; the base is fault truncated (Figure 4 and 5). Abruptly above the contact lava flows are strikingly absent and clastic sedimentary rocks are the dominant strata deposited in a sagging basin after active extension ended. The clastic sedimentary strata above this contact consists mostly of conglomerate and sandstone with a cumulative exposed thickness of more than 5,700 m; the top is not exposed (Figure 4 and 5). While generally absent, a thin package of mafic to intermediate volcanic rocks (Lake Shore Traps) deposited as a shield volcano interfingers with clastic sedimentary rocks of the Copper Harbor Conglomerate. The very last magmatic activity in the MCR is the lone Bear Lake alkaline igneous body near the middle of the clastic sedimentary strata. Stop 7: Great Sand Bay Latitude: 47. 446140N; Longitude: -88. 216411W Directions: Continue driving northeast (right from parking area) on M-26 for 4.5 miles until the Great Sand Bay paved pullover with overview and beach access. The Great Sand Bay overlook provides a beautiful view of Lake Superior (Figure 19). Very large volumes of water filled the Lake Superior basin as a result of melting of the glaciers, turning it into a glacial lake. The levels of the glacial lakes depended on the position of the ice front, outlets, and crustal rebound. There are 15 lake stages recognized in the Lake Superior basin (Farrand 1960). As the lake levels receded to the current level of Lake Superior, more and more of the Keweenaw Peninsula emerged. At the road level, the sand dunes are remains of the Lake Nipissing Stage (4,000 to 5,000 years ago) when the lake level was about 9 m (30 feet) higher than today. After lake stages at about 3,200, 2,000, and 1,000 years ago, the waters receded toward the present level termed Lake Superior. The underlying bedrock is the Copper Harbor Conglomerate. In the Keweenaw Peninsula the Lake Shore Traps are interbedded near the middle of the Copper Harbor Conglomerate (see Stop 9). The massive interiors of these lava flows are more resistant to erosion than the underlying and overlying conglomerates and sandstones of the Copper Harbor Conglomerate. As a result, harbors such as those at Eagle Harbor and Copper Harbor are maintained by lava flows visible at their mouths. While not visible, lava flows occur at the mouth of Great Sand Bay too. There are many extensive underwater fissure vein deposits which crosscut the Eagle River shoals located about 0.5 to 1 km offshore. To date, there have been a total of 36 underwater copper veins discovered from the eastern tip of Great Sand Bay (visible at this stop) to Eagle River, about 3.2 km west. Some of these submerged veins likely connect with veins recognized from on land exposures (Figure 19). The native copper that is naturally on the bottom lands of Lake Superior are grouped as “lake copper.” The largest lake copper specimen ever recovered underwater was a massive 19-ton unattached copper slab in July of 2001. It was recovered from one of these vein deposits north of Jacobs Creek in about 9 m of water. This large underwater native copper vein is on display at the A.E. Seaman Mineral Museum in the outside copper pavilion. 34 �Many of the submerged veins are often quite rich in native copper and can contain long continuous stringers protruding up to 1.5 m in height and extending almost 6 meters in length. Most of the veins are less than 50 cm in width and are primarily composed of quartz or calcite with minor amounts of laumontite, datolite, prehnite, and traces of silver. Veins will locally contain clay pockets associated with well-defined copper crystal specimens. Bornhorst and Barron (2017) provide additional information about the Guiness World record tabular 19-ton native copper mass. Figure 19. Geologic and location map of the 19-ton submerged native copper vein recovered from Great Sand Bay, Keweenaw Peninsula, Michigan (from Bornhorst and Barron, 2017). 35 �Stop 8: Copper Harbor Conglomerate, J. & M. Lizzadro Lakeshore Preserve By Daniel J. Lizzadro-McPherson Latitude: 47. 479128N; Longitude: -87.979576W Directions: Continue east-northeast on M-26 from Great Sand Bay to Eagle Harbor. Continue on M-26 towards Copper Harbor for 9.2 miles (14.8km) until the sign for the preserve appears on the lakeward side of the road. Park at the pull-off on the north-side of M-26 for beach access. PLEASE DO NOT DAMAGE THE OUTCROP. NO HAMMERS ALLOWED. COLLECTION OF BEACH ROCK ONLY. Figure 20: Overview of the J. & M. Lizzadro Lakeshore Preserve, which encompasses the entire shoreline between private properties (shaded, cross-hatched areas) along M26. The Joseph & Mary Lizzadro Lakeshore Preserve is located near the northern-most point on the Keweenaw Peninsula and is host to prominent outcrops of Copper Harbor Conglomerate, colorful cobble-pebble beaches, and iconic views of Lake Superior. This site is notable due to the diverse facies of CHC, rare occurrences of stromatolites (genus Colleria) and raindrop impressions found among the wave-washed bedrock exposures. Established as a preserve in 2003 by the Houghton Keweenaw Conservation District and the Keweenaw Land Trust, the Lizzadro Lakeshore Preserve protects over 640-feet of undeveloped shoreline and several small islands (Figure 20). The preserve showcases one of only three A-ranked Michigan occurrences of the globally rare imperilied plant community-type (G2) bedrock beaches. Thanks to a generous donation by Gina Nicholas, the preserve was named in honor of my grandparents, Joseph & Mary Lizzadro, with the hope that this significant Geoheritage site remains protected for many future generations to enjoy. 36 �The bedrock geology of the preserve consists of red-colored clastic sedimentary rocks grouped under the stratigraphic formation of the Copper Harbor Conglomerate (Figure 5). The Copper Harbor Conglomerate. ranges from 490 m thick near the Wisconsin border, to about 1,310 m thick on the Keweenaw Peninsula, reaching a maximum exposed thickness of 2,000 m on the shores of Isle Royale. Overall, the Copper Harbor Conglomerate is generally a medium reddishbrown colored wedge of fluvial siliciclastic conglomerates and sandstones that rapidly filled-in the rift basin as volcanism waned and subsequently terminated (Daniels, 1982; Cannon and Nicholson, 2000; Woodruff et al., 2020). The base of the Copper Harbor Conglomerate. locally interfingers with the uppermost subaerial basaltic lava flows of the Portage Lake Volcanics (Figure 5). Near the stratigraphic lower-third of the Copper Harbor Conglomerate there is a succession of basaltic to intermediate subaerial lava flows, informally named the Lakeshore Traps (Figure 5). Outcrops of Copper Harbor Conglomerate. exposed along the Lake Superior shoreline at the Lizzadro Lakeshore Preserve (Figure 21) are stratigraphically above Lakeshore Traps (Cornwall, 1954). Figure 11: Overview of geologic features present at the J. & M. Lizzadro Lakeshore Preserve. 37 �Nearby at well-studied Dan’s Point, outcrops of Copper Harbor Conglomerate exhibit lithologic facies that are characteristic of the upper two-thirds of the formation. The conglomeratic facies (Figures 21 and 22: Points A, C, and F) are primarily clast-supported and comprised of rounded to well-rounded poorly sorted clasts, consisting of a 2:1 silicic-to-mafic volcanic rock fragment ratio with minor pyroclastic, plutonic, and metamorphic rocks (Elmore, 1984). The conglomerate matrix is comprised of coarse sand-sized subangular grains cemented with carbonate and iron oxides. The sandstone facies (Figures 21 and 22: Points B and E) are predominantly subangular to angular, lithic graywackes which exhibit a number of sedimentary structures including: current-ripples, cross beds, and parting lineations. Many of the coarser sandstones and conglomerates in the upper section have calcite-rich cement in the matrix, consistent with a vadose or semiarid, caliche-style environment (Kalliokoski, 1986). Two noteworthy outcrop features include: 1) a thin continuous zone of laminated cryptoalgal carbonate where laterallylinked stromatolite are draped over cobbles and over contorted sandy siltstone layers (Figures 21 and 22: Point D); and 2) raindrop imprints preserved in fine- to medium-grained sandstone lenses (Figure 21: Point G). At the time of deposition, the region was nearly equatorial in geographic position and the climate was likely arid with seasonal rainfall patterns conducive to flashfloods and the development of vadose carbonate (Elmore and Vander Voo, 1982; Kalliokoski, 1986). The raindrop imprints in sandstone (Figures 21 and 22: Point G) support this paleoclimate assumption. Details surrounding the origin and depositional setting of the Copper Harbor Conglomerate and overlying Nonesuch Formation (Figure 5) have recently been reevaluated. The long-held inference of the origin for these two formations has been interpreted as a non-marine, fluvial-tolacustrine couplet (White and Wright, 1960; Elmore, 1983, 1984; Ojakangas et al., 2001). The Copper Harbor Conglomerate closely resembles modern-day examples of coalescing fluvial and prograding alluvial fan deposits with varying facies that exhibit proximal-to-distal braided streams, sheet flooding and sand flat features (Elmore, 1984). Isolated cryptoalgal carbonate and ooid lenses are interpreted by Elmore (1983) to have formed in shallow, medial fan lakes and possibly in abandoned or low-water stream channels with limited sediment input (Elmore, 1983). However, marine sedimentological features often resemble and can be easily mistaken for nonmarine features unless contextualized with additional evidence, such as isotopic geochemistry. New research presents evidence for a shallow-marine estuarine origin for at least the upper-third of Copper Harbor Conglomerate and overlying Nonesuch Formation based on new sedimentological observations (Jones et al., 2023) and geochemical analyses (Stüeken et al., 2020; Jones et al., 2020). Sedimentological observations include periodic to rhythmic flaserwavy-linsen-pinstripe bedding, superimposed sets of ripple cross-laminations with bimodal (herring-bone) sediment transport directions, desiccation cracks and hummocky crossstratification (Jones et al., 2023). Periodic to rhythmic textures are indicative of tidal-influenced marine depositional settings. Geochemical evidence indicates that gypsum evaporite fabrics have a marine sulfur isotopic composition (Stueken et al., 2020) and that pseudomorphs after gypsum formed in a saline-to-brackish waterbody (Jones et al., 2020). Both studies conclude that the upper section of the Copper Harbor Conglomerate and overlying Nonesuch formation were deposited in a braided fluvial-evaporitic, sabkha-like, tidally-influenced shallow marine embayment rather than fluvial-lacustrine non-marine depositional setting. 38 �Figure 22: Lithologic column of measured section at the Lizzadro Lakeshore Preserve (data collected by Lizzadro-McPherson, Bornhorst, and Vye (2023). Bedding about E-W strike and 35 to 40o N dip. 39 �Stop 9: Copper Harbor Conglomerate and interbedded Lakeshore Traps at Hunter’s Point Park Latitude: 47.474355N; Longitude: -87.899199W Directions: Continue driving east on M-26 for 3.7 miles to North Coast Road. Turn left (northwest) on North Coast Road and proceed 0.3 miles to Harbor Coast Lane. Turn right and drive 0.3 miles to the parking area for Hunter’s Point Park at end of the road. Figure 23: Geologic map of the Copper Harbor area taken directly from Cornwall (1955) showing the location of Hunter’s Point (Stop 9) and Brockway Nose (part of Stop 10). Geology from Cornwall (1954). Hunter’s Point Park was established in 2005 when funding provided by the Michigan Natural Resources Trust Fund and many generous private donors (www.hunters-point.org) allowed the land to be purchased (Figure 23). Prior to becoming an official park the point was a popular hiking destination for visitors. The landowners subdivided the area for residential housing which would have restricted public access without its conversion into a park. The origin of the name Hunter’s Point is uncertain, but it could have been named after A.W. Hunter, an early resident in the town of Copper Harbor who purchased the point from the U.S. Government. The Copper Harbor Conglomerate is overall composed of volcanogenic clastic sedimentary rocks, dominantly conglomerates with lesser sandstone, siltstone, and shale such as observed at Stop 8. These rocks were deposited in a fining upward prograding alluvial fan complex (Elmore, 1984). Typically conglomerates are composed of clasts with a ratio of mafic-tointermediate+felsic composition of about 2:1 (Daniels, 1982). Towards the tip of the Keweenaw Peninsula, the Copper Harbor Conglomerate is informally subdivided into an inner (land side) “member” and an outer (lake side) “member.” Between these two “members” there is a thin 40 �succession of interbedded lava flows collectively known as the Lake Shore Traps (Figure 23). The Lake Shore Traps consist of Fe-rich olivine tholeiite, basaltic andesite, and andesite lava that were erupted during a time of waning volcanism within the MCR at 1087.2 +/- 1.6 Ma (Davis and Paces, 1990). The thickest section of the Lake Shore Traps is about 15 km to the east at the tip of the peninsula. Volcanologically, the lower lava flows are interpreted as erupted as ponded sheets while the upper lava flows erupted on a low positive slope such as a shield volcano. The Lake Shore Traps were subaerially erupted pahoehoe lava flows. At Hunter’s Point, the top of the andesitic lava flows of Lake Shore Traps are conformably overlain by conglomerates of the Copper Harbor Conglomerate (Figure 23). The strike of bedding is about E-W and dip is about 36o to the north (towards the lake). The orientation of the contact is roughly parallel to the orientation of Hunter’s Point. From the Hunter’s Point parking lot, follow the walkway to beach towards the west side of the point. As the walkway ends, you will be on outcrops of lava flows of the Lake Shore Traps. Walking to the east, the beach gives way to a rocky shoreline. In erosional coves, you can see contacts between lava flows, represented by vesicular to amygdalodoidal andesitic lava flow top overlain by massive interior of the overlying lava flow. The massive lava flow interiors within the Lake Shore Traps often retain relict olivine and interstitial glass due to the overall low degree of alteration (hydrothermal and weathering). In contrast, in massive lava flow interiors within the Portage Lake Volcanics the olivine and interstitial glass are completely replaced by Mg-Fe phyllosilicates and amygdule filling minerals are equivalent to higher degree of metamorphism. Secondary minerals filling amygdules include agate, chalcedony, quartz, laumontite, analcite, calcite, and smectite. The Lake Shore Traps are geographically more distal to the thermal high and increased hydrothermal activity that resulted in the native copper deposits, hence, lower degree and grade of burial metamorphic/hydrothermal alteration. Highly visible red hematitic bands form circular patterns within the massive interior; this banding is interpreted to be the result of alteration related to weathering rather than hydrothermal fluids. To the west from the walkway, you can see a rocky point extending towards Lake Superior, the rocks in this point are conglomerates of the Copper Harbor Conglomerate. The sharp contact between the uppermost lava flow of the Lake Shore Traps and the conglomerates can be viewed on the eastern edge of this rocky point. The conglomerate above the contact is dominated by rounded to sub-rounded boulders that are matrix-supported. There are proportionately more basaltic and andesitic clasts in this conglomerate bed than stratigraphically higher elsewhere along the Lake Superior shoreline such as at Stop 8 as these clasts are likely derived from erosion of strat equivalent to the Lake Shore Traps updip towards the highlands of the Keweenaw Peninsula on the edge of the rift (the updip rocks are now missing having been removed by erosion). The very poor sorting and fine matrix-supporting the clasts suggest this conglomerate could have been deposited as a debris flow. Sedimentary debris flows are common in alluvial fan depositional environments. The Copper Harbor Conglomerate was deposited in an alluvial fan derived from highlands to the southeast in the vicinity of Keweenaw Bay. 41 �Additional outcrops of the Copper Harbor Conglomerate can be seen on the far western end of the pebble to cobble beach. These outcrops consist of interbedded conglomerates and sandstone that are typical of the formation as a whole. These conglomerates are similar to those described at Stop 8. There are several prominent, white-colored calcite-filled fractures (calcite veins) within these outcrops. The calcite veins are northerly oriented consistent with the orientation of faults cutting the Portage Lake Volcanics about 5 km to the south. Calcite veins are a common occurrence in the Copper Harbor Conglomerate and some of them contain native copper such as those described at Stop 7, Great Sand Bay. Stop 10: Overview at Brockway Nose Latitude: 47.467061N; Longitude: -87.898581W Directions: Return from Hunter’s Point to M-26. Turn left on M-26 towards Copper Harbor and drive 0.3 miles (0.5km) to Brockway Mountain Drive. Turn right, uphill, on Brockway and proceed 0.6 miles (1.0km) to Brockway Nose pullover on the left. Brockway Nose provides an excellent view of Copper Harbor and Lake Fanny Hooe (Figure 23). Copper Harbor and several other harbors between here and Eagle River have the Lake Shore Traps at the harbor entrance as the dipping massive interiors of these basaltic to andesitic lava flows are relatively more resistant to erosion. From Brockway Nose viewpoint, the town of Copper Harbor is a prominent visible feature. The town of Copper Harbor began as a boom town in 1843, following the nearby discovery of native copper. Porter's Island, at the mouth of Copper Harbor on the west side of the harbor's Lake Superior entrance (left) was the site of the first government land office. Hunter's Point is west of Porter's Island (Figure 23). On the east side of the mouth of Copper Harbor, the Copper Harbor Lighthouse, built in 1866, is visible. Near the lighthouse on the Lake Superior shoreline is the famous "green rock". The "green rock" is a vein that was described by Douglass Houghton. The vein contained native copper and secondary copper alteration minerals. This location and others in the Keweenaw Peninsula became the foundation of the geological investigations of Douglass Houghton. Houghton's report to the Michigan legislature that sparked the first major mining rush in North America to the Keweenaw Peninsula. Lake Fanny Hooe is located southeast of Copper Harbor. Fort Wilkins is located on the north shore of Lake Fanny Hooe on the thin strip of land between the lake and harbor. Nearby, the Estivant Pines is a 0.8 mi2 nature sanctuary established in 1973, containing one the last stands of virgin white pines in the Midwest and the last stand in the Upper Peninsula. Some of the trees are up to 600 years old (www.michigannature.org). In 1955, the white pine was designated the state tree of Michigan. 42 �Stop 11: Overview at Brockway Mountain Latitude: 47.464260N; Longitude: -87.969506W Directions: Continue uphill and towards Brockway Mountain for 3.4 miles (5.5km). The top of Brockway Mountain is accessed by continuing upwards from Brockway Nose. Brockway Mountain is a conglomerate ridge that reaches an elevation of over 400 m, with excellent views of the ridge and valley topography of the northern shore of the Keweenaw Peninsula. At Brockway Mountain, the Lake Superior shoreline is oriented about east-west From the Brockway Mountain viewpoint there are an excellent 360o views. Underfoot, the Copper Harbor Conglomerate dips about 20o to the north. Near the base of the ridge on the south side, opposite Lake Superior, there is an exposure of a single basaltic lava flow erupted as part of the Lake Shore Traps. With care, at the southwest end of the rock wall, one can view the dipping conglomerates of the Copper Harbor Conglomerates and see the lava flow near the base of the ridge. To the west, the Lake Shore Traps form island chains and a prominent ridge in the vicinity of Agate Harbor and Esrey Park. The ridges of the Lake Shore Traps and Copper Harbor Conglomerate along the Keweenaw Peninsula’s north shore are also the site of numerous shipwrecks. Lake Bailey (with the small island) and Lake Upson occupy a topographically low valley underlain by a finer-grained clastic horizon (sandstone and siltstone) within the Copper Harbor Conglomerate which was easier to erode by the glaciers than conglomerates. Just to the south of Lake Bailey, is the ridge of Mt. Lookout, marking the contact between the basal conglomerates of the Copper Harbor Conglomerate and the uppermost basalt lava flows of the Portage Lake Volcanics. This contact was viewed at Stop 6. The inland lake almost directly south, is Lake Medora, and just before the lake is a prominent ridge which marks the stratigraphic position of the Greenstone flow as also seen at Stop 3. In the distance, farther to the south across Lake Medora, is Mount Bohemia, a dioritic stock-sized intrusion within the lower section of the Portage Lake Volcanics. To the southwest, a distant ridge is Gratiot Mountain, which is a small shallow rhyolite intrusive body that cuts the Portage Lake Volcanics. To the east are the communities of Copper Harbor and Lake Fanny Hooe not easily viewed from Brockway Mountain (better viewed from Brockway Nose). Just south of Copper Harbor is a golf course that is part of Brockway Mountain lodge. Brockway Mountain lodge was built during the Great Depression in the 1930’s by the WPA. To the north, Lake Superior is the prominent feature. On the skyline roughly 50 miles (80km) away, is Isle Royale National Park, which can be visible on a clear day. The skyline of Isle Royale is formed by the Greenstone Flow, as it is on the Peninsula. The beds on Isle Royale dip towards the Keweenaw Peninsula forming the Lake Superior “syncline.” Viewed from here, the Midcontinent 43 �Rift proper extends from the Keweenaw Fault, near the edge of the rift, just south of Mt. Bohemia to the Isle Royale Fault, also originally a graben bounding fault on the edge of the rift on the other side of Lake Superior, just northwest of Isle Royale. Glacial erosion exposed Keweenawan and pre-Keweenawan relatively hard and competent bedrock on the edges of the MCR. Dipping well-cemented conglomerates of the Copper Harbor Formation are exposed at Brockway Mountain and basaltic lava flows of the Portage Lake Volcanics are exposed when viewing south. Both are relatively resistant to glacial erosion. On Isle Royale, on the southeast (Keweenaw side) are exposed the same conglomerates of the Copper Harbor Formation and on the northwest side, there are exposed basaltic lava flows of the Portage Lake Volcanics. In the center of what is now Lake Superior, much less competent, nearly flat lying, very fine sandstone and siltstone of the Freda Formation was at the bedrock surface. The latest glacial advance(s) preferentially eroded out the less competent rocks in the center of the rift, resulting in present day Lake Superior following the horseshoe shape of the 1.1 billion year old MCR. Very large volumes of water filled the Lake Superior basin as a result of melting of the glaciers, turning it into a glacial lake. The Duluth Glacial Lake was the largest of these glacial lakes and only elevations above roughly 400 m (1,300 ft) were emergent such as here at Brockway Mountain and the visible Mt. Bohemia. Stop 12: Float Copper at US-41 Calumet Latitude: 47.241989N; Longitude: -88.448427W Directions: Follow US-41 from Copper Harbor to Calumet. Across the street from the headquarters of the Keweenaw National Historical Park. Google Maps shows the float copper as “Float copper memorial.” Figure 24: Float copper exhibit along US-41 near headquarters of the Keweenaw National Historical Park. 44 �A glacially transported native copper mass is on exhibit at this stop (Figure 24). It weighs 4,263 kg (9,392 lbs) and was found about 7 miles SW of Calumet in less than three feet of surficial sediment/soil. Native copper deposits of the Keweenaw Peninsula were exposed at the bedrock surface at the time of Pleistocene glaciations. The glacial ice entrained masses laying at the surface from previous erosion and plucked masses of malleable native copper from the tabular lodes and veins/fissures. These originally irregular masses were largely cleaned of other minerals and were smoothed and flattened by abrasion from other rocks carried by the glacial ice. The native copper masses were "floating" in the glacial ice, hence locally called “float” copper. When the glaciers retreated about 10,000 years ago, unconsolidated rock debris was left behind by the melting ice as deposits of gravel, sand, and clay. Masses of native copper were scattered among the other sediments carried by the glacier. While some of the rocks in the glacial deposits are from far north of the Keweenaw Peninsula, most of them are recognizable as from local strata exposed in the Keweenaw Peninsula. Most of the large float copper masses did not move far from their bedrock source in the Keweenaw Peninsula, but smaller masses have been transported quite far and have been found southward in Lower Michigan, Indiana, and Illinois (Bornhorst, 2017). The largest known float copper was discovered in the early 2000s and weighed about 35 tons (~70,000 lbs) near the Houghton County airport; it was cut into smaller masses and sold to be smelted and refined. Most pieces of float copper are small, ranging from a few to 50 cm across. The world’s largest existing float copper weighs 26.6 tons (53,200 lbs) was discovered on Quincy Mine claims near Hancock. It is exhibited at a museum in China. The famous Ontonagon boulder was a 1,700 kg (3,708 lbs) float copper mass much smaller than the float copper on exhibit at this stop. The Ontonagon boulder was visited by numerous early European explorers. After Michigan became a territory, Henry Rowe Schoolcraft led an expedition in 1820 with a special goal of seeing the Ontonagon boulder. In 1831, Douglass Houghton accompanied Schoolcraft and visited the boulder too. Pieces of native copper were hacked off of the boulder by Houghton and one of these pieces is part of the University of Michigan mineral collection held by the A. E. Seaman Mineral Museum under the Michigan Mineral Alliance. The Ontonagon boulder was removed from the Keweenaw Peninsula to the nation’s capital in 1843 and is now part of the National Museum of Natural History, Smithsonian Institution’s collection. Float copper masses were altered by oxygenated groundwater and precipitation since the glaciers retreated. Many masses likely had smoothed fresh copper surfaces as abrasion in the glacial ice cleaned off and smoothed the surfaces. The alteration of these surfaces would have occurred in the last 10,000 years. This supergene alteration produced a surface coating on the native copper consisting of varying amounts of cuprite (copper oxide; Cu2O), tenorite (copper oxide; CuO), malachite (hydrated copper carbonate; (Cu2(CO3)(OH)2) and rarely azurite (hydrated copper carbonate, (Cu3(CO3)2(OH)2) (Figure 24). When small 10s of cm sized masses of float copper are cut, the typical surface alteration is often less than several mm thick. While native copper is not stable in contact with water at typical oxidizing surface conditions, the coating of copper oxides, in particular cuprite, inhibits surface oxidation and thereby protects the native copper from extensive alteration. An open access article provides more about float copper (Bornhorst, 2017). The basalt mine rock buildings are part of the Keweenaw National Historical Park. They were once all part of the Calumet and Hecla Mining Company (Bornhorst and Molloy, 2017). The Calumet and Hecla Mining Company was incorporated in 1871 as a consolidation of the Calumet 45 �(formed in 1865), Hecla (formed in 1866), Portland, and Scott Mining Companies. The buildings are built, as are many of the buildings, of local materials, including rock from the Calumet & Hecla Mining Company mines. The national park was established on October 27, 1992, by U. S. Congress Public Law 102-543. The enabling legislation ascertained that the Keweenaw was nationally significant because of its unique geology, the prehistoric use of its copper by Native Americans, the importance of the region as a past leading copper producer and developer of new technologies, its long history of corporate paternalism, and because it became home to so many European ethnic groups that immigrated to the United States. Older mining districts, such as the Keweenaw Peninsula, typically had only single-industry economies and when the mines shut down, the communities suffered major contraction. In 1910, nearly 40,000 people resided within a few miles of this stop whereas now, fewer people live in all of Houghton County. Behind the float copper stands the statue of Alexander Agassiz. Alexander was the son of famous Harvard biologist Louis Agassiz. Alexander was the president of the Calumet & Hecla Mining Company for over 40 years. The statue was moved here from its previous location near Agassiz Park near downtown Calumet in the 1960s. It now stands in front of the Keweenaw History Center, the location of the archives of the Keweenaw National Historical Park. This building was the Calumet & Hecla Library. It is said that at one time this library had more volumes in its collection than the Michigan State Library. Built in 1898, it served as an employee library and bathhouse. The baths were in the basement, until a new bathhouse was constructed in 1911 allowing the basement to be remodeled into additional library space. Stop 13: Freda Sandstone at McLain State Park Latitude: 47.238371N; Longitude: -88.613116W Directions: Follow US-41 to M-203 to McLain State Park. There is an entrance fee. From the pay station turn right towards the campground. Park near the large open area and walk towards the covered shelter and gazebo. Walk down a sandy slope from the gazebo to the lake shore and look around for blocks and slabs of red-colored sandstone. The Freda Sandstone is generally poorly exposed in the Keweenaw Peninsula except for numerous cliff exposures along the shore of Lake Superior southwest of this stop. At this stop, depending on the level of Lake Superior, slabs and blocks of Fred Sandstone can be found along the beach. If the lake level is low enough, then at the shoreline the bedrock of the Freda Sandstone is partially exposed in shallow water and just off shore. The Freda consists of red-colored fine sandstone and siltstone. The red is interrupted by whiteish reduced zones and spots. There are occasional outcrops of Freda Sandstone landward of the Lake Superior shoreline in the area north and south of Portage Channel which are shown on U.S. Geological Survey geologic quadrangle maps and generally located along creeks (Cornwall and Wright, 1956). There are good exposures of Freda Sandstone on the Lake shore between McLain State Park and Porcupine Mountains State Park. The bedding of the Freda at McLain State Park dips about 5OW as compared to the underlying Nonesuch at Hancock Campground and boat launch (Stop 14) where it dips 25OW. This shallowing of dip up-section is typical of the rift-filling strata, and is mostly due to syn-depositional down warping of the rift-filling strata. The Freda Sandstone is generally fine sandstone which is interpreted to have been deposited in a shallow fluvial environment. 46 �There are multiple excellent well-described stops in the vicinity of White Pine, Michigan to examine the Freda Sandstone and these stops are well described by Woodruff et al. (2013). Stop 14: Nonesuch Formation at Hancock Campground and Boat Launch Latitude: 47.133755N; Longitude: -88.620581W Directions: Follow US-41 to M-203 to Hancock Boat Launch and Campground. Drive towards the boat launch and park. At the shoreline you will find a small outcrop of Nonesuch Formation. Walk towards the tree area approximately perpendicular to the Portage Canal shore line and boat launch. About 150 ft from the pavement, you will find the long ago abandoned rock quarry. The Nonesuch Formation is generally poorly exposed in the Keweenaw Peninsula. At this stop the Nonesuch Formation crops out around the margin of a historic rock quarry which is northeast of the Hancock boat launch. Here the Nonesuch Formation is a fine- to-medium grained, gray-to reddish brown sandstone with subordinate interbedded reddish-brown laminated siltstone and shale. The attitude of bedding is about N30OE and 25OW (Cornwall and Wright, 1956). Overall, the Nonesuch Formation consists primarily of siltstone and shale with subordinate amounts of sandstone. At Hancock campground area the formation is coarser grained since this locality is on the northern fringe of the depositional basin centered some 60 km southwest of this stop near White Pine, Michigan. The Nonesuch can be distinguished from the formations below and above by its generally grayish color. Most Nonesuch is a ripple, laminated siltstone with reddish-gray partings. Siltstones and sandstones of the Nonesuch are composed of around 30 to 40 % rock fragments and 60 to 70 % mineral grains. The rock fragments are mostly volcanic with a 2:1 ratio of mafic-tosilicic + intermediate composition (Daniels, 1982). There are multiple excellent well-described stops in the vicinity of White Pine, Michigan to examine the Nonesuch Formation and these stops are well described by Woodruff et al. (2013). Acknowledgments I thank Allan Blaske for his review of this field guide. His comments made this a better guide. References Cited Blattler, C.L., Bergmann, K.D., Kah, L.C., Gomez-Perez, I., and Higgins, J.A., 2020 Constraints on Meso-Neoproterozoic ancient evaporite deposits: Earth and Planetary Science Letters, 532:115951. Bodden, T.J., Bornhorst, T.J., Bégué, F., and Deering, C., 2022, Sources of hydrothermal fluids inferred from oxygen and carbon isotope composition of calcite, Keweenaw Peninsula native copper district, Michigan, USA: Minerals, v. 12, 474. https://doi.org:10.3390/min12040474 47 �Bornhorst, T.J., 2022, Evolved seawater as the source of salinity for metamorphic-dominated ore-forming hydrothermal fluids of the Keweenaw Peninsula native copper district, Michigan: 67th Institute on Lake Superior Geology Proceedings, v. 67, Part 1, Program and Abstracts, p. 5-6. Bornhorst, T. J., 2017, Float copper, Keweenaw Peninsula, Michigan: A. E. Seaman Mineral Museum, Web Publication 3, 4p. Bornhorst, T.J., 1997, Tectonic context of native copper deposits of the North American Midcontinent Rift system: Geological Society of America Special Paper 312, p. 127-136. Bornhorst, T. J. and Barron, R. J., 2017, Discovery and geology of the Guinness world record Lake Copper, Lake Superior, Michigan: A. E. Seaman Mineral Museum, Web Publication 2, 8 p. Bornhorst, T.J. and Barron, R.J., 2013, Geologic overview of the Keweenaw Peninsula, Michigan: 59th Institute on Lake Superior Geology Proceedings, Part 2, Field Trip Guidebook, v. 59, p. 1-42. Bornhorst, T.J., and Barron, R.J., 2011, Copper deposits of the western Upper Peninsula of Michigan: Geological Society of America Field Guide, v. 24, p. 83-99. Bornhorst, T. J., and Lankton, L. D., 2009, Copper mining: A billion years of geologic and human history: in Schaetzl, R., Darden, J., and Brandt, D. (eds.), Michigan Geography and Geology, Pearson Custom Publishing, New York, p. 69-90. Bornhorst, T.J. and Mathur, R., 2018, Copper isotope constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA: Reply. Minerals, v. 8, 508. https://doi.org:10.3390/min8110508. Bornhorst, T.J. and Mathur, R., 2017, Copper isotope constraints on the genesis of the Keweenaw Peninsula native copper district, Michigan USA: Minerals, v. 7, p. 185, https://doi.org:10.3390/min7100185 Bornhorst, T.J., Paces, J.B., Grant, N.K., Obradovich, J.D., and Huber, N.K., 1988, Age of native copper mineralization, Keweenaw Peninsula, Michigan: Economic Geology, v. 83, p. 619-625. Bornhorst, T. J. and Robinson, G.W., 2004, Precambrian aged supergene alteration of native copper deposits in the Keweenaw Peninsula: Michigan: 50th Institute on Lake Superior Geology Proceedings, part 1, Program and Abstracts, v. 80, p. 40-41. Bornhorst, T.J., and Rose, W.I., Jr., 1994, Self-guided geological field trip to the Keweenaw Peninsula, Michigan: 40th Institute on Lake Superior Geology Proceedings, Part 2, Field Trip Guidebook, v. 40, 185 p. Bornhorst, T.J., Rose, W.I., Jr., and Paces, J.B., 1983, Field guide to the geology of the Keweenaw Peninsula, Michigan: 29th Institute on Lake Superior Geology, Part 2, Field Trip Guidebook, v. 29, 116p. Bornhorst, T.J. and Williams, W.C., 2013, The Mesoproterozoic Copperwood Sedimentary Rock-Hosted Stratiform Copper Deposit, Upper Peninsula, Michigan. Economic Geology, v 108, p. 1325-1346. 48 �Bornhorst, T.J. and Molloy, L.J, 2017, Geological and historical field trip to the Keweenaw Peninsula, A tribute to Douglass Houghton, Michigan’s Pioneer Geologist: Michigan Basin Geological Society, Geological and Historical Excursion, September 10th-12th, 89p. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenaw: Geological Society of America Bulletin, v. 46, p. 503-558. Broderick, T.M., 1931, Fissure vein and lode relations in Michigan copper deposits: Economic Geology, v. 26, p. 840-856. Broderick, T.M., and Hohl, C.D., 1935, Differentiation in traps and ore deposition: Economic Geology, v. 64, p. 342-346. Brown, A.C., 2006, Genesis of native copper lodes in the Keweenaw Peninsula, Northern Michigan: A hybrid evolved meteoric and metamorphogenic model: Economic Geology, v. 101, p. 1437–1444. Butler, B.S., and Burbank, W.S., 1929, The copper deposits of Michigan: U.S. Geological Survey Professional Paper 144, 238 p. Cannon, W. F., 1994, Closing of the Midcontinent Rift - A far field effect of Grenvillian contraction: Geology, v. 22, p. 155-158. Cannon, W.F., 1992, The Midcontinent Rift in the Lake Superior region with emphasis on its geodynamic evolution: Tectonophysics, v. 213. p. 41-48. Cannon, W. F., Green, A. G., Hutchinson, D. R., Lee, M.W., Milkereit, B., Behrendt, J.C., Halls, H.C., Green, J.C., Dickas, A.B., Morey, G.B., Sutcliffe, R., and Spencer, C., 1989, The North American mid-continent rift beneath Lake Superior from Glimpse seismic reflection profiling: Tectonics, v. 8, p. 305-332. Cannon, W.F., and Hinze, W.J., 1992, Speculations on the origin of the North American Midcontinent rift: Tectonophysics, v. 213, p. 49-55. Cannon, W.F., and Nicholson, S.W., 2000, Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan: U.S. Geological Survey, pamphlet to accompany I-MAP 2696, 7 p., https://doi .org /10 .3133 /i2696. Cannon, W. F., Peterman, Z.E., and Sims, P.K. 1993, Crustal-scale thrusting and origin of the Montreal River monocline - A 35-km-thick cross section of the Midcontinent Rift in northern Michigan and Wisconsin: Tectonics, v. 12, p. 728-744. Catacossinos, P.A., Harrison, W.B., Reynolds, R.F., Westjohn, D.B., and Wollensak, M.S., 2001, Stratigraphic lexicon for Michigan: Michigan Department of Environmental Quality, Geologic Survey Division Bulletin 8. 56p. Cornwall, H.R., 1951a, Differentiation in lavas of the Keweenawan series and the origin of the copper deposits of Michigan: Geological Society of America Bulletin, v. 62, p. 159-201. 49 �Cornwall, H.R., 1951b, Differentiation in magmas of the Keweenaw series: Journal of Geology, v. 59, p. 151-172. Cornwall, H.R., 1951c, Ilmenite, magnetite, hematite, and copper in lavas of the Keweenawan series: Economic Geology, v. 46, p. 51-67. Cornwall, H.R., 1954, Bedrock Geology of the Lake Medora Quadrangle Michigan: Geologic Quadrangle Maps of the United States. United States Geological Survey, Map GQ-52, scale 1:24,000. Cornwall, H.R. and Wright, J.C., 1956, Geologic map of the Hancock quadrangle, Michigan: U.S. Geological. Survey Mineral Investigations Field Studies Map MF 46. Daniels, P. A., 1982, Upper Precambrian sedimentary rocks: Oronto Group: Geological Society of America Memoir 156, p. 107-134. Davis, D.W., and Paces, J.B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. DeGraff, J.M., and Carter, B.T., 2023, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulleting, v. 135, p. 449-466, https://doi.org/10.1130/B36186.1. Elmore, R.D., 1983, Precambrian non-marine stromatolites in alluvial fan deposits, the Copper Harbor Conglomerate, upper Michigan: Sedimentology, v. 30, p. 829-842. Elmore, R.D., 1984, The Copper Harbor Conglomerate: A late Precambrian fining-upward alluvial fan sequence in northern Michigan: Geological Society of America Bulletin v. 95, p. 610-617. Elmore, R.D. and Van der Voo, R., 1982. Origin of hematite and its associated remanence in the Copper Harbor Conglomerate (Keweenawan), Upper Michigan. Journal of Geophysical Research: Solid Earth, 87(B13), pp.10918-10928. Farrand, W.R., 1960, Former shorelines in western and northern Lake Superior basin: unpublished Ph.D. dissertation No. 5366, University of Michigan, Ann Arbor, 226p. Heaman, L.M., Easton, R.M., Hart, T.M., MacDonald, C.A., Hollings, P., and Smyk, M., 2007, Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario: Canadian Journal of Earth Sciences, v. 44, p. 1055-1086. Hinze, W.J., Braile, L.W., and Chandler, V.W., 1990, A geophysical profile of the southern margin of the Midcontinent rift system in western Lake Superior: Tectonics, v. 9, p. 303-310. Hodgin, E.B., Swanson-Hysell, N.L., DeGraff, J.M., Kylander-Clark, A.R.C., Schmitz, M.D., Turner, A.C., Zhang, Y., and Stolper, 2020, Final inversion of the Midcontinent Rift during the Rigolet phase of the Grenvillian Orogeny: Geology, v. 50, No. 5, p. 547-551, https://doi.org/10.1130/G49439.1. 50 �Hoffman, P. F., 1989, Precambrian geology and tectonic history of North America: in Bally, A.W., and Palmer, A.R., eds., The Geology of North America-An overview, Boulder, Colorado, Geol. Soc. America, The Geology of North America, v. A, p. 447-512. Huber, N.K., 1975, The geologic story of Isle Royale National Park: U. S. Geological Survey Bulletin 1309, 66p. Johnson, R.C., 1985, Documentation of a subaqueously emplaced volcanic horizon in the upper Portage Lake Volcanics, Keweenaw Peninsula, Michigan: 29th Institute on Lake Superior Geology, Part 2, Part 1 Program and Abstracts, v. 31, p. 38-39. Jolly, W.T., 1974, Behavior of Cu, Zn, and Ni during prehnite-pumpellyite rank metamorphism of the Keweenawan basalts, northern Michigan: Economic Geology, v. 69, p. 1118-1125. Jones, S., Prave, A.R., Raub, T.D., Cloutier, J., Stüeken, E.E., Rose, C.V., Linnekogel, S., and Nazarov, K., 2020, A marine origin for the late Mesoproterozoic Copper Harbor and Nonesuch Formations of the Midcontinent Rift of Laurentia: Precambrian Research, v. 336, 105510. Kalliokoski, J., 1982, Jacobsville Sandstone: Geological Society of America Memoir 156, p. 147-155. Kalliokoski, J., 1986, Calcium carbonate cement (caliche) in Keweenawan sedimentary rocks (~1.1 Ga), Upper Peninsula of Michigan: Precambrian Research, v. 32, p. 243-259. Kalliokoski, J., and Welch, E.J., 1985, Keweenawan-age caliche paleosol in the lower part of the Calumet and Hecla Conglomerate, Calumet, Michigan: Geological Society of America Bulletin, v. 96, p. 11881193. Kelly, D., 2020, Fluid inclusion study of selected calcite associated with native copper, Quincy Mine, Keweenaw Peninsula, Michigan: Open Access Master's Report, Michigan Technological University, 65p.2020. Kelly, D., Bornhorst, T.J., and Deering, C., 2022, Fluid inclusions in euhedral calcite crystals from the Quincy Mine, Keweenaw Peninsula native copper district, Michigan: 68th Institute on Lake Superior Geology Proceedings, v. 68, Part 1, Program and Abstracts, p. 35-36. Kulakov, E., Bornhorst, T.J., Deering, C., and Moore, J.B., 2018, The youngest magmatic activity of the Midcontinent Rift at Bear Lake, Keweenaw Peninsula, Michigan: 64th Institute on Lake Superior Geology Proceedings, v. 64, Part 1, Program and Abstracts, p. 61-62. Lane, A.C., 1911, The Keweenawan series of Michigan: Michigan Geological and Biological Survey Publication 6 (Geology series 4), 297p. Livnat, A., 1983, Metamorphism and copper mineralization of the Portage Lake Lava Series, northern Michigan: Ph.D. Dissertation, University of Michigan, Ann Arbor, 292p. Longo, A.A., 1982, A geochemical correlation, with correlative inferences from petrographic and paleomagnetic data, of the Greenstone flow, Keweenaw Peninsula and Isle Royale, Michigan: 28th Institute on Lake Superior Geology Proceedings, Part 1, Program and Abstracts, 28, p. 22-23. 51 �Maki, J.C., and Bornhorst, T.J., 1999, The Gratiot chalcocite deposit, Keweenaw Peninsula, Michigan: 44th Institute on Lake Superior Geology Proceedings, Part 1, Program and Abstracts, v. 44, p. 33-34. Mauk, J.L., Brown, A.C., Seasor, R.W., and Eldridge, C.S., 1992, Geology and stable isotope and organic geochemistry of the White Pine sediment-hosted stratiform copper deposit: Society of Economic Geologists Guidebook Series, v. 13, p. 63-98. Merk, G.P., and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks: Geological Society of America Memoir 156, p. 97-105. Moore, P.B., 1971, Copper-nickel arsenides of the Mohawk No. 2 mine, Mohawk, Keweenaw Co., Michigan: American Mineralogist, v. 56, 1319-1331. Nicholson, S.W., 1991, Geochemistry, petrography, and volcanology of rhyolites of the Portage Lake Volcanics, Keweenaw Peninsula, Michigan, U. S. Geological Survey Bulletin, 1970B, p. B1-B57. Nicholson, S.W., and Shirey, S.B., 1990, Evidence for a Precambrian mantle plume: a Sr, Nd, and Pb isotopic study of the Midcontinent Rift System in the Lake Superior region: Journal of Geophysical Research, v. 95, p. 10851-10868. Nicholson, S.W., Shirey, S.B., Schulz, K.J., and Green, J.C., 1997, Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: implications for multiple mantle sources during rift development: Canadian Journal of Earth Sciences, v. 34, p. 504-520. Ohr, M., 1993, Geochronology of diagenesis and low-grade metamorphism in pelites: Ph.D. dissertation, The University of Michigan, Ann Arbor, MI.,161 p. Ojakangas, R.W., Morey, G.B., Green, J.C., 2001. The Mesoproterozoic midcontinent rift system, Lake Superior region, USA. Sedimentary Geology, v. 141, p. 421–442. Paces, J.B., 1988, Magmatic processes, evolution and mantle source characteristics contributing to the petrogenesis of Midcontinent rift basalts: Portage Lake Volcanics, Keweenaw Peninsula, Michigan: Ph.D. Dissertation, Michigan Technological University, Houghton, 413p. Paces, J.B., and Bell, K., 1989, Non-depleted sub-continental mantle beneath the Superior Province of the Canadian Shield: Nd-Sr isotopic and trace element evidence from Midcontinent rift basalts: Geochimica Cosmochima Acta, v. 53, p. 2023-2035. Paces, J.B., and Bornhorst, T.J., 1985, Geology and geochemistry of lava flows within the Copper Harbor Conglomerate, Keweenaw Peninsula, Michigan: 31st Annual Institute on Lake Superior Geology Proceedings (Kenora, Ontario), p. 71-72. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of the Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagmatic, and tectnomagmatic processes associated with the 1.1 Ga Midcontinent Rift system: Journals of Geophysical Research, v. 98, p. 13,997-14,013. 52 �Püeschner, U.R. Very low-grade metamorphism in the Portage Lake Volcanics on the Keweenaw Peninsula, Michigan, USA. Ph.D. Dissertation, University of Basel, Basel, Switzerland, 2001; pp. 1– 81. Schmidt, S.T.; and Robinson, D. Metamorphic grade and porosity and permeability controls on mafic phyllosilicate distributions in a regional zeolite to greenschist facies transition of the North Shore Volcanic Group, Minnesota. Geological Society of America Bulletin 1997, p. 683-697. Stoiber, R.E., and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250-1277, p. 1444-1460. Stüeken, E.E., Jones, S., Raub, T.D., Prave, A.R., Rose, C.V., Linnekogel, S., and Cloutier, J., 2020, Geochemical fingerprints of seawater in the Late Mesoproterozoic Midcontinent Rift, North America: Life at the marine-land divide: Chemical Geology, v. 553, p. 119812 Velbel, M.A., 2009, The “Lost Interval”: Geology from the Permian to the Pliocene: in Schaetzl, R., Darden, J., and Brandt, D. (eds.), Michigan Geography and Geology, Pearson Custom Publishing, New York, p. 60-68. Weege, R.J., and Pollack, J.P., 1971, Recent developments in native-copper district of Michigan: Society of Economic Geologists Field Conference, Michigan Copper District, September 30 - October 2, 1971, p. 18-43. Weege, R.J., Pollock, J.P., and the Calumet Division Geological Staff, 1972, The geology of two new mines in the native copper district: Economic Geology, v. 67, p. 622-633. Weege, R.J., and Schillinger, A.W., 1962, Footwall mineralization in Osceola amygdaloid, Michigan native copper district: A.I.M.E. Transactions, v. 223, p. 344-350. White, W.S., 1960, The Keweenawan lavas of Lake Superior, an example of flood basalts: American Journal of Science, v. 258A, p. 367-374. White, W.S., 1968, The native-copper deposits of northern Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933-1967 (the Graton Sales volume), American Institute of Mining, Metallurgical, and Petroleum Engineering, New York, p. 303-325. White, W.S., 1971, Field Trip A-2 – Houghton to Calumet via South Range quarry and Eagle River: Society of Economic Geologists, Guidebook for field conference, Michigan copper district, Sept. 30-Oct. 2, 1971, p. 68-75. White, W.S. and Wright, J.C., 1960. Lithofacies of the Copper Harbor conglomerate, northern Michigan. U.S. Geological Survey Prof. Paper 400-B, 5-7. Williams, W.C. and Bornhorst, 2023, Controls on the stratiform copper mineralization in the western syncline, Upper Peninsula, Michigan: Minerals, v. 13, p. 927-950. https://doi.org/10.3390/min13070927 53 �Woodruff, L.G., Cannon, W.F., Nicholson, S.W., and Schulz, K.J., 2013, Geology of Keweenawan Supergroup, Porcupine Mountains, Ontonagon and Gogebic Counties, Michigan: 59th Institute on Lake Superior Geology Proceedings, v. 59, Part 2, Field Trip Guidebook, p. 69-96. Woodruff, L.G., Daines, M.J., Cannon, W.F., and Nicholson, S.W., 1995, The thermal history of the Midcontinent Rift in the Lake Superior region: implications for mineralization and partial melting: in International Geological Correlation Program, Field Conference and Symposium on the Petrology and metallogeny of volcanic and intrusive rocks of the Midcontinent rift system, Duluth, Minnesota, v. 336, p. 213-214. Woodruff, L.G., Schulz, K.J., Nicholson, S.W., and Dicken, C.L., 2020, Mineral deposits of the Mesoproterozoic Midcontinent Rift system in the Lake Superior region — A space and time classification: Ore Geology Reviews, v. 126, p. 1–21, https://doi.org /10.1016/j.oregeorev .2020 .103716. 54 �Field Trip 2 Mining History and Geology of the Quincy Mine, Keweenaw Peninsula Native Copper District, Michigan Theodore J. Bornhorst1, James M. DeGraff2, Tom Wright3, and Katherine Langfield2 1 Department of Geological and Mining Engineering and Sciences and A.E. Seaman Mineral Museum, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 2 Department of Geological and Mining Engineering and Sciences, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 3 Quincy Mine Hoist Association, 49750 US-41, Hancock, MI 49930 Objectives of Field Trip The historic Quincy Mine was the fourth largest copper mine in the Keweenaw Peninsula native copper district. From 1851 to 1967, mining and processing of native copper ore produced ca. 488 million kilograms of refined copper via several shafts sunk along the top of the Pewabic basaltic lava flows. The Quincy Mine is interpreted and made accessible to the public by the Quincy Mine Hoist Association. The field excursion include tours of: the Quincy No. 2 shaft-rockhouse, the largest steam-driven mine hoist in the world, geology exposed along 675 m of an adit that intersects the historic Quincy Mine workings at the No. 5 shaft on the 7th level (107 ft below surface), the Quincy smelter works on the shore of Portage Lake, and two sites on Torch Lake for extraction of native copper from mined ore. Dress appropriately for the underground portion of the tour where the temperature averages 7o C (45 o F). Walk-in is on a wet surface and will access areas not normally visited by the public. Hard hats and lights will be provided. Brief history of the Quincy Mine Douglass Houghton's copper report in 1841 sparked the beginning of the first mining rush of North America to the Keweenaw Peninsula. This human event has its true beginning in the origin of the rocks and the native copper they host. The human story begins with native people's exploitation of native copper and their introduction of native copper to European explorers. Houghton's copper report led to human migration to the Keweenaw Peninsula, the discovery of the first native copper mine in 1845, the Cliff Mine, and the beginning of modern mining. The mining district quickly developed into the most significant copper district in the United States with peak copper production between 1890 and 1915. The district began to decline from 1920 to the end of mining in 1968 and the decline was accompanied by human exodus; the local population continues to decline today. The Keweenaw Peninsula exhibits the classic boom and bust cycle that is often associated with mining. In 1992, a national park was created to preserve and interpret the rich human and geologic history of the now dormant native copper district. 55 �The Quincy Mining Company was established in 1846 and was termed “Old Reliable” for its reliable payment of dividends to its shareholders. From 1866 to 1890 the Quincy Mine area developed into a robust mine. The Quincy Mine was one of the first mines in the Keweenaw Peninsula to evaluate their operations to maximize efficiency and hence, maximize profits. In 1866 they were the third mine to install a man-engine. They experimented with Burleigh power drills in 1868, but the large and cumbersome drills proved a failure. They built a rock house complete with rock crushers in 1873 which eliminated the time and labor involved in the old kiln houses. In 1879, black powder was replaced by dynamite and most hand drilling was eliminated when they adopted Rand Company's "Little Giant" power drills. While these innovations were adapted to increase efficiency, other changes were made to solve problems. The Quincy Mine could not find enough water in the abandoned shafts for its steam plant near the mine up on the top of Quincy hill which led to installation of a pumping station to pump water uphill from Portage Lake. In 1887, they closed their stamp mill on Portage Lake as the tailings they deposited into the lake began to hinder navigation. Quincy proceeded to build a new mill on Torch Lake. By building a new mill they were able to adopt steam-powered stamps rather than the old Cornish drop stamp technology (Lankton and Hyde, 1982). Quincy was able to continue to adapt because they had sufficient copper ore to mine. The Quincy Mining Company began to rebuild itself during the boom years for the whole Keweenaw Peninsula native copper district from 1890 to 1915. It acquired more powerful engines and hoists and began to raise two skips at a time in balance with each other. In 1891, they built the photogenic and functional No. 6 combined shaft and rockhouse. The man-engine reached its maximum depth in 1892 and as a result Quincy began using man-cars to raise and lower workers using the same hoist they used for ore skips. They built their own smelter on Portage Lake on the old Pewabic Mill site in 1898. In 1905 they began to replace their 2-cylinder engines with 4-cylinder engines to get better use of the steam and reduce coal consumption. Underground mining was changing too. Miners switched from candles to paraffin-based lamps in 1896-97 and to the less-smoky calcium carbide lamps in 1912-14. Miners began using machines to cut up masses in 1906 rather than drills. Quincy became the first mine in the district to modernize tramming and hauling when they installed a haulage system with a GE batterystorage locomotive in 1901. Quincy designed and patented their own side-dumping tramcars. By 1903 Quincy had 15 electric locomotives. They experimented without success with power shovels underground. In 1905, they reduced the wait time to dump cars underground by digging 500-ton underground storage bins into the hanging wall above the inclined shafts and thereby were able to hoist 25 % more ore to the surface. In 1910, Quincy operated 160 two-man drills, each of which weighed 245 pounds. The lighter one-man drills significantly decreased the cost of mining but this new technology left a miner alone underground which became one issue of the 1913 strike (Lankton, 1991). The Keweenaw Peninsula native copper mining district never fully recovered after the 1913 strike. The Quincy Mining Company continued to move forward after the strike, and they installed the world's largest steam hoist. Quincy constructed the No. 2 hoist house in 1918 and began operating the world’s largest steam hoist in 1920 as the shaft reached an incline depth of 7750 (2360 m) feet. In 1920 Quincy increased efficiency of processing and smelting by adding 56 �Wilfley tables to their stamp mill and adding a casting wheel at the smelter to eliminate hand pouring of ingots. As the underground workings went deeper, mining became much more difficult. In 1926, they had to install additional pumps to reduce the time used waiting for hoisting water-bailing skips rather than rock skips. In 1927, there was a major underground fire that impacted production. As the mine went deeper, they had to install fans to reduce the temperature at the bottom where miners still sometimes had to work at temperatures of 98oF (Lankton and Hyde, 1982). The Great Depression closed most Keweenaw mines. The Quincy Mine closed in 1930. The Calumet & Hecla Mining Company closed most of its mines except for a lucky few that operated on reduced shifts. The Quincy Mining Company reopened the No. 6 and No. 8 shafts on a limited basis in 1937. It wasn't until World War II and the advent of price controls that a larger production schedule was resumed. District-wide production resumed on a broader scale when price controls were lifted on August 31, 1945 and Quincy permanently ended its underground mining. The reclamation mill continued to operate and make a profit. In 1948, on its 100th anniversary, Quincy paid a dividend of 25 cents per share due only to the copper produced by the reclamation from tailings in Torch Lake plant (Lankton and Hyde, 1992). The Quincy smelter reopened in the mid-1950s after being closed for about 15 years as Quincy could no longer send reclamation concentrates to the Calumet & Hecla Mining Company smelter. The Quincy smelter remained open until the reclamation plant closed in 1967. The mines were allowed to begin flooding in 1970 (Thurner, 1994). The Keweenaw Peninsula native copper mining district has remained dormant in the 54 years to follow except for several episodes of exploration. Highland Copper Company, from 2011 to 2015, has been the latest explorer to attempt to reopen native copper mines in the Keweenaw Peninsula. The economies of mining districts are typically sustained by one principal industry, mining. When the mines are profitable and expanding the local communities also do well and when the mines suffer decline the local communities also suffer decline. This creates the boom to bust mining cycle. The local population follows this boom-and-bust trend. During the boom of mining Calumet was a vibrant city and since the mines have closed it has contracted. The last value obtained from the mining industry is selling the useful equipment to other mines followed by the dismantling of buildings to sell for scrap. Evidence of mining such as shaft-rockhouses and industrial buildings disappeared too. The surface rock piles left from mining once dotted the landscape of the Keweenaw Peninsula, but over time they too are disappearing as they are an inexpensive source of crushed stone for roads and other purposes. In the late 1980s Calumet community leaders envisioned that the past might be the key to the future of Calumet and they sought development of historical tourism. This led to creation of the Keweenaw National Historical Park in 1992. The park consists of limited park owned lands/structures and multiple Keweenaw Heritage Sites which are public, private, and non-profit. Together the park and its cooperative sites preserve and interpret the mining history of the Keweenaw Peninsula and supports historical tourism. The brief history of the Quincy Mine was slightly modified from text written by Larry Molloy, published by Bornhorst and Molloy (2016), and republished by Bornhorst (2022). 57 �Geologic Overview of the Quincy Mine Readers are referred to Bornhorst (this volume) and Bornhorst and Lankton (2009) for the geologic setting of the Quincy Mine and its native copper deposits hosted by the Portage Lake Volcanics. This overview of the geology of the Quincy Mine is from Bornhorst and McDowell (1992), Bornhorst et al. (1986), and Butler and Burbank (1929). The Portage Lake Volcanics comprise several hundred subaerial lava flows erupted within the Midcontinent Rift of North America about 1.1 billion years ago. There are occasional interbedded sedimentary rock layers dominated by conglomerate (Bornhorst, this volume). The native copper ores at the Quincy Mine occur in tabular bodies hosted by the originally porous and permeable tops of subaerial basalt lava flows. Ore-forming hydrothermal fluids precipitated native copper in the open spaces some 30 million years after the lava flows were erupted. About 50 lava flows of the Portage Lake Volcanics are exposed along the adit, twelve of them beneath the interflow sedimentary layer termed the Allouez conglomerate. The Allouez conglomerate and overlying Greenstone flow can be traced from the Houghton-Hancock area to the tip of the Keweenaw Peninsula (Bornhorst, this volume). A clay gouge along a bedding plane fault with undetermined slip occurs at the top of the Allouez conglomerate (Bornhorst and McDowell, 1992). Similar bedding plane faults are common at the tops and bases of conglomerate layers throughout the district. Native copper ore at the Quincy Mine is hosted by a group of relatively thin porous tops of lava flows that are difficult to correlate laterally without mapping the flows in detail (Butler and Burbank, 1929). The productive tops of the lava flows at Quincy, termed the Pewabic amygdaloids, are not brecciated as is common in the larger flow-top mines in the district. Cavernous zones within the Pewabic flows began as open spaces and subsequently were filled with hydrothermal minerals described above. There is much variability within the tabular lode from well to poorly banded and from high-grade of copper ore to practically barren poor rock (Butler and Burbank, 1929). Stratigraphically, about 12 lava flows with a cumulative thickness of about 100 m occur between the Allouez conglomerate and the overlying Pewabic flows which are the host rocks for the native copper deposits at the Quincy Mine. However, at this location along the adit, the Pewabic flows are not mineralized as they are on the northwest side of the Hancock fault. There are about 14 additional lava flows until the Hancock fault is reached. The Hancock fault is marked by a distinctive clay gouge, almost pure corrensite, and a green corrensite-rich brecciated mineralized zone adjacent to the gouge (Bornhorst and McDowell, 1992). The Hancock Mine produced native copper from a mineralized segment of the Hancock fault, suggesting that it may have been a feeder of ore-forming hydrothermal fluid into void spaces in the tops of the Pewabic flows (Bornhorst and McDowell, 1992). The amygdaloidal flow tops exposed by the adit are filled with a number of hydrothermal alteration minerals. Butler and Burbank (1929) describe the main-stage hydrothermal minerals at the Quincy Mine: quartz and calcite are abundant throughout the lode, commonly as euhedral crystals in open cavities; pumpellyite is less abundant but is present throughout the lode; epidote is less abundant than 58 �pumpellyite but is a common hydrothermal mineral; chlorite is particularly abundant in amygdules near the bases of Pewabic lava flows and is locally replaced by quartz and calcite; prehnite is present but not common; and datolite is present only in upper levels of the mine. The Pewabic lode of the Quincy Mine is notable for spectacular euhedral calcite with visibly unaltered pink to rose colored inclusions of native copper, which are highly sought by mineral collectors. Native silver is closely associated with native copper, although abundance is low. Laumontite is sparse and associated with small fissures. Thus, it may be a late-stage hydrothermal mineral rather than main-stage (Bornhorst, this volume). Butler and Burbank described early pumpellyite and epidote followed by quartz, calcite, and native copper. Bumgarner (1980) described amygdules indicating that prehnite and chlorite were early hydrothermal minerals followed by quartz, then chlorite, and lastly calcite. Overview from native copper ore to copper products At the Quincy Mine and elsewhere in the Keweenaw Peninsula native copper was extracted from tabular ore bodies by underground mining methods. Quincy Mine yielded about 42,870,000 tons of ore (1 ton = 2,000 lbs) with recovered refined copper totaling 1,077,000,000 lbs at an average grade of 1.26 % copper per ton of ore. The amount of silver in the native copper ore can be estimated from incomplete production statistics in Butler and Burbank (1929) to be roughly 0.2 oz of silver per ton of ore. The ore is blasted underground into small enough size to be able to be hoisted to the surface. Rock lacking sufficient native copper was sent to the poor rock pile or into abandoned underground mine openings. Prior to being sent to the mineral processing plant to recover native copper, the broken ore is sized by a slatted grating, “grizzly”. The broken ore passing through the grating (most of the ore) is sent to the mineral processing plant and those fragments too large are broken further at the surface near the shaft rock-house with a steam driven hammer. One reason a fragment could be too large is because it is mostly native copper. Native copper is malleable and large masses are not readily fragmented by underground blasting. Once most of the rock was removed from the larger fragments, the copper-dominant fragments were put into barrels (barrel copper) or, if they were too big, they were put onto a flat rail car and shipped directly to the smelter instead of to the mineral processing plant. The ore from the Quincy Mine was processed to separate native copper from the barren host rock and barren minerals in order to produce a product sufficiently enriched in copper to be smelted. The ruins of the Quincy processing plant will be visited at Stop 4. The first essential step in processing was crushing the ore into sand and smaller sized fragments using stamp mills. The crushing aims to produce fragments which are mostly native copper or mostly rock and thereby liberates the native copper from the rock. Because native copper is much denser than the host rock (about 3 times denser than the barren host rock), fragments of native copper can be separated from the barren host rock using water and gravity methods such as jigging. Hence, the mineral processing plant usually was constructed near a body of water. The mineral processing plant produced a “concentrate” which was composed of sand-sized and finer native copper with some fragments or partial fragments of barren rock because no separation method is able to completely separate every particle. The ore 59 �mined at Quincy averaged about 25 lbs of copper in a ton of ore. The copper concentrate was more than 50 % copper, hence most of the sand and smaller size fragments from the crusher ended up being waste, which still contained some copper. This waste, called tailings, was transported by water slurry and dumped into lakes, especially Torch Lake. The amount of native copper in a sand-sized fragment may have been so low that it was correctly separated into the tailings. In other fragments there was enough copper in them but they were incorrectly separated into the tailings. For example, the copper could have been finer grain size than the fragment and it was diluted by barren host rock and minerals. By crushing such fragments to a finer grain size, more copper could have been liberated from the barren host material. Quincy Mine kept track of the lost copper as it dumped tailings into Torch Lake. They later went back and recovered much of the lost copper by reprocessing the tailings using newer more efficient technology. The mineral processing plant and recovery of lost copper are discussed at Stop 4. The copper concentrate from the processing mill was shipped to the Quincy Smelter Works which is discussed further at Stop 2. The smelting and refining process resulted in solid Quincy copper ingots of up to 99.8 % pure copper. The copper ingots transported to markets by ships. The copper mined and processed by Quincy was sufficiently pure to be fabricated into a variety of usable copper products such as electrical wire. Copper ore to copper products text from previously published field trip guide by Bornhorst (2022) with modification. Field Trip Stops Figure 1: Map showing approximate stop locations of Field Trip 2 to the Quincy Mine. 60 �Stop 1: Quincy Mine, Keweenaw Heritage Site of the Keweenaw National Historical Park Latitude: 47.137137N; Longitude: -88.574875W Directions: From Michigan Tech drive west on US-41 (left from parking lot by the MUB) and continue through downtown Houghton across the Portage Lake lift bridge through downtown Hancock and uphill to the Quincy Mine No. 2 shaft rock-house turning right into the parking lot just past the shaft rock-house. The Quincy Mining Company was incorporated in 1846 and operated until 1967. Quincy mined underground from nine shafts on the Pewabic flow top and there was an industrial complex associated with mining (Figure 2). Throughout its history, Quincy Mining Company paid dividends on such a regular basis it was nicknamed "Old Reliable". Quincy Mining Company produced a total of 1.08 billion pounds of refined copper and approximately 100 million oz of silver from approximately 43 million tons of ore at an average grade of 25.1 lbs. of copper per 2000 lb. ton of ore (including copper reclaimed from Quincy tailings). The Quincy Mine ranks as the fourth largest mine in the native copper district. In 1921 the No. 2 shaft was the world's deepest. The Nordberg steam hoist is the world’s largest. Figure 2: The Quincy Mining Company complex ca. 1900. The No. 2 shaft-rockhouse is near the center of the drawing. From Molloy (2011) with permission. 61 �The No. 2 shaft of the Quincy Mine opened in 1858. At the beginning of mining a simple house was built over the shaft. By 1892, Quincy introduced the concept of hoisting the ore and doing initial crushing and sorting of the ore in the same building, a shaft-rock house. The current Quincy No. 2 shaft rock house was built in 1908 (Figure 3). The Quincy No. 2 shaft rock house is 147 feet (45 m) tall and the angle on the side of the building facing US-41 is at the dip angle of the native copper deposit. Behind the shaft rock house, there are two of the original eight pulley stands and stanchions that were used to support a steel cable extending to the No. 2 hoist house built in 1919. Mining at the No. 2 shaft ended in 1931. Figure 3: Quincy Mine No. 2 shaft-rockhouse. This drawing is based on Historic American Engineering Record drawing, MI- 2,19/34, Durward W. Potter, Jr., 1978 and Richard K. Anderson, Jr., 1979. From Molloy (2007). By 1917, the No. 2 shaft had reached such great depths that the hoist engine housed in the 1895 hoist house was no longer adequate. The Quincy Mine needed a large and faster hoist to continue its production. In 1918, the No. 2 hoist house was constructed but World War I delayed 62 �delivery of a new hoist until 1919. The Nordberg hoist began operating in 1920 as the shaft reached an incline depth of 7750 (2360 m) feet. The Nordberg hoist consists of four cross-compound steam engines that work as one (Figure 4a and 4b). The new hoist could move an ore skip carrying 10 tons of rock (13 tons total weight) up at 3200 feet per minute (36 miles per hour) and was more energy efficient than the hoist it replaced. The Nordberg hoist, the world's largest, operated 24 hours per day for 11 years until mining ended in 1931; to a depth of over 9000 feet (2743 m) on the incline (Molloy, 2007). Stairs - down Entrance from the 1895 Hoist House Down Hoist Rope Slots DisplaysModel of #6, Mine Cross Sections Up Overhead Crane Low Pressure Cylinder High Pressure Receiver Oil For Hydraulics Stored Under Here Low Pressure Receiver High Pressure Cylinder Condenser Under Here Oiler's Gallery Hoisting Drum 30' Maximum, 16' Minimum Diameter D i s p l a y s Vacuum Pump Low Pressure receiver Miniatures High Pressure Cylinder Displays High Pressure Receiver Operator's Platform Overhead Door Stairs to Platform Top Of Water Circulating Pump Lily Hoist Controler Displays Oil Pump Drive Low Pressure Cylinders Up Corliss Steam Engine Flywheel Display Of Large Tools Down Figure 4a: Quincy Mining Company No. 2 shaft Nordberg hoist diagram. This drawing is based on HAER drawing, MI-2,14/34, Durward W. Potter, Jr., 1978. From Molloy (2007) A steam engine functions by using alternating intake and exhaust valves to allow steam to enter a chamber, expand inside of the chamber, and use the force of the expansion to push a piston as the steam expands. The double-acting pistons used here can be pushed both up and down in the cylinder by the expanding steam. The entire engine occupies 60 feet by 54 feet of floor space and is 60 feet tall. It is a cross-compound steam engine, an engine where steam is used twice. This common technique accounts for the “choo-choo-choo-choo” sound one hears near steam powered trains. Today the hoist remains an engineering marvel and is still the world’s largest steam mine hoist. 63 �Miniatures H ois ting D rum Operator's Platf orm Brak e Main C rank Oiler's Gallery Low Pres s ure Throttle H igh Pres s ure Throttle Steam Supply Line H igh Pres s ure Low Ex haus t to Pres s ure Equalizing Line Pres s ure C ondens er C y linder C y linder H igh Press ure Low Pres s ure Steam R ec eiv er Steam R ec eiv er Figure 4b: This diagram illustrates the major features of the hoist and traces the flow of steam through the hoist. It is based on HAER drawing, MI-2,13/34, Jon R. Carter, 1978. From Molloy (2007). At the Quincy Mine and elsewhere in the Keweenaw Peninsula native copper was extracted from tabular ore bodies by underground mining methods. The ore is blasted underground into small enough size to be able to be hoisted to the surface. Prior to being sent to the mineral processing plant to recover native copper, the broken ore is sized by a slatted grating, “grizzly.” Those fragments too large are broken further by steam hammers. The native copper-dominant fragments were put into barrels (barrel copper) or, if they were too big, they were put onto flat rail cars. The barrel copper and larger masses were shipped directly to the smelter located downhill from the shaft rock-house. Next to the Quincy Mine No. 2 shaft rock house is a specimen of mass copper weighing hundreds of lbs. that would have been shipped directly to the smelter. Text from previously published field trip guide by Bornhorst (2022) with limited modification. 64 �Stop 2: Quincy Smelter Works Latitude: 47.126688N; Longitude: -88.565290W Directions: From Stop 1 turn left from Quincy Mine returning downhill to Hancock, just before the Portage Lake lift bridge follow M-26 through underpass and from bridge continue 0.4 miles (0.65 km) to the Quincy Smelter Works. The Quincy Smelter was constructed in 1898 and initially consisted of four or five reverberatory furnaces until switching to two larger furnaces in 1920. The purpose of the smelter was to produce bars of copper with as few as possible impurities. Copper with low enough impurities was ready to be made into copper products. The copper concentrate from the mill, barrel copper, and larger masses are melted, turned from solid to liquid in a furnace. Smelting is melting at temperatures higher than the melting point. By being higher than the melting point the liquid metal separates from the liquid silicate rock. Since the density of metallic copper is much higher than other components in the liquid rock, the liquid copper sinks to the bottom of the furnace while the other components, molten slag (waste liquid) float to the top. Men skimmed off the molten slag and it was dumped on a pile where it was left to cool into glass and minerals. Across from the parking lot opposite the agent’s house/office is a pile of solidified slag. The molten copper was tapped from the bottom of the furnace into a refining furnace where it was rabbled and poled. Rabbling (stirring) agitates the molten copper and allows the introduction of small amounts of air which oxidizes the impurities (copper has less tendency to oxidize than impurities). The oxidized impurities are lighter than liquid copper and thus, rise to the surface and are skimmed off the molten copper. After the impurities are skimmed off of the molten copper, green sapling poles are inserted into the molten copper (poling). Poling introduces carbon (wood) which reduces the amount of copper oxides in the molten copper. The refined copper was ladled and poured into molds and sprayed with water to cool it. The solid copper shapes were then dumped into a tank of water to complete cooling. Quincy cast copper ingots of several shapes and sizes (bars, wedges, and cakes). Refined copper from Quincy was up to 99.8 % copper which was sufficient for fabrication of copper products in the early 1900s. Some copper ingots had to undergo further refining. Today, the copper would undergo electrolytic refining to make it more than 99.99 % pure copper. Quincy constructed the smelter to be able to refine and ship its own copper. It also accepted custom work from neighboring mining operations. While underground mining ended in 1945, the Quincy smelter remained open until 1971. After closure of the underground mine, Quincy was actively recovering copper from reprocessing of tailings from Torch Lake. Fortunately, the smelter site remained intact after closing and is now open for guided tours. In 2014, the Keweenaw National Historical Park Advisory Commission acquired the smelter from Franklin Township (Figure 5). Text from previously published field trip guide by Bornhorst (2022) with limited modification. 65 �Figure 5: The historic Quincy Smelter Works. View July 2022 towards the north from Houghton waterfront. Stop 3: Quincy Mine Adit to 7th Level Underground Workings Latitude: 47.130383°N; Longitude: 88.573824°W Directions: Turn left onto M-26 heading west and drive 0.5 mi (0.8 km) to its junction with US41 north of the Portage Lake lift bridge. At the stop sign, merge onto US-41 and continue west for two blocks (~0.1 mi, ~0.15 km) to Dunstan Street on the right before a BP gas station. Turn right onto Dunstan and drive uphill for three blocks on the right (~0.15 mi, ~0.25 km) to Mason Avenue. Turn right onto Mason and drive east about 0.2 mi (0.3 km) to near a sharp right-hand curve. Just before the curve, turn left to enter an unpaved driveway that leads to the adit. The Quincy adit was first opened in 1892 by the Quincy Mining Company and subsequently widened in the 1970s by Michigan Tech mining engineering faculty and students for an underground educational and research facility. The adit enters the south side of Quincy hill at a point located ~690 m SSE of the iconic Quincy No. 2 shaft house along US-41 at the top of the hill. From the portal, the adit follows an azimuth of 331° for 675 m, where it intersects the 7th level workings at the Quincy No. 5 shaft (Bumgarner, 1980). The average strike of PLV layers here is 213° (right-hand rule), which means that the adit cuts across them in a direction 30° clockwise from the dip direction. Approximately fifty lava flows and one conglomerate layer, dipping on average 50° NW, are exposed along the adit (Bumgarner, 1980; Bornhorst et al, 1986). Geologic sites of interest in the adit and side passages are described as sites 3A to 3E in the following text and shown in Figure 6. Underground workings of the Quincy Mine were developed along a series of parallel, relatively thin, lava flow tops, referred to collectively as the Pewabic flow top within the Portage Lake Volcanics. The mine was developed to a vertical depth of 1897 m (6225 ft) comprising 92 levels. The ore body decreases in dip from 54o at the surface to 32o at the bottom levels. Pewabic flows are characterized by large cavernous zones up to 1.5 m thick, interpreted by Butler and Burbank (1929) as coalescing vesicles and large gas cavities. Alternatively, the large cavities could have 66 �been caves or lava tubes formed by lava drainage beneath a solidified flow surface. Openings were connected up to 100s m along formation strike and, where especially well developed, they may host 2 to 10 high-grade copper zones. An interconnected series of such openings would have provided continuous flow paths for ore-forming hydrothermal solutions. Several prominent and steeply dipping veins extend throughout the mine. They probably helped to integrate the hydrothermal system as their mineralogy is similar to that of the hydrothermal mineral assemblage in the flow tops. Figure 6: Map of Quincy adit and 7th level mine workings (modified from Bumgarner, 1980). Six geological sites of interest are labeled 3A through 3F. Numbers 1 – 19 along adit are distances in hundreds of feet. 67 �Site 3A: Contact between two basaltic lava flows. [~75 m from portal] The contact between the two lava flows at this site shows many characteristics that are common in the Portage Lake Volcanics of the Keweenaw Peninsula. Contacts between successive subaerial lava flows are recognized by textural and color differences between the top of the older layer and base of the younger one, as well as by the geometry of their boundary. Massive flow interiors grade into margins with finer grain size and abundant vesicles often arranged in bands parallel to flow contacts. Flow tops have the highest abundance of vesicles. Upper flow surfaces were exposed to the atmosphere and escaping gases during and after emplacement, and later to hydrothermal fluids permeating along flow tops that filled many voids (amygdules) with an assemblage of minerals (Butler and Burbank, 1929; Stoiber and Davidson, 1959; White, 1968; Bornhorst, 1997), thus modifying their color as seen here. Looking at the adit’s northeast wall (right side walking in), the top of the older flow toward the southeast is highly vesicular and has a lighter greenish tone relative to the younger to the northwest. In this case, the distinctive lighter tone and greenish tinge of the flow-top rock results from secondary epidote, pumpellyite, and various copper minerals, which are not present in the base of the overlying flow. The adit cuts nearly perpendicular across the contact between the flows, such that their boundary can be traced from one side of the adit across its ceiling to the other side. This exposure is nearly ideal for measuring strike and dip of the contact because it is exposed in 3-D over a sufficient distance to allow visual averaging of irregularities that are typical of flow contacts. Site 3B: Allouez conglomerate and the Greenstone flow. [~290 m from portal] The Allouez conglomerate and overlying Greenstone flow are well correlated stratigraphic units along the strike of the historic copper mining district (Butler and Burbank, 1929; Stoiber and Davidson, 1959). They can be traced from near the tip of the Keweenaw Peninsula to southwest of the Quincy Mine, a strike length of 80 kilometers. In the Quincy adit, the Allouez conglomerate is a 2-m-thick layer and the overlying Greenstone flow is only 10-15 m thick, far less than its maximum thickness elsewhere. The conglomerate here is typical of most conglomerates interbedded with mafic lava flows of the Portage Lake Volcanics. It is largely clast-supported and contains rounded to subrounded cobbles and pebbles of felsic volcanic rocks and subordinate mafic rocks. At this site, the bedding surface between conglomerate and basalt is marked by a clay seam, or “fluccan” following Cornish mining terminology (Hubbard, 1898). Hubbard (1898) systematically documented such clay seams in mines accessible at the time and he noted that they typically follow contacts between interflow sedimentary layers and lava flows, but also occur at contacts between flows. The clay seams are commonly associated with polished surfaces, fault gouge, brecciation and alteration of adjacent units, and secondary mineralization in fractured zones generally less than a couple of meters thick. As noted by Hubbard (1898), these phenomena indicate that many layer boundaries in the Portage Lake Volcanics have slipped during one or more deformation events. Such surfaces are essentially layer-parallel faults that slipped because of their weaker mechanical strength relative to the layers themselves. 68 �Site 3C: Hancock fault at the adit and in drift to the northeast. [~570 m from portal] The Hancock fault is a major splay of the Keweenaw fault system that intersects the main Keweenaw fault about 14.5 km northeast of here and downdip at a depth of around 3 km (Cannon and Nicholson, 2001; DeGraff and Carter, 2023). Over its 18-km length, the Hancock fault strikes 234° (right-hand rule) and cuts obliquely across the exposed Portage Lake Volcanics in a direction that is ~25° clockwise from formation strike and dips northwest at a steeper angle than layering. It cuts the Pewabic flows of the Quincy and Hancock mines. The Hancock fault had a strong influence on the distribution of copper in these two mines as follows: 1. A portion of the fault in the Hancock Mine had copper ore that was exploited; 2. Copper is also abundant along the Hancock fault in the Quincy Mine; 3. Copper mineralization in Pewabic beds of the Quincy Mine is restricted to the hanging wall northwest of the fault. The Hancock fault has been proposed as an important pathway for ore-forming fluids to access porous zones at the Quincy and Hancock Mines (Bornhorst et al., 1986). Figure 7: Cross-sectional view of the Hancock fault looking northeast at the wall of the adit. Height of the view is about two meters. The slip surface is marked by a clay seam. 69 �The Hancock fault is best exposed and investigated in the Quincy Mine workings, where it is cut by the adit and drifts leading northeast and southwest from the adit (Figure 7). At this site, the Hancock fault is observed crossing the adit and following the northeast drift for about 50 meters, so that measuring its orientation is easy. At the adit, the fault strikes 239° and dips 54° NW, in contrast to stratigraphic layering that strikes 213° and dips a bit less than layering. The fault zone here has a thin (~3 cm) medial clay seam, marking the main slip surface, that is contained within a breccia envelope of disaggregated fragments. Outside of the breccia envelope, country rock is highly fractured near the fault but the rock is still intact. As the fault is followed northeastward along the drifts orientation varies and the thicknesses of its clay seam and surrounding breccia increase and decrease and are not always symmetrically arranged. Site 3D: Ropy pahoehoe at the top of a Pewabic flow in the first northeast drift. [~570 m from portal; ~75 m along drift] Farther along the same drift at Site 3D is a good exposure of the surface of one of the Pewabic flows (Figure 8). Like subaerial mafic lava flows elsewhere, the tops of Portage Lake Volcanics flows show characteristics of two fundamental types – a smooth or ropy geometry (pahoehoe, locally termed amygdaloid) and a rough blocky geometry (aa, locally termed fragmental amygdaloid). Most Portage Lake Volcanics lava flows have smooth flow tops and yet ropy pahoehoe is rarely observed, probably because plan views of flow surfaces are uncommon and because of degradation of flow surfaces between successive extrusive events. The ropy pahoehoe observed on the northwest side of the drift is well preserved. The view here is upward at the base of an overlying flow, and so the pahoehoe feature is really a mold of the upper surface of the underlying flow top that has been removed along the drift. The curved geometry of pahoehoe ropes results from local movement of partly solidified lava crust that forms arcuate patterns that are convex in the local direction of flow (Fink and Fletcher, 1978; Self et al., 1998). The local flow direction indicated by the convexity of the ropes seen here is updip and toward the southwest, i.e. from the center towards the edge of the rift. Most flow-top native copper ore bodies are hosted by brecciated flow tops because their relatively large volume of open space was well connected and provided relatively easy movement of ore-forming fluids (Butler and Burbank, 1929; White, 1968; Bornhorst, 1997). Flows with smooth to ropy pahoehoe tops are usually not favorable because vesicles have limited volume of not well connected open space which hindered movement of ore-forming fluids. However, Pewabic flows with pahoehoe tops had economic grades of copper mineralization because they had large connected openings up to 1.5 m wide and extending up to 100s m along strike. Butler and Burbank (1929) proposed that the exceptional Pewabic lode was the result of an extremely gaseous flow that produced a great abundance of vesicles that coalesced to produce large connected voids. An alternative hypothesis is that the large openings resulted from lava draining from pools and tubes beneath a solidified flow surface. 70 �Figure 8: Ropy pahoehoe in the hanging wall of the first drift northeast from the adit. View is to the northwest. The two highlighted patterns indicate flow updip and toward the southwest. Height of the view is about six meters. Site 3E: Hancock fault in drift to the southwest. [~675 m from portal; ~55 m along drift] This site provides another opportunity to examine the Hancock fault where it follows much of the drift leading southwest from the No. 5 shaft to the No. 7 shaft (Figure 6). From Site 3C at the adit, the fault angles across the corner of unmined rock between the adit and southwest drift and is next exposed on the southeast wall of the drift at Site 3E. From here, the fault trace rises up the southeast wall, gradually angles across the ceiling, and descends the northwest wall where it enters the drift’s hanging wall before reaching the No. 7 shaft. Native copper is frequently found in the fault’s hanging wall up to the breccia zone but has not been found in the footwall. Here, the “medial” clay seam is generally thicker than at Site 3C but its thickness varies considerably along the fault trace, as does the thickness of the disaggregated breccia envelope. It is difficult to estimate the thickness of the still-intact zone of fractured rock 71 �that encloses the breccia zone because, as seen at other faults examined in detail (Caine et al., 1996; Caine and Forster, 1999), its intensity gradually decreases away from the fault to a background value for the system. Study of exposures of the Hancock fault and nearby satellite faults in the Quincy Mine is needed to better understand the slip characteristics and wall-rock modification of the Hancock Fault. This could also help understand the influence of the Hancock fault on copper mineralization. Fault slip is being investigated by the measurement and analysis of slip indicators – slickenlines and steps – on the surfaces of the many small faults associated with the Hancock fault. Observations of how rocks along the Hancock fault were modified physically and chemically have been mostly qualitative so far, though with some exceptions (Bornhorst and McDowell, 1992; Langfield et al., 2023). Site 3F: Hanging wall of Pewabic flow in drift northeast of No. 5 shaft. [~675 m from portal; ~30 m along drift] Along the drift leading northeast from the No. 5 shaft to the No. 4 shaft (Figure 6), the hanging wall of the drift and attached stope exhibit slickenlines directed parallel to dip of the lava flows. One may need to search a little and use oblique lighting to see these fault surface features, which manifest layer-parallel dip slip on the boundary between two lava flows. Another surface with similarly oriented slickenlines occurs in a parallel drift a few tens of meters northwest beyond the hanging wall of this drift. As discussed at Site 3B, Hubbard (1898) documented 12 layer boundaries with layer-parallel slip, but this surface and the other northwest of here were not among them. He mentioned polishing and slickensides on such surfaces but did not specify their orientation. It is likely that such layer-parallel slip is far more common than has been observed because, like the ropy pahoehoe texture, it can only be observed where an ideal exposure permits viewing. The documented layer-parallel slip within the PLV section is strong evidence for a detached style of thrusting, which was used recently to model the cross-sectional geometry of the Keweenaw and Hancock faults (DeGraff and Carter, 2023). 72 �Stop 4: Quincy Mining Company Processing Plant and Dredge Latitude: 47.146295N; Longitude: -88.460474W, Directions: From Quincy Smelter Works turn right (east) and continue 5.7 miles (9.2 km) to ruins of the Quincy processing plant on left carefully pulling into open lot on west side of ruins. The Quincy Mine dredge No. 2 is located on the edge of Torch Lake on the other side of the road. Figure 9: The Quincy Mining Company mills, 1890-1928. Star shows the location of the Quincy dredge No. 2. From Molloy (2011) with permission. The Quincy Mining Company had to move their mill from its Portage Lake site below Quincy Hill because tailings deposited in the lake were beginning to hinder navigation. Construction began on the Quincy mill at this site in 1888 (Figure 9). Mill No. 1 began with three rock crushing stamps and two additional were added in 1892. The building closest to the dredge on the north side of the road contained the 1890 mill which was modified over time. The square building adjacent to it was a turbine building that was built in 1921. As production increased, Stamp Mill No. 2 was built to the north of the No. 1 mill in 1900 and had three stamps. Underground mining activities at the Quincy Mine focused on mining ore (rock with sufficient recoverable copper to make a profit). Inevitably the mine also produced waste (uneconomic) rock along with the ore rock. Some of this waste rock can be seen today throughout the Keweenaw Peninsula as poor rock piles. Some of the waste rock was used underground as fill for already mined out stopes. The broken ore from underground blasting that is small enough to pass through a coarse grating was sent by train to the processing mill. 73 �The purpose of the mill was to remove as much rock as possible from the native copper producing a product where the percent of contained copper is up to 20 times higher than the percent of copper in the ore. The copper-rich product is sand to smaller sized fragments of native copper mixed with similar sized rock and mineral fragments (termed “copper concentrate”). The inefficiencies in separating native copper from rock and minerals fragment results in some amount of waste rock and minerals in the copper concentrate. At the end of processing in the mill, most of the rock and minerals end up as fine sand to sand of waste containing only a small amount of copper (termed tailings). The Quincy Mill used several techniques to separate the copper from the rock and minerals. The essential first step in milling begins with crushing the ore rock to a small enough size to liberate the unwanted rock and minerals from the native copper. The ore rock and minerals containing disseminated copper of various sizes was crushed by steam stamps. Much of the rock was liberated from the native copper by crushing the broken ore fragments derived from mining to fragments 0.0165 to 0.188 inches in diameter (fine to very fine sand size). Larger masses of native copper were removed prior to crushing at the mine and sent directly to the smelter. Since the density of native copper is much higher than the liberated particles of rock and mineral, gravity and water methods could be used to separate the waste rock and minerals (tailings) from the copper. Early mines used jigging to concentrate the native copper from the tailings. Jigging was a well-developed mineral separation technology prior to the first mining of native copper in the Keweenaw Peninsula beginning in 1845. Jigging is accomplished by placing the sand sized particles on a screen where pulsating water allows the heavier copper particles to settle while the lighter particles rise to the top and overflow the screen or are skimmed off the top as waste tailings. Jigging resulted in a “concentrate” of sand sized native copper particles with some rock and minerals that were not copper-bearing (tailings), about 50 % copper and the rest waste rock and mineral. The concentrate was sent to the smelter to be turned into nearly pure copper. The waste tailings were dumped into nearby Torch Lake. However, using jigging up to 25 % of the native copper was incorrectly classified as waste (tailings) and dumped the copper was lost as the tailings were dumped into nearby Torch Lake. Over time new technologies were introduced into the mills by Quincy to increase efficiency and loose less copper into the tailings. Quincy used froth flotation in its processing circuit as early as 1920s. Violent agitation of copper and rock/mineral particles in an oily water along with frothing agents and other chemicals cause bubbles to rise to the surface with copper particles attached to their surface. The bubbles and copper particles were captured from the top of the flotation tank while the waster rock/mineral (tailings) sank to the bottom. and was slurried to Torch Lake. The heavier copper particles were carried upward by the floatation bubbles rather than sinking due to gravity by jigging. The mineral processing circuit could begin with jigging and with the tailings after jigging sent to floatation cells to recover more copper. Later Wilfley tables were added to the mineral processing circuit to help minimize loss of copper from finer grain sizes. A Wilfley table utilizes gravity and water to separate denser particles. A shaking ribbed table with a film of water flowing along the long axis results in the higher density copper particles concentrating in beds behind the riffles. 74 �The Quincy Mining Company knew that the tailings contained a lot of copper that they were unable to recover with technology available at that time. The company had considerable foresight and kept detailed maps each year of the copper content of the tailings that were deposited into the lake. As technology improved, they were able to reclaim copper from the tailings at a profit. Quincy built a special reclamation processing mill near here in 1942-43 for $1.2 million. The main building, 124'x255', had six Harding ball mills to grind the tailings even finer than the stamp mills in order to release more fine particles of copper from the rock/mineral and facilitate addition of Wilfley tables and flotation cells to mineral processing circuit. Across the road is Quincy Mining Company dredge No. 2 on the shore of Torch Lake. Torch Lake was filled with several 100 millions of tons of tailings since not only did Quincy Mine operate a mill on its margin so did many other companies, especially Calumet and Hecla Mining Company. The tailings were sucked up via the dredge and sent to the reclamation mill to recover more copper from the tailings. The reprocessed tailings were redeposited back into Torch Lake. This dredge was built in 1913 by Calumet & Hecla Mining Company. In 1951, the Quincy Mining Company purchased the dredge and it became known as Quincy Dredge No. 2. It could process over 10,000 tons of tailings per day and it had 141 ft suction pipe that could work 115 ft below the surface of the lake (Figure 10). Tailings were conveyed to the mill via a tube held up with pontoons. Quincy recovered 100 million lbs. of copper from tailings in Torch Lake from 1943 until it closed in 1967 or about 10 % of total production. In the 1800s and early 1900s, depositing 100s of millions of tons of tailings into Torch Lake was acceptable practice and the environmental consequences were not considered. Today, the environmental impact of tailings must be carefully considered to obtain a permit, "social license" to operate a mine. The mining companies did not just put tailings into Torch Lake, they also used it to dispose of other waste such as that from electrical systems and barrels filled with chemicals. The early processing plants used only water to separate the copper from the rock. Later floatation cells were used in processing ore from the mine and in processing reclaimed copper from the tailings. The floatation cells used chemicals in water. These chemicals along with the tailings were put into Torch Lake. Discovery of fish with tumors in Torch Lake led to its being designated an U.S. Environmental Protection Agency Superfund site. Some of these chemicals were biodegradable and are no longer present in the Torch Lake water but would have been present decades ago, thereby could have readily caused tumors in older fish. There are far too many tons of tailings in Torch Lake to remove them and thus, the mitigation strategy is to simply cover them with soil. Fortunately, the copper ores of the Keweenaw Peninsula lack pyrite that is known under certain environmental settings to produce acid drainage and in turn can result in significant environmental impact. The lack of acid generating potential and the otherwise mostly inert minerals in the waste rock has greatly lessened the environmental impact of the tailings themselves. Today crushed poor rock from the mines is used directly as aggregate and is also crushed for use as aggregate. Text from previously published field trip guide by Bornhorst (2022) with limited modification. 75 �Figure 10: Quincy Mining Company dredge No. 2 working on Torch Lake, ca. 1920s. From Molloy (2011). Stop 5: Ahmeek Mining Company Stamp Mill Latitude: 47.168633N; Longitude: -88.435810W Directions: From Quincy Mill Ruins and Dredge carefully pull out of gravel lot and continue east on M-26 for 1.9 miles (3 km) to stamp mills of the Ahmeek Mining Company. This is the only remaining steam-powered stamp in the Keweenaw Peninsula. The Ahmeek Mining Company had four of these Nordberg compound steam-powered stamps installed in 1910, and four additional stamps were added in 1914. Rail cars brought rock to the mill using the trestle, located above the trees across the street from the stamp. The compound-expansion nature of the stamps represented a major improvement in processing of copper ore. The stamp could strike approximately 104 24-inch blows per minute. The mill could process approximately 7,000 tons of ore in a 24-hour period. This is not part of the Quincy Mine but we stop here to see a steam-powered stamp used for crushing the native copper ore. Text from previously published field trip guide by Bornhorst (2022) with limited modification. 76 �References Cited Bornhorst, T.J., this volume, 2024, Mesoproterozoic Midcontinent Rift-filling Strata and Native Copper Deposits of the Keweenaw Peninsula, Michigan Field Trip 1: Institute on Lake Superior Geology, Field Trip Guidebook, 70th Annual Meeting, Houghton, MI v. 70, part 2, p. this volume. Bornhorst, T. J., 1997, Tectonic context of native copper deposits of the North American Midcontinent Rift system: Geological Society of America Special Paper 312, p. 127-136. Bornhorst, T.J., 2022, Field guide to the geology and native copper mining history of the Keweenaw Peninsula: Field Trip Guidebook for American Institute of Professional Geologists 2022 National Conference held in Marquette, Michigan August 6-9, 68p. Bornhorst, T.J., Kalliokoski, J.O., and Paces, J.B., 1986, The Keweenaw native-copper district: in Brown, A.C. and Kirkham, R.V. (eds.), Proterozoic Sediment-hosted Stratiform Copper Deposits of Upper Michigan and Belt Supergroup of Idaho and Montana: Geological Survey of Canada, Contribution Series 13386, p. 21-36. Bornhorst, T. J., and Lankton, L. D., 2009, Copper mining: A billion years of geologic and human history: in Schaetzl, R., Darden, J., and Brandt, D. (eds.), Michigan Geography and Geology, Pearson Custom Publishing, New York, p. 69-90. Bornhorst, T.J., and McDowell, S.D., 1992, Michigan Tech Earth Science Laboratory and Experimental Mine connecting with the Quincy native copper mine, Michigan: Society of Economic Geologists Field Conference Guidebook Series, v. 13, p. 100-104. Bornhorst, T.J., and Molloy, L.J., 2016, Geological and Historical Field Trip to the Keweenaw Peninsula: A Tribute to Douglass Houghton "Michigan's Pioneer Geologist". Michigan Basin Geological Society, 65 p. Bornhorst, T. J., and Molloy L.J., 2016, Geological and historical field trip to the Keweenaw Peninsula, A tribute to Douglass Houghton: “Michigan’s Pioneer Geologist: Michigan Basin Geological Society Geological and Historical Excursion September 10th-12th, 89 p. Bumgarner, E.L., 1980, The Geology of the Portage Lake Volcanics in the M.T.U. Mining Laboratory, Hancock, Michigan: Michigan Technological University, M.S. thesis, 138 p. Butler, B. S., and Burbank, W. S., 1929, The copper deposits of Michigan: U.S. Geological Survey Professional Paper 144, 238 p. Caine, J.S., Evans, J.P., and Forster, C.B., 1996, Fault zone architecture and permeability structure: Geology, v. 24, no. 11, p. 1025-1028. Caine, J.S. and Forster, C.B., 1999, Fault zone architecture and fluid flow: Insights from field data and numerical modeling: in Faults and Subsurface Fluid Flow in the Shallow Crust, American Geophysical Union, Geophysical Monograph 113, p. 101-128. Cannon, W.F. and Nicholson, S.W., 2001, Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan: United States Geological Survey, Map I-2696, Scale = 1:100,000. 77 �DeGraff, J.M. and Carter, B.T., 2023, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulletin, v. 135, no. 1/2, p. 449–466. https://doi.org/10.1130/B36186.1 Fink, J.H. and Fletcher, R.C., 1978, Ropy pahoehoe: surface folding of a viscous fluid: Journal of Volcanology and Geothermal Research, v. 4, p. 151–170. Hubbard, L.L., 1898, Keweenaw Point with particular reference to the felsites and their associated rocks: Geol. Survey Michigan, v. 6, part 2, 155 p. Langfield, K.M., DeGraff, J.M., and Gamet, N.G., 2023, Slip kinematics of the Keweenaw and Hancock faults within the Midcontinent Rift System, Upper Peninsula of Michigan: Institute on Lake Superior Geology, 69th Annual Meeting, Eau Claire, Wisconsin, Part 1 – Program and Abstracts, v. 69, p. 5051. Lankton, L.D., 1991, Cradle to Grave: Life, Work, and Death at the Lake Superior Copper Mines, Oxford University Press, 319 p. Lankton, L.D. and Hyde, C. K., 1982, Old Reliable: An Illustrated History of the Quincy Mining Company, Quincy Mine Hoist Association, 159 p. Molloy, L. J., 2011, A guide to Michigan's historic Keweenaw copper district: published by Great Lakes Geoscience LLC, 122 p. Molloy, L. J., 2007, A Visitor's Guide to the Historic Quincy Mine: published by Great Lakes Geoscience LLC, 61 p. Self, S., Keszthelyi, L., and Thordarson, T., 1998, The importance of pahoehoe: Annual Review of Earth and Planetary Sciences, v. 26, p. 81-110. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250-1277, p. 1444-1460. Thurner, A. W., 1994, Strangers and Sojourners: A History of Michigan's Keweenaw Peninsula, Wayne State University Press, 404 p. White, W. S., 1968, The native-copper deposits of northern Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933-1967 (the Graton Sales volume), American Institute of Mining, Metallurgical, and Petroleum Engineering, New York, p. 303-325. 78 �Field Trip 3 Geoheritage of Buffalo Reef: Industrial Impact on Land, Culture, and Fish Sovereignty Erika Vye Great Lakes Research Center, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 Charlie Kerfoot Great Lakes Research Center, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 Stephanie Swart Michigan Department of Environment, Great Lakes, and Energy, 525 West Allegan Street, Lansing, MI, 48909 Dione Price Keweenaw Bay Indian Community, Natural Resources Department, 14359 Pequaming Road, L’Anse, MI 49946 Evelyn Ravindran Keweenaw Bay Indian Community, Natural Resources Department, 14359 Pequaming Road, L’Anse, MI 49946 INTRODUCTION Buffalo Reef is a geoheritage site with scientific, educational, cultural, and aesthetic value. This field trip explores the relationship between geology, mining waste, and culture of Buffalo Reef a 2,200-acre natural cobble feature of Lake Superior’s lakebed southeast of the Keweenaw Peninsula and about 20 miles northeast of Houghton. Finely crushed waste rock - stamp sand from copper ore milling operations at the community of Gay have been moved by currents along the shoreline of the Keweenaw Peninsula to Big Traverse Bay, thus covering this highly productive spawning ground for lake trout and whitefish. This has negative implications for commercial fisheries, local economies, subsistence uses, and the spiritual, physical, and cultural well-being of tribal nations that identify as fishing people. Further, this has adverse impacts on tribes’ ability to exercise their treaty rights to fish in this area (Buffalo Reef Task Force, 2024). Geoheritage is a nascent yet evolving field in the United States that considers the protection, interpretation, and management of geologic features with significant scientific, educational, cultural, or aesthetic value (Brocx & Semeniuk, 2007; Geological Society of America, 2017; National Park Service & American Geosciences Institute, 2015; Reynard & Brilha, 2017). More 79 �distinctively, geoheritage emphasizes the importance of the varied personal values people have for geologic features and explores the wide-ranging relationships people have with landscape. The rich geodiversity of the Keweenaw has fostered relationships for millennia and has imbued our place with significant sites that provide opportunities to broaden both Earth science and cultural literacy (Rose & Vye with Martin, 2017; Vye, 2016). The rich geosites of the Keweenaw provide an accessible platform for people to learn about deep time, Earth's dynamic processes, and importantly, the diverse relationships and reciprocity people have with our geologic underpinnings. The Keweenaw is renowned for Earth's largest native copper deposits that became the first great copper mining district in the United States. From 1845 to 1968, over 11 billion pounds of refined copper were produced in Keweenaw mines, making it a cornerstone of the American economy in the 19th and 20th centuries (Bornhorst & Lankton, 2009; Bornhorst & Barron, 2011). Interpretations and public educational programming depicting the relationship between people and geology have largely focused on stories and heritage associated with the European diaspora that fueled the Copper Boom of 1845-1968 and how copper’s prolific use for transatlantic cables, telegraphs, electricity, and the auto industry ultimately modernized the country (Bornhorst & Lankton, 2009). Less interpreted, yet central to our history, is how geology has shaped, and continues to shape, the ancestral, traditional, and contemporary lands, waters, and livelihoods of the Anishinaabeg- the Three Fires Confederacy of Ojibwe, Odawa, and Potawatomi peoples and their many more-than-human relatives. As such, this field trip visits three stops (Figure 1) to explore mining impacts on culture, subsistence uses, and the wellness of all beings. Figure 1: Map of field trip site locations, courtesy of D.J. Lizzadro-McPherson, MTU 80 �Stop 1 - Mohawk, MI: The trip begins at the poor rock pile where the Mohawk No. 4 mine shaft once stood - a native copper host rock from which some of the Gay stamp sands were generated. Stop 2 - Gay, MI: Participants will then travel to the town of Gay to walk the stamp sands and learn how Tribal, State, Federal, and academic partnerships are collaborating to mitigate environmental damage and ultimately restore Buffalo Reef to the ecological resource that has sustained both tribal and non-tribal communities for generations. Stop 3 - Big Traverse Bay & Buffalo Reef, MI: From Gay, we will travel to Big Traverse Bay to learn more about why shoreline and habitat restoration efforts are necessary and how stakeholders and rights holders are working together to address this environmental justice issue in our community. Participants will benefit from visiting Buffalo Reef aboard Michigan Tech’s Research Vessel Agassiz. This part of the trip enables participants to compare healthy parts of the reef with areas that have been inundated with stamp sands. STOP 1 - MOHAWK, MI At this site, we will learn more about the source rock for the Gay stamp sands after a brief overview of the geological history of the Keweenaw region. Participants will have time to explore the poor rock pile before departing for Gay. Directions: Leave downtown Houghton and head north on U.S. 41 towards Calumet. Stay on U.S. 41 until you reach Mohawk; turn right on 6th street, just past E Phoenix Street there is a place to park on the left-hand side of the road. This space provides access to the Mohawk No. 4 poor rock pile (Figure 2). Coordinates: 47.301203, 88.363369 Figure 2: Parking location to visit Mohawk No.4 Geological Origin Story Michigan’s Keweenaw Peninsula has a rich and globally significant geodiversity in tandem with a fascinating cultural story. This is the site of the largest native copper dominated deposits known on Earth, the oldest metal workings in the Western Hemisphere, and a recent diaspora of 81 �European cultures that flocked to the region for copper mining in the late 1800s – this has shaped an entangled mosaic of cultural, mining, and industrial heritage. Importantly, the Keweenaw Peninsula offers an important window to Earth’s past, exposing the heart of the Mesoproterozoic Mid-Continent Rift. Located on Lake Superior in Michigan’s Upper Peninsula (Figure 3); the abundant geodiversity sites are the result of a flood basalt sequence comprised of hundreds of voluminous lava flows, interbedded and covered by a redbed clastic sedimentary rocks. An upwelling of heat and magma from a hot spot initiated great lava flows erupting from the rifting of supercontinent Rodinia. The rift created a ~3000 km U-shaped feature in the center of North America that extends from Kansas, through what is now Lake Superior and terminated in what is now Michigan (Cannon, 1994, Cannon and Nicholson, 2001, Stein et al., 2015). Figure 3: Extent of rifting associated with the Mid-Continent Rift (K. Schulz, USGS) Some of the largest lava flows on Earth erupted and ponded in the Mid-Continent rift over many centuries (Huber, 1983). During quiet times, red-brown conglomerates and sandstone were deposited between flows in high-energy alluvial fans (Elmore, 1984). The interbedded lava flows and sedimentary layers were normally faulted resulting in a syncline feature that extends from Isle Royale to the Keweenaw Peninsula, now the basin for Lake Superior (Figure 4). Copper was brought to the surface by hydrothermal systems mineralizing permeable layers such as the amygdaloids of lava flow tops and the cracks and crevices of conglomerate rocks (Bornhorst & Barron, 2011, Nicholson et al, 1997, Cannon, 1984). Figure 4: Cartoon depicting interbedded lava flows and minor sedimentary rocks (Huber, 1983. 82 �The Keweenaw is noted for mining nearly 9000 years ago (Martin, 1995, 1999). The valued red metal has since been traded up and down the Mississippi by the Ojibwa caretakers of this landscape and used in ceremony today. From 1845 to 1968, ~11 billion pounds of refined copper were produced from Keweenaw Peninsula mines making it one of the cornerstones of the American economy and the first great metal mining district in the United States (Bornhorst and Barron, 2011, Bornhorst and Lankton, 2009). The region has been extensively mapped and researched since the mid-1800s because of the discovery of copper and the subsequent mining boom. This field trip explores the impacts related to one of the many mining sites in operation from the late 1800s to mid-1900s in the Keweenaw region - Mohawk Mine, a native copper host rock from which some of the Gay stamp sands were derived. Mohawk No. 4 This field stop explores the site of the Mohawk mine, specifically the poor rock pile associated with the Mohawk No. 4 shaft (Figure 5). Rock from this site is the main source for the Gay stamp sands. Following the discovery of copper on the property in 1896 by lumberman Ernest Koch, the Mohawk Mining Company was founded. It was incorporated in 1898 and lasted until 1932 (John Stanton as president, later replaced by Joseph Gay). In 1923 the Mohawk Mining Company took over the neighboring Wolverine Figure 5: A group of Keweenaw youth explore the poor rock Copper Mining Company and the pile at Mohawk No. 4 (photo credit Erika Vye) Michigan Copper Mining Company. In 1934 the company was purchased by the Copper Range Company (Molloy, 2008). The Mohawk Mine had six shafts numbered 1 through 6 running from north to south along what is now US 41. The was a profitable mine paying out over $15 million in shareholder dividends between 1906 and 1932 (Clark, 1978). The No. 4 shaft of the Mohawk Mine was constructed at this site in 1901 and stayed open until the mine closed in 1932 (Figure 6). In the early days of operation, the shaft reached a depth of 501 feet. Technological advances in 1904 led to equipping the No. 1, 2, and 4 shafts with Nordberg Conical Drum Hoists (Figure 7) enabling depths of up to 6000 feet. With this technology, the shaft reached a depth of 900 feet by 1906, 1,175 feet by 1908, and by 1922 a final depth of 2,832 feet. In 1914, the No. 4 shaft was producing between 450 and 500 tons of ore per day. Mining continued from the No. 4 shaft until 1924, with a brief lull in operations until it was reopened in 1926, eventually closing in 1932 (Clark, 1978). 83 �Figure 6: No 4 shaft in Mohawk, MI (photo courtesy of the MTU Archives) Figure 7: Image of Nordberg hoist; the world's largest Nordberg hoist can be visited at the Quincy Mine in Hancock, MI, pictured here (photo courtesy of the MTU Archives) 84 �Ore Deposit and Significant Minerals The Kearsarge lode at Mohawk is a native copper-dominated deposit with minor native silver hosted by basalt lava flows of the Portage Lake Volcanics (about 1.1 billion years old). The strike of the Kearsarge orebody is N45E, dips at 35W, and is 2.9 meters thick, 1,490 meters wide, with a total length of 3,250 meters spanning an area of 250 hectares. The productive part of the fragmental amygdaloidal lode was richer at greater depths than nearer to the surface where the lode consisted of more massive basalt. The Kearsarge lode was the second largest in the district and averaged 6 to 13 feet thick (Butler & Burbank, 1929; White et al, 1953; and USGS, 2005). The fragmental amygdaloid ore of the Mohawk mines is associated with arsenic-rich minerals, more common than in most of the other Keweenaw deposits. The Mohawk mine is well known among mineral collectors for its large occurrence of mohawkite - a mixture of algodonite, domeykite, and copper (Moore, 1971). Mohawkite was first found on the property in 1901, on the first level north of the No. 1 shaft. In addition to copper, the mine also produced a small amount of native silver (Figure 8). Figure 8: Left -Polished mohawkite, a rare mixture of copper and copper arsenides, is named after the Mohawk-Ahmeek area of the Keweenaw (Photo by Robert M. Lavinsky); Right – native copper in amygdaloidal basalt. Geologic features of note include the occurrence of the Mohawkite Fissure that crossed the Kearsarge lode. From 1900-1901, 105 metric tons of mohawkite ore was produced from the Mohawk Mine at the No. 1 shaft. From 1902 through 1925 the No. 1 shaft produced about 117,000 metric tons of refined copper. Additional veins were discovered south of the No. 2 shaft in 1901 resulting in 230,000 pounds of mohawkite (Butler and Burbank, 1929). Mohawkite proved to be challenging in the Keweenaw as smelters were not able to process it on account of the high arsenic levels and the deadly fumes produced. A unique smelter was built in Hackensack Meadows, New Jersey for the specific purpose of processing the ore; it became 85 �operational in 1901. The mohawkite ore contained mostly copper and arsenic, it also contained small amounts of nickel and cobalt, as well as about 20 ounces of silver per ton of ore. (Stevens, 1902) Copper-bearing rocks were transported 11 miles by rail to the town of Gay for milling near the mouth of the Tobacco River on Traverse Bay. This is the next stop on the field trip. STOP 2 – GAY, MI This part of the field trip begins at the Gay Sands sign just outside of the town of Gay. This stop is intended to engage participants in a discussion of how the stamp sands were generated and to learn how Tribal, State, Federal, and academic partnerships are collaborating to mitigate environmental damage and ultimately restore Buffalo Reef to the ecological resource that has sustained both tribal and non-tribal communities for generations. Participants will have an opportunity to walk the stamp sands (accessed just south of the Gay Sands sign): note that at times large trucks are moving through this area; always exercise caution and stay together. Directions: From Mohawk, travel to the town of Gay; follow the Mohawk-Gay Road. When you arrive in Gay, turn right on Main Street, then left on 2nd Street (which becomes the Gay Lac la Belle Rd), park on the right-hand side of the road beside the smokestack and local signage that shares information about the Gay stamp sands (Figure 9). Coordinates: 47.226766, -88.161933 Figure 9: Left - Gay Sands signage; Right – Gay mill smokestack (photo credit Erika Vye) How were the stamp sands created? Liberating the copper from the host rock required a large water source - in this instance, Lake Superior. In 1900, the Wolverine mine and mill opened in Gay. This piqued the interests of New York financiers of the Central, Atlantic, and Baltic mining companies and shortly thereafter the Mohawk mines and mills were opened. The two mills were built in Gay by the Mohawk and Wolverine mining companies enabling the processing of copper ore. A railroad was built to 86 �transport the copper-bearing rocks from Mohawk to Gay; poor rock was left at the mine sites in Mohawk remaining in piles today. A dock was built nearby to import coal to power operations and to load copper on ships to transport to other places (Keweenaw County Historical Society). Note: A QR is included in the resources section of this guide leading to the recently developed Gay Mills Exhibit created by the Keweenaw County Historical Society. An unusual landscape & vastly different soundscape When visiting this site take note of what you hear; try to imagine what the soundscape of this place might have been like in the early 1900s. At that time, the stamps at both mills were running constantly. Imagine the ground shaking with over 70 stamps per minute crushing pieces of rock brought up from underground to free the copper from the matrix. The next step required washing the material to separate the copper and produce a copper-rich mineral concentrate to then be sent to the smelter and formed into copper ingots (Lankton, 2005). The material was brought to the top of the mill with a railway line. To process the copper and create the concentrate, water was pumped from Lake Superior, and the tailings and waste slurry were dumped back into the lake with conveyors. The length continued to grow as the tailings built up along the shoreline (Keweenaw County Historical Society). Figure 10 shows an image of this process on the left, with what remains of this structure today. Figure 11 illustrates the milling process. Figure 10: Left - Conveyor sending tailings slurry back to the lake (Photo credit: MTU Archives) during milling operations in Gay; Right - wood beams left from conveyor structure as sands are continually swept away by wind and currents over time (Photo by Erika Vye) What is happening to the sands? From 1900-1930 the mills flushed over 22.7 million metric tons of tailings to Lake Superior leaving a large bank of black sand, the consistency of kitty litter, along the shore. This finely crushed waste rock has moved, and continues to move, along the southeast shoreline of the Keweenaw Peninsula to Grand Traverse Bay Harbor threatening the nearby Buffalo Reef. Since the 1930s Lake Superior’s fierce storms and strong currents have eroded the stamp sand bank, pushing the tailings into the lake and gradually moving them southward along the shoreline to 87 �the Traverse River. These stamp sands contain high amounts of copper and cover 1,426 acres of shoreline and lakebed. Currently, 30% of the reef has been impacted by stamp sands; modeling predicts that by 2025 stamp sands will impact 60% of the reef. The next stop focuses on the importance of understanding the impacts of these predictions and what is happening for restoration. Before traveling to the last stop we will have lunch at the Gay Park. This site also hosts the Gay Historic School and Museum open from 1 PM to 4 PM on Wednesday and Saturday. 88 �Figure 11: This image describes how copper was processed in the mills - first by gravity and large amounts of water through steam stamps, the rock was funneled into a trommel that sorted and classified the pieces by size. A jig then separated the copper from the mine rock. Next, a series of vibrating Wilfley tables separated the tailings from the small-sized copper. This image was recently modified for a Keweenaw County Historical Society exhibit on the Gay Mills (a link for the exhibit is found in the Resources section of this guide). Original delineation by the Historic American Engineering Record, Heritage Conservation & Recreation Service, Eric M. Hansen, 1978. Modification by David A. Vago, MTU, for the Houghton County Historical Society, 2005; updated 2021. STOP 3 - BIG TRAVERSE BAY & BUFFALO REEF. MI At this site, we will explore how the Gay sands are impacting life and culture in the region, learn about remediation efforts, and how we can share in educating ourselves and others about this environmental justice issue. Directions: From the Gay Park by the Historic School and Museum travel left on Lake Street, then right on 1st Street (becomes the Lake Linden-Gay Rd). Turn left onto Rice Lake Rd, which becomes the Big Traverse Rd. Turn left on the Traverse River Rd, please drive slowly along this road as there are families and small children frequently playing here. This takes approximately 15 min from Gay to Big Traverse. Note that the dock is on the other side of the harbor; to get there simply head back to Big Traverse Rd, then turn left. The dock is about ¼ mile ahead. Coordinates: Big Traverse Bay 47.189857, -88.236644, Dock to board Agassiz 47.190769, 88.237154 What is Buffalo Reef? Buffalo Reef is a natural cobble 1 feature in Lake Superior, located just off the eastern edge of the Keweenaw Peninsula in the U.P. of Michigan (Figure 12). The reef has historically maintained an invaluable spawning habitat for fish species such as lake trout and lake whitefish. Buffalo Reef is estimated to supply 33% of the tribal harvest of lake trout and lake whitefish from Michigan waters of Lake Superior (i.e. 136,375 pounds of whitefish and 61,830 pounds of lake trout average annual yield 2001-2016). Figure 11: Location of Buffalo Reef, also not the locations of Additionally, if the stamp sands both Field Trip Stop 2 and 3, marked by stars. migrate south of Grand Traverse Harbor, they will threaten the undisturbed native sand that serves as habitat for juvenile whitefish (Kerfoot et al, 2012 & 2021). Juvenile whitefish produced on Buffalo Reef migrate south of 89 �Grand Traverse Harbor to sandy, shallow-water habitat where they feed before migrating to the deeper water they inhabit as adults. Without this habitat, whitefish recruitment in the vicinity of Buffalo Reef would be greatly diminished. Whitefish provide the bulk of the commercial, cultural, and spiritual value for the tribal communities that use this resource (BRTF, 2024). How are the stamp sands impacting Buffalo Reef? Most of the cobbles are glacial rocks, scattered around the Jacobsville sandstone bedrock highs of the reef. During spawning, fish drop eggs into the crevices between rocks. Cobbles are coated with a natural organic film, the basis of a food web for feeding fish. Stamp sands move into the northern cobble field of Buffalo Reef burying cobbles and killing living communities on rocks along the leading edge of the sands. (Figure 13). These impacts to fish habitat create a risk for a decline in commercially and culturally important fish keynote species. Importantly, a decline in species impacts the ability to exercise treaty rights. The sands also have high enough copper concentration (about two-eighths of a percent) to be toxic to fish and other organisms that live in Grand Traverse Bay. There are additional impacts to human health through fish consumption. Other concerns include the impacts of the copper-toxic sands on coastal wetlands medicine chests to the KBIC - as the material migrates up streams thereby affecting plant and amphibian habitat (Kerfoot et al, 2012, 2021, in prep). The sands also impact the aesthetics and sense of place inspired by the landscape; the aerial photos in Figure 14 illustrate the movement of the stamp sands inundating white sand Figure 12: Healthy reef habitat progressively beaches along the south shore of the inundated with stamp sands until covered completely Keweenaw Peninsula. The stamp sands also (Photos by Charlie Kerfoot) create challenges for people coming and going from the Big Traverse Bay Harbor; the sands have repeatedly blocked the harbor stopping boat traffic. For example, in 2015, Big Traverse Bay Harbor was dredged removing 4,500 cubic yards of stamp sand. Dredging happens repeatedly here, without this continued maintenance there is a great risk of harming the region’s fishing industry. As such, local stakeholders are working with the Army Corps of Engineers on a long-term solution. 90 �Figure 13 Figure 14: Aerial views of the entry of Traverse River into Lake Superior. The regular movement of stamp sands over the top of the breakwater requires annual or biennial dredging to keep the small Traverse River Harbor, home of a commercial fishing fleet, open to entry. Note the black sands on the left to the north of the channel compared to the white (natural) sands to the right. Left photo credit: Neil Harri; Right photo credit: Charlie Kerfoot Impacts on Fish Sovereignty Buffalo Reef lies within the ceded-territory homelands established by the Treaty of 1842 where 11 Lake Superior Bands of Ojibwa retain rights and responsibilities to harvest fish from the Michigan waters of Lake Superior. Buffalo Reef has always been considered a culturally significant harvesting ground for local communities. Fishing is the strand of the cultural core that ties history to the present day and the future; it is a vital part of the foundation for cultural beliefs and values, traditional lifeways, and even individual identity (Gagnon, 2018; KBIC, 2017). The KBIC identify as fishing people and have always had a strong focus on cultivating and protecting relationships within ecosystems that support healthy food sovereignty initiatives within the community (Figure 15). The Anishinaabeg teachings and ways of life emphasize that landscapes and waters are an intricate system of diverse relationships, and interconnected rights and responsibilities rooted in an acknowledgment and understanding that humans and nature are relatives. These sentient elements have been honored in ceremony since time immemorial and these important teachings Figure 14: Fresh catch on Keweenaw Bay 91 �and traditions continue today. These relationships are founded in the long-standing nation-tonation agreements between the Anishinaabe Ojibwa and all orders of creation from rock, water, fire, and wind; the physical world of sun, stars, moon and earth; plant beings; animal beings; and human beings - all rooted in the First Treaty with Gichi Manidoo (the Creator), also known as Sacred Law, Original Instructions, and Natural Law (Johnston, 1976; Keweenaw Bay Indian Community, 2021). Today, Tribal, State, Federal, and Academic partnerships are combining efforts to mitigate damages and ultimately restore Buffalo Reef as the ecological resource that has sustained both tribal and non-tribal communities for generations. Buffalo Reef Remediation Efforts This is a complex environmental justice issue requiring local, regional, and state stakeholders and rights holders to work together on research and restoration efforts for Buffalo Reef. It was tribal fishermen who first alerted our communities of this issue, underscoring the vital need to bridge knowledges for a holistic understanding of what is happening within our landscape and to recognize the gifts that different knowledges share. Research over the past years has included: a) modeling wave action, currents, and how the sands are migrating across the coastal shelf and along the shoreline; b) use of LiDAR and sonar assessments to understand the extent of the sands underneath water; c) submerging remotely operated underwater vehicles to take pictures of the boulder and cobble fields to assess the quality of the remaining fish habitat; d) researching environmental impacts on the benthic and fish communities; e) exploring considerations for building a revetment to hold back stamp sands from further entering the bay; f) conducting archaeology to understand industrial heritage, mining legacies and Native American uses of the area prior to colonization; and f) and meeting with community members to understand social and economic impacts on the communities involved. After years of observation, scientific study, and dredging at Big Traverse, the EPA funded a feasibility study for a long-term solution. In 2017 the USEPA endorsed the formation of a Buffalo Reef Task Force (BRTF) comprised of multiple state, federal, and tribal agencies. In addition, several academic institutions and private entities have joined the team, recognizing that this issue is larger than any single entity can accomplish on its own. The Buffalo Reef Final Alternatives Analysis Report (Report) was recently on public notice from January 30 to March 1, 2024. This report provides an overview of efforts made by the BRTF “in 2019, the BRTF identified 13 potential alternatives to remediate the stamp sands and restore the habitat. The alternatives were screened based on constructability, operation and maintenance requirements, environmental impact, ecological sustainability, initial costs and legacy costs, regulatory requirements, public input and opinion, time needed for implementation, impact to local populations, and potential for beneficial use of the stamp sands”. Three alternatives were selected for further consideration that included the dredging and disposal of stamp sands in the following locations: 1) White Pine Mine, a closed tailings basin; 2) a Lakeside Placement site; and 3) an Upland Placement site. In 2022, a public meeting was held to discuss the one alternative that would be feasible - the removal of the stamp sands to a regulated and lined landfill to be constructed near Gay. These remediation efforts require land ownership, 92 �both at the shore for a proposed jetty to impede migration of the stamp sands and an upland placement area to move the mining waste. The Report indicates that the BRTF’s preferred remedial alternative and “Potential Plan” identifies the “Upland Placement Alternative” as the BRTF’s preferred remedial alternative (Figure 16). The study compares three scales of implementation for the Upland Alternative are compared in the report. “The scale of implementation differs based on the volume of stamp sands to be dredged and disposed of during the implementation phase. Additionally, the study provides an assessment of the impact the volume of stamp sands removed during implementation has on the cost and duration of the operation, maintenance, repair, replacement, and rehabilitation phase.” Figure 16: Upland Placement Alternative: Small, Medium, All Dredging Scales represented (Left to Right). S Shoreline – South Shoreline; M Shoreline – Middle Shoreline; and N Shoreline – North Shoreline. The Upland Placement footprint required to dispose of the volume of stamp sands removed during project implementation varies per dredging scale. In the placement site measure, the solid white line represents the estimated placement site footprint to contain the stamp sands dredged during the project implementation phase. The dashed white line represents the estimated placement site footprint to contain stamp sands dredged during the OMRR&R project phase (sourced from page ES-5 of the Buffalo Reef Final Alternatives Analysis Report). RETURN TO HOUGHTON Billion-year-old geologic processes brought copper to the surface where people could find it - a gift from the deep Earth. Relationships with the red metal have varied over millennia resulting in different values and actions within our shared lands and waters. Further efforts are required by all stakeholders and rights holders to communicate and elevate the importance of this environmental issue with decision-makers, government officials, and environmental advocacy groups. This field trip is meant to deepen our understanding of these relationships and to reflect on the following questions: What are the relationships between people, Earth, and Buffalo Reef? Why does this matter? How have people impacted Buffalo Reef in the past, and how will they in the future? What can you do to help with the remediation efforts of this place? 93 �Directions: From Big Traverse Bay Harbor, head north on S Big Traverse Rd and continue along Rice Lake Rd. Take M-26 S to US-41 S in Houghton. EDUCATIONAL RESOURCES Access the following websites and videos by following the QR codes. Saving Buffalo Reef Website (DNR) Saving Buffalo Reef Video (GLIFWC) Buffalo Reef Restoration (Great Lakes Now, Ep. 1006 Segment 3) Gay Milling at Gay A Lake Superior Story - REFERENCES CITED Bornhorst, T. J. and Barron, R. J. (2011). Copper deposits of the western Upper Peninsula of Michigan. Geologic Society of America, Field Guide, 24, 83-99. Bornhorst, T. J. and Lankton, T. J. (2009). Copper Mining: A Billion Years of Geologic and Human History, in Schaetzl, R., Darden, J. and Brandt, D. (eds.) Michigan Geography and Geology. United States of America: Pearson Custom Publishing, 150-173. Brocx, M. and Semeniuk, V. (2007). Geoheritage and geoconservation - history, definition, scope and scale. Journal of the Royal Society of Western Australia, 90, 53-87. Buffalo Reef Task Force (2024). DRAFT Buffalo Reef – Final Alternatives Analysis. Retrieved from: https://www.michigan.gov/dnr/-/media/Project/Websites/dnr/Documents/Fisheries/BuffaloReef/00DRAFT-Buffalo-Reef-Main-ReportJAN2024.pdf?rev=1ebf68cee9ae428881d8d6991b4d7471&hash=48BD2B6EA77CD5C430FD63757863 2B28 94 �Butler, B.S. & Burbank, W.S. (1929). The Copper Deposits of Michigan. USGS Professional Paper No. 144 Cannon, W. F. (1994). Closing of the Midcontinent Rift: a far-field effect of Grenvillian compression. Geology 22, pp. 155-158. Cannon, W. F. and Nicholson, S. W. (2001). Geologic Map of the Keweenaw and Adjacent Area Michigan 1:100,000. USGS Map I-2696 Clarke, D. (1978). Copper mines of Keweenaw; no. 12: Mohawk Mining Company. ASIN B0066RONSQ. Elmore, R. D. (1984). The Copper Harbor Conglomerate: A late Precambrian fining-upward alluvial fan sequence in northern Michigan. Geological Society of America Bulletin 95, pp. 610-617. Gagnon (2018). A Tribute to Our Fisherman -Minaadowenjigaaziwaat Gidoo giigoonkeninii-minaanik. Retrieved from: https://nrd.kbicnsn.gov/sites/default/files/A%20Tribute%20to%20our%20Fishermen%20-%20handout.pdf Geological Society of America (2017). GSA Position Statement: Geoheritage. Retrieved from: https://www.geosociety.org/documents/gsa/positions/pos20_Geoheritage.pdf. Huber, N. K. (1983). The geologic story of Isle Royale National Park. United States Geologic Survey Bulletin (1309), pp. 66. Johnston, B. (1976). Ojibway Heritage. Toronto: McClelland and Stewart. Kerfoot C., Yousef F., Green A., Regis R., Shuchman R., Brooks N., Sayers M., Sabol B., and Graves M. (2012). LiDAR (Light Detection and Ranging) and multispectral studies of disturbed Lake Superior coastal environments. Limnol. Oceanogr. 57: 749–771. https://doi.org/10.4319/lo.2012.57.3.0749 Kerfoot C., Hobmeier M., Swain G., Regis R., Raman V., Brooks C., Grimm A., Cook C., Shuchman R., and Reif M. (2021). Coastal Remote Sensing: Merging Physical, Chemical, and Biological Data as Tailings Drift onto Buffalo Reef, Lake Superior. Remote Sensing. 2021, 13 (13), 2434. https://doi.org/10.3390/rs13132434 Kerfoot. C., Swain, G., Regis, R., Raman, V.K., Brooks, C., Cook, C and Reif, M. (in prep). Coastal Copper Tailings Dispersal: 3D Mapping and Shoreline Impacts, Particle Migration, Leaching, And Toxicity. Remote Sensing, 2024, 16. Keweenaw Bay Indian Community (2017). Testimony of Warren C. Swartz Jr. Before the Senate Committee on Commerce, Science & Transportation. Retrieved from: https://www.michigan.gov/dnr//media/Project/Websites/dnr/Documents/Fisheries/BuffaloReef/TribalTestimonyADA1.pdf?rev=2c9d195 864e44557bc3bc315ed93e4a6 Keweenaw Bay Indian Community (2021). Who We Are. Keweenaw Bay Indian Community Natural Resources Department. Retrieved from http://nrd.kbic-nsn.gov/about-us. Keweenaw County Historical Society (2022). Copper Milling at Gay - A Lake Superior Story. Retrieved from: https://www.keweenawhistory.org/Copper-Milling-At-Gay 95 �Lankton, L. (2005). Keweenaw National Historical Park Historic Resource Study. Prepared for the National Park Service, United States Department of the Interior. Retrieved from: http://npshistory.com/publications/kewe/hrs.pdf Martin, S. R. (1995). Michigan prehistory facts: The state of our knowledge about ancient copper mining in Michigan. The Michigan Archaeologist, 41(2-3), pp. 119-138. Martin, S. R. (1999) Wonderful Power: The Story of Ancient Copper Working in the Lake Superior Basin Wayne State University Press, Detroit, MI, p. 284 Molloy, Lawrence J. (2008). A Guide to Michigan's Historic Keweenaw Copper District: Photographs, Maps, and Tours of the Keweenaw, Past and Present. Hubbell, Michigan: Great Lakes GeoScience. p. 66. ISBN 978-0-979-1772-1-7. Moore, P. (1971). Copper-Nickel Arsenides of the Mohawk No. 2 Mine, Mohawk, Keweenaw Co., Michigan. American Mineralogist, Volume 56, pages 1319-1331. National Park Service and American Geosciences Institute (2015). America’s Geologic Heritage: An Invitation to Leadership. NPS 999/129325. National Park Service, Denver, Colorado. Nicholson, S.W., Shirey, S.B., Schulz, K.J., and Green, J.C. (1997). Rift-wide correlation of 1.1 Ga Midcontinent Rift System basalts; implications for multiple mantle sources during rift development. Can. J. Earth Sci., v. 34, pp. 504-520. Reynard, E. and Brilha, J. (2017). Geoheritage: Assessment, protection, and management. Elsevier, ISBN: 9780128095317. Rose, W.I. and Vye, E. with Martin, V. (2017). How the Rock Connects Us: A Geoheritage Guide to Michigan’s Keweenaw Peninsula and Isle Royale. Isle Royale and Keweenaw Parks Association, ISBN 9780935289213. Stein, C. A., Kley, J., Stein, S., Hindle, D. and Keller, G. R. (2015). North America’s Midcontinent Rift: When Rift met LIP. Geosphere, 11(5), pp. 1607-1616. Stevens, Horace J. (1902). The Copper Handbook: A Manual of the Copper Industry of the United States and Foreign Countries. Vol. II. Houghton, Michigan: Mines Publications. US Geological Survey (USGS) (2005). Mineral Resources Data System (MRDS). Vye, E. (2016). Geoheritage of the Keweenaw Peninsula (Doctoral dissertation). Michigan Technological University. White, W.S., Cornwall, H.R., & Swanson, R.W. (1953). Bedrock Geology of The Ahmeek Quadrangle. USGS Map GQ-27, Scale 1:24000 96 �Field Trip 4 Keweenaw Fault System Geometry and Kinematics: Clues to Its Nature and Origin James M. DeGraff, Katherine M. Langfield Department of Geological and Mining Engineering and Sciences Daniel J. Lizzadro-McPherson Geospatial Research Facility, Great Lakes Research Center Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 Objectives This field trip is designed to demonstrate four fundamental attributes of the Keweenaw fault system along the Keweenaw Peninsula: (1) geometry of the fault network and individual faults; (2) style of deformation of hanging-wall and footwall strata; (3) zonation of deformed rocks in fault zones; and (3) kinematic slip indicators on individual faults. Stops in this guide were chosen and grouped into four areas to illustrate the segmented geometry of the Keweenaw fault system and to point out fault blocks defined by intersections between faults in three main directions. Kinematic slip indicators observed at some stops manifest a preponderance of oblique slip with components of dextral strike slip and northwest-side-up reverse slip. Based on this information and fault network geometry, the overall nature of the fault system is interpreted to be transpressional and consistent with forcing by the Grenville orogeny. Introduction The Keweenaw fault extends southwest from the tip of the Keweenaw Peninsula in Michigan’s Upper Peninsula to near Ashland, Wisconsin (Fig. 1), a distance of about 250 kilometers. It is one of two faults along the south shore of western Lake Superior with reverse movement that juxtaposes Mesoproterozoic volcanic layers against Meso-Neoproterozoic clastic sedimentary strata, the other being the Douglas fault in Wisconsin and Minnesota. Irving and Chamberlin (1885) first established the existence of the Keweenaw fault by combining detailed observations in outcrops and trenches with astute reasoning to settle a long-running debate about the nature of the contact between volcanic layers to the northwest and sandstone strata to the southeast. Prior to their work, Wadsworth (1884) had argued that the sandstone was older and dipped northwest beneath the volcanic layers based on their similar dip at some locations along their contact. Afterward, this idea was resurrected intermittently until the mid-1970s, when deep drilling for oil and gas established the younger age of sandstone in the Keweenaw fault’s footwall once and for all. 97 �Figure 1: Mesoproterozoic Keweenawan Supergroup of the Midcontinent Rift System (inset map modified from Stein) in the Lake Superior region. For sources of geologic units and faults, see DeGraff and Carter (2023). KF‒Keweenaw fault; LOF‒Lake Owen fault, DF‒Douglas fault; IRF‒ Isle Royale fault, MIF‒Michipicoten Island fault, TF‒Thiel fault; MF‒Munising fault (provisionally named). Red “U” on upthrown sides of faults. Tectonic Evolution The Keweenaw fault and related major faults along the southern edge of the western Lake Superior basin cut rocks of the Midcontinent Rift System (Fig. 1) and have slipped several kilometers in a reverse sense (Cannon and Nicholson, 2000, 2001; DeGraff and Carter, 2023). Ideas to explain the origin and evolution of the Keweenaw fault differ in relation to the roles of rifting and orogenesis on fault initiation and movement over time. The Midcontinent Rift System (MRS), formed by extension of Laurentian crust in Mesoproterozoic time, was accompanied by voluminous mafic volcanism followed by a period of crustal sag with siliciclastic sediment filling the resulting basin (Cannon et al., 1989; Cannon, 1992; Hinze et al., 1990; Stein et al., 2015). Woodruff et al. (2020) defined stages of magmatism and tectonism in MRS evolution as follows: (1) Plateau Stage with widespread volcanism and distributed minor extension (c.1112 to c.1105 Ma); (2) Rift Stage when volcanism and extension reached maximum intensity along a central subsiding rift basin (c.1102 to c.1090 Ma); (3) Late-Rift Stage with declining volcanism transitioning to sedimentary infill of the rift basin (c.1090 to c.1083 Ma); and (4) Post-Rift Stage with sedimentary infill of a sag basin (c.1083 to c. 1060 Ma). Prior to recognition of the MRS, the Keweenaw fault was interpreted as a thrust that formed during an unspecified compressional event following eruption of lava flows and deposition of siliciclastic strata in the Lake Superior basin (Irving and Chamberlin, 1885; Butler and Burbank, 1929, White, 1968). After recognition of the rift, a new model for formation and evolution of the Keweenaw fault and others around the Lake Superior basin proposed that they formed as normal faults during stages 1 and 2, and then were inverted as reverse faults by post-rift Grenville compression (Cannon et al., 1989; Hinze et al., 1990; Cannon, 1994), i.e. the fifth 98 �Compressional Stage of Woodruff et al. (2020). A recent model, discussed below in relation to the inversion model, is that the Keweenaw fault formed by thrusting during post-rift Grenville compression and did not exist as a normal fault during MRS extension or sag (DeGraff and Carter, 2023). In some ways, the latter model reverts to earlier ideas about the Keweenaw fault. Ideas about the timing of reverse slip on the Keweenaw fault have evolved from the original ideas of Irving and Chamberlin (1885), who inferred two episodes of movement – one prior to deposition of the footwall sandstone and a second afterward. Early thrusting elevated the region northwest of the fault, creating a highland of mafic volcanic layers that shed debris into the tectonic basin southeast of the fault. A second episode of thrusting occurred after most of the sandstone deposition based on deformed footwall strata with steep to overturned attitudes toward the southeast. Later workers have suggested quasi-continuous fault slip that began before Jacobsville deposition and continued during most or all of its deposition (Cannon and Nicholson, 2000), and others have argued for a late reactivation of the fault system during one or more phases of the Appalachian orogeny (Craddock et al., 1997). Stratigraphy Extension during MRS evolution followed by compression during the Grenville Orogeny produced a broad syncline with strata dipping toward an axis beneath Lake Superior (Fig. 1). The related rocks in the vicinity of the Keweenaw Peninsula are well described by Cannon and Nicholson (2000, 2001), whose stratigraphic column and nomenclature are adopted here (Fig. 2). Here, the main geologic units of the Keweenawan Supergroup are from oldest to youngest: (1) Siemens Creek Volcanics and Kallander Creek Volcanics (Powder Mill Group) with basaltic to andesitic lava flows; (2) Portage Lake Volcanics (Bergland Group) mostly composed of basaltic to andesitic flows with lesser conglomerate and sandstone layers; (3) Oronto Group strata beginning with the Copper Harbor Conglomerate and locally interbedded basalt-andesite flows, continuing with the Nonesuch Formation composed of siltstone and shale, and ending with the Freda Sandstone composed of lithic sandstone and siltstone; and (4) Jacobsville Sandstone mostly composed of quartzose to subarkosic sandstone and generally correlated with the Bayfield Group in Wisconsin, USA. Archean granite and gneiss of the Superior craton, with a Paleoproterozoic cover of graywacke and slate (Michigamme Formation), lie beneath the Keweenawan rocks south of Keweenaw Bay. The following descriptions focus on the two geologic units that are juxtaposed along the Keweenaw fault system, namely the Portage Lake Volcanics in the hanging wall and the younger Jacobsville Sandstone in the footwall (Fig. 3). Both units are stratified and have compositional and textural variations between layers that likely influenced their mechanical behavior, which in turn influenced fault initiation and propagation. A more complete description of other Precambrian units along the Keweenaw Peninsula is provided elsewhere in this field trip volume (see Field Trip 1 in this volume). 99 �Figure 2: Left. Regional stratigraphy following Cannon and Nicholson (2001). For sources of radiometric ages in red italics, see DeGraff and Carter (2023). Right. Stratigraphy of the Portage Lake Volcanics from USGS bedrock geology maps of the Keweenaw Peninsula. Intense green units are major lava flows: pcc‒Copper City; pgf‒Gratiot; psc‒Scales Creek; pk‒Kearsarge; pg‒ Greenstone. Letter codes on left side are sedimentary layers, except for one: pu‒unnamed conglomerate (cgl), pbc-pl‒Baltic-Lac La Belle cgl; ps‒St. Louis cgl; pb‒Bohemia cgl; poc‒Old Colony sandstone; pw‒Wolverine sandstone; pkc‒Kingston cgl; pc‒Calumet and Hecla cgl; ph‒ Houghton cgl; pa‒Allouez cgl; pp‒Pewabic West cgl; paf‒ashbed flow top; phc‒Hancock cgl. Bold red bars mark units with layer-parallel slip observed in mines and trenches. Letters on right side indicate where slip occurred (T‒top; B‒bottom; A‒top and bottom). The Portage Lake Volcanics (PLV) exposed along the Keweenaw Peninsula is truncated on the southeast by the Keweenaw fault system, leaving an undetermined thickness of PLV in the footwall beneath Jacobsville Sandstone. The PLV section in the fault’s hanging wall is estimated to be 3000 to 5000 m thick and to contain about 300 flows (Cannon and Nicholson, 2000). It mostly consists of subaerial basaltic flows with less abundant andesitic flows, rhyolitic to dacitic extrusive domes, and associated pyroclastic layers (Butler and Burbank, 1929; White, 1968; Cannon and Nicholson, 2000, 2001). Six named basalt flows are sufficiently traceable along strike due to their 100 �great thickness and distinctive texture to serve as marker units (Fig. 2). The thickest of these, the Greenstone flow, in the upper part of the section is traceable for 80 kilometers in outcrop and drill holes and has a precise radiometric age date of 1091.6 ± 1.3 Ma (Swanson-Hysell et al., 2019; cf. 1094.0 ± 1.5 Ma, Davis and Paces, 1990). The next thickest flow, the Copper City flow, in the lower part of the section is traceable for 25 kilometers and is precisely dated at 1093.4 ± 1.4 Ma (Swanson-Hysell et al., 2019; cf. 1096.2 ± 1.8 Ma of Davis and Paces, 1990). About 3% of the PLV section consists of conglomerate and sandstone deposited between some of the lava flows (Butler and Burbank, 1929; White, 1952; Merk and Jirsa, 1982). Eleven named interflow units (Fig. 2) are traceable along strike for considerable distances up to 90 km (Bornhorst and Barron, 2011), and thus are useful for correlation. Interflow sedimentary layers mostly consist of clast-supported, pebble-to-cobble conglomerate with a gravelly to sandy matrix, which is well indurated and tends to form prominent strike ridges. Conglomerate layers are coarsely bedded and poorly stratified, except where sandy lenses or conglomeratic sandstone occur. Less common are sandstone and siltstone that may occur as interbeds within a conglomerate layer or locally may make up an entire interflow layer. Interflow sedimentary layers may be up to 40 m thick and locally may pinch to near zero thickness (Butler and Burbank, 1929; Merk and Jirsa, 1982; White, 1968). Clasts and matrix grains in the interflow layers were derived from volcanic rocks of the rift basin, with felsic material generally being far more abundant than expected from the small proportion of felsic volcanic rocks that make up the PLV section (< 1% according to Nicholson, 1992). These so-called felsic conglomerates may occur by themselves or in association with mafic conglomerates, in which case the felsic layer tends to lie atop the mafic layer lying atop the underlying lava flow (Butler and Burbank, 1929). Stops of this field trip are all within the lower part of the PLV section exposed in the fault’s hanging wall. For the first half of the trip, the thick Copper City flow is an important stratigraphic reference that be traced for 25 km along strike. Another important stratigraphic reference with a greater strike extent is the St. Louis conglomerate (#6 on USGS bedrock geology maps), which lies at the base of the Copper City flow in many places but elsewhere is separated from it by a thinner basalt flow. For the second half of the trip, the key stratigraphic reference is the Lac La Belle conglomerate (#3 on USGS maps), which lies 580 m to 1050 m stratigraphically below the St. Louis conglomerate. Other lava flows and interflow sedimentary layers in the lower part of the PLV have not yet been correlated well enough to be useful as regional stratigraphic references. A few intrusions cut the lowermost PLV layers along the Keweenaw Peninsula, such as the Mt. Bohemia syenodiorite stock (Cornwall, 1954a) and scattered dikes largely of intermediate composition (Robertson, 1975). Jacobsville Sandstone (JS) in the Keweenaw fault’s footwall fills a sub-basin that extends southeast beneath Keweenaw Bay to an onlap with Paleoproterozoic metasedimentary rocks, northeast to near Stannard Rock, and southwest to Lake Gogebic (Fig. 1). The unit may reach to 23 kilometers in depth based on gravity modeling and early seismic reflection data (Bacon, 1966; Aho, 1969; Kalliokoski, 1982). An exploratory drill hole (Mayflower #41) through the fault near Calumet penetrated JS to a total depth of 803 m (White, 1985), and a deeper drill hole 8.6 km southeast of the fault (Rice Lake #1) reached a total depth in sandstone at 1106 m (Keweenaw NHP, 2016). Regionally correlated units are not well defined for the unit because of lateral facies variability and lack of marker beds. However, Hamblin (1958) recognized the following 101 �succession: (1) basal “conglomerate facies” with locally-sourced clasts deposited adjacent to topographic highs; (2) “lenticular sandstone” facies dominated by planar and trough cross-bedding; (3) “massive sandstone” facies with laterally persistent layers and occasional planar cross-bedding; and (4) “red siltstone” facies with thinly bedded, fine-grained, siliciclastic layers and local trough cross-bedding. Based on this facies succession, Hamblin (1958) interpreted Jacobsville depositional environments as transitioning from (1) alluvial-fluvial at the base, (2) to dominantly fluvial in the lower cross-bedded part of the unit, (3) to dominantly lacustrine in the upper massive part of the unit, and (4) to variably lacustrine and fluvial in the uppermost thinly bedded part of the unit. He inferred that the general sequence of facies and depositional environments was time transgressive, representing both a vertical time sequence at any given point as well as a basinward change of depositional environment at any given time. The JS section along the Keweenaw Peninsula consists of siliciclastic strata that generally conform to the facies of Hamblin (1958) but with some variations. Proximal to the fault system, the lower parts of exposed sections commonly have brownish conglomerate layers consisting of subangular volcanic clasts chaotically dispersed in a poorly indurated muddy matrix, and interbedded with soft, fissile, reddish-brown siltstone and shale (Irving and Chamberlin, 1885; Hamblin, 1958; DeGraff, 1976; Brojanigo, 1984). In such sections with muddy conglomerate and shaly strata, interbeds of whitish to orangish to pinkish, fine- to medium-grained sandstone occur as isolated thin beds near the base and become more abundant and thicker upward in the section until muddy strata are rare. The quartzose to subarkosic sandstones are locally conglomeratic and often crossbedded, which is typical of most JS strata exposed away from the fault system to the southeast. Sand-prone JS strata also occur near the fault system where the muddy conglomerate and shaly facies is absent. Brojanigo (1984) interpreted the muddy conglomerate layers as debris flows derived from an upland of PLV rocks to the northwest, and the more mature sandy strata as fluvial deposits derived from older quartzo-feldspathic rocks to the south. We interpret this bimodal alluvial-fluvial assemblage to be basal Jacobsville, whose PLV-derived detritus is evidence of prior reverse slip on the Keweenaw fault system that elevated the northwest hanging wall and allowed volcanics there to be weathered, eroded, and transported southeastward into the JS sub-basin. The time span of JS deposition has been difficult to determine due to a lack of fossils and igneous rocks interbedded with or crosscutting Jacobsville strata (Kalliokoski, 1982). Deposition probably did not occur prior to reverse slip on the Keweenaw fault system (KFS) because conglomerate low in the JS section near the KFS contains PLV detritus sourced from an elevated region to the northwest (Brojanigo, 1984; Cannon and Nicholson, 2000). The earliest slip on the fault system is generally taken to be ~1060 Ma based on Rb-Sr ages of gangue minerals in fractures associated with native copper mineralization of the Keweenaw Peninsula (Bornhorst et al., 1988) and reset biotite ages in Archean granite gneiss uplifted along related faults west of Lake Gogebic (Cannon et al., 1993). Later reverse slip on the Keweenaw fault that deformed adjacent Jacobsville strata is relatively well constrained at 985 ± 30 Ma by a U-Pb date for late-kinematic vein calcite in the fault zone, in combination with a maximum depositional age of ~993 Ma for deformed strata high in the Jacobsville section (Hodgin et al., 2022). Most Jacobsville deposition probably occurred in the period 1060-985 Ma, although somewhat younger layers could have been deposited in the region (Craddock et al., 2013; Malone et al., 2016). 102 �Keweenaw Fault System – Key Observations and Concepts The Keweenaw fault has been described as a strike fault because of the general parallelism between its map trace and PLV layers in its hanging wall (Fig. 3). Butler and Burbank (1929) also noted a remarkable similarity in dip of hanging-wall layers and the fault, such that PLV layers change dip along strike by about the same amount and in the same sense as changes in the underlying fault surface. Where differences in dip exist, the fault cuts 5° to 17° more steeply and upward across PLV layers in a southeasterly direction, i.e. in the thrusting direction (DeGraff and Carter, 2023). Related to these surface observations, Hubbard (1898) had systematically catalogued in mine workings many layer-parallel faults along contacts between volcanic and interflow sedimentary layers (Fig. 2). These bedding-plane faults are manifested by fault gouge, polished surfaces, breccia with alteration, and secondary mineralization in fractured zones up to 8 m thick (65% ≤ 1.5 m). Hubbard’s observations indicate that PLV layer boundaries were relatively weak and became detached during one or more deformation episodes. Furthermore, his observations along the Keweenaw Peninsula mining district northeast of Portage Lake document layer-parallel slip throughout the PLV section. The surface and subsurface evidence of layer-parallel slip within the PLV section is consistent with knowledge about PLV stratigraphy. The lava flows have variations in texture and mineralogy across their thickness that likely influence their mechanical properties. Massive holocrystalline flow interiors grade into margins with finer grain size and abundant vesicles and amygdules, often arranged in bands parallel to the contacts. Flow tops have the highest abundance of amygdules, are commonly brecciated, and often have been modified by weathering between eruptions or by mineralizing fluids that later migrated along these once-permeable zones (Butler and Burbank, 1929; Stoiber and Davidson, 1959; White, 1968; Bornhorst, 1997). Where one flow lies directly atop another, a significant mechanical contrast exists across their comparatively weak contact. Contrasts in layer characteristics and properties are even more significant at contacts between interflow sedimentary layers and lava flows. Altogether, the evidence just summarized implies a detached style of formation for the Keweenaw fault and related splays (DeGraff and Carter, 2023). Although the Keweenaw fault has been described as a high-angle reverse fault, its northwesterly dip at the surface varies from as low as 20° up to 70° (Butler and Burbank, 1929). Cross-section construction along a transect with abundant constraining data from mining operations and surface mapping implies that the fault is nearly horizontal northwest of its surface trace at Hungarian Falls (DeGraff and Carter, 2023, their Fig. 6), one of the stops on this trip (see Stop 2-1, Fig. 8). Several cross-sections on USGS bedrock geology map sheets from the 1950s show the fault dipping ≤ 25° or show nearly horizontal PLV layers near surface that imply a similarly-dipping fault below (e.g., Laurium, Ahmeek, Mohawk, and Bruneau Creek quadrangles). Thus, the fault and overlying PLV strata dip between nearly horizontal up to 25° NW at several locations and, there, the hanging-wall PLV block has overridden footwall JS strata by as much as 2.5 kilometers. Between 2017 and 2022, three mapping projects funded by the USGS EDMAP program have refined fault and stratal geometries along the Keweenaw fault, and the results indicate that what was largely considered to be a single fault is better characterized as a fault system (Tyrrell, 2019; Mueller, 2021; Lizzadro-McPherson, 2023; Gamet, 2023, Langfield, 2024). The Keweenaw fault 103 �system (KFS), as used here, refers to an ensemble of fault segments whose collective motion has a significant component of dextral strike slip in addition to the long-recognized component of reverse slip with northwest side up. The fault system consists of segments that define three main directional sets: (1) a dominant set that defines the trend of the fault system and locally separates more steeply dipping PLV layers to the northwest from less steeply dipping PLV layers to the southeast; (2) splay faults that are angled 15-30° clockwise from set 1; and (3) connector faults angled 35-75° counterclockwise from set 1 that join footwall splays to the main fault trend (Fig. 3). The three directional fault sets maintain these angular relationships among each other as the curved KFS changes direction from a 35° azimuth near Houghton to a 95° azimuth near the tip of the peninsula. The interconnected nature of the three fault sets defines fault blocks with long dimensions parallel to the local trend of the KFS. Fault-slip indicators measured on ~400 fault surfaces show that the collective ratio of reverse slip to dextral slip on the KFS varies from 1:1 near Houghton to 1:2 or more near the tip of the peninsula. In other words, strike slip is twice as large as dip slip on the KFS near the tip of the peninsula where fault azimuth is 60° clockwise from its azimuth near Houghton (Tyrrell, 2019; Mueller, 2021; Lizzadro-McPherson, 2023; Gamet, 2023; Langfield, 2024). This change in the ratio of strike slip to dip slip is expected as the fault’s azimuth approaches the estimated 105° azimuth of maximum compressive stress that is attributed to the Grenville orogeny. The leftstepping arrangement of footwall splay faults and the fault blocks they help to define is consistent with a transpressional fault system as indicated by the fault-slip data. The relatively short, north- to northeast-trending, connector faults (set 3) are associated with similar-trending fold axes at relatively high angles to the estimated maximum compression direction and shortening direction. The connector faults are inferred to have mostly reverse slip with west side up and to accommodate northeast to east transport of footwall fault blocks associated with dextral transpressional slip of the entire KFS. Why concern ourselves with the geometric details and timing of slip on the KFS? From a science perspective, the arrangement of fault segments in the system along with fault-slip indicators like slickenlines provide clues to the mechanics of fault initiation and kinematics of fault slip. Improved understanding of these aspects of the KFS should apply to similar faults around Lake Superior and help to understand their causative tectonic events and stress regimes. From a practical perspective, faulting along the Keweenaw Peninsula and on strike to the southwest provided pathways for upward migration of mineralizing fluids (Bornhorst, 1997), leading to copper deposits that once supported a thriving mining industry and are still prospective today. Native copper is commonly found along major and minor faults in the mining district. The Hancock fault cutting the Quincy and Hancock mines is an example of a major fault with copper mineralization concentrated in its hanging wall. Another example is the Allouez Gap fault that bisects the Kearsarge flow-top copper deposit, the largest of this type in the district (Bornhorst, 1997). Faults likely provided pathways for upward-moving ore fluids into vesicular flow tops at the Baltic and Isle Royale deposits and others in the Greenland-Mass subdistrict (Broderick, 1931). The earliest native copper deposits exploited in the district east of Eagle River were along subvertical fracture zones and minor transverse faults with displacements less than 200 m (Butler and Burbank, 1929). Therefore, a better understanding of fault geometry and timing may provide insights about the distribution of known deposits and about the possible presence of undiscovered deposits. 104 �Figure 3: Geologic map of the Keweenaw Peninsula showing the Keweenaw fault system north of Portage Lake and field trip stops within the four focus areas. Faults are indicated by curved black lines. Field Trip Stops The field trip stops described below are grouped into four areas to illustrate themes related to fault system geometry, stratal relationships and deformation, fault blocks, deformation fabric in fault zones, and slip kinematics. Each area has an introductory overview of the key themes and nature of the stops, followed by individual stop descriptions. Reported strike and dip values follow a right-hand-rule convention. The dip value is followed by letters indicating the cardinal direction of dip, which is redundant but makes for clarity. About half of the stops in this guide are on public land. Those on private land are specified in the stop descriptions as requiring permission from the owners to access. 105 �Figure 4: Geologic map of Area 1 with the Keweenaw fault system (KFS) and field trip stops 1-1 to 1-3. Geologic unit codes: pbc – Baltic conglomerate, ps – St. Louis conglomerate, pb – Bohemia conglomerate, psc – Scales Creek flow, pk – Kearsarge flow with Wolverine sandstone at its base. Teeth along reverse faults are on upthrust sides. 106 �Area 1: Hungarian Fault Block ‒ Southwest End STOPS IN THIS AREA ARE ON PRIVATE LAND AND REQUIRE PERMISSION TO ACCESS. The three stops in Area 1 are within the vehicle testing grounds of Michigan Tech’s Keweenaw Research Center (KRC), under lease from the Houghton County Memorial Airport (Fig. 4). From west to east, the stops are on the main Keweenaw fault zone (1-1), in a basalt quarry within a faultbounded block (1-2), and on a footwall splay fault (1-3) that passes through Hungarian Falls to the northeast in Area 2. Within the fault-bounded block, an unconformity between the PLV and JS is interpreted to dip shallowly southwest. These three stops illustrate an en echelon, overlapping, fault geometry that define a fault block whose long dimension is parallel to the trend of the Keweenaw fault system (KFS). Recent mapping shows that such fault patterns and fault-bounded blocks are repeated along the KFS north of Portage Lake (Fig. 3). A similar configuration of faults with the enclosed block having a west-dipping PLV-JS unconformity occurs in Area 4 (Figs. 3 and 13). Stop 1-1: Gooseneck Creek fault exposure Directions: From the Portage Lake lift bridge between Houghton and Hancock, follow US-41 north for 6.7 mi (10.8 km) to Airpark Boulevard on the right. Turn right toward Houghton County Memorial Airport and drive 0.5 mi (0.8 km) to the Keweenaw Research Center (KRC) on the right. Enter the KRC parking area and wait in vehicles. We may be escorted by KRC staff for 1.5 mi (2.4 km) to the south edge of their vehicle testing grounds, where we will park and walk. [Lat: 47° 9.259'N | Lon: 88° 29.895'W] The fault exposure on Gooseneck Creek is part of the main Keweenaw fault zone that is traced by means of outcrops, drill holes, and water wells along a line bearing 36° from the Michigan Tech campus to the intersection of Airport Park and Forsman roads, about one kilometer southwest of this stop (Fig. 4). Northeast from that intersection, the fault’s map trace curves eastward so that here it trends 72°, as do the hanging-wall PLV strata. This stop is the most northeasterly site where this segment of the KFS can be observed because the flat upland to the northeast, where the airport is located, has little to no bedrock exposure. Hubbard (1898) seems to be the first geologist to describe this site. While his report puts the outcrop about 80 m south of its actual location, his geologic description is very similar to what was observed and measured during the 2021-2022 EdMap project (Langfield, 2024). “A conglomerate here, underlain by trap, strikes N. 72° E., and dips northerly 44°, the trap being in contact on the south with the sandstone, which is much broken and disturbed but appears to dip rather flat to the N. E.” (Hubbard, 1898) The fault’s main slip surface is not exposed but its position is determined to within a couple of meters by the proximity of hanging-wall PLV outcrops to footwall JS outcrops. PLV strata in the hanging wall, striking 252° and dipping 40-44° NW, change stratigraphically upward from amygdaloidal basalt at the fault at creek level to a felsic pebble conglomerate, and then to a series of basaltic flows for as far as outcrop exists to the north and northwest. The stratigraphic 107 �position of the conglomerate layer suggests that it is the Baltic (#3) conglomerate shown on the USGS Hancock and Chassell bedrock geology maps (Cornwall, 1956a; White, 1956). Abundant fractures within the basalt flows are not obviously systematic, although detailed work might reveal dominant sets. Jacobsville strata in the footwall commonly appear massive due to being thickly bedded to locally cross-bedded, which makes their attitude difficult to measure. In general, JS strata dip gently both toward and away from the fault, suggesting an open anticlinal structure with an axis that trends approximately east-west (Fig. 4). Figure 5: Gooseneck Creek cross-section in progress using outcrop and drill hole data (Langfield, 2024). Red lines below topography are New Arcadian drill hole trajectories. Colors and letter codes of geologic units are explained in Figure 2. KFS-P = Keweenaw fault system - Portage segment; KFS-H = Keweenaw fault system - Hungarian segment. Dashed orange line above KFSP marks what may be the Baltic (#3) conglomerate. Diamond drill holes (DDH) of the Calumet and Hecla Consolidated Copper Company provide data that are critical for the interpretation of this site, situated on a NW-trending line of four New Arcadian holes drilled in 1911-1912 (Fig. 4). Southeast of here, three drill holes penetrated the following beneath glacial overburden (hole depth converted to vertical depth): DDH #17 about 140 m SE cut 46 m of JS sandstone followed by 109 m of PLV basalt; DDH #15 about 205 m SE cut 69 m of JS sandstone and conglomerate followed by 14 m of PLV basalt; DDH #13 about 355 m SE cut 37 m of JS sandstone (Fig 5). Southeast of the fault, therefore, drilling reveals a veneer of JS strata less than 70 m thick overlying PLV basaltic lava flows. About 135 m northwest of the fault, DDH #11 inclines 52° toward this site and reaches a total depth of 457 m. It cuts a single felsic conglomerate layer between depths of 93 m and 109 m (16 m apparent thickness) that we correlate to the 6-m-thick conglomerate layer seen here in outcrop, which yields an average stratal dip of 53° NW. Below the conglomerate, DDH #11 penetrated ~2 108 �meters of sludge that we interpret as fault gouge, and then continued through basaltic flows to its bottom at a vertical depth of 363 m below the DDH #17 surface location to the southeast. The position of the fault below the conglomerate in DDH #11 and not far below the conglomerate at the surface indicates that the fault dips nearly parallel to hanging-wall PLV strata. While at the surface the fault juxtaposes PLV strata against JS strata in the footwall, at depth in DDH #11 the fault’s hanging wall and footwall both have PLV strata, which is consistent with the thin veneer of JS strata penetrated by DDH #17 and DDH #15 southeast of here. Stop 1-2: Basalt quarry of the Keweenaw Research Center Directions: Return to vehicles and drive north 0.15 mi (0.25 km) to KRC perimeter road. Turn right and drive southeast for 0.75 mi (1.2 km) to a basalt quarry on the right. Pull off road into a gravel terrace on the right and park. [Lat: 47° 9.144'N | Lon: 88° 29.023'W] The KRC basalt quarry was opened in 2018-2019 to provide materials for expansion of their vehicle testing facilities. The quarry lies between the fault segment just visited at Gooseneck Creek and a parallel segment to be visited at the next stop (Fig. 4). The quarry exposes portions of at least two basalt lava flows that dip shallowly southwest. The shallow dip is roughly manifested by subhorizontal benches of the quarry and can be measured on the first dry bench west of the quarry pond, where the upper surface of a lava flow has been exposed. Inspection of the irregular subhorizontal surface reveals isolated patches of sediment whose stratification yields an average strike of 125° and dip of 19° SW. The shallow southwesterly dip of PLV strata is important to the understanding of structural geometry. Early geologists noted that older PLV strata near the Keweenaw fault and its splays commonly have anomalous orientations relative to younger PLV strata away from the fault zone, which have a well-defined regional trend (Hubbard, 1898; Butler and Burbank, 1929). In most of the PLV section, strata generally strike northeast to east and dip 35° – 55° northwest to north. At this stop and for ~3 kilometers north and northeast, PLV strata dip less than 25° in various directions, including counter-regional to the southeast. Such anomalies are clues to the structural configuration of the area along the Keweenaw fault system. Specific to this stop, the shallow southwesterly dip of PLV stratal is consistent with data from DDHs #17 and #15, where a thin veneer of JS strata overlies PLV basaltic rocks. The nature of the PLV-JS contact is not described in the core logs, but the normal stratigraphic sequence indicates that it is an unconformity. The unconformity dips shallowly southwest to south based on the two cited DDHs and DDH #20 located ~510 m southwest, which penetrates the unconformity ~35 m lower relative to a common datum. Projecting the unconformity updip brings it to the surface southwest of this stop. Therefore, we interpret that basalt at the quarry roughly correlates with basalt below JS strata in the three DDHs by passing beneath an erosional wedge of JS strata on a SW-dipping unconformity (Langfield, 2024). This new interpretation differs from one involving a transverse fault shown on USGS bedrock geology maps for the Hancock and Laurium quadrangles (Cornwall and Wright, 1956a, 1956b). 109 �Stop 1-3: East branch of Quincy Creek fault exposure Directions: Return to vehicles and drive east on the perimeter road for 0.25 mi (0.4 km) to an intersection with a gravel road on the left. Turn left and drive ~0.35 mi (~0.6 km) to a clearing on the right. Turn into the clearing and park. [Lat: 47° 9.282'N | Lon: 88° 28.548'W] The east and west branches of Quincy Creek cross a segment of the Keweenaw fault system that is about 750 meters southeast of the fault segment at Gooseneck Creek and subparallel to it. Both branches of Quincy Creek constrain the position of the fault to within 8-10 m by the proximity of hanging-wall PLV outcrops to footwall JS outcrops, but the fault zone itself is not exposed. Outcrops along the west branch of Quincy Creek are the most southwesterly constraint on the position of this fault segment because of glacial deposits that cover bedrock southwest of here. However, we interpret the fault to continue southwesterly to an acute intersection with the fault segment seen on Gooseneck Creek at a point about halfway to Portage Lake (Fig. 4). Northeast from this stop, the fault segment is easily traced by means of outcrops and water wells along an azimuth of 42° for a distance of 3 km to the upper Hungarian Falls in Area 2. We will focus on the east branch of Quincy Creek because it provides better exposures near the fault. Again, Hubbard (1898) appears to have been the first geologist to describe outcrops at this site as well as other outcrops in stream valleys to the northeast that cross the fault line. Although his report puts the outcrop 150-175 meters north-northeast of its actual location, his geologic description of part of the outcrop is very similar to what was observed and measured during the 2021-2022 EdMap project (Langfield, 2024). “In Sec. 22 . . . occur outcrops of sandstone and of a conglomerate with a very sandy matrix. The pebbles in the conglomerate are subangular and some of them are of quartz porphyry. The dip is about 50°-54° N. W., strike about N. 45°-50° E.” (Hubbard, 1898) The outcrop just described begins 60 meters downstream from the gravel access road and extends another 30 m downstream. The sedimentary layers here are well indurated and well stratified, having an average strike of 225° and dip of 35° NW. A reddish-brown sublithic sandstone is the dominant rock type along the semi-continuously exposed section in the creek bed, with subordinate conglomeratic sandstone and pebble-to-granule conglomerate that ranges from matrix-supported to clast-supported. Clasts are mostly subrounded to subangular and have a variety of compositions but are dominantly felsic. Whereas Hubbard (1898) thought that these were JS strata, we interpret them as PLV strata because of their induration, lithic nature, and attitude that are similar to other PLV sedimentary units in the area and differ from JS sandstone strata to be seen downstream. The south end of the 30-m extent of indurated sandstone and lesser conglomerate coincides with a sharp deflection in the creek by ~20 meters east before the creek resumes its southerly course at a sharp right bend. Downstream from this point for ~30 meters, intermittently exposed sandstone and minor conglomerate differ in many aspects from the sedimentary strata upstream of the creek’s deflection. The sandstone is lighter toned and locally streaked off-white to beige, is less 110 �indurated and commonly friable, and has a more quartzose composition. The pebble-to-granule conglomerate layer in the first outcrop downstream from the creek’s deflection has a muddy to silty matrix, is poorly indurated, and has subrounded to rounded clasts with a variety of compositions. These characteristics of the sandstone and one conglomerate layer are typical of Jacobsville strata observed elsewhere in fault juxtaposition with hanging-wall PLV strata. The sharp deflection in the creek is interpreted, therefore, as marking a fault contact between PLV sedimentary strata upstream and JS strata downstream. This interpretation is supported by structural observations. Strata in the first outcrop south of the creek’s deflection strike 220° and dip 65° NW (overturned), but become less steeply dipping over a short distance as the creek is followed downstream to the south. These stratal attitudes and their significant change going downstream from the creek’s deflection contrast with stratal orientation and its consistency over a similar distance upstream of the deflection. About 15 meters south of the creek’s deflection, a small fault striking 225° and dipping 80° N cuts thickly bedded JS strata in a larger outcrop along the west bank of the creek. South of the fault, deformation bands in the sandstone are expressed as quasi-linear to broadly sinuous ridges on the outcrop surface. Deformation bands are cataclastic shear zones that develop during compression of partly indurated, porous, clastic material (Fossen et al., 2007). They are generally more cemented than the host material, accounting for their raised relief on erosional surfaces, and have not been observed in PLV sedimentary strata. Farther downstream, JS strata are abundantly displayed for a distance of 1.4 km, nearly down to the derelict Quincy Mining Company stamp mill along state highway M-26. Over that distance, JS strata generally dip less than 15° NW and display a few broad open folds with NNE-trending axes. Area 2: Hungarian Fault Block ‒ Northeast End The first two stops in Area 2 are on the same fault segment seen at Quincy Creek (2-1) and on its curved portion (2-2) that connects back to the main Keweenaw fault zone to the north (Fig. 6). A PLV sedimentary layer, usually conglomerate but locally sandstone, is traceable in the hanging wall from Quincy Creek through the east branch of Dover Creek near Hungarian Falls, where it begins a smooth northward curve from 42° to 345° azimuth, a change of over 55°. From this curved stratal geometry in map view, we infer a single smoothly curved fault along the southeast and east edges of the Hungarian fault block. The long straight part of the fault is the block’s southeast edge that parallels the overall KFS, whereas the short curved part is the block’s east edge and connects the fault segment back to the main Keweenaw fault zone. This geometry and a northwesterly decrease in stratal dip based on drill hole data define a single scoop-shaped fault rather than an intersection of two distinct faults. Stop 2-2 illustrates a common dynamic of the KFS – northeast and east edges of fault-bounded blocks were thrust eastward along west-dipping reverse faults. The third stop in Area 2 is on the main Keweenaw fault zone (2-3), which aligns with its counterpart in Area 1 (Fig. 3). The relationship between the main fault zone and the connector fault may involve the connector fault terminating against a main fault zone that continues to the southwest (Fig. 6 at “?”). Another option is that the hanging-wall sedimentary layer is continuous from Stop 2-2 to Stop 2-3 and is draped over a lateral ramp in the KFS that steps up in stratigraphy to the northeast. The stratigraphic relationships across the Hancock fault are discussed in the Stop 2-3 description. 111 �Figure 6: Geologic map of Area 2 with the Keweenaw fault system (KFS) and field trip stops 2-1 to2-3. Geologic unit codes: ps – St. Louis conglomerate, pcc – Copper City flow; pb – Bohemia conglomerate, psc – Scales Creek flow, poc – Old Colony sandstone; pk – Kearsarge flow with Wolverine sandstone at its base. Teeth along reverse faults are on upthrust sides. See Figures 4 or 13 for symbology. 112 �Stop 2-1: Dover Creek fault exposure at Upper Hungarian Falls Directions: Return back to the KRC perimeter road, then turn right and follow it back to the KRC entrance on Airpark Boulevard. Turn left and drive 0.5 mi (0.8 km) to US-41. Turn right and drive 1.6 mi (2.5 km) to Oneco Road. Turn right onto Oneco and drive 3.1 mi (5.0 km) to Amygdaloid Street. Turn left and follow Amygdaloid and Tamarack Hill Road for 0.3 mi (0.5 km) to M-26. Turn left and drive 0.35 mi (0.56 km) to 6th Street in Hubbell. Turn left and then, after the second house on the left, veer left onto Golf Course Road going uphill. Drive 0.5 mi (0.8 km) to a rutted gravel road on the left. Depending on conditions, we may turn left and take the gravel road. Otherwise, park along Golf Course Road and walk to the stop at Upper Hungarian Falls. [Lat: 47° 10.440'N | Lon: 88° 27.086'W] The fault segment crossed by Dover Creek is near the northeast end of the segment seen at Quincy Creek, and is where the fault’s surface trace begins to curve northward (Fig. 6). Dover Creek has three sets of falls that are worthwhile visiting. The two downstream falls have larger drops entirely over Jacobsville Sandstone. We will visit the upper set of falls at the fault contact between PLV strata upstream in the hanging wall and JS strata in the footwall. This site has been visited by geologists since the mid-1800s and is considered a classic exposure of the Keweenaw fault (original sense). The most insightful description by early geologists is in the work of Irving and Chamberlin (1885), whose diligent field work, keen observations, and logical reasoning convinced the geological community of the time that the contact between PLV strata and JS strata was a large fault. Prior to their work, some geologists argued that JS strata lay stratigraphically below PLV strata based in part on their similar dip here and at Houghton-Douglass Falls on Hammell Creek (Stop 2-3). Of historical interest, Roland Duer Irving is this year’s nominee for recognition by the ILSG as a Pioneer of Lake Superior Geology, and Thomas Chrowder Chamberlin is another wellknown geologist of his time, famous for his classic 1890 work “The method of multiple working hypotheses” published in Science. Both were contemporaries of John Wesley Powell, a U.S. Army officer during the American Civil War, famed explorer of the American west, and second director of the U.S. Geological Survey from 1881–1894. The faulted relationship between PLV and JS strata at this stop was revealed by excavations made by a “force of miners” hired to trench across the PLV-JS contact at three locations on the southwest valley wall (Fig. 7). The trenches exposed a fault zone dipping 30-35° NW along the contact, which has the following internal zonation from hanging wall to footwall, as summarized from Irving and Chamberlin (1885) and converted to true thickness. 1. Trap [basalt]: highly fractured but in place. (2.57 m) 2. Trap debris: disintegrated basaltic fragments in a lumpy crudely laminated clay, having a transitional boundary with zone 1. (0.39 m) 3. Clay: red and “shaly” with light grayish-green spots, some sandy seams, and occasional lumps of disintegrated trap. (0.13 m) 4. Trap debris: similar to zone 2 but with more clayey material, whose dark color contrasts with adjacent red clay. (0.13 m) 113 �5. Trap debris mixed with red clay: trap debris is similar to zone 4 but red clay and minor sand gives zone 5 a reddish tint. (0.17 m) 6. Sandstone: light reddish and quartzose. (0.51 m) Footwall JS strata near the fault contact dip 10° or less, but at the fault contact they are bent downward to be nearly parallel with the fault surface. The trench observations indicate that the fault propagated upward across subhorizontal JS strata and the overriding PLV strata crushed and abraded the truncated edges of JS strata. Figure 7: Trenches at upper Hungarian Falls that exposed relationships across the fault, marked by the red lines (Irving and Chamberlin, 1885). Downstream from the trenches, JS strata generally dip 10-20° NW toward the fault but exhibit a few broad open folds similar to what is observed downstream along Quincy Creek. Upstream from the trenches, PLV strata in the hanging wall begin with a fractured basalt flow at the minor falls below the main falls, and then progress stratigraphically upward to a felsic cobble-pebble conglomerate at the main falls, followed by a series of basaltic flows intermittently exposed for over two kilometers upstream. Stratal dip decreases upstream from 25-30° NW at the main falls to flat-lying and then to 15° SE to define an open syncline, which is succeeded upstream by an open anticline before reaching the Hancock fault (Fig. 8). A well-laminated, 1-m-thick sandstone layer at the base of the 6-m-thick conglomerate layer provides a confident formation strike of 205° and dip of 30° NW, which is essentially parallel to the underlying fault surface. This geometry indicates that the hanging-wall PLV section at this location became detached along 114 �layering somewhere downdip to the northwest and was thrust southeast and upward to its current position along a ramp that cuts upward across younger layers. The fault segment exposed at this stop is penetrated by the vertical Oneco #9 DDH located 1.7 km west-northwest, at a depth of 556 m, which gives an average fault dip over this distance of 19° NW after accounting for topography (Fig. 8; DeGraff and Carter, 2023). Because the fault dips 30-35° NW at the surface, it must dip less than 19° NW over some portion of its trajectory between here and the Oneco #9 DDH. That is, its dip must shallow going in a northwesterly direction similar to the shallowing of PLV stratal dips observed upstream along Dover Creek, which is characteristic of a detached style of faulting with layer-parallel slip. Figure 8: Cross-section along Dover Creek based on outcrop and drill hole data (DeGraff and Carter, 2023). Long bar inclination of L-shaped symbols at land surface shows apparent dip. Thin black lines below topography are drill hole trajectories. Colors and letter codes of geologic units are explained in Figure 2. KF‒Keweenaw fault; HF‒Hancock fault; B‒Bacon (1966) seismic experiment. Stop 2-2: Beaudoin Creek fault exposure Directions: Return to Golf Course Road and turn left to go uphill. Drive 0.5 mi (0.8 km) on Golf Course Road to Beaudoin Creek. We will park along the west shoulder of the road north of the creek culvert. This will require turning vehicles around at the first driveway north of the creek. [Lat: 47° 10.806'N | Lon: 88° 27.049'W] THIS STOP IS ON PRIVATE PROPERTY. PERMISSION IS REQUIRED TO OBTAIN ACCESS. 115 �The small creek crossed by Golf Course Road is unofficially called Beaudoin Creek after the property owner, who also owns the Wood’n Spoon specialty food and gift shop in Mohawk, MI. We will walk upstream to the west for 300 meters to outcrops first described by Hubbard (1898), who traced the PLV-JS fault contact throughout this area and noted remarkable changes in its strike. Between Quincy Creek and the west branch of Dover creek (not visited), the Hungarian fault segment has an azimuth of 42°, but it begins to curve northward at the east branch of Dover Creek, where it has an azimuth of 25° (Fig. 6). The gradual change in fault direction continues from the last stop to this one such that here the fault trace and hanging-wall PLV strata have an azimuth of 345°, which completes a total change in fault strike of 55-60° along a smooth arc. The NNW-trending portion of the fault segment extends more than a kilometer north to a point along another smooth curve of the fault toward the northeast, which re-aligns the fault with the trend of the Portage fault segment. It is unlikely that the position of the second broad curve in the fault north of here is a coincidence, and more likely that it manifests in some way a continuation of the KFS-Portage segment seen at Stop 1-1. Along Beaudoin creek east of the fault, JS strata are intermittently exposed over a distance of 170 meters and mostly consist of yellowish quartzose sandstone with occasional layers of reddish siltstone and conglomerate. Over most of this distance, JS strata dip less than 15° W toward the fault, but within 20 meters of the fault they dip more steeply at 70° E to vertical. The fault contact between PLV basaltic rock to the west and JS sandstone to the east is located to within a meter by the exposures, but the fault zone is not well exposed due to the degraded basaltic rock in the hanging wall. PLV stratigraphy here is very similar to that observed at Hungarian Falls, beginning with a basaltic lava flow of low relief that extends upstream to a small pond below a 6-m-tall waterfall. The waterfall is over a NNW-trending ridge of felsic cobble-pebble conglomerate ~10 m thick that has a meter-thick basal layer of siltstone to fine-grained sandstone, as seen at the previous stop. West of the conglomerate ridge, a series of basaltic flows crops out along the creek bed for another 200 meters. A reliable measurement of PLV strata orientation from the basal unit of the conglomerate layer gives a strike of 170° and dip of 45° W, which probably is also the attitude of the fault surface by analogy with Hungarian Falls and based on the interpretation of a detached fault system. The smooth curve of the fault segment and subparallel PLV strata that are traceable from southwest of Stop 2-1 to north of Stop 2-2, combined with the decrease in dip of the fault and PLV strata toward the Oneco #9 DDH, imply a curved fault surface in three dimensions. A number of geometries involving smaller faults and folds are possible, but the overall geometry implies a larger scoop-shaped fault surface that plunges between southwest and west. Further work to integrate surface mapping with subsurface DDH data are needed to fully define the fault and stratal geometries in this area. For now, we interpret the curved fault segment as part of the Hungarian segment of the KFS, which defines the long southeast edge and shorter east edge of the Hungarian fault block (Fig. 6) with relatively shallow dipping PLV strata. 116 �Stop 2-3: Hammell Creek fault exposure at Houghton-Douglass Falls Directions: Drive southeast on Golf Course Road 1.0 mi (1.6 km) to M-26. Turn left and drive 2.6 mi (4.2 km) to 10th Street in Lake Linden, where M-26 makes a 90° left turn. Turn left and drive 2.0 mi (3.2 km) to a parking area on the right. Turn in and park. [Lat: 47° 12.413'N | Lon: 88° 25.611'W] Houghton-Douglass Falls (a.k.a. Douglass Houghton Falls) was purchased by the State of Michigan in 2018 and, as of this writing, is being converted into a day park with walking trails and signage. The work is not yet complete and access is still somewhat limited but allowed. We will view the site from overlooks at the top of the steep canyon walls and will not descend to the fault contact near the base of the falls due to time constraints. The total vertical drop of 34 m (110 feet) makes Houghton-Douglass Falls the tallest in Michigan. This stop is another classic exposure of the Keweenaw fault (original sense) that has been investigated by geologists since the mid-1800s. The trail to the overlook area crosses the Hancock fault, not yet found in outcrop, and PLV strata in the Keweenaw fault’s hanging wall. The Hancock fault has been traced 16 km on an azimuth of 55° by means of drill holes from the Hancock and Quincy mines to an intersection with the Keweenaw fault one kilometer northeast of the falls (Fig. 3). The Hancock fault seems to have had an important role in the occurrence and distribution of native copper at those two mines (Bornhorst et al., 1986; Field Trip 2 in this volume). Copper mineralization at the base of Houghton-Douglass Falls next to the Keweenaw fault was investigated in an adit opened by the Douglass Houghton Mining Company, organized in 1845 (Stephens, 1902), and recently observed in veins (Gamet, 2023). The geometry of two PLV layers near the intersection of the Hancock and Keweenaw faults is critical to understanding geologic relationships at Houghton-Douglass Falls (Fig. 6). The Laurium bedrock geology map shows the St. Louis (#6) conglomerate and overlying Copper City flow in the hanging walls of the Hancock and Keweenaw faults north and west of their intersection but not to the southwest in the acute fault wedge containing Houghton-Douglass Falls (Cornwall and Wright, 1956b). The two units are easily recognized and correlated in drill holes and outcrops from many kilometers northeast of Calumet-Laurium in a southwesterly direction to the Hancock fault. The St. Louis conglomerate is a felsic, pebble-cobble, clast-supported conglomerate with locally significant lithic and conglomeratic sandstone that is associated with rhyolitic rocks along strike (Hubbard, 1898; White et al., 1953; Nicholson, 1992; Gamet, 2023). The Copper City flow is recognized for its anomalous thickness of 180 m at a point 7 kilometers to the northeast, coarse grain size, and pegmatitic segregations that have been precisely dated (Fig. 2). Recent mapping aided by drill hole data has allowed these two units to be correlated across the Hancock fault into the acute fault wedge, where they are identified in outcrop at Houghton-Douglass Falls (Fig. 6). The main drop at Houghton-Douglass Falls is over the Copper City flow, which extends from upstream of the waterfall down to a ledge ~10 meters above its base. From the north side of the gorge, a planar fabric with meter-scale spacing over much of the flow thickness dips gently 117 �upstream. Observations at the top of the waterfall suggest that this fabric results from amygdule layers that dip 20-25° NW. Below the main waterfall on the ledge above the base, a 3-m-thick sedimentary layer, first noted by Hubbard (1898), consists of a felsic pebble-granule conglomerate and coarse lithic sandstone whose layering provides a reliable strike of 225° and dip of 20° NW, i.e. parallel to amygdule layers at the top of the waterfall. This is interpreted to be the St. Louis (#6) conglomerate below the anomalously thick Copper City flow. Both layers project northeast along strike to intersect the Hancock fault at a point where their map offsets across the fault match the offsets of PLV layers previously correlated across the fault (Fig. 6). Below the St. Louis conglomerate is a basalt lava flow that becomes increasingly fractured at the foot of the falls, at which point sheared basaltic rock is observed along the south face of the gorge. Figure 9: Trenches below Houghton-Douglass Falls that exposed relationships across the fault, marked by the bold red line (Irving and Chamberlin, 1885). Irving and Chamberlin (1885) focused their investigation of Houghton-Douglass Falls along the bottom and walls of the gorge below the falls, again combining careful field observations with trenching across the fault surface. Two trenches running up and down the south valley wall and a third trench along the fault surface (Fig. 9) revealed similar relationships to those observed in the trenches at Hungarian Falls but with some important differences. Basaltic rock in the hanging wall has a clay seam at the fault surface that transitions upward to a clayey breccia and then to fractured but intact basalt as seen in the Hungarian trenches. However, footwall JS strata here are generally poorly indurated, red, shaly conglomerate with subordinate whitish quartzose sandstone layers, which is the opposite relationship of dominant to subordinate lithologies at Hungarian Falls. The downward flexing of subhorizontal JS strata to dips of 20-30° close to the fault surface is again 118 �observed, but the flexing is spread over a larger horizontal distance than at Hungarian Falls. The wider zone of flexure here may result from the poor induration and ductility of the red shaly conglomerate here relative to the moderately indurated sandstone strata at Hungarian Falls. Irving and Chamberlin (1885) estimated a fault dip of 25-30° NW based on their excavations, which is similar to their estimate of PLV stratal dip of 25° NW in the hanging wall. Recent field work yielded a fault dip of 20° NW based on a three-point method using surveyed points across the gorge and by visually siting upward along the fault surface (Gamet, 2023). This result for fault dip matches the PLV stratal dip measured on the St. Louis conglomerate and on amygdule layers in the Copper City flow. While earlier and recent dip values are slightly different, both studies agree that hanging-wall PLV strata are essentially parallel to the underlying fault surface, which is indicative of a detached thrust system. A recent cross-section through Houghton-Douglass Falls uses concepts related to detached thrusting, conservation of volume, and ductile portions of the JS section to model fault geometry and deformation of strata in the hanging wall and footwall of the fault system (Fig. 10). Figure 10: Cross-section along Hammell Creek at Houghton-Douglass Falls based on outcrop data and drill hole correlations (Gamet, 2023). Geologic unit codes: pcc – Copper City flow; psc – Scales Creek flow, pk – Kearsarge flow; pg – Greenstone flow. KFS-M = Keweenaw fault system Mayflower segment; HF = Hancock fault. Area 3: Snake Creek Fault Block – Keweenaw Fault Zone at Lake Gratiot The three stops in Area 3 (Fig. 11) are on the east boundary fault of the Snake Creek block (3-1), on the main Keweenaw fault zone north of Lake Gratiot (3-2), and at the intersection of these two fault trends (3-3). The Keweenaw fault zone roughly parallels the north edge of Lake Gratiot and, relative to Areas 1 and 2, it trends more easterly with an azimuth of 72° and dips more steeply northwest. Other fault segments in Area 3 are similarly oriented clockwise relative to their counterparts in Areas 1 and 2. South of the main Keweenaw fault zone, two fault-bounded blocks have long dimensions oriented parallel to the KFS (Fig.3). West of Lake Gratiot, the Snake Creek block is bounded on the southeast by a NE-trending connector fault, along which PLV layers are 119 �thrust southeast over JS strata (Fig. 11). Deformed hanging-wall PLV strata and footwall JS strata have NE-trending fold axes parallel to their fault contact. Fold axes in the hanging wall plunge 23° with an azimuth of 44° (Mueller, 2021). The southern boundary fault of the Snake Creek block is an ESE-trending footwall splay of the main Keweenaw fault zone (Fig. 3) that juxtaposes PLV strata on the north against JS strata to the south. Similar to the northeast end of the Hungarian block (Fig. 6), this footwall fault splay appears to curve north and merge seamlessly into the connector fault along the southeast edge of the Snake Creek block. Figure 11: Geologic map of Area 3 with the Keweenaw fault system (KFS) and field trip stops 3-1 to 33. Geologic unit codes: pb – Bohemia conglomerate, pgf – Gratiot flow. Teeth along reverse faults are on upthrust sides. See Figures 4 or 13 for symbology. The main Keweenaw fault zone in this area is well exposed along several creeks that empty into Lake Gratiot and, based on outcrop relationships and cross-section models, it consists of two parallel branches (Fig. 11). The northern branch has a well-developed gouge and breccia zone that is at least 20 m wide in places and perhaps as much as 45 m wide. This branch juxtaposes PLV basaltic flows on the north against presumably younger basaltic flows on the south, whereas the southern branch juxtaposes basaltic flows on its north against JS strata on the south. The double fault zone north of Lake Gratiot continues in a west-southwest direction past the termination of the 120 �connector fault intersecting from the southwest and forms the northern boundary of the Snake Creek block. This main fault zone trajectory differs from the 1950s USGS bedrock geology maps and was first proposed by Cannon and Nicholson (2001) in their map compilation. We have adjusted the position of their proposed fault based on a combination of outcrop relationships, drill hole data, and topographic features, and we consider evidence for its existence to be compelling. Stop 3-1: Unnamed creek fault exposure along Iron Gate Road Directions: Continue driving north on M-26 for 2.0 mi (3.2 km) to Hecla Street. Turn right and drive through historic downtown Laurium for four blocks (0.5 mi, 0.8 km) to 1st Street, a.k.a. School Street. Turn left and drive 0.35 mi (0.56 km) to US-41. Turn right and drive 17.6 mi (28.3 km) past the road to Eagle Harbor to historic Central Location. Turn right onto Gratiot Lake Road and drive ~4.8 mi (~7.7 km) to unpaved Iron Gate Road on the right. Turn right and drive 0.5 mi (0.8 km) to an unimproved dirt road on the right. Turn into the side road and park. [Lat: 47° 21.222'N | Lon: 88° 9.340'W] This stop will be a quick show-and-tell to explain fault and stratal geometries at the east edge of the Snake Creek fault block that extends 5 kilometers to the west (Fig. 11). A short walk northwest along the two-track road leads to a 3-m-tall outcrop of JS in the creek northeast of the road. This outcrop is much larger than other JS outcrops sometimes exposed for 35 meters upstream in the creek bed, depending on spring run-off. About 80 meters upstream is the first PLV basalt outcrop where the creek emerges from the upland to the northwest. The boundary between the upland with PLV bedrock and the lower flatter area to the southeast with JS bedrock has a trend of 42° and it extends ~3 kilometers from the southeastern rounded corner of the Snake Creek fault block to the main Keweenaw fault zone at Nine Thirty Two Creek (Stop 3-3). Several small creeks flowing southeast from the upland toward Lake Gratiot cross this boundary and expose bedrock, constraining the position of the geologic contact but not exposing it. The sandstone strata here strike 36° and dip 63° SE in the inferred direction of stratigraphic up, indicating that they have been rotated down to the southeast (Lizzadro-McPherson, 2023). Similar orientations of JS strata are noted at the mouths of other creek valleys where they emerge from the upland. Scattered JS outcrops to the southeast have nearly flat-lying strata, indicating that tilting of JS strata is negligible beyond 100 to 150 meters from the PLV-JS contact. In the upland northwest of the contact, fractured PLV strata with veins of secondary minerals generally do not present good opportunities to determine strike and dip. Where possible to measure, consistent northeasterly strikes with dips both to the northwest and southeast define an anticlinesyncline pair with NE-trending fold axes that parallel the PLV-JS contact. The relationships along the east edge of the Snake Creek block are evidence of a NE-trending fault along which PLV strata to the northwest were thrust over JS strata to the southeast. Similar to the curved fault at the northeast end of the Hungarian block, the fault at the east end of the Snake Creek block also has a curved geometry where it wraps around the block’s southeast corner and gradually changes direction by 55° to a west-northwesterly trend. Along the fault’s 121 �NE-trending section, its position and nature in the latest map (Fig. 11) do not differ much from what is shown on the Bruneau Creek bedrock geology map (Wright and Cornwall, 1954). However, the earlier map labels this fault the “Keweenaw fault,” whereas we interpret it to be part of a curved splay in the footwall of the main Keweenaw fault that lies to the north, which we will visit at the next stop. Stop 3-2: Main Keweenaw fault zone at Eister Creek and Falls Directions: Return 0.5 mi (0.8 km) on Iron Gate Road back to Gratiot Lake Road. Turn left and drive 0.2 mi (0.3 km) to East Gratiot Lake Road. Turn right and drive 1.0 mi (1.6 km) to a parking area along the road. [Lat: 47° 21.975'N | Lon: 88° 7.967'W] Eister Creek near the falls provides excellent exposures across the northern branch of the main Keweenaw fault zone where PLV strata in the hanging wall are juxtaposed against presumably younger PLV strata in the footwall (Figs. 11 and 12). Jacobsville strata that commonly occur in the footwall of the main fault zone are not present here, though they may constitute bedrock south of the southern branch of the main fault zone. Elsewhere nearby in the footwall, the JS unit has thicknesses ranging up to 130 m confirmed in outcrop and greater than 135 m in a water well northwest of Lake Gratiot. In general, the thickness of the JS unit in this area appears to be much less than to the southwest near Houghton, where the unit is known to be at least 785 m thick at the fault system and at least 1,100 m thick away from it to the southeast, but could be 2,000 to 3,000 m thick based on geophysical data. Figure 12: Cross-section along Fault Creek east of Eister Creek (Lizzadro-McPherson, 2023). Geologic unit codes: pb – Bohemia conglomerate; pgf – Gratiot flow; psc – Scales Creek flow. KFS = Keweenaw fault system. Walking north up Eister Creek from the parking area, scattered outcrops of PLV basaltic lava are first encountered at the mouth of the incised creek valley. About 80 meters into the narrow gorge 122 �where it becomes deeper, the basaltic rocks become more fractured and are locally sheared, brecciated, and gougy. Over the next 40-50 m upstream to the base of Eister Falls, fracture intensity increases and cataclastic shearing becomes more prominent until the rock is essentially a breccia cut through by shear zones. The area around the base of the falls is at the core of the main Keweenaw fault zone that is up to 45 meters wide along the creek, depending on how its northern and southern edges are defined. A rock wall perhaps 4 meters wide that projects from the eastern wall of the gorge consists of fault breccia and gouge that is better indurated that the surrounding material, which is also brecciated and gougy. This ridge is inclined steeply upstream, and is taken to define the orientation of the fault zone as striking 255° and dipping 76° N. Upstream from the projecting wall of breccia, the long gradual rise of Eister Falls exposes highly fractured basaltic rocks with some shear zones, but the rock mass is mostly intact and unlike the completely brecciated fault core. The fault-core relationships seen at Eister Creek are even better displayed along another creek located ~800 m east-northeast of here at a locality informally named “Fault creek” (Fig. 12). Stop 3-3: Nine Thirty Two Creek Directions: Return 1.0 mi (1.6 km) on East Gratiot Lake Road to Gratiot Lake Road. Turn right and drive 0.4 mi (0.6 km) to a narrow driveway on the right. Either turn into the driveway and park where possible or park along the right shoulder of the paved road. [Lat: 47° 21.711'N | Lon: 88° 8.730'W] THIS STOP IS ON PRIVATE PROPERTY. PERMISSION IS REQUIRED TO OBTAIN ACCESS. A walk of about 300 meters down the overgrown old road to Lake Gratiot leads to a hairpin turn in Nine Thirty Two Creek that marks the intersection of two fault trends (Fig. 11). The south branch of the main Keweenaw fault zone generally follows the creek valley upstream from the hairpin turn toward the west and, in the opposite direction, it follows an ENE-trending path to the north shore of Lake Gratiot. The thrust that defines the eastern edge of the Snake Creek block follows the western side of the creek downstream from the hairpin turn and terminates northward against the main Keweenaw fault zone. The Keweenaw fault zone upstream of the hairpin turn is manifested by basaltic rocks that are fractured, brecciated, and altered for a few hundred meters to the west. Its east-northeast path is marked by a linear depression that connects to the neighboring creek valley where altered basalt occurs in a cutbank. PLV strata north of the Keweenaw fault zone generally strike east-west and dip moderately north based on two nearby creek traverses. These hanging-wall strata are juxtaposed against presumably younger footwall PLV strata west of the creek’s hairpin turn and against footwall JS strata east of it (Fig. 11). This change in juxtaposition of geologic units along the Keweenaw fault zone occurs because the thrust fault intersecting it on the footwall side raises PLV strata on the west over JS strata to the east. South of the creek’s hairpin turn, JS strata crop out for 235 meters along the creek bed and valley walls and consist of yellowish to reddish, medium-grained, quartzose sandstone that is poorly 123 �laminated along with subordinate reddish, muddy-to-silty, clast-supported conglomerate that is poorly indurated. The exposed JS strata are generally subhorizontal but their dip increases to 69° SE with a strike of 58° within 30 meters of the hairpin turn. The rotation of JS strata downward to the southeast is consistent with components of reverse slip on the intersecting faults that contain the sandstone within their obtuse angle (Fig. 11). Above the sandstone outcrops to the west, the upland caprock is a layer of trachyandesite overlying a basaltic layer, whose contact dips about 10° NE. This stratal orientation may represent a plunging fold axis that is parallel to fold axes near the southeast corner of the Snake Creek block. Some important questions arise from the geometric relationships observed at the intersection of the two faults. For example, what happens to the main Keweenaw fault zone west and south of this fault intersection? Wright and Cornwall (1954) show the Keweenaw fault coming from Eister Creek as bending southwest to follow the PLV-JS fault contact discussed at Stop 3-1. They also show a splay of the Keweenaw fault continuing along Nine Thirty Two Creek as far as Gratiot Lake Road. Cannon and Nicholson (2001) continued this splay fault in a broad arc parallel to regional strike to a reconnection with the Keweenaw fault of Wright and Cornwall (1954) about 6 kilometers east of Mohawk. Based on new mapping and integration of DDH data, we have modified the trajectory of the fault extension proposed by Cannon and Nicholson (2001) and we propose that this is actually the main Keweenaw fault zone. The corollary to this interpretation is that the thrust fault along the east edge of the Snake Creek block is a footwall splay of the main fault zone. In other words, we think that the main Keweenaw fault zone is not always the one that juxtaposes PLV strata in the hanging wall against JS strata in the footwall. Area 4: Keweenaw Fault Zone with Footwall Splays, Lac La Belle to Bête Grise The three stops in Area 4 are along part of the KFS that changes direction from a 72° azimuth to nearly east-west (Fig. 3). The first stop is in the deformed hanging wall of the main Keweenaw fault zone (4-1) that runs along the northwest edge of Lac La Belle, past the southern base of Mt. Bohemia, and along most of the paved road to Bête Grise Bay east of here (Fig. 13). In a westerly direction, the main fault zone forms the northern boundary of the Deer Lake block, whose long dimension is again parallel to the KFS. The Deer Lake block is limited on the south by a footwall splay that diverges from the main fault zone north of Lake Gratiot and juxtaposes PLV basaltic flows on the north against nearly vertical JS strata at the Little Gratiot River (Lizzadro-McPherson, 2023; DeGraff, 1976). Based on diamond drill hole data, the eastern edge of this fault-bounded block is a connector fault where PLV strata are thrust eastward over JS strata, whereas the block’s western edge has a thin cover of Jacobsville Sandstone unconformably overlying weathered basaltic rock. Field relationships and magnetic data suggest that the footwall fault splay curves north and merges into the connector fault along the east edge of the Deer Lake block. The other two stops in Area 4 are at historic localities on the shore of Bête Grise Bay that Irving and Chamberlin (1885) investigated as part of their USGS Bulletin 23 titled “Observations on the junction between the eastern sandstone and the Keweenaw series on Keweenaw Point, Lake Superior”. The Bête Grise block is defined by the main Keweenaw fault zone on the north, by a footwall splay that diverges from it onshore and passes offshore while remaining visible in shallow 124 �Figure 13: Geologic map of Area 4 with the Keweenaw fault system and field trip stops 4-1 to 4-3. Teeth along reverse faults are on upthrust sides. 125 �water (4-2), and by an inferred thrust along the east edge of the block (4-3). The thrust is inferred from a NE-trending belt of intense fracturing and veining in altered basaltic rock that follows the shoreline parallel to the strike of the PLV-JS unconformity exposed to the east along the shore. Thrusting of hanging-wall PLV strata toward the southeast has tilted footwall PLV strata and JS strata above the unconformity 50° SE. Stop 4-1: Haven Falls Directions: Get back onto Gratiot Lake Road and drive 4.3 mi (6.9 km) back to US-41. Turn right and drive 5.7 mi (9.2 km) to Lac La Belle Road. Turn right and drive 4.2 mi (6.8 km) to a Yintersection. Veer right and then through the sharp right curve for 0.5 mi (0.8 km) to Haven Falls Park on the right. Enter the park and park. [Lat: 47° 22.913'N | 88° 1.716'W] The small but beautiful park at Haven Falls spans a terrace formed by a previous higher stand of Lake Superior that was about 10 meters above the current lake level. The cliff of felsic conglomerate over which Haven Creek flows was probably a shoreline cliff at the time of that higher lake level. This stop is in the proximal hanging wall of the main Keweenaw fault zone (Fig. 13) and its stratigraphy is exposed almost continuously from south of Lac La Belle Road, which is privately owned, to well upstream of the falls. About 650 meters east of here and south of the main fault zone, an east-directed thrust fault, cored by the Deer Lake #2 DDH, defines the east edge of the Deer Lake block (Fig. 13A). Slip on this thrust fault has pushed PLV basaltic lavas on the west up and over JS strata to the east (Lizzadro-McPherson, 2023) in a manner similar to what occurs at the east edge of the Snake Creek block. The Haven Falls stop is, therefore, analogous to the Eister Creek stop except that the fault core here is not as well exposed south of the paved road (cf. Figs. 12 and 14). The stratigraphic sequence in the hanging wall begins with a highly fractured, veined, and locally brecciated and sheared lava flow that crops out on both sides of the paved road, but please stay on the north side to respect the private property on the south side. This strongly deformed lava flow lies along a topographic step up from the lowland at the lakeshore to the old lake terrace, and it probably marks the northern edge of the core of the fault zone. Upstream from this first lava flow, a 12-m-wide belt of conglomerate is followed by a 30-m-wide belt of ophitic basalt that locally is highly fractured, veined, and sheared. The felsic cobble-pebble conglomerate at the main falls is largely clast-supported and has a massive appearance. It extends for a horizontal distance of 16 meters along the creek to well above the top of the falls, where it is brecciated along a fault zone that cuts slightly up section toward the east. A reliable formation strike of 245° and dip of 65° NW comes from a sandstone layer above the falls near the northern edge of the second conglomerate layer. The two conglomerate layers here are collectively known as the Lac La Belle conglomerate (Cornwall, 1954a) and have been tentatively correlated with the Baltic (#3) conglomerate near Houghton. Although there is considerable uncertainty about this correlation due to the distance involved, the Lac La Belle conglomerate lies well below the St. Louis (#6) conglomerate seen at many of the earlier stops of this field trip. This means that the Keweenaw fault system here cuts the PLV section at a significantly deeper level than near Calumet, Laurium, and Lake Linden. 126 �The stratigraphic units at the falls have been traced by detailed mapping along strike in both directions. About 350 meters east-northeast, the two conglomerate layers merge into one layer where the intervening basalt flow pinches out, but otherwise the layers can be traced continuously along strike. The only structural complications observed along strike are a few faults that cut at acute angles upward across layers toward the east and have small reverse offsets, similar to the fault at the top of Haven Falls. Detailed mapping in 2019-2020 did not find evidence of four transverse faults shown on the Delaware bedrock geology map as offsetting the Lac La Belle conglomerate, neither in terms of offsets nor enhanced fracturing (LizzadroMcPherson, 2023). In fact, the kinematics of slip along the main Keweenaw fault zone would argue for a system of smaller subparallel faults rather than a series of faults normal to the main fault zone. Figure 14: Cross-section along Haven Creek at the falls (Lizzadro-McPherson, 2023). Geologic unit codes: pb – Bohemia conglomerate; psc – Scales Creek flow. KFS = Keweenaw fault system. THE NEXT TWO STOPS ARE ALONG APACHE LANE, WHICH IS PRIVATELY OWNED AS ARE ALL PROPERTIES ALONG IT. PERMISSION IS REQUIRED TO OBTAIN ACCESS. Stop 4-2: Bête Grise Shoreline, Irving & Chamberlin Historic Site Directions: Exit Haven Falls Park and drive east back to the stop sign at the Y-intersection. Turn sharply right onto Bête Grise Road and drive 3.2 mi (5.2 km) to Apache Lane on the left. [Geology Note: at 1.9 mi / 3.1 km along BG Road, an outcrop to the north is the location of the dated calcite vein in the fault zone.] Turn left, drive 0.5 mi (0.8 km), and then park along the right side of the road. [Lat: 47° 23.345'N | Lon: 87° 56.905'W] We will walk down a moderately steep slope to the shore, where Irving and Chamberlin (1885) used a “force of miners” to strip the shoreline bare in order to better expose the contact between PLV layers on the north and JS strata to the south (Figs. 13B and 15). This is probably not a field 127 �practice we could get away with today even if the site was not privately owned. Depending on the lake level, we may be able to see the contact between highly fractured, veined, and partly altered basaltic rock at the base of the shoreline scarp and JS strata that strike 105° and dip 55° S. An aerial image of the shoreline at this stop shows a sharply defined line with an azimuth of 105° that separates uniformly dark-toned PLV basaltic rocks on the lake bottom and along the shore to the east from variably lighter-toned layers of JS strata to the south and west (Fig. 16). This is the fault line that may be observed onshore or can be closely constrained by nearby outcrops. The aerial image shows many small faults as darker lines and narrow zones that cut JS strata at angles approaching 90° and offset strata by less than a meter or two. Near the fault line, splay faults break the JS unit into blocks up to 30 meters long parallel to the fault line and 4 meters wide. Figure 15: Cross-sectional view of a segment of the KFS exposed by excavation along the Bête Grise Bay shoreline. Fault strike = 100°, dip = 55° S (Irving and Chamberlin, 1885). Circle with black dot indicates movement toward viewer; circle with cross indicates movement away. Onshore north of the fault line, PLV strata are highly fractured, veined, and sheared for at least 55 meters along the shoreline to the east, which is about 25 meters perpendicular to the fault. Basaltic outcrops along Apache Lane and to the north do not exhibit such deformation. Following the shore to the west and south, JS strata change in terms of both facies and structural orientation. The basal part of the section consists of reddish, thin-bedded, siltstone and mudstone with minor fine-grained sandstone (6-7 m true thickness), followed upward by a lighter-toned package of silty to fine-grained sandstone with minor silty pebble conglomerate that forms a resistant ridge (~2 m), and then an interval of reddish siltstone and muddy conglomerate (~4 m). 128 �From this point southward and up section, JS strata tend to be sand-prone but alternate between: (1) pinkish to orange, fine to medium grained, quartzose sandstone; (2) red, thinly bedded, siltstone to mudstone; and (3) muddy to silty, poorly indurated, conglomerate layers. In summary, the JS unit tends to clean upward from a silt- and mud-dominated basal section with conglomeratic units near the fault to a quartzose sand-prone section away from the fault. Along with these stratigraphic changes, the dip of JS strata decrease from 55° S near the fault to about 20° S at a perpendicular distance of 60 meters from the fault, and presumably becomes subhorizontal not much further to the south. Figure 16: Aerial image of Stop 4-2 showing the south boundary fault of the Bête Grise block. The fault is interpreted to have dominant strike slip. Stratigraphic up in the JS is to the south. It is clear that movement along the fault has juxtaposed older PLV strata to the north against younger JS strata to the south and that the north side has a component of upward movement, as noted elsewhere. However, what is the nature of this fault? The work by Irving and Chamberlin (1885) and their team exposed a fault surface that dips about 55° S, essentially parallel to adjacent JS strata (Fig. 15). Based on textbook definitions, this would be a normal fault with younger JS strata in the hanging wall to the south above older PLV strata in the footwall to the north. Something about this interpretation seems paradoxical, however, because at previous stops 129 �the main fault zone dipped north or northwest and also because the tectonic setting of the Keweenaw fault system was compressional. Part of the paradox results from textbook definitions of reverse and normal faults that are based on idealized planar fault surfaces that have mostly dip slip. In the case of curved or corrugated fault surfaces with mostly strike slip, the textbook nomenclature for dip-slip faults may lead to confusion. Depending on the portion of a corrugated fault surface that is exposed, a mostly strike-slip fault with a smaller dip-slip component may exhibit an apparent normal or reverse component of dip-slip even though the actual dip-slip component is the same everywhere along the fault. The Keweenaw fault system in this area trends nearly east-west and is dominated by right-lateral strike slip with lesser north-side-up dip slip (2:1 ratio of strike-to-dip slip), and we infer that motion on this fault is dominantly right-lateral strike slip. The fault forms the southern edge of a fault-bounded block (Fig. 13B) whose east side will be visited next. Stop 4-3: Bête Grise Shore, PLV-JS Unconformity and Fault Directions: Continue driving east on Apache Lane for 0.4 mi (0.6 km) to the end of the road. Park where space allows. [Lat: 47° 23.437'N | Lon: 87° 56.350'W] We will walk 100 meters east and 50 meters south to access the shoreline, where geologists traveling along the coast by boat in the mid-1800s described impressive layers of sandstone on the rocky bottom of Lake Superior (Figs. 13B and 17). This area was examined later by none other than Irving and Chamberlin (1885) and then by Cornwall (1954b). The aerial image of the shoreline and offshore region reveals what the early explorers reported, a set of well-defined parallel layers that curve sharply from NE-trending layers on the western side to EW-trending layers along the shore to the east. The shoreline stop is at the western edge of the JS strata where an unconformity between PLV and JS strata is tilted about 50° SE. Depending on water level and shoreline erosion, we may be able to see the unconformity between saprolitized PLV basaltic lava to the northwest and JS strata to the southeast. If the saprolite is exposed, please do not disturb it by digging, picking at it, or walking on it. The basaltic protolith has been completely converted to clay minerals and still retains its original textures, including whitish veins that are approximately normal to the tilted unconformity. Northwest of the unconformity, i.e. deeper below the paleosurface, PLV basaltic rocks do not exhibit such alteration. Saprolitic basaltic rock that retains original textures, such as ophitic texture, has been observed elsewhere in the area where the PLV-JS unconformity is inferred, such as the east end of the Deer Lake block (Lizzadro-McPherson, 2023; DeGraff, 1976). East of the unconformity along the shore, a recessive basal part of the JS section consists of thinly bedded, reddish siltstone and mudstone with minor interbedded fine-grained sandstone. The recessive strata here strike northeast and dip moderately southeast over a distance of 25 meters to the first small resistant sandstone layer (1-2 m thick). Next in the section is another recessive interval (6-7 m wide) of reddish siltstone with interbeds of poorly indurated muddy conglomerate, followed by a larger ridge of resistant sandstone that begins a sequence of 130 �alternating resistant sandstone beds, recessive reddish siltstone, and reddish poorly indurated conglomerate. Thus, the basal JS section here is very similar to the section at Stop 4-2. The main difference is in their structural attitude, which differs in strike by 55-60°. At Stop 4-2, the dip direction of JS strata is 195° and away from the inferred strike-slip fault on the south side of the Bête Grise block, whereas the dip azimuth of JS strata on the east side of the fault block is 138° and away from the tilted PLV-JS unconformity (Fig. 13B). We infer that southeast tilting of the PLV-JS unconformity resulted from southeast thrusting along the east edge of the Bête Grise fault block, based in part on intense fracturing observed along the shoreline northwest of the unconformity at stop 4-3. Figure 17: Aerial image of Stop 4-3 showing the north and east boundary faults of the Bête Grise block. The east boundary fault is interpreted to have dominant dip slip with west side thrust eastward, whereas the north boundary fault is interpreted to have dominant strike slip. Stratigraphic up in the JS is to the southeast and south. If time permits, we will ascend the shoreline scarp to the flat bench above and walk another 100 meters to reach the eastern edge of JS outcrop along the shore. Here, JS strata strike nearly eastwest and are vertical to slightly overturned to the south, forming narrow ridges and eroded furrows and clefts due to differential erosion of the resistant and recessive layers (Fig. 17). Near the eastern edge of JS outcrop, vertical JS strata are flanked on the north by PLV strata that begin 131 �with a felsic conglomerate and continue upslope with PLV basaltic lavas. The contact between PLV strata on the north and vertical JS strata to the south is a major fault that intersects the shoreline, where a fault breccia is exposed several meters east of the last onshore JS outcrop. From this point, the fault turns eastward and runs along the shoreline for 200 meters before continuing offshore and splitting into two branches. This is the last stop and we hope that you had a good experience that will help you to understand other fault systems. Thank you for your participation! Acknowledgements We thank the following M.S. graduates and their assistants, whose field mapping was funded by U.S. Geological Survey EDMAP projects G17AC00115, G19AC00140, and G21AC10681: Colin Tyrrell (M.S.), Sophie Mueller (M.S.), Nolan Gamet (M.S.), Graham Hubbard, Ian Gannon, Ginny Hemmila, Gabe Ahrendt, Jack Hawes, Braxton Murphy, Breeanne Heusdens, and Dillon Breen. We also thank many who have expressed interest in this work and have provided helpful comments. References Cited Aho, G.D., 1969, A Reflection Seismic Investigation of Thickness and Structure of the Jacobsville Sandstone, Keweenaw Peninsula, Michigan: Michigan Technological University, MS thesis, 104 p. Bacon, L.O., 1966, Geological structure east and south of the Keweenaw fault on the basis of geophysical evidence: in Steinhart, J.S. and Smith, T.J. (eds), The Earth Beneath the Continents: Am. Geophys. Union, Geophysical Monograph 10, p. 42-55. Bornhorst, T.J., 1997, Tectonic context of native copper deposits of the North American Midcontinent Rift System: in Ojakangas, R.W., Dickas, A.B., and Green, J.C. (eds.), Middle Proterozoic to Cambrian Rifting, Central North America: Boulder, CO, GSA Special Paper 312, p. 127-136. Bornhorst, T.J., and Barron, R.J., 2011, Copper deposits of the western Upper Peninsula of Michigan: Geological Society of America Field Guide, v. 24, p. 83-99. Bornhorst, T.J., Paces, J.B., Grant, N.K., Obradovich, J.D., and Huber, N.K., 1988, Age of native copper mineralization, Keweenaw Peninsula, Michigan: Economic Geology, v. 83, p. 619-625. Broderick, T.M., 1931, Fissure vein and lode relations in Michigan copper deposits: Econ. Geol., v. 26, p. 840-856. doi:10.2113/gsecongeo.26.8.840 Brojanigo, A., 1984, Keweenaw Fault; Structures and Sedimentology: Houghton, Mich., Michigan Technological University, unpublished M.S. thesis, 124 p. Butler, B.S., and Burbank, W.S., 1929, The copper deposits of Michigan: U.S. Geological Survey Professional Paper 144, 238 p. 132 �Cannon, W.F., 1992, The Midcontinent Rift in the Lake Superior region with emphasis on its geodynamic evolution: Tectonophysics, v. 213. p. 41-48. Cannon, W.F., Green, A.G., Hutchinson, D.R., Lee, M., Milkereit, B., Behrendt, J.C., Halls, H.C., Green, J.C., Dickas, A.B., Morey, G.B., Sutcliffe, R., and Spencer, C., 1989, The North American Midcontinent Rift beneath Lake Superior from GLIMPCE seismic reflection profiling: Tectonics, v. 8, p. 305-332. Cannon, W.F., Peterman, Z.E., and Sims, P.K. 1993, Crustal scale thrusting and origin of the Montreal River monocline – a 35-km-thick cross section of the Midcontinent rift in northern Michigan and Wisconsin: Tectonics, v. 12, p. 728 - 744. Cannon, W. F., 1994, Closing of the Midcontinent Rift - A far field effect of Grenvillian contraction: Geology, v. 22, p. 155-158. Cannon, W.F. and Nicholson, S.W., 2000, Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan to accompany Map I-2696: U.S.G.S Pamphlet, 7 p. Cannon, W.F. and Nicholson, S.W., 2001, Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan: United States Geological Survey, Map I-2696, Scale = 1:100,000. Cornwall, H.R., 1954a, Bedrock Geology of the Delaware Quadrangle, Michigan: U.S. Geological Survey, Washington, D.C., Geologic Quadrangle Map GQ-51, scale 1:24,000. Cornwall, H.R. and Wright, J.C., 1956a, Geologic Map of the Hancock Quadrangle, Michigan: U.S. Geological Survey, Washington, D.C., Mineral Investigations Field Studies Map MF-46, scale 1:24,000. Cornwall, H.R. and Wright, J.C., 1956b, Geologic Map of the Laurium Quadrangle, Michigan: U.S. Geological Survey, Washington, D.C., Mineral Investigations Field Studies Map MF-47, scale 1:24,000. Craddock, J.P., Pearson, A., McGovern, M., Kropf, E., Moshoian, A., and Donnelly, K., 1997, Postextension shortening strains preserved in calcites of the Midcontinent Rift: Geological Society of America, Special Paper 312, p. 115-126. https://doi.org/10.1130/0-8137-2312-4.115 Craddock, J.P., Konstantinou, A., Vervoort, J.D., Wirth, K.R., Davidson, C., Finley-Blasi, L., Juda, N.A., and Walker, E., 2013, Detrital zircon provenance of the Mesoproterozoic Midcontinent Rift, Lake Superior region, USA: Journal of Geology, v. 121, no. 1, p. 57-73. Davis, D.W., and Paces, J.B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. DeGraff, J.M., 1976, Structural and Age Relationships of Rocks Associated with the Lac La Belle Magnetic Anomaly, Keweenaw County, Michigan: Michigan Technological University, M.S. thesis, 130 p. 133 �DeGraff, J.M. and Carter, B.T., 2023, Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System: Geological Society of America Bulletin, v. 51, no. 1, p. 449–466. https://doi.org/10.1130/B36186.1 Fossen, H., Schultz, R.A., Shipton, Z.K., and Mair, K., 2007, Deformation bands in sandstone: a review: Journal of the Geological Society, v. 164, p. 755-769. Gamet, N.G., 2023, Structural Analysis and Interpretation of Deformation along the Keweenaw Fault System from Lake Linden to Mohawk, Michigan: Michigan Technological University, M.S. thesis, 122 p. Hamblin, W.K., 1958, The Cambrian Sandstones of Northern Michigan: Michigan Department of Conservation, Geological Survey Division, Lansing, MI, Publication 51, 55 p. Hinze, W.J., Braile, L.W., and Chandler, V.W., 1990, A geophysical profile of the southern margin of the Midcontinent Rift System in western Lake Superior: Tectonics, v. 9, no. 2, p. 303-310. Hodgin, E.B., Swanson-Hysell, N.L., DeGraff, J.M., Kylander-Clark, A.R.C., Schmitz, M.D., Turner, A.C., Zhang, Y., and Stolper, D.A., 2022, Final inversion of the Midcontinent Rift during the Rigolet Phase of the Grenvillian orogeny: Geology, v. 50, no. 5, p. 547-551. Hubbard, L.L., 1898, Keweenaw Point with particular reference to the felsites and their associated rocks: Geological Survey of Michigan, v. 6, part 2, 155 p. Irving, R.D. and Chamberlin, T.C., 1885, Observations on the junction between the eastern sandstone and the Keweenaw series on Keweenaw Point, Lake Superior: U.S. Government Printing Office, Washington, D.C., U.S. Geological Survey, Bulletin No. 23, 58 p. Kalliokoski, J., 1982, Jacobsville Sandstone: in Wold, R.J. and Hinze, W.J. (eds.), The Geology and Tectonics of the Lake Superior Basin, Geological Society of America Memoir, No. 156, p. 147-155. Keweenaw National Historical Park, 2016, Calumet & Hecla Records – 00019/004.02.01.03-007 Microfiche Drill Core Log Library: Calumet, Michigan, National Park Service, U.S. Department of the Interior, on microfiche. Langfield, K.M., 2024, Slip Kinematics and Structural Analysis of the Keweenaw Fault System from Lake Linden to Hancock, Michigan: Michigan Technological University, M.S. thesis, in preparation. Lizzadro-McPherson, D.J., 2023, Structural Analysis and Slip Kinematics of the Keweenaw Fault System between Bête Grise Bay and Gratiot Lake, Keweenaw County, Michigan: Michigan Technological University, M.S. thesis, 140 p. Malone, D.H., Stein, C.A., Craddock, J.P., Kley, J., Stein, S., and Malone, J.E., 2016, Maximum depositional age of the Neoproterozoic Jacobsville Sandstone, Michigan: implications for the evolution of the Midcontinent Rift: Geosphere, v. 12, no. 4, p. 1271-1282. 134 �Merk, G.P., and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks: Geological Society of America Memoir 156, p. 97-105. Mueller, S.A., 2021, Structural Analysis and Interpretation of Deformation Along the Keweenaw Fault System West of Lake Gratiot, Keweenaw County, Michigan: Michigan Technological University, M.S. thesis, 69 p. Nicholson, S.W., 1992, Geochemistry, Petrography, and Volcanology of Rhyolites of the Portage Lake Volcanics, Keweenaw Peninsula, Michigan: U.S.G.S. Bulletin 1970, Chapter B, p. B1-B57. Robertson, J. M, 1975, Geology and mineralogy of some copper sulfide deposits near Mount Bohemia, Keweenaw County, Michigan: Economic Geology 70 (7) 1202-1224. Stein, C.A., Kley, J., Stein, S., Hindle, D., and Keller, G. R., 2015, North America’s Midcontinent Rift: When rift met LIP: Geosphere, v. 11, no. 5, p. 1607-1616. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district, parts I and II: Economic Geology, v. 54, p. 1250–1277 and 1444-1460. doi:10.2113/gsecongeo.54.7.1250/ Swanson-Hysell, N.L., Ramezani, J., Fairchild, L.M., and Rose, I.R., 2019, Failed rifting and fast drifting: Midcontinent Rift development, Laurentia’s rapid motion and the driver of Grenvillian orogenesis: Geological Society of America Bulletin, v. 131, nos. 5-6, p. 913-940. Tyrrell, C.W., 2019, Keweenaw Fault Geometry and Slip Kinematics – Bête Grise Bay, Keweenaw Peninsula, Michigan: Michigan Technological University, M.S. thesis, 30 p. Wadsworth, M.E., 1884, On the relation of the Keweenawan series to the eastern sandstone in the vicinity of Torch Lake, Michigan: Boston Soc. Natural Hist. Proc., v. 23, p. 172-180. White, W.S., 1952, Imbrication and initial dip in a Keweenawan conglomerate bed, J. Sediment. Petrol., v. 22, pp. 189-199. White, W.S., 1956, Geologic Map of the Chassell Quadrangle, Michigan: U.S. Geological Survey, Washington, D.C., Mineral Investigations Field Studies Map MF-43, scale 1:24,000. White, W.S., 1968, The native copper deposits of northern Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933-1967 (Graton-Sales Vol.): New York, Am. Inst. Mining Metall. Petroleum Engineers, v. 1, p. 301-325. White, W.S., 1985, “Unpublished diamond drillhole core logs”: U.S. Geological Survey, Field Records Collection, Boxes 282, 287-290. Woodruff, L.G., Schulz, K.J., Nicholson, S.W., and Dicken, C.L., 2020, Mineral deposits of the Mesoproterozoic Midcontinent Rift system in the Lake Superior region – A space and time classification: Ore Geology Reviews, v. 126, p. 1-21. 135 �136 �Field Trip 5 Geology and History of a Native Copper Mine: Adventure Mine, Ontonagon County, Michigan Theodore J. Bornhorst Department of Geological and Mining Engineering and Sciences and A.E. Seaman Mineral Museum, Michigan Technological University, 1404 E. Sharon Avenue, Houghton, MI 49931 Matt Portfleet Department of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 [Latitude: 46.777224; Longitude: -89.081906] Directions: Leave downtown Houghton and head south on M-26 towards South Range. Stay on M-26(highway turns into M-38 past the Mass City turnoff). Stay on M-38 towards Ontonagon. Follow signs to Adventure Mine. The Adventure Mine is privately owned and operated as a publicly available mine tour Introduction The historic Adventure Mine is part of the Greenland-Mass subdistrict of the Keweenaw Peninsula native copper district of the western Upper Peninsula of Michigan (Figures 1 and 2). The Adventure Mining Company began mining native copper in 1850. It permanently ceased mining in 1917 at the time when most small mines of the subdistrict ceased mining operations. From the 1980s to today, the mining activities at the Adventure Mine have yielded specimens of massive native copper and copper crystals for purchase by tourists and mineral collectors. The Adventure Mine is a Keweenaw Heritage Site of the Keweenaw National Historical Park. It is located in the Greenland-Mass subdistrict about 40 km southwest of the Baltic Mine in Painesdale, the southernmost major native copper mine in the district (Figure 2). The subdistrict yielded about 85 million lbs (39 million kg) of refined copper at grades ranging from 0.5 to 1.25 percent (Butler and Burbank, 1929; Weege and Pollock, 1971). The Adventure Mine was the second largest producer in the subdistrict, yielding about 11 million lbs. (5 million kg) of refined copper from the tops of five different basaltic lava flows (Butler and Burbank, 1929). Despite the relatively low production of copper from the Greenland-Mass subdistrict (~0.8 % of the total district production of ~ 5 billion kg (11 billion lbs), the geologic characteristics of the Greenland-Mass subdistrict deposits are typical of the native copper deposits elsewhere in the Keweenaw Peninsula (e.g., Stoiber and Davidson, 1959; Butler and Burbank, 1929; etc.). Since 137 �mining in the Keweenaw Peninsula native copper district ceased in 1968, underground access to observe or study the native copper deposits has been limited. Currently there is access to only two mines in the main area of the district (Quincy and Delaware) and two mines in the Greenland-Mass subdistrict (Adventure and Caledonia). These mines are operated as underground experiences for tourists, except for Caledonia. This field trip guide relies on existing publications by Bornhorst and Whiteman (1995); Bornhorst et al. (2013); Bornhorst and Barron (2011); and Butler and Burbank (1929). The overview of the geologic and part of the human history is summarized from Bornhorst and Lankton (2009), Bornhorst and Mathur (2016), and Bodden et al. (2022). Brandon Erickson prepared a brief history of the Adventure Mine which is included in this guide. Figure 1: Simplified bedrock geology of the Mesoproterozoic Midcontinent Rift around Lake Superior. Modified after Bornhorst et al., 2013) Overview of Geologic History The largest known accumulation of native copper in the world is the Keweenaw Peninsula native copper district (Figure 2). In comparison to other copper mining districts where major copper ore 138 �minerals are sulfides, nearly all of the copper in the district occurs as native copper. About 5 billion kg (11 billion lbs) of refined copper were extracted from about 380 million tons of ore between 1845 and 1968 via underground mines (Weege and Pollock, 1971). Small quantities of native silver occur with the native copper. An estimate using incomplete records suggests the amount of silver was between .05 to .5 oz per ton of ore. Native copper and silver were coprecipitated. The native copper deposits are hosted by the Mesoproterozoic Midcontinent Rift (MCR) (Figures 1 and 2). More than 25 km of volcanic rocks and 8 km of clastic sedimentary rocks fill the center of the MCR (Cannon et al., 1989 and 1993). These rift-filling rocks were emplaced between about 1.15 to ~1 Ga (Cannon et al., 1989; Davis and Paces, 1990; Kulakov et al., 2018; Heaman et al., 2007). Figure 2: Simplified geologic map of the Keweenaw Peninsula and vicinity modified from Bornhorst et al. (2013). At the White Pine mine “Keweenawan” native copper cuts across diagenetic the shale-hosted chalcocite deposit. Early eruptions of MCR basaltic lava flows were scattered on a broad land area above a developing mantle plume. These early eruptions were followed by many eruptions from fissure vents concentrated in the center part of the MCR (now buried under the center of Lake Superior). These eruptions were dominated by fissure volcanoes along linear faults. The Portage Lake Volcanics and Porcupine Volcanics are rift-filling basaltic volcanic rocks erupted about 1.1 billion years ago 139 �during the active rifting of the MCR (Figure 3). The MCR was bounded on the edges by down dropped normal faults resulting in the MCR being a faulted basin. The basin progressively dropped down by stretching and by magma erupted at the surface during active rifting. Eruptions of basalts of the Portage Lake Volcanics were on land surface (subaerial). Subaerially erupted basalt lava flows have either a vesicular or brecciated and vesicular top (pahoehoe or aa lava flow). Mineral filled vesicles are termed amygdules and flow tops dominated by vesicles are termed amygdaloids and those dominated by breccia clasts of amygdaloidal basalt are termed fragmental amygdaloids. The top of a subaerial lava flow is underlain by a massive (relatively vesicle-free) basalt. Massive basalt flow interior in thinner flows is fine grained and in thicker flows it is coarse-grained (ophitic). Thin flows can be vesicular throughout with vesicles more abundant at the top. The typical flow is 10 to 20 m thick. Eruptions of basaltic lavas were cyclical and during eruptive hiatuses minor gravel and sand were deposited on top and infiltrated in the tops of occasional lava flows. These clastic sedimentary layers are overlain by basalt lava flows. A desert environment 1.1 billion years ago resulted in red coloration of these clastic sedimentary rocks. Figure 3: Stratigraphic column for the Adventure Mine region with approximate ages. Active rifting and basaltic volcanic activity ended over a short period of time, but the rift basin continued to passively sag and was progressively filled with clastic sedimentary rocks from the Copper Harbor Conglomerate to the Freda Sandstone (Figure 3). In the Adventure Mine region, the 140 �rift-filling volcanic rocks (Porcupine Volcanics and Portage Lake Volcanics, Figure 3) were first covered by red-colored gravels and sands (Copper Harbor Conglomerate. Overlying the Copper Harbor Formation are black- to gray-colored muds and silts (Nonesuch Formation). Lastly the rift was filled with a thick section of red-colored fine sandstones (Freda Sandstone). Today, the rocks of the Keweenaw Peninsula and Adventure Mine region span the edge of the MCR, and consist of a thick section of rift-filling subaerial basaltic lava flows overlain by a thick section of rift-filling clastic sedimentary rocks (Figures 1, 2, and 3). The last and final phase of the MCR resulted from a regional compressional event due to collision of continental land mass along the eastern edge of North America at that time (Grenville Orogeny, Cannon, 1994). Compression resulted in reverse and thrust faults as well as folding and fracturing of rift-filling volcanic and clastic sedimentary rocks. Native copper and related minerals were emplaced during this regional compressional event (Bornhorst, 1997). From the beginning of regional compression at about 1.06 to 1 billion years ago the Jacobsville Sandstone was deposited in a rift-flanking basin until about 1 billion years ago (Figure 2). There were no recorded geologic events by rocks of Michigan’s Upper Peninsula from about 1.0 billion years ago to 500 million years ago. Erosion likely exposed the native copper deposits at the surface and downward percolating oxidizing groundwaters had access to alter the native copper (Bornhorst and Robinson, 2004). The MCR rocks were buried by Phanerozoic rocks deposited from 500 to 175 million years ago (Catacosinos and others 2001). The native copper deposits of the Keweenaw Peninsula were again at the surface after erosion of overlying rocks by Pleistocene glaciers over the last 2.5 million years. Native Copper Deposits of the Keweenaw Peninsula The cumulative pre-mining geologic copper resource of the Keweenaw Peninsula native copper district totaled about 9 billion kg of copper (20 billion lbs; Bornhorst and Barron, 2011). About ½ of the geologic resource was recovered. Speculative concentrations of copper in rocks are even greater. These concentrations have not been mined for various reasons such as too low of grade or too deep below the surface. Permeable and porous primary geologic settings that have sufficient open spaces that were sufficiently connected with each other facilitated the movement of ore-forming hot waters (hydrothermal fluids) from which native copper and other minerals were precipitated. Compression of the MCR strata integrated the primary permeability and porosity of the hydrothermal plumbing system with compression generated faults/fractures (Bornhorst, 1997). The absolute age of the main-stage of hydrothermal activity coincides with the age of the regional compressional event at about 1.06 to 1.04 billion years ago (Bornhorst et al., 1988). The permeable and porous tops of amygdaloidals and fragmental amygdaloids hosted ~58.5% of produced native copper. Horizons of conglomerate and sandstone between lava flows, which are also permeable and porous, hosted ~39.5% of produced native copper. Native copper ore bodies are "sandwiched" on the bottom side by the massive basalt interior of the flow whose top hosts the native copper ore body. On the top side the ore bodies are sandwiched by massive basalt of the overlying lava flow. The sandwiched ore-bodies are geometrically approximately tabular 141 �(called lode) with a thickness between 3 and 5 m and the same orientation as surrounding host lava flows. The typical lode extends down-dip 1.5 to 2.6 km and has a lateral extent of 1.5 to 11 km (Butler and Burbank, 1929; White, 1968). Open spaces in amygdaloidal lava flow tops (vesicles) and sandstones/conglomerates are typically up to a cm across. They are typically filled dominantly by gangue minerals and lesser native copper. Less frequently the entire open space was filled with masses of native copper. Open spaces between breccia fragments in the top of a lava flow (fragmental amygdaloid) or between clasts in conglomerate will tend to have larger masses of native copper and can weigh up to several lbs, to tens of lbs to hundreds of lbs. and rarely weighing tons. A minor amount of the total produced native copper, ~ 2%, was from sub vertical tabular open spaces (veins when filled with minerals) that follow faults and fissures that perpendicularly cut across the volcanic-dominated strata. Ore-forming hydrothermal fluids readily moved along faults and fissures since they have a relatively large amount of interconnected open-space; these ore-bodies are also tabular lodes. Since the size of open space is large the corresponding size of masses of native copper can also be large weighing multiple tons with the largest masses being several hundred tons. Native copper is closely associated with about 22 common and many more uncommon minerals (Bodden et al., 2022; Butler and Burbank, 1929; White, 1968). These minerals fill the same open spaces along with and instead of native copper. The suite of minerals is similar to those found where rocks have undergone very low to low grade burial metamorphism at less than about < 300OC (Bodden et al., 2022). Thermal modeling suggests that peak burial metamorphic conditions at depth were between 400 to 500oC (Woodruff, 1995). Burial metamorphic processes resulted in ore-forming hydrothermal fluids carrying copper leached from the tops of buried riftfilling basalt lava flows. Batches of metamorphogenic-dominated hydrothermal fluid generated over time were similar to one another. The rift-filling volcanic rocks were very low in sulfur when they erupted, and the little contained sulfur degassed into the atmosphere. During subsequent deposition of rift-filling clastic sedimentary rocks there was an incursion of seawater into the rift for a significant amount of time. This resulted in seawater deeply penetrating into the underlying rift-filling volcanic rocks (Figure 4A). During burial, the rift-filling volcanic and clastic sedimentary rocks were progressively heated and during initial heating the seawater evolved to be depleted in sulfur similar to expelled modern sea floor hydrothermal fluids (Figure 4B). Continued heating during burial resulted in burial metamorphic-dominated hydrothermal fluids with copper leached from the rift-filling volcanic rocks. These fluids were well mixed with the evolved seawater resulting in hybrid metamorphic-dominated ore-forming fluids (Figure 4C). These main-stage hybrid metamorphic-dominated ore-forming hydrothermal fluids moved upwards from the source zone through the same very sulfur poor strata as in the source rocks (Figure 4D). As they moved upwards they cooled, interacted with host rocks, and in the relatively shallow zone of precipitation they variably mixed with sulfur-poor reduced meteoric water (Figure 4D; Bodden et. al, 2022). These processes resulted in precipitation of native copper and main-stage hydrothermal minerals. Higher temperature main-stage mineral assemblages are spatially associated with the area of native copper deposits where the thermal anomaly was greatest 142 �because of focused hydrothermal fluids. Within the native copper district, the suite of main-stage minerals that is associated with native copper and is followed by late-stage minerals precipitated at lower temperature than the main-stage. Figure 4: Cartoon cross sections showing conceptual genetic model of the native copper deposits of the Keweenaw Peninsula formed at about 1060 to 1040 million years ago. Modified from Bodden et al. (2022). A. Marine incursions and seawater penetration during deposition of volcanic and sedimentary rocks in MCR. B. Area prior to burial metamorphism with sulfur depleted evolved seawater providing salinity for ore-forming fluids. C. Burial metamorphic fluids mixing with evolved seawater produce hybrid ore-forming fluids. D. Precipitation of main-stage minerals, including native copper, as a result of mixing of ore-forming fluids with meteoric water, decreasing temperature, and water-rock reactions. 143 �Figure 5: Bedrock geologic map and cross sections of the Greenland-Mass subdistrict of the Keweenaw Peninsula Native Copper District. Modified from Whitlow (1974). 144 �The Evergreen Succession Butler and Burbank (1929) recognized the Evergreen lava flow and a succeeding number of lava flows of the Portage Lake Volcanics as having distinctive lithologies and hosting the native copper deposits in the Greenland-Mass subdistrict (Figure 3 and 5). These are informally termed the Evergreen Succession (Figure 3). The Evergreen Succession is stratigraphically about 150 m (500 ft) above the Bohemia (No. 8) conglomerate (Butler and Burbank, 1929). The Evergreen Succession basaltic lava flows are slightly more intermediate in composition than other lava flows within the PLV (Butler and Burbank, 1929). They are characterized by porphyritic or glomerporphyritic texture although thicker flows are ophitic. It is difficult to correlate individual lava flow with one another except in developed areas for mining of native copper where individual lava flow can be traced along strike from mine to mine. In the Greenland-Mass subdistrict most of the native copper was produced from the tops of lava flows of the Evergreen Succession. Those flow tops hosting native copper are generally fragmental amygdaloidal lodes with the best areas for native copper being where the flow top is thicker. Thin amygdaloidal only flow tops or those with areas of massive basalt mixed in the flow top are typically lower grade. The Evergreen Succession is at a similar stratigraphic position as those lava flows developed at the Isle Royale Mine to the north of the subdistrict in the Houghton area of the main district (Butler and Burbank, 1929). The Evergreen flows were also developed for native copper in the Winona area in the middle between the main district and the subdistrict. The individual copper-rich lava flows within the Evergreen succession were each informally named (Figure 3). The Evergreen flow is a 3 to 15 m thick plagioclase porphyritic lava flow. The Ogima flow is a 30 to 43 m thick slightly plagioclase glomerophyritic basalt lava flow. The Butler flow is a 15 to 27 m thick plagioclase glomerporphyritic basalt lava flow. The Mass and Merchant flows are up to about 25 m thick. The South Knowlton flow is up to 15 m and is a plagioclase glomeroporphyritic basalt. At the top of the Evergreen succession is the Knowlton flow which is a 9 to 21 m thick plagioclase glomeroporphyritic basalt. Between the Butler and Knowlton flows there are a number of thin flows of plagioclase glomeroporphryitic basalt with total thickness of 75 to 90 m thick (Calumet and Hecla, 1958). The tops of the Evergreen lava flows were productive over a strike length of about 5 km. Native copper mined from the Evergreen Succession was extracted from many different mines with some of them connecting with others. The Butler flow top yielded the most copper followed by the Evergreen and Knowlton flow tops which also yielded significant amounts of copper. Vesicle- and inter-fragment void-fillings consist of quartz, calcite, K-feldspar, epidote, prehnite, pumpellyite, and chlorite (Table 1). Less abundant main-stage minerals are native copper, native silver, and datolite. Laumontite and adularia are common late-stage minerals. 145 �Table 1: Percent amygdule-filling minerals estimated from rock piles adjacent to mines/shafts of the Greenland-mass subdistrict. Unpublished data by Stoiber and Davidson 1959). % Amygdule-Filling Mineral Quartz Calcite Mine/Shaft Adventure #1 Adventure #2 Adventure #3 Adventure #4 National #2 Old Mass Mass C Mass 1 &2 Mass B Mass A Michigan Michigan Flintsteel #1 Flintsteel #2 Butler Knowlton Red KFeldspar Epidote Prehnite Pumpellyite Chlorite 52 5 6 26 2 9 tr 30 20 5 40 0 1 4 11 13 30 37 5 1 3 36 22 17 22 55 19 45 63 21 18 23 20 30 27 17 21 10 23 22 16 27 30 52 45 45 38 0 3 40 45 0 40 trace trace 35 18 18 20 15 2 5 15 19 22 18 35 5 3 5 5 5 6 24 53 4 0 0 0 trace 5 10 0 0 0 8 10 0 2 3 trace trace 3 0 0 trace 0 10 0 1 0 1 1 trace 1 1 0 0 7 9 0 8 The Evergreen Succession in the Greenland-Mass subdistrict dips about 45o NW and forms a local broad open anticline (Fig. 6). The largest mine, the Mass Mine, occurs near the maximum bend in this anticline. Most faults have displacement of < 1 m while those faults with significant vertical displacement are uncommon. There are multiple veins in tension fractures in the area of maximum bend that cut perpendicular across the lava flows (Butler and Burbank, 1929). There are some veins that are parallel to the strike of the lava flows but dip in the opposite direction. In the stratigraphically equivalent Isle Royale lode, Broderick (1931) describes similar strike parallel veins which he interpreted to be feeders of ore-forming fluid into the top of the lava flow. The Adventure Mine The Adventure Mine was very small, producing only about 5 million kg (11 million lbs) of refined copper, in context of all mines in the district which produced about 5 billion kg (11 billion lbs. Most of the production of native copper from the Adventure Mine came from the top of the Knowlton basalt lava flow (Knowlton lode; Figure 6 and 7). There was also significant 146 �production from the Butler lode and minor production from the Evergreen, Ogima, and Merchant lodes (Figure 6 and 7). Figure 6: Historic 1902 sketch cross section showing the lodes of the Evergreen succession at the Adventure Mine. Adits perpendicular to strike of the lava flows are shown and drifts parallel to the strike are indicated by black squares. The field excursion utilizes the adit near the No. 1 shaft. Figure 7: Longitudinal sections (parallel to strike) of the Evergreen succession native copper lodes showing underground workings (openings) for the Adventure Mine shafts #1 to #4. Section from Butler and Burbank (1929). 147 �The Knowlton was the focus of native copper mining at the Adventure Mine. The Knowlton lava flow top is a fragmental amygdaloid. In the subdistrict, the Knowlton flow top was developed for about 3000 m along strike and to a maximum depth of about 375 m. At the nearby Mass Mine (Fig 5), the Bulter lava flow top was the principal focus of native copper mining. It was the second focus of mining at the Adventure Mine. In the subdistrict the Butler lava flow top was developed for about 2000 m along strike and to a maximum depth of 300 m down dip. The most abundant secondary minerals in the Butler are quartz and calcite with slightly lesser amounts of K-feldspar and epidote (Table 1). Prehnite and pumpellyite are usually much less abundant and chlorite is present in amounts < 1 %. The Butler contains a high number of veins. Usually, the veins strike subparallel to the strike of the Butler lava flow top and have dips both similar to the dip of bedding and at a high angle to bedding (Butler and Burbank, 1929). The average thickness of the Knowlton lava flow top is about 2.5 m but locally it can thicken to around 6 m (Calumet and Hecla, 1958). In general, a thicker flow top results in better ore. While most of the ore occurs in the top of the Knowlton lava flow top, there are pockets of ore that extend into the underlying Knowlton massive flow interior (footwall) and are closely associated with strikeparallel fractures and veins which were likely feeders of hydrothermal fluids (Bornhorst et al, 2013). At the Adventure Mine, on average the most abundant main-stage minerals filling amygdules and spaces between fragments is quartz which is closely followed by epidote and then calcite and red K-feldspar (Table 1). There are lesser amounts of prehnite, pumpellyite, and chlorite. Native copper is present in small amounts with average grades of between 0.5 to 1.25 % copper with native copper associated epidote, quartz, and calcite. Native silver and datolite are present in much lesser amounts. Least abundant are the late-stage hydrothermal minerals precipitated after native copper that occur in open space fillings as coatings on earlier formed minerals; late-stage minerals include calcite, laumontite, and adularia and in cross cutting fractures and veins. Alteration of hydrothermal mineral is most obvious for native copper. Tenorite and cuprite (Cu oxide) often but not always occurs as a thin coating on native copper that is found in open space fillings. The tenorite and cuprite likely formed by downward-percolating groundwater when the native copper deposits were sufficiently near the surface (supergene alteration) as they are today. In addition to tenorite and cuprite, there are occasional copper carbonate minerals (such as malachite), brochantite (hydrated Cu sulfate) and atacamite (hydrated Cu chloride). These are likely to be supergene in origin. At least one mineral, gerhardtite (hydrated Cu nitrate) is the result of chemical reactions involving explosives. At the Adventure Mine a near horizontal cross-cut adit beginning at Shaft No. 2 connects to the near horizontal Butler drift (Figure 8). To the southeast the Butler drift daylights at the Overview Entrance/Exit. To the northwest the Butler drift connects with the Shaft No. 1 cross-cut adit and with the cross-cut adit to the Ogima lode where there is a large, in place mass, of native copper (Figure 8). The underground of the Adventure Mine is at a stable temperature of about 6oC and is relatively dry and regular field shoes are usually sufficient; hard hats and lights are required and provided by Adventure Mining Company (tour operator). The field trip involves an easy walk 148 �underground to observe the character of native copper mineralization in a horizontal adit that cross cuts the lava flows and a horizontal drift that parallels the strike of the top of the Butler lava flow which hosts a tabular native copper ore body (lode) (Figure 8). The character of native copper mineralization is readily observable in adits, drifts, and stopes (Figure 9). Figure 8: A. Longitudinal section of the Butler lode at the Adventure mine showing workings/openings projected to the vertical and locations for the field trip. B. Geologic map of the Adventure Mine showing workings/openings projected to the horizontal and locations for the field trip. Modified from Butler and Burbank (1929). 149 �Figure 9: Cross section sketch of the topography at the Adventure Mine showing top of the Butler lava flow and the Shaft No. 1 crosscut adit. Overview of the Human History As the land surface of the Keweenaw Peninsula emerged above the progressively retreating glacial lake levels by ca. 7,000 years ago native people took an interest in native copper since its malleability facilitated making tools. At first native peoples likely found boulders of native copper deposited from the glaciers (locally termed float copper) along with gravels and sands derived from erosion of local bedrock and bedrock north of Lake Superior in Canada. These boulders of native copper have a distinctive weathered surface crust of malachite, a green copper-bearing mineral. The green color would have made the relatively infrequent float copper boulders stand out among the other brown, gray, red, and white rocks. The float copper would have also been much heavier than other rocks of the same size. The native people shaped the native copper into tools and decorations. After they depleted the float copper boulders on the surface, they needed a new source of native copper to be able to continue making and trading these items. The native peoples likely found native copper in bedrock because of the green coloration as compared to black- or red-colored host rocks and then became prehistoric miners. There are many shallow mine pits throughout the Greenland-Mass subdistrict. Early European explorers were shown specimens of float copper by native inhabitants which created interest in the Keweenaw Peninsula. In 1841, Douglass Houghton’s report to the Michigan legislature (Michigan’s first state geologist) sparked the first major mining rush in North America. The first significant discovery of native copper was in 1845 at the Cliff Mine which in 1849 became the first profitable native copper mine in the Keweenaw Peninsula native copper district. There were only a few profitable native copper mines from 1845 to the early 1860s. The Minesota Mine, in the Greenland-Mass subdistrict (Figure 6) southwest of the Adventure Mine, became profitable a few years after the Cliff Mine. Many discoveries led to the opening of many mines in the early 1860s. But by 1880, the fate of most of these mines was the same as described below. Initial excitement of possible riches from mining copper was promoted by discoveries of mass copper that implied high grade ore (Figure 10C). Unfortunately, the existence of masses of copper did not necessarily indicate high grade ore. These masses represent the sampling problem termed the “nugget effect.” When the deposit formed there was a clustering of copper in distinct parts of the ore body into a “nugget”. If the mass of copper was missed during exploration the estimate of the grade of the ore body could be far too low and if a 150 �Figure 10: Historic photos from the Adventure Mine. mass is found the grade can be far too high. Mining decisions, such as putting in a shaft or constructing an oversized mill, made from discovery of masses of copper can be costly mistakes especially when funds are limited. Many of the mining projects were underfunded making it difficult to succeed and as a result of lack of funds the operations had to frequently close and in many cases the company merged with another company if they could convince shareholders of potential to discover a large ore body with high grade. There were also frequent shareholder assessments. Rather than paying a dividend to each shareholder from excess funds (profits) an 151 �assessment is the opposite and required each shareholder to pay the company a fee for each share. The fate of the Adventure Mine briefly described below follows this fate and was permanently closed and abandoned by 1917. Adventure Mine History (modified with permission from text provided by Brandon Erickson) In 1848 the Adventure Mining Company began exploration for native copper in the GreenlandMass subdistrict. Exploration activities were focused on a topographic bluff where several different lodes were exposed at the surface. By 1850, the Butler lode appeared to have best potential and the first production of native copper began in 1850. Despite the initial promise the mine struggled to turn a profit as the Butler lode was very rich in copper in some areas and in other areas it was barren. By 1855, the Adventure Mining Company itself ceased mining and to survive in 1855 the company introduced a tributing system. Under tributing, miners would receive a percentage of copper profits instead of a daily wage. In 1856, during financial troubles, a water-powered stamp mill was built along nearby Adventure Creek. By the start of the Civil War in 1861, the richest known ore shoots had been mined out and in 1864 the mine was sold to new investors. The new Adventure Copper Company explored the Butler lode on the eastern side of the bluff but also started an exploration crosscut on the northern slope. The purpose of this adit was to cut across all the lodes. Today’s mine tours enter the mine using this adit (Figure 8, Shaft No. 1 crosscut.) By 1869, the adit had reached the Butler lode and the miners commenced drifting along the lode. Several years later this zone proved rich enough to warrant the sinking of a shaft from the top of the bluff, which is seen on today’s tours as the “skylight stope.” (Figure 8). Mining was centered around this area until an economic downturn in 1877 forced the mine to cut costs and once again only support a small handful of tribute miners. In 1890, the tribute miners uncovered the Knowlton lode, which, unlike the others, cropped out at the base of the bluff. The deeping of shaft No. 1 started immediately and soon reached sufficient depth to begin drifting along the Knowlton lode. The Knowlton lode was very rich in stamp rock (fine sand sized copper disseminated throughout the ore body and lacking the nugget effect). The high-grade copper ore incentivized the miners to continue sinking the shaft to 200 feet deep. At these depths, work was severely hindered by the lack of more modern equipment, and without financial backing the Knowlton efforts ceased by 1893. Adventure Mine was revived again in 1898, as the Adventure Consolidated Mining Company and listed on the Boston stock exchange. This new company was backed by 2.5 million dollars perhaps prompted by ”riches” from mass copper (Figure 10C). The new investment at Adventure Mine was sufficient to build a company town, put in a railroad spur, purchase modern drills, construct and equip a state-of-the-art stamp mill, and install an electric tram line. The company first dewatered the No. 1 shaft and started sinking No. 2 shaft. The promising initial results prompted the company to start a new fully modern third No. 3 shaft (Figure 10A and 10B). This shaft is near the present-day parking lot. By 1903, the No. 1 shaft production had declined and was abandoned at a depth of 700 feet. In response, the company started a fourth shaft on the 152 �eastern limit of their lands (Figure 8). This shaft was a failure and was abandoned after a short time. Shipments of ore from the No. 3 shaft (Figure 10A and 10B) to the stamp mill declined in tonnage and grade. The mine was forced to use diamond drilling to explore for a new ore shoot. In 1909, they found a series of promising new lodes, but to reach them a vertical shaft would need to be sunk. This endeavor around 1910 was Adventure Mines’s “ last hope.” The Adventure Consolidated Mining Company diverted all resources to sink a shaft to 1,500 feet and explored several different lodes along the way. Unfortunately, this exploration was a failure as the ore bodies were not large enough or with high enough grade to make them profitable. The Adventure Mine was more or less abandoned in 1910 but one last attempt was made in 1916 when copper prices increased. The No. 3 Shaft (Figure 10A and 10B) was dewatered down to 700 feet and soon after they were shipping 300 tons of concentrate per day to the smelter. This effort was short-lived and on October 27, 1917 the company ceased all mining and processing activities. Keweenaw National Historical Park The historical significance of the Keweenaw Peninsula native copper district can readily be deduced from the fact that 80% of the new copper for the entire United States was produced from the district in 1880. This was the peak of significance of native copper mining in the district. By 1900, the Keweenaw Peninsula produced only 25 % of the United States new copper. However, absolute copper production from the district peaked in 1916 at an annual production of 121 million kg (267 million pounds). Mining ended in the Keweenaw Peninsula native copper district in 1968. The Adventure Mine peaked in production of copper between 1902 and 1907 at a total of about 3.9 million kg (8.5 million lbs.). The Keweenaw National Historical Park was created in 1992 to preserve and interpret the historical importance of native copper mining to the history of the U.S. The national park visitors center in Calumet provides an excellent overview of the historical significance of the district. Keweenaw Heritage Sites are affiliated with and support activities of the national park. The A.E. Seaman Mineral Museum and Quincy Mine are heritage sites and support the activities of the national park. The Adventure mine is also a Keweenaw Heritage Site and welcomes tourists and visitors seeking an underground mining experience. ACKNOWLEDGMENTS We thank Brandon Erickson for his brief Adventure Mine history summary which we modified for this field guide. We thank Allan Blaske for his review of this field guide that provided significant improvements to this guide. REFERENCES CITED Bodden, T.J., Bornhorst, T.J., Bégué, F., and Deering, C., 2022, Sources of hydrothermal fluids inferred from oxygen and carbon isotope composition of calcite, Keweenaw Peninsula native copper district, Michigan, USA: Minerals, v. 12, 474. https://doi.org:10.3390/min12040474 153 �Bornhorst, T.J., 1997, Tectonic context of native copper deposits of the North American Midcontinent Rift System: Geological Society of America Special Paper 312, p. 127-136. Bornhorst, T.J., and Barron, R.J., 2011, Copper deposits of the western Upper Peninsula of Michigan: Geological Society of America Field Guide, v. 24, p. 83-99. Bornhorst, T.J., Barron, R.J., and Whiteman R.C., 2013, Caledonia Mine, Keweenaw Peninsula native copper district, Ontonagon County, Michigan: 59th Institute on Lake Superior Geology Proceedings, v. 59, part 2, p. 43-57. Bornhorst, T.J., and Lankton, L.D., 2009, Copper mining: A billion years of geologic and human history: in Schaetzl, R., Darden, J., and Brandt, D., eds, Michigan Geography and Geology, Pearson Custom Publishing, New York, p. 150-173. Bornhorst, T.J. and Mathur, R., 2017, Copper isotope constraints on the genesis of the Keweenaw Peninsula native copper district, Michigan USA: Minerals, v. 7, 185, https://doi.org:10.3390/min7100185 Bornhorst, T.J., Paces, J.B., Grant, N.K., Obradovich, J.D., and Huber, N.K. 1988. Age of native copper mineralization, Keweenaw Peninsula, Michigan: Economic Geology, v. 83, p. 619-625. Bornhorst, T. J., and Robinson, G.W., 2004, Precambrian aged supergene alteration of native copper deposits in the Keweenaw Peninsula: Michigan; Institute on Lake Superior Geology Proceedings and Abstracts, v. 50, part 1, p. 40-41. Bornhorst, T.J., and Whiteman, R.C., 1995, Native copper and associated minerals in basalts at the Caledonia Mine, western Upper Michigan: 41st Institute on Lake Superior Geology Proceedings, v. 41, part 1, p. 34. Bornhorst, T.J., and Whiteman, R.C., 1992, The Caledonia native copper mine, Michigan: Society of Economic Geologists Guidebook Series, v. 13, p. 139-144. Butler, B.S., and Burbank, W.S., 1929, The copper deposits of Michigan: U.S. Geological Survey Professional Paper 144, 238 p. Calumet and Hecla, 1958, Unpublished report for Defense Minerals Exploration Administration, 29p. Cannon, W.F., 1994, Closing of the Midcontinent Rift – A far field effect of Grenvillian contraction: Geology. 22, p. 155-158. Cannon, W. F., Green, A. G., Hutchinson, D. R., Lee, M.W., Milkereit, B., Behrendt, J.C., Halls, H.C., Green, J.C., Dickas, A.B., Morey, G.B., Sutcliffe, R., and Spencer, C., 1989, The North American mid-continent rift beneath Lake Superior from Glimpse seismic reflection profiling: Tectonics, v. 8, p. 305-332. Cannon, W. F., Peterman, Z.E., and Sims, P.K. 1993, Crustal-scale thrusting and origin of the Montreal River monocline - A 35-km-thick cross section of the Midcontinent Rift in northern Michigan and Wisconsin: Tectonics, v. 12, p. 728-744. 154 �Catacossinos, P.A., Harrison, W.B., Reynolds, R.F., Westjohn, D.B., and Wollensak, M.S., 2001, Stratigraphic lexicon for Michigan: Michigan Department of Environmental Quality, Geologic Survey Division Bulletin 8. Lansing, MI. Davis, D.W., and Paces, J.B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. Heaman, L.M., Easton, R.M., Hart, T.M., MacDonald, C.A., Hollings, P., and Smyk, M., 2007, Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario: Canadian Journal of Earth Sciences, v. 44, p. 1055-1086. Stoiber, R.E., and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250-1277, p. 1444-1460. Weege, R.J., and Pollack, J.P., 1971, Recent developments in native-copper district of Michigan: Society of Economic Geologists Field Conference, Michigan Copper District, September 30 - October 2, 1971, p. 18-43. White, W.S. 1968, The native-copper deposits of northern Michigan: in Ridge, J.D., ed., Ore Deposits of the United States, 1933-1967 (the Graton Sales volume). American Institute of Mining, Metallurgical, and Petroleum Engineering, New York: p. 303-325. Whitlow, 1974, Geologic map of the Greenland and Rockland quadrangles, Ontonagon County, Michigan: U.S. Geological Survey Miscellaneous Field Studies Map MF-596. Woodruff, L.G.; Daines, M.J.; Cannon, W.F.; Nicholson, S.W., 1995, The thermal history of the Midcontinent Rift in the Lake Superior region: implications for mineralization and partial melting: in International Geological Correlation Program, Field Conference and Symposium on the Petrology and metallogeny of volcanic and intrusive rocks of the Midcontinent rift system, Duluth, Minnesota, v. 336, p. 213-214. 155 �156 �Field Trip 6 Southern Complex Granitoids, Gneisses, and Migmatites: New Data, Discoveries, and Perspectives Chad D. Deering Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931 Introduction The Superior Province is part of the Archean Canadian Shield in North America and represents one of the oldest and most stable cratonic regions on Earth, encompassing parts of Canada and the United States, including Michigan, Wisconsin, and Minnesota. The Archean craton in Northern Michigan is divided into a Northern Complex and Southern Complex, which are separated by the Great Lakes Tectonic Zone (GLTZ) (Morey and Sims, 1976; Sims et al., 1980). The northern portion of the Southern Complex consists of classic ‘dome-and-keel’ structures characterized by domes of Archean basement surrounded by keels of Paleoproterozoic Marquette Range Supergroup lithologies (Annhaeusser et al., 1969). The Archean rocks include a complex assemblage of granitoids, gneisses, and migmatites intruded by numerous mafic dikes and/or sills. Our recent research on the area has revealed new aspects of the igneous and metamorphic evolution that have improved our understanding of the assembly of this large igneous-metamorphic complex through the Archean-Proterozoic transition, but numerous questions regarding the origin evolution of these rocks remain unresolved. This field excursion will include the exploration of a number of different terrains representative of the magmatic, metamorphic, and structural evolution of the Southern Complex and the overlying metasedimentary rocks; highlighting new discoveries while at the same time providing an opportunity to investigate still unresolved questions regarding the geologic evolution of the region. Figure 1. Regional map outlining the location of the Southern Complex Mineral District near Marquette, Michigan. 157 �Evolution of the Superior Craton Mesoarchean The Mesoarchean evolution of the Superior Craton in North America encompasses a critical period of crustal evolution between 3.2 to 2.8 billion years ago. During this time, significant tectonic and magmatic processes shaped the early Earth's crust and laid the foundation for the stable continental core we recognize today. In the early Mesoarchean, around 3.2 billion years ago, smaller continental fragments began to accrete and amalgamate due to tectonic processes related to subduction and associated magmatic activity (Percival et al., 2012; Thurston et al., 2008; Wyman, 2010). These proto-continents served as the building blocks for the Superior Craton (Percival et al., 2012). Intense magmatic activity occurred, leading to the generation and growth of the continental crust within the Superior Craton, as magma intruded into and solidified within the existing crust (King et al., 1998). Greenstone belts, characterized by volcanic and sedimentary rocks, also began to form during this period. These belts, such as the Abitibi and Wawa greenstone belts of Canada (Thurston, 2002) and the Ishpeming greenstone belt of the Upper Peninsula, Michigan, USA (Bornhorst and Johnson, 1993), are important features of the Superior Craton and provide insights into early Earth processes, including volcanic activity and the nature of oceanic environments. The rocks of the Superior Craton underwent significant metamorphism and deformation during the Mesoarchean and high temperatures and pressures caused by tectonic activity led to the development of foliations and other prominent structural features in the rocks. Neoarchean During the Neoarchean Eon, which lasted from approximately 2.8 to 2.5 billion years ago, the crust of the Superior Craton underwent further significant geological evolution. This involved the continued accretion of smaller continental blocks and terranes through tectonic processes such as subduction, collision, and magmatic activity (Mole et al., 2021). In particular, the Minnesotan orogeny occurred around 2.7 to 2.6 billion years ago. This was a period of intense tectonic activity characterized by the collision and amalgamation of various smaller continental blocks and island arcs, leading to the formation of a larger continental mass (Schmitz et al., 2018). The collisional process resulted in the growth of the Superior Province and the formation of the granite-greenstone terranes that comprise much of the region. The amalgamation of these crustal fragments contributed to the expansion and stabilization of the Superior Craton. Neoarchean rocks include extensive granitic intrusions, which formed through the partial melting of existing crustal rocks or through the emplacement of mantle-derived magmas (Mole et al., 2021). These granitic intrusions contributed to the growth of the continental crust and are often associated with mineralization and hydrothermal activity (Mole et al., 2021). Greenstone belts, characterized by volcanic and sedimentary rocks, continued to develop during the Neoarchean within the Superior Craton (Polat et al, 1998; Polat and Kerrich, 2000). These belts represent ancient oceanic crust and island arc environments, and they are interspersed with granitic intrusions. Metamorphic processes affected both the greenstone belts and the granitic intrusions within the craton. Hydrothermal activity continued to play a significant role in the formation of mineral deposits within the Superior Craton during the Neoarchean. Ore deposits such as gold, iron, and copper formed in association with granitic intrusions, greenstone belts, and hydrothermal alteration zones, contributing to the economic significance of the region (Mole et al., 2022). 158 �Southern Complex, Marquette District: Compeau Creek and Bell Creek batholith The southern complex is located south of the Marquette synclinorium and is dominated by the Archean Bell Creek batholith, which consists primarily of coarse-grained megacrystic, high-K igneous rocks with minor amounts of mafic gneiss and metasedimentary rock layers typically found concordant with the foliation of the gneiss. Bell Creek includes trondhjemite-tonalitegranodiorite (TTG), granites, gneisses, and migmatites. Migmatite comprises only a small portion of the complex, distributed at irregular intervals throughout the region and is assigned to a unit referred to as Compeau Creek. The age and origin of the Southern complex of the Marquette region has been debated for decades. It was originally thought to be genetically related to similar lithologies found in the nearby Northern Complex (Cannon and Simmons, 1973; Van Schmus and Woolsey, 1975). However, the Southern Complex is separated from the Northern complex by the Great Lakes Tectonic Zone (GLTZ), which is a continental scale suture/fault zone (Morey and Sims, 1976; Sims et al., 1991). The only age information available before our study of the Bell Creek batholith was obtained by Tinkham (1997) from a single zircon with a U-Pb age of ~2.61 Ga. This period marks the onset of the Archean-Proterozoic transition, which is associated with a shift from the production of dominantly mantle-derived magmas that differentiated to form new continental crust to the early stages of significant recycling of crustal material (Taylor & McLennan, 1995; Valley, 2005). This is a crucial period in Earth’s history due to a decrease in global heat flow, and potentially the onset of ‘modern style’ subduction (Brown et al., 2020) and an increased number of sedimentary environments (Taylor and McLennan, 1995). The origin of trondjemite-tonalite-granodiorite (TTG) and high-K granites during the Archean Eon, including those produced in the Bell Creek batholith, is closely linked to the evolution of continental crust. Several models have been proposed to explain the formation of TTGs during the Archean: 1) Partial melting of pre-existing continental crust. During the Archean, the Earth's crust was thicker and more mafic (rich in magnesium and iron) compared to modern crust (Tang et al., 2016). As a result, when portions of this crust were subjected to high temperatures and pressures, particularly in subduction zones or during collisional events, they could undergo partial melting to produce high potassium granites. 2) Partial melting of the mantle. In this scenario, mantle-derived melts ascend through the crust, assimilating and interacting with continental crust along the way. These interactions can lead to the enrichment of potassium and other incompatible elements in the melts, ultimately resulting in the formation of high potassium granites. 3) Derivation from hybrid sources. It is also possible that the formation of high potassium granites during the Archean involved a combination of crustal and mantle processes. This hybrid model suggests that both the crust and mantle contributed to the source materials for the granites, with melting and mixing occurring at various depths within the Earth's crust. New petrogenetic insights on the origin of Bell Creek batholith Our new bulk-rock major and trace element data and U-Pb zircon dates (including oxygen and LuHf isotopes) provide insight into several aspects of the origin of these rocks. First, extensive U-Pb zircon dating of Bell Creek and Compeau Creek rocks from several recent Michigan Tech geology graduate student studies (Table 1; Petryk, 2019 and Barth, 2023) indicates that the bulk of the magmas were emplaced during a single tectonic event between ~2.4 to 2.6 Ga and is attributed to the collision of the Paleoarchean Minnesota River Valley Terrane (MRVT). Second, bulk-rock 159 �major and trace element compositions of the Compeau Creek migmatite/gneiss and Bell Creek granitoids/gneisses are consistent with formation in a continental arc type tectonic environment (Figure 2). Table 1. Age summary for Bell Creek granitoids (data from Petryk, 2019) Bell Creek granitoid subgroups Sample U-Pb crystallization age (Ga) Inherited grains (Ga) Metamorphic grains (Ga) CLG-14B 2.42 ±0.042 2.8-3.6 2.3 CCG-12A BCG-4A BCG-1A BCG-8B CCG-9D BCG-7C CCG-9E 2.43 ±0.160 2.51 ±0.021 2.58 ±0.056 2.54 ±0.040 2.59 ±0.028 2.61 ±0.047 2.56 ±0.038 2.7 2.8-3.9 (4.2) 2.7-2.8 3.1 3.3-3.5 2.7-3.3 2.7-2.8 2.0 2.3, 2.4 2.3, 2.4 Fine-grained CCG-6A 2.53 ±0.070 - 2.3, 2.4 Clotted BCG-8A CCG-1A 2.55 ±0.017 2.55 ±0.033 2.7-2.9 2.7-3.2 2.2, 2.3 1.8, 2.3 Normal' Foliated 2.3 Figure 2. Left: Tectonic discrimination diagram showing a volcanic arc to syn-collision tectonic setting for Bell Creek granitoids and gneissic rocks (blue) and two younger alkaline granites consistent that formed within-plate following the emplacement of the Bell Creek batholith. Right: Arc rock discrimination diagram showing the high-K nature of most of the Bell Creek and Compeau Creek rocks. Note that the mafic rocks plotted here represent dikes/sills of varying and relatively unknown age. 160 �Third, the oxygen isotopic composition of zircon from the granitoids is dominated by mantle-like values (5.3±0.3) indicating additional of a significant amount of juvenile magma to the crust; however, the hafnium isotopic compositions of the same zircons are heterogeneous and have model ages that indicate the involvement of older Mesoarchean crustal lithologies at the source and during emplacement in the mid- to upper-crust. Our current interpretation is that the granitoids, gneisses, and migmatites were formed through a hybrid process, initially by partial melting of an isotopically heterogeneous Mesoarchean lower crust followed by assimilation of mid- to uppercrustal lithologies. Continental arc subduction produces TTGs when high heat flow facilitates partial melting of lower crust and potentially later as the magma reaches the level of final emplacement in the mid- to upper-crust. Interestingly, the high oxygen isotopes (δ18O > 6‰) and εHf isotopes, with a range between -2 and -24, together indicate a potentially greater role for older Mesoarchean crust in the formation of the Southern Complex magmas than what has been found in the Canadian portion of the Superior craton. Therefore, it appears as if the evolution of the southernmost region of the Superior Craton involved a much greater contribution from crustal lithologies than what has currently been found in the well-studied Canadian segment of the Superior Craton (Mole et al., 2019). Figure 3. Hf-O isotopic compositions of zircon from Bell Creek TTGs Mid- to upper-crustal level mixing and assimilation The Archean granitoids of the Bell Creek batholith also display field evidence of assimilation and mafic-felsic magma mixing at the level of emplacement. Small (up to a cm or two) xenoliths that appear as clots throughout the granitoids in the area consist of biotite, chlorite, garnet and quartz indicative of assimilation of pelitic crust. However, basement crustal lithologies of this type are apparently not well exposed. In our investigation we have identified several outcrops that have quartzite and schist in contact with, or within, gneissic or granitoid host rocks, but the ages have yet to be determined (in progress). These metasedimentary rocks outcrop within the igneous intrusions and are considered to be the best possible candidates for remnants of Archean supracrustal material that was assimilated into the felsic magmas. In addition, our new O and Hf isotope data from single, inherited zircons indicate incorporation of Mesoarchean age crustal lithologies (Table 1 and Figure 3). Major and trace element data reveal a slightly peraluminous 161 �character (Figure 4), high-K (Figure 2), and enrichment of incompatible trace elements (Figure 2) and are best explained as reflecting the assimilation of metasedimentary crustal lithologies. The mafic intrusions also show evidence of felsic ‘blebs’ and complex interactions with the host granitoids throughout the region and are interpreted to reflect magma mixing, which would indicate that at least some of them are sills rather than dikes. However, later generations of mafic intrusions clearly crosscut the dominant foliation, have sheared boundaries, and/or sharp contacts with the host rock and represent at least four to five distinct episodes of magmatism related to younger events unrelated to the granitoids. Figure 4. Shand's index for peraluminosity of Compeau Creek and Bell Creek granitoid, gneissic and migmatitic rocks. Paleoproterozoic During the Paleoproterozoic Eon (roughly 2.5 to 1.6 billion years ago), the Superior Craton underwent significant geological evolution, marked by a series of tectonic, magmatic, and metamorphic events. The early Paleoproterozoic was dominated by the development of rift basins during the breakup of the Superia supercraton during rifting that began ~2.1 Ga, which separated the Wyoming Province from the Superior Province (Drenth et al., 2021). These rift basins accumulated thick sequences of sedimentary rocks, including sandstones, shales, and iron formations that are today known in the Lake Superior region as the Marquette Range Supergroup and Huronian Supergroup (Ojakangas et al., 2001). The Penokean Orogeny, which occurred around 1.85 to 1.75 billion years ago, resulted from the collision of the Superior Craton with other continental blocks that contributed to the growth of Laurentia, leading to crustal thickening, mountain-building, and metamorphism (Schulz and Cannon, 2007). Hydrothermal activity during the Paleoproterozoic played a significant role in the formation of mineral deposits that include iron-rich sedimentary deposits, such as banded iron formations (BIFs), which were deposited during this time, along with important mineral deposits such as iron, copper, and gold (DeMatties, 2022). Following the main tectonic events of the Paleoproterozoic, the Superior Craton experienced episodes of post-orogenic magmatism, marked by the emplacement of large igneous provinces and granitic intrusions. 162 �Field Trip Objectives This field trip is designed to provide a geologic overview of the formation of the Neoarchean Bell Creek batholith including associated metasedimentary rocks and the Paleoproterozoic metasedimentary rocks that filled the deep basins. Figure 5. Generalized geologic map of the Southern Complex Mineral District. 163 �Stop 1: Paleoproterozoic Negaunee Iron Formation (FR/Xn) and mafic dike Directions: Leaving Michigan Technological University drive south along US-41 ~63 miles to the Michigamme Roadside Park. N 46° 32’ 20” W88° 5’ 31” The outcrop is prominently exposed along the northern side of US-41 across from the Michigamme Roadside Park, which overlooks Lake Michigamme to the south. Paleoproterozoic Negaunee Iron Formation that is weakly magnetic containing hematite-goethite with banded chert as fine laminations. The formation is part of a westward plunging syncline conformably overlying Siamo Slate or Ajibik quartzite with a gradational contact and lies unconformably over the Archean basement complex (Gair and Thaden, 1968). This unit includes sideritic slates, grunerite-magnetite-schists; ferruginous slates, ferruginous cherts and jaspilite (Van Hise and Bayley, 1895; Cannon and Gair, 1970). Here, the iron formation is dipping ~65° to the SW and is in sharp contact with the adjacent massive, medium-grained to porphyritic amphibolite dike. A younger, near vertical dike can be observed on the east side of the outcrop in sharp contact with the older amphibolite dike/sill. Stop 2: Paleoproterozoic Ajibik quartzite (Xa) Directions: Heading east along US-41 ~0.5 miles exposure of Ajibik quartzite outcrops along the northern edge of the road. N 46° 32’ 35” W88° 4’ 16” The Ajibik consists of basal conglomerates, slates, and graywackes that grade into the overlying quartzite. At this location, the small exposure of the Ajibik is massive, thick bedded white to buff orthoquartzite. Some relic cross-bedding may be present, but clear evidence of ripple marks or other features reflecting the original depositional environment are not present. A mafic dike crosscuts the quartzite roughly NW-SE and is highly sheared along a sharp contact. Bedding is difficult to identify, but it appears to be dipping ~60° to the SW. Stop 3: Paleoproterozoic Michigamme formation (Xms) Directions: Head east on US-41 S toward Orange Rd. 8.4 miles. Turn right onto M-95 S, and drive ~7.3 miles, crossing the Michigamme River basin to destination. N 46° 24’ 37” W87° 59’ 45” This exposure is of the lower slate member, which includes laminated iron-rich rock consisting of biotite-garnet-cummingtonite-quartz schist with thin beds of quartzite. Minor fold axes are prominent here as chevron folds plunging to the NW and reflect the regional fold axis orientation. Boudinage, which form when single, competent layers are stretched into separate pieces through plastic and/or brittle deformation mechanisms and reflect the presence of minor quartzite layers or lenses within the schist. 164 �Stop 4: Archean Bell Creek batholith granitoid (Wbcf) Directions: Head southwest on M-95 N ~0.5 miles to destination. N 46° 24’ 13” W87° 59’ 52” The most common form of Bell Creek batholith is exposed here as a medium to coarse-grained granitoid that is locally porphyritic with sparse megacrysts of alkali-feldspar (up to several cms). Minerals include alkali-feldspar, oligoclase, biotite, oxides with apatite and zircon as common accessory phases. The abundance of mafic xenoliths (clots) (Figure 6) within the granitoids is correlated with the degree of peraluminosity of the host rock. Some minor pegmatitic veins are also present. Small mafic injections are in sharp contact with the granitoid indicating emplacement that post-dates the main magmatic episode. There is some weak alignment of alkali-feldspar megacrysts that can be best observed on the top of the outcrop. Kfs Grt Iron-Chl 250 μm Figure 6. Left: Mafic clot containing Fe-chlorite or biotite, K-feldspar, and garnet (almandine). Garnet-biotite geothermometry yields an equilibration temperature range between 450°C and 550° C. Right: Example of mafic xenoliths clustered within granitoid. 165 �Stop 5: Undivided granitic rocks (Wgu) Directions: Head south on M-95 toward Co Rd 601 ~4.8 miles to destination. Outcrop is located just south of the city park along the Michigamme river. N 46° 20’ 13” W087° 58’ 22” A metasedimentary sequence is exposed here, which doesn’t appear on the regional geologic map. Blonde and gray/black feldspathic quartzite forms alternating beds with gradational contacts dipping to the north (Figure 7). The blonde quartzite is dominated by quartz, with minor amounts of feldspar and sparse garnet (1-2mm). The gray/black quartzite has similar proportions of quartz and feldspar to the blonde quartzite but includes muscovite, biotite and oxides nearing the abundance of feldspar. Complex interaction with mafic dikes/sills also appear in this outcrop with minor ptygmatic folding and mafic enclaves throughout. Vertical dike contacts are sharp, whereas an apparently older generation of mafic intrusions have more complex contact margins with the host rock. Near vertical mafic dikes on both ends of the outcrop have sharp contacts with the host rock penetrating locally as splays or fingers. Figure 7. Metasedimentary sequence dominated by blonde quartzite and a grey to black quartzite. Lunch Stop: Leif Erickson Roadside Park along the Michigamme River 166 �Stop 6: Archean Bell Creek batholith and Compeau Creek gneiss/migmatite (Wbcf/Wccg) Directions: Drive north along M-95 towards Welsh’s Rd. ~5.7 miles to destination. Outcrop exposed prominently on the east and west sides of the road. N 46° 24’ 54” W87° 59’ 31” The contact between Compeau Creek to the south and Bell Creek batholith to the north is clearly exposed at this outcrop. A zircon U-Pb date of 2426±160 Ma was obtained for the Bell Creek granitoid at this location. The granitoid is fine- to medium-grained, typically equigranular and has an apparently gradational contact with the adjacent migmatite/gneiss. Migmatite/gneiss with ptygmatic folding is best exposed in the outcrop on the west side of the road, but the highly deformed continuation of this rock type is prominently exposed with mafic intrusions on the east side of the road. Stop 7: Archean Bell Creek batholith (Wbcg) Directions: Drive north along M-95 ~2.1 miles to destination. N 46° 26’ 16” W87° 57’ 48” Exposure of Bell Creek megacrystic granitoid similar to Stop 4. Minerals include alkali-feldspar, oligoclase, biotite, oxides and apatite with apatite and zircon as common accessory phases. A strong foliation is not apparent here, but the mafic xenoliths (clots) are well represented as mm- to cm-sized dark spots typically clustered and randomly oriented. Pegmatitic veins are common and vary in width up to tens of centimeters. Stop 8: Archean Migmatite (Wbsc); Compeau Creek? Directions: Drive north along M-95 ~0.8 miles to destination. N 46° 26’ 53.7” W087° 57’ 20.0” This exposure is likely the Compeau Creek quartofeldspathic migmatite/gneiss dipping to the south. The highly deformed migmatite/gneiss includes numerous mafic inclusions and enclaves (Figure 8). However, it is unclear how much of the mafic-felsic segregations are representative of the initial magma mixing followed by deformation or melanosome-leucosome complementary rocks derived by melting. Ptygmatic folding is prominently displayed and likely represents felsic segregations that have buckled during deformation. A zircon U-Pb date of 2525±70 Ma was obtained for the gneiss, which overlaps in time with the dates obtained for other Bell Creek granitoids along the M-95 corridor. 167 �Figure 8. Near vertical mafic dike cross-cutting migmatite with chaotic mixture of mafic-felsic components. Stop 9: Archean Compeau Creek migmatite/gneiss (Wccg) Directions: Drive north along M-95 ~1.4 miles to destination. N46° 27’42” W87° 56’ 05” This outcrop is mapped as Compeau Creek migmatite/gneiss that is presumed to be older than the adjacent Bell Creek granitoid/gneiss. A zircon U-Pb date for the migmatite is slightly older (2633±46 Ma) than the pink, clotted granite, which has been dated to 2550±33 Ma. Inherited zircon grains range in age from 2717 to 3200 Ma. The Compeau Creek gneiss/migmatite on the northern end of this outcrop appears to include a sliver of what might be Archean quartzite (Figure 9); note that the Paleoproterozoic Goodrich quartzite is mapped directly to the north and would, therefore, be in direct contact with the migmatite/gneiss. There are numerous mafic dikes/sills that manifest as either single generation dikes that clearly cross-cut the existing foliation or more complex dismembered dikes (possibly sills) associated with mixing at the time of felsic magma emplacement (Figure 10). Inclusions of felsic material (either bulk rock or individual feldspar crystals) can be found in some of the composite dikes/sills indicative of magma mixing that may have occurred contemporaneously between the mafic magma and a liquid dominant felsic host magma. The foliation is steeply south-dipping (~70°). 168 �Figure 9. Band of quartzite concordant with the foliation of gneiss/migmatite fabric. Relict feldspar crystals ~ 4 cm Figure 10. Mafic intrusion with felsic xenocrysts/xenoliths interpreted to have likely formed through mixing with the host magma during emplacement. This particular intrusion has a Nd model age of ~2.57 Ga, which is within error of the age obtained for the Bell Creek gneiss at this location. 169 �References Barth, Elana G. Age and chemistry of Bell Creek batholith (MS report), Michigan Technological University (2023) Bornhorst, Theodore J., and Rodney C. Johnson. Geology of volcanic rocks in the south half of the Ishpeming greenstone belt, Michigan. No. 1904. US Government Printing Office, 1993. Brown, Michael, Tim Johnson, and Nicholas J. Gardiner. "Plate tectonics and the Archean Earth." Annual Review of Earth and Planetary Sciences 48 (2020): 291-320. Cannon, W. F., and J. E. Gair. "A revision of stratigraphic nomenclature for middle Precambrian rocks in northern Michigan." Geological Society of America Bulletin 81, no. 9 (1970): 2843-2846. Cannon, W. F., and George C. Simmons. "Geology of part of the southern complex, Marquette district, Michigan." J. Res. US Geol. Surv 1 (1973): 165-172. DeMatties, Theodore A. "Exploration-resource assessment of productive felsic volcanic centers in the Paleoproterozoic Penokean Volcanic Belt of northern Wisconsin, Michigan and east-central Minnesota, USA." Ore Geology Reviews 141 (2022): 104489. Gair, Jacob Eugene, and Robert E. Thaden. Geology of the Marquette and Sands Quadrangles, Marquette County, Michigan. No. 397. 1968. King, Elizabeth M., John W. Valley, Don W. Davis, and Garth R. Edwards. "Oxygen isotope ratios of Archean plutonic zircons from granite–greenstone belts of the Superior Province: indicator of magmatic source." Precambrian Research 92, no. 4 (1998): 365-387. Mole, D. R., C. L. Kirkland, M. L. Fiorentini, S. J. Barnes, K. F. Cassidy, C. Isaac, E. A. Belousova, M. Hartnady, and N. Thebaud. "Time-space evolution of an Archean craton: A Hfisotope window into continent formation." Earth-Science Reviews 196 (2019): 102831. Mole, D. R., P. C. Thurston, J. H. Marsh, R. A. Stern, J. A. Ayer, L. A. J. Martin, and Y. J. Lu. "The formation of Neoarchean continental crust in the south-east Superior Craton by two distinct geodynamic processes." Precambrian Research 356 (2021): 106104. Mole, D. R., B. M. Frieman, P. C. Thurston, J. H. Marsh, T. R. C. Jørgensen, R. A. Stern, L. A. J. Martin, Y. J. Lu, and H. L. Gibson. "Crustal architecture of the south-east Superior Craton and controls on mineral systems." Ore Geology Reviews 148 (2022): 105017. Morey, G. B., and P. K. Sims. "Boundary between two Precambrian W terranes in Minnesota and its geologic significance." Geological Society of America Bulletin 87, no. 1 (1976): 141-152. Ojakangas, R. W., G. B. Morey, and D. L. Southwick. "Paleoproterozoic basin development and sedimentation in the Lake Superior region, North America." Sedimentary Geology 141 (2001): 319-341. 170 �Percival, John A., Tom Skulski, Mary Sanborn-Barrie, Greg M. Stott, Alain D. Leclair, M. Tim Corkery, and Michel Boily. "Geology and tectonic evolution of the Superior Province, Canada." In Tectonic styles in Canada: the LITHOPROBE perspective, vol. 49, pp. 321-378. Saint‐John's, Newfoundland: Geological Association of Canada, 2012. Petryk, Brandi. "The origin of an Archean batholith in Michigan’s Upper Peninsula.”. (MS thesis) Michigan Technological University (2019). Polat, Ali, and Robert Kerrich. "Archean greenstone belt magmatism and the continental growth– mantle evolution connection: constraints from Th–U–Nb–LREE systematics of the 2.7 Ga Wawa subprovince, Superior Province, Canada." Earth and Planetary Science Letters 175, no. 1-2 (2000): 41-54. Polat, A., R. Kerrich, and D. A. Wyman. "The late Archean Schreiber–Hemlo and White River– Dayohessarah greenstone belts, Superior Province: collages of oceanic plateaus, oceanic arcs, and subduction–accretion complexes." Tectonophysics 289, no. 4 (1998): 295-326. Schmitz, M. D., D. L. Southwick, M. E. Bickford, P. A. Mueller, and Scott Douglas Samson. "Neoarchean and Paleoproterozoic events in the Minnesota River Valley subprovince, with implications for southern Superior craton evolution and correlation." Precambrian Research 316 (2018): 206-226. Sims, Paul Kibler. Great Lakes tectonic zone in Marquette area, Michigan: implications for Archean tectonics in north-central United States. No. 1904. US Government Printing Office, 1991. Tinkham, D. K. Tectonic Evolution of the Southern Complex Regiong of the Penokean Orogenic Belt, Upper Peninsula Michigan: The Formation of Precambrian Dome-and-Keel Architecture (MS), University of Illinois. (1997). Tang, Ming, Kang Chen, and Roberta L. Rudnick. "Archean upper crust transition from mafic to felsic marks the onset of plate tectonics." Science 351, no. 6271 (2016): 372-375. Taylor, Stuart Ross, and Scott M. McLennan. "The geochemical evolution of the continental crust." Reviews of geophysics 33, no. 2 (1995): 241-265. Thurston, P. C. "Autochthonous development of Superior Province greenstone belts?." Precambrian Research 115, no. 1-4 (2002): 11-36. Van Hise, Charles Richard, and William Shirley Bayley. Preliminary report on the Marquette ironbearing district of Michigan. US Government Printing Office, 1895. Valley, J. W., J. S. Lackey, A. J. Cavosie, C. C. Clechenko, M. J. Spicuzza, Miguel Angelo Stipp Basei, I. N. Bindeman et al. "4.4 billion years of crustal maturation: oxygen isotope ratios of magmatic zircon." Contributions to Mineralogy and Petrology 150 (2005): 561-580. 171 �Wyman, Derek, and Robert Kerrich. "Mantle plume–volcanic arc interaction: consequences for magmatism, metallogeny, and cratonization in the Abitibi and Wawa subprovinces, Canada." Canadian Journal of Earth Sciences 47, no. 5 (2010): 565-589. 172 �Field Trip 7 Landslides on the Ontonagon River at Military Hill Stanley J. Vitton Civil, Environmental, and Geospatial Engineering, Professor Emeritus, Geological and Mining Engineering and Sciences, Adjunct Professor Emeritus, Michigan Technological University, Houghton, MI 49931 Mohammad Sadeghi Civil, Environmental, and Geospatial Engineering, Assistant Professor, Geological and Mining Engineering and Sciences, Affiliated Assistant Professor Michigan Technological University, Houghton, MI 49931 Figure 1: 2003 landslide east of US-45 on the East Branch of the Ontonagon River. 173 �Introduction An impressive sight, at least to geologists and engineers, are the landslides along US-45 as it descends into the Ontonagon River Valley at Military Hill. US-45 follows the trail used by Indigenous peoples such as the Menominee, Dakota and Anishinaabe (Ojibwe/Chippewa) tribes, and later fur traders making their way to and from to the mouth of the Ontonagon River at Lake Superior. In 1844, U.S. Secretary of War William Wilkins, proposed a road between Fort Howard in Green Bay, WI to Fort Wilkins just north of Copper Harbor, MI to create a supply route to the Army posts and to improve access to frontier communities such as Copper Harbor and other neighboring mine sites. Congress, however, did not fund the road. In 1862, with British troops in nearby Ontario and the prospect of Great Britian entering the war on the side of the confederacy, the road became a national security issue. According to a Michigan historian, Le Roy Barnett, “More than half the copper used in the United States came from mines along the proposed frontier passage. As a report of the U.S. Senate Committee on Military Affairs noted, "In case of hostilities with Great Britain, and a descent upon this important portion of our lake coast, there would be no means of affording succor without a road [to the region], and these valuable deposits of copper and other ores might be lost to us. Senator Jacob Howard pressed the point, explaining that if the Soo Canal were "seized and closed ... there would be no means of getting into the [Keweenaw] country or out of the country, either with troops or munitions of war or without them, except by means of some such road as this." (The Free Library, 2024) On March 3, 1863, Abraham Lincoln signed an Act of Congress authorizing construction of the military road. Road construction was started in 1863 but was not completed until 1872. Following construction, the road was used primarily for timber and other commercial interests until the railroad network in the western Upper Peninsula became operational a few years later. Again, according to LeRoy Barnett, “Despite the years of work put into the route, it never became the avenue of settlement and commerce its supporters anticipated. As legislators in the early 1860s had feared, railroads--built shortly after the road's completion--soon siphoned traffic. Furthermore, parts of the road were poorly maintained. "There was no surfacing on most of the road," wrote Upper Peninsula author/historian Knox Jamison of a trip in 1915, "and if it had rained recently, you had better not try it." Getting up and down the Military Hill--a massive body of slippery, wet clay through which the Ontonagon River had cut a 300foot gorge--took him at least two hours.” In 1923, the Michigan Highway Department added Military Road into the state’s transportation network as a section of State Highway M-26 but did not appreciably improve the road, leaving it with a gravel surface and in general following the route’s topography. In 1957, the Michigan State Highway Department added this section of M-26 to the federal highway system as US-45. 174 �Becoming a federal highway requires the road to meet both state and federal road design standards, such as the highway having a maximum grade of less than 8%. This required significant excavation of the glacial clay slopes and most likely the start of the Military Hill landslides. Construction was completed in 1959 with a concrete pavement and a grade meeting state and federal specifications. While the Military Hill clay soils are known for their difficult road construction issues, the highway department most likely did not fully appreciate the difficulty with the excavation and long-term behavior of the slopes. An investigation, either upstream or downstream of the US-45 river crossing, for example, would have shown many old and new landslides not to mention the red silt laden river itself that never changes throughout the seasons. The landslides are in the glacial lacustrine and till sediments in the Ontonagon Basin formed during the area’s deglaciation. One of the more recent landslides near the river crossing, which occurred in 2003, is shown in Figure 1, is just upstream of US-45 and one of the sites we will visit. Figure 2 shows the US-45-Ontonagon River crossing and the location of the landslide north of the confluence of the East and Middle Branches of the Ontonagon River. The steep slopes and the meandering of the river are evident. Figure 2 also shows the stops that we will be making at Military Hill. The clays in the Military Hill area were deposited in the final stages of the Late Wisconsin glacial period, estimated to be at its maximum at about 26,000 BP with deglaciation ending about 9,500 years BP when the Superior Lobe of the Laurentide Ice Sheet retreated into the Superior Basin for the last time (Attig et al., 1985). Fortunately, the northern Great Lakes region is known as the “type area” for the stratigraphic subdivisions of the late-glacial period of North America so the area has been investigated in some detail (Evenson et al., 1976). The first and the most detailed investigation of the glacial sediments in the Ontonagon area was conducted between 1905 and 1919 by Frank Leverett who identified the area’s main glacial features including Glacial Lake Ontonagon and Duluth (Leverett, 1928). Later, Hatch (1965) investigated the postglacial drainage evolution and stream geometry in the Ontonagon area while detailed mapping was conducted by Peterson (1985 and 1986). The area’s prominent feature is the Copper Range, a topographic ridge formed by the Portage Lake Volcanics. The Copper Range was influential in the formation of the Ontonagon River Basin shown in Figure 3 and Figure 4. As shown in these figures, the Ontonagon River System converges at a gap along the Copper Range. According to Leverett (1928), the Copper Range formed an ice-margin boundary during the last couple of glacial advances resulting in the formation of a series of proglacial lakes shown in Figure 5. The proglacial lakes Ontonagon, Ashland, Brule and Duluth formed along this ice-margin with drainage flowing westward to the St. Croix River. As isostatic rebound occurred and the Superior Lobe retreated into the Superior Basin, the drainage merged through a gap in the Copper Range. Leverett notes that it was probable that Lake Goebic was in a pre-glacial valley that extended northward to Lake Superior but was prevented from draining into Lake Superior by a moraine that filled the gap. Thus, the West and South Branch of the Ontonagon River flowed eastward along the Copper Range to where it drained into the present Ontonagon River. 175 �Another distinct feature of the area is a series of parallel rivers that formed between Copper Range and Lake Superior as shown in Figure 6 and 7. Hatch (1965) investigated the drainage system indicating that “it was strongly grooved by glacial flutings parallel to the direction of ice motion. In places the grooves are buried by lacustrine sediments of glacial Lake Duluth.” It is possible that the Ontonagon River, as it began flowing through the Copper Range gap at Military Hill, followed one of the parallel drainages. Due to a greater volume of water, however, it has significantly cut through the Lake Ontonagon and Duluth sediments as shown in Figure 6. Figure 2: Military Hill along US-45 showing Field Trip Stops (Google Maps, 2024). Figure 3: Ontonagon River Basin location (USACE, 2010). 176 �Figure 4: Ontonagon drainage basin showing river recreation, science, and wild designations (Ontonagon, 2023). Figure 5: Development of proglacial lakes along the Superior Lob (Farran and Drexler, 1985). Figure 6: Parallel drainage system on the Ontonagon Plain by glacial grooving (Hatch, 1965). 177 �Figure 7: Aerial photo of the parallel river systems on the Ontonagon till plain. Figure 8: Bedrock geology of the Military Hill area (Cannon et al., 1995). 178 �Background Information Bedrock Geology The landslides at Military Hill are located over the Jacobsville Sandstone, just south of the Keweenaw Fault, as shown in Figure 8. Ontonagon River Watershed Overview The Ontonagon River Watershed, at 1,348 sq. miles, is the second largest watershed entering Lake Superior behind the St. Louis watershed west of Duluth, MN, at 3,584 sq. miles. What makes the Ontonagon River watershed distinctive, however, is the large amount of red sediments that continually flows into Lake Superior. In 1987, the National Geography Magazine, ran an article on “The Great Lakes Trouble Waters” showing an aerial view of the sediment discharge from the Ontonagon River into Lake Superior with the caption, “Each year millions of tons of sediment – like this red clay silt spilling into Lake Superior from Michigan’s Ontonagon River – enters the lakes from tributary stream. Many contaminated with agricultural chemicals and industrial wastes (National Geographic, 1987).” The cover and photo of the Ontonagon River are shown in Figure 9. In the early 2000s, the US Corps of Engineers (USACE, 2010) conducted a 516e sediment study on the Ontonagon River to determine the source of this large quantity of sediments to estimate future dredging requirements. After its investigation, the USACE reported: “The Ontonagon River watershed is primarily undeveloped and consists of forested land uses with little urbanization or agriculture. Much of the watershed experiences significant erosion of the incised valley walls due to the highly erodible soils associated with the lacustrine geology of the lower reaches. Based on the comparison of historic and present-day river morphology it is concluded that the valley walls and river banks have been a large contributor of sediment long before logging or other anthropogenic disturbances were present in the watershed. Therefore, the primary contributor of sediment yield in the watershed is natural processes, rather than anthropogenic alterations. Based on this conclusion, a quantification of geologic time scale sediment yields was conducted.” The report went on the state: There is evidence that the deep valleys and steep walls that exist today are due to natural sediment transport processes and landscape scale geomorphic evolution that have carved out the valleys and deepened the Ontonagon River and its tributaries. Frequent examples of mass wasting of the valley walls exist throughout the downstream reaches of the Ontonagon River and a flat terrace with steep valley walls adjacent to a meandering channel with a narrow beltwidth are typical in the lacustrine areas of the watershed…..Moreover, an average sediment yield of 2.4 million tons per year is more than an order of magnitude greater than current sediment yields of similar watershed sizes in the Great Lakes.” The USACE report did not investigate which branch of the river produced the greatest amount of 179 �sediments. Based on a study by Weidner et al., (2019), however, it would appear the East and Middle Branches produce the most sediment based on the frequency of observable landslides. This would be constitent with Peterson’s 1985 mapping showing that the East and Middle Branches are mostly located in the Glacial Lake Ontonagon sediments as seen in Figure 10, which is a portion of Peterson’s glacial geology map. The length of the East and Middle Branches of the Ontonagon River can also be seen in the soils map from the USDA Natural Resources Conservation Service landform map shown in Figure 11 where the East and Middle Branch extend to the southern end of the lake sediments. Figure 9: July 1987 issue of the National Geographic Magazine (1987). Review of Landslide Activity on the Ontonagon River Travelers along US-45 can view a landslide just to the west of the US-45 – Ontonagon River crossing. A 1,000-foot walk upstream on the East branch of the Ontonagon River will provide the opportunity to inspect a large-scale landslide that occurred in 2003. If you continue to walk upstream from the 2003 landslide, about every bend in the river will show landslide activity, either current or past as shown in Figure 12. Weidner et al., (2019) studied the landslide activity in the Military Hill area (Figure 13a) for the development of a landslide susceptibility map based on riverbank erosion-triggering. Additional landslide studies were conducted by Koons (1965), Dyl (1979), and Smith (2012), all master theses or reports at Michigan Tech. The Weidner et al., study utilized aerial and satellite imagery from the United States Geological Survey (USGS) EarthExplorer web tool for the years 1992 through 2016 identifying 21 landslides. The landslide locations in the study area are shown in Figure 13(a). 180 �Figure 10: A portion of the USGS map of the glacial history of Iron River 1° x 2° Quadrangle (Peterson, 1985). Figure 11: Landforms map of the study area adapted from Jerome (2006), showing the main soil regimes. River hydraulic data were obtained from a USGS gauging station downstream. The USGS Scoops3D limit-equilibrium analysis software was used to develop a “factor of safety” map of the study area, which is shown in Figure 13(c). A significant portion of the Ontonagon River slopes have a factor of safety less than one, which is supported by the observable landslide activity shown in Figure 13(b) through the lacustrine sediments of Glacial Lake Ontonagon and Duluth. 181 �Figure 12: Landslide activity upstream of US-45 on the East Branch of the Ontonagon River (Google Map, 2024). Figure 13: Weidner et al., Military Hill landslide investigation, (a) study area, (b) observed landslides between 1992 and 2016, and (c) Scoops3D factor of safety assessment. 182 �Objectives of the field trip: The objective of the field trip is to investigate landslides in the sediments deposited in the former Glacial Lakes Ontonagon and Duluth. In general, the sediments consist of lacustrine sediments deposited in Glacial Lake Ontonagon and later in Lake Duluth which overlay older till deposits. The first stop, however, will be at Quincy Hill, north of Hancock, MI to observe glacial grooving and striations in the Portage Lake Volcanics indicating the direction of glacial lobe movement across the Keweenaw Peninsula. The second and third stops will be in the US-45 Military Hill area. A summary of the stops are as follows: • Stop 1: Top of Quincy Hill, north of Hancock, to view glacial grooving in the Portage Lake Volcanics indicating the direction of Keweenaw Bay Lobe movement westward into the Ontonagon Lobe that formed Lake Ontonagon. • Stop 2A: The north side of Military Hill to observe the effects of vegetation on limiting landslide development. • Stop 2B: US-45 Military Hills Roadside Park: 2003 Large landslide on the East Branch of the Ontonagon River • Stop 2C: Lower Military Hill Erosion with Slope Movement • Stop 2D: Middle Military Hill with Partial Vegetation and Some Slope Movement • Stop 2E: Middle Military Hill with More Vegetation and Limited Slope Movement • Stop 2F: Middle Military Hill with Some Vegetation and Varved Clay Slope Movement • Stop 2G: Upper Military Hill with Active Slope Movement on both Sides of Highway in non-varved clay • Stop 3: Slope movement two miles south of Military Hill, across from Primrose Acres, where a recently excavated slope on the east side of US-45 has been moving for about eight years. Stop 1: Glacial Grooves at the Quincy Hill Historic Park Lookout Directions: From Michigan Tech drive west through Houghton on US-41 and cross the Houghton-Hancock Bridge, staying on US-41 going into Hancock. In Hancock, go straight uphill, passing Hancock’s main street, onto East White Street. East White Street will take you to US-41 bypassing downtown Hancock. At the US-41 stop, take a right turn, going uphill to the Quincy Mine Hoist. Directly across from the entrance from the Quincy Mine Hoist take a left turn onto No. 2 Road. Follow No. 2 Road a short distance until you come to a two-track road on your left that takes you to the Keweenaw National Historic Park’s “Quincy Mine Dryhouse Ruins” parking lot. The glacial grooves are a short distance from the parking lot. From Michigan Tech to the parking lot is 3.6 miles. Lat: 47.135904°, Lon: -88.577986° 183 �Figure 14: View, looking west, of glacial grooves sculptured into the Portage Lake Volcanics at the Keweenaw National Historic Park. Glacial grooving and striations are common along the Keweenaw Peninsula as the glaciers moved over the Portage Lava Volcanics, which were resistant to glacial erosion. It is generally assumed glaciers came from northeastern Canada moving south to southwest but are surprised to see grooves heading due west as shown in Figure 14. The reason for this direction is the movement of the Keweenaw Bay Lobe filled Keweenaw Bay and then moved west, south, and east as shown in Figure 15. The Keweenaw Bay Lobe then was stopped by the Ontonagon Lobe and to the west by the Michigamme Lobe to the east. Figure 15: Location of glacial lobes in the western Lake Superior Basin (from Attig et al., 2013). Stop 2: Military Hill – Seven Stops – Safety instruction will be provided at the site Directions: From Michigan Tech drive west through Houghton on US-41 to M-26. At the Houghton-Hancock Bridge go straight through the intersection to access M-26. Stay on M-26. Going southwest 37.8 miles to the M-26/M-38 intersection. Take a left turn, staying on M-26 through Mass City, to the M-26/US-45 intersection, 5.5 miles. Take a left turn at the M-26/US-45 intersection headed south 1.8 miles to Stop 2A. Lat: 46.705726°, Lon: -89.159581° 184 �Stop 2A: North US-45 - Slope with Vegetation and Small Slope Movement In the Military Hill area, the north side slopes required less excavation than on the south side and therefore there is less slope movement. In addition, where the slopes were excavated, they tend to be more vegetated as seen in Figure 16. This is due (possibly) to the north facing slope losing the spring snow before the south facing slopes and thus having longer growing season. Figure 16: Stop 1 (a) descending Military Hill going south and (b) vegetated slopes with some slope movement. Stop 2B: US-45 Military Hill Roadside Park: 2003 Large landslide on the East Branch of the Ontonagon River Directions: From Stop 2A to Stop 2B go 0.4 miles south on US-45 to the Military Hills Roadside Park parking lot on the east side of US-45. Starting at the rest area facilities (outhouses) on the northside of the parking lot, walk northeast through the woods to the landslide. There is no path, but the woods are relatively easy to walk through. The 2003 large scale landslide is approximately 1,400 ft (411 m) northeast of the parking lot as shown in Figure 17. There is a smaller landslide north of the path, which has been active for many years, but is difficult to access. The slope debris, below the landslide, has a thick undergrowth, which is difficult to walk through. Military Hills Roadside Park: Lat: 46.699650°, Lon: -89.158627° Military Hill 2003 Landslide: Lat: 46.703234°, Lon: -89.154132° In 2003, a large-scale landslide occurred on the East Branch of the Ontonagon River as shown in Figure 1 and Figure 17. The landslide’s stratigraphy consisted of lacustrine varved clay over a clean alluvial sand that grades downward into a red silty sand, silt and then clay till as illustrated in Figure 18 and Figure 19. While the failure mechanism is unknown, it is speculated that the spring runoff and possibly high-water table caused the alluvial sand to liquefy causing the massive landslide. As the liquefied sand lost strength, it started to flow outward into the river channel as shown in Figure 20(b) and (c). During the slope’s collapse, a sliding plane formed in the varved clay as shown in Figure 20(a) allowing the varved clay to fail over the alluvial sand. Liquefaction boils are shown in Figure 20(b) and (d). 185 �It will take about 20 minutes to walk to this landslide through the woods from the roadside park. While there is no path, the woods are fairly open and easy to walk in. However, the landslide itself is more difficult due to the landslide debris and the vegetation that has developed over the years. Caution must be observed when walking over this site and it is highly recommended that the landslide slopes are not accessed. Figure 17: Stop 2B Military Hills Roadside Park and path to the 2003 landslide. Figure 18: Assumed stratigraphy of the 2003 landslide (Smith, 2012). 186 �Figure 19: 2003 landslide illustrating the varved clay directly over an alluvial sand. Figure 20: Landslide illustrating (a) a sliding plane on the varved clay, (b) liquefaction boils in the varved clay, (c) the flow debris into the river's channel, and (d) a large sand boil. 187 �Stop 2C: Lower Military Hill Erosion with Slope Movement Directions: From Stop 2B go 0.8 miles south on US-45 across the US-45 bridge to Stop 2C, which is the start of the lower landslides with significant erosion. Lat: 46.690087°, Lon: -89.165513° At the following five stops we will travel up Military Hill’s southside. In general, the soils traveling up the south side of Military Hill are like the sediments seen at Stop 2B except for the alluvial sands. The varved clays overlie a sandy brown silt, which have significant erosion (Figure 21). The base of the varved clay can be seen moving over the sandy silt. As we moved up US-45 at Stop 2C a short distance, MDOT has been attempting to stabilize a small landslide just below the base of the varved clay as shown in Figure 22. The clay content appears to be higher in this area. On the west side of US-45 you can observe the steep US-45 embankment that descends down to Sandstone Creek, exposing the Jacobsville Sandstone. Figure 21 Stop 2C showing the contact between the varved clay and a brown/red sandy silt, which is eroding. Figure 22 Stop 2C small landslide. 188 �Figure 23 Stop 2C showing the US-45 embankment that descends to Sandstone Creek on the Jacobsville Sandstone. Stop 2D: Middle Military Hill with Partial Vegetation and Some Slope Movement Directions: From Stop 2C go 0.23 miles south on US-45 Stop 2D, which is at the middle landslides. Lat: 46.686869°, Lon: -89.164320° Stop 2D is a short distance up US-45 and is in the same sediments as Stop 2C, which also are sloping uphill as seen in Figure 24. Movement of the varved clay base can be seen in the upper portion of Figure 24. Figure 24 Stop 2D varve clay movement over the lower sandy silt but without the erosion seen at Stop 2C. 189 �Stop 2E: Middle Military Hill with More Vegetation and Limited Slope Movement Directions: From Stop 2D go 0.30 miles south on US-45 Stop 2E, an excavated slope that is now partially vegetated. Lat: 46.682564°, Lon: -89.164857° At Stop 2E, the slope has much more vegetation with limited apparent slope movement. Figure 25 Stop 2E, slope with more vegetation and limited slope movement. Stop 2F: Middle Military Hill with Some Vegetation and Slope Movement Directions: From Stop 2E go 0.34 miles south on US-45 Stop 2F, a slope with vegetation that had was excavated for the construction of US-45. Lat: 46.677892°, Lon -89.166195° At Stop 2F, there is again less vegetation but more slope movement Figure 26. The clay soils at this elevation are not varved. Figure 26: Stop 2F showing partial vegetation and upper slope movement. 190 �Stop 2G: Upper Military Hill with Active Slope Movement on both Sides of Highway Directions: From Stop 2F go 0.23 miles south on US-45 Stop 2G, a slope with active slope movement. Lat: 46.674640°, Lon -89.167126° At Stop 2G, landslides occur on both sides of the highway as shown in Figure 27. Figure 27(a) shows slope movement on the west side of US-45, which has less movement than on the eastside of US-45 shown in Figure 27 (b), (c) and (d). These landslides have been moving for many years and appear to be in a non-varved clay. While limited soil investigation has been conducted in these sediments, it appears that at the higher elevations in the Military Hill area, a non-varved lacustrine soil overlies the varved clay soils indicating that it possible that this sequence might indicate when Glacial Lake Duluth and Lake Ontonagon combined. An interesting feature of Glacial Lake Ontonagon is that it is at a much higher elevation at 1,320 feet than Glacial Lake Duluth. Isostatic rebound would have had to occur for the lakes to combine. Figure 27 Stop 2G near the top of Military Hill showing slope movements on both sides of the highway with (a) west side, (b) top of east side, (c) south section of slope movement on east side, and (d) north portion of slope movement on the east side. 191 �Stop 3: US-45 Recent Excavation and Resulting Slope Movement Directions: From Stop 2G go 3.4 miles south on US-45 Stop 3, a slope with active slope movement. Lat: 46.627240°, Lon -89.178520° Stop 3 is at a recent location where MDOT excavated a natural slope to improve drainage along the eastside of US-45. The natural slope was excavated at a 2H:1V angle, the same slope as the highway embankment as can be seen in Figure 28. Soon after excavation, however, the slope started to move and has been moving ever since. Figure 29 was taken one year after the photo in Figure 26. The US-45 embankment was constructed with the local clay soil but was compacted, whereas the natural slope was not. The clay soils at this site and at Stop 2G have relatively high plasticity and are at the interface of the low (CL) and high (CH) plasticity soils defined by the Unified Soil Classification System (USCS) with moisture contents in the 20 to 25% range. As we saw at Stop 2F, the lacustrine clay soils are not stable at the angles at which they were excavated, unless compacted. Figure 28 Stop 3 showing a recent excavation into the clay soil at a 2(H):1(V) angle. Figure 29 Stop 3 - excavated slope one year after the photo in Figure 26 was taken. 192 �References Cited Attig, J.W., Clayton, L., and D.M. Mickelson, 1985. Correlation of late Wisconsin glacial phases in the western Great Lakes area, Geological Society of America Bulletin, v. 96, p. 1585-1593. Black, R.F., 1969, Valderan glaciation in Western Upper Peninsula, Proc. 12th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., p. 116-123. Cannon, W.F, Nicholson, L.G., Woodruff, C.A, Hedgman, C.A. and K.J. Schulz, 1995. Geologic Map of the Ontonagon and Part of the Wakefield 30’ x 60’ Quadrangle, Michigan, USGS. Creech, C., Selegean, J., and T. Dahl, 2010. Historic and modern sediment yield from s forested watershed, 2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1. Dyl, Stanley, 1979. Engineering geologic factors affecting the stability of slopes in the Ontonagon Clay at the Military Hill Slide, U.S. Highway 45, Ontonagon County, Mi. In: M.S. Thesis. Michigan Technological University, pp. 92. Farran, W.R and C.W. Drexler. 1985. Late Wisconsinan and Holocene History of the Lake Superior basin. In Quaternary Evolution of the Great Lakes, eds. P.F. Karrow and P.E. Calkin, Geological Association of Canada Special Paper 30:17–32. Gunderman, B.J. and E. A. Baker, 2008. Ontonagon River Assessment, Michigan DNR, Fisheries Division, Special Report 46, Hack, J.T. Postglacial drainage evolution and stream geometry in the Ontonagon area, Michigan. US Geological Survey, 1965. Jerome, D.S., 2006. Landforms of the Upper Peninsula of Michigan. 1:750,000. USDA Natural Resources Conservation Service, pp. 17. Koons, G.J., 1969. Some geologic and engineering properties of the Pleistocene Ontonagon Clays at Victoria, Ontonagon County, Mi. In: M.S. Thesis. Michigan Technological University, pp. 110. Leverett, Frank, 1928, Moraines and shorelines of the Lake Superior region: U.S. G. S. Prof. Paper 154A, p. 1-72. Ontonagon River. (2023, Nov. 12). In Wikipedia. https://en.wikipedia.org/wiki/Ontonagon_River Peterson, W. L., 1985, Surficial geologic map of the Iron River 1° x 2° quadrangle, Michigan and Wisconsin: U.S. Geological Survey Miscellaneous Investigations Series Map I-1360-C, scale 1:250,000. Peterson, W.L., 1986. Late Wisconsinan glacial history of northeastern Wisconsin and western upper Michigan. USGS Bulletin 1652, p. 1-14. Smith, J., 2012. Large scale landslide on the Ontonagon River, Michigan. In: M.S. Report. Michigan Technological University. http://digitalcommons.mtu.edu/etdrestricted/146. The Free Library. S.V. 2024. Through the wilderness, Retrieved Mar 19 2024 from https://www.thefreelibrary.com/Through+the+wilderness.-a0452051967. USACE, 2010. Ontonagon River Watershed 516e Sediment Study, USACE Great Lakes Hydraulics and Hydrology Office, Detroit District, p. 90. 193 �Weidner, L. DePrekel, K., Oommen, T. and Vitton, S., 2019, Investigating large landslides along a river valley using combined physical, statistical, and hydrologic modeling. Engineering Geology, v. 259, p. 1-12. http://doi.org/10.1016/j.enggeo.2019.1051169 194 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2024 Description An account of the resource Institute on Lake Superior Geology. Houghton, Michigan. May 15-18, 2024. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2024-05 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English Type The nature or genre of the resource Text https://digitalcollections.lakeheadu.ca/files/original/9e4f1e28865f88aa5567c5ffccfdf06c.jpg 816ea836c5c7a8b2e6847b11745202e3 https://digitalcollections.lakeheadu.ca/files/original/d571f4b511d43c8f66923f64afef600f.jpg 8c870cbadb19e215fba98cfb751fce7f Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay Finnish Canadian Historical Society Collection Subject The topic of the resource Finnish-Canadians Life in Thunder Bay Description An account of the resource Photographs collected by the Thunder Bay Finnish Canadian Historical Society from a wide range of collectors, documenting Finnish immigration to and life in Thunder Bay. Creator An entity primarily responsible for making the resource Thunder Bay Finnish Canadian Historical Society Publisher An entity responsible for making the resource available Lakehead University Library Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Play entitled "Bajaderi" Subject The topic of the resource Arts Theatre Description An account of the resource Play entitled "Bajaderi" performed at Big Finn Hall, 314 Bay Street, Thunder Bay. People in photo: (left to right) Ted Lake, Hulda Makela, Onni Paavi, Mamie Paavi. Donor: Lauri Lahti. 2 copies. Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource JPG Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context MG8_D11Bi11-1 MG8_D11Bi11-1a Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay Canada - Ontario - Port Arthur https://digitalcollections.lakeheadu.ca/files/original/77671b7bb528411f5e55f3cf5b30cd3d.jpg 890b17f8f01493f9ca773e7152f65923 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay Finnish Canadian Historical Society Collection Subject The topic of the resource Finnish-Canadians Life in Thunder Bay Description An account of the resource Photographs collected by the Thunder Bay Finnish Canadian Historical Society from a wide range of collectors, documenting Finnish immigration to and life in Thunder Bay. Creator An entity primarily responsible for making the resource Thunder Bay Finnish Canadian Historical Society Publisher An entity responsible for making the resource available Lakehead University Library Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Play entitled "Avioliitto Loma" Subject The topic of the resource Arts Theatre Description An account of the resource Play entitled "Avioliitto Loma" performed at the Big Finn Hall, 314 Bay Street, Thunder Bay, December 18, 1960. People in photo: (back, left to right) Linda Murto, Mr. Elo, Leo Villa, name not known, J. Bjorn, Inkeri Kaukovalta (seated left). Donor: Linda Murto. Date A point or period of time associated with an event in the lifecycle of the resource 1960-12-18 Format The file format, physical medium, or dimensions of the resource JPG Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context MG8_D11Bi12-1 Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay Canada - Ontario - Port Arthur https://digitalcollections.lakeheadu.ca/files/original/a535a1c0bcaa6ab95272fb2535026773.jpg 7383304937c00603548382d31f24b1b1 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Thunder Bay Finnish Canadian Historical Society Collection Subject The topic of the resource Finnish-Canadians Life in Thunder Bay Description An account of the resource Photographs collected by the Thunder Bay Finnish Canadian Historical Society from a wide range of collectors, documenting Finnish immigration to and life in Thunder Bay. Creator An entity primarily responsible for making the resource Thunder Bay Finnish Canadian Historical Society Publisher An entity responsible for making the resource available Lakehead University Library Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Play entitled "Onnellinen Sakari" Subject The topic of the resource Arts Theatre Description An account of the resource Play entitled "Onnellinen Sakari" performed at the Big Finn Hall, 314 Bay Street, Thunder Bay. Donor: T. Yrjana. Format The file format, physical medium, or dimensions of the resource JPG Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context MG8_D11Bi13-1 Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Canada - Ontario - Thunder Bay Canada - Ontario - Port Arthur