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[email protected] 5691 (inside Canada, United States) Crown Copyright Queen’s Printer Local: (416) 326-2678 Toll Free: 1-800-668-9938 [email protected] (inside Canada, United States) Ministry of Northern Development © and Mines Ontario Ontario Geological Survey Open File Report 5820 Alkalic Rocks of the Thunder Bay Area 1992 Ministry of Northern Development and Mines Ontario ONTARIO GEOLOGICAL SURVEY Open File Report 5820 Alkalic Rocks of the Thunder Bay Area By M.W. Carter 1992 Parts of this publication may be quoted if credit is given. It is recommended that reference to this publication be made in the following form: Carter, M.W. 1992. Alkalic rocks of the Thunder Bay area; Ontario Geological Survey, Open File Report 5820, 46p. © Queen's Printer for Ontario, 1992 Ontario Geological Survey OPEN FILE REPORT Open File Reports are made available to the public subject to the following conditions: This report is unedited. Discrepancies may occur for which the Ontario Geological Survey does not assume liability. Recommendations and statements of opinions expressed are those of the author or authors and are not to be construed as statements of government policy. This Open File Report is available for viewing at the following locations: (1) Mines Library Ministry of Northern Development and Mines 8th floor, 77 Grenville Street Toronto, Ontario M7A 1W4 (2) The office of the Regional or Resident Geologist in whose district the area covered by this report is located. Copies of this report may be obtained at the user's expense from a commercial printing house. For the address and instructions to order, contact the appropriate Regional or Resident Geologist's office(s) or the Mines Library. Microfiche copies (42x reduction) of this report are available for $2.00 each plus provincial sales tax at the Mines Library or the Public Information Centre, Ministry of Natural Resources, W-1640, 99 Wellesley Street West, Toronto. Handwritten notes and sketches may be made from this report. Check with the Mines Library or Regional/Resident Geologist's office whether there is a copy of this report that may be borrowed. A copy of this report is available for Inter-Library loan. This report is available for viewing at the following Regional or Resident Geologist's offices: Sudbury,159 Cedar St.,2nd Floor,Sudbury P3E 6A5 Thunder Bay,435 James St.,Box 5000,Thunder Bay P7 6E3 The right to reproduce this report is reserved by the Ontario Ministry of Northern Development and Mines. Permission for other reproductions must be obtained in writing from the Director, Ontario Geological Survey. V.G. Milne, Director Ontario Geological Survey iii Contents Page Abstract ix Introduction ^ Mineral Exploration 2 Base Metal Sulphide Mineralization 2 Feldspar 4 Gold 5 Iron 8 Molybdenum 21 Nickel 22 General Geology 13 Precambrian 14 Archean 14 Proterozoic 24 Phanerozoic 24 Metamorphism 2 5 Magnetic Trends 25 Structural Geology 26 Folding 2 6 Foliation 27 Lineation 2 8 Faults and Lineaments 29 Shear Zones 31 Unconformity 32 Economic Geology ^3 Base Metals Sulphide Deposits 33 v Feldspar 34 35 Gold with Silver 37 Iron and Sulphur Molybdenum 39 References 41 Conversion table 46 MAPS IN BACK POCKET Shebandowan Area Sunshine Area Marks Lake Area Kakabeka Falls Area vii ABSTRACT The map area is about 635km2 in areal extent, and is centred about 55 km northwest of Thunder Bay. It stretches from Kaministiquia on Highway 11A-17A in the east to just west of Shebandowan on Highway 11 at Shebandowan Lake on the west. The region straddles the boundary between the Quetico Subprovince lying to the north and the Wawa Subprovince to the south. The rocks are Precambrian (Archean to Proterozoic) and Phanerozoic (Pleistocene to Recent) in age. This project is a summary report on areas mapped by the author between the period 1984 and 1989 (Carter, 1984, 1985a,b,c, 1986a,b,c, 1987a,b,c, 1988, 1989, 1990 a,b,c) and represents a compilation of these data. The emphasis of the work during 1987- 1989 was on a special study of the alkalic (shoshonitic) rocks of the region and the reader is referred to the above-mentioned reports for details on the chemistry, petrography and geological setting of these rocks. The rocks resemble similar rocks in the Kirkland Lake area where they are associated with gold mineralization. The Archean rocks comprise Keewatin-type metavolcanics and metasediments; Quetico-type clastic metasediments; intrusive ultramafic, mafic, and felsic rocks; Timiskaming-type metavolcanics and metasediments; diabase and lamprophyre dikes and a lamprophyric diatreme. Shoshonitic metavolcanic rocks occur in the Keewatin-type and Timiskaming-type rocks. ix The Keewatin-type Metavolcanic-Metaseiimentary Rocks are the oldest rocks in the map area. They comprise an isoclinally folded interlayered sequence of komatiitic, tholeiitic, calc- alkalic, high potassium calc-alkalic, and shoshonitic rocks, associated with intercalated metasediments. These rocks form about 60% of the exposed rocks and underlie the southern two- thirds of the region. The fold axes are curvilinear veering from east-west in the west to southeast in the southeastern part of the area as far as the Mokomon Fault. Southeast of this fault the fold axes trends northeasterly. The shoshonitic metavolcanic rocks occur mainly in the central part of the eastern boundary of the area, and in the southern part of the western limit of the region. The rocks comprise absarokite, shoshonite, and latite and range in colour from mauve to brick red. The suite consists primarily of pyroclastic rocks. The associated flows are aphyric to porphyritic. The pyroclastics indicate that two volcanic centres are present: one occurs in the east-central part of the area about the sub-volcanic Tower Stock, and the other lies in the western part of the area. The Timiskaming-type Metavolcanic-Metasedimentary Rocks occur in a northern and southern belt and unconformably overlie the Keewatin-type Metavolcanic-Metasedimentary Rocks (on the basis of local truncation of fold-axes trends), the Metamorphosed Mafic to Ultramafic Intrusive Rocks, and the early Felsic Intrusive Rocks. The latter are overlain locally by outliers of xi the Timiskaming-type rocks. Shoshonitic rocks in the Timiskaming-type rocks comprise brown to brick-red absarokite, shoshoshonite, latite and toscanite flows and pyroclastics. Two eruptive centres have been located in the northwestern part of the map area in Conacher Township.