Ontario Division of Mines THE BLIND RIVER URANIUM DEPOSITS: THE ORES AND THEIR SETTING by James A. Robertson MISCELLANEOUS PAPER 65 1976 MINISTRY OF NATURAL RESOURCES Ontario Division of Mines HONOURABLE LEO BERNIER, Minister of Natural Resources DR. J. K. REYNOLDS, Deputy Minister of Natural Resources G. A. Jewett, Executive Director, Division of Mines E. G. Pye, Director, Geological Branch THE BLIND RIVER URANIUM DEPOSITS: THE ORES AND THEIR SETTING1 by James A.Robertson MISCELLANEOUS PAPER 65 1976 MINISTRY OF NATURAL RESOURCES 1A paper presented at a workshop sponsored by the United States Geoloqical Survey on The Genesis of Uranium—and Gold-Bearing Precambrian Quartz- Pebble Conglomerates at Golden, Colorado, October 13 to 14, 1975. ©ODM 1976 Publications of the Ontario Division of Mines and price list are obtainable through the Ontario Ministry of Natural Resources, Map Unit, Public Service Centre Queen's Park, Toronto, Ontario and The Ontario Government Bookstore 880 Bay Street, Toronto, Ontario. Orders for publications should be accompanied by cheque, or money order, payable to Treasurer of Ontario. Parts of this publication may be quoted if credit is given to the Ontario Division of Mines. It is recommended that reference to this report be made in the following form- Robertson, James, A. 1976: The Blind River Uranium Deposits: The Ores and Their Setting; Ontario Div. Mines, MP 65, 45p. 3000-300-1976-BP CONTENTS PAGE Abstract ;• Introduction I Regional Geology 1 Table of Formations 2-3 Archean (Early Precambrian) ."> Keewatin-Type rocks 5 Algoman Granitic rocks S P.oterozoic (Middle Precambrian) 9 Huronian Supergroup 9 Elliot Lake Group 11 Matinenda Formation 11 McKim Formation 11 Volcanic Rocks I 3 Hough Lake Group 13 Ramsay Lake Formation 11 Pecors Formation 1-1 Mississagi Formation i 5 Quirke Lake Group !.ri Brace Formation 15 Espanola Formation Hi Serpent Formation Ki Cobalt Group Hi Gowganda Formation 17 Lorruin Formation IS Gordon Lake Formation IS Bar River Formation 19 Summary of Huronian 19 Post Huronian Events 121 The Uranium Deposits 121 Distribution of Uranium Ore Deposits Blind River-Elliot Lake 23 Lithology and Mineralogy of Uranium Ore Deposits 2<> Agnew Lake Area 31 Cobalt Embayment 31 Production 32 Reserves 32 Origin of the Uranium Deposits of Blind River-Elliot Lake-Agnew Lake Type 33 Acknowledgments 35 References 3(i TABLES PAGE 1 — Table of Formations, Blind River-Elliot Lake area 2-3 2 — Schemes of Huronian Stratigraphic Nomenclatures 1 3 — Summary of Huronian Stratigraphy in the Blind River-EDiot Lake area 20 4 — Uranium, thorium, and titanium contents of Blind River Brannerite (from Robertson HiriHb) 2S 5 Uranium and thorium contents in Blind River Uraninite (from Robertson 196Sb) 29 6 — Analyses of Blind River Monazi'.e (from Robertson 19t>Kb) 29 FIGURES 1 — Location of Blind River-Elliot Lake area r' 2a- Generalized geological map of Blind River-Elliot Lake area <i 2b—Schematic cross-section Elliot Lake area "1 3 — Formation of regolith 10 •1 - Lateral variation of the Huronian Supergroup, Elliot Lake 12 "i - Alkali content, Huronian polymictic conglomerates 22 fi — Silica/Alumina, Ferric Iron/Ferrous Iron, Soda/Potash ratios. for Huronian argillaceous rocks 22 7 - Uranium deposits in Quirke Syncline 2 1 S — Cross-section New Quirke Mine 2 1 9 — Correlation of quartz-pebble conglomerate reel's, Quirke Zone 25 ABSTRACT In the Blind River area, Proterozoic clastic sedimentary and minor volcanic rocks of the Huronian Supergroup unconformably overlie and transgress northward over dom- inantly granitic Early Precambrian (Archean) terrain (2,500 million years) and are in- truded by Nipissing Diabase (2,150 million years). Deformations and metamorphic events later than these have bee.i recognized. The Matinenda Formation (basal Huronian) comprises northward-derived arkose, quartzite, and pyritic, uraniferous oligomictic conglomerate that contain 75 percent of Canada's uranium reserves. Historic grades approximate 2 lbs. U308/ton, but lower grade material can be mined as the price of uranium increases. Some thorium and rare earths have been marketed. The general absence of gold reflects a lack of this metal in the source area. The conglon.erate beds occur in southeasterly striking zones controlled by base- ment topography down-sedimentation from radioactive Archean granite. The distribu- tion of monazite relative to that of uraninite and "brannerite" and the presence of uranium values in overlying polymictic conglomerates which truncate the ore-beds, indicate that the mineralization is syngenetic, probably placer. The role of peneeonlem- poraneous mafic volcanic rocks is problematical, but these could have been a source for sulphur in the pyrite. Drab-coloured rocks, uranium and sulphide mineralization, and a post-Archean regolith formed under reducing conditions, suggest a reducing environment. Sedimentary features indicate deposition in fast-flowing shallow water, and possibly a cold climate. In the upper Huronian (Lorrain Formation), a monazite-iron oxide assemblage associated with red beds suggests a change to oxidizing conditions. Similar deposits occur at Agnew Lake, and polymictic conglomerate ar.il siltstone found north of Sudbury carry minor uranium, and locally gold values. Provenance, lack of oxygen, transportation and depositional processes, and no major modification by later events n.re the dominant factors in the formation and preservation of the ore bodies. Research is needed on: mineralogicai relationships; detailed sedimentology of the conglomerates; and, on the volcanic rocks, their nature and role, if any, in the formation of the uranium deposits. HUDSON BA> Figure 1 — Location of Blind River-Elliot Lake area. THE BLIND RIVER URANIUM DEPOSITS: THE ORES AND THEIR SETTING by James A. Robertson1 INTRODUCTION The Blind River uraniferous pyritic oligomictic conglomerates were found in 1953 since which date the activities of mining companies, the universities, and of both Canadian and Ontario Government geologists have given rise to a large body of literature and other data. This paper is an attempt to summarise the present state of knowledge, to provide guidelines for the exploration geologist, or to the geologist in the field who could be in favourable terrain. The paper is in three sections; first, a description of the regional geology; second, a description of the ore- bearing conglomerates; and third, a discussion of those factors that are of genetic significance. REGIONAL GEOLOGY Blind River (Figure 1) lies on the North Shore of Lake Huron, halfway between Sudbury and Sault Ste. Marie. The town of Elliot Lake built to service the uranium mines lies 32 km (20 miles) northeast of Blind River. The region lies on the boundary between the Southern and Superior Provinces of the Canadian Shield. The Superior Province (Goodwin et al. 1972) comprises Archean rocks which were affected by the Kenoran Orogeny (2,500 million years) and the Southern Province (Card et al. 1972) includes Proterozoic rocks affected by the Penokean Orogeny (1,750 million years). The Blind River-Elliot Lake area lies at the margin of early Proterozoic sedimentation and of the mid-Proterozoic metamor- phism. Table 1 is a Table of Formations using the nomenclature recommended by the Federal-Provincial Committee on Huronian Stratigraphy (J.A. Robertson et al. 1969) and Table 2 permits comparison with schemes used in publications before 1969. Table 3 provides a synopsis of the strati- graphy and the relationship to mineralization (see section on "Summary"). The bedrock of the area falls into three broad units, the distribution of which is shown on Figure 2a. These are: (1) the Archean basement, consisting of Keewatin-type "greenstone", Algoma granite and minor mafic intrusive rocks; (2) the haronian sedimentary rocks and metasediments with local minor mafic volcanic rocks and (3) the post-Huronian intrusive 1Chief, Mineral Deposits Section, Geological Branch, Ontario Division of Mines, Toronto. Manuscript accepted for publication by the Director, Geological Branch, Ontario Di- vision of Mines, May 10th, 1976. TABLE 1 TABLE OF FORMATIONS FOR THE BLIND RIVER-ELLIOT LAKE AREA. UNIT CODE DOMINANT AGE LITHOLOGY (Million Years) PHANEROZOIC CENOZOIC PLEISTOCENE AND RECENT Sand, gravel, till UNCONFORMITY PALEOZOIC ORDOVICIAN (20) Limestone PRECAMBRIAN PROTEROZOIC (LATE AND MIDDLE PRECAMBRIAIMI KEWEENAWAN SUPERGROUP Sudbury Dikes (19) Olivine diabase 1,225 INTRUSIVE CONTACT Mount Lake Dike Quartz diabase INTRUSI\ ~ CONTACT WITH NIPISSING DIABASE HUDSONIAN Croker Island Complex (18) Gabbro, granite 1,445 Cutler Batholith (18) Granite 1,750 INTRUSIVE CONTACT PENOKEAIM Nipissing (17) Quart; diabase, diorite 2,155 INTRUSIVE CONTACT HURONIAN SUPERGROUP Cobalt Group Bar River (16) Quartzite Gordon Lake (15) Siltstone, sandstone Lorrain (14) Quartzite, conglomerate, arkose Gowganda (13) Conglomerate, greywacke, quartzite UNCONFORMITYDISCONFORMITY Quirke Lake Group Serpent (12) Quartzite Espanola (11) Limestone, siltstone Bruce (11) Conglomerate LOCAL DISCONFORMITY Hough Lake Group Mississagi (10) Quartzite Pecors (9) Argillite Ramsay Lake (8) Conglomerate LOCH. DISCONFORMITY UNIT CODE DOMINANT AGE LITHOLOGY (Million Years) Elliot Lake Groun** McKim (71 Argillite Matinenda (5) Quartzite, ± U-conglomeiate Conglomerate Arkose ± U-conglomerate regolith UNCONFORMITY ARCHEAN (EARLY PRECAMBRIAN) LATE ARCHEAN INTRUSIVES Diabase 2,500 INTRUSIVE CONTACT KENORAN (ALGOMAN) (3) Granite 2,500+ INTRUSIVE CONTACT EARLY ARCHEAN INTRUSIVES Gabbro