Abstract

The B.E.A.R. silver-pitchblende deposit at Contact Lake, Great Bear Lake area, lies in granodiorite, 500 feet from granite. There are three types of veins: Type I, dark gray quartz veins; Type II, finely banded, white, comb-quartz veins, mineralogically and texturally similar to the large quartz veins of the Great Bear Lake area; Type III, carbonate veins with cobalt, nickel and silver minerals.Six stages of mineral deposition are recognized in the formation of the Main Vein, as follows: (1) tabular bodies of altered granodiorite; (2) magnetite-hematite veins; (3) veins of Type I, gray quartz veins; (4) aplite dikes; (5) veins of Type II, white, finely banded, comb-quartz veins; (6) veins of Type III, carbonate veins with cobalt, nickel, bismuth, silver, and uranium minerals. Periods of marked deformation separate stages (3), (4), (5), and (6). The wall rock alteration and mineralogy of each stage are described.The first three stages are classed as pneumotectic to hypothermal; stage (5) mesothermal; and stage (6) mesothermal to epithermal. Native silver was deposited above a temperature of 200 degrees C., contains minute amounts of mercury, and is largely hypogene. The lead-uranium ratio in the pitchblende indicates an age of 650 million years or Keweenawan.Evidence is presented to show that the silver and pitchblende of this deposit are either co-magmatic with the late quartz dia-base dikes and sills of probable Keweenawan age, the youngest exposed intrusives of the region, or are related to some younger, unexposed intrusive.Evidence from a large number of occurrences in the metallogenic province in which the B.E.A.R. deposit occurs, indicates that the silver and pitchblende of these deposits, likewise, were deposited subsequent to minor deformation which followed the intrusion of the late quartz diabase dikes and sills.

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