Abstract

The oldest uranium mineralisation found in the Great Bear batholith during this study may be hydrothermal pitchblende–hematite veins at Hottah Lake. Their apparent age of 2058 ± 34 Ma can also be explained by the contamination of deposits only 440 ± 57 Ma old, which is the age of pitchblende veins nearby. Numerous pendants of metamorphosed, uraninite-bearing "black sand" placers in a north-trending belt west of the Wopmay Fault are 1860 ± 20 Ma old, the age of the granites that intrude them. Mineralisation at Echo Bay is from 1500 ± 10 to 1424 ± 29 Ma old, and extends up to 30 km north and 40 km south of Echo Bay. The JD claims contain small quartz vein deposits dated at 535 ± 164 and 1092 ± 115 Ma. At Mountain Lake, pitchblende in Helikian sandstones overlying the batholith is 1076 ± 96 Ma old. Polymetallic veinlets at Mazenod Lake are 457 ± 26 Ma old. Pitchblende in a giant quartz vein at the Rayrock mine is 511 ± 86 Ma old. Small pitchblende veins east of the batholith along the Coppermine River are between 400 and 660 Ma old.All the deposits are either between ~395 and 660 Ma old, or indicate remobilization during this interval. These events may be related to a marine transgression and regression approximately 600 and 350 Ma ago, respectively.

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