The geochronology of uranium deposits in the Great Bear batholith, Northwest Territories

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.