Mineralogy, geochronology, and genesis of the Andrew Lake uranium deposit, Thelon Basin, Nunavut, Canada

摘要

The Thelon Basin located in Nunavut, Canada, shares many similarities with the U-producing Athabasca Basin in Saskatchewan. The Kiggavik project area, located near the northeastern edge of the Thelon Basin, contains U deposits and showings along the similar to 30 km long NE-SW Kiggavik-Andrew Lake structural trend. The Andrew Lake deposit is near the southern end of this trend. Pre-mineralization is characterized by quartz +/- carbonate veins that occupy fault systems later reactivated as conduits for U-mineralizing fluids. A four-phase genetic model is proposed for the Andrew Lake deposit. Phase 1 comprises vein-style uraninite (U1; 1031 +/- 23 Ma) that is associated with illite and hematite, and contains variable PbO contents (0.2-9.5 wt.%). Phase 2 is characterized by altered uraninite (U2; similar to 530 Ma) that is associated with coffinite. Altered uraninite (U3; <1 Ma) characterizes phase 3 and occurs as centimetre-scale "roll-fronts". In phase 4, all three uraninite stages, and coffinite, are altered to boltwoodite. Although the oldest uraninite U-Pb age is similar to 1030 Ma, illite associated with the U mineralization gives Ar-40/Ar-39 ages of 941 +/- 31 and 1330 +/- 36 Ma. The younger age is similar to the age for U1, suggesting that there was a fluid event that either precipitated U1 or reset the U-Pb isotopic system at similar to 1000 Ma. While the older age for illite (1330 Ma) does not correlate with Andrew Lake U-Pb uraninite ages, it does correlate with ages previously reported for uraninite and clay alteration minerals in the Kiggavik area.