Y and HREE Mineralization in the MAW Zone, Athabasca Basin: Petrography and Fluid Inclusion Studies

English Abstract:

The MAW Zone REE deposit represents one of the largest heavy REE and Y concentrations inside the Athabasca Basin in northern Saskatchewan. The deposit is located in the southern part of the basin between the Key Lake and McArthur River unconformity-related uranium deposits. The spatial association of this deposit with unconformity-related uranium deposits and faults that parallel a basement high (“quartzite ridge”) led geologists to consider a genetic relationship between each.

Petrographic examination of the host sandstone shows that it has been subjected to silicic, argillic, and dravitic alteration, and is cut by abundant fractures filled with dravite and drusy quartz. Also present in the altered sandstones are minor amounts of zircon, clays, iron oxides, and galena. Xenotime as the ore mineral is generally scarce in the samples examined, but is locally abundant in brown patches in the sandstones. Petrographic studies suggest that mineralization took place after significant compaction of the sandstones. The drusy quartz contains liquid-rich biphase inclusions, vapour-dominated inclusions with various vapour percentages, and daughter-mineral–bearing inclusions. The coexistence of these fluid inclusions suggests a boiling hydrothermal fluid system and heterogeneous trapping of fluid inclusions. Homogenization temperatures of the liquid-dominated biphase inclusions range from 71° to 138^oC, and the ice-melting temperatures range from -10.4° to -27.1^oC, corresponding to salinities from 14.4 to 24.9 wt.% NaCl equivalent. The ice-melting temperature and salinity data are comparable to those reported for unconformity-type uranium deposits present in the same general area, but the homogenization temperatures are relatively low. The potential genetic relationship between the REE mineralization and the unconformity-type uranium deposits needs to be further constrained from geochronological and stable isotopic studies.