Compositional and Thermal Characterization of Basinal Fluids in the Athabasca Basin: Implications for Unconformity-related Uranium Deposits
Haixia Chu, Guoxiang Chi and Ryan Scott, University of Regina, Department of Geology, Regina, SK, Canada
Contact First Author: Haixia Chu; chu207@uregina.ca
Previously Published Material: Chu, H., Chi, G., Scott, R. 2014. Thermal Profiles Inferred from Fluid Inclusions and Illite Geothermometry - Implications for Fluid Flow Patterns in the Athabasca Basin. Saskatchewan Geological Survey Open House 2014 (Dec 1 – 3, 2014, Saskatoon). The results are being prepared for a scientific journal but not yet have been under review now.
English Abstract:
The Athabasca basin hosts the largest high-grade unconformity-related uranium deposits in the world. It is generally agreed that the mineralizing fluids were basinal brines of evaporitic origin, which became enriched in U and Ca through fluid-rock interactions. However, it remains controversial whether these metals were extracted from the basin or the basement, and what driving forces were responsible for fluid flow. In order to address these problems, fluid inclusions entrapped in quartz overgrowths as well as authigenic illite from four drill cores in the central part of the Athabasca basin (DV10-001, Rumpel Lake, WC-79-1 and BL-08-01), away from any known mineralization, were examined in this study.
Liquid-vapor inclusions have Tm-ice from -17.0o to -50.0oC, with salinities from 20.2 to 31.0 wt.%; Halite-bearing inclusions have Tm-halite from141o to 218 oC, with salinities from 29.3 to 32.9 wt.%. Low Tm-ice values suggest the potential existence of Ca2+ and this was confirmed by cryogenic Raman spectroscopy with clear Ca-hydrates peaks and calculated NaCl/ (NaCl+CaCl2) molar ratios from 0.2 to 0.8. Homogenization temperatures for all the inclusions range from 50o to 250oC. Temperatures estimated from illite geothermometry were mostly from 200 o to 250 oC and documented the maximum burial temperatures. No systematic changes in temperature were observed vertically within individual cores or laterally from core to core.
These results suggest that basinal fluids in the Athabasca basin are characterized by high salinities and elevated Ca, which are similar to those found in the uranium deposits. The presence of Ca-rich brines in area away from the basement, which is common in many sedimentary basins, suggest that at least some Ca in the ore fluids may have been derived from the sediments within the basin.The absence of horizontal and vertical thermal gradients may be best explained by basin-scale dynamic thermal convection.
