| Geochemical analyses on samples from the Mississippi Valley Type Gayna River deposit, Northwest Territories, Canada, have resulted in the definition of three ore stages and a deposit genesis model. Pb/Pb and Re/Os isotopic analyses indicate that the mineralization at Gayna River was emplaced during the Cretaceous -- Tertiary. The sphalerites at Gayna River contain at least 21 trace elements including abnormally high Ga concentrations. Trace elements and 87Sr/86Sr ratios, ranging up to 0.7219 in the ore stage, indicate that underlying shales were the source of metals. The main stage of mineralization resulted from a hot saline brine probably derived from evaporated seawater. Stable isotopes suggest that thermochemical sulphate reduction (TSR) of local gypsum was the source of main and late stage sulphide. Fluids circulating through shale units, by tectonically driven flow, reacted with local gypsum causing TSR and resulting in the deposition of Pb and Zn sulphides at Gayna River. |
