Application of sulphur isotopes to discriminate Cu–Zn VHMS mineralization from barren Fe sulphide mineralization in the greenschist to granulite facies Flin Flon–Snow Lake–Hargrave River region, Manitoba, Canada

Abstract

The Flin Flon Belt in northern Canada is one of the largest Palaeoproterozoic volcanic-hosted massive sulphide (VHMS) districts in the world, but up to 20 000 km 2 of prospective Palaeoproterozoic basement south of this belt is buried beneath 10 to 100 m of Phanerozoic calcareous cover. The recent acquisition of airborne SPECTREM geophysics data south of the Flin Flon Belt has resulted in the discovery of Cu-Zn sulphide prospects comprising pyrrhotite, pyrite, chalcopyrite, sphalerite and galena, but numerous barren Fe sulphide occurrences comprising only pyrite and pyrrhotite have also been intersected. The problem for explorers is trying to determine whether a barren Fe sulphide intersection that has just been cored is part of a larger Cu-Zn mineralized system, or nothing more than a pyrite–pyrrhotite occurrence. A sulphur isotope study of sulphides from the Flin Flon–Snow Lake–Hargrave River–Talbot area shows that sulphides from the Cu-Zn VHMS deposits have δ 34 S values that range between −1.4 and 6.4‰, with a mean δ 34 S value of 1.6 ± 1.7‰ (2σ error). More than 95% of these samples have δ 34 S values of <3.3‰. In contrast, pyrite and pyrrhotite separates from barren Fe sulphide deposits have δ 34 S values between 1.8 and 10.0‰, with a mean δ 34 S value of 4.3 ± 1.8‰ (2σ error). In this case, >84% of these samples have δ 34 S values of >3.3‰. The results imply that the barren Fe sulphide deposits can be statistically distinguished from Cu-Zn VHMS mineralization based on S isotopic composition, which should make future exploration drilling decisions easier.