Trace element and sulphur isotope geochemistry of sulphide deposits from the Flin Flon and Snow Lake areas of Saskatchewan and Manitoba
Sangameshwar, Salem Ramachandra Rao
The Precambrian massive sulphide deposits of the Flin Flon and Snow Lake areas of Saskatchewan and Manitoba have been classified into a "barren" group, containing dominantly pyrrhotite and/or pyrite or arsenopyrite with or without nominal amounts of other sulphides, and an "economic" containing, in addition to pyrrhotite and pyrite, minable amounts of sphalerite and chalcopyrite. The "barren" deposits occur in Amisk volcanics, Missi sediments, and Kisseynew gneisses, whereas, the "economic" deposits are restricted to Amisk volcanics and Kisseynew gneisses. δS³⁴%° values of pyrite, pyrrhotite, arsenopyrite, sphalerite, and chalcopyrite from the "barren" group generally lie within the range of +10 to -1, whereas, those from the "economic" deposits generally lie within the range +4 to -1 relative to the standard (Canon Diablo meteoritic troilite). Trace element analyses of the different sulphide minerals from both groups of deposits indicate that minerals from the "economic" deposits generally contain more cobalt than nickel, whereas, those from the "barren" deposits generally contain more nickel than cobalt. Selenium and tellurium contents of sulphides from both groups of deposits are similar. Vanadium was not found in any of the samples. The ores have been metamorphosed. An attempt was made to estimate the temperature and/or pressure of metamorphism, using iron contents of sphalerite, arsenic:sulphur ratios of arsenopyrite, nickel and cobalt partitioning in coexisting pyrrhotite and pyrite pairs, and sulphur isotope partitioning between several coexisting phases. These estimated temperatures and pressures exhibit wide ranges, suggesting a lack of preservation of equilibrium compositions between coexisting phases, if equilibrium was ever attained. The "barren" deposits are believed to be the result of sulphidation of the iron-rich country rocks. The source of sulphur was probably hydrothermal solutions associated with the emplacement of granodiorites. The "economic" deposits are believed to be the result of "volcanogenic hydrothermal activity" during Amisk volcanism.