Biogeochemistry of the 1640 Ma McArthur river (HYC) lead-zinc ore and host sediments, Northern territory, Australia

The formation of the McArthur River lead-zinc deposit involves thermogenic or biologic oxidation of sedimentary organic matter, the products of which generated a massive stratiform sulfide ore body, and secondary carbonate and silica precipitates formed within the sediment pile down the flow pathway and above the reaction zone. The fine-grained texture of the mineralization indicates that primary ore texture is preserved, and coupled with the regional thermal maturity, indicate that this deposit is an ideal location to study organic matter signals related to ore formation and the sedimentary environment. Biomarker data point to a marine environment of deposition and are consistent with data previously collected from the host Barney Creek Formation in the adjacent Glyde Subbasin. An unusual biomarker distribution found in some samples from within two-orebody is considered to be related to the presence of sulfide-oxidizing bacteria. These organisms flourished after turbidite deposition, when oxygen in the upper part of the water column was mixed down to the sediment water interface. The biomaker data are supported by micropalaeontologic observations from the same samples and are consistent with intermittent oxygenation of the water column to the sediment water interface. This observation suggests an extension of the known occurrence of sulfide-oxidizing bacteria back in time by 800 million years, to 1640 Ma.