Geology and Geochemistry of Late Devonian-Mississipian Sediment-Hosted Barite Sequences of the Selwyn Basin, NWT and Yukon, Canada

A sediment-hosted barite horizon occurs in the upper part of the lower Earn Group in the Selwyn Basin, NWT, Canada. This horizon consists of synsedimentary, laminated barite and diagenetic, nodular barite which are hosted in shale, siltstone and mudstone. The lithogeochemistry of the sediments associated with these horizons indicates a reducing, oxygen-depleted environment of deposition. Stable isotope geochemistry indicates a limited supply of sulphate in the Selwyn Basin at this time.;Epigenetic barite and witherite, intergrown with base-metal sulphides is hosted by the lower Earn Group in the Walt/Tryrala/Hess occurrences in the Mac-Millan Pass District, Yukon and has similar geochemical characteristics.;A reducing, Ba and H2S-rich fluid transported along faults; was carried to the seawater-interface where it precipitated barite from seawater and porewater sulphate in the NWT study area. A fluid of similar composition reacted with an oxidized, Zn-Pb-SO4-CO3(aq)-bearing brine to form the mineral assemblages in the Walt/Tyrala/Hess occurrences in the Yukon.