3.26 GA Black Smoker-Type Textures and Setting of VMS Mineralisation in the Pilbara Craton, Western Australia: Ancient Analogues of Modern Pacific-Rim Processes

Kerrich R,
Organization: The Australasian Institute of Mining and Metallurgy
Pages: 4
Publication Date: Jan 1, 1995
Early-Archaean (3.26 Ga) volcanogenic massive sulphide (VMS) deposits located within the low strain and sub-prehnite- pumpellyite metamorphic-grade Strelley greenstone belt, East Pilbara, Western Australia, contain exceptionally well preserved sulphide textures which are directly analogous to those of sulphide chimneys formed by black smokers at present- day submarine hydrothermal vents. The VMS deposits are associated with seafloor alteration zones in and below silica- carbonate laminites, at the top of tholeiitic to calc-alkaline intermediate and felsic rocks. VMS mineralisation comprises stratabound Zn-rich sulphide lenses with significant Cu and barite, and variable Pb and Ag, above Cu-rich stringer zones, all of which are similar to Phanerozoic polymetallic or Kuroko VMS deposits. Sulphide-sulphate mineralisation implicates hydrothermal discharge into sulphate-bearing ocean waters, ruling out a globally anoxic Archaean hydrosphere. The volcanic rocks and co-magmatic sub-volcanic intrusion hosting the VMS deposits are characterised by the conjunction of LILE>LREE>HREE, and Phanerozoic La/Yb with negative normalised anomalies of Nb, P and Ti, consistent with derivation via subduction zone hydrous metasomatism fusing the mantle lithosphere.
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