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.