Proterozoic stratiform (Sedex) zinc-lead-silver deposits of the Carpentaria Zinc Belt, northern Australia

CIM Vancouver 2006
Ross R. Large, Stuart Bull,
Abstract In terms of zinc, lead, and silver metal endowment, sedimentary
basins of northern Australia rank number one in the world. The
late Palaeoproterozoic to earliest Mesoproterozoic Mt Isa-
McArthur basin system hosts four supergiant, stratiform,
sediment-hosted Zn-Pb-Ag deposits (McArthur River, Century,
Mt Isa, and Hilton-George Fisher). These deposits exhibit many
similar geological and geochemical features including: 1)
location close to regionally extensive normal and strike-slip
synsedimentary faults, 2) organic-rich black shale and siltstone
host rocks, 3) laminated, bedding-parallel synsedimentary
sulfide minerals, 4) stacked ore lenses separated by pyritic and
Fe-Mn carbonate-bearing siltstones, 5) lateral zonation
exhibiting an increasing Zn/Pb ratio away from the feeder fault,
6) vertical zonation exhibiting decreasing Zn/Pb ratio up-
stratigraphy, 7) an extensive stratabound halo of iron- and
manganese-rich alteration in the sedimentary rocks surrounding
and along strike from ore, 8) a broad range of d34S values for
sulfide minerals, from about 0 to +20‰, with pyrite exhibiting a
greater spread than base metal sulfides, and 9) lead isotope
ratios that indicate derivation of lead from intrabasinal sources
with interpreted lead model ages being similar to the measured
zircon U-Pb ages of the host rocks. These common features
demonstrate that the stratiform Zn-Pb-Ag ores formed
approximately contemporaneously with sedimentation and (or)
diagenesis.
This presentation will summarise key features of these deposits,
it will compare exhalative-inhalative (‘Sedex’) genetic models
with subsurface replacement concepts for the zinc-lead ores,
and it will discuss the exploration and genetic implications of
new ideas about Proterozoic ocean chemistry.
Keywords: Proterozoic, SEDEX, Geology, stratiform, Zinc, Ore, Australia
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