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Numerical Heat and Fluid-Flow Modeling of the Panorama Volcanic-Hosted Massive Sulfide District, Western Australia

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Schardt, C and Yang, J and Large, RR (2005) Numerical Heat and Fluid-Flow Modeling of the Panorama Volcanic-Hosted Massive Sulfide District, Western Australia. Economic Geology, 100 (3). pp. 547-566. ISSN 0361-0128

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Abstract

Exceptional exposure of the Archean Pilbara block in Western Australia reveals a cross section through an
Archean massive sulfide-hosting volcanic succession with underlying subvolcanic intrusion in the Panorama
district. A numerical model based on available detailed geologic information has been constructed to simulate
heat and fluid flow in the Panorama district. The modeling provides insight into the evolution of the hydrothermal
system and evaluates key geologic parameters and their influence on fluid-flow, hydrothermal circulation,
and the genesis of massive sulfide orebodies. The model simulates important aspects of the Panorama
massive sulfide district, such as temperature distribution, relative alteration zonation, and the size and distribution
of orebodies. Predicted temperatures ranging from 150ºC at the top of the volcanic pile to ~400ºC at the
andesite-diorite interface are comparable to temperature estimates based on previously published oxygen isotope
mapping. Modeled fluid discharge temperatures are highest for the Sulphur Springs deposit (300º–400ºC)
and lower for the Kangaroo Caves and other deposits (250º–350ºC). The most favorable conditions to reproduce
the orebodies and their related alteration zonation occur at anisotropic rock permeabilities comparable
to the upper oceanic crust (10–15–10–14 m2) and higher fault permeabilities (10–14–10–13 m2) with a specific fault
arrangement similar to that mapped in the field. The 4.6 million metric tons (Mt) Sulphur Springs orebody is
predicted to form in less than 5,000 yr, assuming a hydrothermal fluid with seawater salinity, 10 ppm base metal
concentration, and a low deposition efficiency (≤10%); other deposits form above the faults under similar conditions.
A large range of base metal concentrations in the fluids can account for the known orebodies, but high
temperatures (≥250ºC) and high-flow velocities (>10–7 m/s) are necessary to produce the observed alteration
patterns and distribution of ore deposits. Results indicate that the establishment of a significant hydrothermal
system capable of forming economic massive sulfide deposits is favored in fresh volcanic rock packages that
have not been affected by earlier compaction or alteration. Under these conditions, economic massive sulfide
orebodies (>5 Mt of 10% Zn + Cu) may form in a few thousand years, although the overall lifespan of the hydrothermal
system may be between 30,000 and ~200,000 yr, depending on the variations in rock and fault permeability
with time.

Item Type: Article
Keywords: VHMS, ore genesis, ore fluids, sea floor ore deposits, VMS, Cu-Pb-Zn
Journal or Publication Title: Economic Geology
Page Range: pp. 547-566
ISSN: 0361-0128
Identification Number - DOI: 10.2113/100.3.547
Date Deposited: 04 Oct 2007 05:58
Last Modified: 18 Nov 2014 03:22
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