|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Department of Earth and Planetary Sciences, Johns Hopkins University Olin Hall, Baltimore, Maryland 21218
Department of Earth Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4
Centre for Ore Deposit Research, University of Tasmania, Private Box 252-79, Hobart, Tasmania, Australia 7001
Corresponding author: e-mail, cschard1{at}jhem.jhu.edu
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 150°C at the top of the volcanic pile to ~400°C 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 (300°–400°C) and lower for the Kangaroo Caves and other deposits (250°–350°C). 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 (>250°C) 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.
This article has been cited by other articles:
|
|
 |
|
  P. M. Carr, L. M. Cathles III, and C. T. Barrie On the Size and Spacing of Volcanogenic Massive Sulfide Deposits within a District with Application to the Matagami District, Quebec Economic Geology, November 1, 2008; 103(7): 1395 - 1409. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. E. Ioannou and E. T. C. Spooner Fracture Analysis of a Volcanogenic Massive Sulfide-Related Hydrothermal Cracking Zone, Upper Bell River Complex, Matagami, Quebec: Application of Permeability Tensor Theory Economic Geology, June 1, 2007; 102(4): 667 - 690. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Yang, R. R. Large, S. Bull, and D. L. Scott Basin-Scale Numerical Modeling to Test the Role of Buoyancy-Driven Fluid Flow and Heat Transfer in the Formation of Stratiform Zn-Pb-Ag Deposits in the Northern Mount Isa Basin Economic Geology, September 1, 2006; 101(6): 1275 - 1292. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Schardt, R. Large, and J. Yang Controls on Heat Flow, Fluid Migration, and Massive Sulfide Formation of an Off-axis Hydrothermal System-- the Lau Basin Perspective Am J Sci, February 1, 2006; 306(2): 103 - 134. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
