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Geochemistry of Porphyry Deposits
Porphyry ore deposits typically form in convergent plate margin or postsubduction settings at depths of 1-6 km. Oxidized hydrous melts derived from the metasomatized mantle wedge transport Cu, Au, Mo, and other metals to upper-crustal magma chambers. Ponding and release of these magmas is promoted by transient compressional events that perturb steady-state subduction processes, such as the subduction of aseismic ridges or oceanic plateaus. Fractional crystallization leads to repeated cycles of volatile exsolution, vein stockwork formation, and hydrothermal brecciation within and above the mineralizing intrusions. Radiometric dating provides evidence for multiple mineralizing episodes over several million years in some deposits and durations of less than a few hundred thousand years for magmatism and mineralization in others.
Metals are transported by high-temperature brines, vapors, or vapor-like supercritical fluids, depending on local confining pressures. Ore deposition may occur due to decreasing temperature, decreasing pressure, sulfate reduction, water-rock interaction, SO2(g) disproportionation, condensation, or combinations thereof. Stable isotopic data indicate a predominance of magmatically derived sulfur, oxygen, deuterium, copper, iron, and molybdenum in the mineralized core of many porphyry deposits. Lead isotopes provide insights into crustal assimilation processes where there are significant differences in the isotopic compositions of local crustal and mantle sources of Pb.
Funding
Australian Research Council
AMIRA International Ltd
ARC C of E Industry Partner $ to be allocated
Anglo American Exploration Philippines Inc
AngloGold Ashanti Australia Limited
Australian National University
BHP Billiton Ltd
Barrick (Australia Pacific) PTY Limited
CSIRO Earth Science & Resource Engineering
Mineral Resources Tasmania
Minerals Council of Australia
Newcrest Mining Limited
Newmont Australia Ltd
Oz Minerals Australia Limited
Rio Tinto Exploration
St Barbara Limited
Teck Cominco Limited
University of Melbourne
University of Queensland
Zinifex Australia Ltd
History
Publication title
Treatise on GeochemistryVolume
13Edition
2ndEditors
H Holland, K TurekianPagination
357-381ISBN
978-0-08-098300-4Department/School
School of Natural SciencesPublisher
ElsevierPlace of publication
ItalyExtent
270Rights statement
Copyright 2014 Elsevier Ltd.Repository Status
- Restricted