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New Advances in Detecting the Distal Geochemical Footprints of Porphyry Systems—Epidote Mineral Chemistry as a Tool for Vectoring and Fertility Assessments

By
David R. Cooke
David R. Cooke
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Mike Baker
Mike Baker
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Pete Hollings
Pete Hollings
Geology Department, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1
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Gabe Sweet
Gabe Sweet
Geology Department, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1Present address: Duluth Metals, 306 West Superior Street, Suite 610, Duluth, Minnesota 55802.
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Zhaoshan Chang
Zhaoshan Chang
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001Present address: School of Earth and Environmental Sciences, Building 34, James Cook University, Townsville, Queensland 4811, Australia.
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Leonid Danyushevsky
Leonid Danyushevsky
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Sarah Gilbert
Sarah Gilbert
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Taofa Zhou
Taofa Zhou
Ore Deposit and Exploration Centre (ODEC), School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, Anhui, China
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Noel C. White
Noel C. White
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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J. Bruce Gemmell
J. Bruce Gemmell
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Shaun Inglis
Shaun Inglis
CODES (Australian Research Council Centre of Excellence in Ore Deposits), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001
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Published:
January 01, 2014

Abstract

Propylitic alteration halos to porphyry deposits are characterized by low- to moderate-intensity replacements of primary feldspars and mafic minerals by epidote, chlorite, calcite ± actinolite, pyrite, prehnite, and zeolites. The pyrite halo that surrounds porphyry deposits typically extends part way through the propylitic halo and provides strong responses to conventional geochemical and geophysical exploration techniques. When exploring outside of the pyrite halo, porphyry deposits have proven to be difficult to detect based simply on the presence of weak epidote-chlorite alteration.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of epidote from propylitic alteration zones around porphyry and skarn deposits in the central Baguio district, Philippines, have shown that low-level hypogene geochemical dispersion halos can be detected at considerably greater distances than can be achieved by conventional rock chip sampling of altered rocks. Epidote chemistry can provide vectoring information to the deposit center and potentially provides insights into the potential metal endowment of the porphyry system, providing explorers with both vectoring and fertility assessment tools.

Epidote chemistry varies with respect to distance from porphyry deposit centers, with the highest concentrations of proximal pathfinder elements (e.g., Cu, Mo, Au, Sn) detected in epidote from close to the potassic alteration zone. Distal pathfinder elements (e.g., As, Sb, Pb, Zn, Mn) are most enriched in epidote more than 1.5 km from the deposit center. Rare earth elements and Zr are most enriched in epidote from the edge of the pyrite halo. The lateral zonation in epidote chemistry implies that at Baguio the geochemical dispersion patterns were produced by lateral outflow of spent fluids from the porphyry center, rather than from ingress of peripheral, nonmagmatic waters.

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Contents

Special Publications of the Society of Economic Geologists

Building Exploration Capability for the 21st Century

Karen D. Kelley
Karen D. Kelley
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Howard C. Golden
Howard C. Golden
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Society of Economic Geologists
Volume
18
ISBN electronic:
9781629499291
Publication date:
January 01, 2014

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