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Using mineral chemistry to aid exploration: a case study from the Resolution porphyry Cu-Mo deposit, Arizona

Citation

Cooke, DR and Wilkinson, JJ and Baker, M and Agnew, P and Phillips, J and Chang, Z and Chen, H and Wilkinson, CC and Inglis, M and Hollings, P and Zhang, J and Gemmell, JB and White, N and Danyushevsky, L and Martin, H, Using mineral chemistry to aid exploration: a case study from the Resolution porphyry Cu-Mo deposit, Arizona, Economic Geology, 115, (4) pp. 813-840. ISSN 0361-0128 (2020) [Refereed Article]

Copyright Statement

2020 Society of Economic Geologists, Inc.

DOI: doi:10.5382/econgeo.4735

Abstract

The giant, high-grade Resolution porphyry Cu-Mo deposit in the Superior district of Arizona is hosted in Proterozoic and Paleozoic basement and in an overlying Cretaceous volcaniclastic breccia and sandstone package. Resolution has a central domain of potassic alteration that extends more than 1 km outboard of the ore zone, overlapping with a propylitic halo characterized by epidote, chlorite, and pyrite that is particularly well developed in the Laramide volcaniclastic rocks and Proterozoic dolerite sills. The potassic and propylitic assemblages were overprinted in the upper parts of the deposit by intense phyllic and advanced argillic alteration. The district was disrupted by Tertiary Basin and Range extension, and the fault block containing Resolution and its Cretaceous host succession was buried under thick mid-Miocene dacitic volcanic cover, obscuring the geologic, geophysical, and geochemical footprint of the deposit.

To test the potential of propylitic mineral chemistry analyses to aid in the detection of concealed porphyry deposits, a blind test was conducted using a suite of epidote-chlorite pyrite-altered Laramide volcaniclastic rocks and Proterozoic dolerites collected from the propylitic halo, with samples taken from two domains located to the north and south and above the Resolution ore zone. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data of epidote provided indications of deposit fertility and proximity. Competition for chalcophile elements (As, Sb, Pb) between coexisting pyrite and epidote grains led to a subdued As-Sb fertility response in epidote, consistent with epidote collected between 0.7 and 1.5 km from the center of a large porphyry deposit. Temperature-sensitive trace elements in chlorite provided coherent spatial zonation patterns, implying a heat source centered at depth between the two sample clusters, and application of chlorite proximitor calculations based on LA-ICP-MS analyses provided a precisely defined drill target in this location in three dimensions. Drilling of this target would have resulted in the discovery of Resolution, confirming that epidote and chlorite mineral chemistry can potentially add value to porphyry exploration under cover.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration Geochemistry
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Copper Ore Exploration
UTAS Author:Cooke, DR (Professor David Cooke)
UTAS Author:Wilkinson, JJ (Professor Jamie Wilkinson)
UTAS Author:Baker, M (Dr Michael Baker)
UTAS Author:Phillips, J (Mr Joshua Phillips)
UTAS Author:Chang, Z (Dr Zhaoshan Chang)
UTAS Author:Chen, H (Dr Huayong Chen)
UTAS Author:Wilkinson, CC (Dr Clara Wilkinson)
UTAS Author:Inglis, M (Mr Shaun Inglis)
UTAS Author:Zhang, J (Dr Lejun Zhang)
UTAS Author:Gemmell, JB (Professor Bruce Gemmell)
UTAS Author:Danyushevsky, L (Professor Leonid Danyushevsky)
ID Code:139367
Year Published:2020
Funding Support:Australian Research Council (IH130200004)
Web of Science® Times Cited:8
Deposited By:CODES ARC
Deposited On:2020-06-12
Last Modified:2020-07-13
Downloads:0

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