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Geochronological constraints on the Tropicana Gold Deposit and Albany-Fraser Orogen, Western Australia

journal contribution
posted on 2023-05-18, 10:14 authored by Doyle, MG, Fletcher, IR, Foster, J, Ross LargeRoss Large, Mathur, R, McNaughton, NJ, Sebastien MeffreSebastien Meffre, Muhling, JR, Phillips, D, Rusmussen, B

Gold mineralization at the Tropicana mine occurs within the Plumridge terrane along the eastern margin of the Archean Yilgarn craton in the Albany-Fraser orogen, Western Australia. Mineralization is hosted in a favorable syenitic lithofacies of the Tropicana Gneiss with a minimum igneous age of 2638 ± 4 Ma (2σ) and which was metamorphosed to mid-amphibolite to lower granulite facies in the period ca. 2638 to 2520 Ma.

The Tropicana Gneiss was exhumed to crustal levels equivalent to greenschist-facies conditions by the time of economic gold mineralization. The major gold-bearing pyrite-biotite-sericite mineralization formed in association with shear zones during northeast-southwest compression (D3) that postdated W- to NW-verging thrusting (D2). The late fluid-induced event (Tropicana event; Doyle et al., 2013; Blenkinsop and Doyle, 2014) produced a mineral assemblage indicative of greenschist-facies conditions. The paucity of water in granulite-facies gneisses under retrograde conditions suggests that fluids were introduced from an external source for both mineralization and the younger metamorphic event. This occurred at ca. 2520 Ma as determined from biotite (ca. 2515 Ma, 40Ar/39Ar age), pyrite (ca. 2505 Ma, Re-Os, Pb/Pb ages), and tungsten-rich rutile (2521 ± 5 Ma, U-Pb age): the latter is considered to provide the best direct measurement age of gold mineralization.

The Tropicana Gneiss was derived from the upthrusted easternmost margin of the underlying Yilgan craton, or represents a relatively small (160 km long × 50 km wide) remnant crustal block accreted to the Yilgarn craton sometime between ca. 2.6 and 2.5 Ga. The timing of the Tropicana mineralization is distinctly younger than greenstone-associated gold deposits elsewhere in the Yilgarn craton. As in the Dharwar craton, India, and the Limpopo belt, Zimbabwe, economic gold mineralization at Tropicana postdates the major peak of Late Archean world-class gold mineralization (ca. 2.65 Ga) by more than 100 m.y.

The Tropicana Gneiss was relatively unaffected during the younger Albany-Fraser orogeny, with only minor remobilization of gold. Deformation may have been localized at the margins of the domain, between constituent ridged structural blocks, and/or within discrete high-strain shears.

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

Economic Geology

Volume

110

Pagination

355-386

ISSN

0361-0128

Department/School

School of Natural Sciences

Publisher

Economic Geology Publ Co

Place of publication

5808 South Rapp St, Ste 209, Littleton, USA, Co, 80120-1942

Rights statement

Copyright 2015 Society of Economic Geologists

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the earth sciences

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