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~1760 Ma magnetite-bearing protoliths in the Olympic Dam deposit, South Australia: Implications for ore genesis and regional metallogeny

journal contribution
posted on 2023-05-20, 10:18 authored by Courtney-Davies, L, Ciobanu, CL, Verdugo-Ihl, MR, Cook, NJ, Ehrig, KJ, Wade, BP, Zhu, ZY, Vadim Kamenetsky
Spatial associations between banded iron formation and iron-oxide Cu-Au (IOCG) style mineralization are well documented in the Gawler Craton (South Australia), but the possible genetic relationships between these two distinct types of mineralization are hitherto unclear. A texturally conspicuous generation of coarse-grained silician magnetite, intergrown with carbonates and quartz, is observed in drillholes intersecting the ‘outer shell’ of the Olympic Dam IOCG-type deposit. This magnetite is characterised by high U-content (~50 ppm), siliceous chemistry, and unusual zonal textures with respect to Si-Fe-nanoprecipitates. Direct dating of this magnetite by laser ablation inductively coupled plasma mass spectrometry yields reproducible 207Pb/206Pb dates (1761 ± 16 Ma) that are significantly older than the granite hosting the deposit (1593 Ma), or the mineralized breccias constituting the Cu-U-Au-Ag resource (~1592–1589 Ma). The older, Fe-rich crustal material can be correlated with the ~1.76–1.74 Ga (meta)sedimentary Wallaroo Group, host to Fe-rich horizons across the Gawler Craton, including locations ~15 km NW of Olympic Dam. A generation of granitic rocks, which intruded bedrock at ~1.75 Ga are present ~30 km NE of Olympic Dam, and likely exsolved hydrothermal fluids that enriched pre-existing magnetite-bearing protoliths in both U and REE. Such material was physically, and likely chemically, incorporated into the ‘outer shell’ at Olympic Dam some ~150 Ma later, during granite uplift along faults. The coincidence between Fe-rich horizons/BIF and ~1750 Ma granitoids may have provided IOCG systems with an additional source of both Fe and U that predates the ~1.59 Ga craton-scale metallogenic event. The uranium concentrations in some South Australian IOCG systems represent major global anomalies in the element. A combination of the fortuitous geological circumstances outlined here, may help explain the highly anomalous accumulation of uranium found at Olympic Dam.

Funding

Australian Research Council

BHP Billiton Olympic Dam Corporation

History

Publication title

Ore Geology Reviews

Volume

118

Article number

103337

Number

103337

ISSN

0169-1368

Department/School

School of Natural Sciences

Publisher

Elsevier BV

Place of publication

Netherlands

Rights statement

© 2020 Elsevier B.V. All rights reserved.

Repository Status

  • Restricted

Socio-economic Objectives

Mineral exploration not elsewhere classified

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    University Of Tasmania

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