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Timing of Iron Oxide Cu-Au-(U) Hydrothermal Activity and Nd Isotope Constraints on Metal Sources in the Gawler Craton, South Australia

Roger G. Skirrow and Evgeniy N. Bastrakov

Geoscience Australia, GPO Box 378, Canberra, A.C.T. 2601, Australia

Karin Barovich

University of Adelaide, Adelaide, South Australia 5005, Australia

Geoffrey L. Fraser

Geoscience Australia, GPO Box 378, Canberra, A.C.T. 2601, Australia

Robert A. Creaser

University of Alberta, Edmonton, Alberta T6G 2H1, Canada

C. Mark Fanning

Research School of Earth Sciences, Australian National University, Canberra, A.C.T. 0200, Australia

Oliver L. Raymond

Geoscience Australia, GPO Box 378, Canberra, A.C.T. 2601, Australia

Garry J. Davidson

University of Tasmania, Hobart, Tasmania 7001, Australia

Corresponding author: email, roger.skirrow{at}ga.gov.aubilliton.com)

The eastern Gawler craton hosts Australia’s premier uranium-bearing iron oxide copper-gold (IOCG) belt, the >500-km-long Olympic Cu-Au-(U) province. In addition to the Olympic Dam Cu-U-Au and Prominent Hill Cu-Au deposits, numerous barren and weakly mineralized IOCG prospects are present in the province. New geochronological data for hydrothermal minerals combined with constraints from host-rock ages demonstrate that alteration and associated IOCG mineralization formed between ~1570 and ~1600 Ma in three districts of the province. This IOCG hydrothermal activity temporally overlaps with magmatism of the Hiltaba Suite and Gawler Range Volcanics. Titanites in paragenetically early magnetite-bearing alteration in the Olympic Dam and Prominent Hill districts yield U-Pb ion probe ages of 1576 ± 5 and 1567 ± 10 Ma, respectively. Molybdenite in veins crosscutting magnetite-biotite and albitic alteration in the Moonta-Wallaroo district have Re-Os ages of 1574 ± 6 and 1599 ± 6 Ma, respectively. These represent minimum ages of the IOCG alteration assemblages in this district. A muscovite ⁴⁰Ar/³⁹Ar age of 1575 ± 11 Ma provides a minimum age of paragenetically later hematitic alteration in the Olympic Dam district.

Neodymium isotope compositions were determined for 44 whole-rock samples from barren and weakly mineralized Cu-Au prospects and host rocks in the Olympic Dam and Prominent Hill districts. The new geochronological framework enables comparison of the Nd isotope data across two IOCG districts at the time of formation of the Olympic Dam deposit (ca. 1590 Ma). Magnetite-rich weakly Cu-mineralized alteration from five prospects yields a relatively narrow range of _Nd(1590) values of –5.8 to –4.1. Both hematite- and magnetite-rich alteration yield generally similar _Nd(1590) values that match values from fresh and weakly altered Paleoproterozoic metasedimentary and metagranitic rocks (–6.6 to –3.5) as well as from most felsic Hiltaba Suite intrusions and Gawler Range Volcanics in the eastern Gawler craton (ca. –6 to –4). These data are consistent with crustal sources for REE and, by implication, for associated copper in the barren and weakly mineralized prospects. Mineralization and alteration in these minor IOCG systems can be geochemically discriminated from the giant Olympic Dam deposit, where greater inputs of mantle-derived REE and other ore components are evident.

This article has been cited by other articles:

				R. G. Skirrow, R. G. Skirrow, and G. J. Davidson A Special Issue Devoted to Proterozoic Iron Oxide Cu-Au-(U) and Gold Mineral Systems of the Gawler Craton: Preface Economic Geology, December 1, 2007; 102(8): 1373 - 1375. [Full Text] [PDF]

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