Zircon U-Pb Dating in the Vicinity of the Olympic Dam Cu-U-Au Deposit,

Isotopic data are presented for granitoids and felsic volcanics from the Stuart shelf of South Australia, some of which are spatially associated with the Olympic Dam Cu-U-Au deposit. Relatively unaltered quartz monzodiorite, more extensively altered quartz syenite, and felsic volcanics yield zircon U-Pb ages of 1,590_+], 1,613_+ • ø,and 1,576_+[ • m.y., respec-tively. The zircons from this group of rocks, the Olympic Dam suite, have similar morpho-logies and similar 2ø6pb/2øspb ratios, suggesting an intimate genetic relationship. Their ages are comparable to the Gawler Range Volcanics cropping out approximately 130 km to the southwest in the Gawler orogenic domain. Close to the Olympic Dam deposit, the zircon U-Pb system of Olympic Dam suite quartz syenite was contaminated by barite precipitated from hydrothermal fluids associated with the mineralization. The barite is readily removed by air abrasion, which restores the re-versely discordant and spuriously young zircons to more normally discordant positions on the concordia diagram. The abraded zircons then have U-Pb ages similar to uncontaminated Olympic Dam suite zircons. The barite lead must be enriched in 2ø6pb which is concluded t