Forsteritic marble and Mg-Skarn from the Coober Pedy Ridge Subdomain, Gawler Craton, South Australia

Abstract

The Olympic Dam iron oxide-copper-gold province is a world-class copper-gold belt which lies on the eastern margin of the Gawler Craton in South Australia. The Olympic Dam province mineralised around ~1590 Ma during the emplacement of voluminous felsic Hiltaba Suite granites and co-genetic mafic Gawler Range Volcanics. Currently, the Cairn Hill deposit in the Mount Woods domain represents the northern extent of the Olympic Dam province. This study examines the geochemistry and age of thermal events at the Mount Brady Prospect, a weakly mineralised copper-bearing sub-economic magnesian skarn system, in the Coober Pedy Ridge domain of the Gawler Craton. Geochronological work completed via LA-ICP-MS U-Pb analyses on apatite and zircon taken from the identified ‘coarse-grained’ magnesian skarn assemblage and nearby intermediate intrusive rocks records felsic magmatism at 1584.08 ± 4.97 Ma, regional cooling between ~1450-1400 Ma, and three enigmatic apatite samples which yield ages between 1300 Ma and 1085 Ma. The broad range of ages obtained in this study reveal a complex post-Hiltaba age thermal history in this region of the Gawler Craton. Original drilling records from 1987 identify an olivine-bearing carbonate lithology as being of either carbonatitic or metasedimentary origin. There are numerous occurrences in the northern Gawler Craton that have been provisionally linked with potential carbonatite complexes but no occurrence to date has been confirmed to be of carbonatitic origin. Correct discrimination between carbonatitic lithologies and high-grade marbles is difficult based on mineralogy due to strong mineralogical similarities. LA-ICP-MS analysis of representative mineral phases from the Mount Brady samples show characteristic metamorphic mineral compositions and trace element trends which prove the Mount Brady prospect is not of carbonatitic origin.