Carrapateena’s silver lining: geochronology and the distribution of Ag in sulphide minerals
Date
2022
Authors
Clegg. E. J. G.
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Abstract
The Carrapateena Iron Oxide Copper Gold (IOCG) deposit is located within the Olympic Copper-Gold (Cu-Au) Province on the eastern margin of the Gawler Craton, South Australia. IOCG deposits are well known for their Cu-Au endowment but also commonly contain economic by-product elements which can include silver (Ag). At Carrapateena, all economic Cu, Au and Ag mineralisation is hosted in the near-vertical Carrapateena Breccia Complex (CBC) where economic Cu is present primarily as chalcopyrite (CuFeS2) and bornite (Cu5FeS4). These minerals are also known to contain accessory Au and Ag but the relationship of these trace metals to the Cu-sulphides has not been constrained. Understanding the timing and distribution of Ag enrichment provides insight into deposit formation, metal mobility and may improve Ag recovery.
Samples were chosen from petrography and μXRF analysis of core from drill holes DD12CAR108 and DD12CAR114. Scanning Electron Microscopy (SEM) and Laser Ablated Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were used to observe and analyse geochronological minerals, Cu-sulphides and trace elements associated with the major sulphides. Pyrite (FeS2) formed during relatively early hydrothermal events in the CBC with Cu-rich fluids subsequently entering the system resulting in chalcopyrite replacing pyrite. Paragenetic relationships indicate that bornite subsequently replaced chalcopyrite, which was followed by selective replacement of bornite by covellite (CuS).
This study identifies covellite to be a significant host of Ag in the system, both at the current mining depth and in the deepest parts of the CBC sampled to date. Ag enrichment within covellite in the deepest drilled parts of the CBC may be the result of relatively low-temperature metal mobility, and provides evidence for a protracted evolution in the CBC with metal mobility potentially continuing until relatively recent times.
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School of Physical Sciences
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Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR
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