The geochemistry of rare earth element-bearing minerals and their relationship to copper sulphide mineralisation at the Carrapateena deposit, South Australia

Abstract

Carrapateena is an Iron Oxide Copper-Gold (IOCG) deposit located on the eastern margin of the Gawler Craton, within the Olympic Copper-Gold Province. In addition to Cu and Au, Carrapateena contains elevated concentrations of REE. Three mineralogical zones in the deposit are distinguished largely on the basis of Cu abundance: the barren zone, chalcopyrite zone and bornite zone, with the latter containing the highest-grade Cu ore. Each zone exhibits distinct whole-rock REE profiles, warranting an investigation into the relationship between REE and Cu mineralisation. However, limited research has been completed in this space, and on Carrapateena in general. This project aims to investigate the textural relationships between Cu- and REE-bearing minerals, determine the U-Pb geochronology of the REE-bearing minerals and characterise their geochemistry in each zone of the deposit. This will ultimately improve understanding of the temporal development of Carrapateena.

Monazite, xenotime and apatite are the most abundant REE-bearing minerals in studied samples. Textural relationships show that while monazite was part of the main Cu-mineralising stage in the formation of Carrapateena, apatite and xenotime were part of a paragenetically earlier mineral assemblage. The geochronology of all three minerals record multiple remobilisation events, almost all of which post-date the published deposit age of ca. 1590 Ma. Based on textural relationships, the dates produced from monazite may be a more appropriate estimate of the introduction of Cu into the Carrapateena mineral system at ca. 1450 Ma. Apatite exhibits three distinct chondrite-normalised REE fractionation trends corresponding to the bornite, chalcopyrite and barren zones of Carrapateena. For the first time, these trends have been compared to those from other IOCG deposits in the Olympic-Cu-Au Province and offer insight into evolving fluid physiochemistry during IOCG deposit formation. These findings are encouraging for the future applicability of apatite geochemistry to mineral exploration.