Fluorite as indicator mineral in iron oxide-copper-gold systems: explaining the IOCG deposit diversity

Abstract

Hydrothermal iron oxide-copper-gold (IOCG) ore deposits are globally important sources of Cu and Au. IOCG systems show many common features, but also considerable diversity in terms of geological setting, mineralization style and ore fluid characteristics. The key factors that control ore formation are controversially debated and no general ore deposit model has been able to explain the diversity of IOCG deposits on the global scale. Building on previous work that characterized four distinct fluid types at the Prominent Hill IOCG deposit, South Australia, we have analyzed the rare earth element (REE) composition of fluorite from the Prominent Hill, Olympic Dam and Ernest Henry IOCG deposits and from two prospects close to Prominent Hill. The REE data of fluorite from Prominent Hill show four distinct chondrite-normalized patterns, which reflect the four fluid types identified as metalliferous volcanic lake water derived fluid, magmatic-hydrothermal fluid, sedimentary basin brine, and wall rock-buffered basement brine. Two strikingly similar REE pattern types were found in fluorite from the Olympic Dam deposit and one in an exploratory data from the Ernest Henry deposit, demonstrating the involvement of the same principal fluid types. We therefore conclude that world-class IOCG deposits can form by interaction of host rocks with different characteristic types of ore fluids and their combinations, thus IOCG deposits do not necessarily form by a single sequence of processes.