TIME-SPACE RELATIONS OF HYDROTHERMAL ALTERATION AND FE-OXIDE-CU-AU DEPOSITS IN THE CLONCURRY AND CURNAMONA REGIONS, AUSTRALIA

Clusters of iron oxide-rich Cu-Au deposits occur in the Curnamona Province (ca. 1600 Ma mineralization; South Australia/New South Wales) and Cloncurry District (mostly 1520-1500Ma; Queensland). In both cases mineralization broadly corresponded with compressional deformation, regional metamorphism and granitoid emplacement. Both regions contain large volumes of profoundly metasomatized rocks with multiphase sodic and sodic-calcic alteration assemblages, some of which predate the syn-ore deformation structures. The Fe-oxide-Cu-Au deposits are in deep-seated (brittle-ductile settings) and display close time-space relationships with distinct alteration styles. Common features amongst the ore systems include one or more phases of sodic±calcic alteration which was invariably succeeded by 300-500° C Fe±K metasomatism in the immediate ore envrionments. Cu-Au-(Co) mineralization either overlapped with this Fe±K stage or with later carbonate deposition. Some major differences between deposits include: substantial bulk chemical variations in the Fe±K stage; relative timing and temperature of Cu-Au deposition; more and less complex paragenetic histories; and variable degrees of complexity of ore-stage element enrichments (in respect to F, Ni, Zn, As, Mo, Ag, Sn, Ba, LREE, W, Hg and U). Cu:Au ratios also vary and show a distinct relationship to the nature of the stable Fe-phases during mineralization (i.e. T-fO2-fS2 conditions). These features suggest the deposits can be regarded as a genuine class linked by a single fundamental genetic process but that there are variations reflecting different fluid inputs, host rock interactions, and mechanisms of metal precipitation. The general genetic model must account for, a) evolution from Na- to Fe-K metasomatism, b) source and cotransport of Fe, Cu, Co and Au, c) low S-content, and d) presence of carbonates.