Krneta and four co-authors reported in 2015 that apatite from igneous rocks hosting the Worldclass Olympic Dam iron-oxide-copper-gold deposit, South Australia is characterized with respect to morphology, chemistry, mineral assemblage and grain-scale compositional zoning. In granites, apatite displays a characteristic core-to rim zonation due to REE content.
Fields of dusty monazite as ‘emulsion’-like cores or symplectite intergrowths with host apatite are recognized. Compositional data, and their correlation with textures, show a complexity but nevertheless, potential for characterizing the igneous-to-hydrothermal evolution at Olympic Dam. Knowledge of the evolution and geochemistry of apatite at Olympic Dam may offer insights into deposit formation and, potentially, be a tool to discriminate Cu-Au mineralized and barren Fe-oxide dominated hydrothermal systems.
The authors concluded that The difference in grain habit of apatite in the RDG and the mafic enclaves hosted within it can be explained by variable rates of cooling. Wyllie et al. (1962) found that at, a near equilibrium cooling rate, small equant apatite grains are formed whereas conditions of significant undercooling lead to skeletal acicular grains often with central cavities. In the case of the RDG enclaves, these central cavities appear to have been subsequently filled with quartz.
Other studies (e.g. Holden et al. 1987) used observations of acicular grains in and around mafic enclaves to imply rapid cooling of the mafic component upon emplacement into a felsic magma. The compositional data, and their correlation with textures, show a complexity but nevertheless, potential for characterizing the igneous-to-hydrothermal evolution at Olympic Dam.
The Cl component of magmatic apatite from granite and picrite differs. Taken together with S, the Cl component of apatite also appears to be a tracer for the magmatic-to-hydrothermal evolution of the deposit and may also assist understanding subsequent reworking of primary mineral generations.
Further work will focus on determining the REY (REE+Y) fractionation trends of different textural categories of apatite in and surrounding the Olympic Dam
deposit, including apatite within sulfide-hosting hematite breccias of the deposit itself. We will also compare and contrast the textural and chemical signature of apatite with that in other IOCG systems in the Gawler Craton, including those with both comparable and distinct alteration features, as well as worldwide.
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