Paragenesis of hydrothermal palladium in the Vulcan Iron Oxide Copper Gold Prospect.
Date
2022
Authors
Browne, J.
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Abstract
The transportation and concentration of Pd and other platinum group elements (PGE) in crustal environments is unequivocally attributed to mafic-ultramafic magmatic processes. The identification of elevated Pd within some porphyry mineral systems combined with Pd thermodynamic modelling has, however, demonstrated Pd can also be efficiently concentrated and transported in hydrothermal fluids. The identification of Pd-elevated intervals up to ~5500ppb across the Vulcan iron-oxide copper gold (IOCG) prospect in the eastern Gawler Craton, South Australia, presents an unprecedented opportunity to investigate the mineralogy and transport of hydrothermal Pd. This study uses geochemical, petrographic, and in-situ micro-chemical methods to identify, quantify, and paragenetically assess the distribution of Pd-bearing minerals within Pd-rich hematite breccia at Vulcan. Furthermore, this study attempts to characterise the physiochemical nature of Pd-mobilising fluids in IOCG systems for the first time.
Pd-enrichment occurs within apatite-rich hematite breccias containing varying amounts of siderite, dolomite, quartz, chlorite, pyrite, and chalcopyrite. Mineralogical hosts for Pd at Vulcan include some Ni-rich pyrite and a variety of Te-Se-Sb-As alloys identified as merenskyite (PdTe2), mertieite (Pd16Sb5As), and kalungaite (PdAsSe). Compositional mapping and trace element quantification of 22 pyrite grains demonstrate a peak Pd enrichment of 125 ppm occurring within Ni-rich (up to ~1 wt%) pyrite. Textural and trace element analysis of pyrite demonstrates compositional zoning in Pd, Ni, and Se within some Pd-rich (> 1 ppm) cores, suggesting primary pyrite as the initial host for Pd at Vulcan. Comparison of Pd-Pt whole rock composition and Pd paragenesis suggests an early introduction of Pd into the Vulcan system by a highly oxidised acidic fluid. Strong compositional distinction in pyrite Ni-Co concentration and apatite Cl content suggests subsequent hydrothermal activity by hotter and more saline fluid.
This geochemical, petrographic, and in-situ micro chemical study presents the first investigation into the Pd-bearing mineralogy and hydrothermal fluid mobility of Pd within global IOCG mineral systems. Furthermore, this study demonstrates Pd can be significantly concentrated in IOCG systems, suggesting an unrecognised potential exists for hydrothermal Pd in the eastern Gawler Craton.
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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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