Trace element mapping of pyrite from Archean gold deposits - A comparison between PIXE and EPMA
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Chemical zoning of pyrites can record the evolution of mineralising fluids at widely varying P-T conditions ranging from diagenesis to medium-grade metamorphism. If preserved, zoning can reveal growth textures, brecciation and veining, resorption and recrystallisation events, thus shedding light on the processes that contributed to ore formation. Chemical zoning of sulfides is invisible in optical microscopy, but can be studied by chemical etching, high-contrast back-scattering electron images, and elemental imaging. In this study we compared micro-PIXE and WDS-EPMA elemental maps on the chemically zoned pyrites in mineralised vein-bearing samples from the Sheba and Fairview gold mines in the Barberton Greenstone Belt, South Africa. Elemental images show complex distribution of trace elements, suggesting multiple events of pyrite crystallisation and gold deposition. EPMA maps show fine-scale variations reflecting growth and recrystallisation textures marked, in particular, by variations of As, Ni, and Co. In PIXE maps, gold occurs both as finely-distributed and discrete inclusions, suggesting incorporation in the pyrite structure as solid solution, and deposition as electrum inclusions, respectively. Micro-PIXE and EPMA provide complementary information, forming together a powerful tool to obtain information on chemical zoning of pyrites in ore deposits.
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Agangi, Andrea; Przybylowicz, W.; Hofmann, A. (2015)Chemical zoning of pyrites can record the evolution of mineralising fluids at widely varying P-T conditions ranging from diagenesis to medium-grade metamorphism. If preserved, zoning can reveal growth textures, brecciation ...
Trace element zoning of sulfides and quartz at sheba and fairview gold mines: Clues to mesoarchean mineralisation in the barberton greenstone belt, south africaAgangi, Andrea; Hofmann, A.; Przybylowicz, W. (2014)The Fairview and Sheba mines are two of the major gold mines in the Paleoarchean Barberton Greenstone Belt of Southern Africa. At these mines, gold is associated with quartz-carbonate. ±. rutile veins and occurs both as ...
Pyrite zoning as a record of mineralization in the ventersdorp contact reef, Witwatersrand Basin, South AfricaAgangi, Andrea; Hofmann, A.; Wohlgemuth-Ueberwasser, C. (2013)The Archean metasedimentary succession of the Witwatersrand basin, South Africa, hosts the largest Au deposit in the world. Gold mineralization is mostly concentrated in conglomerate horizons, or "reefs," and is tightly ...