Characterization of pentlandite-bearing quartz veins of Kambalda, Western Australia
The Kambalda Dome of the Yilgarn Craton is located in Western Australia and has been historically mined for Ni after the discovery of magmatic sulfide orebodies in 1966. The Ni orebodies consist of komatiite-associated magmatic sulfide deposits which have experienced deformation, metamorphism and plutonism. A complex geologic history at the Kambalda Dome has resulted in the formation of various types of cross-cutting quartz veins that have not yet been fully described and classified. During recent mining activities at the eastern flank of the Kambalda Dome, three types of quartz veins have been observed: barren quartz veins, auriferous quartz veins and pentlandite-bearing quartz veins. Timing and formation conditions of these quartz veins are unknown and pentlandite-bearing quartz veins are of particular interest as pentlandite usually occurs in magmatic or volcanic settings, such as layered mafic-ultramafic intrusions, mantle xenoliths and komatiite-associated magmatic sulfide deposits. Characterization of these quartz veins and understanding of timing and formation conditions have been determined through detailed optical petrography, scanning electron microscopy techniques, cathodoluminescence imaging and electron microprobe analysis. Microanalytical work indicates that pentlandite occurs in four distinct mineralization styles at Kambalda. Mineralization Style I represents the historically mined komatiite-hosted deposits formed through magmatic processes. Mineralization Style II represents carbonate-rich Ni-arsenide bearing quartz veins that are hydrothermal in nature and bear great similarity to profuse hydrothermal Ni occurrences globally. Mineralization Style III represents quartz veins with pentlandite intergrown with pyrrhotite and gangue minerals such as quartz, feldspar and biotite. Pentlandite, co-genetic pyrrhotite and gangue minerals formed by precipitation from metamorphic fluids. Mineralization Style IV represents fractured or brecciated quartz veins with pentlandite, pyrrhotite, pyrite and chalcopyrite mechanically remobilized and localized in late fractures. This study focused on understanding the formation of hydrothermal pentlandite-bearing quartz veins which, through aforementioned techniques and thermodynamic modelling, have been determined to have formed between 2660 ± 4 Ma and ~ 2,625 Ma, from metamorphic fluids at near-neutral pH and reduced conditions. Age constraints are delimited through hostrock U-Pb zircon ages and deformation event ages available in literature. The results of this study are principally important in building on knowledge of crustal fluids that are capable of mobilizing and consequently precipitating Ni minerals such as pentlandite. This study is also relevant to exploration efforts considering such data can be utilized to effectively characterize Ni deposits based on mineralogical and geochemical characteristics of rocks observed.
Kambalda Dome, Ni mobility, Yilgarn Craton, metamorphic fluid, hydrothermal, pentlandite
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