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The Agnew-Wiluna greenstone belt of Western Australia is the largest komatiite-hosted nickel sulfide belt in the world and contains two world-class Ni-Cu-(PGE) deposits and a host of smaller deposits. This study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite-hosted Ni-Cu-(PGE) deposits, with specific focus on camp to district controls. We apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems, but above all that the sulfur required to generate world-class deposits is most likely derived from barren volcanic massive sulfide lenses, which are spatially and genetically associated with felsic volcanic and volcaniclastie sequences that were emplaeed eoevally with large komatiitie sills and ehannelized lava flows. Multiple sulfur isotope data can be utilized in exploration at the deposit to district scales. At the deposit scale, the spatial pattern of mass-independent S isotope values (Δ33S) provides crucial insight into the identification of proximal high-grade and high-tenor ores in mineralized systems. In fact, sulfur data reflect the assimilation process that occurred upon komatiite emplacement, whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero Δ33S values, whereas less turbulent flows interacted with distal sulfidie shales having Δ33S values above 0 per rot. Accordingly, the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high-grade ores of poorly known systems. At the district scale, rather than ascertaining what controls the distribution of komatiite-hosted Ni-Cu-(PGE) deposits, the appropriate question to ask is what controls the distribution of count1y rock sulfides, considering that exhalative sulfides may be crucial to ore genesis in komatiite systems. We propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data. This work provides the first step in identifying district-scale control on komatiite-hosted Ni-Cu-(PGE) deposits. This is the scale that has high impact on exploration for new komatiite-hosted nickel sulfide belts globally. [ABSTRACT FROM AUTHOR]

The location of magmatic Ni-Cu-PGE sulfide deposits is related to lithospheric architecture, particularly that of the subcontinental lithospheric mantle (SCLM). At crustal levels, this relationship is manifest by a close proximity to craton and paleocraton margins. Deposits are associated with mafic-ultramafic rocks and many show a close spatial relationship with a coeval large igneous province (LIP). Meted quantities and tenors observed in deposits require segregation of a magmatic sulfide melt from a large volume of parental ultramafic melt. Generation of these parental melts requires melting of upwelling mantle rising to depths of 100 km or less. The timing and tectonic setting of deposits indicates that this most likely occurs when mantle plumes impact on the base of the SCLM and are channeled laterally to areas of thinnest SCLM, where they undergo decompression melting. Alternatively, the setting of some smaller deposits suggests that upwelling may be induced by syn- to post-collisional lithospheric delamination. Craton margins are generally zones of relatively thin lithosphere and are the focus of strain during regional tectonism, providing points of dilation along active translithospheric faults. These faults facilitate melt introduction into the crust. The craton margin zone of thin lithosphere and active faulting may be adjacent to a neighboring block of continental lithosphere (paleocraton margin) or adjacent to a flanking narrow marginal basin (underlain by asthenosphere). All deposits form during periods of active regional tectonism, most commonly under mildly compressional to transpressional conditions. These different settings and conditions may result in differing depths of melting and differing depths and degrees of crustal interaction. The latter is believed to be a key factor for the development of a metal-rich sulfide melt, which is ultimately emplaced in the deposit environment. These variations can account for the observed range of ore and host rock types. Most large deposits are associated with intracontinental settings or with (former) passive margins at the edge of small marginal basins. No significant deposits are associated with the margins of large oceans or with supra-subduction zone environments, possibly reflecting poor preservational potential or (with the latter) limitations to plume interaction with continental lithosphere. A craton-margin model for the genesis of magmatic Ni-Cu-PGE deposits is proposed. This model provides a framework for further examination of deposit-forming processes and also provides a coherent predictive framework for mineral exploration. [ABSTRACT FROM AUTHOR]