Origin of Cu-Ni-PGE Mineralization at the Manchego Prospect, West Musgrave Province, Western Australia

The late Mesoproterozoic Giles Complex of the West Musgrave province hosts one of the largest concentrations of mafic-ultramafic layered intrusions on Earth. Therefore, the area is highly prospective for hosting significant Ni-Cu and platinum-group element (PGE) mineralization, especially following the discovery of a large magmatic sulfide deposit at Nebo-Babel in 2000. More recently, a significant occurrence of massive to disseminated sulfide mineralization reaching up to 0.62 wt % Cu, 0.47 wt % Ni, and 1 ppm Pt + Pd was identified at the Manchego prospect. The magmatic sulfide mineralization at Manchego is hosted by a range of gabbronoritic rock types situated below a linear magnetic anomaly interpreted to be a magnetite layer belonging to the layered mafic-ultramafic Jameson Range intrusion, which predates the Manchego intrusion. The principal ore minerals comprise massive to disseminated pyrrhotite, chalcopyrite, pentlandite, magnetite, and ilmenite. The presence of several geochemically distinct gabbronoritic lithotypes and an abundance of xenoliths strongly indicate a dynamic magmatic plumbing system, such as a conduit-type environment. Whole-rock samples of sulfide-rich gabbronoritic lithologies have delta S-34 values ranging from -11.8 to 8.4 parts per thousand, which clearly demonstrates the addition of crustal sulfur at Manchego and therefore the availability of crustal sulfur in the West Musgrave province. In comparison to Nebo-Babel, the lithologies intersected at Manchego geochemically resemble the high Ti basaltic NB-4 dikes described by Godel et al. (2011), which are compositionally distinct from the proposed parental magma for the Nebo-Babel intrusion. Therefore, the Manchego prospect provides evidence for the prospectivity of intrusions derived from high Ti basalts in the area, such as the Alcurra Dolerite. Manchego shares many genetic similarities with the Pants Lake intrusion in northern Labrador; both are situated in a magma conduit-type system and assimilated crustal sulfur. However, neither intrusion was sufficiently dynamic to allow the emplacement of chalcophile-undepleted magma pulses, which could have led to an upgrading of metals. Based on present knowledge, this very important step in the formation of economic sulfide deposits is seemingly missing at Manchego; however, exploration is at an early stage.