An integrated study of magmatism, magmatic Ni-Cu sulphide mineralization and metallogeny in the Umiakoviarusek Lake Region, Labrador, Canada

摘要

The OKG prospect in the Umiakoviarusek Lake region of Labrador provides an excellent laboratory to study anorthosite-mangeric-charnockite-granite (AMCG) magmatism and pyroxenite-leucotroctolite hosted magmatic Ni-Cu sulphide mineralization. The prospect consists of anorthositic and granitoid rocks, with lesser Archean gneisses and mineralized pyroxenitic rocks. The REE- and PGE-depleted natures of the surface pyroxenitic rocks show some similarities to spinel lherzolites and peridotites from the sub-continental lithospheric mantle (SCLM). The similarity to the SCLM suggests that the OKG pyroxenitic rocks were derived from the partial melting of a refractory, depleted, garnet-free or garnet-poor SCLM. The presumed Mesoproterozoic age for the pyroxenitic dikes suggest that melting was initiated by basaltic underplating associated with plumes associated with the Nain Plutonic Suite (NPS). Pyroxenitic magmas underwent both fractionation and assimilation of Nain Province crustal material resulting in LREE and LFSE enrichments, negative Th and Nb anomalies, and low #epsilon#Nd signatures. This crustal contamination felsified the pyroxenitic magmas and induced sulphide saturation and, with continued rising into the crust, were emplaced into their anorthositic hosts. Upon emplacement, sulphide segregation occurred resulting in the subsurface base-metal sulphide occurrences.