Constraints on the formation of mineralization and volatile activity in the layered mafic-ultramafic Caribou Lake Gabbro, Northwest Territories, Canada

Abstract

The Caribou Lake Gabbro, NT, Canada is a small layered mafic-ultramafic intrusion hosting minor Ni-Cu-PGE sulphide mineralization. Sulphide mineralization is described in detail and directly compared to early magmatic sulphide melt inclusions. Constraints on the initial silicate melt and R factors to produce the sulphide mineralization are determined. As well, it is demonstrated that sulphide melt inclusion compositions provide a reasonable estimate for metal tenor in sulphide mineralization. Melt and fluid inclusions present in mafic pegmatites and gabbros allow for a study of the volatile history and fluid and melt evolution of the system. Melt inclusion compositions indicate the system formed from an evolved metal-depleted melt. Fluid inclusions preserve the trapping of immiscible carbonic-aqueous brine fluids that may have been exsolved from different parts of the intrusion. This process has been described in economic Ni-Cu-PGE deposits, suggesting the presence of these fluids is not directly related to mineralization potential.