Geochemical and mineralogical characterisation of the Caribou Zn-Pb VMS deposit, Bathurst Mining Camp, New Brunswick, Canada

Abstract

The Caribou Volcanogenic Massive Sulphide (VMS) Zn-Pb deposit in the Appalachians of Eastern Canada is hosted by Middle Ordovician shale and felsic volcanic rocks and deposited in a back-arc environment. The entire mineralised system is characterised by a strong mineralogical and geochemical zonation that is likely related to the zone-refining process. Based on petrographic evidence four paragenetic stages of the mineralisation can be distinguished. The initial i) syngentic precipitation of which framboidal and colloform pyrite have been preserved, ii) the zone refining, iii) the waning state when less reducing conditions incur and is associated with the precipitation of arsenopyrite, cassiterite and later magnetite, and lastly, iv) the metamorphism and deformation that overprinted texturally and chemically most of the mineral phases precipitated during the earlier stages. The zonation of the system allows for the implementation of pyrite as a proxy to the vent complex of the deposit. Particularly, pyrite exhibits increasing As contents with distance from the feeder zone of the system in vertical and lateral directions. Two additional geochemical signatures of the pyrite are suggested exclusively for the vertical zonation; the Co contents of pyrite that increases towards the feeder zone and Au that shows the opposite trend. Besides their applications in mineral exploration, these geochemical signatures provide critical information about the ore genesis of the hydrothermal systems.