The Cantung W (Cu,Au) skarn deposit, Northwest Territories, Canada is a world-class calc-cilicate skarn deposit hosted by the Cambrian Sekwi Formation limestone, near its contact with the Cretaceous Mine Stock monzogranite. The limestone was affected by the Mine Stock in three ways, i) contact metamorphism during initial emplacement and cooling of the intrusion, ii) magmatic fluids associated directly from the intrusion and iii) fluids that used the same pathways as the magma that formed aplitic dykes. Skarn mineralization (scheelite) occurred from magmatic fluids derived either from the proximal intrusion or by late-stage aplitic dykes. Previous work on the Mine Stock monzogranite, immediately below the E-zone orebody, identified coeval silicate melt and fluid inclusions, and zircon inclusions, in apatite. All which provide a unique opportunity to understand the enrichment in, and transfer of, metals between fractionated granitic melts and immiscible aqueous fluids responsible for the formation of the high-grade W-skarn deposits.
Preliminary fluid inclusion petrography indicate very small (~5 µm wide) liquid-rich fluid inclusions with a minor vapour bubble. This study will investigate the melt and fluid inclusion systematics of the apatite from the Mine Stock. A multi-microanalytical approach will be undertaken to determine the i) minimum entrapment temperatures, fluid composition and salinity using microthermometric analysis of the fluid inclusions, ii) major element composition including halogens of quenched melt inclusions to classify the melts, iii) temperature of apatite crystallization (i.e., inclusion entrapment) using electron probe microanalysis of biotite/apatite pairs for F/Cl thermometry, and iv) temperatures of zircon crystallization via LA-ICP-MS using Ti-in-zircon thermometry. Results will be used to model P-T-X conditions during inclusion entrapment. Fluid inclusion data will be compared to the already established fluid inclusions systematics of the ore zone in order to constrain mineralizing fluid compositions and model processes of W enrichment in the granitic intrusions.