Iron-bearing skarns of the Uhuk Massif, Northwest Territories, Canada

The focus of this project is the skarns associated with the Uhuk Massif in Northwest Territories, Canada. Field examination, microscope examination, bulk chemical analysis, and mineral analysis by electron microprobe were used to investigate the processes responsible for the formation of these skarns. The Uhuk Massif is the remnant of a feeder-dike/sill complex, which formed when magma from an underlying sill moved upwards due to fault mediated magmatic propagation. Three known Fe-bearing skarns are located at the eastern end of the Uhuk Massif. The major focus of this study was on the main skarn at Uhuk, which is the coarsest-grained and largest of the three. The dominant calc-silicate mineral assemblage that makes up the main skarn is vesuvianite, andradite-grossular type garnets, and diopside. The goal of this project is to determine what cations must have been introduced to the host rock metasomatically to produce the observed skarn minerals, and to determine the order of crystallization within the skarn to better understand the temperature and composition of the fluids responsible for the observed phases of skarn genesis.;In order to determine the mineral assemblage of the skarns, optical identification, X-ray diffraction, and microprobe analysis was used. DCP-AES analysis was used to determine the bulk rock compositions of the skarns, and surrounding country rock samples, to determine what elements were added to the host rock to produce these skarns. The phases of the skarn's genesis were determined by textural and microprobe analysis, in order to gain an understanding of the order in which the minerals crystallized, and also the zoning patterns within the crystals.;Compared to the country rock samples analyzed, the Main Skarn at Uhuk is enriched in Si, Al, Fe, Mg, Cu, Mn, P, Na, Ti, Co, Cr, Ni, Sc, V, and Zr. At least four phases of mineral growth are observed in the skarn rocks. The first phase was a thermal contact metamorphic phase, where anhydrous calc-silicate minerals began to form in the silty layers of the host rock. The second phase of genesis consisted of metasomatic crystal growth driven by the introduction of H2O-rich fluids. The third phase was a period of retrograde metamorphism/alteration of pre-existing skarn minerals. The final phase resulted in the formation of Fe-oxides and Fe-Sulfides cross-cutting the earlier minerals. The large Main Skarn at Uhuk is associated with a comparatively small igneous intrusion, but large amounts of fluid, supplied by magma passing upwards through the feeder-dike system, allowed for fluids to be transported into the host rock from a larger magma volume, resulting in the formation of these skarns.