Integrated chemical and mineralogical characterization of the Alta Skarn, Utah

The nature of calc-silicate contact metamorphism of skarns depends on factors like depth, temperature, protolith composition, reaction potential, fluid interactions, and the proximity to the main intrusive body, which typically yield characteristic mineralogical zonation. Through transmitted and reflected light petrography, Raman spectroscopy, and XRD, EPMA, cathodoluminescence and fluid inclusion analyses, the Alta Skarn, related to the Eocene Alta Stock and associated to the Sevier Orogeny, was studied to establish a paragenetic model on the genesis of mineral phases already proposed and others not yet reported. This helped to identify the chemical changes of mineral phases resulting from retrograde metamorphism, hydration reactions, and mineral assemblage changes due to protolith variations, fluid interactions and impurities-driven reactions in the CaO-MgO-SiO2-H2O-CO2 (CMS-HC) system. Among the most relevant findings, are the presence of malachite and hydrogrossular in the ludwigite zone, as well as ludwigite inclusions in brucite pseudomorphs after periclase. Moreover, we identified vesuvianite zonation in birefringence heterogeneity due to elemental variations from the inner to the outer zone of the crystal of: Al, Fe, Mg and Ti, also related to textural reactions forming skeletal calcite and diopside crowning around vesuvianite crystals.