Abstract
This study evaluates epidote chemistry as a discriminator of and vector to skarn mineralization, based on LA-ICP-MS analyses of epidote from the Devonian Dolphin Tungsten (W) skarn and Neoproterozoic mafic volcanic rocks (up to 6.5 km northeast from the deposit) on King Island, Tasmania. Epidote from the mafic volcanics has distinctive compositions relative to skarn epidote and metamorphic signatures and records a distal footprint of magmatic-hydrothermal fluids > 4.5 km from Dolphin. Exoskarn epidote, replacing garnet during retrograde alteration, has low Fe/Al ratios (< 0.5) and high Sn (mean > 100 ppm) and Bi (mean > 10 ppm). Endoskarn epidote, replaced feldspar phenocrysts and/or occurs in veins, and is enriched in B, Li, As and Sb (mean > 5 ppm). U-Pb dating of exoskarn epidote yielded a 356.7 ± 8.9 Ma age, which is within uncertainty of the Sandblow Granodiorite (~ 351 Ma), whereas the City of Melbourne Bay Volcanics epidote yielded a 394 ± 65 Ma age consistent with the emplacement of the Tabberabberan‑orogeny intrusions in western Tasmania. A comparative analysis, involving a compilation of 6,008 analyses from previous studies, confirms that epidote compositions vary significantly between magmatic-hydrothermal and metamorphic systems. Arsenic is higher in porphyry epidote, Bi is a distinctive tracer of skarn epidote and elevated Sn is characteristic of W-skarn systems. The LREE/HREE ratios in metamorphic epidote (< 5) are typically lower than in magmatic-hydrothermal epidote (> 5). Additionally, the Sn/HREE ratio discriminates epidote associated with W systems (> 25), Cu deposits (1–25) and metamorphic environments (< 1). Our findings confirm that epidote chemistry is a robust tool for evaluating ore potential and distinguishing skarn from porphyry and metamorphic systems.