Geochemical characteristics of sphalerite from Puharje mine

The Puharje ore deposit is a low-temperature, epigenetic, carbonate-hosted Zn–Pb deposit located on the margin of the Kamnik–Savinja Alps within the Southern Alpine domain. Mineralization, dominated by sphalerite and galena, is hosted in bituminous dolostones of the Late Permian Bellerophon Formation, with minor shale intercalations. This study focuses on evaluating the trace element distribution within four textural types of sphalerite, analyzed by in-situ laser ablation with inductively coupled plasma mass spectrometry (LA-ICP-MS). These data are used to constrain the physicochemical conditions of ore formation, fluid evolution and establishment of a rigid genetic model as well as to assess the critical strategic metal potential of the deposit. Sulfur isotope data from sphalerite (Drovenik et al., 1976) complement the geochemical dataset and provide insights into the source of sulfur and reduction mechanism of sulfate. Sphalerite compositions define two geochemical groups: one enriched in As, Tl, and Pb, and another in Ag, Cu, and Hg, corresponding to two distinct mineralization stages. Stage 1 reflects high-salinity, acidic, reducing fluids strongly influenced by organic matter, while Stage 2 resulted from the influx of more oxidized fluids, promoting precipitation of Cu-, Ag-, and Hg-rich sphalerite compared to Stage 1. Estimated formation temperatures (130–145 °C) and ?34S values (?34S ? +12 ‰) suggest low- to intermediate sulfidation conditions and total reduction of sulfate via thermochemical sulfate reduction (TSR). The sulfate source is most likely related to either the Carboniferous-Permian or Permo-Triassic evaporites from the basement units of Southern Alps. Sphalerite from Puharje is moderately enriched in Ge (up to 112 ppm), particularly in early-stage dark brown varieties, while Ga, In, and Sb are depleted. A negative correlation between Ge and Cd suggests Cd may serve as a proxy for Ge enrichment. Although the deposit shares features with both Mississippi Valley-type (MVT) and Alpine-type (APT) deposits, its Permian host rocks preclude a strict APT classification.