The Huoyanshan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the North Qilian Orogenic Belt, China, is of significant economic importance. This study provides new constraints on the ore-forming processes through high-resolution in situ trace element and sulfur isotope analyses of pyrite and sphalerite using LA-(MC)-ICP-MS. Petrographic and geochemical investigations identified three distinct generations of pyrite (Py l to Py III). Early-stage Py I and Py II are characterized by high trace element contents (Au, As, Bi, Cu, Pb), elevated Co/Ni ratios (>1–10), and enriched δ34S values (+4.98‰ to +7.47‰). These signatures indicate precipitation from high-temperature, reduced magmatic–hydrothermal fluids influenced by thermochemical sulfate reduction (TSR). Late-stage Py IIl exhibits markedly lower Co/Ni ratios (<0.1) and lighter δ34S values (+3.72‰ to 3.89‰). This geochemical shift reflects a transition toward a cooler, more oxidized environment driven by the incursion and mixing of ambient seawater as the hydrothermal system waned. Trace element geochemistry of sphalerite reveals an average crystallization temperature of 265.8 °C (derived from the “GGIMFis” geothermometer), consistent with fluid inclusion data and representing a thermal “snapshot” of the waning hydrothermal stage. Systematic discriminant analysis using Ga/In, Ge/In, and Co-Ni-As systematics further confirms a strong magmatic–hydrothermal affiliation.
Zhang et al. (Sun,) studied this question.
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