Multi-stage Au–Sb–W enriched mineralization in the Zhaishang deposit, western Qinling, central China

Abstract

Mineral deposits with Au − Sb − W metal association are rare worldwide, but the Zhaishang deposit in the western Qinling Orogen, central China, is one of such deposits. This deposit formed through complex ore-forming processes comprising two main ore stages, stage II marked by Au − As mineralization and stage III by Au − Sb − W mineralization. Four types of pyrite (i.e., Py0, Py1, Py2, Py3) and two types of arsenopyrite (i.e., Apy1, Apy2) were recognized based on their texture, geochemistry, and sulfur isotopic signature. The Py0 has diagenetic origin with the lowest As compared to Py2 and Py3. The syn-ore Py2 in stage II can be subdivided into three sub-types, which have the highest Au and As (up to 57.7 ppm and 72,380 ppm, respectively) and show similar positive correlations among Pb, Zn, Ag, Sb and/or Cu. The values of δ³⁴S were similar in all three Py2 sub-types namely 14.2–16.7‰ (Py2a), 10.0–14.4‰ (Py2b), and 13.6–16.6‰ (Py2c). The core–rim textures of arsenopyrite and the dissolution − reprecipitation textures of Py2 imply that the deposition of Au − As was driven by fluid–rock interaction, and the dissolution–reprecipitation reactions resulted from multiple pulses of hydrothermal fluids that originated from a common sedimentary sulfur source. Gold in Stage III occurs as native Au and gold tellurides. Py3 is enriched only in Sb and depleted in other ore-forming elements, such as Au, Ag, As, Cu, Pb, and Zn. Sulfur dominantly originates from a sedimentary sequence and only small fraction has a magmatic origin. Based on thermodynamic modeling, assuming a fluid pH of 4 to 6.6, fluid processes such as oxidation and cooling of fluid induced the formation of the Au − Sb mineralization, while the addition of Ca²⁺ promoted the W mineralization, due to boiling, fluid mixing and fluid–rock interaction. This study highlights that the unique Au − Sb − W metal association reflect diverse fluid sources and dynamic precipitation mechanisms.