Hydrothermal alteration, fluid inclusions and stable isotope characteristics of the Shaquanzi Fe–Cu deposit, Eastern Tianshan: Implications for deposit type and metallogenesis

Abstract

The Shaquanzi Fe–Cu deposit is an important Fe (–Cu) deposit in the Yamansu Fe mineralization belt, Eastern Tianshan. Five-stage (Stage I to V) hydrothermal alteration/mineralization have been recognized: The early skarn (Stage I) and late skarn (Stage II) stages are featured by extensive garnet and amphibole alteration, respectively. Magnetite mineralization stage (Stage III) is associated with pervasive K+Fe±Ca alteration, forming magnetite, mushketovite, K-feldspar, epidote, magnetite, pyrite and quartz. Chalcopyrite mineralization stage (Stage IV) has an ore mineral assemblage of chalcopyrite, bornite, acicular hematite and sphalerite, accompanied with broad epidote+chlorite+calcite alteration. The late veins stage (Stage V) occurs mainly as epidote+calcite veins crosscutting the host rocks and earlier-stage minerals.Stage I hydrothermal fluids have high temperatures (>600°C), medium-high salinities, with magmatic δ18Ofluid=+6‰ to +11.7‰. Stage III ore-forming fluids are medium-high-temperature (ca. 470–570°C) with medium salinity. Stage III minerals were formed under δDfluid=−45.7‰ to −24.3‰, δ18Ofluid=+5.8‰ to +9.1‰ and δ34Sfluid=−1.7‰ to +4.7‰, indicative of magmatic fluids mixed with minor seawater. In contrast, Stage IV fluids have low temperatures (ca. 160°C), medium-low salinities and are Ca-rich, with isotopic compositions reflecting basinal brine mixed with meteoric water (δ13Cfluid=−6.6‰ to −2.3‰; δ18Ofluid=−3.3‰ to +2.8‰ and δ34Sfluid≥+24.8‰).The Shaquanzi diorite (zircon U–Pb age: 298±5Ma) is broadly coeval with previous Re–Os ages of the Shaquanzi magnetite and pyrite (303±12Ma and 295±7Ma, respectively), indicating that the Shaquanzi Fe–Cu metallogeny may have been genetically linked to the regional magmatic–hydrothermal activities led by the Yamansu arc-backarc basin inversion. Features of hydrothermal alterations, mineral assemblages, ore-forming fluids and tectonic setting all suggest that the Shaquanzi Fe–Cu deposit is an IOCG-like deposit, similar to those in the Cenozoic Central Andes.