Metallogenesis and fluid evolution of the Huangtupo Cu–Zn deposit, East Tianshan, Xinjiang, NW China: Constraints from ore geology, fluid inclusion geochemistry, H–O–S isotopes, and U–Pb zircon, Re–Os chalcopyrite geochronology

Abstract

The recently discovered Huangtupo Cu–Zn deposit is located in the Dananhu–Tousuquan arc, East Tianshan, NW China. Orebodies are hosted in volcano-sedimentary rocks of the Late Ordovician–Early Silurian Daliugou Formation. The metallogenic physicochemistry, ore-forming fluids, and metallogenesis of the deposit were investigated through orebody features, fluid inclusion microthermometry, laser Raman spectroscopy, and synchrotron-radiation X-ray fluorescence (SRXRF). The results indicate that the deposit includes an upper sedimentary exhalative ore belt (stage I) as well as a lower vein-stockwork ore belt in a hydrothermal fluid supply channel (stage II) associated with silicification, chloritization, epidotization, pyrophyllitization, and beresitization alteration. The Re–Os isochron age of 429.5 ± 10 Ma obtained from primary chalcopyrite. The LA-ICP-MS zircon U–Pb age of 423.3 ± 2.9 Ma for the host hangingwall tuff. Fluid inclusion (FI) microthermometry and geological characteristics were applied to constrain hydrothermal processes and ore genesis. Quartz and barite were collected from the massive sulfide and vein ores for FI study. Four types of FI were identified: liquid-rich L-type, vapor-rich V-type, daughter-mineral-bearing S-type, and C-type containing CO2–H2O. Stage I barite FIs yield homogenization temperatures of 232–364 °C (peak value 265 °C), with salinities of 4.85–10.94 wt% NaCl equiv., whereas stage II quartz FIs yield temperatures of 270–400 °C (peak value 350 °C), with salinities of 2.41–13.72 wt% NaCl equiv (peak value 6.28 wt%). Laser Raman spectroscopy analyses of FI gas compositions indicate that the FIs contain mainly H2O with minor CO2 and N2. Initial ore-forming fluids comprise a medium-high-temperature, low-salinity system of hot evolved seawater that was cooled and diluted by mixing with cold seawater. Fluid mixing and local boiling would have facilitated mineralization. SRXRF analyses indicate that the liquid phase is enriched in Cu and Zn. The δ34S values of sulfide indicate that the sulfur was derived from the magma (host volcanic rocks). Oxygen and hydrogen isotopic data also imply that the ore-forming fluids were mainly derived from deep circulation of seawater, and mixed with minor magmatic fluids. The estimated trapping pressures for vein-stockwork mineralization fluids range from 20 to 60 bar (average 40 bar) at a depth of ~0.4 km. The ore fluids ascenting along faults and fracture networks at or near the seafloor played important roles in oreforming processes of the Huangtupo VMS Cu–Zn deposit.