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The Hongshi lode-type copper deposit is located in the Kalatag region in the East Tianshan, Xinjiang, NW China. The lode ore bodies are hosted in the Late Ordovician to Early Silurian Daliugou Formation, and the Cu mineralization is closely associated with andesite. Minor amounts of intrusive rocks, such as the quartz porphyry, are also exposed. The country rocks have undergone extensive silicification, chlorite alteration and sericite alteration. The metallic minerals are pyrite and chalcopyrite, with minor magnetite, sphalerite and galena. The gangue minerals are quartz, sericite, epidote, calcite and chlorite. The mineralized veins in the Hongshi deposit can be divided into: an early quartz–pyrite vein stage, the main quartz–chalcopyrite–pyrite ± sphalerite vein stage, and a late quartz–calcite–chlorite vein stage. Fluid inclusion petrography shows that two-phase liquid-rich (type I), two-phase vapor-rich (type II), and daughter-bearing multiphase (type III) fluid inclusions are present in the hydrothermal quartz-sulfide veins in the Hongshi deposit. The fluid inclusions in the early-stage minerals are mainly type I and type II with minor type III. Their homogenization temperatures and salinities range from 198 °C to 315 °C (with a peak value of 253 °C) and from 1.40 to 8.81 wt% NaCl equiv., respectively. The coexistence of type II and type III inclusions and their similar homogenization temperatures but contrasting salinities suggest that fluid boiling processes occurred in the early stage. The main-stage minerals feature dominantly type I and type II inclusions, with homogenization temperatures and salinities of 168 °C–280 °C (with a peak value of 209 °C) and 1.40–6.16 wt% NaCl equiv., respectively. The late-stage minerals feature dominantly type I and type II inclusions, with homogenization temperatures and salinities of 109 °C–179 °C (with a peak value of 157 °C) and 0.53–3.23 wt% NaCl equiv., respectively. The initial ore-forming fluids of the Hongshi deposit were therefore associated with an H2O–NaCl system with a near-neutral pH, low–intermediate temperatures and low salinities. The oxygen and hydrogen stable isotopic analyses of FIs in quartz from the different ore-forming stages show that the ore-forming fluids were of volcanic origin, with gradually increasing proportions of meteoric water during/after mineralization. The δ34S values of chalcopyrite and pyrite from the main ore-forming stage vary between 1.9% and 11.9%, suggesting a volcanic source. The 3He/4He ratios of fluid inclusions in the main-stage pyrite mainly range from 0.12 to 1.40 Ra, and the 40Ar/36Ar values vary from 310 to 337. All these isotopic characteristics suggest that the ore fluids were likely derived from a combination of crustal and mantle components. Combining the integrated analysis of ore deposit geology, the fluid evolutionary process, and H–O–S–He–Ar isotopes, we suggest that the Hongshi deposit should be classified as a volcanic–subvolcanic hydrothermal copper deposit. Processes including local fluid unmixing, decreasing temperature and fluid mixing may have been responsible for the hydrothermal alteration and Cu precipitation.

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.