Genesis and fluid evolution of the Huangtan Au-Cu deposit in the Kalatag district, Eastern Tianshan, NW China: Constraints from geology, geochronology, fluid inclusions, and H-O-S-Pb isotope geochemistry

The 3D plotting of gold solubility and gold fineness aims to illustrate how to quantify their correlations with ore-forming conditions in hydrothermal gold deposits. The thermodynamic calculation of the Au-Ag solid solutions in Mathematica and the 3D plotting in MATLAB are used to build isopleths of gold solubility and gold fineness at different temperatures (200℃, 400℃), pressures (0.1, 5 kbar), salinities (1, 40 wt% NaCl eq.), and sulfur concentrations (0.01, 0.5 mol/kg). The plot indicates that the ore-forming conditions have different correlations with gold solubility and gold fineness. Average rates of change for the correlations are quantified, showing distinct values in the four pH-logfO2 fields of (I) HSO4−, (II) SO42−, (III) H2S, and (IV) HS−, where dominant gold and silver complexes have different dependencies on the conditions. The quantification of the plots illustrates that a decrease in gold solubility by one order of magnitude is possibly caused by a decrease in temperature of ≥40℃, the salinity of ≥9.6 wt% NaCl eq. or sulfur concentration of ≥0.14 mol/kg, or an increase in pressure of ≥3 kbar, while a decrease in gold fineness by 100 units is possibly caused by a decrease in temperature of ≥14 ℃, pressure of ≥1.4 kbar, or salinity of ≥4 wt% NaCl eq., or an increase in sulfur concentration of ≥0.07 mol/kg. Quantification results suggest that a sharp decrease in temperature may result in large-scale gold mineralization and a great variation in gold fineness. In addition, the quantification reveals that the correlation between gold solubility and gold fineness can be expressed by a function, providing a rapid method for 3D plotting.

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Superimposed Mineralization in the Xiaorequanzi Cu Deposit, Xinjiang: Evidence from Fluid Inclusions, H-O-S Isotopes, and Pyrite Trace Elements

Hao,

Li,

Xia

et al. 2024

Minerals

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The Xiaorequanzi Cu deposit is located in the western part of the Dananhu–Tousuquan Island arc in eastern Tianshan, Xinjiang. It includes stratiform and epithermal-related veinlet mineralization. However, the genesis of this deposit remains controversial. Therefore, fluid inclusions, H–O isotopes, in situ S, and trace elements in pyrite were employed in this study to constrain the origins of the deposit. The Xiaorequanzi Cu deposit’s mineralization stages can be categorized into the following three phases: I. volcanogenic massive sulfide (VMS) mineralization; II. quartz–chalcopyrite–pyrite; and III. quartz–chalcopyrite–sphalerite stages. Fluid inclusion studies suggest that Stage I is distinguished by high-temperature (peak: 320–360 °C) and moderate-salinity (peak: 7–9 wt%) fluids belonging to the H2O–NaCl ± CO2 system. Stages II–III only exhibit vapor–liquid inclusions, with mineralizing fluids belonging to the medium-to-low-temperature (Stage II peak: 160–180 °C; Stage III peak: 120–130 °C) and medium-to-low-salinity (Stage II peak: 5–7 wt%; Atage III peak: 4–6 wt%) H2O–NaCl system. The H–O isotopic data suggest that mineralizing fluid in Stage I is a blend of magmatic and paleo-seawater sources, while in Stages II–III, meteoric water predominates, accompanied by low mineralizing temperatures. In situ S isotope results indicate that the source of mineralizing materials in Stage I (2.52–4.48‰) were magmatic rocks, whereas the markedly higher δ34S values in stages II–III (4.68–6.60‰) suggest sulfur isotope leaching from sedimentary rocks by meteoric water as the main source. The LA–ICP–MS data of pyrite in the Xiaorequanzi Cu deposit suggest that Py1 was formed through volcanic processes, whereas Py2 and Py3 exhibited epithermal characteristics. Throughout the mineralization process, a trend in increasing oxygen and decreasing sulfur fugacity occurred, accompanied by a decreased mineralization temperature. This observation corresponds with the temperature data derived from the fluid inclusions. Additionally, the principal components of different generations of pyrite segregated as two clusters representing the VMS (Stage I) and epithermal mineralization (stages II–III). In summary, based on comprehensive research and previous geochronological studies, it is suggested that the Xiaorequanzi Cu deposit experienced two mineralization stages. The early stage is related to the volcanic activity of the Early Carboniferous (354 Ma), whereas the later stage is associated with Carboniferous–Permian (266–264 Ma) volcanic intrusions.

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Genesis and fluid evolution of the Huangtan Au-Cu deposit in the Kalatag district, Eastern Tianshan, NW China: Constraints from geology, geochronology, fluid inclusions, and H-O-S-Pb isotope geochemistry

Cited by 3 publications

References 58 publications

Evolution of an ancient VMS ore-forming system recorded by pyrite and sphalerite mineral texture, trace elements, and sulfur isotope: A case study from the Huangtupo Cu-Zn (-Au) deposit, Eastern Tianshan, NW China

Evolution of an ancient VMS ore-forming system recorded by pyrite and sphalerite mineral texture, trace elements, and sulfur isotope: A case study from the Huangtupo Cu-Zn (-Au) deposit, Eastern Tianshan, NW China

3D Plotting of Gold Solubility and Gold Fineness: Quantitative Analysis of Ore-Forming Conditions in Hydrothermal Gold Deposits

Superimposed Mineralization in the Xiaorequanzi Cu Deposit, Xinjiang: Evidence from Fluid Inclusions, H-O-S Isotopes, and Pyrite Trace Elements

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