Miao Sun

The Xianglin Sn polymetallic deposit, located on the northwestern margin of the Cuonadong dome in the eastern Tethyan Himalaya, represents an important Sn-W-Be polymetallic system recently recognized in southern Tibet. This study investigates the nature and evolution of the ore-forming fluids and the mechanisms of cassiterite precipitation. Fluid inclusion petrography, microthermometry, and laser Raman spectroscopy were applied to inclusions from the cassiterite–sulfide, proximal cassiterite–quartz vein, distal cassiterite–quartz vein, and late fluorite–quartz vein stages. The fluid inclusions mainly comprise liquid-rich, vapor-rich, H₂O-CO₂ three-phase, and minor daughter-mineral-bearing inclusions. The cassiterite–sulfide stage contains the most complex inclusion assemblage, with homogenization temperatures of 326–399 °C and salinities of 2.4–10.5 wt.% NaCl equiv. The proximal cassiterite–quartz vein stage yields homogenization temperatures of 280–361 °C and salinities of 2.4–9.6 wt.% NaCl equiv., whereas the distal cassiterite–quartz vein stage records lower temperatures of 195–295 °C. The fluorite–quartz vein stage is characterized by low-temperature and low-salinity fluids. Raman spectra identify CO₂, N₂, CH₄, H₂S, and CaCO₃ daughter minerals, indicating a volatile-rich, relatively reduced H₂O-CO₂-NaCl hydrothermal system. These features suggest that the principal ore-forming fluids were dominantly magmatic–hydrothermal fluids exsolved from highly fractionated Miocene leucogranites. During upward and outward migration from the main detachment zone to peripheral fractures, the fluids experienced boiling, cooling, mixing, and multistage hydrothermal overprinting. Cassiterite precipitation during the cassiterite–sulfide stage was mainly triggered by boiling or phase separation, whereas the proximal cassiterite–quartz veins were controlled by progressive cooling and local phase separation. In contrast, distal cassiterite precipitation was more strongly influenced by fluid mixing and cooling. These results indicate that the Xianglin deposit records a structurally controlled proximal-to-distal magmatic–hydrothermal Sn mineralizing system related to the Cuonadong dome.

The Nuri deposit is currently the only Cu-W-Mo deposit in the Gangdese metallogenic belt, Tibet, China, that contains large-scale tonnages for both Cu and WO₃ resources, accompanied by a medium-scale Mo resources. Previous studies have suggested the potential presence of concealed porphyry-type orebodies at depth, yet effective exploration tools for verifying this hypothesis remain lacking. In this study, microscopic identification, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were integrated to investigate the mineral chemical characteristics of chlorite from the Nuri deposit. The aim was to evaluate the effectiveness of chlorite geochemistry as an exploration vector for predicting deep concealed porphyry orebodies and to establish corresponding exploration indicators. Chlorite in the deposit can be genetically classified into metasomatic (Chl-I) and hydrothermal (Chl-II) types. Both types are Mg-rich varieties, indicating formation under conditions of low oxygen fugacity and low pH. With decreasing vertical distance to the orebody and toward the southeast direction of the exploration section, the contents of Ti (10–950 ppm) and V (50–820 ppm), as well as the Ti/Sr, Ti/Mn, Ti/Li, and V/Li ratios, progressively increase. In contrast, the concentrations of Li (36–390 ppm), Mn (1270–6730 ppm), Sr (1–510 ppm), and Zn (110–1100 ppm) systematically decrease. These systematic compositional variations demonstrate that chlorite geochemistry is an effective exploration tool in the Nuri mining area and suggest the presence of a concealed mineralization center or porphyry orebody beneath the interval from ZK4501 to ZK4502.

The Wubaduolai copper deposit, a newly discovered porphyry-type deposit located in the western section of the Gangdese metallogenic belt, shows great potential for mineralization. Investigating the ore-bearing potentiality of the adakitic granite in this area is crucial for identifying concealed ore bodies and assessing the metallogenic potential. This paper presents the zircon U-Pb dating, Hf isotope analysis, and whole-rock major and trace geochemical analysis of the plutons in the Wubaduolai mining area. The results indicate that the zircon U-Pb concordia age of the monzogranite is 15.7 ± 0.1 Ma, while the granodiorite porphyry has a concordia age of 15.9 ± 0.2 Ma, both corresponding to a Miocene diagenesis. The geochemical data show that both plutons belong to the high-K calc-alkaline series, characterized by a relative enrichment of large-ion lithophile elements (K, Rb, Ba, and Sr) and a depletion of high-field-strength elements (Nb, Ta, and Ti). Both plutons are characterized by low Y, low Yb, and high Sr/Y values, displaying the typical geochemical characteristics of adakites. Their mineral composition is similar to that of adakite. The ε_Hf(t) values of the monzogranite and granodiorite porphyry range from −5.34 to −2.3 and −5.2 to −3.43, respectively, with two-stage model ages (T_DM2) of 1246–1441 Ma and 1318–1432 Ma. Based on the regional data and this study, the plutons in the Wubaduolai mining area formed in a post-collision setting following the India–Asia continental collision. The magma source is identified as the partial melting of a thickened, newly formed lower crust. The above characteristics are consistent with the diagenetic and metallogenic ages, magma source, and dynamic backgrounds of the typical regional deposits.

The Xiongcun Cu–Au ore district is in the southern middle Gangdese Metallogenic Belt, Tibet, and formed during Neo-Tethyan oceanic subduction. The Xiongcun ore district mainly comprises two deposits, the No. I and No. II deposits, which were formed by two individual mineralization events according to deposit geology and Re–Os isotopic dating of molybdenite. The No. I deposit is similar to a reduced porphyry copper–gold deposit, given the widespread occurrence of primary and/or hydrothermal pyrrhotite and common CH₄-rich and rare N₂-rich fluid inclusions. The No. II deposit, similar to classic oxidized porphyry copper–gold deposits, contains highly oxidized minerals, including magnetite, anhydrite, and hematite. The halogen chemistry of the ore-forming fluid from the No. I and No. II deposits is still unclear. Biotite geochemistry with halogen contents was used to investigate the differences in ore-forming fluid between the No. I and No. II deposits. Hydrothermal biotite from the No. I deposit, usually intergrown with sphalerite, is Mg-rich and classified as phlogopite and Mg-biotite, and hydrothermal biotite from the No. II deposit is classified as Mg-biotite. Hydrothermal biotite from the No. I deposit has significantly higher SiO₂, MnO, MgO, F, Li, Sc, Zn, Rb, Tl, and Pb contents and lower Al₂O₃, FeO_tot, Cl, Ba, Cr, V, Co, Ni, Y, Sr, Zr, Th, and Cu contents than the biotite from the No. II deposit. Hydrothermal biotites from the No. I and No. II deposits yield temperatures ranging from 230 °C to 593 °C and 212 °C to 306 °C, respectively. The calculated oxygen fugacity and fugacity ratios indicate that the hydrothermal fluid of the No. I deposit has a higher F content, oxygen fugacity, and log(fHF/fHCl) value and a lower log(fH₂O/fHF) value than the hydrothermal fluid from the No. II deposit. The biotite geochemistry shows that the No. I and No. II deposits formed from different hydrothermal fluids. The hydrothermal fluid of the No. I deposit was mixed with meteoric waters containing organic matter, resulting in a decrease in oxygen fugacity and more efficient precipitation of gold. The No. I and No. II deposits were formed by a Cl-rich hydrothermal system conducive to transporting Cu and Au. The decreasing Cl, oxygen fugacity, and temperature may be the key factors in Cu and Au precipitation. Biotite geochemistry allows a more detailed evaluation of the halogen chemistry of hydrothermal fluids and their evolution within porphyry Cu systems.