Qin Wang

The Duolong porphyry copper–gold district, located in the northwestern segment of the Bangongco–Nujiang metallogenic belt on the southern margin of the South Qiangtang terrane (Tibet), hosts typical porphyry-style Cu-Au mineralization with well-defined alteration zoning from potassic through chlorite–sericite to propylitic assemblages. Based on integrated in situ major/trace element and sulfur isotope analyses of pyrite and chalcopyrite from different alteration zones, we identify two discrete episodes of magmatic-hydrothermal activity that exerted distinct controls on metal endowment. Sulfur isotope signatures define a systematic evolution from the earliest, high-temperature potassic stage (δ³⁴S: Py-I −3.70 to −1.16‰, mean −2.14‰; Cp-I −4.92 to −0.90‰, mean −2.54‰) through propylitic alteration (Py-II: 1.20‰–5.16‰, mean 3.06‰) to the later chlorite–sericite stage (Py-III: −2.00 to 1.86‰, mean 0.06‰; Cp-II: −2.50 to 0.58‰, mean −0.77‰), tracking progressive fluid cooling and changing fluid sources. Trace element systematics further discriminate these episodes: sulfides from potassic and chlorite–sericite zones are enriched in trace elements, whereas propylitic pyrite is depleted, with potassic pyrite recording the highest Cu concentrations (559–7256 ppm, mean 2302 ppm) and chlorite–sericite pyrite containing the lowest Au contents (0.01–0.59 ppm, mean 0.10 ppm). Gold mineralization occurs as native gold exsolved from chalcopyrite, and the markedly low Au concentrations in chlorite–sericite pyrite (0.01–0.59 ppm, mean 0.10 ppm) demonstrate that gold exsolution was largely completed during the first, high-temperature magmatic-hydrothermal stage. Collectively, these results establish a detailed geochemical framework linking sulfide composition to specific hydrothermal stages, providing new constraints on the processes of porphyry copper–gold mineralization in a collisional setting.

Magnetite is extensively developed within various alteration zones of the mining district. Some magnetite is closely associated with copper mineralization, possessing significant research value. The Duobuza Cu (Au) deposit is a typical porphyry-type deposit within the Bangong Co-Nujiang metallogenic belt and was the first porphyry Cu-Au deposit discovered in the Duolong copper–gold ore district. Currently, this deposit contains copper resources exceeding 3 million tons @0.46%, with associated gold resources exceeding 80 tons @0.19 g/t. This study focuses on magnetite from the Duobuza deposit. Through field geological logging and microscopic identification combined with electron microprobe analysis (EMPA) and in situ LA-ICP-MS testing, mineralogical and mineral chemical research on magnetite is conducted. This research aims to elucidate the genesis of magnetite in the Duobuza deposit and its implications for mineral exploration. Five magnetite types with different occurrences can be distinguished in the Duobuza deposit: Mt₁ is magmatic magnetite; Mt₂, Mt₃, Mt₄, and Mt₅ are hydrothermal magnetite, with Mt₅ being closely associated with copper mineralization. Mt₁ is relatively enriched in Ti, V, Al, and Cr but depleted in Mn and Si; Mt₂ is relatively enriched in Ti and Al but depleted in Si and Cr; Mt₃ is relatively enriched in Al but depleted in Mg; Mt₄ is relatively enriched in Ti, Al, V, Zn, and Mn; and Mt₅ is relatively enriched in Mg, Si, Ti, Al, Mn, and Zn but depleted in Cr. Based on the Al + Mn vs. Ti + V discrimination diagram, magnetite formed in a medium- to high-temperature environment, with hydrothermal magnetite Mt₄ forming at the lowest temperature. Vanadium (V) content can be used to estimate the oxygen fugacity (fO₂) during mineralization. Mt₁ exhibits the highest V content, indicating relatively low oxygen fugacity, whereas Mt₄ shows the lowest V content, suggesting relatively high oxygen fugacity. Mt₅ has a higher V content compared to other early-stage hydrothermal magnetites, suggesting that a lower fO₂ formation environment favors the precipitation of metal sulfides in the mining district. Trace element analysis of magnetite from the Duobuza, Bolong, and Naruo mining districts reveals that magnetite from all three deposits is enriched in Si and Al and depleted in Ca and Ni. Magmatic magnetite from the Naruo and Duobuza deposits exhibits similar elemental distribution patterns. Hydrothermal magnetite from the Duobuza deposit shows significantly higher Ti and V contents compared to magnetite from the Bolong and Naruo deposits.

Magmatic activity is crucial for identification of the tectonic framework of the ancient oceanic crust. In this study, systematic investigation, including a field survey, zircon LA-ICP-MS U-Pb dating, and whole-rock geochemical analysis, has been carried out on the intrusive quartz- and granodiorites within the Meso-Tethyan Shiquanhe Ophiolitic Mélange (SQM), Tibet. Zircon U-Pb dating yields the weighted mean ages of 174.7 ± 1.4 Ma (quartz diorite) and 178.9 ± 1.2 Ma (granodiorite), respectively, demonstrating the Early Jurassic formation age. The quartz diorite samples are metaluminous (A/NKC = 0.77–0.95) (molar/Al₂O₃/(CaO + Na₂O + K₂O)), while the granodiorite samples are weakly peraluminous (A/NKC = 0.95–1.21), and both of them exhibit tholeiitic to calc-alkaline geochemical characteristics and can be classified as I-type granites. The right-dipping rare-earth element (REE) patterns, enrichment in large ion lithophile elements (LILEs: Rb, Ba, Th), and depletion in high-field-strength elements (HFSEs: Nb, Ta, Ti), as well as relatively high (La/Yb)_N ratios, are features compatible with an island arc setting. Combined with previous works, we suggest that the Shiquanhe ophiolitic mélange not only preserves records of mid-late Jurassic island arc magmatic activity but also contains evidence of island arc magmatism from the late Early Jurassic.

The magmatic activity is crucial for identify the tectonic framework of ancient ocean. In this study, a systematically work including field survey, zircon LA-ICP-MS U-Pb dating, and whole-rock geochemical analysis is carried on to investigated the intrusive magmatic rocks of quartz diorite and granodiorite within the Meso-Tethyan Shiquanhe Ophiolitic Mélange (SQM), Tibet. Zircon U-Pb dating yields the weighted mean ages of 174.7±1.4 Ma (quartz diorite) and 178.9±1.2 Ma (granodiorite) respectively, indicating the Early Jurassic formation age. The quartz diorite is metaluminous (A/NKC = 0.77-0.95), while the granodiorite is weakly peraluminous (A/NKC = 0.95-1.21), and both of them exhibit tholeiitic–calc-alkaline geochemical characteristics and classified as I-type granites. The right-dipping rare earth element (REE) patterns, enrichment in large ion lithophile elements (LILEs: Rb, Ba, Th), and depletion in high field strength elements (HFSEs: Nb, Ta, Ti), as well as relatively high (La/Yb)N ratios represent the is-land arc TTG-like magmatism origin. Combine with the previous works, we suggest the Shiquanhe opiolitic mélange represent an island arc and back-arc assemblage rather than an independent ocean basin. Meanwhile, this Early Jurassic island arc magmatism initiated a new era of the Mesozoic mineralization in Shiquanhe area.

One of the most important characteristics of porphyry copper deposits (PCDs) is the type and distribution pattern of alteration zones which can be used for screening and recognizing these deposits. Hydrothermal alteration minerals with diagnostic spectral absorption properties in the visible and near-infrared (VNIR) through the shortwave infrared (SWIR) regions can be identified by multispectral and hyperspectral remote sensing data. Six Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) bands in SWIR have been shown to be effective in the mapping of Al-OH, Fe-OH, Mg-OH group minerals. The five VNIR bands of Landsat-8 (L8) Operational Land Imager (OLI) are useful for discriminating ferric iron alteration minerals. In the absence of complete hyperspectral coverage area, an opportunity, however, exists to integrate ASTER and L8-OLI (AO) to compensate each other’s shortcomings in covering area for mineral mapping. This study examines the potential of AO data in mineral mapping in an arid area of the Duolong porphyry Cu-Au deposit(Tibetan Plateau in China) by using spectral analysis techniques. Results show the following conclusions: (1) Combination of ASTER and L8-OLI data (AO) has more mineral information content than either alone; (2) The Duolong PCD alteration zones of phyllic, argillic and propylitic zones are mapped using ASTER SWIR bands and the iron-bearing mineral information is best mapped using AO VNIR bands; (3) The multispectral integration data of AO can provide a compensatory data of ASTER VNIR bands for iron-bearing mineral mapping in the arid and semi-arid areas.