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The Tiegelongnan Cu (Au) deposit is the largest copper deposit newly discovered in the Bangong-Nujiang metallogenic belt. The deposit has a clear alteration zoning consisting of, from core to margin, potassic to propylitic, superimposed by phyllic and advanced argillic alteration. The shallow part of the deposit consists of a high sulphidation-state overprint, mainly comprising disseminated pyrite and Cu-S minerals such as bornite, covellite, digenite, and enargite. At depth porphyry-type mineralization mainly comprises disseminated chalcopyrite, bornite, pyrite, and a minor vein molybdenite. Mineralization is disseminated and associated with veins contained within the porphyry intrusions and their surrounding rocks. The zircon U-Pb ages of the mineralized diorite porphyry and granodiorite porphyry are 123.1 ± 1.7 Ma (2σ) and 121.5 ± 1.5 Ma (2σ), respectively. The molybdenite Re-Os age is 121.2 ± 1.2 Ma, suggesting that mineralization was closely associated with magmatism. Andesite lava (zircon U-Pb age of 111.7 ± 1.6 Ma, 2σ) overlies the ore-bodies and is the product of post-mineralization volcanic activity that played a critical role in preserving the ore-bodies. Values of −4.6 ‰ to + 0.8 ‰ δ34S for the metal sulfides (mean − 1.55 ‰) suggest that S mainly has a deep magmatic source. The H and O isotopic composition is (δD = −87 ‰ to −64 ‰; δ18OH2O = 5.5 ‰ to 9.0 ‰), indicating that the ore-forming fluids are mostly magmatic-hydrothermal, possibly mixed with a small amount of meteoric water. The zircon εHf(t) of the diorite porphyry is 3.7 to 8.3, and the granodiorite porphyry is 1.8 to 7.5. Molybdenite has a high Re from 382.2 × 10−6 to 1600 × 10−6. Re and Hf isotope composition show that Tiegelongnan has some mantle source, maybe the juvenile lower crust from crust-mantle mixed source. Metallogenesis of the Tiegelongnan giant porphyry system was associated with intermediate to acidic magma in the Early Cretaceous (~120 Ma). The magma provenance of the Tiegelongnan deposit has some mantle-derived composition, possibly mixed with the crust-derived materials. [ABSTRACT FROM AUTHOR]

The Lakange porphyry Cu-Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern-central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai-Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U-Pb age, and molybdenite Re-Os age data for the deposit. The ore-bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90-1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51-19.77 and (La/Yb)N values of 29.65-41.05. The intrusion is enriched in the large-ion lithophile elements (LILE) and depleted in the HREE and high field-strength elements (HFSE). The ore-bearing porphyritic granodiorite yielded a Miocene zircon U-Pb crystallization age of 13.58 ± 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re-Os ages of 13.20 ± 0.20 and 13.64 ± 0.21, with a weighted mean of 13.38 ± 0.15 Ma and an isochron age of 13.12 ± 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore-bearing porphyritic granodiorite yielded zircon εHf( t) values between −3.99 and 4.49 (mean, −0.14) and two-stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6-835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu-Mo deposit and numerous associated porphyry-skarn deposits in the eastern Gangdese porphyry copper belt (17-13 Ma) formed in an extensional tectonic setting during the India-Asia continental collision. [ABSTRACT FROM AUTHOR]

The Miocene Qulong porphyry Cu-Mo deposit, which is located at the Gangdese orogenic belt of Southern Tibet, is the largest porphyry-type deposit in China, with confirmed Cu ∼10 Mt and Mo ∼0.5 Mt. It is spatially and temporally associated with multiphase granitic intrusions, which is accompanied by large-scale hydrothermal alteration and mineralization zones, including abundant hydrothermal anhydrite. In addition to hydrothermal anhydrite, magmatic anhydrite is present as inclusions in plagioclase, interstitial minerals between plagioclase and quartz, and phenocrysts in unaltered granodiorite porphyry, usually in association with clusters of sulfur-rich apatite in the Qulong deposit. These observations indicate that the Qulong magma-hydrothermal system was highly oxidized and sulfur-rich. Three main types of fluid inclusions are observed in the quartz phenocrysts and veins in the porphyry: (i) liquid-rich; (ii) polyphase high-salinity; and (iii) vapor-rich inclusions. Homogenization temperatures and salinities of all type inclusions decrease from the quartz phenocrysts in the porphyry to hydrothermal veins (A, B, D veins). Microthermometric study suggests copper-bearing sulfides precipitated at about 320-400°C in A and B veins. Fluid boiling is assumed for the early stage of mineralization, and these fluids may have been trapped at about 35-60 Mpa at 460-510°C and 28-42 Mpa at 400-450°C, corresponding to trapping depths of 1.4-2.4 km and 1.1-1.7 km, respectively. [ABSTRACT FROM AUTHOR]

The Sharang porphyry Mo deposit is the first discovered Mo porphyry-type deposit in the Gangdese Metallogenic Belt. The orebody is hosted by the Eocene multi-stage composite intrusive complex which is emplaced in the Upper Permian Mengla Formation and cut by the Miocene dykes. Granite porphyry is recognized as the ore-bearing porphyry in the complex, which consists of quartz diorite, quartz monzonite, granite, prophyritic granite and post-mineral lamprophyre. Granodiorite porphyry and dacite porphyry intrude the granite porphyry. Geochemical data indicate that Sharang complex has a High-K calc-alkalinc to shoshonitic, metaluminous to slightly peraluminous composition. The Sharang complex rocks are enriched in large ion lithophile elements, depleted in high-field strength elements, Nb, Sr, P and Ti. REE patterns show slight enrichments in light REE relative to heavy REE and weak negative Eu anomalies. All rocks in this complex have a wide range of initial 87Sr/86Sr ratios (0.705605∼0.712496) and lower εNd(t) values (−0.61∼−7.80). The geochemical data suggest highly oxidized-evolved magma and old continental materials may have been the magma source for the Sharang intrusive complex that host porphyry Mo mineralization. Eocene pre-ore and ore-forming rocks at Sharang may have formed by partial melting of mantle wedge and by mixing with old continental crust at the lower crust level. In contrast the post-ore rocks may have formed by partial melting of enriched lithospheric mantle. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Duolong gold-rich porphyry copper deposit is a newly discovered deposit with proven 5.38 Mt Cu resources of 0.72% Cu and 41 t gold of 0.23 g t−1 in northern Tibet. Granodiorite porphyry and quartz diorite porphyrite are the main ore-bearing porphyries. A wide range of hydrothermal alteration associated with these porphyries is divided into potassic, argillic and propylitic zones from the ore-bearing porphyry center outward and upward. In the hydrothermal alteration zones, secondary albite (91.5-99.7% Ab) occurs along the rim of plagioclase phenocryst and fissures. Secondary K-feldspar (75.1-96.9% Or) replaces plagioclase phenocryst and matrix or occurs in veinlets. Biotite occurs mainly as matrix and veinlet in addition to phenocryst in the potassic zone. The biotite are Mg-rich and formed under a highly oxidized condition at temperatures ranging from 400°C to 430°C. All the biotites are absent in F, and have high Cl content (0.19-0.26%), with log (XCl/XOH) values of −2.74 to −2.88 and IV (Cl) values of −3.48 to −3.35, suggesting a significant role of chloride complexes (CuCl2- and AuCl2-) in transporting and precipitating copper and gold. Chlorites are present in all alteration zones and correspond mainly to pycnochlorite. They have similar Fe/(Fe+Mg), Mn/(Mn+Mg) ratios, and a formation temperature range of 280-360°C. However, the formation temperature of chlorite in the quartz-gypsum-carbonate-chlorite vein is between 190°C and 220°C, indicating that it may have resulted from a later stage of hydrothermal activity. Fe3+/Fe2+ ratios of chlorites have negative correlation with AlIV, suggesting oxygen fugacity of fluids increases with decreasing temperature. Apatite mineral inclusions in the biotite phenocrysts show high SO3 content (0.44-0.82%) and high Cl content (1-1.37%), indicating the host magma had a high oxidation state and was enriched in S and Cl. The highest Cl content of apatite in the propylitic zone may have resulted from pressure decrease, and the lowest Cl content of apatite in the argillic zone may have been caused by a low Cl content in the fluids. The low concentration of SO3 content in the hydrothermal apatite compared to the magmatic one may have resulted from the decrease of oxygen fugacity and S content in the hydrothermal fluid, which are caused by the abundant precipitation of magnetite. [ABSTRACT FROM AUTHOR]

An exploration targeting model for Gangdese porphyry copper deposit in Tibet, China, is constructed based on (i) the age of porphyry intrusions within Gangdese magmatic arc; (ii) the regional-scale normal E-W, N-S and N-E striking faults; and (iii) comprehensive anomalously high concentrations of Cu-Mo-Au-Ag-Pb-Zn. These targeting elements are derived from geological map and geochemical dataset, and are integrated by weights of evidence with the aid of geographic information system (GIS). The resulting prospectivity for porphyry copper deposits delineated by posterior probability demonstrates that the target areas extend along the Yaluzangbujiang River and contain the two large deposits, Qulong and Chongjiang, located in the eastern and central part of the Gangdese belt, respectively. These results indicate that the proposed exploration targeting model is a potential tool to map regional-scale mineral prospectivity. The target areas with high values of favorability, especially where high concentrations of Cu-Mo-Au-Ag-Pb-Zn are present, are the potential areas for finding undiscovered porphyry copper deposits. [ABSTRACT FROM AUTHOR]