Xiang Fang's research while affiliated with Chinese Academy of Geological Sciences and other places

Jiama is a giant, high‐grade porphyry copper system in the Gangdese metallogenic belt, Tibet. Multistage intermediate‐felsic porphyries intruded in this deposit, some of which are strongly associated with copper–polymetallic mineralization. These ore‐bearing porphyries include monzogranite, granodiorite, and quartz diorite porphyries. A new granite aplite dyke was found in the south of Jiama. Its age, genesis, and relationship with ore‐related magmatism are obscure. Here, its emplacement age and petrogenesis were determined using mineralogy, zircon U–Pb dating, geochemistry, and Sr–Nd–Pb isotope studies. The zircon LA–ICP–MS U–Pb age of the aplite dyke is 16.66 ± 0.21 Ma (n = 14, MSWD = 0.66), earlier than that of the ore‐bearing porphyries (∼15 Ma) in Jiama. Furthermore, the aplite exhibits high amounts of silicon (SiO2 = 73.39%–74.74%), potassium (K2O = 5.12%–6.61%), aluminum (Al2O3 = 14.25%–14.69%), and light/heavy rare earth elements (LREE/HREE = 12.12–16.19) as well as negative europium (δEu = 0.47–0.72) and weak negative cerium anomalies (δCe = 0.84–0.93). The aplite dyke is characteristic of metaluminous–peraluminous I‐type granite, which is rich in large‐ion lithophile elements (Rb, Ba, Th, and U) and depleted in high‐field‐strength elements (Nb, P, and Ti). The aplite dyke and ore‐bearing porphyries in the Jiama deposit are the results of a partial melting of the juvenile lower crust, according to whole‐rock geochemistry and Sr–Nd–Pb isotope data, but the dyke and ore‐bearing porphyries were emplaced from the same magma chamber at different times. Thus, the aplite dyke shows the composition of the early evolution stage of shallow magma in the Jiama deposit and is the product of rapid condensation and crystallization.

The Tiegelongnan deposit is a giant deposit (>10 million tons Cu resources with an average grade of 0.53%) located in the west of the Bangong Co‐Nujiang metallogenic Belt, where typical porphyry and epithermal types of alteration and mineralization are developed. A compilation of geological features and mineralogical studies revealed that the Tiegelongnan deposit developed two stages of hydrothermal alteration. The early stage was related to porphyry emplacement, developing potassic, phyllic and propylitic alterations, telescoped by the late advanced argillic alteration in the shallow levels. Correspondingly, two stages of mineralization occurred, the early porphyry‐type mineralization being overlapped by the late high‐sulfidation epithermal mineralization. Due to differences in pH, log fO2, K+ activity and temperature of ore‐forming fluids, distinct sulfide minerals of low to extremely high sulfidation states, such as chalcopyrite, tennantite, enargite and covellite, precipitated throughout the entire hydrothermal process. The Tiegelongnan deposit is a complex porphyry metallogenetic system of ‘multiple structures’. The Early Cretaceous andesitic volcanic rocks of the Meiriqiecuo Formation exposed on the surface act as a cap for the ore body, beneath which an oxidizing‐leaching zone lies. Under the cap and the oxidizing‐leaching zone, a porphyry ore body is remoulded by high‐grade high‐sulfidation epithermal hydrothermal mineralization, which gradually transitions to continuous porphyry‐type mineralization at depth. On the basis of fieldwork and drill core logging data, combined with mineralogical studies, the Tiegelongnan deposit's hydrothermal alteration, mineralization and their correspondence are deciphered, while the controlling factors and geochemicophysics of alteration and mineralization are summarized and discussed, and the metallogenic model is established, with the aim to fertilize the ore‐prospecting theory of the porphyry–epithermal metallogenic system, providing guidance for regional exploration.

The Naruo porphyry copper deposit containing more than 2 Mt of copper is located in the Duolong ore district in the west of the Bangongco‐Nujiang belt in central Tibet. New zircon U‐Pb, biotite 40Ar/39Ar, zircon (U‐Th)/He ages, published age data together with thermal modeling were presented in this paper to investigate the thermal history of Naruo deposit. Thermal modeling reveals a prolonged magmatic‐hydrothermal evolution firstly cooling from ∼700 °C to ∼350 °C at 120 Ma, then cooling to 230 °C at 106 Ma and maintaining at 200 °C from 106 to 90 Ma which is attributed to multiple magmatic events and thermal effect of strike‐slip fault. Affected by thrust nappe structure, the sample was consistent with 120 °C from 70 Ma to 63 Ma. The Naruo deposit started to experience exhumation at a rate of ∼0.07 km/m.y since 60 Ma which is related to India‐Asia collision. The prolonged magmatic‐hydrothermal evolution process is crucial to the formation of giant ore body in the Naruo deposit. The ore‐related intrusions preserved in the foot walls of strike‐slip fault and thrust nappe structure are the objects of future exploration in the Duolong ore district.

Shangxu is an orogenic gold deposit in the Bangong-Nujiang suture zone, central Tibet, China, formed in the Early Cretaceous orogene, related to convergence and collision between the Qiangtang and Lhasa terranes. The mineralization at Shangxu is hosted by Jurassic turbidite sedimentary rocks of the Mugagangri Group, and is associated with a regional fault system. Hydrothermal minerals develop muscovite, carbonate, sulfides and chlorite. Hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis. The earliest is barren quartz stage (H1), which is pre-ore. During the early mineralization quartz-pyrite stage (H2a), defined by massive quartz veins with minor euhedral pyrite and gold, hydrothermal fluids had a δ¹⁸Ofluid of 6.1–6.4‰, δD of −74 to −116‰, δ¹³CCO2 of −5.4 to −7.6‰, and δ³⁰Si of −0.1‰. In the quartz-pyrite-sulfides stage (H2b), characterized by abundant quartz, granular pyrite, muscovite with minor chalcopyrite, galena, sphalerite and gold, fluids had a δ¹⁸Ofluid of 7–8.2‰, δD of −109 to −120‰, δ¹³CCO2 of −9.6‰ and δ³⁰Si of −0.1 to −0.2‰. During the ankerite-sulfide stage (H3a), distinguished by abundant ankerite, muscovite, sulfides with minor quartz and chlorite, hydrothermal system had a fluid with δ¹⁸Ofluid of 4.9–5.3‰, δD of −125.3‰, δ³⁰Si of −0.1‰, δ¹³CCO2 of −12.4‰ in quartz inclusion fluid and δ¹³CCO2 of −2.7‰ in ankerite. The calcite-sulfide stage (H3b) is characterized by calcite, sulfides, with minor quartz and chlorite. Quartz formed earlier than calcite from a fluid having a δ¹⁸Ofluid of 6.4‰, δD of −112.6‰, δ³⁰Si of −0.1‰, and δ¹³CCO2 of −7.4‰, after which calcite precipitated from a hydrothermal fluid with δ¹⁸Ofluid of 5.5–9‰, δ¹³CCO2 of −0.5 to −2.8‰. Hydrothermal fluids in H2b pyrite have ³He/⁴He ratios of 0.27–0.42Ra and ⁴⁰Ar/³⁶Ar ratios of 313–372. The stable isotope composition of hydrothermal fluids from the Shangxu gold deposit is similar to that of typical orogenic gold deposits. The early stage (H1), methane-bearing fluids were probably sourced from the basin sediments, leading to precipitation of early barren quartz veins and siderite alteration. From the quartz-sulfide stage (H2) to carbonate-sulfide stage (H3), hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth. The decreasing δD and δ¹³C of the ore-forming fluids from early to late suggests mixing with δ¹³C-depleted oxidized graphite in sedimentary rocks, meteoric waters or reation between δD-depleted organic matters. Generally, these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the Mugagangri Group. Sulfur and gold, by inference, likely originated from sedimentary/diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies, and migrated with the metamorphic fluids. During transportation to the site of deposition, gold-bearing fluids variably reacted with country rocks.

Shangxu is an orogenic gold deposit within the Bangong-Nujiang suture zone, central Tibet, China. It is hosted by turbidite sedimentary rocks of the Jurassic Mugagangri Group. The host rocks were metamorphosed to subgreenschist facies prior to being hydrothermally altered adjacent to mineralization. Hydrothermal minerals in wall rocks consist of muscovite, carbonate, sulfides and chlorite. Whole rock geochemistry indicates hydrothermal alteration is characterized by the introduction of K2O, CO2 and S, and leaching of Na2O. Increasing 3K/Al and decreasing Na/Al alteration indexes approaching the ore correlate to muscovitization. CO2 concentration reflects the degree of carbonation, which in conjunction with molar (Mn+Fe)/(Fe+Ca+Mg+Mn) and CO2/CaO can be used to distinguish siderite from ankerite in carbonate alteration. Mass transfer analysis shows gains in As, Au, CO2, W, Ca, Cd, Ni, Cr, Sr, Rb, K and losses in Na, Pb, Cu during hydrothermal alteration. In the muscovite alteration zone, muscovite within shear zones (Ms1) shows an increase in Fe, Mg and Na towards the ore, whereas metamorphic muscovite along cleavage planes and in pressure shadows (Ms2), and hydrothermal muscovite (Ms3) change in composition from phengitic (Mg, Fe) distal to mineralization, to paragonitic (Na) adjacent to gold. In carbonate alteration, the composition in carbonate phases changes from early magnesian siderite to ankerite, and then to calcite and dolomite during the evolution of the hydrothermal system. Siderite spots in host rocks and ankerite in veins, wall rock or its replacement of siderite are all enriched in Fe, Mn and depleted in Mg from proximal to distal alteration zones. Pyrite is a dominant mineral in sulfide alteration of the Shangxu deposit. The earliest framboidal pyrite (Py1) formed during diagenesis, and overprinted by Py2, which is recrystallized pyrite associated with burial metamorphism. Py3 rims and enlarges previous pyrite aggregates, or recrystallizes into cubic grains with cracks and quartz pressure shadows during deformation. Py4 is ore-related euhedral pyrite, disseminated near gold, and formed in hydrothermal stage. Vein pyrite (Py5) coexists with marcasite, and fills cracks in quartz veins. Hydrothermal alteration minerals form overlapping alteration haloes surrounding the main auriferous lodes. Distal muscovitization, carbonatization and proximal sulfidation constitute a progressive alteration front from gold. The alteration envelope is tabular in shape, following the strike and dip of the mineralization, and tends to be the widest around the thickest parts of the ore, such that the occurrence and thickness of the alteration envelope can be used as an approximate guide to the size of gold mineralization. Shangxu shares many diagnostic features with turbidite-hosted orogenic gold deposits, such as Bendigo, Reefton and Meguma districts, in deposit geology, alteration mineralogy and lithogeochemistry.

The newly discovered Tiegelongnan Cu (Au) deposit is a giant porphyry deposit overprinted by a high-sulfidation epithermal deposit in the western part of the Bangong–Nujiang metallogenic belt, Duolong district, central Tibet. It is mainly controlled by the tectonic movement of the Bangong–Nujiang Oceanic Plate (post-subduction extension). After the closure of the Bangong–Nujiang Ocean, porphyry intrusions emplaced at around 121 Ma in the Tiegelongnan area, which might be the result of continental crust thickening and the collision of Qiangtang and Lhasa terranes, based on the crustal radiogenic isotopic signature. Epithermal overprinting on porphyry alteration and mineralization is characterized by veins and fracture filling, and replacement textures between two episodes of alteration and sulfide minerals. Alunite and kaolinite replaced sericite, accompanied with covellite, digenite, enargite, and tennantite replacing chalcopyrite and bornite. This may result from extension after the Qiangtang–Lhasa collision from 116 to 112 Ma, according to the reopened quartz veins filled with later epithermal alteration minerals and sulfides. The Tiegelongnan deposit was preserved by the volcanism at ~110 Ma with volcanic rocks covering on the top before the orebody being fully weathered and eroded. The Tiegelongnan deposit was then probably partly dislocated to further west and deeper level by later structures. The widespread post-mineral volcanic rocks may conceal and preserve some unexposed deposits in this area. Thus, there is a great potential to explore porphyry and epithermal deposit in the Duolong district, and also in the entire Bangong–Nujiang metallogenic belt.

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.