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Shoshonitic rocks are widely distributed in post-collisional settings and provide key information on deep geodynamic mechanisms and magmatic evolution. In this paper, we present petrographic, zircon U-Pb age-related, trace elemental, Hf isotopic, bulk-rock elemental, and Sr-Nd isotopic data of the Dalongtan shoshonitic syenite porphyries (DSSPs) in central Yunnan, southeastern Tibet. The DSSPs formed at 33.2 ± 0.3 Ma in a post-collisional setting. They define linear trends on Harker diagrams, and they display similar trace element patterns and enriched bulk-rock Sr-Nd isotopes [(87Sr/86Sr)i = 0.70964–0.70968, εNd(t) = −12.9 to −12.7] and zircon Hf isotopes (εHf(t) = −15.7 to −13.1) to the coeval mantle-derived potassic mafic rocks. This suggests that the DSSPs were fractionated from the lithospheric mantle-derived mafic magmas. The DSSPs, along with the coeval felsic and mafic magmatic rocks (37.2–32.3 Ma), exhibit a planar distribution on the SE Tibet and predate the left-lateral shearing of the Ailaoshan–Red River shear zone (ARSZ) (32–22 Ma), suggesting that there are no genetic relationships between them. The DSSPs have geochemical characteristics similar to those of A-type granites, with high total alkalinity (10.39–11.17 wt.%), HFSE concentrations (Zr + Nb + Ce + Y = 890.2–1054.3 ppm), Ga/Al ratios (10,000 × Ga/Al = 2.95–3.46), whole-rock zircon saturation temperatures (906–947 °C), and oxygen fugacity (ΔFMQ = +3.30–+4.65), indicating that they are products of the high-temperature melting of the lithosphere as a result of asthenosphere upwelling in extensional settings. Based on our data and regional observations, it is proposed that the generation of the DSSPs may be linked to the convective thinning of the thickened lithospheric mantle following the India–Asia collision. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Bangbule skarn lead‐zinc (Pb‐Zn) deposit (>1 Mt Zn + Pb) is located in the western Nyainqentanglha polymetallic metallogenetic belt, central Tibet. Lenticular orebodies are all hosted in skarn and developed in the contact zone between the quartz porphyry and carbonate strata of the mid Paleozoic Middle to Upper Chaguoluoma Formation as well as in carbonate and sandstone beds of the Upper Paleozoic Laga Formation. As a newly discovered skarn deposit, the geological background and metallogenesis of this deposit remain poorly understood. Detailed petrological, geochemical and geochronological data of the ore‐related quartz porphyry, helps constrain the mineralization age and contributes to discussion on the ore genesis of the Bangbule deposit. Both endoskarn and exoskarn are identified in the Bangbule deposit. From quartz porphyry to carbonate formation, the exoskarn is zoned from proximal garnet skarn to distal pyroxene skarn. Zircon U‐Pb dating results show that the quartz porphyry formed at 73.9 ± 0.8 Ma. Geochemical analysis results show that the quartz porphyry has high contents of SiO2 (71.40–74.94 wt%) and K2O + Na2O (3.76–8.46 wt%) with A/CNK values of 0.69 to 1.06. Besides, the quartz porphyry is enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and have low εNd(t) (from –8.25 to –8.19) and high initial (87Sr/86Sr)i values (0.713611–0.714478). Major, trace elements and whole‐rock F concentration analysis results from the endoskarn samples show higher TFe2O3, MgO, CaO, Pb + Zn, W, Sn, Mo and F etc., and lower alkalis (K2O, Na2O, Sr and Ba) than those of fresh quartz porphyry, indicating that the early ore‐forming fluids were an Ca‐Fe‐F‐enriched fluid. Massive ore in the proximal skarn might be related to the high F content in the magma, which lowered the solidus temperature of the quartz porphyry magma and caused a lower temperature of the ore‐forming fluids, as well as facilitating the precipitation of sphalerite and galena. Based on the geochemical characteristics presented in this study, we propose that the ore‐related quartz porphyry was formed by partial melting of crust materials with some juvenile crustal component input. The partial melting of the middle‐upper crust after the initial enrichment of lead and zinc elements are important for the formation of Pb‐Zn deposits. The case study of the Bangbule deposit has proven that there is still a crust‐derived magmatic source region in the western segment of the central Lhasa terrane. Therefore, there is still great potential for Pb‐Zn mineralization and Pb‐Zn exploration. [ABSTRACT FROM AUTHOR]

The Mamupu skarn‐type Cu‐Au polymetallic deposit represents the first discovery of a medium deposit in the southern Yulong porphyry copper belt (YPCB), eastern Tibet. The Cu‐Au mineralization mainly occurs as chalcopyrite in breccia, within the plate‐like carbonate interlayer, being closely related to chloritization (e.g., chlorite, magnetite and epidote) and skarnization (e.g., diopside, tremolite and garnet). The ore‐related quartz syenite porphyry (QSP) and granodiorite porphyry (GP) were emplaced at 40.1 ± 0.2 Ma and 39.9 ± 0.3 Ma, respectively. The QSP of Mamupu is an alkaline‐rich intrusion, relatively enriched in LREE, LILE, depleted in HFSE, with no significant negative Eu and Ce anomalies, slightly high (87Sr/86Sr)i, low ∊Nd(t), uniform (206Pb/204Pb)i and ∊Hf(t) values, which indicates that the porphyry magma may be caused by both the mixing of metasomatized EM II enriched mantle and thickened juvenile lower crust. The QSP in the Mamupu deposit shares a similar genesis of petrology to other ore‐related porphyries within the YPCB. High oxygen fugacity and water content of the magmas are essential for the formation of porphyry and skarn Cu deposits. The QSP has similar high magmatic oxidation states and water content to the Yulong deposit, which indicates that the Mamupu has a high prospecting potential. Differences in the geological characteristics and scale of mineralization between the Mamupu and other YPCB deposits may be due to the different emplacement depths of ore‐related intrusions, as well as differences in the surrounding rocks. [ABSTRACT FROM AUTHOR]

Crustal growth is commonly associated with porphyry deposit formation whether in continental arcs or collisional orogens. The Miocene high-K calc-alkaline granitoids in the Gangdese belt in southern Tibet, associated with porphyry copper deposits, are derived from the juvenile lower crust with input from lithospheric mantle trachytic magmas, and are characterized by adakitic affinity with high-Sr/Y and La/Yb ratios as well as high Mg# and more evolved isotopic ratios. Researchers have argued, lower crust with metal fertilization was mainly formed by previous subduction-related modification. The issue is that the arc is composed of three stages of magmatism including Jurassic, Cretaceous, and Paleocene--Eocene, with peaks of activity at 200 Ma, 90 Ma, and ca. 50 Ma, respectively. All three stages of arc growth are essentially similar in terms of their whole-rock geochemistry and Sr-Nd-Hf isotopic compositions, making it difficult to distinguish Miocene magma sources. This study is based on ~430 bulk-rock Sr-Nd isotope data and ~270 zircon Lu-Hf isotope data and >800 whole-rock geochemistry analyses in a 900-km-long section of the Gangdese belt. We found large scale variations along the length of the arc where the Nd-Hf isotopic ratios of the Jurassic, Cretaceous, and Paleocene--Eocene arc rocks change differently from east to west. A significant feature is that the spatial distribution of Nd-Hf isotopic values of the Paleocene--Eocene arc magmas and the Miocene granitoids, including metallogenic ones, are "bell-shaped" from east to west, with a peak of εNd(t) and εHf(t) at ~91°E. In contrast, the Jurassic and Cretaceous arc magmas have different isotopic distribution patterns as a function of longitude. The isotopic spatial similarity of the Paleocene--Eocene and Miocene suites suggests that the lower crust source of the metallogenic Miocene magmas is composed dominantly of the Paleocene--Eocene arc rocks. This is further supported by abundant inherited zircons dominated by Paleocene--Eocene ages in the Miocene rocks. Another important discovery from the large data set is that the Miocene magmatic rocks have higher Mg# and more evolved Sr-Nd-Hf isotopic compositions than all preceding magmatic arcs. These characteristics indicate that the involvement of another different source was required to form the Miocene magmatic rocks. Hybridization of the isotopically unevolved primary magmas with isotopically evolved, lithospheric mantle-derived trachytic magmas is consistent with the geochemical, xenolith, and seismic evidence and is essential for the Miocene crustal growth and porphyry deposit formation. We recognize that the crustal growth in the collisional orogen is a two-step process, the first is the subduction stage dominated by typical magmatic arc processes leading to lower crust fertilization, the second is the collisional stage dominated by partial melting of a subduction-modified lower crust and mixing with a lithospheric mantle-derived melt at the source depth. [ABSTRACT FROM AUTHOR]

Large‐scale Cenozoic magmatic rocks from the interplay between the Indian and Eurasian plate are exposed in the Yulong porphyry copper belt in the northern Jinshajiang–Ailaoshan domain. Alkali‐rich magmas along the Yulong porphyry copper belt can reveal the tectono‐magmatic processes in the Sanjiang region. In this study, we present new zircon U–Pb–Hf isotopes and whole rock geochemistry of Cenozoic granitoids from the Zhalaga area in the northern Yulong porphyry copper belt. The Zircon U–Pb dating results show that the Zhalaga granitic porphyry crystallized at ca. 42–38 Ma. These porphyry deposits are depleted in Nb, Ta, Sr, and Ti enriched in alkaline and rare earth elements (REEs), and exhibit high zircon saturation temperatures, that strongly indicate A‐type affinity. These data and the generally positive ∊Hf(t) values (2.0–4.5) suggest the magmas originated from a hybrid of partial melting of subduction‐modified lithospheric mantle, possibly triggered by upwelling of the asthenospheric mantle. Geochronological and geochemical data of the current and previous studies distinguish three magmatic phases during the Cenozoic in the Jinshajiang–Ailaoshan region: (1) ca. 62–48 Ma; (2) ca. 44–30 Ma; and (3) ca. 28–16 Ma. The strong collision between the Indian and Eurasian plates produced relatively fast convergence rates during the first episode (ca. 62–48 Ma), whereas the subsequent right‐lateral strike‐slip faulting in the Jinshajiang fault zone initiated at ca. 43 Ma is associated with the relatively low India–Eurasia convergence rates during ca. 44–30 Ma. These significantly impacted the nature and spatial distribution of the magmatism and the large‐scale metallogeny during the Cenozoic in the Sanjiang region. We suggest that the Zhalaga alkali‐rich magmas occurred in a transition period from involving soft to hard collisional settings. This remarkable example demonstrates that alkali‐rich magmas with A‐type affinity are also generated in an orogenic tectonic setting. [ABSTRACT FROM AUTHOR]

The Zegulangbei deposit develops a complete porphyry metallogenetic system, whose magmatic emplacement and mineralization was similarly related to an isolated apophysis derived from a uniform shallow magmatic chamber as the Main deposit. Jiama is a complex porphyry metallogenetic system composed of several isolated magmatic-hydrothermal centers. Multi-types of mineralization and alteration coexist among these metallogenetic centers, partially overlapped, developed with complicated and various metallogenic elements. [Display omitted] • Geological features of Zegulangbei deposit were identified in the Jiama ore district. • Precise geochronology redefine the magmatism, alteration and mineralization age. • Main deposit and Zegulangei deposit have originated from the same magma source. • Jiama is a polycentric, complex porphyry mineralization system. Jiama is a typical giant-scale collisional-type porphyry mineralization system of in the Gangdese metallogenic belt, Tibet. The Zegulangbei deposit is located in the northern part of the ore district, which was a recent discovery. In the Zegulangbei deposit, intrusions have developed in multiple stages and led to the formation of complex porphyry intrusions (2# porphyries), of which granodiorite porphyry and Ⅱ-quartz diorite porphyry occurred related to mineralization. Hydrothermal alteration surrounding the 2# porphyries is characterized by potassic, phyllic, and chlorite–sericite alteration, with minor propylitization, argillization and tourmalinization. Furthermore, veinlet-disseminated copper and molybdenum mineralization mainly occurred within the potassic and phyllic alteration zones. Partial copper mineralization developed within the chlorite–sericite alteration zone. The mineralization is comprised of porphyry Cu–Mo, hornfels Cu–Mo and skarn Cu–polymetallic ore bodies. Hydrothermal vein system developed well, including 5-staged veins (M-, A-, B-, C-, and D-type vein). The similar ages of intrusive rocks (15.8–14.5 Ma, U–Pb), biotite and sericite alteration minerals (15.04–15.02 Ma, 40Ar–39Ar), and molybdenite (14.9 Ma, Re–Os) indicate that the intermediate–felsic magmatic rock emplacement triggered the hydrothermal alteration and mineralization in the Zegulangbei deposit. Geochemistry and Sr–Nd–Pb isotopes of the intrusions in Zegulangbei are consistent with those of the intrusions in the Main deposit (1# porphyries) and the Miocene adakites that developed in the eastern Gangdese belt, implying they were generated from the partial melting of the thickened phlogopite-bearing juvenile crust that had been reworked by diapirs of the arc magma during subduction. The evidence presented in this study suggests that Zegulangbei developed a complete porphyry Cu–polymetallic mineralization system, which was related to the same magma chamber in the upper crust that caused the mineralization in the Main deposit. [ABSTRACT FROM AUTHOR]

The Baomai porphyry Cu-Mo deposit is a newly discovered deposit located in the northern section of the Yulong porphyry Cu belt, eastern Tibet. It is associated with Eocene biotite monzogranite intrusions that were emplaced into Paleoproterozoic Ningduo Group and Middle-Upper Triassic sedimentary rocks. A biotite monzogranite porphyry with a zircon U-Pb age of 42.7 Ma was intruded by several post-ore diorite porphyry dikes (ca. 37.8 Ma). Alteration mineral assemblages consistent with argillic, phyllic, and hornfels were identified in ore-bearing porphyries and host rocks at Baomai. Argillic and phyllic alteration assemblages are spatially related to high-grade Cu and Mo mineralization, whereas hornfels alteration is accompanied by weak Cu mineralization. Molybdenite from the mineralized porphyry returned a Re-Os isochron age of 42.6 Ma, and is considered to represent the age of porphyry-style mineralization at the deposit. Ore-bearing porphyries in Baomai are high-K (K 2 O/Na 2 O >1), alkaline-rich intrusions rich in LREE, LILE (e.g., Rb, U, K), depleted in HFSE (e.g., Nb, Ta, P and Ti) and contain absent or slightly negative Eu anomalies and no significant Ce anomalies. Slightly high 87 Sr/ 86 Sr ratios (0.7064–0.7076), low ε Nd(t) values (−2.5 to −4.6), uniform ( 206 Pb/ 204 Pb) i ratios (18.70–18.75) and positive ε Hf(t) values (0–5.3) of ore-bearing porphyries at Baomai indicate that they share the same or similar petrogenesis to other mineralized porphyries within the Yulong porphyry Cu belt. The porphyries were likely generated from partial melting of phlogopite-bearing amphibolite or amphibolite eclogite with a low degree of crystal fractionation, and related to enrichment mantle (EMII) transformed or mixed by older subducted slab-derived fluid. Actually, there are no significant three stages of ore-bearing magmatic activities in Yulong porphyry Copper belt (Hou et al., 2003b), Eocene intrusions (37–43 Ma) and regional strike slip faulting were all important factors in controlling the formation of these Cu-polymetallic deposits during the Eocene India-Tibetan collision. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Indian slab to the eastern of 93 °E constantly subducted with shallow angle beneath Tibetan lithosphere. • Juvenile pre-collisional magmas restored within Tibetan arc root are the key for porphyry mineralization in southeastern Tibet. • Shallow subducted Indian slab triggered reactivation of juvenile arc root material and caused porphyry mineralization. The 1500-km long Gangdese belt in southern Tibet shows uneven distribution of giant to large porphyry deposits over 45 Mt Cu mainly in the middle-east segment between longitude 87–92°E. However, the western (80–86°E) and eastern end (92–96°E) is generally barren. The recent discovery of Demingding, Cuibaizi and Tangbula porphyry deposits in the east of 92°E has attracted great attention on their origin. Recent high-resolution seismic imaging shows the torn Indian lithosphere subducts with diverse angle. In contrast to the middle-east segment with moderate angle Indian plate subduction, the southeastern Tibet is characterized with a shallow dip of subduction (eastern of Comei rift), where Demingding, Cuibaizi and Tangbula deposits are located. To reveal the formation mechanism of these deposits as well as the Indian slab motion pattern beneath them, we compiled reported whole rock major and trace elements, Sr and Nd isotope signature, zircon trace element, U-Pb ages and Hf isotope data of Miocene ore-related adakitic rocks from Demingding and Tangbula to the north, and Oligocene ore-barren adakitic rocks from Linchi to the south. There is a clear negative correlation between zircon U-Pb ages of rocks and their distance to Indus-Yarlung Zangbo suture: Linchi is around 20 km away from the suture, with an average U-Pb age of 27.1 Ma, while Demingding and Tangbula rocks are 50 and 90 km away from the suture, with ages of 20.3 and 19.7 Ma respectively. Granitoids from Linchi have less compatible element Ni and Cr contents of 4.07 and 5.84 ppm on average respectively, while those of Demingding (20.1 and 43.4 ppm) and Tangbula (5.52 and 7.90 ppm) are much higher. Ni and Cr as compatible elements are concentrated in mafic minerals, and are thus proper indicators for mantle imprint indicators. In addition, as shown by Sr-Nd isotopes, Linchi granitoids have features of ancient crust [(87Sr/86Sr) i = 0.7059 to 0.7085, ε Nd (t) = − 6.20 to −2.90], while Demingding and Tangbula granitoids show less radiogenic features [(87Sr/86Sr) i = 0.7059 to 0.7068, ε Nd (t) = − 3.27 to −1.70], which are more similar to coexisting juvenile arc. Demingding and Tangbula granitoids also show signature of high f O 2 and hydrous melt condition, as indicated by calculated f O 2 of ΔFMQ + 2, and amphibole fractionation indicated by decreasing Dy/Yb with SiO 2 , since amphibole favors MREE (Dy) rather than HREE (Yb). Combining above, our work shows that the Indian slab constantly subducted shallowly beneath these deposits, given no mantle-like signature of near-suture Oligocene adakitic rocks. We suggest the cause to the formation of Demingding, Tangbula and Cuibaizi deposits is the reactivation of pre-enriched arc root materials, triggered by constant northward migration of Indian slab. This is supported by similar isotope signature between Miocene Demingding and Tangbula ore-related porphyries and coexisting arc, and absence of coeval pre-collisional porphyry deposits. The essential components for these porphyry deposits, high f O 2 and water content, were also likely contributed from the pre-enriched juvenile arc root. [ABSTRACT FROM AUTHOR]

The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-(Au) deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet (China). Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate-felsic intrusions (ca. 123-120 Ma). Various epithermal ore and gangue mineral types were discovered in the middle-shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/39Ar dating of hydrothermal biotite (potassic zone), sericite (phyllic zone), and alunite (advanced argillic zone) in/around the ore-bearing granodiorite porphyry yielded 121.1±0.6 Ma (1σ), 120.8±0.7 Ma (1σ) and 117.9±1.6 Ma (1σ), respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb-Sr dated to be 117.5±1.8 Ma (2σ), representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic-hydrothermal system. The Tiegelongnan super-large Cu-(Au) deposit may have undergone a prolonged magmatic-hydrothermal evolution, with the major mineralization event occurring at ca.120-117Ma. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Luerma is the firstly discovered porphyry in western Gangdese. • The metallogenic of Luerma occurred at ca. ∼ 212 Ma, which thus represents the oldest known porphyry deposit in the Gangdese belt. • Five stages of porphyry copper (molybdenum-gold) mineralization has been put forward in Gangdise porphyry copper belt. Due to the difference of lithospheric structure between the eastern and western segment of Gangdese metallogenic belt, it is generally believed that porphyry copper deposits are mainly developed in the east. However, the newly discovered of Luerma porphyry copper deposit in the western segment of Gangdese provides an excellent research object for us to supplement this understanding. The molybdenite re-Os isotope dating of two samples from quartz veinlet ores (ca. 213.1 ± 5.2 Ma and ca. 212.0 ± 3.7 Ma), combined with the LA-ICP-MS zircon U-Pb dating of three ore-bearing quartz monzonite porphyry samples (ca. 212.7 ± 0.9 Ma, 213.1 ± 1.1 Ma, and ca. 211.8 ± 1.8 Ma), indicates a new generation of Late Triassic Luerma copper porphyry-type mineralization events in the western Gangdese magmatic belt. The Luerma porphyry is a strongly peraluminous shoshonite series rock, is rich in silicon total alkalis, potassium and aluminum, has low contents of calcium, magnesium, and iron. It is enriched in light rare earth elements and large ion lithophile elements, relatively depleted in heavy rare earth elements and high field strength elements, and has negative Eu anomalies and no Ce anomalies. The porphyry exhibits relatively low (87Sr/86Sr) i values (0.705617 on average), high ε Nd (t) values (0.63 on average), high ε Hf (t) values (11.98 on average), and young two-stage Hf model ages. The Luerma ore-related porphyries are most likely generated dominantly from partial melting of juvenile crust that formed by metasomatized mantle during the subduction of the NeoTethys Ocean to the Lhasa terrane and underwent crystal fractionation during the process. The deposit is currently the oldest and westernmost porphyry deposit in the Gangdese porphyry copper belt, providing evidence that porphyry copper mineralization in this belt began in at least the Late Triassic. [ABSTRACT FROM AUTHOR]

The Zhibula Cu skarn deposit (19.5 Mt ore @ 1.64%), near the Qulong porphyry Cu–Mo deposit, is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic-hydrothermal fluids and calcareous host rocks. Stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the Jurassic Yeba Formation. Endoskarn zonations for an outward trend are observed in the granodiorite, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and a dark red-brown garnet-bearing granodiorite. The Zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry (SIMS) zircon U–Pb ages of 16.9 ± 0.3 Ma and 17.0 ± 0.2 Ma, respectively. They exhibit different fractional crystallization from granodiorite (SiO 2 = 64.8–69.3 wt.%) to monzogranite (SiO 2 = 72.3–76.8 wt.%). Both the granodiorite and monzogranite are characterized by high Al 2 O 3 (12.6–16.7 wt.%) and K 2 O (1.5–5.5 wt.%) contents, high Sr/Y (35–151) and La/Yb (19–48) ratios, and variable MgO (0.16–3.91) and Mg# (31–61) values. They display features of enrichment in large ion lithophile elements (LILEs, e.g., Rb, Ba, Sr, and K), depletion in high field strength elements (HFSEs, e.g., Nb, Ta, Ti, and P), and moderate negative Eu anomalies (δEu = 0.58–0.98). They show restricted in situ zircon Hf isotopic compositions (+6.7 to +8.8; only one sample is +4.5) and consistent δ 18 O values (+6.0‰ to +6.6‰). The geochemical data indicated that the Miocene Zhibula granitic intrusions formed by the magma that were characterized by high Sr/Y ratios and were derived from the partial melting of the thickened juvenile lower crust, which may have been metasomatized by the slab melts during subduction of the Neo-Tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere. In addition, the Zhibula Cu skarn deposit and the Qulong Cu–Mo deposit form a significant porphyry–skarn ore system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Here we characterize the geology and mineralization of the Sangri porphyry-skarn Cu-Mo deposit. • Zircon and garnet U-Pb, molybdenite Re-Os and K-feldspar Ar-Ar geochronology link magmatism, mineralization and alteration. • The Multi-isotopic dating could help to construct the defined time-framework of porphyry system. Obtaining a precise time framework has been a key but difficult problem for the study of metallogenic porphyry systems. This is more complicated when there are several stages of intrusion emplacement, different alterations, and mineralization events. To solve this problem, the Sangri porphyry-skarn Cu-Mo deposit in the Bangongco-Nujiang metallogenic belt, Tibet, was used as a study site for multiple isotopic dating studies. Zircon U-Pb dating of different intrusions shows that the magmatism of intermediate-felsic intrusions dates from 83.2 ± 0.8 Ma to 81.7 ± 0.7 Ma. Garnet U-Pb dating places the skarn as being formed in 83.2 ± 2.3 Ma. Re-Os dating of molybdenite in quartz-molybdenite vein and Ar-Ar dating of K-feldspar indicate ore-forming and alteration periods of 82.6 ± 0.6 Ma and 80.3 ± 1.8 Ma, respectively. The Sangri deposit is a product of magmatic-hydrothermal mineralization between 84 and 80 Ma in the Late Cretaceous. The mineralization of the Sangri deposit and precise geochronology data indicate that there was a Late Cretaceous metallogenic event in the Central Bangongco-Nujiang metallogenic belt, which provides a new clue for regional exploration and metallogeny. Finally, multi-element isotopic dating is shown to be an important method for constructing the time framework of porphyry systems. [ABSTRACT FROM AUTHOR]

Abstract: The Duolong porphyry Cu–Au deposit (5.4Mt at 0.72% Cu, 41t at 0.23g/t Au), which is related to the granodiorite porphyry and the quartz–diorite porphyry from the Bangongco copper belt in central Tibet, formed in a continental arc setting. Here, we present the zircon U–Pb ages, geochemical whole-rock, Sr–Nd whole-rock and zircon in-situ Hf–O isotopic data for the Duolong porphyries. Secondary ion mass spectrometry (SIMS) zircon U–Pb analyses for six samples yielded consistent ages of ~118Ma, indicating a Cretaceous formation age. The Duolong porphyries (SiO2 of 58.81–68.81wt.%, K2O of 2.90–5.17wt.%) belong to the high-K calc-alkaline series. They show light rare earth element (LREE)-enriched distribution patterns with (La/Yb)N =6.1–11.7, enrichment in large ion lithophile elements (e.g., Cs, Rb, and Ba) and depletion of high field strength elements (e.g., Nb), with negative Ti anomalies. All zircons from the Duolong porphyries share relatively similar Hf–O isotopic compositions (δ18O=5.88–7.27‰; εHf(t)=3.6–7.3), indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization. This, along with the general absence of older inherited zircons, rules out significant crustal contamination during zircon growth. The zircons are mostly enriched in δ18O relative to mantle values, indicating the involvement of an 18O-enriched crustal source in the generation of the Duolong porphyries. Together with the presence of syn-mineralization basaltic andesite, the mixing between silicic melts derived from the lower crust and evolved H2O-rich mafic melts derived from the metasomatized mantle wedge, followed by subsequent fractional crystallization (FC) and minor crustal contamination in the shallow crust, could well explain the petrogenesis of the Duolong porphyries. Significantly, the hybrid melts possibly inherited the arc magma characteristics of abundant F, Cl, Cu, and Au elements and high oxidation state, which contributed to the formation of the Duolong porphyry Cu–Au deposit. [Copyright &y& Elsevier]

Abstract: We have determined the ages of the ore-bearing Bangpu porphyries and the age of formation of an associated Mo–Cu ore deposit using the LA–ICPMS zircon U–Pb and the molybdenite Re–Os methods. Zircons from two adamellite porphyries give ages of 14.07±0.08Ma and 14.96±0.16Ma, and zircons from a diorite porphyry give an age of 15.30±0.25Ma. The ages of three molybdenite samples are 14.96±0.23Ma, 15.08±0.23Ma and 16.61±0.23Ma. Light Rare Earth Elements (LREE) are enriched in the ore-bearing adamellite, which is shoshonitic and peraluminous, while Heavy Rare Earth Elements (HREE) and Y are strongly depleted, indicating an adakitic affinity. In contrast to other deposits formed in the post-collisional Gangdese belt, the Rb/Sr ratio in Bangpu is high, demonstrating more crustal contamination. The geochemistry of the ore-bearing diorite porphyry differs significantly from that of the ore-bearing adamellite. The diorite porphyry displays a reverse slope in its REE (Rare Earth Element) pattern, and is shoshonitic and metaluminous. The geochronology and geochemistry of both ore-bearing rocks indicate that the Bangpu ore deposit is related to two different source regions in a post-collisional environment. The metallic minerals formed mainly during the older diorite porphyry stage, but they were recycled and reactivated during adamellite magmatism. The sources of the mineralising fluids, and the evolution of the northern GPCB (Gangdese Porphyry Copper Belt), where the Bangpu ore deposit is located, are more complex than in the southern GPCB. [Copyright &y& Elsevier]

Abstract: 40Ar–39Ar step-heating experiments on eleven mineral separates have been conducted on eight volcanic rocks and a granite-porphyry dike from the Yangying and Wuyu basins in the middle Gangdese Belt, southern Tibet. New radiometric ages for sanidine and biotite separates in four volcanic rock samples from Yangying ranges from 10.32±0.07 to 11.40±0.11Ma, whereas plagioclase and biotite separates from a stratigraphic section of the Gaza Cun Formation in the Wuyu basin give ages from 12.57±0.08 to 13.2±0.2Ma. A granite-porphyry which cuts the lower part of the Gaza Cun Formation gives an age of 11.09±0.07Ma, and a dacite from the margin of Wuyu basin gives an age of 15.48±0.11Ma. These age data, in conjunction with geochemical data, suggest that the mid-Miocene post-collisional volcanic rocks from these two basins have both similarities and difference in their petrogenesis. The high [Sm/Yb]N (>7) ratio and high Sr concentration (423–1065ppm) in both suites are consistent with their parental melts derived from partial melting of eclogitized lower crust. However, the Yangying samples are more evolved than the Wuyu samples as manifested by lower MgO, Sr/Sr∗, Eu/Eu∗, and normative plagioclase. It is likely that the source material for the Yangying suite is likely more enriched in K2O than that of the Wuyu suite, perhaps has a greater contribution from metasomatized lithospheric mantle. It is apparent that the post-collisional volcanism in southern Tibet occurred spatially scattered and temporally within a short period in each volcanic basin. [Copyright &y& Elsevier]

The Lakang'e porphyry Mo (Cu) deposit, intermediate to large in size, is located in the eastern part of the southern Gangdese metallogenic belt. It is associated with a Miocene granodiorite porphyry (GDP). The alteration styles are mainly potassic and phyllic alteration, with minor argillic, chlorite, and carbonation alteration. In this study, we present whole-rock geochemical compositions, zircon LA-ICP-MS U-Pb data, zircon Hf isotope analyses, and zircon and apatite major and trace element compositions for the ore-bearing GDP and postmineralization quartz diorite porphyry (QDP) to constrain the formation of the Lakang'e Mo (Cu) deposit. The ore-bearing GDP, with a zircon U-Pb age of 13.83 ± 0.20 Ma, was intruded after mineralization by the QDP, which was emplaced at 13.00 ± 0.16 Ma. The GDP and QDP are high-K calc-alkaline series rocks with adakite-like features characterized by high contents of K 2 O and Al 2 O 3 , high Sr/Y ratios, strongly fractionated REE patterns, LILE enrichment, and HFSE depletion. The GDP and QDP have relatively low (87Sr/86Sr) i values (0.7051–0.7054) and high εNd(t) values (−0.87 to 0.59). Zircon grains from the QDP have high εHf(t) values (7.0–9.6), while zircon grains from the GDP show large εHf(t) variations ranging from −4 to 9.6, indicating that the magma source of the ore-bearing GDP included more continental crust than that of the postmineralization QDP. The zircon Ce4+/Ce3+ and Eu/Eu* ratios and apatite Mn and SO 3 contents indicate that the postmineralization QDP had higher oxygen fugacity than the ore-bearing GDP. The oxygen fugacity of the ore-bearing magma present during apatite crystallization (generally below the Ni-Ni-O (NNO) buffer), was lower than that present during zircon crystallization (above the hematite-magnetite (HM) buffer). The F, Cl, and S contents in apatite show that the GDP and QDP were F and S rich and that the GDP had a higher F content than the QDP. A high oxygen fugacity, a F- and S-rich magma and a Mo-rich crustal source were the key factors for the formation of the Lakang'e porphyry Mo (Cu) deposit. From Lakange Mo (Cu) deposit to Jiama Cu polymetallic deposit to Qulong Cu-Mo deposit to Xiongcun Cu-Au deposits, the Cl contents in apatite gradually increase, but the F contents in apatite gradually decrease, and the S content is similar but variation. It indicates that the Mo-dominated porphyry deposit formed from F-S-rich magma, whereas the Cu-dominated porphyry deposit formed from Cl-S-rich magma. Unlabelled Image • Geological features were identified in the Lakange porphyry Mo (Cu) deposit. • Precise geochronology redefines the magmatism and mineralization age. • High f O 2 , F- and S-rich and Mo-rich crustal source are favorable for mineralization. [ABSTRACT FROM AUTHOR]