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We present in‐situ zircon laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U–Pb ages, whole‐rock geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern margin of the Qiangtang Block, Tibet, western China. The zircons yield a U–Pb age of ca. 123 Ma. The hornblende‐bearing monzogranite shows metaluminous to weak peraluminous and high‐K calc‐alkaline characteristics exemplified by high silica (SiO2 = 67.57–70.57 wt%), high aluminium (Al2O3 = 14.68–15.78 wt%), high potassium (K2O = 4.00–5.14 wt%), high alkali (K2O + Na2O = 7.88–8.62 wt%), and low calcium contents (CaO = 1.72–2.17 wt%), with the aluminium saturation index (A/CNK) ranging from 0.98 to 1.09, suggesting that the Mugagangri monzogranite is a metaluminous to weak peraluminous I‐type high‐K calc‐alkaline granite. Geochemically, similar to the arc magmas, the monzogranite is enriched in large‐ion lithophile elements, and relatively depleted in high‐field‐strength elements. The monzogranite displays relatively high (87Sr/86Sr)i values (0.70972–0.71240), uniform εNd(t) values (−2.24 to −3.40), variable zircon εHf(t) values (−14.1 to +8.0), and high radiogenic Pb isotopic values (206Pb/204Pb = 18.588–18.790, 207Pb/204Pb = 15.616–15.642, and 208Pb/204Pb = 38.838–39.053). These geochemical characteristics indicate that the monzogranite was derived from a mixed source comprising ancient crustal and mantle materials, and experienced fractional crystallization during emplacement. We propose that the parental magma of the Mugagangri monzogranite was most likely generated during northward subduction of the Bangong Co‐Nujiang Meso‐Tethys Ocean. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is characterized by the largest crustal thickness on Earth, although the timing of formation of the plateau remains debated. In this study, we present in situ laser ablation‐inductively coupled plasma‐mass spectrometry zircon U–Pb ages and Hf isotopes, and whole‐rock geochemical data on porphyritic granitoids of Sebuta in the central Lhasa block. Our zircon U–Pb data indicate that these rocks emplaced at ca. 89 Ma, in the early Late Cretaceous. Geochemically, the Sebuta biotite granite porphyry can be broadly divided into two subtypes, namely metaluminous porphyry and peraluminous porphyry. The metaluminous porphyry has high SiO2, Al2O3, Sr, low Y and Yb contents, and high Sr/Y and LaN/YbN ratios, showing adakitic features. These rocks have high K2O and Th contents, low Ti/Eu and Nd/Sm ratios, indicative of a continental crust affinity. Positive zircon εHf(t) values, along with high Mg#, Cr and Ni, imply that the Sebuta adakitic porphyry was most likely derived from partial melting of a delaminated thickened juvenile lower crust, and that the initial melts interacted with mantle peridotite during ascent. The field features, petrographic characteristics, formation age, ore‐bearing potential, and Hf isotope of the peraluminous porphyry are similar to those of the Sebuta adakitic porphyry, indicating that the peraluminous porphyry was likely formed by contamination with ancient crustal material and fractional crystallization from the same primary adakitic magmas which generated the Sebuta adakitic porphyry. Residual phases of amphibole + plagioclase + garnet + rutile in the source region, together with previous studies, suggest that the crust beneath the central‐northern Lhasa block experienced thickening during the early Late Cretaceous, and had already been thickened to more than 50 km by the Late Cretaceous (ca. 89 Ma). [ABSTRACT FROM AUTHOR]

Himalayan leucogranites are widely distributed in the North Himalayan gneiss dome (NHGD) and at the top of the Greater Himalayan Crystalline Complex (GHC) and are generally controlled by detachment faults. The ages of these prekinematic, synkinematic, and postkinematic leucogranites can be used to limit the activity of detachment structures (such as the South Tibetan Detachment System, STDS). Research on the STDS activity time in the eastern Himalayas is relatively sparse. In this study, the zircon and monazite U–Th–Pb geochronology of synkinematic and postkinematic leucogranites, which are affected by the STDS and NHGD, in four areas (Lhozhag, Kuju, Xiaozhan, and Cuonadong) in Shannan City, Tibet, China, was measured. The results show that the oldest synkinematic two‐mica granite from Lhozhag, which is affected by the STDS, is 24–25 Ma, so the time of STDS activity is at or slightly earlier than 25 Ma. The youngest synkinematic leucogranite is the garnet‐bearing muscovite granite in Cuonadong at 18.4 Ma. The oldest undeformed postkinematic leucogranite (not affected by the STDS) is the muscovite granite in Xiaozhan at 17.4 Ma. Therefore, the end of STDS activity can be limited to 18.4–17.4 Ma. The STDS includes three forms: detachment fault in the NHGD (northern extension of the STDS), the inner STDS between the GHC and Tethyan Himalayan Sequence, and the outer STDS at the bottoms of synformal klippes. In this paper, the active time limits of the above three kinds of detachment zones are comprehensively summarized. Based on this work, the northward extension (ductile deformation) time of the STDS in the region is considered to be 28–17 Ma. The exhumation of the GHC is mainly controlled by in‐sequence shearing: first, the South Tibet Thrust system (predecessor of the STDS) at the top of the GHC thrust southward at 45–28 Ma, then the High Himalayan Discontinuity fault in the middle of the GHC forms south‐vergent ductile thrusts at 28–17 Ma, and finally, the Main Central Thrust at the bottom of the GHC thrust southward at 17–9 Ma. [ABSTRACT FROM AUTHOR]

Miocene postcollisional potassic and adakitic rocks are widely distributed in the southern Lhasa terrane and western central Lhasa terrane. However, coeval potassic and adakitic rocks in eastern central Lhasa terrane were rarely recognized, and their origins and formation mechanism remain controversial. In this paper, we provide new geochronological and geochemical data for the Miocene postcollisional potassic and adakitic intrusions exposed in the Qingdu area, eastern central Lhasa terrane, southern Tibet. The Qingdu Miocene intrusions consist of quartz monzonite porphyry and biotite granite with coeval zircon U–Pb ages of 14.1 Ma and 14.0 Ma, respectively. They have high SiO2 (67.98–75.32 wt.%), Al2O3 (14.13–14.78 wt.%), and K2O (4.06–6.18 wt.%) and low MgO (0.25–1.46 wt.%) contents. They are both enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with high (La/Yb)N (25.37–42.32) ratios. The biotite granite samples have low Y (7.10–9.96 ppm) and Yb (0.61–0.85 ppm) contents, and high Sr (229–384 ppm) contents and high Sr/Y (30–41) ratios, which show adakitic geochemical characteristics, whereas the quartz monzonite porphyry samples show potassic geochemical characteristics. They display initial (87Sr/86Sr)i ratios of 0.7083–0.7103, εHf(t) values of −6.7 to −0.1, εNd(t) values of −8.96 to −7.44, (208Pb/204Pb)i ratios of 39.028–39.110, (207Pb/204Pb)i ratios of 15.662–15.684, and (206Pb/204Pb)i ratios of 18.541–18.577. These signatures indicate that both the potassic and adakitic intrusions are more likely to originate from partial melting of a thickened lower crust, which were mainly the products of the binary mixing between the juvenile and ancient crust components. Based on the spatial distributions and isotopic features of the postcollisional potassic and adakitic rocks in the Lhasa terrane, we suggest that the differences of the lower crustal composition played a crucial role in causing the geochemical variations of the Miocene postcollisional adakitic and potassic rocks in Lhasa terrane. [ABSTRACT FROM AUTHOR]

The Duolong porphyry Cu-Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole-rock elemental and Sr-Nd-Pb isotope and zircon Hf isotopic data of syn- and post-ore volcanic rocks and barren and ore-bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu-Au mineralization. LA-ICP-MS zircon U-Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore-bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post-ore basaltic andesite. All the samples show high-K calc-alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc-type magmas. Syn- and post-ore volcanic rocks show initial Sr ratios of 0.7045-0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408-18.642, (207Pb/204Pb)t of 15.584-15.672 and positive zircon εHf(t) values of 1.3-10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore-bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054-0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5-9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong-Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Bangong- Nujiang suture ( BNS) between the Lhasa and Qiangtang terranes is an important boundary and its petrogenesis is controversial. Diabase from the accretionary prism in the southern Qiangtang terrane yields a zircon U- Pb age of 181.3 ± 1.4 Ma. All the diabases show tholeiitic basalt compositions, gentle enrichment patters of light rare earth elements ( REE), variable enrichment in incompatible element concentrations (e.g. Th and Rb), and no anomaly in high field strength elements (e.g. Nb and Ta), similar to that of enriched mid-ocean ridge basalt ( E- MORB). They have relatively homogeneous whole rock Nd (ε Nd(t) = 7.3-9.1) and zircon Hf- O isotopic compositions (ε Hf(t) = 14.8-16.1, and δ18 O = 4.57-6.12‰), possibly indicating melting of the depleted mantle and no significant crustal contamination during the petrogenesis. The element variations suggest that the diabases were formed by plume-ridge interaction at a mid-ocean ridge within the Bangong- Nujiang ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • Skarn-type mineralization of the Cuonadong Sn-W-Be polymetallic deposit occurred at ca. 15 Ma. • Skarn-hosted scheelite can be divided into an older type 1 scheelite and a younger type 2 scheelite. • The ore-forming fluid was exsolved from the Cuonadong Miocene leucogranite. • Geochemically and isotopically, the ore-forming fluid was modified by intense fluid-rock interaction during skarnization and greisenization. The Cuonadong Sn-W-Be polymetallic deposit is the first rare-metal deposit with an extraordinary metallogenic potential that has been discovered in the Tethyan Himalayan metallogenic belt. The deposit shows a wide range of different mineralization types, including greisen-, pegmatite-, skarn-, and hydrothermal vein-type mineralization. Of these mineralization types, the skarn-type has the largest inferred resources. In order to constrain the source and evolution of the ore-forming fluid, we conducted a detailed study of the skarn-hosted scheelite, including cathodoluminescence imaging, in-situ trace elemental analysis, and bulk Sr isotope analysis. In addition, bulk Sr isotope analysis of fluorite, phlogopite 40Ar-39Ar dating, and marble whole-rock geochemical analysis were also conducted. Phlogopite 40Ar-39Ar dating indicates that the skarn was formed at ca. 15 Ma, which is close to the formation age of the Cuonadong muscovite granite reported in previous studies. Cathodoluminescence images indicate that skarn-hosted scheelite can be subdivided into an older type 1 scheelite and a younger type 2 scheelite. Type 1 scheelite is characterized by a negative Eu anomaly, whereas type 2 scheelite shows a positive Eu anomaly. Considering the close temporal and spatial relationship between the Cuonadong Miocene leucogranite and the ore-bearing skarn, and their similar lanthanide tetrad effect as observed in the REE patterns, we propose that the negative Eu anomaly was inherited from the Cuonadong Miocene leucogranite, while the positive Eu anomaly resulted from the addition of Eu2+ to the ore-forming fluid during greisenization. Sr isotope data show that the fluorite (87Sr/86Sr) i value of 0.728885 is within the range of the Cuonadong Miocene leucogranite (87Sr/86Sr) i values, while scheelite (87Sr/86Sr) i values (0.709717–0.713480) are similar to those of the Cuonadong marble (0.709525–0.712146). Since scheelite is intergrown with fluorite, we propose that the hydrothermal fluid that exsolved from the Cuonadong Miocene leucogranite is responsible for formation of both fluorite and scheelite. Water-rock interaction between this magma-derived fluid and the marble is responsible for the loss of the scheelite magmatic Sr isotopic signature. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Jigongcun Mo deposit formed during the early Miocene. • High Re concentrations are due to isovalent Re substitution for Mo in molybdenite. • Relatively oxidized fluids caused Re enrichment in the Jigongcun deposit. The Jigongcun Re-rich quartz vein-type Mo deposit is located in the Gangdese porphyry Cu belt, southern Tibet, China. The stratiform and lenticular orebodies are hosted within the quartz veins and are controlled by the NW-/EW-trending faults. In this study, we have identified four hydrothermal stages, namely the (1) pre-ore stage (stage Ⅰ) characterized by the development of thick Mo-free quartz veins; (2) stage Ⅱ, mainly forming thick quartz veins with Re-rich massive molybdenite (Mo1-type; mean = 1811 ppm) and bladed molybdenite (Mo2-type; mean = 1312 ppm); (3) stage III, mainly forming quartz veins with Re-barren bladed molybdenite (Mo3-type) and abundant galena and pyrite; (4) the post-ore stage (stage Ⅳ) characterized by formation of thick ore-barren quartz–calcite veins. Both electron probe micro-analysis and in situ laser ablation–inductively coupled plasma–mass spectrometry analysis of different types of molybdenite show that high Re concentrations are due to isovalent Re substitution for Mo in molybdenite. Fluid evolution during the four stages of mineralization was constrained by a detailed fluid inclusion study. Fluid inclusions during the formation of the early pre-ore stage indicate relatively high-temperature (311–337 °C), high-pressure (1300–1600 bars), low-salinity (0.2–2.6 wt% NaCl-equiv.), and CO 2 -rich hydrothermal fluids. Fluid immiscibility assemblages in CO 2 -rich inclusions coexisting with aqueous inclusions occur in quartz–K-feldspar veins of stage Ⅱ, and likely record phase separation at a temperature of 262–300 °C and pressure of 900–1100 bars, with the precipitation of Re-rich molybdenite. The subsequent fluid mixing occurs at a temperature of 220–271 °C, with the precipitation of Re-barren molybdenite at stage III. H–O–S isotope compositions show that sulfur and ore-forming fluids are derived from a deep-seated igneous source. Re-Os dating of molybdenite samples yielded an isochron age of 22.0 ± 0.4 Ma, indicating that the Jigongcun deposit formed in the Early Miocene, which is earlier than most of the porphyry Cu deposits in the Gangdese porphyry Cu belt. Combined our new geochemical and isotopic results with previous regional investigations, we suggest that the Re-rich Mo mineralization of Jigongcun deposit may be related to the Early Miocene northward subduction of the Indian continental plate. [ABSTRACT FROM AUTHOR]

• Magmatic-hydrothermal water was dominant at the Rongna deposit. • The epithermal mineralization was partially related with the dissolution and re-precipitation of porphyry-style sulfides. • Leaching downward of contracted vapor formed telescoped epithermal alteration and mineralization. • Zinc (Zn) was enriched in the distal fluid of the Rongna deposit. The giant Rongna Cu-(Au) deposit is a recently discovered low-grade composite porphyry-high sulfidation epithermal system in the Duolong ore district of central Tibet. We present fluid inclusion petrography, microthermometry, stable isotope (H, O), and fluid-compositional data (LA-ICP-MS) to constrain the fluid evolution of the Rongna deposit. Hydrothermal quartz and muscovite formed in the porphyry stage yielded fluid values of 8.2 ± 1.0‰ δ18O H2O , and −75 ± 19‰ δD H2O (n = 13). Pyrophyllite, kaolinite, and dickite define the isotopic composition of the epithermal fluid (δ18O H2O = 2.2–8.3‰, δD H2O = −87 ~ −45‰). This epithermal fluid of lighter oxygen isotope and heavier hydrogen isotope composition still has a magmatic-hydrothermal signature and rules out any significant involvement of meteoric water. The very high concentration of Cu in fluid inclusions from epithermal veins and the common sulfide replacement features suggest that the epithermal mineralization may be partially related with the dissolution and re-precipitation of the porphyry-stage sulfides. Combined with fluid inclusion petrography and microthermometric data, it is indicated that a single-phase fluid exsolved from magma at depth and underwent boiling and cooling, forming the porphyry alteration and mineralization. With decrease of temperature and pressure, the ascending vapor contracted into acid aqueous fluid, leaching downward to develop the telescoped high-sulfidation epithermal alteration and mineralization. [ABSTRACT FROM AUTHOR]

• The Mingsai deposit formed during the Miocene (16.03 ± 0.31 Ma). • The sulfur of the Au-bearing pyrite has a deep source. • The Mingsai deposit is an orogenic-type Au deposit. Mingsai is a newly discovered Au deposit located in the eastern part of the Tethys Himalayan Au–Sb polymetallic metallogenic belt. The stratiform and lenticular orebodies are hosted within Middle Jurassic metamorphic tuff and quartz-sericite veins and controlled by an interlayer-gliding fracture zone with extensive hydrothermal alteration. In this study, at least three alteration/mineralization stages of the deposit were recognized as follows: (1) pre-ore stage (Stage Ⅰ), forming mainly ore-barren fine quartz veins without sulfides; (2) main ore stage (Stage Ⅱ), forming mainly thick quartz veins with abundant coarse-grained or fine-grained euhedral and subhedral Au-bearing pyrite, arsenopyrite and sericite; and (3) post-ore stage (Stage III), which is characterized by formation of thick barren quartz–calcite veins with few sulfides. Three types of fluid inclusions were identified as follows: (1) pure carbonic (V-type) inclusions, (2) aqueous-carbonic (C-type, including three-phase C1-type and two-phase C2-type) inclusions and (3) aqueous (L-type) inclusions. Fluid inclusions during the pre-ore stage are mainly C1-type, C2-type and V-type. The main ore stage contains mainly C1-type, C2-type, L-type and limited V-type, whereas the post-ore stage contains mainly L-type (with limited C2-type) fluid inclusions. From stages Ⅰ to III, microthermometric data show homogenization temperatures of 292–362 °C (mean = 309 °C), 247–320 °C (mean = 285 °C), and 206–272 °C (mean = 244 °C), respectively, and fluids with salinities of 0.2–8.3 (mean = 2.8) wt% NaCl equiv., 0.2–13.1 (mean = 5.8) wt% NaCl equiv., and 0.8–15.2 (mean = 8.3) wt% NaCl equiv., respectively. The δD values of the fluids from stages I to III range from −129.1‰ to −131.8‰, −137.5‰ to −137.4‰, and −143.6‰ to −138.6‰, respectively. The δ18O H2O values of the fluids from stages Ⅰ to III range from 13.3‰ to 13.6‰, 13.0‰ to 13.2‰, and 11.0‰ to 11.9‰, respectively. The δD and δ18O H2O values may reflect meteoric water involvement in ore-forming fluids sourced from either crustal metamorphism or mantle devolatilization. Fluid mixing is the crucial mechanism that controlled the deposition of the Au-bearing sulfides. In situ δ34S values of the Au-bearing pyrite range from 1.06‰ to 2.41‰, whereas δ34S values of the barren pyrite from the slate range from 8.19‰ to 15.86‰, indicating that sulfur of the Au-bearing pyrite has a deep source. The 40Ar–39Ar plateau age of hydrothermal ore-bearing sericite from the main ore stage is 16.03 ± 0.31 Ma, indicating that the mineralization time of the deposit is Miocene, which is different from other major gold deposits (Eocene) in the Tethys Himalayan Au–Sb polymetallic metallogenic belt. Consequently, taking the data together, it is suggested that the Mingsai is an orogenic-type Au deposit in the Tethys Himalayan Au–Sb polymetallic metallogenic belt. [ABSTRACT FROM AUTHOR]

A new high sulfidation epithermal Cu–Au occurrence (Nadun) has been discovered adjacent to the Cretaceous Duolong porphyry Cu–Au deposit within the Bangong–Nujiang metallogenic belt, central Tibet. The Nadun Cu–Au mineralization is hosted in a tectonic–hydrothermal breccia with advanced argillic alteration, which occurs above sandstone, associated with quartz–pyrite veins. The granodiorite porphyry with strong argillic alteration yields a zircon U–Pb age of 119.1 ± 1.3 Ma, whereas the weakly argillic granodiorite porphyry intruded into the breccia has a younger age of 116.1 ± 1.3 Ma. This indicates that Cu–Au epithermal mineralization likely occurred between ~ 116 Ma and ~ 119 Ma, consistent with the duration of magmatic–hydrothermal activity at Duolong (~ 115–118 Ma), and providing evidence that Nadun and Duolong were formed during the same event. Moreover, the Nadun and Duolong porphyries have similar Hf isotopic compositions (εHf(t) values ranging from − 8.8 to 8.1; mean = 5.0 ± 1.1, n = 32), likely indicating that the deposits are comagmatic. In addition, boiling assemblages in vapor-rich inclusions coexisting with brines occur in early stage quartz–pyrite veins, and likely record phase separation at a temperature of > 550–300 °C and pressure of 700–110 bars. Most liquid-rich fluid inclusions formed at the breccia stage show similar salinity (1.7–19.3 wt.% NaCl equiv) to vapor-rich inclusions from the underlying quartz–pyrite veins, likely indicating vapor contraction during cooling at elevated presssure. This suggests that quartz–pyrite veins may act as conduits for ore-forming fluid traveling from the porphyry to the epithermal hydrothermal system. O and H isotopic compositions (δ 18 O fluid = 0.42–9.71‰ and δD = − 102 to − 66‰) suggest that ore-forming fluids are dominantly from a magmatic source with a minor addition of meteoric water at a later stage. The S and Fe isotope compositions of sulfides (δ 34 S = − 5.9 to 0.5‰ and δ 57 Fe = − 2.15 to 0.17‰) decrease from the quartz–pyrite vein to breccia ore, indicating that ore-forming fluids gradually become SO 4 2 -enriched and relatively oxidized. This body of evidence suggests that the Nadun Cu–Au mineralization may represent the root of a high sulfidation epithermal deposit. [ABSTRACT FROM AUTHOR]

Abstract: Mesozoic intermediate–felsic intrusions are widely distributed in the southern Qiangtang terrane, central Tibet. Zircon U–Pb dating shows that these intrusions formed in two periods in the Jurassic (169–150Ma) and Cretaceous (127–113Ma). They mostly belong to the high-K calc-alkaline series, and show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, and Ti, and negative Ba anomalies on primitive mantle-normalized diagrams. P2O5 contents decrease with increasing SiO2 content, and Th contents increase with increasing Rb content, consistent with the evolution trend of I-type magmas. These intrusions show a wide range of zircon εHf(t) values from −19.4 to 11.2, including in rocks with similar SiO2 contents, suggesting variable contributions from mantle and Qiangtang crustal sources. Fine-grained mafic to intermediate igneous enclaves in Jurassic intrusions have similar zircon U–Pb ages and similar or slightly higher zircon εHf(t) values to the host rocks, suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers. Magma mixing is also supported by the wide range of zircon Hf isotopic compositions (εHf(t)=−19.4 to 2.5) from within individual Jurassic and Cretaceous intrusions, and Jurassic enclaves. The Jurassic–Cretaceous magmas likely formed in a continental arc setting during subduction of the Bangong–Nujiang ocean between 170 and 110Ma, and evolved in the upper plate crust by MASH processes. [Copyright &y& Elsevier]

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: Porphyry Cu–Mo deposits, related to the Miocene adakitic porphyries from the Gangdese porphyry copper belt in the southern Tibet, formed in a post-collisional setting. Here, we present the new zircon U–Pb ages, whole-rock chemical, and Sr–Nd and zircon Hf isotopic data for the ore-bearing adakitic porphyries from Gangdese porphyry copper belt. LA-ICP-MS zircon dating for six samples yielded ages ranging from 19Ma to 14Ma, indicating they formed in the Miocene. The ore-bearing adakitic porphyries show SiO2 of 61.47–71.67%, K2O of 3.29–4.74%, and high Sr content (394–1106ppm), high Sr/Y ratios (63–158), and low Y (6.12–10.3ppm) and heavy rare earth element contents (e.g. Yb=0.52–0.91ppm). They show steep fractionated REE and flat HREE patterns, and strong enrichment in large ion lithophile elements (Cs, Rb, Ba, Th, and U) and depletion of high field strength elements (Nb), with positive Sr and negative Ti anomalies. There are no linear variations of Ba, La, Sr/Y, Dy/Yb, (87Sr/86Sr)i, and εNd(t) with increasing SiO2 content. Combined with the zircon positive εHf(t) values, and wide range of (87Sr/86Sr)i (0.70559 to 0.70908) and of εNd(t) (−6.8 to 0) values for all the adakitic samples, they were likely derived from the melting of garnet-bearing amphibolite in the juvenile arc mafic lower crust. Additionally, the adakitic porphyries with low Th/Nb ratios have lower initial 87Sr/86Sr, and higher εNd(t) and εHf(t) values, and those with high Th/Nb show higher initial 87Sr/86Sr, and lower εNd(t) and εHf(t) values. This indicates that the juvenile arc lower crust is derived from the melting of the mantle wedge that was metasomatized by slab fluid or sediment melt during the Neotethyan ocean subduction. Significantly, the juvenile arc lower crust possibly inherited the arc magma characteristics of abundant in F, Cl, and Cu and high oxidation state, which contributed to the porphyry Cu–Mo deposits in the Gangdese porphyry copper belt. [Copyright &y& Elsevier]

The Galale Cu Au skarn deposit is located on the southern margin of the Bangong-Nujiang metallogenic belt, Tibet, and the Cu Au mineralization is related to the Late Cretaceous granodiorite. The orebodies occurring as stratiform, lenticular and vein types are hosted within the skarn along the contact between the granodiorite and dolomitic marble or calcitic marble of the Jiega Formation. At least four hydrothermal alteration stages of the deposit have been recognized: prograde magnesian and calcic skarn stage (Stage 1), retrograde skarn stage (Stage 2), hydrosilicate alteration stage (Stage 3), and phyllic alteration stage (Stage 4). Fluid inclusions from skarn rocks and quartz veins are indicative of multiple fluid events. The prograde skarn was formed from a medium-salinity, hot (466–518 °C), high pressure (>1000 bar) homogenous magmatic-hydrothermal fluid, under its possible direct separation from crystallizing magma. The subsequent retrograde skarn was formed from a slightly lower temperatures (370–460 °C) and lower pressure (~800 bar) homogenous magmatic-hydrothermal fluid that could be supplied by crystallizing magma. Sharp drop of pressure (from 800 bar to 300 bar) and significant decrease of temperatures (low to 300 °C) may be related to fracturing and increase of porosity during alteration of skarns, and caused the fluid boiling in hydrosilicate alteration stage. The fluid from the latest phyllic alteration stage is characterized by dominant meteoric water and more lower temperatures (low to 178 °C). Decrease of fluid temperatures and pressures, fluid boiling and changes of redox regime are considered the crucial mechanisms for controlling the precipitation of the ores. The δ34S values of the sulfides range from −4.4 to 6, primarily from −0.9 to 1.7, that suggest a magmatic source. The sulfides yield narrow ranges of 206Pb/204Pb ratios (18.141–18.871) and 207Pb/204Pb ratios (15.588–15.701) and a wide range of 208Pb/204Pb ratios (38.359–39.008), indicating a mixed crust-mantle ore-forming metal source. The 40Ar 39Ar plateau age of phlogopite from the chalcopyrite-bearing phlogopite tremolite skarn (Stage III) is 87.5 ± 0.6 Ma, which is consistent with the crystallization age of the Late Cretaceous granodiorite. Consequently, taking the data together suggests that the Galale Cu Au deposit is a typical oxidized Cu Au skarn deposit related to the Late Cretaceous magmatic-hydrothermal systems. • Both the calcic skarn and magnesian skarn have been observed in the Galale deposit. • The timing of mineralization is 87.5 ± 0.6 Ma, indicating that the Galale deposit formed in the Late Cretaceous. • The galale deposit is typical oxidized Cu-Au skarn deposit associated to the collision-related Late Cretaceous magmatism [ABSTRACT FROM AUTHOR]

[Display omitted] • The Cuonadong composite leucogranites resulted from at least three-period magmatism from Oligocene to Miocene. • The Cuonadong skarn contains multiple generations, and the age and composition of titanite from skarn record three-stage hydrothermal events. • Miocene Sn-rich titanite coexisting with garnet and interstitial cassiterite implies that hydrothermal Sn metasomatism occurred after garnet crystallization. The newly discovered Cuonadong Sn-W-Be skarn deposit is related to fractionated leucogranitic intrusions hosted in the Cenozoic Himalayan gneiss dome, Tibet, however, temporal and genetic relationships between composite magmatism, skarn and mineralization remain unclear. Based on age and compositional features, three types of titanite were identified: Ttn1 and Ttn2 in the diopside-dominated skarn and adjacent greisenized granitic dike, and Ttn3 (subdivided into Ttn3a and 3b) in the Sn-mineralized garnet skarn. Ttn1 has a higher Ti content and yielded a U-Pb age of ∼35 Ma, consistent with the U-Pb ages of monazite from the pegmatitic granite (35.0 ± 0.6 Ma). Younger, recrystallized Ttn2 (∼28–27 Ma) is characterized by higher Al, F, Ta, Nb, Sn and Y contents and was likely formed by interaction between early Ttn1 and late fluids as indicated by the monazite U-Pb age of two-mica granite (28.8 ± 0.3 Ma). These two types of hydrothermal titanite are confined to the Oligocene unmineralized skarn and adjacent greisenized granitic dike. Titanite from the garnet-bearing Sn-mineralized skarn (Ttn3) provides the age of mineralization (16.8 ± 1.6 Ma), slightly younger than the emplacement age of the Miocene granite (monazite U-Pb age: 19.9 ± 0.3 Ma and columbite: 19.0 ± 0.4 Ma). The Sn-rich Ttn3b coexisting with garnet and interstitial cassiterite shows a deficit of Y and HREE and a high (Dy) N /(Yb) N ratio, implying that hydrothermal Sn metasomatism of Ttn3 occurred after garnet crystallization. Overall, our results shows that the Cuonadong multigenerational skarns were generated during three episodic magmatic-hydrothermal events, and mineralization occurred in the Miocene. [ABSTRACT FROM AUTHOR]