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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 Bangong–Nujiang suture zone (BNSZ), which separates the Gondwana-derived Qiangtang and Lhasa terranes, preserves limited geological records of the Bangong–Nujiang Ocean (BNO). The timing of opening of this ocean has been hotly debated due to the rare and complicated rock records in the suture zones, which span over 100 Ma from Carboniferous–Permian to Early Jurassic time, based on geological, palaeontological and palaeomagnetic data. A combination of geochemical, geochronological and isotopic data are reported for the Riasairi trachytes, central BNSZ, northern Tibet, to constrain its petrogenesis and tectonic settings. Zircon U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yields mean ages of 236 Ma. Geochemically, these rocks are high-K calc-alkaline with moderate SiO2 (59.1–67.5 wt%) and high K2O + Na2O (8.1–11.6 wt%) contents. They are enriched in light rare earth elements with negative Eu anomalies, and show enrichments in high-field-strength elements with positive 'Nb, Ta' anomalies, similar to the intra-continental rift setting-related felsic lavas from the African Rift System. The high positive zircon ϵHf(t) and bulk ϵNd(t) values, as well as high initial Pb isotopes, imply a heterogeneous source involving both asthenospheric and subcontinental lithospheric mantle. The field and geochemical data jointly suggest that the Riasairi trachytes within the Mugagangri Group were formed in a continental rift setting. We interpret that the continental-rift-related Riaisairi trachytic lavas as derived from the southern margin of the Qiangtang terrane, implying that the BNO would have opened by Middle Triassic time, well after the commonly interpreted break-up of the Qiangtang terrane from Gondwana. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang collision zone (BNCZ) is an ideal area for studying postcollisional magmatism. A series of late Early Cretaceous Cu‐bearing magmas are found in this collision zone, which has implications for studying the sources of postcollisional magmas. We completed detailed fieldwork and reported zircon U–Pb and Hf‐isotopic and whole‐rock geochemical data on the Daguo volcanics, Shesuo monzogranite‐granodiorites, and Xiongmei granodiorite porphyries, which represented different types of the Cu‐bearing rocks in the BNCZ. The Shesuo samples are characterized by high contents of SiO2, K2O, and total alkali, with high contents of heavy rare earth elements (HREEs) and Y, and are enriched in large‐ion lithophile elements (LILEs), depleted in Nb and Ta, with a marked negative Eu anomaly (0.29–0.92). The Xiongmei granodiorite porphyries are characterized by moderate SiO2 and MgO, high Al2O3 contents, depletion in Nb, Ta, Ba, Sr, and Ti, enrichment in LILEs, high HREEs and Y contents, and relatively low Sr/Y ratios. Both Shesuo monzogranites and Xiongmei granodiorites belong to calc‐alkaline I‐type magmas, which are associated with a wide range of zircon εHf(t) values (−15.3 to +5.8; −15.4 to +3.2). These geochemical features suggest that the Xiongmei granodiorite porphyries and Shesuo monzogranite‐granodiorites are derived from the melting of a juvenile mafic crust with ancient crustal contamination, and the juvenile mafic crusts are derived from a lithospheric mantle enriched by slab melt (including recycled subducting sediments). The Daguo basalt is derived from the partial melting of a mantle wedge metasomatized by subduction‐related fluids and/or melts and the involvement of asthenospheric mantle. The Daguo intermediate‐felsic rocks are derived from the partial melting of a juvenile crust from a metasomorphic mantle wedge. Our study implies that the genesis of these Cu‐bearing magmas is associated with slab break‐off at the end of the southward subduction of the Bangong–Nujiang Ocean lithosphere. In addition, the postcollisional magmas are multisourced, with a juvenile component from either the metasomorphic lithosphere mantle or the juvenile crust, an ancient crustal component and a subducted‐related component from the recycled subducting sediments, the subducted slab, and/or the asthenosphere. [ABSTRACT FROM AUTHOR]

The mechanisms triggering the emplacement of Cretaceous magmatic rocks related to Neo-Tethyan subduction in the southern Lhasa subterrane (SLT) remain controversial because geochronological, geochemical, and isotopic data from the Cretaceous magmatic rocks in the western portion of the SLT are lacking. This paper provides the first report indicating that the Dazhuqu hornblende gabbro and Xietongmen granite porphyry were generated in the Late Cretaceous (ca. 100 Ma and ca. 68 Ma, respectively) in the western portion of the SLT. The Dazhuqu hornblende gabbro is characterized by high MgO, Na2O, Cr, Co, and Mg# values, enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and depletion in high field strength elements with no Eu anomalies. The Xietongmen granite porphyry displays high SiO2, low MgO, Mg#, Cr, Co, and Ni, enrichment in LREEs and LILEs, flat heavy rare earth element (HREE) patterns and negative Eu anomalies. Zircons from the Dazhuqu hornblende gabbro and Xietongmen granite porphyry display high positive εHf(t) ranges from 11.79 to 14.91 and from 9.05 to 12.38, respectively. The Dazhuqu hornblende gabbro was produced by the partial melting of 12–15% garnet peridotite in the depleted mantle that was metasomatized by fluids released from the dehydrating subducted Neo-Tethyan oceanic slab. This magma was then emplaced at an upper crustal depth of 5.3–7.0 km. The Xietongmen granite porphyry was generated by the partial melting of underplated basaltic crust during the subduction of the Neo-Tethyan oceanic crust and formed in the presence of pyroxene, plagioclase, and minor hornblende in its magmatic source. In combination with previously published data from Cretaceous magmatic rocks in the SLT, our data suggest that the petrogenesis of the Dazhuqu hornblende gabbro was related to flat or low-angle slab subduction of the Neo-Tethyan oceanic crust during 109–97 Ma and that the formation of the Xietongmen granite porphyry was related to lithospheric delamination in the western portion of the SLT after ca. 68 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • Accessory minerals geochemistry characteristics are affected by prior or cocrystallizing minerals. • The Cl contents in melts are important for forming porphyry Cu-Au deposits. • Zircon and apatite geochemistry combination is useful for refining targets in the SLT. The products of long-lasting magmatism (ca. 170 Myr) related to the northward subduction of the Neo-Tethys Ocean are preserved in the southern Lhasa subterrane (SLT). However, only a few large porphyry Cu–Au deposits related to these igneous rocks have been discovered in the Xiongcun ore concentration area. Here, we present zircon and apatite data on Jurassic fertile suites (FS), barren suites (BS), and recently proposed prospecting target suites (PTS) in the SLT, intending to present a case study of the regional-scale porphyry metallogenic potential. The zircon geochemical data with Rayleigh fractionation modeling show that the zircon geochemical characteristics of the FS and PTS were affected by high proportions of amphibole and titanite crystallization, whereas the zircon geochemistry of the BS displays the effects of plagioclase fractionation or mixing with the least evolved melts. The zircon Ce4+/Ce3+ and Eu/Eu* values cannot be used to trace the oxygen fugacity of the magma due to prior or simultaneous mineral crystallization. However, the zircon Ce/Ce* and Ce/Nd ratios may be used as semiquantitative measures of the magma redox conditions. This result is similar to that calculated by the new magmatic oxybarometer using trace elements in zircon, showing that the FS (ΔFMQ = 1.21 ± 0.42) and PTS (ΔFMQ = 1.29 ± 0.51) have higher oxygen fugacity levels than the BS (ΔFMQ = 0.40 ± 0.88). The melt S contents estimated from magmatic apatites are lower in the FS and PTS than in the BS, which is attributed to prior anhydrite crystallization under high oxygen fugacity and low temperature conditions. The higher Cl in the melt of the FS (average 0.098 wt%) than in the melts of the PTS (average 0.045 wt%) and BS (average 0.04 wt%) shows that elevated Cl contents in melts are likely important for forming porphyry Cu–Au deposits. The combined geochemical characteristics of zircon and apatite suggest that a high oxygen fugacity (ΔFMQ > 1.2), prior or concurrent anhydrite crystallization, and high zircon Eu/Eu* (>0.6), Ce4+/Ce3+, and (Yb/Dy) N values can be used to refine potential porphyry Cu–Au targets on a regional scale in the SLT. High melt Cl contents and apatite MnO and Pb contents can effectively indicate fertile suites at the deposit scale. [ABSTRACT FROM AUTHOR]

• The Shesuo deposit is related to the intermediate-felsic magmatism (117–112 Ma). • The Shesuo deposit associated with slab break-off during a postcollisional period. • The addition of reducing materials limited the magma fertility. The Bangong-Nujiang metallogenic belt is a newly discovered copper-polymetallic belt in the Tethyan domain. To date, the Shesuo skarn Cu-polymetallic deposit is the only productive Early Cretaceous Cu deposit in the middle segment of this belt. We conducted zircon U-Pb and molybdenite Re-Os dating of this deposit, and the results show that the Shesuo skarn Cu-polymetallic deposit formed at 117–112 Ma. Within the mining area, granodiorites and monzogranites are the main metallogenic granitic bodies. The petrogeochemical features imply that the granodiorites and monzogranites were derived from the partial melting of juvenile lower crust resulting from mantle-derived magmatic underplating, with the additional involvement of ancient crust in the magma chamber, whereas the monzogranites experienced significant fractional crystallization. The δ34S values of sulfide ores suggest that they were mainly sourced from the magma and slightly contaminated by surrounding strata. The Pb isotope compositions of sulfides and Re contents of molybdenite indicate that the metals were derived from the juvenile lower crust, with a small fraction from ancient crustal materials. Our study suggests that the generation of the Shesuo deposit was most likely triggered by slab breakoff during the southward subduction of the Bangong-Nujiang Ocean lithosphere. The Shesuo and Xiongmei deposits have low zircon Ce4+/Ce3+ and Eu N /Eu* ratios and low whole-rock average V/Sc, Sr/Y and (Eu N /Eu*)/Yb N ratios. We propose that these values are due to the input of reduced components, leading to the generation of metallogenic magmas with relatively low magmatic oxidation states and water contents and rendering the magmas infertile for later porphyry-skarn Cu formation in the Xiongmei area. [ABSTRACT FROM AUTHOR]