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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]

[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]

• 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]

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]