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[Display omitted] • The initial ore-forming fluids were magmatic water, with input of meteoric water with time. • Fluid phase separation and mixing triggered the Pb-Zn-Ag and Sb precipitation, respectively. • Keyue is the distal Pb-Zn-Sb-Ag mineralization centered on the Cuonadong leucogranites. • Pegmatite-skarn-type W-Sn-Be deposits may occur at deeper sites beneath the Keyue area. The Keyue Pb-Zn-Sb-Ag polymetallic deposit is located within the North Himalayan Metallogenic Belt (NHMB). This study aims to clarify whether the Keyue deposit has close association in time and space with magmatism, and discuss the significance for further exploration. Orebodies are hosted by the Lower Jurassic Ridang Formation black carbonaceous slate and controlled by the NE-trending faults. Keyue is characterized by multiple stages of hydrothermal veins, including Mn-Fe Carbonate-sulfide (I), quartz-sulfide-sulfosalt mineral (II) and quartz-calcite-stibnite veins (III). Hydrothermal minerals contain six types of fluid inclusions, including H 2 O-rich bi-phase aqueous (type I), pure CO 2 (type II), CO 2 -rich H 2 O-CO 2 -NaCl tri-phase (type III), H 2 O-rich H 2 O-CO 2 -NaCl tri-phase (type IV), halite-bearing tri-phase (type V) and halite-bearing H 2 O-CO 2 -NaCl multiphase inclusions (type VI). All six types of inclusions were observed in stage II quartz, whereas only types I and III inclusions in stage I siderite and sphalerite and type I inclusions in stage III quartz and calcite. Type I inclusions in stage I display total homogenization temperatures (T h, total) ranging from 250.1 to 289.3 °C, with salinities of 9.6–16.3 wt% NaCleq. Types I, III, IV and V inclusions in stage II yield T h, total of 175.5–282.7 °C, 188.8–286.3 °C, 214.3–287.5 °C and 198.3–266.0 °C, with corresponding salinities of 4.0–21.5 wt% NaCleq, 0.6–2.9 wt% NaCleq, 0.0–11.0 wt% NaCleq and 30.1–33.2 wt% NaCleq, respectively. Type I inclusions in stage III have T h,total values of 172.3–240.7 °C and salinities of 3.1–12.6 wt% NaCleq. Fluid phase separation occurred in stages I and II, resulting in CO 2 and H 2 S release, pH increase and rapid Pb-Zn-Ag precipitation, whereas mixing of magmatic fluids and meteoric water in stage III caused the cooling, dilution and stibnite precipitation. Fluid inclusion analysis and C-H-O isotopic compositions indicate that the initial hydrothermal fluids were magmatic water, with increasing input of meteoric water with time. The δ34S CDT values of sulfides from three stages are similar and range from 4.8 to 10.3 ‰ (average 7.7 ‰), showing characteristics of mixture of magmatic and sedimentary sulfur. The Pb isotopic compositions of sulfides are closely consistent with those of Cenozoic leucogranite and Precambrian metamorphic crystalline basement in the NHMB, suggesting that the ore-forming metals were sourced from the hidden causative Himalayan leucogranite formed by the decompression melting of metamorphic crystalline domains. Combining evidence from geochronology, fluid inclusions, isotopes suggest that the Keyue Pb-Zn-Sb-Ag and Cuonadong W-Sn-Be mineralization at different locations around the Cuonadong Dome constitute an integrated magmatic-hydrothermal system, with the distal end-member Pb-Zn-Sb-Ag veins centered on the Cuonadong leucogranites-related W-Sn-Be mineralization. Pegmatite-skarn-type W-Sn-Be polymetallic mineralization may occur at deeper sites beneath the Keyue area, and the distal Pb-Zn-Sb-Ag veins controlled by faults within strata also need more attention around these leucogranite domes in the NHMB. [ABSTRACT FROM AUTHOR]

Initial opening time of Neotethyan ocean in the eastern Gondwana realm is still controversial. Ocean plate stratigraphy (OPS) forming in or near middle ocean ridges is of significance to trace the early stage of seafloor spreading. An over 10-km-long and ~ 5-km-wide Gongzhu seamount OPS is well preserved in the western Yarlung Zangbo suture zone (Southern Tibet), and consists mainly of neritic limestone, siliceous limestone, mudstone, mud-riched basaltic tuff, globular basalt and basaltic breccia interbedded with basaltic lava flows, and basaltic tuffaceous breccia. Geochemical and isotopic compositions of basaltic tuffceous breccias and basaltic lavas exhibit OIB-type affinities, basaltic lavas display slightly high (87Sr/86Sr) t ratios of 0.70430–0.70523, low (143Nd/144Nd) t ratios of 0.51244–0.51247 and ε Nd (t) values of +2.21 to +2.84, initial ratios of 206Pb/204Pb = 17.571–18.176, 207Pb/204Pb = 15.612–15.652, and 208Pb/204Pb = 37.290–38.706. These features are similar to those of alkaline basalts from the Vening-Meinesz Seamount Province in the northeast Indian ocean. The Gongzhu basaltic rocks are geochemically comparable with the mixing products of melts derived from the Pacific/Atlantic MORB and a metasomatized subcontinental lithosphere mantle. In-situ U--Pb zircon dating of two basaltic tuffaceous braccias has yielded mean ages of 245.1 ± 2.5 Ma and 241.9 ± 4.1 Ma. We propose that 272–290 Ma Panjal tholeiitic lavas exposed in the Kashmir region of NW India in the Himalayan orogenic belt developed during rifting of the Gondwana continental margin, whereas the slightly younger, 242–245 Ma Gongzhu seamount OPS formed during the initial seafloor spreading stage of the opening of the Neotethyan ocean. [Display omitted] • The early Middle Triassic Gongzhu seamount is the oldest seamount in the YZSZ. • The Gongzhu seamount represents the initial seafloor spreading phase in Neotethys north of India. • The Gongzhu seamount mantle source was hybrid, containing delaminated SCLM and recycled lower crust. • Gongzhu lavas are akin to basalts of the Vening-Meinesz Seamount Province in the NE Indian Ocean. [ABSTRACT FROM AUTHOR]