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The Pulang porphyry copper deposit recently discovered in northwestern Yunnan province, China, is located at the south end of the Triassic Yidun island arc. To date, 15 mineralized porphyry deposits have been defined in the Pulang area and the copper resource is estimated to exceed 10 Mt. The Pulang deposit, as currently defined, is made up of five ore-bearing porphyry deposits, covering an area of approximately 9 km2. Intermediate acidic porphyritic intrusions composed of quartz-diorite, monzodiorite, quartz-monzonite, and granodiorite are widespread in the Pulang area. The alteration zones identified with the porphyry deposits include silicic, potassium silicate, quartz-sericite, and propylitic zones. The porphyry deposits have hornfels at the contact with slate, sandstone, and andesite. Re-Os ages of molybdenite, and Ar/Ar and K-Ar dating of biotite indicate that the Pulang porphyry copper deposit formed during the Indosinian tectonic episode, with the main ore formation taking place from 216 to 213 Ma (Late Triassic, Norian); however, the whole process of hydrothermal activity, including overprinting, may have extended from 235 to 182.5 Ma.

The Baiyinchang massive sulfide Cu deposit (Zheyaoshan and Huoyanshan mines) is hosted by an early Cambrian, submarine, felsic volcanic succession within an extrusive cryptodome associated with an overlying basaltic flow, in a Late Proterozoic-early Paleozoic submarine volcanic belt in the north Qilian orogen, northwestern China. The deposit is comprised of two mineralized zones: a 30-cm-thick, strata-bound Zn-rich sulfide lens associated with hematitic Fe-Mn cherts, and an underlying, discordant massive ore-dominated sulfide zone enveloped by a hydrothermal alteration pipe that is zoned from chlorite in the center to quartz-sericite at the margin. The discordant sulfide zone accounts for 90 percent of the Cu reserves of the Zheyaoshan mine. It consists of four main ore types: (1) pipelike pyrrhotite-pyrite ± chalcopyrite ore, (2) massive sulfide ore, (3) a disseminated ore halo, and (4) footwall stringer ore. The pyrrhotite-pyrite ± chalcopyrite pipe has an elliptical shape in plan and is 30 × 50 m across. The pipe partially replaces the overlying massive pyrite lens and extends downward at least 150 m, to be gradually replaced by chalcopyrite-rich stringer veins and chalcopyritebearing quartz veins surrounded by a discordant hydrothermal alteration envelope. Massive chalcopyrite-pyrite lenses discordant to volcanic bedding, containing relict patches of felsic volcanic host rocks, are commonly enveloped by a disseminated sulfide halo within a chloritized volcanic unit. These features suggest that Zheyaoshan is a pipe-style deposit that formed mainly by subsea-floor replacement of volcanic host rocks. Studies of fluid inclusions indicate that there are four types: (1) type I two-phase, aqueous fluid inclusions, (2) type II daughter mineral-bearing, multiphase fluid inclusions, (3) type III CO2-rich fluid inclusions, and (4) type IV CH4-rich fluid inclusions. Type II inclusions have high homogenization temperatures (Th) ranging from 320° to 430°C, contain high salinity fluids (31‐38 wt % NaCl equiv), and coexist with CO2-rich fluids found in vapor-rich, high-Th (up to 487°C), moderate salinity (10‐16 wt % NaCl equiv) inclusions in the discordant sulfide zone and associated altered rocks, suggesting a possible contribution of a magmatic fluid to the hydrothermal system. The coexistence of vapor-rich, high-Th (>300°C) and aqueous, low-Th (

The Yulong porphyry copper belt is the most significant porphyry copper belt in Tibet and is located in the Qiangtang terrane of the Himalayan-Tibetan orogen. The terrane is a collage of continental blocks joined by ophiolitic sutures and volcano-plutonic arc complexes. The Yulong belt is approximately 300 km long and 15 to 30 km wide, contains one giant, two large, and two medium- to small-sized porphyry copper deposits, and more than 20 mineralized porphyry bodies. The Yulong belt is located in the Changdu continental block that comprises Proterozoic to early Paleozoic crystalline folded basement and middle to late Paleozoic platform facies carbonate and clastic sedimentary rocks similar to the Yangtze continent. The porphyry belt is closely associated with Tertiary potassic volcanic rocks and alkali-rich intrusions in the area and controlled by north-south-north-northwest, large-scale, strike-slip faults, which are perpendicular to the collision zone between the Indian and Asian continents. Isotopic age determinations of the ore-bearing porphyries indicate that the magmatism occurred over at least three stages, peaking around 52, 41, and 33 Ma, respectively. The timing of middle and late shallow-level emplacement of these magmas is consistent with the ages of associated potassic volcanism and alkali-rich magmatism in the area. Although the porphyry deposits in the Yulong belt were developed in the intracontinental convergent environment, their mineralization styles and features are comparable to porphyry copper deposits in arc environments. Compared to ore-bearing calc-alkaline porphyries in island arcs or continental margin arcs, the porphyritic intrusions in the Yulong belt are characterized by high K2O contents and enrichment in Rb and Ba, suggesting a shoshonitic magmatic affinity. Strong negative anomalies for Nb, Ta, P, and Ti and positive anomalies for Rb, Ba, Th, and LREE, normalized by chondrite, are characteristic of arc magmas. These intrusions yield a narrow 143Nd/144Nd range varying from 0.51243 to 0.51253 and 87Sr/86Sr values from 0.7065 to 0.7077, which are transitional between type II enriched mantle and mid-ocean ridge basalt (MORB) values and closer to the former in terms of epsilon Nd- epsilon Sr. This suggests that the porphyritic magmas were derived either from a hydrous-enriched mantle metasomatized by components such as H2O, K, Rb, Ba, Th, and LREE or by melt derived from the subducted oceanic slab of the Paleozoic Jinshajiang oceanic plate. The hypothesis is supported by Pb isotope data for the intrusions. Large-scale strike-slip faults in eastern Tibet, which accommodated the compressive strains produced by the Asian-Indian continent collision, also localized the porphyry Cu mineralization. North to north-northeast-directed convergence and collision produced a dextral strike-slip fault system around 60 to 70 Ma. Northeast-directed wedging of the Indian continent and subsequent collision with the Yangtze continent during the Paleocene- Eocene produced conjugate strike-slip fault zones. The transition from a dextral strike-slip fault system to conjugate strike-slip zones resulted in stress relaxation and formation of strike-slip pull-apart basins. Crustalscale strike-slip faulting may have caused upwelling and partial melting of the hydrous-enriched mantle by decompression and facilitated the rise of a large volume of volatile-enriched porphyry magma that had ponded near the base of the lithosphere during this period.

The Gacun polymetallic, Ag-rich, volcanic-hosted massive sulfide deposit occurs in a Triassic submarine calc-alkaline volcanic belt that forms part of the Yidun collisional orogenic zone of southwestern China. The deposit is hosted in felsic volcanic rocks associated with an underlying mafic unit (a bimodal suite), which formed in an intra-arc rift basin at about 1,000 m water depth. The volcanic rocks underwent regional lower greenschist facies metamorphism and related deformation during the Yanshan-Himalayan orogeny, resulting in folding and shearing of the ore lenses. The deposit is made up of three mineralized zones: a sheet-like upper massive sulfide zone with exhalite (barite, chert, and jasper), a middle stringer-stockwork strata-bound zone hosted in rhyolitic volcanic rocks, and an underlying lower stringer strata-bound zone in dacitic volcanic rocks. Fluid inclusion studies indicate that two-phase primary fluid inclusions in quartz in the lower stringer ore zone homogenized between 299° and 319°C (average temperature 308°C), whereas those in sphalerite yielded a temperature range from 185° to 260°C (average temperature 241°C). Homogenization temperatures of fluid inclusions in quartz from the middle stringer-stockwork zone ranged from 150°to 350°C and averaged 243°C. The homogenization temperature of fluid inclusions in quartz and sphalerite from the massive sulfide zone show a bimodal distribution corresponding to temperatures from 250° to 150°C for quartz and from 200° to 140°C for sphalerite. Fluid inclusions in barite fragments from an interpreted submarine vent recorded higher homogenization temperatures ranging from 208° to 358°C, whereas those in fined-grained barite from the upper gray-white massive baritic ore gave lower homogenization temperatures ranging from 98° to 125°C. Salinities of fluid inclusions show a wide range from 4.2 to 21.3 wt percent NaCl equiv in the three mineralized zones. Fluid inclusions in quartz from the lower stringer zone have the highest salinities (17.1–21.3 wt % NaCl equiv), whereas those in barite from gray-white massive baritic ores have the lowest salinity (average 4.0 wt % NaCl equiv), close to that of normal seawater. Salinities of fluid inclusions in sphalerite ranged from 5.1 to 14.5 wt percent NaCl equiv, and the high-salinity end member was found mainly in the massive sulfide zone. Preliminary laser Raman spectroscopic analysis of fluid inclusions from the three mineralized zones identified CO 2 , CH 4 , and H 2 S. Oxygen isotope compositions of eleven quartz samples separated from the stringer and stockwork ores and of two silica breccias in the basal sulfide massive ores yielded a limited range from 13.7 to 16.4 per mil. Fourteen host felsic volcanic rock samples and seven quartz samples separated from several alteration zones display a wide range in bulk rock δ 18 O values from 8.0 to 17.1 per mil. For the volcanic rocks in various alteration zones, a significant increase in δ 18 O value was recorded in the deposit outward from the orebodies and downward from upper to lower volcanic units. The most strongly altered quartz-hyalophane zone gave a bulk rock δ 18 O value of 11.3 to 14.4 per mil. The moderately altered sericite-quartz zone yielded slightly higher bulk rock δ 18 O values of 12.5 to 15.4 per mil. The weakly altered lower volcanic unit has much higher bulk rock δ 18 O values ranging from 15.1 to 17.1 per mil; these values are comparable to those measured for the zeolite zone in the Kuroko deposits of Japan. The hydrothermal system that formed the Gacun deposit was relatively high temperature (up to 350°C); it had a relatively high gas content and high salinity and was enriched in 18 O. These data suggest that the dominant 18 O-rich hydrothermal fluid was derived from a felsic magma chamber at depth. The high-salinity fluid inclusions in the massive sulfide zone suggest that ore formed in a sea-floor brine pool filled by episodic venting of mixed subsea-floor fluids. Fluid inclusions with salinities close to that of normal seawater and homogenization temperatures around 250°C in sphalerite and barite within the ore zone suggest that seawater was heated to that temperature by felsic intrusions. Near the mineralized center and main path of hydrothermal fluid discharge at Gacun, fluid inclusions in the strata-bound zone recorded that a minor amount of cold seawater mixed with magmatic fluid. In comparison, away from the mineralized center, a large amount of cold seawater mixed with magmatic-derived fluid and heated seawater in the strata-bound zone.