Xiongcun District Research Articles

Typomorphic characteristics and geological significance of pyrite from No. 1 deposit in the Xiongcun district，Tibet

Typomorphic characteristics and geological significance of pyrite from No. 1 deposit in the Xiongcun district，Tibet

Cathodoluminescence and geochemical characteristics of Apatite: Implications for mineral exploration in the Xiongcun District, Tibet, China

Apatite grains from the No. 2 porphyry Cu–Au deposit in the Xiongcun district of Tibet, China, have a range of physical and compositional features. This study investigates the potential use of apatite associated with hydrothermal alteration as a tool for mineral exploration. In situ textural, cathodoluminescence (CL), and chemical analyses were performed on thin sections containing apatite from various alteration zones in the deposit. No clear variation was seen in apatite from rocks of the potassic, sodic–calcic, chlorite–sericite, phyllic, and propylitic alteration zones using visible light and scanning electron microscopy; however, distinct variations were observed in optical cathodoluminescence (OP-CL) (dark yellow to green, orange to green, yellow–brown to green, yellow-orange to brown, and light yellow–brown to green luminescence for the respective zones). The alteration-related differences in luminescence were a result of the interaction between Fe and Mn; the Na and Cl contents; and depletion in total heavy rare earth elements (ΣHREE) and Y. The variations in the REE contents of apatite from different types of altered rock record reactions with Cl- and F-rich fluids. The partitioning behavior of Cl between apatite and hydrothermal fluids is influenced by pressure, temperature, pH, and fluid composition, whereas the partitioning of F between apatite and fluids is dependent on the fluid composition and not the temperature. At high temperatures, Eu3+ is reduced to Eu2+, which results in negative Eu anomalies in apatite from the potassic-altered rocks and propylitic-altered rocks. Apatite grains in the sodic–calcic-altered rocks and chlorite–sericite-altered rocks show a similar enrichment in light REEs (LREEs) that resulted from REE and Y incorporation as follows: Na+ + (Y + REE)3+ = 2Ca2+. Apatite grains in the phyllic-altered rocks are enriched in the middle REEs. This study confirms that the luminescence, chemical composition (including Fe, Mn, Na, Cl, ΣHREE, and Y contents), and REE patterns of apatite can be affected by hydrothermal alteration; therefore, these results may be used to constrain the evolution of ore-forming hydrothermal fluids and may offer an effective tool for mineral exploration.

Application of exploration geochemistry data to identify anomalies in the plateau region: a case study from the Xiongcun district in the Gangdese metallogenic belt, Tibet, China

This paper describes the discovery of porphyry Cu–Au ore bodies (No. 2 and No. 3) in Xiongcun, Tibet, China, through the investigation of stream sediments, soils and rocks. The study area (Xiongcun), located in the city of Xigaze, has a complex topography due to its complicated geological background. The Xiongcun No. 1 ore body will soon be mined, 15 years after its discovery. However, recent research on stream sediments, soils and rocks around the No. 1 ore body has revealed notable Cu anomalies on the periphery. With the successful application of exploratory geochemistry data in the anomaly locations, the No. 2 and No. 3 ore bodies have been revealed. The ore reserves of the No. 2 and No. 3 ore bodies are estimated to reach 1.64 million tons of Cu, more than 80 tons of Au and 200 tons of Ag. We expect that our findings will not only enhance the understanding of the reanalysis of anomalies surrounding the discovered deposits but also contribute to the evaluation of the ore-prospecting potential of this plateau region.

Reduced fluids in porphyry copper-gold systems reflect the occurrence of the wall-rock thermogenic process: An example from the No.1 deposit in the Xiongcun district, Tibet, China

High fO2 conditions characterize the majority of global porphyry copper deposits and contain highly oxidized minerals, such as magnetite and anhydrite. In contrast, the No. 1 porphyry Cu–Au deposit in the Xiongcun district (Tibet, China) has abundant pyrrhotite, reduced fluids (CH4 ≫ CO2), and a relative lack of highly oxidized minerals, which are indicative of low fO2 conditions. Scanning electron microscopy, fluid inclusion, C–H–O–He–Ar isotopes, and whole-rock organic carbon contents and isotope analysis were used to constrain the evolution of ore-forming fluid, the origin of CH4 and metal deposition mechanisms for the No. 1 deposit. The He–Ar isotopic compositions (3He/4He = 0.11–0.96 Ra, 40Ar/36Ar = 418.7–2920.2) suggest that the ore-forming fluids predominantly derived from crust source with minor mantle input. The H–O isotopic analysis results (δ18OH2O = −1.8 to +5.2‰, δD = −106 to −89.9‰) indicate that the ore-forming fluids were derived from a magmatic source that mixed with some meteoric waters. The element compositions of zircons and fluid/melt inclusions from the mineralized Middle Jurassic quartz diorite porphyry reveal that the primary magma was characterized by high log fO2 (>NNO) conditions. The quartz diorite porphyry intruded into the carbon-bearing wall rocks produced abundant CH4 by thermal decomposition of organic matter (δ13CCH4 = −26.3 to −28.5‰), which changed the redox state of the porphyry copper system from oxidized to reduced condition. Ore elements were deposited via fluid boiling as a consequence of the rapid decrease in temperature and pressure.

Hydrothermal evolution and ore precipitation of the No. 2 porphyry Cu–Au deposit in the Xiongcun district, Tibet: Evidence from cathodoluminescence, fluid inclusions, and isotopes

The No. 2 porphyry Cu–Au deposit in the Xiongcun district forms part of the Gangdese porphyry copper belt of Tibet. This study clarifies the fluid evolution and ore precipitation mechanisms of the magmatic-hydrothermal system that formed the deposit by combining the results of fluid inclusion petrography, microthermometry, scanning electron microscope-cathodoluminescence imaging, and stable isotope analyses of multiple quartz-dominated veins. Four distinct sets of quartz-dominated veins and eight generations of quartz (Q1–Q8) within the veins were identified, namely from early to late, early barren quartz veins (V1) comprised of equigranular CL-bright Q1 quartz, quartz–pyrite–chalcopyrite ± magnetite veins (V2) containing early equigranular CL-bright Q1 quartz and later CL-gray or CL-dark Q2–3 (Q2 + Q3) quartz grains intergrown with Cu–Fe sulfides, quartz–molybdenite ± pyrite ± chalcopyrite veins (V3) comprised of quartz grains (Q4–Q6) characterized by subhedral comb-like textures with well-developed oscillatory growth zoning, and late quartz veins (V4) containing CL-gray Q7 quartz with euhedral growth zones and later CL-dark Q8 quartz. Fluid inclusions in these veins can be classified into six types: B40, B40H, B80, B15H, B15H+, and B15. The B40 and B40H inclusions; B80 inclusions; and B15, B15H, and B15H+ inclusions contain vapor bubbles occupying 30–60 vol%, >70 vol%, and 5–25 vol%, respectively; in addition, B15H, B15H+, and B40H inclusions contain transparent daughter minerals (halite, and in some cases, sylvite). Raman spectra showed that CO2 is only present in B40 and B80 inclusions. In the Q1 quartz in V1 and V2 veins, the dominant type of inclusions is B40, which have homogenization temperatures (Th) of 278 °C–389 °C (peaking at 310 °C–330 °C) and salinities of 2.0–12.8 wt% NaCl equiv. In Q2–3 quartz in V2 veins, all inclusion types were observed. These were trapped at temperatures of approximately 325 °C–340 °C and had salinities of 1.8–69.7 wt% NaCl equiv. In V3 veins, only B15H and B15 inclusions were observed, which had Th values of 171 °C–320 °C (peaking at 240 °C–260 °C) and 173 °C–317 °C (peaking at 210 °C–230 °C) and salinities of 28.7–33.9 wt% NaCl equiv and 5.6–23.1 wt% NaCl equiv, respectively. In V4 veins, only B15 inclusions were observed. Primary B15 inclusions in V4 veins yielded Th values of 166 °C–229 °C (peaking at 170 °C–200 °C) and salinities of 5.1–17.1 wt% NaCl equiv. The 3He/4He and 40Ar/36Ar ratios of the fluid inclusions exhibited the ranges of 0.08–0.84 Ra and 451.3–1567.8, respectively, and the δ18Ofluid and δDfluid values varied from −3.2‰ to 5.8‰ and −92.8‰ to −80.3‰, respectively. By integrating all results from the fluid inclusion, cathodoluminescence, and isotopic analyses, we conclude that the initial ore-forming fluids of the No. 2 deposit were low-salinity, CO2-rich single-phase fluids of magmatic origin. Subsequently, fluid immiscibility developed in the initial ore-forming fluids, generating hypersaline liquid and low-salinity vapor phases and leading to the separation of a CO2 phase plus chalcopyrite precipitation from the fluids. As meteoric water was injected into the hydrothermal system, the ore-forming fluids gradually evolved to become meteoric water-dominated, low temperature, low-salinity, and CO2-poor; in addition, fluid-cooling due to the meteoric water input resulted in molybdenite precipitation.

Early Jurassic volcanic rocks in the Xiongcun district, southern Lhasa subterrane, Tibet: Implications for the tectono-magmatic events associated with the early evolution of the Neo-Tethys Ocean

Early Mesozoic (Late Triassic to Middle Jurassic) igneous rocks in the southern Lhasa subterrane, Tibet, record important information on the early tectono-magmatic evolution of the Neo-Tethys Ocean. This paper presents petrological, geochronological, and geochemical data for the Xiongcun Formation ignimbrites, to constrain the petrogenesis and tectonic setting of these rocks in the southern Lhasa subterrane. The Xiongcun Formation is dominated by andesitic and dacitic rocks. These rocks yield Early Jurassic (195–176 Ma) zircon UPb ages and display typical arc-like geochemical signatures, being enriched in large-ion lithophile elements (e.g., Rb, Ba, and U) and depleted in high-field-strength elements (e.g., Nb, Ta, and Ti). Sr–Nd–Pb–Hf isotopic compositions are highly depleted. These chemical and isotopic data suggest that the Xiongcun Formation ignimbrites probably formed in an intra-oceanic island arc setting related to the northward subduction of the Neo-Tethys oceanic slab. The parental magmas were derived from a depleted mantle source modified by fluids released from the Neo-Tethys oceanic slab. Combined with previously reported data, we suggest that the volcanic rocks in the Early Jurassic Xiongcun and Yeba formations of the southern Lhasa subterrane were generated by a single subduction system, but developed on oceanic and continental crust, respectively.

Petrogenesis and tectonic implications of the ore-bearing porphyries in the Xiongcun district: Constraints from the geochronology and geochemistry

Petrogenesis and tectonic implications of the ore-bearing porphyries in the Xiongcun district: Constraints from the geochronology and geochemistry

Detrital zircon geochronology and geochemistry of Jurassic sandstones in the Xiongcun district, southern Lhasa subterrane, Tibet, China: implications for provenance and tectonic setting

AbstractJurassic sandstones in the Xiongcun porphyry copper–gold district, southern Lhasa subterrane, Tibet, China were analysed for petrography, major oxides and trace elements, as well as detrital zircon U–Pb and Hf isotopes, to infer their depositional age, provenance, intensity of source-rock palaeo-weathering and depositional tectonic setting. This new information provides important evidence to constrain the tectonic evolution of the southern Lhasa subterrane during the Late Triassic – Jurassic period. The sandstones are exposed in the lower and upper sections of the Xiongcun Formation. Their average modal abundance (Q21F11L68) classifies them as lithic arenite, which is also supported by geochemical studies. The high chemical index of alteration values (77.19–85.36, mean 79.96) and chemical index of weathering values (86.19–95.59, mean 89.98) of the sandstones imply moderate to intensive weathering of the source rock. Discrimination diagrams based on modal abundance, geochemistry and certain elemental ratios indicate that felsic and intermediate igneous rocks constitute the source rocks, probably with a magmatic arc provenance. The detrital zircon ages (161–243 Ma) and εHf(t) values (+10.5 to +16.2) further constrain the sandstone provenance as subduction-related Triassic–Jurassic felsic and intermediate igneous rocks from the southern Lhasa subterrane. A tectonic discrimination method based on geochemical data of the sandstones, as well as detrital zircon ages from sandstones, reveals that the sandstones were most likely deposited in an oceanic island-arc setting. These results support the hypothesis that the tectonic background of the southern Lhasa subterrane was an oceanic island-arc setting, rather than a continental island-arc setting, during the Late Triassic – Jurassic period.

Apatite and zircon geochemistry of Jurassic porphyries in the Xiongcun district, southern Gangdese porphyry copper belt: Implications for petrogenesis and mineralization

The Xiongcun district, a unique area where oxidized porphyry copper-gold deposits (OPCD) and reduced porphyry copper-gold deposits (RPCD) coexist, is located in the central part of the Gangdese porphyry copper belt (GPCB) in Tibet, China, and hosts the only known mineralization related to the Neo-Tethyan oceanic subduction. Apatite and zircon major and trace elements, in situ oxygen isotopes in zircon from fertile quartz diorite porphyry (QDP) of the No. I deposit, fertile hornblende quartz diorite porphyry (HQDP) of the No. II deposit, and barren hornblende quartz diorite porphyry with coarse quartz eyes (QQDP) in the Xiongcun district were determined by EPMA, LA-ICP-MS, and SHRIMP II ion microprobe to investigate the petrogenesis, magma oxidation state, and mineralization differences between the No. I and No. II deposits, as well as the potential of apatite as a metallogenic indicator. The results from this study show that a combination of REE, Ti, oxygen isotopes, and the Th/U ratios in zircon and REE as well as Sr in apatite can be used to track the magma compositions and crystallization histories in porphyry systems. Multiple indicators, including the apatite SO3 content, apatite Mn oxybarometer, and zircon Ce4+/Ce3+ ratio, indicate that (1) the parental magmas of fertile QDP and HQDP containing Cu and Au mineralization were more reduced than that of barren QQDP; (2) despite barren QQDP having higher oxygen fugacity than QDP and HQDP, the lower Cu and water contents in the magma result in a lower potential for ore formation; and (3) the similar oxidation states of QDP and HQDP show that the mineralization differences between RPCD (No. I deposit) and OPCD (No. II deposit) were not caused by the oxidation states of the magmas but were likely caused by the different processes of hydrothermal fluid evolution. Apatite grains from fertile porphyries (QDP and HQDP) have much higher Cl/F ratios than those from barren porphyry (QQDP), indicating that the Cl/F ratio of apatite can be used as a proxy for porphyry Cu-Au mineralization related to the Jurassic porphyry intrusions in the Gangdese porphyry copper belt.

New Discovery of the 341 Ma Gabbro at Xiongcun District in the Southern Margin of Lhasa Terrane, Tibet

New Discovery of the 341 Ma Gabbro at Xiongcun District in the Southern Margin of Lhasa Terrane, Tibet

Geological characteristics and genesis of the Jurassic No. I porphyry Cu–Au deposit in the Xiongcun district, Gangdese porphyry copper belt, Tibet

The Xiongcun district, located in the western segment of the Gangdese porphyry copper belt (GPCB), hosts the only known Jurassic mineralization in the GPCB, Tibet, PRC. The No. I deposit in the Xiongcun district is related to the Middle Jurassic quartz diorite porphyry (167–161Ma) and the mineralization was formed at ca. 161.5±2.7Ma. Ore-bearing Middle Jurassic quartz diorite porphyry emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. Veinlets and disseminated mineralization developed within the Middle Jurassic quartz diorite porphyry and the surrounding metamorphosed tuff, hosting a measured and indicated resource of 1.04Mt copper, 143.31t gold and 900.43t silver with an average grade of 0.48% copper, 0.66g/t gold, and 4.19g/t silver. The mineralization can be assigned to four stages, including three main stages of hypogene mineralization and one epigenetic stage. The main alteration associated with mineralization is potassic. Seven mineralization-related hydrothermal veins have been recognized, including quartz–sulfide, biotite–sulfide, magnetite–sulfide, quartz–molybdenite–sulfide, chalcopyrite–pyrite–pyrrhotite, pyrite and polymetallic veins. The S and Pb isotopic compositions of the ore sulfides and the Re contents of the molybdenite suggest a mantle source for the ore-forming materials with minor contamination from the subducted sediments. Hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore-forming process. The ore-bearing porphyry (167–161Ma) and ore-forming (161.5±2.7Ma) ages of the No. I deposit correspond to the time of northward subduction of Neo-Tethys oceanic slab. The geochemical data of the ore-bearing porphyry indicate that the No. I deposit formed in an intra-oceanic island arc setting and the ore-bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments. The genesis of the ore-bearing porphyry and No. I deposit is interpreted as being related to northward intra-oceanic subduction of Neo-Tethys oceanic slab in the Middle Jurassic time (167–161Ma).

CH4‐Rich Fluid of the No.I Porphyry Copper‐Gold Deposit in the Xiongcun District, Gangdese Porphyry Copper Belt, Tibet, PRC

CH₄‐Rich Fluid of the No.I Porphyry Copper‐Gold Deposit in the Xiongcun District, Gangdese Porphyry Copper Belt, Tibet, PRC

The Genetic Types of Mineral Deposits of Xiongcun District, Gangdese Porphyry Copper Belt, Tibet, PRC

The Genetic Types of Mineral Deposits of Xiongcun District, Gangdese Porphyry Copper Belt, Tibet, PRC

Elements Spatial Distribution and Ore Prospecting of the No.II Porphyry Copper - Gold Deposit in the Xiongcun District, Tibet

Xiongcun district is located in the western segment of the Gangdese porphyry copper belt, Tibet. Exploration activities in the No.I, No.II and No.III deposits in the past decade suggest that it would be a large prospective for porphyry copper-gold resources. In this paper, we focus on the systematical research of the elements spatial distribution of the No.II porphyry copper-gold deposit in the Xiongcun district. The results show, from center to the outer parts of the orebody, the elements distribution can be divided into Cu, Au, Ag, K, Mo and Ba → Co, Ni and Mn → Na and Ca → Pb, Zn, Cd, Bi, Sb and As. The No.II deposit is still open down-dip to the north and along the NW-striking, it need to conduct additional exploration.

Geological Characteristics and Exploration Potential of the NO.III Deposit in the Xiongcun District, Tibet, China

The Xiongcun district is located along the south margin of the Gangdese porphyry copper belt, approximately 53 km west of the Xigaze. No.III deposit is a newly discovered porphyry copper-gold deposit in the Xiongcun district. This paper first reports geological characteristics and exploration potential of No.III deposit. No.III deposit is hosted by Early Jurassic hornblende quartz diorite porphyry. Pervasive alteration is dominated by a well-mineralized potassic alteration. Major ore-bearing vein types include quartz-sulfide and chlorite-sulfide veins. Drilling holes and geochemical anomaly indicated the No.III deposit has excellent potential for exploration.

U–Pb and Re–Os geochronological evidence for the Jurassic porphyry metallogenic event of the Xiongcun district in the Gangdese porphyry copper belt, southern Tibet, PRC

Two large copper–gold porphyry deposits (No.I and No.II) were discovered in the last decade within the Xiongcun district, which is located along the south margin of the Gangdese porphyry copper belt. These two deposits are hosted by two porphyries that were emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. The porphyries are both quartz diorite bodies, with one of these distinguished by its large quartz eyes. Our new molybdenite Re–Os and zircon U–Pb dates for No.I and No.II deposits and host intrusions reveal the presence of two Middle Jurassic ore-forming episodes in the Xiongcun district. The No.II deposit is related to the 181–175Ma quartz diorite porphyry and formed ca. 172.6±2.1Ma. The No.I deposit is related to the 167–161Ma quartz diorite porphyry with large quartz eyes and formed ca. 161.5±2.7Ma. Geochronological and geochemical features of the Jurassic ore-bearing porphyries in the Xiongcun district indicate that the porphyry copper–gold mineralization formed in an island arc setting, which is related to the northward subduction of the Neo-Tethys oceanic plate. These observations, in combination with geochronological data reported at Gangdese porphyry copper belt, indicated four major metallogenic events existed in the Gangdese porphyry copper belt at 172–161Ma, 65–48Ma, 40–23Ma, and 20–12Ma. We have identified two mineralization episodes comprise Middle Jurassic metallogenic event (172–161Ma) in the Xiongcun district, which provides new constrains for the Middle Jurassic metallogenic event in the Gangdese porphyry copper belt.

Xiongcun, Tibet: A telescoped system of veinlet-disseminated Cu (Au) mineralization and late vein-style Au (Ag)-polymetallic mineralization in a continental collision zone

The Xiongcun Cu–Au deposit occurs in the western part of the Gangdese porphyry and skarn Cu–Au mineralization belt in the Himalayan–Tibetan Orogen and was formed in an intracontinental orogenic environment related to the India–Asia collision. Sericite 40Ar/ 39Ar dating of the Xiongcun deposit indicates that ore formation occurred around 38.11 ± 0.90 Ma, much earlier than the main ore-forming ages (20 to 14 Ma) of the Gangdese Cu–Au metallogenic belt. The potassium feldspar K–Ar age of the sulfide-bearing pegmatoid dyke in the Xiongcun district is 47.62 ± 0.70 Ma. These ages indicate that the mineralization in Xiongcun is related to relaxation (ca. 52 to 40 Ma) and subsequent uplift (40 to 38 Ma) of the orogen. In the Xiongcun deposit, mineralization, hosted by Jurassic pyroclastic rocks and controlled by NW-striking faults, can be divided into two styles, i.e. veinlet-disseminated Cu ± Au mineralization and vein-style Au ± Ag-polymetallic mineralization. The former is associated with local remnant K-silicate alteration, extensive phyllic alteration and peripheral widespread propylitization. The latter, overprinting the former, is associated with strong silicification, chloritization and kaolinization. The early veinlet-disseminated Cu ± Au mineralization is similar to porphyry-type mineralization and has a mineral assemblage of quartz–sericite–pyrite–chalcopyrite–bornite–magnetite–pyrrhotite–sphalerite ± rutile ± anhydrite. The late vein-style Au ± Ag-polymetallic mineralization, characterized by a mineral assemblage of quartz–pyrite–pyrrhotite–sphalerite (rich in Fe)–chalcopyrite–galena–native gold–electrum–chlorite–kaolinite ± barite ± calcite ± siderite ± hematite, belongs to a sulfide-rich low-sulfidation-type epithermal system. The H, O and S isotopic compositions and high salinities of fluid inclusions indicate a magmatic contribution and increasing contents of meteoric water in the mineralized system from early to late stage. The wide range of homogenization temperatures (380 to 120 °C), homogenization pressures (45.92 to 1.94 bar) and salinities (36.61 to 1.23 wt.% NaCl equiv.) suggest rapid uplift and are consistent with the geological setting. Because of uplift, the hydrothermal system of Xiongcun evolved from a porphyry system to an epithermal system, resulting in an immature porphyry system and the telescoping of late vein-style Au ± Ag-polymetallic mineralization onto the early veinlet-disseminated Cu ± Au mineralization.