Quartz-sulfide Stage Research Articles

Geochemistry of multi-stage scheelite in the skarn: Constraints on ore-forming processes of the Machangqing Cu-Mo polymetallic deposit in Yunnan Province, southwest China

The Machangqing Cu-Mo (-Au) deposit lies in the middle of the Jinshajiang-Ailaoshan alkaline porphyry metallogenic belt, and skarn is one of the main mineralization styles in the deposit. Scheelite from the Machangqing skarn occurs as discrete grains present in the early to late skarnization stages of the deposit, which can be divided into three types based on their occurrence: scheelite I in the prograde skarn, scheelite II (including the early scheelite II-a and the late scheelite II-b) in the retrograde alteration and scheelite III in the quartz-sulfide stages. In the CL images, scheelite grains of all three types have core- (mantle-) rim textures displaying CL-dark cores and CL-bright rims. The REE content could act as quenchers reducing CL intensity of the Machangqing scheelite. The Mo content of these scheelite types ranges from 0.5% to 13.6%, and Scheelite II-b is significantly enriched in MoO3 compared to other scheelite. Scheelite I and scheelite II-b exhibit right-dipped REE patterns, whereas scheelite II-a and scheelite III exhibit slightly middle rare MREE enriched patterns and flat REE patterns, respectively. The Eu anomaly differs between different types of scheelite, most of which exhibit variable negative Eu anomalies. Our study reveals that the substitution mechanism of REE for Ca in the Machangqing scheelite was probably 3Ca2+ =2REE3+ + □Ca and 2Ca2+ = REE3+ + Na+. The ore-forming fluids may be magma-derived. Mo contents of the Machangqing scheelite are generally controlled by the temperature and fO2 of the ore-forming fluids. The Mo variations in scheelite from different stages indicate a temperature decrease from the prograde to the early retrograde skarn stages, followed by fO2 increasing from the early retrograde to the late retrograde skarn stages, then decreasing to the quartz-sulfide stage. The Eu anomaly of scheelite was probably inherited from the ore-forming fluids and not dependant on the fO2 of hydrothermal fluids in the Machangqing deposit.

Origin of the Erdaohe Ag–Pb–Zn deposit, central Great Xing’an Range, northeast China: Constraints from fluid inclusions, zircon U–Pb geochronology, and stable isotopes

The large-scale Erdaohe Ag–Pb–Zn deposit in the central Great Xing’an Range, China, contains > 9.04 Mt of ore reserves. The deposit consists of skarn-type Ag–Pb–Zn orebodies located within a contact zone that is mainly between an Early Cretaceous porphyritic granite and Jurassic calcareous tuff. The deposit records four stages of formation, which are skarn, early quartz–sulfide (disseminated ores), late quartz–sulfide (veined ores), and carbonate stages. Fluid inclusion microthermometry indicates that skarn stage fluids were higher temperature (330 °C to > 500 °C) and more saline (up to 59.8 wt% NaCl equivalent) than the early quartz–sulfide (250 °C–300 °C, <36.1 wt% NaCl equivalent) and late quartz–sulfide stage (160 °C–220 °C, <32.1 wt% NaCl equivalent) fluids. Fluid inclusions of the carbonate stage record even lower temperatures (150 °C–170 °C) and have generally low salinity (2.1–5.1 wt% NaCl equivalent). Raman microprobe data indicate that these fluids are dominated by H2O–NaCl ± CO2 system phases. Sulfides formed during the early and late quartz–sulfide stages of mineralization have a relatively narrow range of δ34S values (4.4‰–8.4‰) that are indicative of sulfur derived from a magmatic source. Quartz samples from the early and late quartz–sulfide stages have δ18Ofluid values of 0.1‰–2.1‰ and from − 5.0‰ to − 3.2‰, respectively, suggesting that the mineralizing fluids were originally magmatic with later stage mineralization involving the addition of meteoric water. LA–ICP–MS U–Pb dating of zircons from the mineralization-related porphyritic granite yielded a weighted mean age of 131.4 ± 0.3 Ma (MSWD = 1.5), indicating that the deposit formed during the Early Cretaceous. Deposit formation involved an aqueous fluid that was exsolved during the final crystallization of the porphyritic granite and ascended along fracture zones until it reacted with Ca-rich wall rocks, cooled to < 300 °C, and boiled under hydrostatic conditions. This caused a decrease in temperature and sulfur fugacity in the ore-forming fluid system, which triggered Ag–Pb–Zn mineralization.

Textural, trace elemental and sulfur isotopic signatures of arsenopyrite and pyrite from the Mandongshan gold deposit (west Junggar, NW China): Implications for the conditions of gold mineralization

The Mandongshan gold deposit, located in the west Junggar region (Xinjiang Province, NW China), is hosted by Carboniferous basalt, tuff, and diabase. The gold ores at Mandongshan gold deposit take the form of hydrothermal veins cutting and disseminations within the altered rocks that host the deposit. A characteristic feature of the Mandongshan is the presence of abundant arsenopyrite. Two gold events have been recorded at Mandongshan: (I) an initial quartz-sulfide stage, and (II) a subsequent calcite-sulfide stage. In situ LA-ICP-MS analyses suggest that arsenopyrite of stage I has higher Te and lower Pb, Bi, Au, Ag, and Cu concentrations than arsenopyrite of stage II. Nano-SIMS δ34S values of pyrite associated with arsenopyrite of stage I and II fall within two ranges of −7.6 to −1.5‰ and −7.8 to −1.6‰. The presence of titanite and lack of rutile in the gold ores were taken to imply that the Mandongshan gold deposit formed from reduced fluids. Titanite crystals recorded in the gold-bearing quartz-sulfide veins show strongly positive Eu anomalies (Eu* = 2.15–3.99) and weakly positive Ce anomalies (Ce* = 1.04–1.58). The δ34S values of pyrite provide evidence for a magmatic sulfur source, which is consistent with the geochemical data obtained from other nearby gold deposits as well as the spatial relationship in the west Junggar region between gold mineralization and widespread felsic intrusions. In addition, our analyses suggest that the native gold of stage I was deposited due to phase separation of the ore-forming fluid. Native gold deposition of stage II can be further subdivided into stages IIa and IIb. The former stage is represented by coarse-grained gold that co-precipitated with arsenopyrite, while stage IIb is represented by fine-grained gold that precipitated as a result of dissolution and re-precipitation process occurring in earlier-formed stage IIa arsenopyrite grains. This model is consistent with our phase equilibrium calculations for the As-Au-Cu-Fe-S-O system of the Mandongshan gold deposit.

The geology, magnetite geochemistry, and oxygen isotopic composition of the Akesayi skarn iron deposit, Western Kunlun Orogenic Belt, Xinjiang, northwest China: Implications for ore genesis

The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite.Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18OV-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18OV-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought.

Genesis of the Shangxu orogenic gold deposit, Bangong-Nujiang suture belt, central Tibet, China: Constraints from H, O, C, Si, He and Ar isotopes

Shangxu is an orogenic gold deposit in the Bangong-Nujiang suture zone, central Tibet, China, formed in the Early Cretaceous orogene, related to convergence and collision between the Qiangtang and Lhasa terranes. The mineralization at Shangxu is hosted by Jurassic turbidite sedimentary rocks of the Mugagangri Group, and is associated with a regional fault system. Hydrothermal minerals develop muscovite, carbonate, sulfides and chlorite. Hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis. The earliest is barren quartz stage (H1), which is pre-ore. During the early mineralization quartz-pyrite stage (H2a), defined by massive quartz veins with minor euhedral pyrite and gold, hydrothermal fluids had a δ18Ofluid of 6.1–6.4‰, δD of −74 to −116‰, δ13CCO2 of −5.4 to −7.6‰, and δ30Si of −0.1‰. In the quartz-pyrite-sulfides stage (H2b), characterized by abundant quartz, granular pyrite, muscovite with minor chalcopyrite, galena, sphalerite and gold, fluids had a δ18Ofluid of 7–8.2‰, δD of −109 to −120‰, δ13CCO2 of −9.6‰ and δ30Si of −0.1 to −0.2‰. During the ankerite-sulfide stage (H3a), distinguished by abundant ankerite, muscovite, sulfides with minor quartz and chlorite, hydrothermal system had a fluid with δ18Ofluid of 4.9–5.3‰, δD of −125.3‰, δ30Si of −0.1‰, δ13CCO2 of −12.4‰ in quartz inclusion fluid and δ13CCO2 of −2.7‰ in ankerite. The calcite-sulfide stage (H3b) is characterized by calcite, sulfides, with minor quartz and chlorite. Quartz formed earlier than calcite from a fluid having a δ18Ofluid of 6.4‰, δD of −112.6‰, δ30Si of −0.1‰, and δ13CCO2 of −7.4‰, after which calcite precipitated from a hydrothermal fluid with δ18Ofluid of 5.5–9‰, δ13CCO2 of −0.5 to −2.8‰. Hydrothermal fluids in H2b pyrite have 3He/4He ratios of 0.27–0.42Ra and 40Ar/36Ar ratios of 313–372.The stable isotope composition of hydrothermal fluids from the Shangxu gold deposit is similar to that of typical orogenic gold deposits. The early stage (H1), methane-bearing fluids were probably sourced from the basin sediments, leading to precipitation of early barren quartz veins and siderite alteration. From the quartz-sulfide stage (H2) to carbonate-sulfide stage (H3), hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth. The decreasing δD and δ13C of the ore-forming fluids from early to late suggests mixing with δ13C-depleted oxidized graphite in sedimentary rocks, meteoric waters or reation between δD-depleted organic matters. Generally, these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the Mugagangri Group. Sulfur and gold, by inference, likely originated from sedimentary/diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies, and migrated with the metamorphic fluids. During transportation to the site of deposition, gold-bearing fluids variably reacted with country rocks.

Dating the Xiaobaishitou skarn W–(Mo) deposit, Eastern Tianshan, NW China: Constraints from zircon U–Pb, muscovite 40Ar–39Ar, and molybdenite Re–Os system

The Xiaobaishitou deposit (36,264 tonnes @ 0.78 wt% WO3) in the Eastern Tianshan orogenic belt is a medium-sized skarn deposit characterized by W–(Mo) ore bodies that developed along contacts between Triassic biotite granite and Mesoproterozoic carbonaceous rocks. Scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and/or quartz–sulfide stage, respectively. Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA–MC–ICP–MS) zircon U–Pb dating of the mineralization-related biotite granites from underground openings and outcrops yields ages of 247.9 ± 1.7 Ma (1σ; N = 22; MSWD = 0.69) and 252.2 ± 3.0 Ma (1σ; N = 12; MSWD = 1.60), implying they were emplaced in the Early Triassic. A muscovite 40Ar/39Ar weighted plateau age of 247.6 ± 2.3 Ma (2σ; MSWD = 2.03) and molybdenite Re–Os model ages ranging from 235.8 ± 5.7 Ma to 249.6 ± 3.6 Ma (weighted mean age = 251.1 ± 1.6 Ma; 2σ; MSWD = 0.70) are interpreted as the time of the hydrothermal activity mineralization. The excellent agreement among the U–Pb, 40Ar–39Ar, and Re–Os chronometers confirms that the Xiaobaishitou deposit formed in the Early Triassic. The Re contents of the molybdenites range from 18,477 to 130,447 ng/g, suggesting that the ore-forming materials were derived from continental crust together with the involvement of abundant mantle components. As one of the representative Triassic deposit in Eastern Tianshan, the Xiaobaishitou provides important chronological evidence for metallogenic regularity in the Eastern Tianshan and the Central Asian Orogenic Belt. The new ages reported here confirm that the Xiaobaishitou deposit represents one of the magmatic–hydrothermal mineralization events that occurred in the Eastern Tianshan orogenic belt in lithospheric extension during the Triassic. It is suggested that mantle material played a role in producing the Triassic mineralization and associated magmatism.

Geology and pyrite sulfur isotopes of the Suoluogou gold deposit: Implication for crustal continuum model of orogenic gold deposit in northwestern margin of Yangtze Craton, SW China

Since the crustal continuum model was proposed mainly based on the variation of mineralization and alteration features of hypozonal, mesozonal, to epizonal deposits, genetic relationship between the different types in one ore belt still requires research. This issue was addressed by the research on the Suoluogou mesozonal orogenic gold deposit and its comparison with the hypozonal orogenic gold deposit in northwestern margin of Yangtze craton. Gold mineralization in Suoluogou is controlled by the bends of roughly EW-trending brittle fault developed in the Late Triassic strata, and it is associated with quartz, sericite, chlorite, carbonate, and sulfide alteration. Pyrite and arsenopyrite are the predominant sulfide mineral, with minor amounts of chalcopyrite, sphalerite, and galena. Four paragenetic stages are divided based on crosscutting relationship and mineral assemblage, including the pre-mineralization stage (stage Ⅰ), the hydrothermal quartz-sulfide stage (stage Ⅱ) and carbonate-quartz-sulfide stage (stage III), and the post-mineralization carbonate-pyrite stage (stage Ⅳ). The δ34S values for pyrite in stage Ⅱ vary from 6.01% to 8.59‰, and those in stage III are from 0.96% to 4.62‰. The decrease of δ34S value from stage Ⅱ to III is explained to the result of the isotope fractionation during separation of oxidised sulfur species in the brecciated space. The sulfide δ34S values in the initial gold mineralization stage of the Suoluogou deposit are similar to those of regional hypozonal orogenic deposit with derivation from metasomatized mantle in the craton margin. This similarity suggests that the mesozonal and hypozonal gold deposits formed in different depths of a crustal continuum model for the deposits sharing similar subcrustal source.

Ore genesis of the Late Cretaceous Larong porphyry W-Mo deposit, eastern Tibet: Evidence from in-situ trace elemental and S-Pb isotopic compositions

The Late Cretaceous (ca. 92 Ma) Larong porphyry W-Mo deposit (39.44 Mt WO3 @ 0.1541%), a newly discovered deposit in the easternmost Bangong-Nujiang metallogenic belt (BNMB), is located in eastern Tibet. The W-Mo mineralization occurs as veins and stock-works hosted in monzogranite porphyry, granodiorite porphyry and surrounding quartz schist, and can be divided into two main paragenetic stages: the W-mineralization stage (Stage I) consists of various K-feldspar-quartz-scheelite veins and the quartz-sulfide stage (Stage II) is dominated by molybdenite and pyrite, of which the latter can be further subdivided into three sub-stages. Here, we present LA-ICPMS in-situ trace elements and S-Pb isotopes of sulfides from the Larong deposit, in order to constrain the sources of ore-forming elements and the processes of mineralization. Our study shows that pyrite is rich in Co and As, molybdenite is rich in W, Pb and Bi, and chalcopyrite has high Sn contents. These results are consistent with the mineralization characteristics of the Larong deposit, where the main metallogenic elements are W and Mo, accompanied by Bi, Sn and Cu. Overall, sulfides from the Larong deposit have calculated δ34SVCDT values ranging from 0.25‰ to 6.37‰, suggesting a predominantly magmatic origin for sulfur. From Stage II-1, to Stage II-2, to Stage II-3, the average δ34SVCDT values of pyrite change from 0.33‰, to 1.88‰, to 5.34‰, showing a progressive and gradual change in redox and temperature conditions. Molybdenite has high Pb isotopic ratios (208Pb/204Pb = 39.356–39.908, 207Pb/204Pb = 15.747–15.928, 206Pb/204Pb = 18.843–20.120) but low Re contents, and pyrite has low Ni contents, implying that the ore-forming materials were mainly derived from the crust. We propose that the W-Mo mineralization is genetically related to the Late Cretaceous monzogranite porphyry, with the mineralization of W and Mo occurring as a result of decreases in temperature and oxygen fugacity of the ore-forming fluid exsolved from the magma. In combination with previous studies, our study led to the identification of three W-dominated polymetallic metallogenic events and mineralization potential of igneous rocks in the BNMB.

Fluid inclusion and stable isotope constraints on the genesis of the world-class Zhuxi W(Cu) skarn deposit in South China

Scheelite mineralization accompanied by traces of chalcopyrite occurs in skarn systems in the giant Zhuxi deposit in the Taqian area, Northeastern Jiangxi province, South China. Three paragenetic stages of skarn with ore deposition have been recognized: the prograde skarn, retrograde skarn and hydrothermal quartz-sulfide stages. Microthermometer data showed that the prograde skarn were formed at relatively high temperatures (450–>500 °C) and pressures (0.97–1.38 kbars) and low oxidation to weak reduction conditions. The Raman microprobe data demonstrated that the fluid of the stage was H2O–NaCl/KCl/CaCl2 ± CH4/C2H4 system. The retrograde skarn alteration formed at 1.24 kbars and relatively medium temperatures (280–320 °C), and the ore-forming fluid was H2O–NaCl/KCl/CaCl2 system. During the hydrothermal quartz-sulfide stage, the fluids were methane-bearing aqueous, low-salinity (0.9–8.0 wt% NaCleqv) and low homogeneous temperature (160–240 °C). Correspondingly, the minimum fluid pressures were evaluated between 75 and 252 bars.The H- and O-isotopic values from the prograde and retrograde stages implied that the mineralizing fluids were derived principally from magmatic water. The mineralizing fluids in the quartz-sulfide hydrothermal stages were mingled with magmatic water with some meteoric water as well as minor contributions of wall rocks. The sulfur and lead isotopes indicated that ore-forming materials including sulfur, lead, copper, zinc and iron in the Zhuxi deposit were derived from local magmatic and sedimentary sources. Geological, fluid inclusion and isotopic data supported that the Zhuxi deposit is a typical skarn-type W(Cu) deposit related to ilmenite-series granitic rocks and formed in a compressional tectonic environment.

Mineralogy, fluid inclusions, and S–Pb isotope geochemistry study of the Tuboh Pb–Zn–Ag polymetallic deposit, Lubuklinggau, Sumatra, Indonesia

The Tuboh Pb–Zn–Ag polymetallic deposit is located in Lubuklinggau, Sumatra, Indonesia. The ore bodies occur within the contact zone between the Eocene Jangkat quartz monzonite and limestone of the Jurassic–lower Cretaceous Rawas Formation and are controlled by skarn and NE–SW faults. In order to reveal the relationship between mineralization and magmatism, a comprehensive study was conducted that included detailed field observation, petrographic study, fluid inclusions, and S–Pb isotope analysis. The results include the following findings. 1) Four mineralization stages were recognized. The prograde stage is characterized by garnet and wollastonite. The retrograde stage is dominated by magnetite, hematite, chlorite, quartz, with minor sulfides. The quartz-sulfide stage is enriched in sphalerite, galena, chalcopyrite, pyrite, pyrrhotite and quartz. The quartz–calcite stage is typified by quartz and calcite. 2) Electron probe microanalysis (EPMA) results revealed that garnet in the Tuboh deposit is rich in andradite (Adr37-99Grs1-59), indicating skarn was formed under relatively oxidized conditions. The temperature and S fugacity for sphalerite crystallization were 270 to 392 °C, and 10−9.7 to 10−7.1 bars, respectively. The decreasing trend between S fugacity with temperature suggests that ore precipitation occurred in a progressive reducing environment. EPMA analyses demonstrate that the Ag is primarily hosted by galena, which is present as solid solution with Bi via coupled substitution of Pb in the galena. 3) Fluid inclusions trapped in garnet indicates that the ore-forming fluid was high in temperature with high to moderate salinity, at 380–450 °C, 9.21–21.4 wt% NaCl equivalent, respectively, which indicates ore-forming fluid may derive from magmatic fluids. Fluid inclusions from quartz suggest ore precipitation from cooler and moderate- to low-salinity fluids, at 337–420 °C and 6.45–11.1 wt% NaCl equivalent, respectively, which is in agreement with the sphalerite crystallization temperature. The fluid inclusions in the quartz and calcite reveal that ore-forming fluid from the post-ore stage was moderate to low in both temperature and salinity, at 151–266 °C and 0.35–7.45 wt% NaCl equivalent, respectively. The positive correlation between homogenization temperature and salinity indicates that the ore-forming fluid mixed with meteoric water. 4) The δ34S values of sulfides range from −2.44 to 2.52‰, suggesting a magmatic origin of S. The Pb isotopic ratios of the galena are very uniform and have low radiogenic Pb, at 206Pb/204Pb = 18.342–18.370, 207Pb/204Pb = 15.576–15.599, and 208Pb/204Pb = 38.369–38.430. This indicates that the metals originated from the Eocene Jangkat quartz monzonite. Finally, in combination of available data suggest that the Tuboh deposit is a typical skarn-type Pb–Zn–Ag polymetallic deposit, which is the result of the Eocene quartz monzonite intruded the Jurassic–Cretaceous Rawas Formation, and ore precipitation is the consequent of the mixture of ore-forming fluid with meteoric water and decreases in S fugacity.

Fluid Inclusions and H-O-C-S Isotopes of the Wushan Copper Polymetallic Deposit in the Suizao Area, Hubei Province: Implications for Ore Genesis

The Wushan copper polymetallic deposit is located in the Tongbai-Dabie orogenic belt in central China. Two small granitoid stocks (Donggushan and Xigushan) occur in the deposit, which is next to the largest Qijianfeng Granite Complex in the Suizao area. The mineralization of Wushan copper polymetallic deposit is mainly composed of ore-bearing quartz veins and quartz stockworks. Two hydrothermal stages are identified as the quartz-sulfide stage (early stage) and the barren quartz stage (late stage). A detailed petrographic study shows four types of fluid inclusions in quartz, including the aqueous fluid inclusions (L+V/V+L), the aqueous-carbonic fluid inclusions (L+V+CO2), the pure carbon dioxide fluid inclusions (pure CO2), and the daughter mineral-bearing multiphase fluid inclusions (S). The daughter mineral-bearing multiphase fluid inclusions (S) are further divided into three subclasses according to their different solid mineral assemblages, including (1) S1: L+V+Hal, (2) S2: L+V+CO2+S (chalcopyrite), and (3) S3: L+V+S (calcite, chalcopyrite, and hematite)±Hal. A laser Raman spectroscopic analysis shows that the main components of fluid inclusions are water and carbon dioxide. The solid minerals of the S-type fluid inclusions include halite, calcite, chalcopyrite, and hematite. The homogenization temperatures of fluid inclusions are 377 to 468°C for the early stage, with a salinity of 11.1 to 34.1 wt.% NaCl equivalent (11.1 to 17.4 wt.% NaCl equivalent and 28.4 to 34.1 wt.% NaCl equivalent, respectively) and an estimated pressure of 89 to 137 MPa. The homogenization temperatures of fluid inclusions in the late stage are 267 to 380°C with salinity of 7.0 to 12.1 wt.% NaCl equivalent and an estimated pressure of 46 to 115 MPa. Therefore, the temperature, salinity, and pressure of the fluid show a decreasing trend from the early to the late stage. In the early stage, the fluid is immiscible, which leads to the precipitation of sulfides. Pyrite shows a δ34S of approximately 0 (-1.8 to +3.4‰), and chalcopyrite also shows a similar δ34S of approximately 0 (+1.5 to +2.4‰), which indicates that the sulfur in the ore-forming fluid is mainly derived from deep-seated magma. Combined with C-H-O isotopic compositions, the initial ore-forming fluid is likely magmatic water, but with the addition of meteoric water in the late stage. By comparing with the typical characteristics of magmatic hydrothermal vein deposit and orogenic deposit related to shear zones, we suggest that the Wushan copper polymetallic deposit is most likely a magmatic hydrothermal vein deposit, which is of great significance for the further exploration work in the Wushan and surrounding areas. This new finding also fills the gap that no magmatic hydrothermal vein type Cu deposits have been found in the Suizao area or even in the Qinling-Dabie orogenic belt in central China.

Genesis of the Panjia Wu‐Cu‐Mo deposit: Evidence from the geochemistry and geochronology of the Datongkeng pluton, northeast South China Block

The Panjia polymetallic deposit, located in the northwestern region of Zhejiang Province, is a newly discovered medium‐ to large‐sized W–Mo–Cu ore deposit belonging to the northern part of the Qinzhou Bay–Hangzhou Bay metallogenic belt. Through investigation in the field and under the microscope, the hydrothermal activity of this deposit can be divided into four stages: pre‐ore stage, silicate oxidation stage, quartz sulfide stage, and post‐ore stage. The Datongkeng pluton, outcroping in Panjia deposit, is one S‐type intrusive rock and characterised by concentrations of SiO2, K2O and Na2O ranging from 67.03 to 71.09%, 3.03 to 4.89%, and 0.24 to 3.37%, respectively. The major elements display peraluminous, high‐K, calc‐alkaline features. Their A/CNK(A/CNK = n (Al2O3)/ [n (CaO) + n (Na2O) + n(K2O)]) ratios, δEu values, and δCe values vary from 0.93 to 1.98, 0.45 to 0.91, and 0.93 to 1.07, respectively. These rocks are enriched in light rare earth elements (all record values of (La/Yb)N &lt;10, except for one) whereas are depleted in Sr, Ba, Nb, P, Eu, and Ti. The end‐member study of the Pb and S isotopes shows that the mantle material plays an important role in the ore‐forming. Zircon U–Pb dating indicates that the second part of the multiperiod magmatism (154–150 Ma) of Datongkeng pluton is the relevant crystallisation age, and the study of metallogenic stage manifests that the molybdenite is formed at the third stage of the mineralisation sequence considered as the main period of mineralisation, subsequent to the mineralogenetic epoch of scheelite. The petrogenesis is related to the materials in the crust and a small amount of materials in the mantle. While the low degree of mantle source and the Proterozoic basement contribute to the Mo, Cu ore‐forming materials. Finally, two types of metallogenic assemblage are formed, including the W‐Mo polymetallic deposit in the Datongkeng pluton and the W‐Cu‐Pb‐Zn‐Ag polymetallic deposit in the veins in the Lantian Formation.

Timing and Source of the Hermyingyi W-Sn Deposit in Southern Myanmar, SE Asia: Evidence from Molybdenite Re-Os Age and Sulfur Isotopic Composition

The Hermyingyi W-Sn deposit, situated in southern Myanmar, SE Asia, is a typical quartz-vein type W-Sn deposit. The ore-bearing quartz veins are mainly hosted by the Hermyingyi monzogranite which intruded into the Carboniferous metasedimentary rocks of Mergui Series. According to mineral assemblages and crosscutting relationships, four ore-forming stages are recognized:(1) silicate-oxide stage; (2) quartz-sulfide stage; (3) barren quartz vein stage; (4) supergene stage. Five molybdenite samples from the deposit yield Re-Os model ages ranging from 67.8±1.6 to 69.2±1.6 Ma (weighted mean age of 68.7±1.2 Ma), and a well-defined isochron age of 68.4±2.5 Ma (MSWD=0.18, 2σ). This Re-Os age is consistent with the previously published zircon U-Pb age of the Hermyingyi monzogranite (70.0±0.4 Ma) (MSWD=0.9, 2σ) within errors, which indicates a genetic link between the monzogranitic magmatism and W-Sn mineralization. The new high-precision geochronological data reveal that the granitic magmatism and associated W-Sn mineralization in southern Myanmar took place during the Late Cretaceous (70–68 Ma). The extremely low Re contents (22.9 ppb to 299 ppb) in molybdenite, coupled with sulfide δ34S values in the range of +1.9‰ to +5.6‰ suggest that ore-forming metals were predominately sourced from the crustal-derived granitic magma.

Fluid Evolution of Fuzishan Skarn Cu-Mo Deposit from the Edong District in the Middle-Lower Yangtze River Metallogenic Belt of China: Evidence from Petrography, Mineral Assemblages, and Fluid Inclusions

The Fuzishan Cu-Mo deposit is located in the Edong district of the Middle-Lower Yangtze River Metallogenic Belt, China. The orebodies mainly occurred as lenticular and bedded shapes in the skarn zone between the Lower Permian Qixia Formation carbonate rocks and the quartz diorite. Four paragenetic stages have been recognized based on petrographic observations: (1) prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage, and (4) carbonate stage. Six fluid inclusion types were recognized: S1(vapor + liquid + halite ± other daughter minerals), S2(vapor + liquid + daughter minerals except halite), LV(rich liquid + vapor), VL(rich vapor + liquid), V (vapor), and L (liquid) types. Fluid inclusion studies show distinct variations in composition, final homogenization temperature, and salinity in four stages. Daughter minerals of the primary fluid inclusions include chalcopyrite, molybdenite, hematite, anhydrite, calcite, and halite in the prograde skarn stage and hematite, calcite, and sulfide (?) in the retrograde skarn stage. No daughter minerals occurred in the quartz-sulfide and carbonate stages. Final homogenization temperatures recorded in these stages are from 405 to &gt;550°C, from 212 to 498°C, from 150 to 485°C, and from 89 to 223°C, respectively, while salinities are from 3.7 to 42.5, from 2.6 to 18.5, from 2.2 to 17.9, and from 0.2 to 11.5 wt.% NaCl equivalent, respectively. The coexisting VLand S1type fluid inclusions show similar homogenization temperature of 550 to about 650°C in the prograde skarn stage, indicating that immiscibility occurred at lithostatic pressure of 700 bars to perhaps 1000 bars, corresponding to a depth of 2.6 km to about 3.7 km. The coeval VLand LVtypes fluid inclusions with homogenization temperature of 350 to 400°C in the late retrograde skarn and quartz-sulfide stages suggest that boiling occurred under hydrostatic pressure of 150 to 280 bars, equivalent to a depth of 1.5 to 2.8 km. Mo mineralization in the retrograde stage predated Cu mineralization which mainly occurred in the quartz-sulfide stage. Fluid compositions indicate that ore-forming fluid has highfO2and rich Cu and Mo concentration in the early stage, while relatively lowerfO2and poor Cu and Mo concentration in the middle to late stages. Microthermometric data show a decreasing trend in temperature and salinity in the fluid evolution process. Decreasing temperature and boiling event may be the main factors that control the ore precipitation.

Ore-forming fluids and isotopic (H-O-C-S-Pb) characteristics of the Fujiashan-Longjiaoshan skarn W-Cu-(Mo) deposit in the Edong District of Hubei Province, China

The Fujiashan-Longjiaoshan deposit is located in the southern area of the Edong District of the Middle-Lower Yangtze River metallogenic belt. W-Cu-(Mo) orebodies are found in the contact zone between the granodiorite porphyry and Carboniferous to Triassic carbonate strata. Four stages of ore formation are identified: (1) the prograde skarn stage, (2) retrograde skarn stage, (3) quartz-sulfide stage (further subdivided into the early 3a and later 3b), and (4) carbonate stage. In this study, we applied fluid inclusion microthermometry, laser Raman spectroscopy, and H-O-C-S-Pb isotopic compositions to constrain hydrothermal processes and ore precipitation mechanisms of the Fujiashan-Longjiaoshan deposit. Early stage (1 and 2) ore-forming fluids belong to a high-temperature (above 550 °C), high-salinity (60–70 wt% NaCl equiv. and 15–20 wt% NaCl equiv, respectively), high-pressure (above 700 bars) and high-oxygen-fugacity NaCl-KCl-H2O system, and in the quartz-sulfide stage 3, the system changes into a NaCl-KCl-CO2-H2O system. Homogenization temperatures and salinities of ore-forming fluids gradually decrease throughout the evolutionary process. Fluid temperatures vary at >550 °C in prograde skarn stage 1, from 350 to 400 °C in retrograde skarn stage 2, from 250 to 300 °C in quartz-sulfide stage 3, and finally from 100 to 150 °C in carbonate stage 4. Salinity levels vary from 15 to 20 wt% NaCl equiv. in prograde skarn stage 1, from 5 to 20 wt% NaCl equiv. in retrograde skarn stage 2, from 10 to 15 wt% NaCl equiv. in quartz-sulfide stage 3a, from 5 to 10 wt% NaCl equiv. in quartz-sulfide stage 3b, and from 0 to 5 wt% NaCl equiv. in carbonate stage 4. The H-O-C isotopic compositions indicate that the ore-forming fluids were derived from magmatic water (δD of −123‰ to −83‰, δ18OV-SMOW of 6.1‰ to 7.4‰) with the input of meteoric water and organic matter in the quartz-sulfide stage (δD of −91‰ to −53‰, δ18OV-SMOW of 2.4‰ to 4.6‰, and δCV-PDB of −14.7‰ to −6.4‰). Sulfur and Pb isotopic compositions show that the ore-forming materials were mainly derived from granitic magma (δ34SV-CDT values of granodiorite-porphyry sulfides and skarns of −5.7‰ to +6.6‰) and in part from host sedimentary strata (δ34SV-CDT values of sulfides of country rocks clustering at −20‰ and at −10‰). Fluid boiling in the retrograde skarn stage gave rise to the first precipitation of scheelite. The precipitation of scheelite, chalcopyrite and molybdenite in the quartz-sulfide stage was probably triggered by the input of meteoric water and organic carbon. According to mineral assemblages and all available geological and geochemical data, we conclude that the Fujiashan-Longjiaoshan deposit is an oxidized skarn-type W-Cu-(Mo) deposit.

Hydrothermal alteration and short wavelength infrared (SWIR) characteristics of the Tongshankou porphyry-skarn Cu-Mo deposit, Yangtze craton, Eastern China

The Early Cretaceous Tongshankou Cu-Mo deposit is located in the eastern Yangtze craton and comprises both porphyry and skarn mineralization. The porphyry ore is hosted in a granodiorite porphyry with the skarn mineralization found along the contacts with the carbonate host rocks. Alteration in the porphyry mineralization can be divided into three stages: potassic alteration, phyllic alteration and a carbonate stage, with phyllic alteration associated with the main porphyry mineralization. No propylitic alteration is present at Tongshankou. The skarn-type alteration comprises five stages: early skarn stage, late skarn stage, oxide stage, quartz-sulfide stage and late vein stage. Short wave-length infrared (SWIR) analysis identified 15 hydrothermal minerals in the Tongshankou deposit, including illite, dickite, halloysite, phengite, talc, muscovite, saponite, gypsum, chlorite, prehnite, montmorillonite, serpentine, phlogopite, actinolite, kaolinite, with montmorillonite, illite and chlorite being the most common. SWIR parameters and the electron microprobe results of chlorites show that chlorites close to the mineralization center tend to be iron-rich and have high FeOH absorption position (Pos 2250 > 2251 nm). Consequently, chlorite may be a useful indicator mineral for mineralization in the Tongshankou deposit. Pos 2250 is not correlated to temperature as calculated using a chlorite geothermometer but does correlate with the iron contents of the chlorites. Our results show that the ore-forming fluids are Fe-rich in the proximity to the mineralization but Mg-rich towards the distal area. Unlike in other porphyry deposits the white mica show no consistent variation in the Tongshankou deposit and cannot be used as vectors towards mineralization. The Fe-Mg-Al poor carbonate host rocks of the Tongshankou deposit restrict the development of a propylitic alteration zone. The Fe-Mg-Al host rocks also prevent Tschermak exchange in white mica ((Siiv(Mg,Fe)vi ↔ AlivAlvi)), making white mica Pos 2200 and Illite crystallinity (IC) randomly distributed. Our results show that SWIR spectroscopy of chlorite may be an applicable exploration tool in skarn-related hydrothermal systems.

Finite difference modeling of metallogenic processes in the Hutouya Pb-Zn deposit, Qinghai, China: Implications for hydrothermal mineralization

The Hutouya Pb-Zn deposit located in Qinghai, China, is a typical skarn-type polymetallic deposit in the Qimantage metallogenic belt. This belt is characterized by extensive magmatic activity, complicated ore-forming element assemblages and various carbonate-bearing strata. Considering the geological features, mineralogy and geochemistry in the field, we have conducted finite difference simulations of the mineralizing process of galena and sphalerite in terms of a temperature-gradient driven flow. Specifically, we have used modern mineralization theory to quantitatively estimate the duration of the mineralizing process of galena and sphalerite in the Hutouya Pb-Zn deposit. The associated computational simulation results have demonstrated that the hydrothermal fluid flow is a key controlling factor of mineralization in this area. The mineralization of galena and sphalerite corresponds to the quartz sulfide stage, whereas the ore-forming time of galena is later than that of sphalerite. The best metallogenic temperatures of the galena and sphalerite are 150°C and 250°C, respectively. These computational results can enhance our understanding of the ore-forming processes in the Hutouya Pb-Zn district.

Alteration, mineralization, and genesis of the Lietinggang–Leqingla Pb–Zn–Fe–Cu–Mo skarn deposit, Tibet, China

The northeastern Gangdese polymetallic belt is one of the most important metallogenic belts in the Tibetan collisional orogen. In this belt, three types of mineralization including skarn type Fe, skarn and breccia type Pb–Zn–Ag, porphyry and skarn type Mo–Cu–W have been recognized. Some deposits are polymetallic deposits with complex metal paragenetic assemblage which needs to be explained. The Lietinggang–Leqingla skarn deposit is the most typical one which have developed Pb–Zn–Fe–Cu–Mo five kinds of metals in the same deposit. Geological field mapping indicates that the ore district is characterized by a regular spatial zoned alteration and mineralization. Garnet skarns with Fe–Cu–Mo mineralization are developed near the intrusion, while the garnet–hedenbergite skarns and the more distal hedenbergite–ferroactinolite skarns with Pb–Zn–Cu mineralization are developed in the carbonate strata. According to the dating date, the Fe–Cu–Mo and Pb–Zn–Cu mineralization formed in the same metallogenic system. Mineralogical studies suggest that from the prograde skarn alteration stage, during the retrograde alteration stage to the oxide stage, and to the quartz–sulfide stage, the fluid conditions for skarns near the intrusion were moderately acidic and weakly oxidizing, relatively oxygenated and alkaline, and weakly oxidizing and alkaline, respectively. However, for the skarns in the carbonate strata, they were lower acidities and weakly reducing, relatively low acidities and reducing, and reducing with a low pH, respectively. Geochemical analyses give information about the elements for the skarnization and mineralization. About the element sources, the host carbonate rocks were mainly responsible for Ca and the magmatic fluids were responsible for Si, Fe and Mg. About the element migration, during the hydrothermal alteration the grossularite skarns and garnet–epidote skarns gained Fe, Mg, Mn, Ca and Sr, but lost Si and K; the andradite skarns, garnet–hedenbergite skarns and hedenbergite–ferroactinolite skarns gained Si, Fe, Mn and Mg, but lost in Ca, K and Sr; and all the skarns gained Co, V, Y, Pb, Zn and Cu, but lost Rb and Ba. The REE migrated mainly in magmatic fluids and enriched in the skarns during the prograde skarn alteration stage. However, they reacted by the ore-forming fluids and migrated out of the system, which process led to the decreasing of these elements in skarns at last. By summarizing studies here and previously published data, a genetic description for the Lietinggang–Leqingla Pb–Zn–Fe–Cu–Mo skarn deposit can be given as follows. The Fe–Cu–Mo mineralization within the garnet-rich zone formed by the interaction between fluids derived from the Jubuzhari composite intrusion and the neighboring carbonate units under a condition of oxidizing and higher temperature. The Pb–Zn–Cu mineralization within the hedenbergite and ferroactinolite-rich zone formed by the interaction between fluids also derived from the Jubuzhari composite intrusion but migrated relative long distance and distal carbonate units under a condition of reducing and lower temperature.

Indium Mineralization in a Sn-Poor Skarn Deposit: A Case Study of the Qibaoshan Deposit, South China

Indium (In) is commonly hosted in Sn-rich deposits but rarely reported in Sn-poor deposits. However, an In-rich and Sn-poor skarn deposit, the Qibaoshan Cu-Zn-Pb deposit, has been identified in south China. Geochemical analyses were undertaken on 23 samples representing the following mineral assemblages: sphalerite-pyrite, pyrite-chalcopyrite, pyrite-sphalerite-galena-chalcopyrite, pyrite, magnetite-pyrite, and magnetite. The results show that In is richest in the sphalerite-pyrite ores, with concentrations of 28.9–203.0 ppm (average 122.8 ppm) and 1000 In/Zn values of 2.7–10.9 (average 7.0). Other ore types in the Qibaoshan deposit are In poor, whereas all are Sn poor (10 to 150 ppm), with most samples having Sn concentrations of ≤70 ppm. Indium is mainly hosted by sphalerite, as inferred from the strong correlation between In and Zn, and weak correlation between In and Sn. Mineral paragenetic relationships indicate sphalerite formed from late quartz-sulfide stage of mineralization processes. Indium in the Qibaoshan deposit is richer in vein-type orebodies than in lenticular-type orebodies occurring at contact zones between carbonate and quartz porphyry, or in carbonate xenoliths. Igneous intrusions that were Sn poor and emplaced at shallow depths formed the In-rich orebodies of the Qibaoshan deposit.

Mineralogy, fluid inclusions, and isotopes of the Cihai iron deposit, eastern Tianshan, NW China: Implication for hydrothermal evolution and genesis of subvolcanic rocks-hosted skarn-type deposits

Most skarn deposits are closely related to granitoids that intruded into carbonate rocks. The Cihai (>100Mt at 45%Fe) is a deposit with mineral assemblages and hydrothermal features similar to many other typical skarn deposits of the world. However, the iron orebodies of Cihai are mainly hosted within the diabase and not in contact with carbonate rocks. In addition, some magnetite grains exhibit unusual relatively high TiO2 content. These features are not consistent with the typical skarn iron deposit. Different hydrothermal and/or magmatic processes are being actively investigated for its origin. Because of a lack of systematic studies of geology, mineral compositions, fluid inclusions, and isotopes, the genetic type, ore genesis, and hydrothermal evolution of this deposit are still poorly understood and remain controversial.The skarn mineral assemblages are the alteration products of diabase. Three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observations, which show a prograde skarn stage (garnet-clinopyroxene-disseminated magnetite), a retrograde skarn stage (main iron ore stage, massive magnetite-amphibole-epidote±ilvaite), and a quartz-sulfide stage (quartz-calcite-pyrite-pyrrhotite-cobaltite).Overall, the compositions of garnet, clinpyroxene, and amphibole are consistent with those of typical skarn Fe deposits worldwide. In the disseminated ores, some magnetite grains exhibit relatively high TiO2 content (>1wt.%), which may be inherited from the diabase protoliths. Some distinct chemical zoning in magnetite grains were observed in this study, wherein cores are enriched in Ti, and magnetite rims show a pronounced depletion in Ti. The textural and compositional data of magnetite confirm that the Cihai Fe deposit is of hydrothermal origin, rather than associated with iron rich melts as previously suggested.Fluid inclusions study reveal that, the prograde skarn (garnet and pyroxene) formed from high temperature (520–600°C), moderate- to high-salinity (8.1–23.1wt.% NaCl equiv, and >46wt.% NaCl equiv) fluids. Massive iron ore and retrograde skarn assemblages (amphibole-epidote±ilvaite) formed under hydrostatic condition after the fracturing of early skarn. Fluids in this stage had lower temperature (220°–456°C) and salinity (8.4–16.3wt.% NaCl equiv). Fluid inclusions in quartz-sulfide stage quartz and calcite also record similar conditions, with temperature range from 128° to 367°C and salinity range from 0.2 to 22.9wt.% NaCl equiv. Oxygen and hydrogen isotopic data of garnet and quartz suggest that mixing and dilution of early magmatic fluids with external fluids (e.g., meteoric waters) caused a decrease in fluid temperature and salinity in the later stages of the skarn formation and massive iron precipitation. The δ18O values of magnetite from iron ores vary between 4.1 and 8.5‰, which are similar to values reported in other skarn Fe deposits. Such values are distinct from those of other iron ore deposits such as Kiruna-type and magmatic Fe-Ti-V deposits worldwide. Taken together, these geologic, geochemical, and isotopic data confirm that Cihai is a diabase-hosted skarn deposit related to the granitoids at depth.