Ore-forming process of the Huijiabao gold district,southwestern Guizhou Province,China: Evidence from fluid inclusions and stable isotopes

The Huijiabao gold district is one of the major producers for Carlin-type gold deposits in southwestern Guizhou Province, China, including Taipingdong, Zimudang, Shuiyindong, Bojitian and other gold deposits/occurrences. Petrographic observation, microthermometric study and Laser Raman spectroscopy were carried out on the fluid inclusions within representative minerals in various mineralization stages from these four gold deposits. Five types of fluid inclusions have been recognized in hydrothermal minerals of different ore-forming stages: aqueous inclusions, CO₂ inclusions, CO₂–H₂O inclusions, hydrocarbon inclusions, and hydrocarbon–H₂O inclusions. The ore-forming fluids are characterized by a H₂O + CO₂ + CH₄ ± N₂ system with medium to low temperature and low salinity. From early mineralization stage to later ones, the compositions of the ore-forming fluids experienced an evolution of H₂O + NaCl → H₂O + NaCl + CO₂ + CH₄ ± N₂ → H₂O + NaCl ± CH₄ ± CO₂ with a slight decrease in homogenization temperature and salinity. The δ¹⁸O values of the main-stage quartz vary from 15.2‰ to 24.1‰, while the δD_H2O and calculated δ¹⁸O_H2O values of the ore-forming fluids range from −56.9 to −116.3‰ and from 2.12‰ to 12.7‰, respectively. The δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal calcite change in the range of −9.1‰ to −0.5‰ and 11.1–23.2‰, respectively. Stable isotopic characteristics indicate that the ore-forming fluid was mainly composed of ore- and hydrocarbon-bearing basinal fluid. The dynamic fractionation of the sulfur in the diagenetic pyrite is controlled by bacterial reduction of marine sulfates. The hydrothermal sulfides and the diagenetic pyrite from the host rocks are very similar in their sulfur isotopic composition, suggesting that the sulfur in the ore-forming fluids was mainly derived from dissolution of diagenetic pyrite. The study of fluid inclusions indicates that immiscibility of H₂O–NaCl–CO₂ fluids took place during the main mineralization stage and caused the precipitation and enrichment of gold.     

Anatomy of a large Ag–Pb–Zn deposit in the Great Xing'an Range,northeast China: metallogeny associated with Early Cretaceous magmatism

The Bairendaba vein-type Ag–Pb–Zn deposit, hosted in a Carboniferous quartz diorite, is one of the largest polymetallic deposits in the southern Great Xing'an Range. Reserves exceeding 8000 tonnes of Ag and 3 million tonnes of Pb?+?Zn with grades of 30 g/t and 4.5% have been estimated. We identify three distinct mineralization stages in this deposit: a barren pre-ore stage (stage 1), a main-ore stage with economic Ag–Pb–Zn mineralization (stage 2), and a post-ore stage with barren mineralization (stage 3). Stage 1 is characterized by abundant arsenopyrite?+?quartz and minor pyrite. Stage 2 is represented by abundant Fe–Zn–Pb–Ag sulphides and is further subdivided into three substages comprising the calcite–polymetallic sulphide stage (substage 1), the fluorite–polymetallic sulphide stage (substage 2), and the quartz–polymetallic sulphide stage (substage 3). Stage 3 involves an assemblage dominated by calcite with variable pyrite, galena, quartz, fluorite, illite, and chlorite. Fluid inclusion analysis and mineral thermometry indicate that the three stages of mineralization were formed at temperatures of 320–350°C, 200–340°C, and 180–240°C, respectively. Stage 1 early mineralization is characterized by low-salinity fluids (5.86–8.81 wt.% NaCl equiv.) with an isotopic signature of magmatic origin (δ¹⁸O_fluid = 10.45–10.65‰). The main ore minerals of stage 2 precipitated from aqueous–carbonic fluids (4.34–8.81 wt.% NaCl equiv.). The calculated and measured oxygen and hydrogen isotopic compositions of the ore-forming aqueous fluids (δ¹⁸O_fluid = 3.31–8.59‰, δD_fluid?=??132.00‰ to??104.00‰) indicate that they were derived from a magmatic source and mixed with meteoric water. Measured and calculated sulphur isotope compositions of hydrothermal fluids (δ³⁴S_∑S?=??1.2–3.8‰) indicate that the ore sulphur was derived mainly from a magmatic source. The calculated carbon isotope compositions of hydrothermal fluids (δ¹³C_fluid?=??26.52‰ to??25.82‰) suggest a possible contribution of carbon sourced from the basement gneisses. The stage 3 late mineralization is dominated (1.40–8.81 wt.% NaCl equiv.) by aqueous fluids. The fluids show lower δ¹⁸O_fluid (?16.06‰ to??0.70‰) and higher δD_fluid (?90.10‰ to??74.50‰) values, indicating a heated meteoric water signature. The calculated carbon isotope compositions (δ¹³C_fluid?=??12.82‰ to??6.62‰) of the hydrothermal fluids in stage 3 also suggest a possible contribution of gneiss-sourced carbon. The isotopic compositions and fluid chemistry indicate that the ore mineralization in the Bairendaba deposit was related to Early Cretaceous magmatism.     

Isotope and fluid inclusion geochemistry of the Cangyuan Pb-Zn-Ag polymetallic deposit in Yunnan,SW China

The Cangyuan Pb-Zn-Ag polymetallic deposit is located in the Baoshan Block, southern Sanjiang Orogen. The orebodies are hosted in low-grade metamorphic rocks and skarn in contact with Cenozoic granitic rocks. Studies on fluid inclusions (FIs) of the deposit indicate that the ore-forming fluids are CO₂-bearing, NaCl-H₂O. The initial fluids evolved from high temperatures (462–498 °C) and high salinities (54.5–58.4 wt% NaCl equiv) during the skarn stage into mesothermal (260–397 °C) and low salinities (1.2–9.5 wt% NaCl equiv) during the sulfide stage. The oxygen and hydrogen isotopic compositions (δ¹⁸O_H2O: 2.7–8.8‰; δD: −82 to −120‰) suggest that the ore-forming fluids are mixture of magmatic fluids and meteoric water. Sulfur isotopic compositions of the sulfides yield δ³⁴S values of −2.3 to 3.2‰; lead isotopic compositions of ore sulfides are similar to those of granitic rocks, indicating that the sulfur and ore-metals are derived from the granitic magma. We propose that the Cangyuan Pb-Zn-Ag deposit formed from magmatic hydrothermal fluids. These Cenozoic deposits situated in the west of Lanping-Changdu Basin share many similarities with the Cangyuan in isotopic compositions, including the Laochang, Lanuoma and Jinman deposits. This reveals that the Cenozoic granites could have contributed to Pb-Zn-Cu mineralization in the Sanjiang region despite the abundance of Cenozoic Pb-Zn deposits in the region, such as the Jingding Pb-Zn deposit, that is thought to be of basin brine origin.     

Study on the evolution of ore-formation fluids for Au-Sb ore deposits and the mechanism of Au-Sb paragenesis and differentiation in the southwestern part of Guizhou Province, China

Ore deposits (occurrences) of Au, As, Sb, Hg, etc. distributed in Southwest Guizhou constitute the important portion of the low-temperature metallogenic domain covering a large area in Southwest China, with the Carlin-type Au and Sb deposits being the most typical ones. In this paper the Au and Sb ore deposits are taken as the objects of study. Through the petrographic analysis, microthermomitric measurement and Raman spectrophic analysis of fluid inclusions in gangue minerals and research on the S and C isotopic compositions in the gold ore deposits we can reveal the sources of ore-forming materials and ore-forming fluids and the rules of ore fluid evolution. Ore deposits of Au, Sb, etc. are regionally classified as the products of ore fluid evolution, and their ore-forming materials and ore fluids were probably derived mainly from the deep interior of the Earth. Fluid inclusion studies have shown that the temperatures of Au mineralization are within the range of 170-361℃,the salinities are 0.35 wt%-8 wt% NaCl eq.; the temperatures of Sb mineralization are 129.4-214℃ and the salinities are 0.18 wt%- 3.23 wt% NaCl eq.; the ore-forming fluid temperatures and salinities tend to decrease progressively. In the early stage (Au metallogenic stage) the ore-forming fluids contained large amounts of volatile components such as CO2, CH4, N2 and H2S, belonging to the H2O-CO2-NaCl fluid system; in the late stage (Sb metallogenic stage) the ore-forming fluids belong to the Sb-bearing H2O-NaCl system. The primitive ore-forming fluids may have experienced at least two processes of immiscibility: (1) when early ore-bearing hydrothermal solutions passed through rock strata of larger porosity or fault broken zones, CO2, CH4, N2 would escape from them, followed by the release of pressure, resulting in pressure release and boiling of primitive homogenous fluids, thereafter giving rise to their phase separation, thus leading to Au unloading and mineralization; and (2) in the late stage (Sb metallogenic stage ) a large volume of meteoric water was involved in the ore-forming fluids, leading to fluid boiling as a result of their encounter, followed by the drop of fluid temperature. As a result, the dissolubility of Sb decreased so greatly that Sb was enriched and precipitated as ores. Due to differences in physic-chemical conditions between Au and Sb precipitates, Au and Sb were respectively precipitated in different structural positions, thus creating such a phenomenon of Au/Sb paragenesis and differentiation in space.     

Migration paths and precipitation mechanisms of ore-forming fluids at the Shuiyindong Carlin-type gold deposit,Guizhou, China

Shuiyindong is one of the largest and highest grade stratabound Carlin-type gold deposits in China. This paper reports on the results of petrographic studies, electron microprobe analyses (EMPA) of arsenian pyrite, and the mass transfer during mineralization and alteration, and it presents the deposit-scale distributions of Au, As, Sb, Hg, Tl, and trace elements in a representative cross section across the Shuiyindong Carlin-type gold deposit, Guizhou Province. The main objectives were to identify the precipitation mechanisms of minerals, or elements from fluids, and the migration paths of ore-forming fluids.Petrographic and EMPA studies indicate that gold in the primary ores is mainly hosted by arsenian pyrite. Mass transfer associated with alteration and mineralization shows that Au, As, Sb, Hg, Tl, and S were significantly added to all mineralized rocks, Fe₂O₃ and SiO₂ were immobile in the main orebodies that are hosted in bioclastic limestone, and CaO, Na₂O, Sr, and Li were removed from country rocks. The relations between Fe and S indicate that the sedimentary rocks at the Shuiyindong deposit contain more iron than is needed to combine with all of their contained sulfur to form pyrite. This suggests that sulfidation and decarbonation were the principal mechanism of gold precipitation at the Shuiyindong deposit. Hg, Sb, and As commonly formed sulfide minerals, such as stibnite, realgar, and orpiment, in late-stage quartz–calcite veins, or absorbed by organic matter in argillite. Fluid cooling presumably led to depositions of stibnite, realgar, and orpiment in late-stage quartz–calcite veins. Organic matter likely served as a reductant in argillite for the ore fluids, causing the precipitation of As, Sb, Hg, and S, as well as Au.Deposit-scale distributions of gold and other relevant elements reflect the passage of fluids through the rocks. Rock strata and structures allowed the ore-forming fluids to migrate horizontally along the unconformity surface of the Middle–Upper Permian, converge on the high position of an anticline, and then ascend into the overlying strata along the anticlinal axis. The distributions of the major and trace elements show that elements that accompanied the ore-forming fluids include Au, As, Sb, Hg, Tl, and S, and that Na₂O and Li were exhausted in the Longtan Formation at the anticlinal core during gold mineralization. The enrichment of Co, Cr, and Ni in the Longtan Formation at the anticlinal core might be associated with deformation that formed the anticline, or with gold mineralization. Different host rocks were preferentially mineralized by different elements. The bioclastic limestone is commonly enriched in Au, whereas the argillite is preferentially enriched in As, Hg, Sb, and Tl. The zonation of ore-forming elements in the deposit appears to be Sb–Tl–As–Hg–Au–Hg–As (from bottom to top). Enrichment of Au, As, Sb, Hg, and Tl provides useful guidance for the exploration for Carlin-type gold deposits in Guizhou. Anomalies of As and Hg in soil or stream sediment might be an important clue and these elements can be used as indicator elements. Ore-forming fluids migrated along the unconformity surface of the Middle–Upper Permian and the anticlinal axis, so these are favorable sites for exploration for Carlin-type gold deposits in Guizhou.     

Early Cretaceous gold mineralization in the Lesser Xing’an Range of NE China: the Yongxin example

ABSTRACT

The northern Lesser Xing’an Range in NE China hosts many gold deposits. However, genesis and tectonic background for the mineralization remain unclear. The newly discovered Yongxin gold deposit in this region provides a good example for understanding the related issues. Two economic orebodies have been recognized at Yongxin and they are mainly hosted in the hydrothermal breccias. Zircon U–Pb ages of granite porphyry and diorite porphyry are 119.3 ± 0.7 Ma and 119.9 ± 0.6 Ma, respectively. These data provide constraints to the upper limit of ore-forming age. The δ³⁴S values of pyrite from orebodies range from 2.3‰ to 5.1‰. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of the pyrite are of 18.126–18.255, 15.492–15.537 and 37.880–38.019, respectively. The δ¹⁸O_H2O and δD values of ore-forming fluids range from ?12.5‰ to 1.8‰ and from ?124.8‰ to ?102.1‰, respectively. The REE compositions of gold-bearing pyrite are similar to those of the volcanic rocks of the Longjiang formation, diorite porphyry and granite porphyry. The combined geological, geochronological and geochemical characteristics of the Yongxin gold deposit indicate that the ore-forming materials were likely sourced from the volcanic rocks of the Longjiang formation, diorite porphyry and granite porphyry, whereas the ore-forming fluids are dominated by meteoric water. The Yongxin gold deposit could be a product of the Early Cretaceous large-scale gold mineralization in northeast China which occurred in an extensional tectonic setting and were related to the rollback of the subducted Paleo-Pacific Oceanic Plate beneath the continental margin of northeast China.     

Fluid properties and sources of Sixiangchang carbonate-associated mercury deposit,southwest China

Mercury mines in Guizhou province are the main base of mercury production and the most important resource base in China. The San-Dan mercury belt in Guizhou province contains a series of important mercury deposits. However, the source of metallogenic materials and the properties of metallogenic fluid of these mercury deposits have long been a controversial issue. In this study, we used cathode luminescence techniques to distinguish different stages of dolomite and calcite, laser ablation inductively coupled plasma mass spectrometry to analyze the trace elements, and stable isotope mass spectrometry techniques to analyze C–O isotopes compositions of dolomite and calcite in the Sixiangchang mercury deposit in San-Dan mercury belt. We also measured the sulfur isotope composition of cinnabar. Our study showed that dolomite can be divided into two stages, the lumpy dolomite associated with cinnabar in Dol 1 stage and dolomite vein in Dol 2 stage, which is associated with Cal 2 stage calcite vein. With the progress of mineralization, Al, As, Mo, Sb, and Sr elements were gradually enriched in the ore-forming fluid. The rare earth element (REE) partition curve of Dol 1 stage dolomite showed a trend of light REE enrichment. Cal 2 stage calcite and Dol 2 stage dolomite exhibited a flat-type REE partition curve, and Dol 2 stage dolomite showed a strong negative anomaly for Eu. δ¹³C of carbonate mineral variation ranges from − 6.89 to − 2.16 ‰, while δ¹⁸O variation ranges from 13.80 to 23.09 ‰, and the δ³⁴S variation range of cinnabar is 16.51–24.28 ‰. Carbonate mineral trace elements and C–O isotopes compositions suggested that early ore-forming fluid was reduced, and late ore-forming fluid was oxidized. The ore-forming fluid of the Sixiangchang mercury deposit is a mixture of deep crustal fluid and meteoric water in deep thermal circulation, and involved in the oxidation of organic matter. The cinnabar δ³⁴S results showed that sulfur mainly came from seawater sulfate with the participation of microbial reduction. Sulfur is sedimentary in origin and was derived mainly from the host-rock strata.

     

Cretaceous–Neogene basin control on the formation of uranium deposits in South China: evidence from geology,mineralization ages,and H–O isotopes

ABSTRACT

The South China Uranium Province (SCUP) contains the largest number of discovered uranium deposits in China. This province includes seven uranium mineralization belts, at Wuyishan, Taoshan–Zhuguang, Chenzhou–Qinzhou, Gan–Hang, Xixia–Luzong, Mufushan–Hengshan, and Xuefengshan–Jiuwandashan. The uranium deposits can be classified according to their ore-hosting rocks into four general types: granite-, volcanic-, black-shale-, and sandstone-related. These uranium deposits crop out at the peripheries of Cretaceous–Neogene (K–N) redbed basins or are connected to the basins by NE–SW- to NNE–SSW-trending regional faults. Most of the volcanic-related uranium deposits were formed during the mid-Cretaceous (118 to 88 Ma); granite-related deposits have a wider range of ages from 124 to 11 Ma; the black-shale-related deposits have ages of 120 to 7 Ma; sandstone-related deposits yield ages of 111 to 22.5 Ma. As such, these four types of uranium deposits in South China have similar ages, irrespective of location, and are similar in age to K–N redbed basins in this region. δD_VSMOW(fluid) and δ¹⁸O_VSMOW(fluid) values of the volcanic-related uranium deposits generally range from – 105.9‰ to – 38.0‰ and – 11.1‰ to +5.3‰, respectively. The black-shale-related uranium deposits yield δD_VSMOW(fluid) and δ¹⁸O_VSMOW(fluid) values of – 74.5‰ to – 33.0‰ and – 4.4‰ to 9.3‰, respectively. However, the granite-related uranium deposits have a much wider range of δD_VSMOW(fluid) and δ¹⁸O_VSMOW(fluid) values from – 104.4‰ to – 23.1‰ and – 9.4‰ to +7.3‰, respectively. H–O isotopic compositions of the SCUP ore-forming fluids are similar to those of basinal fluids, again demonstrating the link between the uranium deposits and the basins. The spatial–temporal relationships and fluid isotopic similarities between the K–N basins and uranium mineralization indicate that the uranium deposits of the SCUP are genetically related to the K–N redbed basins, and are unconformity-related uranium deposits.     

Geological,fluid inclusion,and O–C–S–Pb–He–Ar isotopic constraints on the genesis of the Honghuagou lode gold deposit,northern North China Craton

The Honghuagou Au deposit is located in the Chifeng-Chaoyang region within the northern margin of the North China Craton. The auriferous quartz veins are mainly hosted in the mafic gneiss and migmatite of the Neoarchean Xiaotazigou Formation along NNW- and NE-striking faults, with pyrite as the predominant ore mineral. The gold mineralization process can be divided into two stages, involving stage I quartz-pyrite and stage II quartz-calcite-polymetallic sulfide. Three types of fluid inclusions (FIs) have been identified in the Honghuagou deposit, namely, carbonic inclusions, aqueous‑carbonic inclusions, and aqueous inclusions. Quartz of stage I contains all types of FIs, whereas only aqueous inclusions are evident in stage II veins. The FIs of stages I and II yield homogenization temperatures of 275–340 °C and 240–290 °C with salinities of 3.4–10.7 wt% and 1.4–9.7 wt% NaCl eqv., respectively. The ore-forming fluids are characterized by medium temperature and low salinity, belonging to the H₂O–NaCl–CO₂ system. The δ¹⁸O_H2O values of the ore fluids are between 2.1‰ and 5.9‰, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ¹³C_PDB = −4.4‰ to −4‰) are also similar to mantle carbon. He-Ar isotope data (³He/⁴He = 0.38–0.44 Ra; ⁴⁰Ar/³⁶Ar = 330–477) of fluid inclusions in pyrite indicate a mixed crustal and mantle source for the ore-forming fluids. Whereas, S-Pb isotope compositions of sulfides reveal that ore metals are principally derived from crustal rocks. On the basis of available geological and geochemical evidence, we suggest that the Honghuagou deposit is an orogenic gold deposit.     

Geochemical Tracing of Ore-forming Material Sources of Carlin-type Gold Deposits in the Yunnan-Guizhou-Guangxi Triangle Area --A Case Study of the Application of the Combined Silicon Isotopes Geochemistry and Siliceous Cathodoluminescence Analysis

This paper deals with characteristics of silicon isotope compositions and siliceous cathodolumines-cence of host rocks, ores and hydrothermal silicified quartz of the Carlin-type ore deposits in the Yunnan-Guizhou-Guangxi triangle area. The study shows that primary silicified quartz is nonluminescent but quartz in host rocks andsecondary silicified quartz are luminescent by the action of cathode rays. Correspondingly, silicon isotope composi-tions of host rocks, ores and hydrothermal quartz veins are clearly distinguished. In strata from the Middle Triassic tothe "Dachang" host bed, δ~(30)Si of the host rocks ranges from 0.0‰-0.3‰, while that of primary ore-forming silici-fied fluids from -0.1‰ to -0.4‰, in the Upper Permian and Lower Carboniferous strata and Indosinian diabasehost beds, δ~(30)Si of the host rocks is from -0.1‰ to -0.2‰ and that of the primary silicified quartz veins from 0.3‰-0.5‰. This pattern demonstrates the following geochemical mineralization process: primary ore-forming sili-ceous fluids migrated upwards quickly along the main passages of deep-seated faults from mantle to crust and en-tered secondary faults where gold deposits were eventually formed as a result of permeation and replacement of thesiliceous ore-forming fluids into different ore-bearing strata. This gives important evidence for the fact that ore-forming fluids of this type of gold deposits were mainly derived from upper mantle differentiation and shows goodprospects for deep gold deposits and geochemical background for large and superlarge gold deposits.     

Geology, Fluid Inclusion and Isotopic Study of the Neoproterozoic Suoi Thau Copper Deposit, Northwest Vietnam

The Sin Quyen-Lung Po district is an important Cu metallogenic province in Vietnam, but there are few temporal and genetic constraints on deposits from this belt. Suoi Thau is one of the representative Cu deposits associated with granitic intrusion. The deposit consists of ore bodies in altered granite or along the contact zone between granite and Proterozoic meta-sedimentary rocks. The Cu-bearing intrusion is sub-alkaline I-type granite. It has a zircon U-Pb age of ~776 Ma, and has subduction-related geochemical signatures. Geochemical analysis reveals that the intrusion may be formed by melting of mafic lower crust in a subduction regime. Three stages of alteration and mineralization are identified in the Suoi Thau deposit, i.e., potassic alteration; silicification and Cu mineralization; and phyllic alteration. Two-phase aqueous fluid inclusions in quartz from silicification stage show wide ranges of homogenization temperatures(140–383℃) and salinities(4.18wt%–19.13wt%). The high temperature and high salinity natures of some inclusions are consistent with a magmatic derivation of the fluids, which is also supported by the H-O-S isotopes. Fluids in quartz have δD values of –41.9‰ to –68.8‰. The fluids in isotopic equilibrium with quartz have δ~(18)O values ranging from 7.9‰ to 9.2‰. These values are just plotted in the compositional field of magmatichydrothermal fluids in the δD_(water) versus δ~(18)O_(water) diagram. Sulfide minerals have relatively uniform δ~(34)S values from 1.84‰ to 3.57‰, which is supportive of a magmatic derivation of sulfur. The fluid inclusions with relatively low temperatures and salinities most probably represent variably cooled magmatic-hydrothermal fluids. The magmatic derivation of fluids and the close spatial relationship between Cu ore bodies and intrusion suggest that the Cu mineralization most likely had a genetic association with granite. The Suoi Thau deposit, together with other deposits in the region, may define a Neoproterozoic subduction-related ore-forming belt.     

Geochemical characteristics and metallogenesis of Carlin-type gold deposits in the Sandu-Danzhai metallogenic zone, Guizhou Province, China

Geochemical studies of the Paiting and Miaolong Carlin-type gold deposits in the Sandu-Danzhai metal-logenic zone,Guizhou Province,have shown that the mineralized-altered rocks show LREE-enrichment patterns,generally displaying negative Eu anomalies(δEu=0.51?0.97) and unobvious negative Ce anomalies(δCe=0.86?0.99).Calcite and fluorite in relation with metallogenesis show MREE-enrichment patterns,generally displaying rather weak negative Eu anomalies(δEu=0.74?0.93) and weak negative Ce(δCe=0.70?0.98) anomalies.The δ13CPDB values of carbon in calcite are-1.61‰?-5.82‰,the δ18OSMOW values of oxygen are 13.97‰?19.24‰,and the δ34SCDT values of sulfur in stibnite are 17.72‰?21.68‰.In regard to δD and δ18O,ore-forming fluids pos-sess the characteristics of metamorphic water.The process of metallogenesis of the Carlin-type gold deposits is con-trolled by the Yanshanian tectonic activities.The Yanshanian movement promoted the migration and mobilization of metamorphic fluids in the extensively developed medium-to high-grade metamorphic rocks in this region,carrying primarily enriched gold and associated elements such as Hg,As,and Sb in the Sinian metamorphosed black shales and Lower Cambrian black shales.The ore-forming fluids found their way into a suitable metallogenic environment along the fault zone,followed by gold precipitation to form gold deposits.     

The Vilalba gold district,a new discovery in the Variscan terranes of the NW of Spain: A geologic,fluid inclusion and stable isotope study

This work defines the Vilalba gold district, a new gold region in the NW of Spain comprising three mineralized areas (Castro de Rei, Valiña–Azúmara and Arcos) and two different types of mineralization: 1) W–Au skarn in Castro de Rei, and 2) Au–As (Ag–Pb–Zn–Cu–Sb) vein/disseminated mineralization in Valiña–Azúmara and Arcos. Mineralization is mainly hosted by impure limestone and black slates (lower Cambrian) and spatially related to Variscan and Late-Variscan structures. Rhyolite dikes occur in Arcos (299 ± 6 Ma) and Castro de Rei, both consisting of peraluminous, high-potassium and calc-alkaline rocks. These dikes represent the fractionated expression of unexposed post-tectonic granitoids located at depth. The Castro de Rei area exhibits a contact aureole with biotite ± cordierite and calc-silicate hornfels. Prograde skarn consists of garnet, pyroxene, quartz, wollastonite and scheelite. The retrograde alteration took place in two stages and mainly consists of amphibole, epidote, zoisite, quartz, calcite, chlorite and sulfides. Gold mineralization in the skarn occurs as invisible gold in sulfoarsenides and as electrum related to Bi–Te–S minerals. The mineralization of Valiña–Azúmara and Arcos comprises two stages. The first consists of As-rich pyrite and arsenopyrite with invisible gold. The second stage mainly consists of base metal sulfides and Ag–Pb–Zn–Cu–Sb sulfosalts.Hydrothermal fluids involved in the skarn formation are low salinity (up to 6.6 wt.% NaCl eq.) aqueous carbonic fluids (H₂O + CO₂ ± CH₄ ± N₂) evolving into aqueous fluids during the last stage of gold mineralization. Stable isotope geochemistry indicates the importance of a magmatic fluid in the early stages (δ¹⁸O_SMOW from 7.5 to 11‰; δ³⁴S_CDT from 2.7 to 5.9‰) that evolved through interaction with host-rocks and mixing with metamorphic and/or meteoric fluids. The δ³⁴S_CDT values (7.8–10.9‰) of second retrograde stage sulfides suggest the incorporation of ³⁴S-enriched from host-rocks. In Valiña–Azúmara and Arcos, the fluid inclusion and isotope studies indicate similar hydrothermal fluids to those associated with the second retrograde skarn stage. Taking into account the fluid inclusion study and mineral geothermometry, an attempt was made to determine the P–T conditions of ore formation. The prograde skarn of Castro de Rei formed at temperatures and pressures ranging from 520 to 560 °C and from 1.7 to 2.5 kb. The mineralization of Valiña–Azúmara formed at minimum P–T conditions of 1.7 kb and 355 °C. The estimated temperatures for the Arcos mineralization are similar to those of Valiña–Azúmara (up to 383 °C) but at lower pressures.We propose the model of intrusion related gold systems (IRGSs) to explain the mineralizations of the Vilalba gold district. In this model, the Castro de Rei skarn and the Valiña–Azúmara mineralization represent a proximal and a distal deposit, respectively, relative to an unexposed granitoid situated at depth. We also consider Arcos as a distal deposit in relation to another unexposed granitoid located further south in the district.     

Two pulses of mineralization and genesis of the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet: Constraints from Fe–Zn isotopes

Zhaxikang is one large Sb–Pb–Zn–Ag deposit located in the North Himalaya of southern Tibet. To date, the genesis of this deposit still remains controversial. Here, we present new pyrite Fe and sphalerite Zn isotopic data for the first three stages of mineralization, Fe–Zn isotopic data for Mn–Fe carbonate that formed during the first two stages of mineralization, and Zn isotopic data for the slate wall rocks of the Jurassic Ridang Formation to discuss the genesis of the Zhaxikang deposit. The overall δ⁵⁶Fe and δ⁶⁶Zn values range from −0.80‰ to 0.43‰ and from −0.03‰ to 0.38‰, respectively. The δ⁵⁶Fe values of Mn–Fe carbonates are lighter than those of associated pyrite in six mineral pairs, indicating that the iron carbonates are preferentially enriched in light Fe isotopes relative to pyrite. The sphalerite has lighter δ⁶⁶Zn values than associated Mn–Fe carbonates in three mineral pairs.The δ⁵⁶Fe values of pyrite that formed during the first three stages of mineralization gradually increase from stage 1 (−0.33‰ to −0.09‰) through stage 2 (−0.30‰ to 0.19‰) to stage 3 (0.16‰–0.43‰). In comparison, the sphalerite that formed during these stages has δ⁶⁶Zn values that gradually decrease from stage 1 (0.16‰–0.35‰) through stage 2 (0.09‰–0.23‰) to stage 3 (−0.03‰ to 0.22‰). These data, in conjunction with the observations of hand specimens and thin sections, suggest that the deposit was overprinted by a second pulse of mineralization. This overprint would account for these Fe–Zn isotopic variations as well as the kinetic Rayleigh fractionation that occurred during mineralization. The temporally increasing δ⁵⁶Fe and decreasing δ⁶⁶Zn values recorded in the deposit are also coincident with an increase in alteration, again supporting the existence of two pulses of mineralization. The δ⁵⁶Fe values of the first pulse of ore-forming fluid were calculated using theoretical equations, yielding values of −0.54‰ to −0.34‰ that overlap with those of submarine hydrothermal solutions (−1‰ to 0‰). However, the δ⁵⁶Fe values of the stage 3 pyrite are heavier than those of typical submarine hydrothermal solutions, which suggests that the second pulse of mineralization was probably derived from a magmatic hydrothermal fluid. In addition, the second pulse of ore-forming fluid has brought some Fe and taken away parts of Zn, which results the lighter δ⁶⁶Zn values of sphalerite and heavier δ⁵⁶Fe values of pyrite from the second pulse of mineralization. Overall, the Zhaxikang deposit records two pulses of mineralization, and the overprint by the second pulse of mineralization causes the lighter δ⁶⁶Zn values and heavier δ⁵⁶Fe values of modified samples.     

Geology and C-O isotope geochemistry of carbonate-hosted Pb-Zn deposits, NW Guizhou Province, SW China

The Pb-Zn metallogenic district in NW Guizhou Province is an important part of the Yun-nan-Sichuan-Guizhou Pb-Zn metallogenic province, and also is one of the most important Pb-Zn producers in China. The hosting rocks of the Pb-Zn deposits are Devonian to Permian carbonate rocks, and the basement rocks are meta-sedimentary and igneous rocks of the Proterozoic Kunyang and Huili groups. The ore minerals are composed of sphalerite, galena and pyrite, and the gangue minerals are include calcite and dolomite. Geology and C-O isotope of these deposits were studied in this paper. The results show that δ13C and δ18O values of hydrothermal calcite, altered wall rocks-dolostone, sedimentary calcite and hosting carbonate rocks range from -5.3‰ to -0.6 ‰ (mean -3.4‰) and +11.3‰ to +20.9 ‰ (mean +17.2‰), -3.0‰ to +0.9 ‰ (mean -1.3‰) and +17.0‰ to +20.8‰ (mean +19.7‰), +0.6‰ to +2.5 ‰ (mean +1.4‰) and +23.4‰ to +26.5 ‰ (mean +24.6‰), and -1.8‰ to +3.9‰ (mean +0.7‰) and +21.0‰ to +26.8‰ (mean +22.9‰), respectively, implying that CO2 in the ore-forming fluids was mainly a result of dissolution of Devonian and Carboniferous carbonate rocks. However, it is difficult to evaluate the contribution of sediment de-hydroxylation. Based on the integrated analysis of geology, C and O isotopes, it is believed that the ore-forming fluids of these carbonate-hosted Pb-Zn deposits in this area were derived from multiple sources, including hosting carbonate rocks, Devonian to Permian sedimentary rocks and basement rocks (the Kun-yang and Huili groups). Therefore, the fluids mixing is the main precipitation mechanism of the Pb-Zn deposit in this province.     

Geology,geochemistry and genesis of the Qianfanling quartz-vein Mo deposit in Songxian County,Western Henan Province,China

The Qianfanling Mo deposit, located in Songxian County, western Henan province, China, is one of the newly discovered quartz-vein type Mo deposits in the East Qinling–Dabie orogenic belt. The deposit consists of molybdenite in quartz veins and disseminated molybdenite in the wall rocks. The alteration types of the wall rocks include silicification, K-feldspar alteration, pyritization, carbonatization, sericitization, epidotization and chloritization. On the basis of field evidence and petrographic analysis, three stages of hydrothermal mineralization could be distinguished: (1) pyrite–barite–quartz stage; (2) molybdenite–quartz stage; (3) quartz–calcite stage.Two types of fluid inclusions, including CO₂-bearing fluid inclusions and water-rich fluid inclusions, have been recognized in quartz. Homogenization temperatures of fluid inclusions vary from 133 °C to 397 °C. Salinity ranges from 1.57 to 31.61 wt.% NaCl eq. There are a large number of daughter mineral-CO₂-bearing inclusions, which is the result of fluid immiscibility. The ore-forming fluids are medium–high temperature, low to moderate salinity H₂O–NaCl–CO₂ system. The δ³⁴S values of pyrite, molybdenite, and barite range from − 9.3‰ to − 7.3‰, − 9.7‰ to − 7.3‰ and 5.9‰ to 6.8‰, respectively. The δ¹⁸O values of quartz range from 9.8‰ to 11.1‰, with corresponding δ¹⁸O_fluid values of 1.3‰ to 4.3‰, and δ¹⁸D values of fluid inclusions of between − 81‰ and − 64‰. The δ¹³C_V-PDB values of fluid inclusions in quartz and calcite have ranges of − 6.7‰ to − 2.9‰ and − 5.7‰ to − 1.8‰, respectively. Sulfur, hydrogen, oxygen and carbon isotope compositions show that the sulfur and ore-forming fluids derived from a deep-seated igneous source. During the peak collisional period between the North China Craton and the Yangtze Craton, the ore-forming fluids that derived from a deep igneous source extracted base and precious metals and flowed upwards through the channels that formed during tectonism. Fluid immiscibility and volatile exsolution led to the crystallization of molybdenite and other minerals, and the formation of economic orebodies in the Qianfanling Mo deposit.     

黔东南平秋金矿成因研究:来自氢、氧、硫同位素的制约

黔东南地处江南造山带西南段雪峰隆起西南端,区内金矿床(点)广布,是湘黔金矿集中区的重要组成部分.平秋金矿是该区金矿床的典型代表,其矿体产于下江群番召组浅变质火山-沉积岩,严格受北东向断裂褶皱控制.为理清其成因,对平秋金矿床含矿石英脉中的石英包裹体进行了氢、氧同位素测试.结果显示,其δD为-51.3‰～-59‰,818O...     

A Study of Ore-forming Fluids in the Shimensi Tungsten Deposit, Dahutang Tungsten Polymetallic Ore Field, Jiangxi Province, China

The Dahutang tungsten polymetallic ore field is located north of the Nanling W-Sn polymetallic metallogenic belt and south of the Middle—Lower Yangtze River Valley Cu-Mo-Au-Fe porphyry-skarn belt.It is a newly discovered ore field,and probably represents the largest tungsten mineralization district in the world.The Shimensi deposit is one of the mineral deposits in the Dahutang ore field,and is associated with Yanshanian granites intruding into a Neoproterozoic granodiorite batholith.On the basis of geologic studies,this paper presents new petrographic,microthermometric,laser Raman spectroscopic and hydrogen and oxygen isotopic studies of fluid inclusions from the Shimensi deposit.The results show that there are three types of fluid inclusions in quartz from various mineralization stages:liquid-rich two-phase fluid inclusions,vapor-rich two-phase fluid inclusions,and three-phase fluid inclusions containing a solid crystal,with the vast majority being liquid-rich two-phase fluid inclusions.In addition,melt and melt-fluid inclusions were also found in quartz from pegmatoid bodies in the margin of the Yanshanian intrusion.The homogenization temperatures of liquid-rich two-phase fluid inclusions in quartz range from 162 to 363℃ and salinities are 0.5wt%-9.5wt%NaCI equivalent.From the early to late mineralization stages,with the decreasing of the homogenization temperature,the salinity also shows a decreasing trend.The ore-forming fluids can be approximated by a NaCl-H_2O fluid system,with small amounts of volatile components including CO_2,CH_4 and N_2,as suggested by Laser Raman spectroscopic analyses.The hydrogen and oxygen isotope data show that δ5D_(V-smow) values of bulk fluid inclusions in quartz from various mineralization stages vary from-63.8‰ to-108.4‰,and the δ~(18)O_(H2O) values calculated from the δ~(18)O_(V-)smow values of quartz vary from-2.28‰ to 7.21‰.These H-O isotopic data are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water in the early stage,and meteoric water was added and participated in mineralization in the late stage.Integrating the geological characteristics and analytical data,we propose that the ore-forming fluids of the Shimensi deposit were mainly derived from Yanshanian granitic magma,the evolution of which resulted in highly differentiated melt,as recorded by melt and melt-fluid inclusions in pegmatoid quartz,and high concentrations of metals in the fluids.Cooling of the ore-forming fluids and mixing with meteoric water may be the key factors that led to mineralization in the Dahutang tungsten polymetallic ore field.     

Cadmium and sulfur isotopic compositions of the Tianbaoshan Zn–Pb–Cd deposit,Sichuan Province,China

Although Zn–Pb deposits are one of the most important Cd reservoirs in the earth, few studies have focused on the Cd isotopic fractionation in Zn–Pb hydrothermal systems. This study investigates the causes and consequences of cadmium and sulfur isotope fractionation in a large hydrothermal system at the Tianbaoshan Zn–Pb–Cd deposit from the Sichuan–Yunnan–Guizhou (SYG) metallogenic province, SW China. Moderate variations in Cd and S isotope compositions have been measured in sphalerite cover a distance of about 78 m. Sphalerite has δ^114/110Cd values ranging from 0.01 to 0.57‰, and sulfides (sphalerite, galena and chalcopyrite) have δ³⁴S_CDT values ranging from 0.2 to 5.0‰. Although δ³⁴S_CDT and δ^114/110Cd values in sphalerites have no regular spatial variations, the δ³⁴S_CDT values in galena and calculated ore-forming fluid temperatures decreased from 2.1 to 0.2‰ and from about 290 to 130 °C, respectively, from the bottom to the top of the deposit. Heavy Cd isotopes are enriched in early precipitated sphalerite in contrast to previous studies. We suggest that Cd isotopic compositions in ore-forming fluids are heterogeneous, which result in heavy Cd isotope enrichment in early precipitated sphalerite. In comparison with other Zn–Pb deposits in the SYG area, the Tianbaoshan deposit has moderate Cd contents and small isotope fractionation, suggesting differences in origin to other Zn–Pb deposits in the SYG province.In the Tianbaoshan deposit, the calculated δ³⁴S∑_S-fluids value is 4.2‰, which is not only higher than the mantle-derived magmatic sulfur (0 ± 3‰), but also quite lower than those of Ediacaran marine sulfates (about 30 to 35‰). Thus, we suggest that reduced sulfur of ore-forming fluids in the deposit was mainly derived from the leaching of the basement, which contains large amount of volcanic or intrusive rocks. Based upon a combination of Cd and S isotopic systems, the Tianbaoshan deposit has different geochemical characteristics from typical Zn–Pb deposits (e.g., the Huize deposit) in SYG area, indicating the unique origin of this deposit.