Origin of the Dachang gold deposit,NW China: constraints from H,O, S,and Pb isotope data

The Dachang gold deposit is located in the Late Triassic Songpan-Ganzi Fold Belt, NE Tibetan Plateau. Gold ore is concentrated as veins along secondary faults and fracture zones in the Bayan Har Group metaturbidites. No exposed felsic plutons are present in the vicinity of the deposit. The auriferous veins contain <15% sulphide minerals, mainly arsenopyrite, pyrite, and stibnite. Gold is commonly enclosed within arsenopyrite and pyrite. Typical alteration around the ore bodies includes silicification, sericitization, and weak carbonatization.

Gold-bearing quartz samples have δ¹⁸O values of 16.9–21.2‰ (V-SMOW) from which δ¹⁸O_H2O values of 6.2–9.6‰ can be calculated from the fluid inclusion temperatures (or 10.0 to 12.7‰ if we used the average arsenopyrite geothermometer temperature of 301°C). The δD values of fluid inclusions in quartz range from –90‰ to –72‰. δ³⁴S values of gold-bearing sulphides mainly range from –5.9‰ to –2.8‰ (V-CDT). Pyrite and arsenopyrite in ores have ²⁰⁶Pb/²⁰⁴Pb ratios of 18.2888 to 18.4702, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.5763 to 15.6712, and ²⁰⁸Pb/²⁰⁴Pb ratios of 38.2298 to 38.8212. These isotopic compositions indicate that the ore-forming fluids were of metamorphic origin, and the S and Pb may have been derived from the host metaturbidites of the Bayan Har Group. The Dachang Au deposit has geological and geochemical features similar to orogenic gold deposits. We propose that the ores formed when the Songpan-Ganzi Fold Belt was intensely deformed by Late Triassic folding and thrusting. Large-scale thrusting resulted in regional allochthons of different scales, followed by secondary faults or fracture zones that controlled the ore bodies.     

Auriferous Quartz Veins from the Dongping Gold Deposit,NW Hebei Province and Metallogenesis—Fluid Inclusion Rb—Sr Isochron Evidence

The Dongping gold deposit, situated on the northern margin of the North China Platform, is a composite deposit composed of auriferous quartz vein-type and altered rock-type ore bodies. It is hosted in the inner contact zone of an alkaline intrusion which was intruded into Archean metamorphic rocks and was formed not later than the Hercynian period. Auriferous quartz veins of the deposit are dated with the fluid inclusion Rb-Sr isochron method at 103 ± 4 Ma, indicating that the gold deposit was formed in the Yenshanian period.⁸⁷Sr/⁸⁶Sr sourcetracing shows the ore forming materials came dominantly from alkaline intrusions. These results, combined with other isotope and REE data, suggest that the Dongping gold deposit is not a traditional magmatic hydrothermal deposit, but a reworked hydrothermal deposit related to heated and evolved meteoric water. This project (49372105) is financially supported by the National Natural Science Foundation of China.     

Genesis of the Bangbu Orogenic Gold Deposit,Tibet: Evidence from Fluid Inclusion,Stable Isotopes,and Ar-Ar Geochronology

The Bangbu gold deposit is a large orogenic gold deposit in Tibet formed during the AlpineHimalayan collision. Ore bodies(auriferous quartz veins) are controlled by the E-W-trending Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Quartz veins at the deposit can be divided into three types: pre-metallogenic hook-like quartz veins, metallogenic auriferous quartz veins, and postmetallogenic N-S quartz veins. Four stages of mineralization in the auriferous quartz veins have been identified:(1) Stage S1 quartz+coarse-grained sulfides,(2) Stage S2 gold+fine-grained sulfides,(3) Stage S3 quartz+carbonates, and(4) Stage S4 quartz+ greigite. Fluid inclusions indicate the oreforming fluid was CO_2-N_2-CH_4 rich with homogenization temperatures of 170–261°C, salinities 4.34–7.45 wt% Na Cl equivalent. δ~(18)Ofluid(3.98‰–7.18‰) and low δDV-SMOW(-90‰ to-44‰) for auriferous quartz veins suggest ore-forming fluids were mainly metamorphic in origin, with some addition of organic matter. Quartz vein pyrite has δ~(34)SV-CDT values of 1.2‰–3.6‰(an average of 2.2‰), whereas pyrite from phyllite has δ~(34)SV-CDT 5.7‰–9.9‰(an average of 7.4‰). Quartz vein pyrites yield 206Pb/204 Pb ratios of 18.662–18.764, 207Pb/204 Pb 15.650–15.683, and ~(208)Pb/204 Pb 38.901–39.079. These isotopic data indicate Bangbu ore-forming materials were probably derived from the Langjiexue accretionary wedge. 40Ar/39 Ar ages for sericite from auriferous sulfide-quartz veins yield a plateau age of 49.52 ± 0.52 Ma, an isochron age of 50.3 ± 0.31 Ma, suggesting that auriferous veins were formed during the main collisional period of the Tibet-Himalayan orogen(~65–41 Ma).     

Intrusion-Related Gold Deposits of North China Craton, People's Republic of China

Abstract. Intrusion‐related gold deposits are widely distributed within the North China craton or along its marginal fold belts. Presently, about 200 individual intrusion‐related gold deposits (prospects) have been discovered, among which Yuerya, Anjia‐yingzi, Linglong, Jiaojia, Chenjiazhangzi, Qiyugou, Jinjiazhuang, Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang are the most important ones. In general, the intrusion‐related gold deposits can be classified into three major groups according to their host rocks: (1) hosted by or related to felsic intrusions, including (la) calc‐alkaline granitoid intrusions and (lb) cryptoexplosion breccia pipes; (2) related to ultramafic intrusions, and (3) hosted by or related to alkaline intrusions. The first group contains the Yuerya, Anjiayingzi, Linglong, Jiaojia, Chenjiazhangzi and Qiyugou gold deposits. Gold mineralization at these deposits occurs within Mesozoic Yanshanian calc‐alkaline granitoid intrusions or cryptoexplosion breccia pipes as gold‐bearing quartz veins and replacement bodies. Pyrite, galena, sphalerite, chalcopyrite, native gold and electrum are major metallic minerals. The Jinjiazhuang deposit belongs to the second group, and occurs within Hercynian diopsidite and peridotite as quartz veins and replacement bodies. Pyrite, marcasite, arsenopyrite, native gold and electrum are identified. The third group includes the Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang deposits. Gold mineralization at these deposits occurs predominantly within the Hercynian alkaline intrusive complexes as K‐feldspar‐quartz veins and replacement bodies. Major metal minerals are pyrite, galena, chalcopyrite, tellurides, native gold and electrum. All these pyrite separates from Hercynian and Yanshanian intrusions or cryptoexplosion pipes associated with the gold deposits show a broad range in δ³⁴S value, which is overall higher than those Precambrian rocks and their hosted gold deposits. For the alkaline intrusion‐related gold deposits, the δ³⁴S values of the sulfides (pyrite, galena and chalcopyrite) from the deposits increase systematically from orebodies to the alkaline intrusions. All of these intrusion‐related gold deposits show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the gold ores plot in between the fields of the intrusions and Precambrian metamorphic rocks. Data are interpreted as indicative of a mixing of sulfur and lead from magma with those from Precambrian metamorphic rocks. Isotopic age data, geological and geochemical evidences suggest that the ore‐forming materials for the intrusion‐related gold deposits were generated during the emplacement of the Hercynian or Yanshanian intrusion. The calc‐alkaline or alkaline magma may provide heat, volatiles and metals for the intrusion‐related gold deposits. Evolved meteoric water, which circulated the wall rocks, was also progressively involved in the magmatic hydrothermal system, and may have dominated the ore fluids during late stage of ore‐forming processes. Therefore, the ore fluid may have resulted from the mixing of calc‐alkaline or alkaline magmatic fluids and evolved meteoric water. All these intrusion‐related gold deposits are believed to be products of Hercynian or Yanshanian calc‐alkaline and alkaline igneous processes along deep‐seated fault zones within the North China craton or along its marginal belts.     

东坪金矿成矿时代研究

东坪金矿是我国在碱性岩中发现的第一个大型金矿,本文在详细野外观察的基础上,用K-Ar法、~(40)Ar/~(39)Ar法测定了成矿期花岗细晶岩脉、主成矿期矿石的同位素年龄,确定东坪金矿成矿时代为燕山期。     

Geology and Metallogenesis of the Sawayaerdun Gold Deposit in the Southwestern Tianshan Mountains, Xinjiang, China

The Sawayaerdun gold deposit, located in Wuqia County, Southwest Tianshan, China, occurs in Upper Silurian and Lower Devonian low‐grade metamorphic carbonaceous turbidites. The orebodies are controlled by a series of NE‐NNE‐trending, brittle–ductile shear zones. Twenty‐four gold mineralized zones have been recognized in the Sawayaerdun ore deposit. Among these, the up to 4‐km‐long and 200‐m wide No. IV mineralized zone is economically the most important. The average gold grade is 1–6 g/t. Gold reserves of the Sawayaerdun deposit have been identified at approximately 37 tonnes and an inferred resource of 123 tonnes. Hydrothermal alteration is characterized by silicification, pyritization, arsenopyritization, sericitization, carbonatization and chloritization. On the basis of field evidence and petrographic analysis, five stages of vein emplacement and hydrothermal mineralization can be distinguished: stage 1, early quartz stage, characterized by the occurrence of quartz veins; stage 2, arsenopyrite–pyrite–quartz stage, characterized by the formation of auriferous quartz veinlets and stockworks; stage 3, polymetallic sulfide quartz stage, characterized by the presence of auriferous polymetallic sulfide quartz veinlets and stockworks; stage 4, antimony–quartz stage, characterized by the formation of stibnite–jamesonite quartz veins; and stage 5, quartz–carbonate vein stage. Stages 2 and 3 represent the main gold mineralization, with stage 4 representing a major antimony mineralization episode in the Sawayaerdun deposit. Two types of fluid inclusion, namely H₂O–NaCl and H₂O–CO₂–NaCl types, have been recognized in quartz and calcite. Aqueous inclusions show a wide range of homogenization temperatures from 125 to 340°C, and can be correlated with the mineralization stage during which the inclusions formed. Similarly, salinities and densities of these fluids range for each stage of mineralization from 2.57 to 22 equivalent wt% NaCl and 0.76 to 1.05 g/cm³, respectively. The ore‐forming fluids thus are representative of a medium‐ to low‐temperature, low‐ to medium‐salinity H₂O–NaCl–CO₂–CH₄–N₂ system. The δ³⁴S_CDT values of sulfides associated with mineralization fall into a narrow range of ?3.0 to +2.6‰ with a mean of +0.1‰. The δ¹³C_PDB values of dolomite and siderite from the Sawayaerdun gold deposit range from ?5.4 to ?0.6‰, possibly reflecting derivation of the carbonate carbon from a mixed magmatic/sedimentary source. Changes in physico‐chemical conditions and composition of the hydrothermal fluids, water–rock exchange and immiscibility of hydrothermal fluids are inferred to have played important roles in the ore‐forming process of the Sawayaerdun gold–antimony deposit.     

Dashuigou Tellurium Deposit in Sichuan Province, China: S, C, O, and H Isotope Data and Their Implications on Hydrothermal Mineralization

Abstract: Dashuigou, a unique tellurium‐dominated deposit over the world, is located in the western margin of the Yangtze cra‐ton in southwestern China. It is characterized by high‐grade tellurium accompanied by bismuth, gold, silver, and sulfur, and occurs in the area of less than one km². The mineralization is divided into three stages, i.e. (1) tellurium‐bearing pyrrhotite–pyrite stage, (2) tetradymite stage, and (3) auriferous quartz veins stage. Tellurium mineralization coexisting with bismuth, silver, selenium, and gold predominantly develops in the stage 2, while the stage 1 is enriched only in sulfur and iron, and the stage 3 is very weakly mineralized with gold. The δ³⁴S values of sulfides in the ore of the deposit vary in a narrow range of –3.1 ‐ +2.8 per mil with –3.1 ‐ +2.8 per mil for the stage 1 and –0.5 ‐ +2.1 for the stage 2, showing the isotopic characteristics of mantle derived sulfur. The δ¹³C values of vein dolomites vary from –5.3 to –7.2 per mil, with –5.3 ‐ –6.6 per mil for the stage 1 and –5.3 ‐ –7.2 per mil for the stage 2, which are significantly different from those of surrounding Triassic marble with δ¹³C values of –0.3 ‐ +2.8 per mil, and show characteristics of mantle derived carbon. The δ¹⁸O values of vein dolomites range from +10.2 to +13.1 per mil, which are higher than those of carbonatite, but lower than those of the marble. Their corresponding δ¹⁸O_water values are +0.6 ‐ +3.9 per mil, with +2.7 ‐ +3.8 per mil for the stage 1 and +0.6 ‐ +3.9 per mil for the stage 2. The data implies that these vein carbonates were formed by the mixing fluids of magmatic or mantle source with meteoric or formation water. The δ¹⁸O values of ore‐forming fluids responsible for the formation of vein quartz are estimated to be +3.2 to +6.8, the δD values of inclusion fluids of the quartz are measured to be –54 to –82 per mil. All those stable isotopic data suggest the involvement of the fluids from mantle and/or mantle‐derived magmas through fault system in the forming process of the Dashuigou tellurium deposit.     

Geology and Geochemistry of the Bianbianshan Au‐Ag‐Cu‐Pb‐Zn Deposit,Southern Da Hinggan Mountains,Northeastern China

The Bianbianshan deposit, the unique gold-polymetal (Au-Ag-Cu-Pb-Zn) veined deposit of the polymetal metallogenic belt of the southern segment of Da Hinggan Mountains mineral province, is located at the southern part of the Hercynian fold belt of the south segment of Da Hinggan Mountains mineral province, NE China. Ores at the Bianbianshan deposit occur within Cretaceous andesite and rhyolite in the form of gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite, chalcopyrite, galena and sphalerite. The deposit is hosted by structurally controlled faults associated with intense hydrothermal alteration. The typical alteration assemblage is sericite + chlorite + calcite + quartz, with an inner pyrite - sericite - quartz zone and an outer seicite - chlorite - calcite - epidote zone between orebodies and wall rocks. δ34 S values of 17 sulfides from ores changing from –1.67 to +0.49‰ with average of –0.49‰, are similar to δ34 S values of magmatic or igneous sulfide sulfur. 206Pb/204Pb, 207Pb/204Pb and 208Pb/ 204Pb data of sulfide from ores range within 17.66–17.75, 15.50–15.60, and 37.64–38.00, respectively. These sulfur and lead isotope compositions imply that ore-forming materials might mainly originate from deep sources. H and O isotope study of quartz from ore-bearing veins indicate a mixed source of deep-seated magmatic water and shallower meteoric water. The ore formations resulted from a combination of hydrothermal fluid mixing and a structural setting favoring gold-polymetal deposition. Fluid mixing was possibly the key factor resulting in Au-Ag-Cu-Pb-Zn deposition in the deposit. The metallogenesis of the Bianbianshan deposit may have a relationship with the Cretaceous volcanic-subvolcanic magmatic activity, and formed during the late stage of the crust thinning of North China.     

Characteristics of Triassic epithermal Au mineralization at the Q prospect,Chatree mining area,Central Thailand

The Chatree deposit is located in the Loei‐Phetchabun‐Nakhon Nayok volcanic belt that extends from Laos in the north through central and eastern Thailand into Cambodia. Gold‐bearing quartz veins at the Q prospect of the Chatree deposit are hosted within polymictic andesitic breccia and volcanic sedimentary breccia. The orebodies of the Chatree deposit consist of veins, veinlets and stockwork. Gold‐bearing quartz veins are composed mainly of quartz, calcite and illite with small amounts of adularia, chlorite and sulfide minerals. The gold‐bearing quartz veins were divided into five stages based on the cross‐cutting relationship and mineral assemblage. Intense gold mineralization occurred in Stages I and IV. The mineral assemblage of Stages I and IV is characterized by quartz–calcite–illite–laumontite–adularia–chlorite–sulfide minerals and electrum. Quartz textures of Stages I and IV are also characterized by microcrystalline and flamboyant textures, respectively. Coexistence of laumontite, illite and chlorite in the gold‐bearing quartz vein of Stage IV suggests that the gold‐bearing quartz veins were formed at approximately 200°C. The flamboyant and brecciated textures of the gold‐bearing quartz vein of Stage IV suggest that gold precipitated with silica minerals from a hydrothermal solution that was supersaturated by boiling. The δ¹⁸O values of quartz in Stages I to V range from +10.4 to +11.6‰ except for the δ¹⁸O value of quartz in Stage IV (+15.0‰). The increase in δ¹⁸O values of quartz at Stage IV is explained by boiling. P_H2O is estimated to be 16 bars at 200°C. The f_CO2 value is estimated to be 1 bar based on the presence of calcite in the mineral assemblage of Stage IV. The total pressure of the hydrothermal solution is approximately 20 bars at 200°C, suggesting that the gold‐bearing quartz veins of the Q prospect formed about 200 m below the paleosurface.     

Thermoluminescence of quartz from Shihu gold deposit, western Hebei province, China: some implications for gold exploration

Thermoluminescence (TL) of monomineralic separates have been widely used in various geosciences fields in order to trace the thermal history and aid in prospecting for gold deposits. Quartz is a ubiquitous mineral in the Shihu gold deposit, which is situated in the northern part of the Taihang orogenic belt in the North China craton (NCC). The deposit is hosted by ductile-brittle faults within an Archean metamorphic core complex of the Fuping Group. This deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins. New TL results have been obtained for quartz, in which four type-TL glow curves were identified. The gold-bearing quartz present type III glow curves that consist of two peak glow curves at the middle and high peak temperatures with the similar TL intensity. In addition, the cross-sections of peak temperatures and TL intensity highlight the valuable area where the Au-bearing quartz present weak TL intensity and low-middle peak temperatures. Our results significantly enhance the usefulness of quartz in metallogenic studies of the North China craton and as an indicator mineral in mineral exploration of the Taihang Mountain region.     

Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge,Russia)

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H₂O-CO₂-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (³He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ³⁴S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).     

Recognition of Yanshanian magmatic-hydrothermal gold and polymetallic gold mineralization in the Laowan gold metallogenic belt,Tongbai Mountains: New evidence from structural controls,geochronology and geochemistry

The Laowan metallogenic belt in China is an important metallogenic belt within the Tongbai orogenic belt, and contains the medium-sized Laowan and Shangshanghe gold deposits, the small Huangzhuyuan lead–zinc–silver–gold deposit and some gold and Cu–Pb occurrences. These deposits are hosted in Mesoproterozoic plagioclase amphibolite (or schist) and mica-quartz schist. The gold ores are mainly quartz veins and veinlets and disseminated altered ores. Subordinate ore types include massive sulfides and breccias. The Laowan gold deposit is characterized by three right-stepping en-echelon fracture-controlled alteration zones that dip gently to the south and includes disseminated, sheeted and stockwork ores. These lodes were formed by the interaction of ore-forming fluid with foliated-to laminated cataclasite within the transpressional faults. The Shangshanghe gold deposit is characterized by parallel ore lodes that dip steeply to the north, and includes quartz veins and breccias in addition to ores in altered wallrocks. These lodes were formed by focusing of fluids into transtensional faults. These ore controlling faults displaced early barren quartz veins 10 m horizontally with a dextral sense of motion. The ore-hosting structures at the Laowan and Shangshanghe deposits correspond to the P and R-type shears of a brittle dextral strike-slip fault system, respectively, which make angles of about 15° and − 15° to the Laowan and Songpa boundary faults. The ore-controlling fault system post-dated formation of a ductile shear zone, and peak regional metamorphism. This precludes a genetic relationship between hydrothermal mineralization and regional metamorphism and ductile shear deformation. These gold deposits are not typical orogenic gold deposits. The metallogenic belt displays district-scale-zoning of Mo → Cu–Pb–Zn–Ag → Au relative to Songpa granite porphyry dike zone, suggesting the mineralization may be closely related to the granite porphyry. Measured δ³⁴S of sulfides and δ¹⁸O and δD of fluid inclusion waters in auriferous quartz also are consistent with a magmatic source for sulfur and ore fluids. The similarity of Pb isotope ratios between the ores and Yanshanian granitoids suggests a similar source. As the age (139 ± 3 Ma) of granite porphyry obtained by zircon U–Pb isotope overlaps the mineralization age (138 ± 1 Ma: Zhang et al., 2008a), the gold and polymetallic metallogenesis of the Laowan gold belt has close spatial, temporal and possibly genetic relationships with Yanshanian high level magmatism.     

冀北东坪金矿床深部-外围的构造-蚀变-流体成矿研究

冀北东坪金矿田是我国首次在碱性杂岩体内发现的金矿床,曾被认为是与碱性岩有关的金矿床。近年来年代学数据表明,东坪-后沟一带金矿的赋矿碱性杂岩体形成于海西期,而成矿却主要发生在燕山期。金矿床严格受构造裂隙控制,构造-蚀变-流体成矿作用显著,钾长石化是最重要的蚀变。由未蚀变岩石向矿体和断裂带中心方向,典型的构造-蚀变-矿化分带依次为:0-原岩(二长岩、正长岩)带,I-微斜长石化带,II硅化绢云母化微斜长石岩带,III碎裂微斜长石岩带,及IV断层泥。从0带到III带,Au含量增加,Ag、Cu、Pb、Zn、Mo也略有增加。东坪金矿构造-蚀变-矿化阶段可分为4个:Ⅰ钾长石-石英脉阶段;Ⅱ黄铁矿-白色石英阶段;Ⅲ多金属硫化物-烟灰色石英脉阶段;Ⅳ晚期碳酸盐阶段。深部中段各阶段脉石英的流体包裹体研究表明, 在I、II、III阶段均发育富CO₂包裹体。第Ⅰ阶段钾长石石英脉L-V型包裹体均一温度(Th)为220.3~359℃,盐度1.1%~3.1% NaCleqv;H₂O-CO₂型包裹体Th在346.5~383.5℃。第Ⅱ阶段黄铁矿白色石英脉中L-V型包裹体Th范围是217.2~372.5℃,盐度在1.1%~5.7% NaCleqv;H₂O-CO₂型包裹体Th在241.2~396.7℃,盐度为2.2%~6.2% NaCleqv。第Ⅲ阶段的烟灰色石英脉中L-V型包裹体Th范围为158.2~350.5℃,盐度在0.7%~5.5% NaCleqv;H₂O-CO₂型包裹体Th范围在215.2~378℃之间,盐度范围在3.0%~6.0% NaCleqv。第Ⅳ阶段晚期石英脉L-V型包裹体Th范围为151.2~249.8℃,盐度在0.9%~8.3% NaCleqv。矿区外围转枝莲矿段的II阶段白色石英脉中包裹体的Th范围为220~416.2℃,III阶段烟灰色石英脉的Th范围为195.3~425℃。富金石英脉形成于中高温(＞300℃,可达400℃以上)、中深压力(70~160MPa以上)条件下。其成矿背景、热液蚀变、矿物共生组合及流体性质与典型的造山型金矿有一定的差别,归属于"与侵入岩有关的金矿床"更合理。     

河北东坪碲金矿床辉钼矿Re-Os及锆石U-Pb年龄研究

东坪碲金矿床是与碱性侵入岩有关的国内规模最大的碲金矿床。虽然前人已对该矿床做过大量研究,但其成矿年龄仍存在较大争议。文章通过对矿床中辉钼矿Re-Os和锆石U-Pb年龄进行研究,对成矿年龄和矿床成因进行限定。矿床中的辉钼矿存在浸染状和细脉状两种产状。浸染状辉钼矿通常产于正长岩,与硫化物共生,Re-Os模式年龄为(401.1±2.1)和(402.8±2.1) Ma。细脉状辉钼矿主要产在石英-硫化物脉中,其内部及裂隙中产出大量自然金,Re-Os模式年龄为(380.3±2.0)和(376.9±2.9) Ma。含金石英脉中的岩浆锆石U-Pb年龄为(394±1.7) Ma,热液锆石U-Pb年龄为(382±4.7) Ma。辉钼矿与锆石年龄一致,且与水泉沟碱性杂岩体侵位年龄相吻合,因此认为东坪碲金矿床存在泥盆纪成矿,可能与水泉沟岩体岩浆活动有关。矿床经历了晚侏罗世—早白垩世岩浆流体的交代、活化、富集过程,最终形成大型碲金矿床。矿床中的碲主要来自上地幔或洋壳物质的部分熔融,水泉沟碱性岩浆出溶的高氧逸度、中偏碱性的流体和脱气作用为碲的迁移和富集提供了重要条件。     

Role of fluid mixing and wallrock sulfidation in gold mineralization at the Semna mine area,central Eastern Desert of Egypt: Evidence from hydrothermal alteration,fluid inclusions and stable isotope data

The Semna gold deposit is one of several vein-type gold occurrences in the central Eastern Desert of Egypt, where gold-bearing quartz veins are confined to shear zones close to the boundaries of small granitoid stocks. The Semna gold deposit is related to a series of sub-parallel quartz veins along steeply dipping WNW-trending shear zones, which cut through tectonized metagabbro and granodiorite rocks. The orebodies exhibit a complex structure of massive and brecciated quartz consistent with a change of the paleostress field from tensional to simple shear regimes along the pre-existing fault segments. Textural, structural and mineralogical evidence, including open space structures, quartz stockwork and alteration assemblages, constrain on vein development during an active fault system. The ore mineral assemblage includes pyrite, chalcopyrite, subordinate arsenopyrite, galena, sphalerite and gold. Hydrothermal chlorite, carbonate, pyrite, chalcopyrite and kaolinite are dominant in the altered metaggabro; whereas, quartz, sericite, pyrite, kaolinite and alunite characterize the granodiorite rocks in the alteration zones. Mixtures of alunite, vuggy silica and disseminated sulfides occupy the interstitial open spaces, common at fracture intersections. Partial recrystallization has rendered the brecciation and open space textures suggesting that the auriferous quartz veins were formed at moderately shallow depths in the transition zone between mesothermal and epithermal veins.Petrographic and microthermometric studies aided recognition of CO₂-rich, H₂O-rich and mixed H₂O–CO₂ fluid inclusions in the gold-bearing quartz veins. The H₂O–CO₂ inclusions are dominant over the other two types and are characterized by variable vapor: liquid ratios. These inclusions are interpreted as products of partial mixing of two immiscible carbonic and aqueous fluids. The generally light δ³⁴S of pyrite and chalcopyrite may suggest a magmatic source of sulfur. Spread in the final homogenization temperatures and bulk inclusion densities are likely due to trapping under pressure fluctuation through repeated fracture opening and sealing. Conditions of gold deposition are estimated on basis of the fluid inclusions and sulfur isotope data as 226–267 °C and 350–1100 bar, under conditions transitional between mesothermal and epithermal systems.The Semna gold deposit can be attributed to interplay of protracted volcanic activity (Dokhan Volcanics?), fluid mixing, wallrock sulfidation and a structural setting favoring gold deposition. Gold was transported as Au-bisulfide complexes under weak acid conditions concomitant with quartz–sericite–pyrite alteration, and precipitated through a decrease in gold solubility due to fluid cooling, mixing with meteoric waters and variations in pH and fO₂.     

Porphyry-Style Petropavlovskoe Gold Deposit,the Polar Urals: Geological Position,Mineralogy, and Formation Conditions

Geological and structural conditions of localization, hydrothermal metasomatic alteration, and mineralization of the Petropavlovskoe gold deposit (Novogodnenskoe ore field) situated in the northern part of the Lesser Ural volcanic–plutonic belt, which is a constituent of the Middle Paleozoic island-arc system of the Polar Urals, are discussed. The porphyritic diorite bodies pertaining to the late phase of the intrusive Sob Complex play an ore-controlling role. The large-volume orebodies are related to the upper parts of these intrusions. Two types of stringer–disseminated ores have been revealed: (1) predominant gold-sulfide and (2) superimposed low-sulfide–gold–quartz ore markedly enriched in Au. Taken together, they make up complicated flattened isometric orebodies transitory to linear stockworks. The gold potential of the deposit is controlled by pyrite–(chlorite)–albite metasomatic rock of the main productive stage, which mainly develops in a volcanic–sedimentary sequence especially close to the contacts with porphyritic diorite. The relationships between intrusive and subvolcanic bodies and dating of individual zircon crystals corroborate a multistage evolution of the ore field, which predetermines its complex hydrothermal history. Magmatic activity of mature island-arc plagiogranite of the Sob Complex and monzonite of the Kongor Complex initiated development of skarn and beresite alterations accompanied by crystallization of hydrothermal sulfides. In the Early Devonian, due to emplacement of the Sob Complex at a depth of approximately 2 km, skarn magnetite ore with subordinate sulfides was formed. At the onset of the Middle Devonian, the large-volume gold porphyry Au–Ag–Te–W ± Mo,Cu stockworks related to quartz diorite porphyry—the final phase of the Sob Complex— were formed. In the Late Devonian, a part of sulfide mineralization was redistributed with the formation of linear low-sulfide quartz vein zones. Isotopic geochemical study has shown that the ore is deposited from reduced, substantially magmatic fluid, which is characterized by close to mantle values δ³⁴S = 0 ± 1‰, δ¹³C =–6 to–7‰, and δ¹⁸O = +5‰ as the temperature decreases from 420–300°C (gold–sulfide ore) to 250–130°C (gold–(sulfide)–quartz ore) and pressure decreases from 0.8 to 0.3 kbar. According to the data of microanalysis (EPMA and LA-ICP-MS), the main trace elements in pyrite of gold orebodies are represented by Co (up to 2.52 wt %), As (up to 0.70 wt %), and Ni (up to 0.38 wt %); Te, Se, Ag, Au, Bi, Sb, and Sn also occur. Pyrite of the early assemblages is characterized by high Co, Te, Au, and Bi contents, whereas the late pyrite is distinguished by elevated concentrations of As (up to 0.7 wt %), Ni (up to 0.38 wt %), Se (223 ppm), Ag (up to 111 ppm), and Sn (4.4 ppm). The minimal Au content in pyrite of the late quartz–carbonate assemblage is up to 1.7 ppm and geometric average is 0.3 ppm. The significant correlation between Au and As (furthermore, negative–0.6) in pyrite from ore of the Petropavlovskoe deposit is recorded only for the gold–sulfide assemblage, whereas it is not established for other assemblages. Pyrite with higher As concentration (up to 0.7 wt %) is distinguished only for the Au–Te mineral assemblage. Taking into account structural–morphological and mineralogical–geochemical features, the ore–magmatic system of the Petropavlovskoe deposit is referred to as gold porphyry style. Among the main criteria of such typification are the spatial association of orebodies with bodies of subvolcanic porphyry-like intrusive phases at the roof of large multiphase pluton; the stockwork-like morphology of gold orebodies; 3D character of ore–alteration zoning and distribution of ore components; geochemical association of gold with Ag, W, Mo, Cu, As, Te, and Bi; and predominant finely dispersed submicroscopic gold in ore.     

Gold-telluride-sulfide association in the Sandaowanzi epithermal Au-Ag-Te deposit,NE China: implications for phase equilibrium and physicochemical conditions

The Sandaowanzi gold-telluride deposit, with a total reserve of ?≥?25 t of Au and an average grade of 15 g/t, is located in the Great Hinggan Range Metallogenic Belt in NE China. This deposit is the first reported case of a dominantly Au (±Ag)-telluride deposit in this area and it reveals highly economic bonanza Au- and Ag-telluride ores. Ore bodies principally occur in quartz veins and stockworks and minor in disseminations hosted by trachyandesites and andesitic breccias. Four paragenetic stages of mineralization are identified, demonstrating an early deposition of sulfides and subsequent precipitation of tellurides, which are mainly composed by petzite, sylvanite and to a lesser extent, hessite, calaverite, altaite, unnamed telluride (Au_1.8Ag_0.2Te), krennerite, empressite, stützite and coloradoite. Abundant telluride assemblages identified from Sandaowanzi ores are mostly attributed to breakdown of early tellurium-bearing phases (i.e., γ- and χ-phases) during cooling. The deposition of substantial Au-Ag-Te minerals are constructed under physicochemical conditions of T?=?240 to 280 °C, pH?=?4.39 to 5.64, logfO₂?=–44.8 to –41.8, logfTe₂?=–9.75 to –9.43, logαAu⁺ _(aq)/αAg⁺ _(aq)?=??6.87 to –6.56, and gold is mostly scavenged from a HTe^?-dominant ore-forming fluid. The unusually high Te concentrations in the Sandaowanzi epithermal system are likely attributed to alkaline to calc-alkaline magmatic degassing.     

Geochemical characteristics of gold mineralization of the Huai Kham On deposit,Sukhothai Fold Belt,Northern Thailand

The Huai Kham On gold deposit is located in the central part of the Sukhothai Fold Belt, northern Thailand. The Sukhothai Fold Belt represents an accretionary complex formed by subduction and collision between the Indochina and Sibumasu Terranes. There are many small gold deposits in the Sukhothai Fold Belt; however, the styles and formation environments of those gold deposits are not clear. The geology of the Huai Kham On deposit consists of volcanic and volcanosedimentary rocks, limestone, and low‐grade metamorphic rocks of Carboniferous to Triassic age. Gold‐bearing quartz veins are hosted by volcanic and volcanosedimentary rocks. The quartz veins can be divided into four stages. The mineral assemblage of the gold‐bearing quartz veins of Stages I and II comprises quartz, calcite, illite, pyrite, native gold, galena, chalcopyrite, and sphalerite. Quartz veins of Stage III consist of microcrystalline quartz, dolomite, calcite, pyrite, native gold, and chalcopyrite. Veins of Stage IV consist of calcite, dolomite, chlorite, and quartz. Fluid inclusions in quartz veins are classified into liquid‐rich two‐phase (Types I_A and I_B), carbonic‐aqueous (Type II), and carbonic (Type III) fluid inclusions. The homogenization temperatures of Types I_A and II fluid inclusions that are related to the gold‐bearing quartz veins from Stages I to III ranged from 240° to 280°C. The δ¹⁸O values of quartz veins of Stages I to III range from +12.9 to +13.4‰, suggesting the presence of a homogeneous hydrothermal solution without temperature variation such as a decrease of temperature during the formation of gold‐bearing quartz veins from Stages I to III in the Huai Kham On gold deposit. Based on the calculated formation temperature of 280°C, the δ¹⁸O values of the hydrothermal solution that formed the gold‐bearing quartz veins range from +3.2 to +3.7‰, which falls into the range of metamorphic waters. The gold‐bearing quartz veins of the Huai Kham On deposit are interpreted to be the products of metamorphic water.     

Timing of mineralization at the Shihu gold deposit in the middle segment of the Taihang Mountain,China

The Shihu gold deposit, located in the middle-south section of the core of the Fuping mantle branch structure, is hosted in the Archean Fuping Group and adjacent to the quartz diorite porphyrite. The gold deposit is the only large gold deposit with reserves of more than 30 tons gold discovered in western Hebei Province so far. In order to constrain the timing of mineralization of this ore deposit, this paper focuses on the isotopic dating of zircon and pyrite. Zircons in gold-bearing quartz veins are magmatic in origin and no hydrothermal zircon has been found in such quartz veins, indicating that zircons were derived from the wall rocks. U–Pb ages of zircons fall mainly in the two domains: 2492 ± 82 and 136 ± 4 Ma, respectively, indicative of the contribution of the Fuping-Group TTG gneiss and Yanshanian igneous rocks, respectively. The Re–Os isotopic compositions of pyrites in the gold-bearing quartz veins yield an isochron age of 127 ± 31 Ma. Combined with other dating results, we suggest that the main metallogenic age of the Shihu gold deposit is 120–127 Ma.     

The Ore-forming Fluid of the Gold Deposits of Muru Gold Belt in Eastern Shandong, China - a Case Study of Denggezhuang Gold Deposit

Abstract. Denggezhuang gold deposit is an epithermal gold‐quartz vein deposit in northern Muru gold belt, eastern Shandong, China. The deposit occurs in the NNE‐striking faults within the Mesozoic granite. The deposit consists of four major veins with a general NNE‐strike. Based on crosscutting relationships and mineral parageneses, the veins appear to have been formed during the same mineralization epochs, and are further divided into three stages: (1) massive barren quartz veins; (2) quartz‐sulfides veins; (3) late, pure quartz or calcite veinlets. Most gold mineralization is associated with the second stage. The early stage is characterized by quartz, and small amounts of ore minerals (pyrite), the second stage is characterized by large amounts of ore minerals. Fluid inclusions in vein quartz contain C‐H‐O fluids of variable compositions. Three main types of fluid inclusions are recognized at room temperature: type I, two‐phase, aqueous vapor and an aqueous liquid phase (L+V); type II, aqueous‐carbonic inclusions, a CC₂‐liquid with/without vapor and aqueous liquid (LCO₂+VCC₂+Laq.); type III, mono‐phase aqueous liquid (Laq.). Data from fluid inclusion distribution, microthermometry, and gas analysis indicate that fluids associated with Au mineralized quartz veins (stage 2) have moderate salinity ranging from 1.91 to 16.43 wt% NaCl equivalent (modeled salinity around 8–10 wt% NaCl equiv.). These veins formatted at temperatures from 80d? to 280d?C. Fluids associated with barren quartz veins (stage 3) have a low salinity of about 1.91 to 2.57 wt% NaCl equivalent and lower temperature. There is evidence of fluid immiscibility and boiling in ore‐forming stages. Stable isotope analyses of quartz indicate that the veins were deposited by waters with δ^O and δD values ranging from those of magmatic water to typical meteoric water. The gold metallogenesis of Muru gold belt has no relationship with the granite, and formed during the late stage of the crust thinning of North China.