The Gol-e-Zard Zn-Pb Deposit,Lorestan Province,Iran: a Metamorphosed SEDEX Deposit

The Gol-e-Zard Zn-Pb deposit is one of several sediment-hosted Zn-Pb deposits found in the central part of the Sanadaj-Sirjan Zone, known as the Isfahan-Malayer belt, western Iran. Mineralization occurs in Upper Triassic to Jurassic phyllites and meta-sandstones. Sphalerite and galena are the most abundant metallic ores, with minor chalcopyrite. Calcite and quartz are the main gangue minerals. Fissure filling, replacement textures and especially mineralized faults, suggest an epigenetic stage in the Gol-e-Zard deposit formation. Geochemical studies of mineralized rocks show high concentrations of Zn, Pb and Cu, (Zn and Pb > 10000 ppm and Cu average 3000 ppm). LREE enrichment (LREE>HREE, La/Lu average 1.44) and positive Eu anomalies (Eu/Eu*>1 average 1.67) indicate reducing conditions during the deposition of deposit. However, some samples do not display negative Ce anomalies, which indicate that localized oxidizing conditions are also present. This study indicates that the Gol-e-Zard deposit formed due to circulating hydrothermal fluids in a marine environment. A SEDEX-type genesis, which is defined by circulating hydrothermal fluids through sediments in a marine environment, and syngenetic precipitation of Zn and Pb sulphides, is suggested for the Gol-e-Zard deposit. Emplacement of some granitoid intrusions such as the Aligudarz granitoid intrusion remobilized mineralizing fluids and metamorphosed the Gol-e-Zard deposit.     

Geological Characteristics and Genesis of the Jiamoshan MVT Pb–Zn Deposit in the Sanjiang belt, Tibetan Plateau

The carbonate-hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust-fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst-controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore-forming fluids belonged to a Mg2+–Na+–K+–SO2-4–Cl-–F-–NO-3–H2 O system at low temperatures(120–130°C) but with high salinities(19–22% NaCl eq.). We have recognized basinal brine as the source of the ore-forming fluids on the basis of their H–O isotopic compositions(-145‰ to-93‰ for δDV-SMOW and-2.22‰ to 13.00‰ for δ18 Ofluid), the ratios of Cl/Br(14–1196) and Na/Br(16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite(-5.0‰ to 3.7‰ for δ13 CV-PDB and 15.1‰ to 22.3‰ for δ18 OV-SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34 S values are low in the galena(-3.2‰ to 0.6‰) but high in the barite(27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo-seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples(18.3270–18.3482 for 206 Pb/204 Pb, 15.6345–15.6390 for 207 Pb/204 Pb, and 38.5503–38.5582 for 208 Pb/204 Pb) are similar to those of the regional Triassic volcanic-arc rocks that formed during the closure of the Paleo-Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.     

The Gol-e-Zard Zn-Pb Deposit,Lorestan Province,Iran: a Metamorphosed SEDEX Deposit简

The Gol-e-Zard Zn-Pb deposit is one of several sediment-hosted Zn-Pb deposits found in the central part of the Sanadaj-Sirjan Zone, known as the Isfahan-Malayer belt, western Iran. Mineralization occurs in Upper Triassic to Jurassic phyllites and meta-sandstones. Sphalerite and galena are the most abundant metallic ores, with minor chalcopyrite. Calcite and quartz are the main gangue minerals. Fissure filling, replacement textures and especially mineralized faults, suggest an epigenetic stage in the Gol-e-Zard deposit formation. Geochemical studies of mineralized rocks show high concentrations of Zn, Pb and Cu,（Zn and Pb 〉 10000 ppm and Cu average 3000 ppm）. LREE enrichment（LREE〉HREE, La/Lu average 1.44） and positive Eu anomalies（Eu/Eu＊〉1 average 1.67） indicate reducing conditions during the deposition of deposit. However, some samples do not display negative Ce anomalies, which indicate that localized oxidizing conditions are also present. This study indicates that the Gol-e-Zard deposit formed due to circulating hydrothermal fluids in a marine environment. A SEDEX-type genesis, which is defined by circulating hydrothermal fluids through sediments in a marine environment, and syngenetic precipitation of Zn and Pb sulphides, is suggested for the Gol-e-Zard deposit. Emplacement of some granitoid intrusions such as the Aligudarz granitoid intrusion remobilized mineralizing fluids and metamorphosed the Gol-e-Zard deposit.     

Dating of the Dachang Superlarge Tin-polymetallic Deposit in Guangxi and Its Implication for the Genesis of the No. 100 Orebody

The Dachang superlarge Sn-polymetal deposit in Guangxi, China, is one of the largest tin deposit all over the world. However, this deposit has long been in debate as to its origin. One of the opinions is that the Dachang deposit was formed by replacement of hydrothermal solution originating from Yanshanian granites, and the other is that this deposit was formed by submarine exhalation in the Devonian. This paper presents some new isotopic geochronology data obtained with the 40Ar-39Ar method for quartz and sanidine from massive ore in the No. 91 and No. 100 orebodies. Analytic results show that the No. 91 orebody was formed at 94.52±0.33 Ma (the plateau age obtained with the 40Ar-39Ar method for quartz) or 91.4±2.9 Ma (the plateau age obtained with the 40Ar-39Ar method for feldspar), while the No. 100 orebody was formed at 94.56±0.45 Ma (the plateau age obtained with the 40Ar-39Ar method for quartz), suggesting that both the No. 91 and the No. 100 orebodies were formed at the Late Yanshanian instead o     

The Zhaxikang Vein‐type Pb‐Zn‐Ag‐Sb Deposit in Himalayan Orogen,Tibet: Product by Overprinting and Remobilization Processes during Post‐collisional Period

The Zhaxikang Pb-Zn-Ag-Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein-type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping veintype orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N–S-striking normal fault system. This deposit records multiple stages of mineralization that include an early period(A) of massive coarse-grained galena–sphalerite deposition and a later period(B) of Sb-bearing vein-type mineralization. Period A is only associated with galena–sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite–sphalerite–pyrite, quartz–sulfosalt–sphalerite, calcite–pyrite, quartz–stibnite, and quartz-only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre-existing Pb–Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive openspace filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low–medium temperature(187–267°C) and low salinity(4.00–10.18% wt. Na Cl equivalent) ore-forming fluids, although variations in the physical–chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with Fe S concentrations of 8.999–9.577, 7.125–9.109, 5.438–1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable(4‰–13‰), varying from 4‰ to 11‰ in period A and 10‰ to 13‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206 Pb/204 Pb vs. 207 Pb/204 Pb and 206 Pb/204 Pb vs. 208 Pb/204 Pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb–Zn sulfides and regional Sbbearing fluids. These features are indicative of overprinting and remobilization of pre-existing Pb–Zn sulfides by Sb-bearing ore-forming fluids during a post-collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang-style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb–Zn exploration in these areas.     

H-O-S-Pb Isotopic Compositions of the Chagele Pb-Zn-Cu-Mo Deposit,Tibet: Implications for the Ore-forming Processes and Comparison with Pb-Zn (Cu-Mo) Deposits in Middle-east Segment of the Nyainqentanglha Metallogenic BeltEI北大核心CSCD

The Chagele is a typical Pb-Zn-Cu-Mo deposit located in the western Nyainqentanglha Pb-Zn-Ag-Fe-Cu metallogenic belt (NPMB) that immediately north of the Gangdese porphyry copper belt, Tibet. The deposit contains three ore types: the porphyry (Cu) Mo ores occur as thin veins hosted in the granite porphyry; the skarn (Cu) Pb-Zn type ores are of vein-type or lenticular-type mainly occurring in the external contact zone and interstratified crack zone; and the hydrothermal vein Pb-Zn type ores are controlled by the NNE-striking faults and situated in the structural fractured zones and the up walls of fault zones. The (Cu) Pb-Zn ores consist mainly of galena, sphalerite, chalcopyrite, pyrite, malachite, showing automorphic granular, hypautomorphic to allotriomorphic granular and metasomatic-relict textures, and exhibiting mainly veined, banded, disseminated and massive structures. Hydrothermal alteration includes skarnization, silicification and limonitization. The (Cu) Mo ores consists mainly of chalcopyrite and molybdenite, and minor pyrite. The (Cu) Mo ores are characterized by scaly texture, veinlet and massive structures. It has reserves of 0.38 Mt Pb, 0.6 Mt Zn and 110.1 t Ag, with average grade of 2.08%, 3.29% and 6.07 g/t, respectively, and is considered as a deposit with huge ore-prospecting potential in western of NPMB. However, the ore-forming material and genesis of the Chagele deposit are still not clear. This paper systematically investigated the H, O, S and Pb isotopes of the Chagele deposit and compared it with the other Pb-Zn (Cu-Mo) deposits in the middle-east segment of NPMB. Isotopic geochemical analyses showed that the fluids have δ18O values of -2.2‰ to 2.9‰ and δD values of -189‰ to -157‰, respectively, indicative of mixing between magmatic and meteoric waters. The bimodal distribution of δ34 S values for sulfides (-5.6‰ to -0.8‰, the average: -3.7‰ and 1.1‰ to 2.6‰, the average: 1.8‰) indicated that sulfur of the ores were derived from both wall rocks and magma, while the Cu-Mo orebodies was mainly derived from the granite porphyry. The sulfides have 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values in ranges of 18.614 to 18.688, 15.657 to 15.747 and 38.988 to 39.269; similarly the granite porphyries have 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18.663 to 19.058, 15.643 to 15.664, and 39.002 to 39.559, respectively, implying that both of them were originated from the upper crust. The H-O-S-Pb isotopic characteristics of the Chagele deposit are similar to those of the Pb-Zn polymetallic deposits in the mid-east NPMB, suggesting that these deposits have similar ore-forming fluid and material sources. It can be concluded that the Chagele deposit is a typical porphyry type Mo deposit + skarn type-hydrothermal vein type of Cu-Pb-Zn deposit. Moreover, we argue that the mineralization is not only confined to the mid-east NPMB, the western segment of the belt with similar tectonic-magmatism also has high potential of ore mineralization. © 2018, Science Press. All right reserved.     

Genesis of the Bianjiadayuan Pb-Zn polymetallic deposit,Inner Mongolia,China:Constraints from in-situ sulfur isotope and trace element geochemistry of pyrite

The Southern Great Xing'an Range(S(GXR)which forms part of the eastern segment of the Central Asian Orogenic Belt(CAOB)is known as one of the most important Cu-Mo-Pb-Zn-Ag-Au metallogenic belts in China,hosting a number of porphyry Mo(Cu),skarn Fe(Sn),epithermal Au-Ag,and hydrothermal veintype Ag-Pb-Zn ore deposits.Here we investigate the Bianjiadayuan hydrothermal vein-type Ag-Pb-Zn ore deposit in the southern part of the SGXR.Porphyry Sn± Cu± Mo mineralization is also developed to the west of the Ag-Pb-Zn veins in the ore field.We identify a five-stage mineralization process based on field and petrologic studies including(i)the early porphyry mineralization stage,(ii)main porphyry mineralization stage,(iii)transition mineralization stage,(iv)vein-type mineralization stage and(v)late mineralization stage.Pyrite is the predominant sulfide mineral in all stages except in the late mineralization stage,and we identify corresponding four types of pyrites:Pyl is medium-grained subhedral to euhedral occurring in the early barren quartz vein;Py2 is medium-to fine-grained euhedral pyrite mainly coexisting with molybdenite,chalcopyrite,minor sphalerite and galena;Py3 is fine-grained,subhedral to irregular pyrite and displays cataclastic textures with micro-fractures;Py4 occurs as euhedral microcrystals and forms irregularly shaped aggregate with sphalerite and galena.LA-ICP-MS trace element analyses of pyrite show that Cu,Pb,Zn,Ag,Sn,Cd and Sb are partitioned into pyrite as structurally bound metals or mineral micro/nano-inclusions,whereas Co,Ni,As and Se enter the lattice via isomorphism in all types of pyrite.The Cu,Zn,Ag,Cd concentrations gradually increase from Pyl to Py4,which we correlate with cooling and mixing of ore-forming fluid with meteoric water.Py2 contains the highest contents of Co,Ni,Se,Te and Bi,suggesting high temperature conditions for the porphyry mineralization stage.Ratios of Co/Ni(0.03-10.79,average 2.13)and sulphur isotope composition of sulfide indicate typical hydrothermal origin for pyrites.The δ~(34)S_(cDT) values of Pyl(0.42‰-1.61‰,average1.16‰),Py2(-1.23‰to 0.82‰,average 0.35‰),Py3(—0.36‰to 2.47‰average 0.97‰).Py4(2.51‰--3.72‰,average 3.06‰),and other sulfides are consistent with those of typical porphyry deposit(-5‰to 5‰),indicating that the Pb-Zn polymetallic mineralization in the Bianjiadayuan deposit is genetically linked to the Yanshanian(Jurassic-Cretaceous)magmatic-hydrothermal events.Variations of δ~(34) S values are ascribed to the changes in physical and chemical conditions during the evolution and migration of the ore-forming fluid.We propose that the high Sn content of pyrite in the Bianjiadayuan hydrothermal vein-type Pb-Zn polymetallic deposit can be used as a possible pathfinder to prospect for Sn mineralization in the surrounding area or deeper level of the ore field in this region.     

U-Pb Geochronology and Geochemistry of Stratiform Garnet from the Aqishan Pb-Zn Deposit, Eastern Tianshan, Xinjiang, NW China: Constraints on Genesis of the Deposit

The Aqishan lead-zinc deposit,located in the Jueluotag metallogenic belt of eastern Tianshan,Xinjiang,Northwest China,has a stratiform occurrence in the marine volcanic tuff of the Yamansu Formation.The ore body has a typical double-layer structure,having a stratified,stratoid,lenticular upper part and a veined,stockwork-like lower part.The occurrence of the upper orebody is consistent with that of the volcanic tuff wall rock.The ore minerals are mainly chalcopyrite,pyrite,sphalerite,galena and magnetite,the altered minerals mainly being silicified,such as sericite,chlorite,epidote,garnet.The garnetized skarn,being stratiform and stratoid,is closely related to the upper part of the orebody.Geological observations show that the limestone in the ore-bearing Yamansu Formation is not marbleized and skarnized.Spatially,it is associated with the ferromanganese deposits in the marine volcanic rocks of the Yamansu Formation.These geological features reflect the likelihood that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit.The results from the EPMA show that the garnet is mainly composed of grossular-andradite series,contents being in a range of 34.791-37.8%SiO₂,32.493-34.274%CaO,8.454-27.275%FeO,0.012-15.293%Al₂O₃,0.351-1.413%MnO,and lower values of 0.013-1.057%TiO₂.The content of SiO₂ vs.CaO and FeO vs.Al₂O₃ has a significant positive correlation.The results of ICP-MS analysis for the garnet show that the REE pattern is oblique to right in general.The total amount of rare earth elements is relatively low,ΣREE=71.045-826.52 ppm,which is relatively enriched for LREE and depleted for HREE.LREE/HREE=8.66-4157.75,La_N/Yb_N=23.51-984.34,with obvious positive Eu and Ce anomalies(δEu=2.27-76.15,δCe=0.94-1.85).This result is similar to the REE characteristics of ore-bearing rhyolite volcanic rocks,showing that the garnet was formed in an oxidizing environment and affected by clear hydrothermal activity.The U-Pb isotopic dating of garnet by fs-LA-HR-ICP-MS gives an age of 316.3±4.4 Ma(MSWD=1.4),which is consistent with the formation time of the Yamansu Formation.According to the study of deposit characteristics and geochemical characteristics,this study concludes that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit,the garnet being caused by hydrothermal exhalative sedimentation.     

Distribution Patterns of Ag in Hydrothermal Precipitates from the Okinawa Trough

The Okinawa Trough is characterized by enrichment of Ag in hydrothermal precipitates; however, the distribution of this enrichment remains poorly constrained. This study presents the results of a field-emission scanning electron microscopy and electron-microprobe analysis based mineralogical and geochemical investigation of the spatial distribution of Ag within Ag-rich sulfide samples from the Okinawa Trough. The tetrahedrite, covellite, and galena in these samples contain high concentrations of Ag(average values of 1.60, 0.78, and 0.23 wt%, respectively) and also various Ag sulfosalts. Examination of the Ag budget of these samples indicates that most of the Ag is hosted by tetrahedrite followed by galena. The Ag within tetrahedrite is incorporated by substitution into the Cu site, whereas galena becomes Ag-enriched by the coupled incorporation of monovalent Ag, Tl, and Cu, and trivalent Sb and Bi into Pb lattice sites. Tetrahedrite and galena containing higher concentrations of Sb favor increased Ag substitution. Four sets of Ag host minerals are identified with distinct ore formation temperatures. Tetrahedrite and galena concentrate the majority of Ag at medium temperatures(150–300°C). Other Ag host minerals concentrate only minor or trace amounts of Ag, including massive sphalerite, chalcopyrite, and pyrite at high temperatures(300°C), colloform pyrite and sphalerite at low temperatures(150°C), and Ag-sulfosalts at even lower temperatures(100°C).     

Hydrothermal Sedimentary Mineralization of the Super‐large Bamianshan Fluorite Deposit in Zhejiang Province,China

The Bamianshan fluorite deposit is a super-large one recently discovered in Zhejiang Province of China. This paper presents an analysis of its geological background, orebody and ore characteristics, petrochemical characteristics of host rocks, rare earth elements (REE) of rocks and ores, fluid inclusions in fluorite and Sm-Nd isotopic features in an effort to study its sedimentary mineralization. The result shows that the super-large Bamianshan fluorite deposit is of hydrothermal sedimentation genesis, deformed by the later hydrothermal fluid. Integrated with host rocks and orebody characteristics, it is inferred that the deposit originates from the Cambrian sedimentary rocks. And the later magmatic activities deformed some orebodies in different degrees, forming steeply dipping vein orebodies in the tectonic belts regionally.     

Petrological geochemistry and chronology of ore-bearing intrusion in Wuxi Porphyry Gold Deposit,in South Anhui ProvinceEI北大核心CSCD

The Wuxi gold deposit is located in Langqiao town, Jingxian county in South Anhui province, which is situated in the Jiangnan orogen, between the Middle and Lower Yangtze polymetallic metallogenic belt and South China metallogenic belt. The LA-ICP-MS dating results for zircons from the drill samples and outcrop rock in ore-bearing granite porphyry are consistent, 139.6±1.7 Ma(ZK7301), 137.3±1.6 Ma(ZK7001), 137.3±1.1 Ma (10WX-1), respectively. This intrusion is controlled by fault structure, and slightly contaminated by the early Archean crustal material. The developed cryptoexplosive breccia and mineralized breccia indicated the Wuxi orebody and granite porphyry were formed contemporaneously. The Wuxi granite porphyry is characterized by peraluminous, enriched in LILE (large ion lithophile elements), depleted in HFSE (high field strength elements) and heavy rare earth elements, significant differentiation between LREE and HREE, slight Eu negative anomaly. The apatite from the Wuxi granite porphyry has similar REE characteristics with those of the Yangtze series, indicating it was affected by mantle derived magmatic fluid activities; and the high δEu value of the apatite implies open tectonic environment and high oxygen fugacity during magma evolution. Zircon oxygen fugacity calculation indicates the granite porphyry formed in a high oxygen fugacity condition, thus it is conducive for precipitation and mineralization of Cu, Au and other ore-forming elements. While the formation of the Wuxi granite porphyry was closely related to the subduction and collision of the Paleo-pacific plate. The developed faults in the deposit provided channels for ore-forming fluid migration, which is conducive to the mineralization. Further prospecting and geochemical work are necessary for the area. ©, 2015, Science Press. All right reserved.     

Genesis of the Gold Deposit in the Indus-Yarlung Tsangpo Suture Zone, Southern Tibet: Evidence from Geological and Geochemical Data

The Nianzha gold deposit,located in the central section of the Indus-Yarlung Tsangpo suture(IYS) zone in southern Tibet,is a large gold deposit(Au reserves of 25 tons with average grade of 3.08 g/t) controlled by a E-W striking fault that developed during the main stage of Indo-Asian collision(~65-41 Ma).The main orebody is 1760 m long and 5.15 m thick,and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic melange in the footwall to the south.High-grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic melange.The wall-rock alteration is characterized by silicification in the fracture zone,serpentinization and the formation of talc and magnesite in the ultramafic unit,and chloritization and the formation of epidote and calcite in diorite.Quartz veins associated with Au mineralization can be divided into three stages.Fluid inclusion data indicate that the deposit formed from H_2O-NaCl-organic gas fluids that homogenize at temperatures of 203℃-347℃ and have salinities of 0.35wt%-17.17wt%NaCl equivalent.The quartz veins yield δ~(18)O_(fluid) values of 0.15‰-10.45‰,low δD_(V-SMOW)values(-173‰ to-96‰),and the δ~(13)C values of-17.6‰ to-4.7‰,indicating the ore-forming fluids were a mix of metamorphic and sedimentary orogenic fluids with the addition of some meteoric and mantle-derived fluids.The pyrite within the diorite has δ~(34)S_(V-CDT) values of-2.9‰-1.9‰(average-1.1‰),~(206)Pb/~(204)Pb values of 18.47-18.64,~(207)Pb/~(204)Pb values of 15.64-15.74,and ~(208)Pb/~(204)Pb values of 38.71-39.27,all of which are indicative of the derivation of S and other ore-forming elements from deep in the mantle.The presence of the Nianzha,Bangbu,and Mayum gold deposits within the IYS zone indicates that this area is highly prospective for large orogenic gold deposits.We identified three types of mineralization within the IYS,namely Bangbu-type accretionary,Mayum-type microcontinent,and Nianzha-type ophiolite-associated orogenic Au deposits.The three types formed at different depths in an accretionary orogenic tectonic setting.The Bangbu type was formed at the deepest level and the Nianzha type at the shallowest.     

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.     

Metallogenic Age and Ore-forming Material Sources of the Dahongshan Fe-Cu Deposit, Yunnan Province: Insights from Molybdenite Re-Os Dating and H-O-S-Pb Isotopes

The Dahongshan Fe-Cu (-Au) deposit is a superlarge deposit in the Kangdian metallogenic belt, southwestern China, comprising approximately 458 Mt of Fe ores (40% Fe) and 1.35 Mt Cu. Two main types of Fe-Cu (-Au) mineralization are present in the Dahongshan deposit: (1) early submarine volcanic exhalation and sedimentary mineralization characterized by strata-bound fine-grained magnetite and banded Fe-Cu sulfide (pyrite and chalcopyrite) hosted in the Na-rich metavolcanic rocks; (2) late hydrothermal (-vein) type mineralization characterized by Fe-Cu sulfide veins in the hosted strata or massive coarse-grained magnetite orebodies controlled by faults. While previous studies have focused primarily on the early submarine volcanic and sedimentary mineralization of the deposit, data related to late hydrothermal mineralization is lacking. In order to establish the metallogenic age and ore-forming material source of the late hydrothermal (-vein) type mineralization, this paper reports the Re-Os dating of molybdenite from the late hydrothermal vein Fe-Cu orebody and H, O, S, and Pb isotopic compositions of the hydrothermal quartz-sulfide veins. The primary aim of this study was to establish the metallogenic age and ore-forming material source of the hydrothermal type orebody. Results show that the molybdenite separated from quartz-sulfide veins has a Re-Os isochron age of 831 ± 11 Ma, indicating that the Dahongshan Fe-Cu deposit experienced hydrothermal superimposed mineralization in Neoproterozoic. The molybdenite has a Re concentration of 99.7–382.4 ppm, indicating that the Re of the hydrothermal vein ores were primarily derived from the mantle. The δ34S values of sulfides from the hydrothermal ores are 2‰–8‰ showing multi-peak tower distribution, suggesting that S in the ore-forming period was primarily derived from magma and partially from calcareous sedimentary rock. Furthermore, the abundance of radioactive Pb increased significantly from ore-bearing strata to layered and hydrothermal vein ores, which may be related to the later hydrothermal transformation. The composition of H and O isotopes within the hydrothermal quartz indicates that the ore-forming fluid is a mixture of magmatic water and a small quantity of water. These results further indicate that the late hydrothermal orebodies were formed by the Neoproterozoic magmatic hydrothermal event, which might be related to the breakup of the Rodinia supercontinent. Mantle derived magmatic hydrothermal fluid extracted ore-forming materials from the metavolcanic rocks of Dahongshan Group and formed the hydrothermal (-vein) type Fe-Cu orebodies by filling and metasomatism.     

Lead isotope geochemical characteristics of Pb-Zn-Cu deposits on the southwestern margin of Tarim, and their significance

The polymetallic(Pb,Zn,Cu,etc) ore belt on the southwestern margin of Tarim is one of the major regions with the greatest prospecting potential in Xinjiang.Reported in this paper are the lead isotope data for 66 sulfide samples(including 50 galena samples,15 chalcopyrite samples and 1 pyrite sample) collected from such representative deposits as Tamu,Tiekelike,Kalangu,Abalieke,etc.in this ore belt.The Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb in the galena samples range from 17.931 to 18.176,15.609 to 15.818 and 38.197 to 38.944,with the average values of 18.017,15.684 and 38.462,respectively.Those in the chalcopyrite samples range from 17.926 to 18.144,15.598 to 15.628 and 38.171 to 38.583,with the average values of 18.020,15.606 and 38.262,respectively.The pyrite sample has the Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb to be 17.980,15.604 and 38.145,respectively.In combination with the previous Pb isotope data for sulfides,it is found that there is only a slight variation in the Pb isotopic composition of galena,chalcopyrite,sphalerite and pyrite in the ore belt.However,there is some difference in Pb isotopic characteristics between galena and chalcopyrite,especially the Pb isotopic composition of galena shows an obvious linear correlation with some other relevant parameters(e.g.β and γ).The comprehensive analysis suggested that lead in galena(maybe including sphalerite and pyrite) was derived principally from wall rocks and underlying basement,and that in chalcopyrite only originated from the basement.The single-stage model ages of these sulfides couldn’t indicate the time limit of metallogenesis(Pb,Zn,Cu,etc.),and the positive linear correlations for the Pb isotopic composition of galena are of no single-stage and two-stage Pb-Pb isochron significance.Furthermore,there are significant differences in Pb isotopic composition characteristics between the genetic type of deposits in this polymetallic ore belt and the Mississippi Valley type(MVT).In addition,the authors also pointed out that there is a phenomenon of differentiation(not paragenesis) for lead and copper elements during the process of metallogenesis in this ore belt.     

A New Variety of Mineral—Argentian Mercurian Gold

Argentian mercurian gold,golden-yellow in colour,is a variety of native gold containing Ag and Hg,coccurring as hexagonal and tetragonal crystals in hairy,milk-droplet or irregular forms.Its microhardness Hv=91kg/mm^2,equivalent to 3.04on Mons‘scale,and the reflectance is 70.35%(589nm).Chemical analysis gave:Au 56.05-67.33,Ag18.29-31.06 and Hg 10-14.82%,as well as minor Cu.In a few samples Bi or Fe was also detected.The simplified formula is (Au0.52Ag0.36Hg0.09Cu0.02)0.99.X-ray analysis suggests the mineral is of isometric system,with space group=Oh^5-Fm3m,a0=0.40803nm,V=0.06739nm^3,and Z=4.Argentian mercurian gold occurs in a Ag-multimetal deposit at Xiacun,Baiyu County,Sichuan Province,As observed in the mining district,the mineral is distributed along the fissures of the main metallic minerals pyrite,tetrahedrite,chalcopyrite,arsenopyrite,galena,sphalerite,etc.,or in the sulfide veinlets developed in the.fissures of these minerals.Also found in the mineral deposit are native gold,argentite,sulvanite,bournonite,boulangrite,etc.     

China’s First Independent Cobalt Deposit and its Metallogenic Mechanism: Evidence from Fluid Inclusions and Isotopic Geochemistry

The Tuolugou cobalt deposit is the first independent large-scale Co- and Au-bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low-grade metamorphic volcano-sedimentary rock series with well-developed Na-rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCl-H2O system, accompanied by NaCl-CO2-H2O-N2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3He/4He range between 0.10 to 0.31Ra (averaging 0.21Ra), and 40Ar/36Ar between 302 and 569 (averaging 373), which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. δ34S values of pyrite approaches to zero (δ34S ranging from ?4.5‰ to +1.5‰, centering around ?1.8‰ to ?0.2‰), reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 206Pb/204Pb>19.279, 207Pb/204Pb>15.691 and 208Pb/204Pb>39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water-dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase (such as pyrite), but cobalt enrichment, and presence and increasing contents of Co-bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata-bound Co-Cu-Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt. All of them are syngenetic hydrothermal exhalative sedimentation in origin.     

中国有色金属工业总公司矿产地质研究院

The Changpo tin-polymetallic deposit occurs in the Upper Devonian marine carbonate rocks and silicious rocks and is controlled jointly by three factors, i.e., strata (D3), structures and magmatic rocks, bearing dual characteristics of the syndepositional deposit and hydrothermal one. According to modes of occurrence and mineral assemblages, it can be divided into two types of mineralizations: stratiform stanniferous sulfides and veinlike cassiterite-sulfides. The former has such characteristics of sedimentary deposits as being controlled by the strata, and possessing typical syndepositional structure, e. g., striped and laminated structure, as well as less developed wall rock alterations. In contrast, veinlike mineralizations are characterized by features of hydrothermal deposits, such as being governed by fracture systems and affected by tectonic activities, showing polystage pulsation and having typical hydrothermal wall rock alterations including sericitization, tourmalinization and fluoritization. The two types display distinct differences not only in geological characteristics, but also in mineral assemblages, metallogenic physical-chemical conditions and temperatures as well as ore-forming time. Nevertheless, there exist close relations between the two mineralizations: (1) they occur in the same spatial position; (2) they have similar vertical mineral zoning: pyrite in the upper part of the orebody and pyrrhatite in the lower; (3) δ34S values of pyrite and sphalerite are similar in the two types, being -4.5‰ - +1.3‰ in the pyrite and -7.1‰ - +0.2‰ in the sphalerite respectively. All this implies that these two mineralizations have intimate relationships and also obvious differences. On the one hand, they were formed in different ore-forming stages and diverse geological conditions; on the other hand, the stratiform mineralization was- superimposed and remolded by the late ore-forming hydrothermal fluids, i. e., veinlike mineralization, whose material sources in turn had something to do with the stratiform mineralization. Studies show that the stratiform mineralization is of sea-floor syndepositional type formed in Late Devonian whose formation was probably related to the eruptive sedimentation of the volcanic hot spring ascending along the deep-seated fractures. The metallogenic elements such as S, Sn, Pb and Zn were derived from the depth of the crust, and the veinlike mineralization resulted from the hydrothermal liquid of Yanshanian granitic magma. Under the action of the magmatic solution and the heat of the magma, the metallogen materials in the stratiform mineralization were activated and transported, and thus provided some ore-forming materials for veinlike mineralization, such as S, Sn, Pb and Zn. It is therefore concluded that the Changpo ore deposit is a composite-origin type formed both by syndeposition, i.e., eruptive deposition from volcanic hot spring at seafloor, and by superimposition-reformation of the magmatic hydrothermal fluids, and that this deposit must have evolved from the stratiform stanniferous sulfide mineralization.     

Geology and Isotope Geochemistry of the Yinchanggou-Qiluogou Pb-Zn Deposit, Sichuan Province, Southwest China

The Yinchanggou-Qiluogou Pb-Zn deposit,located in the western Yangtze Block,southwest China,is hosted by the Upper Sinian Dengying Formation dolostone.Ore bodies occur in the Qiluogou anticline and the NS-and NNW-trending faults.Sulfide ores mainly consist of sphalerite,pyrite,galena and calcite,with subordinate dolomite and quartz.Seventeen ore bodies have been discovered to date and they have a combined 1.0 million tons of sulfide ores with average grades of 2.27wt%Zn and 6.89wt%Pb.The δD_(H2O-SMOW) and δ~(18)O_(H2O-SMOW) values of fluid inclusions in quartz and calcite samples range from-68.9‰ to-48.7‰ and 7.3‰ to 15.9‰,respectively,suggesting that H_2O in the hydrothermal fluids sourced from metamorphic water.Calcite samples have δ~(13)C_(PDB) values ranging from-6.2‰ to-4.1‰ and δ~(18)O_(SMOW) values ranging from 15.1‰ to 17.4‰,indicating C and O in the hydrothermal fluids likely derived from a mixed source of metamorphic fluids and the host carbonates.The δ~(34)S_(CDT) values of sulfide minerals range from 5.5‰ to 20.3‰,suggesting that thermal chemical reduction of sulfate minerals in evaporates were the most probable source of S in the hydrothermal fluids.The ~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb ratios of sulfide minerals fall in the range of 18.11 to 18.40,15.66 to 15.76 and 38.25 to 38.88,respectively.The Pb isotopic data of the studied deposit plot near the upper crust Pb evolution curve and overlap with the age-corrected Proterozoic basement rocks and the Upper Sinian Dengying Formation hosting dolostone.This indicates that the Pb originated from a mixed source of the basement metamorphic rocks and the ore-hosting carbonate rocks.The ore geology and C-H-O-S-Pb isotopic data suggest that the YinchanggouQiluogou deposit is an unusual carbonate-hosted,strata-bound and epigenetic deposit that derived ore-forming materials from a mixed source of the underlying Porterozoic basements and the Sinian hosting carbonates.     

Hydrothermal sedimentation characteristics of the Dajiangping superlarge pyrite deposit, Yunfu, Guangdong

The Dajiangping pyrite deposit is hosted in a carbonate-clastic rock series which is characterized by a bioreef-chert suite in its middle part.Conformable lenses of various sizes constitute the orebodies which often branch transitionally into the surroundings.Syngenetic deformation fabrics can be observed in orebody NO.3.Orebody No.4 is composed almost entirely of massive pyrite,with conspicuous hydrothermal sedimentation and bacterium-alga features.The hydrothermal sedimentation origin is also reflected by simple chemistry of the ore (predominated by quartz and pyrite),the presence of U and Th,and the REE compositions of pyrite and ankerite.The ores are rich in organic matter and the difference in organic content between the banded ores and the massive ores is mainly owing to the difference in the clastic components they contain rather than to the subsequent processes of reworking .Co/Ni rations in the ore may reflect the temperature pattern during hydrothermal sedimentation.