Epithermal deposits in South China: Geology,geochemistry, geochronology and tectonic setting

South China Block (SCB) is the broad area including the Yangtze Craton in the northwest and Huanan Orogen in the southeast. It is an important epithermal metallogenic province in China, containing at least 1 high-sulfidation (HS) and 42 low-sulfidation (LS) Au-Ag ± Cu ± Pb-Zn ± Sb epithermal deposits. Porphyry-type mineralization was recognized in four of the LS deposits, and thus they were regarded as LS–P type. These 43 deposits are mainly located in: (1) the Lower Yangtze River Belt and (2) the Northeastern Jiangnan Orogenic Belt in the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt and (4) the Southeast Coastal Volcanic Belt in the Huanan Orogen. They are mostly located in Mesozoic volcanic basins, especially where the regional faults and their subsidiaries occurred. The host rocks include Jurassic–Cretaceous volcanic-sedimentary rocks, coeval or slightly older subvolcanic, granitoids and breccias, and metamorphic basement rocks. The alteration of the HS epithermal deposit (Zijinshan Cu-Au) zoned from silicic (vuggy quartz), through alunite, to dickite and phyllic alteration zones, from the ore veins outwards. The alteration of the LS deposits is zoned from adularia-chalcedony-bladed calcite (or quartz pseudomorphs after bladed calcite) in ore veins to distal illite-sericite-chlorite-kaolinite assemblages. For those LS–P systems, besides the dominated LS alteration assemblages, phyllic and potassium silicate alteration related to porphyry mineralization were identified. Acid leaching textures and vein, stockwork and breccia structures are common in HS deposit, while the LS epithermal deposits are characterized by open-space filling, crustifications, colloform banding and comb structures. The ore-forming fluids are low-temperature, low-salinity meteoric water-dominated in most epithermal deposits in SCB, with variable input of magmatic water. The ore components were derived from both the deep magma and host rocks, and transported upwards or laterally and precipitated in the fracture systems by fluid boiling, mixing and cooling. Most of the epithermal deposits are formed at depth of < 1.5 km and < 300 °C, with few exceptions containing porphyry-type mineralization, such as the Zhilingtou, Yinshan and Longtoushan deposits. Deep drilling is suggested in these deposits as more epithermal and/or porphyry mineralization could be expected. The mineral systems were formed in Early Yanshanian (180–130 Ma) and Late Yanshanian (120–90 Ma) periods. The Early Yanshanian epithermal ore systems are mainly located in a series of E–W-trending metallogenic belts to the west of the Lishui–Haifeng Fault, which were formed in a syn- or post-collision tectonic setting by the collision between the SCB and its surrounding plates. The Late Yanshanian epithermal deposits are mainly located in Southeast Coastal Volcanic Belt, genetically related to the westward subduction of the paleo-Pacific plate.     

Genesis of the giant Zijinshan epithermal Cu-Au and Luoboling porphyry Cu–Mo deposits in the Zijinshan ore district,Fujian Province,SE China: A multi-isotope and trace element investigation

The Zijinshan ore district occurs as one of the largest porphyry-epithermal Cu–Au–Mo ore systems in South China, including the giant Zijinshan epithermal Cu–Au deposit and the large Luoboling porphyry Cu–Mo deposit. The mineralization is intimately related to Late Mesozoic large-scale tectono-magmatic and hydrothermal events. The Cu–Au–Mo mineralization occurs around intermediate-felsic volcanic rocks and hypabyssal porphyry intrusions. In this study, we summarize previously available Re–Os isotopes, zircon U–Pb age and trace elements, and Sr–Nd–Pb isotope data, and present new Pb–S and Re–Os isotope data and zircon trace elements data for ore-related granitoids from the Zijinshan high-sulfidation epithermal Cu–Au deposit and the Luoboling porphyry Cu–Mo deposit, in an attempt to explore the relationship between the two ore systems for a better understanding of their geneses. The ore-bearing porphyritic dacite from the Zijinshan deposit shows a zircon U-Pb age of 108–106 Ma and has higher zircon Ce⁴⁺/Ce³⁺ ratios (92–1568, average 609) but lower Ti-in-zircon temperatures (588–753 °C, average 666 °C) when compared with the barren intrusions in the Zijinshan ore district. Relative to the Zijinshan porphyritic dacite, the ore-bearing granodiorite porphyry from the Luoboling deposit show a slightly younger zircon U–Pb age of 103 Ma, but has similar or even higher zircon Ce⁴⁺/Ce³⁺ ratios (213–2621, average 786) and similar Ti-in-zircon temperatures (595–752 °C, average 675 °C). These data suggest that the ore-bearing magmatic rocks crystallized from relatively oxidized and hydrous magmas. Combined with the high rhenium contents (78.6–451 ppm) of molybdenites, the Pb and S isotopic compositions of magmatic feldspars and sulfides suggest that the porphyry and ore-forming materials in the Luoboling Cu–Mo deposit mainly originated from an enriched mantle source. In contrast, the ore-bearing porphyritic dacite in the Zijinshan Cu–Au deposit might be derived from crustal materials mixing with the Cathaysia enriched mantle. The fact that the Zijinshan Cu–Au deposit and the Luoboling Cu–Mo deposit show different origin of ore-forming materials and slightly different metallogenic timing indicates that these two deposits may have been formed from two separate magmatic-hydrothermal systems. Crustal materials might provide the dominant Cu and Au in the Zijinshan epithermal deposit. Cu and Au show vertical zoning and different fertility because the gold transports at low oxygen fugacity and precipitates during the decreasing of temperature, pressure and changing of pH conditions. It is suggested that there is a large Cu–Mo potential for the deeper part of the Zijinshan epithermal Cu–Au deposit, where further deep drilling and exploration are encouraged.     

Gold mineralization in the Jiangnan Orogenic Belt of South China: Geological,geochemical and geochronological characteristics,ore deposit-type and geodynamic setting

Located in the southeastern margin of the Yangtze Block and generally interpreted as the Neoproterozoic collisional product of the Yangtze with the Cathaysia Blocks of South China, the Jiangnan Orogenic Belt (JOB) contains a number of gold (Au) (-polymetallic) ore deposits and mineral showings, mostly hosted by Neoproterozoic low-grade metamorphic volcaniclastic and sedimentary rocks. The mineralization styles mainly include auriferous quartz veins and disseminated mineralization in altered mylonite and cataclasite that are developed along shear zones, fracture zones and inter- or intra-formational fault zones closely related to regional folding and shearing deformation. Three gold mineralizing epochs are recognized in the JOB. The ca. 423–397 Ma mineralization was associated with the early Paleozoic tectonothermal event(s), which induced widespread emplacement of Silurian S-type granites, low-grade metamorphism and enrichment of gold in the Neoproterozoic rocks (i.e., forming Au source beds). The second Au mineralization epoch, occurring at ca. 176–170 Ma (Jurassic), was related to the subduction of the Paleo-Pacific plate beneath the South China continental margin. The third and most important Au mineralization epoch took place at ca. 144–130 Ma (early Cretaceous), when a Basin-and-Range tectonic pattern was developed, characterized by NE–NNE-trending strike-slip faults, granitic domes and metamorphic core complexes (MCC), and basins filled with red bed lithologies. C, H, O, He-Ar, S and Pb isotopic and fluid-inclusion data suggest that the ore fluids were predominantly metamorphic and/or magmatic, with variable input of mantle-derived fluids and the progressive involvement of meteoric waters in the later stages of mineralization. Ore materials were mostly contributed by the Neoproterozoic source beds, plus a possible contribution from mantle- or magma-derived components. The Au (-polymetallic) deposits in the JOB, particularly those formed in the early Cretaceous, share many geological and geochemical features with the orogenic-type and Carlin-type deposits. In the context of tectonic evolution of South China, the gold mineralization in the JOB may be considered an “intracontinental reactivation type”, characterized by synchronous development of Au–polymetallic mineralization, reactivation of stuctures developed in Neoproterozoic metamorphic rocks, and widespread granite emplacement in the late Mesozoic.     

Cenozoic metallogeny of Greece and potential for precious,critical and rare metals exploration

The Cenozoic metallogeny in Greece includes numerous major and minor hydrothermal mineral deposits, associated with the closure of the Western Tethyan Ocean and the collision with the Eurasian continental plate in the Aegean Sea, which started in the Cretaceous and is still ongoing. Mineral deposits formed in four main periods: Oligocene (33–25 Ma), early Miocene (22–19 Ma), middle to late Miocene (14–7 Ma), and Pliocene-Pleistocene (3–1.5 Ma). These metallogenic periods occurred in response to slab-rollback and migration of post-collisional calc-alkaline to shoshonitic magmatism in a back-arc extensional regime from the Rhodopes through the Cyclades, and to arc-related magmatism along the active south Aegean volcanic arc. Invasion of asthenospheric melts into the lower crust occurred due to slab retreat, and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates. These geodynamic events took place during the collapse of the Hellenic orogen along large detachment faults, which exhumed extensive metamorphic core complexes in mainly two regions, the Rhodopes and the Cyclades. The detachment faults and supra-detachment basins controlled magma emplacement, fluid circulation, and mineralization.The most significant mineralization styles comprise porphyry, epithermal, carbonate-replacement, reduced intrusion-related gold, intrusion-related Mo-W and polymetallic veins. Porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos, whereas in other cases alteration is of restricted development and mainly structurally controlled. Porphyry deposits include Cu-Au-, Cu-Mo-Au-Re, Mo-Re, and Mo-W variants. Epithermal deposits include mostly high- and intermediate-sulfidation (HS and IS) types hosted in volcanic rocks, although sedimentary and metamorphic rock hosted mineralized veins, breccias, and disseminations are also present. The main metal associations are Cu-Au-Ag-Te and Pb-Zn-Au-Ag-Te in HS and IS epithermal deposits, respectively. Major carbonate-replacement deposits in the Kassandra and Lavrion mining districts are rich in Au and Ag, and together with reduced intrusion-related gold systems played a critical role in ancient economies. Finally hundreds of polymetallic veins hosted by metamorphic rocks in the Rhodopes and Cyclades significantly add to the metal endowment of Greece.     

Geological,fluid inclusion and isotopic studies of the Yinshan Cu–Au–Pb–Zn–Ag deposit,South China: Implications for ore genesis and exploration

The Yinshan Cu–Au–Pb–Zn–Ag deposit is located in Dexing, South China. Ore bodies are primarily hosted in low-grade phyllite of the Neoproterozoic Shuangqiaoshan Group along EW- and NNW-striking fault zones. Pb–Zn–Ag mineralization is dictated by Jurassic rhyolitic quartz porphyries (ca. 172 Ma), whereas Cu–Au mineralization is associated with Jurassic dacite porphyries (ca. 170 Ma). The main ore minerals are pyrite, chalcopyrite, galena, sphalerite, tetrahedrite–tennatite, gold, silver, and silver sulphosalt, and the principal gangue minerals are quartz, sericite, calcite, and chlorite. Two-phase liquid-rich (type I), two-phase vapor-rich (type II), and halite-bearing (type III) fluid inclusions can be observed in the hydrothermal quartz-sulfides veins. Type I inclusions are widespread and have homogenization temperatures of 187–303 °C and salinities of 4.2–9.5 wt.% NaCl equivalent in the Pb–Zn–Ag mineralization, and homogenization temperatures of 196–362 °C and salinities of 3.5–9.9 wt.% NaCl equivalent in the Cu–Au mineralization. The pervasive occurrence of type I fluid inclusions with low-moderate temperatures and salinities implies that the mineralizing fluids formed in epithermal environments. The type II and coexisting type III inclusions, from deeper levels below the Cu–Au ore bodies, share similar homogenization temperatures of 317–448 °C and contrasting salinities of 0.2–4.2 and 30.9–36.8 wt.% NaCl equivalent, respectively, which indicates that boiling processes occurred. The sulfur isotopic compositions of sulfides (δ³⁴S = −1.7‰ to +3.2‰) suggest a homogeneous magmatic sulfur source. The lead isotopes of sulfides (²⁰⁶Pb/²⁰⁴Pb = 18.01–18.07; ²⁰⁷Pb/²⁰⁴Pb = 15.55–15.57; and ²⁰⁸Pb/²⁰⁴Pb = 38.03–38.12) are consistent with those of volcanic–subvolcanic rocks (²⁰⁶Pb/²⁰⁴Pb = 18.03–18.10; ²⁰⁷Pb/²⁰⁴Pb = 15.56–15.57; and ²⁰⁸Pb/²⁰⁴Pb = 38.02–38.21), indicating a magmatic origin for lead in the ore. The oxygen and hydrogen isotope compositions (δ¹⁸O = +7.8‰ to +10.5‰, δD = −66‰ to −42‰) of inclusion water in quartz imply that ore-forming fluids were mainly derived from magmatic sources. The local boiling process beneath the epithermal Cu–Au ore-forming system indicates the possibility that porphyry-style ore bodies may exist at even deeper zones.     

Review of Mesozoic multiple magmatism and porphyry Cu–Mo (W) mineralization in the Yidun Arc,eastern Tibet Plateau

The Yidun Arc was formed in response to the westward subduction of Garze–Litang Ocean (a branch of Paleotethys) in the Late Triassic, where abundant porphyry Cu–Mo deposits (221–213 Ma) developed along the regional NW–SE sinistral faults and emplaced in the southern portion of the arc. The ore-related porphyries are mostly metaluminous or slightly peraluminous, belonging to shoshonitic high-potassium calc-alkaline I-type granites, with ε_Hf(t) values of −6.64 to +4.12. The ore-bearing magmas were probably derived from the partial melting of subduction-metasomatic-enriched mantle, with the contamination of underplated mafic materials. The Late Cretaceous (88–80 Ma) highly fractionated I-type granite belt and related porphyry Cu–Mo deposits and magmatic-hydrothermal Cu–Mo–W deposits occur along approximately N–S-trending faults in the Yidun Arc. This belt extended across the Yidun Arc and Garze–Litang suture zone to the north and across the Yangtze Craton to the south, intruding the Late Triassic porphyry belt. The ore-related porphyries are characterized by high silica and high total alkalis, with enrichment in large ion lithophile elements (LILEs; Rb, U and K) and depletion in high field strength elements (HFSE; Nb, Ta, P and Ti) and Ba. They have lower ε_Hf(t) values varying from −9.55 to −2.75, and significant negative Eu anomalies, indicating that the ore-bearing porphyritic magmas originated from ancient middle-upper crust. Two-stage magmatism and mineralization were superimposed in the Xiangcheng-Shangri-La district. Some ore deposits comprise two episodes of magmatism and associated mineralization such as both 207 ± 3.0 Ma granodiorite and 82.1 ± 1.2 Ma monzogranite intruded in the Xiuwacu deposit, causing Cu–Mo–W polymetallic mineralization. To date, 11 Late Triassic porphyry Cu deposits (e.g. the Pulang giant deposit with 5.1 Mt Cu), and five Late Cretaceous porphyry Cu–Mo (W) deposits (e.g. Tongchanggou Mo deposit with 0.59 Mt Mo) have been evaluated in the Xiangcheng-Shangri-La district. The continuity and inheritance of multiphase magmatism and the new understanding of superimposed mineralization will help to guide future exploration.     

Geology,geochronology, geochemistry and ore genesis of the Wangu gold deposit in northeastern Hunan Province,Jiangnan Orogen,South China

The Wangu gold deposit in northeastern Hunan, South China, is one of many structurally controlled gold deposits in the Jiangnan Orogen. The host rocks (slates of the Lengjiaxi Group) are of Neoproterozoic age, but the area is characterized by a number of Late Jurassic–Cretaceous granites and NE-trending faults. The timing of mineralization, tectonic setting and ore genesis of this deposit and many similar deposits in the Jiangnan Orogen are not well understood. The orebodies in the Wangu deposit include quartz veins and altered slates and breccias, and are controlled by WNW-trending faults. The principal ore minerals are arsenopyrite and pyrite, and the major gangue minerals are quartz and calcite. Alteration is developed around the auriferous veins, including silicification, pyritic, arsenopyritic and carbonate alterations. Field work and thin section observations indicate that the hydrothermal processes related to the Wangu gold mineralization can be divided into five stages: 1) quartz, 2) scheelite–quartz, 3) arsenopyrite–pyrite–quartz, 4) poly-sulfides–quartz, and, 5) quartz–calcite. The Lianyunshan S-type granite, which is in an emplacement contact with the NE-trending Changsha-Pingjiang fracture zone, has a zircon LA-ICPMS U–Pb age of 142 ± 2 Ma. The Dayan gold occurrence in the Changsha-Pingjiang fracture zone, which shares similar mineral assemblages with the Wangu deposit, is crosscut by a silicified rock that contains muscovite with a ca. 130 Ma ⁴⁰Ar–³⁹Ar age. The gold mineralization age of the Wangu deposit is thus confined between 142 Ma and 130 Ma. This age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of NE-trending extensional faults, the emplacement of Late Jurassic–Cretaceous granites and the formation of Cretaceous basins filled with red-bed clastic rocks in northeastern Hunan, which forms part of the Basin and Range-like province in South China. EMPA analysis shows that the average As content in arsenopyrite is 28.7 atom %, and the mineralization temperature of the arsenopyrite–pyrite–quartz stage is estimated to be 245 ± 20 °C from arsenopyrite thermometry. The high but variable Au/As molar ratios (>0.02) of pyrite suggest that there are nanoparticles of native Au in the sulfides. An integration of S–Pb–H–O–He–Ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks, possibly driven by hydraulic potential gradient created by reactivation of the WNW-trending faults initially formed in Paleozoic, with possible involvement of magmatic and mantle components channeled through regional fault networks. The Wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic, epithermal and Carlin-type gold deposits, and may be better classified as an “intracontinental reactivation” type as proposed for many other gold deposits in the Jiangnan Orogen.     

Late Permian–Triassic metallogeny in the Chinese Altay Orogen: Constraints from mica 40Ar/39Ar dating on ore deposits

The Central Asian Orogenic Belt (CAOB) constitutes the largest Phanerozoic accretionary orogen on Earth. It extends over 5000 km and hosting numerous metal deposits. The Chinese Altay Orogen, an important element of the CAOB, hosts abundant Devonian (ca. 410–370 Ma) deposits. The ⁴⁰Ar/³⁹Ar dating of seven mica separates from the representative samples syngenetic with orogenic-type mineralization is summarized to record a poorly studied Permian to Triassic metallogenic episode in the Chinese Altay Orogen. The Kelan and Maizi basins in the Chinese Altay Orogen, which likely represent an arc accretionary complex, contain a series of polymetallic lode deposits hosted in low-grade metamorphic volcano–sedimentary rocks. Two muscovite and five biotite separates were obtained from the ore-forming veins paragenetically associated with Au-bearing polymetallic sulfides in the Keketale Pb–Zn, Wulasigou Cu, Tiemurt Pb–Zn, Dadonggou Pb–Zn and Sarekuobu Au deposits. These separates yielded ⁴⁰Ar/³⁹Ar plateau ages ranging from 260 Ma to 205 Ma. Integration of these results with other published geological and geochronological data indicates that the Au–Cu–Pb–Zn mineralization post-dated the final CAOB assembly, with fluid movement and mineralization possibly driven by regional metamorphism and deformation. It is herein proposed for a metallogenic model that the metamorphic fluid migration following final assembly of the CAOB results into the formation of the deposits.     

Genesis of Luobuzhen Pb–Zn veins: Implications for porphyry Cu systems and exploration targeting at Luobuzhen-Dongshibu in western Gangdese belt,southern Tibet

Porphyry systems are known to form in magmatic arc environment and commonly include porphyry Cu, epithermal Pb–Zn–Au–Ag, skarn polymetallic mineralization, etc. The systems are rarely reported in collisional zones, such as the Gangdese belt in southern Tibet where many postcollisional porphyry copper deposits occurred. In addition, other types of mineral systems are rarely present except porphyry copper mineralization in the Gangdese belt. In this study, we present Pb–Zn-bearing quartz veins at Luobuzhen in the western Gangdese belt. The Luobuzhen Pb–Zn veins cross-cut dacite of the Linzizong Group with zircon U–Pb age of 50.1 ± 0.2 Ma and monzogranite with zircon U–Pb age of 17.1 ± 0.1 Ma. Ore minerals include sphalerite, galena, chalcopyrite, and pyrite; gangue minerals are quartz with minor chlorite and sericite. Primary fluid inclusions of quartz are liquid-rich, aqueous, and two-phase inclusions. The homogenization temperatures of these primary inclusions are moderate to high (267–400 °C), and salinities range from 8.9 to 18.4 wt.% NaCl equiv. Quartz has δ¹⁸O_SMOW values of 6.2–9.3‰, while sulfides have δ³⁴S_V-CDT values of −5.1‰ to 0.1‰, ²⁰⁶Pb/²⁰⁴Pb of 18.722–18.849, ²⁰⁷Pb/²⁰⁴Pb of 15.640–15.785, and ²⁰⁸Pb/²⁰⁴Pb of 39.068–39.560. These data suggest that magmatic fluids with contribution from meteoric water, magmatic sulfur, and lead derived from upper crust and metasomatized mantle by Indian continental materials would be critical for the Luobuzhen base metal mineralization.The Dongshibu area, located at ∼2 km east of the Luobuzhen, is characterized by high concentrations of Cu (up to 1450 ppm) and Mo (up to 130 ppm) of stream sediments, which is quite different from high concentrations in Pb, Zn, Ag, and Au shown in the Luobuzhen area. In addition, porphyry copper mineralization-related alteration and veins/veinlets occur in the Miocene monzogranite at Dongshibu. The monzogranite is characterized by high Sr/Y ratios, which are also shown on ore-forming intrusions in the Gangdese postcollisional porphyry copper deposits, and shows similar zircon Hf isotopes to the ore-related high Sr/Y intrusions from the Zhunuo porphyry copper deposit which is located ∼20 km northeast of the Luobuzhen-Dongshibu. A comprehensive analysis allows us to infer that the base metal veins at Luobuzhen are components of a porphyry Cu system with porphyry Cu mineralization likely present at Dongshibu and epithermal Au–Ag veins possibly occurring at Luobuzhen, which are indicative of the existence of porphyry copper systems in collisional zones. The potential porphyry Cu mineralization and epithermal Au–Ag veins should be targeted in future exploration at Luobuzhen-Dongshibu.     

Geology and molybdenite Re–Os age of the Dahutang granite-related veinlets-disseminated tungsten ore field in the Jiangxin Province,China

This is a brief research report about the recently-discovered and currently being explored Dahutang tungsten deposit (or ore field) in northwestern Jiangxi, south-central China. The deposit is located south of the Middle–Lower Yangtze River valley Cu–Au–Mo–Fe porphyry–skarn belt (YRB). The mineralization is genetically associated with Cretaceous porphyritic biotite granite and fine-grained biotite granite and is mainly hosted within a Neoproterozoic biotite granodiorite batholith. The Dahutang ore field comprises veinlets-disseminated (~ 95% of the total reserve), breccia (~ 4%) and wolframite–scheelite quartz vein (~ 1%) ore styles. The mineralization and alteration are close to the pegmatite shell between the Cretaceous porphyritic biotite granite and Neoproterozoic biotite granodiorite and the three styles of ore bodies mentioned above are related to zoned hydrothermal alteration that includes greisenization, K-feldspar alteration, silicification, carbonatization, chloritization and fluoritization arranged in time (early to late) and space (bottom to top).Five samples of molybdenite from the three types of ores have been collected for Re/Os dating. The results show Re/Os model ages ranging from 138.4 Ma to 143.8 Ma, with an isochron age of 139.18 ± 0.97 Ma (MSWD = 2.9). The quite low Re content in molybdenite falls between 0.5 ppm and 7.8 ppm that is indicative of the upper crustal source. This is quite different from molybdenites in the YRB Cu–Au–Mo–Fe porphyry–skarn deposits that contain between 53 ppm and 1169 ppm Re, indicating a mantle source.The Dahutang tungsten system is sub-parallel with the YRB porphyry–skarn Cu–Au–Mo–Fe system. Both are situated in the north margin of the Yangtze Craton and have a close spatial–temporal relationship. This possibly indicates a comparable tectonic setting but different metal sources. Both systems are related to subduction of the Paleo-Pacific plate beneath the Eurasian continent in Early Cretaceous. The Cu–Au–Mo–Fe porphyry–skarn ores are believed genetically related to granitoids derived from the subducting slab, whereas the porphyry W deposits are associated with S-type granitoids produced by remelting of the upper crust by heat from upwelling asthenoshere.     

Genesis of the Zhengguang gold deposit in the Duobaoshan ore field,Heilongjiang Province,NE China: Constraints from geology,geochronology and S-Pb isotopic compositions

The Zhengguang gold deposit in the Duobaoshan ore field, hosted in volcanic rocks of the Middle Ordovician Duobaoshan Formation, is one of the largest gold deposits in the Northeastern Great Xing’an Range of the Central Asian Orogenic Belt (CAOB). The deposit comprises the No. I, II and III ore zones with a total resource exceeding 35 tonnes of Au, 100,000 tonnes of Zn and 100 tonnes of Ag. A genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry-type and epithermal mineralization. Zircon LA-ICPMS U-Pb dating reveals that the tonalite porphyry was emplaced at 462.1 ± 1.8 Ma (Middle Ordovician). The δ³⁴S_V-CDT values of sulfide minerals range from −3.0‰ to −1.7‰ with an average of −2.33‰, indicating that sulfur was mainly derived from a magmatic source. The Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb ranging from 17.572 to 17.629, ²⁰⁷Pb/²⁰⁴Pb from 15.424 to 15.486, and ²⁰⁸Pb/²⁰⁴Pb from 37.206 to 37.418) suggest a major mantle component for Pb and, by inference, for other ore metals. Therefore, we suggest that the ore-forming elements in the Zhengguang gold deposit may be related to the mantle-sourced tonalite porphyry. On the basis of the geological characteristics and geochemical signatures documented in this study, we conclude that the Zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry, as part of the Duobaoshan porphyry-epithermal ore system that is related to the subduction of the Paleo-Asian Ocean during the Ordovician.     

Timing of skarn deposit formation of the Tonglushan ore district,southeastern Hubei Province,Middle–Lower Yangtze River Valley metallogenic belt and its implications

The Tonglushan ore district in the Middle–Lower Yangtze River Valley metallogenic belt includes the Tonglushan Cu–Fe, the Jiguanzui Au–Cu, and the Taohuazui Au–Cu skarn deposits. They are characterized by NE-striking ore bodies and hosted at the contact of Triassic carbonate rocks and Late Mesozoic granitoid deposits. New Sensitive High-Resolution Ion Microprobe (SHRIMP) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA–ICP-MS) zircon U–Pb, molybdenite Re–Os, and phlogopite ⁴⁰Ar–³⁹Ar ages indicate that these skarn deposits formed between 140.3 ± 1.1 and 137.3 ± 2.4 Ma. These dates are identical to the zircon U–Pb ages for host quartz diorites ranging from 140 ± 2 to 139 ± 1 Ma. These results confirm that both skarn mineralization and related intrusions were initiated during the Early Cretaceous. The high rhenium contents (261.4–1152 μg/g) of molybdenites indicate that a metasomatic mantle fluid was involved in the ore-forming process of these skarn ore systems. This conclusion is consistent with previously published constraints from sulfur, deuterium, and oxygen isotope compositions, and the geochemical signatures, and Sr–Nd isotopic data of the mineralization-hosting intrusions. Geological and geochronological evidence demonstrates that there were two igneous events in the Tonglushan ore district. The first resulted in the emplacement of quartz diorite during the Early Cretaceous (140 ± 2 to 139 ± 1 Ma), and the second is characterized by the eruption of volcanic rocks during the mid-Early Cretaceous (130 ± 2 to 124 ± 2 Ma). The former is spatially, temporally and genetically associated with skarn gold-bearing mineralization (140.3 ± 1.1 to 137.3 ± 2.4 Ma). The recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the Middle–Lower Yangtze River Valley metallogenic belt.     

Mesozoic multiphase magmatism at the Xinan Cu–Mo ore deposit (Zijinshan Orefield): Geodynamic setting and metallogenic implications

The Xinan Cu–Mo deposit, newly-discovered in the Zijinshan Au–Cu–Mo Orefield (the largest porphyry–epithermal system in SE China), is featured by the presence of abundant multi-phase granitoids, which reflects the complex Mesozoic tectono-magmatic evolution in the region.New and published LA-ICP-MS zircon U–Pb age data reveal that the Mesozoic Zijinshan magmatism occurred in two major phases: (1) Middle to Late Jurassic (ca. 169–150 Ma), forming the Zijinshan complex granite and the Xinan monzogranite; (2) late Early Cretaceous to earliest Late Cretaceous (ca. 112–98 Ma), forming the Shimaoshan volcanic rocks, Sifang granodiorite, and the Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and late aplite dykes. Additionally, a possible earliest Cretaceous magmatism (ca. 141 Ma) may have occurred based on inherited zircon evidence. Major and trace element geochemistry indicates that all the Zijinshan igneous rocks show subduction-related geochemical affinities. Zircon Ce^4 +/Ce^3 + values of the late Early Cretaceous to earliest Late Cretaceous granitoids (Ce^4 +/Ce^3 + = 190–1706) are distinctly higher than the Middle to Late Jurassic ones (Ce^4 +/Ce^3 + = 27–457), suggesting that the former were derived from more oxidized parental magma. The Middle to Late Jurassic Zijinshan complex granite and monzogranite have ε_Hf (t) values of − 8.02 to − 10.00, with the two-stage Hf model ages (T_DM2) of 1.72 to 1.84 Ga (similar to the Paleoproterozoic metamorphosed Cathaysia Block basement), suggesting that they were derived from partial melting of the basement. The late Early Cretaceous to earliest Late Cretaceous Sifang granodiorite and Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and aplite dykes contain higher and wider range of ε_Hf (t) values (0.66 to − 6.05), with T_DM2 of 1.12 to 1.56 Ga, indicating that they were also partial melting product of the Cathaysia basement but with more mantle and/or juvenile mafic lower crustal input. We propose that the Zijinshan Orefield was in a compressive, Pacific subduction-related tectonic setting during the Middle to Late Jurassic. The regional tectonic regime may have changed to extensional in the late Early Cretaceous to earliest Late Cretaceous, during which the Pacific plate subduction direction change and the accompanying subduction roll-back and slab window-opening occurred. The tectonic regime transition, high oxygen fugacity and mantle/mafic lower crustal materials involvement in the late Early Cretaceous to earliest Late Cretaceous may have generated the Zijinshan porphyry-related Au–Cu–Mo mineralization.     

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.     

Geodynamic setting of the Zijinshan porphyry–epithermal Cu–Au–Mo–Ag ore system,SW Fujian Province,China: Constrains from the geochronology and geochemistry of the igneous rocks

Zijinshan is a large porphyry–epithermal Cu–Au–Mo–Ag ore system located in the Zijinshan mineral field (ZMF) of southwestern Fujian Province, China. Although it is commonly accepted that the early Cretaceous magmatism and the metallogenesis of the mineral field are closely related, the tectonic setting for the ore-forming event(s) has been controversial and regarded as either extensional or subduction-related. New U–Pb zircon geochronology, Sr–Nd–Pb isotopic systematics, and geochemical data presented here from granites and volcanic rocks in the mineral field help to clarify this uncertainty.LA–MC–ICP-MS U–Pb zircon analyses yield weighted mean ages of between ca. 165 and 157 for the monzogranite, ca. 112 Ma for granodiorite, and between ca. 111 and 102 Ma for nine samples of volcanic units in the study area. These dates, integrated with previous geochronological data, indicate that there were two magmatic events in the area during the Middle to Late Jurassic and the Early Cretaceous. Major and trace element geochemistry indicates that these rocks are high-K, calc-alkaline granites, are enriched in LREE and Th, U, Ta, Nd, Sm and Yb, and depleted in Ba, K, Sr, P, Ti and Y. These features are characteristic of volcanic-arc granites or active-continental margin granites. The Middle to Late Jurassic monzogranitic plutons in the region have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7096 to 0.7173, εNd_T values of − 10.1 to − 7.6, ²⁰⁶Pb/²⁰⁴Pb isotope ratios of 18.51–18.86, ²⁰⁷Pb/²⁰⁴Pb isotope ratios of 15.64–15.73, and ²⁰⁸Pb/²⁰⁴Pb isotope ratios of 38.76–39.18. The Early Cretaceous granodiorite and volcanic rocks are distinctly different with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7055–0.7116, εNd_T values of − 8 to 0.5, ²⁰⁶Pb/²⁰⁴Pb ratios ranging between 18.49 and 19.77, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.63–15.71, and ²⁰⁸Pb/²⁰⁴Pb ratios of 38.71–40.62. These characteristics suggest that the source for the Middle to Late Jurassic monzogranitic plutons is a partially melted Mesoproterozoic substrate, with a minor component from Paleozoic material, whereas the Early Cretaceous granodiorite and volcanic rocks may represent mixing of crustal and mantle-derived melts. It is therefore suggested that the Middle to Late Jurassic monzogranitic plutons, and the Early Cretaceous granodiorite and volcanic rocks in the ZMF are the result of an active continental-margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. Given that the mineralization and the early Cretaceous granodiorite and volcanic rocks in the area are genetically related, the Zijinshan porphyry–epithermal ore system formed in the subduction-related tectonic setting.     

The trinity pattern of Au deposits with porphyry,quartz–sulfide vein and structurally-controlled alteration rocks in Ciemas,West Java,Indonesia

The Ciemas gold mining area is located in the Sunda arc volcanic rock belt, West Java, Indonesia. Ore bodies are associated with Miocene andesite, dacite and quartz diorite porphyrite. To constrain ore genesis and mineralization significance, a detailed study was recently conducted examining these deposits, which included detailed field observation, petrographic study, petrochemistry, sulfur isotope analyses, zircon U–Pb dating, and fluid inclusion analysis. The results include the following findings. 1) Ore types have been identified as porphyry, a quartz–sulfide vein, and structure-controlled alteration rocks. 2) In host rocks, zircon LA–ICP-MS U–Pb dating of quartz diorite porphyrite, amphibole tuff breccia and andesite yield ages of 17.1 ± 0.4 Ma, 17.1 ± 0.4 Ma and 17.5 ± 0.3 Ma, respectively. 3) Fluid inclusions in the quartz from ore are given priority to liquid and gas–liquid phases, and their components are of the NaCl–H₂O system with homogenization temperatures of 240–320 °C, salinities of 14–17%, densities of 0.85–0.95 g/cm³, and fluid pressure values between 4.1 and 46.8 MPa, corresponding to metallogenic depths from 150 to 1730 m. Fluid characteristics are identified as similar to those of high sulfur epithermal deposits. 4) The sulfur isotopic compositions are notably uniform, the δ³⁴S values of wall rocks range from 3.71 to 3.85‰, and the δ³⁴S values of ores vary from 4.90‰ to 6.55‰. The sulfur isotopic composition of ores is similar to that of the wall rocks, indicating a mixed origin of mantle with a sedimentary basement. 5) The trace element patterns of different ore types are similar, which indicates that they originate from the same source. Au deposits primarily occurred during the late magmatic activity. Finally, we have set up the regional metallogenic model, confirming that this gold deposit in the Sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type.     

Geology and genesis of Kafang Cu–Sn deposit,Gejiu district,SW China

Kafang is one of the main ore deposits in the world-class Gejiu polymetallic tin district, SW China. There are three main mineralization types in the Kafang deposit, i.e., skarn Cu–Sn ores, stratiform Cu ores hosted by basalt and stratiform Cu–Sn ores hosted by carbonate. The skarn mainly consists of garnet and pyroxene, and retrograde altered rocks. These retrograde altered rocks are superimposed on the skarn and are composed of actinolite, chlorite, epidote and phlogopite. Major ore minerals are chalcopyrite, pyrrhotite, cassiterite, pyrite and scheelite. Sulfur and Pb isotopic components hint that the sources of different types of mineralization are distinctive, and indicate that the skarn ore mainly originated from granitic magma, whereas the basalt-hosted Cu ores mainly derived from basalt. Microthermometry results of fluid inclusions display a gradual change during the ore-forming process. The homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages. The salinities and freezing temperatures exhibit similar evolutionary tendencies with the T _{homogenization}, while the densities of the different types keep constant, the majority being less than 1. Oxygen and hydrogen isotopic values (δ¹⁸O and δD) of the hydrothermal fluids fall within ranges of 3.1 to 7.7‰ with an average of 6.15‰, calculated at the corresponding homogenization temperature, and − 73 and − 98‰ with an average of − 86.5‰, respectively. Microthermometry data and H–O isotopes indicate that the ore-forming fluid of the Kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage. Molybdenite Re–Os age of the skarn type mineralization is 83.4 ± 2.1 Ma, and the stratiform ores hosted by basalt is 84.2 ± 7.3 Ma, which are consistent with the LA-ICP-MS zircon age of the Xinshan granite intrusion (83.1 ± 0.4 Ma). The evidence listed above reflects the fact that different ore styles in the Kafang deposit belong to the same mineralization system.     

Cenozoic high-K alkaline magmatism and associated Cu–Mo–Au mineralization in the Jinping–Fan Si Pan region,southeastern Ailao Shan–Red River shear zone,southwestern China–northwestern Vietnam

The Jinping–Fan Si Pan (JFP) Cenozoic magmatic and Cu–Mo–Au metallogenic belt in the southeastern part of the Ailao Shan shear zone host the Tongchang, Chang′an, Habo, and Chinh Sang Cu–Mo–Au deposits. These deposits form an integrated epithermal-porphyry regional mineralization system associated with 40–32 Ma high-K alkaline magmatism. The magmatic rocks in the belt have relatively low TiO₂ (<0.73 wt%), P₂O₅ (<0.29 wt%), and FeO^* (<4.99 wt%), and high Na₂O (2.86–4.75 wt%) and K₂O (4.01–7.98 wt%). They also have high contents of incompatible trace elements, and are enriched in LILE (Rb, Ba, K, Sr) and LREE. They have marked Nb, Ta, Ti and P depletion in primitive mantle-normalized spidergrams, and plot close to the EMII mantle field in the Sr–Nd isotopic diagram. These characteristics are similar to those of the Eocene high-K alkaline rocks along the northern Ailao Shan belt, eastern Tibet plateau. The sulfur and lead isotope analyses of sulfide minerals from both the ores and related magmatic rocks confirm the involvement of a magmatic ore fluid. The Cenozoic alkaline intrusions and Cu–Mo–Au mineralization in the JFP were formed prior to the initiation of left-lateral shearing along the Ailao Shan shear zone. The magmas appear to have been derived from enriched mantle, possibly with mixing of materials from the buried Tethyan oceanic lithosphere, and/or crust.     

Sulfidic and non-sulfidic indium mineralization of the epithermal Au–Cu–Zn–Pb–Ag deposit San Roque (Provincia Rio Negro,SE Argentina) — with special reference to the “indium window” in zinc sulfide

At San Roque in Patagonia's Rio Negro Province, Argentina, an In–Au–Cu–Zn–Pb–Ag mineralization (< 0.24 wt.% In, < 7 ppm Au, < 0.45 wt.% Cu, < 14.1 wt.% Zn, < 0.55 wt.% Pb, < 60 ppm Ag) is bound to lava, and volcaniclastics of Triassic through Jurassic age. The polymetallic sulfidic and non-sulfidic indium mineralization is attributed to the low-sulfidation (LS) to intermediate sulfidation (IS) epithermal type of mineralization. Its vein-type and stockwork mineralization developed at 39.2 bars under hydrostatic conditions, corresponding to a depth of 400 m below the water level of the paleoaquifer. In the redox-controlled hypogene mineralization, the temperature increased from 130 °C up to as much as 250 °C at depth, while the pH regime changed from slightly acidic near surface to more alkaline conditions around pH 8 at a depth of approximately 150 m. The monophase mineral associations composed of sphalerite, Ag–Bi-enriched and inclusion-free galena (< 1.7 wt.% Ag, < 3.7 wt.% Bi), chalcopyrite, pyrite, gold, silver, digenite, various In–Cu- and Pb–Zn–Ag “intermediate products”, wittichenite, roquesite, sakuraiite, dzhalindite, brochantite, antlerite, cerussite, and “manganomelane” in a quartz and muscovite-rich gangue have been subdivided into three different stages: (1) Stockwork mineralization of LS to IS epithermal type (hypogene), (2) quartz vein mineralization (hypogene), and (3) salar mineralization (supergene–hypogene).Salt–mud flats controlled the youngest mineralization with Mn, Li, Ca, Mg, V, Sr, Cu, Ag and In bound to oxides, hydroxides, sulfates and subordinate carbonates. The quartz vein mineralization is made up of oxides, hydroxides prevailing over sulfides and containing W, Fe, Au, As, Pb, In, and Cu. It formed at the passage from the vadose into the phreatic zones under oxidizing to slightly reducing conditions. The level marks the boiling level of the hydrothermal solutions involved in the mineralizing process. The hypogene stockwork mineralization is exclusively made up of sulfides containing Zn, Pb, Cu, In, Ag and Bi in the phreatic zones. It developed under reducing conditions. Indium is present at all levels within the volcanic rocks and has been derived from sphalerite rich in Cd (< 1.6 wt.% Cd), In (< 7.3 wt.% In) and Cu (< 7.2 wt.% Cu) while the Fe contents are moderate in sphalerite (< 6.8 wt.% Fe). Indium reached economic grade only through the segregation of a Cu–In–S phase in the “indium window” which is defined by a Cd content of sphalerite in the range 0.2–0.6 wt.% Cd. This concentration of In is controlled by the crystal morphology and the lattice parameters of the minerals involved. It is described as a two-stage process with interdiffusion processes in an Fe-enriched system (stage I) and zoned replacement in an Fe-poor system enriched in indium (stage II). Cu-bearing sphalerite decomposed into sphalerite poor in trace elements and into Cu–In-bearing sphalerite. Further indium concentration took place, when roquesite and sakuraiite decomposed along with an increase in oxygen pressure under hypogene and supergene conditions into dzhalindite. The physical–chemical conditions of the mineralogy and chemical changes in the system In–Cu–Zn–Cd observed in nature have been approximated based upon the results obtained during laboratory studies in material sciences that were focused on solar energy.     

Geochronological and petrogeochemical constraints on the skarn deposits in Tongshanling ore district,southern Hunan Province: Implications for Jurassic Cu and W metallogenic events in South China

Southern Hunan Province, South China, is located in the central part of the Qin–Hang metallogenic belt and is characterized by abundant Cu–Pb–Zn and W–Sn polymetallic ore deposits. The Cu–Pb–Zn deposits are associated with Jurassic granodiorite porphyries whereas the W–Sn deposits occur within Jurassic granite porphyries. Here we present geochronologic and geochemical data for the Tongshanling Cu–(Mo)–Pb–Zn deposit and the Weijia W deposit in the district of Tongshanling, southern Hunan. Zircon U–Pb dating and molybdenite Re–Os geochronology indicate that the emplacement of the Tongshanling granodiorite porphyry and the associated Cu mineralization occurred at 162–160 Ma, slightly earlier than the formation of the Xianglinpu granite porphyry and associated W mineralization at 159–158 Ma. The Tongshanling granodiorite is high-K calc-alkaline, weakly peraluminous, and weakly fractionated with zircon ε_Hf(t) values of − 15.1 to − 5.6. In contrast, the Xianglinpu granite is alkaline, peraluminous, and highly fractionated, with ε_Hf(t) values of − 9.5 to 0.9. Our data indicate that the Tongshanling granodiorite is relatively oxidized and was formed by the partial melting of Paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction-modified lithospheric mantle. In contrast, the Xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle. The difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies.