Quartz Vein Type Research Articles

Cathodoluminescence and Trace Element Composition of Scheelite from the Middle‐Lower Yangtze River Metallogenic Belt (MLYB): Implications for Mineralization and Exploration

AbstractThe Middle–Lower Yangtze River Metallogenic Belt (MLYB) is known to contain abundant copper and iron porphyry‐skarn deposits, with an increasing number of tungsten deposits and scheelite in Fe–Cu deposits being discovered in the MLYB during recent decades. The ore genesis of the newly‐discovered tungsten mineralization in the MLYB is poorly understood. We investigate four sets of scheelite samples from tungsten, iron and copper deposits, using CL imaging and LA–ICP–MS techniques to reveal internal zonation patterns and trace element compositions. The REE distribution patterns of four studied deposits show varying degrees of LREE enrichment with negative Eu anomalies. The oxygen fugacity of ore‐forming fluid increased in Donggushan, while the oxygen fugacity of ore‐forming fluid decreased in Ruanjiawan, Guilinzheng and Gaojiabang. The scheelites from the Donggushan, Ruanjiawan, Guilinzheng and Gaojiabang deposits show enrichment in LREEs and HFSE, with Nb/La ratios ranging from 1.217 to 52.455, indicating that the four tungsten deposits are enriched in the volatile fluorine. A plot of (La/Lu)N versus Mo/δEu can be used to distinguish quartz vein type, porphyry and skarn tungsten deposits. This study demonstrates that scheelite grains can be used to infer tungsten mineralization and are effective in identifying magmatic types of tungsten deposits in prospective mining sites.

Implications of aplite dykes for mineralization in the Late Cretaceous vein-type Xiuwacu W-Mo deposit in the southern Yidun Terrane, SE Tibetan Plateau

Abstract The Xiuwacu W-Mo deposit with 24,000 t of Mo and 23,000 t of WO3, is located in the Southern Yidun terrane (SYT), SW China; being the only quartz-vein type W-Mo deposit in the region. In the deposit, aplite dykes are spatiotemporally associated with W-Mo orebodies; however, their genetic relationship remains unclear. Here we present the result of a study of the petrography, zircon U-Pb dating, whole-rock geochemistry, Sr-Nd-Pb isotopes, zircon trace elements and Hf isotopes of the aplite dykes. The Xiuwacu aplites are emplaced at 78.7 ± 1.9 Ma and have high-silica, alkali-rich and metaluminous -peraluminous compositions. They are enriched in light rare elements (LREEs), large-ion lithophile elements (LILEs; U, Rb, Th), and depleted in heavy rare earth elements (HREEs), high-field strength elements (HFSEs; Nb, P, Ti), and with strong negative Eu anomalies (δEu = 0.09–0.58, average = 0.36). The aplites have an average estimated crystallization temperature of 700 °C, and relatively low magmatic oxygen fugacity ([log(fo2)] = −33.2 to −16.1 average = −26.1) which is substantially lower than the Late Triassic biotite granite but similar to the Late Cretaceous porphyritic monzogranite in the deposit. All the aplite samples have varying (87Sr/86Sr)i ratios (0.701240–0.719258), negative eNd(t) values (−10.33 to −3.22), negative eHf(t) values (−5.3 to −3.3), and ancient two-stage Hf depleted-mantle model ages (TDM2(Hf) = 1886–2070 Ma). These geochemical characteristics demonstrate that the aplite dykes were formed by the partial melting of the ancient lower crust under an extensional setting, which was triggered by the NW-SE ward subduction of the neo-Tethys ocean slab during the Late Cretaceous. The ancient lower crust is interpreted to have provided the main source of W and Mo for the Xiuwacu deposit. The enrichment of W and Mo by fractional crystallization of the aplite magmas played an important role in concentrating W-Mo during the formation of the deposit. Aplite dykes have also been found in several Late Cretaceous Mo and/or Cu deposits in the SYT. Considering their common occurrence within the orebodies, the aplite dykes could be an effective prospecting indicator.

The world-class Jiangnan tungsten belt: Geologicalcharacteristics, metallogeny, and ore deposit model

The Jiangnan tungsten belt (JNB), a newly identified in the past decade, has a total resource of more than 6 Mt WO3 and still has a good potential for further prospecting. The JNB, located along the Jiangnan Massif (JM) and its eastern extensional areas, is adjacent to and parallel with the Middle-Lower Yangtze River porphyry-skarn Cu-Mo-Au-Fe belt (MLYRB) at north. Both JNB and MLYRB have the same mineralization periods, i.e., 150–135 and 130–125 Ma. The tungsten mineralization in JNB developed at the proximal contact of granite plutons, whereas the Pb-Zn±Cu veins occurs at the distal areas, exhibiting an obvious zoning in space. Apart from the Dongping quartz vein wolframite deposit, the other W deposits in the JNB belong to porphyry and skarn types. The Zhuxi scheelite skarn deposit with 3.44 Mt of WO3 is the largest one over the world. Meanwhile, the exploration of the Dahutang super-large, and Dongyuan and Yangchuling large porphyry W deposits has proven the porphyry is a new major W type except for both skarn and quartz vein types which were recognized before. Moreover, it is interesting to find unusual scheelite-bearing anorthosite and albitite dikes, which cut through the skarn ores in the Zhuxi deposit area. The scheelite-bearing albitite is proposed to crystallize from Al-, Si-, P-, W-, and F-rich residual magma whereas the scheelite-bearing anorthosite formed when the residual magma was contaminated by pure limestone in a reducing environment. The granitoids associated with W deposits and W-Mo deposits in the JNB are biotite monzonite and granodiorite, respectively. According to the petrology, geochemistry and major accessory minerals, the ore-related granitoids can be recognized as S type (or ilmenite series) with peraluminous nature and I type (or magnetite series) with metaluminous nature. Geochemical and Sr-Nd-Hf isotopic data indicate the W deposits-related granitoids were derived from the remelting of the Neoproterozoic phyllite and slate and the W-Mo deposits-related granitoids were also derived from the same strata but with input of mantle materials. According to the sources of granitoids and the skarn mineral assemblages as well as mineral chemistry it can be recognized as reduced W and the oxidized W-Mo deposits. Usually the reduced W deposit appears as large and super-large scale, such as the Zhuxi and Dahutang whereas the oxidized W-Mo as relatively smaller. A tectonic model is suggested to explain the two periods of mineralization in both JNB and MLYRB, which are corresponding to oblique subduction of Izanagi plate in 150–135 Ma at quite low angle and the extension tectonic regime of post-subduction at 130–125 Ma, respectively. The porphyry-skarn Cu-Mo-Au-Fe system in early period and apatite-magnetite system in late period along MLYRB are related to the granitoids derived from the slab subducted slab and the stagnant slab whereas tow periods of porphyry-skarn as well as quartz vein type W(Sn) deposits are associated with the granitoids which were remelted from the Neoproterozoic phyllite deduced from mantle underplated. Moreover, a deposit model is set up for the relationship among the porphyry-skarn W and W-Mo, and distal Pb-Zn-Ag±Cu veins, which can be referenced for the further prospecting in JNB and the regions with similar tectonic setting.

In situ LA-ICP-MS analyses of mica and wolframite from the Maoping tungsten deposit, southern Jiangxi, China

The Maoping tungsten deposit is located in the Nanling W–Sn metallogenic belt in South China. Greisen and quartz vein types of mineralization developed in this deposit. Protolithionite occurs in the granite. Zinnwaldite is occurs mainly in greisen and wolframite–quartz veins whereas phengite is found in the underground quartz veinlets. In granite and greisen, protolithionite, and zinnwaldite are partly replaced by Li-phengite. LA-ICP-MS trace element analyses of micas and wolframite are employed to characterize the ore-forming source and evolution of ore-forming fluids. Micas show compositional variation trend in vertical directions with a decrease of W, Sn, Nb, and Ta and an increase of MgO, V, Ni, and Co. Wolframite in greisen has higher Mo, Sn, Nb, Ta, and REEs than those in quartz veins. All wolframites show similar REE patterns with enrichment of HREE. Wolframites in greisen and quartz veins have negative Eu anomalies, while wolframites in quartz veinlet display positive Eu anomalies. Compositions of mica and wolframite from different mining levels of the Maoping deposit suggest that the ore-forming fluids are dominated by magmatic hydrothermal fluids in the deep with a slight addition of meteoric water in the shallow. Brittle fracture-induced depressurization and fluid mixing controlled the evolution of ore-forming fluids and possibly lead to the wolframite deposition.

Research and Application of Nelson Concentrator in Beneficiation Test of Quartz Vein Type Gold Ore

A gold deposit in Shandong belongs to Quartz vein type gold-bearing deposit, the main gold minerals are natural gold and silver-gold minerals, there are a few metallic minerals such as pyrite, the main gangue minerals are quartz, feldspar, sericite and so on, the average size of gold minerals is 62.37 microns, the particle size of the cloth is coarse. As a kind of gravity separation equipment, Nelson concentrator is more and more favored by mines because of its high enrichment ratio, high recovery rate and extremely friendly to environment, the experimental research of Nelson concentrator was carried out, and the gold concentrate with gold grade of 385.06 G / T and recovery of 62.21% was obtained.

Vendian-Cambrian granites of the Ufaley block (Middle Urals): a new isotope data, source composition, potential ore content

Relevance. The junction zone between the Uralian mobile belt (UMB) and the East European Platform (EEP) is long, heterogeneous and characterized by asynchrony in the geodynamic settings. For many of its constituent parts, the age, source composition and ore content of magmatic complexes, which are necessary to build a complete picture of geological history, are not completely clear. The aim of this work is to study petrogeochemistry, age, isotopic parameters, and reconstruction of the source composition for granites of the Bitim complex in the eastern part of the Ufaley block (Middle Urals). This structure is considered to be a fragment displaced from the EEP to the east. Research methodology. The analysis of rocks for petrogenic and rare components, microprobe studies of the composition of minerals and isotope studies of U–Pb, Lu–Hf (LA–ICP–MS) were performed. Petrocheochemical comparison was made, author’s data about Ar–Ar, Rb–Sr age and the behavior of Sr and Hf isotopes were analyzed. Results. Granitoids of the Bitim complex formed over a long time interval – 579–520 Ma, corresponding to the Upper Vendian (taking into account errors – to the boundary with the Cambrian). The isotopic labels of the studied granites are as follows: 87Sr/86Sr = 0.703389, εHf (t) is +1.5...+12.5, 176Hf/177Hf = 0.28253–0.282797. Conclusions. The geodynamics of the Vendian stage is the activation of movements along previously existing riftogenic faults. Deep source of magma generation for granites was heterogeneous: the mantle played a significant role, the crustal component was represented by ancient graywacks. U–Pb dating of zircons transformed as a result of the post-Cambrian tectonothermal activity is comparable with the ages of the main geodynamic events in UMM (spreading, subduction, collision). The behavior of F, Cl, S in apatites, which is an indicator of the fluid regime, shows that gold mineralization of the quartz-vein type can be associated with the Bitim granites. Studies are clarified the imagination about the structure of the junction zone between UMM and EEP and can be used in geological and metallogenic mapping.

Regional low-temperature fluid flow indicated by quartz mineralization in Silesicum, NE Bohemian massif

The crystalline rocks of the Silesicum unit of the Bohemian Massif host two principal types of hydrothermal quartz veins. Veins associated with granitoids are primarily quartz with wollastonite and epidote and accompanied by hydrothermal alteration of host rocks whereas others are of the more complex Alpine-type. L+ V + S (liquid + vapour + solid phase) fluid inclusions within quartz crystals contain muscovite and +/- calcite (+/- haematite) as solid phases and homogenisation temperatures are between 124 and 176 degrees C. Trapped fluids are uniformly of the H2O-NaCl-CaCl2 +/- MgCl2 +/- KCl system with a salinity between 9.1 and 26.8 mass % (NaCl+CaCl2). The variable Na/Ca ratios result from different intensity of fluid-rock reactions. The ubiquitous muscovite is a product of fluid-rock interactions. Oxygen isotope evidence indicates that the fluids were a mixture of meteoric and marine waters in deep regional-scale convection systems. The studied type of fluids represents a post-Variscan hydrothermal system and shows the extent of migration pathways in the upper crust on the north-eastern edge of the Bohemian Massif.

Geology, fluid inclusions, H-O isotope, and hydrothermal zircon U-Pb geochronology of the Daqingshan orogenic gold deposit in Beishan orogenic belt, Xinjiang, NW China

The Daqingshan gold deposit, located in the Beishan orogenic belt, northwestern China, is hosted in a Carboniferous greenschist facies metavolcanic-sedimentary sequence. Three periods of metamorphic and deformational events were recognized, corresponding with the three types of quartz veins in the deposit area. Quartz veins formed in the second period (D2) are the main auriferous ones that are strictly controlled by the subsidiary structures of the Kuluke shear zone. Gold mineralization occurs both as quartz veins and as enveloping altered wall rocks. Native gold, pyrite, and arsenopyrite are the primary ore minerals, while quartz and sericite are the main gangue minerals. Wall-rock alteration predominantly consists of silicification, sericitization, arsenopyritization, and pyritization. Systematic fluid inclusion investigation shows that CO2-H2O three-phase inclusions are the dominant type of fluid inclusions in the auriferous quartz veins, suggesting that the ore-forming fluids belong to a CO2-H2O ± CH4 ± N2 system that is particularly rich in CO2. The ore fluids are characterized by medium to high temperature (230~380 °C), low salinity (2~8% NaCleqv.), and medium density (0.8~0.9 g/cm3). Oxygen isotopes (δ18Ofluid = 11.3‰ to 13.9‰) indicate that the ore-forming fluids were most likely derived from metamorphic water. Fluid immiscibility might be the critical mechanism leading to the deposition of gold. The U-Pb dating results of hydrothermal zircons from auriferous quartz veins indicated that the maximum timing of the gold mineralization at Daqingshan was 295 Ma, the Early Permian. Comprehensive studies suggest that the Daqingshan deposit is a typical orogenic gold deposit formed during the subduction-accretionary phase of the Beishan orogenic belt. Significantly, recognizing the ore genesis of the Daqingshan gold deposit has an important implication for deep and regional mining exploration of southern Beishan.

Epithermal gold mineralization in Cretaceous volcanic belt, SE China: Insight from the Shangshangang deposit

Low sulfidation (LS) epithermal gold deposits within the Southeastern China Fold Belt (SCFB) are generally associated with Early Cretaceous volcanism (91–110 Ma). The Shangshangang (SSG) gold deposit (3 t Au @ 2.7 g/t) is proposed to be a LS ore system hosted by Early Cretaceous volcanic-subvolcanic rocks in the Dongkeng Basin (DVB), northern SCFB. Early Cretaceous felsic volcanic-subvolcanic rocks within the DVB possess high-K calc-alkaline and metaluminous to weakly peraluminous signatures. They show rare trace element (REE) and trace element patterns resembling those of Early Cretaceous A-type granites and rhyolites in the SCFB with significantly Eu negative anomalies (Eu/Eu* = 0.1–0.3). These volcanic-subvolcanic rocks are potentially formed by mixing of melts from crust and Early Cretaceous enriched mantle under an extensional tectonic setting. This is indicated by their negative εHf(t) values (−8.8 to −5.2), young two-stage Hf model ages (TDM2 = 1.32–1.48 Ga), and variable Sr-Nd isotopic compositions.The epithermal event at SSG is represented by three mineralization stages characterized by four distinct quartz vein types. These are: (1) greyish green crustiform comb quartz veins (type A) and smoky grey fine-grained (<0.5 mm) quartz veins (type B) in the early stage, (2) ivory medium- to coarse-grained (>1 mm) quartz veins (type C) in the middle stage, and (3) late white calcite-rich quartz veins (type D). Quartz veins are typically accompanied by hydrothermal alteration with zoning (kaolinite-illite-chlorite zone, adularia-chlorite-quartz zone, and adularia-sericite-quartz zone). Gold mineralization is identified in the early stage and free gold exists as micrometer-sized inclusions of native gold within pyrite. Pb–Zn mineralization dominates the middle stage. Hydrothermal fluids within the ore system are of low salinity (<7 wt% NaCl) and gas-poor. The fluid temperatures decreases from 224 − 316 °C for Au mineralization to 190–261 °C for Pb-Zn mineralization. No indication for fluid boiling is found. The H–O isotopes indicate mixing of magmatic and meteoric fluids and a larger portion of meteoric water at a later stage. The δ34S values of pyrite related to Au mineralization are 1.1–2.0‰ and of sphalerite and galena related to Pb-Zn mineralization range from −1.8 to 2.5‰. The Pb isotopic compositions of sulfides from the early and middle stages are relatively homogeneous and similar with those of subvolcanic rocks within the DVB. Deposit geology, microthermometric result, and isotopic data support a LS epithermal origin for the SSG gold deposit, and therefore suggest a co-existing relationship between low and intermediate sulfidation epithermal gold mineralization within the DVB.

Ore-forming fluids of the Fancha gold deposit, Lingbao, Henan Province

The Fancha gold deposit is a representative of the auriferous quartz vein type gold deposits in the Xiaoqingling gold district where the ore-forming fluid is one of the key controlling factors in the deposits formation, and also the main focus of ore deposit research. Here, the geological characteristics and fluid inclusions of the Fancha deposit are presented in detail, with a description of the potential origin and evolution of the fluid and the genesis of the deposit. Field investigation and petrographic observation show that ore-bodies in the Fancha deposit are preferentially hosted in the amphibolites of the Taihua Group and are controlled by brittle fracture. Hydrothermal alteration in the Fancha deposit includes silicification, potash feldspathization, sericitization, pyritization and carbonatization. The mineral assemblage, cross-cutting and replacement relationships indicate that the ore-forming process can be divided into quartz-K-feldspar (I), quartz-coarse pyrite (Ⅱ), quartz-fine pyrite (III), quartz-polymetallic sulfide (IV) and carbonate stages (V). Gold is mainly precipitated in stages III and IV. Three types of fluid inclusions have been identified in the Fancha deposit, based on their characteristics at room temperature: three-phase CO2-rich, three-phase CO2-bearing and two-phase aqueous inclusions. The fluid inclusions demonstrate the modes of homogenization temperatures of 363.3℃, 325.5℃, 273℃, 258.62℃ and salinities of 14.53, 9.59, 11.61, 8.03 wt% NaCl.equiv., for stages II, III, IV, and V respectively. The ore-forming fluid in the Fancha deposit belonged to the CO2-H2O-NaCl-(±CH4) fluid system with mid-low temperature and mid-low salinity. The δ18OH2O of the metallogenic fluids was between 1.36 and 6.28, and the δDH2O was between -87 and -53.1. Hydrogen and oxygen isotope data indicate that the ore-forming fluids were dominated by metamorphic fluids in the early stage, and that the metamorphic fluid gradually mixed with circulating meteoric water during the later stages. Petrographic observation and microthermometry suggest that fluid mixing and immiscibility obviously occurred during the main metallogenic stage. Fluid mixing and fluid immiscibility probably led to gold deposition in the Fancha deposit.

Metal content and P-T evolution of CO2-bearing ore-forming fluids of the Haftcheshmeh Cu-Mo porphyry deposit, NW Iran

The Haftcheshmeh Cu-Mo porphyry deposit is located in the NW part of the Arasbaran Metallogenic-Magmatic Zone, NW Iran. Ore mineralisation is generally hosted within the gabbro-diorite and granodiorite porphyry stocks, presenting various types of hydrothermal quartz veins and veinlets associated with potassic to sericitic alteration.Stage I corresponds to barren quartz-K-feldspar-biotite-anhydrite veins (A veins), with minor metal sulphides (pyrite ± chalcopyrite), surrounded by K-feldspar and biotite halos related to potassic alteration. Stage II is described with quartz-molybdenite-chalcopyrite-pyrite-bornite-magnetite-hematite-biotite veins, predominantly occurring in the potassic alteration halos (B veins). Stage III shows pyrite-quartz-chalcopyrite ± molybdenite-galena-sphalerite associated with sericitic alteration halos (D veins). The coexistence of halite-saturated aqueous-rich and low-salinity vapour-rich fluid inclusions in the H2O-NaCl-CO2 system is evidence of fluid boiling in each alteration/mineralising stage. This process was subsequently followed by meteoric water input diluting the CO2-bearing ore-forming fluid. LA-ICPMS data of fluid inclusions associated with the successive stages reveal elevated Na, K, Fe, Mn, Cu and Mo content. The metal content of fluid inclusions of Stages II and III is in large part due to accidentally trapped minerals. Molybdenite and chalcopyrite started precipitating between stages I and II from a metal-poor fluid. The long-duration (>1 Ma) of the magmatic-hydrothermal activity and associated CO2 fluxes and repeated fluid boiling events lead to ore deposition at temperatures of 450 to 250 °C and at depths between 3.0 and 1.0 km from near-lithostatic to near-hydrostatic conditions.

He-Ar, S, Pb and O isotope geochemistry of the Dabaiyang gold deposit: Implications for the relationship between gold metallogeny and destruction of the North China Craton

The Dabaiyang gold deposit is located within the Zhang-Xuan gold mineralized zone, along the northern margin of the North China Craton (NCC). The ore mineralization is hosted within Precambrian metamorphic rocks, and is a typical quartz-vein type gold deposit with minor sulfide mineralization. Here we report He-Ar, S, Pb and O isotopes from this deposit with a view to trace the source of the ore-forming fluids and metals, and to evaluate the relationship among ore-formation, magmatism and craton destruction in the NCC. The ratios of 3He/4He and 40Ar/36Ar of the fluid inclusions in the pyrite of the Dabaiyang ores show a range of 1.4Ra–1.8Ra and 4974.4–15669.5, respectively, with the concentrations of 4He and 40Ar varying from 0.8 to 6.6 (10−7 cm3 STP/g) and 4.3 to 218.1 (10−7 cm3 STP/g), respectively. Our data suggest that mixed mantle and crust derived fluids were involved in the Dabaiyang gold mineralization, with ca. 17.1%–27.6% mantle-derived helium, as computed from crust-mantle mixing model. The δ34S values in the pyrite range from −10.40‰ to −11.90‰, with an average of −10.96‰, suggesting that the sulfur in the ore forming fluids was derived from a mixed-source of the Precambrian metamorphic basement and mantle. The Pb isotopic ratios in the pyrite from the ores show 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in the range of 16.82 to 17.16, 15.33 to 15.43 and 36.77 to 37.22, respectively, indicating that the ore forming fluids, and by inference, the ore metals, were mainly derived from lower continental crust with minor contribution of mantle. The δ18OH2O values of the fluid inclusions in the gold-bearing quartz veins range from −1.04‰ to 4.36‰, suggesting the dominant role of magmatic water with minor contribution of meteoric water in the ore precipitation. Based on the analytical results of the isotopic compositions obtained in this study, combined with the previously published geochronological and He-Ar/S/Pb/O isotopic data, we suggest that the ore fluids and metals were derived from a mixed source involving contributions from mantle, crust and atmospheric water, and that the ore formation was associated with destruction of the North China Craton.

Double-vein (ore-bearing vs. ore-free) structures in the Xitian ore field, South China: Implications for fluid evolution and mineral exploration

Two types of spatially and temporally associated hydrothermal veins, ore-bearing and ore-free, occur as double vein structures in the Xitian ore field, South China. Here, we investigated the genetic relationship, material provenance, fluid properties, and prospecting significance of the co-developed veins in the granite-related, fault-controlled vein-type Xiangdong W, Goudanlan W, Chaling Pb–Zn and Xinggao fluorite deposits of the Xitian ore field, focusing on two common minerals: quartz and zircon. Petrographic, CL, microthermometric and H–O isotopic analyses of Stage I and Stage II quartz in both the ore-bearing and ore-free veins of these deposits document two episodes of hydrothermal activity. The first episode involved a high-temperature (up to 370 ℃), high-salinity (up to 28% NaCl equiv.), high-δ18O (–2.1‰ to +7.2‰), and high-δ2H (–82‰ to –54‰, mean = –68‰, n = 13) fluid that corresponds to the main magmatic-hydrothermal stage of the deposits, and the second episode involved a low-temperature (down to 90 ℃), low-salinity (down to 1% NaCl equiv.), low-δ18O (–8.8‰ to –5.3‰), and low-δ2H (–83‰ to –60‰, mean = –73‰, n = 6) fluid that represents an accessary mineralization stage. Variations in fluid inclusion types and compositions indicate that the processes of fluid mixing, boiling, cooling, and degassing played important roles in mineralization, and that magmatic fluid became less important than meteoric water along during the formation of ore-free veins. LA-ICPMS U–Pb dating reveals totally different age populations for these veins: zircons from the ore-bearing quartz veins yield older and more variable ages (pre-Devonian: >400 Ma, n = 68) that are similar to that of the local basement/sedimentary rocks, whereas zircons from the ore-free quartz veins yield younger and less variable ages (Triassic: 250–200 Ma, n = 31; and Jurassic: 170–140 Ma, n = 13) that are identical to those of the host granite zircons. In addition, the ore-free veins show lower temperatures, salinities, and total REEs (as recorded by quartz) but greater alteration (as reflected by CL and trace element features of hydrothermally-altered zircons) and wider vein size than the ore-bearing veins. We propose a “mineral–water separation” model to explain the formation of the double-vein structures. In this model, ore-bearing veins and ore-free veins formed in succession during faulting events: ore-bearing veins formed first in the smaller fractures and were the dominant sites of mineralization, whereas the ore-free veins served as dissipating passageways for residual water and silica in larger fractures. We suggest that the mineral-water separation model has good application prospects in mineral exploration, and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins.

Genesis of the Shangjinshan W–Mo polymetallic deposit in the Eastern Jiangnan tungsten belt: Evidences from geochemistry, geochronology and zircon Hf isotope analyses

The newly discovered Shangjinshan W–Mo polymetallic deposit, located at the southern Anhui, southeast China, is a large-scale skarn-type tungsten polymetallic deposit. According to mineral assemblages, ore textures/structures and superposition relationships of the mineralization, three ore types have been recognized: veinlet-disseminated skarn (the primary type), quartz vein type and porphyry type. The mineralized event of this deposit could be divided into four stages: (I) the prograde skarn stage, (II) retrograde skarn stage, (III) quartz-sulfide vein stage, and (IV) quartz-calcite vein stage. The intrusion in the tungsten-rich district of the Shangjinshan is mainly composed of the granodiorite with zircon U–Pb ages of 138.4 ± 1.2 Ma to 136.7 ± 1.3 Ma. Meanwhile, Re–Os isotopic dating of five molybdenite samples yields an isochron age of 141.9 ± 3.1 Ma and a weighted average age of 139.3 ± 1.7 Ma, respectively. The ore-forming ages are consistent with the rock-forming ages within errors, indicating that the W-Mo mineralization is genetically related to the Shangjinshan granodiorite. The granodiorite is I-type granites, characterized by metaluminous to slightly peraluminous and high-K cal-alkaline compositions. They are also enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs) and heavy rare earth element (HREEs), with obviously negative Eu anomalies (Eu/Eu* = 0.50–0.84). The zircon εHf (t) values and two-stage Hf model ages (TDM2) fall into the range −6.18 to −2.04 and 1.5–1.3 Ga, respectively. The relatively low rhenium contents in molybdenite and high radioactive Pb isotopes of the pyrites from stage II indicate that the ore-forming material was derived from Shangjinshan granitic magmatism. Together with previously published data, we propose that the W-related granitoids in the JNB were likely generated by partial melting of the Shangxi Group with some additional mantle materials. The granitic magmatism was caused by the asthenosphere upwelling, triggered by the roll-back of subduced Paleo-Pacific plate during Late Jurassic to Early Cretaceous. These granitic stocks predominately contributed to the production of skarn alteration and mineralization, resulting in the giant tungsten polymetallic district in the Jiangnan tungsten belt.

Genesis of the Banxi Sb deposit, South China: Constraints from wall-rock geochemistry, fluid inclusion microthermometry, Rb–Sr geochronology, and H–O–S isotopes

The Banxi Sb deposit is located in the world-class central-western Hunan Sb belt in South China, with quartz-vein type Sb-only mineralization hosted by Neoproterozoic epimetamorphic clastic sedimentary rocks. In this contribution, microthermometric, Rb–Sr geochronological and H–O isotopic analyses on fluid inclusions trapped in quartz, S isotopic studies on stibnite, and major-trace elemental measurements on fluid-altered and unaltered wall-rocks are presented to constrain the genesis of the deposit. The fluid inclusions are characterized by low homogenization temperature (170–260 °C) and low salinity 3–7 wt% NaCl equiv., with a low fluid density of 0.72–0.93 g/cm3 and a pH of 5.59. The low δDw (fluid δ2H, –140‰ to –107‰) whereas positive δ18OV-SMOW (15.9–17.2‰) and δ18Ow (fluid δ18O, 5.9–8.4‰) values in quartz indicate that the mineralizing fluid was generated from the low-grade metamorphic basement rocks and received a certain input of meteoric water. The Rb–Sr isotopic compositions of quartz samples yielded an isochron age of 196 ± 4 Ma (1σ, MSWD = 0.70) for quartz-stibnite ores. A highly radiogenic 87Sr/86Sr value (0.72663–0.74002, initial 87Sr/86Sr = 0.72640) indicates that ore-forming materials are derived mainly from basement rocks, and a direct material contribution from local granitic rocks can be ruled out. The δ34SV-CDT values of stibnite range narrowly from 4.81‰ to 6.72‰ and are in the δ34SV-CDT range of the metamorphic rocks, indicating that the sulfur was sourced from the basement rocks by sulfate reduction. Compositional differences between fluid-altered (decolorized) and unaltered wall-rocks are obvious: the migrated SiO2, SO3, LREE, Hf, Nb, Zr, Ta, Th, U, Mo, Sn, W into altered wall-rocks suggests a deep basement metamorphic rocks-derived Si-rich alkaline brine for the fluid-rock interaction; while the leached Fe2O3, MgO, MnO, TiO2, Ba, Cs, Rb, As, Co, V, Ni, Sb, Sc, Cu, Pb and Zn from the altered rocks imply a material contribution of Banxi Group wall-rocks during the Sb mineralization process. Consequently, we conclude that the quartz-stibnite stage of the Banxi Sb deposit was formed during the Late Triassic orogeny in the Xuefeng Mountain region. Heated by granitic magmatism, Sb and S were leached from the basement rocks, forming an initial Si-rich and alkaline ore-bearing fluid. Precipitation of stibnite from the fluid resulted from interacting with wall-rocks and mixing of meteoric water, coupled by releasing of stress, decreasing of temperature and lowering of the pH at higher crustal levels.

Formation of the Granodiorite-Hosting Magushan Cu–Mo Polymetallic Deposit in Southern Anhui, Eastern China: Evidences from Geochronology and Geochemistry

The newly discovered Magushan Cu-Mo polymetallic deposit, located in southeastern Anhui, eastern China, is a middle-scale skarn-type polymetallic deposit with different ore types of veinlets-disseminated skarn (the primary type), quartz veins, and porphyry. LA-ICP-MS zircon U–Pb analyses yielded a crystallization age of 135.7 ± 1.5 Ma for the ore-related granodiorite in Magushan. The granodiorites are I-type granites in nature, characterized by metaluminous and high-K calc-alkaline characteristics. They are enriched in large ion lithophile elements (LILEs, e.g., Ba, Th, and U) and light rare earth elements (LREEs), and depleted in high field strength elements (NFSEs, e.g., Nb, Ta, and Ti) and heavy rare earth element (HREEs), with slightly negative Eu anomalies (Eu/Eu* = 0.81–0.86). These granodiorites show high Mg# (mainly &gt; 40) values, high MgO (1.73–1.96 wt. %) and low Na2O (&lt;4.21 wt. %) contents, with whole-rock (87Sr/86Sr)i ratios (0.708877 to 0.710398), negative εNd(t) values of −5.4 to −5.2, and negative zircon εHf(t) values of −4.60 to −1.37, with old two-stage Hf model ages (TDM2) between 1.2‒1.5 Ga. Besides, they are characterized by high radiogenic Pb isotopic compositions with (206Pb/204Pb)i = 18.44–18.56, (207Pb/204Pb)i = 15.66–15.67, and (208Pb/204Pb)i = 38.77–38.87. These granodiorites are characterized by high zircon Ce4+/Ce3+ ratios (average 893) and Eu/Eu* ratios (average 0.51), indicating high magmatic oxygen fugacities. The distinct geochemical and isotopic features suggest that the Magushan granodiorites could be formed by metasomatized mantle-derived magmas, mixing with materials from Neoproterozoic crust that is widely distributed in the Southern Anhui. This study concludes that the formation of the Magushan Cu-Mo polymetallic deposits may largely depend on an oxidizing environment and multi-sources mixed of mantle- and crust-derived materials.

Structural characteristic of the hydrothermal-ore system of the Bambukoy river basin, Western Transbaikalia

The hydrothermal ore system of the Bambukoy basin of the Western Transbaikalia is located within the South Muya Ridge is a set of quartz veins with different orientations, performing fissure paragenesis, formed during the development of thrust and shear deformations. The rocks enclosing are terrigenous deposits of the Amatkan Formation of the Vendian age, presented in the form of interbedded aleurolites and sandstones of varying grain size. The terrigenous deposits intensively deployed in inclined, recumbent, diving folds. In the structure of the zone, there are two types of quartz veins. The first type includes veins concordant stratification and cleavage, the second type are counter veins. Due to the kinematic reconstruction was revealed that the formation of sub - concordant veins is associated with the initial stages of the formation of the thrust system. In turn, the counter veins are derived from the subsequent stages of deformation, expressed in the development of left-side shifts that complicate the thrust system.

Fluid inclusion and isotopic (C, H, O, S and Pb) constraints on the origin of late Mesozoic vein-type W mineralization in northern Guangdong, South China

Northern Guangdong of South China occurs many large tungsten deposits, including Shirenzhang, Meiziwo and Yaoling quartz-vein type wolframite deposits. In this study, we carried out a detailed study on fluid inclusions and C-H-O-S-Pb isotopic analyses of mineral separates for these three deposits, in order to resolve the origin and evolution of ore-forming fluids and the ore deposition mechanism. The ore veins in these deposits present a similar mineral paragenesis that could be divided into three stages: (I) pre-ore stage, (II) syn-ore stage, and (III) post-ore stage. The pre-ore stage is the magmatic-hydrothermal transition stage, which is marked by fluid exsolution from the highly fractionated granites, accompanied with potassic alteration and greisenization. The syn-ore stage can be further divided into two stages: silicate-oxide stage (stage II-1) that is characterized by significant tin-tungsten mineral deposition, and sulfide stage (stage II-2) that is characterized by abundant sulfide minerals deposition. The post-ore stage is dominated by quartz and fluorite. The three deposits show similar temperature and salinity variations for syn-ore and post-ore stages. In the Shirenzhang deposit, the fluid temperature and salinity range from 239 to 301 °C and 1.4 to 8.7 wt% NaCl equiv in stage II-1, from 206 to 256 °C and 1.4 to 7.0 wt% NaCl equiv in stage II-2, and from 186 to 236 °C and 1.4 to 8.6 wt% NaCl equiv in stage III. In the Meiziwo deposit, the fluid temperature and salinity range from 242 to 310 °C and 1.1 to 8.6 wt% NaCl equiv in stage II-1, from 196 to 252 °C and 1.4 to 8.1 wt% NaCl equiv in stage II-2, and from 188 to 234 °C and 1.2 to 7.3 wt% NaCl equiv in stage III. In the Yaoling deposit, the fluid temperature and salinity range from 230 to 304 °C and 1.2 to 9.0 wt% NaCl equiv in stage II-1, from 203 to 258 °C and 1.4 to 6.5 wt% NaCl equiv in stage II-2, and from 184 to 231 °C and 1.6 to 8.3 wt% NaCl equiv in stage III. The ore-forming fluids in the three deposits belong to a medium temperature, low-salinity H2O-NaCl system, with trace amounts of volatile components including CO2, CH4 and N2. The C-H-O isotope data (δ13CCO2 = −18.9 to −6.7‰; δ18Owater = +1.1 to +6.3‰; δDH2O = −78 to −55‰) indicate that the ore-forming fluids were mainly magmatic water, which might be modified by fluid-rock interaction and mixing with meteoric water. Sulfur (δ34S = −7.0 to +0.3‰) and Pb isotope data (206Pb/204Pb = 18.531–18.693, 207Pb/204Pb = 15.728–15.753, 208Pb/204Pb = 38.902–39.081) suggest that the ore metal and sulfur are of magmatic origin. The involvement of both organic matter in metasedimentary rocks during fluid-rock interaction and oxidized meteoric water may have been responsible for the negative δ34S and δ13C values. Fluid boiling, fluid-rock interaction and minor input of meteoric water might have been effective factors for the precipitation of wolframite, cassiterite and scheelite. The sulfide precipitation may have resulted from cooling and dilution of magmatic fluids by mixing with meteoric water.

Trace Element Geochemistry in Quartz in the Jinqingding Gold Deposit, Jiaodong Peninsula, China: Implications for the Gold Precipitation Mechanism

Lots of studies on gold precipitation mechanisms have focused on fluid inclusions within quartz. However, the trace elements in quartz reflect the properties of the ore fluid, and a comparison of the trace element content in different types of quartz can reveal the precipitation mechanism. The Jinqingding gold deposit is the largest gold deposit in the Muping–Rushan gold belt and contains the largest single sulfide–quartz vein type orebody in the gold belt. This study distinguished four types of quartz in this orebody through field work and investigations of the mineralogy and cathodoluminescence (CL) of the quartz and crosscutting relationships as seen under a microscope. In situ studies via electron probe micro-analyzer (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were used to determine the trace element content of the different quartz types. Type Qa displayed a comb structure in the field and zoning under the microscope and in CL. Milky white and smoke grey Qb was the most common quartz type and hosted the most sulfide and gold. Qc was Qa and Qb quartz that recrystallized around pyrite or overgrew and appeared different from Qa and Qb in CL images. Qd occurred within fractures in pyrite. Qa formed prior to the mineralization of gold, and Qd formed post-mineralization. Qb and Qc provided information regarding the ore fluid during mineralization. Sericites occurred with pyrite in fractures in the quartz, and some, along with free gold, filled in fractures in pyrite. Free gold occurred within Qa, Qb, Qc, and in brittle fractures in pyrite. Qc had the lowest Al content of all of the quartz types. As Al content is related to the acidity of the ore fluid in previous study, this indicated an acidity decrease during mineralization, which could be attributed to the sericitization. Sericitization could indicate a potential gold occurrence. The Ti content decreased from Qb to Qc, indicating a decrease in temperature during quartz overgrowth formation. Change in acidity and cooling can therefore be identified as possible causes of gold precipitation in the sulfide–quartz vein type in the Jinqingding gold deposit.

Genesis of the Xiaolonghe quartz vein type Sn deposit, SW China: Insights from cathodoluminescence textures and trace elements of quartz, fluid inclusions, and oxygen isotopes

Quartz textures revealed by scanning electron microscope cathodoluminescence (SEM–CL) images suggest that quartz in the Xiaolonghe Sn deposit formed in at least three fluid episodes. Quartz (Q1) in the pre-ore silicification zone has homogeneous texture, high CL intensity and high Ti content (19–53 ppm). Fluid inclusions hosted in Q1 are vapor-rich (V1-type) and homogenized as supercritical fluid at ∼570 °C. Quartz (Q2) in the syn-ore topaz-cassiterite-quartz veins has lower CL intensity and is characterized by euhedral growth zones with lower Ti content (1.3–12 ppm). Fluid inclusions hosted in Q2, topaz and cassiterite are liquid-rich fluid inclusions of moderate salinity (∼15 wt% NaCl equiv) (L1-type) which homogenized at ∼423 °C. The post-ore quartz (Q3) closely associated with sericitization of topaz generally crosscuts Q2, and has dark CL intensity and much lower Ti concentration (<1.5 ppm). In Q3, the vapor-rich (V2-type) fluid inclusions coexist with the halite-bearing (S-type) fluid inclusions, which homogenized at ∼269 °C, 0.05 kbars.The upper limits of T–P conditions of pre-ore and syn-ore stage are constrained by the intersection of NaCl–H2O fluid inclusion isochores and Ti-in-quartz isopleths, and the lower limits are based on microthermometry results of fluid inclusions. Combined with the δ18Ofluid value (8.3‰) of Q1, it indicates that the pre-ore supercritical fluid was directly exsolved from a granitic magma at T = 570–600 °C and P = 0.70–0.77 kbars, corresponding to a maximum depth of 2.8 km under lithostatic pressure. The syn-ore subcritical fluid (8.0‰ > δ18Ofluid > 6.3‰) mixed with some meteoric water was under 423–450 °C, 0.32–0.45 kbars. The transition from the pre-ore supercritical fluid to the syn-ore subcritical fluid indicates boiling condition (probably at 512 °C, 0.62 kbars), which was likely caused by hydraulic fracturing under high pressure. Both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in Xiaolonghe Sn deposit. In the post-ore stage, the coexisting S-type and V2-type fluid inclusions in Q3 indicates a second fluid boiling at 269 °C, 0.05 kbars, which was probably caused by decompression due to rapid denudation of the overlain strata. The low salinity (5.5 wt% NaCl equiv) L2-type fluid inclusions hosted in fluorite homogenized at 199 °C and <0.02 kbars, indicating that fluorite veins probably formed in open fractures. The δ18Ofluid results from sericite (5.1–5.0‰), quartz (−1.3 to −2.0‰), and chlorite (−7.9‰) suggest that increasing meteoric water was involved after second fluid boiling.