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Wolframite-quartz vein-type tungsten deposits constitute the world's major tungsten resources and are integral to tungsten production. A major share of this mineralization product is found in Southeast China, with other significant resources in the Central Andean belt, the East Australian belt, the Karagwe-Ankole belt and the European Variscan belt. In the past few decades, extensive studies on wolframite-quartz vein-type tungsten deposits have been conducted, but many key questions concerning their ore-forming fluid and metallogenic mechanism remain unclear. Additionally, a summary work on the global distribution and fluid characteristics of these wolframite-quartz vein-type tungsten deposits is still lacking. In this contribution, recent progress regarding several major issues related to the fluid processes involved in the forming of these veins are overviewed, and challenges in terms of future research are proposed. These issues include the nature of ore-forming fluids, their sources, and their transportation and wolframite deposition mechanisms. In particular, the affinity between veins and the exposed granitic intrusion from the Zhangtiantang-Xihuashan ore district, where an as-yet undiscovered deep intrusion, rather than the exposed granitic intrusion, was probably responsible for the formation of the wolframite-quartz veins, is reevaluated. This study also reviews the existing fluid and melt inclusion data from several tungsten deposits to address whether the mineralization potential of the magmatic-hydrothermal systems was directly correlated with the metal contents in the granitic melts and the exsolving fluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrothermal process is divided into four stages from early to late, and two stages of Sn mineralization are identified. • Fluid mixing may be the predominant mechanism for the minor Sn mineralization occurred in stage II. • Fluid cooling may be the predominant mechanism for the abundant cassiterite precipitation in stage III. • The ore-forming fluid mainly derived from highly evolved granitic magma, and the genesis of cassiterite is consistent with typical skarn-type Sn deposits. The Xianghualing Sn-polymetallic deposit is a large skarn-type Sn deposit located in the Nanling polymetallic metallogenic belt, South China. The ore bodies are controlled by NE-trending faults and mainly hosted in the contact of Middle Devonian carbonate rock and granite. The Xianghualing deposit is divided into four mineralization stages, and two stages of Sn mineralization are identified. The mineralization stages from early to late include stage I (prograde stage), stage II (retrograde stage), stage III (cassiterite-magnetite-arsenopyrite-topaz-quartz stage), stage IV (sphalerite-galena-pyrite-chalcopyrite-quartz-calcite stage). Stage II is the initial stage of Sn mineralization where only minor cassiterite precipitates, and stage III is the main Sn mineralization stage where abundant cassiterite precipitates. On this basis, fluid inclusion microthermometry and Raman spectroscopy analyses were carried out for ore and/or gangue minerals at different stages. In addition, trace element composition analysis was also conducted on cassiterite. These data can contribute to reveal the fluid properties, evolution and formation mechanism of Xianghualing deposit. Three types of fluid inclusions were identified in different mineralization stages, including halite-bearing multi-phase inclusions (Type B), liquid-rich two-phase inclusions (Type L) and vapor-rich two-phase inclusions (Type V). Garnet (stage I) contains Type B inclusions and Type V inclusions, with homogenization temperatures and salinities of 511–549 °C, 37.6–48.9 wt% NaCl equiv. and 551–559 °C, 4.0–5.1 wt% NaCl equiv., respectively. Topaz (stage II) contains Type L inclusions with homogenization temperatures of 408–445 °C and salinities of 9.5–12.4 wt% NaCl equiv. Cassiterite (stage III) contains Type L inclusions with homogenization temperatures of 368–417 °C and salinities of 8.7–11.5 wt% NaCl equiv. Quartz (stage IV) contains Type L inclusions with homogenization temperatures of 162–227 °C and salinities of 2.6–5.0 wt% NaCl equiv. The temperature and salinity of the fluid from stage I to stage II decreased significantly, recording intense meteoric water mixing. The temperature of the fluid decreased from stage II to stage III, while the salinity changed little, indicating that, except for minor meteoric water mixing, cooling of fluid is predominant. The temperature and salinity of the fluid from stage III to stage IV continued to decrease, recording the further mixing of meteoric water. From stage II to stage III, the evolution temperature of the fluid is basically consistent with the temperature indicated by trace elements (Nb, Ta, Ti) of cassiterite in the two stages. Fluid mixing may be the predominant mechanism for the minor Sn mineralization occurred in stage II. Fluid cooling may be the predominant mechanism for the abundant cassiterite precipitation in stage III, which is accompanied by redox reactions of Sn (II)-Cl complexes with As (III) and/or CO 2 as potential oxidants, and acid neutralization of carbonate rocks. Combined with the cassiterite composition, it is indicated that the ore forming fluid of the Xianghualing deposit mainly derived from the highly evolved granitic magma in the region, and the genesis of cassiterite is consistent with that of typical skarn-type Sn deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Dulong skarn-type deposit developed two stages of Sn mineralization. • Detailed fluid study suggest mixing is the main mechanism for Sn mineralization. • Difference of trace elements in two stages of cassiterite also imply a mixing trend. Dulong Sn polymetallic deposit is a world-class skarn tin deposit situated at the Youjiang basin with a reserve of 0.4 Mt Sn at 0.56 %, 5.0 Mt Zn at 5.12 %, together with 7 kt In. The deposit predominantly occurs within the Neoproterozoic Xinzhaiyan Formation and is controlled by NS-trending faults. Based on elaborate field and petrographic observations, the Dulong Sn polymetallic deposit was divided into four mineralization stages: stage 1 (prograde stage), stage 2 (retrograde stage), stage 3 (quartz-sulfide stage) and stage 4 (carbonate stage). Tin mineralization primarily occurs as cassiterite during stage 2, with additional cassiterite-stannite formation noted in stage 3. Analysis of fluid inclusions across these stages reveals the evolutionary history of the mineralizing fluids and the precipitation mechanisms at Dulong. During stage 1, diopside hosts both daughter-bearing multiphase inclusions and vapor-rich inclusions. The daughter-bearing multiphase inclusions exhibit homogenization temperatures ranging from 510 to 574 °C and salinities between 44.7 and 49.6 wt% NaCl equiv., whereas the vapor-rich inclusions display homogenization temperatures of 573–586 °C and salinities from 2.9 to 4.0 wt% NaCl equiv., indicating a boiling fluid process. Cassiterite (stage 2) features primarily liquid-rich two-phase inclusions, with homogenization temperatures of 351–410 °C and salinities of 6.3–9.6 wt% NaCl equiv. These inclusions document the mixing of magmatic fluid with meteoric water, which is likely the principal mechanism driving initial tin mineralization. Similarly, the same type of inclusions is also recorded in cassiterite of stage 3. The homogenization temperature of the inclusions in cassiterite is 290–334 °C and the salinities of the inclusions is 3.4–8.4 wt% NaCl equiv. Comparatively, the temperature continued to decrease in stage 3, indicating that fluid mixing may have persisted during this stage which could also explain the occurrence of cassiterite and stannite in this stage. In addition, redox reaction where CO 2 and/or As (III) serve as oxidants may also be another mechanism to exact cassiterite from ore-forming fluid. Our Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data suggests that cassiterite of the Dulong deposit involves a variety of complex substitutional mechanism. Due to the differing geochemical properties of the elements and variations in their concentrations, there is an indication that two phases distinct mineralizing fluids may have been present. The varying geochemical properties and concentrations of elements such as Nb, Ta, Zr, Fe, In, and Ga align with microthermometric results, indicating a reduction in magmatic hydrothermal fluid contribution and/or a transition from high to low temperatures in the hydrothermal system. This variation is also likely attributable to fluid mixing processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wolframite- and scheelite-bearing quartz veins share the similar ore-forming fluid. • Magma source fluid responsible to the Chuankou W deposit. • The Ca-rich mineral in sandstone contributes Ca to precipitate scheelite. • Fluid-rock interaction exert a principle control on scheelite precipitation. The large-scale Chuankou W deposit is located in the north part of the Nanling metallogenic belt, South China. It comprises independent quartz vein-type scheelite and wolframite mineralization, both associated with the underlying granitic intrusion spatially. The scheelite-bearing quartz veins occur invariably in sandstone and slate to the west, whereas the wolframite-bearing quartz veins are mainly hosted by the granite to the east. To reveal the fluid characteristics of the two mineralizing vein systems, detailed petrography, microthermometry, and Raman spectroscopic analyses were carried out on fluid inclusions in scheelite, wolframite and their coexisting quartz. Major and trace element concentrations of fluids were obtained from individual fluid inclusions in quartz via LA-ICP-MS analysis. Wall-rock alteration of both vein systems were evaluated by TESCAN Integrated Mineral Analyser (TIMA) analysis, and based on which the bulk geochemical data of wall-rock as a function of distance from the vein were obtained for scheelite-bearing quartz vein. These data aid elucidation on the nature of fluids in the two types of W mineralization. Fluid inclusions in quartz and its coexisting tungsten minerals share similar homogenization temperature and salinity, suggesting near concurrent formation of quartz and ore minerals. LA-ICP-MS analyses on pseudosecondary fluid inclusions in quartz associated with ore minerals show considerable concentrations of W in both mineralizing fluids, whereas Fe, Mn and Ca are generally absent irrespective of their higher detection limits. This may imply that Ca, Fe, and Mn were not initially derived from the granitic magma. The fluid compositions of both types of W mineralization display similar Rb/Na, K/Na, and Rb/Cs ratios, indicating a similar initial fluid source. The TIMA image shows that the host rock (sandstone) of scheelite-bearing quartz vein contains abundant Ca-rich minerals, such as apatite and calcium feldspar, indicating wall-rock as potential source providing Ca for the precipitation of scheelite. This assumption is strongly supported by bulk geochemical data of wall rock as a function of distance from hydrothermal quartz vein. In contrast, the tourmaline-rich granite hosting wolframite quartz veins may be a potential source of Fe for the precipitation of wolframite. Study on fluid composition combined with wall rock alteration suggest that the magmatic-sourced fluids and fluid–wall-rock interactions exerted primary control on the large-scale variations in mineralization types in the deposit, with scheelite- and wolframite-bearing quartz veins being both genetically and spatially related. Results of this study provide new guidelines for mineral exploration, suggesting a homologous scheelite-dominated deposit being likely to exist in association with a wolframite-dominated deposit, where the lithology of Ca-bearing formations may indicate potential prospecting areas. [ABSTRACT FROM AUTHOR]

The Shangshan'gang Au deposit is located in the Cretaceous Dongkeng volcanic basin of northern Fujian Province in southeast China. The deposit is hosted by altered intermediate to silicic volcanic rocks along NE–SW- and ENE–WSW-trending faults. The main types of wall-rock alteration are silicification, sericitization, argillization, and chloritization. Ore mineralization occurred in three stages, which were the base metal, Au Ag, and post-ore stages. Electrum and kustelite are the main Au Ag minerals. Laser ablation–inductively coupled plasma–mass spectrometry analyses revealed different compositions for the two stages of pyrite, galena, and sphalerite, which reflect changing mineralization conditions. Fluid inclusions revealed an epithermal mineralization environment with low–moderate temperature and salinity. Mixing of ore fluids is the main ore-forming mechanisms which occurred from the early to late stages, as evidenced by the H and O isotopic compositions of the ore-forming fluids. The proportion of meteoric fluid in the ore-forming hydrothermal fluid gradually increased with time. Fluid boiling may have locally occurred in the early stage and promoted ore precipitation. Our results show that the Shangshan'gang Au deposit is an intermediate-sulfidation-type epithermal deposit that gradually changed to a low-sulfidation-type during late mineralization. Given the close temporal and spatial relationship between intermediate-sulfidation-type and porphyry deposits, there is potential for porphyry deposits to exist in the Zhenghe–Jian'ou area. • An intermediate-sulfidation genesis was proposed to the Shangshan'gang deposit. • In-situ major and trace element of sulfides reveals divers mineralization conditions. • Ore-forming fluid were characterized by low-medium temperature and salinity fluids. • Mineralization was induced by mixing of dominant meteoric and minor magmatic fluids. [ABSTRACT FROM AUTHOR]

• The Luoyang deposit records three episodes of fluid ascent from the parental magma. • Two-stage fluid boiling occurs in the Luoyang deposit. • The Luoyang skarn system was formed in a more shallow depth than the Makeng skarn system. The Luoyang Fe skarn deposit is located in the Yong'an–Meizhou depression belt in Fujian Province, eastern China. Skarn alteration and mineralization are concentrated in a zone adjacent to an early Yanshanian granite porphyry (146 Ma), within limestone of the upper Carboniferous Chuanshan and lower Permian Qixia formations. Petrographic observations reveal five paragenetic stages of skarn formation and ore deposition: Stage 1 (early skarn; andradite); Stage 2 (diopside + magnetite); Stage 3 (late skarn; actinolite + chlorite + tremolite + magnetite + pyrite); Stage 4 (quartz + calcite + fluorite + pyrite + hematite + sphalerite + galena + chalcopyrite); and Stage 5 (calcite + quartz). We analyzed fluid inclusions in garnet, diopside, calcite, and quartz from stages 1, 2, 4, and 5, and measured H–O isotopic compositions of fluid inclusions in garnet, magnetite, and quartz from stages 1, 2, and 4. Observations of fluid compositions and phase assemblages allow three types (and two subtypes) of fluid inclusions to be distinguished: halite-bearing (type 1a) and hematite-bearing (type 1b), vapor-rich (type 2), and liquid-rich aqueous inclusions (type 3). In stage 1 garnet contains type-1a, -1b, and -2 primary fluid inclusions, which comprise two immiscible phases that formed through boiling. In stage 2 diopside contains type-1a and -2 fluid inclusions that also record boiling, which resulted in the precipitation of magnetite. In stage 4 quartz contains type-3 primary inclusions that are related to sulfide mineralization. In stage 5 calcite and quartz contain type-3 fluid inclusions, which represent the post-sulfide mineralization fluids. Microthermometric and H–O isotopic data indicate that multiple episodes of fluid flow occurred in the Luoyang deposit. During the early skarn stage, an initial supercritical fluid that exsolved during crystallization of the parent granitic magma ascended and underwent a first boiling event at 488 °C–536 °C and 380–438 bar (lithostatic pressure), which produced two fluids with differing salinities, represented by type-1a and -2 inclusions. This stage of boiling resulted in minor magnetite precipitation and type 1b fluid inclusions associated with this stage contain hematite. The magnetite stage was associated with a second episode of fluid ascent as the parent magma cooled to 454 °C–498 °C, which triggered a second boiling event and abundant magnetite precipitation at 336–449 bar (lithostatic pressure). The sulfide stage is associated to a third period of fluid ascent and occurred at 220 °C–261 °C at the same pressure conditions as the second boiling event (~380 bar). This stage included the input of meteoric water, which resulted in sulfide precipitation. Late-stage carbonate crystallization involved the influx of further meteoric water at lower temperatures (144 °C–193 °C) and the same pressure (~380 bar), representing the collapse of the skarn system. These observations suggest that the Luoyang deposit formed at a shallower depth than the Makeng deposit, which is located within the same belt. Variations in skarn alteration and magnetite mineralization are ascribed to the difference in depth between the two skarn systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two independents W and Cu mineralization styles were identified in the Shiweidong deposit. • The elemental content of the W and Cu mineralizing fluids was significantly different. • Fluids with distinct sources were responsible for W and Cu mineralization, respectively. The Shiweidong W-Cu deposit, located within the giant Dahutang W-Cu ore field, contains quartz vein type W-Cu and veinlet-disseminated type W mineralization. These ore veins are mainly hosted in the Jinningian biotite granodiorite. Two distinct mineralization stages were identified in association with quartz, namely wolframite-quartz veins and chalcopyrite-scheelite-quartz association. The deposit represents an example of a complex of economically valuable W and Cu, with resources of 0.3 Mt WO 3 and 0.24 Mt Cu. The characteristic and origin of the W and Cu mineralizing fluids remain debated. In our study, homogenization temperature (Th) and salinity were determined for fluid inclusions (FIs) in ore or associated gangue minerals. Additionally, we use the trace element compositions of fluid inclusions obtained by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to clarify fluid characteristics responsible for W and Cu mineralization. Primary fluid inclusions (FIs) trapped in wolframite display high Th ranging from 305 to 352 °C and have moderate salinity from 3.2 to 5.0 wt% NaCl equiv., quartz associated with chalcopyrite exhibit a close syngenetic relationship, and a significant low-temperature (248 ∼ 271 °C) fluid was recorded by FIs in quartz. Wolframite-hosted FIs were characterized by high concentrations of incompatible lithophile element Cs and volatile elements including Li and B, indicating that W mineralization fluid was derived from highly fractionated granitic systems. All FIs in wolframite display the absence of Cu. In contrast, FIs hosted in quartz coexisting with chalcopyrite have the high Cu concentrations with average value of 1033 ppm. Giving the lower Cs content in FIs from quartz coexisting with chalcopyrite, we suggest that the Cu-rich ore-forming fluid released from a less fractionated magma. These results indicate that W and Cu mineralization at Shiweidong was introduced by distinct fluids. Fluid simple cooling is likely a major driving factor in wolframite formation, while fluid boiling accompanied chalcopyrite deposition. Our new findings illuminate that the existence of independent Cu mineralization events in the W deposit in northern Jiangxi. [ABSTRACT FROM AUTHOR]

• LA–ICP–MS analysisof fluid inclusions indicates a common magmatic–hydrothermal fluid source. • Halite bearing fluid inclusions in deep level of quartz veins contain significant amounts of Pb, Zn, and Cu. • Result of fluid inclusion mapping agrees well with the fluid evolution trend obtained through fluid inclusion LA–ICP–MS analysis. The Xianhualing District at Jinzhai in the northern Dabie Orogen, China, is a significant area for Pb–Zn–Cu–Au polymetallic exploration. The main rocks in the area are mica–quartz schist of the Neoproterozoic Foziling Group, and magmatic rocks which are controlled by two sets of faults striking NNE and NW. Recent drilling has revealed that the orebody occurs mainly in mica–quartz schist in the form of breccia and veinlets. Major ore minerals include pyrite, sphalerite, galena, chalcopyrite, magnetite, gold, silver, and silver sulfosalts, with alteration assemblages of predominantly quartz, sericite, calcite, and chlorite. Three types of fluid inclusions occur in quartz–sulfide vein samples collected from eight drill-holes: two-phase liquid-rich inclusions (type I), two-phase vapor-rich inclusions (type Ⅱ), and halite-bearing inclusions (type III). Microthermometric studies of type I and Ⅱ fluid inclusions indicate homogenization temperatures of 161–378 °C and salinities of 0.5–7.8 wt% NaCl equivalent. Fluid inclusion microthermometric data and mineralization and alteration characteristics indicate an intermediate-sulfidation epithermal environment. Current exploration is focused on the location of potential deep porphyry mineralization associated with epithermal mineralization. In this study, 28 drill-core samples from different levels were selected for fluid inclusion microthermometry to elucidate fluid-evolution pathways and hence to determine the likelihood of porphyry bodies. The consistent fluid inclusion petrography, distribution patterns, and fluid-evolution trends indicate that the deeper part of the Dongchong area may have been the regional thermal center of fluid flow. The estimated mineralization depths of type III fluid inclusions are in the range 0.4–1.5 km, indicating a relatively shallow formation. Fluid chemical compositions obtained from single-inclusion laser-ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) analyses support the occurrence of a single magmatic–hydrothermal fluid source, which has a degree of mixing with meteoric water and a small amount of basinal brines during the migration path, and the fluid evolution pattern agrees well with the fluid inclusion mapping result. Quartz-vein hosted fluid inclusions contain significant amounts of Pb, Zn, and Cu, indicating good exploration prospects for porphyry Cu mineralization at depth. [ABSTRACT FROM AUTHOR]