Magmatic-hydrothermal Fluids Research Articles

Coupled evolution of basin structure and fluids recorded by microfractures: A case study of deep-buried ordovician in the tarim basin

The fluid activity in the deep strata of sedimentary basins is commonly related to tectonic activity, and the cements filled in fractures are a good carrier for the tectonic-fluid coupling evolution. Compared to macrofractures, microfractures have characteristics of high frequency and easy identifiable periods. Abundant microfractures infilled by carbonate cements (MCCFs) developed in carbonates of the Ordovician Yingshan and Yijianfang formations in the platform basin area of the Tarim Basin. Based on the study of petrology, U-Pb dating, and geochemical characteristics, this study determined the stages of MCCFs and clarified the tectonic-fluid coupling evolution process recorded by MCCFs in the study area. The formation order of these MCCFs is D1, C1, C2, D2, C3, and C4. The precipitation times of MCCFs have a good correspondence with orogeny around the Tarim Basin and active times of strike-slip faults in the platform basin area. The six stages of MCCFs in the Ordovician Yingshan and Yijianfang formations in the SLU recorded the tectonic-fluid coupling evolution process of concentrated seawater in the late Middle Ordovician, meteoric water at late Ordovician, organic acids during the Silurian, Mg-rich hot brine at the end Devonian-early Carboniferous, and magmatic hydrothermal fluids during the Permian. This not only indicates a close connection between fluid activity and tectonic activity in sedimentary basins, but also confirms that the formation of MCCFs in carbonate formations is closely related to regional tectonic-fluid coupling activities. This study provides a good example for studying macro scale tectonic-fluid coupling activities in basins using microfractures.

Coupling mechanism of trace elements and maceral in medium and high sulphur coal in the Jurassic terrestrial environment of Zhongyuan mine in the Hengshan mining area and adjacent areas

ABSTRACT Considering the urgency of resource utilization and environmental protection, the geochemistry of anomalous trace transition metal elements in coal formed in terrestrial environments has been studied using methods such as inductively coupled plasma atomic emission spectrometry analysis, electron probe micro-area analysis, sequential chemical extraction procedures, and correlation analysis. The results indicate that minerals in the coal samples included pyrite, kaolinite, quartz, dolomite, calcite, and celestite. Furthermore, compared with the average values of coals in China and the upper continental crust, the coal samples were rich in transition metal trace elements such as Ni, Cr, and Sr and were deficient in Be, Cd, Cu, Co, Ga, Mo, Sb, Tl, V, Zn, and Ti. We found that Ni preferentially occurred in the organic matter over minerals, while Cr primarily bonded with sulfide minerals and to a lesser extent with the iron-manganese oxide minerals. Sr had a low correlation with organic matter but adhered to clay minerals and celestite. Ni enrichment in coal samples was the result of terrigenous input, while the Cr enrichment was related to intrusion of magmatic hydrothermal fluids. Sr enrichment was caused by the presence of SO4 2- in the terrigenous debris and the influence of Sr-rich water underground.

Multistage fluid mixing events induced Sn polymetallic super-enrichment at Dulong in Yunnan Province, South China

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 CO2 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.

Genesis studies of Li–Rb deposits in pegmatites from Bailongshan, western China: Evidence from chronology, fluid inclusions, and H–O isotope analysis

The Bailongshan Pegmatite deposit, located in the West Kunlun Orogenic Belt, Northwest China, is a newly discovered, super-large Li–Rb (Be–Ta–Nb) rare-metal deposit. Since complex magmatic-hydrothermal processes are responsible for the mineralization of such rare-element pegmatites, it is desirable to study the evolution and sources of ore-forming fluids to analyze the genesis of ore deposits. In this study, the 40Ar/39Ar plateau ages of muscovite and biotite were determined to be 171.36 ± 1.87 and 172.39 ± 1.66 Ma, respectively, indicating that the duration of hydrothermal mineralization was approximately 170 Ma. Based on the zonal nature of the mineral assemblage, the Bailongshan area was divided into four zones and stages (I–IV), namely the albite–quartz–lithium tourmaline (AQT, stage I), albite–quartz-bearing mica (AQM, stage II), albite–quartz–spodumene (AQS, stage Ⅲ), and spodumene–quartz (SQ, stage IV) zones. Among these, AQS and SQ were the main ore-bearing areas. In terms of the fluid inclusions found in quartz and spodumene, the different types include a gas-rich phase (V-type), a liquid-rich phase (L-type), a daughter mineral-bearing three-phase (S-type), and a carbon dioxide-bearing phase (C-type). In stage I, the homogeneous temperatures of the V- and S-type fluid inclusions varied from 365 to 415 °C, while their corresponding salinities were 8.5–12.9 and 44.8–47.2 wt% NaCl equiv., respectively. In stage II, the homogeneous temperature and salinity of the L-type inclusions were 315–365 °C and 9.9–13.3 wt% NaCl equiv., respectively, while in stages Ⅲ and IV, the homogeneous temperatures of the L- and S-type fluid inclusions were between 235 and 335 °C, while their salinities were 7.2–12.3 and 32.1–37.0 wt% NaCl equiv., respectively. Furthermore, for the C-type inclusions, the homogeneous temperature and salinity were 235–320 °C and 4.9–10.6 wt% NaCl equiv., respectively. The laser Raman results showed that the fluid in the metallogenic stage was an H2O–NaCl–CO2–CH4 system. Based on the homogeneous temperature and salinity results, the fluid capture pressure from stage III to stage IV was calculated to be 280–150 MPa, and the depth of the capture was >6 km. Moreover, the H–O isotope results suggested that the early ore-forming fluids are mainly magmatic hydrothermal fluids, whereas the later (stage IV) mineralizing fluids may be mixed with a small amount of meteoric water. The subsequent immiscibility of the fluid may be one of the factors responsible for the discharge and precipitation of minerals.

Geochemical Evidence of Ore-Forming Processes in the Shuiyindong Gold Deposit of Southwest Guizhou Province, China.

The Shuiyindong deposit is one of the ultralarge Carlin-type gold deposits in Southwest Guizhou Province, China. Gold mineralization mainly occurs in the Permian Longtan Formation and the early Triassic Yelang Formation. It is controlled by both strata and faults. Detailed studies of the mineralogy and geochemistry characteristics of the Shuiyindong deposit are conducted to investigate the ore-forming process. Arsenian pyrite and arsenopyrite are the main Au-hosting minerals. Three types of pyrite can be recognized, including euhedral and subhedral pyrite, framboidal pyrite, and bioclastic pyrite. The euhedral and subhedral pyrite is the main Au-hosting type. The Au appears as a solid solution (Au+) and natural nanoscale gold (Au0) in the sulfide minerals. The Co/Ni ratios of sulfides (0.07-3.13) reveal that the ore-forming fluids were mainly affected by hydrothermal activity, but magmatic activity cannot be excluded. Organic matter in the ores is abundant (0.11-3.04%), which might provide sulfur for pyrite and favor an increase in the porosity and permeability of the host rocks by releasing organic acids. The REE and trace element results suggest that halogens (F and Cl) were contained in the reducing magmatic hydrothermal fluids. The sulfur isotopic data (from -8.64‰ to 27.17‰) suggest that the source of sulfur is complicated and is probably a combination of a magmatic source, the reduction of marine sulfate, and bacterial sulfate reduction. The Pb isotopic data of the sulfides indicate that Pb is from a mixture of crust and mantle sources. The obvious enrichment zones exist along the boundary faults in the geochemical map of As, implying that As may originate from the deep crust and then move to the strata with basinal fluids. By combining these results, it can be inferred that the ore-forming fluids were a mixture of basinal and deep source fluids. A probable ore-forming model of the Shuiyindong gold deposit is established.

Hidden deposit exploration using the tectono-geochemistry method in the western Xicheng ore field, China

Geochemical anomalies involve complex geological and geochemical processes. Integrating metallogenic processes into the interpretation of geochemical data can promote mineral exploration. In this study, 3080 subsamples were collected from the western Xicheng ore field and combined into 1312 composite samples using the tectono-geochemistry method. Nineteen elements were analyzed for each composite sample. Factor analysis based on the CLR-transformed data yielded four factors, including the Ag–Sb–Hg–Pb–Au–(B–Ba) association of F1, Zn–Cd–Pb association of F2, Bi–Sn–(Au–As) association of F3, and W–Sn–(Cu) association of F4. Thresholds of each factor were obtained using the concentration–number (C–N) fractal model. Six targets were delineated based on the factor anomaly maps, and one Pb–Zn and two Au deposits were discovered in Targets I and II, respectively. These discoveries and the good spatial correspondence between known deposits and anomalies provide compelling evidence for the effectiveness of the tectono-geochemistry method in the study area. More importantly, a model for the genetic relationship between geochemical anomalies and metallogenesis was constructed. The late tectonic-magmatic-hydrothermal transformation dominated the geochemical pattern in the study area. The degree of interaction between the Au-rich magmatic-hydrothermal fluids and SEDEX-style Pb–Zn mineralizations yielded leakage halos with various elemental assemblages. In addition, W–Sn anomalies may serve as auxiliary exploration indicators for Au mineralizations.

The orientation of intra-arc crustal fault systems influences the copper budget of magmatic-hydrothermal fluids

Some of the largest magmatic-hydrothermal copper ore deposits and deposit clusters are associated with arc-oblique fault systems. Whether this structural context impacts the geochemistry of hydrothermal fluids, including their copper contents, remains unknown. Here, we investigate the copper concentration and helium isotope signature of geothermal fluids as modern analogs of hydrothermal ore deposits in the Andes of central-southern Chile. We show that fault systems broadly parallel to the regional stress field facilitate the early release of fluids from deep primitive magmas. By contrast, fault systems oblique to the regional stress field prevent the early escape of fluids and promote magmatic enrichment in copper, volatiles, and ligands, enhancing the potential to form copper deposits. We conclude that the orientation of fault systems actively influences the copper budget of ascending hydrothermal fluids, explaining the contrasting distribution of metals along distinct structures often observed in porphyry-epithermal systems and other types of magmatic-hydrothermal deposits.

Episodic fluid charging and mixing triggers calcite-bearing agates in the Permian Emeishan Basalt, SW China

ABSTRACT Agate, a distinctive form of banded chalcedony, derives its characteristic appearance from the deposition of silica and the presence of impurities. A significant variety of agate-bearing calcite was identified in the Permian Emeishan Basalt located in the southwestern Sichuan Basin. This calcite-bearing agate provides valuable insights into the complex interplay and evolution of fluids and minerals. This study aims to provide a detailed description and analysis of the microscopic textural and geochemical characteristics of the agate, while elucidating the sequence of mineral deposition, fluid properties, and the genetic mechanism underlying its formation. The findings reveal that the agate primarily consists of lamellar calcite and banded chalcedony, exhibiting a variety of textures, thicknesses, and colours. Through the analysis of the transformation and precipitation of epidote and allanite, and the identification of four types of calcites and five micro-silica textures, it has been confirmed that the early stage of fluid in geodes involved the mixing of meteoric water with post-magmatic hydrothermal fluid. The middle and late stages involve the mixing of magmatic-hydrothermal fluid with organic-acid fluid. The charging of silica-rich hydrothermal fluids and the generation of hydrocarbons from organic matter cause fluctuations in SiO2 concentration, pH, and crystallization rates, contributing to the diversity of silica minerals, such as chalcedony and quartz. The interlayered growth observed between chalcedony and calcite is attributed to secondary metasomatism, which occurs after the dehydration and transformation of chalcedony due to increasing temperatures. Notably, the internal texture of the agate is somewhat influenced by pressure variations caused by the episodic charging of the fluid.

Mineral chemistry of the Geyer SW tin skarn deposit: understanding variable fluid/rock ratios and metal fluxes

AbstractThe Geyer tin skarn in the Erzgebirge, Germany, comprises an early skarnoid stage (stage I, ~ 320 Ma) and a younger metasomatic stage (stage II, ~ 305 Ma), but yet, the source and distribution of Sn and the physicochemical conditions of skarn alteration were not constrained. Our results illustrate that contact metamorphic skarnoids of stage I contain only little Sn. REE patterns and elevated concentrations of HFSE indicate that garnet, titanite and vesuvianite of stage I formed under rock-buffered conditions (low fluid/rock ratios). Prograde assemblages of stage II, in contrast, contain two generations of stanniferous garnet, titanite-malayaite and vesuvianite. Oscillation between rock-buffered and fluid-buffered conditions are marked by variable concentrations of HFSE, W, In, and Sn in metasomatic garnet. Trace and REE element signatures of minerals formed under high fluid/rock ratios appear to mimic the signature of the magmatic-hydrothermal fluid which gave rise to metasomatic skarn alteration. Concomitantly with lower fluid-rock ratio, tin was remobilized from Sn-rich silicates and re-precipitated as malayaite. Ingress of meteoric water and decreasing temperatures towards the end of stage II led to the formation of cassiterite, low-Sn amphibole, chlorite, and sulfide minerals. Minor and trace element compositions of cassiterite do not show much variation, even if host rock and gangue minerals vary significantly, suggesting a predominance of a magmatic-hydrothermal fluid and high fluid/rock ratios. The mineral chemistry of major skarn-forming minerals, hence, records the change in the fluid/rock ratio, and the arrival, distribution, and remobilization of tin by magmatic fluids in polyphase tin skarn systems.

Late Palaeozoic high-K calc-alkaline to shoshonitic series magmatism and related W(–Mo–Cu–Au) metallogeny of the Kyrgyz Tien Shan, Central Asia

In the Kyrgyz Tien Shan, numerous high-K calc-alkaline to shoshonitic series intrusions are associated with the large fault system known as the ‘Major structural line of Tien Shan’, or ‘Nikolaev Line’. During the Carboniferous, this lineament represented a zone of intracontinental, possibly back-arc rifting associated with a north-dipping subduction, whereas in the Late Carboniferous to Permian it was part of a larger continental collision structure. These Late Paleozoic high-potassic intrusions comprise numerous intrusive phases that vary in composition from the early mafic (monzogabbro, monzodiorite) through intermediate (monzonite, syenite, quartz syenite) to late stage and more evolved (quartz monzonite, granodiorite, monzogranite, leucogranite–alaskite) members locally intersected by monzodiorite–porphyry and lamprophyre dykes. They can be related to low degrees (from ∼1–2 to 2–2.5 vol%) of partial melting of metasomatically enriched upper mantle followed by magma fractionation and emplacement at shallower crustal levels. In summary, the high-K magmas formed in continental- and post-collisional arc settings with a progressive input of crustal material. From the west to the east, the potassic intrusions contain progressively higher Nb and Y concentrations, reflecting their derivation in a post-collisional setting. The A-type granite signatures also become more distinct in this direction. This is consistent with the tectonic model implying the ‘scissor-like’ closure of the Late Paleozoic Turkestan palaeo-ocean from east to west. These high-potassic intrusions are accompanied by W–Mo–Cu–Au skarn/porphyry to Au(–W) replacement-style deposits, which are part of the extended Au (Au–W–Mo–Cu) metallogenic belt of Tien Shan. The association of skarn and porphyry-style W–Mo to Mo–Cu–Au–W mineralization defines these ‘porphyry–skarn’ systems as a distinct group containing strongly oxidized andradite-dominant skarns. An early W partitioning into magmatic–hydrothermal fluid, together with Mo and Cu, is typical of this magmatic–hydrothermal system and can be explained by an early H 2 O saturation of the parental magma. The late-stage mafic dykes including lamprophyres probably reflect the presence of another, but concealed, mafic intrusion releasing CO 2 and metals, such as Au, As, Sb, Bi and Te, into the hydrothermal mineral system.

Textural and compositional evolution of quartz and cobalt-bearing minerals from the Wubaoshan Deposit, Jiangxi Province, South China: Implications for cobalt mineralization

Cobalt resources are primarily derived from hydrothermal-related deposits; however, our understanding of the mechanisms governing cobalt transportation and deposition, particularly for cobalt arsenides and sulfarsenides within hydrothermal fluids, remains limited. In this study, we present a comprehensive investigation into the Wubaoshan cobalt deposit located in the Qin-Hang ore Belt, South China. This deposit exhibits mineralization associated with multiple hydrothermal fluids, resulting in complex paragenesis and the formation of cobalt minerals. By employing a combination of petrographic and geochemical observations, we explore the conditions of the ore-forming fluid and the hydrothermal mechanisms underlying cobalt mineralization. Our analysis reveals three distinct hydrothermal stages of mineralization: Stage 1 is characterized by quartz-arsenopyrite-pyrite assemblages formed at relatively high temperatures (352–390 °C), neutral pH, and high fS2 (log fS2 = −6.9 ∼ −8.8); Stage 2, the pivotal stage for cobalt mineralization, displays various sulfides-sulfarsenides formed at lower temperatures (229 ± 6.0 °C), under acidic conditions, and low fS2 (log fS2 = −12.0 ∼ −14.0); and Stage 3 comprises minor sulfides and carbonates formed at relatively lower temperature and pH. Sulfur isotope analysis of pyrite from Stage 1 (+13.49 to +14.30 ‰) and sphalerite from Stage 2 (+5.53 to +9.21 ‰) suggests a mixed sulfur source derived from both Permian seawater sulfate and related magmatic rocks. Additionally, our results reveal that a transformation from cobalt arsenide to sulfarsenide during Stage 2, likely influenced by the change of As/S ratio in ore fluids, which is affected by the influx of external sulfur from magmatic hydrothermal fluids. Our findings, together with the previous thermodynamic modelling results, indicate that the variations of the ore fluid condition, particularly temperature and pH, govern the precipitation and dissolution of mineral during cobalt mineralization. These findings contribute to our understanding of the formation processes of the Wubaoshan deposit and provide valuable insights into the mechanisms of cobalt enrichment.

Cobalt enrichment and metallogenic mechanism of the Galinge skarn iron deposit in the Eastern Kunlun metallogenic belt, western China

Skarn iron deposits, as representative examples of Co-rich magmatic-hydrothermal deposits, are attracting increasing attention due to rising cobalt demand worldwide. However, the specific Co enrichment mechanisms and metallogenic processes in skarn deposits remain elusive. This study presents high-precision in situ U–Pb geochronological data for garnet from skarns, major and trace element analyses of sulfarsenides and sulfides, and X-ray mapping in the Galinge deposit. The Galinge skarn iron deposit formed at 237.1 ± 0.3 Ma (garnet U–Pb dating), during which time the region was in the post-collisional stage. During this period, the crust was thickened, causing delamination of the lithospheric mantle, which further led to the upwelling of asthenospheric materials and partial melting of the lower crust. As the resultant mixed magma ascended, it reacted with carbonate strata to form skarn deposits. Cobalt shows two occurrence modes in the Galinge deposit: independent cobalt minerals such as skutterudite and cobaltite, and isomorphic substitution of Co with other metals in ore minerals (arsenopyrite, pyrrhotite, sphalerite, pyrite, magnetite, and chalcopyrite). Our results revealed that arsenopyrite is the most cobalt-enriched ore mineral in the Galinge deposit, with an average Co content of 34,077 ppm. Other minerals generally contain insignificant Co contents of less than 500 ppm, including sphalerite (471 ppm) > pyrite (194 ppm) > pyrrhotite (145 ppm) > alabandite (∼100 ppm) > magnetite (7 ppm) > chalcopyrite (2 ppm). In arsenopyrite, cobalt and nickel replace iron in accordance with the inverse correlation between the concentrations of cobalt and nickel (wt%) and that of iron. In pyrite and chalcopyrite, a portion of the isomorphic cobalt substitutes for Fe or Cu. The weak correlation between Co (ppm) and Cu or Fe (wt%) indicates that only isomorphic cobalt is carried out by substituting Fe or Cu. The negative correlation between Co + Fe and Zn or Mn suggests that cobalt and iron replace Zn or Mn in sphalerite and alabandite. No evidence of element substitution was observed in pyrrhotite. Our study highlights that during the early mineralization stage, cobalt in the magmatic-hydrothermal fluids migrated in the form of CoCl42-. Subsequently, under the influence of an increase in pH, CoCl42- reacts with H3AsO30 to form CoAs3 (skutterudite). With the continuous precipitation of arsenides and sulfarsenides, the As/S (reduced) ratio decreased, leading to the CoAs3 (skutterudite) changing to CoAsS (cobaltite).

MINERAL PARAGENESIS OF EARLY BIOTITE VEINS AT THE KUH-E JANJA Cu-Au PORPHYRY DEPOSIT, SOUTHEASTERN IRAN: IMPORTANCE OF MICROTEXTURAL OBSERVATIONS IN STUDIES CONSTRAINING THE RELATIVE TIMING OF HYPOGENE Cu MINERALIZATION

Abstract Veins consisting primarily of biotite are the earliest stockwork vein type recognized at the Kuh-e Janja Cu-Au porphyry deposit in southeastern Iran. These early biotite veins may contain quartz and minor amounts of sulfide minerals such as chalcopyrite and pyrite. Observations at the hand-specimen scale do not provide reliable constraints on the paragenetic relationships, as the early biotite veins have been repeatedly overprinted during the evolution of the magmatic-hydrothermal system. Microscopic investigations show that the sulfide minerals in the early biotite veins are texturally late, providing evidence that sulfide deposition did not occur at the high temperatures of biotite formation and potassic alteration of the host rocks. Chalcopyrite primarily occurs along hairline fractures that crosscut or refracture the earlier biotite veins. Biotite in contact with the chalcopyrite can be apparently unaltered or is replaced by chlorite, depending on the degree of wall-rock buffering of the magmatic-hydrothermal fluids that caused hypogene Cu mineralization. The findings add to the growing body of evidence that Cu mineralization in this deposit type occurs at temperatures close to the transition from ductile to brittle conditions (<450°C) following a drop in the pressure regime from lithostatic to hydrostatic conditions.

Fluid origin and evolution of the Taolin Pb-Zn deposit in northeastern Hunan Province, South China: Insights from fluid inclusions and H-O-He-Ar isotopes

Situated in northeastern Hunan Province, the vein-type Pb-Zn orebodies at Taolin are mainly hosted in NE-/NEE-trending faults between Dayunshan-Mufushan pluton and Neoproterozoic metasedimentary rocks of the Lengjiaxi Group. Hydrothermal mineralization can be divided into five stages: (1) coarse-grained quartz stage, (2) quartz-fluorite-base metal stage, (3) quartz-barite-fluorite-base metal stage, (4) pale pink and colorless quartz stage, and (5) fine-grained quartz stage. In this research, fluid inclusions as well as stable (H-O) and noble gas (He-Ar) isotope compositions were performed to uncover the nature, origin, and evolution of the ore-forming fluids, ore precipitation mechanisms, and mineralization process of the Taolin deposit. Four types of fluid inclusions, i.e., liquid-rich two-phase inclusions (LV-type), pure liquid phase inclusions (PL-type), vapor-rich two-phase inclusions (VL-type), and pure vapor phase inclusions (PV-type), were distinguished in sphalerite, quartz, and fluorite. Microthermometric analysis of fluid inclusion assemblages in sphalerite, quartz, and fluorite from different stages indicates that from the Stage 1 to Stage 5, the homogenization temperatures vary between 168 and 211 °C, between 151 and 198 °C, between 131 and 180 °C, between 132 and 164 °C, and between 118 and 138 °C, respectively, whereas the fluid salinities vary from 12.4 to 16.9 wt% NaCl equivalent, from 9.7 to 14.6 wt% NaCl equivalent, from 5.6 to 10.3 wt% NaCl equivalent, from 3.6 to 9.7 wt% NaCl equivalent, and from 0.9 to 3.8 wt% NaCl equivalent, respectively. The H-O isotope data of quartz and the He-Ar isotopic compositions of sulfide crystals suggest that the ore-forming fluids were a mixture of crust-derived magmatic hydrothermal fluid and meteoric water. Fluid mixing and cooling were likely the crucial mechanisms for ore precipitation.

The role of CO2 in the genesis of Dabie-type porphyry molybdenum deposits

Porphyry-type molybdenum deposits, many of which are in China, supply most of the World’s molybdenum. Of particular importance are the molybdenum deposits located in the Qinling-Dabie region that are responsible for more than half of China’s molybdenum production. A feature that distinguishes this suite of deposits from the better-known Climax and Endako sub-types of porphyry molybdenum deposits is their formation from CO2-rich magmatic-hydrothermal fluids. The role of CO2, if any, in the transport of molybdenum by these fluids, however, is poorly understood. We conducted experiments on the partitioning of molybdenum between H2O-CO2, H2O-NaCl, and H2O-NaCl-CO2 fluids and a felsic melt at 850 °C and 100 and 200 MPa. Here we show that the exsolution of separate (immiscible) brine and vapor leads to the very high brine DMo values needed for efficient extraction of Mo from the magmas forming Dabie-type porphyry molybdenum deposits.

Genesis of Hongqiling Sn-W polymetallic deposit in Dongpo ore concentration field, southern Hunan: Evidences from U-Pb chronology and trace element geochemistry of cassiterite

Hongqiling deposit is one of the most typical hydrothermal vein type Sn-W polymetallic deposits in the Dongpo ore field, southern Hunan. It is an ideal object to study the Sn-W mineralization in the Nanling metallogenic belt and even in the whole South China Block, and to reveal the regional metallogenetic regularity. Based on the detailed investigation of the deposit geology, this paper discusses the mineralization age and processes of the Hongqiling hydrothermal vein type Sn-W polymetallic deposit by LA-MC-ICP-MS in-situ U-Pb dating and trace element geochemistry of cassiterite from the quartz vein type Sn-W ore body. Cathodoluminescence (CL) imaging shows that cassiterite in Hongqiling deposit can be divided into two generations.primary cassiterite (Cst-I) and altered cassiterite (Cst-II). The LA-MC-ICP-MS in-situ U-Pb age of the two groups of Cst-I samples are 158.9 ± 0.7 Ma and 158.4 ± 0.8 Ma, respectively, which are well consistent with the mineralization ages of most Sn-W deposits in the Nanling metallogenic belt, and are also consistent with the ages of middle to late Jurassic magmatic activity represented by the Qianlishan intrusion. This indicates that the Hongqiling deposit, like many Sn-W deposits in the Nanling metallogenic belt, is genetically related to the regional Middle to Late Jurassic granitic magmatic activities. LA-ICP-MS trace element analysis shows that trace elements such as Na and Cs are mainly distributed in fluid inclusions in cassiterite, while the major elements such as Mg, Al, and Si are mainly distributed in the mineral inclusions, and other elements such as W, U, Zr, Hf and Ti are mainly distributed in the cassiterite by isomorphic substitution. The high Fe and W contents in both primary and altered cassiterite indicate that the ore-forming fluid of Hongqiling deposit is mainly derived from granitic magma. The fluctuating variation of Fe, V, Sc, Ti, Zr, Hf, Nb and Ta in the primary cassiterite with the crystalline bands indicates that there are two large-scale pulses of magmatic hydrothermal fluid during the mineralization process, while the altered cassiterite is relatively depleted of Ti, Sc, Zr and U elements, and enriched in Pb which may represent the compositional characteristics of the late-stage fluid. In summary, the Hongqiling hydrothermal vein type Sn-W polymetallic deposit was formed by the pulsating exsolution of magmatic hydrothermal fluid of late Jurassic granitic magmatism. The trace elemental compositions of primary cassiterite are generally controlled by the compositions of ore-forming fluid and the rate of crystallization.

W-rich zircons from the granite in the Hukeng tungsten deposit, South China: Genesis and exploration significance

South China is endowed with copious hydrothermal tungsten ore deposits, which are generally suggested to be associated with highly fractionated granites. However, the mechanism of tungsten enrichment and mineralization during magmatic-hydrothermal processes is not clear. Here, we clearly identified W-rich zircons (up to several thousand ppm) from the granite in the Hukeng tungsten deposit in South China. W-rich zircons are generally dark in cathodoluminescence images with irregular cracks, cavities and blurry oscillatory zones. They also show high contents of U, Nb, REEs, and high W/Gd ratios, which are not possible to be produced only by magma differentiation. Raman spectra of zircons indicate that these W-rich zircons have experienced different degrees of metamictization. Thus, these W-rich zircons should be crystallized from the late magma and subsequently altered by W-rich magmatic-hydrothermal fluids. W-rich zircons record the activity of W-rich ore-forming fluids which were exsolved from the granitic magma. We suggested that the W/Gd ratios of > 0.2 of zircons can be used as an indicator to estimate the W mineralization potential of a granite. This study provides a new pathway for using zircon to record tungsten mineralization processes and to guide tungsten ore prospecting.

Lithospheric influence on metallogenesis in the East Kunlun Orogen: Insights from isotopic and geochemical mapping

This study examines the influence of lithospheric architecture on regional metallogenesis, using geological and geochemical data from the East Kunlun Orogen (EKO). We explore how specific lithospheric components and structures affect the formation of orogenic gold and various polymetallic mineral deposits. The study reveals that metallogenic processes in the EKO initially targeted sources within the metasomatized-enriched subcontinental lithospheric mantle (SCLM) and reactivated lower crust during the Paleozoic era.Lithospheric architecture, shaped by crust-mantle interactions occurred in the Early Mesozoic led to variations in the sizes of orogenic gold deposits between the eastern and western EKO. In the west, smaller gold deposits are linked to moderate mantle underplating and slightly enriched SCLM. Gold-bearing fluids released by mantle devolatilization mixed with metamorphism fluid in collision stage, contributing to the formation of these deposits. In contrast, the eastern EKO hosts larger gold deposits, resulting from significantly enriched SCLM. Extensive lithospheric thinning process in post-collision stage lead to the mixing of gold-bearing mantle-derived and magmatic-hydrothermal fluids. Fertilized magma differentiation potentially increases gold concentrations in this region.Additionally, Triassic-era melting of the lower crust led to diverse mineralization types in porphyry-skarn-epithermal deposit systems. Key findings include the role of juvenile fertile lower crustal materials in forming copper polymetallic deposits, the importance of metamorphic basement reworking for molybdenum and tungsten deposits, and the influence of lead and zinc leaching from old sedimentary rocks on the formation of silver‑lead‑zinc deposits. This study broadens our understanding of the geological factors influencing metallogenesis and provides a framework for future exploration and research in regions with similar lithospheric architectures.

Quartz fluid inclusions and trace elements in the Lailisigaoer porphyry Mo deposit, Western Tianshan, Xinjiang: Fluid evolution and metallogenic mechanism in magmatic-hydrothermal system

The Lailisigaoer deposit is a typical porphyry Mo deposit located in the late Paleozoic Boluokenu metallogenic belt of Western Tianshan, NW China. This study aims to understand molybdenum mineralization and the dynamics of magmatic-hydrothermal fluid within the porphyry system, focusing on fluid inclusion, cathodoluminescence textures, and trace elemental composition in various generations of quartz. Six vein types in the Lailisigaoer deposit are classified as comb quartz veins with unidirectional solidification texture (UST, QI), actinolite/biotite ± quartz veinlets (M-type, QII), quartz-chalcopyrite vein (A-type, QIII), quartz-molybdenite vein (B-type, QIV), quartz-pyrite vein (D-type, QV) and quartz-carbonate vein (E-type, QVI). Micro thermometry data indicate decreasing homogenization temperatures in primary fluid inclusions from UST to E-type veins. The magmatic-hydrothermal fluids associated with UST and M-, A-, B-, D-, E-type veins underwent a transition from high temperature (342–495℃), high-pressure (∼1.25 kb), and variable salinity (6.7–41.1 wt%NaCl) in the H2O-CO2-NaCl system to low-temperature (142–238℃), low-pressure (∼0.25 kb), and low-salinity (1.6–5.1 wt%NaCl) in the H2O-NaCl system. This evolution is reflected in the proportion of quartz with oscillatory zones decreasing and irregular quartz increasing, indicating a shift from turbulent to stable fluid conditions. Furthermore, a gradual reduction in Ti concentration (from 79 ppm in UST to 1.4 ppm in E-type quartz) suggests a decrease in fluid temperature during the magmatic-hydrothermal evolution. Mineralization primarily occurs in A- and B-type veins, with molybdenum precipitation attributed to fluid immiscibility in a medium–high temperature (240–368 ℃) and high pressure (∼0.95 kb) environment. The A-type veins (mean 31 ppm in Ti concentrations) consist of equigranular (dark-core) (QIII-1) and patchy inhomogeneous CL-gray quartz (QIII-2). The B-type veins (mean 24 ppm in Ti concentrations) are characterized by equigranular (bright-core) inhomogeneous quartz (QIV-1) with growth zones that are cemented by later mosaic homogeneous CL-gray quartz (QIV-2). Based on the quartz-Ti thermometer, the mineralized veins (A- and B-type) were confined to be formed at depths of 2.8–3.6 km, with molybdenum mineralization occurring at 3.4–3.6 km. Molybdenum mineralization initiates during the QIV-1 crystallization period in magmatic-hydrothermal fluids and terminates in the QV-2 generation.

A reinterpretation of the mineralization processes involved in the formation of the Tomnadashan sulfide deposit, Loch Tay, Scotland, UK

The Tomnadashan sulfide deposit, which is located on the southern margin of Loch Tay (Scotland, UK), was mined for copper during the 19th century. The genetic processes at Tomnadashan remain poorly understood, and the mineralization has never been dated. To gain an improved understanding of this mineral system, we have dated the molybdenite at Tomnadashan using the Re–Os chronometer. Furthermore, we have contextualized these ages within a paragenetic interpretation. Our results show that the age of the molybdenite is c. 423–419 Ma, and it occurs early in the paragenesis (the second stage out of six). Based on the paragenesis of molybdenite, this age is likely to reflect the initial Caledonian mineralization event at Loch Tay. Our new data and literature review suggest that although Tomnadashan is a magmatic-related ore deposit, the porphyry that crops out is unlikely to have provided the mineralizing fluids associated with the mineralization. A concealed intrusion or granitic dykes within the porphyry may be the source of the magmatic–hydrothermal fluids. The age data indicate that the Tomnadashan mineralization is coeval with gold mineralization at Cavanacaw in Northern Ireland, giving rise to the possibility of a previously unrecognized mid-Silurian magmatic–hydrothermal episode of gold and base metal mineralization throughout the Grampian Terrane. Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/topic/collections/early-career-research