Search Results (90)

The Weishan rare earth element (REE) deposit, located in western Shandong, North China Block, is a typical carbonatite REE deposit and constitutes the third largest light REE resource in China. Its mineralization is closely related to the multi-stage evolution of a carbonatite magma–hydrothermal system. However, the mechanisms governing REE enrichment, migration, and precipitation remain insufficiently constrained from a mineralogical perspective, which hampers the understanding of the ore-forming processes and the establishment of predictive exploration models. Apatite is a pervasively developed REE phase in the Weishan deposit which occurs in multiple generations, and thus represents an ideal recorder of the magmatic–hydrothermal evolution. In this study, different generations of apatite hosted in carbonatite orebodies from the Weishan deposit were investigated using cathodoluminescence (CL), electron probe microanalysis (EPMA), and in situ LA-ICP-MS trace element analysis. Three types of apatite were identified. In paragenetic sequence, Ap-1 occurs as polycrystalline aggregates coexisting with calcite, is enriched in Na, Sr, and LREEs, and shows high (La/Yb)_N ratios, suggesting crystallization from an evolved carbonatite magma. Ap-2 and Ap-3 display typical replacement textures: both contain abundant dissolution pits and dissolution channels within the grains, which are filled by secondary minerals such as monazite and ancylite, and thus exhibit characteristic features of fluid-mediated dissolution–reprecipitation during the hydrothermal stage. Ap-2 is commonly associated with barite and strontianite, whereas Ap-3 is associated with pyrite and monazite and is characterized by relatively sharp grain boundaries with adjacent minerals. From Ap-1 to Ap-3, total REE contents decrease systematically, whereas Na, Sr, and P contents increase. All three apatite types lack Eu anomalies but display positive Ce anomalies. Discrimination diagrams involving LREE-Sr/Y and log(Ce)-log(Eu/Y) indicate that apatite in the Weishan REE deposit formed during the magmatic to hydrothermal evolution of a carbonatite, and that the dissolution of early magmatic apatite, followed by element remobilization and mineral reprecipitation, effectively records the progressive evolution of the ore-forming fluid. Full article

The Hadamengou gold deposit, hosted in the Precambrian metamorphic basement, is a super-large gold deposit occurring along the northern margin of the North China Craton. Despite extensive investigation, the genesis of the gold mineralization is poorly understood and remains highly debated. This study integrates a comprehensive dataset, including fluid inclusion microthermometry and C-H-O-S-Pb isotopes, to better constrain the genesis and ore-forming mechanism of the deposit. Hydrothermal mineralization can be divided into pyrite–potassium feldspar–quartz (Stage I), quartz–gold–pyrite–molybdenite (Stage II), quartz–gold–polymetallic sulfide (Stage III), and quartz–carbonate stages (Stage IV). Four types of primary fluid inclusions are identified, including pure CO₂-type, composite CO₂-H₂O-type, aqueous-type, and solid-daughter mineral-bearing-type inclusions. Microthermometric and compositional data reveal that the fluids were mesothermal to hypothermal, H₂O-dominated, and CO₂-rich fluids containing significant N₂ and low-to-moderate salinity, indicative of a magmatic–hydrothermal origin. Fluid inclusion assemblages further imply that the ore-forming fluids underwent fluid immiscibility, causing CO₂ effusion and significant changes in physicochemical conditions that destabilized gold bisulfide complexes. The hydrogen–oxygen isotopic compositions, moreover, support a dominant magmatic water source, with increasing meteoric water input during later stages. The carbon–oxygen isotopes are also consistent with a magmatic carbon source. Sulfur and lead isotopes collectively imply that ore-forming materials were derived from a hybrid crust–mantle magmatic reservoir, with minor contribution from the country rocks. By synthesizing temporal–spatial relationships between magmatic activity and ore formation, and the regional tectonic evolution, we suggest that the Hadamengou is an intrusion-related magmatic–hydrothermal lode gold deposit. It is genetically associated with multi-stage magmatism induced by crust–mantle interaction, which developed within the extensional tectonic regimes. Full article

Fluorite, a key accessory mineral associated with rare earth element (REE) deposits, exerts a significant influence on REE migration and precipitation through complexation, adsorption, and lattice substitution within fluorine-bearing fluid systems. It therefore provides a valuable archive for constraining REE enrichment processes. The Weishan alkaline–carbonatite-related REE deposit, the third-largest LREE deposit in China, is formed through a multistage magmatic–hydrothermal evolution of the carbonatite system. However, limited mineralogical constraints on REE enrichment and precipitation have hindered a comprehensive understanding of its metallogenic processes and exploration potential. Here, cathodoluminescence imaging and LA-ICP-MS trace element analyses were conducted on fluorite of multiple generations from the Weishan deposit to constrain the physicochemical conditions of mobility and precipitation mechanisms of this REE deposit. Four generations of fluorite are recognized, recording progressive evolution of the ore-forming fluids. Type I fluorite, which coexists with bastnäsite and calcite, is LREE-enriched and exhibits negative Eu anomalies, indicating precipitation from high-temperature, weakly acidic, and reducing fluids. Type II fluorite occurs as overgrowths on Type I, while Type III fluorite replaces Type II fluorite, with both displaying LREE depletion and MREE-Y enrichment, consistent with cooling during continued hydrothermal evolution. Type IV fluorite, which is interstitial between calcite grains and associated with mica, is formed under low-temperature, oxidizing conditions, reflecting REE exhaustion and the terminal stage of fluorite precipitation. Systematic shifts in REE patterns among the four generations track progressive cooling of the system. The decreasing trend in La/Ho and Tb/La further suggests that these fluorites record dissolution–reprecipitation events and associated element remobilization during fluid evolution. Full article

The Sanjiang Tethys orogenic belt in Southwest China is a globally important polymetallic metallogenic domain, hosting numerous world-class Cu-Pb-Zn deposits. Among these, the Lanping Basin is a typical ore concentration area, characterized by complex tectonic evolution and extensive hydrothermal mineralization. Although numerous vein-type Cu deposits occur in the northern and western parts of the basin, research in the north region remains less comprehensive. This study investigates three typical vein-type Cu deposits (Hetaoqing, Hemeigou, and Songpingzi) in the northern Lanping Basin using rare-earth element (REE) analysis, S-Pb-Sr isotope determinations, and tectonic stress inversion. Results show that ²⁰⁶Pb/²⁰⁴Pb ratios range from 18.374 to 18.691, and δ³⁴S_V-CDT values vary from –11.7‰ to +9.4‰, indicating mixed sources of ore-forming materials dominated by deep magmatic sources, particularly related to alkaline rocks around the basin. Sulfur sources are closely associated with thermochemical sulfate reduction (TSR). Additionally, ⁸⁷Sr/⁸⁶Sr ratios range from 0.710949 to 0.711864, ΣREE values range from 85.87 × 10^–6 to 111.86 × 10^–6, Ce/Ce* ratios range from 0.86 to 0.92, and Eu/Eu* ratios range from 1.06 to 2.99. Fluid inclusion microthermometry yields temperatures of 217–252 °C (average 238 °C), indicating that ore-forming fluids experienced water–rock interaction during migration and ultimately exhibited mixed properties. Tectonic stress field inversion reveals that the structures formed by NE–SW compressive stress field before mineralization stage provided ore-hosting spaces and fluid migration pathways, while a late Cenozoic abrupt stress field change promoted the precipitation of ore-forming materials. Full article

The Sepid-Sarve copper deposit is part of an Eocene volcano-sedimentary sequence located in the southern Sabzevar Zone. The copper mineralization occurs at the contact between pyroclastic and lava units with various limestone layers (including marly, Nummulitic, sandy, and clastic limestones). The ore minerals consist of malachite, azurite, chalcocite, digenite, cuprite, tenorite, covellite, and occasionally native copper. The associated hydrothermal fluids show moderate to high salinities, ranging from 3.08 to 13.38 wt.% NaCl equivalent, with homogenization temperatures between 90 and 356 °C, indicating fluid mixing during ore formation. Chalcocite is rarely accompanied by quartz, suggesting low silica content in the ore-forming fluids. The δ³⁴S values of sulfide samples from the Sepid-Sarve deposit range from −23.9 ± 0.3‰ to −2.9 ± 0.2‰, while δ³⁴S values of hydrothermal H₂S range from −24.1 ± 0.3‰ to −21.0 ± 0.3‰. The δ¹⁸O values of hydrothermal fluids associated with mineralization fall within the range of basaltic rocks, meteoric waters, and sedimentary rocks. Geochemical variations in major and trace elements suggest the involvement of continental crustal contamination in the magmatic evolution. The studied volcanic rocks fall within the calc-alkaline to shoshonitic fields, formed in a continental arc setting, and are derived from an enriched mantle source influenced by subduction-related fluids. These rocks are characterized by HREE depletion, moderate LREE enrichment, and a weak negative Eu anomaly. Based on the results, the Sepid-Sarve deposit is classified as a stratabound (Manto-type) copper sulfide deposit, formed in a volcano-sedimentary setting associated with a subduction-related magmatic arc environment. Full article

Jiaodong Gold Province is a globally rare giant gold cluster, with ongoing debates regarding its metallogenic material sources and mineralization mechanisms. This study focuses on the Linglong quartz-vein-type gold deposit within the Zhaoping Fault Zone, conducting in situ trace element and S-Pb isotope analyses of pyrite from different mineralization stages. The trace element characteristics were investigated to explore the sources of metallogenic materials, the evolution of ore-forming fluids, and the mechanisms of gold precipitation. The main findings are as follows: (1) In the Linglong gold deposit, gold primarily enters the pyrite lattice as a solid solution (Au⁺) through Au-As coupling. From the Py1 to Py3 stages, Co and Ni contents significantly decrease, while Cu, As, Au, and polymetallic element contents continuously increase. Additionally, Cu mainly replaces Fe²⁺ in the form of Cu²⁺, whereas Pb predominantly exists as micro inclusions of galena. (2) The S isotope (Py1: δ³⁴S = +7.60‰–+8.25‰, Py2: δ³⁴S = +6.15‰–+8.15‰, Py3: δ³⁴S = +6.90‰–+9.10‰) and Pb isotope (²⁰⁶Pb/²⁰⁴Pb = 16.95–17.715, ²⁰⁷Pb/²⁰⁴Pb = 15.472–15.557, ²⁰⁸Pb/²⁰⁴Pb = 37.858–38.394) systems collectively constrain the ore-forming materials such that they are dominated by metasomatized enriched lithospheric mantle, with simultaneous mixing of crustal materials. (3) The ore-forming fluid underwent a continuous evolution process characterized by persistently decreasing temperatures and a transition from mantle-dominated to crust–mantle mixed sources. The Py1 stage was predominantly composed of mantle-derived magmatic fluids uncontaminated by crustal materials, representing a high-temperature, closed environment. In the Py2 stage, the fluid system transitioned to an open system with the incorporation of crustal materials. Through coupled substitution of “As³⁺ + Au⁺ → Fe²⁺” and dissolution–reprecipitation processes, gold was initially activated and enriched. During the Py3 stage, pyrite underwent dissolution–reprecipitation under tectonic stress and fluid activity, promoting extraordinary element enrichment and serving as the primary mechanism for gold precipitation. Concurrently, bismuth–tellurium melt interactions further facilitated the precipitation of gold minerals. Full article

The Chuankou deposit is a super-large W deposit formed during the Indosinian collision event in South China, and its mineralization is suggested to be related to the Indosinian muscovite granite. However, two types of W mineralizations were discovered in the Caledonian granite porphyry in the Chuankou W deposit: disseminated scheelite and quartz-wolframite-scheelite vein mineralizations. The genesis of W mineralization in the Caledonian granite porphyry is not yet clear. This paper focuses on fluid microthermometry and stable isotopes (C, H, O, S) analysis of the quartz and scheelite in the ores in the Caledonian granite porphyry in the Chuankou W deposit. The aims are to determine the nature and evolution of the ore-forming fluids, the origin of the ore-forming materials involved in the two types of W mineralization in the Caledonian granite porphyry, and to provide a detailed discussion of the deposit’s genesis. Microthermometry results of fluid inclusions with scheelite and quartz from two stages show that the average homogenization temperature in the quartz-veins within the Caledonian granite porphyry is 248 °C, and the average salinity is 6.31 wt.% NaCl eq (n = 85), the average homogenization temperature in the quartz-veins within the slate is 219 °C, and the average salinity is 5.57 wt.% NaCl eq (n = 49). The ore-forming fluids experienced an evolution from high temperature and high salinity to low temperature and low salinity. Sulfur isotope compositions show that the δ³⁴S values of pyrite and arsenopyrite in the quartz-veins within the Caledonian granite porphyry are 2.06 to 3.28‰ and −0.38 to 0.21‰, respectively, and the δ³⁴S value of pyrite in the quartz-veins within the slate is −1.72 to 0.47‰. The δ³⁴S values of each stage are close to 0‰, indicating that the origin of sulfur mainly from magma. The H-O isotope compositions of the quartz indicate that the ore-forming fluid was primarily magmatic water. The low δ¹⁸O_H2O values (1.74 to 1.58‰) are influenced by fluid–rock interactions or the incorporation of atmospheric precipitation. The carbon isotopes (δ¹³C = −9.5 to 8.3‰) indicate a magmatic origin, but the C isotopes of quartz in the quartz-veins within the slate shift toward sedimentary rocks, reflecting the incorporation of rock components in the late mineralization period. These isotopic differences indicate that the fluid–rock interaction gradually strengthened during fluid evolution. Full article

The evolution of ore-forming fluids in gold precipitation is a key aspect in understanding the genesis of orogenic gold deposits. Traditional fluid inclusion analyses are often limited in revealing the fluid property changes during mineralization, leading to significant debates on the mineralization temperature and fluid sources. In this study, we selected the Liba gold deposit in the West Qinling orogen and employed scanning electron microscope–cathodoluminescence (SEM-CL) and laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) to analyze the microstructure and trace element characteristics of quartz veins, revealing the multi-stage evolution of ore-forming fluids and the mineralization mechanisms. SEM-CL imaging identified five distinct quartz stages. The pre-mineralization (Qz0) and early-stage mineralization (Qz1) fluids were predominantly magmatic–metamorphic in origin, as indicated by relatively high δ¹⁸O and δD values. During the primary metallogenic (Qz2a, Qz2b) and late-stage mineralization (Qz3), temperatures progressively decreased, and the gradual mixing of meteoric water and formation water was observed, which promoted gold precipitation. And the content of trace elements in post-mineralization quartz (Qz4) is significantly lower and similar to that in the Qz0 stage. Through the analysis of quartz trace elements (e.g., Al/Ti, Ge/Al ratios) and isotope data (δ18O = 8.25‰ to 12.67‰, δD = −119.1‰ to −79.8‰), the results indicate that the Liba gold deposit is a medium- to low-temperature orogenic gold deposit. Furthermore, the gold enrichment process was primarily driven by a hydrothermal system, with variations in the fluid composition during mineralization contributing to the concentration of gold. Full article

The Dulong Sn-polymetallic deposit in Yunnan Province of southwestern China serves as a unique case study for unraveling the evolution of skarn systems and tin mineralization. Four distinct garnet types (Grt I to Grt IV) were classified based on petrographic observations. Compositional analysis reveals a progression from Grt I to Grt III, marked by increasing andradite components, and elevated tin concentrations, peaking at 5039 ppm. These trends suggest crystallization from Sn-enriched magmatic-hydrothermal fluids. In contrast, Grt IV garnet exhibits dominant almandine components and minimal tin content (<2 ppm). Its association with surrounding rocks (schist) further implies its metamorphic origin, distinct from the magmatic origin of the other garnet types. Combined with previously published sulfur and lead isotopic data, as well as trace element compositions of garnet, our study suggests that Laojunshan granites supply substantial ore-forming elements such as S, Pb, W, Sn, In, and Ga. In contrast, elements such as Sc, Y, and Ge are inferred to be predominantly derived from, or buffered by, the surrounding rocks. The geochemical evolution of the garnets highlights the critical role of redox fluctuations and fluid chemistry in controlling tin mineralization. Under neutral-pH fluid conditions, early-stage garnets incorporated significant tin. As the oxygen fugacity of the ore-forming fluid declined, cassiterite precipitation was triggered, leading to tin mineralization. This study reveals the interplay between fluid redox dynamics, garnet compositional changes, and mineral paragenesis in skarn-type tin deposits. Full article

The metallogenic process of gold deposits is typically characterized by multi-stage mineralization and complex tectonic evolution. Precise determination of metallogenic age is thus critical yet challenging for establishing ore-forming models and tectonic evolutionary frameworks. The Koka gold deposit in Eritrea represents the largest gold discovery to date in the area, though its metallogenic age and tectonic evolution remain debated. This study employs in situ micro-analysis techniques to investigate major/trace elements and U-Pb geochronology of hydrothermal monazite coexisting with gold mineralization, providing new constraints on the metallogenic timeline and tectonic setting. Petrographic observations reveal well-crystallized monazite with structural associations to pyrite and native gold, indicating near-contemporaneous formation. Trace element geochemistry shows peak formation temperatures of 270–340 °C for monazite, consistent with fluid inclusion data. Genetic diagrams confirm a hydrothermal origin, enabling metallogenic age determination. Monazite Tera–Wasserburg lower intercept ages and weighted mean ²⁰⁸Pb/²³³Th ages yield 586 ± 8.7 Ma and 589 ± 2.3 Ma, respectively, overlapping error ranges with published sericite ⁴⁰Ar/³⁹Ar ages. This confirms Ediacaran gold mineralization, unrelated to the Koka granite (851 ± 2 Ma). Statistical analysis of reliable age data reveals a three-stage tectonic evolution model: (1) 1000–875 Ma, Rodinia supercontinental rifting, with depleted mantle-derived mafic oceanic crust formation and Mozambique Ocean spreading; (2) 875–630 Ma, subduction-driven crustal accretion and Koka granite emplacement; and (3) 630–570 Ma, post-collision crustal/lithospheric remelting, with mixed metamorphic–magmatic fluids and meteoric water input driving gold precipitation. Full article

The Xiaobaihegou fluorite deposit is located in the southwest of the Altyn-Tagh Orogen, NW China. However, the provenance, thermodynamic properties, and enrichment mechanisms of the ore-forming fluids in this deposit remain unclear. Fluorite mineralization primarily occurs in the vicinity of the contact zone between the granite and the wall rocks. The zircon U-Pb age of the alkali-feldspar granite in the Xiaobaihegou fluorite deposit is 482.3 ± 4.1 Ma. The ore-hosting lithologies are mainly calcareous rock series of the Altyn Group. The ore bodies are controlled by NE-trending faults and consist primarily of veined, brecciated, massive, and banded ores. The ore mineral assemblage is primarily composed of calcite and fluorite. The rare earth element (REE) patterns of fluorite and calcite in the Xiaobaihegou deposit exhibit right-dipping LREE enrichment with distinct negative Eu anomalies, which closely resemble those of the alkali-feldspar granite. This similarity suggests that the REE distribution patterns of fluorite and calcite were likely inherited from the pluton. The ore-forming process can be divided into an early stage and a late stage. The massive ores formed in the early stage contain mainly gas-rich two-phase fluid inclusions and CO₂-bearing three-phase inclusions, with homogenization temperatures ranging from 235 °C to 426 °C and salinities from 28.59% to 42.40% NaCl equivalent. In the late stage, brecciated and stockwork ores were formed. They host liquid-rich two-phase and gas-rich two-phase fluid inclusions, with homogenization temperatures ranging from 129 °C to 350 °C and salinities from 0.88% to 21.61% NaCl equivalent. The results of hydrogen and oxygen isotope studies indicate that the ore-forming fluids were derived from a mixture of magmatic–hydrothermal and meteoric water. Fluorite precipitation in the early stage was mainly due to the mixing of magmatic–hydrothermal solution and meteoric water, as well as a water–rock reaction. In the late stage, fluid mixing further occurred, resulting in a decrease in temperature and the formation of brecciated and stockwork ores. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of fluorite from the deposit range from 0.71033 to 0.71272 and 0.511946 to 0.512073, respectively, indicating that the ore-forming material originates from the crust. Based on the ore-forming characteristics, it is proposed that Ca may be primarily leached from the strata formation, while F may predominantly originate from magmatic–hydrothermal solutions. The formation of fluorite deposits is closely related to the transition of the Central Altyn-Tagh Block and Qaidam Block from a compressional orogenic environment to an extensional tectonic environment. Full article

The Qiubudong silver deposit on the western margin of the Fuping ore cluster in the central North China Craton is a representative breccia-type deposit characterized by relatively high-grade ores, thick mineralized zones, and extensive alteration, indicating considerable potential for economic resource development and further exploration. Previous studies on this deposit have not addressed its genetic mineralogical characteristics. This study focuses on pyrite and quartz to investigate their typomorphic features, such as crystal morphology, trace element composition, thermoelectric properties, and luminescence characteristics, and their implications for ore-forming processes. Pyrite crystals are predominantly cubic in early stages, while pentagonal dodecahedral and cubic–dodecahedral combinations peak during the main mineralization stage. The pyrite is sulfur-deficient and iron-rich, enriched in Au, and relatively high in Ag, Cu, Pb, and Bi contents during the main ore-forming stage. Rare earth element (REE) concentrations are low, with weak LREE-HREE fractionation and a strong negative Eu anomaly. The thermoelectric coefficient of pyrite ranges from −328.9 to +335.6 μV/°C, with a mean of +197.63 μV/°C; P-type conduction dominates, with an occurrence rate of 58%–100% and an average of 88.78%. A weak–low temperature and a strong–high temperature peak characterize quartz thermoluminescence during the main mineralization stage. Fluid inclusions in quartz include liquid-rich, vapor-rich, and two-phase types, with salinities ranging from 10.11% to 12.62% NaCl equiv. (average 11.16%) and densities from 0.91 to 0.95 g/cm³ (average 0.90 g/cm³). The ore-forming fluids are interpreted as F-rich, low-salinity, low-density hydrothermal fluids of volcanic origin at medium–low temperatures. The abundance of pentagonal dodecahedral pyrite, low Co/Ni ratios, high Cu contents, and complex quartz thermoluminescence signatures are key mineralogical indicators for deep prospecting. Combined with thermoelectric data and morphological analysis, the depth interval around 800 m between drill holes ZK3204 and ZK3201 has high mineralization potential. This study fills a research gap on the genetic mineralogy of the Qiubudong deposit and provides a scientific basis for deep exploration. Full article

This study presents a comprehensive case analysis of pyrite-hosted solid inclusions and their metallogenic significance in the Bainaimiao porphyry Cu deposit in NE China, which is genetically linked to the early Silurian granodiorite intrusion and porphyry dykes. Solid inclusions in pyrite from the deposit’s southern ore belt were analyzed across distinct mineralization stages. Using Electron Probe Micro-Analysis (EPMA) and in situ sulfur isotope analysis (MC-ICP-MS), inclusion assemblages in pyrite were identified, including pyrrhotite-chalcopyrite solid solutions, biotite, and dolomite. The results demonstrate that these inclusions primarily formed through coprecipitation with pyrite during crystal growth. Early-stage mineralizing fluids exhibited extreme temperatures exceeding 700 °C, coupled with low oxygen fugacity (fO₂) and low sulfur fugacity (fS₂). Sulfur isotope compositions (δ³⁴S: −5.85 to −4.97‰) indicate a dominant mantle-derived magmatic sulfur source, with contributions from reduced sulfur in sedimentary rocks. Combined with regional geological evolution, the Bainaimiao deposit is classified as a porphyry-type deposit. Its ore-forming materials were partially derived from Mesoproterozoic submarine volcanic exhalative sedimentary source beds, which were later modified and enriched by granodiorite porphyry magmatism. Full article

The Shabaosi gold field is located in the western Mohe Basin, part of the northern Great Xing’an Range, NE China, and contains multiple gold deposits. However, the sources of the ore-forming materials, the fluid evolution, and the genesis of these gold deposits have been disputed, especially regarding the classification of these deposits as either epithermal or orogenic gold systems. Based on detailed field geological investigations and previous research, we conducted systematic research on the Shabaosi, Sanshierzhan, Laogou, and Balifang gold deposits using fluid inclusion and H-O-S-Pb isotope data, with the aim of constraining the fluid properties, sources, and mineralization processes. Fluid inclusion analyses reveal diverse types, including vapor-rich, vapor–liquid, CO₂-bearing, CO₂-rich, and pure CO₂. Additionally, only a very limited number of daughter mineral-bearing fluid inclusions have been observed exclusively in the Laogou gold deposit. During the early stages, the peak temperature primarily ranged from 240 °C to 280 °C, with salinity concentrations between 6 and 8 wt% NaCl equiv., representing a medium–low temperature, low salinity, and a heterogeneous CO₂-CH₄-H₂O-NaCl system. With the influx of meteoric water, the fluids evolved gradually into a simple NaCl-H₂O system with low temperatures (160–200 °C) and salinities (4–6 wt%). The main mineralization stage exhibited peak temperatures of 220–260 °C and salinities of 5–8 wt% NaCl equiv., corresponding to an estimated formation depth of 1.4–3.3 km. The δD_V-SMOW values (−138.3‰ to −97.0‰) and δ¹⁸O_V-SMOW values (−7.1‰ to 16.2‰) indicate that the magmatic–hydrothermal fluids were progressively diluted by meteoric water during mineralization. The sulfur isotopic compositions (δ³⁴S = −0.9‰ to 1.8‰) and lead isotopic ratios (²⁰⁸Pb/²⁰⁴Pb = 38.398–38.579, ²⁰⁷Pb/²⁰⁴Pb = 15.571–15.636, and ²⁰⁶Pb/²⁰⁴Pb = 18.386–18.477) demonstrate that the gold predominantly originated from deep magmatic systems, with potential crustal contamination. Comparative analyses indicate that the Shabaosi gold field should be classified as a epizonal orogenic gold system, which shows distinct differences from epithermal gold deposits and corresponds to the extensional tectonic setting during the late-stage evolution of the Mongol–Okhotsk orogenic belt. Full article

The Cuyu gold deposit in central Jilin Province in Northeast China is located in the eastern segment of the northern margin of the North China Craton (NCC), as well as the eastern segment of the Xing’an–Mongolian Orogenic Belt (XMOB). Gold ore-bodies are controlled by NW-trending faults and mainly occur in late Hercynian granodiorite. The mineralization process in the Cuyu deposit can be divided into three stages: quartz + coarse grained arsenopyrite + pyrite (stage I), quartz + sericite + pyrite + arsenopyrite + electrum + chalcopyrite + sphalerite (stage II), and quartz + calcite ± pyrite (stage III). Stage II is the most important for gold mineralization. We conducted analyses including petrography, microthermometry, laser Raman spectroscopy of fluid inclusions, and H–O–S–Pb isotopic analysis to elucidate the mineralization processes in the Cuyu deposit. Five types of primary fluid inclusions (FIs) are present in the hydrothermal quartz and calcite grains of the ore: liquid-rich two-phase aqueous fluid inclusions (L-type), vapor-rich two-phase aqueous fluid inclusions (V-type), CO₂-bearing two- or three-phase inclusions (C1-type), CO₂-rich two- or three-phase inclusions (C2-type), and pure CO₂ mono-phase inclusions (C3-type). From stages I to III, the fluid inclusion assemblages changed from L-, C2-, and C3-types to L-, V-, C1-, C2-, and C3-types and, finally, to L-types only. The corresponding homogenization temperatures for stages I to III were 242–326 °C, 202–298 °C, and 106–188 °C, and the salinities were 4.69–9.73, 1.63–7.30, and 1.39–3.53 wt.% NaCl equiv., respectively. The ore-forming fluid system evolved from a NaCl-H₂O-CO₂ ± CH₄ ± H₂S fluid system in stage I and II with immiscible characteristics to a homogeneous NaC-H₂O fluid system in stage III. Microthermometric data for stages I to III show a decreasing trend in homogenization temperatures and salinities. The mineral assemblages, fluid inclusions, and H–O–S–Pb isotopes indicate that the initial ore-forming fluids of stage I were exsolved from diorite porphyrite and characterized by a high temperature and low salinity. The addition of meteoric water in large quantities led to decreases in temperature and pressure, resulting in a NaCl-H₂O-CO₂ ± CH₄ ± H₂S fluid system with significant immiscibility in stage II, facilitating the deposition of gold and associated polymetallic sulfides. The Cuyu gold deposit has a similar ore genesis to those of gold deposits in the Jiapigou–Haigou gold belt (JHGB) of southeastern Jilin Province indicating potential for gold prospecting in the northwest-trending seam of the JHGB. Full article