Potassium-argon illite geochronology is widely applied to constrain the timing of hydrothermal alteration in mineral systems; however, its reliability in tectonically complex and long-lived magmatic arcs remains problematic. This study evaluates the applicability and limitations of K-Ar illite dating in the Eastern Pontides, Türkiye where Late Cretaceous mineral systems were overprinted by post-mineralization tectono-magmatic thermal events. New K-Ar ages obtained from hydrothermal < 0.2 µm illite fractions from the Yanıklı intermediate-sulfidation epithermal system yield ages of 72.4 ± 1.0 Ma, 68.6 ± 0.9 Ma, and 55.3 ± 0.7 Ma, which are systematically younger than the independently constrained timing of hypogene hydrothermal alteration and mineralization.These apparent age offsets of up to ∼ 10 m.y.r. younger are attributed to partial isotopic resetting and mixed age signals resulting from prolonged thermal histories, fluid circulation, and structural reactivation during the Late Cretaceous-Paleogene evolution of the Eastern Pontides. Episodic magmato-tectonic reactivation, including faulting, uplift, and extension, likely promoted argon mobility along grain boundaries and crystal defects at temperatures below canonical closure values (∼200-250 °C) for illite.Comparison with regional thermochronological constraints and independent geochronometers indicates that K-Ar illite ages in the Eastern Pontides predominantly record the timing of the last thermal or hydrothermal perturbation associated with Paleocene syn-collisional and Eocene post-collisional geodynamics and magmatism rather than primary Late Cretaceous hydrothermal alteration. This study highlights the need for cautious interpretation of K-Ar illite ages in tectonically complex regions and emphasizes the importance of integrating petrography, alteration paragenesis, structural context, and complementary geochronological methods for robust temporal reconstructions of mineral systems. Future studies should also evaluate these limitations through systematic analysis of multiple grain-size fractions and application of Illite Age Analysis (IAA) approaches where appropriate in the Eastern Pontides.
The thick evaporites within the Qianjiang depression are frequently considered a significant source of potassium-rich brine in the depression. This study conducted mineralogical, geochemical, and isotopic analyses on the late Eocene evaporites in the Qianjiang depression to investigate the origin and evolution of the evaporites. Based on field core descriptions and microscopic observations, the evaporites are primarily composed of dolomite, anhydrite, glauberite and halite. They display complete salinization cycles involving carbonate, sulfate, and chloride phases, along with two binary sedimentary cycles that sulfate to chloride and carbonate to sulfate. The high 1000 × Br/Cl ratio (0.37) and the low δ37Cl value (–0.41 ‰) observed in one sample do not necessarily indicate that the threshold of the potash stage has been reached. Instead, these values are more likely attributable to anomalies arising from the dissolution–recrystallization process. These results collectively suggest that the study area experienced a dry and hot climate, with significant warming and cooling processes, developing different sedimentary sequences. The obvious climate fluctuations during the Late Eocene led to the dominance of halite deposition in the saline lakes.
Porphyry deposits are the world’s most important source of Mo and Cu resources and typically exhibit pronounced metallogenic specialization, with Mo and Cu rarely occurring together in similar abundances within a single deposit. Whether the Mo mineralization and its associated Cu mineralization in porphyry Mo deposits share a unified source, and whether mantle components participated in the formation of these deposits, remains unclear. To address this issue, we selected the Lower Urgen Mo deposit in the northern Great Xing’an Range as a case study. This deposit features veinlet-disseminated- and quartz-vein-type Mo mineralization, accompanied by minor Cu mineralization. Through detailed studies of deposit geology, in-situ lead and sulfur isotopes, helium and argon isotopes, and pyrite geochemistry, we have constrained the genesis of the Lower Urgen deposit. The hydrothermal mineralization process can be divided into four stages: Stage 1 is characterized by magnetite, quartz, and K-feldspar; Stage 2 is the main stage of Mo mineralization; Stage 3 is involved in Pb-Zn-Cu mineralization; and Stage 4 features calcite, quartz, fluorite, and minor pyrite. In-situ δ34S values of pyrite from various stages display a narrow range (6.0 ‰ to 8.3 ‰), and their lead isotope ratios (206Pb/204Pb = 18.332–18.502; 207Pb/204Pb = 15.539–15.574; 208Pb/204Pb = 38.126–38.320) are homogeneous and overlap with those of the ore-bearing granite porphyry, suggesting a common and predominantly magmatic source for sulfur and lead, derived from the associated granitic magma. Consistent Co/Ni (mostly 1–10) of pyrite from three stages suggests that the multistage hydrothermal fluids originated from a common source-the coeval granite porphyry. Fluid inclusions in hydrothermal pyrite have 3He/4He ratios of 0.73 to 2.10 Ra and 40Ar/36Ar ratios of 318 to 336, indicating substantial mantle-derived volatile contributions. The variations in mineral assemblages indicate a progressive decrease in oxygen fugacity within the Lower Urgen mineralization system. Fluid cooling and immiscibility could dominate the massive precipitation of molybdenite at Stage 2, whereas the large-scale precipitation of chalcopyrite at Stage 3 may be closely related to the incursion of meteoric water into the hydrothermal system. After the precipitation of molybdenite and chalcopyrite, the remaining ore-forming elements continued to precipitate in Stage 4 pyrite. Our findings highlight the significance of noble gas isotope and in-situ mineral geochemical analyses in revealing the genesis of porphyry Mo deposits, which is critical for elucidating detailed ore-forming processes of porphyry mineralization systems in Northeast China and globally.
Lithology modeling and grade estimation are foundational to mineral resource assessment. However, existing deep learning methods often lack effective integration of geological priors and make insufficient use of heterogeneous geological data and spatial continuity information, limiting their geological consistency and predictive robustness. To address these limitations, we propose the Enhanced Cascade Mixture Density Network (ECMDN), a deep learning framework with Geological Prior Encoding through neighborhood feature engineering. ECMDN integrates geological data, spatial continuity priors, and neighborhood feature learning to improve three-dimensional (3D) lithological probabilistic modelling and grade estimation. Specifically, spatial continuity-guided neighborhood probability features (FeatAug-1) are constructed from boreholes, geological maps, and exploration sections, enabling quantitative representation of local lithological continuity. Furthermore, lithology-constrained grade feature engineering (FeatAug-2) is introduced to characterize spatial grade variability under geological controls. The proposed method quantitatively encodes geological priors into machine-learning feature representations, thereby improving geological plausibility and predictive performance. Finally, the proposed method is validated using the Qulong porphyry copper deposit in Tibet, China. The results demonstrate a lithology prediction accuracy of 0.9371, significantly outperforming Random Forest (RF) (0.8632) and Deep Neural Network (DNN) (0.9250). For grade estimation, ECMDN achieved optimal performance (R2 = 0.8331), exceeding IDW(0.4315), Ordinary Kriging(0.5765), RF (0.7898), and DNN (0.7821). The resulting geological model exhibits geologically coherent lithology and copper-grade distributions, providing a reliable basis for 3D mineral resource modeling.
The mechanisms of gold mineralization, as well as post-mineralization modifications such as tectonic exhumation and preservation are critical to exploration. The Haigou deposit, located between the North China Block and the Xingmeng Orogenic Belt, is a representative Te-rich gold deposit with reserves of ∼ 40 t at an average grade of 3.4 g/t. Previous studies have focused largely on its origin, timing, ore-fluid sources, and metallodynamic setting, whereas the mineralization processes and post-ore modifications have received less attention. To address this gap, we conducted detailed field investigations, trace-element analyses of ores, apatite fission-track thermochronology, and thermal-history modeling of the Haigou deposit. Our primary objectives were to constrain the gold mineralization processes and to evaluate post-mineralization exhumation and preservation potential. Micro-textural analyses reveal that the main metallic minerals include pyrite, chalcopyrite, galena, Te-bearing galena, nickeline (NiTe2), native gold, argentite, calaverite (AuTe2), mercurian telluride (HgTe), and hessite [(Au,Ag)Te2]. Gold occurs predominantly as micro-sized native gold, nano-sized gold, and tellurides hosted in sulfides. Integration of published S-isotope and fluid-inclusion data indicates that the ore-forming materials were derived from mantle sources. Thermal-history modeling further reveals three episodes of rapid uplift at ca. 160–85 Ma, 28–14 Ma, and 8.5 Ma–present, corresponding to exhumation from depths of 5.2 ± 0.4 km. Compared with deposits that have undergone significant post-mineralization modification, the Haigou deposit is remarkably well preserved, and its ore-forming depths of ca. 5.1–9.8 km point to substantial untapped potential for gold mineralization at depth.
Carbonatite-related deposits host critical metals including rare earth elements (REEs) and high-field-strength elements (HFSEs; e.g., Nb, Zr, and Ti), which serve as indispensable raw materials for high-tech and green energy industries. Recent inclusion investigations of carbonatite-related deposits revealed that their ore-forming fluids (or carbonatitic brine-melts) are not Cl-dominated brines, but fluids enriched in carbonate and sulfate. Although the contribution of sulfate- and carbonate-rich fluids to the formation of REE deposits has been verified, the mechanisms controlling the co-enrichment of HFSEs and REEs remain unclear. In this study, we used a hydrothermal diamond anvil cell (HDAC) to investigate the dissolution behavior of Nb2O5(s), ZrSiO4(s), and TiO2(s) in CO32−-, SO42−-, and OH−-bearing fluids under high P–T conditions. Our experiments led to three key findings: (1) Alkaline (i.e., OH−-rich) fluids can directly dissolve traditionally insoluble components, including Nb, Zr, and Ti; (2) The solubility of these components is further enhanced in CO32−-bearing alkaline fluids; (3) Compared with CO32−-bearing alkaline fluids, SO42−-rich fluids can dissolve Nb on the same order of magnitude, but exhibit a relatively weaker ability to dissolve Zr and Ti. The varying mobilities of HFSEs in these fluids are consistent with mineralization of carbonatite-related deposits, which are characterized by co-enrichment of Nb with REEs but lesser extents of Zr and Ti enrichment. We propose that in carbonatite-related ore-forming systems, the early-stage carbonatitic brine-melts can co-mobilize REEs, Nb, Zr, and Ti, whereas the late-stage sulfate-rich aqueous fluids can further selectively transport REEs and Nb. Late-stage fluid activity sustains REE and Nb mobilization and promotes the formation of high-grade mineralization, accounting for the greater enrichment of REE-Nb over Zr-Ti in these deposits.
The Beishan Orogenic Collage records prolonged tectonic evolution accompanied by widespread granite emplacement and extensive Cu, W, and Au mineralization. At the Xichangjing W-Cu deposit, scheelite- and chalcopyrite-bearing mineralization is spatially associated with biotite granite and hosted by fracture-controlled veins. To clarify the origin of the biotite granite and its relationship with mineralization, we integrated whole-rock major- and trace-element geochemistry, LA-ICP-MS zircon U-Pb geochronology, zircon Hf isotope analyses, Ti-in-zircon thermometry, and zircon oxybarometry. Zircons yield weighted mean 206Pb/238U ages of 421.9 ± 1.7 Ma and 422.9 ± 2.0 Ma, constraining emplacement of the biotite granite to the Late Silurian. The biotite granite is high-K calc-alkaline and weakly peraluminous (SiO2 = 70.05 % ∼ 71.59 wt%; A/CNK = 1.02 ∼ 1.10), and its elevated Rb/Sr ratios, negative Eu anomalies, and depletions in Ba, Sr, P, and Ti indicate appreciable magmatic differentiation. Negative zircon εHf(t) values (−8.63 to − 4.58) and two-stage Hf model ages (1700 ∼ 1950 Ma) indicate that the intrusion was mainly produced by remelting of ancient continental crust, with additional input from mantle-derived melts, forming hybrid magmas. Ti-in-zircon temperatures are mainly 740 ∼ 780 °C, and zircon oxybarometry yields ΔFMQ values of − 2.35 to − 0.19, indicating an evolved granitic system that crystallized under relatively reducing conditions. The deposit formed in a post-collisional tectonic environment between the Gongpoquan and Huaniushan arcs, where slab break-off likely induced asthenospheric upwelling and crust–mantle interaction. The resulting peraluminous, high-temperature, relatively reduced magmas provided favorable physicochemical conditions and crust-derived materials for tungsten mineralization.
The Dayaocun high-grade Fe skarn deposit (6.03 million tonnes at 51.41 % TFe), recently discovered in the northern section of the Tongling ore-cluster area within the Middle-Lower Yangtze River Metallogenic Belt (MLYB), represents a significant addition to our understanding of the genesis and metallogenic potential of skarn Fe deposits in eastern China. Zircon U-Pb dating of the ore-related granodiorite yields an age of 140.1 ± 2.5 Ma, indicating that skarn formation was contemporaneous with early Cretaceous magmatic activity in the region. Garnet U-Pb dating (137.0 ± 1.4 Ma) and trace element geochemistry reveal two distinct generations of garnet (Grt I and Grt II), formed under contrasting fluid redox conditions and temperature regimes. Major and trace element compositions of magnetite define two mineralization stages. Magnetite I displays low Ti and V contents and formed under moderate temperature (∼500 °C) and relatively reducing conditions, whereas magnetite II is characterized by higher Mg and Mn but lower Ti, V, and Cr contents, suggesting late-stage oxidation and hydrothermal re-equilibration. The progressive increase in oxygen fugacity (fO2) during Fe enrichment is evidenced by decreasing HFSE and REE contents and elevated Eu anomalies. Integrating petrography, U-Pb chronology, and mineral chemistry, the Dayaocun Fe skarn deposit formed during an early-stage magmatic-hydrothermal system. The localized Fe enrichment and evolved magmatic signature suggest a distinct hydrothermal regime within the Tongling ore cluster, independent from Cu-Au skarn systems. These findings provide new constraints on genesis of Fe skarn deposits in the MLYB, highlighting the role of redox evolution and fluid-rock interaction in controlling high-grade Fe mineralization. The study not only refines the metallogenic model of the Tongling ore-cluster region, but also enhances regional exploration criteria for high-grade Fe skarn deposits in eastern China.
The Farhadabad Cu prospect in western Iran is a volcanic-hosted Cu occurrence developed within Eocene andesitic and basaltic-andesitic volcanic rocks. Mineralization occurs as veins, veinlets, and disseminations of chalcopyrite, bornite, chalcocite, covellite, malachite, and azurite, accompanied by magnetite, pyrite, quartz, calcite, clay minerals, hematite, goethite, and Mn oxides. Although volcanic-hosted Cu deposits are commonly associated with complex hydrothermal systems, the sources of ore-forming fluids and metals, as well as the processes controlling ore deposition, remain poorly constrained at the Farhadabad prospect. To constrain the origin and evolution of the mineralizing system, petrographic observations, fluid inclusion microthermometry, and stable isotope (O and S) analyses were conducted. Hydrothermal alteration of the host rocks is characterized by silicification, sericitization, chloritization, carbonatization, and argillization. Fluid inclusion data from sulfide-associated quartz and calcite indicate ore formation at temperatures of 130–280 °C from aqueous fluids with low to moderate salinities of 0.53–16.05 wt% NaCl equivalent. Magnetite δ18O values range from +8.6 to +11.3 ‰, corresponding to calculated equilibrium fluid δ18O values of +16.9 to +19.6 ‰ at an average homogenization temperature of 160 °C, supporting a significant contribution from evolved basinal/metamorphic fluids. Sulfur isotope compositions of pyrite and chalcopyrite (δ34S = −5.0 to +7.0 ‰) yield calculated mineralizing-fluid δ34S values of −7.2 to +4.8 ‰. These values are compatible with a possible magmatic sulfur contribution and do not exclude sulfate-bearing basinal fluids; sulfur isotope fractionation during hydrothermal fluid evolution, potentially involving sulfate reduction, may also have contributed to the observed range. Fluid inclusion and oxygen isotope data are consistent with mixing of hot, saline basinal/metamorphic fluids with meteoric water. These fluids, possibly derived in part from Lower Cretaceous strata, are interpreted to have migrated upward along thrust-related faults into the Eocene volcanic succession, where fluid–rock interaction promoted hydrothermal alteration and may have contributed to Cu enrichment through leaching of the volcanic host rocks. Subsequent fluid evolution and mixing likely promoted the destabilization of dissolved metal complexes and precipitation of epigenetic Cu sulfides. The observed geological, mineralogical, and geochemical characteristics are broadly consistent with a Manto-type interpretation; however, in the absence of subsurface and drilling data, the Farhadabad Cu occurrence is considered a Manto-type prospect rather than a definitively established Manto-type deposit.
The Huangniping Au deposit represents a typical example of metasediment-hosted gold mineralization in the northern Longmenshan orogenic belt, yet the processes controlling gold enrichment and redistribution remain poorly constrained. In particular, the role of multistage pyrite growth in recording fluid evolution, metal remobilization, and gold precipitation has not been systematically evaluated. Here we integrate petrographic observations, back-scattered electron (BSE) imaging, in-situ LA–ICP–MS trace element analysis, and LA–MC–ICP–MS sulfur isotope data to investigate seven generations of pyrite formed during sedimentary-diagenetic (Py0a–Py0b), metamorphic hydrothermal (Py1–Py3), and hydrothermal vein (Py4–Py5) stages.Gold is predominantly hosted as lattice-bound solid solution within pyrite, but exhibits systematic decoupling from As across successive pyrite generations, indicating that Au incorporation was not solely controlled by As substitution. Elemental zoning and relic cores in Py1 indicate inheritance and mobilization of Au and trace elements from early diagenetic pyrite during metamorphism. Py2 and Py3 display rhythmic zoning and enhanced Au, As, Cu, and Sb contents, suggesting progressive fluid enrichment. Py4 contains the highest Au contents (average 167 ppm, up to 393 ppm), with textures and zoning patterns indicative of episodic injections of Au-rich fluids and metal remobilization. In contrast, Py5 is characterized by low Au and base metal depletion. Sulfur isotope compositions of metamorphic hydrothermal stage (δ34S ranging from 15.0 to 27.5‰) and hydrothermal vein stage (19.3–22.8‰) overlap significantly, indicating a common ore-forming fluid source likely derived from metamorphism of the Cambrian Niutitang Formation sediments.This study demonstrates that multistage pyrite growth effectively archives the physicochemical evolution of ore-forming fluids in metasediment-hosted gold systems and highlights metasomatic overprinting, progressive metal remobilization, and cyclic fluid ingress as key processes governing gold enrichment in the northern Longmenshan orogenic belt.
The first discovered nickel orebody in the Shuiluo Ni-Zn-Sb occurrence (1.53% Ni, 1.01% Zn, and 0.94% Sb) occurs as a lenticular body within Late Devonian Wuzhishan Formation (D3w) limestone and is spatially associated with paleo-manganese nodules in the Wuxu Sb-Zn-Sn district of the Danchi Fold-and-Thrust Belt (DFTB), South China. The nickel orebody of the Shuiluo occurrence offers an opportunity to understand the ore-forming process and genesis of this unusual nickel mineralization in the world-renowned tin belt. Field observations, micro-X-ray fluorescence (μ-XRF) mapping, TESCAN Integrated Mineral Analyzer (TIMA) analysis, and electron probe microanalysis (EPMA) indicate that the Shuiluo orebody records three stages: an early sedimentary Ni-Mn pre-enrichment stage, a later Zn-Sb hydrothermal overprinting stage, and a final supergene enrichment stage. Nickel occurs mainly in three species: Ni hosted by Mn-rich phases and limonite, Ni associated with Zn-W-bearing hydrothermal overprinting, and discrete Ni-rich minerals, including josephinite, annabergite, and Ni-bearing chlorite. We propose that regional Late Devonian Mn-bearing strata provided a Ni-bearing background, whereas paleo-manganese nodules acted as the primary trap for Ni pre-enrichment under oxidizing marine conditions. Subsequent Late Cretaceous Zn-Sb-W-bearing hydrothermal fluids modified the Ni-enriched nodules along permeable structures, and post-Cretaceous weathering and leaching further upgraded Ni to form the local ore-grade Shuiluo Ni orebody. This multi-stage process differs from typical magmatic sulfide, lateritic, hydrothermal, and marine sedimentary Ni deposits, and may represent a previously under-recognized style of Ni mineralization in Sn-polymetallic metallogenic belts. The Late Devonian Mn-bearing Wuzhishan and Liujiang formations in South China may be prospective for similar Ni-Co mineralization where Mn-nodule-rich horizons have experienced hydrothermal overprinting and subsequent supergene weathering and oxidation.
Epithermal Ag–polymetallic deposits commonly display pronounced vertical metal zonation, yet the timing of ore formation and the physicochemical processes responsible for upward metal redistribution remain difficult to resolve because hydrothermal systems are commonly overprinted by repeated veining and fluid pulses. The Nagengkangqie’er Ag-polymetallic deposit in the East Kunlun Orogen, northwestern China, provides an excellent natural laboratory, with mineralization changing vertically from deep Cu–Pb–Zn ores to middle Ag–Pb–Zn ores and shallow Ag-rich sulfide–sulfosalt assemblages. Here we combine in situ U–Pb dating of argentite-bearing calcite, sphalerite major- and trace-element geochemistry, principal component analysis, and in situ sulfur isotope analyses of sphalerite and coexisting sulfides. Ore-related, argentite-bearing calcite yields a lower-intercept U–Pb age of 211 ± 4 Ma. Because the dated calcite is spatially and paragenetically associated with argentite and Ag-bearing sulfide–sulfosalt assemblages, this age constrains the timing of an Ag-bearing hydrothermal event within the Late Triassic ore-forming window, rather than the crystallization age of argentite itself. Three sphalerite generations record progressive vertical and temporal fluid evolution: deep Sp1 formed from a relatively reduced, Cu–Zn–Cd–In–Pb-rich fluid; middle Sp2 records enhanced Mn–Sn–Ag enrichment and Cu–Ag–Sn–In coupled substitution; and shallow Sp3 is Fe–Mn-rich, Zn-poor, and associated with abundant discrete Ag minerals. Sulfur isotope variations are consistent with changes in sulfur reservoirs, degrees of inter-mineral isotope equilibration, and precipitation conditions during successive hydrothermal pulses, but these isotope data are interpreted as complementary evidence rather than as a unique proof of any single process. We infer that the Nagengkangqie’er metal zonation was generated by structurally focused multiphase fluid ascent, accompanied by cooling, pressure decrease, boiling, fluid mixing, and changes in sulfur activity. These results link Nagengkangqie’er Ag mineralization to Late Triassic magmatic–hydrothermal activity and show that ore-related calcite U–Pb dating, when integrated with sphalerite geochemistry and sulfide sulfur isotopes, provides a useful framework for dating, interpreting, and exploring vertically zoned epithermal Ag–Pb–Zn systems.
The Qiushulin molybdenum deposit, located in the central Taihang Mountains of the North China Craton (NCC), is hosted at the contact zone between the quartz monzonite porphyry and the Neoarchean Fangli gneiss. LA-ICP-MS zircon U-Pb dating of the quartz monzonite porphyry yielded a weighted mean206Pb/238U age of 132 Ma. Combined with whole-rock geochemical characteristics, indicated that it was formed by the partial melting of mantle-derived amphibolite/basalt in the Early Cretaceous, which was caused by the subduction of the Paleo-Pacific plate (PPP) beneath the NCC and subsequent plate rollback. Re-Os dating was performed on molybdenite, obtaining two stages of metallogenic ages. The former metallogenic age is130 Ma, which is broadly consistent with the age of the quartz monzonite porphyry and comprises the first two mineralization stages: (Ⅰ) quartz pyrite, (Ⅱ) quartz polymetallic sulfides. The latter metallogenic age is 113 Ma, which comprises the last mineralization stage: (Ⅲ) quartz carbonate. The petrography, microscopic thermometry, and laser Raman results of fluid inclusions indicate that the main component of the inclusions is CO2, dominated by three-phase primary inclusions, with liquid-rich secondary inclusions also observed. The primary inclusion for stages I and II mineralization temperatures are 357–427 ℃ and 257–381 ℃, with salinities of 6.54–9.44 wt% and 2.96–11.61 wt%, respectively. The calculated capture pressures for stages I and II mineralization are 200–276 MPa and 203–248 MPa, and the ore-forming depth is about 8.34 km. H-O isotope analysis reveals that for stage I, the ranges of δDV-SMOWand δ18OH2Oare − 58.1 to − 59.0 ‰ and 5.37 to 6.07 ‰, respectively, plotting near the primary magmatic water field. For stage II, the ranges of δDV-SMOWand δ18OH2Oare − 59.4 to − 60.8 ‰ and 4.40 to 4.48 ‰, respectively, shifting towards the meteoric water line. This indicates that the ore-forming fluid was mainly primary magmatic water, and as the mineralization proceeded, meteoric water was added. Combined S-Pb isotope composition indicates that the metallic minerals are mainly derived from the mantle-lower crust. Based on the research of the Qiushulin molybdenum deposit and host rock quartz monzonite porphyry, together with previously regional tectonic-magmatic events, ore geology, and the geochronologic and isotopic data, we suggest that the Qiushulin molybdenum deposit is a typical porphyry-type deposit. Its formation is attributed to the crust-mantle magma interaction triggered by lithosphere extension and asthenosphere upwelling during the rollback of the subducted PPP beneath the NCC, accompanied by multi-stage tectonic magmatic activities and mineralization superposition.
Despite the economic significance of gold skarn deposits, the processes driving ore-forming fluid evolution, particularly the role of discrete magmatic fluid pulses, remain enigmatic. Here, we integrate garnet paragenesis, U-Pb geochronology, geochemistry, and fluid inclusion microthermometry with phase-equilibrium modeling from the large, reduced Laozuoshan gold skarn deposit to address this issue. Textures and crosscutting relationships document five andradite-grossular (Adr-Grs) garnet generations (Grt1–Grt5) in prograde anhydrous skarn and one hydrogrossular-dominated generation (Grt6) in late retrograde sulfide-carbonate assemblages. Garnet U-Pb ages constrain the gold skarn formation to ca. 108–105 Ma, broadly linking gold mineralization to the Early Cretaceous diorite stocks rather than the previously proposed late Permian granodiorite. The compositions of Grt1–Grt5 record a stepwise evolution from Adr96–99Grs0–2 through Adr46–76Grs22–51 and Adr25–43Grs55–72 to Adr0–14Grs86–100, then to Adr22–32Grs66–73. Microthermometric data indicate a trapping temperature of > 556 °C for Grt1, whereas Grt2–Grt5 record alternating temperature-pressure variations (491–640 °C, 360–1006 bar). Phase-equilibrium modeling indicates that the stepwise Adr-Grs evolution was controlled primarily by staged shifts in effective composition of the fluid-rock reacting system, rather than by pressure variations. These results reveal that multiple batches of magmatic fluids were episodically introduced into the fracture system. Higher concentrations of gold-associated metals in Grt6 than those in Grt1–Grt5 suggest that gold was likely transferred from the incoming magmatic fluids into reacted fluids via prograde metasomatism during episodic fluid activity. Consequently, gold precipitated from successive reacted fluids and progressively accumulated in pore-fracture networks, forming the Laozuoshan gold skarn ores.
Silver is widely associated with Pb-Zn mineralization worldwide, however, the genesis of high-grade silver ores in these systems remains highly debated. Here, we choose the newly-discovered Erdaokan Ag-Pb-Zn deposit (∼1800 t Ag with an average grade as high as 431 g/t) in northeastern (NE) China as a case study to decipher the above issue. The studied mineralization comprises four stages, among which three pyrite generations (Py1, Py2, Py3), two types of sphalerite (Sp1, Sp2) and galena (Gn1, Gn2) have been identified. In situ trace element analyses reveal that Py1 contains higher Mn, Pb, Zn, Co, and Ni than Py2 and Py3. The Py2 exhibits the highest Ag, As, Cu, Sb, and Tl contents, and Py3 shows wide variations in Ag, Cu, Pb, Zn, As, and Ni. Gallium, Cd, and In are generally low in all pyrite types, mostly below the detection limits. Trace element compositions reveal that the studied deposit formed under low temperature and low fO2 conditions, with significant fluid-rock interactions during mineralization process. Extracted fluid inclusions in pyrite show elevated 3He/4He values (0.83–2.08 Ra) and 40Ar/36Ar ratios (320.6–410.2), indicating the presence of crust-mantle end-member reservoirs, along with meteoric water contributions to the ore-forming system. In situ Pb isotope contents of sulfides suggest that the metals are predominantly derived from magmatic sources. These new data collectively indicate that the formation of the Erdaokan high-grade Ag ores is caused by fluid-rock interactions. Combined with ore deposit geology, gangue assemblages and geochemical data, we interpret the Erdaokan deposit as an epithermal type silver deposit.
Sandstone-hosted uranium deposits are a globally significant uranium resource and are widely distributed in the Meso–Cenozoic sedimentary basins of northern China. This paper systematically reviews the basin geodynamic setting, geological characteristics, and the nature, origin, and precipitation mechanisms of ore-forming fluids associated with these deposits. This review also provides a comparative discussion with other uranium deposit types worldwide. The formation of sandstone-hosted uranium deposits in northern China was controlled by the combined effects of Paleo-Pacific plate subduction and the India–Eurasia collision. Large-scale uranium mineralization occurred predominantly from the Eocene to Miocene, closely linked to regional tectonic uplift that drove massive basinal fluid flow. The ore-forming fluids are characterized by low temperatures (generally < 200 °C) and low to moderate salinities (mostly < 15 wt% NaCl equiv.), consistent with a shallow, low-temperature metallogenic environment. This signature is also common in other uranium deposit types, implying that the involvement of basinal fluids may have broader significance than previously thought. The transport of uranium depends on the specific combination of ligand species, concentration, pH, and temperature, rather than on the absolute predominance of a single ligand. There is a clear discrepancy between fluid inclusion data and modern fluid compositions: paleo-ore-forming fluids contain significantly higher uranium concentrations than present-day basinal waters, suggesting that simple inheritance or direct correspondence between them is unlikely. The most uranium-rich basinal fluids currently known are those from unconformity-type uranium deposits, yet their chemical conditions differ markedly from those of sandstone-hosted systems, indicating that uranium enrichment in basinal fluids is not tied to a single fluid type. Potential uranium sources are not limited to eroded basement highs at basin margins; uranium-rich accessory minerals, carbonate detritus, and black organic-rich shales within the basin fill can all serve as viable uranium suppliers. Fluid sources include meteoric/surface water, formation water, and deep hydrocarbon fluids. The first two act as uranium carriers, whereas hydrocarbon fluids provide critical reductants. Redox reactions are the core mechanism for uranium precipitation, achieved through fluid mixing, water–rock interaction, and microbial sulfate reduction. Adsorption, an additional pathway independent of redox, plays a significant role under low-temperature, low-uranium-concentration conditions. Testing and refining these concepts depend critically on the acquisition of direct compositional data from ore-forming fluids. The development of in situ LA-ICP-MS analysis of single fluid inclusions offers the potential to fundamentally overcome this limitation. It will provide key constraints on fluid origin, evolution, and precipitation mechanisms, thereby enabling a more robust metallogenic model for sandstone-hosted uranium deposits.
As the primary global source of lithium, LCT-type pegmatites warrant detailed study of their mineralization in LCT-type pegmatite is of paramount importance for their exploration and development. This study investigates the Murong pegmatite (Asia’s largest single-vein LCT-type pegmatite) through a systematic geochemical analysis of columbite-group minerals (CGMs), tourmaline, and apatite. In addition, the fluid exsolution was investigated by comparing the geochemical characteristics of apatite from the No. 134 pegmatite, a typical LCT-type deposit in the Jiajika of the Songpan-Ganzé orogenic belt (SGOB). The CGMs U-Pb dating shows that the Murong Pegmatite was intruded between 193.2 and 199.2 Ma, which is consistent with the end of the Late Triassic Barrovian-Buchan metamorphism in the SGOB. The substitution between Li and Mg in tourmaline reveals the limited efficiency of B-rich fluids in transporting Li into the surrounding hornfels. A comparative analysis of apatite between the Murong and the Jiajika No. 134 pegmatites reveals a single fluid exsolution at Murong, contrasting with the multi-stages fluid exsolution at No.134. Fluid exsolution shifted the melt toward a slightly alkaline, low alkali-to-lithium ratio (low (Na + K)/Li ratios), which triggered spodumene crystallization. We conclude that fluid exsolution plays a regulatory role in the melt environment during pegmatite formation. Furthermore, the escape of a large volume of volatiles caused the melt liquidus temperature to rise, leading to fast crystallization and limiting Li diffusion into the wall rocks, thus facilitating the formation of single, super-large Li deposits with pervasive mineralization throughout the entire vein.
Pegmatite-type lithium (Li) deposits are a crucial source for modern batteries, yet their formation remains contentious due to limited understanding of their timing and processes. The existence of Indosinian lithium mineralization in the Altun region and the mechanisms of lithium migration and enrichment during magmatic-hydrothermal processes are particularly debated. The Kumusayi Li deposit, situated in biotite schist with muscovitization and greisenization halos around ore veins, provides significant insights. U-Pb dating of cassiterite (219.7 ± 5.2 Ma) from Kumusayi spodumene-bearing pegmatites confirms an Indosinian mineralization age. In-situ Rb-Sr isotopic analysis of micas reveals two metallogenic episodes: recorded by magmatic-hydrothermal muscovite P1 (206.8 ± 1.9 Ma) and hydrothermal muscovite H1 (196.2 ± 7.1 Ma). Microanalytical data of mica generations reveal a systematic geochemical evolution: Nb-W-Sn-Ta contents increase from P1 to H1-H3, while Li-Rb-Co-Ni decrease, with peak concentrations in H1 (Li2O = 1.8–2.3%). Altered biotite schist shows significant lithium depletion (primary biotite: Li2O = 0.18–0.25% vs. Re-equilibrated biotite: 0.03–0.06%), indicating substantial lithium mobilization during hydrothermal alteration. The metallogenic process comprises three stages: early magmatic crystallization of spodumene depletes lithium; late magmatic formation of lower-Li muscovite P1 (Li2O = 0.83–1.33%); and hydrothermal overprinting, where Li-enriched fluids precipitate high-Li muscovite H1, followed by progressive lithium depletion through H2-H4 (Li2O = 0.08–0.15%). This magmatic-hydrothermal mechanism is appears to be essential for Li enrichment leading to Li mineralization. Recognizing Indosinian lithium mineralization at Kumusayi and understanding lithium recycling between magmatic and hydrothermal systems offers new genetic models and exploration strategies for rare-metal deposits in the Altun belt. Notably, lithium replenishment from country rocks during hydrothermal alteration provides a novel perspective for regional prospecting.
As an important part of the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province (SYGMP), the Wuzhishan ore field in Puding, Guizhou, SW China, is situated on the southwestern margin of the Yangtze Block. More than 20 different scale Pb-Zn deposits and occurrences have been explored in the area. Among them, the Nayongzhi deposit represents the first large-scale Pb-Zn deposit identified in the Wuzhishan ore field, with proven Pb + Zn resources exceeding 1.35 Mt. Most Pb-Zn orebodies occur as stratiform and are hosted in dolostone of the Lower Cambrian Qingxudong Formation, and the Dujiaqiao deposit is the only one hosted in dolostone of the Late Ediacaran Dengying Formation in the ore field. Although the Dujiaqiao deposit is medium-sized, its mineral assemblage and wall-rock alteration similar to those of the Yuhe ore block in the Nayongzhi deposit. Establishing a genetic link between the Late Ediacaran-hosted cross-stratal vein-type mineralization at Dujiaqiao and the Cambrian-hosted stratiform mineralization at Nayongzhi is a key scientific problem for understanding multi-stratal Pb-Zn mineralization and further exploration guidance. Moreover, the critical metals, including Cd, Ge, Ga, and In, are mainly recovered as by-product and hold considerable economic significance, and its enrichment characteristics and mechanisms in the Dujiaqiao deposit remain unclear. Sphalerite from the Dujiaqiao deposit was divided into three generations: early-stage black (Sp1), middle-stage reddish-brown (Sp2), and late-stage light-yellow (Sp3). In-situ trace‑element and sulfur-isotope analyses of sphalerite and other sulfides were performed using LA-ICP-MS and LA-MC-ICP-MS, respectively. The results demonstrate that sphalerite from both the Dujiaqiao and Nayongzhi deposits exhibits similar trace-element patterns, with enrichment of low-temperature elements (e.g., Cd, Ge) and depletion in high-temperature elements (e.g., Mn, Co, In, Sn). Concentrations of Ge (0.75–225 ppm, avg. 61.3 ppm, n = 98) and Cd (301–3858 ppm, avg. 1348 ppm, n = 98) meet or exceed the threshold grades for potential by-product recovery. Notably, Ge is enriched in Sp1 and Sp2, whereas Cd is most enriched in Sp2, followed by Sp3. These elements are incorporated into sphalerite by lattice substitution; Ge enters via coupled substitution dominated by 3Zn2+ ↔ Ge4+ + 2(Ag+, Cu+), and Cd via Zn2+ ↔ Cd2+ replacement. Trace-element geothermometry yields ore-forming temperatures of 104.3–231.5 °C (avg. 145.4 °C, n = 71), indicating low‑ to moderate‑temperature hydrothermal conditions, slightly higher than that of the Nayongzhi deposit. Sphalerite δ34S values (+18.0‰ to + 24.7‰, avg. + 21.5‰, n = 49) closely resemble that of the Late Ediacaran marine sulfate, indicating that the sulfur was derived mainly from thermochemical sulfate reduction (TSR) of sulfate hosted in Dengying Formation. Overall, the Dujiaqiao and Nayongzhi deposits share similar geological and geochemical characteristics except for its host rocks. It is suggested that both belong to MVT Pb-Zn deposits formed during the same mineralizing event. The Dujiaqiao deposit represents deeper, structurally controlled channel-facies mineralization, whereas the Nayongzhi deposit records shallower, bedding‑parallel replacement mineralization. The research provides new geological and geochemical constraints on the Late Ediacaran‑hosted cross‑stratal vein‑type Pb‑Zn mineralization in the Wuzhishan ore field and offer implications for future Pb-Zn exploration in the area
The Dashui gold deposit, a large and high-grade gold deposit in the western Qinling orogen, is distinguished by intense hematite–silica–calcite alteration and sulfide-poor oxidized ores. Its mineralization timing and ore-forming fluid evolution have long been controversial due to the lack of conventional geochronometers. This study presents new in-situ calcite U–Pb dating, trace element concentrations, and Sr isotope compositions to constrain the timing of ore-stage hydrothermal activity and fluid evolution. Petrographic and cathodoluminescence (CL) examinations recognize three distinct calcite generations: early-stage Cal-1, ore-stage Cal-2, and late-stage Cal-3. In-situ U–Pb dating of the ore-stage Cal-2 from two mineralized samples yielded well-defined lower intercept ages of 195.0 ± 1.4 Ma and 193.8 ± 1.8 Ma. These dates constrain ore-stage calcite precipitation to the Early Jurassic. Given the textural association between Cal-2, native gold, and hematite, these ages provide an important constraint on the timing of main-stage gold mineralization. Cal-1 exhibits elevated 87Sr/86Sr ratios (0.70836–0.70848), indicating crustal stratigraphic fluids that acquired radiogenic 87Sr from deep Rb-rich basement sources. Ore-stage Cal-2 shows lower and more variable 87Sr/86Sr ratios (0.70675–0.70839), overlapping with regional Mesozoic granitoids and suggesting involvement of magmatic-hydrothermal fluids, with elevated Mn/Sr and Fe/Sr ratios and non-linear Sr isotope arrays reflecting intensified fluid–rock interaction during the main mineralization stage. Cal-3 exhibits the highest 87Sr/86Sr ratios (∼0.70860), coupled with decreased Sr contents, reflecting late-stage meteoric water influx. Geochemically, the transition from dark red CL in Zone A to brilliant orange-red CL in Zone B within Cal-2 is principally controlled by fluctuations in the activator/quencher Mn2+/Fe2+ ratio and total REE abundances. Zone B preserves relatively uniform REE patterns and weak HREE fractionation, whereas Zone A shows stronger REE fractionation and variable Y/Ho ratios, indicating changes in fluid composition, fluid flux, and fluid–rock interaction during calcite growth.
