Search Results (60)

To support drilling gas influx control, saline aquifer CO₂ sequestration and CCUS development under the dual carbon goals, this study proposes a high-precision calculation method for the solubility of high-temperature, high-pressure, CO₂-rich natural gas in formation water. An activity–fugacity coupling model is established: fugacity coefficients of gas components are solved via the dimensionless Helmholtz free energy equation of state, and liquid-phase activity coefficients are characterized by the Pitzer electrolyte model. Comparative experiments with three natural gas and three formation water samples are carried out at 393.15–453.15 K and 5–100 MPa to analyze the influences of temperature, pressure, salinity and CO₂ content on solubility for model verification. The overall relative error between calculated and experimental data is below 10% (max 4.5%). Solubility rises rapidly with pressure then plateaus, declines with salinity, and grows with CO₂ content; CO₂ solubility far exceeds that of alkanes. This efficient, widely applicable model cuts engineering costs and guides safe oil-gas exploitation and CCUS deployment. Full article

The Dadonggou Mo deposit in Western Hebei, within the Yanshan–Liaoning Mo metallogenic belt, is a newly recognized medium-sized porphyry Mo system. Exploration has delineated 126 orebodies, most of which are blind, with identified resources of ~22,000 t Mo at an average grade of 0.071% Mo. Integrated lithogeochemistry, zircon U-Pb chronology, molybdenite Re-Os geochronology, quartz fluid-inclusion microthermometry, and H-O-S isotope analyses constrain the mineralization age, ore-fluid evolution, and sources of ore-forming materials. The zircon U-Pb dating of the ore-bearing granite porphyry and quartz porphyry from the Dadonggou molybdenum deposit yields ages ranging from 135.8 Ma to 141.5 Ma. The low Ti content in zircons indicates that they are super-wet magmatic rocks. The magmatic evolution experienced a change in oxygen fugacity from oxidizing to reducing conditions, which facilitated the initial enrichment of molybdenum. Molybdenite yields a Re-Os isochron age of 135.9 ± 4.0 Ma and a weighted mean model age of 134.2 ± 1.6 Ma, indicating Early Cretaceous mineralization. Ore fluids evolved from an early CO₂-H₂O-NaCl system with relatively high temperature and salinity to a later H₂O-NaCl system with lower temperature and salinity. Isotopic data indicate progressive meteoric-water incorporation into dominantly magmatic fluids. Sulfur isotopes and high Re contents in molybdenite indicate a mixture of mantle magma mixed with some seawater. Lower late-stage trapping pressures record post-ore depressurization and hydrothermal-system shallowing. Full article

Continental remobilization is a crucial driver of metallogenesis and the formation of ore deposits. Some of the world’s largest mineral deposits of the economically valuable elements tin (Sn), tungsten (W), gold (Au), copper (Cu), lead (Pb), and zinc (Zn) formed during the Mesozoic Era. Additionally, the chemistry and distribution of the elements Sn and W have been investigated in previous studies to understand planetary formation and differentiation processes. These two elements are largely co-located during certain South China Mesozoic metallogenic events but are not co-located during other time periods in the same regions. Here, we investigated the mineral chemistry network similarities and dissimilarities of Sn and W to understand their mineral formation and distribution during the Mesozoic Era and throughout Earth history. Mineral chemistry network community detection analysis and electronegativity associations among mineral constituent elements of Sn minerals and W minerals indicate that the elements have similar chemistry among their oxide minerals. However, Sn forms a much wider range of minerals that also contain S compared to W, which occurs in a limited number of S-containing minerals. The divergent constituent element interactions among S-containing Sn minerals and W minerals reflect the redox sensitivity and importance of oxygen (O) fugacity in Sn mineral formation. Conversely, extensive W mineral deposits are known to form at both high and low O fugacities. The similarities and differences between the mineral chemistry networks of Sn and W reflect the mineral distribution of the two elements in the Sn-W mineralization event from 160 to 139 Ma vs. the Sn–uranium (U) mineralization event from 125 to 98 million years ago (Ma). The mineral chemistry and distribution of Mesozoic Sn and W deposits illustrate the contrasting importance of redox and O fugacity on the mineral formation of different elements, and the dynamic crustal evolution that took place during this period of Earth history. Full article

Magnetite is extensively developed within various alteration zones of the mining district. Some magnetite is closely associated with copper mineralization, possessing significant research value. The Duobuza Cu (Au) deposit is a typical porphyry-type deposit within the Bangong Co-Nujiang metallogenic belt and was the first porphyry Cu-Au deposit discovered in the Duolong copper–gold ore district. Currently, this deposit contains copper resources exceeding 3 million tons @0.46%, with associated gold resources exceeding 80 tons @0.19 g/t. This study focuses on magnetite from the Duobuza deposit. Through field geological logging and microscopic identification combined with electron microprobe analysis (EMPA) and in situ LA-ICP-MS testing, mineralogical and mineral chemical research on magnetite is conducted. This research aims to elucidate the genesis of magnetite in the Duobuza deposit and its implications for mineral exploration. Five magnetite types with different occurrences can be distinguished in the Duobuza deposit: Mt₁ is magmatic magnetite; Mt₂, Mt₃, Mt₄, and Mt₅ are hydrothermal magnetite, with Mt₅ being closely associated with copper mineralization. Mt₁ is relatively enriched in Ti, V, Al, and Cr but depleted in Mn and Si; Mt₂ is relatively enriched in Ti and Al but depleted in Si and Cr; Mt₃ is relatively enriched in Al but depleted in Mg; Mt₄ is relatively enriched in Ti, Al, V, Zn, and Mn; and Mt₅ is relatively enriched in Mg, Si, Ti, Al, Mn, and Zn but depleted in Cr. Based on the Al + Mn vs. Ti + V discrimination diagram, magnetite formed in a medium- to high-temperature environment, with hydrothermal magnetite Mt₄ forming at the lowest temperature. Vanadium (V) content can be used to estimate the oxygen fugacity (fO₂) during mineralization. Mt₁ exhibits the highest V content, indicating relatively low oxygen fugacity, whereas Mt₄ shows the lowest V content, suggesting relatively high oxygen fugacity. Mt₅ has a higher V content compared to other early-stage hydrothermal magnetites, suggesting that a lower fO₂ formation environment favors the precipitation of metal sulfides in the mining district. Trace element analysis of magnetite from the Duobuza, Bolong, and Naruo mining districts reveals that magnetite from all three deposits is enriched in Si and Al and depleted in Ca and Ni. Magmatic magnetite from the Naruo and Duobuza deposits exhibits similar elemental distribution patterns. Hydrothermal magnetite from the Duobuza deposit shows significantly higher Ti and V contents compared to magnetite from the Bolong and Naruo deposits. Full article

We have investigated the major- and trace-element composition of hydrothermal pyrite, magnetite, and Ti-magnetite, and of the principal Cu-minerals chalcopyrite and chalcocite, to constrain ore-forming processes in the northeastern Saveh district (central Urumieh–Dokhtar magmatic arc, Iran). Our data provide new constraints on the magmatic–hydrothermal evolution and subsequent hydrothermal–supergene modification of the ore system. Ti-magnetites hosted in monzodioritic intrusions are enriched in Ti–V–Al, plot below the magnetite–ulvöspinel join and record high crystallization temperatures (<500 °C) under relatively low oxygen fugacity. By contrast, magnetite from silica-rich hydrothermal veins is Fe-rich with very low TiO₂; it formed at intermediate temperatures (~200–300 °C) under higher fO₂ and is markedly depleted in Ti and V compared with the intrusive oxides. Textures and oxide systematics (Al + Mn vs. Ti + V; V/Ti–Fe) document repeated hydrothermal pulses, Fe²⁺ leaching and element redistribution during cooling and fluid–rock interaction. Geochemical trends indicate progressive evolution from a magmatic fluid to later meteoric water overprint, with increasing As contents reflecting cooling and mixing with meteoric waters. Vertical elemental zoning suggests that most samples represent mid- to deep-level sections of the epithermal system. Elevated Cu contents (up to 0.95 wt.%) highlight pyrite as a significant Cu host. Co/Ni ratios between 1 and 10 further corroborate a magmatic–hydrothermal origin. Chalcopyrite is the principal economic Cu carrier at Northeast Saveh. Replacement follows a temperature- and fluid-controlled pathway (chalcopyrite → covellite → chalcocite). At lower temperatures (<~200 °C) replacement proceeds more slowly, producing chalcocite/digenite under prolonged reaction conditions. Chalcocite commonly occurs as thin replacement rims and fracture fills that concentrate remobilized copper. Collectively, the investigated oxide and sulfide proxies provide robust discriminants for separating magmatic versus hydrothermal domains and for vectoring toward higher-temperature feeders and zones of remobilized copper. Full article

Skarn deposits, as one of the most widespread ore deposit types, commonly contain economically subordinate Co, which can locally reach ore-grade concentrations in arsenide and sulfarsenide minerals. However, the partition behavior of Co during skarn mineralization and the key physicochemical factors governing its enrichment remain unclear. The Haisi Fe-Co deposit in the eastern segment of the East Kunlun Orogenic Belt is an ideal case for understanding Co mineralizing processes. Based on mineral paragenesis and texture observation, the chemical compositions of magnetite and Fe, Co-, and As- mineral phases were obtained using the EPMA and LA-ICPMS methods. Low Co concentrations (<7 ppm) in magnetite suggest a low partition coefficient of magnetite relative to skarn fluids. During the sulfide stage, abundant glaucodot, alloclasite, cobaltite, and Co-rich arsenopyrite were formed, following earlier native bismuth, safflorite, and löllingite mineralization. The observed paragenetic evolution from diarsenides to sulfarsenides likely records a progressive increase in oxygen fugacity (fO₂) and an increase in the S/As ratio of ore-forming fluids. Thermodynamic modeling using CHNOSZ corroborates that the continuous increase in fO₂ and sulfur fugacity (fS₂), coupled with a possible decrease in pH, promoted the sequential precipitation of diarsenides, sulfarsenides, and ultimately sulfides. These findings imply that dynamic redox and sulfur activity gradients are critical drivers for Co concentration in skarn systems. Full article

The Yawan gold deposit, located in the Western Qinling Orogen, contains gold mineralisation that is predominantly controlled by approximately east-west-trending fault systems. This study integrates field geology, petrography, cathodoluminescence imaging, electron probe microanalysis of gold-bearing minerals (pyrite and arsenopyrite), and in situ laser ablation U-Pb dating of calcite to constrain the timing of mineralisation and to elucidate the mechanisms of gold enrichment. This study reveals that the deposit is significantly structurally controlled and comprises two discrete mineralisation stages: a quartz-pyrite (Py1)-arsenopyrite (Apy1)-chalcopyrite assemblage (Stage 1), and a quartz-calcite-pyrite (Py2)-arsenopyrite (Apy2)-stibnite-sphalerite-galena assemblage (Stage 2). Py1 displays distinct zonation, with rim As contents notably higher than core values, while Co and Ni contents gradually decrease from core to rim. Py2 is characterised by high As (0.00%–4.72%), low Fe/S ratios, and a porous texture, containing gold and arsenopyrite inclusions. Invisible gold occurs in lattice-bound form in both Py1 and Py2. The As-Fe-S ternary diagram of pyrite indicates that Au⁺ likely entered the crystal lattice as a solid solution. Arsenopyrite geothermometry yields a mineralisation temperature of 389 ± 44 °C, and sulfur fugacity (ƒS₂) decreased markedly from Stage 1 to Stage 2. Combined with the S and Fe characteristics of pyrite, these features support a medium-temperature metamorphic hydrothermal environment. U-Pb dating of calcite from Stage 2 yields an age of 215.6 ± 7.1 Ma. In summary, the Yawan gold deposit belongs to the orogenic gold system, with its gold precipitation and enrichment controlled by sulfidation triggered by Late Triassic tectono-fluid activity. Full article

The Yixingzhai deposit is a giant gold system containing four cryptovolcanic breccia pipes, several of which host significant porphyry-type gold orebodies at depth. A key exploration target is the Tietangdong cryptovolcanic breccia pipe, characterized by skarn alteration in its upper zones. However, the evolution of early hydrothermal fluids and their implications for gold enrichment potential remain poorly understood. This study employs an integrated approach—combining petrography, electron probe microanalysis, laser ablation-inductively coupled plasma–mass spectrometry (LA-ICP-MS), and LA-ICP-MS elemental mapping—to analyze zoned garnets within the Tietangdong skarn, with the aim of deciphering changes in magmatic–hydrothermal composition and physicochemical conditions, as well as their influence on gold enrichment. Textural and compositional data reveal three distinct generations of garnets. Garnets from generations I and III consist of a grossular–andradite solid solution and commonly exhibits optical anisotropy. In contrast, generation II garnet is predominantly andraditic and optically homogeneous. LA-ICP-MS elemental mapping of generations I and III indicates that both generations contain significant Al and Fe, with their optical anisotropy attributed to a high degree of Fe³⁺/Al³⁺ cationic ordering. Compared to generations I and III, generation II garnet displays distinct geochemical characteristics, including enrichment in Fe, As, Sn, W, and U, patterns enriched in light rare earth elements, a positive Eu anomaly, and a wide range of Y/Ho ratios. Garnets from generations I and III crystallized under relatively high-pressure, high-temperature, and low-oxygen fugacity conditions, whereas generation II garnets formed under lower pressure–temperature conditions and higher oxygen fugacity. Moreover, concentrations of Co, Ni, and Cu increase systematically from generation I to generation III. We interpret the sharp compositional break at generation II as recording of the pulsed injection of magmatic–hydrothermal fluids, which enhanced the potential for gold mineralization. The zoning patterns in garnet provide a robust record of the temporal evolution of physicochemical conditions and fluid composition in the hydrothermal system. Full article

Sulfide geochemistry has been widely employed to constrain formation processes in various deposit types; however, its use in porphyry W-Mo metallogenic systems is still relatively scarce. The Sansheng porphyry W-Mo deposit (Mo 24,361 t @ 0.226% and WO₃ 17,285 t @ 0.569%), situated in eastern Inner Mongolia, northeastern China, features with quartz vein and veinlet-disseminated W-Mo orebodies primarily localized within the cupolas of an Early Cretaceous granitic intrusion. This contribution provides a comprehensive analysis of the deposit’s geology, in situ sulfur isotopic signatures, and geochemical characteristics of wolframite and sulfides to decipher the formation of the Sansheng deposit. A narrow δ³⁴S range (2.15‰–7.14‰) for sulfides, consistent Y/Ho (5.09–6.23) and Nb/Ta (7.20–19.96) ratios in wolframite, and pyrite Co/Ni (1–10) and As/Ni (>10) ratios collectively point to a shared source—the highly fractionated Sansheng granitic magma. Wolframite, pyrite, arsenopyrite, and chalcopyrite all host significant trace elements, though their enrichment patterns differ considerably among these minerals. Temporal variations in trace element concentrations in wolframite and sulfides reveal a decline in fluid temperature and oxygen fugacity from early to late stages. Greisenization is associated with tungsten mineralization, whereas sericitization facilitates Stage III sulfide precipitation. Full article

A large, low-grade Fe–Ti–V oxide deposit occurs within the Xiaohaizi Ultramafic–Mafic intrusion. Based on petrographic observations and electron probe microanalysis (EPMA) of amphibole, this study examines the magmatic evolution and ore-forming processes of the intrusion through analyses of amphibole occurrence, mineral chemistry, and crystallization conditions. Five textural types of amphibole were identified: (i) inclusions, (ii) co-crystallization with early silicates, (iii) reaction rims, (iv) co-crystallization with late Fe–Ti oxides, and (v) phenocrysts. The amphiboles are calcic varieties, mainly composed of magnesio-hastingsite, kaersutite, and tschermakite. Crystallization occurred at temperatures of 901–1013 °C and pressures of 254–424 MPa, with ΔNNO values ranging from −1.3 to +2.8 and estimated melt H₂O contents of 3.3–7.1 wt.%, corresponding to crystallization depths of 9.6–16.0 km. Importantly, the crystallization interval of the Fe–Ti oxides is defined by these amphibole-assemblage conditions, as evidenced by their direct intergrowth. Integration of mineralogical and geochemical data indicates that the Xiaohaizi intrusion underwent four distinct stages of magmatic evolution. During these stages, the crystallization of Fe–Ti oxides was accompanied by notable fluctuations in oxygen fugacity and melt water content. These results suggest that fractional crystallization played a dominant role in ore formation, with possible late-stage liquid immiscibility observed at the mineral scale. Overall, this study proposes that the Xiaohaizi Fe–Ti–V oxide deposit represents a magmatic conduit-type ore-forming system developed within a crystal mush. The enrichment of Fe–Ti oxides is strongly associated with hydrous melts and elevated oxygen fugacity conditions. Full article

The processes responsible for high-grade disseminated gold mineralization remain poorly constrained, hindering effective exploration. This study integrates petrography, BPMA, and LA-ICP-MS analysis of magnetite from marble- and granite-hosted ores with contrasting gold grades, to constrain wall-rock-induced changes in the thermodynamic environment. BPMA results show distinct mineral assemblages: granite-hosted ores are characterized by quartz (52.31%)-K-feldspar (19.65%)-sericite (9.56%)-pyrite (8.36%), whereas marble-hosted ores feature pyrrhotite (33.90%)-chlorite (27.50%)-pyrite (15.22%)-magnetite (1.94%). The closed intergrowths of magnetite with gold and sulfides, along with the magnetite Ga-V (Grant-Vaughan) discrimination diagram, indicate a hydrothermal origin for magnetite formed during the mineralization stage. Geochemical data show that marble-hosted magnetite has lower V and chalcophile element (Co, Ni, Sn, Zn) concentrations than granite-hosted magnetite. Considering the partitioning behavior of these elements in magnetite, these differences indicate magnetite crystallization under increasing oxygen fugacity (fO₂) and decreasing sulfur fugacity (fS₂). Thermodynamic modeling results demonstrate that these changes in fO₂ and fS₂ destabilized gold-sulfur complexes in the ore-forming fluid, significantly enhancing gold precipitation efficiency and ultimately leading to the formation of high-grade ores in marble. Full article

The Evevpenta gold–silver epithermal deposit, belonging to an adularia–sericite or low-sulfidation type, is in the northern part of the Kamchatka Peninsula within the Oligocene–Quaternary Central Kamchatka volcanic belt. Variously native gold, silver, and Au–Ag chalcogenides, including calaverite, petzite, hessite, acanthite, uytenbogaardtite-petrovskaite, and naumannite, constitute its Au–Ag mineralization. Extensive fluid inclusion studies, involving fluid inclusion petrography, Raman spectroscopy, and microthermometry, revealed that quartz from gold-bearing adularia–quartz veins crystallized from low-salinity fluids (T ice melting from −0.1 to −3.3 °C) at moderate to low temperatures (140 to 364 °C). The mineralizing fluids consisted of Na, K, and Mg sulfate and bicarbonate-bearing aqueous solutions and low-density CO₂. The gold-bearing mineral assemblages were formed within narrower temperature ranges. The gold–telluride–quartz assemblage was deposited between 325 and 175 °C, while the telluride–sulfide–quartz formed between 219 and 258 °C. Possible influx of meteoric waters led to progressive cooling and a decrease in salinity from the early to late fluid generations during mineral deposition. Overall data on ore and associated with metasomatic alteration mineralogy indicate that the ore formation occurred under relatively reduced or neutral conditions from weakly acidic to near-neutral aqueous solutions, possessing relatively high sulfur and tellurium fugacity. Full article

Gallium (Ga) enrichment in sphalerite has been widely recognized; however, its enrichment mechanisms remain insufficiently understood. The South Hunan district, located at the intersection of the Nanling Region and the Qin-Hang Metallogenic Belt in South China, is characterized by abundant Jurassic magmatic-hydrothermal Pb–Zn deposits, which typically host Ga-depleted sphalerite. Recently, Ga-enriched sphalerite (up to 385 ppm by LA-ICP-MS) has been identified in newly drilled cores at Zhaojinci, adding complexity to the regional Pb–Zn metallogenic framework. EPMA elemental mapping and LA-ICP-MS time-resolved spectra indicate that Ga is homogeneously distributed within sphalerite, excluding the presence of micron-scale Ga-bearing mineral inclusions. A strong positive correlation between Ga and Cu concentrations suggests that Ga incorporation is facilitated by the coupled substitution of Zn²⁺ by Cu⁺. Sphalerite geothermometry yields formation temperatures of 118–138 °C (average 126 °C for GGIMF is and ~129 °C for SPRFT), accompanied by intermediate sulfur fugacity conditions (lg fS₂ = −22.9 to −21.2), which appear to favor Ga enrichment in sphalerite. The trace element geochemistry of the Zhaojinci sphalerite (Ga-Ge-Cd-enriched and Mn-In-Sn-Co-depleted), combined with its formation under low-temperature (120–180 °C) and intermediate fS₂ conditions (within the pyrite stability field), is consistent with MVT-like mineralization. This interpretation is supported by multiple lines of geological evidence, including the strict confinement of stratabound Pb–Zn mineralization to the Devonian Xikuangshan Formation limestone, structural control by syn-sedimentary normal faults, pervasive dolomitization of the host rocks, and the absence of genetic relationship to magmatic activity. Moreover, the sphalerite geochemical signature, corroborated by an XGBoost-based machine learning classifier, reinforce the MVT-like affinity for the Zhaojinci mineralization. This study not only emphasizes the importance of low-temperature and intermediate-fS₂ conditions in Ga enrichment within sphalerite, but also highlights the significance of discovering MVT-like sphalerite for Pb–Zn resource exploration in the South Hunan district, providing valuable new insights and directions for mineral prospecting in this geologically important region of South China. Full article

Skarn-type iron ore is economically significant, and numerous skarn ore deposits have been identified in the North China Craton. The newly discovered orbicular diorite in this region is distinguished from other analogous rocks due to the accumulation of large magnetite particles, which may shed new light on the genesis of this ore type. The magnetite in different parts of the orbicular structure exhibits distinct compositional differences. For example, magnetite at the edge has a small particle size (200 μm) and is associated with the minerals plagioclase and hornblende, indicating that it crystallized from normal diorite magma. By contrast, magnetite in the core has a relatively large particle size (>1000 μm), is associated with apatite and actinolite, and contains apatite inclusions as well as numerous pores. The size of magnetite in the mantle falls between that of the edge and the core. The syngenetic minerals of magnetite in the mantle include epidote and plagioclase. The magnetites in the cores of orbicules have a higher content of Ti, Al, Ni, Cr, Sc, Zn, Co, Ga, and Nb than those in the rim. The δ⁵⁶Fe value of the core magnetite (0.46‰–0.78‰) is much higher than that of the mantle and rim magnetite in orbicules. Moreover, the δ⁵⁶Fe value of magnetite increases as the V content of magnetite gradually decreases. This large iron isotope fractionation is likely driven by liquid immiscibility that forms iron-rich melts under high oxygen fugacity. The reaction between magma and carbonate xenoliths (Ca, Mg)CO₃ during magma migration generates abundant CO₂, which significantly increases the oxygen fugacity of the magmatic system. Under the action of CO₂ and other volatile components, liquid immiscibility occurs in the magma chamber, and Fe-rich oxide melts are formed by the melting of carbonate xenoliths. Iron oxides (Fe₃O₄/Fe₂O₃₎ will crystallize close to the liquidus due to high oxygen fugacity. These characteristics of magnetite in the Tanling orbicular diorite (Wuan, China) indicate that diorite magma reacts with carbonate xenoliths to form “Fe-rich melts”, and skarn iron deposits are probably formed by the reaction of intermediate-basic magma with carbonate rocks that generate such “Fe-rich melts”. A possible reaction is as follows: diorite magma + carbonate → (magnetite-actinolite-apatite) + garnet + epidote + feldspar + hornblende + CO₂↑. Full article

A solubility model of SO₂ in multi-ion electrolyte solutions has been developed by the activity-fugacity relation at vapor-liquid equilibria. The fugacity coefficient of SO₂ in the vapor phase is calculated by the equation of state (EOS) of pure SO₂, and the activity coefficient of SO₂ in the liquid phase is calculated by the Pitzer activity coefficient theory. The model can reproduce the reliable solubility data of SO₂ in pure water and multi-ion electrolyte solutions (Na⁺, K⁺, Cl⁻, ${\mathrm{SO}}_4^{2-}$) within or close to experimental uncertainties. Although the second-order and third-order interaction parameters between SO₂ and Mg²⁺ and Ca²⁺ have been adopted by an approximation, the solubility model can also be extended to predict the SO₂ solubility in seawater. In addition, combining with the EOS of a CO₂-SO₂ fluid mixture, the model can be used to predict the solubility of a CO₂-SO₂ mixture in aqueous electrolyte solutions. The calculated results are consistent with experimental data, which indicates that the solubility model has certain predictive ability. Full article