Search Results (327)

Hydrothermal cobalt (Co) deposits are a significant source of Co; however, the sources of Co and hydrothermal fluids for such deposits remain poorly understood. This study addresses this issue through an investigation of the geology, mineralogy, and in situ sulfur isotopes of the Qibaoshan Co-Pb-Zn-Cu deposit, a typical hydrothermal Co deposit in South China, to constrain the occurrence of Co and the sources of Co and hydrothermal fluids. Detailed scanning electron microscopy (SEM), TESCAN Integrated Mineral Analyzer (TIMA), and electron microprobe (EPMA) mapping analyses reveal that Co in the Qibaoshan deposit occurs predominantly as Co-bearing minerals in veinlet mineralization, mainly including cobaltite, skutterudite, and smaltite. EPMA elemental mappings reveal that cobaltite grains commonly show a compositional evolution from Ni-S-rich and As-Fe-poor cores to As-Fe-rich and Ni-S-poor rims. This evolution indicates a decrease in fluid temperature and Ni content, coupled with an increase in the As/S ratio during ore-forming processes. In situ S isotope analyses of various sulfides (pyrite, chalcopyrite, sphalerite, galena, and arsenopyrite) yield a wide range of δ³⁴S_V-CDT values from 0.24‰ to 19.08‰, with two dominant clusters at 2–5‰ and 15–17‰. This suggests two end-member sources for sulfur and hydrothermal fluids in the Qibaoshan deposit: magmatic and sedimentary sources. Arsenopyrite, which is closely associated with Co minerals, yields δ³⁴S_V-CDT values ranging from 2.17‰ to 5.99‰, pointing to a magmatic origin for Co in the Qibaoshan deposit. The Pb-Zn and Cu mineralization of the deposit was also likely mainly derived from magmatic sources, with the incorporation of sedimentary sulfur and fluids during the ore-forming processes. This study demonstrates that magmatic–hydrothermal fluids derived from depth can serve as sources of Co, even in hydrothermal deposits where no magmatic rock is exposed, which provides crucial implications for the metallogenic models and mineral exploration of hydrothermal Co deposits. Full article

The Nanping pegmatite-type Nb-Ta deposit is one of the large-scale Li-Cs-Ta (LCT)-type pegmatite deposits in Southeast China. Nevertheless, the mineralization mechanism of this ore deposit remains unclear, primarily due to the lack of systematic research on the characteristics of ore-forming fluids and mineralization processes. To address this issue, analyses of the fluid inclusion characteristics, hydrogen–oxygen isotope compositions and in situ U-Pb geochronology of Nb-Ta minerals were performed on the No. 31 vein of the Nanping pegmatite deposit. In situ U-Pb dating of the Nb-Ta minerals with varying textures from different zones yields main mineralization ages clustered between 390 and 370 Ma, along with isolated younger ages around 270 Ma in specific mineral zones, indicating multiple mineralization episodes. The fluid inclusion homogenization temperatures of different zones range from 130 to 382 °C, and salinities between 2 and 16 wt% NaCl eqv, consistent with a medium-to-low temperature and salinity fluid system. Hydrogen and oxygen isotope data show that the ore-forming fluids were predominantly derived from magmatic fluids, mixed with later meteoric waters. This study clarifies the multistage mineralization history and fluid evolution of the Nanping pegmatite-type Nb-Ta deposit, providing key constraints for metallogenic models of pegmatite-hosted rare-metal deposits. Full article

The Kocayayla Pb–Zn ± Cu vein-type mineralization is located in the Biga Peninsula, northwestern Türkiye. This study aims to constrain the geological, geochemical, and isotopic characteristics of the mineralization and to clarify its genetic classification. The deposit is hosted mainly by andesitic and basaltic andesitic rocks as well as schists and is structurally controlled by E–W-trending strike-slip faults. Mineralogical and petrographic identifications, XRD analyses, whole-rock geochemistry, and sulfur isotope data were integrated to evaluate ore-forming processes. Mineralization is temporally and spatially associated with propylitic and phyllic to argillic alteration and is concentrated within zones of intense silicification and chloritization, accompanied by quartz, sericite, kaolinite/nacrite, chlorite, and carbonate assemblages. The ore assemblage is dominated by galena, sphalerite, and subordinate chalcopyrite, with minor fahlore-group minerals. Rare earth element patterns of ore samples (whole rock) overlap with those of the wall rocks, whereas Pb–Zn enrichment reflects selective hydrothermal metal transport. Sulfur isotope compositions show limited internal variation and indicate sulfur derived predominantly from H₂S-dominated magmatic–hydrothermal fluids. Regional comparison of δ³⁴S datasets and reported Au contents across the Biga Peninsula indicates that Au-rich intermediate-sulfidation epithermal systems exhibit broader and more variable sulfur isotope ranges, whereas Au-poor intermediate-sulfidation epithermal systems show relatively restricted and near-zero δ³⁴S values. These features collectively support the classification of the Kocayayla mineralization as an Au-poor intermediate-sulfidation epithermal Pb–Zn system. Full article

The physicochemical controls on gold precipitation in orogenic gold deposits remain poorly constrained, with traditional fluid inclusion and isotopic studies often yielding ambiguous results due to overprinting or incomplete records. This study addresses this challenge using chlorite—a sensitive mineral proxy for fluid conditions—as a quantitative sensor in the Jinshan orogenic gold deposit (>200 t Au) of the Jiangnan orogenic belt, South China. Hosted in Neoproterozoic phyllite within NE–NNE-trending ductile–brittle shear zones, Jinshan features auriferous quartz–polymetallic sulfide veins with prominent chlorite alteration. Integrating high-resolution SEM-EPMA analyses of multi-generational chlorite with thermodynamic modeling, we reconstruct the temporal evolution of temperature, oxygen fugacity (fO₂), pH and sulfur fugacity (fS₂) during ore formation. Four paragenetic stages are identified: Stage 1 (ankerite–quartz), Stage 2 (pyrite–arsenopyrite–quartz), Stage 3 (quartz–gold–polymetallic sulfide), and Stage 4 (chlorite–carbonate–quartz). Electron microprobe analysis reveals that the chlorite composition changes from Fe-rich chamosite (Stage 2) to Mg-rich clinochlore (Stage 3) and then to Fe-rich chamosite (Stage 4). Chlorite from Stage 2 (Chl-1) formed metasomatically at low fluid/rock ratios, while Stage 3 and 4 chlorites (Chl-2 and Chl-3) precipitated directly from higher fluid/rock ratio fluids. Chlorite compositions record a critical Stage 2–3 transition involving cooling from ~320 °C to ~260 °C, reduction (log fO₂ from −33.6 to −39.7), and alkalinization, and sulfur fugacity remained stable within a narrow range (log fS₂ = −13.6 to −8.0), followed in Stage 4 by minor reheating to ~280 °C, re-acidification, and a slight rebound in oxygen fugacity. Thermodynamic simulations reveal that the destabilization of Au(HS)₂⁻ complexes, primarily driven by the synergistic effects of cooling, pH increase, and decreasing oxygen fugacity, triggered gold precipitation during the main ore stage. Results demonstrate that abrupt cooling coupled with fluid alkalinization and reduction exerted the dominant control on gold precipitation in Jinshan, resolving long-standing debates on ore-forming mechanisms and highlighting chlorite as a robust quantitative sensor for fluid evolution. Full article

The North China Craton (NCC) hosts numerous world-class Au deposits and these Au deposits can be classified into the Au-only and Ag-Au polymetallics, respectively. The former is mostly located in the eastern NCC, such as in the giant Jiaodong Province, and the latter is mostly distributed along the northern and southern margins of the NCC. Compared with Au-only deposits, the ore genesis of the Ag-Au deposits remains controversial. This paper focuses on the Niujuan Ag-Au deposit in the Fengning ore cluster of the northern margin of the NCC. Detailed deposit geology investigation, texture analysis, and analyses of the in situ trace element and sulfur isotope compositions of pyrite, coupled with H-O isotope compositions of quartz from different stages, were conducted to elucidate the ore-forming processes and metal sources. The results showed that the formation of the Niujuan deposit can be divided into four stages, including a pre-ore siliceous breccia stage (stage 1), syn-ore quartz-pyrite stage (stage 2), syn-ore polymetallic sulfide stage (stage 3), and post-ore fluorite-calcite stage (stage 4). Among these, stage 3 represents the major Ag-Au mineralization stage. Pyrite is well developed within stage 2 and stage 3, representing the intensive sulfidation of the wall rock. Microscopic analytical techniques including gamma-enhanced reflected light and scanning electron microscopy backscattered electron (BSE) reveal that pyrite samples from stage 2 and stage 3 have distinct textures. Pyrite (Py1) from stage 2 is homogeneous but with numerous pores. In contrast, pyrite (Py2) from stage 3 has overgrowth textures, and be divided into three sub-stages from core to rim (Py2a, Py2b, and Py2c) with different BSE brightness levels. LA-ICP-MS trace elements analyses results show that these different stages of pyrite show different composition such as Au, As, Ag, Co, and Ni. Py1 has low Au and Ag concentrations ranging from <0.1 ppm to 0.02 ppm and <0.1 ppm to 21.8 ppm, respectively. Py2a has low Au and Ag concentrations ranging from <0.1 ppm to 0.4 ppm and 0.4 ppm to 118.4 ppm, respectively. Py2b is characterized by high As and low Au contents, with average values of 6670.8 ppm for As and 1.4 ppm for Au. Py2c shows relatively low Co and Ni concentrations ranging from 0.02 ppm to 255.2 ppm and <0.1 ppm to 9.9 ppm, respectively. The sulfur isotope composition of Py1 and Py2 is relatively consistent, ranging from 3.8‰ to 6.7‰. The H and O isotope compositions of quartz from stage 1, stage 2, and stage 3 have insignificant variations, ranging from −119.5‰ to −101.3‰ for δD and −6.8‰ to −3.7‰ for δ¹⁸O_fluid, respectively. The results show that sulfur and, possibly, Au and Ag were mainly derived from magmatic hydrothermal fluids, and a significant amount of meteoric water was involved. Combined with the published mineralizing ages (~140 Ma), this paper suggests that the Niujuan Ag-Au deposit formed during the Early Cretaceous under an extensional setting in response to the eastward retreating subduction of the Paleo-Pacific oceanic plate. Evidence from deposit geology and geochemistry reveals that the mixture of magmatic and meteoric water, together with intensive sulfidation, is the key factor controlling Au and Ag deposition. Full article

The Maoniuping deposit, recognized as the world’s third-largest light rare earth (LREE) deposit, is characterized by exceptional ore-forming conditions and considerable exploration potential. Based on systematic mineralogical investigations of chevkinite, allanite, and bastnäsite, this paper synthesizes the trace elements and rare-earth element (REE) geochemical characteristics of these minerals to elucidate their enrichment mechanisms and metallogenic processes. The results reveal a crystallization sequence of chevkinite → allanite → bastnäsite, accompanied by a progressive decrease in the content of Nb, Ta, Zr, Hf, Sr, and Ba. This trend indicates continuous magmatic–hydrothermal evolution of the ore-forming fluids. REE enrichment exhibits distinct stages: early-stage enrichment of HREE, mid-stage enrichment of Ce, Pr, and Nd, and late-stage dominance of La. For chevkinite (δCe = 0.98–1.11, avg. 1.05; δEu = 0.75–0.87, avg. 0.82) and bastnäsite (δCe = 0.81–1.15, avg. 0.88; δEu = 0.58–0.79, avg. 0.66), the evolution process of the continuous increase in oxygen fugacity within the metallogenic system is recorded. The low-temperature, high-oxygen fugacity environment facilitates the incorporation of LREEs into bastnäsite lattices, enabling the formation of large-scale REE ore bodies at structurally favorable positions. These findings provide direct mineralogical evidence for understanding REE enrichment mechanisms in alkaline magmatic–hydrothermal systems and offer crucial insights for metallogenic process inversion and exploration assessment of analogous REE deposits. Full article

The Bagenheigqier medium-sized Pb-Zn deposit is located in central-southern segment of Great Xing’an Range, northeastern China, where its vein-type orebodies are hosted within the structural contact zone between the Lower Permian Dashi Formation and granite porphyry intrusions. Five mineralization stages are divided into skarn (I), oxide (II), quartz-pyrite-arsenopyrite (III), quartz-polymetallic sulfide (IV), and quartz-calcite-pyrite (V). Three types of fluid inclusions (FIs) are identified in Bagenheigeqier Pb-Zn deposit, including daughter mineral-bearing three-phase (SL-type), vapor–liquid two-phase (VL-type), and vapor-rich two-phase (LV-type) FIs. All FI types occur in Stages I–III, with homogenization temperatures (Th) of 423–486, 389–441, 362–408 °C, and salinities of 1.1–49.2, 0.9–43.9 and 0.9–38.8 wt.% NaCl equiv, respectively. Stage IV hosts only VL- and LV-type FIs (Th: 277–319 °C; salinity: 2.1–8.7 wt.% NaCl equiv), whereas Stage V contains exclusively VL-type FIs with Th of 173–214 °C and salinity of 1.2–5.7 wt.% NaCl equiv. The H-O isotopic results of quartz in stage II–IV (δD = −103.5‰–−99.1‰, −115.7‰–−107.8‰ and −121.5‰–−117.2‰; δ¹⁸O_H2O = 4.4‰–7.1‰, 1.1‰–3.5‰ and −4.6‰–−3.5‰) indicate the ore-forming fluids are predominantly of magmatic origin with subordinate meteoric water mixing. Fluid boiling and the mixing of meteoric water may lead to the precipitation of metal. The in situ trace elements analyses indicate that sphalerites in main mineralization stage are enriched in Fe, Mn, Co and In and depleted in Ga and Ge. The calculation results suggest that the sphalerites crystallized under moderate temperature conditions (286–330 °C) and intermediate f_S2 (−10.5 to −9.2) conditions. The geological, fluid inclusion, isotopic and trace element evidences indicate that the Bagenheigeqier deposit is classified as a skarn-type deposit. Full article

This text systematically investigates the Laotudingzi monzogranite (a gold-hosting intrusion) and the Dongbaligou gold ore deposit in the Laoling gold ore belt through comprehensive geochronological, whole-rock geochemical (macroelement and microelement), strontium-neodymium-lead-hafnium isotopic and in situ sulfur-lead isotopic analysis of pyrite, combined with hydrogen-oxygen isotopic studies of hydrothermal quartz. The results demonstrate a significant Early–Middle Jurassic magmatic-mineralization event in southern Jilin Province (Ji’nan). The gold mine is structurally controlled by detachment fractures within the Laoling metamorphic core complex, which developed in an extended environment. The metallogenic materials are primarily derived from adakitic magma, supporting a “decratonic-type” genetic model. By integrating geochronological, geochemical, and isotopic datasets from the ore-related intrusions and gold deposits, as well as fluid inclusion characteristics, we elucidate the metallogenic mechanism linking Jurassic gold mineralization to subduction-related cratonic destruction. The process involved lower crustal thickening induced by Paleo-Pacific Plate subduction, lithospheric destabilization via gravitational foundering and delamination, and syn-extensional magmatism that sourced ore-forming fluids during cratonic lithosphere thinning. This work establishes a genetic framework connecting plate subduction, lithospheric removal, and gold endowment in convergent margin settings. Full article

The Xiaotunxiang deposit, a newly discovered large-scale fluorite resource (1.28 Mt ore reserves) in southwestern Guizhou Province, China, provides a critical case study for understanding fluorite mineralization in the region. To constrain its genesis, this study integrates detailed ore deposit geology with mineralogy, trace element geochemistry, and strontium isotope analysis of fluorite. The ore mineral assemblage is dominated by fluorite, quartz, and calcite, with minor amounts of barite and pyrite. Trace element data reveal significant enrichment in Ti, Cr, Mo, and Sb relative to the upper continental crust. Fluorite exhibits moderate total REE contents (26.8–138 ppm), slight heavy REE enrichment (ΣLREE/ΣHREE = 0.17–1.88), pronounced negative Ce anomalies (δCe = 0.59–0.72), and negligible Eu anomalies (δEu = 0.95–1.14). These geochemical signatures are closely comparable to those of nearby fluorite deposits (Qinglong, Gaoling, and Getang), indicating a shared source of ore-forming materials. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr = 0.707468–0.707682) are consistent with local carbonate wall rocks, confirming their role as the primary source of calcium. We conclude that the Xiaotunxiang deposit formed from a low-temperature hydrothermal system where fluorine and associated metals were likely sourced from the Emeishan basalts, while calcium was derived from the interaction of acidic fluids with carbonate host rocks. Precipitation was ultimately triggered by fluid–rock (water/rock) interaction, classifying Xiaotunxiang as a carbonate-hosted hydrothermal deposit. Full article

The Zhunuo ore district, at the western end of the Gangdese porphyry Cu belt, hosts significant Cu mineralization and newly recognized W mineralization dominated by scheelite. However, the genetic relationship between scheelite and porphyry mineralization, and the evolution of ore-forming fluids remain poorly constrained. To address this, scheelite samples from multiple locations were analyzed for major elements (EMPA), in situ trace elements (LA-ICP-MS), and internal textures (cathodoluminescence, CL). These data, combined with machine learning methods, were used to determine scheelite genetic types and reconstruct fluid evolution. REE patterns and CL textures reveal three scheelite generations in Yalongri (early Sch I c, middle Sch I b, late Sch I a), two in Zhigunong (early Sch II a, late Sch II b), and one in Xiongbaxi (Sch III). Low Na (0–329 ppm) and Nb (3.9–39 ppm) relative to high ΣREE + Y-Eu (16–3857 ppm), indicate that the dominant substitution mechanism is 3Ca²⁺ = 2REE³⁺ + □Ca (□Ca = Ca vacancy). δEu values > 1 in Sch I a, Sch I b, Sch II a, and Sch II b indicate reducing fluids, whereas δEu < in Sch I c and Sch III reflects oxidizing conditions. Variations in REE, Mo, and Sr contents suggest that ore-forming fluids in Yalongri evolved from oxidizing to reducing conditions, with late-stage scheelite undergoing dissolution–reprecipitation. Zhigunong records two reducing stages: an early REE-rich-Mo-poor stage and a later REE-poor-Mo-rich stage. Xiongbaxi records a single oxidizing, REE-rich, Mo-rich stage. Scheelite exhibits low-to-moderate Sr/Mo ratios (0.02–6.10), consistent with a magmatic–hydrothermal origin, and relatively uniform Y/Ho ratios (12–59) indicating stable crystallization conditions. A Random Forest model classifies scheelite into orogenic, porphyry, skarn, and greisen types. Overall, the results indicate that ore-forming fluids evolved from oxidizing to reducing conditions, favoring metal transport and enrichment. Integrated geochemical and machine learning evidence suggest, strong potential for porphyry-type Cu-W(-Mo) mineralization in Yalongri and Zhigunong, and skarn-type W-Mo mineralization in Xiongbaxi, providing important guidance for future exploration in the western Gangdese metallogenic belt. 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

This study investigates the genesis of gold mineralization at the Rodruin prospect in the central Eastern Desert (CED) of Egypt, with the aim of constraining the relative contributions of metamorphic and magmatic fluids to ore formation. Gold mineralization at Rodruin is hosted by quartz–carbonate veins emplaced within a shear zone that transects low-grade metasedimentary sequences intruded by Ediacaran post-tectonic granitoids. It exhibits characteristics transitional between orogenic turbidite-hosted and polymetallic vein-type mineralization. Although metamorphic devolatilization is interpreted to have generated the dominant ore-forming fluids, adjacent granitoid intrusions acted primarily as a thermal engine, with only a limited direct input of magmatic-hydrothermal fluids. This interpretation is supported by the occurrence of magmatic-affiliated mineral inclusions (monazite, cassiterite, and zircon) coupled with generally low concentrations of trace elements typically enriched in granitic magmatic-hydrothermal fluids (Sb, Bi, Mo, W, Sn, Nb, and Ta), collectively indicating a subordinate magmatic contribution. Rare earth element (REE) patterns of the ore samples closely resemble those of the nearby granitoids, displaying LREE enrichment; however, a distinct positive Eu anomaly is restricted to the ore assemblages and is attributed to hydrothermal feldspar alteration supporting magmatic involvement in ore formation. Carbon and oxygen isotope compositions (δ¹³C = −6.6 to −2.36‰; δ¹⁸O = +15.7 to +19.7‰), together with REE signatures comparable to primitive mantle values and textural evidence for synchronous sulfide–carbonate precipitation, manifested by rhythmic banding of carbonates and sulfides unequivocally indicate a hydrothermal–metasomatic origin. Collectively, these lines of evidence support a hybrid metamorphic–magmatic model in which gold and associated base metals were predominantly transported by metamorphic fluids, whose mobilization and focusing were enhanced by the thermal influence of Younger granitic intrusions, whereas magmatic-hydrothermal fluids contributed only a minor proportion to the overall metal budget. Full article

The Lanuoma sediment-hosted lead–zinc (Pb–Zn) deposit, situated in the central part of the Sanjiang base metal metallogenic belt (SMB) within the Changdu Basin, is hosted by Triassic Bolila Formation limestone. The source of metals and sulfur (S), as well as the ore-forming processes for the deposits in this belt, are contentious. To constrain the metal and sulfur sources and to define the ore-forming mechanism, we analyzed Zn, Pb, and S isotopes of sphalerite and robinsonite, as well as Zn isotopes of the host limestone and the metamorphic basement. Sphalerite shows homogeneous δ⁶⁶Zn values (−0.31‰ to −0.12‰; mean = −0.20‰). The calculated δ⁶⁶Zn of the ore-forming fluid (~0.00‰) matches that of the Triassic limestone, indicating a sedimentary Zn source (δ⁶⁶Zn = −0.11‰ to −0.09‰; average 0.00‰). Robinsonite displays a wider δ⁶⁶Zn range (−0.22‰ to 0.44‰), reflecting a mixture of sedimentary and metamorphic sources (δ⁶⁶Zn = 0.12‰ to 0.42‰; average 0.22‰). Lead isotopes of sphalerite are uniform (²⁰⁶Pb/²⁰⁴Pb = 19.041–19.079) and indicative of a sedimentary rock source, whereas robinsonite shows wide variation (²⁰⁶Pb/²⁰⁴Pb = 19.070–19.156) and linear trends between low- and high-radiogenic end-members, indicating mixed Pb sources from sedimentary rocks and metamorphic basement. Sulfur isotopic compositions of sulfides (δ³⁴S = −1.4‰ to 2.6‰; mean = −0.1‰) cluster near 0‰, consistent with a deep magmatic origin. A strong linear correlation between ²⁰⁶Pb/²⁰⁴Pb and δ⁶⁶Zn, coupled with a lack of correlation between both ²⁰⁶Pb/²⁰⁴Pb and δ³⁴S and δ⁶⁶Zn and δ³⁴S in the sulfides, indicates that Pb and Zn were derived from a common metal source, whereas sulfur originated from a distinct reservoir. Combined with previously published fluid inclusion, rare earth element, and multi-isotopic constraints, these results suggest that Pb–Zn mineralization at Lanuoma was controlled by a mixing between metal-rich basinal brines and sulfur-rich deep-sourced fluids, leading to sulfide precipitation dominated by open-space filling. This study provides new insights into the genesis and mineralization process of sediment-hosted Pb–Zn deposits in the Sanjiang metallogenic belt. Full article

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