Non-silicate chromian spinel coexisting with the silicates like olivine and pyroxenes in the mantle-related rocks is nominally Si-free, but is expected to contain some Si due to chemical equilibrium. This anticipation has long been verified. How Si enters spinel, what the solubility is, what factors affect the Si-incorporation process, and what the implications are remain largely unexplored though. By performing high-P experiments in the system MgO-Al2O3-SiO2 and examining the literature data in other composition systems, we have found that (1) Si enters spinel via the substitution reaction Si4++ M2+= 2 M3+ (M2+: Mg2+, Fe2+, etc.; M3+: Al3+, Cr3+, etc.); (2) its solubility in spinel coexisting with olivine can reach the level of weight percent, and positively correlates with P, T, and compositional parameters Cr# and Mg# of the spinels; (3) the SiO2 contents of the chromian spinels from various mantle-related rocks of different petrological or tectonic origins can be very different. Interacting with Earth's major elements Mg, Fe, Al and Cr, attaining high levels of abundance for easy quantification, and possessing significantly different abundance variations among spinels from different types of mantle-related rocks, Si in nominally Si-free chromian spinel has the potential to be a powerful petrogenetic probe for the upper mantle.

The Paleoproterozoic banded iron formation (BIF) at Changyi in the eastern North China Craton is a rare example of a Superior-type BIF in China. However, its genesis, depositional age, and tectonic setting remain poorly constrained and highly debated. In this study, we integrated zircon U-Pb geochronology, whole-rock geochemistry, Fe-O isotopes, and P-T phase equilibrium modeling to systematically constrain the formation age, provenance, and depositional environment of the Changyi BIF. Detrital zircon U-Pb geochronology reveals a provenance derived from both Archean cratonic basement (similar to 2.9 Ga and similar to 2.7 Ga) and Paleoproterozoic magmatic materials (similar to 2.45 Ga and similar to 2.2 Ga). The detrital zircon age spectrum shows a distinct peak at similar to 2.45 Ga, providing clear evidence for a major magmatic event of this age in the source region, while the youngest zircon population (2243 Ma) constrains the maximum depositional age of the BIF. The ores are dominated by SiO2 and total Fe2O3 (TFe2O3). The increasing contents of Al2O3 and TiO2 from Type I to Type III ores indicate progressively enhanced detrital input. The REY distribution patterns are characterized by LREE depletion, positive La, Eu, and Y anomalies, and low RREY. Mixing model results indicate that the ore-forming materials were mainly derived from seawater, with minor contributions from high-temperature hydrothermal fluids and continental solutes. Wholerock b18 O values range from 8.8%0 to 10.9%0, with reconstructed original b18 O values between 8.8%0 and 12.25%0. The b18 O values of different ore types are jointly controlled by mineral proportions and the intensity of metamorphic/fluid processes, with Type III ore exhibiting the lowest b18O values, reflecting fluid-rock exchange and isotopic resetting. However, large-scale isotopic homogenization did not occur regionally, and most ores largely preserve their primary oxygen isotope signatures. Iron isotope analysis showed that ore b56Fe values ranged from -0.44%0 to +1.17%0, with predominantly positive values and the highest values in Type III ore. The b56Fe values covaried with Fe3+/(Fe2+ + Fe3+) ratios among different ore types, reflecting fluctuations in redox conditions during deposition and the geochemical response to oceanic oxidation events, providing robust geochemical evidence for the local manifestation of the Great Oxidation Event (GOE) within the depositional basin. Phase equilibrium modeling indicated that the Changyi BIF experienced peak amphibolite-facies metamorphism at 785 degrees C/6.2 kbar, recording an incomplete prograde P-T path indicative of rapid burial and crustal thickening. Collectively, our results support a genetic model in which the Changyi BIF was deposited in a Paleoproterozoic back-arc basin along an active continental margin, demonstrating that such settings can provide transiently stable depositional environments for Superior-type BIF formation. The deposit systematically documents geochemical responses to both global (GOE) and regional (metamorphism) events, providing new constraints on the genesis and paleoenvironmental evolution of BIFs in the eastern North China Craton. (c) 2026 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). Thi s is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Mafic microgranular enclaves (MMEs) are typically considered products of magma mixing, preserving distinct physicochemical signatures relative to their host rocks. In this study, we investigate the Late Cretaceous Huanggang MME-bearing granite pluton in the southern Great Xing'an Range (SRXR) and demonstrate that MMEs share similar crystallization physicochemical conditions with the host granites. Integrated crystallization temperature and pressure calculations, based on in-situ mineral compositions (zircon, apatite, hornblende, and feldspar), reveal overlapping thermal (620-700 degrees C) and pressure (0.05-0.53 GPa) conditions. Despite these similarities, MMEs exhibit higher oxygen fugacity (Delta FMQ =- 0.75 to + 4.84) and water activity (H2Omelt = 3.1-3.8 wt%) compared to host granites (Delta FMQ =- 0.45 to + 2.30, H2Omelt = 2.9-3.3 wt%). These variations suggest MMEs formed under more oxidizing and hydrous melt conditions. Apatite geochemistry shows pronounced fluorine enrichment, with F/Cl ratios (19.2-92.6) and F concentrations (2.56-2.92 wt%) indicating a fluorine-rich source, likely from slab dehydration in subduction zones. While thermobarometric conditions suggest a genetic relationship between MMEs and host granites, differences in redox-sensitive element ratios imply distinct melt evolution pathways. We propose that MMEs formed either from localized mixed melts during the late-stage homogenization of the magma chamber or from the early crystallization of post-mixed melt. This study highlights that MMEs can form both during active melt interaction and subsequent crystallization processes. The subduction of the Paleo-Pacific plate serves as the geodynamic driver for magma mixing in the SGXR, which is also linked to the Early Cretaceous polymetallic metallogenies in this region.

The majority of light rare earth element (LREE) resources are derived from carbonatite-associated deposits at cratonic margins. However, the origin of ore-forming carbonatite magmas remains unclear. Here, we conducted high pressure-temperature experiments to investigate LREE behavior during carbonate-rich sediment recycling. Results show that, during subduction, the calcic carbonates progressively concentrate LREE, becoming the principal LREE carriers and, upon melting at higher pressures, generate LREE-rich melts. As the melts ascend through cratonic lithospheric mantle, precipitation of extremely LREE-poor magnesite induces further enrichment, producing melts with LREE concentrations up to 156 times those of sedimentary carbonates. These melts are comparable to natural ore-forming carbonatites, highlighting that craton-margin lithosphere drives LREE ore-forming carbonatite magmatism. Our global compilation shows that LREE concentrations in carbonatites positively correlate with the associated deposit tonnage, suggesting that ore-forming carbonatites fundamentally control the deposit reserve magnitude. These findings provide a unified framework for the formation and global distribution of carbonatite-hosted deposits at cratonic margins.

The genesis of the Huachanggou gold (Au) deposit in the Qinling orogenic belt has been controversial due to the absence of direct geochronological constraints. To resolve this, we investigated hydrothermal xenotime and monazite occurring in Au-bearing quartz-albite veins and alteration halos, which are texturally and paragenetically coeval with gold mineralization. LA-ICP-MS analyses reveal that these phosphates are MREE-HREE enriched, have low U and Th concentrations, and exhibit subdued Eu anomalies-all diagnostic of a hydrothermal origin. SHRIMP U-Pb dating yields weighted mean 206Pb/238U ages of 208.8 +/- 2.2 Ma and 210.4 +/- 2.4 Ma for xenotime, consistent with the 206.9 +/- 4.0 Ma age for monazite, tightly constraining the gold mineralization to the Late Triassic (ca. 210-207 Ma). This age coincides with a regional compressional event attributed to the final collision between the South Qinling and Yangtze blocks. Our results demonstrate that hydrothermal xenotime-monazite U-Pb chronometry provides a robust and high-temperature geochronometer for orogenic gold systems, overcoming limitations of low-temperature isotopic systems (e.g., Ar-Ar on mica or fuchsite). This approach refines the timing and tectono-metallogenic framework of orogenic gold deposits in the Qinling belt and similar collisional settings.

Early Cretaceous granitoids are widespread in the southern margin of the North China Craton (SNCC), and record geologic information about the regional lithospheric evolution. The Niangniangshan pluton in the Xiaoqinling terrane of the SNCC comprises three lithological phases: (1) medium-grained biotite monzogranite, (2) fine- to medium-grained biotite monzogranite, and (3) fined-grained monzogranite. They have zircon U - Pb ages of 142 - 139 Ma, 135 - 132 Ma and similar to 123 Ma, respectively. Phases 1 and 2 are metaluminous to slightly-peraluminous and high-K calc-alkaline affinity, showing adakite signatures such as high Sr/Y and no Eu anomalies; whilst phase 3 has higher SiO2 content, lower Sr/Y and (La/Yb)(N) ratios, and clear negative Eu anomalies compared to phases 1 and 2. These results, combined with the published data, indicate that phase 1 and 2 were formed by partial melting of the Neoarchean-Paleoproterozoic metamorphic basement within a still-thickened crust, whilst phase 3 was formed from partial melting of the samebasement during lithospheric thinning. This phase-by-phase contrast refines the tectono-magmatic transition from crustal thickening to lithospheric thinning and indicates that crustal thickening in the SNCC has continued to similar to 132 Ma, , whereassubsequent lithospheric thinning had formed the felsic plutons at similar to 123 Ma. The phase 2 magma forming the Niangniangshan pluton is relatively oxidized (log fO(2) = -20.57 to -8.61; Delta FMQ = -2.99 to 6.71), and had favorable conditions for Mo transportation and mineralization. Exploration for porphyry systems in the Xiaoqinling terrane may be limited by poor preservation, because the area underwent similar to 7 km of exhumation during similar to 140-120 Ma, likely strongly eroding the shallow porphyry-style hydrothermal system.

The contributions of mantle plumes to the formation of magmatic nickel–copper–platinum-group element sulfide deposits remain poorly characterized. Here, we assess this ambiguity by utilizing the Hg isotope composition of sulfide ores from the giant Jinchuan deposit and those within the Central Asian Orogenic Belt, which represent magmatic sulfide deposits that formed within intracratonic and orogenic settings, respectively. The Δ199Hg values of the sulfide ores within the Central Asian Orogenic Belt (0.01 ± 0.16‰, 2 SD) and Jinchuan (−0.03 ± 0.11‰, 2 SD) are similar to those of mantle plumes (0.0 ± 0.1‰, 2 SD), but distinctly different from those of metasomatized lithospheric mantle (non-zero). This supports a plume origin for magmatic sulfide deposit formation, regardless of their formation in intracratonic or orogenic settings. These findings help to better understand the genesis of magmatic sulfide deposits in a diversity of tectonic settings and provide new insights into Hg isotope behavior during magmatic sulfide mineralization. Δ199Hg values in Central Asian Orogenic Belt and Jinchuan sulfide ores match mantle plume signatures and differ from metasomatized lithospheric mantle, indicating a mantle plume origin for these deposits, according to Hg isotope analysis of the Ni–Cu PGE ore samples.

The dynamic interplay between melt evolution and fluid activity plays a crucial role in rare metal enrichment in highly fractionated granites, yet the specific mechanisms remain inadequately understood. This study explores the recently discovered Tailaihua Be-Nb-Ta deposit in the southern Great Xing'an Range (SGXR) to elucidate these processes. By integrating monazite U-Pb geochronology, whole-rock geochemistry, and electron probe microanalysis (EPMA) of major minerals, we establish a comprehensive magmatic-hydrothermal evolution sequence and explores the behavioral dynamics of melt-fluid interactions within highly fractionated granitic systems exhibiting Be-Nb-Ta mineralization. LA-ICP-MS U-Pb dating of Tailaihua ore-forming granite yielded ages of 143.4 +/- 1.9 Ma for the monzonitic granite (MG), 142.1 +/- 2.3 Ma for the alkali-feldspathic granite (AFG), and 140.0 +/- 3.0 Ma for the albite granite (AG). The Tailaihua ore-forming granites are characterized by high SiO2, Al2O3, alkalis (K2O + Na2O), and A/CNK ratios (>1.1), with depleted CaO, MgO, FeOT, indicating high-K peraluminous compositions. Trace elements show Rb-Th-U-Ta enrichment and Sr-Ba-Eu depletion, confirming highly fractionated I-type granitic magmas, accompanied by strongly REE tetrad effects. Progressive crystal fractionation of biotite, K-feldspar, and plagioclase within the MG-AFG-AG sequence drove magma evolution. Our key finding reveals that extreme rare metal enrichment resulted from a two-stage process: 1) initial magmatic concentration through fractional crystallization, followed by 2) significant hydrothermal remobilization driven by volatile exsolution (H2O-F), inducing pervasive metasomatism and characteristic REE tetrad effects. This study quantitatively links magma differentiation to ore formation, offering a robust model for exploring similar rare-metal deposits.

The Yunzhongshan (YZS) massif, located in the central Trans-North China Orogen (TNCO), preserves crucial Neoarchean to Paleoproterozoic volcanic records for understanding the tectonic evolution of the North China Craton (NCC), and offers valuable insights into global Archean geodynamic processes. However, the precise magmatic processes and the tectonic setting of these rocks remain contentious. This study presents an integrated investigation of field geology, petrography, whole-rock geochemistry, whole-rock Nd-Hf isotopes, and zircon U–Pb-Hf isotopes for the YZS meta-volcanic rocks. We report crystallization ages of 2516 ± 7 Ma for meta-basalt and 2519 ± 13 Ma for meta-dacite, alongside captured zircon ages of ∼ 2.55 Ga and ∼ 2.70 Ga. The volcanic suite displays significant geochemical diversity, evolving from tholeiitic basalts to calc-alkaline dacites, yet consistently preserves subduction-related signatures (e.g., Nb, Ta depletion) and homogeneous, depleted mantle-like isotopic compositions (εNd(t) = +1.9 to + 4.0; εHf(t) = +5.7 to + 12.2). Petrogenetic analysis and modeling suggest these rocks formed via fractional crystallization transitioning to assimilation fractional crystallization from a slab-fluid-modified depleted mantle source. Critically, the coexistence of arc-like signatures with extensional indicators (flat HREE patterns, high Ti/V ratios) and regional coeval alkaline granites supports a continental back-arc setting. Therefore, we interpret the ∼ 2.52 Ga YZS meta-volcanic rocks as products of a back-arc basin. This study reveals that the YZS magmatism records a pivotal tectonic transition from subduction-driven compression to back-arc extension within the central NCC, providing robust evidence for the operation of modern-style plate tectonic regimes.

The timing, petrogenesis, and tectonic setting of the Paleo-Mesoproterozoic (similar to 1.6 Ga) alkaline magmatism and associated rare earth element (REE) mineralization in the southern North China Craton (SNCC) remain contentious. The Longwangzhuang (LWZ) deposit is a recently discovered REE deposit in the SNCC. It is hosted within the region's largest Late Paleoproterozoic granite pluton, namely the LWZ REE-bearing granite. In this study, we present an integrated study of zircon U-Pb geochronology, whole-rock geochemistry, and Sm-Nd and zircon Lu-Hf isotopes on the LWZ REE-bearing granite. Zircon U-Pb dating yields a crystallization age of 1613 +/- 6 Ma, implying that the pre-enrichment of REEs occurred in the late Paleoproterozoic. The granite exhibits A-type characteristics, including high SiO2, alkalis, and FeOT/(FeOT + MgO) ratios, with strong enrichment in LREEs and strong negative Eu anomalies. Whole-rock epsilon(Nd) (t) values range from -6.2 to -4.9, and zircon epsilon(Hf)(t) values vary from -4.8 to +0.8, indicating derivation primarily from the partial melting of ancient Mesoarchean crustal sources (Taihua Group). Geochemical tectonic discrimination diagrams consistently suggest an intraplate extensional setting. We conclude that the LWZ A-type granite formed during the Columbia supercontinent breakup. The primary enrichment of REEs was governed by extensive fractional crystallization of the magma, with late-stage hydrothermal activity contributing to the final ore-grade mineralization. This study not only clarifies the origin of the LWZ granite but also establishes a link between Proterozoic intracontinental rifting and REE metallogeny in the SNCC.

This study reports Mo isotope data for molybdenite and whole-rock samples from the giant Leimengou porphyry Mo deposit in the Qinling Orogen (China), and interprets the Mo isotope fractionation as being due to magmatic-hydrothermal processes. The average δ98/95Mo values of syn-ore porphyritic monzogranite (PMG) and porphyritic K-feldspar granite (PKG), post-ore quartz monzonite porphyry (QMP), and Taihua Supergroup gneiss are + 0.29 ‰, − 0.26 ‰, 0 ‰, and + 0.14 ‰, respectively. The values for molybdenite decrease from + 0.19 ± 0.17 (‰) in Stage II quartz-molybdenite veins to − 0.53 ± 0.22 (‰) in Stage III quartz-pyrite-molybdenite veins. The εNd(t) values of the PMG and PKG are negative, consistent with a crust-dominated source for these intrusions; the PKG is an evolved peraluminous granite interpreted to have formed by fractional crystallization of the magma that generated the PMG. In addition, the more evolved PKG (high SiO2 content and Mo/Ce ratio) has a negative δ98/95Mo value, whereas the PMG from which it was derived (less fractionated with a lower SiO2 content and Mo/Ce ratio) has a positive δ98/95Mo value. The lower δ98/95Mo value of the PKG is interpreted to reflect fractional crystallization of plagioclase. Significantly samples of PMG and PKG with high Mo contents and Mo/Ce ratios have low δ98/95Mo values, whereas those with low Mo contents and Mo/Ce ratios have high δ98/95Mo values. The samples with low Mo contents represent magma that lost Mo to magmatic fluid, and therefore their high δ98/95Mo values are interpreted to indicate that the light Mo isotope preferred the fluid. This unusual Mo isotopic behavior is likely universal for collision-type porphyry Mo deposits but is different from that of Climax-type porphyry Mo deposits and may reflect the high content of CO2 in collision-type fluids and its low content in Climax-type fluids.

Fluorite is a critical strategic non-metallic mineral resource with wide industrial applications. Here, we provide new constraints for the granite-related fluorite mineralization processes in the Zhangcuo-Banling ore belt in Shaowu of South China. We present geochronological constraints from granite zircon U-Pb, fluorite Sm-Nd, and quartz Rb-Sr dating. The results suggest that the fluorite mineralization ages (137 f 27 Ma and 143 f 14 Ma) are likely younger than the intrusion age of the granite (151.0 f 1.3 Ma). Analyses of fluid inclusions reveal that the ore-forming fluids represent a NaCl-H2O fluid system with characteristics of medium-to-low temperature and low salinity. The delta DV-SMOW values of fluorites range from-71.3 %o to-61.9 %o, and the delta 18OV-SMOW values range from-2.9 %o to 2.6 %o, suggesting that the ore-forming fluids were primarily derived from meteoric water. The (87Sr/86Sr)t ratios of fluorite range from 0.716235 to 0.716635, while for quartz, the ratios range from 0.717106 to 0.720313. These values are consistent with the reported (87Sr/86Sr)t ratios of granite from South China, indicating that the Ca came from the ore-bearing granite. Considering the background of diagenesis and mineralization, along with the significantly high F content (1800 x 10-6 to 7400 x 10-6) in the granite, we propose that F originated from the leaching of biotite in the granite and the gaseous HF released from magma. This study establishes a granite-related hydrothermal fluorite mineralization model for the Shaowu region of South China.

This contribution presents a case examination of high-Mg andesite formation through magma mixing and its contribution to gold mineralization. The Axi high-Mg andesites from northwest China are host to a large epithermal gold deposit. They are porphyritic, with 15-40 vol% macrocrysts, primarily plagioclase (the dominant phase), along with clinopyroxene, amphibole, and quartz. Textural and compositional analyses of plagioclase macrocrysts reveal a variety of zoning types, including un-zoned, oscillatory-zoned, sieve-zoned, and patchy-zoned textures, often indicative of a multi-stage growth process. Compositions of the plagioclase macrocrysts vary significantly, with anorthite contents ranging from 10% to 78% for plagioclase, while some feldspars exhibit albite contents as high as 95%-99%. Clinopyroxene occurs either as macrocrysts or glomerocrysts, displaying both normal and reverse zoning patterns. Amphibole macrocrystals are found as opacitized grains or pseudomorphed by chloride, quartz, calcite, and Fe-Ti oxide. Quartz macrocrysts occasionally show corroded or embayed boundaries. The occurrence of alkali feldspar macrocrysts is limited, with some being replaced by plagioclase. Taken together, the sieve and patchy zoning in plagioclase, reverse zoning in clinopyroxene, and resorption of quartz macrocrysts suggest open-system processes, likely driven by mafic magma recharge within a silicic magma reservoir. The formation of high-Mg andesite through magma mixing is conducive to gold mineralization, as mafic magma recharge may introduce sulfur and gold into the system.

The North China Craton underwent extensive lithospheric thinning and crustal reworking during the Mesozoic, challenging classic views of craton stability. This period marks a transition from tectonic quiescence to widespread reactivation, but timing and magnitude remain poorly constrained. Here we reconstruct crustal thickness evolution along the southern margin of the North China Craton using strontium to yttrium and lanthanum to ytterbium ratios, plus neodymium isotopic data from granitoids. Thickening began in the Jurassic and peaked around 130 Ma, when crustal thickness exceeded 70 km and palaeoelevation surpassed 5 km, forming a plateau comparable to the Tibetan Plateau. After similar to 128 Ma, thickness and elevation decreased to 30-40 km and <3 km by 125-110 Ma. These shifts parallel sedimentary, structural and geophysical evidence. We interpret this evolution as two stages: initial thickening from North China-Yangtze collision, followed by extensional collapse and lithospheric thinning likely driven by Paleo-Pacific plate rollback.

The Liaoshang gold deposit in the Jiaodong Peninsula is a tectonically controlled pyrite-carbonate vein-type system, genetically distinct from the Jiaojia-type altered rock-hosted and Linglong-type quartz-vein gold deposits in the region. Due to the considerable resource potential of Jiaodong gold deposits, extensive research has been conducted on their temporal and metal sources, yet the geological framework of individual mining districts such as the Liaoshang deposit remains poorly constrained. This study integrated petrography, geochemistry, and U - Pb geochronology of zircon, apatite and monazite from local granitiods to elucidate the tectonic history and mineralization processes. Two granite types were identified: plagioclase granites emplaced at 2.14-2.09 Ga, which underwent regional metamorphism at 1.98-1.83 Ga, and monzogranite dykes intruding the meta-sedimentary rocks of the Paleoproterozoic Jingshan Group crystallized at 1.85-1.84 Ga. Apatite from the dykes records a metamorphic age of 248 +/- 15 Ma, indicating involvement in the Triassic Sulu ultrahigh-pressure orogeny. Hydrothermal monazite from the monzogranite yields a lower intercept U-Pb age of 140 +/- 5.7 Ma, predating the main mineralization event at Liaoshang (similar to 116 Ma) and other Jiaodong deposits (similar to 120 Ma) by approximately 20 Ma. Petrographic and microstructural evidence further suggest an early hydrothermal event, implying that ore formation was a prolonged, multi-stage process lasting at least similar to 20 Ma. Whole-rock geochemistry shows that, compared to those of weakly altered granites, mineralized plagioclase granites are significantly enriched in Ag, Pb, As, Te, Sb and Bi. These elements also correlate strongly with Au and total Fe2O3, indicating co-precipitation with polymetallic sulfides and native gold. In addition, As-rich zonation also exists in pyrite formed during the main mining period. Combined with the elevated arsenic content and the obvious Au - As correlation, these findings highlight the important contribution of Precambrian basement rocks, particularly the Jingshan Group metasediments, to the metal endowment of the Liaoshang gold system.

Interaction between organic and inorganic fluids can facilitate formation of mineral deposits. Organic acids are common in oilfield brines, and their decomposition can generate H2O, CO2 and CH4 that are abundant in fluid inclusions from hydrothermal mineral deposits. However, little research has been performed on the interaction between organic acid-bearing solution and metals. This study insights into the role of organic acids in metal transportation by examining the thermal persistence of silver acetate at high temperatures and pressures using a hydrothermal diamond anvil cell. The experimental results indicate that silver acetate becomes more persistent at higher pressure at the same temperature. The presence of pyrite facilitates the decomposition of silver acetate at temperatures of 150-330 degrees C under geothermal gradient of 25 degrees C/km. Our thermodynamic modeling results also show that organic matter could generate silver acetate and acetic acid at high temperature and pressure, furthermore, silver acetate remain stable and maintain higher concentrations under a lower geothermal gradient with temperatures below 500 degrees C and pressure above 500 MPa. These observations accord with the geologic fact that large-scale orogenic-type mineralization of Ag, Au and Cu generally occurred in the post-orogenic thermal extension. They also consist with the numerous observations of CO2- H2O inclusions, the carbonate and hydroxylic alterations in the orogenic-type mineral deposits, and the widespread presence of pyrite formed during earlier mineralization stages. This research provides new understanding of organic-inorganic interaction during hydrothermal mineralization, orogeny and thermal evolution of sedimentary basins.

In the early Paleoproterozoic, the Earth's atmosphere-ocean system shifted from a reducing to an oxidizing state, triggering the extensive deposition of banded iron formations (BIFs) in the Siderian period (2.5-2.3 Ga). As a key sedimentary formed during the hydrospheric oxidation stage, BIFs are expected to preserve abundant microbial fossils or organic carbon. However, evidence for contemporaneous widespread biological activity remains limited. This paper focuses on C-O isotopes and the trace element geochemistry of the 2.5 Ga Jining BIF to constrain the redox state of paleo-oceans and associated biogeochemical cycling during BIF deposition. The delta C-13(carb) values of the BIF samples range from -18.6 parts per thousand to -9.6 parts per thousand, with an average of -12.7 parts per thousand, exhibiting a notable negative value, and TOC contents (0.04-0.19 wt.%) are extremely low. This suggests the incorporation of oxidized organic carbon to pore water via ferrihydrite reduction during early diagenesis process. The globally negative delta C-13(carb) value of BIFs and iron-rich carbonates reflect enhanced biological activity at similar to 2.5 Ga. REE patterns reveal negative Ce/Ce*((SN)) and Eu/Eu*((CN)) anomalies, and the presence of primary hematite mesobands together indicate that the Jining BIF records a redox transition in seawater from reducing to oxidizing conditions.

The Huoqiu Group is located in the southern margin of the North China Craton and is considered an Archean geologic body. Its supracrustal rocks are divided into the Huayuan, Wuji, and Zhouji formations in ascending order. The Wuji and Zhouji formations contain large BIF-type iron deposits. The BIFs show geological and geochemical features of Paleoproterozoic Lake Superior-type rather than Archean Algoma-type. The study of the formation ages and evolutionary history of the Huoqiu Terrane will provide significant guidance for the mineralization and exploration of the Huoqiu iron deposits. In this paper, we collected all available isotopic ages and Hf isotopic compositions obtained from the Huoqiu Terrane and reassessed their accuracy and geological meanings. We conclude that the Wuji and Zhouji formations were not older than 2343 Ma. Therefore, the BIFs hosted in the Wuji and Zhouji formations must be of Paleoproterozoic age. The magmatic zircons from the TTG gneisses and granite yield U-Pb ages of Neoarchean Era, indicating that the Wuji and Zhouji formations of the Huoqiu Group were deposited on an Archean granitic basement that mainly comprises the trondhjemite-tonalite-granodiorite (TTG) gneisses and granites of the “Huayuan Formation”. The Early Precambrian crystalline basement in the Huoqiu area can be divided into the Huayuan Gneiss Complex and the Huoqiu Group, comprising the Wuji and Zhouji formations. The tectonic scenario of granitic complexes overlain by supracrustal rocks in the Huoqiu Terrane has been recognized in the Songshan, Zhongtiao, Xiaoshan, and Lushan Early Precambrian terranes in the southern margin of the North China Craton. As indicated by the zircon U-Pb ages and εHf(t) data, the crustal growth of the Huoqiu Terrane occurred mainly at ~2.9 Ga and ~2.7 Ga. Based on the sedimentary age, environment, and rhythm, the BIFs in the Huoqiu region are considered to be of Lake Superior type and of great potential for Fe ore exploration.

The Proto-Tethys Ocean has played a significant role in the geological history of Earth. However, ongoing debates persist regarding the timing and polarity of its early subduction. Volcanic rocks associated with iron deposits in the Bulunkuole Complex, West Kunlun Orogen, offer insights into both the complex’s formation age and Proto-Tethys evolution. This study presents newly obtained zircon U–Pb age data (~536 Ma) along with comprehensive whole-rock major and trace element and Sr–Nd–Hf isotope analyses of these volcanic rocks. Our dataset implies that the Bulunkuole Complex partly formed in the early Paleozoic rather than entirely in the Paleoproterozoic, as previously suggested. Geochemically, the volcanic rocks exhibit enrichments in large ion lithophile elements and light rare earth elements, along with depletions in high-field strength elements. They also display elevated initial 87Sr/86Sr values (0.71093, 0.72025) and negative εNd(t) values (−5.13, −6.18), classifying them as continental arc volcanic rocks. These geochemical fingerprints, complemented by zircon εHf(t) values (−12.7 to −1.6), indicate that the parental magmas of the volcanic rocks were produced by partial melting of the lithospheric mantle wedge, which had been metasomatized by subducted sediment-derived melts. The available data, in conjunction with previously published findings, strongly suggest that the Proto-Tethys Ocean subducted southward prior to approximately 536 Ma due to the assembly of Gondwana. Subsequent slab rollback may have resulted in a crustal thinning of 9–25 km during 536–514 Ma. Further shifts in subduction dynamics led to the transition from high-angle subduction to either normal or low-angle subduction, facilitating the formation of a thicker crust ranging from 39 to 70 km between 514 and 448 Ma. This study, therefore, provides valuable insights into the early evolution of the Proto-Tethys Ocean and contributes significantly to our understanding of the tectonic history of the West Kunlun Orogen.

The origin of CO2-dominated fluids in orogenic gold deposits is usually mired in controversy. The Dunbasitao gold deposit is the largest among several gold deposits along the Armantai suture zone, East Junggar, China. Orebodies are hosted in volcano-sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation and porphyritic quartz diorite and are controlled by shear zones. Based on the cross-cutting relationship of veins, the hydrothermal process can be divided into the early, middle, and late stages and the gold only occurred in the middle stage. Seven types of fluid inclusions (FIs) were identified in the Dunbasitao deposit: Type-1 FIs (L-H2O + L-CO2 or L-H2O + L-CO2 + V-CO2) that homogenized to H2O phase or show critical homogenization; Type-2 FIs (L-H2O + L-CO2 or L-H2O + L-CO2 + V-CO2) that homogenized to CO2 phase; CO2-dominated Type-3 FIs (L-CO2 or L-CO2 + V-CO2); Two-phase aqueous Type-4 FIs (L-H2O + V-H2O) that homogenized to liquid phase; Type-5 FIs are composed of three phases (L-H2O + V-H2O + Solid), which homogenized to liquid phase; Type-6 and Type-7 FIs refers to FIs composed of a single liquid or vapor H2O phase, respectively. Microthermometry and laser Raman spectroscopy (LRS) analyses show that the initial ore-forming fluids in the early stage were moderate-T-h (326-342 degrees C), low salinity (2.4 to 4.7 wt% NaCl equiv), and homogenous H2O-CO2-NaCl liquid fluids, containing 13-33 mol% CO2 and a small amount of CH4, H2S, and N-2. The calculated delta O-18(H2O) (V-SMOW) values are 7.5-8.5 parts per thousand, delta D-18(H2O) (V-SMOW) values range from -100 to -96 parts per thousand, and delta C-13(fluid) (PDB) range from -3.8 to -2.5 parts per thousand. In the middle stage, two typical immiscible fluid inclusion assemblages (FIA.18 and FIA. 27) composed of both Type-1 and Type-2 FIs were measured. The salinity of FIA.18 is 3.3 wt% NaCl equiv. and T-h is 320 degrees C. For FIA.27, the salinity is 2.2 wt% NaCl equiv. and T-h is 298 degrees C. The salinities of Type-4 FIAs vary from 5.9 to 14.4 wt% NaCl equiv., significantly higher than Type-1 and Type-2 FIs (1.7 to 3.5 wt% NaCl equiv). The salinities of three isolated Type-5 FIs (halite-bearing) range from 30.3 to 32.9 wt% NaCl equiv. and T-h vary from 257 to 277 degrees C. These facts indicate extreme unmixing between carbonic and aqueous fluids in the middle stage, which led to gold precipitation. The Type-3 FIs represent the salt-free, H2O-lost, CO2 end-member composition, whilst the Type-5 FIs and high-salinity Type-4 FIs represent the highly saline aqueous end-member composition. Late-stage fluids are initially liquid, very low-salinity (1.4 to 2.6 wt% NaCl equiv), and low-T-h (176-233 degrees C) aqueous fluids. Two immiscible carbonic FIAs from the middle stage yield a trapping pressure (P-t) of 86.9-133.9 MPa. Considering the rapid pressure fluctuations during fluid immiscibility, using hydrostatic or lithostatic pressure alone cannot get the real mineralization depth, Therefore, we use the lithostatic pressure for the P-t maximum and hydrostatic pressure for the P-t minimum and calculated a mineralization depth of 5.3-8. 9 km, which doesn't represent the change but uncertainty for depth. Combining the characteristics of ore-forming fluids with the hydrothermal alteration and mineral compositions of ores, the Dunbasitao gold deposit is determined as a mesozonal orogenic gold deposit and there is considered to be prospecting potential in the deep.