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The redox condition, a key parameter of mineralization, is one of the most difficult parameters to constrain precisely. Here we employ electron probe and X-ray photoelectron spectroscopy (XPS) to analyse sulphur (S) in apatite grains from five granitoid plutons that are differentially related to gold mineralization in the world-class gold fields of Jiaodong, Xiaoqinling, and Wutai-Hengshan within the North China Craton (NCC) to constrain the redox condition of melt. The results show increasing order of the apatite S content and S6+/ΣS ratios in the Linglong (only spatially close the Jiaodong gold deposits), Sunzhuang (related with the Yixingzhai gold deposits), Huashan (weakly related with the Xiaoqinling gold deposits), Wenyu (closely related with the Xiaoqinling gold deposits) and Guojialing plutons (closely related with the world-class Jiaodong gold deposits), indicating that the oxidation state increased from the Linglong pluton to the Guojialing pluton. The S concentrations of Guojialing, Wenyu, Huashan and Sunzhuang plutons, are estimated using previous methods are, 120–208 ppm, 107–138 ppm, 72–77 ppm and 10–74 ppm, respectively. Combined with the regional differences in gold mineralization in the North China Craton, the gradual increase in mineralization scale is consistent with the trend of increasing oxidation state in the granitoid plutons from Wutai-Hengshan to Xiaoqinling to Jiaodong goldfields, thus also underpinning the contribution of Mesozoic granites to gold mineralization in the North China Craton through providing the thermal energy and medium for the activation and migration of ore-forming fluids. [ABSTRACT FROM AUTHOR]

The large‐scale concentration of Au associated with Mesozoic granitoid intrusions in the North China Craton (NCC) has inspired many investigations to explore the genetic relationship between the magmatism and gold metallogeny. The Xiaoqinling gold province is located in the southern margin of the North China Craton. The Wenyu and Huashan monzonitic granites formed at Early Cretaceous represent two of the important intrusions in this region, and a large number of gold deposits occur around the Wenyu pluton. Here we present results from an integrated study using in situ zircon U–Pb ages, trace elements, and Hf isotope to infer the composition and environmental changes during different evolution stages of the fertile Wenyu pluton and compare with the infertile Huashan pluton. The Huashan pluton was emplaced at 144.0 ± 0.6 Ma, whereas the fertile Wenyu pluton experienced multistage magmatic activity from 141.4 ± 0.6 to 129.6 ± 0.5 Ma. Temperatures computed from Ti‐in‐zircon thermometry indicate that the late‐stage Wenyu magma crystalized at 644°C, the Huashan magma, and early‐stage Wenyu magma crystalized at around 750°C. And the oxygen fugacity (Ce4+/Ce3+ > 200 and Eu/Eu* > 0.7) and the water content of the late‐stage Wenyu magma stay at higher levels. The U/Yb–Hf and U/Yb–Y relationship with εHf(t) (−15.63 to −17.89) of the late‐stage Wenyu magma suggest that the ancient lower crust with subsequent inputted basaltic components make up the source of the fertile and infertile plutons. Combined with previous geochronological data and geodynamics studies, we propose that the late‐stage intrusion of the Wenyu pluton experienced intensive magma mixing. And the formation of Wenyu pluton created conducive heat energy, oxygen fugacity, and water conditions for the formation of high‐grade gold deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Erdaokan is a magmatic-hydrothermal deposit genetically linked with bitumen. • Bitumen is of biogenic origin, and was sourced from the adjacent sedimentary strata. • Organic matter that formed bitumen significantly interacted with ore-forming fluids. The newly discovered Triassic Erdaokan Ag-Pb-Zn deposit having an ore reserve of 2964 kt, with an average grade of 517 g/t Ag, 0.6 wt% Pb and 0.4 wt% Zn, is the only known bitumen-bearing magmatic-hydrothermal Ag-Pb-Zn deposit in the northeastern segment of the Great Xing'an Range, NE China. Its genetic relationship with organic matter remains elusive. In this contribution, we present results from detailed geochemistry, isotope and biomarker studies on bitumen and discuss the genesis of bitumen and its relationship with Ag-Pb-Zn mineralization. The carbon isotope and biomarker analyses suggest a biogenic origin for the organic matter that formed bitumen. We infer that the organic matter was most likely sourced from the carbonaceous shale and limestone belonging to Niqiuhe Formation. Significant interaction between the organic matter and ore-forming fluid is indicated. The light n-alkanes and analogs, alkali elements, vanadium and nickel in the bitumen were removed by the ore-forming fluid, and a variety of metal elements entered into the bitumen. The thermochemical oxidation of methane induced by high-valence metal oxides and thermochemical sulfate reductions were the two main interaction mechanisms between the organic matter and ore-forming fluid, which made an effective contribution to metal precipitation in the Erdaokan Ag-Pb-Zn deposit. On this basis, we propose a genetic model for the genesis of the Erdaokan Ag-Pb-Zn deposit and other hydrocarbon-bearing magmatic-hydrothermal deposits which envisages a significant role played by the organic matter sourced from the sedimentary rocks in ore concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bitumen Sm-Nd age of 234.6 Ma is interpreted as the hydrocarbon deposition timing. • The ore-forming age of Erdaokan is constrained at middle Triassic. • Bitumen Sm-Nd can be used to constrain the hydrothermal mineralization age. Dating of bitumen can potentially constrain both the timing of mineralization and hydrocarbon deposition in hydrocarbon-bearing hydrothermal deposits. Here we report for the first time direct Sm-Nd dating on bitumen from the Erdaokan Ag-Pb-Zn deposit, a newly discovered, large, hydrocarbon-bearing hydrothermal deposit with 2964 kt of ore and 1535 t Ag with an average grade of 517 g/t Ag, 0.6 wt% Pb and 0.41 wt% Zn in the Back-Arc basin of NE Great Xing'an Range, NE China. Dating results show that Sm-Nd isochron age of four bitumen samples is 234.6 ± 1.2 Ma and an isochron age that includes three galena and four bitumen samples is 234.9 ± 1.4 Ma. In order to verify these ages, we performed Rb-Sr dating on pyrite and galena from the same deposit and U-Pb dating of zircon from the adjacent diorite porphyrite dike, which yielded ages of 232.9 ± 2.3 Ma and 234.2 ± 2.8 Ma, respectively. The highly concordant ages from multiple techniques confirms that bitumen Sm-Nd isotopic dating is reliable, and that the ages obtained in our study represent the hydrocarbon deposition as well as mineralization timing in the deposit. We conclude that, in the Duobaoshan metallogenic belt, the Erdaokan Ag-Pb-Zn deposit is the first identified large, Middle Triassic, hydrocarbon-bearing silver-lead–zinc deposit and is of great significance to the regional metallogenesis research and prospecting work in the Great Xing'an Range. [ABSTRACT FROM AUTHOR]

• Silver occurs as argentite, pyrargyrite and invisible silver in tetrahedrite. • The ore-forming fluids were mainly of magmatic origin. • Mixing of hydrocarbon and ore-forming fluids resulted in the precipitation of Ag. The recently discovered Erdaokan Ag-Pb-Zn deposit is located in the Duobaoshan gold-copper metallogenic belt in the eastern part of the Central Asian Orogenic Belt. The ore-bodies occur mainly as veins hosted in the breccia. Three stages of mineralization, including early magnetite-quartz-pyrite, middle silver-sulfide-bitumen-quartz and late carbonate stages, were recognized. Here we report results from electron microprobe analysis (EPMA), S-Pb-H-O isotopes and fluid inclusions studies to gain insights into the salient characteristics of the ore mineralization and mechanism of silver precipitation. The silver occurs mainly as argentite, pyrargyrite and invisible silver in the tetrahedrite grains, in which Ag, Fe and As isomorphically substituted Cu, Zn and Sb, respectively. The homogenization temperatures of fluid inclusions in the early, middle and late stage mineralisation range from 96 to 179 °C, 78 to 178 °C, and 98 to 191 °C, respectively. The fluid salinities vary from 0.35 to 5.54 wt.%NaCl equiv. The δ34S values of the pyrite and galena show a range from −0.97‰ to +9.31‰. 206Pb/204Pb vary from 18.0125 to 18.1864, 207Pb/204Pb, from 15.561 to 15.081, and 208Pb/204Pb, from 38.0445 to 37.6979, with a mean of 18.0298, 15.5125 and 37.7281 respectively. The δD and δ18O water values of the quartz from the ore body range from −119.1‰ to −109.7‰ and −4.64‰ to 1.98‰, respectively. Based on these results, we argue that the ore-forming fluids were derived from a magmatic source, with fluid mixing as the dominant mechanism for silver precipitation, involving hydrocarbon fluid interaction as inferred from the presence of bitumen in the ore. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study deepens understanding of the spatial and temporal evolution of minerals in the Bayan Obo Deposit. • Detailed mineralogical assemblages and fabric features of each ore are presented. • This study established the formation mechanism of different REE-Nb-Fe minerals and the metallogenic process of the deposit. The Bayan Obo deposit in the northern margin of the North China Craton is a world-class REE-Nb-Fe deposit, the complex mineralization history of which remains unresolved. In this study, we employ SEM and Image J software combined with mineralogical data obtained by in-situ EDS and EPMA analyses to analyze petrographic images rapidly and to investigate the mineralogical assemblages of each type of rocks/ores from the Main Orebody in an attempt to understand the mineralization process and ore-formation mechanism of this deposit. We identify three metallogenic periods and six ore-forming stages based on the field occurrence of ores combined with published geochronological data. The Mesoproterozoic magmatic event comprises two stages, which were distinguished as the coarse-grained dolomite stage (stage 1) and the fine-grained dolomite stage (stage 2). Three stages were recognized in the Mesoproterozoic shear deformation-hydrothermal mineralization period, including the disseminated mineralization stage (stage 3), the banded mineralization stage (stage 4) and the massive mineralization stage (stage 5). The Paleozoic hydrothermal period involved the vein mineralization stage (stage 6). Based on detailed studies of the mineral assemblages and paragenesis, as well as the complex textures of the ores, we propose a model of the multi-stage metallogenic process as follows: (1) The REE minerals and rutile occurring as inclusions wrapped within magmatic idiomorphic dolomite grains indicate that the REE-Nb mineralization might have started during the magmatic period. (2) The Nb minerals, such as fergusonite and ilmenorutile, intergrown with REE minerals, such as monazite and bastnäsite, indicate that the Nb and REE were transported by the same ore-forming magma or fluid and precipitated during the same metallogenic process. (3) From the fine-grained dolomite stage to the massive mineralization stage (from stage 2 to stage 5), the mineral assemblages become more complex, with a gradual increase in the degree of hydrothermal alteration suggesting that more hydrothermal fluid was involved in the ore mineralization. (4) The complex mineralogical assemblages and textural relationships indicate multiple formation mechanisms for the REE-Nb-Fe minerals. We propose that the unusually large volume of REE-Nb-Fe resources in the Bayan Obo deposit was the result of combined magma and hydrothermal fluid activities in the Mesoproterozoic (from stage 1 to stage 5), whereas the fluids only caused reactivation of the ore materials previously deposited without the addition of exogenous materials in the Paleozoic stage (stage 6). [ABSTRACT FROM AUTHOR]

The North China Craton (NCC) hosts the world's most typical example of "decratonic" gold deposits including lode, porphyry, cryptoexplosive breccia, and skarn subtypes. The lithospheric structure in the ore fields show "triple-junctions" of basement microblocks, zones of lithospheric thinning, and "hotspots" with abnormal crustal heat flow. The basement rocks are dominantly composed of trondhjemite-tonalite-granodiorite (TTG) suite and amphibolites. The intermediate-felsic calc-alkaline plutons with crust-mantle mixed origin and formed under high oxygen fugacity, volatile-rich and moderately fractionated conditions, together with dyke swarms of diverse compositions are indicators for the gold mineralization. The mantle under the gold field shows metasomatic or juvenile "EM2" or "EM2 + EM1" characteristics. The gold deposits are closely associated with craton destruction, heterogenous reactivation, large-scale magmatic intrusion and eruption, and upwelling of voluminous ore-bearing fluids within a transitional tectonic regime. The presence of mantle-derived mafic rocks, mafic microgranular enclaves (MME) and amygdaloidal bodies, minerals rich in Te, Ni, Cr, Mg, C and N, He and stable isotopes with mantle signature, among other features, indicate that the ore-forming metals and fluids have mixed mantle and deep crustal origin. Gold deposits coexisting or closely associated with mafic dykes and crust-mantle-derived stocks indicate that the upwelling of ore-forming fluid and localization of the ore-materials were facilitated at least partly by the intrusion of deep magma. The spatial distributions of altered rocks with alkali-feldspar-hematite zone distal to the orebody (barren) and pyrite-phyllite (sericite) zone proximal to the ore (ore-bearing zone) indicate a marked physico-chemical interface at the final stage of evolution of the ore-forming fluid. The presence of wide alteration zone indicates that the ore-controlling faults were in a compressive stress state, whereas narrow alteration zone is generally associated with a tensile stress state. The cataclastic, poikilitic, interstitial and zonal textures displayed by the various stages of ore minerals are related to the impact of alternating local tectonic stress fields in the faults, as well as fault-valve mechanism. Intense gold mineralization is typically associated with the development of polymetallic sulfide minerals and complex mineral assemblages. The major gold mineralization is also commonly related with pyrite with xenomorphic or complex forms, rich in As, Se, and Te, with large unit cells, wide X-ray diffraction peaks, and high P/(P + N) values corresponding to thermoelectric conductive type. Quartz grains formed in the main gold mineralization stage are generally fine grained and irregular, occasionally occurring as grain clusters, and showing complex thermoluminescence patterns with both high and low temperature peaks. Multiple rhythmic zones in quartz, pyrite or other ore minerals with various impurities in between the different zones indicate the pulses of ore fluid flow toward the upper part of the orebody. In contrast, minerals with few or no zones may indicate an ore-fluid reservoir typically in the middle to lower parts of orebody. • Indicators of decratonic gold mineralization include geodynamic background and mineralizing processes. • Five subcategories of indicators for geodynamic background are discussed. • Mineralizing processes are indicated by six subcategories of evidences. • Indicators are summarized as references for prospecting similar gold deposits elsewhere. [ABSTRACT FROM AUTHOR]

[Display omitted] • Apatite from both the Huashan and Wenyu plutons are fluorapatite of magmaticorigin. • Wenyu apatite formed under a higher oxidation state and incorporated more mantle-derived materials than Huashan apatite. • Wenyu apatite crystallized earlier than feldspar and Huashan apatite was affected byfeldsparcrystallization. • The magma of the Wenyu pluton incorporated more intensive fluid exsolution during crystallization. • Wenyu pluton is more favorable to gold mineralization than the Huashan pluton. The relationship between granitic magmatism and lode gold mineralization has remained as a controversial topic among economic geologists. In this paper, we report in situ elemental and Sr isotopic signature of apatite from the Wenyu and Huashan granitic plutons in the Xiaoqinling goldfield, southern margin of the North China Craton (NCC), intending to provide further constrain the relationship between magmatism and metallogeny. The formation ages of Huashan and Wenyu granitic plutons are coeval with the gold mineralization, but most of the gold deposits are clustered nearing the Wenyu pluton, and only a few small gold deposits are found adjacent to the Huashan pluton. Although apatite from both plutons is all fluorapatite, characterized by negative Eu anomaly and enrichment of LREEs, the apatite from the two plutons shows different signatures. Based on these differences, the apatite from the Huashan pluton is divided as group A (HS-A) and group B (HS-B). The δEu, δCe values and MnO and Ga contents of the Wenyu and HS-A apatite indicate high oxygen fugacity range from MH to NNO for the magma, whereas the HS-B apatite shows low oxygen fugacity range from NNO to FMQ. The 87Sr/86Sr, REE, Th/U, and Ce/Y values of the apatite suggest that the magma for the Wenyu pluton incorporated more mantle-derived materials in contrast to Huashan pluton. Sr/Y ratio and REE content of the apatite indicate that WY apatite crystallized earlier than feldspar and Huashan apatite was affected by feldspar crystallization. The fluid-volatiles exsolution texture and S content of the apatite indicate higher content of volatiles in the Wenyu pluton magma, where the magma experienced more intense fluid exsolution than that of the Huashan pluton during apatite crystallization. The characteristics of many mantle-derived materials, high oxygen fugacity, and higher volatiles as revealed by the apatite data show that the magmatism of Wenyu pluton was more conducive to the mineralization of gold deposits than that of the Huashan pluton and is more closely related to gold deposits. [ABSTRACT FROM AUTHOR]

• Magnetite from fertile intrusion shows magmatic and hydrothermal origin. • Magnetite from barren intrusion is of typical magmatic origin. • The fertile Wenyu pluton formed at higher oxygen fugacity and lower temperature compared to the barren pluton. • Deep sourced was fluid involved in the formation of the Wenyu pluton. The Xiaoqinling district in the southern margin of the North China Craton is the second largest gold enriched area in China. The Huashan and Wenyu plutons represent two typical Mesozoic magmatic intrusions in this region and were coeval with the gold mineralization. Here we report the geochemistry and Mössbauer spectral characteristics of magnetite from the two plutons with a view to explore the role of the granitic magmatism in the gold enrichment. The results of EPMA and Mössbauer spectroscopy suggest that the average values of Fe2+/Fe3+ in the magnetite from the two intrusions are lower than the standard value of 0.50, indicating an oxidizing environment. The estimated oxygen fugacity is higher for the Wenyu pluton than that of the Huashan pluton, which is also supported by the occurrence of hematite in the former, and the distinct δEu-δCe anomalies for magnetite from the two intrusions. The Sn content in magnetite indicates lower formation temperatures of the Wenyu pluton as compared to that of the Huashan pluton. The results of LA-ICP-MS analysis demonstrate similar multi-element variation patterns for the two intrusions. Titanium vs. Ni/Cr relationship suggests that the magnetite from the Huashan pluton is of typical magmatic origin, whereas that from the Wenyu pluton shows both magmatic and hydrothermal signature. The Ni/Co ratio of magnetite from the Wenyu granite is higher than that of the Huashan granite, which indicates a deeper source for the Wenyu pluton. The comparatively more favorable physico-chemical conditions, such as higher oxygen fugacity, lower temperature, as well as the involvement of deep-sourced material are envisaged to have provided better metallogenic environment for generating the gold mineralization around the Wenyu pluton. [ABSTRACT FROM AUTHOR]