This study conducted a systematic investigation on the petrology and geochronology of granulites exposed in the Huangtuling area in the Dabie orogen, China. The results demonstrate that the rocks experienced at least two periods of granulite facies metamorphism (GFM), including an older high-pressure (HP) GFM and a younger low-pressure (LP) GFM related to two orogenic cycles in the Paleoproterozoic and Cretaceous, respectively. Dating of different accessory minerals yielded two groups of metamorphic ages: similar to 2.0 Ga recorded by zircon and similar to 120 Ma recorded by rutile and apatite. Combined with their trace element compositions, it is suggested that zircon ages represent the timing of older GFM and rutile and apatite record the timing of younger GFM. This demonstrates that accessory minerals can differentially record the timing of different periods of GFM. Zircon retains comprehensive information about the older event but lacks information on the younger one, while rutile and apatite exhibit the opposite pattern. The high temperature and low melt/fluid activity of LP GFM may be potential factors driving contrasting responses of accessory minerals to thermal overprinting, given their different Pb closure temperatures and limited Zr reactivity in the bulk rock during Cretaceous metamorphism. Therefore, this study supports petrologic evidence that the Huangtuling granulites experienced two periods of GFM. Based on the well-constrained regional background, it can be concluded that the Paleoproterozoic GFM was produced by a collisional orogeny associated with the assembly of the Columbia Supercontinent, and the Cretaceous GFM was induced by extension and collapse of a Triassic orogen. This study highlights the importance of simultaneously dating accessory minerals with different closure temperatures in U-Pb isotopic systems to distinguish between multiple orogenies, especially in ancient rocks preserving multi-stage granulite-facies mineral assemblages.

The origin and evolution of dolomitization in carbonate-hosted Zn-(Pb) deposits are essential for understanding ore-forming processes and reconstructing ancient marine environments. However, establishing a temporal link between dolomitization and mineralization in these deposits remains challenging due to the scarcity of direct geochronological constraints. This limitation hinders a comprehensive understanding of metallogenic processes and paleoenvironmental reconstructions. To address this issue, we present an integrated study of the Aozigang Zn deposit in Hubei Province of South China. We reveal distinct generations of dolomite, which include sedimentary breccia dolomite (SBD), fascicular fast dolomite (FFD), fascicular slow dolomite (FSD), bladed dolomite (BD), radial slow dolomite (RSD), and medium-crystalline to coarse-crystalline dolomite (MD). The dull-red CL color and fabric features of the FSD suggest that dolomitization occurred under near-surface to shallow-burial, anoxic marine conditions. Uranium-Pb dating of FSD yields an age of 546.9 +/- 7.4 Ma (MSWD = 2.8, n = 74), indicating that dolomitization took place during the Neoproterozoic. By combining the in situ carbon isotope composition of sedimentary dolomite, we provide direct chronological evidence for the delayed oxygenation of the Neoproterozoic ocean. The elevated Mn/Sr ratios and Mn enrichment observed in later MD are consistent with hydrothermal recrystallization under reducing conditions. The clear rim and cloudy core of MD serve as direct petrography evidence of the recrystallization from early dolomite. Meanwhile, the 513C and 518O values of hydrothermal calcite (peak at +0.27%o to +1.43%o and-11.81%o to-7.40%o, respectively) reflect the influence of relatively high-temperature fluids and lower oxygen fugacity. The Pb isotopes of sphalerite indicate a mixed metal source that involves contributions from both the upper crust and basement. This study integrates geochronological and geochemical methods to provide direct dating evidence for Precambrian dolomitization, which is associated with the global oxygenation event known as the Neoproterozoic Oxygenation Event (NOE). The results offer a new perspective for investigating carbonate-hosted ore deposits on a global scale.

The Yashan granitic complex, a multiphase, highly evolved granitic system, hosts one of the largest Ta-Nb-Li deposits in South China. Spatially, it comprises a composite pluton intruded by multiple albitite dikes (AD). The pluton exhibits a vertically zoned sequence of granitic rocks, progressing from two-mica granite (TMG) at the base through Li-mica granite (LG) and topaz lepidolite granite (TLG) to lepidolite quartz rock (LQR) at the top. Apatite is widespread in the Yashan complex and displays distinct morphologic and chemical variations. Three genetically distinct types have been identified: magmatic (Ap1), magmatic-hydrothermal overprinted (Ap2), and later hydrothermal (Ap3) apatite. Ap1 yields concordant U-Pb ages of 152.5 +/- 0.6 Ma and exhibits geochemical characteristics similar to those of typical S-type granites. Fractional crystallization of plagioclase, monazite, and garnet controls the distribution of Sr, REE, and trace-elements. Ap2 displays porous textures, elevated Sr contents (up to 15,705 ppm), and high Sr-87/Sr-86 isotopic ratios, along with scattered U-Pb ages. The spatial association of Ap2 with hydrothermal Li-rich mica, as well as its enrichment in Nb and Ta, suggests fluid-mediated remobilization of rare metals. These features reflect metasomatic overprinting by hydrothermal fluids exsolved from the evolved magma. Ap3 records a discrete hydrothermal event with a late Cretaceous age of 87.2 +/- 2.9 Ma. Collectively, these findings indicate that although hydrothermal alteration significantly modified mineral chemistry, magmatic differentiation remained the dominant control on rare-metal enrichment. Furthermore, the study highlights that Sr-rich apatite with low Th/U ratios (<1) in highly evolved granites can serve as a valuable indicator for constraining the timing of hydrothermal alteration.

Graphite can preserve crucial information related to the carbon cycle in metamorphic, magmatic, and hydrothermal systems. However, traditional bulk isotope analysis often obscures significant microscale heterogeneity. This study establishes a reliable protocol for in situ carbon isotope analysis of graphite using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Two critical challenges were addressed: the mass loading effect and the scarcity of appropriate reference materials. Mass loading induces significant carbon isotope fractionation, with the delta 13C deviation showing a linear dependence on the 12C+ intensity ratio of sample to standard (12C+Isam/12C+Istd). This deviation intensifies as the ratio diverges from 1, surpassing |2%o|at values of 0.2 and 2.6. The application of a linear regression correction reduces the deviations at these extreme ratios (0.2 and 2.6) from over |2%o|to within 0.50%o. Commercial pencil leads were validated as cost-effective reference materials for the in situ C isotope analysis of graphite. The 2H grade exhibited excellent micro-scale homogeneity (0.30%o, 2SD), performing slightly better than pressed pellets of the United States Geological Survey graphite standard USGS24 (0.50%o, 2SD), and negligible inter-matrix fractionation between these two samples (|Delta delta 13C| <= 0.22%o). Calibration of variable-grade pencil leads (2B to 6B) achieved precisions ranging from 0.12%o to 0.58%o (2SD), with deviations within 0.18%o of IRMS values. The method provides high spatial resolution with sub-permil accuracy, enabling resolution of intra-crystalline delta 13C zoning in graphite. It offers a robust framework for reconstructing metamorphic temperature histories, tracing carbon sources, and investigating fluid-mediated carbon precipitation in geological systems.

Tungsten (W), lithium (Li), and other rare metals are essential components in various industries. The coexistence of tungsten and lithium deposits represents a deposit type with great economic potential. However, the process of W-Li co-mineralization remains poorly understood, presenting challenges in elucidating the mechanisms governing their concurrent presence. This study focuses on the Gaoaobei tungsten (W) deposit, notable for its substantial lithium (Li) content, classifying it as a greisen-type W-Li deposit. Specifically, what is the process of Li enrichment and mineralization within tungsten deposits, and which factors play a critical role in controlling the occurrence of Li mineralization events in tungsten deposits. The monazite U-Pb dating indicates that the medium-coarse-grained biotite monzogranite in the Gaoaobei deposit formed at 226.3 f 1.9 Ma, while the medium-grained muscovite granite was dated at 160.0 f 1.4 Ma. The cassiterite U-Pb ages of results for the medium-coarse-grained biotite granite (wall rock), medium-grained muscovite granite (metallogenic granite), and aplite indicate that the hydrothermal stage Li mineralization in the Gaoaobei W-Li deposit ranges from approximately 159.0 f 4.6 Ma to 155.3 f 4.5 Ma. The Gaoaobei W-Li deposit is characterized by early-stage alterations, including biotitization, albitization, and muscovitization, followed by late-stage silicification and sericitization. The study reveals that the mica types in the Gaoaobei W-Li deposit are predominant Zinnwaldite, Protolithionite, and Lepidolite, characterized by high Al and Fe contents and low Ti, Ca contents, among other features. The mineral compositions of various mica types demonstrate an evolutionary trend from early to late stages, showing an increase in Li, Rb, Ta, and Zn contents, and a decrease in W, Sn, and Nb contents. The magmatic muscovite exhibits Nb/Ta ratios mostly exceeding 4 and Li/Rb ratios mostly below 1.5. In contrast, hydrothermal muscovite displays lower Nb/Ta ratios (mostly below 4) but higher Li/Rb ratios (mostly above 1.5). Re-equilibrated muscovite falls within the intermediate range of these two categories (Nb/Ta = 0 to 4; Li/ Rb = 0.1 to 2), highlighting that a Li/Rb ratio greater than 1.5 can serve as a criterion for evaluating the potential for Li mineralization. The majority of Zr/Hf ratios of muscovite in the Gaoaobei deposit are below 10, suggesting promising prospects for W, Sn, Mo, and other deposits. This study establishes the initial determination of the granite-forming ages for the Yanshanian period granite in the Gaoaobei mining area and links the hydrothermal stage Li mineralization age of the Gaoaobei deposit to the Late Jurassic large-scale W-Sn mineralization event in the Nanling Range. These findings provide valuable insights for the exploration of rare metal deposits such as Li in W mines in the Nanling Range and similar deposits worldwide.

The Tong’an-Baishuidong mining district (TBMD), located in the eastern section of the Jiangnan Orogen, is a newly discovered granite-type lithium mining district. Thisstudy presents new monazite U–Pb chronological, whole-rock geochemical, and Nd–Pb isotopic data to reveal the petrogenesis and geodynamic setting of the Wutang granites in the TBMD. The monazite U–Pb age of 145.8 ± 1.0 Ma indicates that the granites were emplaced at the end of the Late Jurassic. Whole-rock geochemical results demonstrate that the Wutang granites are enriched in SiO2 (72.80–73.40 wt

Rare-metal granites are highly evolved, peraluminous intrusions characterized by extreme enrichments in incompatible elements. However, the mechanisms responsible for such enrichment remain contentious. The Yashan granitic complex in South China, renowned for its well-developed Li-Ta-Nb mineralization, consists of three granite groups and a stockscheider, arranged from the base to the top of the pluton, as well as several albitite dikes that intruded the pluton later. Geochemically, the Yashan granites are strongly peraluminous and enriched in PRO5 and rare metals (including Li, Rb, Be, Cs, Sn, Nb, Ta, and W) while being depleted in Ca, Fe, Ti, and Mg. This compositional signature suggests an S-type granitic magma derived from partial melting of metasedimentary rocks. This study identified abundant Li-bearing minerals, such as lepidolite, petalite, amblygonitemontebrasite, and elbaite, as well as beryl in certain granites within the complex. Detailed mineralogical analyses indicate that these minerals are predominantly of magmatic origin. Rapid crystallization of K-feldspar in the stockscheider appears to have generated a flux-rich boundary layer, which, combined with the accumulation of a magmatic volatile phase, promoted the precipitation of rare-metal minerals in the upper part of the pluton. Moreover, sustained thermal energy within the magma chamber likely facilitated the upward migration of residual melt, ultimately leading to the formation of the mineralized albitite dikes. These integrated findings advance our understanding of rare-metal granite genesis by highlighting the combined roles of magmatic fractionation, volatile-driven differentiation, and magma chamber dynamics in the concentration of incompatible elements.

The high background of Chlorine (Cl) signals in the carrier gas and the influence of apparent halogen signals have posed challenges for determining Cl content in apatite using Laser Ablation Inductively Coupled Plasma (quadrupole) Mass Spectrometry (LA-(Q)ICP-MS), which hinder simultaneous determination of U-Pb ages, trace element in apatite. In this contribution, we present an enhanced Cl content calibration method using Iolite software 3D Trace Elements DRS. We analyzed six reference materials (RMs) at spot sizes of 44 mu m, 32 mu m, and 24 mu m. The U-Pb ages (corrected against Madagascar apatite), and the trace element concentrations (calibrated using NIST SRM 610), respectively, were consistent with the recommended values. We thus compared two methods for calibrating Cl content: (1) using a single RM (Durango with analyzed Cl content) and (2) employing multiple RMs (Madagascar, Mud Tank, Durango, Otter Lake with Slyudyanka as monitor). The former method yielded Cl contents that deviated from Electron probe microanalyzer analysis (EPMA) results due to the "apparent halogen signal," while the latter provided consistent results across all spot sizes. As analytical uncertainties increase with decreased spot sizes, we recommend >= 44 mu m spot size for routine analysis. Our findings suggest that combinations of Madagascar, Mud Tank, Durango, Otter Lake and NIST SRM 610 can be used to determine U-Pb ages, trace element concentrations, and Cl contents simultaneously using LA-(Q)ICP-MS, where Madagascar and NIST SRM 610 are recommend to corrected U-Pb age and calibrate trace element contents, respectively.

Five fossil beds containing fossil specimens of Hipparion chiai, which is the most widespread index fossil in Late Miocene strata in northern China, were identified. The biological apatite (carbonated hydroxyapatite) in the teeth fossils of Hipparion chiai has a high mu value (initial 238U/204Pbi) and limited Th content. The fossilized tooth enamels remain relatively unchanged due to their resistance to diagenetic alterations. Here, for the first time, we precisely dated six fossil teeth of Hipparion chiai from the Wangdafuliang section in Fugu, Shaanxi Province, using the LA-ICP-MS U-Pb geochronology method. The U-Pb dates obtained from the six fossil teeth of Hipparion chiai range from 6.87 +/- 0.13 Ma to 7.71 +/- 0.39 Ma (2 s), with an average of 7.26 Ma. The ages of the tooth enamels of a Samotherium sp. and a Rhinocerotidae (genus and species unidentified) are consistent with the ages of the tooth enamels of the Hipparion chiai. The analytical method developed for this study provides a new benchmark for dating Neogene fossils.

Hydrothermal alteration can be utilized to constrain element migrations during mineralization, as it records the effects of fluid-rock interactions. Previous studies have suggested that uranium in deposits primarily originates from uranium-bearing granites; however, limited knowledge exists regarding the leaching mechamisms of this element and rare earth elements (REEs) from these rocks. In recent years, the Xiaoshan Deposit, a newly discovered medium-sized uranium deposit, has been discovered in the central part of the Lujing uranium ore field, South China. In this study, we examine this deposit to investigate hydrothermal alterations and their impact on elemental mass change. The deposit exhibits seven types of alteration including K-feldspar, albite, illite, sericite, muscovite, quartz and chlorite alteration. These alterations follow a certain sequence, starting from chlorite alteration, followed by widespread K-feldspar alteration, then to albite alteration, accompanied by muscovite alteration, and finally illite, sericite and quartz alteration. The main uranium mineralization stage was coeval with the late acid siliceous hydrothermal fluid, illite and sericite alteration. The pre-ore alkaline alteration (K-feldspar alteration) resulted in the leaching and extraction of uranium, leading to the precipitation of a significant amount of apatite in mineral interstices and initial uranium enrichment (Delta Ci (U) = 16.52 ppm). This process facilitated material preparation for subsequent acidic alterations and localized ore enrichment. The original dense rock structure was disrupted, creating fractures/cavities that served as conduits for uranium mineralization. Moreover, under alkaline metasomatism, uranium and REEs was extensively leached out of uranium-bearing accessory minerals such as the apatite. According to apatite compositional variations and alteration geochemistry, these variations reveal the process of uranium dissolution, migration, and precipitation enrichment into ore bodies. Uranium was completely released during alkaline metasomatism, causing a sharp decline in U content from 53.1 ppm to 0.96 ppm. The formation of alkaline alteration fluids facilitates the extraction of uranium from the surrounding rocks (the Indosinian granite).

Robust U-Pb dating of accessory minerals (e.g., apatite, titanite, wolframite, and cassiterite) by LA-ICP-MS is often impeded by variable contents of common Pb in matrix-matched reference material (RM). Therefore, common Pb needs to be corrected in these RMs analyses that are used as standards to calibrate isotope fractionation during data reduction. In this study, a novel stand-alone computer program (called Isoclock) focused on the deduction of common Pb from RM, and the corrected RM were used for isotope fractionation. A new common Pb correction method was introduced into the program that allows the deduction of common Pb not only in 206Pb and 207Pb, but also in 208Pb, so that both U/Pb and Th/Pb age calculations can be performed. The software contains several processing steps for the raw files of different mass spectrometers. The processing interface contains data import and view, background correction and filtering of outliers, calculation of common Pb for RMs, fractionation calibration, and age calculation. Isoclock is written using the free and open-source Python language and can either run the code directly or by using a graphical interface. Finally, we discuss the main advantages of this software and its geological application using six examples of apatite, cassiterite, titanite, monazite and wolframite U-Pb dating. New software, Isoclock, focuses on deducing common Pb from reference materials or samples. A novel common Pb correction method has been introduced into the program to process data from hydrothermal/accessory mineral LA-ICP-MS U-Th-Pb dating.

Giant granite-type lithium (Li) deposits in northern Jiangxi province (South China), such as the Shiziling-Baishuidong (1.1Mt @ 0.3 wt% Li2O) and Yichun #414 (0.6 Mt @ 0.39 wt% Li2O), are tectonically located in the Jiangnan Orogen. The concentration and enrichment mechanism of rare metals (incl. Li) in northern Jiangxi is still unclear. Mica is widely distributed in this Li-ore type and is closely ore-related. Therefore, we used mica geochemistry to determine the mineralization process and mechanism of the Shiziling-Baishuidong and Yichun #414 deposits. At Shiziling-Baishuidong, lithium mineralization is concentrated along the intrusive endocontact of Early Cretaceous highly-fractionated S-type muscovite granite. Early albite and muscovite (with Li-rich mica) alterations, and late greisen (muscovite and quartz) alterations are common in the ShizilingBaishuidong and Yichun #414 deposits. The hydrothermal and magmatic muscovite is mostly lepidolite and zinnwaldite, respectively. At Yichun, the biotite- or two-mica granite may have altered by F- and Na-rich magmatic-hydrothermal fluids, leaching the Li-Nb-Ta-W for the subsequent mineralization in the muscovitization and greisenization stages. The re-equilibrated muscovite (M2r), a metasomatic(altered) equilibrated muscovite in the altered granite, has the lowest Li (663 ppm), Nb (15.2 ppm), Ta (16.7 ppm), and W (6.12 ppm) contents. At both Shiziling-Baishuidong and Yichun, the magmatic muscovite has the highest Nb/Ta (mostly > 8) but lower Li/Rb (mostly 1.5), whereas the hydrothermal muscovite has the lowest Nb/Ta (mostly similar to 4) but higher Li/Rb (mostly > 1.5). The re-equilibrated muscovite has Nb/Ta = 4 to 8 and a wide Li/Rb range (0.1 to 2.0). When lithium was precipitated, the re-equilibrated and hydrothermal muscovite mineralogy and chemistry show that hydrothermal alteration was essential in the granite-type Li ore formation at Shiziling-Baishuidong.

High-purity quartz (HPQ) has extremely low total impurity content (<20 ppm, IOTA CG, a HPQ standard of Unimin) and is indispensable to many high-tech optoelectronic industries. Whilst the controlling factors for the granite-hosted HPQ formation are yet to be well resolved, it is generally considered to be related to temperature and pressure, and/or specific purification processes. Here, we analyzed the chemical compositions of quartz and muscovite from various HPQ occurrences in South China. The results indicate that the F content in muscovite and Ti content in quartz provide useful indicators for exploring and characterizing the granite-hosted HPQ. More specifically, we found that granites containing muscovite with <= 0.100 wt% F have the potential to form 4 N5-grade (SiO2 >= 99.995 wt%) HPQ, whereas those with 0.1-1 wt% F have the capacity to generate 3 N-(SiO2 >= 99.900 wt%) to 4 N5-grade HPQ. The ideal quartz crystallization temperature (titanium-in-quartz geothermometer (TitaniQ)) to generate 4 N-(SiO2 > 99.990 wt%) grade HPQ is 420 to 490 degrees C. Higher F content in the granitic melt, which implies higher volatile content, would lower the magma solidus and contribute to the incorporation of impurities such as lattice-bound Ti-Al and fluid inclusions. We propose that in-situ analysis of muscovite and quartz supports rapid assessment of the metallogenic potential of granite-hosted HPQ.

A new software, Brama, was used for processing of large amounts of individual low-count data from LA-ICP-MS U–Pb scans. The data processed by the software can be analyzed with Bayesian regression to calculate age and common Pb.

The coal metamorphism in Central Hunan provides valuable information about hydrothermal activity and water/rock reactions. Learning how to collect age data on hydrothermal fluid systems is necessary for understanding the history and genetic mechanisms of large-scale coal-generated graphite deposits. The Shihangli graphite deposit, formed by significant siliceous hydrothermal alteration, is the most distinctive in Central Hunan. Re–Os dating of pyrite from the Shihangli graphite deposit demonstrates that the coal-generated graphite mineralization age is ~ 127.6 ± 3.8 Ma. Based on in - situ mineral analysis, the hydrothermal pyrite in the Shihangli graphite deposit is mostly enriched in Sb, As, Au, W, Ag, Cu, Pb, and Zn. Based on the pyrite Re–Os isochron, the initial ( 187 Os/ 188 Os) values of pyrite were 1.03 ± 0.24 and the Os(t) values varied from 571.8 to 755.1. Pyrite from the Shihangli graphite deposit comprises a Pb isotope composition similar to that of the Madiyi Formation bulk rock and stibnite from the Xikuangshan Sb deposit. Based on the Re–Os, Sr, S, and Pb isotopic compositions of sulfides in the graphite and Sb deposits in Central Hunan, the Madiyi Formation was likely the primary source of ore-forming elements (Sb, Au, and As). The Re–Os and Pb isotope compositions of pyrite most likely reflect when large-scale fluid migration and coal-generated graphite mineralization occurred in Central Hunan.

The Changjiang U ore field developed typical granite-related U mineralization in the Zhuguangshan complex, China. Pitchblende is the most important ore mineral in these mineralizations. In this study, the mineralogy and geochemistry of pitchblende were investigated by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to identify the genesis of the Changjiang U ore field. Pitchblende exhibits colloidal, fragmented, spherulitic and fine-grained crystals in U ores. Its geochemical compositions are similar to those of other granite-related U deposits in South China, which have elevated contents of U, Sr, As and W; low contents of Pb, Th, Zr, Nb, Ta, Hf, Co, Ni and rare earth elements (REEs); and variable amounts of Ca, Si, Bi, Y, V and Zn. These geochemical signatures suggest that mineralization occurred through hydrothermal genesis and that the hosting Youdong and Changjiang granites acted as the dominant U sources. The uraninite in these granites might be the major U source mineral. Uranium mineralization occurred under the following conditions: low temperature (<250 degrees C), low oxygen fugacity (log f(O2) = -29.5 - -25.5), weakly acidic (pH = 5.3-5.9), high CO32- and F- contents and a silicon-saturated solution. Rapid changes in the physicochemical conditions of the ore-forming fluid are responsible for the precipitation of pitchblende. Combined with previous studies, we propose that U-rich granites, Cretaceous-Tertiary crustal extensions, regional faults and hydrothermal alterations were the critical factors for U formation in the Changjiang ore field.

位于南岭成矿带南西部的鹿井矿床是华南热液型铀矿的典型代表.为查明其成矿流体来源、性质与演化以及成矿机制,开展了不同成矿阶段石英、萤石及方解石中流体包裹体的显微测温和不同阶段石英的氢?氧同位素分析.矿床地质特征表明成矿过程可划分为(I)粗晶石英+黄铁矿±绿泥石±绢云母、(II)沥青铀矿+硫化物+绿泥石+绢云母+暗灰色微晶石英、(III)紫黑色萤石+肉红色方解石+灰色微晶石英+赤铁矿+铀石±黄铁矿和(IV)梳状石英+浅色萤石+白色方解石四个阶段;其中阶段II和III代表成矿主阶段.成矿早阶段和主阶段捕获水溶液包裹体和少量含CO2包裹体,而晚阶段仅见水溶液包裹体.早、主、晚阶段包裹体的均一温度依次为186～317、169～236、149～189℃,盐度依次为9.9～12.9、6.3～9.9、4.5～7.0 wt％NaCleqv.成矿流体自早阶段至晚阶段逐渐由中低温、中低盐度的NaCl-H2O-CO2体系演化为低温、低盐度的NaCl-H2O体系,期间由压力降低引发的流体沸腾作用是重要的成矿机制.H-O同位素数据表明,初始成矿流体来自岩浆水与大气降水的混合,成矿过程伴随着大气降水的持续加入.

赣南草桃背铀矿床位于会昌地区河草坑铀矿田,是一个大型火山岩容矿的铀矿床,成因机制存在较大争议.矿床内发育有大面积的花岗岩和火山岩,矿体主要赋存在火山隐爆角砾岩和震碎花岗岩中.文章以该矿床内花岗岩、火山岩及矿石中广泛发育的蚀变矿物绿泥石为研究对象,采用电子探针及LA-ICP-MS原位微区分析技术对其矿物化学组成进行分析.分析结果表明,花岗岩和矿石中的绿泥石主要为富铁的鲕绿泥石和蠕绿泥石,火山岩中的绿泥石则为相对富镁的密绿泥石.各类绿泥石阳离子置换关系主要以Fe、Mg置换为主,同时存在一定的Tschermak(TK)和二八—三八面体(DT)替换机制.矿石中绿泥石具有相对较高含量的Ti、Li、Be、B、Zn、Ga、Ge、Sn、Cs、U、Rb和Ba等元素,并显示出较低的Th/U比值.矿石中绿泥石的结晶温度区间为201～269℃,平均值为242℃,属于中低温热液作用的产物.矿石中绿泥石的氧逸度(log f O2)变化于-48.4～-41.2之间,平均值为-44.5,硫逸度(log f S2)变化于-7.5～+2.8之间,平均值为-1.8,草桃背铀矿床的铀矿化主要形成于低氧逸度、高硫逸度的环境.

In this paper, the major, trace and rare earth elements of representative fresh samples of granites, altered rocks and ores were studied from the mineralization-alteration cross section in Mianhuakeng uranium deposit, northern Guangdong Province. Using the method of mass balance calculation, the migration law of components in each alteration zone was discussed to solve the problems of the source of ore-forming materials, source of ore-forming fluids and their properties. The results show that the mineralization-alteration cross section has obvious horizontal zoning characteristics, which can be divided into the fresh granite zone (V), the alkali metasomatic alteration zone (IV), the chloritization alteration zone (III), the hydromicatization alteration zone (II) and the hematitization alteration zone (I). From the lateral alteration zone (the alkali metasomatic zone) to the central mineralization zone (the hematite alteration zone), the immigration rate of Si02 (0. 27% 40. 21% 40. 50% 40. 70%) was positive to the immigration rate of U element (4. 73% *8.07% *39.26% 08. 29%). K' and Na were mutually exclusive and incompatible, Mg0 and Mn0 exhibit a negative relationship, which might show a balanced convection migration. Th, Pb, Cs, Mo and As elements have the highest immigration rate in the central mineralization zone, while Ba, Sr, Co and V elements have the lowest migration rate in the central mineralization zone, which could be used as a good indication for uranium mineralization. According to the content, ratio and migration characteristics of the elements in each alteration zone and combine to the previously published data, it is considered that the ore-forming materials of the deposit are mainly contributed by the host rock, the Changjiang granite. The ore-forming fluids were rich in volatiles and mineralization agents (CO2, F, H2 0, etc.), alkali metals (K, Cs, Rb) and HREE with relatively high oxygen fugacity, and its sources were a mixture of mantle fluids and meteoric waters during the deep circulation. The introduction of volatiles and mineralization agents were the important mechanism for mineral migration of the deposit, and the environment from oxidation to reduction with CO2 escape was an important mechanism for mineral precipitation of the deposit.

Early Cretaceous felsic volcanic-intrusive complexes are widespread in the Gan-Hang Volcanic Belt (GHVB) and accompany abundant uranium ore resources. However, the petrogenesis and tectonic significance of these rocks are not well understood. We present zircon U-Pb geochronology, major- and trace-element geochemistry, and Sr-Nd-Hf isotopic compositions of the Yuhuashan Complex and hosted mafic microgranular enclaves (MMEs) from the southwestern part of the GHVB. The Yuhuashan Complex consists of rhyolitic porphyritic lava and subvolcanic porphyritic granite that are metaluminous to weakly peraluminous and have pronounced A-type geochemical characteristics. They were formed at a high temperature and can be further classified as of A2 subtype affinity. The Yuhuashan A-type granitic rocks were generated largely by partial melting of Proterozoic metamorphic rocks. Our new data, together with previously published data, suggest that the Early Cretaceous A2-type granitic rocks formed along the GHVB during an extensional event. The MMEs hosted in the Yuhuashan porphyritic granite exhibit igneous textures, suggesting quenching of mafic magmas that comingled with the host granitic magma. Zircons from the MMEs have similar U-Pb ages but higher εHf(t) values, compared to the host granite. Hence, the MMEs and host granite likely crystallized from different magma sources, providing direct evidence for mafic-felsic magma-mingling processes. The MMEs have high MgO and K2O contents and show shoshonitic affinities. Geochemical and isotopic data imply that the MMEs were derived from a phlogopite-bearing lithospheric mantle source that had been metasomatized by previous subduction-related fluids or melt. Underplating of such high-temperature mafic magmas could have induced lower-crustal rocks to partially melt and generate the Yuhuashan A-type complex. A backarc extensional setting, related to the rollback of a subducted paleo-Pacific-derived plate, is favored to explain the petrogenesis of the Yuhuashan Complex and MMEs.