Zhenzhen Li

The Dajing Cu-Sn polymetallic deposit, situated within the southern Great Xing’an Range of northern China, is a representative Mesozoic magmatic–hydrothermal system within a major Cu–Sn–Ag–Pb–Zn metallogenic belt. Located at the junction between the Siberian and North China plates, the deposit occurs within a composite tectonic domain overprinted by the Paleo-Asian, Mongol–Okhotsk, and Paleo-Pacific systems. Building on field geological constraints and detailed ore petrography, this study utilizes SEM–CL imaging and in situ LA–ICP–MS trace-element analysis of hydrothermal quartz to reconstruct the multistage physicochemical evolution and fluid dynamics of the ore-forming system. Three quartz generations record successive mineralization stages: early QI forms grain cores associated with Stage I cassiterite–arsenopyrite–quartz mineralization; main-stage QII crystallized during or shortly after Stage II chalcopyrite precipitation and exhibits well-developed oscillatory zoning; and late QIII occurs mainly as rim overgrowths and fracture fillings and postdates Stage III ore-mineral precipitation. Quartz is characteristically Ti-poor (4.7–22.8 ppm), and its trace-element systematics indicate a low- to intermediate-temperature hydrothermal signature and a granitic magmatic–hydrothermal affinity. Al, Li, Na, K, and Ge show coupled behavior consistent with heterovalent substitution and vary markedly among quartz generations, with CL-bright QIIa showing relatively higher Al, Ge, and Na relative to CL-dark QIIb, whereas QIII is generally characterized by lower Al, Li, and Ge. Localized anomalously high Cu and Sn values are mainly attributed to the co-ablation of fine-grained mineral inclusions, metal-rich fluid inclusions, or fracture-filling components. These features indicate a chemically heterogeneous fluid reservoir with inferred relatively acidic conditions during the initial Sn-mineralization stage. The fluid system subsequently experienced recurrent physicochemical fluctuations associated with pulsed fluid input during the principal Cu-mineralization stage. QIII records a trace element-depleted late-fluid system associated with the terminal pyrite–quartz stage. Late fluids migrated along earlier quartz boundaries and fractures and may have undergone further cooling and dilution through fluid mixing and/or water–rock interaction. Overall, the fluid system shows a progressive shift in inferred fluid chemistry, consistent with decreasing acidity during hydrothermal evolution.

The Dajing giant Cu–Sn polymetallic deposit is located in the Cu–Sn–Ag–Pb–Zn polymetallic belt of the southern Great Xing’an Range, NE China. Research on its ore genesis is of great significance for understanding Sn polymetallic mineralization in this region. In this study, pyrite, arsenopyrite, and sphalerite were analyzed by electron-microprobe analysis (EMPA) and in situ S–Pb isotope analysis. Previously published fluid-inclusion microthermometric and H–O isotope data were also incorporated to constrain fluid evolution and ore genesis. Both in situ S and Pb isotopic compositions fall within short ranges. The δ³⁴S values suggest a sulfur reservoir with possible magmatic contribution, whereas Pb isotopes indicate a mainly crustal Pb signature in an orogenic setting. Arsenopyrite records variations in As, S, Fe, and Co contents from core to rim. The Co-rich core shows Co enrichment accompanied by Fe depletion, consistent with Co-for-Fe isomorphous substitution. These features indicate changes in local fluid chemistry during arsenopyrite growth. Sulfur isotope geothermometry based on coexisting late-stage pyrite–sphalerite pairs yields 118–233 °C, with an average of 159 ± 49 °C, indicating medium- to low-temperature hydrothermal activity during the late sulfide stage. The Dajing deposit is interpreted as a fault-controlled hydrothermal vein-type Cu–Sn polymetallic deposit formed in a Late Jurassic extensional setting. Ore precipitation was likely promoted by cooling during upward fluid migration away from the magmatic heat source, pressure release, meteoric-water mixing, and fluid–rock interaction with granitic rocks and Linxi Formation wall rocks. This study provides mineral-scale constraints on fluid evolution and ore genesis in the Great Xing’an metallogenic belt.

大兴安岭南段是我国重要的锡多金属成矿带，锡找矿潜力巨大，小乌兰（宝盖沟）锡铁矿是该带腹地一处小型锡矿床。为取得进一步找矿突破，本次研究采用蚀变矿物勘查方法，在小乌兰矿区开展了系统的短波红外光谱（SWIR）和绢云母矿物化学分析（电子探针主量元素和LA-ICP-MS微量元素），结合锡石原位U-Pb定年，揭示成矿流体运移路径，圈定找矿靶区。研究结果显示，该矿床锡矿化形成于143.2±0.8Ma，是大兴安岭南段燕山期大规模锡多金属成矿事件的组成部分。小乌兰矿区围岩蚀变以硅化、白云母化、绢云母化、绿泥石化为主，少量电气石化和黄玉化，蚀变整体呈带状分布，分带不明显，矿化与云英岩化密切相关。绢云母Pos2200整体偏低（2198~2209nm），与围岩为酸性花岗质岩石有关。空间分布上，绢云母Pos2200在西半区呈现中部高且向南东和北西变低的趋势，是热液流体pH和成分变化的直接体现，Pos2200高值区 (>2205nm)内流体pH略偏中性，更靠近高温热液中心，靠近云英岩化矿脉，流体转变为偏酸性，Pos2200降低（2203~2206nm）。矿物化学结果显示西半区中部绢云母更富集Fe、Sn、Li和Rb，而向北西和南东方向更富集流体活动性元素Nb、W、Cu、Pb、B和Ga，暗示西半区的中部更靠近热液活动中心，且流体沿断裂向北西和南东方向迁移。短波红外光谱和矿物化学结果均展现出西半区中部为更高温的热液活动中心，流体沿北西-南东向构造迁移成矿的特征，显示出绢云母可作为有效的矿物指针示踪流体演化与迁移路径，也为区内同类型锡多金属矿床的找矿勘查提供一定的理论依据。

The Mapeng pluton in the central Taihang Mountains hosts significant gold mineralization; however, the magmatic processes controlling its emplacement, crystallization, and potential role in ore genesis remain debated. Previous petrological and geochemical studies have identified three internal lithofacies zones and suggested magma mixing. However, it remains uncertain whether these zones formed through in situ fractional crystallization or multiple intrusive pulses, and how magmatic dynamics contributed to gold enrichment. To address these questions, we applied quantitative crystal size distribution (CSD) analysis to constrain the intrusion history and evaluate its implications for mineralization. The CSD curves of quartz in the Mapeng granite are typically concave, with characteristic lengths (CLs) ranging from 0.78 to 1.43 mm, slopes from −1.29 to −0.70, and intercepts from −2.10 to 0.95. These variations indicate strong fluctuations in crystal growth and nucleation rates, suggesting a major influence of magma mixing. For plagioclase, the CL values range from 0.56 to 2.50 mm, slopes from −4.40 to −1.33, and intercepts from −1.21 to 3.48, further supporting the idea of multistage magma injection and crystal coarsening. Regarding crystal spatial distribution and alignment, the crystal aggregation degree (R value) ranges from 0.79 to 1.14, and the alignment factor (AF value) ranges from 0.01 to 0.19. These values suggest that the crystals tend to aggregate spatially, with their alignment degree being extremely weak, which indicates rapid magma flow disturbed by mixing processes. Notably, the R value and AF value show a negative correlation (R² > 0.6) in the central facies and a positive correlation in the transitional facies, revealing differences in crystal accumulation mechanisms among different lithofacies zones. By synthesizing the covariance of CSD parameters and texture indices, this study infers that the Mapeng pluton experienced multiple batches of magma injection during its emplacement and consolidation. These injection events accelerated crystal dissolution and regrowth, thereby promoting crystal coarsening and textural reorganization. This study provides new quantitative mineral–textural evidence.

伟晶岩壳的形成与相关花岗质岩体的演化及其中的Sn-W金属矿化有密切联系，但目前针对伟晶岩壳的研究还相对薄弱。大兴安岭南段白音乌拉钨锡矿床内与成矿有关黑云母花岗岩发育显著的岩相分带：深部为主体中粗粒黑云母花岗岩，向上过渡到细粒黑云母花岗岩，最上部为由伟晶岩-细晶岩层组成的伟晶岩壳。在详细的岩相学观察基础上，本文对不同岩相带和热液脉中的黑云母开展了电子探针主量元素点分析和面扫描以及LA-ICP-MS微量元素分析。结果显示，相比其他两个岩相，伟晶岩壳中岩浆成因黑云母具有最高的FeO、MgO、Cl含量，最低的Al₂O₃、K₂O、F、Li、Sn、W、Nb、Ta含量，表明伟晶岩壳具有最低的演化程度，而细粒黑云母花岗岩演化程度最高。伟晶岩壳中以钾长石定向生长为特征的单向固结结构十分发育，其中黑云母可见蠕虫状石英+黑云母增生边，其形成与富水岩浆过冷有关。因此，伟晶岩壳相对深部岩体而言，其形成时间更早，属于岩浆房的早期冷凝边。伟晶岩壳形成之后，可作为“盖层”而促进深部岩浆房的演化，并使Sn、W等不相容元素富集于晚期演化程度最高的岩相内，随后发生流体出溶而成矿。伟晶岩壳和细粒黑云母花岗岩内，岩浆黑云母外增生的热液成因黑云母证实了这一流体出溶过程的发生。白音乌拉矿床内不同岩相带内黑云母较高的Sn和W含量指示成矿岩体具有良好的成矿物质条件，但不同产状的热液型黑云母中Sn含量差异较大，而W在所有产状的热液型黑云母中含量均很高，可能暗示Sn与W成矿是由不同批次的流体形成，但二者均具有较好的成矿潜力。

Fluorite is a widespread mineral in porphyry and hydrothermal vein Mo-polymetallic deposits. Here, fluorite is utilised as a probe to trace the fluid source and reveal the fluid evolution process in the Chalukou giant Mo (Pb–Zn) deposit, Northeast China, which is characterised as early porphyry Mo and later vein-style Zn–Pb mineralisation. A detailed rare earth element (REE) and Sr–Nd isotope study of fluorite combined with Sr isotopes of sphalerite is conducted for the Chalukou deposit. The chondrite-normalised REE patterns of fluorites from molybdenite veins show light REE (LREE)-enriched patterns, with negative Eu anomalies (δEu = 0.60) and weakly negative Y anomalies (Y/Y* = 0.72). The fluorites associated with sphalerite veins exhibit rare earth element (REE)-flat patterns with negative Eu anomalies (δEu = 0.65 to 0.99) and positive Y anomalies (Y/Y* = 1.37 to 3.08). In addition, during the progression from Mo to Zn–Pb mineralisation, the total concentration of REEs decreases from 839 ppm to 53.7 ppm, and Y/Ho ratios increase from 22.1 to 92.5. These features may be explained by the different mobilities of REE complexes during fluid migration. The Eu anomalies are considered to be inherited from source fluids. All the initial ⁸⁷Sr/⁸⁶Sr ratios of fluorite and sphalerite are between those of ore-forming porphyries and wall rocks (rhyolite), with fluorite ratios ranging from 0.706942 to 0.707386 and sphalerite ratios varying from 0.705221 to 0.710417. The majority of εNd(t) values of fluorite varying from −6.4 to −3.6 are also located between the ratios exhibited by ore-forming porphyries and rhyolite, whereas three εNd(t) values of fluorites ranging from −0.26 to 0.36 are close to those of ore-forming porphyries. All the isotopic features indicate that the Sr-Nd isotope ratios of hydrothermal fluid are derived from porphyries and disturbed by fluid–rock reactions. Together with a two-stage Sr–Nd isotope mixing model, we suggest that different sources and fluid–rock interactions (syn-ore intrusions and strata) finally influence the Sr–Nd isotopes of the ore-forming fluids, which are recorded by the majority of fluorite and sphalerite.