内蒙古双尖子山银多金属矿区及外围岩浆活动与银多金属成矿作用

发布时间：2018-06-12 02:11

  本文选题：叠合成矿作用 + 年代学　； 参考：《中国地质大学》2017年博士论文

【摘要】：内蒙古双尖子山银多金属矿床位于大兴安岭南段黄岗-甘珠尔庙成矿带,为超大型热液脉型矿床,在时空分布上与中-晚侏罗世构造-岩浆活动关系密切。双尖子山银多金属矿化产出在下二叠统大石寨组火山-沉积岩内,并且构成似层状、(长)扁豆状、透镜状和囊状等脉型矿体,且被中侏罗世火山岩所覆盖。矿区内三种主要矿化类型被认知:主要赋存在蚀变围岩中的浸染-细脉状矿化、寄宿在北西向和北东向的脉和断层中的角砾状矿化。根据不同矿化类型的切割关系,双尖子山银多金属矿化系统可能是相对较早的石英-细脉状矿化被相对后期的脉型和角砾状矿化所叠加。锆石LA-ICP-MS U-Pb测年结果基本厘定了双尖子山矿区及外围侵入-火山岩的年代学格架,确定岩浆活动主要分三个阶段,分别为262~238 Ma、169~159 Ma和142~131 Ma,主要集中在晚二叠世-早三叠世、中-晚侏罗世和早白垩世三个阶段。此外,北西向含矿石英脉的白云母Ar-Ar坪年龄为147±2 Ma和硫化物(毒砂、黄铁矿)的Re-Os等时线年龄为159±6 Ma,以及含矿石英脉的锆石U-Pb加权平均年龄给出了三组年龄值,分别为263±2 Ma,177±2 Ma和148±1 Ma。其中最年轻的一组数据(148±1 Ma)指示着岩浆热液锆石的年龄或石英脉形成的最晚时限。这些数据均显示了双尖子山脉型矿化可能与中晚侏罗世热事件有关。矿床稳定和放射性同位素地球化学指示,石英脉和角砾岩型矿石的成矿流体主要由岩浆水和高度演化的大气降水组成,流体缓冲作用和成矿流体的混合是重要的成矿机理。C和S同位素均指示成矿流体中的碳和硫主要源于岩浆,并混染了部分围岩。铅同位素同样证实了成矿流体的混合模式,成矿系统(浸染-细脉状、脉型和角砾状矿石)的铅同位素呈现线性分布,主要分布在壳源铅和地幔铅之间,同样也指示了成矿流体中的铅源自深源,并混入了壳源铅。根据矿石组合和矿石地球化学,双尖子山矿床是一个中温中硫的银多金属矿床,其氧逸度和硫逸度分别是-35.1~-30.5和-17.2~-13.1,主成矿温度为250~240℃,成矿物质的沉淀主要是在流体混合和沸腾作用下由混合流体沉淀而成。与双尖子山银多金属主矿化有关的中-晚侏罗世岩浆活动可能是蒙古-鄂霍茨克洋闭合后的后造山伸展及古太平洋板块俯冲共同作用的结果。这种联合的动力机制,引起构造体制从挤压到拉张的转变,随后引发大规模加厚下地壳和岩石圈地幔拆沉。岩石圈拆沉及随后上涌的软流圈地幔诱发大量岩浆的侵入,这些岩浆从深部带来了大量的硫和其他金属成矿元素,为后期大规模的热液成矿提供了充足的物质准备,双尖子山热液脉型矿化就形成于这样的构造背景之下。
[Abstract]:The Shuangjianzishan silver polymetallic deposit in Inner Mongolia is located in the Huanggang-Ganjuermiao metallogenic belt in the southern section of the Daxinganling Mountains. It is a very large hydrothermal vein type deposit and is closely related to the tectonic-magmatic activity of the Middle-Late Jurassic in time and space. Shuangjianzishan silver polymetallic mineralization occurred in volcanic-sedimentary rocks of the Lower Permian Dashizhai formation, and formed a lamellar (long) lentil, lenticular and cystic vein orebody, which was covered by the volcanic rocks of the Middle Jurassic. Three main types of mineralization are recognized in the mining area: leaching and veinlike mineralization in altered surrounding rocks, and breccia mineralization in veins and faults in NW and NE directions. According to the cutting relationship of different mineralization types, the bangjianzishan silver polymetallic mineralization system may be superimposed by the relatively late vein type and breccia mineralization in the relatively early quartz-veinlike mineralization system. The zircon LA-ICP-MS U-Pb dating results have basically determined the geochronological framework of the intrusion-volcanic rocks in the Shuangjianzishan ore area and its periphery, and determined that magmatic activity is mainly divided into three stages, namely, 262an238Ma-169159Ma and 142Pn-131Ma, mainly concentrated in the late Permian-early Triassic. Middle-late Jurassic and early Cretaceous. In addition, the Ar-Ar plateau age of Muscovite and Re-Os isochron of sulfide (arsenopyrite, pyrite) in NW direction is 147 卤2 Ma and 159 卤6 Ma.The zircon U-Pb weighted mean age of ore-bearing vein gives three sets of age values. It is 263 卤2 Ma 177 卤2 Ma and 148 卤1 Ma respectively. The youngest set of data (148 卤1 Ma) indicates the age of magmatic hydrothermal zircon or the latest time limit for the formation of quartz veins. All these data suggest that the bipine-type mineralization may be related to the middle and late Jurassic thermal events. The deposit stability and radioisotope geochemistry indicate that the ore-forming fluid of quartz vein and breccia type ore is mainly composed of magmatic water and highly evolved atmospheric precipitation. The mixing of fluid buffer and ore-forming fluid is an important metallogenic mechanism. Both C and S isotopes indicate that the carbon and sulfur in the ore-forming fluid are mainly derived from magma and mixed with part of the surrounding rock. The lead isotopes also confirmed the mixed model of ore-forming fluids. The lead isotopes of the ore-forming systems (leaching-vein-vein, vein-type and breccia ores) showed a linear distribution, mainly between crust-derived lead and mantle lead. It also indicates that the lead in the ore-forming fluid originates from the deep source and mixed with the shell source lead. According to ore assemblage and ore geochemistry, Shuangjianzishan deposit is a medium temperature medium sulfur silver polymetallic deposit with oxygen fugacity and sulfur fugacity of -35.1 ~ 30.5 and -17.2 ~ (-2) ~ (-1), respectively. The main ore-forming temperature is 250 ~ 240 鈩，

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