大兴安岭南段道伦达坝铜多金属矿床成矿作用及铜-钨-锡-银共生分离机制

The southern Great Xing'an Range is the most important copper–tin–silver–polymetallic ore cluster in northern China, where a large number of copper–tin–silver–lead–zinc–(tungsten–iron) deposits, such as Huanggangliang, Weilasituo, Dajing, Daolundaba, Baiyinchagan, Maodeng, and Bianjiadayuan, occur. However, the mineralization of these deposits, especially the paragenesis and separation mechanism of Cu–W–Sn–Ag (lead–zinc) has not been well studied. The Daolundaba deposit is located in West Ujimqin Banner, southern Great Xing'an Range, and is a Cu-based, associated with W–Sn–Ag medium-sized deposit. The deposit includes Cu orebody, W orebody, Sn orebody, Cu–W orebody, Cu–Sn orebody, W–Sn orebody, and Cu–W–Sn orebody, with associated Ag. These ore bodies occur not only as alien symbiosis, but also intergrowth symbiosis; therefore, the Daolundaba deposit is an ideal object to study the Cu–polymetallic mineralization and the mechanism of Cu–W–Sn–Ag paragenesis and separation. This project is based on the study of the mechanism of Cu–W–Sn–Ag paragenesis and separation, and the laser in situ analysis technique will be widely used in the process of research. Our study will focus on ore-forming fluid system, micro mineralogy, and petrpgenesis of ore causative intrusion. The purpose of the study is to find out the partition coefficients of elements between magma and fluid; the ore-forming fluid characteristics, exsolution, evolution, and mineralization process; the origin, migration, enrichment, and precipitation condition of ore-forming elements; the mechanism of Cu–W–Sn–Ag paragenesis and separation; and the constraints of magma source and magma evolution on mineralization. This study can not only obtain innovative results on paragenesis and separation mechanism of Cu–W–Sn–Ag and mineralization in the Daolundaba copper–polymetallic deposit but also can enrich the metallogenic theory of copper–tin–polymetallic deposits in China, and solve the genesis of copper–tin–polymetallic deposits in the southern Great Xing'an Range.

大兴安岭南段是我国北方最重要的铜锡银多金属矿集区，然而关于这些矿床的成矿作用，尤其是铜钨锡银（铅锌）元素共生分离机制的研究尚处于起步阶段。道伦达坝铜多金属矿床位于大兴安岭南段的西乌珠穆沁旗，是一个以铜为主，共伴生钨、锡、银的中型矿床，矿床内产出铜钨锡同体共生和异体共生矿体，是研究铜多金属成矿作用和铜钨锡银元素共生分离机制的理想对象。本项目以铜钨锡银元素共生分离机制研究为主线，充分利用激光原位分析技术，通过成矿流体系统、微区矿物学和成矿岩体成因研究，查明元素在岩浆和流体中的分配系数、成矿流体出溶、演化与成矿的关系，成矿元素起源、迁移、富集、沉淀条件和元素共生分离机制，及岩浆源区成分和岩浆演化过程对成矿的控制作用。本项目不但有望在道伦达坝矿床铜钨锡银元素共生分离机制和成矿作用等方面取得创新性成果，而且可以丰富我国铜锡多金属矿床成矿理论，回答大兴安岭南段铜锡多金属矿床成因问题。

道伦达坝铜锡钨银矿床位于大兴安岭南段。该矿床的成矿岩体及成矿时代存在较大争议，锡钨铜银元素共生分离机制尚不清楚。本项目对该矿床开展了矿床地质特征、成矿流体系统、成矿流体和成矿物质来源、成岩成矿时代、成矿岩体源区组成及成因、元素共生分离和矿质沉淀机制研究。研究表明，道伦达坝矿床属于典型的断控中高温岩浆热液矿床，成矿与硅化、萤石化、黄铁绢英岩化关系密切，成矿过程经历了气成-高温热液阶段（Ⅰ阶段）、高温热液阶段（Ⅱ阶段）、中温热液阶段（Ⅲ阶段）和低温热液阶段（Ⅳ阶段），其中Ⅰ、Ⅱ和Ⅲ阶段是主成矿阶段。Ⅰ、Ⅱ、Ⅲ和Ⅳ阶段流体包裹体均一温度和盐度分别介于309～389℃和6.2%～46.3%NaCleqv、242～339℃和5.3%～41.4%NaCleqv、153～268℃和3.5%～35.4%NaCleqv、114～188℃和2.1%～7.6%NaCleqv，由早阶段到晚阶段，成矿流体温度和盐度逐渐降低。石英和萤石的H-O同位素组成表明，Ⅰ和Ⅱ阶段流体主要为岩浆水，Ⅲ阶段流体为岩浆水与天水的混合，Ⅳ阶段主要为大气降水。硫化物S-Pb同位素组成表明，成矿物质主要来自岩浆。LA-ICP-MS锡石U-Pb、独居石U-Pb和绢云母40Ar-39Ar定年分别获得136.8±7.4Ma～134.7±6.6Ma、137.8±1.8Ma～134.7±2.8Ma和140.0±1.1 Ma的年龄；成矿岩体的LA-ICP-MS锆石U-Pb年龄介于136Ma～134Ma；成岩成矿时代均属早白垩世。成矿岩体具有高硅、富钾、低钙、贫镁特征；稀土配分曲线呈强烈铕负异常的海鸥式，四分组效应明显；岩石富集Rb、Th、U、K，亏损Ba、Sr、P、Ti、Nb、Zr等元素；岩体具有正的εHf(t)值（4～10.7）和年轻的Hf同位素模式年龄（505～931 Ma），暗示花岗岩的源区主要为起源于亏损地幔的新元古代新生下地壳物质。岩体中的云母为铁锂云母和锂云母，磷灰石为氟磷灰石，成矿岩体为典型高分异I型花岗岩。岩浆低的氧逸度和富氟对W和Sn的活化、迁移、富集起着重要作用；成矿流体的多次沸腾及流体混合是矿质沉淀的主要机制。本研究成果对理解大兴安岭南段锡多金属成矿作用具有重要的理论意义。