滇西北衙金矿床富碱斑岩岩浆氧逸度对成矿的制约

发布时间：2018-02-24 21:51

本文关键词： 氧逸度富碱斑岩锆石北衙金矿滇西　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：斑岩型矿床是世界上铜、钼的主要来源,很多斑岩型铜矿富含金,可构成超大型金矿,也是金的重要来源。世界上许多的超大型-大型斑岩矿床的产出环境往往与与板块俯冲有关,主要包括岛弧和陆缘弧环境。近年的研究工作发现在陆内环境、后碰撞环境中,也发育一系列大型-超大型斑岩矿床。这些斑岩矿床与弧环境产出的斑岩矿床有着较多相似之处,但其成岩成矿的年龄均与后碰撞和碰撞构造背景密切相关,而与弧环境以及洋壳俯冲没有直接的关系。相对而言,产于弧环境中的斑岩型矿床的岩浆氧逸度较高,而对于后碰撞陆内环境斑岩矿床岩浆氧逸度及其成矿制约尚缺乏系统论述。滇西北衙矿集区位于印度-欧亚大陆碰撞后形成的陆内环境,是该区域规模最大的金多金属矿床,斑岩体在矿区呈岩株状广泛出露,但除了在万硐山、红泥塘、马头湾、南大坪等几个斑岩体中先后发现金矿体,周围很多斑岩体并无矿化。对于斑岩型矿床的含矿与无矿斑岩体,它们之间的差别一直备受关注。论文通过岩相学和岩石地球化学特征,对比分析了北衙矿区发育的富碱斑岩岩相学、地球化学特征、锆石微量元素特征以及岩浆氧逸度的差异,探讨了岩浆氧逸度对成矿的制约。取得的主要认识如下:1、锆石LA-ICP-MS测年显示,北衙矿集区的含矿岩体与无矿岩体的年龄接近,集中在36 Ma左右。2、通过锆石微量元素对各个岩体进行对比研究,北衙金矿床的含矿岩体的锆石Ce~(4+)/Ce~(3+)比值普遍高于无矿岩体,并且含矿岩体的岩浆氧逸度也普遍高于无矿岩体。3、北衙金矿床富碱斑岩有着与埃达克岩相似的地球化学特征,其源区为加厚下地壳,含矿岩体的源区可能受到富集地幔物质的影响,使其具有不同的特征。富集地幔经历过洋壳的俯冲改造,有着高的S含量和高的氧逸度,在较高的氧逸度条件下,S以SO_4~(2-)的形式在岩浆中高度富集,使得亲铜元素Cu、Au不断富集,为该区的斑岩型Cu-Au矿化提供了成矿物质来源。
[Abstract]:Porphyry deposits are the main source of copper and molybdenum in the world. Many porphyry copper deposits are rich in gold and can form super-large gold deposits. It is also an important source of gold. The occurrence environment of many super-large porphyry deposits in the world is often related to plate subduction, including island arc and continental margin arc environment. A series of large and super-large porphyry deposits are also developed. These porphyry deposits are similar to porphyry deposits in arc environment, but their diagenetic and metallogenic ages are closely related to the post-collision and collisional tectonic setting. In contrast, porphyry deposits occurring in arc environments have higher oxygen fugacity of magma. However, the oxygen fugacity of magma and its ore-forming constraints in post-collision continental environment porphyry deposits are not discussed systematically. The Ya ore concentration area in northwest Yunnan is located in the intracontinental environment formed after the India-Eurasia collision, and is the largest gold polymetallic deposit in this region. The porphyry is widely exposed in the mining area, but gold ore bodies have been discovered in Wandong Mountain, Hongjitang, Matou Bay, Nandaping and other porphyry bodies. Many porphyry bodies are not mineralized. The differences between ore-bearing and ore-free porphyry bodies in porphyry deposits have been paid close attention to. The differences in lithology, geochemistry, trace element characteristics of zircon and oxygen fugacity of magma developed in Beiya mining area are compared and analyzed. The constraints of magmatic oxygen fugacity on mineralization are discussed. The main conclusions are as follows: 1. Zircon LA-ICP-MS dating shows that the age of ore-bearing rock mass in Beiya ore concentration area is close to that of ore-free rock mass. Concentrated at 36 Ma or so, the zircon trace elements were used to study each rock mass. The results show that the ratio of zircon Ce~(4 / CEO _ 3 in the ore-bearing rock body of Beiya gold deposit is generally higher than that of the ore-free rock mass. The oxygen fugacity of magma of ore-bearing rock is generally higher than that of ore-free rock. The alkali-rich porphyry of Beiya gold deposit is similar to that of adakite, and its source area is thickened lower crust. The source region of the ore-bearing rock may be affected by the enriched mantle material, which has different characteristics. The enriched mantle has undergone subduction transformation of the oceanic crust, with high S content and high oxygen fugacity. Under the condition of high oxygen fugacity, S is highly enriched in magma in the form of so _ 4C _ 4 ~ (2), which leads to the continuous enrichment of Cu _ 2O _ (-au), which provides a source of ore-forming material for porphyry type Cu-Au mineralization in this area.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.51

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