论文部分内容阅读
川西冕宁-德昌喜马拉雅期稀土元素成矿带长约270km,宽15km,包括牦牛坪超大型、大陆槽大型、木落寨中型和里庄小型REE矿床以及一系列矿点和矿化点。该矿带在空间上位于攀西二叠纪古裂谷中,但岩体和矿体均形成于喜马拉雅期,年龄为40~10Ma。REE成矿作用与喜马拉雅期碳酸岩-碱性杂岩体有关,受印度-亚洲大陆碰撞带东部一系列新生代走滑断裂系统控制。碳酸岩-碱性杂岩体主要侵位于元古代结晶基底和古生代—中生代沉积盖层内。矿区蚀变以霓长岩化为特征,在杂岩体和矿体中形成规模不等的霓长岩蚀变晕。REE成矿作用主要有3种样式,即大陆槽式、牦牛坪式和里庄式。大陆槽式以爆破角砾岩筒矿化为特征,牦牛坪式以典型的脉状矿化系统为标志,里庄式则以浸染状矿化为特色。主要矿石类型有伟晶岩型、碳酸岩型、角砾状和网脉状,矿物组合主要为重晶石+萤石+霓辉石+方解石+氟碳铈矿。流体包裹体和稳定同位素研究表明,成矿流体来源于碳酸岩-正长岩不混溶岩浆系统,但在流体演化的晚期阶段有外部流体的加入。根据综合分析研究,笔者提出了一个可能的REE成矿作用模式。该模式强调,成矿热液流体系统经历了一个复杂的演化过程:从不混溶碳酸岩-正长岩岩浆系统分离出高温、含硫酸盐富REE的NaCl-KCl卤水,到流体沸腾导致REE-氟碳酸盐和硫酸盐有效沉淀,最后与雨水混合导致少量硫化物沉积。在空间上形成了一个“三层楼”式的REE成矿系统:在深部层位,形成细脉-浸染状矿体(如里庄式矿床);在中部层位,形成脉状矿体(如牦牛坪式矿床);在上部层位,形成角砾岩筒矿体(如大陆槽式矿床)。成矿系统发生于喜马拉雅期大陆碰撞带从压扭向张扭转变过渡的构造背景下,新生代大规模走滑断裂及其派生的拉分构造和张性裂隙带促进了含REE岩浆-热液系统的形成。
The Mianning-Dechang Himalayan REE belt in western Sichuan is about 270km long and 15km wide. It includes the Maoniuping mega-scale, continental channel large-scale, Muluozhai medium-sized and Lizhuang small REE deposits and a series of ore-hosting and mineralization sites. The ore belt is spatially located in the Permian ancient rift in Panxi, but both the rock mass and the ore body were formed in the Himalayan period with an age of 40-10 Ma. REE mineralization is related to the Himalayan carbonate-alkaline complex and controlled by a series of Cenozoic strike-slip faults in the eastern Indo-Asian collision zone. Carbonatite-alkaline complex mainly intruded in Proterozoic crystalline basement and Paleozoic-Mesozoic sedimentary cover. The alteration of the mining area is characterized by the rifloraization of the niobium, and the alteration of the rifnium of the Niobium type is formed in the complex bodies and ore bodies. REE mineralization mainly has 3 kinds of styles, namely continental trough type, yak type and Lizhuang type. The continental trough is characterized by the mineralization of the brecciated breccia tube. The typical yak type is marked by a vein-type mineralization system, while the Li-Zhuang style is characterized by disseminated mineralization. The main types of ore are pegmatite type, carbonate type, breccia and reticulate vein. The mineral assemblages are mainly barite + fluorite + nihuiite + calcite + bastnaesite. Fluid inclusions and stable isotope studies show that the ore-forming fluid is derived from the carbonate-syenite immiscible magmatism system, but an external fluid is added in the late stage of fluid evolution. According to comprehensive analysis and research, the author proposed a possible mode of REE mineralization. This model emphasizes that the fluid-forming hydrothermal fluid system undergoes a complex evolutionary process: the high temperature, sulfate-rich REE-rich NaCl-KCl brine is separated from the immiscible carbonate-syenite magma system, and fluid boiling leads to REE - Fluorocarbons and sulphates precipitate effectively, and finally mixing with rain leads to small amounts of sulfide deposits. A “three-story” REE metallogenic system has been spatially formed: at the deep level, veinlets-disseminated ore bodies (eg, Li Zhuang-type deposits) are formed; at the middle level, vein-shaped ore bodies (Such as the Maoniuping deposit). In the upper layer, breccia tube bodies (such as continental trough deposits) are formed. The metallogenic system occurred in the tectonic setting of the Himalayan continental collision zone transition from compression and torsion to torsional deformation. The Cenozoic large-scale strike-slip faults and their derived pull-apart structures and zonal fractures promote the formation of REE- The formation of the system.