【作者】 曾荣；

【导师】 薛春纪； 裴先治；

【作者基本信息】 长安大学 ， 地质工程， 2007， 博士

【摘要】 西南三江中段兰坪盆地因产有包括金顶超大型铅锌矿床及其外围一系列矿床而成为引人注目的巨型矿集区。虽然大规模成矿作用发生在中新生代沉积地层当中,但这里的大型矿床与以沉积岩为主岩的MVT矿床、SST矿床、Sedex型矿床均不可类比,成矿机制独特。在对兰坪盆地铅锌铜大型矿集区内矿床的众多研究中不难发现,后生特点明显,热液成矿特征显著,由此可见,兰坪盆地铅锌铜大型矿集区内矿床形成机制认识的关键性问题之一就是流体的问题。笔者正是在注意到兰坪盆地成矿作用的独特性以及流体对认识成矿作用的重要性的基础上,通过对区域成矿地质背景的分析,选取盆地内的两个超大型矿床作为研究对象,以揭示其流体成矿作用机制。金顶矿床以白垩系和第三系陆相碎屑岩为主岩,拥有2亿吨矿石,平均品位Zn6.08%、Pb1.29%（1500万吨金属）,是目前中国最大的Zn-Pb矿床,也是世界上形成时代最新且唯一陆相沉积岩容矿的超大型Zn-Pb矿床。不同于世界上人们公认的沉积岩容矿基本类型,金顶矿床也许代表了沉积岩容矿Zn-Pb矿床的一个新类型。位于金顶超大型铅锌矿床北部30公里的白秧坪Cu-Ag-Co多金属矿床,是继金顶之后在兰坪盆地发现的又一个大型甚至超大型多金属矿床。因此,如能将金顶矿床的成矿流体研究与白秧坪矿床的流体研究结合起来,相互对比,彼此借鉴,就可以明显地推进兰坪盆地的成矿学研究。本研究是在前人研究所积累丰富地质资料的基础上,通过系统详尽的矿相学研究,在查清矿石中矿物共生、伴生和世代关系以及不同矿化阶段矿物共生组合特点的基础上,以不同矿化阶段所形成的典型矿物组合及流体包裹体为对象,通过对流体包裹体的岩相学特征、冷热台研究以及流体包裹体的气液相成分、稀土微量元素的研究,来了解成矿流体的基本性质及演化。通过对流体包裹体的H、O同位素、He、Ne、Ar、Xe同位素,矿石硫化物硫、铅同位素以及碳酸盐矿物碳、氧同位素的研究来帮助进一步判断成矿流体的性质及来源,并结合区域地质构造背景对兰坪盆地大规模成矿过程进行了研究。主要取得以下几个方面的进展:1.首次对金顶矿区不同矿化阶段流体包裹体中的稀土和微量元素进行了测试,发现从成矿早阶段到成矿晚阶段,成矿流体SREE逐步升高,轻重REE分异越趋显著,系统从还原性演化为氧化性,微量元素组合趋于复杂,流体中成矿元素不断富集,而且在早-中阶段的流体成矿可能是快速的,中-晚阶段趋缓,深、浅部两种不同性质流体的混合可能是流体成矿的基本过程。2.对金顶和白秧坪矿床成矿主阶段热液矿物内流体包裹体的惰性气体同位素组成进行了研究,发现成矿流体是壳幔不同性质流体系统混合的结果。3.利用Basin2^TM软件对兰坪盆地的流体压力进行模拟,发现盆地沉积和压实产生的流体超压可以忽略,区域构造推覆体最多仅能产生170×10⁵Pa的流体超压,由流体包裹体获得的高达1364×10⁵ Pa的流体超压不可能是由沉积压实以及推覆体产生的,结合其深部背景研究以及地球物理研究认为成矿流体超压很可能是深部富CO₂含矿流体注入引起的,进一步证明了兰坪盆地成矿流体是一种壳幔混合流体。4.对兰坪盆地的流体成矿过程进行了研究,认为深、浅部两种不同性质流体的混合是流体成矿的基本过程。5.鉴于金顶超大型铅锌矿床有别于MVT、SST和SEDEX型铅锌矿床的独特特征,提出铅锌矿床的新类型——“金顶型”。更多还原

【Abstract】 The Lanping basin, Yunnan, SW-China, is famous for the giant Jinding deposit and the new-discovered Baiyangping Cu-Co-Ag super-large deposit. Differing from known major types of sediment-hosted Zn-Pb deposits in the world, including SST, MVT and Sedex, the metallogenetic mechanisms of Zn-Pb deposits in the Lanping basin are unique, although the large-scale mineralization occurred in the Mesozoic-Cenozoic strata. Because of the remarkable characteristics of epigenetic alterations and hydrothermal mineralization of the deposits in the large Pb-Zn-Cu ore concentration area, Lanping basin, the key point is about fluid for making clearly the metallogenetic mechanisms. Based on these, through the analysis of regional ore-forming geological setting, this article takes the two super-large deposits as the examples for revealing the fluid metallogenetic mechanisms.With a reserve of～200 Mt ore grading 6.08% Zn and 1.29% Pb （i.e. a metal reserve of～15 Mt） hosted in Cretaceous and Tertiary terrestrial rocks, the Jinding deposit is the largest Zn-Pb deposit in China, and also the youngest sediment-hosted and the only continental sediment-hosted super-large Zn-Pb deposit in the world. Differing from known major types of sediment-hosted Zn-Pb deposits in the world, the Jinding represents a new type of sediment-hosted Zn-Pb deposits. The Baiyangping Cu-Ag-Co polymetallic deposit is another super-large deposit found in the north of Jinding in the Lanping basin. So, it can improve the metallogeny study of the Lanping basin, with the comparation of metallogenetic fluids between the Jinding and Baiyangping deposits.Based on the abundant geological data collected, through the detailed study on mineragraphy for checking out the symbiotic, associated and generation relationship of the minerals and mineral assemblage in the different mineralization stages, we studied the petrography, homogeneous temperature, salinity, gas and luqid components, and rare element compositions of fluid inclusions, in order to recognizing the basic charateristics and evolution of the ore-forming fluids. Then, combing the regional geological structure setting with the H-O、He-Ne-Ar-Xe isotopes of fluis inclusions, S、Pb isotopes of sulfide ores and C-O isotopes of carbonate minerals, we have studied the metallogenic process in the Lanping basin.The major advances are as follows.Ⅰ. Rare element compositions of fluid inclusions in the various mineralization stages of the Jinding ore district shows that from the early to late mineralization stage of the fluid mineralization processes, SREE and LREE / HREE increased in the ore-forming fluid respectively, and the fluid system became more oxidizing. The rare element assemblage of the ore-forming fluid became more complex, the metallogenic element was richer in the ore-forming fluid. The fluid mineralization may be quick during the early-middle stage and slower during the middle-late stage. A mixing of a deep- and a shallow- fluid may be the essentials for the large-scale mineralization in the Jinding.Ⅱ. The compositions of noble gas isotopes of fluid inclusious in the hydrothermal minerals of the main mineralization stage of the Jinding and Baiyangping deposits indicates that metallogenetic fluids were the mixiture of two different fluids with different characteristics from the crust and mantle.Ⅲ. The mineralizing system was strongly injected by a deep overpressure fluid based on observations of hydraulic fractures, fluid inclusion data and the basin fluid modeling. The fluid pressures of （513～1364）×10⁵ Pa are revealed in CO₂-rich fluid inclusions. The basin fluid dynamic modeling results indicate that the overpressures could not have been produced by normal sediment compaction, a fluid overpressure of 170×l0⁵Pa could have been made by the thrusting nappe. An injection process of mantle-derived fluids are likely responsible for the building-up of the high overpressures. The mixing of two types of fluids in a structural-lithologic trap may have been the key dynamic process for the large-scale mineralization in Lanping basin.Ⅳ. With the study on the fluid metallogenetic process of the Lanping basin, we find out that the mixing of a deep- and a shallow- fluid may be the essentials for the large-scale mineralization.Ⅴ. Because of the unique characteristics of the Jinding super-large Zn-Pb deposit, which is different from the MVT、SST and SEDEX type Zn-Pb deposits, it may be a new type of Zn-Pb deposit named "Jinding type".更多还原