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湖南黄沙坪多金属矿床成矿流体演化及矿床成因
黄诚
导师李晓峰
2014
学位授予单位中国科学院研究生院
学位授予地点北京
学位名称博士
学位专业矿物学、岩石学、矿床学
关键词成矿流体演化 矿床成因 矽卡岩型多金属矿床 湖南黄沙坪
摘要黄沙坪多金属矿床是一个典型的矽卡岩型多金属矿床,是南岭多金属成矿带的重要组成部分。矿区内发育不同类型金属元素组合,是研究矿床流体演化与成因以及华南地区燕山期大规模岩浆活动与钨钼铜铅锌多金属成矿作用的耦合关系及其深部动力学机制的理想对象。本文以黄沙坪花岗质斑岩及所形成的钨钼铅锌铜多金属矿床为研究对象,运用岩石学、元素地球化学、同位素地球化学和流体包裹体等方法手段,对花岗质斑岩的成因和形成构造环境、成矿物质与成矿流体的来源、成矿年代学、成矿流体的演化及成岩成矿的地球动力学背景等方面进行了系统研究,对该矿床的成因和成矿过程取得了初步的认识。 1. 流体包裹体特征表明,形成不同矿化类型的流体性质具有很大的差别。早矽卡岩阶段石榴石中Type Ib和Type IIa包裹体共存,并且具有高温(>528℃),压力大(600~800bar)的特点,说明在成矿作用早期流体发生不混溶作用,该流体代表了直接来源于岩浆成因的热液。晚矽卡岩阶段与W成矿有关的流体还是以高温高盐度为特征,成矿流体温度集中在400℃~460℃,盐度集中在40~45%NaCleqv,压力为200~400bar。而硫化物期,与Mo成矿有关的流体温度集中在300~340℃,盐度集中在12-14%NaCleqv,压力介于100~200bar之间。与Zn-Pb成矿有关的流体温度进一步降至160~240℃,盐度集中在4~10%NaCleqv和14~18%NaCleqv。早期石榴石等矽卡岩矿物和白钨矿的结晶与后期硫化物的矿化过程均受岩浆热液流体的控制。不同阶段形成了不同类型和温压条件的包裹体,反映了成矿流体性质受深部岩浆房分异出的超临界流体沿着不同的路径演化所控制。成矿早期流体具有较高的氧逸度,成矿晚期氧逸度逐渐减小。而与Cu成矿有关(Cu矿化、Cu-Mo矿化、Cu-W)的流体则为另一期的成矿流体作用所形成。 2. 利用岩体锆石U-Pb定年和辉钼矿Re-Os定年方法,确定不同岩体的成岩年龄相差不大,属晚侏罗世的产物,并结合岩石地球化学等数据初步得出岩体的演化顺序。成矿年龄则与成岩年龄相一致,表明二者存在紧密的联系。 3.氧化物(白钨矿)、硫化物(方铅矿、闪锌矿、磁黄铁矿、黄铜矿、辉钼矿)和脉石矿物(方解石、萤石)铅同位素,硫化物(方铅矿、闪锌矿、磁黄铁矿、黄铜矿、辉钼矿)硫同位素以及方解石碳氧同位素组成表明成矿物质主要来自岩浆,是幔源物质上涌导致的地壳物质重熔的产物,少量来自地层。与Cu有关的矿化类型和与W、Mo矿化、Zn-Pb矿化有关的矿化类型具有不同的成矿特点,前者矿体中地层提供了较多的成矿物质,成矿流体可能直接来源于岩浆,而后者的成矿流体是与碳酸盐岩地层的水-岩反应的产物。 4. 通过系统研究萤石和方解石微量元素特征,表明不同矿化类型的微量元素含量变化很大。萤石的稀土分配模式除了受离子半径影响,更主要受热液体系中形成的REE络合物的控制。萤石的稀土元素配分曲线与成矿斑岩很相似,都具有明显负Eu异常和不明显的Ce异常。但是,成矿斑岩中的稀土含量明显高于萤石中的含量,而萤石则具有明显的Y正异常。上述特点表明了形成萤石的流体可能由成矿斑岩分异作用所产生,并且流体经历了远距离的运移过程。热液中氟的离子配体具有很强的搬运各种金属元素的能力,富含氟的热液流体持续不断的供给促使形成黄沙坪多金属矿床。方解石微量和稀土元素特征表明,与Cu矿化有关的流体和与W-Mo-Pb-Zn有关的流体具有明显的区别,表明二者不是同一期成矿流体作用所形成。 5.在总结黄沙坪矿床成岩和成矿作用特征基础上,结合湘南乃至华南地区中生代金属矿床的成矿规律,认为黄沙坪矿床形成的动力学背景是中-晚侏罗世活动的Farallon-Izanagi洋岭和转换断层俯冲触发作用导致陆内发生转换拉伸。在此过程中,由于地幔物质上涌导致的壳幔混合作用是黄沙坪矿床形成大规模矿化的重要因素。黄沙坪矿区由于花岗质岩体在演化过程中形成的岩体具有不同的地球化学组成,再加上成矿流体和成矿物质组成的差别,形成了矿区矿化类型及规模的差异。其中深部岩浆所形成的超临界成矿流体在上升过程中不断与已经结晶的花岗岩及围岩相互作用,并萃取其中的成矿物质。成矿流体从深部向上运移过程中,首先与矿区石磴子组地层发生水岩交换反应,在二者的接触带形成高温高盐度的矽卡岩型钨钼矿体,随着温压降低和岩石韧-脆性条件的转换,后期流体沿着早先形成的断裂和裂隙在远离岩体的碳酸盐地层中的有利构造位置充填形成脉状铅锌矿体。而黄沙坪矿床与铜矿化有关的矿化类型的成矿流体则直接来源于岩浆。
其他摘要Huangshaping deposit is a typical skarn-type polymetallic deposit, which is also an important part of the Nanling polymetallic mineralized belt. Different types of assemblages of metal elements are well developed in mining area. Thus, it is an ideal object for researching ore-forming fluid evolution and genesis. Moreover, it also can provide evidence for coupling relationship between the extensive magmatic activity in Yanshanian period in south China and W-Mo-Cu-Pb-Zn polymetallic mineralization, and its deep dynamical mechanism.This doctoral dissertation is focused on granites and associated polymetallic deposit in Huangshaping, respectively. Based on research of petrology, elemental geochemistry, isotopic geochemistry and fluid inclusions, we mainly discussed the petrogenesis and tectonic setting of the granitic intrusion in this area, the sources of ore-forming materials and fluids, metallogenic chronology, ore-forming fluid evolution, as well as the corresponding metallogenic geodynamic setting. Finally, following preliminary knowledge of ore genesis and ore forming process is obtained. 1. Fluid inclusion data show that the fluid property of different mineralization types varies widely. The fluid inclusions in garnet and actinolite are characterized by coexisting brine and vapor-rich fluid inclusions, also, high homogenization temperatures ( 528℃ to > 600℃) and pressure 600~800 bar) , indicating that immiscible condition occurred during early stage and fluid exsolved directly from magma. Tungsten mineralization from later skarn stage was characterized by fluid inclusion with high temperature ( 400~460℃) ,high salinity ( 40%~45% NaCleqv). The pressure is estimated to be 200~400bar. At the sulfide stage,molybdenum mineralization was characterized by fluid inclusion with temperature from 300~ 340℃, salinity from 12~14% NaCleqv and pressure from 100~200bar.The fluid inclusions associated with Zn-Pb mineralization are almost liquid-rich fluid and the ore-forming temperature drops to 240~160℃ and salinity shows mainly between 4~10% and 14~18%NaCl eqv. The process of crystallization of skarn minerals, scheelite and mineralization of later sulfides are controlled by fluid related to magma intrusion. In General, different types of fluids formed under wide range of temperatures and pressures representing different mineralization stages indicate that characteristics of ore-forming fluid were controlled by different evolution paths of supercritical fluid exsloved from deep magma chamber. Oxygen fugacity of ore-forming fluid decreased gradually from early to late metallogenic stage. While Cu mineralization(Cu,Cu-Mo,Cu-W) was formed by another stage of fluids, different from W-Mo-Pb-Zn mineralization. 2.The radioactive age of zircons by LA-ICP-Ms U-Pb dating method and Re-Os dating of the molybdenite were repoorted from the Huangshaping polymetallic deposit. The results show that different types of granitic plutons are of similar ages. Mineralization age is coincide well with the intrusion age of granitic plutons, both of which belong to the production of late Jurassic period. Based on the field inverstigation, petro-geochemical data, we concluded the evolutionary sequence of the Huangshaping granites. 3. Systematic studies of Pb isotopes of oxides(scheelite), sulfides (galena, sphalerite, pyrrhotite and molybdenite) and gangue mineral(calcite and fluorite) ;S isotopes of sulfides (galena, sphalerite, pyrrhotite and molybdenite) and C-O isotopes of calcite and associated gangue minerals from different mineralization stages argue that ore-forming materials were mainly derived from the magma, which was the production of the remelting of the deep crust caused by upwelling of the mantle source material. And also, sedimentary rocks contributed small part of ore-forming materials. There were different characteristics between Cu mineralization and W-Mo-Pb-Zn mineralization. The former shows higher proportion of ore-forming m
学科领域矿床地球化学
语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/5882
专题研究生_研究生_学位论文
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黄诚. 湖南黄沙坪多金属矿床成矿流体演化及矿床成因[D]. 北京. 中国科学院研究生院,2014.
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