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云南大红山层状铜矿床地球化学及成矿机制研究
其他题名A study on geochemistry and ore-forming mechanism of the Dahongshan stratiform copper deposit in Yunnan province
吴孔文
2008-08-22
学位授予单位中国科学院地球化学研究所
学位授予地点地球化学研究所
学位名称博士
关键词云南大红山 铁铜矿床 层状铜矿 火山岩型块状硫化物矿床 成矿流体 变质条件 矿床地球化学
摘要云南省大红山铁铜矿床位于康滇地轴南端西缘,介于红河深断裂与绿汁江深断裂所夹持的滇中台坳内,赋存于中元古代大红山群海相火山喷流-沉积岩系中,是我国典型的火山岩型块状硫化物(VHMS)矿床之一。该矿床包括一系列与火山喷发-岩浆侵入活动相关但成因有一定差别的矿床,被统称为“大红山式”铁铜矿床。该矿床经济价值巨大,铁、铜储量均达超大型矿床规模,但其研究程度较低,多停留在矿区地质特征层面上,地球化学研究较为薄弱。本次工作系统地研究了大红山层状铜矿床中各类岩石的岩相学特征,对特征矿物做了电子探针定性和定量分析,挑选火山质岩石中锆石做定年分析,系统分析了岩石的主量元素和微量元素,测定了硫化物的硫和铅同位素,并选取了与富集型硫化物相关的石英脉矿物和碳酸盐矿物分别做流体包裹体和碳、氧同位素研究。论文取得的主要认识如下: 1.红山群曼岗河组火山喷流-沉积年代约为1687±8Ma,即形成于早-中元古代,因此不可能遭受如前人所说的吕梁运动改造作用。在700 ~ 800Ma左右,即晋宁运动期本区遭受了强烈的变质变形以及流体蚀变改造作用。 2.层状铜矿中岩石类型主要为黑云母片岩、白云石钠长石岩和白云石大理岩。黑云母片岩中主要矿物为黑云母、钠长石、铁白云石和石榴子石;白云石钠长石岩中主要矿物为钠长石、铁白云石、石榴子石及少量的黑云母;白云石大理岩中主要矿物为铁白云石,含少量的钠长石和黑云母。岩石原岩恢复表明,三类岩石原岩为火山物质、泥质沉积物和喷流热水沉积混合组成,其中黑云母片岩以泥质为主,包含火山质物质和喷流热水沉积物质;白云石钠长石岩以火山物质和喷流热水为主,含少量的泥质;白云石大理岩以热水喷流沉积为主。 3.本区至少遭受过三期变质作用:区域高温变质作用、流体蚀变改造作用和变形变质作用。区域高温变质作用变质温度最高可达可达660℃,主要集中在600 ~ 630℃之间,形成压力约为4.9 ~ 5.0Kbar。三期变质改造使原岩发生了绿帘-角闪岩相的变质作用,变质过程中,稀土元素(特别是轻稀土元素)和部分高场强元素发生了迁移;流体蚀变改造富集了早期的贫铜矿胚,使之形成工业矿床。 4.硫化物硫同位素研究显示,其δ34S值为-0.6 ~ +10.9‰,主要集中在+5.0 ~ +10.9‰之间。这一组成表明富集型硫化物大体继承了早期硫化物硫源特征,并在改造过程中富集重硫。早期硫化物硫源主要来自岩浆硫和海水无机还原硫。硫化物铅同位素范围为:206Pb/204Pb= 18.985 ~ 23.318,均值为21.222;207Pb/204Pb=15.581 ~ 15.904,均值为15.747;208Pb/204Pb=39.803 ~ 45.652,均值为42.540。显然,本区硫化物具有极高含量的放射性成因铅,部分放射性成因铅含量稍低的样品与前人所圈定的改造型矿床的硫化物铅同位素范围较为吻合。分析认为,本区硫化物铅同位素代表了两种不同铅源的混合,即早期硫化物的普通铅和围岩中的放射性成因铅。硫铅同位素示踪以及矿相学研究表明,本区早期铜质来源于海底火山喷流-沉积,而晚期富集型铜矿铜质继承了早期铜质,同时也不排除晚期流体中所带来的铜质。 5.流体包裹体研究表明,本区改造型流体中包括三种流体体系:①中-低盐度H2O-NaCl±KCl±FeCl3 ±CaCl2流体,盐度范围为0.53 ~ 24.59 % NaCl equiv.,密度为0.80 ~ 1.16 g/cm3;②高盐度高密度H2O-NaCl±CaCl2流体,盐度为31.2 ~ >59.76% NaCl equiv,密度为1.14 ~ 1.45 g/cm3;③纯液相CO2流体,流体密度为0.77 ~ 1.09 g/cm3。流体包裹体均一温度在100 ~ 456℃之间,主要集中在150 ~ 260℃和260 ~ 456℃两个温度区间。方解石碳、氧同位素范围分别为-5.6 ~ -3.1‰和12.4 ~ 15.5‰。综合分析表明,流体主要来自海底下伏岩浆房的出溶或喷流的高温高盐度流体,部分与海水混合。流体在热液改造过程中活化富集了早期硫化物,经过短距搬运而沉积形成了晚期富集型硫化物。 6.本次研究确定该矿床的成矿机制为:早-中元古代,本区的陆内裂谷作用为火山喷发提供了构造条件,海底火山喷流-沉积形成了早期的贫铜矿胚。元古代末期,本区遭受了强烈的区域变质、变形和流体蚀变改造作用,使原先的贫铜矿胚得到活化富集,形成了工业矿床。
其他摘要The Dahongshan iron-copper deposit in Yunnan province is located in the southwestern margin of the Kangdian Axis, belonging to the central Yunnan synclise between the Honghe and Luzhijiang deep fault. This deposit is hosted in the Mesoproterozoic Dahongshan Group comprising volcano exhalative-sedimentary rocks, and is one of the typical VHMS deposits in China. There are a series of deposits in the ore district,so called as “Dahongshan-type” deposits. All these deposits characterized by different ore-forming mechanism are related to the volcano exhalative and magmatic emplacement events. The economic value of these deposits is significant due to the giant reserves of iron and copper. Previous studies focused on the geological characteristics of the ore deposit, while the geochemical study was relatively poor. Thus, a detailed study on the stratiform copper ore body has been conducted in this work including elaborate petrography study on various types of rocks;qualitative and quantitative study of typical minerals by electron probe;U-Pb dating of zircon from volcanic rock; major elements and trace elements analysis of various rocks; S and Pb isotope of sulfide; fluid inclusion study of quartz-vein and C、O isotope of calcite related to sulfide-rich sample. Finally, the above mentioned studies lead to the following conclusions: 1. The emplacement age of the volcano exhalative-sedimentary rocks of the Mangganghe Group is about 1687±8Ma. It is therefore impossible that the Dahongshan Group had been altered by Lvliang Movement as previously suggested. During 700 ~ 800Ma, the Jinning Movement strongly affected the Dahongshan Group by metamorphism, deformation and fluid alteration. 2. The rocks in the stratiform copper deposit are mainly biotite schist, dolomite-albite rock and dolomite-marble. The main minerals of biotite schist are biotite, albite, ankerite and garnet; main minerals in dolomite-albite rock are albite, ankerite, garnet and minor biotite; those of dolomite-marble are ankerite, with minor albite and biotit. Their protolith are composed of volcanic material, pelitic sediment and exhalative sediment with various proportions. 3. There are at least three stages of metamorphism happened, namely high temperature regional metamorphism, fluid alteration and deformation. The highest temperature of regional metamorphism is 660℃, mainly between 600℃ and 630℃, with the pressure range of 4.9 ~ 5.0kbar. These metamorphism made the protolith altered to epidote-amphibolite facies. REE, especially LREE,and part of HFSE were mobilized during metamorphism. Alteration caused by metamorphic fluid enriched the earliest metal-poor ore body and made it economicly utilized. 4. The study on the sulfur isotope of sulfide indicates that the δ34S range is -0.6 ~ +10.9‰, mainly in +5.0 ~ +10.9‰. It is suggested that the sulfide-rich ores inherited the sulfur characteristics of the earliest sulfide-poor ores and absorbed heavy S during alteration. The sulfur of early-stage sulfide may derived from magma and seawater. The Pb isotopic ratios of sulfides are: 206Pb/204Pb= 18.985 ~ 23.318, with an average of 21.222; 207Pb/204Pb=15.581 ~ 15.904, with an average of 15.747;208Pb/204Pb=39.803 ~ 45.652, with an average of 42.540. It is obvious that the sulfides are enriched in radiogenic Pb. Some sulfides with relatively low content of radiogenic Pb are consistent with those of the sulfides in reworked ore body reported before. The Pb isotopic characteristics of sulfides represent the mixture of two types of Pb, namely common Pb of the earliest sulfide and radiogenic Pb from the wallrock. The characteristics of S and Pb isotopes of sulfides suggest that the copper of the earliest chalcopyrite came from submarine volcano exhalative-sedimentation, while that of late chalcopyrite-rich ores is inherited the copper from the earliest chalcopyrite and the cu-bearing fluid. 5. The study of fluid inclusion indicate that there were three types of fluid system: ①low-medium salinity H2O-NaCl±KCl±FeCl3±CaCl2 fluid which salinity of 0.53 ~ 24.59% NaClequiv. and density of 0.80 ~ 1.16 g/cm3; ②high salinity and high density H2O-NaCl±CaCl2 fluid, with salinity of 31.2 ~ >59.76% NaCl equiv. and density of 1.14 ~ 1.45 g/cm3; ③ pure liquid CO2 fluid, with density of 0.77 ~ 1.09 g/cm3. The homogenization temperature is 100 ~ 456℃, clustering in two ranges: 150 ~ 260℃ and 260 ~ 456℃. The δ13C and δ18O of calcite are -5.6 ~ -3.1‰ and 12.4 ~ 15.5‰, respectively. Fluid inclusion from quartz and C、O isotope characteristics of calcite suggest that the ore-forming fluid may mainly originate from magma chamber beneath seafloor, and partly mixed with seawater. The ore-forming fluid dissolved the earliest sulfide during alteration, and deposited sulfide-rich ores after short-distance transport. 6. The mechanism of mineralization is summarized as below: During the Mesoproterozoic, the continental rifting induced the submarine volcano exhalative-sedimentation, thereafter gave rise to the metal-poor ore body during this period. In late Neoproterozoic, regional metamorphism, deformation and fluid alteration rebuilt the Dahongshan Group and concentrated the copper from the earliest copper-poor ore body, resulting in the formation of economically utilized ore bodies.
页数127
语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/3442
专题研究生_研究生_学位论文
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吴孔文. 云南大红山层状铜矿床地球化学及成矿机制研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2008.
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