滇中郝家河砂岩型铜矿床成岩期和改造期热液蚀变作用——来自组分迁移计算的证据  

Hydrothermal Alteration during Diagenesis and Reworked Periods in the Haojiahe Sandstone-type Copper Deposit, Yunnan, Southwest China: Evidence From Mass Balance Calculation of Migrated Components

作　　者：吴海枝[1] 韩润生[1] 吴鹏[1] 和继圣 冯兴杰 梁徐文[1] 孙晓栋[1] 

机构地区：[1]昆明理工大学国土资源工程学院有色金属矿产地质调查中心西南地质调查所,云南昆明650093 [2]云南星焰有色金属股份有限公司,云南楚雄675000

出　　处：《大地构造与成矿学》2014年第4期866-878,共13页Geotectonica et Metallogenia

基　　金：教育部博导基金项目(编号:20115314110010);全国危机矿山重大专项(编号:20089943;1212011220725);国家自然科学基金项目(批准号:U1133602;41102049);云南省矿产预测评价工程实验室及省创新团队;云南省科技计划(编号:2010CC005);中国科学院矿床地球化学国家重点实验室开放研究基金(编号:201109)联合资助

摘　　要：通过牟定郝家河砂岩型铜矿床两类典型矿化的围岩蚀变类型、空间分布、蚀变矿物组合特征的综合分析,识别出该矿床存在成岩期与改造期两期热液蚀变。成岩期热液蚀变分布于浅紫交互带浅色砂岩一侧,呈现大范围面状硅化、碳酸盐化、黄铁矿化,并具蚀变分带:全浅色砂岩中的强硅化、黄铁矿化亚带;浅紫过渡砂岩中的强碳酸盐化、绢云母化、绿泥石化、弱硅化亚带,并具辉铜矿-斑铜矿-黄铜矿-黄铁矿的金属矿物分带。改造期热液蚀变主要分布于断裂、节理旁侧,表现为带状、网脉状的硅化、碳酸盐化。以1580 m中段实测剖面为研究对象,采集各蚀变亚带的代表样品,以紫色砂岩为原岩,进行主量元素、微量元素及稀土元素的组分迁入、迁出计算,结果显示各亚带组分的迁入、迁出特征与镜下观察的蚀变矿物组合吻合。分析表明,蚀变矿物组合与组分迁移特征还间接指示了不同亚带的形成条件:成岩期紫色砂岩(围岩)呈氧化-碱性条件,浅色砂岩呈还原-酸性条件,浅紫过渡矿化带则处于氧化还原-酸碱转化面上;改造期构造热液属还原-中偏碱性的中温构造流体。在此基础上,探讨了两期成矿流体分别形成层状矿体及脉状富矿体的机理,为深化研究该类矿床的"矿源-构造-流体耦合成矿"机制提供了重要证据。On basis of study of the spatial distribution features, mineral assemblages of alteration and mineralization characteristics of the Haojiahe deposit, two kinds of the hydrothermal alteration in the diagenesis period and the tectonic-reworking period have been identified. The hydrothermal alteration of the diagenesis period includes silicification, carbonatization and pyritization, occurred widely in the grey sandstone. There are two alteration subzones in this period： the main subzone and the transitional subzone. The main alteration subzone consists of carbonatization, sericitization, chloritization and the latter weak silicification at the purple-grey interface. Besides, there is also a horizontal metallic mineral zonation in this subzone, i.e., hematite→chalcocite→bornite→chalcopyrite→pyrite from purple stone to grey sandstone. Whereas the banded and veined silicification and carbonation formed in the hydrothermal alteration of tectonic-reworked period occur along the fractures and joint fissures. Taking the purple sandstone as the original rock and Ti as the referential object, samples selected in different subzone from the 1580 m level cross-section are used to calculate the mass balance of migrated components including main elements, trace elements and rare earth elements. The results show that the amount of migrated components in each subzone is consistent with the corresponding mineral assemblages. Moreover, it also reflects indirectly the physicochemical conditions of hydrothermal fluid in different alteration subzones. The condition of diagenesis-period fluid in the purple sandstone was oxidizing and alkaline, while the fluid condition in the grey sandstone should be reducing and acidic; consequently, the interface between purple bed and grey bed was the Eh and pH boundary. The hydrothermal fluid of tectonic-reworked period was strong reducing, weak-alkaline and high temperature. Combined the results of migrated component calculation with the physicochemical conditions of ore-forming fluid, it

关 键 词：砂岩型铜矿床 蚀变作用 组分迁移计算 成岩期 改造期 郝家河 滇中 

分 类 号：P618.41[天文地球—矿床学] P614[天文地球—地质学]