德兴铜厂斑岩铜矿流体过程  

Ore-forming Fluid Process in the Dexing Porphyry Copper Deposit, Jiangxi Province: Evidence from Clay Mineralogy, Fluid Inclusion and Isotope Tracing

作　　者：朱金初[1] 金章东[1,2] 饶冰[1] 李福春[1,3] 

机构地区：[1]南京大学地球科学系,内生金属矿床成矿作用国家重点实验室 [2]中国科学院南京地理与湖泊研究所,南京210008 [3]南京农业大学资源与环境科学学院,南京210095

出　　处：《南京大学学报（自然科学版）》2002年第3期418-434,共17页Journal of Nanjing University（Natural Science）

基　　金：国家自然科学基金重点项目 (4 973312 0 )

摘　　要：从德兴斑岩铜矿床中蚀变矿物、包裹体记录及同位素组成的时空变化 ,示踪成矿热液流体来源、演化过程及迁移途径 .氧、锶同位素空间变化表明 ,虽然与铜厂斑岩铜矿成矿过程有关的热液流体至少有 3种 ,包括高温岩浆流体、来自深部围岩的非岩浆流体和大气降水 ,但是起主导作用的是岩浆流体 .岩浆流体通过沸腾作用或不混溶作用而形成 ,它携带成矿物质从深部向上部及边部迁移、聚集 ,并在演化过程中引起围岩蚀变和金属矿化 .铜厂地区存在着两种不同成因的伊利石 ,热液成因的伊利石以 1M型、结晶度较差和含膨胀层为特征 ,而沉积浅变质成因的伊利石以 2M1 型、结晶度完好和不含膨胀层为特征 ,而且前者在空间上分布在离接触带不到2km的范围内 ,从而指示了热液流体活动的空间规模 .Nd、Sr同位素在空间上的变化则表明 ,在成矿流体作用过程中 ,Nd同位素相对稳定 ,斑岩的εNd变化在 - 0 76～ - 3 6 0范围内 ,表明岩浆系壳 -幔混合来源 .而Sr同位素初始比由斑岩体内部向围岩接触带则呈有规律升高(87Sr / 86Sr) i,0 70 5→ 0 .711) 。By using clay mineral characteristics, fluid inclusion and independent isotopic composition as tracer, the source, evolution process and transportation behavior of ore_forming fluids in the Tongchang porphyry copper ore field are investigated in this paper. According to O and Sr isotope varitations in the Tongchang porphyry system, at least three types of hydrothermal fluids are detected: the magmatic fluid, the deep_seated nonmagmatic fluid and the meteoric water. The magmatic fluid plays a determining role in the ore_forming process. It is generated by the second boiling or immiscible separation. Carrying enriched ore_forming materials and volatiles, it flows upward to the upper portions of the porphyry cupola and along its contact with the wall rocks, resulting in hydrothermal alteration and intense mineralization. There exist two typical kinds of illite within the Tongchang copper ore field. The first is of 1M polytype, with lower crystallinity and interstratified layer. It is formed by hydrothermal alteration. The second is of 2M 1 polytype, with higher crystallinity and no interstratified layer. It is sedimentary_weakly metamorphic in origin. The former illite is distributed in an area less than 2 km from the contact. The illite distribution can be used as a tracer for spatial scope of hydrothermal fluid activity. Nd isotope composition (ε Nd=_0.76～_3.6)is relatively stable and indicative of mixed crustal_mantle source for the porphyry. Increasing from 0.705 to 0.711, gradual change of Sr isotope composition from interior to contact zone within the porphyry body indicates quantitatively that the ore_forming elements mostly come from the parent magma. They are transported by hydrothermal fluids to the upper portions of the cupola and the contact zone where they concentrated.

关 键 词：斑岩铜矿 热液流体 伊利石 同位素 包裹体 示踪 

分 类 号：P618.41[天文地球—矿床学] P595[天文地球—地质学]