斑岩铜(钼-金)矿床的成矿流体

斑岩铜矿是主要的铜资源,是矿床研究和勘查的重要目标。斑岩铜矿按其与板块构造的关系可分为2种:俯冲带斑岩铜矿和碰撞造山带斑岩铜矿,它们在成矿流体方面有很多区别,其中较大的差别是碰撞造山带斑岩铜矿的钾化蚀变带比俯冲带斑岩铜矿的钾化蚀变带强得多,且范围也相对较宽。文章简述了这2种斑岩矿床的主要地质特征,着重从流体包裹体、蚀变作用和稳定同位素研究来探讨斑铜矿床成矿流体的主要特征,包括成矿流体的成分、形成温度和压力,氢、氧、碳和硫稳定同位素组成。这两种类型的斑岩铜矿中主要发育5种包裹体:M熔体包裹体;Ⅰ液体包裹体;Ⅱ气体包裹体;Ⅲ含子矿物的多相包裹体和CO2_H2O包裹体。Ⅱ类和Ⅲ类包裹体常共存,且均一温度相似,表明成矿流体经历了不混溶和沸腾作用。在Ⅲ类含子矿物的包裹体中发现了含金属硫化物(黄铜矿、黄铁矿)和氧化物(赤铁矿、磁铁矿)子矿物。在斑岩金矿和碰撞造山带的斑岩铜矿中出现CO2_H2O包裹体,在斑岩的斑晶和一些早期石英脉的石英中可见到熔体包裹体以及熔体_流体包裹体,它们代表斑岩岩浆的样品,说明斑岩铜矿的形成经历了岩浆和热液阶段。最近的研究表明,斑岩铜矿的初始流体是中等盐度和密度的岩浆流体。这种流体在上升过程中因压力释放而发生沸腾,形成气体包裹体和含子矿物的高盐度包裹体。

Ore-forming fluids of porphyry copper (molybdenum-gold) deposits

Porphyry copper deposits are currently the largest source of copper ore. Porphyry copper deposits are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals followed by stockwork and veins. According to the relationship between plate tectonics and mineralization,the deposits could be divided into two types:deposits associated with convergent plate boundaries and deposits occur in collisional orogeny setting. Understanding the behavior of Cu,Au and Mo in magmatic-hydrothermal systems is essential for studying the development of a porphyry copper deposit. Porphyry copper deposits in subduction environment provide some of the best examples of the effects of fluid-assisted mass and energy transport in the Earth''s crust. Much of our understanding of the physical and chemical conditions attending magmatic-hydrothermal fluid flow in the porphyry environment has come from fluid inclusion studies. During the earliest stage of magma crystallization,a liquid+vapor zone exists immediately above the pluton. Copper transported in the original magmatic fluid would be partitioned into the high salinity liquid and vapor phases. This higher density phase would flow downward along the side of pluton,whereas the copper-vapor phase would move upwards into the shallower part. Above the liquid+vapor zone,a small vapor+halite zone exists. Inclusion trapped here would be vapor-rich inclusions (with occasional halite). There are two types of magmatic and magmatic-hydrothermal phase inclusions:Silicate melt inclusion and melt-fluid inclusion. Four types of fluid inclusions are found:liquid inclusion; vapor inclusion; daughter mineral bearing inclusion and H₂O-CO₂ inclusion. Recent researches are focused on the primary composition of ore-forming fluid derived from the magma and copper transition by vapor or liquid phases.