国外铁氧化物铜—金矿床的特征及其研究现状

THE CHARACTERISTICS OF THE OVERSEAS IRON-OXIDE CU-AU DEPOSITS AND THE PRESENT SITUATION OF THE STUDIES

铁氧化物铜—金矿床是一类具许多共同特征但成因联系不太密切的矿床类型,近来已成为国外铜—金勘探的主要矿床类型之一。该类矿床以矿石中含有大量的铁氧化物(磁铁矿或赤铁矿)且伴有很强的区域性钠(—钙)质蚀变为特征,可以产于元古代克拉通内或新生代大陆边缘岛弧环境,其周围具火成岩或含蒸发盐层,时空上与之有关的侵入岩为磁铁矿系列花岗岩,矿化主要产于近区域主断裂的羽状次级断裂中。部分该类矿床的形成与一定的主岩类型有关,而多数矿床可能由高盐度H2O—CO2—盐混合流体的不混溶作用形成,且矿化通常与钾化有关。对成矿流体是主要来自岩浆还是受围岩控制尚有争论,成矿模式有蒸发盐来源模式、外来流体加热模式和岩浆—热液流体模式。但对部分该类矿床详细的流体包裹体和稳定同位素研究表明成矿流体主要源于岩浆。对该类矿床进行地球物理勘探需要考虑磁铁矿、硫化物和Cu—Au矿化之间的相互关系。在我国开展对该类矿床的研究将有益于发现新的铜资源基地。

The ironoxide CuAu deposits is a class of loosely related ores that share a pool of common characteristics but no common genetic relationship, it has become one of the major targets of CuAu exploration industry over the last decade. This class of deposits is characterized by the abundance of iron oxide (magnetite or hematite) in the ores and the associated intensive regional sodic(calcic) alteration. They may occur in Proterozoic intracraton or Phanerozoic continental margin volcanic arcs with nearby intrusive complex or evaporite. The spatially and temporally associated intrusive rocks are magnetiteseries granitoids. Mineralization mainly occurs in second order echelon structures near the main regional structure. The mineralization of a number of deposits of this class were associated with certain types of host rocks, but the most were formed by the unmixing of H2OCO2salt fluid with very high salinities and the mineralization is commonly linked to potassic alteration. There is argument whether the fluids responsible for mineralization is a dominant magmatic source or controlled by host rocks. The main genetic models include 'an evaporite source model', 'a fluid heating model' and 'a magmatichydrothermal model'. However, detailed fluid inclusion and stable isotope studies at several deposits have indicated a dominant magmatic component to the fluids responsible for mineralization. The sorts of relationships between magnetite, sulphides and CuAu mineralization in Feoxide CuAu systems should be considered in the geophysical exploration. To study this type of deposits will be helpful for the discovery of new Cu resources base in China.