中国与火山岩—斑岩有关的金银多金属矿成矿地质特征

与火山岩—斑岩有关的金银矿矿集区和大型矿床的形成是多种因素综合作用的结果,特别是火山盆地类型及结构、大地构造背景、基底断裂、火山岩岩相和岩类、基底矿源层、火山机构内部构造、流体系统等对于矿床的形成起着决定性的作用。上叠式火山盆地能否成矿,关键是基底是否具备初始矿源层,岩浆是否起源于上地幔并同熔了老基底中的矿源层。继承性火山盆地能否形成金银矿,关键在于上下两套建造中火山岩的发育程度和火山—沉积建造的连续性,一般底部构造层中发育玄武岩、科马提岩、枕状熔岩等中基性、碱性火山岩,顶部构造层以中—酸性火山岩为主时,对成矿有利。大地构造位置上为两个构造单元的接合部位,与金银矿成矿有关的火山盆地或其基底都经历过裂陷拉张环境,不管是盖层还是基底,必有其一为裂谷或岛弧环境岩石建造。许多中大型矿床和矿集区都分布在多次开合的裂谷环境中。斑岩体岩石类型、成分、形态、产状控制矿体的定位和展布,潜火山岩、斑岩体与金银矿存在空间上的不可分割性、时间上的同一性和成因上的内在联系。单一的火山熔岩很少形成矿床,形成金银矿床的火山岩常为凝灰岩、凝灰质集块岩、凝灰质火山熔岩,岩相上常为从火山岩向沉积岩过渡的地方,岩石组合为火山碎屑岩+凝灰岩+杂砂岩、粉砂岩+熔岩+泥质岩+碳酸岩。“三重结构”构造控矿,即深层次基底断裂,中深部位的盖层断裂,超浅、近地表—地表构造。以火山机构为中心从下向上形成多位容矿裂隙：侵入体(斑岩)顶部裂隙系统,隐爆角砾岩筒裂隙系统,破火山口裂隙系统。潜火山岩发生多期隐爆形成具一定延深的角砾岩筒,往往存在多个热流体系统,补给系统和排放系统完全时对成矿有利。

Metallogenic Characteristics of Au-Ag Polymetallic Deposits Related to Volcanic Rocks and Porphyries in China

Controlled by divers complicated factors, large sized Au Ag deposits or their concentrated areas are mainly controlled by the types of volcanic basin s and their configuration, tectonic settings, basement faulting, volcanic facies, por ph yry, and basement ore source bed. For an overlaid volcanic basin, the orig in al basement ore source bed and the magma derived from mantle and co melting th e old basement are the main ore controlling factors. As for an inherited basin, the development of volcanism and succession of volcano sedimentary formation domina t e the metallogenesis. Ore deposits are generally located at the transitional sec ti on o f two different tectonic units, and are related either to a rift or an island fo rmation. The types, chemical composition, configuration and attitude of porphyries are decis i ve for the location and distribution of ore deposits in space, time and origin. Au A g deposits are generally formed at the transitional section from volcanic rocks to s edimentary rocks, representing the transition from intensive volcanism to vo lcanic tranquility. The "three level" structures, i.e. deep seated basement f aulting, over burden faulting and subsurficial faulting, are conducive to metallogenesis. From the volcanic apparatus downwards,there are multiple ore hosting fissure sy stems: the top fissure system in porphyries, the f i ssure system in breccia pipes and th fissure system in caldera. Th e cons iderable extension of breccia pipes, existence of more than one fluid system an d compl etion of fluid feeding and fluid drainage systems are decisive factors for the f ormation of ore deposits.