中国东部中生代浅成热液金矿的类型、特征及其地球动力学背景

Geology, Distribution, Types and Tectonic Settings of Mesozoic Epithermal Gold Deposits in East China

中国东部中生代浅成热液金矿可以划分为与花岗岩和与碱性岩有关的两种类型;也可以分为高硫型和低硫型两大类,而且以后一种为主。这些金矿的形成和分布受区域构造制约,具体地说是受破火山口、火山角砾岩筒以及与火山机构有关的断裂控制。成矿围岩为火山岩类及同源花岗质岩石和周围地层。主要的蚀变组合为冰长石-玉髓-绢云母或明矾石-高岭石-石英(玉髓)。成矿年龄分布在180～188Ma,135～144Ma,127～115Ma和94～105Ma四个区间,前三组年龄分别响应于中生代华北板块与扬子克拉通的造山碰撞后陆内造山的伸展过程、构造体制大转折以及岩石圈大减薄,后一组为华南地区岩石圈再一次强烈伸展期间的产物。虽然这些矿床的形成时间有差异,但都是发育于大陆伸展环境中。

We preliminarily describe the basic characteristics of the epithermal gold deposits in East China. The epithermal gold deposits in East China can be divided into low-sulfidation and high-sulfidation types, which are related to granitic and alkaline series magmatic rocks. Except for the Zijinshan in Fujian province and the Tiantoushan in Anhui province, the others are low- sulfidation epithermal gold deposits. The Guilaizhuang in the west Shandong and possibly the Yixingzhai in northwestern Shanxi are alkaline rock-related gold deposits. The epithermal gold deposits in East China are spatially distributed in the faulting-depressing volcanic basins or along the magmatic-volcanic zones in the uplift areas. Most of them are structurally controlled by calderas, craters, diatremes and related faults and hosted in volcanic rocks, intrusions and sur- rounding strata. The alteration assemblages are mainly adularia-chalcedony-sericite for low-sulfi- dation gold deposits, and alunite-kaolinite-quartz (chalcedony) for high-sulfidation gold deposits. In general, the alterations in these Mesozoic gold deposits do not show the obvious zoning as those in the Cenozoic gold deposits in the southeast Pacific islands and Japan. The ore-forming ages of the epithermal gold deposits in East China are within four pulses of 180-188 Ma, 135-144 Ma, 127-115 Ma and 94-105 Ma, respectively. The former three pulses geodynamically correspond to the extensional periods of post-collision orogenic process between North China and Yangtze cra- tons, transformation of the tectonic regime from NS- to nearly EW-directions, and significant thinning process of the lithosphere; The latter pulse is the products of the lithosphere extension in South China. We suggest that all the epithermal gold deposits in East China are the products of magmatic heat events in the extensional tectonic setting within the continental margin.