中国陆区大规模成矿的地球动力学:以夕卡岩型金矿为例

THE GEODYNAMIC SETTING OF LARGE-SCALE METALLOGENESIS IN China's Mainland, EXEMPLIFIED BY SKARN TYPE GOLD DEPOSITS

系统总结了中国不同构造单元 70个夕卡岩型金矿床的基本地质特征 ,其中 1个为超大型、1 9个大型和 2 4个中型矿床 ,总储量超过 1 0 0 0t,占全国探明储量的约 2 0 % ,表明夕卡岩型金矿是我国最重要金矿类型之一 ,值得今后地质研究和勘探工作重视。通过编制中国夕卡岩型金矿分布图 ,发现它们产于碰撞造山带、断裂岩浆带和活化克拉通边缘等 3类地区 ,所有夕卡岩型金矿集中区均受到显生宙陆陆碰撞的影响。通过对各成矿省夕卡岩型金矿和相关热液矿床及花岗岩类的同位素年龄统计 ,结合地质分析 ,发现中国夕卡岩型金矿的形成时间总晚于各成矿省最晚一次的洋盆闭合或陆陆碰撞的开始时间 ,约滞后 5 0Ma ,因此排除了它们形成于大洋板块俯冲所致的岩浆弧背景的可能性 ;通过联系各成矿省地质构造演化与碰撞造山带 p T t轨迹 ,确定各成矿省成矿作用和花岗岩浆作用均爆发于陆陆碰撞过程挤压伸展转变期的减压升温体制 ,而不是碰撞后。基于碰撞造山带构造几何和造山机制 。

This paper summarizes the geological characteristics of seventy skarn-type gold deposits occurred in various tectonic units of China. They include 1 super-large, 19 large and 24 medium-sized, and contain a total resource of approximately 1 000 tons of gold, accounting for 20% of China's gold reserves. This shows that skarn-type gold is one of the most important kinds of gold resources and worth of more attention in geological research and gold exploration. In compiling a distribution map of skarn-type gold deposits, it is found that gold-bearing skarns are sited in collisional orogenic belts, fault-controlled magmatic belts and reactivated cratonic margins. All of the Chinese skarn gold provinces were affected by Phanerozoic collisional orogenesis. On the basis of compiling the data set of isotope ages for skarn-type gold deposits and other kinds of hydrothermal deposits and their related granitoids, combined with a synthesis of geological evolution of different tectonic units, it is revealed that the metallogenesis of skarn-type gold deposits in China always postdated the final oceanic closure or the beginning of inter-continent collision in each tectonic unit by about 50 Ma. This rules out the possibility that these skarn-type gold deposits were formed in a magmatic arc setting resulted from oceanic plate subduction. Linking the common p-T-t path for collisional orogeny to the tectonic evolution of metallogenic provinces in China shows that the large-scale granitic magmatism and metallogenesis in China occurred in a decompression-geothermal increase regime during tectonic transition from collisional compression to extension, instead of post-collisional tectonism. Therefore, the CMF model, which is based on the architecture and dynamic mechanism of collision orogens, can be used to interpret the temporal and spatial distribution and the genesis of the skarn gold deposits in China.