钦杭结合带成矿地质背景及成矿规律

钦杭成矿带是钦州湾-杭州湾成矿带的简称,具有矿床规模大、矿床分布密集、矿床类型齐全、伴生组分多样的显著特点,是中国地质调查局规划的全国重点成矿区带。钦杭成矿带又称为钦杭(构造)结合带,大地构造位置对应于扬子板块和华夏板块的接合带。研究显示,钦杭带是一条古老俯冲带。它在古生代仍存在洋壳,属于洋陆俯冲体系。中生代构造转换是一个重要的地质事件,它使钦杭带由特提斯构造域卷入到西太平洋构造域中,大地构造性质从华夏和扬子板块之间的板块构造机制为主,转为陆内岩石圈拉张伸展构造环境,并产生巨大的地质效应,最突出的是燕山期岩浆的大规模活动以及成矿作用的大爆发。燕山期花岗岩存在确切的幔源端元信息,幔源物质参与了许多矿床的形成,并为最近钨多金属矿床北拓找矿所验证。钦杭结合带是重要的斑岩铜(钼)矿带,斑岩铜(钼)矿在钦杭结合带北、中、南三段均有产出,它们的主成岩成矿年龄是燕山期,但带有古老俯冲带岛弧体系的基因。钦杭带也是一条古海洋喷流热水沉积矿床密集分布带,VMS型铜多金属矿床和SEDEX型铅锌多金属矿床发育。钦杭带是一条古老俯冲带改造成矿带,古老俯冲带经燕山期改造/叠加成矿是钦杭成矿带的重要成矿机制。

Geological settings and metallogenesis of Qinzhou Bay-Hangzhou Bay orogenic juncture belt, South China

The Qinzhou Bay (Q) to Hangzhou Bay (H) metallogenic belt situated in South China, is one of national-wide key metallogenic zones recognized and planned by the China Geological Survey, and quite famous due to its scale, clustering of deposits and variety of deposit types and useful associate metals. It is also called the Qinzhou Bay to Hangzhou Bay orogenic juncture belt, corresponding to the transitional tectonic zone separating the Yangtze plate and the Cathaysian plate. It is shown that the Q-H belt is an ancient subduction system. Besides Neoproterozoic, there existed Paleozoic continent-oceanic subduction system as evidenced by the occurrence of fossil oceanic crust. The Mesozoic tectonic trasition is a greatly significant geological event, and it made the Q-H belt change from the Tethyan tectonic domain to the West Pacific tectonic domain, resulting in intra-continental lithosphere stretching and thinning and finally the outburst of Yanshanian magmatism and mineralization in the belt area. Mantle-derived end character is observed, indicating that mantle source materials were involved in the mineraization. The Q-H belt may be referred to as a porphyry copper (molybdenum) deposit belt and a fossil ocean-floor exhalation-hydrothermal deposit belt, since granitic porphyry Cu(Mo) deposits are scattered over it, as well as rich VMS and SEDEX types of deposits do. It is concluded that the Q-H belt is a fossil subduction system-reworked metallogenic belt, characterized by mineralization of Yanshannian reworking/superimposing on fossil plate subduction system. The Yanshanian granitic porphyry Cu(Mo) deposits originated from partial melting of the island-arc basaltic rocks associated to subduction of the fossil oceanic plate.