初论华南加里东花岗岩与大规模成矿作用的关系

Relationship BeMtwieneenr aCliazlaetdioonn iiann S Gourathn iCtohidinsa and Large-scale

华南加里东期的花岗岩类在强度和广度上仅次于燕山期花岗岩,是华南大花岗岩省的重要组成部分。但是前人对于加里东期花岗岩类与成矿关系的报道较少,早期的研究甚至认为加里东期花岗岩一般不成矿。本文根据对近年来在某些地区和矿床出现的加里东期花岗岩类及相关矿化现象的初步研究成果,并结合对相关文献的调研,提出华南地区加里东期花岗岩类与该地区钨锡等金属大规模成矿作用之间具有相当密切的关系。这种关系主要表现在三个方面:(1)某些加里东期花岗岩、尤其是那些演化比较充分的加里东晚期花岗岩可能在晚阶段直接形成矿床,如湘东南的彭公庙、桂北的牛塘界、桂东北的桂岭、右江地区的钦甲等花岗岩体,但是其重要性相对较小;(2)某些加里东期花岗岩可能为该地区较晚期的成矿作用提供部分成矿物质来源,如在赣南的石雷、粤北的梅子窝等钨矿床可能有这种情况,在湘南的益将,加里东期的石英闪长岩为风化壳型稀土-钪矿化直接提供了成矿物质来源。(3)更为重要的是华南地区正是从加里东期开始进入了陆内演化的阶段,加里东期花岗岩类开启了以地壳物质重熔为主的华南大花岗岩省形成和发展的重要一幕,标志着华南陆壳进入不断成熟、亲石成矿元素不断向陆壳富集的阶段,多旋回花岗岩浆活动及其演化使钨锡等金属元素在燕山期花岗岩中高度富集,并最终导致了华南地区举世瞩目的燕山期大规模成矿作用。

The Caledonian granites take the second importance among the multi-aged granitoids in so-called South China Large Granite Province. However, the pervious studies show less concern on the metallogenic aspects of Caledonian granites. Some early studies considered no important mineralization related to Caledonian granites. Based on some newly discovered granitic intrusions of Caledonian ages, together with the synthetic assessment of related literature, the present paper reviews the general character of Caledonian granites and discusses the relationship between Caledonian granites and large scale rare metal metallogeneses in South China. Although the large-scale rare metal mineralization mainly took place in the Yanshanian Period of Late Jurassic Era,Caledonian granitoids of mostly Silurian Era made great positive effects. Some well-evolved Caledonian granites, such as those in Penggongmiao of southeastern Hunan, Niutangjie of northern Guangxi, Guiling of northeastern Guangxi, and Qingjie of Youjiang area, can cause W, Mo and Sn mineralization. Some others might serve as rare metal supply for mineralization associated with late-staged granites, such as Shilei of southern Jiangxi and Meiziwo of northern Guangdong. At Yijiang of southern Hunan, the weathering products of Caledonian quartz diorite form a unique REE-Sc deposit. The most important significance, however, is that the Caledonian Orogeny started the intra-continental crust evolution of South China. The Caledonian granitoids resulted mainly by melting of crust materials, instead of adding of mantle material. The following tectonic episodes such as Variscan, Indo-sinian, and Yanshanian, together with the accompanying granitic magmatism, promoted the forward evolution of crust. As a result, the crust of South China became highly matured, which is indicated by high enrichment of felsic components and lithophile rare metals, and finally yielded the largest rare metal mineralization in the world.