关于“碱质交代成矿模式”的几点看法

SOME OPINIONS ABOUT METALLOGENIC MODEL OF ALKALINE METASOMATISM

胡受奚教授等,主要根据对华南与钨锡矿床有关的花岗岩特别是西华山花岗岩体的研究,提出了“碱质交代成矿模式。他们认为,花岗岩的交代蚀变过程,“是以钾交代为主导,由强基(K)向较弱的基(Li)或氢交代的发展过程”;与其有关的钨锡矿床成矿过程,表现为“在时间上从早到晚,空间上自下而上,从碱质交代转移浸出带→蚀变交代转移富集带”的过程;“矿脉及其两旁岩石中的钨、锡、钼、铋等造矿元素的含量,是随着碱性长石化加强和云英岩化减弱而变贫”;蚀变交代时间上由早到晚,在空间上由下到上,由钾长石化→钠长石化→云英岩化,而钾长石化带的下部“是各种成矿元素的活化转移带。

Taking Xihuashan in Jiangxi province as an example, the author advances his opinions on the 'metallogenic model of alkaline metasomatism related to granites' put forward by professor Hu Shouxi et al. The geological observations and petrological, mineralogical and geochemical studies have revealed the following facts: 1) The lower parts and roots of the ore veins and the related redfeldspathization are almost all confined to medium fine grained granite (γ_5^(2b)), which is a product of albitization in closed and planar forms. The redfeldspathization alongside the Ore veins occurs in open and linear forms and was formed later than the albitized granite(γ_5^(2b)). 2). Beneath the red-feldspathization zone, i. e., towards the greater depth of the granite body, there is a white-albitization zone formed later than redfeldspathization. 3). The formation of ore veins in the medium-fine grained granite mainly proceeded downward, so the intense red-feldspathization at the root of the ore veins occurred latest and marked the end of the mineralization. 4).The red-feldspathized rock is usually in company with greisen. The red-feldspathized rock in the greisen zone contains relatively high tungsten, whereas greisen in red feldspathization zone only has rather weak mineralization. The red-feldspathized rock and greisen are two different parts separated contemporaneously from residual melt-fluids. 5) Tungsten is unevenly distributed in the Xihuashan granite body, and the lower and upper parts of the rock body show considerable difference in its contents: from only 4.8 ppm at the depth to some 50 ppm (sporadically in excess of 100 ppm) in the upper part. Based on these facts, the author considers that the metallogenic model of alkaline metasomatism seems not to hold water in Xihuashan area.