摘要:
四川西部是我国松潘—甘孜造山带的主体,区域内中—上三叠统分布极其广泛,其中陆陆碰撞壳源改造型花岗岩类不均匀集中侵入于该套地层中,并衍生出以锂为主的稀有金属花岗伟晶岩,最有代表性的是甲基卡和可尔因花岗伟晶岩型稀有金属矿田,目前在二者中均勘察出超大型锂矿床。矿化伟晶岩脉主要由富锂辉石的白云母-钠长石-钾长石型花岗伟晶岩脉构成,它们分布在离母岩-二云母花岗岩外围热接触变质的蚀变中—上三叠统沉积岩系中,和围岩侵入关系清楚,并对围岩均有不同程度的接触交代蚀变作用。鉴于这些共同点,长期以来,人们对这两个矿田成矿作用的认识和找矿思路统一用甲基卡矿田成矿模式来看待。但随着研究工作的不断深入,发现它们既有相似处,但也存在较大的差异。比如:两个矿田形成时的构造-岩浆环境、花岗伟晶岩产出的围岩岩性和蚀变作用、矿化伟晶岩脉的结构-构造、成矿矿物的多样性等方面各有其不同的特征,本文在分别概述各自特征基础上,对产生差异的原因做了初步分析,为提升川西花岗伟晶岩成岩成矿理论和开辟新的找矿方向提供新依据。
Abstract:
The Songpan–Ganzi orogenic belt is mainly located in western Sichuan in China, and Middle–Upper Triassic strata are widely distributed in the region. Continental-continental collision crust-derived modified granitoids are unevenly concentrated in the strata, from which rare metal granitic pegmatites dominated by lithium are derived. The most representative are the Jiajika and Keeryin granitic pegmatite rare metal ore fields.At present, super-large lithium deposits have been explored in both of them. The mineralized pegmatite veins are mainly composed of spodumene-rich muscovite-albite-K-feldspar type granitic pegmatite veins, which are distributed in the Middle–Upper Triassic sedimentary rock series of thermal contact metamorphism in the periphery of the mother rock-two-mica granite. These veins are related to the intrusion of the surrounding rock and show different degrees of contact metasomatic alteration with the surrounding rock. In view of these common points, our understanding of the mineralization of these two ore fields and prospecting ideas have, for a long time,been unified with the metallogenic model of the Jiajika ore field. However, with advances in research, it has been found that they have both similarities and differences. For example, the structure-magma environment of the two ore fields, lithology and alteration of the surrounding rock produced by the granitic pegmatite, structure of the mineralized pegmatite vein, and diversity of ore-forming minerals have different characteristics. Based on a summary of their respective characteristics, this study describes a preliminary analysis of the causes of the differences, which provides a new basis for improving the diagenesis and mineralization theory of the granitic pegmatite in western Sichuan and opening new prospecting directions.
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