论南岭区域复式花岗岩体及稀有金属花岗母岩的分异演化作用

南岭区域不同时期花岗岩体及与其有关的稀有金属矿床的形成,除了受区域混合岩化作用以及区域花岗岩浆分异演化作用的制约外,还受到遍布于南岭区域的每一个多期多阶段复式花岗岩体的自身分异演化作用的深刻的影响。在那些复式岩体中,只有在岩体分异演化的晚期阶段,才会出现稀有金属花岗岩母岩。现仅将本区域复式岩体和成矿母岩的分异演化及其与成矿作用的关系论述如下。

On Differentiation And Evolution Of Complex Granites And Granitic Parent Rocks Of Rare Metals In Nanling Region

1. The composite granites in Nanling region all underwent rather thorough differentiation during hundreds of million years to over one thousand million years of evolution. This evolution was controlled by certain regularity which might find its expression in the following facts: In an area where diverse intrusives make up a composite granite, with the advance of geologic time, magmatic intrusion were gradually reduced in scale, intrusive bodies occurred at shallower and shallower depths, metasomatism grew stronger and stronger, and rock-forming minerals, accessory minerals and metallic minerals appeared in greater and greater diversities. Petrochemically, granitic rocks of different periods tended to be gradually depleted in Ti, Fe, Ca, Mg and enriched in SiO2, alkali-metals, rare elements and volatile mineralizers such as F, Cl, B and CO2. Rare elements were originally extracted through migmatization from source bed, then migrated and concentrated in the mixed granitic magma where they were extracted again during the plane-form alkali replacement. Later, these ore-forming elements accumulated and ascended towards the top of the late stage Yenshaniian granitic magma, forming successively numerous granitic parent rocks of rare metals. 2.By the time granitic parent rocks of rare metals formed, the rare element abundances of these rocks had already become several times, tens of times or even hundreds of times higher than those of ordinary granites. These rocks, being usually small stocks or dykes located at the shallow part of the composite granites, are characterized by poorer Ti, Fe, Ca and Mg and richer SiO₂, alkali-metals, volatiles, mineralizers and rare elements. With the progress of such metasomatism as potash-feldspathization, albitization and greisenization developed through permeation along cracks of parent rocks, the intrusive bodies altered in upward succession from coarse-grained porphyritic biotite granite through medium-grained microporphyritic muscuvite-biotite granite to fine-grained muscovite granite. In the upper part of the last granite, albitization, lepidolitization, lepidolite-muscovitization and greisenization gradually intensified, accompanied by a tremendous increase in Na-, Li-bearing minerals of late generation in place of the early stage potash-feldspathization, causing a tendency of Na₂O>K₂O. The whole process of the evolution of these granitic parent rocks of rare matals were essentially another process of extraction, migration and concentration of rare elements which led to the formation of Ta-rich rare metal deposits in the intense albitization, lepidolitization and lepidolite- muscovitization zones. Such a metallogenic process could be observed from place to place in the whole Nanling region, which ultimately gave rise to large-scale extensive and intense rare and nonferrous metallization of middle and late Yeushanian period, and produced in time and space genetic zoning of a series of mineralizations surrounding granitic parent rocks of rare matals, together with Jots of primary geologic and geochemical indicators which play a substantial role in the search for ore deposits of rare and nouferrous metals in the whole region.