摘要
从花岗岩原地重熔说的角度 ,对热液铀矿床研究中存在的诸如矿岩时差 ,大小岩体矿化特征 ,产铀岩体判别指数以及与钨 (锡 )、铌、钽矿化 ,红层和构造运动等关系问题进行了初步的探讨。重熔说认为 ,岩体只是重熔界面凸起而被剥蚀的地方 ,岩体的大小仅反映剥蚀程度的大小 ,而无本质的区别。由于铀沉淀的“位源距”较大 ,铀总是沉淀于岩体的外接触带中。外接触带作为成矿围岩 ,既可以是沉积岩 (包括红层 )、变质岩 ,也可以是早期的花岗岩 ,前二者反映剥蚀程度较小 (“小岩体”) ,后者反映剥蚀程度较大 (“大岩体”)。由于后者的成矿围岩为花岗岩 ,所以产生了矿岩时差大的错觉。用化学成分计算出的指数与铀矿化没有直接的关系。此外 ,铀矿化一般晚于钨 (锡 )、铌、钽等矿化 ,故多与“大岩体”有关 ,其成矿壳层较低 ,成分也较为简单。铀的化学性质非常活泼 。
In this paper, we try to discuss come problems concerned the origin of hydrothermal uranium(U) deposit from the point of remelting in situ view about granite formation. The problems include the time differences between mineralization and country rock (granite), characteristics, differences between “large granite bodies” and “small granite bodies”, granite discriminant that is used to judge whether or not granite produce U deposit as well as relationship of U mineralization to W (Sn), Nd, Ta mineralization, red beds and tectonic movements. According to the theory of remelting in situ, granite bodies in the same period that can be investigated are actual doming portions of the same remelting layer, which had be so stripped by erosion that granite bodies resulted. Thus the size variation of granite bodies implies only the fact of different erosional levels. Since U always moves in long distance with hydrothermal solution from its parent granite, it always deposits in outer contact zone, which, as a kind of country rock, might be sedimentary rock (including red bed), metamorphic rock, of early period granite. The two former situations indicate less erosional levels (small granite bodies) while the later situation indicates larger erosional levels (large grannite bodies). Because the country rock of later is granite, an illusion of large time difference between mineralization related granite and granite might be made. Also, there is no direct and simple connection between U mineralization and discriminant which is calculated from primary chemical composition of granite and has been unsuccessfully used as an index to judge whether of not a granite body would produce U mineralization because in this situation the granite is only country rock. Besides, the U mineralization is later than the one of W (Sn), Nd, Ta in general so that it often relate to “large granite bodies”, in which “mineralization crust” is lower than the one of W (Sn), Nd, Ta and mineral composition is relatively simple. Last, owing to
出处
《华东地质学院学报》
2001年第2期98-103,共6页
Journal of East China Geological Institute
基金
国家自然科学基金资助项目(49871 0 1 3)
