南岭地区花岗岩型铀矿的特征及其成矿专属性

摘要

南岭地区是我国花岗岩型铀矿的重要矿集区。该区产铀岩体的成因类型以S型(改造型)花岗岩为主，对岩性没有明显的选择性。构造是控制铀成矿的重要因素之一，几乎所有热液铀矿体都分布在一定的断裂或破碎构造中，并且与穿切于花岗岩中的中基性岩脉密切相伴。产铀岩体的热液蚀变发育，规模大、范围广、类型全的热液蚀变是判别产铀岩体的重要标志。产铀岩体的主要成岩时代为印支期和燕山期，铀成矿作用则主要发生于燕山晚期-喜山期，成岩成矿具有明显的时差，指示成岩和成矿作用是两次或两次以上不同的地质作用。印支期和燕山期花岗岩主要提供成矿铀源和成矿围岩，而铀矿成矿作用与燕山晚期-喜山期伸展断裂构造和蚀变交代的关系更为密切。对于南岭地区的花岗岩型铀矿，燕山晚期-喜山期的伸展构造活动及其伴随的中基性-酸性岩浆活动比印支期-燕山期的花岗岩更具有成矿专属性。%The Nanling region is an important area of granite-hosted uranium deposit cluster in China. The genetic type of the uranium-bearing granites is mainly of S type (reworking type) granite without lithology preference. Regional tectonics is one of the key factors controlling uranium mineralization, almost all of the hydrothermal uranium ore bodies occur in faults or fracture zones, and spatially associated with medium-mafic dikes that intrude into the granites. The uranium-bearing granites are characterized by pervasice and intensive hydrothermal alteration of diverse types. The formation times of the uranium-bearing granites are mainly Indosinian and Yanshanian, however, the mineralization times of uranium are mainly late Yanshanian and Himalayan, thus there is significant time difference between granite formation and uranium mineralization, which indicates that the granite formation and uranium mineralization are of two or more different geological processes. Granites of Indosinian and Yanshanian are the main source and wall-rock for the uranium mineralization, while the uranium mineralization is closely associated with extensional fault structures and alteration of the late Yanshanian and Himalayan. Thus, for the granite-hosted uranium deposits in the Nanling region, the extensional faults and accompanying medium-mafic magmatism and the late Yanshanian and Himalayan alteration have more metallogenic specialization than the Indosinian and Yanshanian granites themselves.