外生-后成渗入型铀矿床的空间定位问题探讨

Discussion on spatial emplacement of exogenic-epigenetic infiltration-type uranium deposit

产于中新生代盆地中的外生后成渗入型铀矿床是一种资源量大、开采成本低、对环境污染小的矿化类型, 是我国当前寻找的重点。通过10 多年的找矿实践, 大家一致认为中亚的成矿模式和找矿评价准则在我国并不完全适用。中国是一个强烈遭受新构造运动的地区, 中新生代盆地受到程度不同的各种改造。根据盆地和造山带的空间关系可划分为: 造山带的盆地、近造山带盆地和远离造山带弱构造活化的盆地。在每个类型中, 按盆缘的结构特征又可进一步划分出相应的亚类。笔者探讨了每类盆地对形成外生后成渗入型铀矿化的有利度, 同时还探讨了成矿的古气候条件, 指出天然地下水补给区小的内陆盆地、干旱的气候期并不完全是成矿的有利因素, 甚至可能是不利因素。相反, 处于潮湿气候区的盆地有利于成矿。为了提高找矿的科学性和找矿效率, 应当尽快建立适合于中国地质情况的外生后成渗入型铀矿成矿模式和找矿评价准则。

Exogenic-epigenetic infiltration-type uranium deposit is a kind of deposit with large resources,low exploitation cost,and less environmental pollution being the recent important prospecting target in China.Prospecting practice for uranium during recent decade indicates that the metallogenic model and prospecting-evaluation criteria obtained from sandstone-hosted uranium deposits in Middle Asia are not applicable to the case in China.China is a country which has been subject to intense neotectonism,and Meso-Cenozoic basins in China have experienced various tectonic reworking.According to the spatial relation to orogenic belts sedimentary basins may be divided into:basins in orogenic belt;basins near orogenic belt and basins with weak tectonic activation far away from orogenic belt.Then,based on the structural features,basins may be further divided into corresponding subtypes .The author discusses the favourability of each type basin for the formation of exogenic-epigenetic uranium mineralization,as well as the paleo-climatic conditions for uranium ore-formation.Then,the author proposes that,for small intracontinental basins recharged by natural groundwater,the arid climatic period is not totally a favourable factor for uranium ore-formation,it even could be an unfavourable factor.In contrast,basins located in humid climatic region may be advantageous to uranium ore-formation.For improving the prospecting efficiency,a metallogenic model for exogenic-epigenetic infiltration uranium deposits and corresponding prospecting-evaluation criteria suitable for geologic situation of China have to be established as soon as possible.