中国北方兴蒙地区叠合盆地砂岩型铀成矿特征及勘查方法综述

中国北方兴蒙地区发育多个中大型叠合盆地,盆地内均发现大型、特大型铀矿床,且最近又有许多新的找矿突破。兴蒙地区叠合盆地在铀成矿及勘查方法等方面具有很多共性。研究发现,铀成矿作用受特定的构造样式和构造演化阶段控制,有利的沉积相主要发育于盆地发展的坳陷期,局部为断陷期,在断陷期和断坳转换期形成了盆地内铀成矿的还原介质,在挤压隆升剥蚀期,构造反转、地层掀斜剥蚀形成剥蚀窗口,有利于含矿流体的运移。盆地内铀成矿作用的类型为:①潜水、潜水-层间和层间氧化作用;②同沉积成矿;③构造热事件叠加成矿;④多种流体混合作用成矿。根据这些成矿特征,盆地内的铀矿勘查可通过以下方式进行:①铀源体可通过源-汇系统进行厘定;②成矿流场和成矿通道通过反转抬升剥蚀窗口和有利沉积相厘定;③沉积建造、油气逸散场可利用其物性特征(电性、放射性等)进行厘定。地质及物化探方法组合可有效地完成上述勘查。

Review on metallogenic characteristics and exploration methods of sandstone-type uranium deposits in superimposed basins in the Xingmeng area, Northern China

There are several medium-large superimposed basins in the Xingmeng area, Northern China, where large and extra-large uranium deposits have been found and many new breakthroughs have been made recently. These basins have many similarities in uranium metallogenesis and exploration methods. It is found that uranium mineralization is controlled by specific structural styles and stages of tectonic evolution in this region. Favorable sedimentary facies were mainly in the depression stage of basin development, locally in fault-depression stage. Reducing medium of uranium mineralization in basins formed in the fault-depression stage and fault-depression transition stage. During compressive uplift and denudation stage, tectonic inversion and strata tilt erosion resulted in denudation windows favorable for migration of ore-bearing fluids. The types of uranium mineralization in the basins include (1) phreatic water, phreatic water-interlayer and interlayer oxidation; (2) synsedimentary mineralization; (3) tectonic thermal events superimposed mineralization; (4) fluid mixing mineralization. The study of the metallogenic process suggests that the exploration of uranium deposits in the basins can be carried out in the following ways: (1) the source-sink system is used to determine uranium source bodies; (2) the metallogenic flow field and channel are determined by inverted uplift and denudation windows and favorable sedimentary facies; and (3) the sedimentary formation and oil-gas escape field are clarified in terms of their physical properties (electricity, radioactivity, etc.). An effective combination of geologic, geophysical and geochemical methods permits to attain these exploration objectives.