摘要
近20年的勘查实践表明,横贯中国北方的古亚洲洋造山带及其两侧的中—新生代陆相沉积盆地,是我国最重要的沉积型铀矿床形成发育的铀成矿构造域。研究认为,古亚洲洋造山带是重要的富铀地质体,盆-山耦合机制制约下的地表水系搬运沉积作用是形成铀源供给系统的必要前提,泥岩型铀矿表现为单一铀源供给系统,而砂岩型铀矿则表现为双重铀源供给系统并且铀储层砂体本身的"再生铀源"不容忽视。在逆冲-造山间歇期或裂后热沉降时期,相对松弛和稳定的大地构造背景有利于沉积-成矿环境的形成,泥岩型铀矿需要同沉积期的稳定构造背景,而砂岩型铀矿不仅需要同沉积期的稳定构造背景,也需要成矿期具有适当掀斜作用的构造背景,有些矿床对成矿期后的构造环境还非常敏感。调查发现,当成矿期的含矿流场与沉积期的古水流体系基本一致时,铀储层砂体中层间氧化效率最高而且铀搬运通量最大,更加有利于成就大型和超大型矿床。在区域古构造等因素的协同影响下,同沉积期的古气候背景是制约铀储层砂体和成矿期层间氧化带发育方向和规模的极为重要的地质因素。同沉积期古气候不仅制约了铀储层砂体发育的结构和规模,同时更重要地制约了铀储层内部和外部还原介质的类型及其空间分布规律。铀储层砂体的形态和结构制约了层间氧化带发育的方向和轨迹,而铀储层内部和外部的还原介质则控制着古层间氧化带推进的里程及前锋线位置,铀矿化作用则与氧化还原地球化学障有关。基于此,毗邻古亚洲洋造山带的中—新生代沉积盆地都是沉积型铀矿勘查的主要远景区,而针对目标沉积盆地,则需要在深入剖析盆地构造格架以及区域含矿流场补-径-排关系基础上,再依据含铀岩系自身的特征(古气候背景、还原介质类型与分布空间)圈定和评价找矿靶区。
Exploration over the past two decades indicates that the Paleo-Asian orogenic belts across north China and Mesozoic-Cenozoic continental basins around their both sides are the most important metallogenic tectonic domain for the formation of the deposition-type uranium deposits in China.The Paleo-Asian orogenic belts are essential uranium-rich geological bodies.The uranium delivery system depends on the transportation of the surface drainage restricted by basin-mountain coupling mechanics.Mudstone-type uranium deposits were fed by the single uranium source,whereas sandstone-type uranium deposits were fed by the double uranium source,and the regenerated uranium source originated from uranium reservoirs is quite important.Slack and sustained geotectonic background during the dormant period of the trust-orogeny process and the post-fault thermal subsidence is a period favorable to the formation of depositional-metallogenic environment.Mudstonetype uranium deposits need synsedimentary sustained tectonic setting.Sandstone-type uranium deposits were formed under not only the synsedimentary sustained tectonic setting,but also the tip-tilting tectonic setting during the mineralization period.Some sandstone-type uranium deposits were obviously affected by the tectonic setting after mineralization.Survey indicates that the efficiency of interlayer oxidation is the highest,and the transported flux of uranium is the largest,and the large even super large uranium deposits tend to be formed when the mineral-charged flow field during the mineralization period was consistent to the synsedimentary palaeocurrent.Synsedimentary palaeoclimate is a significant geologic factor affecting the development of uranium reservoirs and interlayer oxidation zone,which constrained not only the architecture and size of uranium reservoirs,but also the types of reductive media inside and outside uranium reservoirs and their spatial distribution.The morphology and architecture of uranium reservoirs restricted the direction and track of interlayer oxidation zone,whereas the reductive media inside and outside uranium reservoirs controlled the advancing mileage and location of frontal line of the interlayer oxidation zone.Uranium mineralization is related to the redox geochemical barrier.This study shows that the Mesozoic-Cenozoic basins around the Paleo-Asian orogenic belts are primary prospective area for deposition-type uranium deposits.Based on the in-depth analysis of the regional tectonic framework and recharge-runoff-discharge system of the mineral-charged flow field,the prospecting target can be delineated and evaluated according to the synsedimentary palaeoclimate,types of reductive media and their spatial distribution of uranium-bearing series in the target basin.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2015年第1期189-205,共17页
Earth Science Frontiers
基金
中国核工业地质局高校科技攻关项目
国土资源部中央地质勘查基金专题研究项目(2008150013
2013150011)
国家自然科学基金项目(40772072
40802023)
中国石油辽河油田分公司重大项目
中国石化河南油田分公司协作项目
关键词
砂(泥)岩型铀矿床
铀成矿构造域
古亚洲洋造山带
中—新生代沉积盆地
sandstone-type（mudstone-type）uranium deposits
tectonic domain of uranium mineralization
Paleo-Asian orogenic belts
Mesozoic-Cenozoic sedimentary basins
