滇西腾冲地块构造-盆地演化与砂岩型铀矿成矿条件

以"煤铀兼探"新思路带动的中国西南地区新一轮砂岩型铀矿勘查,首选滇西腾冲地块新近纪盆地群为突破口。从容矿主岩沉积建造、铀源地质体配置、成矿作用驱动3个方面,总结了腾冲地块构造-盆地演化对铀成矿的影响。在大陆汇聚构造体制下,地块内发育一系列受断裂制约的狭长状断陷盆地和冲积扇、扇三角洲、辫状河、湖泊的复合沉积体系,扇中辫状河道、三角洲前缘席状砂、水下分流河道等是赋铀砂体发育的有利沉积微相。中特提斯洋俯冲碰撞形成的燕山期中酸性花岗岩和经历多期构造变质的高黎贡山群花岗片麻岩、混合花岗岩为区内铀成矿提供了充足的物质来源。而赋矿层同沉积期的新近纪构造运动,以及第四纪以来的地壳差异升降,驱动了产铀盆地内部的潜水氧化和后期叠加的层间氧化成矿过程。基于上述认识,提出当前区内的铀矿勘查应加强沉积微相和岩相古地理研究,建立赋矿有利相带的空间分布模式;同时加强不同蚀源区地质体的铀源能力分析和成矿作用类型的甄别,更准确地锁定潜在铀矿体的定位规律。

Tectonic-basin evolution in Tengchong block, western Yunnan Province, and minerogenetic conditions of sandstone type uranium deposits

A new round exploration for sandstone type uranium deposits led by China Geological Survey focuses on the Tengchong block in western Yunnan Province at present. This paper mainly analyzes the relationship between tectonic-basin evolution and uranium mineralization in Tengchong block in three aspects, i.e., the sedimentology of host rocks, the uranium source and the oreforming process. A compound sedimentary system consisting of alluvial fan, fan delta, braided river, fluvial delta and lacustrine facies was formed in the small graben basins on Tengchong block during Pliocene epoch. The host rocks of uranium deposits were generally developed in special microfacies such as braided channel, delta front sheet sand and distributary channel. The acidic granites from Yanshanian orogeny and the metamorphic rocks in Gaoligongshan Group provided main uranium source for mineralization. Moreover, the neotectonic movements, either in host rocks depositional stage or in the post-depositional stage, drove the multiperiodic ore-forming processes, including phreatic oxidation and interlayer oxidation. Based on the above results, the authors hold that the study of microfacies, large-scale lithofacies paleogeography, uranium source capacity in different geological bodies and the analysis of mineralization types constitute the keys to present exploration in Tengchong block.