Genetic Analysis of the Bottom Sandstone of Zhiluo Formation,Northeastern Ordos Basin: Predictive base of spatial orientation of sandstone-type uranium deposit
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摘要: 砂体的结构和规模因沉积体系的不同而异,它们对铀成矿贡献的差别很大。作者通过露头调查、钻孔岩心分析和砂分散体系制图,对鄂尔多斯盆地东北部直罗组下段进行了成因分析。研究发现,直罗组底部砂体并非传统认识上的辫状河成因。实际上,它可以分为上、下两个亚段。虽然两个亚段的物源和砂分散方向具有很好的继承性(北西—南东向),但成因完全不同。下亚段主要由辫状河体系和辫状河三角洲体系构成,其中辫状河三角洲平原构成了研究区的主体。上亚段主要由曲流河体系和(曲流河)三角洲体系构成,虽然(曲流河)三角洲平原也是研究区的主体构成部分,但是(曲流河)三角洲前缘却占据了一定的空间,这是湖泊向西北方向扩展的结果。正是由于上、下亚段成因的不同,导致了下亚段砂体具有较大的规模和较好的连通性,而上亚段砂体规模变小、非均质性增强。砂岩型铀矿勘探的实践证明,矿体主要聚集于下亚段砂体中。因此看来,上述认识可以用于砂岩型铀矿成矿规律的总结和铀成矿空间的定位。Abstract: The sandstone structure and scale vary with different depositional systems, and have different contribution to uranium mineralization. According to outcrop research, drilling core analysis, and sand distributed system drawing,we analyzed the lowermember of Zhiluo Formation, northeastern Ordos basin. The results show that the lowermember of Zhiluo Formation is not formed by braided stream in traditional recognition. In fact, it can be divided into the upper and lower sub-members. Although the upper and lower sub-members have well inheritance in provenance and sand distributed direction-which is NW-SE, they have different genesis. The lower sub-member of Zhiluo Formation com-prise braided stream system and braided delta regime, and braided stream delta plain is the main body; the upper sub-member of Zhiluo Formation comp rise meandering river system and meandering river delta regime, and meandering river delta plain is the main body, meandering river delta front take up some space also, which is the result of lake extension to northwest. So, the low sub-member has larger scale and better connectivity, while up sub-member has smaller scale and higher heterogeneity. The practices of sandstone-type uranium exploration also p rove that the ore mainly occurred in low sub-member of Zhiluo Formation. Therefore, the genetic recognition is favorable for the rule summary and space orientation of uranium mineralization.
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