Forecasting the occurrence of sandstone-type uranium deposits by spatial analysis: An example from the northeastern Ordos Basin, China

Abstract

Spatial orientation analysis of sandstone-type uranium mineralization is closely linked to sedimentology in the northeastern Ordos Basin. The Zhiluo Formation in this area is an integrated third-order sequence, which can be divided into three depositional system tracts. The sandstone-type uranium deposits mainly lie in the lowstand systems tract (LST) which can be divided into two parasequence set— an upper parasequence set and a lower parasequence set by outcrop study, drill core analysis, and sand distribution system mapping. The lower parasequence set comprises a braided stream system and a braided delta system. The braided delta system mainly consists of a delta plain, which has extensive sandstones and good connectivity and favours uranium mineralization and is thus the main uranium mineral host unit. The upper parasequence set, which comprises a meandering river system, and a meandering river delta system has less sandstone, and is the secondary uranium mineral host unit. The high-grade mineralization zone is mainly in a braided distributary channel, which sandstone heterogeneity research shows to be a transfer sedimentary facies from the braided stream sedimentary system to the braided delta sedimentary system. The highest-grade zones always exist in the branching area of the braided distributary channel at the margin of channel sandstones where isolated barrier bedcause abrupt facies changes. The frequency and quality of uranium mineralization decrease when the number and thickness of isolated barrier beds increase. Statistical results show that medium grained and fine-grained sandstones are best for uranium mineralization. Uranium deposits always occur in the middle-lower part of braided distributary channel sandstone in each vertical sequence unit. These sedimentological features are the basis of analysis of the spatial orientation and forecasting of uranium mineralization.