GEOCHEMICAL EVIDENCE FOR SEDIMENTARY PROVENANCE OF MIDDLE JURASSIC SANDSTONES IN DONGSHENG AREA,INNER MONGOLIA
Li Hongtao1, Cai Chunfang1, Luo Xiaorong1, Sun Xiyong2
1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
2. Liaohe Petroleum Bureau, China National Petroleum Corp., Panjin, Liaoning 124010
Sandstone-hosted roll-type uranium deposits have recently been found in the Middle Jurassic Zhiluo Formation in Dongsheng area, northern part of the Ordos Basin. In order to assess the sandstone provenance and geochemical characteristics of the uranium mineralization, the host sandstones were analyzed for rare earth elements(REE) and trace elements. The sandstone samples contained different kinds of metamorphic rock fragments. Meanwhile, the granitic gneiss and amphibolite sampled from outcrops north to the Ordos Basin were analyzed for REE. The results showed that ratios of LREE/HREE were 19.02 for the granitic gneiss and 4.47 for the amphibolite, respectively. The LREE/HREE ratios were close to the highest and the lowest LREE/HREE ratios of the sandstones with well-compared chondrite-normalized REE patterns, respectively. So these results consistently indicated that parent rocks of sandstones were mainly contributed from these two kinds of metamorphic rocks. There was a very high Th/U ratio for the granitic gneiss, which was a mainly potential uranium resource. Interestingly, the uranium contents of the sandstones were positively correlated to LREE/HREE ratios and contents of sulphophile element, such as Pb, Zn and Mo. These characteristics were important marks of uranium mineralization.
Li Hongtao,Cai Chunfang,Luo Xiaorong et al. GEOCHEMICAL EVIDENCE FOR SEDIMENTARY PROVENANCE OF MIDDLE JURASSIC SANDSTONES IN DONGSHENG AREA,INNER MONGOLIA[J]. Chinese Journal of Geology, 2007, (2): 353-361.