The Genesis and Characteristics of Calcified-Wood Alike Carbonation in Zhiluo Group of Ore-Bearing Strata in Dongsheng Uranium Deposit

Dongsheng deposit at the northeast Ordos Basin is one of the largest sandstone-type uranium deposits in China. Its characteristics are quite different from that of sandstone-type uranium deposit in Turpan Basin and Yili Basin, Xinjiang province. One of the important aspects is that Zhiluo group of ore-bearing stratum in Dongsheng deposit was developed with more discontinuous lenticular carbonation and phenomenon of calcified wood rather than the unique non-plant fossils. This phenomenon of calcified-wood alike carbonation is rarely observed in other uranium deposits in Ordos Basin. The identified rock slice is composed of micritic calcite cemented sandstone and crystalline calcite. The former was formed by sedimentary diagenesis. The latter consists of calcite inclusions, which have been observed in water-based solution and CO2 or CH4-based gas inclusions. The temperature of the most inclusions were in the range of 140~170°C. It indicated that carbonate played an important role as hydrothermal fludis in the process of the formation of calcified wood. The analytic results of sparry calcite carbon and oxygen isotope showed that the most of the carbon sources were provided by the organic matter rather than from the process of diagenesis. Combined with the formation and characteristics of Dongsheng deposit where the area oil and gas dispersion exists, the formation of calcified-wood alike carbonation was the result of geological dispersion of oil and gas, which came from the middle of the basin area in the Paleozoic atmosphere filled by calcite crystals. Understanding the formation mechanism of Zhiluo group of ore-bearing stratum has great significance in prospecting for Dongsheng deposit.