The different characteristics and geological significance of reduction alteration of sandstone-type uranium deposits in Northwest Region of China

摘要

Based on isotope trace studies of sandstone-type uranium deposits in Dongsheng area of Ordos basin, south margin in Yili basin and Turpan-Hami basin, such as geological attitude, carbon and oxygen isotope in fluids, hydrogen and oxygen isotope, sulfur isotope in pyrite and carbon isotope in "detritus pot top gas" of mineral-bearing stratum, this paper reveals the different features of the reduction and alteration among the formation of three uranium deposits. The differences are mainly reflected on the types of organic matter and the reduction alteration scale. These differences are the main reason to cause apparent epigenetic alteration types and intensity of uranium mineralization. It is concluded that the reduction of coal bed methane dissipation from the Neopaleozoic is the main feature of Dongsheng deposit, which leads to the abroad development of green-color alteration and bleaching phenomenon. The reduction of bacteria is the main feature of Yili deposit, which leads to a small range of weaker fading alteration and much more framboidal spherules pyrited mineralization. The organic acid from dispersed coal particles in stratum is the main feature of Turpan-Hami basin deposit, which is the main reductant of the uranium deposit. According to the above-mentioned characteristics, we think that the types, characteristics, and the scale of reductant are the important factors in determining the types of uranium deposits and the differences between the scales. This recognition has an important theoretical and practical significance to research genetic types of uranium deposits and their exploration methods.