The Cenozoic Basins And Sandstone-type Uranium Mineralization In Western Yunnan

This dissertation was directed by the metallogenic theories of exogenic-epigenetic sandstone-type uranium deposits. By collecting datum of regional geology, remote sensing, geophysics, hydrology and hydrochemistry, uranium deposits and uranium occurrences systematically, developing field geologic investigation, radioactive geophysics method, drilling validation, inside test and combination with synthetical studies, and the central studies concentrated on the characteristics of depositional systems, sequence stratigraphy , evolvement of sedimentary basins and basin-mountain coupling , hydrology and hydrochemistry, oxidation zone and Uranium mineralization. the author summarized the metallogenic conditions on sandstone-type uranium deposits systematically, and established the metallogenic model of phreatic interlayer oxidation zone sandstone-type uranium deposits in Cenozoic basins Western Yunnan. The author acquired some innovative outcomes and recognitions:1. According to the difference of basin sedimentary evolvement and tectonic evolvement controled by strike-slip activity of orogen in different areas Western Yunnan, the author divided in 2 sorts of Cenozoic basins. In sedimentary basin stage, the degree of intense strike-slip activity of orogen was different, it brought difference in the types and space deployment of depositional systems, intense degree of the volcano activity and developable frequency of lacustrine basin.In reformed basin stage, the form even the intense degree of tectonic activity was different, and it brought difference in the degree of uplift and denudation, intense degree of the volcano activity and physiognomy.2. The types of oxidation zone and the metallogenic process are different in different sorts of basins. The cover of Cenozoic basins in northern Tengchong area mostly developed phreatic interlayer oxidation process, and the cover of Cenozoic basins in southern Ruili area mostly developed phreatic oxidation process, and the sandstone-type uranium deposits have relationship with phreatic interlayer oxidation metallogenic process in Cenozoic basins western Yunnan.3. The period of metallogenic process of sandstone-type uranium deposits corresponded with stage of violent activity of basin tectonic, that is to say, it corresponded with forming stage of tectonic sequence boundaries. It is considered that the tectonic sequence boundary one provided the seeped channels for ground water bearing O and U under the cover, and provided the developed spaces for phreatic interlayer oxidation zone, collected spaces for sandstone-type uranium deposits, and the forming of the tectonic sequence boundary two and the tectonic sequence boundary three were correlative with the metallogenic process of phreatic interlayer oxidation sandstone-type uranium deposits.4. The metallogenic conditions of sandstone-type uranium deposits are different in different sorts of basins and different stages of basin evolvement.The advantaged basins for prospecting sandstone-type uranium deposits are those basins that developed regional isolatable water layers, continued rising in reformed basin stage, developed phreatic interlayer oxidation metallogenic process, existed volcano activity and deep incised physiognomy being low mountain-hill-river valley terraces in northern Tengchong area..5. In this dissertation, the author discussed metallogenic model and the located model of uranium orebody in different tectonic position of phreatic interlayer oxidation zone sandstone-type uranium deposits in western Yunnan.It is considered, besides tonguelike vanguard oxidation-reduction interface like interlayer oxidation zone, it also developed oxidation-reduction interface in upper and lower limb inner the typical phreatic interlayer oxidation zone, thereby, it could develop 3 planar or lentoid uranium orebody in tonguelike vanguard, upper and lower limb along the interface of phreatic interlayer oxidation zone, it is neither similar to curly uranium orebody located in vanguard near by oxidation-reduction interface of interlayer oxidation zone, nor to stratiform and stratoid uranium orebody located in floor near by oxidation-reduction interface of phreatic oxidation zone. Moreover, the author pointed out, in slope belt, uranium orebody located in tonguelike vanguard, upper and lower limb along the interface of phreatic interlayer oxidation zone, and fault depression belt, uranium orebody located in tonguelike vanguard and upper limb along the interface of phreatic interlayer oxidation zone.Those innovative outcomes and recognitions acquired by the author will not be only provide with important function in deploying prospecting sandstone-type uranium deposits of the minitype intermontane basins developed inner orogenies belt in western Yunnan, further more, it perfected and enriched the theories of sandstone-type uranium deposits own in china.