Phase Mountain Region Remote Sensing Application Technology Demonstration Study

The post-remote sensing application technology refers to a kind of information deepening application technology by combing the remote sensing technology with traditional technologies in various fields and modern information technology and it covers information processing, information interpretation, information analysis, information presentation and information application etc.In the field of uranium resource exploration, the idea of applying the concept of post-remote application technology is to fully dig out the information on prospecting for uranium deposits in the remote sensing images, to comprehensively analyze it by combining with other geologic information, summarize and find out the regularity, to visualize the obtained understanding and regularity and to represent geological processes, providing powerful support for uranium resource exploration and prospective prognosis.Xiangshan area is an important production base of hard rock type uranium resources, where the largest and richest volcanic uranium orefield in China is located. Uranium deposits occur in Xiangshan volcanic - intrusive complex of over 300km in area, they are controlled by structures, porphyry mass and thermal alteration and thus there is a large prospect. As a kind of bran-new technology, the post-remote sensing application technology is applied on trial in Xiangshan area, which is of important significance on the development of post-remote sensing application technology and on the further prospecting for uranium deposits in Xiangshan area.Under the direction of scientific theories of earth system, based on processing and analyses of basic geology, remote sensing, airborne radioactive, gravitational, magnetic and DEM information and by taking the deep digging and application of multi-source information in the field of uranium resource exploration and the determination of further prospecting direction in Xiangshan as objectives, emphases are put on these researches, including the overall research on Xiangshan volcanic - intrusive complex, the research on neotectonic movements, comparative study of northwestern and southeastern parts in Xiangshan area, the research on the degree of erosion and preservation conditions and that on red basins in South China and the preservation of uranium. By searching references related, collecting data and creating a spatial database and though geologic investigation and comprehensive analyses, the following innovative achievements or conclusions are obtained.(1) Through the comprehensive analyses on tectonic and magmatic evolution in South China, it is proposed for the first time that Xiangshan volcanic—intrusive complex is under the control of the belt of Xuefeng Mountain—Wugong Mountain—Guangze, the northernmost belt among six EW-trending granite belts in South China, the tectonic setting for its formation is related to EW-trending tectonic process before Jurassic, undergoing "open-close" alternative tectonic evolution of squeezing before Jurassic - squeezing and twisting in Jurassic—stretching and thinning from Cretaceous to Paleogene and squeezing and uplifting since Miocene, and uranium mineralization was formed in the specific stage of tectonic evolution of stretching and thinning from Cretaceous to Paleogene.(2) The detailed interpretation on remote sensing image of Xiangshan area shows NE, NNW, SN, NWW and EW linear structures and these structural features most are products due to the reactivation of palaeostructures caused by neotectonic movement, that is to say, they have features of neotectonic movement. It is proposed for the first time that the neotectonic movement is one of dominant factors that affect the spatial distribution of uranium deposits.(3) Gravitational and magnetic data of Xiangshan area are developed secondarily using GeoExpl software developed in 2005 by Development Research Center of Geologic Survey Bureau, China. Upward continuations of gravitational and magnetic anomalies at different heights and calculation results of directional derivatives of gravitational and magnetic anomalies at different heights show there are three groups of major basement structures in Xiangshan area: EW, NE and NW trending. NW trending Xiangshan - Furongshan basement structure (F2) divides Xiangshan volcanic—intrusive complex into the northwestern and southern parts with different structural features.(4) Xiangshan volcanic - intrusive complex consists of acid pyroclastic rocks interbedded with sedimentary rocks, acidic lava, intermediate—acidic shallow—super-shallow intrusive rocks. The U-Pb age of single grain zircon of rhyolitic dacitic porphyry that was considered as volcanic rock of effluent facies is 129.54±7.93Ma, which is less than the age of porphyroclastic lava, the main rock in Xiangshan volcanic - intrusive complex. Combined with features in its occurrence and shape, it is believed that the rhyolitic dacitic porphyry is a post-volcanic shallow or super shallow intrusive body. Referring to the fact that the boundary age of Jurassic and Cretaceous is 145.5Ma, it is proposed for the first time that the formation age of Xiangshan volcanic—intrusive complex is early Cretaceous.(5) SiO₂ content, Rb/Sr, Rb/Ba ratios of Xiangshan volcanic - intrusive complex decrease from eruption - effluent - intrusion and however, TFe (Fe₂O₃+FeO) , CaO, MgO, TiO₂, and P₂O₅ contents, solidification index SI and 8Eu increases, and the magmatic evolution is contrary to the magmatic differentiation of normal magmatic chamber whose acidity increases gradually, which is called as reverse magmatic evolution series. Ratios of incompatible elements such as Th/U, Rb/Ba, Th/Nb, Th/Ta, Nb/Ta and La/Nb vary in relatively large amplitude, which is of no evident positive or negative relation with major components such as SiO₂ and so on, REE distribution patterns are not identical totally and therefore, it is believed that rocks of eruptive, effluent and intrusive facies are from different source areas, breaking through the former understanding that "that magma for various complex in Xiangshan area is not only from a same source but also the product of magmatic differentiation from a same magmatic chamber."(6) Through the principal component conversion and ratio processing of ETM⁺ data of Xiangshan uranium orefield where vegetation is well developed, the effect of vegetation is eliminated to some extent and good remote sensing anomaly information on alteration of hydrous minerals is acquired, where the remote sensing anomalies of alteration distributed in the porphyroclastic lava in the northwest or metamorphic rocks in the western section in the north of Xiangshan uranium orefield are caused by hydrothermal hydromicazation and this is an important criteria for ore prospecting.(7) Aimed at the metallogenic characteristics of Xiangshan uranium orefield, the concept of U-Th concentration coefficient (FD=U X Th / K) is presented in this dissertation, FD reveals the combined U and Th mineralization information and thus it is related to (volcanic) magmatic hydrothermalism. The U-Th concentration coefficient has a certain correlation with the distribution of deposits in Xiangshan area; namely, uranium (thorium-bearing) deposits are distributed mostly in or near the areas with relatively high FD.(8) Deposits occur in the interior and outside of Xiangshan volcanic - intrusive complex, fewer deposits are distributed in the southeast and however, whether the number or grade of deposits in the northwest is evidently better than that in the southeast. The calculation results of DEM-based area vs elevation curves show that the earth is eroded seriously in Xiangshan, but the degree of erosion is heterogeneous due to differences in lithology of matter at the earth surface and in intensity of geologic and tectonic activities. Through comparative analyses on geomorphic features, occurrences of granite porphyry, physical and chemical properties of porphyroclastic lava, metallogenic type and characteristics, it is proposed for the first time that the degree of erosion in the northwest is different from that in the southeast of Xiangshan uranium orefield, deposits are characterized by unbalanced occurrence, which is not caused by the differences in mineralization or geologic framework, but by the different degree of erosion. From the northwest to the southeast of Xiangshan uranium orefield, the erosion depth of deposits increases gradually. There are better preservation conditions for deposits in the northwest of orefield and most uranium deposits are well or relatively well kept, which thus is of important significance in the prospecting for uranium deposits in Xiangshan area in the future.(9) Red beds of South China have a close relation of time and space with the uranium mineralization and were formed in the pull-apart tectonic setting from Cretaceous to Paleogene. From a new view, namely, the preservation of red basins in South China to uranium deposits and reconsidering the time and space relation between red basins in South China and uranium deposits, it is proposed for the first time in this dissertation that red basins are under the control of epigenetic faulted structures (neotectonics) and they are residual structural basins; deposits occurring near red basins were covered by red beds and thus area near and in the deep of red beds are favorable for mineralization preservation, which is the prospecting direction as well.The application of post-remote sensing technology promotes its development, plays a role in demonstrating the application and a series of creative achievements or conclusions have obtained in the aspects of tectonic - magmatic activities, metallogenic conditions - preservation conditions for deposits, prospecting direction and so on, providing a new idea to further prospect for new large and high-grade uranium deposits in Xiangshan orefield and its adjacent areas.