The Study On Geologic-landform Environment And Metallogenic Mechanism Of Karst Type Bauxite In Pingguo,Guangxi

The study on Geologic-landform Environment and Metallogenic Mechanism of Karst-type Bauxite in Pingguo, GuangxiWestern Guangxi is China’s bauxite concentration area and develops well karst type deposit combined by accumulative and primary bauxite ores. They contain more abundant mineralization information than the single type deposit. The Pingguo bauxite deposit, a representative of this area, provides typical instance for probing the karst type bauxite mineralization regularities and genesis and the study of on it should have universal and theoretical significance.The accumulative ore deposit in Pingguo orefield has been formed on the surface of the earth in recent geological era. This dissertation discusses the local environment features and causes which make the accumulative ores preserving during strongly denudating process in modern orogenic belt and express the new understandings as below.1) Discovered the zonal regularity of the accumulative ore and landform types in the Pingguo orefield.The landform types formed in different evolution stages follow zonal distribution rule and ore bodies’morphology and mineralization elements of the accumulative ore show the zonal distribution too. Karst landform in the mining area presents the ring-shaped zonage which is consistent with the anticlines and forming karst peak-forest and the hill belts respectively in the cores and wings of anticlines. Correspondingly, in the accumulative ore mineralization zonage, the ore body distribution patterns and the bauxite mineralization elements change regularly with the landforms and their zonages. The accumulative ore zonage change shows the differences in the degree of weathering and corresponds to the differences in the karst landform development degree.2) It has been recognized that the structure-lithology-landform constraint mechanisms control the accumulative ore landform zonage in the ore fieldThe temporary primary datum role of primary bauxite seams in the mine landform development results alternating cycles development of landform on both sides of the seams. In the ordinal erosion process, the changes of stratum attitude of anticline control the degree of karst landform development, and the karst landforms of the mine area are in different developmental stages. The lithologic difference of insoluble primary seam in karst stratigraphic system of mine area changes the dynamics balance of landform development, resulting in geomorphologic zonation of the accumulative ores.3) The preservation role and the developmental process of accumulative ore have been revealed.The accumulative ore distribution is essentially limited to the seam outcrop line, displaying a close relationship between the preservation of the accumulative ore and landform zonage. REE features show that accumulative mineral soil and primary ore are homologous, indicating a high preserved degree of accumulative ore. The degree of weathering of the accumulation ore is proportional to the increase of aluminum concentration, showing that new weathered mineralization of accumulative ore occurred. The structure-lithology controls changes of development degree of karst water system the mine area. The unique karst diversion channel intercepts the surface water in the peripheral mine area, and the development of karst water system in the internal mine area is immature because of geomorphic cycles. The karst water systems respectively from the horizontal and vertical space make the accumulative ore effectively closed down in the primary seam confining zone controlled by anticline.4) Materialization controlled by the landform evolution and water system patterns has been discussed.With the strengthening of the development degree of the karst landforms in the mine area, the closed environment formed by the temporary primary datum of the primary seam is destroyed gradually, and its landmark commonly appears in the form of tower peaks manifesting the change of development of karst groundwater systems from the horizontal to the vertical. This controls the new distribution patterns of the accumulative ores, and the preservation of the accumulative ore will be constrained in the marginal zone range. There is a sign of loss of accumulation ore in Taiping mine are, which means the crisis of the change of preservation degree of the accumulative ore.The sedimentary primary ore in Pingguo orefield is a karst deposit which is formed in the platform island environment. The primary ore sedimentary types are studied in this dissertation to explore the distribution pattern of the primary ore. The points of view are as follows.1) The regional geological background of the primary bauxite mineralization in Pingguo is analyzed.Pingguo primary bauxite formed in the platform basin environment of Youjiang basin. The platform uplifted into island during Dongwu movement in Permian. The distribution of the organic reefs indicates that the Pingguo orefield is an isolated platform, and its primary ore formed in the island environment which is a special tectonic environment for karst bauxite. This background controlled the primary ore’s mineralization conditions, scale, distribution and characteristics.2) The primary ore formed in Delta mineralization model is presented.The overall distribution pattern of the primary ore is fan-shaped. The studies of primary ore distribution characteristics, ore structure, mineral composition and geochemistry indicate that the primary ore is a delta sedimentary ore. Based on the ore structures distribution, the shapes of sand dam and river sediment zone are determined. With the coal seam, the sedimentary facies of middle bay zone and branch channel are divided. These sedimentary microfacies reflect the internal components characteristics of the Delta. The distribution of the primary ore texture and the structure of ore seam profile show anti serial sequence in upstream and normal serial sequence in downstream, indicating that the spatial variation from the delta plain to the delta front. The strontium isotope features also show the transitional type sedimentary property between sea and land facies of the primary ore.The Pingguo accumulative ore formed at the edge of the modern orogenic belt, and the primary ore in the Permian island plain. Two karst bauxite mineralization characteristics show the differences owing to different regional tectonic settings. Comparing accumulative ore and primary ore mineralization environment and mineralization process, it reveals the common geological features of karst-type bauxite mineralization and reflects the consistency of the karst-type bauxite mineralization mechanism. That is to say, these two types of bauxite have experienced the denudation in the source area and the transportation mineralization process before deposition. Perhaps, it’s the major advantage and the universal way of karst-type bauxite’s mineralization by the karstification where non-soluble bauxite substances can be fully separated and preserved.