CHEN Jian1, XIANG Zhen-zhong2,3, YAN Qi1*, XI Wei-yao1, WANG Xing-wei1, CHEN Jun2, CHEN Yi-ping1, YIN Qi1, WU Tao2,3, GU Jing2
(1. The Sixth Geological Team, Guizhou Province Bureau of Nonferrous Metals and Nuclear Industry Geological Exploration, Kaili 556000, China;
2. The State Key Laboratory of Ore Deposit Geochemistry, Chinese Academy of Science, Guiyang 550081, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China）
Abstract:The large-scale Tiechanggou Bauxite deposit, located in the southeastern Guizhou, hosts 2.98 million tons of proved ores. Its ore bodies, hosted in the Middle Permian Liangshan Formation (Fm.), occurred as layered, lenticular and funnel-shaped on the paleo-eroded surface of dolomite in the Upper Devonian Gaopochang Fm., with usual siderite nodules in the bottom part of the ore bodies. The overlying strata of the ore body is usually carbonaceous shale or coal seams, with limestone of the Permian Qixia Fm. Locally. They consist of a typical coal-bauxite-iron structure in the Kaili-Huangping area. In this paper, we have collected samples of kaolinite rocks from cores of a drill hole in the center of the aluminum-forming basin of the Tiechanggou bauxite deposit for analyzing their elemental geochemical characteristics, then have discussed the weathering, sedimentation, and diagenesis processes of the center of the aluminum-forming basin. The main conclusions are given below. (1) The characteristics of immobile elements (e.g., Al2O3/TiO2 ratios, and Zr-Ta, Zr-Nb, and lgCr-lgNi diagrams) indicate that the ore-forming materials of the Tiechanggou bauxite deposit could be mainly sourced from the Silurian strata in the basement. (2) The first elevation of this area occurred in the Permian, caused the outcropping and denudation of the basin and its periphery area. The weathering products were migrated to and deposited in the central part of the basin with initially deposited kaolinite rock (consisting of dominant kaolinite and enriched accessory minerals such as anatase and zircon). Compared with the Silurian shale, the initial kaolinite rock was characterized with low contents of K, Mn, Cs, Rb, Sr, and Ba, and high contents of Al, Sr, Th, Nb, Zr, Y, and REE, withgeneral negative Ce anomalies in the profile, indicating that its sedimentary environment is general weakly reduced environment. (3) The second elevation caused a certain degree weathering and leaching transformation of sediments in the central part of the basin, but the overall Al/Si ratios of samples in the section are changed relatively slight, indicating that only a certain amount of iron was leached away. The ratios of V/Cr (average 1.96), Th/U (average 3.40), and Co/Ni (average 0.39), of samples from the upper kaolinite rock layer all reflect characteristics of their weathering occurred under weakly oxidized condition. Weathering and leaching caused the migration of the rare earth elements (REE) especially the light rare earth elements away from the upper kaolinite rock layer. This finally changed the REE distribution patterns of samples in the upper and lower kaolinite rock layers. The lower kaolinite rock layer is characterized by rich siderite nodules. The iron leached from the upper part and the periphery of the basin during the weathering process was migrated to and enriched in the lower part of the section. It is believed that siderite nodules were formed by the reaction of initial iron nodules with organic carbon surrounding those iron nodules in the diagenesis process.
Keywords: kaolinite rock series; geological and geochemical characteristics; ore genesis; Tiechanggou deposit; Guizhou
ACTA MINERALOGICA SINICA Vol. 41, No.4/5, 2021, page 494-508