Study on Permian Basalt Weathering Crust and Enrichment of Rare-earth Element in Western Guizhou Province, China
|Course||Mineralogy , petrology study of ore deposits|
|Keywords||Forming mechanism rare earth deposit weathering crust E’meishan basalt Guizhou Province|
E’meishan basalt in western Guizhou Province has been the focus of academic research in recent years. Researchers have interested in the relationship between E’meishan basalt and mineralization. E’meishan large igneous provinces was put out by Mei Houjun in 1962, E’meishan basalt character and eruption were discussed by Song Xieyan (1998, 2002), Wang Yangeng (2003), He Bin (2003, 2004, 2005). Guizhou Geology and Mineral Seminar held in 2001, 2003, 2005, the E’meishan basalt was main topic. A lot of researchers of E’meishan basalt were reported in the seminars.The deposits of Guizhou Province, including in gold, copper, antimony, mercury, bauxite, and many other non-metallic metal deposit, are closely related with E’meishan basalt, e.g. well-known Laowanchang gold deposit, Weining copper depost, Linkou pyrite deposit. The mineralization mechanism, material sources, background of mineralization and mineral character of these deposits have been studied by geologists, such as Chen Lv-an (2000), Yang Zhusen (2000), Yang Yuangeng(2003).E’meishan basalt weathering crust and rare-earth deposit of weathering crust are rarely involved in past. On the basis of the basalt weathering profiles at Heishitou, Weining County and Yemachuan, Hezhang County, and previous studies of the Lufang, Weining County, Shiyakou, Hezhang County and Yuwanchong, Bijie County, author tested content of rare-earth element in the basalt weathering profiles. Additionally, enrichment factors and mineralization mechanism were discussed in the paper. Lastly, author put forward distribution region of rare earth depositMany deposits are closely related with E’meishan basalt weathering crust in Guizhou Province. Mineralization took place near the horizon of E’meishan basalt. The weathering crust in the boundary of Middle-Upper Permian was divided into 4 types according to weathered rock and locality, these are (1) the basalt weathering crust at karst surface of the top of Maokou Fm.; (2) manganese (iron) weathering crust on carbonate laterite; (3) high alumina and kaolinite weathering crust within E’meishan basalt; (4) kaolinite clay weathering crust at the top of the basalt and the base of Longtan (Xuanwei) Fm.The third sub-layer (upper basalt) is rich in Cu, Fe, rare earth elements; it is an important source of mineralization. A lot of deposits, such as iron, manganese, gold, copper, rare earth deposit were formed on the weathering crust. Especially, gold, copper and rare earth deposits formed commonly in the weathering crust of the top basalt with high content of Cu, Fe and rare earth elements. The basalt was weathered into kaolinite clay at hill of razed surface in Quaternary because of long-term exposure and weather. Therefore, kaolinite clay rich in rare earth element formed in the weathering process. Especially, rare earth deposit formed in the weathering kaolinite clay crust of the top basalt with high content of Cu, Fe and rare earth elements. Additionally, because of kaolinite strongly adsorptive for rare earth element, rare earth element gathered in white kaolinite clay on weathering crust of razed hill. More than kaolinite clay of weathering crust at the low-lying terrain has low enrichment of rare earth element because of weak weathering process.At the same time, author suggests that concentration of rare earth element are easily at alkaline, humid climate and oxidation condition, and rich in iron and manganese environment. Lastly, rare-earth deposit mineralization model was established.Through field testing and geochemical analysis of the basalt weathering crust, rare earth mineralization points have been found in Hezhang, Weining, Bijie County. Therefore, author suggests that the weathering crust at the top of basalt is an important horizon to find rare earth deposit. At the same time, rare earth deposit in the basalt weathering crust was reconsidered a new type.As the rare earth mineralization type with higher content of rare earth element is widely distributed in the weathering crust at the top of Permian basalt, therefore, it is likely a large-scale perspective region of rare earth mineralization. At the same time, Cu accumulation in the weathering crust was fund. Content of Cu is up to 0.5%. Cu is easily extracted by chemical method due to Cu preserved in the kaolinite clay. Therefore, the horizon of basalt weathering crust may be an important prospecting horizon.