| Bauxite is the main raw material for industrial aluminum extraction.Western Guangxi is one of the dominant areas for aluminum resource production in China.The aluminum industry is an important pillar industry in the economic development of Guangxi.Depositedtype bauxite is the main type of bauxite for industrial utilization,but after years of mining,the amount of aluminum resources has decreased sharply.Permian sedimentary bauxite in western Guangxi is a potential replacement resource.Paleoclimate is one of the important conditions for the mineralization of sedimentary bauxite.The metallogenic paleoclimate of sedimentary bauxite can be studied by analyzing the changes in mineral composition and ore characteristics.The sedimentary bauxite is studied for its geological and geochemical characteristics as well as its mineralization paleoclimates using methods such as field geological survey,optical microscope,scanning electron microscope experiments,XRD and XRF,as well as ICP-MS testing and analysis,and the following conclusions are obtained:(1)Through field investigation and petrographic observation,the sedimentary bauxite ore-bearing rock series in western Guangxi can be divided into "iron layer-aluminous layerclay layer" from bottom to top.The ore-bearing rock series occurred in the form of stratified or stratified-like structure,partly in the form of lenticular.(2)The ore texture has subhedral-euhedral,cementation,mud crystal-microcrystal and clastic texture,and the ore structure is dense massive,pisolitic(oolitic),soil or semi-soil,layered,brecciated and honeycomb or porous.(3)The ore-bearing rock series are mainly aluminum minerals(diaspore),clay minerals(kaolinite,pyrophyllite,chlorite,etc.)and iron minerals(pyrite,goethite,hematite,etc.),followed by anatase and calcite.(4)The ore-bearing series showed variations of light red-light green(ferroaluminite),greenish-gray-light gray(bauxite ore),light gray-light purple(bauxite rock),and black(carbonaceous mudstone),which reflected the transformation of the paleoclimate between hotdry and warm-humid.(5)The upper and lower parts of the ore-bearing rock series were characterized by a high content of kaolinite and less chlorite and pyrophyllite,while the middle part was the opposite,indicating that the ore-bearing rock series was relatively dry and hot in the early stage but warm and humid in the middle stage.The results of XRF and ICP-MS tests showed that the Si O2/Al2O3 ratio of the ore-bearing rock series(0.03~7.7)was relatively large in the upper and lower parts and relatively small in the middle part.The Sr/Cu ratio(0.06~637.5)was relatively large in the middle and lower part and small in the upper part.This reflected the ore-forming paleoclimate of ore-bearing rock series,with relatively high humidity in the middle stage and low humidity in the early and late stages,and a transformation to a dry climate during the oreforming process.The CIA values(mostly between 80 and 100)were high in the lower and upper parts and low in the middle,indicating that the early and late stages were hot and the middle stage was warm.(6)The paleoclimate change characteristics of ore-bearing rock series can be divided into six stages: stage Ⅰ was the hot and arid climate,which mainly formed iron-aluminum rock;stage Ⅱ was the warm and humid climate,which mainly deposits soil and pisolitic(oolitic)bauxite;stage Ⅲ was warm and humid climate,and the humidity is lower than that of stage II,mainly forming soil,honeycomb or porous bauxite.Stage IV was the hot and humid climate,mainly forming dense massive bauxite,stage V was the warm and humid climate.The temperature and humidity were further lower than stage IV,mainly forming sand debris and dense massive bauxite,stage VI was the hot and arid climate,mainly forming aluminous clay rock and carbonaceous mudstone.During the deposition of sedimentary bauxite,several climate changes occurred.There were alternating paleoclimate processes such as transformation from warm and humid to dry and hot. |
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