Geological and geochemical characteristics of primary sedimentary bauxite in Pingguo, Guangxi and its metallogenic environment

The Pingguo bauxite mining area in Guangxi is an important bauxite producing area in China. There are two types of bauxite ores: Karst accumulation type and primary sedimentation type. Previous researches mainly focused on the genesis of accumulative bauxite, but no specific analysis has been carried out on the sedimentary facies, paleogeomorphology, sedimentary environment and its control on the formation of primary sedimentation type ore. In this paper, detailed mineralogical and geochemical studies have been carried out on a variety of primary ores in the Pingguo area. The results show that the primary bauxite ore is generally enriched in Zr, Ga, Th, U and V but depleted in Sr and Ba. The 87Sr/86Sr values are generally high, mostly between 0.7080 and 0.7085. Energy spectrum scanning electron microscope and electron probe microanalysis of oolites in primary ore show that different samples have variable contents of O, Al, Si, Fe, K, Ti and Ga. Combined with the field occurrences and spatial location of the ore bodies, this study puts forward that the paleogeomorphic characteristics of the Pingguo mining area are that the terrain in the east and north is higher, whereas the terrain in the south and west is lower. The sedimentary environment from the Taiping area to Nadou area and then to Xin'an area in Pingguo changed from near-land to far-land, and from shallow-water to deep-water, presenting the pattern of sea-land intersection sedimentary environment. The primary bauxite ore-forming materials were transported and deposited from Taiping to Nadou and then to Xin'an. On the whole, it was a delta sedimentary environment which can be divided into more detailed sedimentary microfacies such as branch fluvial facies, swamp facies and sandbank facies. It is pointed out that sandbank microfacies were most conducive to the enrichment of primary ore. Therefore, the Narong and Tangqin areas in Pingguo were most conducive to the deposition of primary ore. © 2022, China Science Publishing & Media Ltd. All right reserved.