The tectonism-sedimentation constraints on Al-Ga coupling relation of coal-bearing strata and prediction of Ga favorable area

This paper is the result of mineral exploration engineering.

Objective The type, location and horizon of coal accumulation basin conducive to aluminum-gallium symbiosis were predicted.

Methods The coupling relationship between coal, aluminum and gallium is discussed through the symbiotic relationship of aluminum and coal - aluminum in coal accumulation basin. Then, based on the differences of coal accumulation strength of different types of coal accumulation basins, combined with the temporal and spatial distribution characteristics of aluminum ore, the types and horizon of coal accumulation basins conducive to the co-occurrence of aluminum and gallium are discussed. Based on the tectono-sedimentary process of coal-bearing rock series during the sedimentary period, combined with the gallium test data in coal, the prediction of gallium-bearing favorable areas in the southern margin of Ordos Basin is carried out.

Results Among the basin types, the large stable craton coal accumulation basin has high coal accumulation strength and obviously strong aluminum (gallium) mineralization. Gallium is the best in the Carboniferous-Permian coal in North China, the second in Late Permian in South China, and the lowest in Early and Middle Jurassic in North China. The content of gallium in the coal of Pubai mining area in the southern margin of Ordos Basin is relatively high, and the content of gallium in the bottom coal seam generally exceeds 30 μg /g, followed by the coal seam of Tongchuan mining area, the weighted average of gallium in coal is 28 μg/g, and there are 450 pieces of gallium content over 30 μg/g in various mining areas of Huanglong Jurassic coal field. The No. 2 coal layer at the top has the highest content of gallium, and gallium is mainly enriched in the roof and floor of coal seam and gangue. The content of gallium in coal seam itself is relatively low. Finally, 4 favorable areas for finding gallium are predicted.

Conclusions Coal and aluminum (gallium) have basically the same ore-forming background and closely related ore-forming conditions, which determines the internal genesis and coupling relationship of coal-aluminum-gallium symbiosis in coal-bearing rock series, and can form coal-aluminum-gallium co-forming ore series. Due to the difference of basement stability and basin formation mechanism, the coal accumulation strength of different types and different times not only causes the difference, but also controls the difference of aluminum-gallium enrichment degree.