Abstract: Dongsheng kaolin deposits lie in Jurassic Yan’an Formation in northeast of the Ordos Basin. Genesis of the kaolinites is disputed. Based on thin section observation, scanning electro microscope (SEM), X-ray diffraction, major elements component (XRF) and REE analysis (ICP-MS), the characteristics of kaolin sandstone deposits in the studied area were determined. By contrasting with country rocks, the orebearing sandstone is white sandstone cemented by kaolinite with coarse and fine fraction in the same sample, and the original rock is red sandstone with clastic kaolinite and illite. The distribution of the ore beds are well correspondent to the oil seepage in northern basin. Field characteristics, petrography, bulk chemistry and natural gas migration and leakage suggest that the kaolin sandstone deposits experienced chemical reduction from the Neopaleozoic gas seepage in field south of the studied area where fluids reduced some Fe³⁺ of iron to Fe²⁺ within the red sandstone, and then the red beds were bleached. At the same time, acid fluid dissolved feldspar grains and transformed feldspar into kaolinite. Kaolin deposits experience later weathering and leaching and improve present scale.

Key words: kaolin deposits, gas seepage, Dongsheng, Ordos Basin