Geochemical Characteristics of Mercury in Near Surface Soil and its Relations to the Accumulation of Oil And Gas in Shaanxi-Gansu-Ningxia Basin

Shaanxi-Gansu-Ningxia Basin is a depression basin, in which a lot of oil and coal formed during the Paleozoic and the Mesozoic.The present landforms can be divided into three belts: desert, loess and the transitional zone betweenthem two. It is confirmed by the experts at home and abroad that the soil-mercury above and around an oil and gas accumulations is relatively abundant. In the study aera, the distribution of soil- mercury in the transitional zone is shown as monopeak; but for desert and loess, and thermal decomposed soil-mercury of transitional zone, are di- and / or polypeaks which coincide with the features of that in oil and gas region.The different distribution of soil-mercury are contribute to the differences of soil and water's chemical composition and geological background, concertration in desert is higher than that in loess and varies widely, the transitional zone shows the mixed feature. For the study of occurence of soil- mercury, two temperature programming experiments were designed, one is from 100℃ to 800℃ with an interval of 50℃ ; the other is 80℃ to 300℃ , steped by 20℃. The results show that two main forms of soil-mercury, i.e.absorbed simple substance mercury and mercury chloride (HgCl₂).but there is no mercury compounds in soil when the temperature is higher than 350℃. Soil-mercury in the basin is combined by two sources, autochthonous and allo chthonous, the undery-ing oil and gas are being the main resources of the allochthonous mercury.