Xueqiu Wang

Interpretation of regional-scale distribution of high Hg in soils of karst area in Southwest China

The abundance and spatial distribution of mercury in soil samples covering nearly the whole of China (c. 9 million km2) were obtained by the China Geochemical Baseline (CGB) project from 2008 to 2015. From the data and maps, it was found that the Hg contents both in the top (0–25 cm) and deep soil (below 100 cm or C-horizon) of the karst area in southwestern China are richer than that of any other geographical landscape areas. Median Hg values for this karst area are 113 and 90 µg/kg respectively (n = 126), in the top and bottom soils, much higher than the corresponding data of 26 and 18 µg/kg for the entire country (n = 3380). This regional-scale high Hg distribution is due mainly to high Hg geochemical backgrounds in bedrock and soil formation on limestone. A large-scale epithermal metallogenic domain developed in southwestern China and the extensive distribution of Lower Cambrian black shale in southwest China led to a high Hg geochemical background for parent rocks of soils. The chemical weathering of carbonate minerals and the geochemical behaviour of Hg in the epigenetic environment result in Hg enrichment by ferric oxides, iron hydroxide and organic carbon in limestone soils. Human activities mostly result in local-scale Hg anomalies, but have little effect on this regional-scale anomaly.

Comparative Study and Spatial-Temporal Distribution of Regolith and Rock Geochemical Data from Xingmeng - North China

Geochemical mapping at national and continental scales continues to present challenges worldwide due to variations in geologic and geotectonic units. Use of the proper sampling media can provide rich information on the geochemical compositions of different geological units as well as geochemical responses to climate change, weathering and various types of mineralization. The abroad study on geochemical transect, is mainly for the North American continent scale geochemical transect research across Canada and the United States (Smith et al., 2008; Drew et al., 2010). However, China is still at the primary systematically studying the content and spatial distribution of geochemical elements on the national or continent scale, especially in the area of the geochemical transect. Different from the China geochemical baseline, which of study rang is a nationwide two-dimension planar, however, the study area of the geochemical transect is a national or continent one-dimension transect. The sampling density of the latter is high(1~4 km/site) along a linear sampling route to collecting regolith and rock samples, through which demonstrating the spatial distribution relationships between element content of sediments or rocks and the various factors, for example, geology, geography, climate et al. In order to study the regional geochemical composition and lateral spatial variation of the geochemical elements, a national-scale geochemical transect across the Xingmeng Orogenic Belt and the North China Craton has been completed as a part of the China Geochemical Baselines Project (Wang et al., 2015). Its purpose is to