National-scale geochemical mapping projects in China

Regional, national and global scale geochemical mapping projects have been carried out in China since the late 1970s, due to the development of cost-effective, low detection limit analytical methods. These projects have provided a huge mass of high-quality, informative and comparable data for mineral resource exploration and are now making contributions to environmental assessment. In this paper, four national-scale geochemical mapping projects are described. (1) The Regional Geochemistry-National Reconnaissance Project (RGNR project), which is China's largest national geochemical mapping project, has covered 6 million km(2) of upland regions since 1978. Generally, stream sediment samples were collected at a density of 1/km(2) and four samples were composited into one sample and analysed for thirty-nine elements. (2) The deep-penetrating geochemical mapping project (DEEPMAP Project) has been conducted since 1994 in covered terrains, including sedimentary basins, at a density of 1 sample per 100 km(2) with thirty to seventy elements determined per sample. In the past 10 years, an area of approximately 800 000 km(2) has been covered and this project has played an important role in finding sandstone-type uranium deposits in basins. (3) The seventy-six geochemical element mapping project (76 GEM project) has been carried out since 1999 and involved the collection of stream sediment samples from the RGNR project targets which were analysed for seventy-six elements. Samples from each 1:50 000 map sheet were composited into one analytical sample (approximately one composite sample per 400 km(2)). Approximately 1 million km(2) have been surveyed to date. (4) The multi-purpose eco-geochemical mapping project has been conducted since 1999 in Quaternary plain areas for environmental and agricultural applications. Surface soils (depths from 0-20 cm) were collected at a density of one sample per km(2), and four samples were composited into one for analysis. Deep soils (from a depth of 150 to 200 cm) were collected at a density of one sample per 4 km(2) and four samples were composited into one analytical sample. All the composite samples were analysed for fifty-four elements.