Multi-scale geochemical mapping in China
|Location||International Geological Congress,oslo 2008|
|Holding Date||29 September 2008|
Regional-, national- and global-scale geochemical mapping projects have been carried out in China since the late 1970s. Four national-scale geochemical mapping projects are: (1) Regional Geochemistry - National Reconnaissance (RGNR) Project, which is China’s largest national-scale geochemical mapping project and has covered more than 6 million km2 of the country’s hilly and mountainous regions since 1978. Generally, stream-sediment samples were collected at a density of 1 sample per km2 and 4 samples were composed into one analytical sample for analysis of 39 elements. (2) Deep-penetrating geochemical mapping (DEEPMAP) project has been conducted in covered terrains, including basins with analysis of 30-70 elements since 1994. An area of approximately 800 000 km2 has been covered. It is playing an important role in finding concealed mineral deposits such as sandstone-type uranium deposits in basins. (3) 76 Geochemical Element Mapping (76 GEM) project has been carried out since 1999. Samples from each 1: 50 000 map sheet are composed into one analytical sample (approximately one composite sample per 400km2) for 76 element analyses. Approximately 1 million km2 has been finished up to now. (4) Multi-purpose Eco-geochemical Mapping project has been conducted in the quaternary plains of eastern China to provide data for environmental regulation and for improvement of agricultural practices since 1999. Surface (0-20cm) soils are collected at a density of 1sample/ km2 and 4 samples are composed into 1 analytical sample, deep soils (150 to 200cm) are collected at a density of 1sample/4km2 and 4 samples are composed into one analytical sample. All the composite samples are analyzed for 54 elements. For many years, China has been a leading participant in international efforts such as the International Geological Correlation Program’s Projects 259 (International Geochemical Mapping) and 360 (Global Geochemical Baselines) and the International Union of Geological Sciences Task Group on Global Geochemical Baselines that have a long-term goal of producing a global geochemical database. The leadership role taken on by China includes: (1) transferring its expertise in sampling, chemical analysis, and map generation to the developing countries through bilateral and multilateral collaboration. (2) Providing chemical analyses of the global-scale mapping samples for 70 elements from developing countries. The distinguishing features of China’s geochemical mapping projects are the close linkage of mapping with mineral exploration at all scales. These geochemical mapping projects have provided a huge mass of high-quality data for mineral resources and are making contributions to environmental assessment.