Analytical requirements in international geochemical mapping

Abstract

The history of the development of geochemical exploration has been closely connected with the progress of geoanalysis techniques and instrumentation. The application of spectrographic methods and the development of sensitive colorimetric methods in analyzing geological materials provided the necessary background for the birth of this new exploration method. The use of atomic absorption spectometry highlighted local and semi-regional scale geochemical exploration in the whole world. Regional and national geochemical mapping became established only when automatic instruments with multielement analysis capability became available (e.g., the XRF spectrometer, the ICP emission spectrometer, and the neutron activation facility). International geochemical mapping is the inevitable outcome in the trend of development of geochemical exploration. But its analytical requirements possess some marked differences with its earlier stages due to its international or global nature. ELEMENTS DETERMINED: Elements determined in existing regional or national geochemical mapping projects have been highly diversified. They should be unified in the International Mapping Program (IGCP 259), but flexibility must be allowed. To solve this problem, the elements will be grouped into six packages and analysis can be made in sequence in these packages according the facility and capability of different laboratories. DETECTION LIMITS: Detection limits of trace and ultratrace elements should be lowered below their crustal abundance in order to make the geochemical maps of these elements much more informative than before. A proposed list of detection limits is given. ACCURACY: Accuracy is the long-time neglected item in geochemical exploration analysis, because the exploration geochemist has been mainly interested in looking for the relative contrast of anomalous values with background values. But in International Geochemical Mapping, the interlaboratory bias must be reduced to a minimum to make the data globally comparable. This could be done by developing unified procedures for selecting optimum methods, and for routine monitoring of the data quality. Primary and secondary standard samples have to be prepared and used in these procedures.