Geochemical Mapping: With Special Emphasis on Analytical Requirements

More than 40 national and regional geochemical mapping projects in the world carried out from 1973 to 1988 do not conform to common standards.In particular they have many analytical deficiencies.In the period 1988 to 1992,the International Geochemical Mapping project(Project 259 of UNESCO's IGCP Program)prepared recommendations designed to standardize geochemical mapping methods.The analytical requirements are an essential component of the overall recommendations. They included the following:71 elements should be analyzed in future mapping projects;the detection limits of trace and ultratrace elements must be lower than the corresponding crustal abundances;and the Chinese GSD and Canadian STSD standard sample series should be used for the correlation of global data.A proposal was also made to collect 5000 composite samples,at very low sampling densities to cover the whole Earth's land surface.In 1997 an IUGS Working Group on Global Geochemical Baselines was formed to continue the work which began with IGCP 259.From 1997 up to now,new progress has been made especially in China and FOREGS countries under the aegis of this working group,including the study of suitable sampling media,development of a multi-element analytical system,new proficiency test for selection of competent laboratories and role of wide-spaced mapping in mineral exploration.One of the major problems awaiting solution has been the inability of many laboratories to meet the IGCP recommendations to generate high quality geochemical maps. Fortunately several laboratories in China and Europe have demonstrated an ability to meet the requirements and they will be well placed to render technical assistance to other countries.