1∶ 250,000 multi-target geochemical mapping is one of the most important regional basic work contents in multi-target geochemical survey, and its working method is basically the same as the national1∶ 200,000 regional geochemical exploration plan, mainly with different sampling media. It collects 1 shallow soil samples every 1km2 in Quaternary plains, basins, offshore beaches, deltas, lake wetlands, loess plateaus and hilly areas in China, and combines them into every 4 km2 1 sample. At the same time, every 16km2 1 deep soil sample was collected for total element analysis. The 54 indexes specified in the unified analysis are Ag, As, Au, B, Ba, Be, Bi, Cd, Co, Cr, Cu, F, Hg, La, Li, Mn, Mo, Nb, Ni, P, Pb, Sb, and Ni specified in the 1∶200000 national regional geochemical exploration plan. On the basis of 39 elements of Mg, considering the research needs of agriculture, environment, health and ecology, three elements of Br, C, Ce, Cl, Ga, Ge, I, N, Rb, S, Sc, Se, Tl, etc. 13, and two indicators of organic carbon and pH value were added for analysis.

According to the characteristics of multi-objective geochemical mapping, the working areas are mostly thick covered areas, mainly collecting and analyzing soil samples, and the geochemical background of their elements has little change in the same geochemical landscape. In order to better reflect the change of geochemical background, the accuracy and precision of analytical methods are highly required, and the most important point is to require a lower detection limit. Therefore, in addition to increasing the number of elements to be analyzed to 54 indicators in the national scanning plan of regional geochemical exploration to 1∶200000, the monitoring requirements for technical indicators and analysis quality of analytical methods are much stricter. Therefore, the supporting analysis method can only take modern large-scale analytical instruments such as inductively coupled plasma mass spectrometer (ICP-MS), inductively coupled plasma emission spectrometer (ICP-AES) and X-ray fluorescence spectrometer (XRF) as the main body, and combine with other special analytical instruments to form an advanced supporting analysis scheme with 54 indexes (Table 84.4), and apply it to large-scale actual sample analysis.

Table 84.4 Matching Analysis Scheme of 54 Indexes in Multi-objective Geochemical Mapping