Influence of variation in element background values in rocks on metallogenic prognosis in geochemical maps
CHENG Zhi-zhong, XIE Xue-jing (China University of Geoscience,Beijing 100038, China; Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, Hebei, China)
Geochemical exploration is mineral exploration carried out by using variations of element contents in various kinds of media. Therefore geochemical mapping is the most fundamental work for geochemists, just as geological mapping for geologists. Variations in element background values in various types of rock have an important influence on the prognostic process during geochemical prognosis of ore deposits. Seven-six elements for geochemical mapping in southwestern China may be divided into two groups: (1) the element group with less influence of lithological variation on metallogenic prognosis, and (2) the element group with more influence of lithological variation on metallogenic prognosis. The first element group consists of Hg, Cd, Sb, Au, Sn, Mo, Ag, U, Pb, Bi and W, which are characterized by the ratios of the highest background values in rocks to the anomaly thresholds in the prognostic region of 1 and the ratios of the maximum background values to the minimum background values of 4. This geochemical method is very effective for searching for minerals of these elements. The second element group consists of Pt, Co, Cr, Cu, Ni, V and Ti, which are characterized by the ratios of their highest background values in rocks to the anomaly thresholds in the prognostic region of 1 and the ratios of maximum background values to the minimum background values of 8. This paper deals with the elements Sn (belonging to the first element group) and Cu (belonging the second element group). Sn deposits in southwestern China are closely related to Sn geochemical anomalies, whereas Cu deposits in southwestern China are not necessarily bound up with giant Cu geochemical anomalies. For the second element group, the multifractal filter technique should be used to suppress different background interferences and extract mineralization information from the geochemical anomalies of the elements.