Geochemical Survey in Mojiang Area of Yunnan Province, China: Geochemical Map and Geochemical Anomaly Map

The geochemical maps and geochemical anomaly maps produced based on the data in the databases of the Regional Geochemistry–National Reconnaissance (RGNR) and the National Multipurpose Regional Geochemistry Survey (NMPRGS) projects have played a crucial role in China’s geochemical exploration. A geochemical survey of the Mojiang area, Yunnan Province, China, has been completed and reveals potential new regions for Ni exploration related to occurrences of serpentinite melanges. The geochemical maps and geochemical anomaly maps need to be drawn in this area. Traditional geochemical maps, heavily dependent on data quantity, are less suitable for consistent comparisons across distinct regions and elements. Here, a fixed value method is proposed to contour the Ni geochemical map on 19 levels, which is convenient for the comparison among elements. On the geochemical maps, the two known Ni deposits are located in a region with Ni surely screening risk level (on the national standard of pollution risk of heavy metals in China) and a region with Ni economic level (Ni as an associate or main economic metal on the national standard of Ni deposit in China), respectively. In addition, we have determined that the Sn and Li levels in this area are at (low or high) background levels compared to other regions. Then, the method of seven levels of classification, which is also suitable for the comparison across different areas or elements, is used to draw the geochemical anomaly maps in the Mojiang area. On the anomaly maps, the two known Ni deposits are located in the regions with Ni anomaly levels not less than four, while the anomaly areas of Sn and Li are sporadic, with anomaly levels not larger than two in this area. These consistent results with the known facts of Ni, Sn, and Li deposits in the Mojiang area not only consolidate the roles of geochemical maps and geochemical anomaly maps but also illustrate the comparison among elements in mineral exploration. Furthermore, we predicted three Ni potential regions in the Mojiang area on the geochemical survey.