A 19-Level Fixed-Value Method to Classify the Cu Concentration and Its Application in the Jinchuan Area of Gansu Province, China

The massive elemental dataset of stream sediments and soils accumulated by the projects of the Regional Geochemistry–National Reconnaissance (RGNR) and the National Multi-Purpose Regional Geochemical Survey (NMPRGS) provide core support for the compilation of geochemical maps and hold irreplaceable significance in the field of mineral exploration and soil environment. Geochemical maps produced by traditional methods are heavily dependent on data volume, which limits the comparisons across different areas and different elements. To facilitate the comparisons, a 19-level fixed-value classification method was proposed for Sn, Li, Mo, Ni, etc. However, the method for Cu is still lacking. Here the method for Cu is proposed to divide Cu content into 19 levels on 18 fixed values which are determined based on many typical values such as the detection limit, quartiles from the RGNR and NMPRGS projects, and cutoff grades. The Jinchuan Cu-Ni deposit is a giant deposit in China which is selected as an illustration on the new method. The elemental data of rocks and stream sediments in the Jinchuan area are used to compile elemental concentration maps and elemental concentration-level maps for the elements of Cu and Ni. The results show that the 19-level fixed-value method can not only effectively evaluate the concentration levels of elements but also enable the comparisons among elements. The Jinchuan Cu-Ni deposit is located in the mineralization areas and high anomaly areas of Cu and Ni. Compared with the previous reported maps of Ni, Sn, and Li in other areas, the new method facilitates the recognition of target metals in geochemical exploration. An element with a concentration level of no less than 15 may be mineralized or is the target metal on the 1:200,000 survey data from sediments. The 19-level fixed-value method may hold significant applications in the fields of mineral exploration and environment assessment.