Lead (Pb) Geochemical Mapping Based on a Fixed-Value Method: A Case Illustration in Wenshan Area, Southwest China

Abstract

An objective understanding of the spatial distribution of Pb concentrations is essential for the rational exploitation of resources and the effective assessment of environmental pollution. The geochemical map is an indispensable tool in mineral exploration and environmental assessment. A 19-level fixed-value method for contouring the geochemical map of Pb is proposed, which is based on various typical values of Pb concentrations, including analytical detection limit, abundance values of soils and stream sediments in China, risk screening values and intervention values for agricultural soils in China, and the cut-off grades of ore deposits. Based on 18 fixed values, Pb concentrations are divided into 19 levels and further categorised into six types. These six types are illustrated in the geochemical map in blue tone, yellow tone, pink tone, red tone, grey tone, and black colour, corresponding to low-background zones (level 1–5), high-background zones (level 6–9), maybe screening risk zones (level 10–12), surely screening risk zones (level 13–15), surely intervention risk zones (level 16–18), and mineralised zones (level 19), respectively. The method is applied in the Wenshan area of Yunnan Province, which is rich in Pb, Zn, and Sn metal resources. The results indicate that the Pb concentration in this area ranges from level 2 to level 19, with most belonging to the high-background zones. Low-background zones are closely related to the spatial distribution of low-Pb rocks in the region, while the zones in maybe screening risk, surely screening risk, intervention risk, and mineralised types coincide spatially with proven Pb-Zn deposits in the area. Geochemical maps generated by traditional cumulative frequency method rely on the existing Pb concentration data from samples, which limits the comparison across different elements and areas. In contrast, the proposed 19-level fixed-value method for Pb represents an objective and innovative approach that facilitates the comparison and provides robust support for mineral exploration and environmental assessment.