Abstract:

The Lanping basin located in the middle section of the Sanjiang range in southwest China is a famous polymetallic mineralization area in which dominant economic metals are copper, lead, zinc, and silver. The regional geochemistry survey with the scale of 1∶250 000 has been completed by Yunnan Geological Survey Institute from 2012 to 2016 in this area. The sampling medium is stream sediment with the size of -10 to +60 meshes, and the averaged sampling density is ca. 1.02 per square kilometer. Based on the analytical results of the regional geochemistry survey, the enrichment coefficients of 29 trace elements on average concentration in the study area are calculated relative to their average background values in the Southwest Sanjiang ore zone and discussed focusing on the main economic metals firstly. The results indicate that it is not suitable to determine economic metals only depending on the enrichment coefficients. Then geochemical anomalies of 29 trace elements are determined and classified in the Lanping basin with an area of 8 800 km² on the method of seven levels’ classification to eliminate the elemental enrichment effects during weathering. The results indicate that the determined anomaly areas are consistent with the known metal deposits spatially and metal deposits with larger scales are commonly located in the anomaly areas with higher levels. The known metal deposits in this area are commonly located in the anomaly areas with levels higher than 3 on the seven levels’ classification method. According to this criterion, two favorable areas are determined for future prospecting for polymetallic deposits. One is the Laojunshan area in the northeast of the basin, and the other is the south section of Baiyangchang area in central-south of the Lanping basin of Yunnan province, China.

Key words: Lanping Basin, regional geochemistry survey, stream sediment, Seven levels’ classification, prospecting area