A discussion on the reasons for discordance between Pb-Zn ore deposits and Pb-Zn geochemical anomalies in Qinling metallogenic belt

In Qinling metallogenic belt，It is frequently seen that Pb-Zn anomaly areas have no lead-zinc ore deposit，and lead-zinc ore districts have no Pb-Zn anomalies. Such a discordance between Pb-Zn ore deposits and Pb-Zn geochemical anomalies causes many Pb-Zn anomalies to have no ore-prospecting significance or even results in mistakes in prospecting evaluation and drilling deployment. Through lots of experimental studies, The authors have found that Pb and Zn in stream sediments are mainly concentrated in coarse-grained samples (-10~+60 meshes) and fine-grained samples (＜140 meshes) , but are poor in medium-grained samples (80~120 items) in Qinling area. Previous work adopted unified granularity (-60 mesh) to delineate the Pb-Zn anomaly, which is actually the reflection of fine-grained sorption-state Pb-Zn enrichment far away from the source area. It is thus suggested that, when large-area chemical prospecting work is conducted in Qinling area, researchers should first perform granularity experiment to set up a reasonable granularity range of metallogenic elements in different backgrounds and thus render samples of different grain sizes (coarse, medium and fine) more representative. In this way, the passive situation in Pb-Zn prospecting work in Qinling area can be changed, and geochemical prospecting can have more directive significance in ore-prospecting work and deployment of exploration and drilling work.