秦岭成矿带Pb、Zn化探异常与铅锌矿常无对应关系的原因

秦岭成矿带中Pb、Zn化探异常区常无铅锌矿，而铅锌矿区又常无Pb、Zn异常，这种Pb、Zn异常与铅锌矿的不对应关系，通常导致大量的Pb、Zn异常无找矿指示意义，甚至给找矿评价、勘查部署选区工作带来了某些误导。本次的大量实验研究表明，秦岭地区水系沉积物中Pb、Zn元素主要在较粗粒级(-10~+60目)组分和细粒(小于140目)组分两端粒级中富集，而在中等粒度(80~120目)中贫化。以往所采用的统一粒度(-60目)样品分析所圈定的Pb、Zn异常，主要是细粒级吸附态的Pb、Zn在远离铅锌矿源区富集的反映，强化了远离矿源“次生富集”的信息。据此建议，在秦岭地区开展的面积性化探工作中，首先通过典型矿区粒级试验，建立区内不同背景区成矿元素的合理粒级范围，使所选用的粒度组合(粗、中、细粒)对在不同粒级中富集的元素更具代表性，改变秦岭Pb、Zn等化探异常指导找矿工作的被动局面，确保化探工作能更好地指导地质找矿和勘查部署选区工作。

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.