云南省芒市弄坎异常查证

Examination and confirmation of Nongkan anomaly in Mangshi,Yunnan

弄坎异常位于"西南三江"多金属成矿带南段,从元素空间分布及组合特征可分为AuAs-Sb和Pb-Zn-Ag-Cu 2个综合异常。经三级查证,下二叠统沙子坡组与上三叠统南梳坝组接触带附近的粉砂岩、碎裂岩为异常源,验证结果虽发现的金矿化较弱,但发现了高含量的钛矿化和铁矿化。研究表明:弄坎金异常的成因为岩浆热液在上升过程中混入地表水(大气降水),形成混合流体,不断萃取沙子坡组碎裂岩、碎屑岩类等富金地层中的金元素形成含金成矿流体,成矿流体通过断裂构造迁移在地层滑脱面、断层交汇处等成矿有利部位沉淀富集形成异常。

The Nongkan anomaly is located in the southern part of the Southwestern Three Rivers metallogenic belt,which can be divided into two comprehensive anomalies,Au-As-Sb and Pb-Zn-Ag-Cu,based on the spatial distribution and assemblage characteristics of the elements. Third grade anomaly inspection found that the siltstone and cataclasite near the stratigraphic contact belt between the Lower Permian Shazipo Formation and Upper Triassic Nanshuba Formation are the anomalous source. In spite of the relatively weak gold mineralization,the inspection discovered high levels of titanium and iron mineralization. The study believes that the ascending magmatic hydrothermal fluids mixed with surface water（ precipitation） into mixed fluids,which extracted gold mineral from the siltstone and cataclasite of Lower Permian Shazipo Formation and formed Au complex ore-forming fluids. In the process of migration through fault structures,the fluids precipitated and enriched into anomalies at the favorable sections like slide faults and fault intersections.