Abstract:

Take the Yangjiaba polymetallic ore field in Lueyang County, Shaanxi Province as an example, systematic research of fluid inclusions from the ores indicates that they can be divided into two distinct areas in space: Areas A and B. Area A is featured by single liquid phase while Area B by larger voluminous, primary two-phases inclusions with large gas: liquid ratios. In Area A, the primary gaseous-liquid phase inclusions consist of H₂O and their homogeneous temperatures are measured at 184℃. The fluid inclusions in Area B are mainly composed of H₂O and C₆H₆ and their homogeneous temperature are concentrated around 260℃ and 330℃. The homogeneous temperature of the Area B is apparently higher than those measured previously, indicating the involvement of higher temperature, reductive fluids in mineralization. Combined with the consideration of the tectonic settings of the Qinling orogenic belt, and of the analysis of trace and REE elements, it is suggested at the present preliminary stage of study that the H₂O-C₆H₆ fluids might belong to mantle fluid moved upwards via large deep-cut faults by rapid surge during intense tectonic movement.  These fluids resulted in crust-mantle superimposed mineralization, being the prelude of intense mineralization in the Qinling orogenic belt.

Key words: fluid inclusion, trace elements and REE, crust-mantle superimposed mineralization, fluid geochemistry tracing, Yangjiaba