Sphalerite Rb-Sr isotopic dating of the Dongyan Pb-Zn deposit in Southeastern Sichuan fold belt and its constraint on the timing of tectonic deformation

The Dongyan Pb-Zn deposit located in the Southeast Sichuan folded belt is a middle-low temperature hydrothermal type lead and zinc deposit, predicted amount of Zn metal is 101400 tons. The orebodies occur along NNE- and NWW-trending faults in veined or stratoid form in the interlayer fracture zone and are hosted in Ordovician carbonate rocks. The formation of this type of Pb-Zn deposit in the southeastern Sichuan fold belt and the relationship with the NNE-trending fault remain unclear. In this paper, Rb-Sr isotopic dating yielded an age of (157.7±3.3) Ma for the sphalerite in the Dongyan Pb-Zn deposit, which represents the main metallogenic age of this deposit and also constrains the formation time of NNE-trending fault of this area. The (⁸⁷Sr/⁸⁶Sr)_i ratio of the sphalerite is 0.71347, which is much more higher than the ratios of the same period or earlier period, and might have been related to atmospheric freshwater. The Southeast Sichuan folded belt of Sichuan Basin is a nappe-detachment thin skinned structure. The main period of the fold deformation was the early Yanshanian stage in the Middle-Late Jurassic period. Rb-Sr isochron age of Dongyan sphalerites is consistent with the tectonic deformation age mentioned above, indicating that the formation of the deposit was related to the Early tectonic deformation in Yanshanian stage.