Genesis of the Zhongshangou Au-Te deposit linked to alkaline magmatism at the northern margin of the North China Block: Evidence from sulfides Re-Os geochronology

Abstract

The northern margin of North China Block (NCB) is a world-class gold metallogenic province with >1000 t gold, where has undergone multiphase tecto-magmatic overprinting since the Archean. Yet the genesis of the mineralization is still in doubt due to poor geochronological constraints using methods such as Ar-Ar and Rb-Sr dating. The Zhongshangou Au-Te deposit is located in the central part of the NCB gold metallogenic province, where it is structurally controlled and hosted by an amphibolite quartz monzonite phase of the Shuiquangou Alkaline Complex (SAC). Hydrothermal alteration at the deposit is characterised by an intense K-silicate assemblage with variable amounts of Fe-Mn carbonate, which is commonly observed in alkaline plutons associated with Au-Te deposits.Pyrite and chalcopyrite associated with the Au-Te mineralization contain very low common Os and yield model ages ranging from ca. 384 to 373 Ma, with a precise Re-Os isochron age of 379 ± 5 Ma (2σ, MSWD = 0.92). Analyses of molybdenite associated with the Au-Te mineralization yield precise model ages ranging from ca. 379 to 375 Ma, with a Re-Os isochron age of 379 ± 4 Ma (2σ, MSWD = 0.3). The Re-Os geochronology thus provides a reliable constraint of ca. 379 Ma for the mineralization, which is coeval with the syenite in the SAC. The Re-Os geochronology of the pyrite and chalcopyrite also yield a very low initial 187Os/188Os value of 0.22 ± 0.11, which indicates a significant source from the mantle material. Our evidence coupled with previous published data in the literature show that the Zhongshangou deposit is an alkaline pluton-hosted epithermal system related to the emplacement of the SAC in an extensional setting. The Re-Os geochronology using the low-level highly radiogenic sulfides has constrained the timing of the gold metallogeny at the northern margin of NCB and has opened new perspectives for gold exploration in the metallogenic province.