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.

Zhongshangou Au-Te deposit, located in the northern margin of the North China Craton (NCC), is a vein-type mineralization and hosted in a strongly altered and locally brecciated sulfide-bearing quartz veins that crosscut granitic host rocks. Paragenetic and structural evidences confirm two modes of the Au-Ag tellurides mineralization: (1) the earlier mode is expressed by sulfides-hosted dispersed ultrafine Au-Ag tellurides (∼2–50 μm) as inclusions; (2) the later mode is represented by combinations of Au filling sulfides fractures and grain borders, associated with minor molybdenite. Re-Os pyrite and chalcopyrite ages are deemed a suitable proxy to constrain the timing of Au based on the occurrence of Au-bearing minerals as inclusions within pyrite and chalcopyrite, whereas Au-bearing minerals associated with minor molybdenite filling pyrite fractures may represent a younger ore-froming stage, which is constrained by Re-Os molybdenite geochronology. In order to understand the petrogenetic link between the Au-Te mineralization and the ore-hosting alkaline intrusion, this paper presents new situ LA-ICP-MS U-Pb dating of zircon, and detailed Re-Os sulfides (molybdenite, pyrite, and chalcopyrite) geochronology. The U-Pb age of zircons from quartz monzonite is 392 ± 3 Ma (MSWD=0.16), which is inconsistent with a previous U-Pb ages of ∼373–410 Ma obtained from Shuiquangou alkaline and granitic batholiths. Moreover, the Re-Os isotope measurement documents two well-defined isochron ages of 379.3 ± 3.8 Ma (2σ, MSWD=0.3) for four molybdenite separates and 379 ± 4.9 Ma (2σ, MSWD=0.92) for five auriferous pyrite and chalcopyrite samples from the Zhongshangou deposit. These data reveal that an important Au-Te mineralization event took place in the northern margin of the NCC at ∼380Ma, and also suggest a genetic connection with the emplacement of alkaline intrusions. [Display omitted] • The Re-Os geochronology using the low-level highly radiogenic sulfide provides a reliable constraint of ca. 379 Ma for the mineralisation. • 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. • The Re-Os geochronology 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. 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. [ABSTRACT FROM AUTHOR]