Re-Os and U-Pb geochronology for the Xiaorequanzi VMS deposit in the Eastern Tianshan, NW China: Constraints on the timing of mineralization and stratigraphy

Abstract

The Xiaoriquanzi volcanogenic massive sulfide (VMS) Cu-Zn deposit occurs at the western part of the Paleozoic Dananhu-Haerlik arc in the eastern Tianshan, Xinjiang, China. Due to a lack of precise mineralization ages, the metallogenesis of the deposit has long been debated. In this study, systematic geochronological methods are used to constrain the mineralization age of the deposit. The deposit is hosted in the Xiaorequanzi Formation volcanic-sedimentary rocks. The orebodies occur as clusters of lenticular bodies with or without banding, and they are controlled by the NW-trending acticline. The ore types contain massive, banded, laminated and chlorite-enriched ores as well as vein-type, veinlet-dissemination and dissemination ores. In this study, Re-Os dating of the chalcopyrite from the Xiaorequanzi deposit yields an isochron age of 354 ± 11 Ma and initial 187Os/188Os ratios of 0.39 ± 0.14, which is consistent with the zircon U-Pb ages of ore-hosted tuff sandstone and dacite at 357.3 ± 2.4 Ma and 359.5 ± 3.4 Ma, respectively. Zircon U-Pb dating reveals that the mineralized granite porphyry formed at 354.7 ± 3.2 Ma, and this age is similar to the exhalative syn-sedimentary mineralization age (354 ± 11 Ma). Thus, precise geochronologic studies reveal that the seafloor volcanic hydrothermal system formed exhalative syn-sedimentary mineralization in the local extensional basin of the Dananhu-Haerlik arc during the Early Carboniferous (354–357 Ma). From Early Silurian to Carboniferous, two epochs VMS and porphyry deposits alternately formed in Dananhu-Haerlik long-lived arc. This reveals complicated arcs-basins tectonic transformation at the island arc setting.