Zircon U-Pb and muscovite 40Ar/39Ar dating of Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province, Jiangnan Orogen: Evidence for large-scale mineralization in South China at ca. 150–120 Ma

Abstract

The Jiangnan Orogen is located between the Yangtze and Cathaysia blocks, and hosts abundant Au, Sb, W, Cu, Pb, Zn, Ag, and Ta-Nb-(Li-Be) deposits. Among these, both the Taolin and Lishan Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province are large Pb-Zn deposits, which are located at the northwestern and southern margins of the Late Jurassic to Early Cretaceous Dayunshan-Mufushan composite pluton, respectively. However, the mineralization ages of these deposits remain controversial and poorly constrained. In this study, muscovite 40Ar/39Ar dating of the Taolin and Lishan deposits along with zircon U-Pb dating and geochemical analysis of the Dayunshan-Mufushan composite pluton were undertaken to constrain the age and nature of the Late Jurassic to Early Cretaceous magmatism and related mineralization in South China. Zircon U-Pb dating of the biotite monzogranite and two-mica monzogranite yielded emplacement ages of ca. 149 and 145–136 Ma, respectively. Muscovite from the ore-bearing granitic pegmatites in both the Taolin and Lishan deposits yielded well-defined 40Ar/39Ar ages of ca. 121 and 129 Ma, respectively. These results and previously published data indicate that the Dayunshan-Mufushan composite pluton was emplaced in several stages at ca. 154–148, 146–137, and 136–127 Ma, and experienced associated, multi-stage, granitic pegmatite magmatism at ca. 142, 131, and 125–120 Ma. Two mineralization events occurred at ca. 141–136 and 133–120 Ma in the Pb-Zn-(Cu-Co-Mo), Ta-Nb-Li-Be, and Au deposits in northeastern Hunan Province, including the Dayunshan-Mufushan region. Zircons from the Dayunshan-Mufushan composite pluton record low oxygen fugacity (ƒO2) conditions, indicating the pluton was likely responsible for the large-scale Pb-Zn mineralization.In addition to the 170–160, 160–150, and 120–80 Ma mineralization events, the Late Jurassic to Early Cretaceous (ca. 150–120 Ma) was also an important period of mineralization in South China. This mineralization was likely initiated by Middle Jurassic to Early Cretaceous extension associated with subduction, subsequent slab rollback, and possible break-off of the Paleo-Pacific plate, which led to lithospheric collapse and thinning.