Geochemical characteristics of A-type granite near the hongyan Cu-polymetallic deposit in the eastern hegenshan-heihe suture zone, NE China: Implications for petrogenesis, mineralization and tectonic setting

Abstract

In the eastern Hegenshan-Heihe suture zone (HHSZ) of NE China, Cu-Au hydrothermal mineralization at the newly discovered Hongyan deposit is associated with the Shanshenfu alkali-feldspar granite (SAFG). Zircon U-Pb dating showed that the inner phase and outer phase of the SAFG were formed at 298.8 ± 1.0 Ma and 298.5 ± 1.0 Ma, respectively. Whole rock geochemistry suggests that the SAFG can be classified as an A-type granite. Halfnium isotopes and trace elements in zircon suggest that the SAFG has high Ti-in-zircon crystallization temperature (721–990 °C), high magmatic oxygen fugacity and largely positive εHf(t) (from +6.0 to +9.9). We proposed that the SAFG was derived from crustal assimilation and fractional crystallization of juvenile crust metasomatized by subducting oceanic crust. The high oxygen fugacity of the SAFG suggests the chalcophile elements (e.g., Cu, Au) remained in the magma as opposed to the magma source. An arc-related juvenile source favors enrichment of Cu and Au in the resulting magma. Combined, these magmatic characteristics suggest Cu ± Au exploration potential for magmatic-hydrothermal mineralization related to the SAFG, and similar bodies along the HHSZ. The results obtained combined with regional geological background suggest that the Permian A-type granites and related mineralization along the HHSZ were formed in a post-collisional slab break-off process.