Petrogenesis and Metallotectonic Implications of the Middle–Late Jurassic Granitoids at the Chadi Cu Polymetallic Deposit, Southern Qin–Hang Belt (South China)

Abstract

Better understanding of shoshonitic rocks is vital to unravel the formation process and spatial distribution of their associated ore deposits. Here, we conducted analyses on the shoshonitic granodiorite and its mafic microgranular enclaves (MMEs) from the Chadi Cu-Pb-Zn polymetallic deposit (South China), with the aim to investigate their petrogenesis and tectonic setting. Zircon U-Pb age of the MMEs (165.0 ± 1.2 Ma) is coeval with that of the host granodiorite (164.8 ± 0.63 Ma). The Chadi granitoids are enriched in large ion lithophile elements and light rare earth elements, but depleted in high-field-strength elements. The granodiorite displays low (⁸⁷Sr/⁸⁶Sr)_i (0.7069–0.7072), and negative ε_Nd(t) (–5.8 to –5.5) and zircon ε_Hf(t) (–3.6 to –0.4) values. These isotopic characteristics of the granodiorite and MMEs indicate the mixing of a mafic magma (formed from the subduction-related, metasomatically-enriched lithospheric mantle) and a felsic magma (formed from the partial melting of crustal materials), which is closely related to the Paleo-Pacific subduction. The Chadi granodioritic magma has likely low oxygen fugacity (<ΔFMQ + 1), low whole-rock Sr/Y ratio (mostly < 30), and low S (0.04 ± 0.02 wt%) and Cl (0.23 ± 0.04 wt%) contents, suggesting that the potential of forming large-scale Cu mineralization is low.

Keywords

Middle–Late Jurassic granitoids / mafic microgranular enclaves / shoshonitic rocks / metallogenic potential / the Qin–Hang belt

RIGHTS & PERMISSIONS

2025 Geological Society of China