The Formation Age and Magma Source of the Xiaonanshan–Tunaobao Cu-Ni-PGE Deposit in the Northern Margin of the North China Craton

Abstract

The Xiaonanshan–Tunaobao Cu-Ni-PGE deposit is located in the northern margin of the North China Craton (N-NCC) in central Inner Mongolia. However, the age, magma source, petrogenesis, and sulfide mineralization mechanism of the ore-related Xiaonanshan-Tunaobao pluton remain unclear. Zircon U-Pb dating indicates the Tunaobao pluton formed at 275.9 ± 2.8 Ma (Early Permian), similar to the Xiaonanshan pluton (272.7 ± 2.9 Ma). The ore-related gabbro is enriched in LREE and LILE (e.g., Rb) and depleted in HREE and HFSE (e.g., Nb and Ti). It likely originated from enriched mantle metasomatized by subduction fluids, supported by enriched Hf-Nd isotopes (–34.34 to –6.16 for zircon εHf(t) and –7.24 to –5.92 for whole-rock εNd(t) values) and high Ba/La but low Rb/Y ratios. The δ34S values of the Xiaonanshan sulfides range from 4.5‰ to 11.4‰, indicating a mantle origin with contribution from surrounding rocks. Combining previous recognition with this study, we propose that the Xiaonanshan–Tunaobao pluton formed in a post-collision extensional setting.