The formation and recycling of Neoproterozoic granitoids in the Jiangnan Orogen, South China: Implications for Mesozoic rare metal mineralization

Abstract

In the era of energy transition on the Earth, rare metal mineralization has attained increased significance for various energy sectors and understanding their formation and evolution in various tectonic settings is of great importance for formulating exploration strategies. The Neoproterozoic Jiangnan Orogen in South China marks the assembly zone of the Yangtze and Cathaysia blocks and carries numerous rare metal deposits. In this contribution, we investigate the Neoproterozoic Jiuling composite batholith to understand the formation of rare metal mineralization. We present new in-situ zircon U–Pb ages and Lu–Hf isotopes, and whole-rock geochemistry and Sm–Nd isotopes of the Banbei biotite granodiorite and the associated rare metal-mineralized Baishawo granites in the western portion of the Jiuling batholith suite. Zircon U–Pb dating indicates that the Banbei biotite granodiorite, and the Baishawo two-mica granite and muscovite granite formed at ca. 820 Ma, 153 Ma, and 142 Ma, respectively. The ε_Hf(t) values of the biotite granodiorite, two-mica granite and muscovite granite are –4.4 to +5.8, –11.8 to –7.0, and –10.5 to –7.3, respectively. The ε_Nd(t) values of the biotite granodiorite, two-mica granite and muscovite granite are –3.88 to –2.73, –10.6 to –10.2, and –9.23 to –9.16, respectively. Zircon Hf isotopes and whole-rock Sm–Nd isotopes suggest that the granite suite was sourced from the Mesoproterozoic crust. Geochemical modeling suggests that the Banbei biotite granodiorite was derived from partial melting of Meso- to Neoproterozoic metasedimentary rocks, whereas the Baishawo two-mica granite and muscovite granite were derived from assimilation–fractional crystallization of the Neoproterozoic Banbei biotite granodiorite and Mesozoic magma with low degrees of differentiation. Combined with previous studies on the granite suites in the Jiangnan Orogen, we suggest that collision between the Yangtze and Cathaysia blocks ceased at least 820 Ma, and that Precambrian rocks might have contributed significantly to the enrichment of rare metal mineralization in Mesozoic granite through reworking.