Petrogenesis and metallogenesis of the Xinjie layered mafic–ultramafic intrusion, China: Modeling of recharge, assimilation and fractional crystallization

• The Xinjie intrusion experienced magma recharge, assimilation, and fractional crystallization (RAFC) processes.
• The new magma was recharged at least once.
• The assimilation was from the underlying Emeishan basalts.
• The recharge might have triggered the early crystallization of Fe–Ti oxides and the formation of the immiscible melts.

The Xinjie layered mafic–ultramafic intrusion in the central Emeishan large igneous province (ELIP), SW China, hosts Fe–Ti–V oxide ore in the upper part and Ni–Cu–platinum-group element (PGE) sulfide deposits in the lower part. In this study, we use published Sr–Nd isotopic data to simulate and evaluate the energy-constrained recharge, assimilation, and fractional crystallization (EC-RAFC) model with a view to track the petrogenesis and mineralization. In contrast to the energy-constrained assimilation fractional crystallization (EC-AFC) model, the EC-RAFC modeling shows that the Xinjie intrusion may represent a shallow crustal magma chamber system, where it experienced the RAFC processes. In the early stage of the magmatic process (Tm = 1460 °C), a pulse of magma was injected into an actively evolving magma chamber. Minor melting (Ma∗ = 0.257) and assimilation of the wallrock (underlying Emeishan basalts) occurred when the temperature of magma (Tm = 1245 °C) decreased close to the equilibration temperature (Teq = 1165 °C). The mass–temperature plots indicate that fractional crystallization was significantly affected by the recharge and assimilation processes, whereas the contaminated magma recharge favored the early crystallization of Fe–Ti oxides as well as the formation of the PGE-bearing immiscible melt in the lower part of the intrusion. In contrast, the formation of the Fe–Ti oxides ores in the upper part occurred probably through fractional crystallization and/or immiscibility of the evolved Fe–Ti-rich magma, resulting in the paragenesis of Fe–Ti–V oxides and Ni–Cu–PGE sulfides in the Xinjie layered intrusion.

We present selected results of the energy-constrained recharge, assimilation, and fractional crystallization (EC-RAFC) simulations to assess quantitatively the petrologic evolution of the Xinjie layered mafic–ultramafic intrusion, China. Consequently, our modeling suggests that the Xinjie intrusion has experienced the RAFC processes. The mass–temperature plots indicate that fractional crystallization was significantly affected by the recharge and assimilation processes, whereas the contaminated magma recharge favored the early crystallization of Fe–Ti oxides as well as the formation of the PGE-bearing immiscible melt in the lower part of the intrusion. In contrast, the formation of the Fe–Ti oxides ores in the upper part occurred probably through fractional crystallization and/or immiscibility of the evolved Fe–Ti-rich magma, resulting in the paragenesis of Fe–Ti–V oxides and Ni–Cu–PGE sulfides in the Xinjie layered intrusion.Figure optionsDownload as PowerPoint slide