The spatiotemporal distribution, petrogenesis, and key ore-forming factors of the Jurassic magmatic arc in the Gangdese belt, Tibet

Abstract

Porphyry Cu deposits (PCDs), especially super-large deposits, have always been the hotspots in research on mineral deposits and prospecting. Xiongcun, as the only super-large PCD in the Gangdese belt formed in an oceanic subduction setting, has not yet had its key ore-forming factors clearly defined. Moreover, the coupling relationship between these ore-forming factors and deep magmatic processes remains underexplored. This study focuses primarily on the Xiongcun ore-forming intrusion, the Karu and Tangbai weakly Cu-mineralized intrusions, and the Yabo and Jiacha barren intrusions within the Jurassic Arc. With the exception of the Jiacha sample located in the eastern segment of the Jurassic Arc (ESJA), all other samples are distributed within the western segment (WSJA). All these intermediate-felsic samples, with ages ranging from 172.2 to 190.4 Ma, are predominantly calc-alkaline or high-K calc-alkaline series, exhibiting characteristics typical of arc magmas. The low MgO contents (0.64–1.98 wt%), depleted Hf-Nd isotopic compositions (ε_Hf(t) = 11.9–16.3, whole-rock ε_Nd(t) = 5.7–6.7), and young two-stage model ages (175–534 Ma) of samples from the WSJA indicate an origin derived from juvenile mafic lower crust, while in contrast, the heterogeneous isotopic signatures observed in the ESJA reflect compositional heterogeneity in the source region, which is ascribed to the presence of relic ancient crustal materials. Then, based on new data, we explored the key ore-forming factors of the Jurassic Arc. The samples from the WSJA collectively exhibit higher zircon Ce⁴⁺/Ce³⁺ ratios, higher ΔFMQ values, lower T(ti-zr) values, and higher whole-rock Ba/La ratios compared to those from the ESJA, indicating that the magmas in the WSJA generally possess higher oxygen fugacity and water content. Consequently, the ESJA exhibits lower metallogenic potential. Furthermore, the differences in mineralization between the WSJA and ESJA can be attributed to the varying degrees of fluid metasomatism experienced by their source regions. Within the WSJA itself, the metallogenic potential varies significantly, ranging from barren intrusions through weakly mineralized intrusions to ore-forming intrusions. This progression corresponds to an increasing trend in magma oxygen fugacity, water content, and volatile content, which is linked to the enhanced intensity of fluid metasomatism affecting the magmatic source regions. These factors are crucial for the formation of the super-large Xiongcun deposit.