Geochemistry and Sr–Nd–Hf–O isotopes of ore-bearing plutons from the Yundukala Au–Cu–Co deposit, East Junggar, Xinjiang, Northwest China: Implications for petrogenesis and tectonic setting

Abstract

Ongoing exploration in East Junggar, Northwest China, has led to the discovery of the intrusion-related Yundukala Au–Cu–Co deposit. The alteration and mineralization in the Yundukala deposit are closely related to diorite and gabbro-diorite, whereas the geochemical features of these ore-related plutons are still unclear. In this study, in order to unlock the nature of the ore-forming magmas, zircon U–Pb dating, whole-rock major and trace elemental and Sr–Nd isotope analysis, as well as zircon O–Hf isotope analysis, were conducted. Our results show that diorite and gabbro-diorite were both generated in the Early Devonian, with ages being 401.3 ± 3.8 Ma and 401.6 ± 4.5 Ma, respectively. Geochemically, they are all characterized by LREE-enriched patterns in chondrite-normalized REE diagrams, and evident enrichment of Rb, U and K and depletion of Nb and Ta contents in primitive mantle-normalized patterns, although the degrees of enrichment and depletion are variable. Isotopically, the diorite and gabbro-diorite display relatively high initial 87Sr/86Sr (0.704966–0.707395) and positive εNd(t) (1.29–3.84) of whole-rock, as well as positive zircon δ18O (5.3–8.9 ‰) and εHf(t) (2.4–18.8). These lines of evidence collectively indicate that these magmatic rocks were generated by mixing between mantle- and crustal-derived melts, and were emplacement in an island arc environment. The magma mixing during the formation of ore-bearing diorite and gabbro-diorite might bring abundant sulfur and metals, thus favoring the formation of Au–Cu–Co mineralization. This work emphasizes that further mineral exploration in East Junggar needs to pay attention to the Early Devonian granitoids.