Geochronological and sulfur isotopic evidence for the genesis of the post-magmatic, deeply sourced, and anomalously gold-rich Daliuhang orogenic deposit, Jiaodong, China

Abstract

The Daliuhang gold deposit (>\u200920\xa0t gold) is located in the central Penglai-Qixia belt of the giant Jiaodong gold province, eastern China. The ore-hosting Guojialing granodiorite and pegmatite were formed at 129.0\u2009±\u20090.6\xa0Ma and 126.2\u2009±\u20090.6\xa0Ma, respectively. Syn-ore monazite, with a U–Pb age of 120.5\u2009±\u20091.7\xa0Ma, represents the timing of gold mineralization. Given at least 5\xa0m.y. between magmatism and mineralization, a genetic relationship to magmatic-hydrothermal activity is negated. Noble gas isotopes of pyrite have crust-mantle-mixed 3 He/ 4 He (1.13 to 1.50 Ra) and air-like 40 Ar/ 36 Ar (327–574). Together with the broadly positive correlation between 3 He and 36 Ar, it is inferred that the initial ore-forming fluids were deeply sourced from the sedimentary wedge overlying the subducted plate and overlying mantle during early Cretaceous paleo-Pacific plate subduction. The pre-ore and post-ore pyrites have low δ 34 S values (3.7–5.6‰ and 5.3–6.4‰, respectively), whereas ore-related pyrites have higher δ 34 S values, especially in As–Au-rich domains (7.8–8.3‰). These positive δ 34 S values also suggest that the initial ore fluid and some of the sulfur component were derived via subduction-related devolatilization. The elevated δ 34 S values of the ore-related pyrite are partly ascribed to mass fractionation and partly to a contribution from sulfur leached from crustal host rocks. This interpretation is also supported by neodymium isotope ratios of monazite (ε Nd (~\u2009120\xa0Ma)\u2009=\u2009−\u200913.7 to −\u200911.6), which correlate well with the ore-hosting Guojialing granodiorite. This study highlights the combined roles of deeply derived fluids and intense interaction with upper crustal rocks in the formation of Jiaodong gold deposits.