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

摘要

The Daliuhang gold deposit (>?20?t 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?±?0.6?Ma and 126.2?±?0.6?Ma, respectively. Syn-ore monazite, with a U–Pb age of 120.5?±?1.7?Ma, represents the timing of gold mineralization. Given at least 5?m.y. between magmatism and mineralization, a genetic relationship to magmatic-hydrothermal activity is negated. Noble gas isotopes of pyrite have crust-mantle-mixed 3He/4He (1.13 to 1.50 Ra) and air-like 40Ar/36Ar (327–574). Together with the broadly positive correlation between 3He and 36Ar, 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 δ34S values (3.7–5.6‰ and 5.3–6.4‰, respectively), whereas ore-related pyrites have higher δ34S values, especially in As–Au-rich domains (7.8–8.3‰). These positive δ34S values also suggest that the initial ore fluid and some of the sulfur component were derived via subduction-related devolatilization. The elevated δ34S 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 (εNd (~?120?Ma)?=???13.7 to ??11.6), 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.