Genesis of the Wulong gold deposit, Liaoning Province, NE China: Constrains from noble gases, radiogenic and stable isotope studies

摘要

The Wulong lode deposit contains over 80 tonnes of gold with an average grade of 5.35?g/t. It is one of the largest deposits in Dandong City, Liaoning Province in northeast China. Previous studies on the deposit focused on its geological characteristics, geochemistry, fluid inclusions, and the timing of gold mineralization. However, controversy remains regarding the origin of the ore-forming fluids and metals, and the genesis of the gold deposit. This paper presents zircon U–Pb and pyrite Rb–Sr ages and S, Pb, He, and Ar isotopic results along with quartz H and O isotopic data for all litho-units associated with the deposit. Laser ablation inductively coupled mass spectrometry measurements yielded zircon U–Pb dates for samples of pre-mineralization rocks like granite porphyry dike, the Sanguliu granodiorite, fine-grained diorite, and syn-mineralization diorite, as well as post-mineralization dolerite, and lamprophyre; their emplacement ages are 126?±?1?Ma, 124?±?1?Ma, 123?±?1?Ma, 120?±?1?Ma, 119?±?2?Ma, and 115?±?2?Ma, respectively. The pyrite Rb–Sr isochron age is 119?±?1?Ma, indicating that both magmatism and mineralization occurred during the Early Cretaceous. Theδ18OH2Ovalues of ore-forming hydrothermal fluids from the quartz–polymetallic sulfide vein stage vary from 4.8‰ to 6.5‰, and theδDV-SMOWvalues are between??67.7‰ and??75.9‰, indicating that the ore-forming fluids were primarily magmatic. The noble gas isotope compositions of fluid inclusions hosted in pyrite suggest that the ore-forming fluids were dominantly derived from crustal sources with minor mantle input. Sulfur isotopic values of pyrite vary between 0.2‰ and 3.5‰, suggesting that S was derived from a homogeneous magmatic source or possibly from fluids derived from the crust. The Pb isotopic compositions of sulfides (207Pb/204Pb?=?15.51–15.71,206Pb/204Pb?=?17.35–18.75,208Pb/204Pb?=?38.27–40.03) indicate that the Pb of the Wulong gold deposit is a mixture of crust and mantle components. Geochronological and geochemical data, together with the regional geological history, indicate that Early Cretaceous magmatism and mineralization of the Wulong gold deposit occurred during the rollback of the subducting Paleo-Pacific Plate, which resulted in lithospheric thinning and the destruction of the North China Craton (NCC), which indicates that the deposit is of magmatic–hydrothermal origin.