Genesis of the Wulong gold deposit, Liaoning Province, NE China:
Constrains from noble gases, radiogenic and stable isotope studies
-
Abstract
TheWulong 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 UePb and pyrite RbeSr 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 UePb 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 RbeSr isochron age is 119 1 Ma, indicating that both magmatism and
mineralization occurred during the Early Cretaceous. The d18OH2O values of ore-forming hydrothermal
fluids from the quartzepolymetallic sulfide vein stage vary from 4.8& to 6.5&, and the dDV-SMOW values
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 ¼ 15.51
e15.71, 206Pb/204Pb ¼ 17.35e18.75, 208Pb/204Pb ¼ 38.27e40.03) 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 magmaticehydrothermal origin.
-
-