Early orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean – Constraints from the Ludousou gold deposit, central China

Abstract

The West Qinling Orogen experienced a complex orogenic history and developed related orogenic gold deposits. Most known orogenic gold deposits in West Qinling are hosted by brittle to ductile shear zones and mainly formed during 220–190 Ma. The Ludousou gold deposit, located in the northwesternmost segment of West Qinling, has breccia gold ores controlled by E-W, NE-, NW-, and N-S trending faults, and is hosted by tuff and quartz diorite porphyry. Uranium-Pb zircon investigations indicate that tuff and quartz diorite porphyry were emplaced at 252.9 ± 4.1 Ma and 247.0 ± 2.2 Ma. Magmatic apatites from the same quartz diorite porphyry crystallized at 243.5 ± 4.8 Ma indicating a rapid cooling history. Hydrothermal sericite coexisting with gold-bearing pyrite and arsenopyrite from mineralized quartz diorite porphyry provided 40Ar/39Ar plateau and inverse isochron ages of 235.68 ± 0.29 Ma and 235.61 ± 0.41 Ma. Hydrothermal apatite separated from the same mineralized quartz diorite porphyry yielded concordant U-Pb age of 235.7 ± 4.9 Ma. Such data bracketed that the Ludousou gold mineralization event occurred at ca. 236 Ma postdating the 252–247 Ma magmatism by approximately 8–11 million years. Combined present field observations and geochronological data with sulfur isotopic and fluid inclusion investigations in literatures, we therefore propose that ore-forming fluids may not be derived from ore-hosting tuff and quartz diorite porphyry, and such rapid cooled host-rocks might even provide little heat source during ore formation. The Ludousou gold deposit is best classified as an orogenic gold deposit, and probably can extend the orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean tracing back to ca. 236 Ma.