Geochronological and He-Ar-S isotopic constraints on the origin of the Sandaowanzi gold-telluride deposit, northeastern China

摘要

Northeastern China is characterized by widespread Mesozoic volcanic rocks and Au-Cu-Mo mineral deposits with a total gold reserve of >2000 t. Amongst those gold deposits, the newly discovered Sandaowanzi has a total reserve of >= 25 t of Au and an average grade of 15 g/t. This deposit is important because it is the first reported case of a dominantly Au(+/-Ag)-telluride deposit containing economically valuable bonanza Au- and Ag-telluride ores in the region. The Sandaowanzi quartz vein system and associated Au-(+/-Ag)-telluride mineralization are mainly hosted by trachyandesites and andesitic breccias. Native gold is closely associated with abundant tellurides including petzite, sylvanite, calaverite, hessite, and altaite. Twelve pyrite samples from the alteration zone yield a well defined Rb-Sr isochron age of 119.1 +/- 3.9 Ma, which is in agreement with a robust Rb-Sr isochron age of 1213 +/- 2.6 Ma derived from 10 auriferous quartz samples. The obtained isochron age of similar to 120 Ma represents the formation of the Sandaowanzi gold-telluride epithermal system, which is much younger than the host trachyandesite with a zircon U-Pb age of 3125 +/- 0.5 Ma and the spatially associated monzogranite with a zircon U-Pb age of 1822 +/- 1.1 Ma. Dating results indicate a close relationship between the local Au-Ag-Te mineralization and a magmatism episode in the Early Cretaceous. Noble gas (He and Ar) isotopes obtained from telluride, sulfide and quartz and sulfur isotopes determined from sulfides including chalcopyrite, sphalerite and pyrite demonstrate clear mixing trends between crustal and mantle-derived components, confirming a significant contribution of fluid produced from mantle-derived magmas into the epithermal system. Like many Mesozoic porphyry Cu-Mo +-/- Au deposits, the coeval epithermal Au-Ag +/- Te deposits in the region are genetically related to magmatism triggered by the subduction of the Pacific oceanic plate beneath the Eurasian continent at the time. (C) 2014 Elsevier B.V. All rights reserved.