Au mineralization-related magmatism in the giant Jiapigou mining district of Northeast China

Abstract

The Jiapigou mining district (JMD) in the northeastern margin of the North China Craton mainly contains quartz vein- and altered rock-type gold deposits that have been prospected and mined for over 200 years. However, the ore-formation mechanism and geodynamic setting are still limited understood. Here we present new geological, mineralogical, gochronological, geochemical and Hf isotopic evidences of the ore-related intrusions from the deposits in the JMD to reveal the tectonic setting and genetic relationship between the Au mineralizitions and synchronic magmatism. The results show the following: (1) zircon U–Pb dating of the ore-related intrusions, such as basic dikes (gabbro and porphyritic gabbro), granites, and acid dikes (granite aplite dike and rhyolite porphyry) bracket their emplacement in the range of 177–171 Ma; (2) The basic dikes are characterized by enrichment in large ion lithophile elements (LILEs; i.e., Rb, Ba, and U), moderately depletion of high field strength elements (HFSEs; i.e., Nb and Ta), and high εHf (t) values (–13 to +12.8), whereas granites are characterized by high SiO2 (73.24–75.12 wt%) and total alkali (K2O + Na2O = 5.74–8.58 wt%) concentrations, low TFe2O3 (0.78–1.43 wt%) and CaO (0.98–1.36 wt%) concentrations, enrichment of LILEs (i.e., Rb, Ba, Th, and K) and depletion of HFSEs (i.e., Nb, Ta, Ti, and P), and low high εHf (t) values (–13.6 to –11.0), which features as well as those of the acid dikes. These results indicate that the ore-related intrusions, such as basic dikes, granites, and acid dikes were emplaced during the Middle Jurassic (177–171 Ma), constrained that the giant Au mineraliziton in the JMD occurred in the Middle Jurassic. And the basic dikes were likely derived from an enriched lithospheric mantle source that has been influenced by fluids expelled from a subducted slab, whereas granites and acid dikes were likely derived from partial melting of Archean crustal materials. Combined with regional geological observations, we conclude that the giant Au mineralization and ore-related magmatism occurred in an extensional setting associated with the subduction of the Paleo-Pacific Plate. The basic dikes and granites can be regarded as a precursor for the Au mineraliziton in the JMD. And mantle- and crustal-fluids and metals substantially contributed to the formation of the giant Au mineralization in the JMD.