Geology, geochronology and tectonic setting of the Chaihulanzi gold deposit in Inner Mongolia, China

Abstract

The Chaihulanzi is a Precambrian metamorphic rock-hosted gold deposit in the northern margin of the North China Craton (NCC). The local outcropping lithologies include mainly Archean metamorphic rock, Paleoproterozoic carbonatite, and Phanerozoic diorite, granite, aplite and mafic to felsic dikes. Due to the lack of data, the deposit was variably proposed to be orogenic, intrusion-related, or mesothermal type, and the mineralization was loosely constrained to be Paleozoic or Mesozoic. Based on field geology, petrological/mineralogical observations, whole-rock geochemistry, and zircon U-Pb-Hf isotopes of ore-related aplite, and sericite Ar-Ar dating of gold-ore veins, we discussed the ore-causative magmatism, and the age and tectonic setting of gold mineralization. Our results show the presence of an early (native gold-dominated) and a late (gold-silver telluride-dominated mineralization) stage: The early-stage gold mineralization was genetically linked to the Middle-Late Permian aplite (LA-ICP-MS zircon U-Pb age: 264.5 ± 1.3 Ma), whose ages are similar to the gold ore veins (sericite Ar-Ar age: 263.67 ± 0.99 Ma). The distinct negative zircon εHf (-18.31 to -15.45) and model age (TDMC = 2.1–2.4 Ga) indicate a crustal magma source, probably from partial melting of the NCC basement. The whole-rock trace element compositions and zircon U-Pb ages, together with the tectonic evolution of northern NCC margin imply a post-collisional extension setting (after the Paleo-Asian ocean closure) for the gold mineralization. The newly-discovered late-stage quartz-carbonate ore veins occur as fracture infill, and crosscut early-stage quartz-sericite veins and Mesozoic volcanic wallrocks, implying that the late-stage mineralization occurred in the Mesozoic or after. The two-stage gold mineralization overprinting makes Chaihilanzi and its periphery highly prospective for gold exploration.