Geochronology and origin of the Sarekoubu gold deposit, southern Altaides, China: Ar-Ar dating of vein quartz and Cu-Zn-Fe isotopes

Abstract

The Sarekoubu gold deposit, located north to Altay city, China, has an unusual feature for abundant carbonic (CO2-CH4-N2)-bearing fluid inclusions. For many years, the ages and origin of the Sarekoubu deposit have been still controversial. The gold deposit occurs in the fractured zone parallel to the strata of lower Devonian Kangbutiebao Formation (D1k22), and has three hydrothermal mineralizing stages: (I) disseminated pyrite and white quartz vein stage; (II) fine quartz and pyrite veinlet stage; and (III) polymetallic sulfides-grey quartz stage. Stages II and III are the main gold mineralization stages. Two gold-bearing chalcopyrite-quartz vein samples from stage III were selected for 40Ar–39Ar age study. The result shows that fluid inclusions in quartz of mineralizing stage have isochronal ages of 216.9 ± 6.7 Ma and 218.0 ± 6.3 Ma, and inverse isochronal ages of 218.3 ± 6.1 Ma and 216.7 ± 6.4 Ma. The Fe isotope analysis shows that the Sarekoubu gold deposit is different from VMS/SEDEX deposits. The δ56Fe values of pyrite from main mineralization stages in the Sarekoubu gold deposit have a large variation of Fe isotope range (from −0.498‰ to 0.759‰), which can be regarded as a closed hydrothermal system for Fe isotopes. The δ65Cu values of chalcopyrite both from the Sarekoubu gold deposit and overprint gold mineralization of adjacent Tiemurte deposit have a narrow range (−0.28–0.922‰), which are not the same as VMS deposits with a wide range of δ65Cu values. The gold mineralization in the Sarekoubu deposit is younger than the gold deposits near regional Irtysh Tectonic Belt. This may be related with the evolution of the thrust of the Irtysh Tectonic Belt in the southern Altaides.