A Middle Triassic gold-forming event of the Jiapigou ore district, northeast China: Evidence from pyrite Re-Os geochronology of the Sandaocha deposit

• The oldest-known Middle Triassic (239 ± 3 Ma) gold mineralization in the Jiapigou ore district (JOD). • The JOD underwent at least three periods of gold mineralization. • The timing and geodynamic settings of the three gold-forming events in the JOD. The Sandaocha lode gold deposit is a representative example of the Jiapigou Ore District (JOD), located at the northeastern edge of the North China Craton. The orebodies are composed of auriferous polymetallic sulfide–quartz veins hosted within Neoarchean to early Paleoproterozoic metamorphosed intrusions and supracrustal rocks, and are governed by NNE-striking ductile–brittle secondary faults. Mineralogical assemblages and cross-cutting relationships reveal that the deposit formed through three mineralization stages: (Ⅰ) arsenopyrite–pyrite–quartz, (Ⅱ) gold–polymetallic sulfide–quartz, and (Ⅲ) carbonate–quartz. The Re-Os isochron age of 239 ± 3 Ma (MSWD = 1.5), obtained from six pyrite samples of stage Ⅱ, constrains the Sandaocha gold mineralization to the Middle Triassic and reveals the oldest-known gold-forming event in the JOD. Geological, chronological, and H-O isotopic results indicate that the Sandaocha gold mineralization has close temporal-spatial and genetic links with coeval magmatic-hydrothermal event. Moreover, chronological data from this and previous studies indicates that the JOD underwent at least three distinct periods of gold mineralization. The ca. 239–204 Ma gold-forming event occurred during the extensional period following the Paleo-Asian Ocean closure, the ca. 178–170 Ma gold-forming event occurred in a compression–extension transitional setting towards the end of Paleo-Pacific Plate subduction, and the ca. 156–152 Ma gold-forming event was associated with the post-subduction extensional setting.