MAGMATIC-HYDROTHERMAL DEPOSITS OF THE HUNJIANG BASIN, JILIN PROVINCE, NE CHINA, WITH A FOCUS ON THE WHITE MOUNTAIN BRECCIA-HOSTED GOLD DEPOSIT

The Hunjiang basin is a large (50 x 80 km), NE-trending sedimentary basin located in Jilin Province, northeastern China. It comprises Proterozoic to Paleozoic sedimentary rocks deposited on an Archean basement. Mesozoic sedimentary and volcaniclastic rocks are exposed within the core of the Hunjiang basin. The basin hosts a diversity of mineral deposits that have been exploited by over 100 past and producing mines of variable sizes. The White Mountain gold deposit represents the most economically significant deposit in the basin, with proven and probable mineral reserves of 612,000 oz Au at an average grade of 3.2 g/t Au. It is hosted by hydrothermal breccias that developed along a regional dolomite-sandstone contact and its classification remains enigmatic.

The majority of the deposits in the Hunjiang basin are of magmatic-hydrothermal or hydrothermal origin, with the exception of sedimentary deposits of coal, hematite, gypsum, and phosphorus. Porphyry Cu, Cu-Au, and Mo deposits and related skarn and epithermal deposits that have been exploited for Au, Ag, Sb, Zn, and Pb, are scattered throughout the basin. The basin also hosts a range of sedimentary rock-hosted gold deposits and occurrences, including White Mountain. The style of mineralization and the alteration assemblage at White Mountain indicate that ore formation occurred at temperatures of less than 200°C from moderately acidic fluids. LA-ICP-MS geochronology of zircons from porphyries, intrusive igneous rocks, and volcaniclastic rocks within the basin give Middle Jurassic to Late Cretaceous magmatic ages. This suggests that the White Mountain gold deposit, along with other magmatic-hydrothermal and hydrothermal deposits in the basin, may have formed during late Mesozoic regional extension.