THE WHITE MOUNTAIN GOLD DEPOSIT, JILIN PROVINCE, CHINA: DEFINING ORE CONTROLS IN AN ENIGMATIC BRECCIA-HOSTED ORE DEPOSIT
Property-scale mapping and detailed core logging have allowed the recognition of multiple breccia types along the ore-bearing horizon. The dominant breccia types include: matrix-supported angular clast dolomite breccia; clast-supported monomictic dolomite crackle breccia; matrix-cement supported angular to scalloped quartz and subangular dolomite clast breccia; matrix-cement supported subrounded to rounded dolomite and quartz clast breccia; and polymictic subrounded to angular dolomite, sandstone, and hematite clast breccia. The polymictic breccia unit is spatially associated with ore. Elevated gold grades (up to 108g/t) typically occur when the breccia is silicified and distinctly vuggy due to the dissolution of dolomite clasts or matrix. The polymict shows evidence for multiple brecciation events and is localized on the mine scale, while the other breccia types appear to be of regional extent.
At White Mountain, gold is associated with pyrite and/or marcasite that are now oxidized to hematite. Barite is abundant within the ore zones. In addition to silicification and hematite alteration, secondary kaolinite and dickite occur in the altered host rocks. It is proposed that White Mountain is a comparably low-temperature hydrothermal deposit formed from moderately acidic fluids. The presence of Jurassic and Cretaceous porphyritic intrusions within the Hunjiang Basin suggests that the deposit may have formed during Late Mesozoic regional extension. Preliminary interpretations will be discussed and will contribute to a deposit model that can be used to derive effective guidelines for both near-mine exploration and the search for similar deposits within the region.