New Data on the Reduced Intrusion-Related Au Mineralization of the Central Kolyma Gold Region: Age, Formation Conditions, Composition, Ore-Controlling Factors

New data are presented on the formation conditions and ages of the reduced intrusion-related Au mineralization of the Vetrenskaya area in the Central Kolyma region. The mineralization is predominantly confined to intersections of Late Jurassic minor intrusive bodies and NE-trending fracture systems and is represented by zones of thin quartz veinlets with sericite–quartz halos. The major ore mineral is gold-bearing arsenopyrite (up to 10%), while minor minerals are represented by lellingite, pyrite, chalcopyrite, and pyrrhotite. Microscopic native gold of a low fineness is paragenetically associated with bismuth minerals (bismuthine, native bismuth, and tellurides of Bi and Au), forming microinclusions (1–10 μm) in the arsenopyrite. The isochronous Re–Os age of the goldbearing arsenopyrite is 137–117 Ma, which suggests the mineralization was formed significantly later than the hosting granitoids (147–153 Ma). The reduced intrusion-related Au ore deposit was formed at shallower depths than orogenic Au deposits were and at lower temperatures in comparison with rare-metal (W, Mo) ore deposits.