Geology and Mine Development of the Red Dog Zinc-Lead Deposit, Brooks Range, Alaska

CIM Vancouver 2006
The Red Dog sediment-hosted zinc-lead deposit is located in the Brooks Range thrust belt in northwest Alaska, approximately 1000 km northwest of Anchorage. The mine constitutes the primary deposit in a 400 square km district, which host several other mineral occurrences. All the known mineralisation is hosted by the Mississippian Ikalukrok Member, deep basinal shale of the Kuna Formation, part of a Devonian to Cretaceous sedimentary sequence. The rocks underwent intense deformation during the Brookian Orogeny in Middle Cretaceous time. Several thrust faults juxtapose the stratigraphy.

The Red Dog mine is composed of four deposits which together contain 110 Mt in resources and reserves. The total resource exceeds 30 Mt of Zn metal, making the Red Dog mine the largest Zn deposit in the world. The mine is an open pit with 25 foot high benches. The biggest challenge is not the Arctic conditions but the metal extraction, due to the fine grained nature of the mineralisation and the variability of the ore. The mine produces Zn and Pb-Ag concentrates that are shipped to smelters around the world from the Red Dog port facilities during the short summer period.

Ore mineralogy is generally simple and composed of sphalerite, pyrite, galena and marcasite. Deposits are generally overlain by thick exhalative barite horizons and exhibit strong silicification, which locally obliterates the original textures. Although described as a world class Sedex-type deposit, a large portion of the mineralisation exhibits sub-surface replacement textures. Moreover, unlike most other Sedex deposits, the reconstruction of the basin is made difficult by the structural complexity of the district. Several assumptions are made regarding the deposit settings relative to metal source, growth faults or crustal extension to assist exploration in the district.
Keywords: Red Dog, SEDEX, Replacement, Alteration, Sediment-hosted, basin, Zinc, Lead, exhalative, Barite
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