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Abstract

The world-class Zn-Pb-Ag deposits of the Red Dog district, Alaska, occur in severely shortened, late Paleozoic sedimentary rocks of the western Brooks Range fold and thrust belt. Red Dog-style strata-bound mineralization occurs within a localized Mississippian black shale facies of the Lisburne Group informally termed the Ikalukrok unit. Prior work has developed paleogeographic models in which the Ikalukrok unit formed in a starved, second-order basin flanked by carbonate platforms. Collision with and northward (modern coordinates) obduction of the oceanic Angayucham terrane telescoped Devonian to Early Jurassic passive margin sediments along thrust faults with displacements ranging from meters to tens or hundreds of kilometers. The most significant thrusts bound allochthons that juxtapose coeval stratigraphy from previously widely separated parts of the former continental margin. Thrusts within the allochthons created structurally and stratigraphically defined thrust plates and subplates, which are in turn deformed internally by smaller faults and associated folds. Steeply dipping extensional faults cut all compressional structures in the district.

The Red Dog mine area and Anarraaq deposits are highly enriched in Zn and Pb owing to the superposition of as many as four phases of sulfide mineralization through carbonate replacement, brecciation, silicification, and veining. Barite and secondary silica are pervasive and intimately associated with base-metal mineralization in the mine area deposits. A giant barite body occurs in the structural hanging wall of the Anarraaq deposit but is spatially separated from it. The Ikalukrok unit hosts other strata-bound Zn-Pb-Ag deposits and occurrences in the Red Dog district that are referred to herein as laminated deposits. Sulfides within laminated deposits such as Su and Lik are typically laminated and brecciated. These deposits lack evidence of associated barite or widespread, multiphase massive base-metal sulfides, which form the high-grade cores of the mine area and Anarraaq deposits. We suggest that differences in character of Zn-Pb-Ag deposits in the Red Dog district can be attributed to variability in the original composition of the Ikalukrok unit host and the location of the deposits within the original subbasin.

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