THE RELATIONSHIP OF ORE AND STRUCTURAL GEOLOGY AT THE RED DOG Zn-Pb-Ag DEPOSIT, WESTERN BROOKS RANGE, ALASKA

Abstract

The Red Dog deposit is a stratabound zinc - lead - silver massive sulfide deposit hosted by black shale and barite of the Carboniferous to early Permian Kuna Formation. Four distinct varieties of ore occur at Red Dog, they are: massive sulfide, mineralized and silicified black shale, mineralized barite, and mineralized and silicified barite. Stratigraphically, the mineralized shale composes the lower portion of the deposit, the massive sulfide is In the center of the deposit, mineralized and silicified barite is above massive sulfide, and the mineralized barite is at the top of the deposit. The Red Dog deposit is proposed to have formed during a period of tectonism and abundant hydrothermal activity in the late Carboniferous to early Permian. The preserved stratigraphy of barren barite down through weakly mineralized barite and into silicified and sulfide mineral replaced barite existed throughout the time of deposit formation. A zone of replacement mineralization below the barite moved upwards with time overprinting earlier barite with quartz and sulfide mineralization. Massive sulfide formed under a barite carapace by replacement and direct precipitation into open space from hydrothermal fluids. The Red Dog Main Deposit is unusually large relative to other similar deposits because the mineralizing system was unusually large. The deposit is unusually high-grade because only the high-grade vent complex and feeder zone are preserved.