Abstract

The Red Dog orebody (western Brooks Range, Alaska) contains reserves of approximately 150 Mt at an average grade of 16.2% Zn, 4.4% Pb, and 110 g/t Ag. Three mineralization facies can be identified within the orebody on the basis of mineralogical, textural, and paragenetic variations. The mineralization facies are termed breccia, transitional, and stratiform, representing a variation from a predominantly early epigenetic style of mineralization (breccia and transitional facies) to features that are more characteristic of syngenetic mineralization (stratiform facies). The primary relationship between the orebody and host rocks has been obscured by postmineralization deformation events that occurred during the Cretaceous Brooks Range orogeny. Therefore, reconstruction of the orebody was established using the mineralization facies model, determining local fault strain kinematics, drawing sections, and contouring the orebody's footwall, which is also a structural horizon. The reconstructed vent field is approximately 2400 m by 400 m, and contains four principal vents: the Hilltop, Main, West, and Aqqaluk. All vents are characterized by breccia facies mineralization that grades rapidly to transitional facies. The stratiform facies defines the periphery of the orebody. The development of the orebody began in the Upper Mississippian when early-stage metal-rich fluids were initially focused into the Main and West vents. All four vents were active during main-stage mineralization, which is characterized by extensive brecciation and sulfide-bearing barite rock and bitumen formation. Near the end of main-stage mineralization, the Aqqaluk vent became the main discharge zone, and fluid flow ceased entirely at the Hilltop vent. During late-stage mineralization, minor sulfide and sulfide-bearing and unmineralized barite rock were deposited. Upper Pennsylvanian strata do not host Zn–Pb mineralization, and they define the end of the ore-forming event at Red Dog. However, stratiform barite rock continued to be deposited, suggesting fluids were discharged at the sea floor until the end of the Pennsylvanian.

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