STRUCTURAL SETTING OF THE RED DOG DISTRICT, WESTERN BROOKS RANGE, ALASKA

The Red Dog district, encompassing the Zn-Pb-Ag deposits at Red Dog (Qanaiyaq, Main, Aqqaluk and Paalaaq) and Anarraaq, hosts the world’s largest reserves of zinc. Understanding the structural geology of the district is the key to future discoveries. Recent structural analysis combined with exploration drilling and previous detailed stratigraphic mapping provides a framework for future exploration.

Three major allochthons have been studied in the Red Dog district. The lowermost of these is the Wolverine Creek allochthon (WC) which is overlain by the Brooks Range (Endicott Mountains) allochthon (BR) and the Kelly River allochthon (KR). The BR is host to all known mineralization in the district. It is dominated by incompetent Mississippian through Triassic shales and cherts that form a duplex with floor, roof and linking thrusts defining several tectono-stratigraphically distinct plates and sub-plates. In contrast, the thick-bedded cherty limestones of both the WC and KR result in fewer internal imbrications. To-date at least three repetitions have been mapped in the WC which form a poorly defined anticlinal stack that uplifts and folds the overlying BR. Preliminary structural mapping in the district indicates a dominant 020 degree vergence direction for folding and thrusting (D1, n > 500) with a single associated cleavage. NE - trending folds are interpreted to reflect underlying lateral or oblique ramps. N-S sinistral oblique-slip faults probably reflect extension subparallel to the tectonic transport direction (D2). The WNW-striking Wrench Creek and Sivukat Mountain extensional faults that bound the district to the north and south respectively have dextral oblique-slip (down to the SSW) movement that cuts the earlier thrusts (D3). Other oblique-slip NW-striking faults have also been mapped, one of which bounds the western side of the Red Dog open pit and separates it from the up-thrown Qanaiyaq (formerly Hilltop) deposit to the south (D3).

Ore-hosting stratigraphy is best preserved to the north of anticlinal stacks in the WC structural footwall.