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de Vera, Jose, 2005

Structure of the Red Dog district, western Brooks Range, Alaska

Bibliographic Reference

de Vera, Jose, 2005, Structure of the Red Dog district, western Brooks Range, Alaska: University of London, United Kingdom, Ph.D. dissertation, xxviii, 633 p. (3 vol.), (some color) illust., (some color) maps.

Abstract

This thesis presents a structural and stratigraphic analysis of the Red Dog district, western Brooks Range, northwestern Alaska. The aims of the research were to define the structure and stratigraphic context of the Red Dog district and, in particular, of the giant Zn-Pb-Ag and barite deposits in the region, in order to develop new tectonostratigraphic models for the area and for the mineralization. The research programme involved extensive periods of regional fieldwork combined with detailed mapping of the Red Dog open pit together with structural analysis, reconstructions and tectonostratigraphic analyses.

The research presented in this thesis has resulted in a new structural interpretation and a new tectonostratigraphy for the Red Dog district, western Brooks Range of Alaska. This has led to a new model for the tectonostratigraphic evolution of the Red Dog district, for the mineralization and also for the western Brooks Range.

The Red Dog district of the western Brooks Range consists of two major allochthonous terranes, the Arctic Alaska and the Angayucham terranes. These form part of a telescoped Devonian through Jurassic continental passive margin and oceanic crust that are now preserved in seven stacked allochthon sheets bounded by regional sub-horizontal thrust systems. These were thrust northwestwards onto the passive margin of northern Alaska in the Mid-Late Jurassic to Late Cretaceous Brookian orogeny, forming a NE-SW-to WNW-ESE-trending and WNW-vergent thin-skinned foreland fold and thrust belt. The Arctic Alaska terrane of the western Brooks Range consists of the lower six allochthons formed by the telescoping of proximal and distal sedimentary sections of the southern passive margin of the ancestral Alaskan continent. The seventh and uppermost thrust sheet consists of the Misheguk Mountain allochthon of the Angayucham terrane. This is interpreted to have formed as Middle Jurassic oceanic crust south of the ancestral passive margin and subsequently obducted northwestwards onto the telescoped passive margin during the Brookian orogeny.

The Zn-Pb-Ag and barite mineralization of the Red Dog district is confined to the Red Dog thrust plate of the Endicott Mountains allochthon of the Arctic Alaska terrane of northern Alaska. The Red Dog plate exhibits a complex stratigraphy reflecting emplacement into a foredeep basin where olistostromal units were being formed and incorporated into the thrust plate itself. The mineralization appears to be structurally controlled by the major NW-trending Wulik Peaks transverse zone within the dominant NE-SW-trending fold and thrust belt of the western Brooks Range. Late Devonian to Late Mississippian extensional faults associated with rifting and passive margin development of the Arctic Alaska terrane controlled the contraction of the passive margin during the Brookian orogeny that formed the western Brooks Range in this region. The Sooner River arch was a WNW-ESE trending basement high that controlled the formation of the Wulik Peaks transverse zone as well as probably localizing the Zn-Pb-Ag and barite deposits of the Red Dog district. These WNW-ESE-trending basement involved faults were also later reactivated by Middle Eocene to Present Day extension. This new tectonostratigraphic model for the world-class Red Dog Zn-Pb-Ag and barite mineralization has important implications for exploration of new deposits within the Red Dog district, as well as elsewhere in the Brooks Range of northern Alaska.

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