structure of the red dog district, western brooks range, alaska

664 Pages·2007·46.3 MB·English

STRUCTURE OF THE RED DOG DISTRICT,
WESTERN BROOKS RANGE, ALASKA
Jose de Vera
A Thesis submitted in the fulfilment of the requirements
of the University of London for the degree
of Doctor of Philosophy
Department of Geology
Royal Holloway, University of London
Egham, Surrey TW20 0EX
United Kingdom
December 2005
Royal Holloway
University of London
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A mis Padres
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Abstract
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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 lead 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 - 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
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Abstract
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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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Contents
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CONTENTS

PAGE No.
Title Page i
Dedication ii
Abstract iii
Contents v
List of Figures xii
List of Tables xxvi
List of Enclosures xxvii
List of Appendices xxviii

CHAPTER 1 INTRODUCTION 1

1.1 Introduction 2
1.2 Location of the Red Dog district 4
1.3 Geology of the Red Dog district 5
1.4 Aims of research 10
1.5 Research methodology 11
1.6 Thesis Outline 12
1.7 Acknowledgements 13

CHAPTER 2 REVIEW OF THE TECTONIC EVOLUTION 15
OF THE BROOKS RANGE, ALASKA

2.1 Introduction 16
2.2 Plate tectonic setting and evolution 17
2.3 The Brooks Range 29
2.3.1 Physiographic elements 29

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2.3.2 Geological framework 30
2.3.3 Structure of the Brooks Range 32
2.3.4 Structural units of the Brooks Range 34
2.3.5 Orogenic events 35
2.4 Arctic Alaska Terrane 44
2.4.1 Tectonic affinity of the Arctic Alaska terrane 47
2.4.2 Origin of the Arctic Alaska terrane 49
2.4.3 Stratigraphy of the Arctic Alaska terrane 51
2.4.4 Structural units of the Arctic Alaska terrane 51
2.5 Angayucham terrane 63
2.5.1 Structural units of the Angayucham terrane 65
2.5.2 Tectonic affinity of the Angayucham terrane 66
2.5.3 Origin of the Angayucham terrane 67
2.5.4 Correlation with other terranes 69
2.5.5 Mechanics of ophiolite emplacement 70
2.6 Mineral deposits of the Brooks Range 70
2.6.1 Pre-accretionary mineral deposits 70
2.6.2 Accretionary and post-accretionary deposits 73
2.7 Summary 74

CHAPTER 3 REVIEW OF THE GEOLOGY OF THE RED DOG 76
DISTRICT

3.1 Introduction 77
3.2 History of exploration and discoveries 82
3.3 Regional stratigraphy 83
3.3.1 Stratigraphic units of the Red Dog district 86
3.3.2 Igneous rocks 97
3.4 Regional structure 98
3.4.1 Structure of the Red Dog district 98
3.4.2 Wrench Creek and Sivukat Mountain Faults 100
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3.4.3 Structural Models 100
3.5 Sediment-hosted Zn-Pb-Ag deposits: An overview 102
3.5.1 Definitions 102
3.5.2 Classification and Nomenclature 102
3.5.3 Examples of sediment-hosted Zn-Pb-Ag deposits 106
3.5.4 General characteristics 106
3.5.5 Tectonostratigraphic setting 109
3.5.6 Temporal distribution of sediment-hosted Zn-Pb-Ag deposits 111
3.5.7 Morphology and structure of sediment-hosted Zn-Pb-Ag deposits 115
3.5.8 Genesis of sediment-hosted Zn-Pb-Ag deposits 118
3.6 Mineralization of the Red Dog district 121
3.6.1 Deposits of the Red Dog district 121
3.6.2 Ore genesis and timing of mineralization 132
3.7 Summary 137

CHAPTER 4 THRUST TECTONICS: A REVIEW 138

4.1 Introduction 139
4.2 Basic Geometric Elements 141
4.2.1 Thrust faults 141
4.2.2 Thrust sheets 146
4.2.3 Thrust fault-related folds 149
4.2.4 Mechanics of thrust faulting 152
4.3 Thrust Systems 155
4.3.1 Duplexes 155
4.3.2 Imbricate thrust systems 160
4.3.3 Triangle zones and mountain fronts 169
4.3.4 Basement-involved thrust systems 174
4.4 3D thrust systems 177
4.4.1 Lateral ramps, tear faults and transverse zones 177
4.5 3D thrust belt geometries 189
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4.6 Thrust Sequences 194
4.6.1 In-sequence thrusting 194
4.6.2 ‘Out-of-sequence’ thrusting 196
4.6.3 Synchronous thrusting 198
4.7 Summary 201

CHAPTER 5 STRATIGRAPHY OF THE RED DOG DISTRICT 202

5.1 Introduction 203
5.2 Nomenclature and rationale of description 203
5.3 Depositional megasequences 209
5.3.1 Ellesmerian stratigraphy (Late Devonian – Late Jurassic) 209
5.3.2 Brookian Stratigraphy (Early Cretaceous) 211
5.4 Stratigraphy of the Arctic Alaska terrane 212
5.4.1 Stratigraphy of the Endicott Mountains allochthon 212
5.4.2 Stratigraphy of the Picnic Creek allochthon 245
5.4.3 Stratigraphy of the Kelly River allochthon 249
5.4.4 Stratigraphy of the Ipnavik River allochthon 259
5.4.5 Stratigraphy of the Nuka Ridge allochthon 259
5.4.6 Stratigraphy of the Copter Peak allochthon 261
5.5 Stratigraphy of the Angayucham terrane 266
5.5.1 Igneous stratigraphy of the Misheguk Mountain allochthon 266
5.5.2 Tectonic affinity of the Angayucham terrane 271
5.6 Foreland basin stratigraphy 272
5.6.1 Early syn-orogenic megasequence 272
5.6.2 Late syn-orogenic megasequence 281
5.7 Summary 284

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CHAPTER 6 STRUCTURAL ANALYSIS OF THE RED DOG 286
DISTRICT

6.1 Introduction 287
6.2 Structural nomenclature and hierarchy 287
6.2.1 Structural units 287
6.3 Arctic Alaska terrane 292
6.3.1 Endicott Mountains allochthon 292
6.3.2 Picnic Creek allochthon 348
6.3.3 Kelly River allochthon 357
6.3.4 Ipnavik River and Nuka Ridge allochthons 370
6.3.5 Copter Peak allochthon 370
6.4 Angayucham terrane 373
6.4.1 Misheguk Mountain allochthon 373
6.5 Structure of the thrust front 389
6.5.1 Amphitheatre Mountain triangle zone 392
6.5.2 The Wulik Peaks transverse zone 398
6.5.3 Amaruk River emergent thrust front 408
6.5.4 Structure of the North Slope parautochthon 414
6.6 Wrench Creek and Sivukat Mountain faults 420
6.6.1 Wrench Creek fault 425
6.6.2 Sivukat Mountain fault 427
6.6.3 Other late extensional faults 433
6.7 Thrust systems and kinematic analyses 438
6.7.1 Thrust systems 438
6.7.2 Kinematic analyses 439
6.7.3 Thrust sequences 442
6.8 Summary 444

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CHAPTER 7 STRUCTURAL ANALYSIS OF THE Zn-Pb-Ag AND 446
BARITE DEPOSITS OFTHE RED DOG DISTRICT

7.1 Introduction 447
7.2 Deposits of the Red Dog Creek area 450
7.2.1 Qanaiyaq deposits (formerly the Hilltop deposit) 458
7.2.2 Main deposit 460
7.2.3 Aqqaluk deposit 500
7.2.4 Paalaaq deposit 503
7.3 Deposits of the Anarraaq-Wulik area 503
7.3.1 Anarraaq deposit 503
7.3.2 Aktigiruq deposit 506
7.4 Deposits of the Su-Lik area 509
7.5 Summary 511

CHAPTER 8 DISCUSSION 513

8.1 Introduction 514
8.2 Tectonostratigraphy of the Red Dog district 514
8.2.1 Introduction 514
8.2.2 Tectonostratigraphy of the Red Dog district 520
8.3 Structural analysis of the Red Dog district 529
8.3.1 Introduction 529
8.3.2 Tectonic events in the Red Dog district, Northwestern 529
Brooks Range
8.3.3 Fold and thrust belt structures in the Red Dog district 531
8.3.4 Tectonostratigraphic model for the evolution of the 552
Red Dog district
8.4 Tectonic evolution of the Western Brooks Range 558
8.4.1 Transverse zones and basement structural inheritance 558

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