Circular 1319

Regional Fluid Flow and Basin Modeling in 

Northern Alaska

Contributors

Robert A. Ayuso Craig A. Johnson Erin E. Marsh

Robert C. Burruss Karen D. Kelley Thomas E. Moore

Julie A. Dumoulin David L. Leach Christopher J. Potter

Garth E. Graham Paul G. Lillis John F. Slack

Anita G. Harris 
Regional Fluid Flow and Basin Modeling in 

Northern Alaska

Contributors: Robert A. Ayuso, Robert C. Burruss, Julie A. Dumoulin, 

Garth E. Graham, Anita G. Harris, Craig A. Johnson, Karen D. Kelley, 

David L. Leach, Paul G. Lillis, Erin E. Marsh, Thomas E. Moore, 

Christopher J. Potter, John F. Slack

Circular 1319

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Kelley, K.D., ed., 2008, Regional fluid flow and basin modeling in northern Alaska: U.S. Geological Survey 

Circular 1319, 45 p.
iii

Contents

1. Introduction.................................................................................................................................................1

2. Depositional Settings and Age of Carboniferous Rocks in the Western Brooks

Range, Alaska ...................................................................................................................................3

3. Geochemistry of Paleozoic Sedimentary Rocks: Metallogenic Significance .................................6

4. Depositional Models for Barite and Zinc...............................................................................................9

5. Insights into the Ore-Forming Fluids.....................................................................................................12

6. Geochemical Indicators of Massive Sulfide Deposits and Vein Breccia Zn-Pb-Ag

Occurrences....................................................................................................................................15

7. Sulfur and Oxygen Isotope Chemistry of Barite .................................................................................18

8. Radiogenic Isotope Studies ...................................................................................................................20

9. Phosphatic Rocks of the Lisburne Group ............................................................................................22

10. Metalliferous Tasmanite and Oil Shale ..............................................................................................25

11. Preliminary Retrodeformable Regional Cross Section, Western Brooks Range ........................28

12. Geologic Rationale for Extensional Basin Framework During Red Dog Mineralization ............32

13. Lisburne Petroleum System .................................................................................................................36

References....................................................................................................................................................40

Glossary of Terms ........................................................................................................................................44
iv

Figures

1.1. Landsat map of northern Alaska showing location of mineral deposits and 

occurrences in the western and central Brooks Range and North 

Slope of Alaska ......................................................................................................................2

1.2. Grade-tonnage diagram showing data for the Red Dog, Anarraaq, and 

 Su-Lik deposits compared with those for other deposits worldwide...........................1

2.1. Map of northern Alaksa showing distribution of Lisburne Group rocks ..........................4

2.2. Depositional setting and stratigraphic context of the Lisburne Group 

succession in the Red Dog area .........................................................................................5

3.1. Plots of organic carbon (Corg) versus sulfur (S) for sedimentary rocks ............................7

3.2. Chondrite-normalized rare earth element (REE) plots of altered (silica-rich 

wall rocks) and mineralized samples from the Red Dog deposits 

and the Anarraaq deposits ..................................................................................................8

4.1. Stratigraphic column for the central Brooks Range showing locations of 

barite and sulfide mineral deposits ..................................................................................10

4.2. Schematic diagram illustrating relative stratigraphic positions of sulfide 

and barite deposits in northern Alaska............................................................................10

4.3. Photos of textures of ore types in northern Alaska...........................................................11 

5.1. Schematic paleogeography of the Red Dog area in Late Carboniferous ......................13

5.2. Reflux brine model for the shale-hosted massive sulfide deposits, 

northern Alaska ...................................................................................................................14

6.1. Whole rock geochemistry of mineralized, visually unaltered, and 

unmineralized samples in and around massive sulfide and 

vein-breccia deposits and occurrences .........................................................................16

6.2. Shaded relief map of the Drenchwater area showing stream sediment 

geochemical anomalies .....................................................................................................17

7.1. Plots of oxygen versus sulfur isotope compositions for Red Dog and 

central Brooks Range barite deposits .............................................................................19

7.2. Histograms of sulfur isotope compositions for barite samples from 

Red Dog and the central Brooks Range, comparing barite-only to 

barite associated with sulfides .........................................................................................19

8.1. Lead isotope diagram for sulfides from Red Dog and from the Brooks Range.............20

8.2. Initial strontium isotope ratios of barite from the Red Dog deposits, 

Anarraaq and other deposits or occurrences in the Red Dog district, 

and from regional deposits or occurrences east of Red Dog in the 

western and central Brooks Range..................................................................................21

9.1. Outcrop and hand sample photographs of phosphorite occurrences in 

northern Alaska ...................................................................................................................23

9.2. Palinspastic restoration of northern Alaska showing location of 

phosphatic strata surrounding the Kuna Basin..............................................................24

 10.1. Shaded relief map of the Howard Pass quadrangle showing locations 

of oil shale and tasmanites sampled during 2005 ..........................................................26

10.2. Outcrop photographs of oil shale occurrences..................................................................27

11.1. Map showing major structures and structural units and location of 

cross section........................................................................................................................30
v

11.2. Cross section from Kugururok River to Tupikchak Creek, Misheguk 

Mountain and De Long Mountains quadrangles............................................................31

12.1. Schematic northwest to southeast cross section depicting the Anarraaq 

deposit in Late Mississippian time ...................................................................................33

12.2. Geologic cross section through the Red Dog district .......................................................34

12.3. Interpreted segment of composite reflection seismic line R1 from 

National Petroleum Reserve–Alaska, approximately 70 km 

north-northeast of Red Dog ...............................................................................................35

13.1. Location map of northern Alaska showing distribution of deep- and 

shallow-water facies of the Lisburne Group, location of North Slope 

wells, and location of samples used for geochemical analysis ..................................37

13.2. Photomicrographs of dead oil that show evidence for petroleum migration................38

13.3. Frequency distribution diagrams showing CAI (conodont alteration 

indices) values of samples of Lisburne Group................................................................39

Table

10.1. Metal concentrations in black oil shale and tasmanite from northern 

 Alaska compared to other metalliferous organic-rich black shale and 

 oil shale localities .....................................................................................................................27
1. Introduction 1

1. Introduction

By Karen D. Kelley

The foothills of the Brooks Range contain an enormous 

accumulation of zinc (Zn) in the form of zinc sulfide and 

barium (Ba) in the form of barite in Carboniferous shale, chert, 

and mudstone (fig. 1.1). Most of the resources and reserves of 

Zn occur in the Red Dog deposit and others in the Red Dog 

district; these resources and reserves surpass those of most 

deposits worldwide in terms of size and grade (fig. 1.2). In 

addition to zinc and lead sulfides (which contain silver, Ag) 

and barite, correlative strata host phosphate deposits (fig. 1.1). 

Furthermore, prolific hydrocarbon source rocks of Carboniferous and Triassic to Early Jurassic age generated considerable 

amounts of petroleum that may have contributed to the worldclass petroleum resources of the North Slope.

Deposits of Zn-Pb-Ag or barite as large as those in the 

Brooks Range are very rare on a global basis and, accordingly, multiple coincident favorable factors must be invoked 

to explain their origins. To improve our understanding of 

these factors and to contribute to more effective assessments 

of resources in sedimentary basins of northern Alaska and 

throughout the world, the Mineral Resources Program and 

the Energy Resources Program of the U.S. Geological Survey 

(USGS) initiated a project that was aimed at understanding the 

petroleum maturation and mineralization history of parts of 

the Brooks Range that were previously poorly characterized. 

The project, titled “Regional Fluid Flow and Basin Modeling 

in Northern Alaska,” was undertaken in collaboration with 

industry, academia, and other government agencies. This Circular contains papers that describe the results of the recently 

completed project. The studies that are highlighted in these 

papers have led to a better understanding of the following:

•	 The complex sedimentary facies relationships and 

depositional settings and the geochemistry of the sedimentary rocks that host the deposits (sections 2 and 3).

•	 The factors responsible for formation of the barite and 

zinc deposits (sections 4 and 5).

0

5

10

15

20

25

0 10 20 30 40 50 60

Zinc (Zn) + Lead (Pb) wt %

Zinc (Zn) + Lead (Pb) Mt

Broken Hill

Howards Pass

McArthur River

Sullivan

Hilton

George Fisher

Century

Jinding

Rammelsberg

Lady Loretta

Mt. Isa

Anarraaq

Red Dog

Su-Lik

•	 The geochemical indicators or exploration tools that 

might be used to locate other large deposits of similar 

character in the Red Dog district and elsewhere (section 6).

•	 The isotopic compositions of barite and sulfide deposits (sections 7 and 8)

•	 The distribution and nature of phosphate and metalliferous oil shale localities (sections 9 and 10).

•	 The architecture, kinematics, and timing of the complex thrust systems that disrupted and redistributed 

the Carboniferous and younger rocks; these studies 

are necessary in order to make a realistic palinspastic 

reconstruction of the basin (sections 11 and 12).

•	 The nature and extent of the petroleum system sourced 

from Mississippian rocks (section 13).

Figure 1.2. Grade-tonnage diagram showing data for the 

Red Dog, Anarraaq, and Su-Lik deposits (indicated by red 

stars) compared with those for other deposits worldwide 

(modified from Large and others, 2002). Other deposits with 15 

Mt or greater and (or) high grade (20 wt percent Pb and Zn) 

are labeled by name.
2 Regional Fluid Flow and Basin Modeling in Northern Alaska

SUDS SU-LIK

HUSKY

WULIK

MOIL

Red Dog district

SU GINNY CREEK

NIMIUKTUK

HOHUM

SAFARI CREEK

IPNAVIK RIVER

1035

KIVLIKTORT

1032 1082

LAKEVIEW

TUCK

KADY

VIDLEE Massive sulfide (Zn-Pb-Ag)

Vein-breccia (Zn-Pb-Ag)Barite

N P R A

Barrow

Lisburne Hills

B E A U F O R T

S E A 

LONGVIEW

WHOOPEE CREEK

ZHAR

Howard Pass Misheguk Mtn Killik River Chandler Lake

De Long Mtns

LISBURNE RIDGE

MOUNT BUPTO

Phosphate

0 50 100

KILOMETERS

IVOTUK HILLS

AHNOWAY

STORY CREEK

DRENCHWATER

ANARRAAQ

Ikpikpuk

MONOTIS CREEK

AKMALIK CREEK

SKIMO CREEK

SHAININ LAKE

ATNEERICH CREEK

AMPHITHEATRE  MOUNTAIN

WULIK PEAKS

GULL

69° 

68° 

162° 159° 156° 

Anchorage

Kotzebue

Anchorage

K

otzebue

Figure 1.1. Landsat map of northern Alaska showing location of mineral deposits and occurrences in the western and central Brooks Range and North Slope of Alaska. Yellow line delineates the National Petroleum Reserve–Alaska (NPRA); blue dashed lines delineate quadrangle boundaries.
2. Depositional Settings and Age of Carboniferous Rocks in the Western Brooks Range, Alaska 3

2. Depositional Settings and Age of 

Carboniferous Rocks in the Western 

Brooks Range, Alaska

By Julie A. Dumoulin and Anita G. Harris

The Kuna Formation of the Lisburne Group (Carboniferous to Permian in age) hosts the giant Red Dog and related 

Zn-Pb-Ag massive sulfide deposits in northwestern Alaska. 

The geography of northwestern Alaska at the time of mineralization (about 330 to 340 million years ago) and the nature 

of the sedimentary basin in which the deposits formed may be 

determined by comparison of Lisburne Group facies between 

the Red Dog district and areas farther east (fig. 2.1). Many factors can be considered, including the character and geometry 

of the basin, the composition of its sediment fill, the timing 

and environments of deposition within it, and its post-depositional thermal history. All of these factors are important for 

deciphering the geologic events that led up to and prevailed 

during mineralization and for assessing where other zinc or 

barite resources might occur (Dumoulin and others, 2004; 

Young, 2004).

New studies of the sedimentology and paleontology of 

the Lisburne Group constrain the setting, age, and thermal 

history of these deposits. In the west and west-central Brooks 

Range, the Lisburne Group includes both deep- and shallowwater sedimentary facies and local volcanic rocks that are 

exposed in a series of thrust sheets or allochthons, which are 

further subdivided into plates (fig. 2.2). Deep-water facies 

in the Red Dog area (the Kuna Formation and related rocks) 

are found chiefly in the Endicott Mountains and structurally 

higher Picnic Creek allochthons (EMA and PCA, respectively). In the Red Dog plate of the EMA, the Kuna consists 

of at least 122 m of thinly interbedded calcareous shale and 

limestone (Kivalina unit) overlain by 30–240 m of siliceous 

carbonaceous shale, mudstone, and limestone including 

carbonate turbidites (Ikalukrok unit). The Ikalukrok unit in 

the Red Dog plate hosts all massive sulfide deposits in the 

area. The Kuna Formation in the Key Creek plate of the EMA 

(60-110 m) resembles the Ikalukrok unit but is unmineralized 

and has thinner carbonate layers that are mainly organic-rich 

dolostone. Correlative strata in the PCA include less shale and 

mudstone and more carbonate. Microfossils indicate an age 

range of Osagian to early Chesterian (late Early-Late Mississippian) for the Kuna in the Red Dog area (fig. 2.2). For 

explanation of the geologic time scale, refer to Gradstein and 

Ogg (2004). Sedimentologic, faunal, and geochemical data 

imply that most of the Kuna formed in slope and basin settings 

characterized by poorly oxygenated bottom-water and locally 

high organic productivity.

Shallow-water facies of the Lisburne Group in the Red 

Dog area occur locally in the EMA and throughout the Kelly 

River allochthon (KRA) and consist of the Utukok and Kogruk 

Formations. The Utukok Formation is an impure limestone 

with disseminated and interbedded noncarbonate mud and 

quartz-rich silt and sand. Clean carbonate predominates in 

the overlying Kogruk Formation, but the formation has been 

widely altered to dolostone and chert. The Utukok Formation 

is mainly Osagean but its base is Kinderhookian. The Kogruk 

Formation is mostly Meramecian (early Late Mississippian) 

in age (fig. 2.2). Most of the rocks of the Kogruk and Utukok 

Formations were deposited in inner to middle platform settings. Deep-water, locally phosphatic facies of the uppermost 

Lisburne Group formed during a platform-drowning event of 

regional extent that began in the late Meramecian. 

In the Howard Pass area, approximately 120–250 km to 

the east, the Lisburne Group includes an array of shallow- and 

deep-water facies that correspond well in age and general 

depositional environment to those in the Red Dog area but 

differ in some details. Deep-water strata generally are thinner, 

include less carbonate, and are formed in settings that were 

deeper and (or) had less detrital input. Shallow-water deposits 

are less extensive, contain less quartz silt and sand, and are 

formed chiefly in middle and outer platform settings. 

Paleogeographic reconstructions of northern Alaska 

imply that carbonate platforms flanked the Kuna basin to the 

north and south in the west, but flourished chiefly north of 

the basin in the east. The basin shows evidence of periodic 

tectonic instability and is interpreted as an extensional passive 

continental margin basin. The platforms provided carbonate 

and perhaps some noncarbonate detritus to the basin; noncarbonate material could also have come from older strata underlying the platforms and (or) the Endicott delta to the north. 

Carbonate turbidite deposition in the Kuna basin occurred 

chiefly during middle Osagean and late Meramecian-early 

Chesterian (late Early and middle Late Mississippian) times 

and ceased when adjacent platforms drowned. A combination 

of local and global factors probably controlled the timing of 

sediment input to the basin and the flooding of the adjoining 

carbonate platforms. Platform drowning occurred at about the 

same time as the start of barite precipitation and sulfide mineralization, implying that regional extension was a significant 

component of all three events. High productivity, locally thick 

calcareous turbidite fill, and proximity to restricted, shallowwater carbonate platform environments are aspects of the 

Kuna basin that appear to have been important in forming the 

giant Red Dog deposits.
4 Regional Fluid Flow and Basin Modeling in Northern Alaska

Figure 2.1. Map of northern Alaska showing distribution of Lisburne Group rocks (blue).

De Long Mts. Quadrangle

Killik River

Misheguk Mt.

Howard Pass

Baird Mts.

Noatak

Quadrangle

Quadrangle

Quadrangle

Quadrangle

Quadrangle

Brooks Range

Arctic Ocean

Chukchi Sea

Alaska

Inigok well

153oW

69o

165oW

N

68oN

0 100 200

KILOMETERS

141oW

Figure 1

Area of

Drenchwater

Lisburne

Peninsula

Prudhoe

Bay

IkpikpukUmiat basin

Red Dog

 district

Arctic Coastal Plain
2. Depositional Settings and Age of Carboniferous Rocks in the Western Brooks Range, Alaska 5

Endicott Mountains

Wolv. Red Key Creek

Port Rd Wulik Amaruk Wulik Amph. Kelly Eli

Kelly River

Plate

Allochthon

Age (Ma)

System

Series

Stage

N. American

Dog Peaks

Picnic

Creek

311

323

333

350

362

Pennsylvanian (part) Mississippian Devonian (part)

Middle (part) Lower Upper

Chesterian Morrowan Atokan Meramecian

Lower

Osagean Kinderhookian

Upper (part)

Famennian

Utukok Fm.

Utukok Fm.

Kayak Sh.

Kogruk Fm.

Siksikpuk Fm.Siksikpuk Fm.Siksikpuk Fm.Siksikpuk Fm.Siksikpuk Fm.

Ikalukrok unit

Kuna Fm.

Kogruk Fm. Utukok Fm.

Kayak Sh.Kayak Sh.Kayak Sh.Kayak Sh.Kayak Sh.

Utukok Fm.

Micritic

Utukok Fm.

Kogruk Fm.

Kogruk Fm.

Siksikpuk Fm.

Kogruk Fm. Utukok Fm.

Unnamed limestone

Eli Limestone

limestone unit

Kanayut Conglomerate

Kanayut Conglomerate

Kivalina unit

Inner and/or middle platform

Outer platform or deeper

Slope and/or basin

Uncertain

? ? ? ?

? ?

Lisburne Group Depositional Settings

Kogruk Fm.

unnamed subunit of Lisburne Group

unnamed subunit of Lisburne Group

Creek

Figure 2.2. Depositional setting and stratigraphic context of the Lisburne Group succession 

in the Red Dog area (modified from Dumoulin and others, 2004). [Amph., Amphitheatre plate; 

Wolv., Wolverine Creek plate; Fm., Formation; Sh., Shale; question marks indicate placement of 

boundary is uncertain]
6 Regional Fluid Flow and Basin Modeling in Northern Alaska

3. Geochemistry of Paleozoic 

Sedimentary Rocks: Metallogenic 

Significance

By John F. Slack

Whole rock geochemical data provide a basis for interpreting the origin and evolution of Paleozoic sedimentary 

rocks, not only in the Red Dog region, but regionally throughout the western and central Brooks Range. Such data are useful for identifying hydrocarbon source rocks, establishing critical background values for documenting the geochemistry of 

hydrothermal alteration in wall rocks to the sulfide deposits of 

the district, and for discerning the nature and history of fluid 

flow in the sedimentary basins (Slack, Dumoulin, and others, 

2004; Slack, Kelley, and others, 2004). 

Concentrations of total organic carbon (TOC) in Paleozoic sedimentary rocks of the region display a large range, 

but the highest values (>4.1 wt percent) occur in black shales 

of the Kuna Formation, making these potentially important 

hydrocarbon source rocks. The organic-rich nature of these 

strata, together with other geochemical attributes, suggest 

that the geochemistry of the Kuna Formation played a fundamental role in formation of the massive sulfide deposits. A 

critical factor may have been the anomalously low average 

Fe/Ti (iron/titanium) ratios for shales of the Kuna Formation 

and Kayak Shale (6.34 and 6.25, respectively), compared to 

those for other Paleozoic shales in the western Brooks Range 

and the average of shales worldwide (10.1–10.6). Within most 

sediments of the Kuna Formation and Kayak Shale, formation of synsedimentary to early diagenetic pyrite was inhibited by the iron-limiting bulk compositions, which resulted 

in generally low S/C (sulfur/carbon) ratios of <0.2 (fig. 3.1). 

These data suggest that in the Kuna basin, reduction of marine 

sulfate by abundant organic matter and restricted formation of 

sedimentary pyrite created significant amounts of H2S within 

anoxic pore fluids. This H2S (hydrogen sulfide) may have been 

crucial to synsedimentary precipitation of the huge tonnages of 

base-metal sulfides in the Red Dog district, providing a local 

source of abundant reduced sulfur in addition to that produced 

by reduction of seawater sulfate and dissolution of barite (Kelley, Leach, and others, 2004). Distal from sites of Zn-Pb-Ag 

mineralization, H2S in the sediments of the Kayak Shale and 

Kuna Formation probably escaped through synsedimentary 

faults or was removed by diagenetic fluids. 

High biological productivity in Mississippian seawater 

also may have indirectly influenced subseafloor hydrothermal fluid flow and Zn-Pb-Ag mineralization in the Red Dog 

district. The upper part ofthe Kuna Formation is very siliceous 

and contains abundant organic carbon and phosphate and 

locally abundant radiolarians (Dumoulin and others, 2004), 

all of which are hallmarks of high biological productivity in 

marine sediments. If these siliceous units became lithified 

during sedimentation or very early diagenesis, they could have 

served as effective hydrologic seals or cap rocks to ascending 

hydrothermal fluids, not only on a district scale but regionally 

as well. Such cap rocks, if not breached by synsedimentary 

faults, also would have partly contained the thermal flux associated with mineralization. This process might have helped 

focus Zn-Pb mineralization within permeable carbonate units 

(for example, calcareous radiolarites), which occur stratigraphically below the black cherts and generally below the bedded 

siliceous rocks of the Kuna Formation. 

Textural and geochemical data record the effects of diagenetic and (or) hydrothermal fluid flow in some of the Paleozoic rocks. Mobility of phosphorus (P), fluorine (F), uranium 

(U), and light rare earth elements (REEs) is documented in 

unmineralized black shales of the Kuna Formation by phosphate replacements of carbonate clasts. A negative cerium 

(Ce) anomaly (see shaded region, fig. 3.2A, B) for phosphoruspoor black shales of the Kuna Formation suggests that the 

diagenetic fluids were oxidizing. Other trace elements that 

document the history of hydrothermal fluid flow that produced 

wall rock alteration adjacent to the sulfide deposits include 

thallium (Tl), antimony (Sb), arsenic (As), germanium (Ge), 

and positive europium anomalies (Eu/Eu*), reflecting enrichment of europium relative to other rare earth elements (Slack, 

Kelley, and others, 2004). The latter suite of elements provides 

a powerful means of distinguishing unaltered and unmineralized rocks from those that were affected by the mineralizing 

hydrothermal fluids, including altered wall rocks (fig. 3.2A, B) 

and highly mineralized zones (fig. 3.2C). 
3. Geochemistry of Paleozoic Sedimentary Rocks: Metallogenic Significance 7

A

SULFUR (S, wt %) SULFUR (S, wt %)

ORGANIC CARBON (Corg, wt %)

0 2 4 6 8

0

1

2

3

4

B

Regression line for

oxidized marine sediments

(S/Corg = 0.36)

 Sulfate- and iron-

 limited sediments

0

1

2

3

4

5

0 5 10 15 20 25

EXPLANATION

Kayak Shale

 Kanayut Conglomerate

Siksikpuk Formation

Kuna Formation

ORGANIC CARBON (Corg, wt %)

Figure 3.1. Plots of organic carbon (Corg) vs. sulfur (S) for sedimentary rocks. A, 

Paleozoic and Mesozoic rocks from northern Alaska. B, Detail of A showing field for 

sulfate- and iron-limited sediments. The low iron of most Kuna Formation samples 

limited the amount of pyrite that formed and increased the amount of sulfur available 

to form zinc- and lead- sulfide minerals. Modified from Slack and others (2004a).
8 Regional Fluid Flow and Basin Modeling in Northern Alaska ROCK/CHONDRITE ROCK/CHONDRITE ROCK/CHONDRITE

0.1

1

10

100

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

C

Anarraaq

1

10

100

1,000

B

Anarraaq altered wall rocks

1

10

100

1,000

A

Main and Aqqaluk

altered wall rocks

Massive sulfide

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Main and Aqqaluk

Figure 3.2. Chondrite-normalized rare earth 

element (REE) plots of altered (silicified wall rocks) 

and mineralized samples from the Red Dog deposits 

(Main and Aqqaluk) and the Anarraaq deposit. 

Unaltered black shales of the Kuna Formation are 

shown as the shaded field. [Element abbreviations: 

La, lanthanum; Ce, cerium; Pr, praseodymium; 

Nd, neodymium; Pm, promethium; Sm, samarium; 

Eu, europium; Gd, gadolinium; Tb, terbium; Dy, 

dysprosium; Ho, holmium; Er, erbium; Tm, thulium; 

Yb, ytterbium; Lu, lutetium]
4. Depositional Models for Barite and Zinc 9

4. Depositional Models for Barite 

and Zinc

By Karen D. Kelley 

Understanding the timing and nature of mineralizing 

processes in northern Alaska allows a better context for relating the mineralizing event to the evolution of the basin, which 

ultimately increases our ability to assess the potential for 

similar deposits in other sedimentary basins. Barite and ZnPb-Ag deposits are regionally widespread in northern Alaska 

(fig. 1.1). Barite occurs as lenses of conformable (parallel to 

bedding) barite in Mississippian rocks, and disseminated or 

bladed barite in shale and chert of Pennsylvanian to Triassic age (fig. 4.1). Some deposits are extraordinarily large; for 

example, barite at the Anarraaq deposit alone is estimated to 

be as much as 1 billion metric tons (King and others, 2002). 

Some deposits have both barite and associated sulfides; the 

sulfide bodies may spatially overlap barite or be separated 

from barite by unmineralized rock. Other barite deposits lack 

associated sulfides (fig. 4.2).

The Zn-Pb-Ag mineral occurrences/deposits can be separated into two groups: shale-hosted massive sulfide (SHMS) 

and Zn-Pb-Ag veins and breccias (termed vein breccias). The 

SHMS deposits are in the Mississippian Kuna Formation 

(fig. 4.1) that includes black shale and lesser carbonate layers. 

Typical of these deposits are mineralized horizons that are 

laterally extensive (several kilometers to tens of kilometers). 

The mineralogy of the massive sulfide deposits is a simple 

assemblage of sphalerite, galena, pyrite, and marcasite. Grain 

sizes and textures of the ores are highly variable (fig. 4.3), 

ranging from very fine-grained and layered (parts of Drenchwater, Anarraaq, and Su-Lik) to extremely coarse-grained 

and fragmental or brecciated (Red Dog deposits). Paragenetic 

studies of the individual deposits underscore a complex history 

of formation (Kelley, Dumoulin, and Jennings, 2004; Kelley, 

Leach, and others, 2004).

The vein breccia occurrences are discordant (cross cut 

bedding) in clastic sedimentary rocks of the Endicott Group 

that stratigraphically underlie the Kuna Formation (fig. 4.1 

and 4.2). These commonly occur as narrow mineralized veins 

or vein sets that are not laterally extensive at the surface. The 

relative proportions of sulfide minerals vary but the dominant 

sulfide mineral is sphalerite with lesser amounts of galena, 

pyrite, and chalcopyrite; quartz is the dominant gangue 

mineral. Textures range from host-rock breccias cemented by 

sulfides and quartz, to veins with color-banded and (or) crustiform sphalerite with lesser banded quartz, to complex breccias 

(fig. 4.3). 

Chemical and isotopic data, as well as absolute ages, 

were obtained for deposits in the Red Dog district. The 

following paragenesis is indicated: (1) deposition of minor 

sulfides with abundant barite immediately beneath the 

seafloor in unconsolidated mud—at Anarraaq, barite replaced 

shallow carbonate lenses; (2) subseafloor hydrothermal 

recrystallization and coarsening of pre-existing barite as a 

result of introduction of the main ore-bearing fluid; and (3) 

open-space deposition of barite and sulfides in veins and 

coeval replacement of barite—at Anarraaq, replacement of 

carbonate was the dominant process of sulfide deposition 

(Kelley, Dumoulin, and Jennings, 2004; Kelley, Leach, and 

others, 2004). 

Geochemical and isotopic characteristics suggest that the 

vein-breccia occurrences are the remnants of hydrothermal 

fluid flow in the clastic aquifer. These fluids ascended along 

faults and formed the overlying SHMS deposits (Young, 1989; 

Kelley and others, 2000; Ayuso and others, 2004). An alternative explanation is that the vein breccias formed along faults 

during the Mesozoic Brookian orogeny, as some vein zones 

parallel fold axes of anticlines (Ellersieck and others, 1982; 

Kurtak and others, 1995), and galena at the Vidlee occurrence 

shows curvature of crystal cleavages. However, other veins 

(for example, Kady) terminate at Mesozoic thrust faults (Werdon, 1999), and 40Ar/39Ar (argon) isotopic dating of recrystallized detrital white mica in sandstone adjacent to a mineralized 

quartz vein at Kady yields an age of 324 Ma (Werdon and others, 2004). In addition, lead isotope compositions of galenas 

from the vein breccias are within the range of compositions 

in the overlying shale-hosted sulfide deposits, suggesting that 

the lead in both types of deposits was derived from a similar 

or perhaps common crustal reservoir and are of similar age 

(Young, 1995; Ayuso and others, 2004; Werdon and others, 

2004). If the veins were significantly younger, radiogenic 

growth of lead would be reflected in the lead isotope ratios of 

galena from the vein breccias.

An absolute age for the SHMS deposits was determined 

by Re-Os (rhenium-osmium) isotopic methods to be 338.3 ± 

5.8 Ma (Morelli and others, 2004). This age overlaps the age 

of minor igneous rocks in the area (Werdon and others, 2004) 

and the age of the host rocks (Dumoulin and others, 2004). 

Based on similar stratigraphic positions, it is inferred that 

barite and phosphate formed coevally with the zinc deposits 

(Dumoulin and others, 2006). The stratigraphic and textural 

information, together with age data, suggest that the initiation 

of barite, phosphate, and zinc mineralization coincided with 

regional drowning of the outboard carbonate platform in Late 

Mississippian time, presumably as a result of extensional tectonism and subsidence along a passive continental margin.
10 Regional Fluid Flow and Basin Modeling in Northern Alaska

?

Zhar

100 METERS

STRATIGRAPHY

 Kanayut Conglomerate

(meandering and braided streams)

Noatak Sandstone

 (shallow marine)

 Hunt Fork Shale

(shallow to deep marine)

Endicott

 Group

Lisburne

 Group

Kayak Shale 

(shallow marine)

Etivluk

Group

DEVONIAN

 MISSISSIPPIAN

PENNSYLVANIAN

PERMIAN

 TRIASSIC

 JURASSIC

CRETACEOUS

 PERIOD

 Kuna Fm

 (deep marine)

Kogruk Fm (shallow marine)

Utukok Fm (shallow marine)

Siksikpuk Fm (mid-shelf or deeper)

Otuk Fm (mid-outer shelf)

Okpikruak Fm (flysch)

 Unnamed marble Baird

(shallow marine) Group Base not exposed

MINERAL DEPOSIT

OR OCCURRENCE

Barite

Stratiform

 massive

 sulfide

Vein or 

breccia

Anarraaq, Gull, 

Lakeview, Moil, 

Nimiuktuk, Red 

Dog, Su, Tuck, 

Wulik

Story Cr, 

Ginny Cr

Anarraaq,

Drenchwater,

Red Dog, Su-Lik, 

Ferric Cr, Wulik

Ahnoway, Hohum, Husky, 

Kady, Kivliktort,

Safari Cr, Ipnavik R, Whoopee

Cr, 

Vidlee,

Husky

shale/mudstone carbonate

shale, mudstone, chert

Figure 4.1. Stratigraphic column for the central Brooks Range showing locations of barite and sulfide mineral deposits 

(modified from Moore and others, 1994; Young, 2004). For locations of deposits, see figure 1.1.

anoxic; dysoxic

Kuna Formation black

 shale/mudstone

siltone, sandstone, conglomerate

barite

V

sulfide

V

V

V

carbonate turbidites

V

superimposed barite and sulfide sulfide and barite are

 separate

barite only sulfide only 

sulfide

Endicott Group siltstone, 

sandstone, or conglomerate

Siksikpuk Formation

red and green shales

oxic

V V V veins

towards carbonate platform

barite

sulfide

vein-breccias

# #

#

# #

#

# #

#

Figure 4.2. Schematic diagram illustrating relative stratigraphic positions of sulfide and barite deposits in northern 

Alaska. Some have superimposed barite and sulfide bodies (for example, Red Dog), some have barite and sulfides that 

are spatially separated (for example, Anarraaq), some are barite only (Moil, Gull), and some are sulfide only (Su-Lik, 

Drenchwater). Modified from Kelley and Jennings (2004).
4. Depositional Models for Barite and Zinc 11

Figure 4.3. Textures of ore types in 

northern Alaska. A, Vein ore from Red 

Dog. B, Banded ore from Anarraaq. 

Cream colored mineral is sphalerite. 

C, Typical vein breccia occurrence 

(Ahnoway) showing vein with adjacent 

breccia.

A

B

2 centimeters

2 centimeters

2 centimeters

C
12 Regional Fluid Flow and Basin Modeling in Northern Alaska

5. Insights into the Ore-Forming Fluids

By David L. Leach

Investigations of fluid inclusions can provide information on the composition, temperature, pressure, and possible 

sources of the hydrothermal fluids responsible for ore and 

gangue minerals. In a broader sense, this information contributes to a better understanding of why and where such giant 

deposits form in the Earth’s crust.

Fluid inclusions in ore-stage sphalerite and post-ore 

quartz gangue in the Red Dog deposits were analyzed (Leach 

and others, 2004). The temperatures of the fluids that deposited the vein sphalerite were probably less than 200°C and perhaps as low as 100°C. The maximum depth of sediment burial 

during mineralization was not greater than 200 m based on 

thickness of the Kuna Formation in the Red Dog area. Therefore, the presence of temperatures of 100 to < 200°C during 

ore deposition less than 200 m below the seawater-Kuna sediment interface requires locally high thermal gradients. 

The origin of these anomalously high temperatures at 

such shallow depths is equivocal. There is no direct evidence 

for major igneous intrusions in the vicinity of the Red Dog 

deposits other than the presence of volumetrically minor 

altered alkali basalt and rhyolite intrusions. The 40Ar/39Ar dates 

of biotite from the altered intrusions overlap a Re-Os date for 

ore-stage pyrite (338 ± 5 Ma) and the age of Kuna Formation 

sedimentation. The presence of a large intrusion below the ore 

deposits during ore deposition cannot be excluded because the 

ore deposits were displaced from their location during Mesozoic thrusting. A plausible source of local heating of the Kuna 

Formation at the Red Dog deposits is avecting hydrothermal 

fluids that acquired geothermal heat at considerable depth in 

the underlying rocks. Assuming normal thermal gradients of 

25 and 35°C per km, with ambient surface temperatures of 

15°C in the Carboniferous, a temperature of 100°C would 

have required fluid circulation to about 3.4 to 2.4 km and 

a temperature of 200°C would have required circulation to 

between 7.4 and 5.3 km. 

Final ice melting temperatures indicate that the fluid 

inclusions in sphalerite have salinities of about 14 to 19 wt 

percent NaCl equivalent. The fluid inclusion electrolyte data 

show that the ore fluid for the vein sphalerite derived its salinity from the evaporation of seawater and has a composition 

that is indistinguishable from evolved basin brines that formed 

Mississippi Valley-type (MVT) deposits (Leach and others, 

2005). The dissolution of evaporites is inconsistent with the 

composition of fluid inclusion electrolyte data. Considering 

the salinity of the vein sphalerite fluid inclusions together with 

the electrolyte data, the seawater evaporative brine was probably initially about 30 wt percent saline fluid and was diluted 

by seawater or meteoric water at some point in its flow path. 

There is evidence for an increasingly arid climate in northern 

Alaska during the Chesterian (Dumoulin and others, 2004; 

Young, 2004), a time that was coeval with the age of Red Dog 

mineralization (see fig. 2.2). The best chance for seawater 

evaporative environments close to the Red Dog deposits was 

in the shallow subtidal to supratidal facies of the Lisburne 

Group (Kogruk Formation) in the Wolverine Creek plate of the 

Endicott Mountains allochthon, located less than 50 to 75 km 

north of the ore deposits prior to Brookian thrusting (fig. 5.1).

The proximity of the Red Dog deposits to broadly coeval 

evaporative environments is consistent with models that call 

upon infiltration of reflux brines during the precipitation of 

MVT lead-zinc ores. 

Fluid inclusions were also studied in the abundant quartz 

that constitutes the majority of the silica rock in the ore 

deposits. This post ore quartz extensively replaced barite and 

was traditionally thought to be part of the main ore event. Primary fluid inclusion assemblages contain two-phase aqueous 

inclusions, single-phase inclusions of dense methane, or both. 

Primary assemblages that contain single-phase, dense methane 

inclusions together with two-phase aqueous inclusions yield 

consistent homogenization temperatures and provide unequivocal evidence for the coeval trapping of immiscible gas- and 

aqueous-rich fluids. The densities of the methane inclusions, 

together with the temperature of homogenization of coexisting 

aqueous fluid inclusions, show that these fluid inclusions were 

trapped between pressures of 800 and 3,400 bars and temperatures between 187 and 214°C. The pressures obtained provide 

unequivocal evidence that the quartz formed after ore deposition in the Carboniferous because such high fluid pressures 

could only have been produced from thrust loading during the 

Mesozoic Brookian orogeny. The observed large variation in 

pressure is best explained by transient fluid pressures from 

hydrostatic to lithostatic conditions during thrust loading. The 

3,400 bars pressure corresponds to about 12 km of lithostatic 

burial, whereas the lower pressure (800 bars) correspond to 

about 8 km of hydrostatic pressure. Because of their low salinity (0 to 5 wt percent NaCl equivalent) the electrolyte compositions of the quartz fluid inclusions do not constrain their 

origin(s).

This study provides the first direct fluid inclusion data on 

the origin of the ore fluids for deposits of this type and yields 

insights into the hydrothermal fluid processes that produced 

this world-class ore deposit. Furthermore, the data show that 

most of the silica present in the ore deposits is unrelated to 

the ore-forming event. Thus, the presence of silica in the host 

rocks cannot be used as a guide to mineralization. Perhaps the 

most important conclusion is that the ore fluid was an evolved 

basin brine that obtained its salinity through the evaporation 

of seawater. These brines were probably sourced by supratidal 

carbonate rocks of the Lisburne Group, infiltrated into the 
5. Insights into the Ore-Forming Fluids 13

underlying rocks of Endicott Group, and extracted metal from 

rock-water reactions within the sandstone and conglomerate 

aquifers or the underlying metasedimentary basement rocks 

(fig. 5.2). In the Red Dog area, the metalliferous fluids 

ascended into the organic-rich rocks of the Kuna Formation 

along zones of active extensional faults or breaches in the 

shale aquitards overlying the aquifers in Endicott Group. The 

mechanisms for ore deposition at the Red Dog deposits are 

not established but probably involved a combination of fluid 

mixing, fluid-rock reactions that include reduction of barite, or 

cooling. Studies show that brine infiltration from evaporative 

environments in carbonate platforms produces temperatures, 

flow rates, and duration of the reflux system sufficient to 

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Angayucham 

Ocean 

Tidal

Shallow Marine

Platform Carbonates

Old Crustal Block

Angayucham

Ocean

Old Crustal Block

Nuka arkose

N

Red Dog

Anoxic

shales

Oxic /Anoxic chert/shales

Sediment -sill

complex

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v 

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Angayucham 

Ocean 

Old Crustal Block

highlands

80 KILOMETERS

tidal

shallow marine

platform carbonates

Angayucham

Ocean

old crustal block

Nuka arkose

N fault

Red Dog

anoxic

shales

sediment-sill

complex

/anoxic chert/shales

oxic

projected axis of future

Sverdrup-Hannah basin

rapid

transgression 

Figure 5.1. Schematic paleogeography of the Red Dog area in Late Carboniferous (modified from 

Young, 2004). A possible source for the evaporatively concentrated seawater (brines) for the ore 

fluids was a sabkha-like environment north of Red Dog. The brines infiltrated fluvial-deltaic rocks 

and extracted metal from sandstone and conglomerates. The fluids ascended into organic-rich 

rocks of the Kuna Formation along zones of active extensional faults.

explain ore formation in the passive margin. Since the brine 

infiltration model calls upon a continued brine recharge into 

underlying rocks and aquifers, it could produce a protracted 

period of mineralization and potentially giant ore deposits 

such as the Red Dog deposits. The genesis of shale-hosted 

ores like the Red Dog deposits may be most favorable in 

siliciclastic-starved, shale and organic-rich passive margin 

sub-basins, that are flanked by carbonate platforms that 

contain evaporative sabka-like environments. Furthermore, 

the important carbonate turbidite fill in many passive margin 

settings that contain flanking carbonate platforms may also be 

an important control in localizing the ore into permeable and 

chemically reactive lithologies. 
14 Regional Fluid Flow and Basin Modeling in Northern Alaska

metal extraction

sabkha

Passive Continental Margin

Reflux brine model for SEDEX deposits

open marine environment evaporative basin

“brine factory”

100 KILOMETERS

5 km

temperature 100-200°C

replacement ore

brine discharge/ brine pool sea level

br ni i e ulf n x

dense hypersaline fluids

“dolomitization”

faults

SEDEX ORES organic-rich mudstone/shale

fluvial-deltaic clastic rocks and (or) basement

carbonate turbidites

calcareous shale

Figure 5.2. Reflux brine model for the shale-hosted massive sulfide deposits, northern Alaska.
6. Geochemical Indicators of Massive Sulfide Deposits and Vein Breccia Zn-Pb-Ag Occurrences 15

6. Geochemical Indicators of Massive 

Sulfide Deposits and Vein Breccia 

Zn-Pb-Ag Occurrences

By Garth E. Graham, Karen D. Kelley, and John F. 

Slack

Geochemical anomalies in regional stream sediment 

samples played a significant role in locating the Red Dog 

deposit (Tailleur, 1970) and other shale-hosted massive 

sulfide (SHMS) deposits in the Red Dog district, as well as 

the Drenchwater deposit (Jansons, 1982) and numerous vein 

breccia occurrences (Duttweiler, 1987; Meyer and Kurtak, 

1992; Kelley and others, 1997). However, the limited suite of 

elements determined and the relatively high detection limits 

of some analytical methods made it difficult to distinguish 

the SHMS deposits from the vein breccia occurrences by an 

evaluation of regional geochemical data. Furthermore, all of 

the deposits and occurrences listed above are at least partly 

exposed at the surface, and therefore, sulfide and gangue 

minerals were affected by surface weathering (mechanical and 

chemical) and oxidation processes. In these environments, 

elements such as lead (Pb) and zinc (Zn) behave in a predictable manner (that is, Pb is relatively immobile compared to 

Zn), allowing for a straightforward interpretation of the stream 

sediment data. In contrast, if the deposits are concealed, the 

mobility and transport of elements may differ, and elements 

other than Pb or Zn may be as good or better pathfinder elements for these deposits.

Using modern analytical techniques, geochemical studies 

were recently undertaken to (1) determine element associations that distinguish these two types of deposits, and (2) 

highlight pathfinder elements that have not traditionally been 

used to delineate SHMS-type deposits. These data allow us to 

assess the resource potential of an area with more certainty. 

Analyses of whole rock and stream sediment samples from 

SHMS and vein breccia occurrences show that both deposit 

types yield similar geochemical signatures with regard to most 

elements including zinc (Zn), lead (Pb), silver (Ag), arsenic 

(As), and antimony (Sb) (Slack, Kelley, and others, 2004; 

Graham and others, in press). Results show: (1) in addition to 

Pb and Zn, most mineralized samples from the SHMS deposits 

contain anomalously high concentrations of As (>40 to 672 

ppm), germanium (Ge; >2 to 823 ppm), Sb (>12 to 919 ppm), 

and thallium (Tl; >1.5 to 313 ppm); (2) Tl shows the greatest 

range in concentration and is consistently elevated in mineralized rocks and altered (but unmineralized) rocks adjacent to 

the SHMS deposits; and (3) geochemical differences between 

the two deposit types include low Tl (<0.7 ppm) and elevated 

copper (Cu; 260 to 2,450 ppm) and gold (Au; 200 to1,010 

ppb) in the vein breccia occurrences compared to the SHMS 

deposits (fig. 6.1). These differences provide a powerful means 

of distinguishing the SHMS from the vein breccia occurrences.

Geochemical data for sediment samples from streams 

draining the SHMS and vein breccia deposits mimic the 

whole-rock patterns described above. In particular, stream sediment samples from drainages near the SHMS deposits contain 

anomalously high concentrations of Tl (>1.3 ppm) compared 

to those near the vein breccia occurrences (approximately 0.5 

to 0.8 ppm). Soil samples collected over buried portions of 

the Su-Lik deposit also show elevated Tl directly over the ore 

body (Kelley and Kelley, 2003). 

Results of a stream sediment survey at Drenchwater 

show that uranium (U) and phosphorus (P) concentrations are 

anomalously high (7.1 to 18.1 ppm and 1,500 to 4,040 ppm, 

respectively) in some samples draining known mineralized 

areas (fig. 6.2). These elements, and mercury (Hg), molybdenum (Mo), and selenium (Se), are also elevated in soil samples 

at the Su-Lik deposit (Kelley and Kelley, 2003), suggesting 

that Tl, U, P, Hg, Mo, and Se may be additional pathfinder elements for SHMS deposits (Graham and others, in press).

The element associations that delineate the Drenchwater deposit are also characteristic of stream sediments from 

Twistem Creek and the Kiligwa River east of Drenchwater 

(fig. 6.2), as well as from Spike Creek, about 130 km west 

of Drenchwater. These data suggest that there is potential for 

additional undiscovered SHMS resources in these areas. 
16 Regional Fluid Flow and Basin Modeling in Northern Alaska

1

1

10

100

1,000

10,000

100,000

1,000,000

0.01 0.1 1 10 100 1,000

Thallium (Tl), in parts per million

Above threshold

10

100

1,000

10,000

100,000

1,000,000

0.1 1 10 100 1,000

Arsenic (As), in parts per million

Strongly

mineralized

Above threshold

0.01 0.1 1 10 100 1,000 10,000

Above threshold

Base metals

anomalous

Low base

metals

1 10 100

Germanium (Ge), in parts per million

C. D.

A.

Antimony (Sb), in parts per million

B.

Zinc (Zn) + Lead (Pb), in parts per million

0.1 1,000

Above threshold

Zinc (Zn) + Lead (Pb), in parts per million

Visually unaltered

Range of unmineralized samples 

Red Dog and Anarraaq Drenchwater Su-Lik Vein breccia

EXPLANATION

Figure 6.1. Whole rock geochemistry of mineralized, visually unaltered, and unmineralized samples in and 

around massive sulfide and vein-breccia deposits and occurrences. A, thallium; B, germanium; C, antimony; D, 

arsenic.
6. Geochemical Indicators of Massive Sulfide Deposits and Vein Breccia Zn-Pb-Ag Occurrences 17

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Eastern

Map

Area

Drenchwater Cr.

False Wager Cr.

Kiligwa R.

Twistem

Cr.

Drenchwater Cr.

Drenchwater Cr.

Drenchwater Cr.

False Wager Cr.

Twistem

Cr.

Twistem

Cr.

Twistem

Cr.

Kiligwa R.

Kiligwa R. Kiligwa R.

Eastern

Map

Area

Eastern

Map

Area

Eastern

Map

Area

False Wager Cr.

False Wager Cr.

A B

C D

Zn (ppm)

28–349

350–499

500–749

750–1,050

TI (ppm)

0.3–1.2

1.3–2.4

2.5–3.9

4.0–12.4

U (ppm)

1.1–4.9

5.0–6.9

7.0–11.9

12.0–18.1

P (ppm)

298–1,099

1,100–1,499

1,500–1,999

2,000–4,040

0 2 4 KILOMETERS

N

Figure 6.2. Shaded relief map of the Drenchwater area showing stream sediment geochemical anomalies. Purple 

shaded regions are outcrop areas of the Kuna Formation. Main sulfide outcrop is indicated; however, disseminated 

sulfides occur along northwest-southeast zone between Drenchwater and False Wager Creeks. A, Zinc (Zn) content 

in parts per million (ppm). B, Thallium (Tl) content in ppm. C, Phosphorus (P) content in ppm. 

D, Uranium (U) content in ppm.
18 Regional Fluid Flow and Basin Modeling in Northern Alaska

7. Sulfur and Oxygen Isotope Chemistry 

of Barite

By Craig A. Johnson

Barite deposits are numerous in northern Alaska (fig. 1.1) 

and many are associated with sulfide mineralization. In the 

Red Dog district, the sulfides are either intergrown with the 

barite (for example, Red Dog deposits) or they occur as separate bodies in stratigraphically underlying rocks (for example, 

the Anarraaq deposit, fig. 4.2). In the Howard Pass quadrangle 

of the central Brooks Range, sulfide mineralization has not 

been recognized intergrown with the barite deposits (fig. 

1.1), but whether or not separate sulfide bodies are concealed 

beneath the outcropping barite is unknown. Tools for determining the presence of underlying sulfides beneath the barite 

deposits would help assess the potential for concealed Zn-PbAg sulfide mineralization.

Johnson and others (2004) suggested that barite-only 

mineralization (that is, barite that has no associated sulfides) 

might be distinguished from barite associated with lead-zincsilver deposits by analyzing sulfur- and oxygen isotopes in the 

barite. Results are reported in δ notation, where δ = [(RSample/

RStandard) -1] x 1,000, and RSample and RStandard are the ratio 34S/32S 

or 18O/16O in sample and standard, respectively. Analyses from 

the Red Dog district suggest that a typical barite-only deposit 

(Anarraaq) shows tight δ18O vs. δ34S correlations extending 

from the isotopic composition of seawater sulfate in Mississippian time to very high δ-values. By contrast, barite associated with sulfide mineralization at the Red Dog mine shows a 

poorer δ18O vs. δ34S correlation with δ18O values that are equal 

to or below seawater sulfate (fig. 7.1A). 

Outcropping barite deposits of the Howard Pass 

quadrangle show fairly tight arrays on a δ18O vs. δ34S plot 

(fig. 7.1B). Linear regression slopes range from 1 to 5, much 

like the slopes that characterize Anarraaq and other barite-only 

deposits in the Red Dog district. The isotopic variations reflect 

barite precipitation from combinations of seawater sulfate, 

which had been isotopically enriched by bacterial sulfate 

reduction, and sulfate from reoxidation of the bacteriallyproduced H2

S.

The Howard Pass barites are compared with Red Dog 

district barite-zinc-lead-silver deposits and Red Dog bariteonly deposits in figure 7.1C. The Howard Pass barites differ 

from Red Dog district barite-only deposits in that they lack 

very high δ-values and show δ18O values equal to or less than 

the value for Mississippian seawater sulfate. Both observations 

suggest a closer affinity to sulfide-associated barite than to 

barite-only mineralization.

Histogram plots (fig. 7.2) show that the Howard 

Pass δ34S distribution resembles the distribution for Red Dog 

district barite-zinc-lead-silver deposits; most notably both lack 

very high δ34S values. However, the Howard Pass distribution 

is displaced to higher δ34S by about 3 per mil. If the Howard 

Pass and Red Dog mineralizations formed simultaneously, as 

the stratigraphic correlations imply, then the δ34S difference 

implies that Howard Pass barite formed in a basin that was 

isolated from the larger Mississippian basin, or that the Red 

Dog and Howard Pass deposits formed in different isolated 

basins. 

Barite associated with Red Dog district Zn-Pb-Ag deposits formed where seawater sulfate was bacterially reduced and 

then reoxidized at a rate that was fast compared to the rate of 

supply of fresh sulfate. This condition would be consistent 

with stagnant basin waters. Stagnation favors anoxia, which 

can ultimately lead to the accumulation of H2S, an essential 

ingredient for the formation of Zn-Pb-Ag sulfide mineralization. Thus, the sulfur and oxygen isotope data for the Howard 

Pass barite occurrences record conditions that would have 

been favorable for the later formation of zinc-lead-silver s

ulfide deposits, and the preservation of these deposits in the 

rock record. The other essential ingredient for sulfide deposits 

is a supply of metals. Whether zinc, lead, silver, and other 

metals were available during formation of the Howard Pass 

barite is a question on which the stable isotope data have no 

direct bearing. 
7. Sulfur and Oxygen Isotope Chemistry of Barite 19

Anarraaq

massive &

laminated

Seawater sulfate in

Mississippian time

Anarraaq

nodules

Red DogAqqaluk

0

10

20

30

40

50

60

5 10 15 20 25 30

15

20

25

30

35

40

10 12 14 16 18 20

Longview Lakeview

Drenchwater

Abby

Tuck

Bion

Stack

Ekakevik

Seawater sulfate in

Mississippian time

0

10

20

30

40

50

60

5 10 15 20 25 30

Howard Pass barites

Seawater sulfate in

Mississippian time

A

B

C

 O18

δ O 18

 O18

 S34  S34  S 34

Longview

Abby

Stack

Drenchwater

Ekakevik

Tuck

Bion

Lakeview

DEPOSIT

Red Dog district barite only

Red Dog district barite-sulfide

Figure 7.1. Plots of oxygen (O) versus sulfur (S) isotope compositions for Red Dog and central Brooks Range barite 

deposits (modified from Johnson and others, 2004). A, Barite from a representative lead-zinc-silver deposit (Red DogAqqaluk) and a representative barite-only deposit (Anarraaq) of the Red Dog district. B, Barite from several deposits 

in the Howard Pass quadrangle, central Brooks Range. C, Comparison of Howard Pass barite deposits and Red Dog 

district barites (including barite-sulfide deposits at Red Dog-Aqqaluk and barite-only deposits in the district).

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

0

2

4

6

8

0 5 10 15 20 25 30 35 40 45 50 55 60

No. of barite samples No. of barite samples

 S34

Seawater 

 sulfate Howard Pass

Seawater 

 sulfate Red Dog barite-zinc-leadsilver (Zn-Pb-Ag) deposits

 S34

Red Dog barite

 deposits

Seawater 

 sulfate

No. of barite samples

 S34

Figure 7.2. Histograms of sulfur (S) isotope compositions for 

barite samples from Red Dog and the central Brooks Range, 

comparing barite-only to barite associated with sulfides.
20 Regional Fluid Flow and Basin Modeling in Northern Alaska

8. Radiogenic Isotope Studies

By Robert A. Ayuso

Radiogenic isotope information (for example, lead and 

strontium isotopes), can be used to evaluate the contributions 

of metal sources (ranging from sedimentary to magmatic 

rocks) and regional fluid flow processes that control metal 

transport and precipitation. Lead (Pb) and strontium (Sr) 

isotope data also provide essential insights into the age of 

mineralization and post-mineralization disturbances.

Lead isotope data were obtained on sulfide minerals 

from the shale-hosted Zn-Pb-Ag Red Dog deposits (Qanaiyaq, 

Main, Aqqaluk, and Paalaaq), other shale-hosted deposits 

near Red Dog, and Zn-Pb-Ag sulfide deposits from the central 

Brooks Range (fig. 8.1). Galena from the main mineralization 

stages in the Red Dog deposits and from the Anarraaq and 

Wulik deposits define a narrow field on standard Pb isotope 

diagrams and they display overlapping Pb isotope compositions (Ayuso and others, 2004). Lead in sulfides of the Red 

Dog district is less radiogenic (lower values of 206Pb/204Pb, 207Pb/204Pb or 208Pb/204Pb) than the average crustal lead evolution model, consistent with a long history of evolution prior 

to the Carboniferous. The overall lead isotope homogeneity in 

the shale-hosted massive sulfide deposits is consistent with a 

homogeneous regional source, with mixing of lead during the 

leaching of a thick sedimentary section and fluid transport, 

and (or) with mixing at the site of deposition. The homogenous compositions indicate that galena deposition resulted 

from largely similar hydrothermal solutions throughout the 

western and central Brooks Range, suggesting a flow system 

that operated at an unusually large scale (many hundreds of 

kilometers). Younger and genetically unrelated fluids did not 

significantly disturb the isotopic compositions of galena and 

sphalerite after the main mineralization event in the Red Dog 

district. 

Strontium isotope data for barite associated with sulfide 

mineralization (for example, the Red Dog deposits) were 

compared with data from sulfide-poor barite occurrences, 

both in the Red Dog district and the central Brooks Range 

(Ayuso and others, 2004). Fluids with heterogeneous Sr 

isotope signatures are indicated in figure 8.2. Barite from 

the Main deposit extends to higher values of 87Sr/86Sr 

(0.709034–0.709899) than barite from the Anarraaq deposit 

(0.708615–0.709256). All barite is more radiogenic than 

Carboniferous seawater. Other Mississippian (?) shale-hosted 

deposits and mineral occurrences containing barite in the 

Red Dog district and barite from regional occurrences east of 

Red Dog in the western and central Brooks Range also have 

heterogeneous 87Sr/86Sr ratios. The compositions of barite from 

the central Brooks Range (Howard Pass quadrangle) overlap 

Carboniferous seawater, at least in part. The variations in Sr 

isotope compositions in barite from deposits and occurrences 

in the Red Dog district and elsewhere in the Brooks Range 

indicate that no single fluid was responsible for their isotopic 

signature. 

The Sr isotope data do not show compelling differences 

between textural varieties of barite (coarse-grained versus 

fine-grained). Higher values of 87Sr/86Sr in barite from the Red 

Dog deposits, compared to massive barite at Anarraaq (and 

other barites that are sulfide-poor) that is not directly associated with massive sulfides, probably reflects the interaction 

between the former and metal-bearing hydrothermal fluid. 

Therefore, values of 87Sr/86Sr in barite may provide a means 

of distinguishing sulfide-associated barite (high values) from 

sulfide-poor barite (low values). 

38.6

37.8

38.2

39

208Pb/204Pb

206Pb/204Pb

Shale hosted massive 

 sulfide deposits

Galena

 field

Sphalerite

Pyrite

Chalcopyrite

Galena

17 18 19 20

Average crustal

 Pb 500 Ma

Figure 8.1. Lead (Pb) isotope diagram for sulfides from 

Red Dog and from the Brooks Range. Average crustal lead 

evolution curve is from Stacey and Kramers (1975).
8. Radiogenic Isotope Studies 21

0.709 

0.707 

Suds

Shear Creek

Other deposits in the Red Dog district Red Dog

Su

Moil

Gull

Wul

87 86 Sr/ Sr (barite) Deadlock

 Mtn.

0.711 

Kivliktort

Tuck

Lakeview

Regional (Howard Pass quadrangle)

Zhar

Carboniferous seawater Triassic 

seawater

Devonian seawater

Permian to Triassic seawater

(clastic-hosted)

Anarraaq

(lenses & veins)

Carboniferous seawater

Evolved Crustal Rocks/Sediments

Seawater Sr Reservoir

More Radiogenic Sr Reservoir

Longview Stack Bion

Stratiform barite

0.711 

0.709 

0.707 

Ekakevik

Abby Creek

Limestone, Howard Pass

Figure 8.2. Initial strontium (Sr) isotope ratios of barite from the Red Dog deposits, Anarraaq, and other deposits or occurrences in the Red Dog district, and from regional deposits or occurrences east of Red Dog in the western and central Brooks Range. The plot shows Sr isotope compositions of barite from the Red Dog district: Su, Gull, Wul, Suds, Moil, Deadlock Mountain (assumed to be Carboniferous), Shear Creek (hosted in the Middle Jurassic to Lower Triassic Otuk Formation), and various regional occurrences east of Red Dog in the Howard Pass quadrangle, including the Mississippian barite deposits, and barite from Kivliktort (Devonian?), Tuck and Lakeview (Pennsylvanian?), and Zhar (Permian to Triassic). Estimated Carboniferous seawater Sr is shown for reference (Veizer and others, 1999).
22 Regional Fluid Flow and Basin Modeling in Northern Alaska

9. Phosphatic Rocks of the Lisburne 

Group

By Julie A. Dumoulin and John F. Slack

Phosphatic rocks are a small but notable part of the 

Lisburne Group (Permian- Carboniferous), a chiefly carbonate platform succession found in outcrop and in the subsurface 

throughout northern Alaska. New sedimentologic, paleontologic, and geochemical data better define the geographic and 

stratigraphic extent of these strata and support tectonic and 

paleogeographic reconstructions (Dumoulin and others, 2006).

Most Lisburne phosphorites are located in a discontinuous outcrop belt that extends for 265 km through the westcentral Brooks Range (fig. 1.1), but similar phosphatic rocks 

also occur in the western Brooks Range and in the subsurface 

in the Ikpikpuk well north of the Brooks Range. Fossils indicate an age of Late Mississippian (mainly early Chesterian) 

for Lisburne phosphatic rocks in all of these areas. Phosphatic 

strata are interbedded with black shale and lime mudstone rich 

in radiolarians and sponge spicules; they formed largely in 

poorly oxygenated outer ramp to slope settings.

Where best developed in the central Brooks Range east 

of the National Petroleum Reserve-Alaska (NPRA), Lisburne 

phosphorites occur as 2- to 40-cm-thick beds of sand-sized 

phosphatic grains cemented by carbonate or silica (fig. 9.1). 

These beds cap sequences of shale and lime mudstone and 

occur through an interval ≤12 m thick. High gamma ray 

response through the phosphatic interval indicates strongly 

condensed facies, likely related to low sediment input and 

hardground development. 

Lisburne phosphorites contain up to 37 wt percent P2O5, 

8.6 wt percent F (fluorine), and 162 ppm U (uranium) but 

their resource potential is limited by relatively low cumulative 

thickness and discontinuous distribution. Interbedded black 

shales have up to 20 wt percent TOC (total organic carbon), 

are potential petroleum source rocks, and typically overlie 

Lisburne dolostone intervals that contain as much as 13 percent vuggy and intercrystalline porosity. These shales are also 

locally metalliferous with up to 1,690 ppm chromium (Cr), 

1,870 ppm vanadium (V), 461 ppm nickel (Ni), 4,670 ppm 

zinc (Zn), and 32 ppm silver (Ag). This geochemical signature 

in the Lisburne phosphatic black shales is similar to that of 

the Nick Ni-Zn-Mo-PGE deposit in Yukon Territory, Canada 

(Hulbert and others, 1992), and the Tian’eshan Ni-Mo-PGE 

deposit in southern China (Coveney and others, 1992). 

Paleogeographic reconstructions of northern Alaska 

imply that Lisburne phosphorites formed in the Ikpikpuk basin 

and along both sides of the mud-rich Kuna basin (fig. 9.2), 

which hosts giant massive sulfide and barite deposits of the 

Red Dog district. Lisburne phosphatic strata are coeval with 

these deposits and formed as part of a nutrient-rich upwelling 

regime. The high productivity characteristic of this regime was 

an important influence on metallogenesis in the Red Dog district, and likely contributed (through nutrification) to the Late 

Mississippian drowning of carbonate platform environments 

throughout the southern NPRA.
9. Phosphatic Rocks of the Lisburne Group 23

A

B C

3 CENTIMETERS

Black shale and phosphorite unit

platform facies of Lisburne Group

Figure 9.1. Outcrop and hand sample photographs of 

phosphorite occurrences in northern Alaska. A, Black 

shale and phosphorite occurs discontinuously above 

platform facies of the Lisburne Group (white rocks to 

right) at the Lisburne Hills occurrence. B, Phosphatic 

rudstone overlain by calcareous radiolarite near the 

Skimo Creek occurrence. C, Phosphatic rudstone 

(phosphate is bright blue in color) from the Skimo Creek 

occurrence.
24 Regional Fluid Flow and Basin Modeling in Northern Alaska

?

+

+

Earliest Chesterian Time

Meade

basin Ikpikpuk-Umiat

basin

Itkilyariak

Akmalik

Nuka

Kuna

basin

Kelly

Platform

(Kogruk)

Lithofacies and Depositional Settings

Nonmarine to shallow-marine

siliciclastic strata

Shallow-water carbonate strata

Deeper water carbonate, shale

and chert

Deep-water chert, lesser shale

and carbonate

Coeval occurrences of phosphatic strata in 

Lisburne Group

RED DOG

DRENCHWATER

200 KILOMETERS

Figure 9.2. Palinspastic restoration of northern Alaska showing location of 

phosphatic strata surrounding the Kuna basin.
10. Metalliferous Tasmanite and Oil Shale 25

10. Metalliferous Tasmanite and 

Oil Shale

By Erin E. Marsh, Julie A. Dumoulin, Karen D. Kelley, 

and John F. Slack

Occurrences of oil shale in the Brooks Range were first 

reported in the literature in the late 1800s. The early explorers commented on the use of this material by natives for fuel. 

Outcroppings were first described by Smith and Mertie (1930) 

from exposures along the Kiligwa River. In the 1950s and 

1960s, Irv Tailleur (USGS) visited and resampled many of the 

sites during studies in the National Petroleum Reserve-Alaska 

(NPRA). Tourtelot and Tailleur (1966) reported exceptionally large oil yields of 146 and 144 gallons per ton from two 

samples of organic-rich shale. Other samples yielded about 25 

to 50 gallons of oil per ton. In addition, semiquantitative spectrographic analyses of some samples indicated that vanadium 

(V), zinc (Zn), and molybdenum (Mo), as well as gold (Au), 

silver (Ag), arsenic (As), nickel (Ni), and mercury (Hg) were 

present in high concentrations compared to other oil shales.

In order to put the oil shales into a modern stratigraphic 

and structural context and to evaluate earlier reports of high 

metal contents, five of the oil shale localities in the Howard 

Pass quadrangle were visited (fig. 10.1). Samples were collected for petrography and selected samples were submitted 

for geochemical analyses using modern techniques. 

Two types of oil shale in northern Alaska (fig. 10.2) are 

tasmanite (made up of algal material) and black oil shale (rich 

in various forms of organic matter). The fossil of unicellular 

marine algae, Tasmanites, has been observed interspersed in 

basinal sediments in many localities worldwide. In a few locations, deposition of massive concentrations of these organisms 

has formed an oil shale consisting almost entirely of telalginite 

derived from Tasmanites (Cook and Sherwood, 1991). 

Although noted in several locations (Sweden, Sahara, 

Alaska, Brazil), the tasmanite deposits in Tasmania are the 

most well-known. In Alaska, tasmanite occurs not only in the 

Brooks Range but also in the Yukon Flats area, although the 

characteristics and extent of these oil shale lenses have yet to 

be determined (Lillis and Stanley, 2005).

The tasmanite in northern Alaska is pale yellowish-brown 

in outcrop, and on freshly broken, unweathered surfaces has 

a dark reddish-brown resinous luster and a woody appearance (fig. 10.2B, C). In thin sections it consists of a mass of 

flattened Tasmanites spores that contain minor barite. The tasmanite is intercalated with white layers that consist of silicafilled (and partly replaced) flattened and unflattened Tasmanites spores. The tasmanite typically includes pyrite nodules (as 

much as 0.5 cm in diameter) that are sporadically distributed. 

The pyrite appears to have formed on or near the surface as the 

spores were deposited. The tasmanite beds are associated with 

radiolarian chert; at one location, tasmanite overlies chert of 

Late Mississippian-Permian age. Some tasmanite samples are 

so oil-rich that they can burn (fig. 10.2D).

Black oil shale in outcrop has a low density; therefore, 

it is very lightweight. In thin section it consists of orange-red 

organic material with disseminated quartz silt. Pyrite typically 

occurs as discontinuous thin (as much as 3 cm thick) lenses 

intergrown with gray shale (fig10.2A). Similar to tasmanite, 

the oil shales are associated with radiolarian chert of unknown 

age.

The pyrite separates are generally low in most metals; 

exceptions include high concentrations of As (2,460 ppm) and 

Ni (290 ppm) in pyrite from tasmanite. High metal concentrations in whole-rock samples of oil shale reported previously 

(Tourtelot and Tailleur, 1966) were largely confirmed by our 

recent data, with a few exceptions. Our samples collected 

in 2005 contain high Cu (copper; as much as 800 ppm), Hg 

(2,410 ppb), Mo (340 ppm), Ni (410 ppm), Se (selenium; 

100 ppm), and V (6,760 ppm). High concentrations of Au and 

Zn reported in previous studies (maximum values of 150 ppb 

and 7,000 ppm, respectively) were not observed in either the 

tasmanite or black shale samples. 

A comparison of Alaskan oil shale samples with other 

organic-rich and oil shale localities (table 10.1) suggests 

some similarities. Some organic-rich (12 to 25 wt percent 

organic carbon) portions of the Devonian-Mississippian New 

Albany Shale in southern Indiana are enriched in cadmium 

(Cd; 130 ppm), copper (Cu; 177 ppm), lead (Pb; 795 ppm), 

molybdenum (Mo; 562 ppm), nickel (Ni; 498 ppm), vanadium (V; 3,200 ppm), and zinc (Zn; 9,725 ppm) (Ripley and 

others, 1990); and the Pennsylvanian-age Mecca Quarry 

Shale and Logan Quarry Shale from Illinois and Indiana, 

respectively, contain enriched concentrations of Mo (1,600 

ppm), Se (400 ppm), U (240 ppm), V (10,100 ppm), and Zn 

(14,300 ppm) (Coveney and Martin, 1983). Known metalliferous oil shales include Devonian kerogenous marine strata in 

central Nevada, which contain anomalously high concentrations of Mo (960 ppm), Se (200 ppm), V (3,200 ppm), and Zn 

(18,000 ppm) (Desborough and others, 1979). 
26 Regional Fluid Flow and Basin Modeling in Northern Alaska _[_[ _[ _[ _[

_[

158°30’W 158°W 157°30’W 157°W 156°30’W

68°45’N68°30’N

68°45’N68°30’N

157°W

159°W

159°W 158°30’W 158°W 157°30’W

0 2.5 5 10

KILOMETERS

EXPLANATION

Colville basin foredeep depositsEndicott Mountains allochthonPicnic Creek allochthonIpnavik River allochthonNuka Ridge allochthonCopter Peak allochthonMisheguk Mountain allochthonthrust faultsTailleur oil shale locations

1113 14

16

19

N

Figure 10.1. Shaded relief map of the Howard Pass quadrangle showing locations of oil shale and tasmanites sampled during 2005 (from Tourtelot and Tailleur, 1966). Also shown is the distribution of structural sequences or allochthons (from Dover and others, 2004).
10. Metalliferous Tasmanite and Oil Shale 27

A 

chert 

white tasmanite

brown tasmanite

A B

C D

Figure 10.2. Outcrop photographs of oil shale 

occurrences. A, Oil shale site no. 11: pyrite 

lens in black shale. B, Tasmanite site no. 14: 

tasmanite contains pyrite nodules. C, Tasmanite 

site no. 14: tasmanite (brown material at top) is 

intercalated with white layers that consist of 

silica in tasmanite. Pyrite nodules occur in the 

brown tasmanite. D, Tasmanite is so oil-rich it 

can burn. For site locations, see figure 10.1.

Table 10.1. Metal concentrations in black oil shale and 

tasmanite from northern Alaska compared to other metalliferous 

organic-rich black shale and oil shale localities. All values in 

parts per million (ppm) except Hg which is in parts per billion 

(ppb). Values listed represent maximum concentrations reported 

in literature. [nd., no data reported. See glossary of terms for 

names of elements (symbols only shown in table)]

Elements

Northern 

Alaska

New Albany 

Shale

Mecca Quarry/

Logan Quarry Nevada

Cd 90 130 nd nd

Cu 800 177 500 nd

Hg 2,410 nd nd nd

Ni 410 498 nd nd

Mo 340 562 1,600 960

Pb 60 795 500 nd

Se 100 nd 400 200

U 70 nd 240 nd

V 6,760 3,200 10,100 3,200

Zn 940 9,725 14,300 18,000
28 Regional Fluid Flow and Basin Modeling in Northern Alaska

11. Preliminary Retrodeformable 

Regional Cross Section, Western 

Brooks Range

By Thomas E. Moore and Christopher J. Potter

The western Brooks Range is a northwest-directed 

foreland fold-and-thrust belt. The Zn-Pb-Ag mineral deposits 

are located in Mississippian basinal rocks that were displaced 

by large-magnitude thrust faults into allochthonous structural 

positions in the Cretaceous and Tertiary (Mull, 1982; Moore 

and others, 1986; Mayfield and others, 1988). A preliminary 

retrodeformational cross section from the Kugururok River 

in the axial part of the Brooks Range to Tupikchak Creek in 

the deformed part of its foreland basin (fig. 11.1) has been 

constructed (Moore and Potter, in press). This cross section 

provides a better understanding of the geologic context of 

the deposits at the time of ore formation, an estimate of the 

amount of crustal shortening that has taken place in the Brooks 

Range, and an opportunity to test the viability of deformational models that call for multiple episodes of deformation in 

the Brooks Range as recently proposed by Moore and others 

(2004). It also provides a mechanism for reconstructing the 

depositional extent of the Mississippian basin that hosted the 

Red Dog massive sulfide deposits and for determining the 

nature of aquifers that served as conduits for hydrothermal 

fluids.

The top of the cross section (fig. 11.2) depicts the 

exposed geology as presently known along the northwest 

trending line of section. Rocks in the section are interpreted 

to compose parts of a south-facing Mississippian to Jurassic 

passive margin that were imbricated by north-directed thrusting during the Brookian orogeny (Moore and others, 1994). 

The structurally lowest and originally the most proximal part 

of the passive margin succession is the autochthon, which 

underlies the North Slope and is interpreted as undeformed 

and gently southward dipping at depths of more than 9 km in 

the cross section. The 2- to 5-km-thick Endicott Mountains 

allochthon, which is divided into Wolverine Creek, Red Dog, 

and Key Creek plates, overlies the autochthon on a regional 

flat thrust developed in Jurassic and Lower Cretaceous strata 

of the autochthon. The most distal parts of the passive margin 

succession are represented by the Kelly River allochthon, a 

tabular structural unit exposed in klippen near the crest of the 

Brooks Range, and the Ipnavik River allochthon, which is 

present only in the southern part of the cross section. These 

allochthons were also emplaced on flat thrusts developed 

in Jurassic strata early during the period of thrusting but 

have been further deformed by younger faults and folds that 

developed after the allochthons were emplaced. The structurally highest rocks of the Brooks Range orogen are klippen of 

igneous rocks that represent the uppermost plate of the orogen, 

beneath which the passive margin was thrust. The Picnic 

Creek allochthon of Mayfield and others (1988) is not present in our line of section and here is regarded to compose part 

of the Key Creek plate of the Endicott Mountains allochthon 

because (1) it is laterally discontinuous in the western Brooks 

Range, and (2) its lithostratigraphy and environments of deposition are similar to those in the Key Creek plate (Dumoulin 

and others, 2004).

Foreland basin deposits are the deposits that were shed 

from the developing mountain belt and are thickest in the 

northern part of the cross section. There, they are mainly 

Aptian to Cenomanian and display relatively simple stratigraphy where deposited on the autochthon. Farther south where 

deposited on allochthonous rocks, foreland basin deposits 

have less certain stratigraphy and age relations because of 

their involvement in complex folds and thrusts associated with 

emplacement of the allochthons. In these areas, the foreland 

basin deposits are latest Jurassic and Neocomian.

Internal thrusting within stratigraphic sequences of the 

allochthons resulted in structural repetition of strata between 

less deformed overlying and underlying strata (duplexes). This 

type of deformation notably affected the host strata for the Red 

Dog mineral deposits, which are located in the Red Dog plate 

of the Endicott Mountains allochthon.

The thrusts at the base of the allochthons are interpreted 

to have originally formed as flat bedding plane thrusts in 

Devonian strata that cut upward to the north, resulting in 

emplacement of the allochthons onto Jurassic and Lower 

Cretaceous strata on adjacent parts of the passive margin. 

Thrusts cut upward into overlying strata progressively through 

time, imbricating units within the allochthons, including the 

duplexes that host the Red Dog mineral deposit. Worldwide, 

flat thrusts and duplexes with large amounts of displacement 

and allochthons with thin stratigraphic thicknesses such as 

those seen in the western Brooks Range are ascribed to thinskinned style thrusting.

Moore and others (2004) proposed that the latest Jurassic 

and Early Cretaceous thin-skinned thrust belt was redeformed 

by a completely separate system of thrusts active in the Early 

Tertiary. This younger system of thrusts deformed a thick 

structural section consisting of the earlier formed stack of 

allochthons, duplexes, and accompanying foreland basin sediments from the earlier deformation. The younger thrusts truncated the earlier generation of thrusts and caused significant 

uplift in the Brooks Range, but produced much less displacement than that seen in the latest Jurassic and Early Cretaceous 

deformational belt. Nonetheless, the later generation of thrusts 

produced some of the most conspicuous folds and faults in the 

young, thick, and previously undeformed parts of the foreland 
11. Preliminary Retrodeformable Regional Cross Section, Western Brooks Range 29

basin. The Early Tertiary deformation produced wide-spaced 

detachment folds in the foothills of the northern Brooks Range 

and, farther south, truncated the Cretaceous thrusts on broadly 

spaced north-directed reverse faults. In addition to these types 

of structures, normal faults were observed along which higher 

allochthons in the orogen were dropped down to the southeast 

and juxtaposed against the Endicott Mountains allochthon. 

Such normal faults are present in the southern part of the cross 

section. The age and cause of the normal faulting are uncertain but the faults are interpreted here to be the northernmost 

faults of the regionally extensive belt of middle Cretaceous 

down-to-the-south extensional deformation in the southern 

Brooks Range (see, for example, Miller and Hudson, 1991). 

Despite differences in their depth of burial at the time of the 

various deformations, the contractional deformations utilized 

the Jurassic and Lower Cretaceous Kingak Shale at the top of 

the autochthon as their primary detachment horizon under the 

northern Brooks Range.

The cross section presented in figure 11.2 is a regional 

section designed to be kinematically retrodeformable, such 

that faults and folds can be sequentially restored to plausible 

pre-deformational stratigraphic locations without significant 

volume changes, crossing faults or other geometric impossibilities. This restoration must be done successively for each 

of the three deformations. A simple cut-and-paste balancing 

of line lengths and areas of the section allows calculations of 

the approximate amount and percent shortening on a regional 

basis. However, the section is not rigorously balanced and 

errors of as much as 20 percent are possible. Duplexes of 

stratigraphic units (for example, Endicott Group, Lisburne 

Group) within some allochthons are illustrated with form 

lines, but no attempt has been made to retrodeform these 

structures. The qualitative section is useful for testing whether 

the structural hypothesis is plausible and suitable for a more 

detailed analysis and modeling. For this reason, the model is 

regarded as approximate and preliminary.

Retrodeformation of the cross section indicates that a 

multi-deformational structural history consisting of (1) thinskinned deformation in the early Cretaceous, (2) extensional 

faulting in the mid-Cretaceous, and (3) thin- to thick-skinned 

deformation in the Early Tertiary is a viable model of deformation for western Brooks Range structures. This qualitative 

restoration suggests shortening on the Early Tertiary structures 

totals about 35 km and about 30 percent shortening over the 

length of the cross section. Shortening during the latest Jurassic and Early Cretaceous deformational event is significantly 

higher, representing about 200 km of shortening. Estimates 

of the total shortening in the Brooks Range range from 500 to 

800 km (Oldow and others, 1987; Mayfield and others, 1988), 

but some workers have argued for much lower amounts of 

total shortening (see, for example, Kelley and Brosgé, 1995). 

Our estimate of shortening in this paper, however, is only for 

the northern Brooks Range and therefore represents only part 

of the total shortening for the Brooks Range. Restoration of 

the Red Dog plate indicates that the Red Dog mineral deposits 

probably formed stratigraphically above the Endicott Group 

but the precise location to which the host strata should be 

restored is poorly constrained because of the complexities of 

restoring the duplexes, especially those that contain the Red 

Dog massive sulfide deposits.

Key assumptions involved in the construction of the 

section include (1) the autochthon is undeformed and (2) the 

Wolverine Creek plate of the Endicott Mountains allochthon 

is thick and extensive at a depth of about 4–10 km in the cross 

section. This cross section interpretation also awaits analysis 

of thermal maturity and thermochronologic data currently in 

progress. Additional information bearing on these and other 

assumptions could support alternative structural models, and 

are the focus of future studies.
30 Regional Fluid Flow and Basin Modeling in Northern Alaska

Cre e k

le ga E

Red Dog

mine

ult fa k. h C nc Wre

eg id R

le ib ss ce ac In

x

x

x

x

x

x

x

x

Mountain F ront

X

X‘

0 10 20

Nanushuk Formation

Cenozoic deposits

Torok Formation

Fortress Mountain Formation

Okpikruak Formation

Misheguk Mtn. and Copter Peak 

allochthons

Ipnavik River allochthon

Kelly River allochthon

Undivided

Key Creek plate

Red Dog plate

Wolverine Creek plate

161° 162° 161° 30’ 69°

68°

KILOMETERS

NATIONAL

PETROLEUM

RESERVE–

ALASKA

AVAN HILLS

Sivukat

Mtn. fault

Sheep Mtn. Amphitheatre

Mtn.

RED DOG

DISTRICT

Chevron Hill

Tingmerkpuk Mtn.

Eagle Creek

well

Poko Mtn.

Igloo Mtn.

Tupikchak

 Mtn.

Tupikchak Creek

Avan River

Kugururok

River

Deadlock Mtn.

Wrench Creek

Kelly

River

Tingmerkpuk

River

Kokolik

River

Surprise Creek

Continental Divide

Red Dog district boundary

National Petroleum Reserve boundary

Syncline

Anticline

Thrust fault, teeth on upper plate

Normal fault, teeth on hanging wall

Contact

Shublik Formation

(parautochthonous)

AlbianCenom. Albian- Cenom. Albian- Aptian

L. Jur.

and

E. Cret.

Dev.-

Jur.

Miss.-

E. Cret.

MissE. Cret. Miss.- E. Cret. L. Dev.- E. Cret. Miss.- E. Cret. Miss.- E. Cret. Triassic

Endicott Mountains allochthon

EXPLANATION

Figure 11.1. Map showing major structures and structural units and location of cross section. Okpikruak Formation 

not shown south of the Continental Divide, except near the Kugururok River. Picnic Creek allochthon included 

with Endicott Mountains allochthon and Nuka Ridge allochthon included with Ipnavik River allochthon. Sources of 

data: Curtis and others (1984, 1990), Ellersieck and others (1990), De Vera and others (2004), and C.G. Mull (written 

commun., 2006). Cross section X-X’ shown on figure 11.2.
11. Preliminary Retrodeformable Regional Cross Section, Western Brooks Range 31 Ko Continental Divide Tingmerkpuk Mountain

0

below

2468

10

02468

10

0246810

NORTH SLOPE 

FORELAND BASIN 

DEPOSITS

Symbols

Ellesmerian sequence

Bend Bend

Pre-Mississippian basement

No vertical exaggeration

Autochthon Endicott Mountains

allochthon

Kelly River

allochthon

Ipnavik River

allochthon

Misheguk Mountain

and Copter Peak 

allochthons, undivided)

Ellesmerian Sequence(Mississippian-Triassic)

Fortress Mountain Formation(Albian)Okpikruak Formation (Neocomian)Kingak Shale(Jurassic-Neocomian)

Okpikruak Formation (Neocomian)Etivluk Group (Permian-Jurassic) andTingmerkpuk sandstone (Neocomian)Endicott Group (Devonian-Lower Mississippian)

Okpikruak Formation (Neocomian) Okpikruak Formation (Neocomian)

Cretaceous thrust fault Contact

Form line

Tertiary thrust faultNormal fault

Etivluk Group (Permian-Jurassic)and Lisburne Group (MississippianPennsylvanian), undivided

Okpikruik Formation(Jurassic-Neocomian)Ophiolite (Middle Jurassic)and associated maficigneous rocks

Etivluk Group (Permian-Jurassic)Lisburne Group (Mississippian and Pennsylvanian)

Lisburne Group (Mississippian and Pennsylvanian)

Baird Group (Devonian)

Fortress Mountain Formation (Albian)

Torok Shale (Albian)Nanushuk Formation(Albian-Cenomanian)Pre-Mississippian basement

Kugururok River Avan Hills

Kelly River Inaccessible Ridge Mountain

 front

Eagle Creek

well

Tupikchak

Creek

North

A.

South

B.

COLVILLE BASIN BROOKS RANGE

Foreland basin

Autochthon

Wolverine Creek plate

Wolverine Creek plate

Key Creek plate

Red Dog plate

Kelly River alloc.

Kelly River alloc.

Key Creek plate

Ipnavik River alloc.

Misheguk Mtn. & Copter Pk. allocs.

0246810

Kilometers

below

sealevel

Kilometers

sealevel

Kilometers

below

sealevel

Kilometers

below

sealevel

0 10 5

KILOMETERS

Figure 11.2. Cross section X-X’ from Kugururok River to Tupikchak Creek, Misheguk Mountain and De Long Mountains quadrangles. 

A, Organization of major 

structural units. Wolverine Creek, Red Dog, and Key Creek plates of the Endicott Mountains allochthon. 

B, Geologic units. Etivluk and Lisburne Groups not distinguished 

in Ipnavik River allochthon (includes local Nuka River allochthon). Gray shading in explanation indicates organization of elements of North Slope foreland basin.
32 Regional Fluid Flow and Basin Modeling in Northern Alaska

12. Geologic Rationale for Extensional 

Basin Framework During Red Dog 

Mineralization

By Christopher J. Potter and Julie A. Dumoulin

In order to understand the ore forming processes for 

a mineral deposit, it is necessary to determine the geologic 

framework that existed when the ore deposit formed. In the 

case of the Red Dog massive sulfide district in the western 

Brooks Range, Alaska, where the mineral deposits formed in 

Mississippian-age deep-water sediments, geologic and isotopic 

studies strongly indicate that mineralization occurred shortly 

after these sediments were deposited on the ocean floor. To 

develop physical and numeric models for the formation of 

these ores, scientists need to infer: (1) the chemical processes 

responsible for the ore formation; (2) the physical conditions 

(pressure, temperature) under which such processes operated; and (3) the geologic framework (configuration of the 

significant strata) at the time of ore formation. This chapter 

addresses the geologic framework of the ore-forming process, 

and specifically how this framework is incorporated into models aimed at simulation of ore-forming processes.

Reactive transport hydrologic models for mineralization 

in the Red Dog massive sulfide district (Schardt and others, 

in press) are based on an interpreted geologic framework 

(fig. 12.1). This framework is necessarily simplified, relative 

to the complex geologic situation that undoubtedly existed 

during ore formation. We use a simplified framework for two 

reasons: (1) the computer-based numerical model cannot 

efficiently handle a geologic configuration that is too complex, 

so there is a trade-off between geologic complexity and computing speed; and (2) the younger geologic history of the ore 

district (after the formation of the ore in Mississippian time) 

is complex, and it is difficult to “see through” the complex 

younger faulting to get at the true original configuration.

Figure 12.2 shows a present-day regional cross section 

through the Red Dog area, from De Vera and others (2004). 

The prominent curved thrust faults on this illustration formed 

in Early Cretaceous time, with additional faulting likely in 

early Tertiary time. These structures produced intense lateral 

shortening and vertical thickening of the original south-facing 

ocean margin that underlay northern Alaska. (In aggregate, the 

faults in figure 12.2 have produced over 200 km of 

northwest-southeast shortening; Moore and Potter, this 

volume, section 11). As a result, the sedimentary rocks that 

represent the deep ocean basin in which the Red Dog deposits 

formed have been severely modified since the ore-forming 

event.

The Mississippian Kuna Formation hosts the Red Dog 

and related ore deposits. This formation consists of black 

shale, chert, limestone and other minor components that accumulated in a deep-water setting (Dumoulin and others, 2004). 

The Kuna basin, in which these rocks accumulated, is estimated to have been anywhere from 0.1 to 2.5 km deep and at 

least 300 km long (Dumoulin and others, 2004; Young, 2004). 

The varied sedimentary facies and locally abrupt thickness 

changes in the Kuna basin strongly suggest that this basin was 

the site of active faulting. Submarine block faulting was likely 

a factor in producing the complex variations in water depth 

and sediment thickness (Dumoulin and others, 2004; Kelley, 

Dumoulin, and Jennings, 2004).

Regional considerations are consistent with an extensional tectonic setting in the Kuna basin. The Hanna trough, 

currently present beneath the Chukchi Sea north-northwest of 

Red Dog, is a north-northwest trending feature that records 

Devonian through early Mississippian extension. The Ikpikpuk-Umiat basin in the subsurface of the North Slope, north 

of the Brooks Range, appears to record extension at that time 

as well (Bird, 2001). Seismic lines on the North Slope, eastnortheast of Red Dog and intermediate in position between 

these two basins (fig. 12.3) also record extensional deformation at this time. It is not unreasonable to conclude that the 

Kuna Basin would have undergone extensional deformation as 

well.

Figure 12.1, a diagram of a basin configuration that was 

used in numerical modeling of the Anarraaq deposit near Red 

Dog (Schardt and others, in press), represents a very small 

extensional basin that would have been a component of this 

much larger, regional extensional province. In this model, this 

subbasin is considered to be of the appropriate scale to model 

the Anarraaq massive sulfide deposit. The basis of the cross 

section is the variation in thicknesses of the stratigraphic units 

of the Kuna Formation in the vicinity of the deposit. These 

thicknesses are accommodated in a structural style called 

an asymmetric graben, which is a basin that has been downdropped between two normal faults that have significantly different amounts of offset. This results in a strongly asymmetric, 

tilted basin that is a common style in the North Sea. The 

modeled basin would be considered to be just one of a large 

number of such subbasins within the regional Kuna basin.
12. Geologic Rationale for Extensional Basin Framework During Red Dog Mineralization 33

Ikalukrok unit: Barite layers

Mineralized shale (ore) 

Ikalukrok unitr: chert, fine-grained limestone, lithic turbidites

NW SE

Kivalina unit

Kivalina unit

Kivalina unit

Endicott Group

Endicott Group

Endicott Group 

0 200 METERS

vertical exaggation ~1.5

"basement"

"basement"

"basement"

Figure 12.1. Schematic northwest to southeast cross section depicting the Anarraaq deposit in Late Mississippian time.
34 Regional Fluid Flow and Basin Modeling in Northern Alaska

? ?

Kelly River

allochthon

WNW ESE

North

Slope

Wulik

Peaks

Wulik Peaks

 synform

Su-Lik North

Basin

Red

Dog

Husky Hills

Rok Hills

 window Kelly River synform

Husky Hills

 antiform

Arctic Slope parautochthon

H=V

Key Creek plate

Red Dog plate

Wolverine Creek

 plate

Endicott Mountains

 allochthon Foreland basin

 strata

Picnic Creek

 allochthon

10 KILOMETERS

Figure 12.2. Geologic cross section through the Red Dog district (from DeVera and others, 2004).
12. Geologic Rationale for Extensional Basin Framework During Red Dog Mineralization 35

Kingak Shale 

 (Jurassic-Neocomian)

Sadlerochit Group (Permian-

 Triassic) & Shublik Formation (Triassic)

Lisburne Group (Mississippian-Permian)

Pre-Mississippian basement 

 (Proterozoic-Devonian)

Nanushuk Formation 

 (Albian-Cenomanian)

Torok and Fortress Mountain Formations 

 (Aptian-Albian)

Endicott Group (Devonian- Mississippian)

Sea Level

-10

Approximate elevation (kilometers)

South North

-5

0 5 KILOMETERS

EXPLANATION

Figure 12.3. Interpreted segment of composite reflection seismic line R1 from National Petroleum 

Reserve–Alaska, approximately 70 km north-northeast of Red Dog, showing a Devonian-Missippian normal 

fault producing an Endicott-age half graben. Normal fault was later reactivated by a thrust fault.
36 Regional Fluid Flow and Basin Modeling in Northern Alaska

13. Lisburne Petroleum System

By Julie A. Dumoulin, Robert C. Burruss, and Paul G. 

Lillis

The Lisburne Group consists mainly of Carboniferous 

carbonate rocks formed in a variety of shallow- and deepwater settings. It crops out throughout the Brooks Range and 

is found in subsurface beneath much of the North Slope in 

northern Alaska (fig. 13.1). Sulfur-rich oils found in a number 

of North Slope wells from the Barrow Arch east to Mikkelsen 

Bay have been interpreted as derived from a Lisburne source, 

although recent studies suggest that only oils in the Mikkelsen 

Bay area, and perhaps at Prudhoe Bay, are truly Lisburnesourced (Lillis and others, 2006). Recent field and geochemical data provide information on generation and migration 

of hydrocarbons within the Lisburne petroleum system 

(Dumoulin and others, 2005).

Potential hydrocarbon source rocks within the Lisburne 

in the western and central Brooks Range are deep-water black 

shales interbedded with radiolarites, carbonate turbidites, and 

local phosphorites (Kuna Formation and related units). These 

units are more than 200 m thick in the Red Dog area (western 

Brooks Range) and at least 30 m thick at Skimo Creek (central 

Brooks Range; fig. 1.1); shales with total organic carbon 

(TOC) values greater than 2 percent (locally as high as 20 

percent) make up more than two-thirds of these units. Coarse 

crystalline dolostones in shallow-water facies of the Lisburne 

that contain vuggy and intercrystalline pores and fractures 

filled with solid hydrocarbons are found locally throughout the 

western and central Brooks Range (fig. 13.2). Although much 

of the Lisburne outcrop reached temperatures too high for oil 

generation, some sections in the Howard Pass and Chandler 

Lake quadrangles are still within the oil window (fig. 13.3). 

Geochemical parameters in rocks with low thermal maturity 

indicate a good match between organic-rich shales of the 

Lisburne, hydrocarbon residues in porous dolostones of the 

Lisburne, and proposed “Lisburne oils” in North Slope wells.

In addition to the evidence for generation of liquid 

hydrocarbons, fluid inclusion observations on cements and 

organic petrography of solid hydrocarbons in fractures in the 

Lisburne demonstrate that deeply buried, organic-rich units 

generated natural gas in the western Brooks Range (Red Dog 

area), central Brooks Range (Lisburne no. 1 well), and central 

North Slope (Inigok no.1 well). Structural studies suggest that 

Lisburne hydrocarbons were generated during the Early Cretaceous as a result of thrust sheet stacking during the Brookian 

orogeny.
13. Lisburne Petroleum System 37

 

 

Deep-water facies North slope well

Lisburne oil in Lisburne Group reservoir

Lisburne oil in Triassic reservoir

Lisburne oil mixed with other oils in

Lisburne Group reservoir

Lisburne oil mixed with other oils in reservoirs

younger than Lisburne Group

Solid hydrocarbon residues in Lisburne Group:

Lisburne source rock, still in oil window,

geochemically matches Lisburne oil

Reported hydrocarbon, not analyzed

Analyzed but too thermally mature or weathered 

to obtain geochemical profile

Geochemically matches Kuna source rock 

and Lisburne oil

Endicott Mtns (EMA), Picnic Cr, Ipnavik R 

allochthons

Mostly shallow-water facies 

Wolverine plate, western EMA; all of central EMA

Shallow-water facies capped by (drowned

by) deep-water facies

Kelly River allochthon

Shallow-water facies

Eastern EMA; North slope sequence, 

Lisburne Penninsula

Potential Lisburne Group source rocks

in subsurface basins

0

0 100 KILOMETERS

100 MILES

NATIONAL PETROLEUM 

RESERVE

Point Barrow

Mikkelsen Bay

Prudhoe Bay

Canada

United States

Cape Lisburne

Noatak River

Colville River

A

R

C T I C

O C E A N

Figure 13.1. Location map of northern Alaska showing distribution of deep- and shallow-water facies of the Lisburne 

Group, location of North Slope wells, and location of samples used for geochemical analysis. [EMA, Endicott Mountains 

allochthon]
38 Regional Fluid Flow and Basin Modeling in Northern Alaska

A A B

4 MILLIMETERS

Figure 13.2. Photomicrographs of dead oil that show evidence for petroleum migration. A, Dead oil in vug lined with quartz and 

dolomite, Kogruk Formation, Lisburne Group Outcrop near Red Dog mine. Pocket knife is shown for scale. B, Dead oil in Lisburne 

Group dolostone, Ivotuk Hills locality. Dead oil was extracted and correlated to Lisburne type oil in North Slope reservoirs.
13. Lisburne Petroleum System 39

OilWindow

GasWindow

West East

Conodont Alteration Index (CAI) measurements,  De Long Mountains Quadrangle

Conodont Alteration Index (CAI) measurements,  Misheguk Mountains Quadrangle

Conodont Alteration Index (CAI) measurements,  Howard Pass Quadrangle

Conodont Alteration Index (CAI) measurements,  Killik River Quadrangle

GasWindow

OilWindow

More

50

353025201510

1 1.5 2 2.5 3 3.5

ycneuqerF

CAI

Conodont Alteration Index (CAI) measurements,  Chandler Lake Quadrangle

More

86420

141210

1 1.5 2 2.5 3 3.5

ycneuqerF

CAI

9876543210

1 1.5 2 2.5 3 3.5 More

CAI

ycneuqerF

OilWindow

GasWindow

0

70

605040302010

1 1.5 2 2.5 3 3.5 More

ycneuqerF

CAI

Oil Window

Gas Window

50

4540353025201510

1 1.5 2 2.5 3 3.5

ycneuqerF

CAI

More

OilWindow

GasWindow

Figure 13.3. Frequency distribution diagrams showing CAI (conodont alteration indices) values of samples of Lisburne Group. In general, thermal maturity of surface samples decreases from west to east, indicating shallower levels of burial and thermal maturation.
40 Regional Fluid Flow and Basin Modeling in Northern Alaska

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44 Regional Fluid Flow and Basin Modeling in Northern Alaska

Glossary of terms

[Taken from Jackon, J.A., ed., 1997, Glossary of geology (4th

ed.): Alexandria, Va., American Geological Institute]

Element symbol definitions

Ag – silver

As – arsenic

Au – gold

Ba – barium

Ce – cerium

Cr – chromium

Cu – copper

Eu – Europium

F – fluorine

Ge – germanium

Hg – mercury

Mo – molybdenum

Ni – nickel

O – oxygen

P – phosphorus

PGE – platinum group elements

Pb – lead

REE – rare earth elements

S – sulfur

Sb – antimony

Se – selenium

Sr – strontium

Tl – thallium

U – uranium

V – vanadium

Zn – zinc

A

allochthon A mass of rock that has been moved from its 

place of origin by tectonic processes.

anoxic Relating to a marked lack or difficiency of oxygen; 

for example, oceanic anoxia refers to an absence of oxygen in 

seawater (<0.1 ml/l).

autochthon A mass of rock that remains at its site of origin, 

where it is rooted to its basement.

B

barite Barium sulfate mineral (BaSO4).

C

calcareous A substance that contains calcium carbonate 

(CaCO3).

carbonate A mineral compound; calcite is an example 

(CaCO3).

chalcopyrite A bright brass yellow mineral composed of 

copper, iron, and sulfur (CuFeS2).

chert A hard, dense, microcrystalline sedimentary rock, 

consisting dominantly of quartz.

conodont Microfossil, commonly toothlike in form made up 

of carbonate and apatite.

contraction Tectonic processes resulting in shortening.

D

diagenetic Chemical, physical, and biologic changes undergone by a sediment after its initial deposition and during and 

after its lithification.

dolomite A rhombohedral mineral (CaMg(CO3)

2

 that is 

white, colorless, or tinged yellow, brown, pink, or gray.

dolostone A rock made up of the mineral dolomite, a mineral with the composition of CaMg(CO3

)

2

.

dysoxic Below normal concentration of oxygen in seawater 

(0.1 to 1.0 ml/l).

E

extension Tectonic process resulting in elongation (pullapart).

F

facies The aspect, appearance, and characteristics of a rock 

unit, usually reflecting the conditions of its origin; a mappable, 

areally restricted part of a lithostratigraphic body, differing 

in lithology or fossil content from other beds deposited at the 

same time.

fluid inclusions In a mineral, a tiny cavity (micron sized 

in diameter), containing liquid and (or) gas, formed by the 

entrapment in crystal irregularities of fluid, commonly that 

from which the rock crystallized.

G

galena Lead sulfide (PbS) mineral.

gangue Valueless rock or mineral aggregates in an ore; that 

part of an ore that is not economically desirable but cannot be 

avoided in mining.

H

hydrothermal Of or pertaining to hot water, to the action of 

hot water, or to the products of this action, such as a mineral 

deposit precipitated from a hot aqueous solution.
Glossary of terms 45

K

kerogenous Said of oil shale or other sedimentary rock containing complex fossilized organic material that is insoluble in 

common organic solvents and yields petroleum on distillation.

klippe An isolated rock unit that is an erosional remnant or 

outlier of a sheetlike allochthonous rock unit.

L

lithology The description of rocks in hand sample or outcrop 

on the basis of such characteristics as color, mineralogic composition, and grain size.

M

marcasite Iron sulfide (FeS2) mineral. It may be differentiated from pyrite based on lower specific gravity, less chemical 

stability, and usually a paler color.

metalliferous Metal-bearing.

mica A group of minerals with low hardness, readily splitting into thin plates.

mudstone An indurated mud having the texture and composition of shale but lacking its fine lamination; fine-grained 

sedimentary rock.

N

nodule A small irregularly rounded mass of a mineral or 

mineral aggregate, usually exhibiting a contrasting composition from the enclosing sediment or rock in which it is embedded.

O

oil shale A general term applied to a fine-grained sedimentary rock containing enough organic material (called kerogen) 

to yield oil and combustible gas upon distillation.

orogeny The process of formation of mountains.

P

paleogeography The study and description of the physical 

geography of the geologic past.

passive margin A continental boundary formed by rifting 

and continental rupture.

per mil Parts per thousand.

phosphate A mineral compound containing PO4

-3 groups.

phosphorite A sedimentary rock with a high enough content 

of phosphate minerals to be of economic interest.

pyrite Iron sulfide (FeS2) mineral. It has a higher specific 

gravity, more chemical stability, and a brighter metallic luster 

compared to marcasite.

Q

quartz Crystalline silica, an important rock-forming mineral 

(SiO2).

R

radiogenic A product of a radioactive process (heat, lead).

radiolarian Microfossil characterized mainly by a siliceous 

skeleton and a marine pelagic environment; the silica is often 

replaced by other minerals.

rudstone A carbonate rock composed of bioclasts or other 

fragments, over 2 mm in diameter, closely packed, in physical 

contact.

S

sabkha Supratidal environment of sedimentation, formed 

under arid to semiarid conditions on restricted coastal plains.

salinity Total quantity of dissolved salts in seawater.

sandstone Medium-grained clastic sedimentary rock composed of abundant rounded or angular fragments of sand size 

set in a fine-grained matrix and united by a cementing material.

shale Fine-grained detrital sedimentary rock, formed by 

the consolidation of clay, silt, or mud; characterized by finely 

laminated structure, which imparts a fissility parallel to the 

bedding. 

siliciclastic Clastic noncarbonate rocks which are almost 

exclusively silicon bearing.

siltstone Indurated silt having the texture and composition 

of shale but lacking its fine lamination or fissility.

sphalerite Zinc sulfide (ZnS) mineral.

strata plural of stratum which is a tabular or sheetlike body or 

layer of a sedimentary rock.

stratiform Having the form of a layer; a stratiform ore 

deposit is one that is strictly coextensive with a given rock 

unit.

sulfide A mineral compound characterized by the linkage of 

sulfur with a metal or semimetal. Examples include sphalerite 

(zinc sulfide), galena (lead sulfide), or pyrite (iron sulfide).

synsedimentary Said of a sedimentary ore deposit in which 

the ore minerals formed contemporaneously with the enclosing rock.

T

turbidite A sediment or rock deposited from a turbidity current.
Ayuso and others—Regional Fluid Flow and Basin Modeling in Northern Alaska—Circular 1319

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