U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 107–03

October 2003

The Natural Dispersal of Metals to the Environment

in the Wulik River–Ikalukrok Creek Area,

Western Brooks Range, Alaska

Introduction

Reconnaissance geologic investigations by I.L. Tailleur in 

1968 noted the presence of widespread iron-oxide staining in 

creek beds in the Wulik River and Ikalukrok Creek drainages 

of the western Brooks Range. A brief examination of one of 

these creeks revealed the presence of weathered sulfide-bearing 

bedrock and stream sediments containing more than 10 percent 

lead (Tailleur, 1970). Tailleur named this creek Red Dog Creek, 

and subsequent exploration in this area resulted in the discovery 

of the huge Red Dog lead-zinc-silver deposit. As exploration 

continued in this region, many other metal-bearing deposits 

were discovered (fig. 1). Today there are at least eight significant areas of high metal concentrations in bedrock at or near the 

surface in the Wulik River and Ikalukrok Creek areas (fig. 1).

Most of the iron-, lead-, and zinc-bearing rocks in the 

western Brooks Range originally formed on or immediately 

below an ancient sea floor about 330 to 340 million years ago 

(Kelley and others, 2003). The sea floor was at the bottom of a 

deep-water basin where thin black shale, chert, and carbonate 

layers were deposited. Metal-bearing fluids deposited minerals 

such as pyrite (iron sulfide), galena (lead sulfide), and sphalerite 

(zinc sulfide). These metal-bearing sedimentary rocks are now 

exposed at the surface and are being eroded and dispersed to the 

environment along the slopes, creeks, and rivers of the region. 

Erosion and dispersion of metal-bearing rocks have been ongoing for at least hundreds of thousands of years and have resulted 

in very large amounts of lead, zinc, and other metals that are 

now found in the Wulik River and Ikalukrok Creek drainages. 

Mining of the Red Dog lead-zinc-silver deposit began in 

1989. Ore is mined in an open pit and transferred to a nearby 

processing facility where it is crushed, ground, and concentrated 

using a flotation process. The process separates metal-bearing minerals (galena and sphalerite) from other minerals in the 

metal-bearing host rock. This processing produces a concentrate 

of fine-grained, clean, and angular galena and sphalerite grains. 

Trucks are used to transport concentrates from the mine to the 

coastal port facility where they are temporarily stored during winter. During the summer, concentrates are transferred to 

barges and then to deep-water ships. Transportation and storage 

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Figure 1. Location map of sulfide mineral deposits and sample sites.

CHUKCHI

SEA

Red Dog

Wulik

River

0 10 Km

Su-Lik

68°00'

163°30'

Barrow 0 100 KM

Arctic

Brooks

Kivalina

Ri

ver

Ikalukrok

Cr

Circle

Range

Area of Map Oak Cub

Ferric Creek

Anarraaq

port facility

port road

02AH28

02AH25

02AH18

02AH24

02AH16

02AH20

Suds

Wulik

02AH15

Sulfide prospect/deposit

Sample site

02AH29

Kivalina

Noatak
of the concentrate has inadvertently resulted in dispersal of dust 

from the concentrates along roads, and around the mine and port 

facility. 

High concentrations of lead or zinc in surface materials in 

northwestern Alaska are of concern to villagers in the region 

(i.e., Kivalina and Noatak) (fig. 1). It is difficult, however, to 

determine whether the source is from natural erosion or dispersion or related to fugitive dust, based solely on high concentrations of lead or zinc. This study shows how metal-rich samples 

that are derived from fugitive concentrate dust can be distinguished from those that are naturally dispersed to the environment by weathering and erosion of metal-bearing deposits.

Natural Metal Dispersal Processes

Natural metal dispersal in the Wulik River and Ikalukrok 

Creek area effectively started several hundred thousand years 

ago when glaciers covered the region. These glaciers physically eroded and moved bedrock materials—including parts of 

metal-bearing deposits in their path—to the limits of glaciation 

that were at or beyond the present coastline (Coulter and others, 

1965). The glaciers eventually melted and retreated to higher 

parts of the nearby mountains, where remnants were still 

present until about 11,500 years ago (Hamilton, 1994).

Since the glaciers retreated from the Wulik River and 

Ikalukrok Creek areas, both physical and chemical weathering 

processes have continued to disperse metals from bedrock 

to the environment. Physical weathering breaks up nearsurface bedrock and creates a cover of soil and rock fragments 

as much as several meters thick. Some of these materials, called 

colluvium, may slowly migrate downslope to valley lowlands 

where they are then eroded and transported by streams to 

lower elevations—thus forming alluvium. Both processes—the 

breaking up of near surface bedrock and deposition of materials in streams—are called mechanical or physical weathering 

processes. Chemical weathering involves the alteration and dissolution of minerals. Oxidation of sulfide minerals, especially 

pyrite (iron sulfide), is a very important chemical-weathering 

process that develops acidic surface materials and waters. The 

acidic conditions and the abundance of oxidized iron enable 

further sulfide-mineral breakdown, precipitation of secondary 

minerals, and dissolution of metals in surface and ground water. 

Metal-bearing bedrock deposits in the Wulik River and Ikalukrok Creek drainages have been affected by chemical weathering 

and physical weathering and erosion for at least the last 10,000 

years. These are the processes that produced very high (greater 

than 10 percent) lead concentrations in the sediments of Red 

Dog Creek before the Red Dog mine existed. 

Distinguishing Naturally Dispersed Metals from 

Mining-Produced Fugitive Concentrate Dust

The complicated processes that lead to naturally dispersed 

metals in the Wulik River and Ikalukrok Creek areas produce 

several characteristics of the resulting metal-bearing materials 

that distinguish them from those that are the product of miningproduced fugitive concentrate dust. Naturally dispersed metals 

can be identified by their patterns of metal concentrations in 

surface materials, their mineralogic character, and their association with certain other elements.

There are two characteristic patterns of metal concentration in natural surface materials of the region. In residual 

colluvium profiles over metal-bearing bedrock deposits, metal 

contents characteristically increase with depth and proximity 

to the metal-bearing bedrock source. The Cub prospect colluvium profile shown in figure 2 illustrates this type of variation. 

The metal-bearing bedrock at the Cub prospect is on a small 

tributary to the upper Ikalukrok River, about 9 km upstream 

from the confluence with Red Dog Creek (fig. 1). The second 

type of metal-concentration variation is developed in silt, sand, 

and gravel (alluvium) deposited by streams in the area. In these 

sediments, metal concentrations remain nearly constant from 

the surface downward through sampled profiles. Data for the 

lower Ikalukrok Creek area (fig. 2) illustrate this type of variation. The physical erosion and transport of alluvium by streams 

effectively mixes and homogenizes metal-bearing material in 

the alluvium. These two types of metal-concentration variation 

distinctly contrast with that developed where mining-produced 

fugitive concentrate dust is the source of high metal concentrations. As one would expect, ore-concentrate dust is localized at 

the surface, and metal concentrations sharply decrease downward in soil profiles (fig. 2). 

The mineralogic character, including mineral species and the 

morphology of specific mineral grains, also distinguishes natural metal-rich surface materials. The effects of chemical weathering, especially oxidation, are evident in natural colluvium 

developed over metal-bearing bedrock. Here, secondary minerals such as jarosite, plumbojarosite, and anglesite are developed; 

sphalerite is lacking, and galena occurs in only minor amounts, 

if at all (samples 02AH16, 20, and 24; table 1). Surface materials at the port facility where fugitive concentrate dust is present, 

contain both galena and sphalerite (02AH28; table 1).

The morphology of galena grains produced by anthropogenic input (mine concentrate and port facility) is different 

than galena that occurs naturally (alluvium and colluvium over 

and surrounding natural deposits) (fig. 3). Individual grains 

of galena and sphalerite in soil at the port facility are angular, 

0

10

20

30

40

50

60

1,0002,0003,0004,0005,0006,00014,000

Cub prospect (colluvium)

LEAD CONCENTRATION (PPM)

DEPTH (CM)

port facility (dust)

Middle Ikalukrok Creek (alluvium)

Figure 2. Diagram showing variation in lead concentrations in profiles 

from the Cub prospect colluvium, middle Ikalukrok Creek alluvium, and 

port facility surficial materials. 
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Figure 3. Scanning electron microscope (SEM) photomicrographs (secondary electron images) showing morphology of galena grains in different surface materials. A, sample 02AH29 of lead concentrate 

from the Red Dog mine showing perfect cubic cleavage of galena that is typical of concentrate; B, 

sample 02AH28 collected adjacent to the road at the port facility—well-developed cubic cleavage is 

evident; C, sample 02AH18 collected from alluvium along Ikalukrok Creek—galena grains are rounded; 

and D, sample 02AH24 collected from the Lik deposit—galena grain is rounded and the surface is 

etched (pitted).

5 μm

02AH29 A

1 μm

02AH28 B

02AH18

2 μm

02AH24

1 μm

C D

Galena Galena

Galena

Galena

Pits on surface of grain

Galena
and galena shows its characteristic cleavage (fig. 3B) that is 

similar in appearance to galena from concentrate (fig. 3A). 

This distinct mineral morphology is to be expected because the 

concentrate material results from the crushing and grinding of 

unweathered Red Dog bedrock deposit materials. The preserved 

sulfide grains in alluvium and colluvium related to natural metal 

dispersal are very different. Such samples are typically etched 

and rounded (figs. 3C, 3D). Alluvial sediments contain smooth 

and well-rounded grains of galena because of the long history 

of physical weathering and mechanical transport in streams (fig. 

3C). Colluvial samples are etched and rounded because they 

have been chemically weathered in an acidic oxidizing environment (fig. 3D).

In addition to mineralogy, the overall geochemical character helps distinguish anthropogenic versus natural soils. Some 

distinguishing geochemical characteristics include:

• Lead-zinc ratios are distinctly higher in colluvium as a 

result of preferential dissolution and removal of sphalerite by chemical weathering (no colluvial samples have 

detectable sphalerite; table 1).

• High molybdenum (Mo) and selenium (Se) contents and 

low calcium (Ca) contents characterize colluvium over 

natural deposits compared to soils near the port facility. 

This is due to more acidic conditions in colluvium over 

mineral deposits (due to the presence of pyrite)—conditions under which elements such as Se and Mo are stable 

and Ca is not.

• Galena has higher concentrations of impurities (such as 

aluminum, potassium, and silica) in colluvium, reflecting the presence of mineral phases such as jarosite 

intergrown with the galena. 

• Compared to fugitive dust collected at the port facility, 

galena-bearing alluvium has increased concentrations 

of elements such as chromium, hafnium, and titanium 

because stream sediments commonly have higher 

amounts of heavy minerals such as pyroxene and zircon 

(fig. 4). 

Conclusion

The Wulik River and Ikalukrok Creek drainages are one of 

the more metal-rich areas in the world due to natural processes. 

Geologic processes formed many small to very large metal-rich 

deposits on or immediately beneath a deep sea floor about 330 

to 340 million years ago. One of these deposits, the largest zinc 

deposit in the world, is now the site of the Red Dog mine. Many 

of these ancient metal concentrations are now exposed at or near 

the surface where physical and chemical processes can naturally 

disperse them to the environment. This natural dispersal of metals, particularly lead and zinc, has occurred widely and in large 

amounts within the Wulik River and Ikalukrok Creek drainages 

and has been underway in this area since the onset of glaciation. 

The long and complicated history of natural metal dispersal 

in the Wulik River and Ikalukrok Creek areas developed characteristic metal variations in surface-material profiles, distinctive 

metal-bearing mineralogic assemblages and morphologies, and 

certain geochemical characteristics that sharply contrast with 

those at places where mining-produced fugitive concentrate dust 

is the source of high metal concentrations. These characteristics 

can be used to readily distinguish natural metal occurrences 

from those associated with fugitive concentrate dust. 

References

Coulter, H.W., Pewe, T.L., Hopkins, D.M., Wahrhaftig, C., Karlstom, T.N.V., and Williams, J.R., 1965, Map showing extent 

of glaciations in Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-415, scale 1:2,500,000.

Hamilton, T.D., 1994, Late Cenozoic glaciation of Alaska, in

Plafker, George, and Berg, H.C., eds., The geology of Alaska: 

Boulder, Colo., The Geological Society of America, The 

Geology of North America, v. G-1, p. 813–844.

Kelley, K.D., Leach, D.L., Johnson, C.A., Slack, J.F., Dumoulin, J.A., and King, A.R., 2003, The giant Red Dog Zn-Pb-Ag 

massive sulfide deposits, northwestern Alaska, USA: Basin 

setting and conditions of ore formation, in Eliopoulos and 

others, eds., Mineral exploration and sustainable development: Athens, Greece, Proceedings of the 7th Biennial SGA 

meeting, 24–28 August 2003, p. 689–692.

Tailleur, I.L., 1970, Lead-, zinc-, and barite-bearing samples 

from the western Brooks Range, Alaska: U.S. Geological 

Survey Open-File Report 445, 16 p. 

Figure 4. Concentration ranges of selected elements in alluvium compared to port facility soil 

showing significantly higher chromium, hafnium, and titanium in alluvial samples. 

Cr (ppm) Ti (%) Hf (ppm)

0 80 160 0 .2 .4 .6 0 4 8

Port facility

Alluvium

Contacts:

Karen D. Kelley Travis Hudson

USGS MS 964 Applied Geology, Inc

Box 25046 902 Vista del Mar

Denver, CO 80225 Sequim, WA 98382

kdkelley@usgs.gov ageology@olypen.com