environmental studies of mineral deposits in alaska

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Right

. A sample of the ore mineral cinnabar (red mineral) collected from one ofseveral abandoned mercury mines in southwestern Alaska. The mines in theregion were studied to evaluate effects of mercury on surrounding ecosystems.

Above

. Geologists from the U.S. Geological Survey collecting water samplesdownstream from a massive sulfide deposit, northwestern Brooks Range, Alaska.Stream characteristics such as trace-element concentrations in stream sedimentsand stream waters, and streamwater pH and conductivity were measureddownstream from several mineral deposits in Alaska to evaluate effects of thesedeposits on surrounding environments.

Front Cover. Acid-mine drainage found below the Duke mine, a massive suldeposit in the Prince William Sound area, Alaska (lower left); collecting water samdownstream from the Drenchwater massive sulfide deposit in the northwestern BRange, Alaska (upper right).

Environmental Studies ofMineral Deposits in Alaska

U.S. GEOLOGICAL SURVEY BULLETIN 2156

M A R C H 3, 1849U

.S.

DE

PARTMENT OF THE

INTER

IOR

Short articles summarize environmental geochemical studies of metallicmineral deposits in Alaska, including massive sulfide, gold, mercury,chromium, and uranium mines and deposits. The studies report metal and acidconcentrations in samples collected around such mines and deposits, andevaluate environmental effects of the deposits. The articles are written in a styleintended to reach a general audience

Edited by John E. Gray and Richard F. Sanzolone

With contributions fromElizabeth A. Bailey Karen D. Kelley Richard F. SanzoloneHelen W. Folger Keith A. Mueller* Elaine Snyder-Conn*Richard J. Goldfarb Steven W. Nelson Clifford D. TaylorLarry P. Gough James K. Otton Peter M. TheodorakosJohn E. Gray John A. Philpotts

*U.S. Fish and Wildlife Service

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996

For sale by U.S. Geological Survey, Information ServicesBox 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only anddoes not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

Environmental studies of mineral deposits in Alaska / edited by John E. Gray and Richard F. Sanzolone ; with contributions from Elizabeth A. Bailey . . . . [et al.].

p. cm.—(U.S. Geological Survey bulletin ; 2156)Includes bibliographical references (p. ).1. Metals—Environmental aspects—Alaska. 2. Mines and mineral resources—

Environmental aspects—Alaska. I. Gray, John E., 1956–. II. Sanzolone, R.F.III. Bailey, Elizabeth A. IV. Series.

TD196.M4E58 1997[QE75.B9]551.9

′

09798—dc20 96–13189CIP

CONTENTS

223

3

71419

192327

. 3

CONTENTS

Introduction ........................................................................................................................ 1Geochemical Processes—How Metals Enter Environments Downstream

From Mineral Deposits.........................................................................................Background Geochemical Studies—The Starting Point ............................................

Studies of Mineral Deposits Rich in Heavy Metals ...........................................................Natural Environmental Effects of Silver-Lead-Zinc Massive Sulfide Deposits

in the Northwestern Brooks Range.......................................................................Acid- and Metal-Rich Waters Associated with Iron-Copper-Zinc Massive

Sulfide Deposits in Prince William Sound...........................................................Environmental Geochemistry of Mercury Mines in Southwestern Alaska........................Environmental Geochemistry of Alaskan Gold Deposits...................................................

Gold-Bearing Quartz Veins in the Pacific Gulf Coastal Forest Ecoregion ................Placer Gold Deposits of the Fairbanks and Nome Districts .......................................

Geochemistry of Surface Waters Draining Alaskan Chromite Deposits ...........................Radioactivity Concerns of Uranium and Thorium Deposits at Bokan Mountain, Southeastern Alaska ..................................................................................................1Summary............................................................................................................................. 35References Cited................................................................................................................. 37Glossary .............................................................................................................................. 39

..... 3

.... 6

.

....

.... 18

...

FIGURES

1. Map showing location of silver-lead-zinc deposits in the northwestern Brooks Range, Alaska ........................... 2. Photographs in the northwestern Brooks Range, of Red Dog Creek mineral deposit prior to mining,

and of intense red-weathering zones near Drenchwater Creek.............................................................................. 4 3. Plots demonstrating how water from Discovery Creek affects dissolved zinc in lower Drenchwater Creek ......... 4. Photograph of a bright-orange iron-oxide layer along False Wager Creek, which drains Drenchwater deposit

on east side............................................................................................................................................................. 7 5. Photograph of mineralized rock from a volcanic-rock-hosted massive sulfide deposit showing veins

with abundant chalcopyrite and pyrrhotite, Prince William Sound ....................................................................... 8 6. Photograph of abandoned tailings piles (background) near the Dutchess mine ......................................................... 9 7. Map showing location of massive sulfide deposits studied, Prince William Sound .................................................. 9 8. Photograph of water effluent discharging from base of tailings piles at the Dutchess mine .................................. 11

9. Photograph of tailings and effluent from the Beatson mine washing into Prince William Sound,and view of flooded Beatson pit............................................................................................................................. 12

10. Map showing location of mercury mines and deposits in southwestern Alaska......................................................... 1411. Photograph of rock sample containing the mercury ore mineral cinnabar ................................................................. 1512. Schematic diagram showing most important sources of mercury............................................................................... 1613. Photograph of heavy-mineral sample, showing abundant cinnabar particles ............................................................. 1714. Plot of mercury in fish muscle versus mercury in fish liver for fish collected throughout southwestern Alaska ...15. Map showing location of gold vein deposits of the Pacific Gulf Coastal Forest Ecoregion.................................... 1916. Photograph showing vein containing quartz and pyrite, and microscopic gold.......................................................... 20

IIIIII

CONTENTS

IV

CONTENTS

IV

..... 28

...

..... 33...... 36

17. Photograph of open-pit cut, Alaska-Juneau mine, near Juneau, Alaska ..................................................................... 2118. Photograph showing geologists sampling waters draining an adit from an abandoned gold mine in

southern Alaska...................................................................................................................................................... 2219. Map showing location of gold placers in Alaska ........................................................................................................ 2420. Photograph showing placer operation near Fairbanks ................................................................................................ 2521. Photograph of Red Mountain chromium deposit, showing color and vegetation contrast between

ultramafic rock and vegetated soil ........................................................................................................................ 2722. Photograph showing a seam of black chromite ore layered within the ultramafic rocks at Red Mountain...........23. Location map of the Alaskan chromium occurrences studied .................................................................................... 2924. Photograph showing water flowing from an abandoned chrome mine....................................................................... 3025. Map showing location of Bokan Mountain uranium deposits, southeastern Alaska ............................................... 3226. Photograph of the granitic intrusion at Bokan Mountain............................................................................................ 3327. Photograph showing previous mining of uranium ore at the Ross-Adams uranium mine ....................................28. Plot of dissolved metal concentrations in water versus water pH for several Alaskan deposit types...................

TABLES

1. Water standards used for reference in these studies.................................................................................................... 52. Geochemical data summary of mineral deposits studied............................................................................................ 36

Environmental Studies of Mineral Deposits in Alaska

Edited by John E. Gray and Richard F. Sanzolone

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INTRODUCTION

Mining of minerals and metals is important in all indus-trialized and developing countries. In the United States, min-ing of metallic mineral deposits is conducted in most States,including Alaska. In the past century, much of the mininghas concentrated on the extraction of metals necessary forthe economic or industrial development of societies, forexample, gold, silver, iron, copper, lead, zinc, chromium,mercury, tin, cobalt, molybdenum, nickel, and uranium.Other metals such as arsenic, cadmium, and selenium areoften enriched in mineral deposits and recovered as by-products. Because many of these metals can be toxic toplants, animals, and humans, their interaction with the envi-ronment is a national concern. To address this concern, stud-ies of natural and man-made environmental interactions ofmetals before, during, and after mining have becomeincreasingly important to society.

The economic success of any mineral depositdepends on a clear understanding of its geology, mineral-ogy, and geochemistry, because these characteristics aidin locating, developing, and extracting metals and mineralsfrom ore deposits. These characteristics also affect sur-rounding environments, because metals can be carrieddownstream from the deposits and into local ecosystems.1

With a thorough understanding of the characteristics ofmineral deposits and their downstream effects, scientistscan predict potential environmental problems and identifysolutions to these problems.

To evaluate environmental concerns, scientists measuremetal concentrations in rock, soil, stream-sediment, water,plant, and sometimes fish samples collected around minesand mineral deposits. Metal concentrations in these samplesare typically compared to Federal and State standards, aswell as to local background concentrations. These measure-ments are the initial steps toward identifying environmentalcontamination problems associated with mineral deposits,both prior to, and resulting from mining.

1Italicized terms are defined in the Glossary; see page 39.

The most important environmental concerns resuing from weathering and mining of mineral deposits aincreased acid and metal concentrations downstream can potentially degrade drinking water and wildlifhabitat. Thus, the primary objectives of the studies psented here are to:

determine metal and acid concentrations in sampcollected downstream from mineral deposits,

assess the degree of metal contamination in lostreams due to weathering and mining of the deposand

evaluate environmental effects related to the minedeposits.

Such studies are particularly important in Alaska: number of known mineral deposits exist that have not been developed, and these studies may be useful for fumining, monitoring, and remediation programs within thState. These studies may also be useful for evaluation, deopment, and remediation of mineral deposits of similar tyin similar geographic and geologic settings.

The U.S. Geological Survey (USGS) is working witseveral agencies in Alaska, including the U.S. Fish aWildlife Service, U.S. Forest Service, National Park Servicand Alaska native corporations, to evaluate the environmtal effects of mineral deposits and their mining. In coopetion with these agencies, the USGS has the unique abilitintegrate aspects of geology, mineralogy, and downstregeochemistry of mineral deposits in Alaska and identify aenvironmental hazards related to these deposits. Studiethe geology, mineralogy, and geochemistry of minedeposits can be integrated with local climatic, hydrologand topographic conditions to address land use and envimental issues. This publication summarizes the results frsome of the first environmental studies of mineral depositsAlaska conducted by the USGS. Some of the text is techcal, and a glossary of some technical terms is providThese technical terms are in italics when first mentionedthroughout the text.

1

ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

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2 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

GEOCHEMICAL PROCESSES—HOW MET-ALS ENTER ENVIRONMENTS DOWNSTREAM

FROM MINERAL DEPOSITS

Rocks and minerals exposed at or near the surface oEarth undergo changes in color, form, and chemical comsition. This process, called weathering, is primarily the resof the action of air, wind, water, snow, ice, and biologicactivity on the rocks and minerals in mined and unminmineral deposits. Weathering can result in the formationacid water and conversion of metals into water solubforms. These acid- and metal-rich waters are commoreferred to as acid drainage. Formation of acid drainagearound mineral deposits is primarily related to oxidation sulfide minerals, especially pyrite (iron sulfide), that pro-duces strong acids like sulfuric acid. Many heavy metals,including arsenic, copper, lead, zinc, and cadmium, cotained within sulfide minerals in the mineral deposits, amore soluble in water containing abundant acid. When thacid- and metal-rich waters flow downstream from a minedeposit, they may be an environmental concern, if thadversely affect local wildlife habitat or human health.

At the same time that rocks and minerals are weathing, they are also being eroded, transported, and redeposdownstream. During this erosion process, the physical achemical changes of the rocks and minerals continue atsite of the mineral deposit, which is the primary source of metals, as well as in streams below the deposits. Therefacid- and metal-rich waters will continue to form until thesmetal sources are removed by natural or human process

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BACKGROUND GEOCHEMICALSTUDIES—THE STARTING POINT

To determine if metal concentrations around minedeposits are of environmental concern, scientists collecseries of samples, chemically analyze these samplesmetal concentrations, and then determine which metal ccentrations are “normal or usual” and which are “high unusual.” Materials sampled for study are usually strewater, stream sediment, soil, and sometimes fish and plaThe initial step in mineral deposit environmental studies iscollect samples upstream from such mineral deposits,from areas where mineral deposits are not known. Sampcollected from such unmineralized areas are referred to“background” samples. When these background sampleschemically analyzed, they provide the chemical concenttions that are considered normal or usual and are unaffeby mineral deposits or mining. These background sampprovide scientists with a reference or starting point agaiwhich to compare chemical data from samples collecdownstream from mined and unmined mineral deposits.many instances, samples collected downstream from mindeposits contain high metal concentrations that greaexceed those in background samples. These high concetions must be closely evaluated to determine if the enviroment has been adversely affected. In the following studdata are presented to examine metal concentrations related hazards around several types of mineral deposits

3

STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS

ALASKA

Area offig. 1

Kotzebue

Drenchwater

Lik

Red Dog

GATES OF THE ARCTICNATIONAL PARK

NOATAK NATIONAL PRESERVE

BROOKS RANGE

NATIONALPETROLEUM RESERVE

IN ALASKA

68˚

164˚

0 50 100 KILOMETERS

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Figure 1.

Location of silver-lead-zinc massive sulfide deposits in the northwestern Brooks Range, Alaska.


Mineral deposits containing large amounts of sulfidminerals are of environmental concern because hemetals such as copper, lead, zinc, and cadmium are higconcentrated in these deposits. Mineral deposits containsuch large amounts of sulfide minerals are commonreferred to as massive sulfide deposits. The State of Alacontains several types of massive sulfide deposits. Tmassive sulfide deposits studied here are (1) those foprimarily in sedimentary rocks in the northwestern BrooRange and (2) those closely associated with volcanic roor lavas in Prince William Sound.

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NATURAL ENVIRONMENTAL EFFECTSOF SILVER-LEAD-ZINC MASSIVE SULFIDE

DEPOSITS IN THE NORTHWESTERN BROOKS RANGE

Silver-lead-zinc massive sulfide deposits in the nortwestern Brooks Range consist of layers rich in sulfide merals that are dispersed in black shale and chert. dominant minerals are sphalerite (zinc sulfide), silver-richgalena (lead sulfide), pyrite, and marcasite (iron sulfides).The deposits currently under study in the Brooks Range Lik, Drenchwater, and Red Dog (Kelley, 1995) (fig. 1). ARed Dog, one of the largest zinc deposits in the world, ming of lead and zinc began in 1990 and continues today. Lik and Drenchwater deposits have not been mined. three deposits are exposed at the surface and were disered by the presence of orange staining on surrounding sides or by the presence of significant heavy meconcentrations in streams draining the deposits (fig. 2).


4

Figure 2A.

Photograph in the northwesternBrooks Range of Red Dog Creek prior to miningwhere it flowed through the mineral deposit. RedDog Creek had significant natural heavy-metal con-tamination that eliminated fish life in the vicinity ofthe deposit. The contamination and resulting mineralstain led to discovery of the Red Dog deposit (photoby C.G. Mull).

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What are the environmental issues of the BrookRange massive sulfide deposits?—The Brooks Rangemassive sulfide deposits have the potential to form acand metal-rich waters that can carry high concentrationstoxic metals such as lead, zinc, and cadmium. Sevethousand people living in the surrounding region traditioally rely on subsistence hunting and fishing for foosources. These silver-lead-zinc massive sulfide depocan be a potential hazard to residents and wildlife, if draage from these deposits enters streams and rivers that port local wildlife habitat. To evaluate stream watquality near the deposits, scientists measured concentions of metals and pH in water collected from streams surrounding these silver-lead-zinc deposits.

5


Table 1.

Water standards used for reference in these studies.

[Concentrations are in ppb (micrograms per liter); --, standard has not been estab-lished]

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________________________________________________Element EPA criteria State of Alaska maximum maximum concentration contaminant (CMC)

1

level (MCL)

2

________________________________________________Arsenic 360 50Antimony -- 6Mercury

3

2.4 2

Copper 18 1,000Lead

4

82 --Zinc

4

120 5,000

Cadmium

4

3.9 5Iron -- 300Sulfate -- 250,000

Chromium III 1,700

5

100Chromium VI 16 --

________________________________________________

1

CMC is the Environmental Protection Agency’s water qual-ity criteria to protect against acute effects in aquatic life andis the highest instream concentration of a toxic pollutant con-sisting of a 1-hour average not to be exceeded more thanonce every 3 years on the average.

2

MCL is the maximum concentration allowed by the Stateof Alaska in public drinking water systems. Concentrationslisted for copper, zinc, iron, and sulfate are secondaryMCL’s that are reasonable totals and provide a generalguideline for public drinking water systems.

3

The CMC for mercury in seawater is 2.1 ppb.

4

These element standards vary with water hardness. Val-ues listed are for a water hardness of 100, which is similar tothat for streams studied here.

5

Standard is for total chromium concentration.

Figure 2B.

Photograph in the northwestern Brooks Range look-ing west across Drenchwater Creek. The weathering of pyrite hasresulted in intense red-weathering zones.

Water quality downstream from massive sulfidedeposits is significantly affected.—Data from the Drench-water deposit indicate that stream waters draining deposit have low pH values (indicating that they are acidand dissolved concentrations of aluminum, arsenic, cmium, copper, iron, lead, manganese, nickel, and zinc several orders of magnitude greater than that in water sples collected upstream (backgrounds) from the deposit (3). The most acidic waters collected range in pH from 2.83.1 and contain as much as 95,000 ppb (parts per billion)aluminum, 26 ppb arsenic, 270,000 ppb iron, 8 ppb cmium, 260 ppb copper, 10 ppb lead, 3,400 ppb mangan290 ppb nickel, and 2,600 ppb zinc; these values are all nificantly above background concentrations (Kelley aTaylor, 1996). Sulfate concentrations (1,180 ppm (parts permillion)) are also high. Although the deposits are rich in sver, water samples contain low silver concentrations (< ppb). Locally, the iron- and sulfate-rich waters have precitated a bright-orange iron-oxide layer that cements stream pebbles and cobbles on the creek bottom (fig. 4).

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Although metal concentrations in waters draining thDrenchwater deposit are higher than streams in unmineized areas, many metals are still present at levels belowState of Alaska drinking water standards. Levels of camium, copper, and zinc exceed the instream criteria mamum concentrations (CMC) that the U.S. EnvironmenProtection Agency (EPA) indicates may acutely affeaquatic life (table 1).


6

Drenchwater

Drenchwater

Creek

DiscoveryCreek

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1,000

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600

400

200

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Figure 3.

Plots demonstrating how the stream water from Discovery Creek, which drains mineralized areas, affects thedissolved zinc in lower Drenchwater Creek. Aluminum, cadmium, copper, iron, lead, manganese, and nickel show varia-tions in concentrations similar to zinc that reflect the input of water contaminated by metals naturally weathering from themineralized area. In addition, the pH of water downstream from the deposit dramatically decreases (acidity increases).Data were collected in July 1994.

The Red Dog massive sulfide deposit contributes hiacid and metal contents to stream waters, similar to Drenchwater deposit. The only significant differencbetween the two is the higher metal concentrations in RDog waters relative to Drenchwater. Water quality dafrom streams draining the Red Dog deposit prior to mini(Dames and Moore, 1983; Runnels and others, 1992) rethat the waters were acidic (as low as a pH of 3.5) and ctained toxic levels of cadmium (as much as 800 ppb), le(2,250 ppb), and zinc (272,000 ppb). These concentratiexceeded the drinking water standards recommended byState of Alaska (5 ppb Cd; 15 ppb Pb; and 5,000 ppb Zand the EPA-CMC standards (table 1). Other metals, sas aluminum, chromium, copper, iron, manganemercury, nickel, and silver, slightly exceeded EPA-CMstandard. Streams immediately draining the Red Ddeposit did not support any significant biota, such as fisuggesting that waters were apparently toxic to maquatic life prior to mining. Stream water quality 15–20 kdownstream of the deposit was also significantly affectezinc and cadmium concentrations were well above the rommended CMC concentrations.

The higher metal concentrations of Red Dog waterelative to Drenchwater are due primarily to the greaamount of sulfide minerals present in the Red Dog depoand the greater extent of exposure of sulfide mineralsweathering at the surface.

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When geology differs, so does the water quality.—TheLik deposit yields waters that are near-neutral to neutral, aconcentrations of all metals except zinc are low relativeDrenchwater and Red Dog. Stream waters collected dostream from Lik have pH values of 6.2 to 8.1. Only one saple from a small tributary contained concentrations cadmium (5 ppb) and zinc (2,000 ppb) that are comparato levels detected below the Drenchwater deposit. Zinc wthe only metal that was consistently high in water sampbelow the deposit, ranging from 380 to 2,000 ppb.

Differences in chemistry between the Drenchwater aLik deposits may be attributed to the presence of carbonrocks, such as limestone, surrounding the Lik deposit. Cbonate rocks tend to neutralize acid in the water and, becametals are more soluble in water containing significant acthese near-neutral waters have a lesser ability to transmost metals in solution.

7


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A bright-orange iron-oxide layer locally covers the botom and cements stream pebbles and cobbles along False WCreek, which drains the Drenchwater deposit on the east side.orange part of the stream in this photo is about 1.5–2 m wide.

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What has the Brooks Range massive sulfide data tous?—These results show that the primary factors affectiwater chemistry are the extent of exposure of the deposthe amount of sulfide minerals present, and the presencabsence of carbonate rocks. In the absence of carborocks, silver-lead-zinc massive sulfide deposits in tBrooks Range can produce significant naturally occurriheavy-metal concentrations in downstream waters. Carbate rocks are not present at the Red Dog and Drenchwdeposits, and waters are highly acidic and metal rich. In ctrast, carbonate rocks are abundant at the Lik deposit, waters are near-neutral and contain low concentrationsmost metals except zinc.

These data are useful for predicting the environmeneffects likely to result from natural weathering of massisulfide deposits and from possible future mining of sudeposits. Furthermore, the data enable mine planners toter anticipate, plan for, and mitigate potential environmenproblems, and are useful for devising realistic plans remediation and monitoring programs.

ACID- AND METAL-RICH WATERSASSOCIATED WITH IRON-COPPER-ZINC

MASSIVE SULFIDE DEPOSITS INPRINCE WILLIAM SOUND

Massive sulfide deposits in Prince William Sound cosist of iron-, copper-, and zinc-rich sulfide minerals in annear volcanic rocks. Many of the deposits were mined froabout 1900 to 1930, but have since been abandoned. Tabandoned mines are located in the Chugach National Foand on private lands within the forest.

Rocks in the Prince William Sound region are domnantly sandstone and slate, with some basalt. The massulfide deposits are most common in basalt, but are foualso in nearby sedimentary rocks. The primary sulfiminerals are pyrite, pyrrhotite, chalcopyrite, and sphalerite(fig. 5). Minor galena is present in some deposits. Sfide-rich bodies range in size from a few centimeters to m wide and a few hundred meters long.

Workings range from small prospect trenches to minwith tunnels hundreds of meters long. The Beatson mcontains more than 4 km of tunnels and a 300 m diameopen pit. Small tailings piles, about 10 to 20 m high, afound at most mine sites (fig. 6). These tailings generally bright red as a result of the weathering of sulfide mineraBright-green to black moss covers metal-rich soils where landscape was stripped for mining. Mine waste piles, undground workings, and unmined ore can potentially foracidic and metal-rich effluent that can enter local streaand rivers; such effluent may eventually reach Prince Wiam Sound, which could present a problem to this locmarine environment. Prior to this study, no detailed hydgeochemical data have been collected to determine extent of acid-mine drainage to Prince William Sound.

Stream waters from tailings versus mine adiwaters.—Waters were collected within, upstream fromand downstream from mines located in three areLaTouche Island (Beatson, Blackbird, Duke, and Dutchemines), Knight Island (Barnes Cove prospect and RCove mine), and Port Fidalgo (Schlosser, Fidalgo, aThreeman mines) (fig. 7). The concentration of metalssurface waters collected from unmineralized areas (baground concentrations) is largely controlled by the chemtry of the rocks and soils. Metal concentrations agenerally low in waters collected from background sitand are 0.3 to 0.6 ppb copper, 0.8 to 1.4 ppb zinc, <0.1 cadmium, <0.5 ppb lead, <20 ppb iron, and 4 ppm sulfaBackground waters generally have pH values near 7.

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Figure 5.

Mineralized rock from a volcanic-rock-hosted massive sulfide deposit showing veinswith abundant chalcopyrite and pyrrhotite, Prince William Sound.


9


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149˚ 147˚

60˚

ALASKA

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Beatson, Blackbird,Duke, Dutchess

0 50 KILOMETERS

Figure 6.

Abandoned tailings piles (background) near the Dutchess mine.

Figure 7.

Location of massive sulfide deposits studied (crossed pick and hammer symbol), PrinceWilliam Sound.


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Waters containing the highest metal concentrationsthe Prince William Sound area were collected from the baof tailings piles (fig. 8). These waters contain as much 3,600 ppb copper, 3,300 ppb zinc, 21,000 ppb iron, 220 plead, 10 ppb cadmium, and 311 ppm sulfate and have pH ues as low as 2.6 (Goldfarb and others, 1996). Waters lected directly from mine adits contained lower metcontents, and pH values of about 6: adit waters containemuch as 1,400 ppb copper, 3,100 ppb zinc, 310 ppb ironppb cadmium, 0.9 ppb lead, and 166 ppm sulfate, but madit waters contained significantly lower metal concentrtions. The much higher metal concentrations and aciditywaters from the tailings piles are the result of weatheringsulfide minerals in the tailings.

Acid- and metal-rich waters emanating from themassive sulfide deposits are rapidly diluted downstreamlarger streams. The large streams below the mines hnear-neutral pH values, and the amount of acid-mine draage from the deposits is too small to affect the acidity, meloadings, and water quality of these larger streams.

The flooded pit at the Beatson mine is about 500 from the shoreline of Prince William Sound and represea potential heavy-metal source. Water discharging from base of the pit (fig. 9) has a pH of 6.5, and waters in thehave a pH of 7.3. Such near-neutral pH values limit the subility of most metals, and thus, the amount of metal thwill be transported in water downstream to Prince WilliaSound. Water discharging from the pit contains 30 piron, 21 ppb copper, 39 ppb zinc, and 6.5 ppm sulfaAlthough these metal concentrations are not as elevatethose collected downstream from other massive sulfdeposits, the volume of water in the pit and the drainaemanating below the pit could deliver a large enouquantity of metal to the near-shore marine environmentpossibly damage Prince William Sound.

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Why do we care about massive sulfide deposits Prince William Sound?—Many of the iron-copper-zincmassive sulfide deposits in the Prince William Sound aproduce metal-rich waters as they weather. Metal concentions and the pH of the acid-mine drainage will depend onumber of factors, including the amount and type of sulfiminerals present, extent of weathering, local hydrology, athe acid-neutralizing capacity of the rocks. Our studies shthat on a local scale, especially where surface waters fthrough tailings piles, acid-mine drainage is a concernPrince William Sound.

Water data show that prior to emptying into majostream channels, surface waters flowing away from mosthe mine workings exceed recommended EPA-CMC cocentrations for copper, lead, zinc, and cadmium (table Furthermore, much of the mine discharge exceeds the Sof Alaska drinking water limits of 5 ppb cadmium, 1,000 ppcopper, and 300 ppb iron; in addition, mine effluent is oftmore acidic than the recommended drinking water pH ranof 6.5 to 8.5. Therefore, at least locally, surface water mnot be suitable for human consumption.

Whether any of these abandoned mines pose a threthe downstream marine life of Prince William Sound is preently unknown. However, acid- and metal-rich wateclearly exit the base of the Beatson mine pit and drain iPrince William Sound a few hundred meters below the miMetal concentrations in these waters are about 10 timhigher than in waters from background sites. Because malife is especially sensitive to elevated heavy-metal conctrations, additional analysis of near-shore waters for meenrichments is warranted.

11


Figure 8.

Water effluent discharging from base of tailings piles at the Dutchess mine.


12

Figure 9A.

Tailings and effluent (foreground) of the Beatson mine, washing into Prince William Sound (background).

13


Figure 9B.

View of the Beatson mine flooded pit.


14

64˚

Mercury mine

Mercury deposit

Studyarea

ALASKA

Sleetmute

Aniak

Bethel

Dillingham

KuskokwimBay

BristolBay

IliamnaLake

Kusko

kwim

River

Yu

k onR

iver

0 100 KILOMETERS50

156˚160˚164˚

62˚

60˚

Figure 10. Location of mercury mines and deposits in southwestern Alaska.

l

tothekid-er-asy).an-

ngell

andjorly theis aagert oftal of

ENVIRONMENTAL GEOCHEMISTRY OF MERCURY MINES IN

SOUTHWESTERN ALASKA

Mercury-rich mineral deposits in Alaska are anothtype of deposit under investigation for natural and mininrelated heavy-metal concentrations in the environmeMercury deposits are scattered over a wide region in souwestern Alaska covering several tens of thousands of squkilometers (fig. 10). The mercury sulfide mineral cinnabaris the most common mercury ore mineral in the deposits (11), but liquid mercury also occurs naturally at some locaties. Several of the mercury deposits have been mined,most of the deposits are small and undisturbed. None ofmercury mines in Alaska are currently operating, due to enomic factors. Mercury is used in the manufacturing of eletrical instruments, fungicides, pharmaceuticals, amunitions, in the production of paper, and in the extractiof gold (amalgamation of gold) in mining.

ion,its.s in

erg-nt.th-are

fig.li- but theco-c-

ndon

Should we be concerned about mercury mineradeposits in southwestern Alaska?—Mercury is a heavymetal that has no known metabolic function and is toxicliving organisms. In humans, mercury adversely affects central nervous system and internal organs such as the neys. In streams and lakes, bacterial activity converts mcury in sediments from inorganic compounds (such cinnabar) to organic forms (such as methylmercurOrganic mercury compounds are easily absorbed by orgisms and are more hazardous than inorganic forms.

The primary sources of mercury are naturally occurrimineral deposits, rocks, soils, and volcanic eruptions, as was man-made industrial sources such as factory effluentsairborne incinerations. Southwestern Alaska has no masources of industrial mercury; however, mercury is highconcentrated around mineral deposits in the region. Thus,presence of mercury deposits in southwestern Alaska potential hazard to residents and wildlife because drainfrom the deposits enters streams and rivers that are palocal ecosystems (fig. 12). To evaluate the environmenconcerns of these mercury deposits, the concentrationmercury was measured in sediment, water, soil, vegetatand fish collected around some of the mercury deposThese data were then compared with those from streamunmineralized (background) areas.

15

ENVIRONMENTAL GEOCHEMISTRY OF MERCURY MINES IN SOUTHWESTERN ALASKA

are8.sitsin-rm inest-

Figure 11.

Rock sample containing the mercury ore mineral cinabar (red mineral). Pencil point for scale.

ryeasllyonsm-am

eon-nic

s,a-

and toen-ts)

cleer-1.34,ausest- ofichn-nts

Measuring mercury levels in stream sedimentsstream water, and fish.—Stream-sediment samples collected near some mines contain total mercury concentratiin excess of 5,000 ppm (Gray, 1994). Stream-sediment sples collected from streams in local unmineralized areas tically contain less than 1 ppm mercury, indicating that tsamples collected near the mines are highly enriched in mcury. These high mercury concentrations in stream sements near the mines are the result of erosion of cinnainto the streams. Cinnabar is resistant to weathering, thus, it remains in streams for long periods of time (fig. 13

Stream waters below the mercury mines generally neutral to slightly alkaline with pH values of about 7 to The formation of acid drainage below some mineral depocontaining sulfide minerals can be of concern; however, cnabar is highly insoluble in water and does not easily foacid drainage during weathering. Thus, acid formationstreams below the mercury mines and deposits in southwern Alaska is probably insignificant.

,-onsam-yp-heer-di-bar

and).

n-

Samples of stream water collected below mercumines contained as much as 0.75 ppb mercury, wherbackground stream and river waters in the region typicacontain less than 0.10 ppb. These mercury concentratiare below the 2.0 ppb drinking water standard recomended by the State of Alaska and the 2.4 ppb instreEPA-CMC standard (table 1).

Although cinnabar is highly insoluble in water, thwater data indicate that minor amounts of mercury are cverted to forms that are soluble in water, probably orgaforms of mercury, that are easily absorbed by organismsuch as fish, living in the stream environment. For this reson, fish were collected throughout southwestern Alaska analyzed for mercury to evaluate the potential for mercuryenter local food sources and the food chain. Mercury conctrations were measured in fish muscle samples (edible filleand livers. Maximum mercury concentrations in the mussamples of freshwater fish collected downstream from mcury mines were about 0.6 ppm (wet weight) and about ppm in the liver samples (fig. 14) (Gray and others, 1991996). These concentrations are considered elevated becsimilar fish collected from background streams in southweern Alaska contained only about 0.2 ppm mercury. Mostthe mercury in the fish (> 90 percent) was the highly toxorganic form of mercury, methylmercury. Although the fiscollected downstream from the mines contain mercury cocentrations higher than background levels, mercury contein the edible portions of the fish were belowthe 1.0 ppm limit established by the Food andDrug Administration (FDA).

Mercury concentrations were also mea-sured in salmon collected from large rivers in theregion because these fish are foods of localresidents and sportsmen. Mercury concentra-tions in salmon muscle samples were low,less than 0.1 ppm (Gray and others, 1996),well below the recommended FDAlimit. These low mercury concentra-tions are understandable becausesalmon spend much of theirlives in the ocean and are incontact with streamwaters in southwesternAlaska only when hatch-ing and spawning.


16

Mercury Cycle

Sources:

1. Industrial (organic Hg)2. Mines & deposits (inorganic Hg)

Water Supplies

Food Chain:

Mercury increases inconcentration as it moves up the food chain

2

3

1

Figure 12.

Schematic diagram of mercury cycle showing the most important sources of mercury—industrial, volcanoes, and mineral de-posits such as those in southwestern Alaska. When mercury from mineral deposits erodes into streams, toxic mercury compounds can beabsorbed by fish and eventually consumed by humans.

17

ENVIRONMENTAL GEOCHEMISTRY OF MERCURY MINES IN SOUTHWESTERN ALASKA

s

- ther in oftedeg-n-

ng toe foraticm-keness

pro-

n

s

b

Figure 13.

Heavy-mineral sample in a gold pan showing abundant cinnabar particles.

Levels of mercury in soil and vegetation aroundmines.—Soil and vegetation samples collected aroumines also contained higher mercury concentrations thlocal background samples. Soils around mines containedmuch as 1,500 ppm mercury, whereas background samples generally contained less than 1 ppm mercuAlder leaves collected near mines contained from 0.030.97 ppm mercury (dry weight), compared to alder leavfrom background sites containing less than 0.2 ppm. Scitists were most interested in the amount of the toxmethylmercury in plants that could be consumed browsing animals in areas near the mines. Unlike fiswhere the highly toxic methylmercury represents the larmajority of the total mercury, only a small fraction of thmercury in vegetation is methylmercury, generally less th5 percent. It is unlikely that mercury contents in such minamounts represent a significant health concern to wildlthat consume such vegetation.

odthisent,tainury

What are the answers to environmental questionabout the mercury deposits?—Stream-sediment, streamwater, soil, vegetation, and fish samples collected nearmines have elevated concentrations of mercury. Cinnabathe mines is the dominant source of this mercury. Erosionthe cinnabar around the mines results in highly elevamercury concentrations in stream sediments, soils, and vetation. The elevated mercury concentrations in fish dowstream from the mines indicate that mercury is beiconverted from inorganic mercury, such as cinnabar,organic mercury that is more biologically available. Thmercury is then transferred to water and to food sourcesthe fish, such as larvae, insects, and other small aquorganisms that live in the streams. Mercury or other containant can concentrate in tissues of organisms when it is taup more rapidly than the organism can eliminate it, a proccalled bioaccumulation. When mercury enters the foodchain it tends to concentrate in the highest predators, a cess called biomagnification; thus, mercury concentrationsin fish are useful for evaluating levels of mercury in the fochain that can eventually affect humans. The results of study suggest that, although samples of stream sedimwater, soil, and vegetation collected near the mines conelevated mercury concentrations, concentrations of mercin fish indicate minor, local effects on food chains.

dan asoilry.

toesen-icyh,geeanorife


18

1.0

0.8

0.6

0.4

0.2

0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

ME

RC

UR

Y, I

N P

AR

TS

PE

R M

ILLI

ON

WE

T W

EIG

HT

IN F

ISH

MU

SC

LE

MERCURY, IN PARTS PER MILLION WET WEIGHT IN FISH LIVER

FDA action level for edible fish

Cinnabar Creek Dolly Varden and Arctic grayling

Kolmakof River Arctic grayling

Chineekluk Creek Arctic grayling

Background Arctic grayling

Salmon

EXPLANATION

Figure 14.

Plot of mercury in fish muscle versus mercury in fish liver for fish collected throughout south-western Alaska.

19

ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS

ed of

ofsednda,d-n-

d-ks.ral

n 3

Southern Alaska Gold Districts

Talkeetna 8. Willow Creek

Chugach-Kenai Mts1. Girdwood2. Hope-Sunrise3. Moose Pass4. Nuka Bay5. Port Wells6. Port Valdez7. McKinley Lake

Juneau Gold Belt 9. Berners Bay10. Alaska-Juneau, Treadwell11. Endicott Peninsula

Chichagof Island

12. Chichagof

60˚

136˚152˚

8

1

2

3

4

56

7

12

9

10

11

Anchorage

Seward

Valdez

JUNEAU

ALASKA

UN

ITED

STA

TES

CA

NA

DA

WRANGELLMOUNTAINS

CHUGACHMOUNTAINS

TALKEETNAMOUNTAINS

KENAI

MTS

BOUNDARYRANGES

COASTAL FOOTHILLS

Prince William Sound

CHILKAT-BARANOFMOUNTAINSGULF OF ALASKA

PACIFIC OCEAN

KodiakIsland 0 150 300 KILOMETERS

Figure 15. Location of gold vein deposits of the Pacific Gulf Coastal Forest Ecoregion.

ENVIRONMENTALGEOCHEMISTRY OF

ALASKAN GOLD DEPOSITS

Mining of gold deposits has been a major industry Alaska since the early 1900’s. Both large gold vein depossuch as the Alaska-Juneau mine, near Juneau, and lplacer gold districts, such as those near Fairbanks and Nohave been economically important in the past and will cotinue to be important in the future. Heavy metals sucharsenic, copper, lead, zinc, and cadmium are associated many of the gold deposits. The following two studies evaate environmental concerns of heavy metals in streams rivers downstream from Alaskan gold deposits.

en-llydarens

oferend

loryeau

initsargeme,n-

aswithlu-and

GOLD-BEARING QUARTZ VEINSIN THE PACIFIC GULF

COASTAL FOREST ECOREGION

The Pacific Gulf Coastal Forest Ecoregion, as definby the U.S. Forest Service, includes the coastal regionssouth-central and southeastern Alaska along the GulfAlaska. In south-central Alaska, these lands are compoof the Kodiak Mountains, Kenai-Chugach Mountains, athe Gulf of Alaska coastal plain. In southeastern Alaskgeographic provinces of the ecoregion include the Bounary Ranges, Coastal Foothills, and Chilkat-Baranof Moutains (fig. 15).

Rocks in this region are predominantly marine sanstone and shale that are intruded by minor granitic rocGold-bearing quartz veins are the most widespread minedeposit in the region (fig. 15). The veins contain less thapercent sulfide minerals (fig. 16) and cut both the sedimtary and granitic rocks. The sulfide minerals are typicapyrite, arsenopyrite, chalcopyrite, galena, sphalerite, anstibnite. Calcite and other carbonate alteration minerals adjacent to the veins. Veins range in length from a few teof meters to more than a kilometer, with maximum widthsabout 5 m. More than 100 of these gold vein deposits wmined in the early 1900’s. Mines range from open cuts ashort tunnels at the smaller deposits, to large open pits (gholes) at the largest deposits, such as the Alaska-Jundeposit (fig. 17).

ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA20

-sidd

inetedhers.ant

ndukaic atsers,

Figure 16. Vein containing quartz (white) and pyrite (brass colored). Microscopic gold is contained within pyrite grains,but because of its fine-grained nature is not visible. Felt marker for scale.


Establishing background concentrations in streamsfor the gold vein studies.—Background concentrations formetals in stream waters that drain unmineralized rocks wfound to be <0.05 ppb silver, <5 ppb arsenic, <1 ppb cmium, ≤1 ppb copper, ≤20 ppb iron, <1 ppb lead, 0.1 to 0.2ppb antimony, 3 to 6 ppb zinc, and 0.7 to 1.7 ppm sulfaThe pH of surface waters varies from 7.2 to 7.9. Waters emnating from weathered, unmined gold vein deposits also ctain low heavy-metal and sulfate concentrations. Fexample, in the Nuka Bay district (fig. 15, locality 4), surfacwaters flowing from small, unmined, gold-bearing veincontain as much as 6 ppb arsenic and 3.6 ppm sulfate (Ctat and others, 1994). Concentrations of 140 ppb iron andppm sulfate were measured in a large stream in the Gwood district (Carrick and Maurer, 1994).

edood

eread-

te.a-

on-oresieu- 4.6ird-

Testing for acid and toxic metals in waters downstream from mines.—Waters emanating from gold mine(fig. 18) have pH values near neutral, indicating that acwater formation is minor. The most acidic water collectehad a pH of 6.4, but most waters contained slightly alkalpH values, similar to background surface waters collecthroughout the region. Most metal concentrations in tmine waters are also similar to that of background wateHowever, because pyrite and arsenopyrite are the dominsulfide minerals found along with gold at the mines, iron aarsenic are generally the most elevated metals. In the NBay district, a maximum concentration of 130 ppb arsenwas measured in water immediately downstream fromsmall vein and tailings pile. In the McKinley Lake distric(fig. 15, locality 7), water-filled prospect pits contained amuch as 94 ppb arsenic and 650 ppb iron (Trainor and oth1996). Mine waters collected from both districts containas much as 5 ppm sulfate. The stream draining the Girdwdistrict contained 8.5 ppm sulfate and 550 ppb iron.

21ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS

ldci-ingra-seate theul-ar

owits.n-ad-

Figure 17. Open-pit cut at the largest gold vein deposit in Alaska, the Alaska-Juneau mine, near Juneau.

The Alaska-Juneau mine was the largest gold lodeAlaska, with more than 109,000 kg (3,500,000 oz) of goproduced from 1893 to 1944. Unlike many of the other gobearing vein deposits in the region, the Alaska-Junedeposit contains abundant sphalerite and galena. Most mdrainage emanates from one tunnel, and this water hameasured pH of 8 and concentrations of <0.5 ppb silver, to 2.7 ppb arsenic, <0.2 ppb cadmium, <2 ppb copper, <1ppb iron, <2 ppb lead, <0.2 ppb mercury, 39 to 52 ppb ziand 230 to 340 ppm sulfate. Except for sulfate and zinc, thdata are similar to those of background waters collected frunmineralized areas.

et-e issee oficen

entedersowte

inldld-auines a0.600

nc,eseom

What are the environmental issues related to the govein deposits?—Compared to mine-drainage waters assoated with other mineral deposit types, waters emanatfrom gold-bearing quartz veins contain low metal concenttions due to the low abundance of sulfide minerals in thegold-bearing vein deposits and mines. In addition, carbonminerals that form adjacent to the veins tend to neutralizeminor amount of acid produced during weathering of the sfide minerals. Water pH is consequently maintained neneutral. In waters of near-neutral pH, most metals have lsolubilities and are not easily transported from the deposEven waters that drain Alaska’s largest lode gold mine cotain total base metal concentrations (copper+lead+zinc+cmium) of less than 100 ppb.

Arsenic and iron are the most commonly enriched mals in waters emanating from mines, and their presencrelated to the sulfide mineralogy of the deposits; but themetal concentrations in the waters rarely exceed the StatAlaska maximum levels for drinking water of 50 ppb arsenand 300 ppb iron. Although higher concentrations have bemeasured in water samples from some localities, effluthroughout this ecoregion is rapidly diluted when discharginto larger stream channels. Metal concentrations in watthat drain Alaska’s largest gold mine are consistently belthe drinking water maximum allowable levels; only sulfaoccasionally exceeds the State limit of 250 ppm.

ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA2222 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 18. Sampling waters draining an adit from an abandoned gold mine in southern Alaska.


hentingits,la-on-inehenders

pos-thesitsalsnd

hered

ral-ofay in

avy canur-

finems

PLACER GOLD DEPOSITS OF THEFAIRBANKS AND NOME DISTRICTS

Placer mining has been an important industry in Alassince the late 1800’s. Although some placer gold mines currently operating in Alaska, many are now abandonPlacer mining has produced about 730,000 kg (23,490,oz) of gold, which represents more than 70 percent of gold produced in Alaska (Swainbank and others, 1995). Ttwo largest Alaskan placer gold districts, Fairbanks aNome, produced about 247,000 kg (7,971,000 oz) a149,900 kg (4,822,500 oz) of gold, respectively. Becauplacer mining has been widespread in Alaska (fig. 19), enronmental concerns related to placer mining are addresby evaluating the water geochemistry of samples collecfrom these two major gold districts.

What are placers?—Placer deposits form in streambeds, on beaches, in deltas, and in marine sediments wthe action of water erodes rocks and minerals, separaheavy minerals from lighter ones. Stream placer deposlike those in the Fairbanks district, are surficial accumutions of stream rock, gravel, and sediment containing ccentrated heavy minerals (fig. 20). Beach and marplacers, like those found in the Nome district, form near tmouths of rivers, and similar to stream placers, gold aother heavy minerals are transported to the seas in rivand streams. After the gold and stream sediment are deited in the marine environment, ocean currents rework sediments, concentrating the heavy minerals in depoalong beaches and in shallow marine settings. Minercommon in most placer deposits include free gold, aoxide and sulfide minerals of tin, tungsten,antimony, copper, zinc, lead, mercury, andarsenic.

During placer mining, water is used toseparate gold from the sediment. During thisprocess, the water becomes turbid and muddy.Present-day placer operations capture this turbidwaste water in nearby, man-made ponds untilenough of the finely suspended sediment and mud hassettled out, and the water can be reused or dischargedback into streams or other water bodies. Because theobjective of placer mining is to remove smallamounts of gold from large volumes of sedi-ment, a significant amount of unwanted orwaste material remains. This waste is com-

kaareed.700allhe

ndndsevi-sedted

posed mostly of rocks, boulders, coarse gravel, and otheavy minerals (placer tailings) that are commonly moundand left in stream valley bottoms.

Environmental issues of placer deposits inAlaska.—The primary environmental concern from placemining is the potential for the generation of acid and metrich water, but increased water turbidity or the addition toxic materials (such as liquid mercury) into the streams malso degrade stream water quality. Enrichment of metalsstreams below placer mines can affect water quality. Hemetals such as arsenic, copper, lead, zinc, and cadmiumbe carried downstream when they are dissolved in water ding weathering or can be transported downstream as sediment. These heavy metals can be toxic to life forwhen concentrations are exceedingly high.


en-air-theenic ofs.are

ethek-r-oesues6.5am

66˚

160˚ 150˚

60˚

ALASKA

Fairbanks

Nome

Norton Sound

Bering SeaGulf of Alaska

ARCTIC OCEAN

Yukon Riv er

Principal gold placer districts

Placer gold districts studied

EXPLANATION

0 250 500 KILOMETERS

Figure 19. Location of gold placers in Alaska.

Metal concentrations in waters below placermines.—To evaluate the adverse effects, metal concenttions in waters collected downstream from placer minwere measured and then compared to local backgroundsState and Federal water quality standards. Stream water sples collected upstream (backgrounds) and downstrefrom two placer mines in the Fairbanks district (Fairbanand Porcupine Creeks) were analyzed for arsenic, zinc, cmium, copper, and lead to address these environmental cerns (Ray and others, 1992). Arsenic concentrationsstream waters on Fairbanks Creek range from 22 to 64 upstream, and from 62 to 112 ppb below the placer. Arseconcentrations in stream water samples from PorcupCreek range from <1 to 15 ppb upstream, and from <1 toppb below the placer deposit (Ray and others, 1992).

be

ra-es andam-amksad-

con- inppbnicine 20

Of most significance are the elevated arsenic conctrations in stream waters collected below the placer on Fbanks Creek compared to the arsenic levels in background stream water samples. These elevated arsconcentrations are probably related to the weatheringarsenopyrite, which is common in the placer tailingAlthough the stream water concentrations of arsenic below the EPA-CMC standard of 360 ppb (table 1), somwater samples collected from Fairbanks Creek exceed 50 ppb maximum level of arsenic recommended for drining water by the State of Alaska (table 1). Acid-water fomation around placer deposits in the Fairbanks district dnot appear to be a significant problem because pH valfor the two stream waters are near neutral, ranging from to 8.1. Concentrations of other heavy metals in strewaters are below the EPA-CMC standard and appear toof minor concern.


Figure 20. Placer operation near Fairbanks showing placer tailings piles and settling ponds.


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no

ma lm

otetiths.mels

on-lowhena-he

llya-l.amrictenic Inhe isin inA- ininor ofup-

Environmental effects related to water turbid-ity.—Highly turbid waters often reduce light transmitted tthe stream bottom, reducing photosynthesis. Excessivturbid waters can smother plant life, destroy habitats benthic organisms, and clog the gills in fish. Prior to the m1980’s, waste water was not held in settling ponds, but woften discharged directly back into streams. Today, turbwater discharges from placer operations are closely motored, and the downstream effects are generally fairly min

Mercury introduced during placer mining.—Liquidmercury has been used for the extraction of gold (amalgaation of gold) for many years. Amalgamation of gold hbeen most often used in placer operations because oftengold is fine grained. Although gold amalgamation is rareused today, some liquid mercury may remain in streanear old placer operations because it was sometimspilled, lost, or discarded.

During the 1980’s and 1990’s, high concentrations mercury and other heavy metals were found in marine wanear the Nome placer deposits. Mercury concerns scienthe most because it is toxic to life forms and can enter food chain and affect the health of wildlife and humanMercury concentrations in seawater collected near the Noplacer district ranged from <0.05 to 0.48 ppb (U.S. MineraManagement Service, 1989). Although these mercury ccentrations are considered high for seawater, they are bethe 2.1 ppb EPA-CMC standard for seawater (table 1). Tsource of mercury was traced to upstream sources of cinbar and liquid mercury used for gold amalgamation in tarea (U.S. Minerals Management Service, 1989).

lyrdasidi-r.

-stheyses

frs

stse

Conclusions of the placer studies.—Placer depositscontain minerals with heavy metals that are potentiatoxic to humans and wildlife, but water quality degradtion downstream from placer mines is relatively minimaFor example, although arsenic concentrations in strewaters sampled below placers in the Fairbanks distexceed the State drinking water standard, these arsconcentrations are also below the EPA-CMC standard.addition, acid-water formation below placer deposits in tFairbanks district is minor because measured water pHgenerally near neutral. Mercury concentrations seawater near the Nome placer district are higher thantypical background seawater, but are well below the EPCMC standard. Most other heavy-metal concentrationswaters near the placers studied here are low and of mconcern. Continued study of the environmental effectsplacer deposits is important, especially in streams that sport wildlife, or in populated areas.

27GEOCHEMISTRY OF SURFACE WATERS DRAINING ALASKAN CHROMITE DEPOSITS

as a

kaists3).a,00geallyakheiteles asinend

Figure 21. The Red Mountain chromium deposit, showing the color and vegetation contrast between thebare, light-orange ultramafic rock (center background), and vegetated soil (left background).

GEOCHEMISTRY OF SURFACE WATERS DRAINING ALASKAN

CHROMITE DEPOSITS

Most of the world’s chromium is found in ultramaficrocks. These ultramafic igneous rock complexes consistdark, layered rocks that are rich in silica, magnesium, iroand calcium, as well as the mineral chromite. These ultramfic rocks generally weather to an orange-brown color duethe formation of iron oxides, and these rocks typically do nsupport vegetation (fig. 21). Chromium ore consists of blalayers or seams that are rich in chromite. Although theseams vary in thickness from the width of a few chromgrains to nearly 2 m, only thick seams are mined (fig. 2Chromium is used in the manufacturing of steel alloys, mals plating, pigments and dyes, wood preservatives, and catalyst in chemical processes.

ofn,a-

tootckse

ite2).et-

There are several chromite deposits throughout Alasthat are associated with ultramafic rocks. USGS scientstudied two of these chromite-bearing occurrences (fig. 2Red Mountain, located 16 km from the town of Seldoviwas the largest chromite mine in Alaska, where over 35,0t of chromium ore was recovered through 1976. Drainafrom the Red Mountain mine enters streams that eventurun into a saltwater fishery in Kachemak Bay. SiniktanneyMountain (fig. 23), in the western Brooks Range, was tsite of USGS study of a second, small, unmined chromseam. At both locations scientists collected water sampdownstream from the mineralized areas (fig. 24), as wellfrom local unmineralized (background) areas to determwater pH, chromium concentrations, and other major- atrace-metal concentrations.


re-ostnd

umoth aretedenkalesn-- asterted

Figure 22. Photograph showing a 60 cm thick seam of black chromite ore layered within the ultramafic rocks at RedMountain.

Potential hazards related to chromium deposits.—Weathering of ultramafic rocks produces two typeof surface waters (Barnes and O’Neil, 1969). The mocommon type is alkaline with pH values of about 8.3 8.6 and is enriched with magnesium bicarbonate. The sond and much less common type is a highly alkaline, ccium hydroxide water with pH values of about 11.2 11.8. Because most chromium deposits are found in ulmafic rocks, it is important to understand how wateflowing from such rocks interact with chromite. Althougchromite is resistant to chemical and physical weatherand highly insoluble in near-neutral surface water, in socases, small amounts of chromium can be found in waas either a trivalent or the highly oxidized hexavalent for(Hem, 1992). Trivalent chromium is the dominant form most surface waters, but in highly oxygenated, alkaliwaters of pH greater than 9, hexavalent chromium pdominates. This hexavalent chromium poses the menvironmental concern because it is toxic to humans aanimals (Simon and others, 1994).

-sst

toec-al-totra-rshingmeterminne

Chromium concentrations in surface waters drainingthe Alaskan deposits.—Waters flowing from the two Alas-kan chromite localities studied are the alkaline, magnesibicarbonate type. Measured pH values of 7 to 8 at bdeposits indicate that the streams draining the depositsneutral to slightly alkaline. Stream water samples collecdownstream from the Red Mountain mine contain betwe0.5 and 1.0 ppb chromium, well below the State of Alasdrinking water standard of 100 ppb (table 1). Water sampcollected downstream from the Siniktanneyak locality cotain chromium below the 0.5 ppb lower limit of determination. Other heavy metals measured in the waters, suchnickel, copper, lead, and zinc, are also below drinking wastandards and similar in concentration to waters collecfrom background sites.

29GEOCHEMISTRY OF SURFACE WATERS DRAINING ALASKAN CHROMITE DEPOSITS

-l-akf

nsed theereinanlity

ro-edtoro-le

ALASKA

Fairbanks

Nome

Bering Sea PACIFIC OCEAN

ARCTIC OCEAN

Yukon Riv er

Chromium deposits and mineral occurrences

Chromium occurrences studied

EXPLANATION

0 250 500 KILOMETERS

Kuskokwim Riv

er

Anchorage

Siniktanneyak

Red Mountain

66˚

160˚ 150˚

60˚

Figure 23. Location map of the Alaskan chromium occurrences studied.

Stream waters contain low concentrations of chromium.—The low chromium concentrations in waters colected from the Red Mountain mine and the SiniktanneyMountain complex are consistent with the low solubility ochromium in slightly alkaline surface water. Concentratioof trivalent and hexavalent chromium were not determinin these studies because the total chromium contents ofwaters were low and because the water pH values wbelow 9. Such waters are unlikely to contain chromium the toxic hexavalent form. Results for these two Alaskchromite deposits suggest no adverse effect on the quaof waters emanating from the deposits. In addition, chmium concentrations entering streams below the RMountain deposit are probably not high enough adversely affect the fishery near Seldovia, although chmium accumulation in bottom sediments and possibtransference to fish were not evaluated.


Figure 24. Water flowing from an adit of an abandoned chromium mine.

31RADIOACTIVITY CONCERNS OF URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST-

ing

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URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEASTERN ALASKA

RADIOACTIVITY CONCERNS OF URANIUM AND THORIUM DEPOSITS

AT BOKAN MOUNTAIN, SOUTHEASTERN ALASKA

Naturally occurring uranium and thorium mineradeposits are of environmental significance because tproduce radon and radium through radioactive decay. Tassociated radioactivity is a health concern because exsive exposure to radioactivity can produce cancer humans. A few small uranium deposits are scattethroughout Alaska, but the only uranium mine (RosAdams) is on Bokan Mountain at the south end of PrinceWales Island about 60 km southwest of the town of Ketckan (fig. 25). Uranium and thorium are most widely usedthe nuclear power industry and for nuclear weapons, current social and political issues have depressed the prand demand for uranium. For these reasons, many uranmines, including the Ross-Adams, are presently closed, uranium deposits in Alaska are not currently under stuHowever, because of the health concerns associated radioactivity, potential hazards of deposits like those Bokan Mountain are summarized here.

Uranium deposits on Bokan Mountain.—In 1955,prospectors found radioactive uranium- and thorium-bearquartz-rich veins in granite over a 30 km2 area on BokanMountain (fig. 26) (Roppel, 1991). These veins are highradioactive and widespread in this area, but most of the veare small, generally 2 cm or less in width. Primary radioative minerals in the prospects include uraninite, thorianite,and uranothorite. Some of the veins at Bokan Mountaiexceed 10 percent thorium ore (ThO2) and 1 percent uraniumore (U3O8), which are considered high concentration(Thompson, 1988). Although several of the veins have beprospected, only the Ross-Adams deposit has been m(fig. 27). Initially at Ross-Adams, a 110 m long, 15 m widand 10 m deep open pit was developed (MacKevett, 196but later underground workings were driven along a 110long pipe. The deposit was mined intermittently from 195to 1971 until the ore was exhausted. Altogether, ab85,000 t of high-grade uranium ore averaging about 1 pcent U3O8 was produced (Staatz, 1978). The Ross-Adaopen pit still contains some stockpiles of radioactive rock

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Human hazards of radioactive deposits.—In certainconditions, radioactivity associated with uranium and thrium deposits can be of environmental concern. The mahealth concerns for humans are long-term exposure to:

Radon in confined air spaces. Radon concentratiocould be high near any radioactive deposit.

Uranium, radium, and radon in drinking wateUranium is easily oxidized by air and water, anoxidized uranium compounds, as well as by-producradium and radon, are soluble in water. Thorium water is generally of lesser concern because it occin low concentrations in most surface waters, athorium minerals do not dissolve easily in water.

Surface radiation and inhalation or ingestion radioactive dust. In all these cases, long-term exposure to radioactiv

must be considered unlikely because the mines on BoMountain are closed and the area is so remote. For examsurface and ground waters near the Bokan deposits cohave high concentrations of dissolved uranium, radium, aradon, but the area is distant from any major water suppl


ALASKA

Prince of Wales Island

Petersburg

Wrangell

Ketchikan

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PRINCE O

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0 50 100 KILOMETERS

57˚

56˚

55˚

54˚

130˚134˚

Figure 25. Location of Bokan Mountain uranium deposits.

33RADIOACTIVITY CONCERNS OF URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST-

Figure 26. View of the granitic intrusion (center) at Bokan Mountain.

Figure 27. Photograph from the 1960’s showing mining of uranium ore at the Ross-Adams mine.

URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEASTERN ALASKA 33

35SUMMARY

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SUMMARY

The studies of Alaskan mineral deposits presenherein show that various types of mineral deposits have vdifferent geochemical characteristics that influence tchemistry of waters draining the mineral deposits. Thecharacteristics are directly related to the mineraloggeochemistry, and geology of each mineral deposit. Fsome deposits, downstream water geochemistry may preenvironmental problems for the local ecosystems. For exaple, the most adverse effects were observed downstrefrom the massive sulfide deposits in the northwestern BroRange and in Prince William Sound, where water sampcontain the highest concentrations of metals and lowestvalues of the deposits studied here (fig. 28). Such acid- metal-rich waters result from the weathering of pyrite aother base-metal sulfide minerals in these deposits that facid and release heavy metals during the process. Wsamples collected near the massive sulfide deposits may tain heavy metal concentrations in excess of State and Feral water standards (table 2). Although waters emanafrom these deposits are high in acid and metal content, thwaters are rapidly diluted downstream, usually within a fekilometers below the deposits (for example, deposits in Brooks Range).

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Most of the other Alaskan deposits studied contain loacid and metal concentrations in water collected downstrefrom the deposits (fig. 28). For example, stream waters clected downstream from mercury deposits in southwestAlaska have near-neutral pH values and contain low merccontents, suggesting that these deposits produce only mamounts of acid and heavy metals upon weathering. The dissolved mercury concentration is due to the presencecinnabar, which is resistant to physical and chemical weaering and does not easily form acid water. A greater envirmental problem of the mercury deposits is the elevamercury concentrations in stream sediment samples andthat were collected downstream from the mines and depohowever, the mercury concentrations in the fish are belthe recommended FDA level for mercury in edible fish, sugesting only minor effects on local food chains. Alaskgold veins and gold placer deposits contain pyrite and otsulfide minerals capable of producing acid water, but tamount of these sulfide minerals is generally small. Thweathering of such deposits does not produce water with nificant concentrations of acid or heavy metals. Similarthe chromium-bearing deposits contain little or no pyritand waters draining these deposits contain low-metal ccentrations and have near-neutral pH values.

The case studies presented herein summarize the eronmental effects of several types of mineral deposits. Tresults emphasize the need for additional, well-designgeochemical studies, which are necessary for the classiftion and understanding of any mineral deposit, but whiwill also address potential environmental concerns. Enviromental geochemical studies are now a common practicethe mining industry, before, during, and subsequent to mining of mineral deposits. These studies help predunique effects of mineral deposits on the surrounding enronments. Environmental geochemistry can be useful inphases of mineral exploration, as well as in mine plannidevelopment, and remediation.


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acid, high metal near neutral, high metalhigh acid, high metal

massive sulfide deposits (northwestern Brooks Range)

ultra high acidand metals

Au deposits

Hg deposits

Cr deposits

massive sulfide deposits (Prince William Sound)

acid, low metal near neutral, low metal

Increasing pyritedecreasing neutralizing capacity

Figure 28. Plot of dissolved metal concentrations in water versus water pH for several Alaskan deposit types. This plot shows that thewaters emanating from Alaskan mercury, gold, and chromium deposits have near-neutral pH and low dissolved metal contents, whereasAlaskan massive sulfide deposits form waters that are often high in acid and metal contents.

Table 2. Geochemical data summary of mineral deposits studied.

______________________________________________________________________________________Deposit type Elements of Element concentrations in water pH range in environmental concern exceeding EPA-CMC standards1 stream water______________________________________________________________________________________Massive sulfides Pb, Zn, Cd, Cu 2,250 ppb Pb, 272,000 ppb Zn, 2.8–8.1 (sedimentary rock 800 ppb Cd, 360 ppb Cu hosted)Massive sulfides Cu, Pb, Zn, Cd 3,600 ppb Cu, 3,300 ppb Zn, 2.6–7.3 (volcanic rock 220 ppb Pb, 27 ppb Cd hosted)

Gold veins As, Pb, Zn, Cd, Sb 6.4–8.0Gold placers As, Pb, Zn, Cd, Hg 6.5–8.1Mercury Hg, Sb, As 7.0–8.4Chromium Cr 6.7–9.3

______________________________________________________________________________________1CMC is the Environmental Protection Agency’s water quality criteria to protect against acute effects in

aquatic life and is the highest instream concentration of a toxic pollutant consisting of a 1-hour average notto be exceeded more than once every 3 years on the average.

37REFERENCES CITED

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REFERENCES CITED

For more information on the silver-lead-zinc mineraldeposits in the northwestern Brooks Range see:

Dames and Moore, 1983, Environmental baseline studies, Red Project: Prepared for Cominco Alaska, Inc., Anchorage, AK

Kelley, K.D., 1995, Natural environmental effects of silver-leazinc deposits in the Brooks Range, Alaska: U.S. GeologiSurvey Fact Sheet 092-95.

Kelley, K.D., and Taylor, C.D., 1996, Natural environmental effecassociated with the Drenchwater zinc-lead-silver massive sfide deposit, west-central Brooks Range with comparisonsthe Lik and Red Dog deposits, in Moore, T.E., and Dumoulin,J.A., eds., Geologic studies in Alaska by the U.S. GeologiSurvey, 1994: U.S. Geological Survey Bulletin 2152, p. 31–4

Runnels, D.D., Shepherd, T.A., and Angino, E.E., 1992, Metalswater—Determining natural background concentrations mineralized areas: Environmental Science and Technology26, p. 2316–2323.

For more information on massive sulfide deposits inPrince William Sound please refer to:

Goldfarb, R.J., Nelson, S.W., Taylor, C.D., d’Angelo, W.M., anMeier, A.L., 1996, Acid-mine drainage associated with volcnogenic massive sulfide deposits, Prince William Sound, Alka, in Moore, T.E., and Dumoulin, J.A., eds., Geologic studiin Alaska by the U.S. Geological Survey, 1994: U.S. Geolocal Survey Bulletin 2152, p. 3–16.

For more information on mercury in southwesternAlaska please refer to:

Gray, J.E., 1994, Environmental geochemistry of mercury mineAlaska: U.S. Geological Survey Fact Sheet 94-072.

Gray, J.E., Meier, A.L., O’Leary, R.M., Outwater, C., and Thodorakos, P.M., 1996, Environmental geochemistry of merry deposits in southwestern Alaska—Mercury contents fish, stream-sediment, and stream-water samples, in Moore,T.E., and Dumoulin, J.A., eds., Geologic studies in Alaska the U.S. Geological Survey, 1994: U.S. Geological SurvBulletin 2152, p. 17–30.

Gray, J.E., Theodorakos, P.M., Budahn, J.R., and O’Leary, R.1994, Mercury in the environment and its implicationKuskokwim River Region, southwestern Alaska, in Till, A.B.,and Moore, T.E., eds., Geologic studies in Alaska by the UGeological Survey, 1993: U.S. Geological Survey Bullet2107, p. 3–13.

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tsul- to

cal6. inin, v.

da-as-esgi-

For more information on southern Alaska gold veindeposits please refer to:

Carrick, S., and Maurer, M., 1994, Preliminary water resouassessment of the Girdwood area, Alaska: Division of Geolical and Geophysical Surveys Public-Data File 94-51, 36 p.

Cieutat, B.A., Goldfarb, R.J., Borden, J.C., McHugh, J.B., and Tlor, C.D., 1994, Environmental geochemistry of mesothermgold deposits, Kenai Fjords National Park, south-central Alka, in Till, A.B., and Moore, T.E., eds., Geologic studies iAlaska by the U.S. Geological Survey, 1993: U.S. GeologiSurvey Bulletin 2107, p. 21–26.

Trainor, T.P., Fleisher, S., Wildeman, T.R., Goldfarb, R.J., aHuber, C., 1996, Environmental geochemistry of the McKinlLake gold mining district, Chugach National Forest, Alaska,inMoore, T.E., and Dumoulin, J.A., eds., Geologic studies Alaska by the U.S. Geological Survey, 1994: U.S. GeologiSurvey Bulletin 2152, p. 47–58.

For more information on Alaskan placer deposits pleaserefer to:

Ray, S.R., Vohden, J., and Morgan, W., 1992, Investigation of trmetals related to placer mining on Fairbanks and PorcupCreeks: Alaskan Division of Geological and Geophysical Sveys, Public-Data File 92-13, 27 p.

Swainbank, R.C., Bundtzen, T.K., Clough, A.H., Henning, M.Wand Hanson, E.W., 1995, Alaska’s Mineral Industry, 199Division of Geological and Geophysical Surveys, SpecReport 49, 77 p.

U.S. Minerals Management Service, 1989, Mercury in the marenvironment, workshop proceedings: OCS MMS 89-0049.


kan.S.

thetan,

m,, v.

ralst-

For more information on chromium studies pleaserefer to:

Barnes, Ivan, and O’Neil, J.R., 1969, The relationship betwefluids in some fresh alpine-type ultramafics and possible mern serpentinization, western United States: Geological Socof America Bulletin, v. 80, p. 1947–1960.

Hem, J.D., 1992, Study and interpretation of the chemical chateristics of natural water: U.S. Geological Survey WateSupply Paper 2254, 263 p.

Simon, N.S., Demas, C., and d’Angelo, W., 1994, Geochemisand solid-phase association of chromium in sediment from Calcasieu River and estuary, Louisiana, U.S.A.: ChemiGeology, v. 116, p. 123–135.

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ds;s;art

enod-iety

rac-r-

trythecal

For more information on the mineral deposit at BokanMountain please refer to:

MacKevett, E.M., Jr., 1963, Geology and ore deposits of the BoMountain uranium-thorium area, southeastern Alaska: UGeological Survey Bulletin 1154, 125 p.

Roppel, Patricia, 1991, Fortunes from the Earth—An history of base and industrial minerals of southeast Alaska: ManhatKans., Sunflower University Press, 139 p.

Staatz, M.H., 1978, I and L uranium and thorium vein systeBokan Mountain, southeastern Alaska: Economic Geology73, p. 512–523.

Thompson, T.B., 1988, Geology and uranium-thorium minedeposits of the Bokan Mountain Granite Complex, southeaern Alaska: Ore Geology Reviews, v. 3, p. 193–210.

For information on water standards please refer to:Alaska Department of Environmental Conservation, 1994, Drin

ing water regulations: State of Alaska, Department of Enviromental Conservation report 18-ACC-80, 195 p.

Environmental Protection Agency, 1992, Water quality standarestablishment of numeric criteria for priority toxic pollutantStates’ compliance; final rule: Federal Register, 40 CFR P131, v. 57, no. 246, p. 60847–60916.

39GLOSSARY

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ral

ussifics

GLOSSARY

amalgamation of gold. A process used for the separatioof gold. Gold, especially fine grained gold, can brecovered using liquid mercury, which has the abilito blend or stick to gold, thereby effectively extractingold particles from stream-sediment samples. Amgamation of gold was widely used in the early 1900for gold extraction in many gold deposits, especialplacer deposits.

acid drainage. The formation of acid water principally bysurface oxidation of rocks containing sulfide mineralsuch as pyrite (iron sulfide). When surface watcomes in contact with the sulfide minerals, sulfuracid is produced, which further dissolves surroundirocks and minerals. Metals are often more solubleacid solutions, and thus, acid drainage generally cries high concentrations of dissolved metals. Suacid waters found downstream from mines are callacid-mine drainage.

arsenopyrite. Iron-arsenic sulfide (FeAsS), steel gray to siver white in color, common in vein gold deposits anin some massive sulfide deposits.

background concentrations. In geochemistry, this refers tochemical concentrations in natural materials that hanot been influenced by the activities of humans. studies of mineral deposits, background samples those collected from unmineralized areas, generaupstream from mines or distant from mineralized areThus, geochemical backgrounds represent concentions that are considered “normal or usual” and aunaffected by mineral deposits or mining.

bioaccumulation. Increase of metal concentrations iorganisms through uptake from water or food source

biomagnification. Increasing element concentrations witascending position in the food chain.

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s,ericng inar-ched

l-d

veInarelly

as.tra-re

n

chalcopyrite. Copper-iron sulfide (FeCuS2), brass yellow incolor, is common in a variety of mineral deposits andan important ore of copper.

chromite. Iron-chromium oxide (FeCr2O4) is a hard, heavymineral, typically black or dark brown. Chromite ifound in mafic and ultramafic rocks and is a commoore of chromium.

cinnabar. Mercury sulfide (HgS) is most commonly a brilliant red color. Cinnabar contains 86 percent mercuand is an important ore of mercury.

ecosystem. An area consisting of the physical environmeand its living elements (such as plants and animals) anonliving elements (such as water, rocks, and sothat might affect this area.

galena. Lead sulfide (PbS) that commonly contains signifcant amounts of silver. Galena is usually silver grayblue gray in color, forms cubes, and is common many vein and massive sulfide deposits. Galena isimportant ore of lead and silver.

heavy metals. These are among the most toxic of the metaCopper, lead, zinc, cadmium, mercury, and iron acommon heavy metals, and such metals have hatomic weights, and therefore are commonly call“heavy metals.” These metals have a high affinity fsulfur and often form sulfur compounds, and becausulfur is easily oxidized by air and water, these metacan be transported in water downstream from minedeposits that contain them.

marcasite. An iron sulfide (FeS2) mineral, commonly lightgray to brassy in color, that has a radiating fibroform, is dimorphous with pyrite, and often resemblepyrite in appearance; but marcasite has a lower specgravity. Marcasite is common in sedimentary rockand some ore deposits.


-

p-f

dds-ts

nin

pH. A measure of the amount of acid or base in a solutipH is related to the concentration of the hydrogen ioNeutral solutions have a pH of 7, whereas the pHacid solutions is less than 7 and alkaline solutions hapH values greater than 7. Acids generally have excess of hydrogen ions (H+) and bases have an excesof hydroxyl ions (OH-). Sulfuric acid (H2SO4) is anexample of a strong acid, and sodium hydroxid(NaOH), a type of lye, is a strong base.

ppb. Abbreviation for parts per billion. This is a concentration measured as micrograms per liter or as micgrams per kilogram.

ppm. Abbreviation for parts per million. This is a concentration measured as milligrams per liter or as milgrams per kilogram.

pyrite. Iron sulfide (FeS2) is one of the most widespreadsulfide minerals and is common in metallic minerdeposits. Pyrite is typically cubic in form and palebronze or brass-yellow in color; it is often calle“fools gold.” The primary concern of pyrite in min-eral deposits is its tendency to form strong acid (sulric acid) upon oxidation.

pyrrhotite. An iron sulfide mineral, generally bronze to redbrown in color, commonly massive and not often founas crystals. Pyrrhotite is common in massive sulfideposits and may contain significant amounts of nickit is therefore a source of nickel in some deposits.

sphalerite. Zinc-iron sulfide ((ZnFe)S), yellow, brown, orblack in color. Sphalerite often contains minor amounof cadmium, arsenic, and manganese, and is a wspread zinc ore.

stibnite. Antimony sulfide (Sb2S3), silver-gray sulfidemineral with a bright metallic luster that commonlforms bladed crystals containing striations. Stibnitethe principal ore of antimony and often contains somsilver and gold.

sulfide minerals. Minerals containing the reduced form osulfur (S2-), which is bound with common metals, sucas iron in pyrite (FeS2), lead in galena (PbS), zinc insphalerite (ZnS), mercury in cinnabar (HgS), amoothers. Sulfide minerals are common in many typesmetallic mineral deposits. Many of these minerals cbe of environmental concern because they can prodacid during oxidation. When acid is formed, it can disolve metals in surrounding minerals and rocks, releing them into surface waters of streams and rivers.

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thorianite. Thorium oxide (ThO2), a thorium ore, generallycubic in form and highly radioactive, containing impurities or rare earth elements such as cerium.

ultramafic rock. A rock composed primarily of mineralssuch as pyroxene and olivine. Ultramafic rocks are tyically of igneous origin, dark in color, and consist operidotite, pyroxenite, and dunite rock types.

uraninite. Uranium oxide (UO2), commonly called pitch-blende, is black, brown or steel gray in color, ancommonly contains thorium, radium, cerium, anlead impurities. Uraninite is highly radioactive, eaily oxidized, and common in vein mineral deposiin granites.

uranothorite. Thorium-uranium silicate ((Th, U)SiO4),highly radioactive, typically brown, or black, and is aore of uranium and thorium found most commonly vein deposits in granites.

Manuscript approved for publication February 28, 1996Published in the Central Region, Denver, ColoradoGraphics by Richard P. Walker, Barbara Ramsey, and

Carol A. QuesenberryPhotocomposition and design by Carol A. QuesenberryEdited by Lorna Carter and Carole A. BalesOnline composition by Joan G. Nadeau

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may be pur-chased by mail and over the counter in paperback book form and as a setof microfiche.

“Publications of the U.S. Geological Survey, 1971-1981”

may bepurchased by mail and over the counter in paperback book form (two vol-umes, publications listing and index) and as a set of microfiche.

Supplements

for 1982, 1983, 1984, 1985, 1986, and for subse-quent years since the last permanent catalog may be purchased by mailand over the counter in paperback book form.

State catalogs

, “List of U.S. Geological Survey Geologic and Wa-ter-Supply Reports and Maps For (State),” may be purchased by mail andover the counter in paperback booklet form only.

“Price and Availability List of U.S. Geological Survey Publica-tions,”

issued annually, is available free of charge in paperback bookletform only.

Selected copies of a monthly catalog

“New Publications of theU.S. Geological Survey” is available free of charge by mail or may be ob-tained over the counter in paperback booklet form only. Those wishing afree subscription to the monthly catalog “New Publications of the U.S.Geological Survey” should write to the U.S. Geological Survey, 582 Na-tional Center, Reston, VA 22092.

Note.

–Prices of Government publications listed in older catalogs,announcements, and publications may be incorrect. Therefore, the pricescharged may differ from the prices in catalogs, announcements, and pub-lications.