Distribution of pH Values and Dissolved 

Trace-Metal Concentrations in Streams

By Winfield G. Wright, William Simon, Dana J. Bove, M. Alisa Mast, 

and Kenneth J. Leib

Chapter E10 of

Integrated Investigations of Environmental Effects of Historical 

Mining in the Animas River Watershed, San Juan County, Colorado

Edited by Stanley E. Church, Paul von Guerard, and Susan E. Finger

Professional Paper 1651

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract .......................................................................................................................................................501

Introduction.................................................................................................................................................501

Purpose and Scope ..........................................................................................................................502

Methods of Study .......................................................................................................................................502

Sample Collection .............................................................................................................................502

Selection of Mines that May Affect the Environment ................................................................515

Geologic Setting .........................................................................................................................................515

Major Events of Mineralization, Alteration, and Igneous Intrusion .........................................515

Hydrothermal Alteration ..................................................................................................................518

Undisturbed Sources........................................................................................................................518

Data Presentation ......................................................................................................................................518

Distribution of pH Values and Dissolved Trace-Metal Concentrations ............................................519

pH Values ...........................................................................................................................................519

Aluminum............................................................................................................................................521

Copper ................................................................................................................................................526

Iron .....................................................................................................................................................527

Manganese ........................................................................................................................................533

Zinc .....................................................................................................................................................535

Other Metals ......................................................................................................................................537

Summary......................................................................................................................................................539

References Cited........................................................................................................................................539

Figures

 1–6. Maps showing:

 1. Locations of water-quality sampling sites where data were collected 

 for construction of low-flow distribution maps ............................................................503

 2. Locations of water-quality sampling sites where data were collected 

 for construction of high-flow distribution maps ...........................................................510

 3. Locations of inactive mines, prospect pits, and mining-related features 

 identified from topographic maps, high-ranking draining mines and 

 waste-rock piles, and permitted sites ............................................................................516

 4. Distribution of pH values in streams during low flow ..................................................520

 5. Distribution of pH values in streams during high flow ................................................522

 6. Distribution of dissolved aluminum concentrations in streams during 

 low flow ...............................................................................................................................523

 7. Photograph showing aluminum hydroxysulfate precipitates in discharge from 

Governor mine (Paradise portal), Middle Fork Mineral Creek subbasin .........................524

 8. Map showing distribution of dissolved aluminum concentrations in streams 

during high flow ........................................................................................................................525

 9. Graph showing relation of pH values to dissolved aluminum concentrations 

in selected streams, compared to solubility lines for gibbsite (log K=9.35) and 

amorphous Al(OH)3

 (log K=10.8) .............................................................................................526
 10. Map showing distribution of dissolved copper concentrations in streams 

during low flow ..........................................................................................................................528

 11. Map showing distribution of dissolved copper concentrations in streams 

during high flow ........................................................................................................................529

 12. Graph showing dissolved copper concentrations in Cement Creek and 

in Animas River downstream from Silverton, showing opposite responses 

to snowmelt runoff during April–September 1997 ...............................................................530

 13. Photographs showing iron oxyhydroxide precipitates in discharge from 

undisturbed springs ..................................................................................................................531

 14. Map showing distribution of dissolved iron concentrations in streams 

during low flow ..........................................................................................................................532

 15. Map showing distribution of dissolved manganese concentrations in streams 

during low flow ..........................................................................................................................534

 16. Photographs showing manganese precipitates in discharge from undisturbed 

springs in California Gulch ......................................................................................................535

 17. Map showing distribution of dissolved zinc concentrations in streams during 

low flow ......................................................................................................................................536

 18. Map showing distribution of dissolved zinc concentrations in streams during 

high flow .....................................................................................................................................538

Tables

 1. Selected water-quality data for construction of the low-flow distribution maps.............504

 2. Selected water-quality data for construction of the high-flow distribution maps ...........511

 3. Selected draining mines, waste-rock piles, and permitted sites in the Animas 

River watershed study area ....................................................................................................517

Abstract

The Animas River watershed study area contains nearly 

5,400 inactive mines, prospect pits, and other mining-related 

features. Many of these features do not affect water-quality 

conditions. For this study, a subset of mines was selected representing draining mines, mine waste-rock piles, and permitted 

mine and mill sites that may affect the environment.

Dissolved trace-metal concentrations and pH values in 

streams throughout the watershed were highly variable and 

depended on factors such as hydrothermal alteration, acidneutralizing capacity of the rocks, and mixing of different 

waters. Hydrothermal alteration was the primary influence on 

distribution of trace-metal concentrations, because the rocks 

in the Animas River watershed have a wide range of mineral 

assemblages. Many of the historical mines are located in 

highly mineralized and altered areas.

Spatial distribution maps prepared for this report display 

areas of hydrothermal alteration and locations of selected 

historical mine sites. They show color ranges for different pH 

values and dissolved trace-metal concentrations in study area 

streams, and they depict low-flow and high-flow conditions of 

the streams.

Because of the combined effects of hydrothermal alteration and historical mines, to attribute low pH values and 

high trace-metal concentrations to either source is difficult; 

however, several historical mines clearly affect the study area 

streams. Several non-mining related iron and manganese 

springs affect low pH values and high trace-metal concentrations, for example, near peak 3,792 m in Mineral Creek basin, 

in Cement Creek, and in California Gulch.

Introduction

Trace metals are inorganic chemicals usually occurring 

in small amounts in nature. In the Animas River watershed 

study area, however, trace metals such as aluminum, copper, 

iron, manganese, and zinc can occur in high concentrations 

due to the weathering of mineralized rocks and drainage 

from historical mines. These high concentrations can be harmful to the aquatic life in the Animas River and its tributaries 

(Besser and Brumbaugh, this volume, Chapter E18; Besser 

and others, this volume, Chapter D). High concentrations of 

copper and zinc in streams can be acutely toxic to fish and 

other aquatic life. High concentrations of aluminum and iron 

cause the precipitation of solids in zones where acidic and 

more neutral waters mix, and the precipitates can reduce 

productivity of food sources for aquatic life or prohibit the 

development or retention of suitable aquatic habitat. High 

manganese concentrations can be toxic to aquatic life and 

are pervasive in streams of the study area because of the abundance of manganese-related minerals (Bove and others, this 

volume, Chapter E3) and the high solubility of manganese at 

the pH range of streams in the study area (Garrels and Christ, 

1965). The pH of stream water is an important control of trace 

metal solubility—where pH values are low, dissolved iron and 

aluminum concentrations generally are high; where pH values 

are high, iron and aluminum concentrations are low.

The study area has deep snowpack in the winter, and 

snowmelt runoff can increase streamflow by several orders 

of magnitude (Mast, Evans, and others, 2000; von Guerard 

and others, this volume, Chapter B), thereby diluting dissolved trace-metal concentrations in streams. Descriptions 

of climate, snowpack, annual streamflow, and the differences 

between low flow and high flow at selected sites can be found 

in Mast, Evans, and others (2000) and Leib and others (this 

volume, Chapter E11). Trace-metal precipitation and annual 

runoff in the study area exhibit some unusual characteristics 

that are not easily explained using accepted hydrologic and 

geochemical principles; some of these unusual characteristics are described in this chapter for the purposes of future 

investigation.

The presence of historical mines may contribute 

to or intensify the characteristics of pH and trace-metal 

distribution. Remediation of historical mines can bring about 

benefits to a watershed in the form of achieving levels of pH 

and trace-metal content closer to those of the undisturbed site. 

Effects of weathering of hydrothermally altered rocks on water 

Chapter E10

Distribution of pH Values and Dissolved Trace-Metal 

Concentrations in Streams

By Winfield G. Wright, William Simon,1 Dana J. Bove, M. Alisa Mast, and Kenneth J. Leib

1

Animas River Watershed Coordinator, Hermosa, Colo.
quality as well as trace-metal discharges from large springs are 

also important to consider, however, in attempts to remediate 

historical mining areas. Better understanding of the complex 

sources of spatial distribution of pH values and trace-metal 

concentrations can be used to indicate areas that might benefit 

most from mine-site remediation.

Purpose and Scope

The purposes of this chapter are the following:

• Describe the distribution of pH values and selected 

trace-metal concentrations in streams during low and 

high flow

• Describe some of the unusual characteristics of tracemetal precipitation and annual runoff in the watershed

• Show photographic examples of features that result 

from high trace-metal concentrations in waters of the 

study area.

Spatial distribution maps are presented using waterquality data collected during 1991–99. For the low-flow 

distribution maps, the data do not reflect a single snapshot of 

pH values and trace-metal concentrations in streams due to the 

wide area covered and the large number of samples that constitute the low-flow data set. For the high-flow distribution maps, 

data from a synoptic sampling of the watershed are presented; 

however, fewer sites are represented by the high-flow data set 

because access to the high country during snowmelt runoff 

was difficult or impossible. Ranges of trace-metal concentrations in streams are indicated on the spatial distribution maps 

to provide a pictorial presentation of the water-quality conditions in the watershed.

Methods of Study

Sample Collection

Low-flow data were collected during 1991–99. These 

data do not represent a steady-state snapshot of conditions 

in the watershed. The primary goal of the low-flow data was 

to show the ranges of water-quality conditions in the highaltitude tributary streams as they are influenced by hydrothermal alteration and the presence of historical mines. The 

ranges of pH and trace-metal concentrations do not substantially vary between years during low flow. Because of snowmelt, the most important contrasts occur between low-flow 

and high-flow conditions. Most of the low-flow data were 

collected by the U.S. Geological Survey (USGS) during late 

summer (Wright and Janik, 1995; Mast, Evans, and others, 

2000; Sole and others, this volume, Chapter G). A few of the 

samples were collected during late fall or mid-winter lowflow conditions. Data gaps were filled in by use of selected 

low-flow samples collected by the Colorado Department 

of Public Health and Environment (CDPHE) (Peter Butler, 

Robert Owen, and William Simon, Unpublished report to 

Colorado Water Quality Control Commission, Animas River 

Stakeholders Group, 2001), Schemel and others (2000), and 

Wirt and others (2001). Locations of the low-flow sampling 

sites are in figure 1, and the data are in table 1.

High-flow data were collected during June 23–25, 

1992, by the CDPHE. These sites were not as numerous as 

the low-flow sites and do not include the high-altitude tributary 

streams. Because of the diurnal streamflow fluctuations during 

snowmelt runoff (Leib and others, this volume, Chapter E11), 

these high-flow samples do not necessarily represent a steadystate snapshot of conditions in the watershed. Locations of the 

high-flow sampling sites are shown in figure 2, and the data are 

listed in table 2.

Site numbers for data collected by the USGS are prefixed 

with UA (upper Animas River site), CC (Cement Creek site), 

MC (Mineral Creek site), and MS (mine site) (table 1). The 

USGS collected samples for seasonal analyses at mainstem 

streams where CDPHE site numbers were used (1996–99 sampling dates), and the sites are prefixed with COA (Colorado 

Animas River site), COC (Colorado Cement Creek site), and 

COM (Colorado Mineral Creek site) (table 1). Site numbers 

for other low-flow sites are prefixed with AR for Animas 

River (Schemel and others, 2000) and PG for Prospect Gulch 

(Wirt and others, 2001). Site numbers for high-flow data 

collected by the CDPHE are prefixed with COA (Colorado 

Animas River site), COC (Colorado Cement Creek site), and 

COM (Colorado Mineral Creek site) (table 2).

At sites where water-quality samples were collected by 

the USGS, field parameters (pH, specific conductance, water 

temperature, discharge, and dissolved oxygen) were measured 

at the time of sample collection. Samples were filtered using 

0.45-μm (micrometer) filters and acidified using concentrated 

nitric acid for analysis of dissolved trace-metal concentrations. Samples were not collected for total (unfiltered) trace 

metals in the high-altitude tributary streams. Samples were 

analyzed within 6 months after collection by using inductively 

coupled plasma–atomic emission spectroscopy (ICP-AES). 

Sample collection methods and quality-assurance information 

for USGS data presented in this study are described in Mast, 

Evans, and others (2000). Methods for collection and analysis of CDPHE data are described in the internal document, 

“Guidance on Data Requirements and Data Interpretation 

Methods Used in Stream Standards and Classification 

Proceedings (July 1993)” (http://www.cdphe.state.co.us/wq/

Assessment/assessment_practices_and_methods.htm accessed 

August 14, 2002).

502 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 503

MC3

MC9

MC22

MC48

MC1

MC2

MC4

MC5

MC7

MC8

MC10

MC13 MC14

MC15

MC16

COM07

MC34

MC39

MC42

MC46

MC47

MC50

MC51

MC52

MC53

MC56

CC2

CC10

CC18

CC27

CC32

CC41

CC53

CC81

CC3

CC4

CC5

CC7

CC8

CC9

CC11

CC12

CC13

CC14

CC15

CC16

CC17

CC19

CC20

CC21

PG2259

CC28

CC31

CC30

CC38 CC51

CC101

COC21

CC58

CC59

CC60

CC61

CC62

CC64

CC78

CC79

CC80

CC134

CC84

CC86

UA1

UA5

UA8

UA9

UA11

UA12

UA13

UA14

UA16

UA17

UA19

UA20

UA22

UA24

UA26

UA28

UA34

UA2 UA3

UA4

UA6

UA7

UA15

UA18

UA21

UA23

UA25

UA27

UA29 UA30

UA31

UA32

UA33

UA42

UA43

UA44

UA45

UA46

UA47

UA48

UA49

UA50

UA51

Silverton

MC90

MC86

MC87

MC79

COM23

COM25

COM26

COM27

COM28

COM34

MC54

MC55

CC70

PG45

CC135

CC129

COC48

COC43

COC31

COC18

COM13

COA70

COA67

COA58

COA59

COA51

COA48

COA30

COA45

COA40

MC17 MC18

MC30

MC28 MC29

MC57

MC40

COM02

COM29

UA10

COA31

COA53

COA33

COA60

COA68

COA72

COC17

COC11

COC34

COC36

COC39

COC41

COM32

7

13A

13B

16

MC89MC88

MS82

MS81

x

Calif.

Mt.

COC06

COC40

AR3

PG347

PG800

PG1800

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

EXPLANATION

USGS sites and number (table 1) MC15, CC38, UA37, MS81

State of Colorado site and number (table 1) COA30, COC06, COM28

7 Photograph location referring to figure

number in text 

Large iron spring

Large manganese spring

Watershed study area

boundary

Red Mountain Pass

AR3, PG45 Other sites (table 1)

Animas Riverwatershed study area

C O L O R A D O

Durango

McCarty

Basin

Ross Basin

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

th Sou k For

Illinois 

Middle Fk M ni eral Cr

Gulch

Eureka

Maggie

Minnie

ou B lde Gulch r

Gulch

Gulch

Animas River

Cement Creek

California Gl

ace Pl Gl r

Picayune

Niagara

Burrows

x Storm Peak

 3,792 m

Ohio xPeak

Browns Gl

Prospect Gl

Topeka Gl

Anvil Mt x

Fork

North

x

Denver Lake

Horses

hoe Cr

Gl

Gl

Dry Gl

Cascade Gl

Hematite Gl

Grouse Gulch

Burns Gulch

Gulch

3745'

107o37'30" 107o45'

37o

52'30"

o

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTI CO NENTAL DIVIDE

OURAY CO Junction mine 

Vermilion Peak

elev. 4,235 m

Figure 1. Locations of water-quality sampling sites where data were collected for construction of low-flow distribution maps.
Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Animas River basin

UA1--- Boulder Gulch near mouth 9/26/97 14:00 5.00 93 7.45 7.4 63 <4 37 <3 25

UA2--- Burrows Creek upstream 

from North Fork

9/05/98 14:45 0.56 181 4.55 16.1 5,350 58 93 2,660 2,330

UA3--- Burrows Creek downstream 

from London mine

9/05/98 11:30 -- 215 4.30 13.0 9,140 66 137 2,540 3,880

UA4--- Burrows Creek downstream 

from wetland

9/05/98 13:40 0.71 192 4.49 15.7 6,230 63 146 2,910 2,510

UA5--- California Gulch upstream 

from mines

8/18/98 14:00 1.74 135 4.9 13.5 3,220 16 67 9,670 1,540

UA6--- California Gulch upstream from 

Mountain Queen mine

8/11/98 14:00 0.52 474 6.63 6.4 <40 10 <30 19 44

UA7--- California Gulch downstream 

from Mountain Queen mine

8/11/98 15:30 0.65 365 6.55 8.8 109 12 <30 143 204

UA8--- Cinnamon Creek near mouth 9/08/98 10:45 2.32 174 7.32 7.4 <40 <4 <30 <3 <20

UA9--- Cunningham Creek near mouth 9/23/98 14:15 7.46 260 8.13 12.1 <40 <4 <30 <3 27

UA10-- Eureka Gulch upstream from 

mines

9/08/98 12:00 0.04 86 5.81 7.5 112 <4 <30 27 198

UA11-- Eureka Gulch upstream from 

sink holes

9/13/98 15:00 0.53 161 6.62 10.8 <40 <4 <30 21 220

1aUA12-- Eureka Gulch downstream 

from cut dike

9/08/98 14:00 0.06 254 6.45 9.7 63 5 <30 1,210 2,070

UA13-- Eureka Gulch downstream 

from Terry tunnel

9/13/98 13:00 2.17 148 6.28 11.3 96 10 <30 287 338

UA14-- Eureka Gulch near mouth 9/14/98 11:30 6.72 308 7.10 8.4 140 6 <30 161 373

UA15-- Grouse Gulch near mouth 9/06/98 12:45 1.76 228 6.97 9.9 <40 <4 <30 <3 <20

UA16-- Hematite Gulch near mouth 9/23/98 13:50 0.68 277 8.24 9.0 <40 <4 <30 <3 <20

UA17-- Horseshoe Creek near mouth 9/04/98 10:40 0.95 109 6.76 8.5 <40 <4 <30 <3 34

UA18-- Lower California Gulch 8/18/98 16:00 2.19 278 5.32 12.3 1,800 8 113 8,640 1,440

UA19-- Maggie Gulch near mouth 9/23/98 12:55 1.98 232 8.49 9.2 <40 <4 <30 <3 <20

UA20-- Maggie Gulch upstream 

from mines

10/03/98 15:00 0.65 193 6.81 7.0 42 <4 <30 25 <20

UA21-- McCarty Basin 9/13/98 16:30 0.37 109 6.67 9.3 57 <4 <30 17 29

UA22-- Minnie Gulch upstream 

from Esmeralda mine

9/29/98 13:30 1.21 185 8.15 8.4 <40 <4 35 <3 <20

UA23-- Minnie Gulch near mouth 9/23/98 12:05 2.71 253 8.42 7.4 77 <4 <30 23 <20

UA24-- Niagara Gulch near mouth 9/09/98 9:40 0.51 195 7.27 6.4 <40 <4 <30 <3 <20

UA25-- North Fork upstream from 

Burrows Creek 

9/05/98 15:30 1.52 105 6.76 15.6 43 <4 <30 <3 44

UA26-- North Fork upstream from 

West Fork

9/06/98 11:30 2.60 114 5.99 10.7 55 9 <30 663 772

UA27-- North Fork downstream 

from Burrows Creek 

9/05/98 16:15 1.88 121 5.41 15.5 360 17 54 920 840

UA28-- North fork Minnie Gulch 10/3/98 13:15 0.26 219 6.79 4.4 <40 <4 <30 <3 <20

UA29-- Picayune Gulch near mouth 9/09/98 8:30 1.09 386 6.86 6.7 62 <4 <30 11 <20

UA30-- Placer Gulch upstream from 

Gold Prince mine

9/23/98 13:30 0.05 171 7.34 6.4 <40 <4 <30 <3 256

UA31-- Placer Gulch upstream from 

Sunbank mine

9/28/98 14:30 0.53 184 6.40 9.7 92 6 <30 270 905

UA32-- Placer Gulch downstream 

from Gold Prince mine

9/23/98 16:30 0.41 141 6.61 9.5 57 <4 <30 736 839

UA33-- Placer Gulch downstream 

from Sunbank mine

9/28/98 15:30 0.63 195 5.93 9.4 362 21 704 1,180 1,210

2bCOA33- Animas River at Eureka 9/23/98 11:05 8.78 219 6.48 6.6 <40 <4 <30 971 573

Table 1. Selected water-quality data for construction of the low-flow distribution maps.

[Some site names are informal place names used on local signage; ft3/s, cubic feet per second; SC, specific conductance; μS/cm, microsiemens per centimeter 

at 25°C; pH, s.u., standard units; temp., temperature; °C, degrees Celsius; Al, aluminum; Cu, copper; Fe, iron; Mn, manganese; Zn, zinc; Diss., dissolved; μg/L, 

micrograms per liter; <, less than; --, no data; BDL, below detection limit; data, unless otherwise indicated, are from Mast, Evans, and others, 2000]

504 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 505

Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Animas River basin—Continued

UA34-- South fork Eureka Gulch 9/07/98 15:00 3.70 307 6.37 10.4 115 5 431 116 46

UA42-- Stream downstream from 

Denver Lake

9/04/98 12:35 0.26 63 7.15 18.0 <40 <4 <30 <3 <20

UA43-- Stream downstream from 

Lucky Jack mine

9/04/98 12:15 0.06 100 6.72 14.1 <40 <4 33 205 665

UA44-- Stream in Placer Gulch 9/23/98 12:00 0.24 100 4.86 6.4 2,200 5 <30 922 154

UA45-- Upper Animas River upstream 

from Cinnamon Creek

9/08/98 11:40 4.80 211 6.22 10.4 369 16 75 3,690 1,430

UA46-- Upper Animas River upstream 

from Silver Wing mine

9/30/98 14:00 10.4 228 6.68 10.2 65 4 <30 1,300 628

UA47-- Upper Burns Gulch 9/07/98 11:00 2.30 147 6.60 6.8 <40 <4 <30 <3 35

UA48-- Upper Burns Gulch 9/07/98 12:00 2.07 160 6.81 8.9 59 28 <30 45 790

1aUA49-- Upper Picayune Gulch 9/08/98 14:00 0.39 208 7.44 16.0 141 <4 <30 96 28

UA50-- West Fork Animas River 

downstream from 

Placer Gulch

8/19/98 12:00 0.31 180 5.75 10.0 606 7 112 4,700 1,070

UA51-- West Fork Animas River 

at Animas Forks

8/19/98 15:00 3.49 190 5.89 13.1 326 19 <30 4,260 1,390

3cCOA60 Animas River downstream 

from Arrastra Creek

8/19/99 12:05 167 175 7.37 9.5 72 <4 <30 243 226

4dCOA68 Animas River at Silverton 9/30/98 13:15 34 295 7.27 11 80 <4 <30 1,220 351

5eCOA72 Animas River downstream 

from Silverton

9/30/98 11:00 111 440 6.73 7.5 77 <4 895 1,100 375

Cement Creek basin

CC2--- Cascade Gulch near mouth 9/04/97 16:20 0.50 243 7.96 7.0 <40 <4 <30 <3 <20

CC3--- Cement Creek upstream from 

Mogul mine

9/10/97 15:15 1.19 199 6.17 10.2 109 66 <30 745 1,200

CC4--- Cement Creek downstream 

from Ross Basin

9/10/97 10:15 0.40 189 6.82 8.1 76 23 <30 47 470

CC5--- Dry Gulch upstream from 

Eveline mine

9/26/97 9:30 0.27 89 3.89 7.3 907 36 155 64 91

CC7--- Fairview Gulch near mouth 9/26/97 12:15 0.71 113 7.50 7.2 <40 <4 <30 <3 <20

CC8--- Georgia Gulch near mouth 9/25/97 16:30 0.65 205 5.86 8.5 43 10 55 323 424

CC9--- Hancock Gulch near mouth 9/04/97 15:20 0.20 236 7.68 8.2 <40 <4 <30 <3 <20

CC10-- South fork, Hancock Gulch 

upstream from adit

8/29/97 14:15 0.20 233 6.93 4.7 <40 <4 <30 <3 <20

CC11-- South fork, Hancock Gulch 

at mouth

9/03/97 15:00 0.37 290 7.23 10.1 73 <4 <30 61 <20

CC12-- Illinois Gulch upstream from 

Yukon adit

9/04/97 17:00 0.05 162 7.91 8.4 <40 <4 <30 <3 <20

CC13-- Middle Fork Cement Creek 

near mouth

9/30/97 12:00 -- 444 6.64 4.6 45 <4 71 575 278

CC14-- Minnesota Gulch near mouth 9/27/97 13:00 0.77 196 6.90 13.8 45 5 <30 364 147

CC15-- Near mouth of gulch in 

drainage from Minnehaha 

Basin

9/30/97 15:45 0.71 144 7.32 7.6 68 6 <30 15 72

CC16-- Niagara Gulch downstream 

from Irene mine

9/28/97 11:25 0.06 437 3.14 11.0 1,530 99 19,370 420 448

CC17-- Niagara Gulch near mouth 9/28/97 14:30 0.49 247 3.51 11.8 2,930 20 2,460 194 93

6fCOC17- South Fork Cement Creek 

at Gladstone

11/03/98 14:30 2.34 700 5.75 2.9 974 42 2,250 2,370 965

Table 1. Selected water-quality data for construction of the low-flow distribution maps.—Continued
Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Cement Creek basin—Continued

CC18-- North Fork Cement Creek 

upstream from Gold King

9/24/99 14:00 0.08 395 4.79 5.5 100 <4 <30 507 64

CC19-- North Fork Cement Creek 

upstream from upper Gold 

King

9/22/99 15:00 0.14 300 3.70 9.7 1,350 136 204 385 549

CC20-- Porcupine Gulch upstream 

from mines

9/29/97 14:30 0.21 168 6.99 8.7 <40 <4 37 <3 <20

CC21-- Porcupine Gulch near mouth 9/29/97 16:00 0.34 655 6.38 10.2 86 <4 3,220 4,760 930

CC27-- Creek upstream from Queen 

Anne adit

9/06/97 13:00 0.20 176 7.20 7.8 <40 <4 <30 <3 96

CC28-- Creek downstream from Queen 

Anne adit near mouth

9/10/97 12:45 0.30 252 5.19 8.9 1,110 55 <30 1,660 1,410

CC30--- South Fork Cement Creek 

upstream from Natalie/

Occidental mine

10/17/96 14:00 0.48 191 5.36 3.8 168 8 <30 61 38

7gCOC31 Cement Creek at Fairview 

Gulch bridge

11/03/98 15:15 10.7 1,010 4.04 6.0 6,560 34 16,310 1,910 957

CC31--- South Fork Cement Creek 

downstream from Big 

Colorado mine

10/17/96 11:30 1.78 603 5.78 3.8 932 17 4,800 1,180 381

CC32--- South Fork Cement Creek 

downstream from Velocity 

Lake

10/17/96 15:30 0.43 150 7.10 3.0 98 <4 <30 10 <20

CC38--- Spring in Dry Gulch 8/12/98 14:00 <0.01 50 4.45 13.1 232 7 50 18 <20

CC41--- Spring in Minnehaha Basin 9/30/97 13:25 0.54 173 6.82 1.4 <40 <4 <30 <3 <20

8hCOC43 Cement Creek near Yukon 

tunnel

8/17/99 15:20 35.7 542 4.22 11 2,970 186 2,500 1,140 1,270

9iCOC48 Cement Creek at Silverton 9/30/98 14:30 18 963 3.78 12 4,810 26 4,100 2,490 605

CC51--- Headwaters of Ross Basin 9/05/97 14:10 0.01 287 6.96 1.2 <40 <4 <30 4 237

CC53--- Spring near Corkscrew Pass 9/07/97 14:35 0.01 76 3.92 11.2 1,000 <4 <30 12 <20

CC58--- Stream downstream from 

Kansas City mine

9/25/97 15:30 0.03 775 3.30 8.4 3,110 619 6,600 10,800 3,950

CC59--- Stream downstream from 

Lead Carbonate Mill

9/30/97 12:30 0.01 565 3.06 16.8 4,690 380 7,450 1,210 3,880

CC60--- Stream in Middle Fork 

Cement Creek

9/30/97 10:00 0.33 63 6.52 6.9 <40 <4 <30 5 <20

CC61--- Stream in Minnesota Gulch 9/27/97 10:00 0.26 146 7.46 12.6 63 <4 <30 13 <20

CC62--- Stream in Minnesota Gulch 9/27/97 11:15 0.07 444 3.32 14.2 2,150 65 2,380 864 763

CC64--- Stream in Niagara Gulch 9/28/97 13:10 0.03 673 2.97 16.7 7,160 41 11,650 332 93

CC70--- Stream in upper Prospect 

Gulch

9/10/97 15:00 0.05 158 6.83 10.0 <40 <4 64 191 <20

CC78--- Stream near Adams mine 10/01/99 13:00 -- 52 4.59 2.5 437 17 <30 61 74

CC79--- Telephone gulch upstream 

from adit

9/05/97 11:05 0.05 124 4.58 7.1 583 19 60 70 42

CC80--- Telephone gulch at mouth 9/05/97 12:15 0.03 160 4.28 10.0 1,750 31 33 149 56

CC81--- Tributary of upper Cement 

Creek

9/07/97 13:45 0.01 163 7.16 16.5 55 <4 <30 9 <20

CC84--- Tributary of upper Cement 

Creek

9/07/97 13:35 0.006 76 6.7 8.4 <40 <4 <30 <3 <20

CC86--- Upper Georgia Gulch 9/25/97 13:25 0.28 316 6.54 9.2 133 <4 <30 559 178

10jCC101-- South Fork Cement Creek 

upstream from Middle Fork

10/17/96 10:00 1.87 640 5.07 1.8 1,030 24 4,130 1,310 473

10jCC129-- Topeka Gulch upstream 

from mines

9/04/94 17:00 0.15 558 3.27 9 6,800 41 13,000 1,200 206

10jCC134-- Topeka Gulch at mouth 9/10/94 17:00 0.19 1,480 6.72 10.1 153 7 870 2,000 74

10jCC135-- Upper Ohio Gulch 9/30/94 14:00 0.001 980 3.34 9.4 11,000 336 2,300 9,900 1,200

Table 1. Selected water-quality data for construction of the low-flow distribution maps.—Continued

506 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 507

Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Mineral Creek basin

MC1--- Bear Creek near mouth 9/27/97 14:30 -- 135 7.51 8.6 78 <4 <30 7 <20

MC2--- Browns Gulch upstream from 

Brooklyn mine

9/18/99 10:40 0.80 281 4.62 4.0 9,110 18 405 569 55

MC3--- Browns Gulch near mouth 7/18/99 15:30 1.40 270 4.30 12.0 4,110 53 376 1,310 940

MC4--- Browns Gulch downstream 

from Brooklyn mine

9/18/99 12:15 1.04 349 4.01 5.6 8,110 67 829 1,470 749

MC5--- Creek draining Crystal Lake 

at mouth

8/27/98 16:35 0.40 204 6.84 12.9 59 <4 <30 <10 <20

11kCOM07 Mineral Creek at Chattanooga 4/06/99 14:15 1.76 205 4.19 0.3 1,080 594 1,060 462 3,050

MC7--- Middle Fork Mineral Creek 

upstream from Paradise 

portal

8/27/98 16:15 1.76 566 6.86 9.8 100 <4 310 <10 52

MC8--- Middle Fork Mineral Creek 

downstream from Paradise 

portal

8/27/98 14:05 3.96 874 5.32 11.4 2,710 <4 14,640 26 164

MC9--- Mill Creek near mouth 8/26/99 11:00 3.83 89 7.69 9.9 <40 <4 <30 <3 <20

MC10-- Mineral Creek near Red 

Mountain Pass

8/25/99 9:40 3.14 77 7.33 8.5 <40 <4 <30 <3 <20

MC13-- North tributary to Big Horn 

Gulch downstream from 

mines

9/21/99 17:00 0.36 200 4.84 8.9 252 69 228 150 494

12lCOM13 Mineral Creek at Burro Bridge 2/24/99 11:15 3.48 691 6.50 0.1 <40 129 <30 522 1,590

MC14-- Porphyry Gulch upstream from 

Bullion King mine

8/24/99 13:25 0.77 52 6.70 12.5 <40 <4 <30 4 <20

MC15-- Porphyry Gulch downstream 

from Bullion King mine

8/24/99 14:30 0.80 60 6.67 10.5 75 <4 <30 73 120

MC16-- Porphyry Gulch downstream 

from Highway 550

8/25/99 10:45 -- 68 7.18 10.4 45 <4 <30 <3 35

MC17-- North-flowing tributary to 

Middle Fork Mineral Creek

10/02/98 9:30 0.86 1,369 3.74 1.4 51,530 22 76,650 1,770 302

MC18-- North-flowing tributary to 

Middle Fork Mineral Creek

10/02/98 10:30 0.84 1,785 3.74 2.6 71,430 <4 117,290 2,150 353

MC22-- North-flowing tributary to 

Middle Fork Mineral Creek

10/2/98 14:30 1.01 1,406 3.32 11.2 54,020 21 69,310 1,840 354

13mCOM27 Mineral Creek upstream from 

South Fork

4/22/98 14:15 19.1 607 4.45 6.2 4,800 115 2,760 642 729

MC28-- Spring on lower Mineral Creek 8/12/98 16:30 0.002 465 3.59 8.3 11,880 147 33,520 1,180 445

MC29-- Spring on lower Mineral Creek 8/12/98 15:30 0.001 459 3.22 8.0 14,380 372 15,050 1,160 580

MC30-- Spring on lower Mineral Creek 8/28/97 17:30 0.001 576 3.02 15.8 7,650 80 4,260 772 314

MC34-- Spring near peak 3,792 m 8/28/97 11:30 -- 675 2.70 10.0 1,630 193 16,200 22 <20

14nCOM34 Mineral Creek at Silverton 9/25/97 12:30 181 203 6.82 7.6 44 <4 281 144 131

MC39-- Stream downstream from 

Congress mine

9/17/99 16:00 0.03 715 2.93 8.9 3,180 8,390 40,540 384 10,940

MC40-- Stream downstream from mine 

in US Basin

9/17/99 15:00 0.06 466 6.59 9.5 129 <4 134 3,970 353

MC42-- Stream east of Chattanooga 

beaver ponds

8/27/99 9:30 0.72 112 6.11 7.8 198 7 105 140 46

MC46-- Stream near Chattanooga 

beaver ponds

8/26/99 13:45 -- 313 3.25 -- 923 32 849 822 310

MC47-- Stream near peak 3,792 m 8/26/97 15:00 -- 377 3.63 -- 2,570 4 645 355 61

MC48-- Stream near peak 3,792 m 9/03/98 16:50 0.10 471 3.45 11.9 2,820 13 4,040 771 90

MC50-- Stream south of Browns Gulch 8/25/99 15:00 1.95 311 3.25 10.1 5,510 78 2,160 271 38

MC51-- Stream south of Browns Gulch 8/25/99 14:00 0.41 70 3.88 9.3 599 <4 211 46 29

Table 1. Selected water-quality data for construction of the low-flow distribution maps.—Continued
Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Mineral Creek basin—Continued

MC52-- Stream south of Browns Gulch 8/25/99 14:30 1.62 355 3.21 9.4 6,640 100 2,950 331 76

MC53-- Stream southwest of Ohio Peak 8/09/99 12:00 -- 1,035 2.61 9.8 14,800 44 36,790 4,130 186

MC54-- Upper Zuni Gulch 8/25/99 10:30 0.18 163 3.18 5.2 1,070 103 490 12 54

MC55-- Upper Zuni Gulch 8/25/99 10:00 0.05 17 5.53 6.9 74 <4 33 <3 <20

MC56-- Zuni Gulch near mouth 8/25/99 13:30 0.22 48 3.90 10.3 315 19 99 9 <20

MC57-- Spring downstream from mine 

northwest of Burro Bridge

9/13/99 17:00 0.36 241 6.24 4.6 71 <4 <30 7 25

MC79-- Middle Fork Mineral Creek 

at mouth

9/28/95 11:00 7.9 796 4.75 4.7 7,200 11 15,600 1,100 230

MC86-- Spring near Ophir Pass road 9/14/95 9:30 0.02 106 6.56 4.3 <1 <1 <1 <1 <1

MC87-- North tributary to Middle Fork 

Mineral Creek

9/19/95 17:00 0.09 180 6.78 13.6 <1 2 <1 <1 5

MC88-- Middle Fork Mineral Creek 

upstream from unnamed 

north-flowing tributary

9/20/95 10:30 5.6 778 6.39 6.7 120 5 10,400 990 72

MC89-- Middle Fork Mineral Creek 

downstream from unnamed 

north-flowing tributary 

9/20/95 12:00 7.2 800 4.58 8.0 7,100 8 18,100 1,100 120

MC90-- North tributary to Middle 

Fork Mineral Creek

9/20/95 14:00 0.06 143 8.02 13.3 30 1 <1 4 <1

MS81-- Koehler tunnel (prior to 

remediation)

9/25/95 10:00 0.02 3,520 2.45 2.3 71,400 98,600 686,000 23,700 228,000

MS82-- Junction mine drainage 

downstream from red pool

9/25/95 10:30 0.15 3,310 2.50 2.5 70,300 61,100 494,000 20,300 157,000

Colorado State sites (Unpub. report to Colorado Water Quality Control Commission, ARSG, 2001)

COA30-- Animas River downstream 

from Burns Gulch

9/11/91 -- 27 178 6.8 6.4 100 24 BDL 1,100 690

COA31-- Animas River upstream from 

Eureka

9/10/91 -- 19 162 7.2 12.2 110 18 BDL 780 570

COA40-- Animas River upstream from 

Minnie Gulch

9/10/91 -- 24 222 7.3 10.1 100 16 BDL 750 500

COA45-- Animas River downstream 

from Maggie Gulch

9/10/91 -- 58 1,900 7.3 12.0 58 5 14 320 340

COA48-- Cunningham Creek near 

mouth

9/10/91 -- 10.5 144 6.7 8.0 BDL BDL 10 BDL 11

COA51-- Cunningham Creek 9/9/91 -- 19.5 97 7.5 11.5 51 BDL 13 BDL BDL

COA53-- Animas River downstream 

from Howardsville

9/10/91 -- 88 160 7.0 7.0 86 BDL 45 230 270

COA58-- Arrastra Creek 9/10/91 -- 13 160 7.8 7.8 BDL BDL BDL BDL 120

COA59-- Upper Arrastra Creek 9/10/91 -- 8.3 150 7.6 5.5 BDL BDL 13 BDL 68

COA67-- Swansea Gulch 9/10/91 -- 1.8 92 6.9 4.9 BDL BDL 24 7 76

COA70-- Idaho Gulch 6/25/92 -- -- -- 8.1 4.7 BDL 9 BDL BDL 50

COC06-- North Fork Cement Creek 

at mouth

9/7/91 -- .18 353 3.1 6.5 8,400 1,400 16,000 2,200 4,200

COC11-- Upper Middle Fork Cement 

Creek

9/8/91 -- .30 227 8.4 5.5 BDL BDL BDL BDL 12

COC18-- Cement Creek downstream 

from North Fork

9/8/91 -- 2.4 376 3.8 6.6 2,700 360 1,300 2,000 3,100

COC21-- Cement Creek downstream 

from South Fork

9/8/91 -- 9.8 575 5.5 7.9 1,600 91 950 2,600 1,800

COC34-- Cement Creek downstream 

from Cascade Gulch

9/7/91 -- 12 735 4.2 9.0 3,900 64 6,200 1,900 1,000

COC36-- Cement Creek downstream 

from Minnesota Gulch

9/7/91 -- 13 705 4.7 9.5 3,900 62 5,700 1,700 960

Table 1. Selected water-quality data for construction of the low-flow distribution maps.—Continued

508 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 509

Site 

number 

(fig. 1)

Site name Date Time

Streamflow 

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp. 

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Diss.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Colorado State sites (Unpub. report to Colorado Water Quality Control Commission, ARSG, 2001)—Continued

COC39-- Cement Creek downstream 

from Porcupine Gulch

9/7/91 -- 19 945 4.0 10.5 4,000 72 5,500 1,800 1,000

COC40-- Ohio Gulch 9/7/91 -- 1.4 970 2.9 9.5 18,000 330 25,000 530 1,000

COC41-- Cement Creek downstream 

from Ohio Gulch

9/7/91 -- 18 650 4.0 10.3 4,900 85 5,800 2,000 960

COM02-- Mineral Creek at Red Mountain 

Pass

9/7/91 -- .50 2,600 2.6 8.5 67,000 62,000 490,000 17,000 180,000

COM23-- Upper South Fork Mineral 

Creek

9/6/91 -- 6.7 167 7.0 9.0 BDL BDL 10 26 13

COM25-- South Fork Mineral Creek 

downstream from Bandora 

mine

9/6/91 -- 8.4 170 6.9 10.1 130 BDL 52 24 95

COM26-- Clear Creek, Ice Lake basin 9/6/91 -- 5.7 126 7.8 10.1 BDL BDL BDL BDL BDL

COM28 South Fork Mineral Creek 9/6/91 -- 23 217 7.6 12.7 87 BDL 330 18 9

COM29-- Mineral Creek downstream 

from South Fork

9/6/91 -- 42 360 6.7 9.5 BDL 31 1,300 290 420

COM32-- Mineral Creek downstream 

from North Star mine

9/6/91 -- 36 260 6.1 14.0 BDL 8 750 260 300

Other sites

AR3--- Animas River upstream from 

Mineral Creek confluence 

(Schemel and others, 2000)

9/19/96 10:00 69 420 6.9 -- 48.5 -- 558 1,110 514

PG45-- Prospect Gulch downstream 

from shaft mines (Wirt and 

others, 2001)

9/29/99 -- .38 356 5.0 -- 750 83 290 290 810

PG347-- Prospect Gulch downstream 

from Lark mine (Wirt and 

others, 2001)

9/29/99 -- .55 556 3.4 -- 3,500 360 5,000 460 1,400

PG800-- Prospect Gulch downstream 

from all mines (Wirt and 

others, 2001)

9/29/99 -- .58 496 3.8 -- 3,900 340 5,400 480 1,700

PG1800 Prospect Gulch upstream from 

Red Spring (Wirt and others, 

2001)

9/29/99 -- .72 497 3.4 -- 4,400 360 4,300 500 1,700

PG2259 Prospect Gulch at mouth 

(Wirt and others, 2001)

9/29/99 -- 1.2 583 3.5 -- 10,000 230 20,000 610 1,500

1aData for these sites are revised from Mast, Evans, and others (2000).

2bSite A33, table 24 (Mast, Evans, and others, 2000).

3cSite A60, table 24 (Mast, Evans, and others, 2000).

4dTable 21 (Mast, Evans, and others, 2000).

5eTable 20 (Mast, Evans, and others, 2000).

6fSite C17, table 24 (Mast, Evans, and others, 2000).

7gSite C31, table 24 (Mast, Evans, and others, 2000).

8hSite C43, table 24 (Mast, Evans, and others, 2000).

9iTable 22 (Mast, Evans, and others, 2000).

10jSole and others (this volume).

11kSite M07, table 24 (Mast, Evans, and others, 2000).

12lSite, M13, table 24 (Mast, Evans, and others, 2000).

13mSite M27, table 24 (Mast, Evans, and others, 2000).

14nTable 23 (Mast, Evans, and others, 2000).

Table 1. Selected water-quality data for construction of the low-flow distribution maps.—Continued
x

California

Mountain

x Storm Peak Ohio x

Peak COM12

COM08

COM18

COM30

COM15

COM17

COM06

COM07

COM11

COM14

COC33 COC15

COC01

COC46

COC47

COC42

COC13

COC35

COC12

COC45

COC38

COC25

COC26

COC11

COC16

COC21

COC08

COC44

COA62

COA17

COA24

COA39

COA37

COA34

COA47

COA03

COA43

COA32

COA9

COA36

COA07

COA25

COA15

COA42

COA05

COA08

COA26

COA22

COA23

COA21

COA04

COA02

COA14

COA28

COA27

COA11

COA10

Silverton

COM22

COM23

COM25

COM26

COM27

COM28

COM34

COC24

COC48

COC43

COC30

COC18

COM13

COA70

COA67

COA58

COA59

COA51

COA48

COA30

COA45

COA40

COM02

COM29

COA31

COA53

COA33

COA60

COA68

COA72

COA20

COA55

COA64

COA65

COC02

COC03 COC06

COC17

COC34 COC36

COC39

COC40

COM01

COM03 COM05

COM10

COM19

COM32

COA13

COA56

COA61

COA66

COC09

COC22

COC23

COC27

COC31

COM20

EXPLANATION

State of Colorado site and number (table 2)

COM28, COA31,COC48

Watershed study area

boundary

Junction mine 

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

3745'

107 37'30" 107 45'

3752'30"

o

o

o o

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

ht Sou k For

Illinois Gl Middle Fk M ni eral Cr 

Gulch

Eureka

Maggie

Minnie

Boulder Gulch

Gulch

Gulch

Anima River s

Cement Creek

Cali of nia r Gl

Prospect Gl

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

CONTINENT L A DIVIDE

OURAY CO

3,792 mx

Vermilion Peak

elev. 4,235 m

Figure 2. Locations of water-quality sampling sites where data were collected for construction of high-flow distribution maps.

510 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 511

Site 

number 

(fig. 2)

Site name Date Time

Streamflow

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp.

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Tot.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Colorado State sites (Colorado Department of Public Health and Environment, unpub. data, 1992)

Animas River basin

COA02 Downstream from Lucky Jack mine 6/25/92 -- -- -- 6.88 18.6 130 4 -- -- 850

COA03 Horseshoe Gulch 6/25/92 -- -- -- 6.86 9.6 BDL BDL -- -- 22

COA04 North Fork Animas River upstream 

from Horseshoe Creek

6/25/92 -- -- -- 7.36 13.6 BDL BDL -- -- 53

COA05 North Fork Animas River upstream 

from Burrows Creek

6/25/92 -- -- -- 7.02 11.0 BDL BDL -- -- 190

COA07 Burrows Creek 6/25/92 -- -- -- 4.61 14.1 3,000 35 67 -- 1,600

COA08 North Fork Animas River 

downstream from Burrows 

Creek

6/25/92 -- -- -- 6.01 9.8 BDL 5 -- -- 430

COA09 North Fork Animas River at Animas 

Forks

6/25/92 -- -- -- 6.43 7.1 BDL 6 62 340 500

COA10 West Fork Animas River at Animas 

Forks

6/25/92 -- -- -- 6.02 7.7 640 23 78 2,900 1,000

COA11 West Fork Animas River downstream from Frisco tunnel6/25/92 -- -- -- 5.88 7.6 730 20 -- -- 960

COA13 West Fork Animas River downstream 

from Placer Gulch

6/25/92 -- -- -- 6.05 9.1 790 20 -- -- 960

COA14 North Fork Animas River 

downstream from Animas Forks

6/25/92 -- -- -- 5.95 6.3 390 17 68 -- 860

COA15 California Gulch downstream from 

Vermillion mine

6/25/92 -- -- -- 5.78 11.2 1,700 17 -- -- 990

COA17 California Gulch midway 6/25/92 -- -- -- 5.89 9.6 2,100 15 -- -- 1,100

COA20 Placer Gulch near mouth 6/25/92 -- -- -- 6.38 8.6 88 22 -- 1,900 950

COA21 Placer Gulch downstream from 

Sunbank mine

6/25/92 -- -- -- 6.23 7.9 190 42 -- -- 1,300

COA22 Placer Gulch upstream from 

Sunbank mine

6/25/92 -- -- -- 6.20 6.2 100 36 -- -- 1,300

COA23 Placer Gulch downstream from 

Gold Prince mine

6/25/92 -- -- -- 5.06 2.0 BDL 9 -- -- 1,100

COA24 Cinnamon Creek 6/25/92 -- -- -- 7.71 5.1 BDL BDL -- -- BDL

COA25 Grouse Gulch 6/25/92 -- -- -- 8.00 7.4 BDL BDL -- -- BDL

COA26 Picayune Gulch 6/25/92 -- -- -- 7.66 9.8 BDL BDL -- -- 14

COA27 Burns Gulch 6/25/92 -- -- -- 7.54 6.4 76 27 BDL -- 710

COA28 Animas River downstream from 

Burns Gulch

6/25/92 -- -- -- 7.35 6.3 53 6 -- -- 490

COA30 Animas River downstream from 

Silver Wing mine

6/25/92 -- -- -- 7.32 5.1 52 10 -- -- 480

COA31 Animas River upstream from 

Eureka Gulch

6/25/92 -- -- -- 7.11 4.1 59 -- -- -- 470

COA32 Niagara Gulch 6/25/92 -- -- -- 7.18 1.5 BDL BDL -- -- BDL

COA33 Animas River at Eureka 6/25/92 -- -- -- 7.13 19.1 67 7 61 -- 460

COA34 Eureka Gulch at mouth 6/25/92 -- -- -- 7.50 6.3 94 11 92 -- 550

COA36 South Fork Eureka Gulch 6/25/92 -- -- -- 7.40 6.5 58 BDL -- -- 25

COA37 Eureka Gulch upstream from 

confluence with South Fork

6/25/92 -- -- -- 7.44 7.7 87 13 -- -- 890

Table 2. Selected water-quality data for construction of the high-flow distribution maps.

[Some site names are informal place names used on local signage; ft3/s, cubic feet per second; SC, specific conductance; μS/cm, microsiemens per centimeter 

at 25°C; pH, s.u., standard units; temp., temperature; °C, degrees Celsius; Al, aluminum; Cu, copper; Fe, iron; Mn, manganese; Zn, zinc; Diss., dissolved; Tot., 

total; μg/L, micrograms per liter; --, no data; BDL, below detection limit]
Site 

number 

(fig. 2)

Site name Date Time

Streamflow

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp.

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Tot.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Colorado State sites (Colorado Department of Public Health and Environment, unpub. data, 1992)

Animas River basin—Continued

COA39 Eureka Gulch downstream from 

former Lake Emma

6/25/92 -- -- -- 7.58 10.1 110 24 -- -- 1,200

COA40 Animas River downstream from 

Eureka braided reach

6/25/92 -- -- -- 7.02 25.3 55 8 -- 800 590

COA42 Minnie Gulch 6/25/92 -- -- -- 7.86 15.8 BDL BDL -- -- 9

COA43 Maggie Gulch 6/25/92 -- -- -- 7.80 20.7 51 BDL -- -- 13

COA45 Animas River downstream from 

Middleton braided reach

6/25/92 -- -- -- 7.20 12.0 68 7 67 -- 410

COA47 Hematite Gulch 6/25/92 -- -- -- 7.65 14.0 BDL BDL -- -- 10

COA48 Cunningham Creek near mouth 6/25/92 -- -- -- 6.60 9.4 BDL BDL -- -- 23

COA51 Cunningham Creek downstream 

from Highland Mary tailings

6/25/92 -- -- -- 7.58 9.1 BDL BDL -- -- BDL

COA53 Animas River at Howardsville 

(gauging station)

6/25/92 -- -- -- 7.25 9.0 BDL 5 -- -- 240

COA55 Animas River 6/25/92 -- -- -- 7.25 14.0 75 7 -- -- 340

COA56 Animas River upstream from 

Arrastra Creek

6/25/92 -- -- -- 7.25 5.0 BDL 8 80 -- 360

COA58 Arrastra Creek at mouth 6/25/92 -- -- -- 8.36 6.5 BDL 6 14 -- 110

COA59 Arrastra Creek downstream from 

talus

6/25/92 -- -- -- 8.48 3.9 BDL 5 -- -- 68

COA60 Animas River downstream from 

Arrastra Creek

6/25/92 -- -- -- 6.71 9.3 BDL 6 79 -- 320

COA61 Animas River downstream from 

Mayflower Mill

6/25/92 -- -- -- 6.59 6.3 BDL 6 -- -- 350

COA62 Boulder Gulch 6/25/92 -- -- -- 6.80 7.2 BDL BDL BDL 89 57

COA64 Animas River downstream from 

Boulder Gulch

6/25/92 -- -- -- 6.83 7.0 51 7 64 -- 340

COA65 Animas River downstream from 

mill tailings

6/25/92 -- -- -- 6.54 6.0 BDL 5 70 -- 350

COA66 Animas River downstream from 

Silver Lake campground

6/25/92 -- -- -- 6.40 7.1 BDL 7 -- -- 360

COA67 Swansea Gulch 6/25/92 -- -- -- 8.25 5.4 BDL BDL 56 -- 68

COA68 Animas River at Silverton 

(gauging station)

6/25/92 -- 421 -- 7.60 5.5 50 7 260 -- 310

COA70 Idaho Gulch 6/25/92 -- -- -- 8.15 4.7 BDL 9 -- -- 50

COA72 Animas River downstream from 

Silverton (gauging station)

6/23/92 -- 965 -- 7.40 8.0 BDL 7 78 350 240

Cement Creek basin

COC01 Cement Creek at upper Ross Basin 6/24/92 -- -- -- 6.27 -- 300 140 500 650 950

COC02 Cement Creek downstream from 

Ross Basin

6/24/92 -- -- -- 4.88 18.1 420 140 -- BDL 1,100

COC03 Cement Creek upstream from 

North Fork

6/24/92 -- -- -- 5.28 10.7 570 130 -- -- 1,100

COC06 North Fork Cement Creek 6/24/92 -- -- -- 3.20 10.0 13,000 2,100 45,000 -- 6,900

COC08 Minnehaha Basin gulch downstream 

from Lead Carbonate mine

6/24/92 -- -- -- -- -- BDL BDL -- -- 13

COC09 Minnehaha Basin gulch midway 6/24/92 -- -- -- 7.30 7.2 100 9 -- -- 87

COC11 Middle Fork Cement Creek 

downstream from Black 

Hawk mine

6/24/92 -- -- -- 7.04 5.1 BDL BDL -- -- 15

Table 2. Selected water-quality data for construction of the high-flow distribution maps.—Continued

512 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 513

Site 

number 

(fig. 2)

Site name Date Time

Streamflow

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp.

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Tot.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Cement Creek basin—Continued

COC12 Minnehaha Gulch at mouth 6/24/92 -- -- -- 7.28 6.7 120 10 230 -- 140

COC13 Middle Fork Cement Creek 

at mouth

6/24/92 -- -- -- 6.52 6.2 67 15 180 -- 230

COC15 South Fork Cement Creek 

downstream from Velocity 

Lake

6/24/92 -- -- -- 6.27 12.7 91 BDL -- -- 35

COC16 South Fork Cement Creek 

upstream from Middle Fork

6/24/92 -- -- -- 6.12 13.0 120 10 -- -- 260

COC17 South Fork Cement Creek 

at Gladstone

6/24/92 -- -- -- 6.16 14.1 63 11 1,600 -- 340

COC18 Cement Creek downstream from 

North Fork

6/24/92 -- -- -- 3.78 8.2 1,600 300 4,100 -- 1,600

COC21 Cement Creek downstream from 

Gladstone

6/24/92 -- -- -- 5.17 6.7 890 160 -- 1,900 1,000

COC22 Prospect Gulch downstream from 

Red Mountain 3

6/24/92 -- -- -- 3.38 5.3 3,300 12 -- -- 46

COC23 Prospect Gulch upstream from 

Galena Queen mine

6/24/92 -- -- -- 6.13 8.6 BDL 27 -- -- 460

COC24 Prospect Gulch downstream from 

Galena Queen mine

6/24/92 -- -- -- 4.45 12.3 660 43 -- -- 360

COC25 Prospect Gulch downstream from 

Lark mine

6/24/92 -- -- -- 3.07 8.8 1,700 240 -- -- 850

COC26 Prospect Gulch at mouth 6/24/92 -- -- -- 3.76 5.3 3,100 310 9,400 -- 950

COC27 Cement Creek downstream from 

Prospect Gulch

6/24/92 -- -- -- 4.90 8.5 1,400 170 4,000 1,700 1,000

COC30 Cement Creek downstream from 

Georgia Gulch

6/24/92 -- -- -- 4.37 11.9 1,900 160 -- -- 1,000

COC31 Cement Creek downstream from 

Fairview Gulch

6/24/92 -- -- -- 4.47 8.7 1,900 150 -- -- 960

COC33 Cascade Gulch 6/24/92 -- -- -- 7.55 6.7 BDL BDL -- -- BDL

COC34 Cement Creek downstream from 

Cascade Gulch

6/24/92 -- -- -- 4.90 8.9 1,700 140 -- -- 870

COC35 Minnesota Gulch 6/24/92 -- -- -- 7.28 9.7 110 BDL 500 -- 85

COC36 Cement Creek downstream from 

Minnesota Gulch

6/24/92 -- -- -- 4.85 6.5 1,700 140 4,800 -- 860

COC38 Porcupine Gulch 6/24/92 -- -- -- 6.98 11.9 220 23 -- -- 810

COC39 Cement Creek downstream from 

Porcupine Gulch

6/24/92 -- -- -- 5.11 5.9 1,800 140 -- -- 920

COC40 Ohio Gulch 6/24/92 -- -- -- 3.74 7.3 2,400 39 -- -- 280

COC42 Illinois Gulch 6/24/92 -- -- -- 7.59 10.0 76 BDL -- -- 59

COC43 Cement Creek downstream from 

Illinois Gulch

6/24/92 -- -- -- 5.72 9.0 1,400 130 4,500 1,500 840

COC44 Topeka Gulch 6/24/92 -- -- -- 4.55 11.4 1,300 12 -- -- 130

COC45 Niagara Gulch 6/24/92 -- -- -- 3.75 12.0 860 11 -- -- 39

COC46 Cement Creek downstream from 

Niagara Gulch

6/24/92 -- -- -- 5.05 11.0 1,500 120 4,600 -- 850

COC47 Cement Creek upstream from 

large spring

6/24/92 -- -- -- 5.05 9.0 1,500 120 -- -- 790

COC48 Cement Creek at Silverton 

(gauging station)

6/23/92 -- 98 -- 5.00 5.0 1,700 110 5,000 1,100 720

Table 2. Selected water-quality data for construction of the high-flow distribution maps.—Continued
Site 

number 

(fig. 2)

Site name Date Time

Streamflow

(ft3

/s)

SC

(μS/cm)

pH

(s.u.)

Water

temp.

(°C)

Diss.

Al

(μg/L)

Diss.

Cu

(μg/L)

Tot.

Fe

(μg/L)

Diss.

Mn

(μg/L)

Diss.

Zn

(μg/L)

Mineral Creek basin

COM01 Mineral Creek at headwaters 6/23/92 -- -- -- 7.04 10.0 BDL BDL 14 BDL 8

COM02 Tributary downstream from 

Junction mine

6/23/92 -- -- -- 2.81 14.4 14,000 14,000 160,000 3,000 40,000

COM03 Tributary downstream from 

Congress mine

6/23/92 -- -- -- 3.58 20.2 680 1,100 5,000 130 1,400

COM05 Mineral Creek upstream from 

Porphyry Gulch

6/23/92 -- -- -- 3.90 14.7 870 900 8,000 200 2,600

COM06 Porphyry Gulch 6/23/92 -- -- -- 6.95 11.1 BDL BDL BDL BDL 57

COM07 Mineral Creek at Chattanooga 6/23/92 -- -- -- 6.65 9.1 91 140 2,300 100 880

COM08 Mill Creek downstream from 

Silver Queen mine

6/23/92 -- -- -- 7.06 10.8 BDL BDL -- -- 13

COM10 Mill Creek at Chattanooga 6/23/92 -- -- -- 7.48 6.6 BDL BDL 30 -- 14

COM11 Mineral Creek downstream from 

Chattanooga

6/23/92 -- -- -- 6.89 9.0 BDL 51 -- -- 540

COM12 Browns Gulch 6/23/92 -- -- -- 4.70 9.1 1,100 42 1,200 -- 700

COM13 Mineral Creek downstream from 

Browns Gulch

6/23/92 -- -- -- 6.65 9.4 BDL 34 -- -- 490

COM14 Tributary draining southwest 

Ohio Peak

6/23/92 -- -- -- 3.70 11.0 2,700 38 -- -- 22

COM15 Middle Fork Mineral Creek 

downstream from Ophir Pass

6/23/92 -- -- -- 6.87 7.0 62 BDL -- -- BDL

COM17 Middle Fork Mineral Creek 

downstream from Governor 

mine

6/23/92 -- -- -- 6.80 -- 180 BDL -- -- 25

COM18 Unnamed north-flowing tributary 

of Middle Fork Mineral Creek

6/23/92 -- -- -- 4.11 5.6 9,500 9 -- -- 110

COM19 Middle Fork Mineral Creek 

downstream from unnamed 

north-flowing tributary

6/23/92 -- -- -- 5.74 7.4 1,200 BDL -- -- 83

COM20 Middle Fork Mineral Creek 

upstream from Bonner mine

6/23/92 -- -- -- 5.82 10.3 370 BDL -- -- 31

COM22 Middle Fork Mineral Creek at 

mouth

6/23/92 -- -- -- 5.72 11.2 2,200 4 4,200 240 47

COM23 South Fork Mineral Creek at 

headwaters

6/23/92 -- -- -- 7.10 -- BDL BDL -- -- BDL

COM25 South Fork Mineral Creek 

downstream from Bandora 

mine

6/23/92 -- -- -- 7.13 -- BDL BDL -- 25 45

COM26 Clear Creek (Ice Lakes) 6/23/92 -- -- -- 7.25 -- BDL BDL -- -- BDL

COM27 Mineral Creek upstream from 

South Fork

6/23/92 -- -- -- 6.40 9.0 140 34 2,100 -- 340

COM28 South Fork Mineral Creek at mouth 6/23/92 -- -- -- 7.35 12.0 77 BDL 160 9 11

COM29 Mineral Creek downstream from 

large springs and Zuni Gulch

6/23/92 -- -- -- 6.95 11.0 53 10 -- -- 120

COM30 Bear Creek 6/23/92 -- -- -- 7.00 18.8 BDL BDL -- -- 13

COM32 Mineral Creek downstream from 

North Star mine

6/23/92 -- -- -- 6.72 16.3 82 10 840 -- 110

COM34 Mineral Creek at Silverton 

(gauging station)

6/23/92 -- 379 -- 7.20 8.0 BDL 8 190 74 110

Table 2. Selected water-quality data for construction of the high-flow distribution maps.—Continued

514 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 515

Selection of Mines that May Affect 

the Environment

Inactive mines can be sources of trace-metal loading 

to streams of the study area (Jim Herron, Bruce Stover, and 

Paul Krabacher, Unpublished Lower Animas River reclamation feasibility report, Upper Animas River Basin, Colorado 

Division of Minerals and Geology, 2000; Unpub. report to 

Colorado Water Quality Control Commission, ARSG, 2001; 

Wirt and others, 2001; Nash and Fey, this volume, Chapter E6; 

Wright, Kimball, and Runkel, this volume, Chapter E23). 

From features indicated on USGS topographic maps 

(C.L. Rich, U.S. Geological Survey, written commun., 2002), 

nearly 5,400 inactive mines, prospect pits, and other miningrelated features lie in the Animas River watershed study area 

(fig. 3), but not all of the sites contribute to environmental 

degradation (Unpub. Lower Animas River reclamation feasibility report, CDMG, 2000; Unpub. report to Colorado Water 

Quality Control Commission, ARSG, 2001; Church, Mast, 

and others, this volume, Chapter E5). The wide distribution of 

these features does not adequately describe the effects of historical mines on the environment because many of the features 

are prospect pits or small mines that have little, if any, environmental effect. Therefore, only a subset of mines thought to 

have some effect on stream-water quality is presented in this 

chapter.

As part of the mine-site ranking process by the Animas 

River Stakeholders Group, 33 draining mines and 32 wasterock piles were identified and ranked as large contributors to 

water-quality degradation (table 3) (Unpub. report to Colorado 

Water Quality Control Commission, ARSG, 2001). In addition to the high-ranking mine sites, seven permitted mine and 

mill sites are undergoing remediation or have been remediated (table 3). The permitted sites are generally some of the 

large mine and mill sites that may contribute metal loads 

to streams, yet they were not included as part of the ARSG 

ranking process due to ongoing regulatory activities. To better 

show the effects of mine sites on the distribution of pH values 

and trace-metal concentrations, only the high-ranking draining mines, waste-rock piles, and permitted mine and mill sites 

are shown on the spatial distribution maps (fig. 3, and section, 

“Data Presentation”). More information about the mineranking process can be obtained through the ARSG Website, 

http://www.waterinfo.org/arsg/ (accessed August 15, 2002).

Geologic Setting

Because water quality is related to geology, a short 

synopsis of bedrock geology, hydrothermal alteration, and 

mineralization of the study area is presented here to establish a geologic framework for the reader for interpretation 

of the variation of pH and trace metals in surface water. 

More detailed descriptions of the geology and alteration 

of the watershed are found in other chapters of this volume 

(Yager and Bove, this volume, Chapter E1; Bove and others, this volume). The study area lies within the western part 

of the San Juan volcanic field, which includes the San Juan, 

Uncompahgre, and Silverton calderas (Lipman and others, 

1976; Bove and others, 2000). The Silverton caldera, a 

large collapsed volcanic depression, nested within the larger 

San Juan caldera, formed in response to the eruption of the 

27.7-Ma Crystal Lake Tuff (Lipman and others, 1976; Bove 

and others, this volume). Within the Silverton caldera, the 

Crystal Lake Tuff is mostly absent due to erosion, and the 

dominant volcanic rock units are a thick sequence of finely 

porphyritic dacitic-andesitic lavas and volcaniclastic rock 

(Silverton Volcanics) (Burbank and Luedke, 1969; Yager 

and Bove, this volume).

The Eureka graben, which is the downdropped, northeasttrending fault zone along the crest of the uplifted dome of the 

coalesced San Juan–Uncompahgre calderas, was an important 

host to mineralization that postdates these calderas by about 

5–15 Ma (Lipman and others, 1976). Although altered and 

mineralized rocks are in close spatial association with the 

San Juan, Uncompahgre, and Silverton calderas, alteration and 

mineralization were rarely contemporaneous with caldera formation (Lipman and others, 1976; Slack and Lipman, 1979). 

The San Juan–Uncompahgre caldera cycle thus provided a 

favorable structural environment for later mineralization. Most 

mineralization and associated hydrothermal alteration in this 

area were temporally and genetically associated with three 

major episodes of high-level magmatism between about 27 

and 10 Ma.

Major Events of Mineralization, Alteration, 

and Igneous Intrusion

More than 90 volume percent of the rocks in the study 

area were affected by low-grade regional metamorphism 

or propylitic alteration, the result of thermal events associated with the San Juan–Uncompahgre and Silverton calderas 

(Burbank and Luedke, 1969; Bove and others, this volume). 

The timing of these events preceded most ore mineralization 

and later episodes of more intense hydrothermal alteration 

by several million years (Lipman and others, 1976; Bove and 

others, 2001). The propylitic mineral assemblage contains 

varying amounts of chlorite, epidote, calcite, and illite, in the 

presence of fresh to weakly altered primary feldspar crystals. 

The regional propylitic event was followed by three major 

periods of magmatism, which were related to most mineralization and hydrothermal alteration in the area (Bove and others, 

this volume). Hydrothermal activity related to these magmatic 

episodes superimposed more intense hydrothermal alteration 

assemblages upon the previously propylitically altered rocks.

The earliest of these magmatic events was associated 

with 26–25 Ma quartz-monzonite intrusive activity, which was 

related to subeconomic porphyry copper-molybdenum mineralization in the area between Middle and South Forks Mineral 

Creek (Ringrose and others, 1986; Bove and others, this volume). The center of the most intense hydrothermal alteration 
Figure 3. Locations of inactive mines, prospect pits, and mining-related features identified from topographic maps, high-ranking draining mines and wasterock piles, and permitted sites (Unpub. report to Colorado Water Quality Control Commission, ARSG, 2001; Church, Mast, and others, this volume).

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENTAL CO

DIVIDE

OURAY CO

51

65

1

2

3

4

5

6

7

8

9

10

11,13

12

14

15,16,17

18

19

20

21

22 23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39 40

41

42

43

44

45

46

47

48

49

50

52

53

54

55

56

57

58

59

60

61

62

63

64

66

67

68

69

70

71

72

72

EXPLANATION

Inactive mine, prospect pit, or mining-related feature identified from USGS topographic maps

18

58

High-ranking draining mine and number  from table 3

High-ranking waste-rock  pile and number from table 3

67 Permitted mine site and number 

 from table 3

71 Permitted mill site and number 

 from table 3

Watershed study area

boundary

Ri ver

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

uth So k For

Illinois Gl

Middle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder Gulch

Gulch

Gulch

 River Animas

Cement Creek

Californ a i Gl

lace P Gl r

Burrows

x Storm Peak Ohio x

Peak

Browns Gl

x

California

Mountain

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

37o

45'

107o37'30" 107o45'

37o

52'30"

3,792 mx

Vermilion Peak

elev. 4,235 m

516 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 517

and mineralized rock was near peak 3,792 m (fig. 1), between 

Middle and South Forks Mineral Creek. In the vicinity of peak 

3,792 m, quartz-molybdenite stockwork veins associated with 

intense quartz-sericite-pyrite (QSP) altered rock are cut by 

molybdenite-bearing quartz stockwork veinlets; these veinlets 

were postdated by base-metal veins, which are present mostly 

on the margins of the porphyry system (R.T. McCusker, 

Unpublished Mount Moly progress report, 1979–1980, 

Drill holes 1–6, 1982). The base-metal veins contain silver 

and some gold in sulfide ores consisting mainly of galena, 

sphalerite, and pyrite with lesser tetrahedrite-tennantite and 

chalcopyrite (Ringrose and others, 1986). A pervasive area of 

QSP-altered rock (3.5 km2

) is centered roughly on the summit 

and is zoned outward into weak sericite-pyrite (WSP) and then 

propylitic alteration assemblages. The weak sericite-pyrite 

assemblage is characterized by partial replacement of plagioclase by sericite, whereas biotite and pyroxene are altered to 

chlorite, sericite, and fine opaque minerals. The rocks are typically less silicified than QSP-altered rocks, and contain fewer 

quartz-sulfide stockwork veinlets.

Table 3. Selected draining mines, waste-rock piles, and permitted mine and mill sites in the Animas River watershed study area.

[Unpub. report to Colorado Water Quality Control Commission, ARSG, 2001]

Map No. 

(fig. 3) Mine or site name Map No. (fig. 3) Mine or site name

Draining mines Waste-rock piles

1 Mogul mine 34 Galena Queen mine, shaft

2 Natalie/Occidental mine 35 Kansas City #2 mine

3 Grand Mogul mine 36 Hercules mine, shaft

4 Mammoth tunnel 37 Upper Joe & Johns mine

5 Anglo-Saxon mine 38 Grand Mogul mine – East

6 Joe & Johns mine 39 Kansas City #1 mine

7 Big Colorado mine 40 Black Hawk mine

8 Porcupine mine 41 Lead Carbonate Mill

9 Eveline mine 42 Henrietta mine (level 3)

10 Columbia mine 43 Ross Basin mine

11 Koehler tunnel 44 Lark mine

12 North Star mine 45 Pride of the Rockies mine

13 Longfellow mine (Junction mine) 46 Henrietta mine (level 7)

14 Bandora mine 47 Mogul mine

15 Upper Bonner mine 48 Brooklyn mine

16 Bonner mine 49 Bullion King mine

17 Lower Bonner mine 50 Unnamed shaft mine, upper Browns Gulch

18 Ferricrete mine 51 Congress mine, shaft

19 Governor mine (Paradise portal) 52 Brooklyn mine, upper waste-rock pile

20 Brooklyn mine 53 Unnamed mine, upper Browns Gulch

21 Little Dora mine 54 Little Dora mine

22 Vermillion mine 55 Brooklyn mine, lower waste-rock pile

23 Columbus mine 56 Ben Butler mine

24 Lower Comet mine 57 Silver Wing mine

25 Unnamed mine 58 Tom Moore mine

26 Sound Democrat mine 59 Eagle mine

27 Mountain Queen mine 60 Lucky Jack mine

28 Silver Wing mine 61 Clipper mine

29 Frisco tunnel 62 Buffalo Boy mine

30 Senator mine 63 Ben Franklin mine

31 Royal Tiger mine 64 Caledonia mine

32 Pride of the West mine 65 Sunnyside mine

33 Little Nation mine

Permitted mine sites

Permitted mill sites 66 Upper Gold King mine

71 Pride of the West Mill tailings 67 American tunnel

72 Mayflower Mill tailings 68 Gold Prince mine

69 Sunnyside mine

70 Terry tunnel
Intrusion of high-level dacite porphyry in the Red 

Mountain Pass and Ohio Peak–Anvil Mountain areas at 

23 Ma caused significant mineralization and formed extensive 

zones of acid-sulfate altered rock (>40 km2

 total). The Red 

Mountain Pass area was developed for silver-copper-leadarsenic ores hosted within breccia pipes and brecciated fault 

zones (Burbank and Luedke, 1969; Bove and others, this 

volume). Although the Ohio Peak–Anvil Mountain system is 

very similar in size and style of alteration, it is largely devoid 

of economic mineral deposits (Bove and others, this volume). 

Zones of acid-sulfate altered rock were localized along fault 

and hydrothermal breccia zones and permeated outward into 

intensely altered wallrock (Bove and others, this volume). 

These acid-sulfate centers are composed mainly of quartz, alunite, pyrophyllite, dickite, and as much as 30 volume percent 

pyrite. Broad expanses of QSP-altered rock, very similar in 

character to that mapped in the area of peak 3,792 m, are generally present between individual acid-sulfate zones. Larger 

areas of QSP-altered rock are particularly well exposed on the 

highly dissected margins of the acid-sulfate systems. Propylitically altered rocks surround the Red Mountain Pass and Ohio 

Peak–Anvil Mountain acid-sulfate systems.

Post-20 Ma vein mineralization produced most of the 

economically important vein minerals in the study area and 

appears to have been closely tied to intrusion of high-silica 

alkali rhyolite (Lipman and others, 1976; Bove and others, 

this volume). Veins are mostly a polymetallic variety (silver, 

lead, zinc, copper, ±gold) and formed as fracture- or fissurefillings (Bove and others, this volume). Many of these veins 

in the Eureka graben area are especially rich in manganese 

silicate gangue minerals (Bove and others, this volume). 

Zones of hydrothermally altered rock related to these post20 Ma veins consist of narrow envelopes that are superimposed over regional propylitically altered rock (Bove and others, this volume). In some areas with high vein concentrations, 

the associated alteration zones can be locally pervasive.

Hydrothermal Alteration

Mineral types and abundances strongly affect water 

quality; for details on the minerals included in the alteration 

assemblages, see Bove and others (this volume). The study 

area has five types of hydrothermal alteration assemblages: 

regional propylitic alteration (PROP); weak sericite-pyrite 

alteration (WSP); vein-related quartz-sericite-pyrite alteration (V-QSP); quartz-sericite-pyrite alteration (QSP); and 

acid-sulfate alteration (AS). The PROP alteration is characterized by an earlier formed regional propylitic assemblage that 

affected most rocks within the Animas River watershed study 

area and vicinity. It is distinguished largely by the absence of 

pyrite, quartz, and chlorite veinlets and the scarcity of finely 

disseminated pyrite. Examples of QSP alteration occur in 

the peak 3,792 m and Red Mountain Pass areas. An example 

of WSP alteration occurs in the area where QSP-altered 

rock grades outward into WSP-altered rock and finally into 

propylitized (PROP) rock (Ringrose and others, 1986; Bove 

and others, 1998). Hydrothermal propylitic alteration that 

formed in association and peripheral to the peak 3,792 m 

hydrothermal system is characterized by the presence of veins 

and fractures filled with pyrite, chlorite, magnetite, and quartz. 

Examples of AS alteration are indicated in the Topeka Gulch 

and Ohio Peak areas (locations, figs. 1, 4). The V-QSP alteration style is illustrated throughout the Animas River watershed 

study area where relatively narrow (1–3 ft) quartz base-metal 

veins are present on the periphery of the other hydrothermal 

systems (Bove and others, this volume). These veins contain 

silver and some gold in sulfide ores of pyrite, sphalerite, 

galena, fine-grained tetrahedrite-tennantite, and chalcopyrite 

in a gangue of quartz, with lesser manganese silicates, barite, 

and carbonates.

Undisturbed Sources

Weathering of rocks that have been hydrothermally 

altered and not disturbed by mining contributes to the low 

pH and observed trace-metal loads in the study area (Wright 

and Janik, 1995; Bove and others, 2000; Mast, Verplanck, 

and others, 2000; Unpub. Lower Animas River reclamation feasibility report, CDMG, 2000; Mast and others, this 

volume, Chapter E7). Metal and acid loading from these 

rocks is considered an undisturbed or background source. 

Background sources enter streams as diffuse ground-water 

inflow and in springs. Background iron and manganese 

springs (fig. 1) have a considerable effect on water quality 

of the study area. Information about iron springs, iron bogs, 

and ferricrete deposits can be found in Stanton, Yager, and 

others (this volume, Chapter E14), Verplanck and others 

(this volume, Chapter E15), and Wirt and others (this volume, 

Chapter E17). Trace-metal loading from diffuse ground-water 

sources in the Cement Creek basin is described in Walton-Day 

and others (2000), Wirt and others (2001), and Kimball and 

others (2002).

Data Presentation

Spatial distribution maps are used in this report to 

describe the distribution of pH values, dissolved aluminum, 

dissolved copper, dissolved iron, dissolved manganese, and 

dissolved zinc for low-flow and high-flow conditions. The 

spatial distribution maps display colors that represent the 

ranges of pH values and dissolved trace-metal concentrations 

for sites throughout the watershed. Colors represent the range 

of the entire data set to show major contrasts between different 

areas of the watershed. The blue and light-blue colors represent lower trace-metal concentrations and higher pH values; 

the green, orange, and red colors represent higher trace-metal 

concentrations and lower pH values. Dissolved iron and manganese concentrations were not available in the CDPHE highflow data set; therefore, high-flow spatial distribution maps are 

not shown for these constituents.

518 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 519

Water-quality standards for protection of aquatic 

life in the study area were recommended by the ARSG 

to the State of Colorado, and the standards were adopted 

in 2002 (Colorado Department of Public Health and 

Environment, Stream Classifications and Water-Quality 

Standards, http://www.cdphe.state.co.us/op/regs/waterregs/

100234wqccsanjuanriverbasintables.pdf, accessed 

September 18, 2003). The standards are either the State of 

Colorado table value standards, which are closely based on 

the national water-quality criteria, or the ARSG’s model of the 

achievable ambient dissolved metal concentration for a particular reach after restoration of historical mines. The standards 

are different for each segment of the watershed (Unpub. report 

to Colorado Water Quality Control Commission, ARSG, 

2001), and the standard for most of the metals varies by hardness concentration. Because of the prevalence of naturally 

occurring dissolved constituents in waters of the study area, 

and the concentrations expected in surface waters after restoration of inactive mine sites, the ARSG-proposed standards may 

exceed the national criteria in certain stream reaches. The 

color ranges on the distribution maps, therefore, do not reflect 

toxicity thresholds or water-quality standards in the watershed 

study area because some of the thresholds and standards are 

exceeded throughout most of the area.

Distribution of pH Values 

and Dissolved Trace-Metal 

Concentrations

The distribution of pH and dissolved trace-metal concentrations differs greatly in streams throughout the Animas 

River watershed study area and depends on many factors, such 

as geologic setting, the presence and size of historical mines, 

and mixing of acidic and more neutral waters. Because of the 

deep snowpack that accumulates during the winter and melts 

during the spring, streamflow in the study area exhibits large 

seasonal differences. This affects the distribution of pH values 

and trace-metal concentrations contrasted between low flow 

(late summer and middle winter) and high flow (snowmelt 

runoff during May through July). In some areas, the presence 

of historical mines does not affect low pH values and high 

trace-metal concentrations in streams. In other areas, the presence of historical mines does affect low pH values and high 

trace-metal concentrations in streams.

pH Values

Although no national water-quality criteria exist for pH 

values in water, the State of Colorado has a statewide standard of pH 6.5–9.0 for protection of aquatic life. Below about 

pH 5.5, more sensitive invertebrate taxa begin to decrease 

or disappear. Whether effects of acidity on invertebrates are 

caused by response to the direct toxicity of extremely low 

pH or whether they have a more indirect cause, the effects of 

acidification on algal food resources, is not clear (Sutcliffe and 

Hildrew, 1989). About 50 percent of European lakes with pH 

below 5.1 are fishless. Populations of salmonid fishes (trout 

and char) are relatively sensitive to the effects of acidification. 

Freshly fertilized eggs are the most sensitive life stage, and 

survival of brown trout eggs can be reduced in the pH range 

of 4.2–5.1. However, adult and juvenile salmonids (across a 

range of species and test waters) can typically tolerate short 

exposures to pH between 4.2 and 5.1. Toxic effects of pH are 

strongly ameliorated by increased calcium concentrations in 

the range of 100–400 eq/L (equivalents per liter) (Brown and 

Sadler, 1989).

The geology in a watershed plays an important role in 

determining the pH of streams. Low pH values in streams 

are related to acid-generating minerals such as pyrite (FeS2

) 

and chalcopyrite (CuFeS2

), whereas neutral to alkaline pH 

values occur where these sulfide minerals generally are 

absent or where minerals such as calcite, with significant 

acid-neutralizing capacity, are abundant (Plumlee and others, 

1993; U.S. Environmental Protection Agency, 1994). Low pH 

values (less than 4.5) were primarily found in streams draining highly altered or mineralized bedrock. Some streams also 

were affected by historical mines. Low pH values in streams 

of the study area generally coincide with high concentrations 

of dissolved trace metals, because acidic conditions contribute 

to trace-metal mobilization and transport (Moran and Wentz, 

1974, p. 23; Kimball and others, 1994; Broshears and others, 

1996). In contrast, high pH values are associated with areas 

where rocks have substantial acid-neutralizing capacity and 

commonly coincide with low concentrations of some trace 

metals, such as aluminum and iron; however, higher pH values 

do not exclude the presence of some trace metals such as zinc 

and manganese, which have high solubilities in circumneutral waters (Stumm and Morgan, 1981, p. 242–243). Mixing 

of low- and high-pH streams contributes to the precipitation 

of some trace metals from the dissolved phase into the solid 

phase, for instance, aluminum and iron. Other trace metals 

such as copper may adsorb to the precipitated solids (Church 

and others, 1997; Schemel and others, 2000). Therefore, the 

concentrations of dissolved trace metals can decrease through 

mixing of waters having different pH.

During low flow, streams that primarily drain intensely 

altered rocks have notably lower pH. For example, rocks in the 

peak 3,792 m area between Middle and South Forks Mineral 

Creek contain as much as 5 volume percent pyrite (Bove and 

others, this volume), and figure 4 shows clearly that during 

low flow, pH values in streams draining that area are very low. 

Low pH values also were present in streams draining the east 

and west sides of Ohio Peak (fig. 4). Extremely low pH values 

of 2.45 and 2.50 were measured in water from the Koehler 

tunnel and Longfellow mine at the headwaters of Mineral 

Creek (MS81 and MS82 in fig. 1 and table 1), and low pH 

values were prevalent throughout most of Prospect Gulch 

(table 1; labeled in fig. 1); Wirt and others (2001) concluded 

that the lower reaches of Prospect Gulch are largely affected 

by ground-water discharge from undisturbed sources.
SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENT OC

AL DIVIDE

OURAY CO

Silverton

Howardsville

Middleton

Chattanooga

Animas

Forks

Gladstone

x Storm Peak

Ohio xPeak

R ver i

Cinnamon Cr

West 

Fork

South

Fork

An mas i

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fork South

Illinois Gulch

Gulch

Eureka

Maggie

Minnie

Boulder Gulch

Gulch

Gulch

Middle Fk M ni eral Cr

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

pH values, in standard units

High-ranking draining mine

High-ranking waste-rock pile

>3.5 - 4.5

>4.5 - 5.5

>5.5 - 6.5>6.5

No data

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

<3.5

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

37o45'

107o37'30" 107o45'

37o

52'30"

3,792 mx

Vermilion Peak

elev. 4,235 m

x

California

Mountain

Figure 4. Distribution of pH values in streams during low flow.

520 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 521

The most noteworthy effects of acid rock drainage were 

observed in the mainstem of Cement Creek (fig. 4), where pH 

values ranged from 3.9 to 5.5 downstream from Gladstone, 

despite the inflow of several high-pH streams draining the 

west slopes of Storm Peak (fig. 4). Metal-loading studies 

done in Cement Creek attributed the low-pH, high-metal 

waters throughout the length of the stream to diffuse groundwater inflows (Walton-Day and others, 2000; Kimball and others, 2002). Several large, low-pH iron springs in the Cement 

Creek basin likely are surface expressions of this ground water 

(fig. 1).

During low flow, high pH values (greater than 6.5) were 

measured in most of the Animas River upstream from Silverton, 

except for a few of the headwater streams in the North Fork and 

West Fork Animas River subbasins (fig. 4). The Animas River 

upstream from Silverton drains propylitically altered rocks 

that contain calcite within the rock matrix (Bove and others, 

this volume), and calcite dissolution likely maintains the high 

pH values. High pH values also were measured in South Fork 

Mineral Creek, which drains sedimentary rocks containing 

calcite.

During high flow, many streams had higher pH values 

compared to those of low flow, including Mineral Creek, 

lower Cement Creek, and the Animas River downstream from 

Silverton. Streams affected by historical mining and geologic 

alteration still had relatively low pH values (less than 4.5). 

These included upper Mineral Creek (COM02, COM03, 

and COM05), north-flowing Red tributary (informal name) 

of Middle Fork Mineral Creek (COM18), tributary draining southwest Ohio Peak (COM14), North Fork Cement 

Creek (COC06), Cement Creek below North Fork (COC18), 

Prospect Gulch (COC26), Ohio Gulch (COC40), and Niagara 

Gulch (COC45) (figs. 2 and 5; table 2).

Aluminum

Aluminum binds with organic and inorganic ligands to 

form compounds that are soluble in acidic and basic solutions 

(aluminum is amphoteric) and quite insoluble in circumneutral solutions. Aluminum is listed as a nonpriority pollutant in 

surface water; it has a continuous concentration standard of 

87 μg/L (micrograms per liter) and a maximum concentration 

standard of 750 μg/L (U.S. Environmental Protection Agency, 

2002). Recent work has noted that colloidal aluminum may 

be the form most toxic to fish (Witters and others, 1996), and 

freshly formed aluminum-hydroxide precipitates may be the 

most toxic to trout. The toxicity of aluminum to brook trout 

is generally thought to be greatest at pH 5.0–5.5 (Cleveland 

and others, 1986; Mount and others, 1988). Water-quality 

standards for aluminum in the Animas River watershed have 

numeric values that vary by month, ranging from 700 μg/L 

in July to 3,550 μg/L in February (Unpub. report to Colorado 

Water Quality Control Commission, ARSG, 2001). Many of 

the aluminum concentrations in the study area exceeded the 

standards; therefore, the colors for the distribution of dissolved aluminum were divided arbitrarily to show the stream 

segments with the highest dissolved aluminum concentrations 

(fig. 6).

During low flow, concentrations of dissolved aluminum 

ranged from a high of 71,400 μg/L in the north-flowing Red 

tributary of Middle Fork Mineral Creek (MC18, undisturbed 

site) and 71,400 μg/L in water from the Koehler tunnel to 

77 μg/L at the outflow of the watershed study area (COA72) 

(fig. 6; table 1). Many stream segments and tributaries had 

aluminum concentrations that were below the detection limit 

(table 1). The distribution of high dissolved aluminum concentrations (green, orange, and red colors on the distribution map) 

reflects the weathering of hydrothermally altered rocks and 

low-pH waters in the study area.

A possible control on the aluminum chemistry of waters 

in the study area could be the leaching of aluminum from 

common aluminosilicate minerals in sulfuric acid solutions 

generated by the oxidation of sulfide minerals (Nordstrom 

and Ball, 1986, p. 55). An example illustrating aluminum 

precipitation that results from high dissolved aluminum 

concentrations is shown in drainage from the Governor mine, 

also called Paradise portal (fig. 7). The white precipitate has 

been identified as aluminum hydroxysulfate, or basaluminite 

(Carlson-Foscz, 1991), and the precipitation of the aluminum 

is generally attributed to mixing of acidic water from deeper 

in the mine with near-surface, circumneutral ground water 

(D.K. Nordstrom, oral commun., 1995). Many other streams 

in the study area also have these aluminum precipitates, such 

as Middle Fork Mineral Creek (MC79), Mineral Creek downstream from the confluence with Middle Fork, Burrows Creek 

(UA2), California Gulch (UA18), and West Fork Animas River 

at Animas Forks (UA51) (fig. 1; table 1). Aluminum precipitates are not everywhere accompanied by high dissolved 

aluminum concentrations. For example, the dissolved aluminum concentration was relatively low at site UA51 (326 μg/L, 

table 1); however, the mixing of acidic and more neutral 

waters causes aluminum precipitation that coats the streambed with a white material. Aluminum colloids also may be 

transported from mixing zones and deposited at downstream 

locations (Schemel and others, 2000, p. 1004); these processes 

occur at numerous locations throughout the watershed.

During high flow, dissolved aluminum concentrations 

were generally not as high as during low flow. Dissolved 

aluminum concentrations ranged from 14,000 μg/L at the 

headwaters of Mineral Creek, and 13,000 μg/L in water from 

North Fork Cement Creek, to below the detection limit at the 

outflow of the study area (fig. 8; table 2). Some stream segments had relatively high dissolved aluminum concentrations 

during high flow, including Burrows Creek, California Gulch, 

Prospect Gulch, most of Cement Creek, and the north-flowing 

Red tributary of Middle Fork Mineral Creek (fig. 8; table 2).

Dissolved aluminum concentrations are highly dependent 

on pH, and dissolved aluminum is not conservative (dissolved 

phase is pH dependent) in the hydrologic system (Stumm and 
SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NT CO NE I NTAL DIVIDE

OURAY CO

Silverton

Howardsville

Middleton

Chattanooga

Animas

Forks

x Storm Peak

Gladstone

Ohio xPeak

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

pH values, in standard units

High-ranking draining mine

High-ranking waste-rock pile

>3.5 - 4.5

>4.5 - 5.5

>5.5 - 6.5>6.5

No data

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

<3.5

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

3,792 mx

Vermilion Peak

elev. 4,235 m

North Fork

R ver i

Cinnamon Cr

West 

Fork

South

Fork

An mas i

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fork South

Illinois Gulch

Gulch

Eureka

Maggie

Minnie

Boulder Gulch

Gulch

Gulch

Middle Fk M ni eral Cr

37o45'

Figure 5. Distribution of pH values in streams during high flow.

522 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 523 Vermilion Peak elev. 4,235 m Silverton HowardsvilleMiddleton

Chattanooga

Gladstone

Animas

Forks

Ohio xPeak

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENT OC

AL DIVIDE

OURAY CO

>10,000

Range of dissolved aluminum concentrations,  in micrograms per liter

>5,000 - 10,000

>1,000 - 5,000

>100 - 1,000

<100

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

3,792 m

x

x Storm Peak

 x

California

Mountain

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mi

ll Cr

Lakes

Cunningham Cr

Cement Creek

South kr Fo

Illinois Gulch

Middle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder

hc Gul

Gulch

Gulch

37o45'

Figure 6. Distribution of dissolved aluminum concentrations in streams during low flow.
Morgan, 1981; Nordstrom and Ball, 1986; Schemel and others, 2000). Aluminum is soluble in acidic solutions, and the 

pH-dependent precipitation of aluminum colloids is illustrated 

by comparison of some of the dissolved and total-recoverable 

aluminum concentrations. For example, precipitated aluminum 

colloids are reflected by the difference between the dissolved 

aluminum concentration (0.45-μm filtration) and the totalrecoverable aluminum concentration (unfiltered). In water 

from the Animas River downstream from Silverton (COA72) 

where the mean pH was 6.4, the mean dissolved aluminum 

concentration was 262 μg/L and the mean total-recoverable 

aluminum was 1,260 μg/L (Mast, Evans, and others, 2000). 

In water from Cement Creek (COC48) where the mean pH 

was 4.2, the mean dissolved aluminum concentration was 

3,080 μg/L, and the mean total-recoverable aluminum was 

12,940 μg/L. In water from a spring located in lower Mineral 

Creek (site MS57 in Mast, Evans, and others, 2000) where the 

mean pH was 2.9, the mean dissolved aluminum concentration 

was 10,260 μg/L, and the mean total-recoverable aluminum 

concentration was 10,270 μg/L.

Four possible controls on the aluminum chemistry in 

waters of the study area are (1) the leaching rate of aluminum 

from aluminosilicate minerals, (2) the solubility of aluminum sulfate minerals (basaluminite, jurbanite, and alunite) 

known to exist under these conditions (Nordstrom, 1982; 

Nordstrom and Ball, 1986), (3) the solubility of gibbsite 

and amorphous aluminum hydroxide minerals (Sullivan and 

Drever, 2001), and (4) the importance of organically bound 

Figure 7. Aluminum hydroxysulfate precipitates in discharge from Governor 

mine (Paradise portal), Middle Fork Mineral Creek subbasin.

524 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 525 Figure 8. Distribution of dissolved aluminum concentrations in streams during high flow. HowardsvilleMiddleton

Chattanooga

Gladstone

Animas

Forks

x Storm Peak Ohio x Peak

Silverton

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

CONTIN NT E L A DIVIDE

OURAY CO

Vermilion Peak

elev. 4,235 m

>10,000

Range of dissolved aluminum concentrations,  in micrograms per liter

>5,000 - 10,000

>1,000 - 5,000

>100 - 1,000

<100

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

3,792 m

x

37o45'

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fo South rk

Illinois Gulch

M di dle Fk M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder

hc Gul

Gulch

Gulch

x

California

Mountain
dissolved aluminum (Nordstrom and Ball, 1986). Regarding 

solubility controls, aluminum should begin precipitating from 

the dissolved to the solid phase at about pH 4.5 and should 

not be present in the dissolved phase by about pH 5.5. In the 

study area, however, aluminum appears to be present in the 

dissolved phase to about pH 6.2 (fig. 9). The cause of this is 

uncertain, except for the possibility that the solubility of aluminum complexes is not following theoretical relations in the 

waters of the study area, or possibly aluminum colloids were 

passing through the 0.45-μm filtration apparatus.

Figure 9. Relation of pH values to dissolved aluminum concentrations in selected streams, compared 

to solubility lines for gibbsite (log K=9.35) and amorphous Al(OH)3

 (log K=10.8) (Sullivan and Drever, 

2001).

Copper

Chronic toxicity of copper is an important factor limiting 

the distribution and abundance of brook trout populations in the 

study area (Besser and others, 2001; Besser and Brumbaugh, 

this volume). Survival of aquatic species exposed to copper 

and other divalent metals decreases when the concentration of 

metal bound to gills or other permeable body surfaces exceeds 

a threshold concentration. Chronic (long-term) toxicity occurs 

when threshold concentrations are achieved at internal target 

0

0.02

0.04

0.06

0.08

0.10

0.12

3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

pH, IN STANDARD UNITS

DISSOLVED ALUMINUM, IN MILLIMOLES PER LITER

Animas River downstream from Silverton

South Fork Cement Creek at Gladstone

Mineral Creek at Chattanooga

Mineral Creek at Silverton

Gibbsite

Amorphous Al(OH)3

EXPLANATION

526 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 527

organs. In acute (7 day) toxicity tests with copper in test 

waters with water quality similar to that of the Animas River, 

median lethal concentrations (LC50) of 35 and 75 μg/L were 

determined for fathead minnows and amphipods, respectively. 

Chronic (30 day) tests with early life stages of brook trout 

determined an LC50 (29 μg/L) similar to those for fathead 

minnows, but significant decreases in growth occurred at 

copper concentrations as low as 8 μg/L (Besser and Leib, this 

volume, Chapter E19). Copper is listed as a priority pollutant 

in surface water; it has a continuous concentration standard 

of 9 μg/L and a maximum concentration standard of 13 μg/L 

(U.S. Environmental Protection Agency, 2002). Copper standards for the Animas River downstream from Silverton are 

hardness-dependent concentrations; for hardness values ranging 

from 20–120 mg/L as CaCO3

, the chronic standard ranges 

from 2.9 to 13.8 μg/L, respectively (Unpub. report to Colorado 

Water Quality Control Commission, ARSG, 2000). Many of the 

dissolved copper concentrations in the study area exceeded the 

standards for aquatic life; therefore, the colors for the distribution of dissolved copper were divided arbitrarily to show the 

stream segments with the highest dissolved copper concentrations (fig. 10).

Dissolved copper concentrations in streams of the 

watershed were generally related to the presence of copperbearing minerals such as chalcopyrite (CuFeS2

) and enargite 

(Cu3AsS4), and the highest dissolved copper concentrations 

generally were downstream from mines that worked these 

deposits. During low flow, dissolved copper concentrations 

ranged from 98,600 μg/L in water from the Koehler tunnel, to 

8,390 μg/L in the stream downstream from the Congress mine, 

and 372 μg/L in water from a non-mining affected spring 

(site MC29) (fig. 10; table 1). In areas where copper minerals 

are not in abundance, such as the Animas River upstream from 

Silverton and parts of South Fork Mineral Creek, the dissolved 

copper concentrations were low and frequently below the 

analytical detection limit (<4 μg/L). Dissolved copper concentrations were elevated in water from a few non-mining affected 

streams and springs (MC29, MC52, and CC135, figs. 1 and 

10; table 1); however, those dissolved copper concentrations were low compared to the concentrations from miningaffected sites, demonstrating the effect that mines can have 

on weathering of copper minerals. The distribution of high 

dissolved copper concentrations (green, orange, and red colors 

on the distribution map) reflects the weathering of hydrothermally altered rocks in the study area.

During high flow, the contrast in distribution of dissolved 

copper concentrations between low flow and high flow was 

not systematic. During snowmelt runoff, dissolved trace-metal 

concentrations typically decrease due to dilution (Sullivan and 

Drever, 2001). In Cement Creek, dissolved copper concentrations were higher during high flow, whereas dissolved copper 

concentrations were lower in Mineral Creek and in other parts 

of the watershed (figs. 2 and 11; table 2). For example, in 

the Animas River downstream from Silverton, the dissolved 

copper concentrations decreased during snowmelt runoff. In 

Cement Creek, the dissolved copper concentrations increased 

during snowmelt runoff (fig. 12); the causes of this opposite 

response are uncertain. It is possible that small colloidal particles may have passed through the 0.45 μm filters; however, 

several replicate analyses were done on samples from Cement 

Creek filtered through 0.1 μm filters, and the results were the 

same as the 0.45 μm filtered analyses.

Dissolved copper is not conservative in the hydrologic 

system and partitions to solids by instream processes, particularly downstream from mixing zones of low- and highpH waters (Church and others, 1997; Nordstrom, Alpers, 

and others, 1999). Copper adsorbs readily to particulates and 

is transported in the sediment and colloidal phases (Schemel 

and others, 2000). In the presence of iron and aluminum 

precipitates, copper concentrations can decrease with increasing pH values (Smith, 1994). The partitioning of dissolved 

copper is illustrated by comparing some of the dissolved 

and total-recoverable copper concentrations. For example, 

in water from the Animas River downstream from Silverton 

(COA72) where mean pH was 6.4 (during all seasons), the 

mean dissolved copper concentration was 13 μg/L and the 

mean total-recoverable copper was 27 μg/L (Mast, Evans, and 

others, 2000). In water from Cement Creek (COC48) where 

mean pH was 4.2, the mean dissolved copper concentration was 68 μg/L and the mean total-recoverable copper was 

144 μg/L (Mast, Evans, and others, 2000). In water from the 

Joe and Johns mine, located in Prospect Gulch (site MS19 in 

Mast, Evans, and others, 2000), the pH value on March 14, 

1997, was 2.54, the dissolved copper concentration was 

597 μg/L, and the total-recoverable copper concentration was 

605 μg/L (Mast, Evans, and others, 2000). These examples 

illustrate how low pH values correlate with high dissolved 

copper concentrations in water of the study area.

Iron

Iron is the main component of the colloidal material 

that forms in the streams of the study area. Therefore, the iron 

colloids may act to cover the food sources for aquatic life, 

can precipitate on fish gills, and can reduce the quantity and 

quality of habitat for benthic invertebrates and for spawning of trout. Toxicity data for iron are limited, and effects of 

aqueous iron on brook trout have been reported to vary widely 

under different test conditions (Besser and Leib, this volume). 

The toxicity of particulate iron to brook trout is low, and the 

standard method for separation of dissolved metals (0.45 μm 

filtration) does not adequately remove iron colloids (Church 

and others, 1997); therefore, dissolved iron concentrations 

tend to be overestimated. The toxicity of iron in stream water 

may best be represented by concentrations of dissolved ferrous 

iron (Fe2+), which is the predominant species in highly acidic 

streams, such as Cement Creek and upper Mineral Creek 
>100

Range of dissolved copper concentration,  in micrograms per liter

>75 - 100

>50 - 75

>25 - 50

<25

No data

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

CONT NENTAL I

DIVIDE

OURAY CO

Silverton

Howardsville

Middleton

Chattanooga

Gladstone

Animas

Forks

Ohio xPeak

Vermilion Peak

elev. 4,235 m

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

Fork

37o45'

i R ver

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fo South kr

Illinois Gulch

M di dle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder Gulch

Gulch

Gulch

California

Mountain

x

3,792 m

x Storm Peak

Figure 10. Distribution of dissolved copper concentrations in streams during low flow.

528 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 529 Figure 11. Distribution of dissolved copper concentrations in streams during high flow.Silverton HowardsvilleMiddleton

Chattanooga

Gladstone

Animas

Forks

x Storm Peak Ohio x Peak

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTI CO NENTAL DIVIDE

OURAY CO

>100

Range of dissolved copper concentration,  in micrograms per liter

>75 - 100

>50 - 75

>25 - 50

<25

No data

Vermilion Peak

elev. 4,235 m

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

37o45'

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

uth oS Fork

Illinois Gulch

M

di dle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

oulder B

Gulch

Gulch

Gulch

3,792 m

x

California

Mountain
(Besser and Leib, this volume). Iron is listed as a nonpriority pollutant in surface water; it has a continuous concentration standard of 1,000 μg/L (U.S. Environmental Protection 

Agency, 2002). Iron standards for chronic toxicity for the 

Animas River downstream from Silverton have numeric values 

that vary by month, ranging from 1,220 to 3,776 μg/L (Unpub. 

report to Colorado Water Quality Control Commission, 

ARSG, 2000). Many of the dissolved iron concentrations in 

the study area exceeded the standards for aquatic life; therefore, the colors for the distribution of dissolved iron were 

divided arbitrarily to show the stream segments with the highest dissolved iron concentrations.

Solubility of iron in streams is dependent on pH: iron is 

soluble at low pH values (less than about 3.2) and insoluble 

at higher pH values (Nordstrom and Alpers, 1999). However, 

iron also can be solubilized by sunlight through a process 

called photoreduction (McKnight and others, 1988). Iron 

precipitates as orange, red, or yellow solids under several 

conditions: (1) ground water with high ferrous-iron concentrations and low pH can discharge at springs or mine entrances 

and the ferrous iron oxidizes to ferric iron, which precipitates 

orange- or red-colored iron oxyhydroxides; (2) low-pH water 

with high dissolved iron concentration mixes with high-pH 

water, resulting in the precipitation of orange iron oxyhydroxides or yellow iron sulfate (for example, schwertmannite 

(Bigham and others, 1996)); (3) ferrous iron is solubilized 

by photoreduction of ferric iron colloids in the stream, and 

reprecipitates as an orange oxyhydroxide. The iron oxyhydroxides and iron sulfates can be transported with the stream 

in a colloidal or sediment form, and iron colloids contribute to 

degradation of both water quality and habitat. Ground water 

discharging from springs or diffusely from the soil zone can 

form ferricrete deposits (Hanshaw, 1974). Because of the 

pervasive presence of iron sulfide minerals, dissolved and colloidal iron are major contributors to water-quality degradation 

in the Animas River watershed study area (Church and others, 

1997; Schemel and others, 2000). Large iron springs and ferricrete deposits are present in many locations throughout the 

watershed (fig. 1); some of the iron springs are quite large and 

contribute to trace-metal loading in the study area. Figure 13 

shows photographs of two large iron springs.

During low flow, dissolved iron concentrations ranged 

from 686,000 μg/L in water from the Koehler tunnel, to 

117,000 μg/L in the north-flowing Red tributary of Middle 

Fork Mineral Creek (undisturbed site), and 25,000 μg/L in 

water from Ohio Gulch. The distribution of dissolved iron 

concentrations greater than 1,000 μg/L (green, orange, and 

red colors) reflects the weathering of hydrothermally altered 

rocks in the study area. In the Animas River upstream from 

Silverton, where hydrothermally altered rocks are less 

Figure 12. Dissolved copper concentrations in Cement Creek and in Animas River downstream from Silverton 

showing opposite responses to snowmelt runoff during April–September 1997.

0

20

40

60

80

100

120

140

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

1997 CALENDAR YEAR

DISSOLVED COPPER,

IN MICROGRAMS PER LITER,

CEMENT CREEK

0

5

10

15

20

25

30

DISSOLVED COPPER,

IN MICROGRAMS PER LITER,

ANIMAS RIVER 

Copper concentrations in Cement Creek, COC48

Copper concentrations in Animas River, COA72

SNOWMELT RUNOFF

EXPLANATION

530 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 531

Cement Creek

Cement Creek road

11 0

Iron springs

A

B

Figure 13. Iron oxyhydroxide precipitates in discharge from undisturbed springs. A, spring in lower Prospect 

Gulch (site CC29, Mast, Evans, and others, 2000); B, springs in Cement Creek downstream from confluence with 

Prospect Gulch (site CC1, Mast, Evans, and others, 2000).
Silverton

Howardsville

Middleton

Chattanooga

Gladstone

Animas

Forks

x Storm Peak

Ohio xPeak

x

California

Mountain

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

CONT NE I

A NT DIVIDE L 

OURAY CO

Vermilion Peak

elev. 4,235 m

>10,000

Range of dissolved iron concentrations,  in micrograms per liter

>5,000 - 10,000

>1,000 - 5,000

>100 - 1,000

<100

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

37o45'

3,792 m

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake Ice Lake

Fuller Lake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fork uth oS

Illinois 

Gulch

M

di dle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

oulder B

Gulch

Gulch

Gulch

Figure 14. Distribution of dissolved iron concentrations in streams during low flow.

532 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 533

abundant, dissolved iron concentrations were below detection 

limit in many stream segments. The dissolved iron high-flow 

data coverage was not nearly as complete as the low-flow data 

coverage; therefore, dissolved iron distribution maps are not 

shown for high-flow conditions.

Dissolved iron is highly dependent on pH and is not 

conservative in the hydrologic system. The pH-dependent 

precipitation of iron solids is illustrated by a comparison of 

some of the dissolved and total-recoverable iron concentrations. For example, in water from the Animas River downstream from Silverton (COA72) where the mean pH was 6.4, 

the mean dissolved iron concentration was 894 μg/L and the 

mean total-recoverable iron was 2,180 μg/L. In water from 

Cement Creek (COC48) where the mean pH was 4.2, the mean 

dissolved iron concentration was 3,590 μg/L and the mean 

total-recoverable iron was 49,240 μg/L. In water from a spring 

in lower Mineral Creek (site MS57 in Mast, Evans, and others, 

2000) where the mean pH was 2.9, the mean dissolved iron 

concentration was 6,560 μg/L and the mean total-recoverable 

iron concentration was 6,980 μg/L. These examples illustrate 

how low pH values correlate with high dissolved iron concentrations in water of the study area.

Manganese

Manganese does not have a national water-quality criterion for surface water. The chronic aquatic life standards for 

manganese established for the Animas River at Silverton have 

numeric values that vary by month, and the values range from 

1,000 to 2,700 μg/L (Unpub. report to Colorado Water Quality 

Control Commission, ARSG, 2000). Many of the dissolved 

manganese concentrations in the study area exceeded the 

chronic standards for aquatic life; therefore, the colors for the 

distribution of dissolved manganese were divided arbitrarily to 

show the stream segments with the highest dissolved manganese concentrations (fig. 15).

The distribution of high dissolved manganese concentrations (greater than 1,000 μg/L) was generally related to the 

presence of deposit-related minerals such as pyroxmangite 

(MnSiO3

), huebnerite or manganese tungstate (MnWO4), 

and rhodochrosite (MnCO3

) (Bove and others, this volume); 

however, dissolved manganese concentrations were relatively 

high in many stream reaches of the study area because of manganese transport downstream from source areas. Manganese 

is soluble and can be transported long distances downstream 

from its source (Hem and Lind, 1994; Kimball and others, 

1995). In addition, mill tailings piles that have large accumulations of tailings processed from manganese-rich ores also are 

sources from which manganese can be leached into streams. 

These factors contributed to the persistent presence of manganese in streams of the study area.

During low flow, dissolved manganese concentrations 

ranged from 23,700 μg/L in water from the Koehler tunnel, to 

2,150 μg/L in the north-flowing Red tributary of Middle Fork 

Mineral Creek (undisturbed site M18, which is away from the 

influence of mine water), and 9,900 μg/L in upper Ohio Gulch 

(table 1). The distribution of high manganese concentrations 

(green, orange, and red colors on the distribution map) reflects 

the weathering of hydrothermally altered rocks. The dissolved 

manganese data coverage for high flow was not nearly as complete as the coverage for low flow; therefore, dissolved manganese distribution maps are not shown for high-flow conditions.

One of the highest dissolved manganese concentrations 

was 56,010 μg/L in a seep below the waste-rock pile at the 

Yukon tunnel (site CC100 in Mast, Evans, and others, 2000; 

Yager and Bove, this volume), located east of site COC43 in 

Cement Creek (fig. 1). This site was a tungsten mine, and the 

primary deposit-related mineral was huebnerite (MnWO4

). In 

many other areas where high dissolved manganese concentrations were present in the water, the huebnerite (or tungsten) 

was not the target economic mineral, and other manganese 

phases were present as a gangue mineral. For example, 

the Sunnyside mine, which consists of more than 166 km 

of underground tunnels between upper Eureka Gulch and 

Gladstone (fig. 15), contained an abundance of pyroxmangite 

(MnSiO2

); and mines that were developed in “Sunnysidetype” deposits (Casadevall and Ohmoto, 1977) tended to have 

elevated dissolved manganese concentrations in mine drainage. The high concentrations of manganese downstream from 

Gladstone (fig. 15) may have been affected by development of 

Sunnyside-type deposits.

High dissolved manganese concentrations were present 

in stream reaches affected by conditions not related to mining. Manganese concentrations in California Gulch (sites UA5 

and UA18, fig. 1) were largely affected by springs on the 

west side of California Mountain. For example, site UA37 

had a dissolved manganese concentration of 74,670 μg/L 

(Mast, Evans, and others, 2000; Yager and Bove, this volume), 

and the “undisturbed” occurrence of manganese is evident 

in this area because of the thick, black manganese-rich 

ledges (called manganocrete (Verplanck and others, this 

volume, Chapter E15)) that are present along the east bank 

of California Gulch (fig. 16).

Dissolved manganese generally is conservative in the 

hydrologic system at all pH ranges (Garrels and Christ, 1965). 

Schemel and others (2000) showed that manganese transport 

from the Animas River, Cement Creek, and Mineral Creek 

to the Animas River downstream of Silverton agreed within 

4 percent. Comparing the dissolved and total-recoverable 

manganese concentrations in the study area can illustrate 

other examples of the persistence of dissolved manganese. 

For example, in water from the Animas River at Eureka on 

September 23, 1998 (site COA33), the dissolved manganese 

concentration was 971 μg/L and the total-recoverable manganese concentration was 1,030 μg/L at pH of 6.4, indicating 

that 94 percent of total manganese was present in the dissolved phase (Mast, Evans, and others, 2000). In water from 

the Animas River at Silverton on January 30, 1997 (site A68 in 

Mast, Evans, and others, 2000), the dissolved manganese concentration was 2,830 μg/L and the total-recoverable manganese 

concentration was 2,950 μg/L at pH of 6.4 (95 percent in the 

dissolved phase). In water from Cement Creek near Silverton 

on January 9, 1997 (site C48 in Mast, Evans, and others, 2000), 
Figure 15. Distribution of dissolved manganese concentrations in streams during low flow.

Silverton

Howardsville

Middleton

Chattanooga

Animas

Forks

x Storm Peak

Ohio xPeak

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENT OC

AL DIVIDE

OURAY CO

Vermilion Peak

elev. 4,235 m

>2,500

Range of dissolved manganese concentrations,  in micrograms per liter

>1,000 - 2,500

>500 - 1,000

>250 - 500

<250

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

37o45'

 River

Cinnamon Cr

West

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fork South

Fairview Gulch

Illinois Gulch

M

di dle Fk

M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder

hc Gul

Gulch

Gulch

3,792 m

x

California

Mountain

Gladstone

534 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 535

Figure 16. Manganese precipitates in discharge from undisturbed springs in California Gulch.

BLACK MANGANESE LEDGES

MANGANESE

PRECIPITATE

the dissolved manganese concentration was 1,810 μg/L and the 

total-recoverable manganese concentration was 1,820 μg/L at 

pH of 3.9 (99 percent in the dissolved phase). In water from the 

Animas River downstream from Silverton on April 28, 1997 

(A72 in Mast, Evans, and others, 2000), the dissolved manganese concentration was 1,100 μg/L and the total-recoverable 

manganese concentration was 1,110 μg/L at pH of 6.96 

(99 percent in the dissolved phase). These examples illustrate 

that manganese remains in the dissolved phase in water of the 

study area regardless of the pH values. However, stream cobbles 

throughout the study area are frequently coated with a black 

manganese precipitate, possibly caused by biological or organic 

complexation of manganese (Morgan, 2000); this indicates 

that some manganese is lost from the dissolved phases to solid 

phases.

Zinc

Zinc is essential for metabolism by most living organisms, but high concentrations of zinc can be toxic to aquatic 

organisms (Muyssen and others, 2002). Dissolved zinc is 

the primary element of concern for survival of aquatic life 

in the Animas River watershed study area because levels of 

zinc exceed aquatic standards in many reaches (Besser and 

Brumbaugh, this volume). Zinc toxicity can be reduced by 

increased pH, hardness, and cadmium concentrations (Barata 

and others, 2002). Hence, aquatic toxicity guidelines and 

standards for zinc encompass complex issues. From laboratory 

tests of upper Animas River water samples, zinc was more 

toxic to amphipods than to fathead minnows, whereas copper was more toxic to minnows than to amphipods (Besser 

and Leib, this volume). Zinc toxicity thresholds (EC50) 

for survival were 200, 704, and greater than 2,000 μg/L for 

amphipods, fathead minnows, and brook trout, respectively 

(Besser and others, this volume). Zinc is listed as a priority 

pollutant in surface water; it has a continuous concentration 

standard of 120 μg/L and a maximum concentration standard 

of 120 μg/L (U.S. Environmental Protection Agency, 2002). 

The chronic aquatic life standards for zinc established for the 

Animas River downstream from Silverton have numeric values 

that differ by month, ranging from 170 to 620 μg/L (Unpub. 

report to Colorado Water Quality Control Commission, 

ARSG, 2000). Many of the dissolved zinc concentrations 

in the study area exceeded the standards for aquatic life; 

therefore, the colors for the distribution of dissolved zinc were 

divided arbitrarily to show the stream segments with the highest dissolved zinc concentrations (fig. 17).

Dissolved zinc concentrations are primarily related 

to the presence of the deposit-related mineral sphalerite (ZnS) 

and trace concentrations of zinc in other sulfide minerals of 

the study area (Bove and others, this volume; Mast and others, 

this volume). During low flow, the highest dissolved zinc concentration in the study area was in water from the Koehler tunnel (MS81), the Longfellow mine (MS82), and upper Mineral 

Creek (COM02) (fig. 17; table 1). The dissolved zinc concentration was 10,940 μg/L in the stream affected by the Congress 
Silverton

Howardsville

Middleton

Chattanooga

Gladstone

Animas

Forks

x Storm Peak Ohio x Peak

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENT OC

AL DIVIDE

OURAY CO

Vermilion Peak

elev. 4,235 m

>1,000

Range of dissolved zinc concentrations,  in micrograms per liter

>500 - 1,000

>250 - 500

>100 - 250

<100

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

37o45'

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mill Cr

Lakes

Cunningham Cr

Cement Creek

Fo South rk

Illinois Gulch

M

di dle Fk M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder

hc Gul

Gulch

Gulch

x

California

Mountain

3,792 m

Figure 17. Distribution of dissolved zinc concentrations in streams during low flow.

536 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 537

mine (MC39, table 1), which was affected by the similar 

geologic setting as the Koehler tunnel and Longfellow mine 

(the Red Mountain district, Bove and others, this volume). 

By the time water in Mineral Creek reached Chattanooga 

(site COM07), the dissolved zinc concentrations were diluted 

considerably, to a concentration of 3,050 μg/L. In water from 

Mineral Creek near Burro Bridge (site COM13), the dissolved 

zinc concentrations were diluted further, to a concentration 

of 1,590 μg/L. These high dissolved zinc concentrations were 

diluted to 729 μg/L at site COM27 upstream from the confluence of Mineral Creek and South Fork Mineral Creek (fig. 1). 

South Fork Mineral Creek (site COM28) had a dissolved zinc 

concentration of 9 μg/L and pH of 7.6; the dissolved zinc concentrations at COM34 were diluted even further, to 131 μg/L 

(figs. 1 and 17; table 1).

One subbasin in particular with high dissolved zinc 

concentrations was Prospect Gulch (fig. 1), where historical mines and a number of non-mining affected springs with 

elevated trace-metal concentrations are located (Wirt and 

others, 2001). Dissolved zinc concentrations were 810 μg/L 

at site PG45 below the shaft mines in upper Prospect Gulch 

(table 1), and the concentrations remained relatively the same 

(at about 1,400 to 1,700 μg/L) for the remaining length of the 

stream. Streamflow discharges increased throughout this reach 

of stream; therefore, other sources—probably diffuse groundwater sources—contributed to dissolved zinc concentrations 

in the reach (Wirt and others, 2001). Dissolved zinc concentrations from non-mining affected springs included a spring 

in lower Prospect Gulch (fig. 13A—1,070 μg/L) and a spring 

downstream from the confluence of Prospect Gulch with 

Cement Creek (fig. 13B—1,280 μg/L) (Mast, Evans, and others, 2000; Mast and others, this volume; Yager and Bove, this 

volume). Discharge from diffuse ground-water sources affects 

dissolved zinc concentrations in many streams of the study 

area, particularly in Cement Creek (Kimball and others, 2002).

Dissolved zinc concentrations were higher in Eureka 

Gulch and the North Fork Animas River during high flow 

than during low flow; however, concentrations were diluted 

in several reaches of the Animas River, Cement Creek, and 

Mineral Creek. Even though the streamflow discharges were 

much greater (as much as twice the discharge as during low 

flow; see fig. 3 in von Guerard and others, this volume), the 

dissolved zinc concentrations were in the same range during 

snowmelt, possibly because of the flushing of zinc from soils 

and waste-rock piles.

Other Metals

Other metals and constituents in the study area may 

be detrimental to the survival of aquatic life. Cadmium is 

highly toxic and tends to bioaccumulate in tissues of aquatic 

and terrestrial biota. Tissues of fish and aquatic invertebrates of the Animas River watershed study area were found 

to contain elevated concentrations of cadmium, although 

bioaccumulation of cadmium was not closely associated with 

observed impacts on stream ecosystems (Besser and others, 

2001; Besser and others, this volume). Cadmium (possibly 

airborne) has been shown to affect ptarmigans in the southern 

Rocky Mountains (Larison and others, 2000). Cadmium concentrations were generally below the detection limits for most 

of the samples in the study area for water-quality samples 

analyzed by inductively coupled plasma–atomic emission 

spectroscopy (ICP-AES) (Mast, Evans, and others, 2000). 

Therefore, water-quality samples from selected sites (COA33, 

COA53, COA58, COA68, and COA72) were reanalyzed for 

cadmium using graphite furnace atomic absorption spectroscopy (GFAA), and the concentrations ranged from 0.6 to 

5.1 μg/L (Mast, Evans, and others, 2000). Cadmium is listed 

as a priority pollutant in surface waters; it has a continuous 

concentration standard of 0.25 μg/L and a maximum concentration standard of 2.0 μg/L (U.S. Environmental Protection 

Agency, 2002). Lead also can be toxic in the environment 

(Prosi, 1989). Lead is listed as a priority pollutant; it has a 

continuous concentration standard of 2.5 μg/L and a maximum concentration standard of 65 μg/L (U.S. Environmental 

Protection Agency, 2002). Several streams in the study 

area had high dissolved lead concentrations (for example, 

COA33, 150 μg/L; COA58, 95 μg/L; COC43, 70 μg/L; 

CC58, 170 μg/L; CC59, 320 μg/L; CC134, 34 μg/L; COM07, 

197 μg/L; COM13, 110 μg/L; COM34, 62 μg/L; MC29, 

140 μg/L, in Mast, Evans, and others, 2000). Mine drainage 

sites had dissolved lead concentrations ranging from less than 

30 to 1,380 μg/L (Mast, Evans, and others, 2000). Lead sorbs 

strongly to colloids and may be transported as bed sediment; 

however, stream sediment was not found to be toxic to aquatic 

organisms in the study area (Besser and Leib, this volume). 

Chromium is known to be toxic to aquatic organisms, but 

toxicity depends on the chromium valence state (Spehar and 

Fiandt, 1986). Hexavalent chromium (chromium VI) is listed 

as a priority pollutant; it has a continuous concentration 

standard of 11 μg/L and a maximum concentration standard 

of 16 μg/L (U.S. Environmental Protection Agency, 2002). 

Trivalent chromium (chromium III) is listed as a priority pollutant; it has a continuous concentration standard of 

74 μg/L and a maximum concentration standard of 570 μg/L 

(U.S. Environmental Protection Agency, 2002). Dissolved 

chromium concentrations (valence not determined as part of 

this study) ranged from less than 2 to 1,980 μg/L in streams, 

springs, and inactive mines of the study area (Mast, Evans, 

and others, 2000). Because of the high detection limits and 

lack of data, distribution maps are not shown for these metals; 

however, the presence of high concentrations of these metals in selected samples indicates that they are present in the 

hydrogeochemical system and are being transported in the 

dissolved, colloidal, or sediment phases.
Silverton

Howardsville

Middleton

Chattanooga

Gladstone

Animas

Forks

x Storm Peak

Ohio xPeak

SAN MIGUEL CO

HINSDALE CO

SAN JUAN CO

NTINENT OC

AL DIVIDE

OURAY CO

Vermilion Peak

elev. 4,235 m

>1,000

Range of dissolved zinc concentrations,  in micrograms per liter

>500 - 1,000

>250 - 500

>100 - 250

<100

No data

EXPLANATION

Alteration types

Acid-sulfate (AS)

Quartz-sericite-pyrite (QSP)

Vein-related quartz-sericite-pyrite (V-QSP)Weak sericite-pyrite (WSP)Propylitic (PROP)

High-ranking draining mine

High-ranking waste-rock pile

Permitted mine site under remediation

Permitted waste-rock pile or mill tailings site under remediation

Base from U.S. Geological Survey1:100,000 Digital Line GraphsAlbers Equal-Area Conic projectionStandard parallels 37o30' and 40o30'

Central meridian 37o00'

0

0

1

1

2

2

3

3

4 MILES

4 KILOMETERS 

107o37'30" 107o45'

37o

52'30"

x

37o45'

 River

Cinnamon Cr

West 

Fork

South Fork

Animas

North Fork

Arrastra

Creek

SilverLake

HighlandMary

South 

Fork

Creek

Bear

Creek

Mineral 

Clear Cr Clear Lake

Fuller Lake

IceLake

Columbine Lake

Mi

ll Cr

Lakes

Cunningham Cr

Cement Creek

Fo South kr

Illinois Gulch

M

di d

el Fk M ni eral Cr

Gulch

Eureka

Maggie

Minnie

Boulder

hc Gul

Gulch

Gulch

x

California

Mountain

3,792 m

Figure 18. Distribution of dissolved zinc concentrations in streams during high flow.

538 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
pH Values and Dissolved Metal Concentrations in Streams 539

Summary

In the Animas River watershed study area, low pH 

and elevated concentrations of trace elements have degraded 

stream and surface water. Water quality is dependent upon 

weathering processes that take place in hydrothermally altered 

rocks and affect water that flows through to the streams. These 

weathering processes accelerate when water passes through 

rock disturbed by historical mining. Ground water draining 

from historical mine sites, and rainfall and snowmelt washing across and through mine-waste piles and mill tailings, 

can cause the release of considerable amounts of acidity and 

trace elements into nearby streams. All of these situations can 

produce high trace-metal concentrations and low pH values that 

degrade the environment and may make stream reaches toxic to 

aquatic life.

The pH of study area streams showed a wide range of low 

and high values, a variation mostly influenced by the presence 

or absence of nearby altered rocks. Where pH values were low 

(below ≈3.5), the dissolved and total-recoverable trace-metal 

concentration values were nearly equal to one another. Where 

pH values were high (above ≈6.5), in some instances dissolved 

trace elements were precipitating or were partitioning to solids, processes influenced by mixing of different-pH waters.

The distribution of trace-element concentrations varied 

greatly: the highest concentrations were evident in headwater 

streams near mine sites that have been suggested for remediation and in areas of highly altered rocks. The lowest traceelement concentrations were generally in headwater streams 

in areas of propylitic alteration, regardless of the presence of 

historical mines.

Because of the combined effects of hydrothermal alteration and historical mines on streams, we cannot distinguish 

their effects and cannot attribute low pH values and high tracemetal concentrations to either. That several historical mines 

have an effect on study area streams, however, has been made 

clear. Finally, some non-mining affected springs in the study 

area themselves contain low pH values and high trace-metal 

concentrations, which may further complicate the determination of the extent to which anthropogenic sources affect the 

dissolved trace-element concentrations and pH of streams.

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