U. S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Geochemical Baselines and Processes Affecting Surface Water, 

Redcloud Peak Area, Colorado

by

William R. Miller*

Open-File Report 98-35

This report is preliminary and has not been reviewed for conformity with the U.S. Geological 

Survey editorial standards and stratigraphic nomenclature. Any use of trade product or firm 

names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

'U.S. Geological Survey, DFC, Box 25046, MS 973, Denver, CO 80225
Introduction

When precipitation, as rain and snow, falls within a drainage basin, water comes into 

contact with rock minerals and chemical weathering is initiated. Chemical weathering within a 

basin involves the congruent dissolution of minerals such as calcite or the incongruent 

dissolution and transformation of minerals such as plagioclase to clay minerals. These processes 

release elements to the natural water of a basin. Therefore the chemical composition of water 

that evolves within a basin that has not been affected by anthropogenic processes, is determined 

primarily by the chemical composition of rocks within the basin. Climate, mainly precipitation 

and temperature plays a role, particularly in the rates of water-rock reactions, but composition of 

the rocks is the fundamental control. The major element composition of most rock types is 

generally known from geologic maps, giving insight into the expected major element 

composition of natural waters of the basin in question. The same is not true with respect to trace 

elements which can vary two or more orders of magnitude within similar rock types.

This background geochemistry of the natural water of a basin can be modified by input 

from anthropogenic processes such as nuclear fallout, atmospheric emissions, or mining wastes. 

There is probably no place in the world in which the natural background composition of waters 

of an area have not been modified to some extent by anthropogenic processes; the effects of these 

processes are always superimposed on the natural background geochemistry. But areas can be 

selected which are only minimally affected by anthropogenic input. Geochemical baselines, at a 

particular point in time for stream waters, can thus be determined, and may approximate the 

natural background geochemistry, in areas of minimal anthropogenic input. This information is 

useful for understanding the processes responsible for the chemical composition of waters of a 

basin. In addition, because stream water geochemistry is sensitive to changes in the 

environment, by monitoring stream water geochemistry in the future, changes in the environment 

within the basin can be determined.

The purpose of this study is to determine the natural baseline geochemistry of stream 

waters in the Redcloud Peak area (fig. 1), in the Southern Rocky Mountains of Colorado, for one 

period of time. Recent advances in analytical technology, particularly inductively coupled 

plasma-mass spectrometry, allow for the determination of a wide range of major and minor 

elements at very low detection limits. The Redcloud Peak area was selected because the study 

area has been shown to have high and moderate potential of several deposit types (Sanford and 

others, 1987) and the area has not been significantly impacted by mining, although some mines 

and prospects exist in the area. Therefore the geochemical baselines of stream waters evolving in 

this mineralized area can be determined and approximates the natural background geochemistry.

The determination of geochemical baselines for the Redcloud Peak area establishes a 

range of element concentrations in stream waters for this minimally impacted mineralized area at 

the time of sampling.

Field and Laboratory Methods

Thirty-three samples of water were collected from streams and one spring in the 

Redcloud Peak area (fig. 2). Samples were collected in high density polyethylene bottles that

1
Redcloud 

Peak Study 

Area

0 5 10 15 miles

Figure 1. Map showing location of Redcloud Peak study area.
29

h- 38° 00'

N

xMine

107° 30' 107° 22'30

I

Figure 2. Map showing locations of sample sites, Redcloud Peak area, Colorado
had been rinsed with 10 % nitric acid. At each site, a 60-ml sample was collected and filtered 

through a 0.45 ^m filter, and acidified to pH< 2 with nitric acid. An additional 500-ml raw 

sample was also collected. The methods and the data are shown in McHugh and others (1995).

At each site the temperature, pH, and conductivity were measured. The pH was 

measured using an Orion' model 250 pH meter with an Orion glass electrode with a Ag/AgCl 

junction. The conductivity was measured using an Orion model 120 conductivity meter. Ferrous 

iron was also determined at each site colorimetrically with a Hach DR/2000 spectrophotometer. 

Calcium, magnesium, sodium, potassium, silica, aluminum, manganese, and total iron were 

determined using the filtered, acidified samples by flame atomic absorption spectrophotometry 

(Perkins-Elmer, 1976). Fluoride, chloride, sulfate, and nitrate were determined by ion 

chromatography using the unacidified samples ( Fishman and Pyen, 1979). Alkalinity, as 

bicarbonate, was determined on the raw samples by Gran's plot potentiometric titration (Orion 

Research, 1978). The remaining elements were determined using the filtered and acidified 

samples by inductively coupled plasma-mass spectrometry.

Study Area

The Redcloud Peak study area is located between the Uncompahgre and Gunnison 

National Forests on federal lands administrated by the Bureau of Land Management. Elevations 

range from around 9400 feet along the Lake Fork of the Gunnison River to 14,034 feet for 

Redcloud Peak. Precipitation ranges from around 20 inches along the lower portion of Henson 

Creek to greater than 40 inches surrounding Redcloud Peak (Colorado Climate Center, 1984). 

Most of the study area is in the alpine zone characterized by alpine tundra and the absence of 

trees. Below this zone, the remaining area is in the subalpine zone, dominated mainly by 

Engelmann spruce and subalpine fir.

Geology and Mineralization

The study area is located within the San Juan volcanic field of southwestern Colorado. 

The study area occurs mainly within the 23.1 Ma Lake City caldera (Lipman, 1976). The caldera 

formed in response to the eruption of the Sunshine Peak Tuff with subsequent eruption of dacite 

lavas and emplacement of felsic plutons and related rhyolitic intrusions (Hon and others, 1983 

and Hon, 1987). Most of the exposed rocks within the study area are part of the caldera-fill 

sequence (Lipman, 1976 and Hon, 1987).

The Redcloud Peak area has approximately 100 quartz veins, of which 30 are more than 

2000 feet long (Hon, 1987). The veins contain quartz and disseminated pyrite with minor 

amounts of galena, chalcopyrite, sphalerite, tetrahedrite, and rhodochrosite (Sanford and others, 

1987). No significant acid-mine drainage occurs within the study area, although natural acidrock drainage is present. The Galena mining district is located adjacent and northwest of the

'The use of trade names in this report is for descriptive purposes only and does not 

constitute endorsement by the U.S. Geological Survey.
Redcloud Peak area. Galena, sphalerite, and pyrite with minor chalcopyrite, silver bearing 

tetrahedrite and native silver occur in the Galena district (Sanford and others, 1987).

The mineral potential of the Redcloud Peak area was evaluated by (Sanford and others, 

1987). They concluded that "much of the Redcloud Peak area has high mineral resource 

potential for precious (silver and gold) and base (principally lead, zinc, and copper, but also 

antimony, barite, bismuth, cadmium, fluorspar, manganese, mercury, selenium, tellurium, and 

tungsten) metals in vein-type and breccia-pipe-type epithermal deposits; the rest of the study area 

has moderate potential for these deposits. Part of the Redcloud Peak study area has high 

potential for uranium in vein-type deposits; other parts of the area have moderate potential for 

this commodity. Parts of the Redcloud Peak study area have moderate potential for molybdenum 

and copper in quartz monzonite-associated porphyry deposits " (Sanford and others, p. Bl, 

1987). The high to moderate potential for several deposit types and the lack of significant 

mining or acid drainage associated with mining allow the determination of geochemical baselines 

of this mineralized area that approximate the natural background geochemistry of stream waters 

at the time of year the sampling was carried out. This information can be used as collaborating 

data for establishing baselines at sites impacted by acid-mine drainage with similar deposit types, 

geology, and climate.

Results

Waters were collected from 32 streams and one spring during July 21-23, 1994 (fig. 2). 

The weather was stable and no precipitation occurred during this time. Spring runoff was over 

and stream flow was less than mean flow (Ugland and others, 1995). The chemical analyses of 

the 33 waters are shown in Table 1. The maximum values of remaining elements not shown in 

Table 1 are shown in Table 2. The quality of the waters ranges from excellent to degraded. The 

waters can be classified by the dominant cation and anion. Eighteen of the waters are calciumsulfate dominant, 9 are calcium-sulfate-bicarbonate dominant and 6 are calcium-bicarbonate 

dominant in composition.

Waters from mineralized areas

The water data delineate four anomalous areas that are related to mineralization of the 

rocks (fig. 3). The northwest Redcloud Peak anomaly (sites 11, 12, 13, 14, 16, 20, 30, and 32) is 

located along the northwestern slope of Redcloud Peak and extends from Redcloud Peak to 

Cooper Creek (fig. 3). The waters in this area are anomalous in sulfate, Zn, rare-earth elements 

La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, and Yb (REE), Mo, Li, U, Be, F, and low pH. The high values 

of sulfate and acid waters indicate surface and near surface oxidation of sulfides, mainly pyrite, 

and potential for epitheral base and precious metal deposits. Sanford and others (1987) 

concluded the most of the Redcloud Peak study area had high potential for precious and base 

metals in vein-type and breccia-pipe-type epithermal deposits. The anomalous values for Mo, Li, 

U, Be, REE, and F indicate the presence of highly evolved igneous rocks characteristic of 

porphyry Mo mineralization in the near surface.

The Alpine Gulch anomaly (fig. 3) is located along lower Alpine Gulch (sites 18 and 19).
Table 1. Analytical data for 33 water samples from Redcloud Peak area, Colorado

Site

RW01

RW02

RW03

RW04

RW05

RW06

RW07

RW08

RW09

RW10

RW11

RW12

RW13

RW14

RW15

RW16

RW17

RW18

RW19

RW20

RW21

RW22

RW23

RW24

RW25

RW26

RW27

RW28

RW29

RW30

RW31

RW32

RW33

Temp 

deg. C

15

8

12

9

7

7

11

9

11

9

10

8

11

13

5

9

10

8

10

9

12

12

11

11

8

14

11

16

14

10

8

6

10

PH

6.86

7.09

5.92

7.55

7.14

7.65

7.1

7.37

6.87

6.73

5.17

4.92

7.18

3.58

6.08

4.17

7

7.92

7.81

6.8

6.91

7

7.42

7.6

7.57

6.06

7.05

7.12

7.53

4.42

6.4

3.9

6.6

Cond 

|jS/cm

128

110

230

119

132

105

195

120

87

117

117

127

143

320

70

148

128

208

622

95

93

94

121

210

87

129

44

115

136

140

55

194

47

Ca

mg/l

15

15

31

17

19

14

25

18

13

14

12

12

17

22

7.8

11

15

28

85

13

12

12

18

33

11

14

6.3

16

18

12

7.6

14

6.7

Mg 

mg/l

2.4

1.7

3.3

1.3

1.5

1.9

5.3

1.8

1

2.5

1.5

2

2.9

4.5

1.2

2

2.4

4.3

10

1.2

1.4

1.4

1.6

2

1.2

2.4

0.5

1.8

2.1

1.4

0.7

2.3

0.7

Na 

mg/l

2.1

0.7

1.5

1

1

1.7

0.4

0.4

0.5

0.4

1

0.6

1.6

2.2

0.6

0.5

2

4.4

26

4

1.2

1.2

2.3

4.4

1.1

1.1

0.9

1.7

2.3

1.2

0.4

1.1

0.4

K

mg/l

0.9

0.5

0.8

0.4

0.5

0.4

0.5

0.4

0.4

0.9

1.2

1.9

1.1

4.5

1.7

3.6

0.9

0.5

1.1

0.4

0.7

0.7

0.3

1.2

1

1.7

0.5

0.8

0.6

1.2

0.4

2.3

0.5

Si02 

mg/l

9

3

9

6

6

8

3

3

4

6

10

9

9

29

16

25

10

12

14

9

6

6

7

8

8

10

6

7

10

10

3

17

4
VVVVVVVVVVVVVVVVVVT-VVVVVVVVVVVV^V

3

O)

o 3

LL

O)

CO

V l°VVV T VVV (N(N

V ^ V V V

ininoLOininr-cMrt-iis^o 

v vcov v v co CM ^ ' o>

-y»

CM

v v v v

CM

CNJ

vvvvvvvvv

V co v « V

oOV V V V

V V ^ V V V V V v ' V ^ ^ V v ' V v ' V V V V V V V V V v ' V V

m co ;« m co m 

v CM £2 v o> v

co T7 T7 CM CM T7 CD

o o ^ o o

m

oVVoVVo^rO^rO^rOCM.OCM^VV^O^VooVoooVCDO

^v v^v v^v'~'v'~'v V V V V V

~\ « \ r~\ ^D < .J f-^ o o V o o

oooopoooooopo-^-oocMpopooooooooooooo

CD CD CD CD O CD o o o o o

C\ji^OOi^i^i^,-^,-vi-vi-v j-^O,piOOOOOOO 

QCDj-JCDCDCDCDCicicD tj v tj vvvvvvv VVVVVVVV

S^q

o o-?

OO r^OOOOOOO'-.-; v^O-OOOOOOOOO.-:OOO,xiO 

V V V V V V V V V CM V V V V V VVVVVVVVV

CO =;

z. £

LL. J25

^

C/3

CM CNjCNjCNjCNjCNjCNjCNjCNj(N^(NCNjCNjCNlCNlCNlCNjCNjCNjCNjCNjCNjCNjO>CMCMCMr^CMC^

CJCMC»CDCD'CD'CD'CD'CD'CD'^-^CD'CD'CDOCDC»CDC»CDC>CDC»^CDCD V VVVVVVVVO^OVVVVVVVVVVVVOVVVOVVV

CO CM T- ^, 00 CO 

CM T

CM _ DCMOOO,V |COCO^'COCMO>Ln .OOCOCMO^HOT-T-CMT-COO

OOCD°CDCDC>CDCDCDCDCD 0 CDCDCDCD O ci O OOOOO v-'OOOOOOV

T~ CM co ^ m co r**- oo 01 CD T~~ CM co ^ in co r*~ oo o> o T~ CM co ^ in co r*~ oo o> CD T~ CM co

CDCDCDCDCDOCDCDO^^^^^^^^^^CMCMCMCMCMCMCMCMCMCMCOCOCOCO 

0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:0:
00

Site

RW01

RW02

RW03

RW04

RW05

RW06

RW07

RW08

RW09

RW10

RW11

RW12

RW13

RW14

RW15

RW16

RW17

RW18

RW19

RW20

RW21

RW22

RW23

RW24

RW25

RW26

RW27

RW28

RW29

RW30

RW31

RW32

RW33

U 

M9/I

0.1

0.1

0.3

1.1

0.5

0.1

<0.1

0.1

0.4

<0.1

2.6

6.6

0.6

3.4

0.2

3.5

<0.11

2.2

0.2

0.3

0.2

2.1

8.1

0.1

2.6

0.6

0.5

0.3

5.2

<0.1

4.6

<0.1

Li 23432321

<13352

162

8.72

4.6

170443

11

2124

4.7223

<1

5.7

<1

Be 

M9/I

<0.2

<0.2

0.8

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

0.2

1.7

2.9

<0.2

6.9

0.6

4.3

<0.2

0.3

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

2.5

<0.2

0.3

<0.2

3.3

<0.21

<0.2

Sc 

M9/I 3234232323234

7.1

4.7

6.15

5.6

7.2

5.4

4.8

4.3

5.4

5.2

6.9

6.67

8.2

7.6

8.9

8.2

8.2

8.1

Cr

0.3

0.3

<0.2

0.3

0.2

0.2

<0.2

0.3

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

0.5

0.5

0.2

<0.2

<0.2

0.2

0.5

<0.2

0.3

0.2

0.5

0.3

<0.2

<0.2

0.2

<0.2

Rb

2.1

1.5

2.3

1.2

0.7

0.9

1.8

0.61

4.1

3.6

6.8

3.2

21

6.2

18

1.9

0.6

4.8

0.6

1.9

1.8

1.2

2.4

2.1

6.6

1.8

1.4

1.34

0.8

9.5

1.1

Sr 

M9/I

170

120

190

140

160

130

83

81

37

55

54

39

170

56

29

35

160

430

>1000

130

140

140

190

320

38

110

39

140

190

49

42

44

79

Y

fjg/i

<0.1

<0.1

4.9

<0.1

<0.1

<0.1

<0.1

0.1

0.1

<0.1

8.8

9.2

0.3

9.2

0.2

3.5

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.1

<0.14

0.1

<0.1

<0.1

13

<0.1

13

<0.1

Cs 

M9/I

<0.2

0.2

0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

<0.2

0.2

1.8

<0.2

2.5

<0.2

<0.2

3.1

<0.2

<0.2

<0.2

0.2

0.4

<0.2

0.2

0.7

<0.2

<0.2

<0.2

<0.2

1.1

0.2
Site Pr Nd Sm Eii Gd Dy Yb 

	M9/I M9/' M9/' M9/' M9/' M9/' M9/'

RW01 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW02 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW03 0.8 3.4 0.7 0.2 1.1 0.6 0.2

RW04 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW05 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW06 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW07 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1

RW08 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1

RW09 <0.1 0.3 <0.1 <0.1 <0.1 <0.1 <0.1

RW10 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW11 2.2 8.7 1.8 0.2 2 1.6 0.6

RW12 1.7 5.8 1.4 0.2 1.8 1.5 0.7

RW13 <0.1 0.3 <0.1 <0.1 <0.1 <0.1 <0.1

RW14 1 4.7 1.2 0.2 1.6 1.3 0.6

RW15 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW16 0.4 1.6 0.3 <0.1 0.4 0.4 0.2

RW17 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW18 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW19 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW20 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW21 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW22 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW23 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW24 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW25 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW26 0.6 2.4 0.5 <0.1 0.7 0.5 0.2

RW27 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW28 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW29 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

RW30 2.8 10 2.2 0.2 2.4 2 0.9

RW31 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1

RW32 2 9 2.1 0.3 2.9 2.2 0.8
Table 2. Maximum values for selected elements.

Element

Ti

V

Ga

Ge

Zr

Nb

Ag

Cd

Sn

Sb

Te

Eu

Tb

Ho

Er

Tm

Hf

Ta

W

Re

Au

Tl

Pb

Bi

Th

Concentrations

2

0.4

0.2

0.2

0.1

0.3

0.1

<2

O.3

0.4

<1

0.2

0.4

0.5

0.6

0.2

0.1

O.I

O.I

0.1

0.1

0.2

<5

0.6

O.4

10
N

Lee Smelter 

Gulch -^ 

Anomaly Lower Alpine Gulch 

Anomaly

38° 00'

Anomaly

107° 30' 107° 22'30"

Figure 3. Map showing locations of anomalies, Redcloud Peak area, Colorado

11
The waters of the area are anomalous in Mo, As, Li, U, F, sulfate, and conductivity. The high 

concentrations of sulfate indicates that oxidation of sulfldes has taken place in the subsurface, but 

not the surface. If sulfide oxidation was occurring at the surface, the acid generated by the 

oxidation would not have time to be buffered and the waters would be acidic. The alkaline pH 

values and the higher alkalinity values indicate that natural acid generated by the oxidation of the 

sulfldes has been buffered, probably by calcite present in the subsurface. Calcite is probably 

associated with propylitic alteration of the rocks. The water chemistry indicates porphyry Mo 

mineralization in the subsurface. This area was considered to have high potential for porphyry 

Mo deposits by Sanford, and others (1987).

The Lee Smelter Gulch anomaly (fig. 3) is located along Lee Smelter Gulch and Copper 

Gulch (sites 3 and 4). The waters of the area are anomalous in sulfate, REE, Zn, Mo, U, F and 

low pH values. The acid waters and the high sulfate concentrations indicate that the area is 

undergoing oxidation of pyrite in the surface and near surface and indicates potential base and 

possibly precious metal mineralization. The anomalous Mo, U, F, and REE indicate the waters 

are in contact with evolved igneous rocks with moderate porphyry Mo mineralization in the 

subsurface. This area was considered to have moderate potential for porphyry Mo deposits by 

Sanford and others (1987).

The Lake Fork anomaly (fig. 3) is located along the lower southern slope of Redcloud 

Peak, above the Lake Fork of the Gunnison River (sites 23, 24, and 27). This anomaly is the 

weakest of the four. The waters of the area are anomalous in Mo, Li, U, and F. The area 

probably contains evolved igneous rocks with weak porphyry Mo mineralization in the 

subsurface.

Other elements associated with the four anomalous areas are Al, Fe, Mn, Co, Ni and Cu. 

The highest values are Al with a maximum value of 4.4 mg/1 at site 32 (fig. 2). Sites 14, 30, 16, 

12, and 11 (fig. 2) have Al concentrations >1 mg/1 (Table 1). At many of these sites, hydrous Al 

oxides are actively precipitating in the stream channel. The oxidation of the sulfldes, mainly 

pyrite, releases acid which dissolves the Al from rock minerals. When the acid waters mix with 

more neutral to alkaline waters, the resulting higher pH values of the mixed waters cause hydrous 

Al oxides or sulfates to precipitate forming white coatings along the stream bottoms and rock 

surfaces. Fe and Mn concentrations in the waters are less than Al. Much less hydrous Fe oxide 

precipitate is present in the stream channels than hydrous Al precipitates. Co and Ni 

concentrations are low; the maximum for both occur within the northwest Redcloud Peak 

anomaly (site 14) with 12 and 7 |ag/l respectively. Cu concentrations are also low with a 

maximum of 6 |ag/l at site 32, which suggests that the waters are not in contact with rocks 

containing Cu-rich minerals.

Alkalinity, which provides acid-buffering capacity to the waters, is highest at sites 19, 24, 

and 18 (fig. 2) with values of 179, 94, and 86 mg/1 respectively (Table 1). These sites occur in 

the lower Alpine Gulch anomaly and the Lake Fork anomaly. The mainly felsic compositions of 

the bedrocks in the study area provide low alkalinity to the waters. Therefore the source of the 

higher values of alkalinity is probably due to calcite present as an alteration mineral in the 

surface or subsurface of the watersheds.

Anomalous concentrations of nitrate occur at sites 2 and 12 (fig. 2) with values of 2 and 

1.1 mg/1 respectively (Table 1). The source of the anomalous nitrate is not the mineralized rocks

12
of the study area but is probably due to anthropogenic sources. The mostly likely cause is air 

pollution from the west. Another possibility is contamination by large animals.

Low ionic-strength waters

Low ionic strength waters are also present in the study area. Low values of conductivity, 

which is a measure of the total dissolved solids, occur at sites 27, 33, 31, and 15 with values of 

44, 47, 55, and 70 (iS/cm. These sites are located along a tributary draining the southeast slope 

of Redcloud Peak, along lower Copper Creek, upper northwestern portion of Copper Creek 

basin, and along lower Silver Creek (fig. 2). These sites contain the most dilute waters in the 

study area. These waters have elevated concentrations of sulfate and pH values that are slightly 

acid to neutral with low alkalinity, probably because of the oxidation of pyrite which is 

pervasive within the study area.

Comparison of Henson Creek with the Lake Fork of the Gunnison River

Comparisons of the water quality can be made of Henson Creek with the Lake Fork of the 

Gunnison River (the two major streams of the study area) by comparing the water quality at sites 

29 and 28 (fig. 2 and Table 3). Henson Creek is higher in pH and alkalinity (which improves 

water quality), but higher in sulfate, Zn, and Cu than the Lake Fork. Fe, Al, and Mn 

concentrations were low at both sites, and As, Ni, and Co concentrations were <1 ug/1 at both 

sites (Table 3). Zn concentration of 26 (ig/1 at site 29 on Henson Creek is the only elevated metal 

in the waters. Both streams are of overall good quality at sites 29 and 28, at the time of 

sampling.

Chemical modeling of the waters

To gain understanding of processes such as speciation of elements and identification of 

minerals that may control the concentration, mobility, and attenuation of elements in the stream 

waters, chemical modeling of the stream waters was carried out using PHREEQC (Parkhurst, 

1995). The modeling program assumes mineral-solution equilibrium. For some chemical 

reactions, particularly with slow kinetics, this may not be the case. The cations in the stream 

waters occur mostly as simple cations or sulfate, carbonate, and bicarbonate complexes. The 

dominate anions are SO42", HCO3", and Cl". The dominant species for selected elements are 

shown in Table 4.

The oxidation potential (Eh) is calculated using PHREEQE, assuming equilibrium of iron 

species in water with ferrihydrite with log KT=17.91 at 25°C. The Eh values were all oxidizing 

and ranged from 0.099 to 0.826 volts. The high values of Eh at sites 14, 32, 16, 12, and 11 (Eh 

from 0.543 to 0.826 volts) are typical of waters in contact with oxidizing sulfide minerals, 

particularly pyrite. These waters are from the northwest Redcloud Peak anomaly. The lowest 

values occur at sites 18, 19, 6, 24, and 29 (Eh from 0.099 to 0.128 volts) and are typical for 

waters out of contact with the atmosphere. Because these are stream waters, except for site 19 

which is a spring, groundwater inflow is probably a major component of flow at these sites.

13
Table 3. Comparison of Henson Creek to Lake Fork of the Gunnison River

Henson Creek (site 29) Lake Fork of the Gunnison River (site 28)

pH

Conductivity

Ca

Mg

Na

K

SiO2

Alkalinity as HCO3

Sulfate

Cl

F

Al

Mn

Fe

Cu

Zn

Mo

Cr

U

7.53

136

18

2.1

2.3

0.6

10

35

31

0.22

0.14

<0.1

0.02

0.02

2

26

0.3

1

0.3

7.12

115

16

1.8

1.7

0.8

7

28

23

0.19

0.16

<0.1

0.01

0.03

<1

<5

0.5

1

0.5

All speicies in mg/l except Cu, Zn, Mo, Cr, and U which are in ug/l, conductivity in 

uS/cm, and pH dimensionless

14
Table 4. Dominant dissolved species for selected elements

Element Dominant Specie Less Dominant Specie

Al AI+3, AI(OH) 4- AIF2+, AISO4+

Alkalinity HCO3-

Ca Ca2+ CaSO4

Cl ClCu Cu(OH), Cu2+ Cu+

F F-, AIF2+

Fe Fe2+ Fe(OH)2+, Fe(OH)+

K K+

Mg Mg2+ MgSO4

Mn Mn2+ MnSO4

Na Na+

S SO42- CaSO4, MgSO4

Si H4SJO4

Zn Zn2+ ZnSO4, ZnCOS

15
Saturation indexes were calculated for a suite of minerals to determine if concentrations 

of trace metals in water were controlled by mineral phases. The saturation index is a 

convenient means of expressing saturation states of minerals (Barnes and Clark, 1969 where:

SI=log, 0 IAP/KT.

In the expression, SI is the saturation index, IAP is the ion activity product, and KT is the 

equilibrium constant of the dissolution reaction at the temperature in question. Mineral phases 

are supersaturated at SI>0, saturated at SI=0, and undersaturated at SI<0.

The waters are supersaturated with respect to calcite only at site 19 (Table 5). Sites 18 

and 24 are slightly undersaturated with respect to calcite. The remaining sites are all significantly 

undersaturated with respect to calcite. Pyrite is common in the rocks of the study area, so the 

oxidation of the pyrite generates acid which will dissolve any calcite present and then consume 

the alkalinity of the water. The felsic composition of the rocks provides low buffering capacity 

to neutralize the acid generated by the oxidation of the pyrite. Therefore the waters should be 

undersaturated with respect to calcite. Site 19 and to a lesser extent sites 18 and 24 are unusual 

in that they are supersaturated or slightly undersaturated with respect to calcite. Site 19 is a 

spring sample. The most likely explanation is that the waters are in contact with abundant 

calcite. The sulfate concentration at site 19 is 176 mg/1 and can be explained by the oxidation of 

pyrite which would generate sulfate and acid. The amount of calcite in which the waters are in 

contact at this site is great enough to neutralize the acid and buffer the pH to 7.81. The presence 

of significant calcite is most likely due to propylitic alteration in the subsurface in the vicinity of 

site 19.

Other minerals which have an influence on the control of species in water is chalcedony. 

Most of the waters are near saturation with respect to chalcedony (Table 5). Therefore, 

chalcedony appears to control the amount of dissolved silica in the waters.

Conclusions and Summary

Waters in contact with mineralized rocks generate natural-acid drainage from two areas, 

the northwest Redcloud Peak and the Lee Smelter Gulch anomalous areas. The natural-acid 

drainage is mostly buffered in downstream Henson Creek and the Lake Fork of the Gunnison 

River and metals have been reduced to low levels. The quality of the waters, as they emerge 

from the area at sites 20 (Henson Creek) and 28 (Lake Fork of the Gunnison River) is good.

Waters from two other anomalous areas, the lower Alpine Peak Gulch area and the Lake 

Fork area (fig. 3), have alkaline pH with moderate concentrations of alkalinity, because of the 

presence of calcite, most likely from propylitic alteration in the subsurface. These waters have 

high concentrations of Mo, Li, U, and F. Arsenic concentration is also high at site 19.

Low-ionic strength waters are also present in the study area. These waters have elevated 

concentrations of sulfate and pH values that are slightly acid to neutral with low alkalinity, 

probably because of the oxidation of pyrite which is pervasive within the study area.

These baselines establish an approximation of background geochemistry of stream waters 

for the time of year in which the sampling was done. These data can be used along with other

16
Table 5. Saturation index values of mineral phases for 

waters collected in the Redcloud Peak area

Site No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

PE

3.95

3.62

7.13

2.51

4.54

1.96

3.54

2.77

4.51

4.99

9.21

11

3.6

14

6.73

13

2.71

1.67

1.92

4.94

4.36

3.62

2.57

2.08

2.47

6.41

3.33

3.15

2.17

12

6

14

5.02

Eh

0.233

0.214

0.421

0.148

0.268

0.116

0.209

0.163

0.266

0.294

0.543

0.649

0.212

0.826

0.397

0.767

0.160

0.099

0.113

0.291

0.257

0.214

0.152

0.123

0.146

0.378

0.196

0.186

0.128

0.708

0.354

0.826

0.296

Calcite

-2.36

-1.89

-1.81

-1.92

-1.46

-1.86

-1.56

-2.24

-2.65

-4.17

-1.97

-3.55

-2.17

-0.36

0.25

-2.07

-2.09

-2.3

-1.24

-0.51

-1.89

-2.32

-1.72

-1.21

-3.12

-2.82

Chalcedony

-0.48

-0.87

-0.45

-0.59

-0.56

-0.44

-0.91

-0.89

-0.78

-0.58

-0.37

-0.35

-0.43

0.06

-0.1

0.04

-0.37

-0.27

-0.23

-0.41

-0.62

-0.62

-0.54

-0.49

-0.45

-0.42

-0.61

-0.6

-0.42

-0.37

-0.87

-0.09

-0.77

17
information to establish geochemical baselines prior to mining at acid-mine drainage sites in 

areas of similar deposit types, geology, and climate. Caution must be exercised when estimating 

trace elements in waters from similar sites because variations in similar rock type can vary up to 

several orders of magnitude.

18
References Cited

Barnes, I. and Clark, F.E., 1969, Chemical properties of ground water and their corrosion and 

encrustation effects on wells: U.S. Geol. Survey Prof. Paper 498-D, 58 p.

Colorado Climate Center, 1984, Colorado average annual precipitation 1951-1980: Compiled by 

Colorado Climate Center, Dept. Atmospheric Science, Colorado State Univ., Fort 

Collins, scale 1:500,000.

Fishman, M.J. and Pyen, G., 1979, Determination of selected anions in water by ion 

chromatography: U.S. Geol. Survey Water Resources Invest. 79-101, 30 p.

Hon, Ken, 1987, Geologic alteration and vein maps of the Redcloud Peak (Lake City caldera)

and Handies Peak Wilderness Study Areas, Hinsdale County, Colorado: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-1949, scale 1:24,000.

Hon, Ken, Lipman, P.W., and Mehnert, H.H., 1983, The Lake City caldera, western San Juan

Mountains, Colorado: Geological Society of America Abstracts with Programs, v. 15, P. 

389.

Lipman, P.W., 1976, Geologic map of the Lake City caldera area, western San Juan Mountains, 

southwestern Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map 

1-962, scale 1:48,000.

McHugh, J.B., Miller, W.R., Meier, A.L., and d'Angelo, W.M., 1995, Chemical analyses of 33 

surface water samples from the Redcloud Peak area, Colorado: U.S. Geological Survey 

Open-File Report 95-79, 5p.

Orion Research, Inc., 1978, Analytical methods guide (9th ed.): Cambridge, MA, 48 p.

Parkhurst, D.L., 1995, User's guide to PHREEQC - a computer program for speciation, reactionpath, advective-transport, and inverse geochemical calculations: U.S. Geological Survey 

Water-Resources Investigations Report 95-4227, 143 p.

Perkin-Elmer Corporation, 1976, Analytical methods for atomic-absorption spectrophotometry: 

Norwalk, Connecticut, Perkin-Elmer Corporation, 586 p.

Sanford, R. F., Grauch, R.I., Hon, K., Bove, D.J., Grauch, V.J.S., and Korzeb, S.L., 1987, 

Mineral resources of the Redcloud Peak and Handies Peak wilderness study area, 

Hinsdale County, Colorado: U.S. Geological Survey Bull. 1715-B, 35 p.

Ugland, R.C., Maura, W.S., Wilson, E.A., and O'Neill, G.B., 1995, Water resources data,

19
Colorado, water year 1994, volume 2, Colorado River basin: U.S. Geological Survey 

Water-Data Report CO-94-2, p. 214.

20