Geochemical Results of a 

Hydrothermally Altered Area at

Baker Creek, Blaine County, Idaho

By James A. Erdman, Falma J. Moye, Paul K. Theobald,

Anne McCafferty, and Richard K. Larsen

U.S. Geological Survey Bulletin 2064-GG

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the Idaho Geological Survey,

Idaho State University, and the University of Idaho
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

This publication is only available online at:

http://geology.cr.usgs.gov/pub/bulletins/b2064-gg/

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and

does not imply endorsement by the U.S. Government

Version 1.0 2001

Published in the Central Region, Denver, Colorado

Manuscript approved for publication March 21, 2001

Graphics by Joe and Alice Springfield

Photocomposition by Gayle M. Dumonceaux
III

Contents

Abstract ......................................................................................................................................... 1

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

Acknowledgments .......................................................................................................... 2

Geologic Setting ........................................................................................................................... 2

Vegetation...................................................................................................................................... 3

Field Methods................................................................................................................................ 3

Upland and Drainage Basin Surveys.............................................................................. 3

Sample Media and Collection.......................................................................................... 3

Plants .......................................................................................................................... 3

Soils............................................................................................................................. 4

Stream Sediments .................................................................................................... 4

Heavy Mineral Concentrates.................................................................................. 4

Aquatic Mosses ........................................................................................................ 5

Sample Preparation and Analysis.............................................................................................. 5

Geochemical Surveys .................................................................................................................. 6

Geochemistry of the Upland............................................................................................. 6

Soils............................................................................................................................. 6

Douglas-Fir................................................................................................................. 6

Big Sagebrush........................................................................................................... 8

Elk Sedge.................................................................................................................... 8

Summary .................................................................................................................... 8

Geochemistry of the Drainage Basins............................................................................ 8

Stream Sediments .................................................................................................... 8

Nonmagnetic Heavy Mineral Concentrates......................................................... 8

Weakly Magnetic Heavy Mineral Concentrates ................................................. 10

Aquatic Mosses ........................................................................................................ 10

Mineralogy of the Nonmagnetic Concentrates ................................................... 10

Summary .................................................................................................................... 10

Drill Hole Results........................................................................................................................... 11

Regional Aeromagnetic Trends.................................................................................................. 12

Conclusions ................................................................................................................................... 12

Observations Concerning Sample Media and Techniques ........................................ 12

Observations Concerning Potentially Mineralized Areas ........................................... 12

References .................................................................................................................................... 14

Appendix ....................................................................................................................................... 15

1. Map showing Baker Creek study area ............................................................................ 2

2. Geologic map of Baker Creek study area ...................................................................... 2

3. Photograph showing view from locality 1 in argillically altered zone ....................... 4

Figures
IV

4-9. Maps showing:

4. Localities of soil and plant samples from upland geochemical survey............. 5

5. Localities of stream-sediment, heavy mineral concentrate, and aquatic

moss samples from drainage basin survey ........................................................... 5

6. Patterns of anomalous elements, upland survey.................................................. 7

7. Patterns of anomalous elements, drainage basin survey ................................... 9

8. Distribution of significant ore-related minerals identified in nonmagnetic

heavy mineral concentrates, drainage basin survey .......................................... 11

9. Relationship between aeromagnetic anomalies and alteration in 

Baker Creek study area and surrounding region ................................................. 13

Metric Conversion Factors

Multiply By To obtain

Miles 1.609 Kilometers

Feet 0.3048 Meters

Inches 2.54 Centimeters

Tons 1.016 Metric tons

Short tons 0.907 Metric tons

Troy ounces 31.103 Grams

Ounces 28.35 Grams
1

Geochemical Results of a 

Hydrothermally Altered Area at

Baker Creek, Blaine County, Idaho

Abstract

The area immediately east of Baker Creek, Blaine County, 

Idaho, is underlain by a thick section of mafic to intermediate 

lava flows of the Eocene Challis Volcanic Group. Widespread 

propylitic alteration surrounds a zone of argillic alteration and 

an inner core of phyllic alteration. Silicified breccia is present 

along an east-trending fault within the zone of phyllic 

alteration.

As part of a reconnaissance geochemical survey, soils and 

plants were sampled. Several species of plants (Douglas-fir 

[Pseudotsuga menziesii], mountain big sagebrush [Artemisia tridentata ssp. vaseyana], and elk sedge [Carex geyerii]) were collected from 10 upland localities and stream sediments, panned 

concentrates, and aquatic mosses were collected from 16 drainage basin localities all of which were generally within the area 

of alteration.

Geochemical results yielded anomalous concentrations of 

molybenum, zinc, silver, and lead in at least half of the seven 

different sample media and of gold, thallium, arsenic, antimony,

manganese, boron, cadmium, bismuth, copper, and beryllium in 

from one to four of the various media. Part of this suite of elements—silver, gold, arsenic, antimony, thallium, and manganese—suggests that the mineralization in the area is epithermal. 

Barite and pyrite (commonly botryoidal-framboidal) are widespread throughout the area sampled. Visible gold and pyromorphite (a secondary lead mineral) were identified in only one 

small drainage basin, but high levels of gold were detected in 

aquatic mosses over a larger area.

Data from the upland and stream sampling indicate two 

possible mineralized areas. The first mineralized area was identified by a grab sample from an outcrop of quartz stockwork that 

contained 50 ppb Au, 1.5 ppm Ag, and 50 ppm Mo. Although 

the soil and plant species that were sampled in the area indicated 

mineralized bedrock, the Douglas-fir samples were the best indicators of the silver anomaly. The second possible mineralized 

area centers on the fault-controlled silicified breccia that is most 

likely the source of anomalous silver and molybdenum levels 

identified in the soils; silver, molybdenum, and manganese in 

stream sediments; thallium in Douglas-fir; bismuth and silver in 

concentrates; and gold, silver, arsenic, antimony, and molybdenum and lead in aquatic mosses.

An interpretation of regional aeromagnetic data delineated 

the subsurface extent of shallow, steeply dipping magnetic 

sources inferred to be shallower parts of an Eocene batholith 

thought to underlie much of the Baker Creek area. The Eocene 

intrusive event(s) may have served as the heat source(s) that 

caused the hydrothermal alteration.

Examination of core from a 1,530-ft-deep (466 m) hole 

drilled in 1982 confirmed a bedrock source for the anomalous 

silver and base-metal suite at the quartz stockwork location, and 

indicated subeconomic levels of molybdenum.

Introduction

In this report, we summarize geochemical data from a 

reconnaissance geochemical survey of a hydrothermally altered 

area located just east of Baker Creek in Blaine County, Idaho, 

relate these data to the geology and structure, and present results 

from a 1,530-ft-deep (466 m) drill hole near one of two mineralized areas that we identified. The hole was drilled in 1982 by the 

Duval Corporation in an attempt to locate a possible porphyry 

molybdenum deposit.

This reconnaissance survey was conducted by Erdman, 

July 24–26, 1986, following a brief 1-day tour with D.H. McIntyre (U.S. Geological Survey). McIntyre had studied the volcanic rocks in the summer of 1985 and thought that local 

conditions were favorable for minable metallic mineral deposits. 

He suggested that biogeochemistry, more specifically, plant 

geochemistry, might be more suitable for study of the area than 

soil geochemistry because of the intense hydrothermal alteration in the area (Hall and McIntyre, 1986) and the possible 

occurrence of deeply leached soils.

The Baker Creek study area is in the Northern Rocky 

Mountains physiographic province. It encompasses about 12 

mi2 (~30 km2) in the northwestern corner of Blaine County and 

is approximately 10 mi (16 km) northwest of Ketchum (fig. 1). 

Access to the study area is provided by the unpaved Baker 

Creek road south of Idaho Highway 75 and by a logging road 

along the East Fork of Baker Creek.

 James A. Erdman, Falma J. Moye, Paul K. Theobald, Anne McCafferty

 Richard K. Larsen 

By

and

 
2 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

Approximate boundary

of study area

0 2 4 MILES

0 2 4 KILOMETERS

SMOKEY MOUNTAINS

BOULDER

MOUNTAINS

Norton

Peak

Fox Peak

Bald

Mountain

Ketchum

Big Woo d

Riv er

Baker

Creek

Warm Springs

Creek

43 ̊

45'

114 ̊30'

75

IDAHO

Baker Creek

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX

PEAK

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

Tri

Trp Tri

Tdi

Tdi

Td

Td

Ta

Ta

Ta

Tri

Approximate

boundary of

study area 

1

2

2

3

4

19

18

26

17

12 13

14 15

16

11

20

21

22

23

24

25

5

6 7

8

9

10

Trp

Tri

Tdi

Td

Ta

Tertiary lithologies

Rhyolite ash-flow tuff of Fox Peak

Porphyritic rhyolite intrusion

Dacite porphyry intrusion

Dacite lava

Andesite lava

Alteration

Silicified breccia

Phyllic alteration

Argillic alteration

Propylitic alteration

Contact—Dashed where approximately located

Fault

Sample locality and number

EXPLANATION Acknowledgments

We especially thank D.H. McIntyre for sharing his field 

observations and suggestions on the Baker Creek area. G.S. 

Plumlee shared his expertise on the role of botryoidal and framboidal pyrite in low-temperature hydrothermal systems. Battle 

Mountain Exploration Company provided extensive geochemical data from an earlier study of the area. Chemical analyses 

were performed in the USGS laboratories by Betty Bailey, R.H. 

Hill, T.A. Roemer, and R.M. O’Leary. Molybdenum and thallium were determined in Douglas-fir samples on an acid digestion of the ash from 30-g aliquots of dry material using 

inductively coupled plasma emission spectroscopy by Geochemical Services, Inc., Sparks, Nev.

Geologic Setting

The Baker Creek area is underlain by a thick section of 

mafic to intermediate lava flows and tuff breccias of the Eocene 

Challis Volcanic Group. Andesitic to dacitic volcanic rocks crop 

out discontinuously (fig. 2), reflecting their original deposition 

on an irregular topographic surface. Volcanic rocks have been 

intruded by a number of small intrusions, ranging from dacite to 

alkali rhyolite in composition. These were emplaced at shallow 

levels; for example, the rhyolite at Fox Peak vented to the surface to form a pyroclastic carapace.

Figure 1. Map showing Baker Creek study area, Blaine County, Idaho. 

Figure 2. Geologic map of the Baker Creek study area, Idaho, showing 

sample localities. 
3

The basal andesite lava flows and tuff breccias range in 

composition from basic andesite containing clinopyroxene as 

the dominant phenocryst to silica-rich andesite that has a phenocryst assemblage of hornblende, plagioclase, and clinopyroxene. Dacite is dominantly of lava flow origin and typically is 

strongly porphyritic, containing as much as 30 percent phenocrysts of varied proportions of hornblende, biotite, and plagioclase; clinopyroxene may be present in minor amounts. Dacite 

also is present as small intrusive bodies that can be distinguished from lava flows only by contact relations. Rhyolite is 

present as two distinct compositional and genetic types. In a 

shallow flow-dome complex at Fox Peak, rhyolite is strongly 

porphyritic, containing as much as 40 percent phenocrysts of 

sanidine, quartz, plagioclase, biotite, and minor hornblende. 

Ages of 49.61±19 Ma (biotite) and 48.3±15 Ma (sanidine) were 

determined by 40Ar/39Ar dating. Other rhyolite intrusive rocks, 

such as the small plug east of Alden Gulch (fig. 2, unit Tri), are 

alkali rhyolite characterized by coarse, pink potassium feldspar 

in a fine-grained groundmass. A similar intrusion 2 mi (3.2 km) 

to the southeast yielded an 40Ar/39Ar age of 47.89±0.14 Ma 

(sanidine).

Hydrothermal alteration has affected an area about 5 sq mi 

(13 sq km) in the study area. A well-developed concentric alteration zone comprises a broad marginal zone of propylitic alteration and a core zone of argillic, phyllic, and silicic alteration. 

Propylitic alteration has affected all volcanic rock types and is 

widespread and generally indistinguishable from deuteric alteration in the mafic and intermediate rocks. Argillic alteration has 

affected mainly dacite intrusive and volcanic rocks and is confined to an area in which there are several small dacite intrusive 

bodies (fig. 2). For this reason, we believe that alteration is 

closely related to emplacement of the dacite intrusions. Intense 

phyllic alteration is present in a central core defined by localities 

2, 4, 5, 7, and 11 (fig. 2). Within this core there are variably 

developed quartz-stockwork and silicified zones, and the most 

intense stockwork zones are proximal to silicified breccia zones. 

Sulfide minerals are concentrated primarily in the phyllic zone 

and in silicified breccia and stockwork, although minor amounts 

of sulfide minerals are present in the weak argillic and propylitic 

zones. In the weak argillic and propylitic zones, pyrite is the 

only sulfide mineral and makes up less than 1 percent of the 

rock. In the phyllic zone and silicified breccia and stockwork, 

pyrite, molybdenite, chalcopyrite, galena, and tetrahedrite are 

the principal sulfide minerals; pyrite is the most abundant.

Vegetation

The terrain in the study area is typically steep and ranges in 

elevation from about 6,600 ft (2,012 m) along the Big Wood 

River to 9,160 ft (2,790 m) at Fox Peak (fig. 1). Because of the 

high relief, the abundant perennial streams that drain the area 

have a high flow rate that tends to scour fine sediments from the 

active channels. Aquatic mosses, which were found to be 

responsive to mineralization in similarly steep terrain in the 

Idaho cobalt belt (Erdman and Modreski, 1984), are quite 

common and provide an alternative to sampling the missing fine 

sediments.

Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) dominates the forested parts of this landscape (fig. 3), but the open 

slopes are covered by mountain big sagebrush (Artemisia tridentata ssp. vaseyana [Rydberg] Beetle), a subspecies that is 

present throughout the upper foothill and mountain areas of 

much of the western interior of the United States. Elk sedge 

(Carex geyerii Boott.) is an herbaceous plant common to the 

area and is easily recognized.

Large blocks of slopes have been clear cut during logging 

operations; these areas support a vegetation rich in herbaceous 

and shrubby species and in young conifers.

Field Methods

Upland and Drainage Basin Surveys

One part of the study consisted of sampling soils, Douglasfir, sagebrush, and sedge from 10 upland localities (fig. 4), 

mainly in the argillically and phyllically altered zones. Douglasfir was selected for its unusual ability to concentrate arsenic 

(Warren and others, 1968) and gold (Erdman and others, 1985); 

sagebrush was chosen because of its demonstrated response to 

gold (Erdman and others, 1988) and base metals (Lovering and 

Hedal, 1983); and sedge was collected because of its ability to 

accumulate molybdenum (Erdman and others, 1985, p. 148). 

Gold, silver, and molybdenum are of particular interest because 

a rock sample from a stockwork-veined outcrop contains 50 ppb 

Au, 1.5 ppm Ag, and 50 ppm Mo.

The purpose of this upland sampling was to determine 

which of these three common and quite different plant species is 

most useful in detecting possible metallization in the underlying 

soils and bedrock and to ascertain how they compare with soils 

as a prospecting medium. As Dunn (1986) expressed so well, 

“The biogeochemical method has the advantage that it may give 

a more representative indication of [in Dunn’s case] gold in the 

environment than a spot soil sample.”

In a second part of the study, stream sediments, panned concentrates, and aquatic mosses were sampled from 16 drainage 

basin localities (fig. 5) generally in the identified alteration zones. 

Boyle (1979, p. 472) reported that it is often useful to sample 

moss where it abounds along stream courses, especially where 

spring flooding occurs, because moss tends to mechanically collect fine (skim) gold, which can be determined chemically in the 

ash. Shacklette (1984) and Smith (1986) detailed the advantages 

of using aquatic mosses in mineral exploration surveys. 

Sample Media and Collection

Plants

At most of the 10 upland localities, plant samples were collected from two sites about 10 m apart because of high local 

chemical variability commonly encountered with plants. Cohen 

and others (1987, p. 66–68) gave the best accounting of this 

Field Methods
4 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

problem in a biogeochemical study at the Hemlo gold deposit. In 

the present study, the outermost 15 cm (5.9 in.) of branches from 

a single Douglas-fir tree were sampled at each site for all localities except locality 6 for a total of 17 samples, and the twigs and 

needles were placed in cloth sample bags. Fifteen samples of 

sagebrush collected at all localities, except localities 6 and 9, consisted of new growth, including the inflorescence, composited 

from several adjacent shrubs. The above-ground portion of several clumps of sedge at all localities was combined into a composite sample for a total of 18 samples. Only a single set of 

samples was collected at locality 5, a small stand of Douglas-fir at 

the base of a silicified outcrop. Sedge was sampled at locality 6, 

a site encrusted with manganese and iron oxides at a small spring.

Soils

Soil samples were collected from shallow pits at all upland 

localities except locality 6. The 18 samples were taken from a 

depth just below 2 in. (5 cm), sieved to a minus 10-mesh (<2 

mm) fraction, and composited. This fraction was later sieved 

into two size fractions, <30 to >80 mesh (<0.6 mm to >0.17 mm) 

and <80 mesh.

Stream Sediments

Stream-sediment samples were analyzed to determine the 

chemistry of rock material eroded from the drainage basin 

upstream from selected sample localities. This information is 

useful in identifying basins that contain concentrations of elements that may be related to mineral deposits. The 16 streamsediment samples consisted of active alluvium collected, with 

few exceptions, from the mouths of unbranched streams. Each 

sample was composited from several sites at the locality plotted 

on figure 2.

Heavy Mineral Concentrates

Heavy mineral concentrate samples were collected from 

the same active alluvium as the stream-sediment samples. The 

nonmagnetic fraction of a concentrate sample is useful in 

detecting mineralized areas because primary and secondary ore 

minerals are commonly in this fraction. This is particularly true 

for uncommon minerals such as gold and cinnabar (mercury 

sulfide). The concentrations of ore and ore-related minerals in 

Figure 3. View from locality 1, Baker Creek study area, Idaho, in the argillically altered zone showing highly altered dacites in foreground and 

mosaic of Douglas-fir forest and sagebrush-dominated clearings. Heavy mineral concentrates at the mouth of the drainage in the immediate foreground contained visible gold and the lead phosphate mineral pyromorphite. Location of locality 1 is shown in figure 2.
5

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

1

2

3 4

5

6 7

8

9

10

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

11

12 13

14

15 16

17

18

19

21 20

22

23

24

26

25

these concentrate samples facilitate determination of elements 

not easily detected in bulk stream sediments. The contrast in 

metal content between geochemical anomalies and normal background is greatly expanded so that anomalies that are fairly subtle in stream sediments are easily recognized in the concentrate 

fraction. Each of the 16 bulk sediment samples was screened 

with a 10-mesh sieve to remove the coarse material. The <10-

mesh fraction was panned in the field until most of the quartz, 

feldspar, clay, and organic matter were removed. This panned 

concentrate was then placed in paper bags for further processing 

in the laboratory.

Aquatic Mosses

Aquatic mosses are an ideal alternative sampling medium 

where steep terrain and the attendant high flow rate of streams 

make it difficult to obtain adequate sediment samples. Heavy 

rain and sleet at the time of collecting made sampling the stream 

sediments very difficult, but mosses were generally abundant 

and easily collected. No attempt was made to identify the moss 

species because previous studies indicate that element contents 

between different species collected at the same site differ little 

(Shacklette and Erdman, 1982, p. 235; Erdman and Modreski, 

1984, p. 75; Smith, 1986, p. 345). The 16 samples were rinsed of 

silt as thoroughly as possible in the stream water, squeezed to 

remove most of the water, and placed in sealed plastic bags.

Sample Preparation and Analysis

The plant samples were washed, oven dried at 40°C, pulverized in a mill to pass a 2-mm screen, and then ashed in an 

electric muffle furnace at 450°C. The heating and cooling cycle 

was 24 hours.

Gold determinations were made on 500 mg samples of ash 

(250 mg samples of moss) by a modified graphite-furnace 

atomic absorption method of Meier (1980), as detailed in 

Erdman and others (1988). Nine ore-related elements—Ag, As, 

Bi, Cu, Cd, Mo, Pb, Sb, and Zn—were determined in 250 mg 

aliquots for Douglas-fir, sedge, and moss (500 mg aliquots for 

sagebrush) by flame atomic absorption spectrophotometry 

(O’Leary and Viets, 1986). Bismuth and antimony were not 

detected in any of the plant samples at a lower limit of 

Sample Preparation and Analysis

Figure 4. Soil and plant sample localities, Baker Creek study area, 

Idaho.

Figure 5. Stream-sediment, heavy mineral concentrate, and aquatic 

moss sample localities, Baker Creek study area, Idaho. Dashed lines 

indicate approximate limits of drainage basins associated with sample 

localities.
6 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

determination of 4 and 8 ppm, respectively (2 and 4 ppm for 

sagebrush), and so are not listed in the tables of analytical 

results given in the appendix tables. 

The soil and stream-sediment samples were air dried, then 

sieved using 30- and 80-mesh stainless-steel sieves. The portion 

of the sediment passing through the sieves was saved for analysis; two size fractions, <30- to >80-mesh and <80-mesh, of the 

soils were analyzed, whereas only the finer fraction of the sediments was retained for analysis.

Samples that had been panned in the field were air dried 

and sieved to <35 mesh; the light minerals remaining in the 

<35-mesh fraction were removed by heavy liquid flotation 

(bromoform, specific gravity 2.85). The heavy mineral 

concentrate samples were then separated into magnetic, weakly 

(para-) magnetic, and nonmagnetic fractions by placing the 

sample in contact with the face of a large electromagnet (in 

this case a modified Frantz Isodynamic Separator). The most 

magnetic material (removed at a setting of 0.25 amperes), 

primarily magnetite, was not analyzed. The second fraction 

(removed at a setting of 1.75 amperes), mostly ferromagnesian 

silicate minerals and iron and manganese oxide minerals, was 

saved for analysis, because this paramagnetic fraction might 

contain limonite and manganese oxide minerals which in turn 

might contain high trace-metal values related to mineral deposits. The third fraction (the nonmagnetic material, which might 

include nonmagnetic ore minerals) was split using a Jones 

splitter. These magnetic separates are the same separates that 

would be produced by using a Frantz Isodynamic Separator set 

at a slope of 15° and a tilt of 10° with a current of 0.2 amperes 

to remove the magnetite and ilmenite and a current of 0.6 

amperes to split the remainder of the sample into paramagnetic and nonmagnetic fractions.

The nonmagnetic fractions were examined visually at 

low magnification (10-30×) to identify the minerals present. 

Nonmagnetic and weakly magnetic fractions were pulverized 

for chemical analysis, and the magnetic fraction was 

archived. 

As with the heavy mineral concentrates, the soil and 

stream-sediment samples were first pulverized to approximately 200 mesh (75 μ) before being analyzed for 31 elements using semiquantitative, direct-current-arc emission 

spectroscopy. The analyses of heavy mineral concentrate samples were performed using the method of Grimes and Marranzino (1968). Gold analyses were conducted by graphite furnace 

atomic absorption spectrophotometry on 10 g aliquots of soil 

samples only.

Geochemical Surveys

Figures 6–8 show the patterns of elements whose concentrations in various sample media were anomalous based 

on visual inspection of the data and experience, not the concentrations themselves. Analytical results for these samples 

are given in appendix tables 1–7. The concentrations given 

in the text that refer to plant samples are expressed on an 

ash basis.

Geochemistry of the Upland

Soils

Only the soils from localities in the zones of phyllic and 

argillic alteration contain anomalous levels of silver, 

molybdenum, lead, and zinc (figs. 2, 6A; appendix table 1). 

Some of the soil samples contain detectible gold at background 

levels of 2 ppb, but the distribution of these samples is widely 

scattered and forms no pattern that corresponds to the mineralized areas identified using other evidence.

The molybdenum, lead, and zinc element suite at locality 7 

reflects the molybdenum-silver-gold anomaly in the nearby 

stockwork-veined outcrop sampled by D. L. McIntyre in the 

summer of 1985. Both the coarse and fine fractions of the soil 

from locality 7 contain the highest concentrations of molybdenum, lead, and zinc (15, 150, and 200 ppm, respectively; appendix table 1). 

In contrast to the above base-metal suite, silver was 

detected only in soils from localities 3 and 4, just north of the 

east-trending fault and associated silicified breccia (fig. 2). 

Silver values range from 1 to 2 ppm in both coarse and fine 

fractions. The two fractions from locality 4 also contain 7 and 

10 ppm Mo, respectively.

Douglas-Fir

Analytical results for Douglas-fir samples (appendix table 

2) generally reveal anomalies (fig. 6B) that are subtle; concentrations are about twice background. Such subtle anomalies 

were also observed with the other two plant species. Results for 

silver, arsenic, and thallium are exceptions, however. 

Concentrations of silver in Douglas-fir from the two sites 

at locality 7 are 3.2 and 3.8 ppm, well above the concentrations 

of ~0.2 ppm at most other localities. Samples of both trees from 

locality 7 also contain anomalous levels of zinc, as compared to 

background levels of ~400 ppm, and of molybdenum, as compared to <1 ppm elsewhere. Only one sample of Douglas-fir 

from locality 7 yielded an anomalous concentration of cadmium, 5.6 ppm as compared to ~2 ppm in other samples. 

Arsenic (160–400 ppm) was detected in the four samples 

of Douglas-fir from localities 9 and 10 (fig. 6B) where the bedrock contains fresh disseminated pyrite. Arsenic levels in Douglas-fir samples from the other localities are less than the 40 

ppm limit of determination. 

Although the only strong multielement anomaly detected 

in Douglas-fir is at locality 7, high thallium concentrations in 

samples from both sites at locality 2 present a curious anomaly 

that is supported by other evidence, including proximity to the 

silicified breccias (fig. 2). Concentrations of 1.8 and 2.1 ppm Tl 

from the Douglas-fir at locality 2 are anomalous as compared to 

most other samples in which thallium was detected in only trace 

amounts (appendix table 2). Boyle (1979, p. 132) reported that, 

Thallium is a trace constituent of most gold deposits 

containing sulphides and sulphosalts * * * It should also 

be mentioned that thallium shows a marked coherence 
7

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

1

2

3

Tl

Zn

As

As, Zn

Ag, Mo, Zn, Cd

Ag,

Mo

Ag

Mo

Zn

Mo, Pb, Zn

4

5

6 7

8

9

10

1

2

3

Mo

4

5

6 7 Cd, Mo, Cu, Pb, Zn

8

9

10

1

2

3 4

5

6 7

8

9

10

1

2

3 4

5

6 7

8

9

10

Mo, Zn

Mo, Cd, Zn

Cd, Zn

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

43 ̊

45'

114 ̊30'

43 ̊

45'

114 ̊30'

43 ̊

45'

A B 114 ̊30'

C D

Geochemical Surveys

Figure 6. Patterns of anomalous elements, Baker Creek study area, Idaho. A, Soils. No sample collected at locality 6. B, Douglas-fir. No 

sample collected at locality 6. C, Sagebrush. No samples collected at localities 6 and 9. D, Sedge.
8 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

with silver and lead * * * Thallium tends to be concentrated in medium and low temperature deposits * * * and 

is enriched in some present day gold-bearing precipitates 

from hot springs.

Warren and Horsky (1986) described the role of thallium in 

plants as a pathfinder for gold. According to Boyle (1979), 

thallium is highly mobile under both acidic and alkaline conditions and therefore is easily dispersed into the water regime. 

Such mobility might account for the strong anomaly in 

Douglas-fir.

A rock-chip sample of outcrop from locality 2 contains 6 

ppm W; it is one of the few rock samples collected by Duval 

Corporation in 1980 (unpublished data) that contained anomalous tungsten. The sample also contained 3.5 ppm Ag.

Big Sagebrush

Only samples of sagebrush from localities 5 and 7 are 

anomalous (fig. 6C). Molybdenum levels in the three samples 

from both localities range from 20 to 72 ppm and are considerably higher than levels of 4–12 ppm in sagebrush samples from 

the other localities (appendix table 3). Locality 7 is again the 

focal point and has a strong base-metal signature of cadmiummolybdenum-copper-lead-zinc. Sagebrush from the two sites at 

this locality contains 26 and 40 ppm Cd, far above the levels of 

0.4–5.0 obtained elsewhere. This represents an anomaly to background contrast of about 10.

Marked cadmium anomalies in plants from mineralized 

environments where cadmium is enriched should be expected. 

Unlike most other elements, cadmium is readily taken up in proportion to its concentration in the soil solution (Kabata-Pendias 

and Pendias, 1984). A similarly strong contrast was found in 

sagebrush associated with an active hot-springs system in 

Nevada where peak levels approached those found at Baker 

Creek (Erdman and others, 1988). The same two sagebrush samples from locality 7 contain the only detectable lead (10 and 20 

ppm) and about twice background concentrations of copper and 

zinc (appendix table 3).

Elk Sedge

The anomaly pattern for the sedge samples (fig. 6D) mirrors that of sagebrush and, to some degree, that of Douglas-fir. 

The molybdenum values of 24–56 ppm at localities 5 and 7 are 

strong outliers as compared to molybdenum concentrations of 

generally 8–12 ppm in the other samples (appendix table 4). 

The anomaly to background contrast of 2 to 1 for cadmium is 

considerably less than that for sagebrush; concentrations in 

sedge samples from localities 6 and 7 range from 5.2 to 7.6, 

and are clearly higher than the range of 0.8–3.2 in samples 

from the other localities. Anomalous zinc levels range from 

880 ppm at locality 5 to >2,000 ppm in the sedge from the 

mineralized seep at locality 6; background concentrations in 

sedge are ~200–400 ppm.

Summary

The results from the upland survey identify locality 7 as 

indicating potential for base-metal mineralization, with some 

potential for silver. The silver-molybdenum anomalies in the 

soils from localities 3 and 4 (and the thallium anomaly in Douglas-fir from locality 2) reveal another possible precious-metal 

mineralized area: the silicified breccia about0.5 km to the north. 

Results of the admittedly limited soil geochemistry tentatively define two areas with potential for mineralization that differ geochemically and, perhaps, structurally.

Geochemistry of the Drainage Basins

Stream Sediments

Stream-sediment samples in 5 of the 16 drainage basins 

sampled—localities 11, 15, 16, 24, and 25—have anomalous 

metal values (fig. 7A, appendix table 5). The only convincing 

silver anomaly, 1.5 ppm, is from sample locality 11, whose west 

fork drains the east-trending fault and associated silicified breccia (fig. 2). This sediment sample also contains the highest manganese and molybdenum concentrations, >5,000 and 10 ppm, 

respectively. Other molybdenum anomalies (7 ppm) were 

detected in samples from basin localities 24 and 25, whose sediments are derived, in part, from the western end of the same 

fault.

At the East Fork of Baker Creek (fig. 7A), the sediment 

sample from locality 16 yielded the only clear lead anomaly 

(150 ppm), the highest concentration of zinc (700 ppm), and 

2,000 ppm Mn. This sample reflects the anomalies associated 

with upland localities 5, 6, and 7, described earlier. The sediment from locality 15 also contains anomalous levels of manganese and zinc, >5,000 and 200 ppm, respectively; the close 

proximity of this locality to locality 16 suggests a broad mineralized system having similar characteristics.

Nonmagnetic Heavy Mineral Concentrates

The nonmagnetic fraction of the concentrates from 7 of the 

16 drainages sampled have anomalous metal values (fig. 7B). 

The lead and copper anomalies from localities 21 and 22 are 

unsupported by results from other sample media and therefore 

most likely reflect metal contamination from nearby cabins. The 

bismuth anomalies at localities 11, 24, and 25, however, coincide with the molybdenum anomalies in the stream sediments 

and strongly suggest that bismuth is enriched in the east-trending fault or its associated breccia. Bismuth concentrations range 

from 70 ppm at locality 11 to 1,000 ppm at locality 25 (appendix table 6). 

Although bismuth commonly indicates high-temperature 

mineralization, it can be associated with arsenic and antimony 

in low-temperature hydrothermal conditions (G.S. Plumlee, oral 

commun., 1990). For example, in a reconnaissance-scale 

geochemical survey of geothermal fields, Zhu and others (1989) 
9

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

43 ̊

45'

114 ̊30'

43 ̊

45'

114 ̊30'

43 ̊

45'

A B 114 ̊30'

C D

11

12 13

14

15 16

17

18

19

21 20

22

23

24

26

25

Mn,

Zn

Mo

Mo

Ag,

Mn,

Mo

Mo, Pb, Zn

11

12 13

14

15

16

17

18

19

21 20

22

23

24

26

25

Ag,

B

Bi

Bi

Bi

Pb

Pb, Cu

Pb,

Mo

11

12 13

14

15 16

17

18

19

21 20

22

23

24

26

25

Ag

Ag

Ag, Be, Zn

11

12 13

14

15

16

17

18

19

21 20

22

23

24

26

25

Au,

Ag,

Zn

Mo, Pb

As

Mo, Pb Au

Sb, As,

Au, Ag

As, Pb,

Zn, Cd

Geochemical Surveys

Figure 7. Anomalous elements detected in drainage basins in Baker Creek study area, Idaho. A, Stream sediments. B, Nonmagnetic heavy 

mineral concentrates. C, Weakly magnetic heavy mineral concentrates. D, Aquatic mosses.
10 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

found that higher bismuth concentrations in soils tend to coincide with near-surface thermal waters from drill holes in the geothermal fields.

The concentrate from locality 16 contains extremely anomalous amounts of molybdenum and lead: 70 ppm Mo, as compared to <10 ppm in the other 16 samples, and 3,000 ppm Pb, as 

compared to normal concentrations of <20 to 50 at all other 

localities except 21 and 22. Also, as shown on figure 7A, the sediment from this locality 16 contains anomalous amounts of zinc.

The concentrate from nearby locality 15 contains anomalous amounts of silver and boron. The sample contains 2 ppm Ag 

and 500 ppm B, as compared to <1 ppm Ag and <20 to 50 ppm 

B in the concentrates from the other 15 localities.

Barium levels in most of the samples exceed the 10,000 

ppm upper limit of determination (appendix table 6). Such levels 

are significant in that they indicate the presence of barite. In this 

terrace, the only source of barite is hydrothermal.

Weakly Magnetic Heavy Mineral Concentrates

We found metal anomalies in this weakly magnetic fraction 

of concentrates from only localities 11, 15, and 16 (fig. 7C). 

Concentrations of silver are anomalous at all three localities and 

range from 1 ppm at localities 15 and 16 to 2 ppm at locality 11; 

silver is below the 1 ppm limit of determination in all other samples. The beryllium content of concentrate from locality 16 is 15 

ppm, well above the <2–5 ppm levels in the other samples. The 

zinc concentration in this sample is 1,000 ppm.

Aquatic Mosses

The analytical results for the moss samples are given in 

appendix table 7. The anomalous patterns (fig. 7D) to some 

extent mirror those for the stream sediments. The following 

anomalies were observed in both media: molybdenum at localities 24 and 25, lead and zinc at locality 16; silver at locality 11, 

and zinc at locality 15.

Analytical methods used for sediment samples will not 

detect low-level gold, arsenic, and antimony, so a comparison of 

the relative merits of the two media is somewhat biased. However, the antimony-gold-silver-arsenic anomaly in the moss at 

locality 11 is far more significant than the anomalies in the 

stream sediments and two fractions of concentrates shown in 

figure 7A–C. Antimony was detected in only this sample, and 

the 72 ppm value far exceeds the 8 ppm limit of determination. 

The silver value of 3.2 ppm is the second highest observed, well 

above the <0.2 ppm levels found in most other samples. The 

gold value of 64 ppb matches that of the sample from locality 

15 and far exceeds the gold concentrations in most of the other 

samples (appendix table 7). Arsenic, antimony, and silver are 

low-temperature “mobile” elements that are commonly characteristic of late stages or fringes of epithermal systems (Plumlee 

and Rye, 1989). Although samples having gold values of 48 ppb 

or higher are fairly widespread, the gold concentrations at localities 11 and 15 are high enough to warrant closer study of those 

localities.

Anomalous metallic elements in the moss sample from 

locality 15 include gold, the highest concentration of silver (5.2 

ppm), and 1,500 ppm Zn. Finally, anomalous metallic elements 

in the moss sample from locality 16 suggest base-metal potential: 160 ppm Pb, >2,000 ppm Zn, 20 ppm Cd, and detectible 

arsenic. The cadmium anomaly in the moss sample from locality 16 (as shown in appendix table 7) may relate to the occurrence of pyromorphite in the nonmagnetic concentrate 

(described below) from locality 16. Boyle (1979, p. 126) 

observed: 

“Where supergene * * * lead minerals such as * * * 

pyromorphite are present cadmium may be significantly 

enriched.”

Analytical results for the aquatic moss samples complement those of the concentrates and may be more informative 

than results for the stream sediments. In retrospect, we probably 

could have combined the advantages of both sediments and 

mosses by simply using the fines entrapped by the moss, as has 

been suggested by Smith (1976) and Boyle (1979). In his work 

with aquatic bryophytes (mostly mosses), Smith (1986) analyzed the plants but maintained that rigorous cleaning actually 

detracts from this plant’s effectiveness as a sample medium.

Mineralogy of the Nonmagnetic Concentrates

Barite and pyrite are the most common and widespread of 

the ore-related minerals identified in the nonmagnetic heavy 

mineral concentrates. Because barite was identified in samples 

from all 16 drainage basin localities, its distribution is not 

shown in figure 8. Barite was either dominant or abundant at all 

localities except 15 and 19. Botryoidal-framboidal pyrite was 

identified in 8 of the 12 samples in which pyrite was identified. 

The source of framboidal pyrite is commonly metalliferous 

black shale. Although such black shale is common east of the 

study area (Hall and others, 1978; Hall, 1985), it does not crop 

out in any of the basins drained by Baker Creek and therefore 

most likely is not the source of the pyrite at Baker Creek. The 

botryoidal-framboidal pyrite in the concentrates at Baker Creek 

may have formed under low-temperature hot-springs conditions. 

Because low-temperature pyrite can break down relatively rapidly in the weathering environment, it must be continuously 

eroding from exposed hydrothermally altered outcrops. Both 

botryoidal pyrite and barite tend to be present in the late, waning 

stages or low-temperature (<200°C) fringes of hydrothermal 

systems (Plumlee and Rye, 1989).

Visible gold and pyromorphite were identified in the nonmagnetic concentrate only from locality 16 (fig. 8). A single, 

extremely small flake of gold in this sample is the only visible 

gold observed in the study. Pyromorphite is a typical secondary 

mineral in the oxidized zone of lead deposits. The presence of 

these ore-related minerals requires that the bedrock source be 

exposed in the watershed above locality 16.

Summary

Results of the drainage basin survey, like those of the 

upland survey, provide evidence of two areas with potential for 
11

as-yet unrecognized mineralization. One area centers on locality 

16, but includes the basin above locality 15 just across the East 

Fork of Baker Creek. The focal point of the second area is the 

east-trending fault and associated breccia delineated by localities 11, 24, and 25.

Drill Hole Results

During 1982, Duval Corp. completed a 1,530 ft (466 m) 

diamond drill hole just east of locality 5 (fig. 2). The purpose of 

the drilling was to test for porphyry molybdenum mineralized 

rock beneath a zone of phyllically altered intrusive dacite and 

local quartz stockwork. The hole was also placed to test a coincident factor analysis anomaly correlating log molybdenum and 

log fluorine with inverse strontium and log zinc as well to test a 

molybdenum-silver geochemical anomaly based on rock chip 

and soil grid sampling. The resulting drill core was megascopically logged and split on alternate 10-foot (3.05-m) intervals for 

assay except in zones of visible mineralized rock where each 

10-foot zone was split and assayed. Twenty-one thin sections 

stained for potassium feldspar were petrographically examined 

to quantify rock type and alteration.

In summary, the corehole penetrated variably altered and 

mineralized dacite porphyry cut by dikes of rhyolite porphyry 

and quartz latite porphyry. The dacite porphyry shows little textural or mineralogic variation downhole and is a gray to green to 

brownish-tan porphyry composed of clear to milky white plagioclase laths as long as 5 cm in an aphanitic groundmass of quartz, 

hornblende, and potassium feldspar. The rhyolite porphyry dikes 

are a distinctive light- pinkish-white intrusive rock that clearly 

cuts the dacite porphyry and consists of greasy, greenish plagioclase phenocrysts, sparse large quartz “eyes,” and abundant 

biotite laths in an aphanitic, pinkish groundmass of potassium 

feldspar and quartz. The only quartz latite dike encountered was 

also distinctive; it is a cream-white porphyry composed of small 

(1-3 cm), clear quartz phenocrysts, sparse white plagioclase 

phenocrysts, and salmon-colored potassium feldspar phenocrysts in a hard, dense, microcrystalline groundmass of quartz 

and potassium feldspar.

Strong phyllic alteration and local quartz stockworks 

development and silica groundmass flooding were logged from 

the collar to 350 ft and (0–107 m) from 950 to 1,200 ft (290–

366 m). These zones range from a uniform gray color to tan 

brown; the brown coloration is due to biotization. The phyllically altered zones are separated by short intervals of argillic 

alteration. Broad zones of propylitic alteration were logged 

from 450 to 850 ft (137–259 m) and from 1,300 to 1,532 ft 

(396–467 m). 

The alteration mineralogy based on thin section petrography is similar to that mapped on the surface and is summarized 

in the following paragraphs.

Intense phyllic alteration: Quartz+serite+pyrite±clay±calcite. This alteration involves almost total obliteration of the original rock textures that yields a light-gray, fractured, and 

brecciated aggregate of sericitized feldspar and introduced silica 

cut by quartz stockworks containing as much as 5 percent pyrite.

Phyllic alteration: Quartz+pyrite±serite±biotite±clay±calcite. This alteration involves partial to total alteration of feldspar 

and generally total alteration of mafic rocks. Ragged biotite is 

locally developed as felty aggregates in the groundmass as well 

as larger phenocrysts visible to the eye. Original rock textures 

are generally preserved, and color ranges from gray to brown in 

biotite-rich zones.

Argillic alteration: Clay±quartz±pyrite±sericite. This alteration involves argillization of feldspar and general preservation 

of rock texture.

Propylitic alteration: Calcite+chlorite+pyrite±clays±epidote. This alteration involves partial to almost total alteration of 

plagioclase and mafic minerals and patchy alteration of groundmass. Propylitically altered rock has a distinctly greenish cast 

and reacts with dilute HCl. 

In addition to pyrite, which varies from less than 1 percent to 5 percent in the most intensely altered zones, three zones 

of lead-zinc-silver-copper mineralized rock were intercepted in 

the drill hole. These zones consist of galena, sphalerite, pyrite, 

and local chalcopyrite associated with pods and veinlets of 

actinolite, chlorite, calcite, and local gypsum. Also, from 150 to 

Drill Hole Results

keer C

rekaB

Big Wood River

East

Fork

South

Fork

Alden

Gulch

Easley Gulch

Easley

Hot Springs

FOX PEAK

0 1 2 MILES

0 1 2 KILOMETERS

43 ̊

45'

114 ̊30'

11

12

13

14

15

16

17

18

19 20

21

22

23

24

26

25

pyrite

(botr)

pyrite

pyrite (botr)

(botr)

pyrite

(botr)

pyrite

(botr)

pyrite

(botr) pyrite

(botr)

pyrite

pyrite

pyrite

gold

pyromorphite

pyrite

pyrite (botr)

Figure 8. Distribution of significant ore-related minerals identified in 

nonmagnetic heavy mineral concentrates, Baker Creek study area, 

Idaho. Dashed lines indicate drainage basins associated with sample 

localities. Screened pattern indicates drainage basin associated with 

sample containing visible gold. Pyrite (botr), botryoidal-framboidal 

pyrite.
12 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

190 ft (46-58 m), traces of molybdenite were logged in zones of 

strong phyllic alteration.

A summary of the drill hole geochemistry includes the 

following groupings:

0-300 ft (0-91 m): 39 ppm Mo

2,650 ppm F

660-710 ft (201-216 m): 3,000 ppm Pb

820-880 ft (250-268 m): 7,000 ppm Pb

500 ppm Zn

1,450 ppm Cu

890-920 ft (271-280 m): 870 ppm Pb

5.9 ppm Ag

980-1,350 ft (299-411 m): 36 ppm Mo

1,333 ppm F

The highest values obtained were 10 ft (3.05 m) of 1.20 percent 

Pb from 810 to 820 ft (247–250 m), 10 ft of 0.29 percent Cu 

from the same interval, and 10 ft of 80 ppm Mo from 1,010 to 

1,020 ft (308–311 m).

Regional Aeromagnetic Trends

Regional aeromagnetic data from the study area were 

extracted and interpreted from a regional data set compiled as 

part of a larger project (McCafferty, 1992). The data originated 

from surveys flown north-south with 1 mi (1.6 km) flightline 

spacing at 11,000–12,000 ft (3,353–3,658 m) barometric elevation. The original data have been filtered to simulate the magnetic field as if it were measured at a constant elevation of 1,000 

ft (305 m) above ground. This representation is shown as a contour map on figure 9.

A combination of magnetic highs and lows is present over 

the Baker Creek area. Magnetization boundaries were inferred 

(Cordell and Grauch, 1985; Blakely and Simpson, 1986) on figure 9. The boundaries represent abrupt lateral changes in the 

magnetic properties of rocks and are inferred to be steep or nearvertical geologic contacts.

Two such boundaries coincide with the Wood River graben 

(fig. 9, loc. A). A magnetic high over the graben suggests that the 

faults may have played a role in the emplacement of Tertiary 

intrusions. Alternatively, it may reflect shallower exposures of an 

Eocene granitic batholith that Hall and McIntyre (1986) felt 

underlies much of the area northwest of Ketchum. Preliminary 

studies of rock magnetization in the surrounding area (J.W. 

Cady, oral commun., 1988) indicate that the Eocene granite has 

relatively high magnetization values as compared to rocks of 

Challis Volcanic Group of similar age.

Similar pairs of parallel northeast-trending magnetization 

boundaries are directly to the northwest and southeast of the 

hydrothermally altered area (fig. 9, locs. B, C). The presence of 

magnetic highs over these areas suggests a similar relationship 

to the Eocene batholith as in the Wood River graben. These 

boundary features may represent major structural features that 

played a role in alteration and mineralization at Baker Creek by 

localization of intrusive and hydrothermal activity. These structures may also control the path for the heated meteoric water at 

Easley Hot Springs just to the north of the Baker Creek altered 

area (see fig. 2).

Conclusions

Observations Concerning Sample Media and 

Techniques

Results of a geochemical survey of a hydrothermally 

altered area at Baker Creek, Blaine County, Idaho, indicate that 

soils are more useful than expected, generally more so than the 

plants, in delineating possible areas of mineralized rock. Silver 

and molybdenum contrasts were about the same in both media, 

but the soil anomalies were more extensive. The better response 

of Douglas-fir to silver, as compared to that of the other two 

plant species sampled, suggests that it is an ideal plant medium 

in precious-metal exploration.

Aquatic mosses are a preferred sample medium, as compared to stream sediments, and results for mosses complement 

results for heavy mineral concentrates. Mineral identification in 

concentrates defined only a single, narrow target based on single 

grains of visible gold and pyromorphite, a secondary lead mineral, in the nonmagnetic concentrate from one locality.

Aeromagnetic data for the area define magnetization 

boundaries that coincide with structural and lithologic contacts 

that may play a role in controlling the hydrothermal activity in 

the Baker Creek Area.

Observations Concerning Potentially 

 Mineralized Areas

Two broad areas with potential for as-yet unrecognized 

mineralization were defined by the geochemical results. One 

area centers on drainage basin locality 16, where visible gold 

and pyromorphite were identified in the nonmagnetic heavy 

mineral concentrate. Locality 15, nearby, may be part of this 

area and warrants more detailed study. Anomalous amounts of 

base-metals characterize this area more strongly than they do 

the other area, and the inferred mineralization at localities 15 

and 16 may reflect a deeply buried, higher temperature porphyry 

system. The second area focuses on silicified breccia along a 

fault zone. The geochemical signature of this latter area—antimony, arsenic, silver, bismuth, thallium, and tungsten—is 

suggestive of a low-temperature system.

Results of a drill hole in the area indicate subeconomic 

mineralization in bedrock underlying the base-metal surface 

geochemical anomaly. Unfortunately, the drilling effort did not 

intersect molybdenum mineralized rock as had been anticipated. 

The geochemical, geologic, and aeromagnetic results, however, 

support further studies in the area.
13

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-200

-100

-100

-200

-100

-100

0

0

0

300

-0

Hydrothermally altered area

Fault—Dashed where approximately located.

Bar and ball on downthrown side

Magnetic contour

Locality discussed in text

EXPLANATION

A

-200

Magnetization boundaries

43 ̊

45'

43 ̊

30'

114 ̊30'

75

75

BOULDER MOUNTAINS

Exposed Batholith Roof Zone

B

C

Norton PeakExposed Batholith

Roof Zone

Baker

Creek

Springs

Creek

Warm

Ketchum

A

Wood River

Graben

Griff Butte

Adams

C A U L D R O N

Chiefly

Paleozoic

Sedimentary Rocks

Deer

Creek

Gulch

Greenhorn

Bald

Mountain

Shaw Mountain

Gulch

Outline of

figure 2

0 2 4 MILES

0 2 4 KILOMETERS

Figure 9. Relationship between aeromagnetic anomalies and alteration in Baker Creek study area and surrounding region, Idaho. Aeromagnetic anomaly map from surveys flown at 1-mi (1.6 km) spacing. Data have been filtered to simulate the magnetic field at 1,000 ft (305 m) above 

terrain. Magnetization boundaries (heavy lines) were inferred from the horizontal gradient method. Hachures indicate areas of magnetic lows. 

Contour interval 20 nanoteslas. 

Conclusions
14 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

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1°×2° quadrangle, Idaho: U.S. Geological Survey Bulletin 1658-L, 

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Erdman, J.A., and Modreski, P.J., 1984, Copper and cobalt in aquatic 

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APPENDIX
16 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

Appendix table 1. Analytical results for selected elements in soils from upland localities in the 

Baker Creek study area, Blaine County, Idaho.

[In parts per million except for gold, which is in parts per billion. Sample localities shown on figure 2; suffixes C 

and F in sample numbers indicate powdered coarse (<30 to <80 mesh) and fine (<80 mesh) fractions of soils, 

respectively. Analyses for Ag, Mo, Pb, and Zn by optical emission spectroscopy and for Au by graphite furnace 

atomic absorption. < indicates trace but less than the lower limit of determination shown in parentheses; N 

indicates not detected; Anomalous values are shown in italics] 

Sample Au Ag Mo Pb Zn

 No. (2) (0.5) (5) (10) (200) 

H01-C N < 7 30 N

H01-F N N < 20 N

H02-C N N N 10 N

H02-F N N N < N

H03-C N 2 < 30 N

H03-F 2 2 5 30 N

H04-C 2 1 7 30 N

H04-F N 1.5 10 50 N

H05-C N < N 70 200

H05-F N N N 50 200

H07-C N < 15 150 200

H07-F N < 15 150 200

H08-C 2 N N 10 N

H08-F N N N 10 N

H09-C N N N 30 N

H09-F 2 N N 20 N

H10-C N N N 15 N

H10-F N N < 10 N

Appendix table 2. Analytical results for selected elements in ash of Douglas-fir branches (stems and needles combined) from 

upland localities in the Baker Creek study area, Blaine County, Idaho. 

[In parts per million except for gold, which is in parts per billion. Sample localities shown on figure 2. < indicates trace but less than the lower 

limit of determination shown in parentheses; N indicates not detected. Analyses for Mo and Tl were on an acid digestion of the ash from 30-g 

samples of dry material by inductively coupled plasma emission spectroscopy at the laboratory of Geochemical Services, Inc., Rocklin, Calif. 

Anomalous values are shown in italics]

Sample Au Ag As Cd Cu Mo Pb Tl Zn

 No. (8) (0.2) (40) (0.2) (20) (20) (~0.6) (20) 

H01-P1 < N N 2.8 60 0.67 < < 600

H01-P2 N 0.8 N 2.0 40 0.57 < < 480

H02-P1 < 0.2 N 2.4 40 0.57 < 2.1 360

H02-P2 8 N N 0.8 40 0.61 20 1.8 240

H03-P1 < 0.6 N 0.4 40 0.52 < 0.7 400

H03-P2 8 0.2 < 0.8 80 0.90 20 < 480

H04-P1 N N N 2.4 40 0.55 < < 400

H04-P2 16 0.4 N 1.2 60 0.74 < < 440

H05-P < 0.2 N 3.6 60 1.10 20 < 1,000

H07-P1 8 3.2 N 5.6 60 1.80 < < 1,000

H07-P2 < 3.8 N 2.4 60 4.00 < 0.6 800

H08-P1 16 N N 2.4 80 0.76 < < 440

H08-P2 N 0.6 N 1.6 40 0.51 < 1.2 360

H09-P1 8 0.4 200 0.8 60 0.97 < < 520

H09-P2 < < 400 0.8 60 0.68 < < 640

H10-P1 < N 160 2.0 60 0.67 N < 680

H10-P2 < 0.4 240 2.8 60 0.83 N < 800
17

Appendix table 3. Analytical results for selected elements in ash of big sagebrush new growth (stems and leaves 

combined) from upland localities in the Baker Creek study area, Blaine County, Idaho. 

[In parts per million except for gold which is in parts per billion. Sample localities shown on figure 2. < indicates trace but less 

than the lower limit of determination shown in parentheses; N indicates not detected. Anomalous values are shown in italics] 

Sample Au Ag As Cd Cu Mo Pb Zn

 No. (8) (0.1) (20) (0.2) (10) (2) (10) (10) 

H01-A1 16 0.1 N 2.6 160 8 N 480

H01-A2 < N N 3.0 380 6 N 360

H02-A1 8 N N 1.0 340 6 N 300

H02-A2 24 N N 1.0 340 12 N 320

H03-A1 8 0.1 N 1.6 320 8 N 380

H03-A2 8 N N 1.2 380 6 N 360

H04-A1 < N N 4.2 460 10 N 400

H04-A2 48 N N 2.8 400 4 N 420

H05-A < N N 5.0 440 20 N 520

H07-A1 < 0.1 N 26 520 20 20 620

H07-A2 8 < N 40 520 72 10 720

H08-A1 < N N 3.6 360 6 N 360

H08-A2 8 N N 1.8 360 10 N 400

H10-A1 < N N 3.2 310 8 < 380

H10-A2 < N N 0.4 440 8 < 320

Appendix table 4. Analytical results for selected elements in ash of elk sedge (above ground parts) from the 

upland localities in the Baker Creek study area, Blaine County, Idaho.

[In parts per million except for gold which is in parts per billion. Sample localities shown on figure 2. < indicates trace but less 

than the lower limit of determination shown in parentheses; N indicates not detected. Anomalous values are shown in italics] 

Sample Au Ag As Cd Cu Mo Pb Zn

 No. (8) (0.2) (40) (0.2) (20) (4) (20) (20) 

H01-C1 < 0.2 N 2.0 60 12 N 480

H01-C2 24 0.4 N 1.6 80 12 N 480

H02-C1 < 0.4 N 1.6 40 4 N 360

H02-C2 N 0.4 N 1.6 40 20 N 400

H03-C1 8 1.4 N 0.8 60 16 N 360

H03-C2 N 0.4 N 1.2 40 12 N 360

H04-C1 N 2.0 N 3.2 60 20 N 600

H04-C2 < 0.4 N 2.4 80 8 N 560

H05-C < N N 1.6 40 28 N 880

H06-C 20 1.2 N 5.2 100 8 N >2,000

H07-C1 N N N 5.2 100 24 N 1,200

H07-C2 < 0.8 N 7.6 60 56 N 1,400

H08-C1 N N N 1.2 40 8 N 280

H08-C2 8 N N 1.2 60 8 N 560

H09-C1 16 N N 0.8 20 4 N 160

H09-C2 8 0.2 N 0.8 20 4 N 180

H10-C1 N 0.4 N 2.0 60 12 N 400

H10-C2 N 0.8 N 1.2 40 8 N 300

Appendix
18 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

Appendix table 5. Analytical results of selected elements in stream sediments from drainage basin 

localities in the Baker Creek area. 

[In parts per million. Sample localities shown on figure 2. Analyses made on <80-mesh (<180-m) fraction by 

optical emission spectroscopy; <, indicates trace but less than the lower limit of determination shown in parentheses; N indicates not detected. Anomalous values are shown in italics]

Sample Ag ppm Mn ppm Mo ppm Pb ppm Zn ppm

 No. (0.5) (10) (5) (10) (200)

H11-SS 1.5 >5,000 10 50 <

H12-SS N 700 N 20 N

H13-SS < 500 < 30 N

H14-SS N 500 N 30 N

H15-SS 0.5 >5,000 < 30 200

H16-SS 0.5 2,000 5 150 700

H17-SS N 500 N 20 N

H18-SS N 300 N 30 N

H19-SS N 150 N 10 N

H20-SS N 100 N < N

H21-SS N 150 N 15 N

H22-SS N 500 N < N

H23-SS N 1,000 N 10 N

H24-SS 0.5 300 7 30 N

H25-SS N 300 7 20 N

H26-SS N 150 N 15 N
19

Appendix table 6. Analytical results of selected elements in the nonmagnetic and weakly magnetic 

fractions of heavy mineral concentrates collected from drainage basin localities in the Baker Creek 

study area, Blaine County, Idaho.

[In parts per million. Sample localities shown in figure 2. Analyses of powdered <80-mesh fractions by optical 

emission spectroscopy; < indicates trace but less than the lower limit of determination shown in parentheses; N 

indicates not detected. Anomalous values are shown in italics] 

Sample Ag B Ba Be Bi

 No. (1) (20) (50) (2) (20)

Nonmagnetic (C3) fraction

H11-H N 20 >10,000 N 70

H12-H N 20 >10,000 N N

H13-H N < >10,000 N N

H14-H N 20 >10,000 N N

H15-H 2 500 10,000 N N

H16-H N 20 >10,000 N 20

H17-H N 20 >10,000 N N

H18-H N < 7,000 2 N

H19-H N 20 700 N N

H20-H N 20 3,000 N N

H21-H N 50 >10,000 < N

H22-H N 20 >10,000 N N

H23-H N 50 7,000 < N

H24-H N 50 2,000 N 100

H25-H N 50 >10,000 N 1,000

H26-H N 30 2,000 < 30

Weakly magnetic (C2) fraction

H11-H 2 < 3,000 5 N

H12-H N < 700 < N

H13-H < < 500 < N

H14-H < < 1,000 < N

H15-H 1 < 1,000 3 N

H16-H 1 < 1,000 15 N

H17-H N < 200 N N

H18-H N < 200 N N

H19-H N < 200 N N

H20-H N < 200 N N

H21-H < < 150 2 N

H22-H N < 500 2 N

H23-H N < 150 < N

H24-H < < 150 2 N

H25-H N < 700 3 N

H26-H N < 200 N N

Appendix
20 Geochemical Results of a Hydrothermally Altered Area at Baker Creek, Blaine County, Idaho

Appendix table 6—Continued. Analytical results of selected elements in the nonmagnetic and 

weakly magnetic fractions of heavy mineral concentrates collected from drainage basin localities in 

the Baker Creek study area, Blaine County, Idaho.

[In parts per million. Sample localities shown in figure 2. Analyses of powdered <80-mesh fractions by optical 

emission spectroscopy; < indicates trace but less than the lower limit of determination shown in parentheses; N 

indicates not detected. Anomalous values are shown in italics] 

Sample Cu Mo Pb Sr Zn

 No. (10) (10) (20) (200) (500)

Nonmagnetic (C3) fraction

H11-H < N < <3,000 N

H12-H < N N 3,000 N

H13-H < N N 5,000 N

H14-H < N 20 3,000 N

H15-H < N 50 500 N

H16-H < 70 3,000 2,000 N

H17-H N N 50 700 N

H18-H < N < < N

H19-H N N N < N

H20-H < N 30 200 N

H21-H < N 700 500 N

H22-H 300 N 300 1,000 N

H23-H 10 N 30 500 N

H24-H < N 30 N N

H25-H < N 20 1,500 N

H26-H N N 30 200 N

Weakly magnetic (C2) fraction

H11-H 100 15 30 < 500

H12-H 70 N < < <

H13-H 100 N 50 < <

H14-H 70 10 70 < <

H15-H 100 15 100 < 500

H16-H 100 < 200 200 1,000

H17-H 70 N 50 N N

H18-H 10 N < N N

H19-H 20 N 50 < N

H20-H 70 N 50 < N

H21-H 100 10 50 N N

H22-H 70 N 20 200 <

H23-H 10 N 20 300 N

H24-H 20 N 100 500 N

H25-H 70 20 70 300 <

H26-H 15 N 30 N N
21

Appendix table 7. Analytical results, including ash yield, for aquatic mosses from drainage basin 

localities in the Baker Creek study area, Blaine County, Idaho.

[In parts per million except for gold which is in parts per billion. Sample localities shown on figure 2. < indicates 

detected but below the limit of determination shown in parentheses; N indicates not detected; leaders (--), no data. 

Anomalous values are shown in italics] 

Sample Au Ag As Sb Mo

 No. (16) (0.2) (40) (8) (4)

H11-M 64 3.2 < 72 8

H12-M Insufficient sample, no data

H13-M 48 N N N8

H14-M 16 N N N 4

H15-M 64 5.2 N N8

H16-M 16 1.6 40 N 8

H17-M -- N N N 8

H18-M 16 N N N N

H19-M < N N N N

H20-M < N N N 4

H21-M Insufficient sample, no data

H22-M < 0.4 N N 4

H23-M < 0.6 40 N 4

H24-M -- 2.2 N N 20

H25-M 16 0.6 N N 16

H26-M -- N N N 4

Sample Cu Pb Zn Cd Ash %

No. (20) (20) (20) (0.2)

H11-M 100 60 720 2.8 15.5

H12-M Insufficient sample, no data

H13-M 60 20 380 1.2 16.8

H14-M 40 20 240 0.8 32.0

H15-M 140 40 1,500 5.6 16.1

H16-M 120 160 >2,000 20 21.4

H17-M 60 < 380 1.6 12.6

H18-M 20 < 360 0.4 56.5

H19-M 80 40 180 1.2 32.3

H20-M 40 < 160 0.8 17.8

H21-M Insufficient sample, no data

H22-M 80 20 300 1.6 17.5

H23-M 80 20 320 1.6 14.3

H24-M 100 100 360 4.4 23.3

H25-M 60 100 180 2.4 38.2

H26-M 60 < 260 0.8 20.2

Appendix