![](media/image1.wmf){width="6.5in" height="1.0138888888888888in"}

Regional Geochemical Results from the Analyses of Rock, Water, Soil,
Stream Sediment, and Vegetation Samples\--Fortymile River Watershed,
East-Central, Alaska, 1998 Sampling

*By* J.G. Crock^1^, L.P. Gough^2^, R.B. Wanty^1^, W.C. Day^1^, B.
Wang^2^,

B.M. Gamble^2^, M. Henning^3^, Z.A. Brown^1^, and A.L. Meier^1^

**Open-File Report 00-511**

This report is preliminary and has not been reviewed for conformity with
U.S. Geological Survey editorial standards or with the North American
Stratigraphic Code. Any use of trade, firm, or product names is for
descriptive purposes only and does not imply endorsement by the U.S.
Government.

^1^ U.S. Geological Survey, Box 25046, MS 973, DFC, Denver, CO
80225-0046.

^2^ U.S. Geological Survey, 4200 University Dr., Anchorage, AK
99508-4667.

^3^ Alaska Department of Natural Resources, Division of Mining and Water
Management, 550 W. 7^th^ Ave., Suite 900 B, Anchorage, AK 99501-3577.

2000

U.S. DEPARTMENT OF THE INTERIOR

Bruce Babbitt, *Secretary*

U.S. GEOLOGICAL SURVEY

Charles G. Groat, *Director*

# 

# 

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

*For additional information Copies of this report can*

*write to:* *be purchased from:*

Chief Scientist, Central Region Books and Open-File Reports

Mineral Resources Program U.S. Geological Survey

U.S. Geological Survey Federal Center

Box 25046, Federal Center Box 25046

Denver, CO 80225-0046 Denver, CO 80225-0046

TABLE OF CONTENTS

Page

LIST OF TABLES
.................................................................... 4

LIST OF
FIGURES....................................................................
6

INTRODUCTION.....................................................................
7

Background.....................................................................
7

Geologic and Hydrologic
Setting.................................\............ 9

STUDY
METHODS.................................................................\...
9

Study Design and Sample
Collection........................................ 9

Sample Preparation and
Analysis..........................................\... 11

ANALYTICAL
RESULTS............................................................ 11

ACKNOWLEDGEMENTS.........................................................\...
12

REFERENCES........................................................................\...
12

LIST OF TABLES

Page

Table 1a. Concentration ranges for major element oxide analyses of rocks
by

> wavelength dispersive X-ray fluorescence
> spectrometry........................... 16

Table 1b. Lower limits of determination for elemental analyses of solid
samples by

> inductively coupled plasma -- mass
> spectrometry.................................... 17

Table 1c. Lower limits of determination for miscellaneous methods of
analyses of

> solid
> samples.............................................................................
> 19

Table 2a. Field and laboratory methods with lower limits of
determination (LLD)

for the analyses of water
samples...................................................... 20

Table 2b. Lower limits of determination for the elemental analyses of
water samples

> by inductively coupled plasma-mass
> spectrometry............\....................\.... 21

Table 3. Description and location of water sampling sites with selected
field

> measurements from the Fortymile River watershed,
> Alaska....................... 22

Table 4. Rock sample descriptions and location of sampling sites,
Fortymile River

> watershed,
> Alaska.......................................................................
> 23

Table 5. Description and location of soil, vegetation, and stream
sediment collection

sites, Fortymile River watershed,
Alaska..........................................\... 25

Table 6. Ion chromatography results for the analyses of water samples
from the

> Fortymile River watershed,
> Alaska.................................................... 26

Table 7. Chemical results for the analyses of major and minor elements
in water

> samples from the Fortymile River watershed,
> Alaska.........................\...... 27

Table 8. Determination of major element concentrations using X-ray
fluorescence for

> selected rock samples from the Fortymile River watershed,
> Alaska.............. 34

Table 9. Rare earth and other element determinations (ICP-MS sinter
method) for

> selected rock samples from the Fortymile River watershed,
> Alaska.............. 36

Table 10. Miscellaneous analytical results for rock samples from the
Fortymile River

watershed,
Alaska.......................................................................
39

Table 11a. Chemical results (dry-weight basis) for soil samples from the
Fortymile

> River watershed,
> Alaska...............................................................
> 59

Page

Table 11b. Chemical results as measured (ash-weight basis, unless noted
with \*)

> For soil samples from the Fortymile River watershed,
> Alaska..................... 74

Table 12a. Chemical results (dry-weight basis) for *Alnus crispa* (green
alder) leaf and

> twig samples from the Fortymile River watershed,
> Alaska......................... 89

Table 12b. Chemical results as measured (ash-weight basis, unless noted
with \*) for

*Alnus crispa* (green alder) leaf and twig samples from the Fortymile
River

watershed,
Alaska.......................................................................
98

Table 13a. Chemical results (dry-weight basis) for *Salix glauca*
(grayleaf willow) leaf

> and twig samples from the Fortymile River watershed,
> Alaska................... 107

Table 13b. Chemical results as measured (ash-weight basis, unless noted
with \*) for

> *Salix glauca* (grayleaf willow) leaf and twig samples from the
> Fortymile
>
> River watershed,
> Alaska................................................................
> 117

Table 14a. Chemical results (dry-weight basis) for *Hylocomium
splendens* (feather

> moss) samples from the Fortymile River watershed,
> Alaska....................... 126

Table 14b. Chemical results as measured (ash-weight basis, unless noted
with \*) for

> *Hylocomium splendens* (feather moss) samples from the Fortymile River
>
> watershed,
> Alaska.......................................................................
> 132

Table 15a. Chemical results (dry-weight basis) for *Peltigera apthosa*
(green dog lichen)

samples from the Fortymile River watershed,
Alaska............................... 137

Table 15b. Chemical results as measured (ash-weight basis, unless noted
with \*) for

> *Peltigera apthosa* (green dog lichen) samples from the Fortymile
> River
>
> watershed,
> Alaska.......................................................................
> 142

Table 16a. Chemical results (dry-weight basis) for *Picea glauca* (white
spruce)

samples from the Fortymile River watershed,
Alaska...........................\.... 147

Table 16b. Chemical results as measured (ash-weight basis, unless noted
with \*) for

> *Picea glauca* (white spruce) samples from the Fortymile River
> watershed,
>
> Alaska..................................................................................\...
> 150

Table 17. Chemical results for stream sediment samples from the
Fortymile River

> watershed,
> Alaska.......................................................................
> 153

LIST OF FIGURES

Page

Figure 1. Figure 1. Location of the Big Delta and Eagle quadrangles
within which

are located the Goodpaster and Fortymile study areas,
respectively....... 8

Figure 2. Study site locations for water, soil, vegetation, and sediment
samples,

Fortymile River watershed.
.......................................................... 15

**INTRODUCTION**

This report briefly describes and presents geochemical and
biogeochemical data for a cooperative study in the Fortymile Mining
District, east central Alaska. This study is being funded by the U.S.
Geological Survey (USGS) Mineral Resources Program through Fiscal Year
2001. Cooperative funds are being provided from various State of Alaska
sources through the Alaska Department of Natural Resources. Results for
the first field season completed in June 1997 are presented in Crock and
others (1999). The study's second field season was completed in June
1998 and the results of the sample analyses for this phase of the study
are presented here.

Primary objectives of this study are:

• Determine the regional baseline geochemistry (waters, soils, rocks,
sediments, and selected terrestrial vegetation) for a section of the
Fortymile River watershed currently being mined for placer gold (suction
dredge and "cat" or dozer operations).

• Determine regional watershed geochemical fluxes.

• Assess the influence of geology on water-rock signatures, and using
these signatures, try to differentiate sources of surface and hyporheic
water (shallow groundwater near a streambed).

• Determine the movement of metals through ecosystems of specific
interest, such as permafrost muskeg terrain, upland alluvial forests,
and riverine floodplain shrub systems.

• Using both a geologic and a hydrologic framework, define the relative
contribution of the various natural sources of arsenic and cadmium and
other environmentally important metals to the landscape.

• Assist the State of Alaska and the U.S. Environmental Protection
Agency (USEPA) in the arsenic risk-assessment process.

**Background**

The USGS and the Alaska Department of Natural Resources (AK-DNR) are
currently investigating the environmental geochemistry of a portion of
the Fortymile and Goodpaster River watersheds (fig. 1). The management
of the region and its resources is complex due to diverse ownership and
the many land-use options. In 1980, the Fortymile River and its major
tributaries were designated a Wild and Scenic Corridor by the Alaska
National Interest Lands Conservation Act (ANILCA). Jurisdiction of the
land bordering the watershed continued to be the responsibility of the
U.S. Bureau of Land Management (USBLM). The AK-DNR has jurisdiction over
the management of the river's recreation (rafting, canoeing, and
fishing) and mining. The USEPA is also involved because mining
discharges require compliance with the National Pollutant Discharge
Elimination System (NPDES) of the Clean Water Act. Finally, both sport
and subsistence hunting are important in the region and are managed by
several Federal and State agencies.

Placer gold was first discovered in the Fortymile River Mining District
in 1886 and has been mined there ever since. Yeend (1996) provides a
summary of the gold mining history of the placers of the Fortymile River
region. Historically from 1886 to 1995, the Fortymile Mining District
has produced about 16,640 Kg (534,974 oz) of gold (Swainbank and others,
1998). Along the North Fork of the Fortymile River, and just above its
confluence with the South Fork, mining is currently limited to a small
number of suction dredges which when combined produce only a few hundred
ounces of gold per year.

![](media/image2.png){width="4.107638888888889in"
height="3.714583333333333in"}

Figure 1. Location of the Big Delta and Eagle quadrangles within which
are located the Goodpaster and Fortymile study areas, respectively.

A cooperative effort between the USGS and the AK-DNR was initiated in
1997 to provide data to address water quality concerns, as well as to
establish regional baseline geochemical and biogeochemical data (Crock
and others, 1999; Wanty and others, 2000). In June 1998, we continued
our work of the previous year (Crock and others, 1999) with field
measurements of pH, turbidity, electrical conductivity, and stream
discharge for the Fortymile River and many of its tributaries. At the
same time, samples of soils, rocks, stream sediments, water, and
vegetation were collected for chemical analysis, and sent to the USGS
laboratories in Denver, Colorado. This report lists the analytical
results of the 1998 sampling. Figure 2 depicts the sampling locations
for the 1998 sampling efforts in the Fortymile watershed. The analytical
results of the 1997 sampling are listed in Crock and others (1999). In
addition, similar studies were initiated at and near the new Teck-Pogo
gold discovery located about forty miles northeast of Delta Junction,
Alaska in the Big Delta quadrangle (fig. 1).

Important to this study's assessment will be the evaluation of the flux
and biogeochemical cycling of arsenic and cadmium between the
terrestrial and aquatic phases. In addition to studying water-rock
processes that mobilize arsenic and cadmium, this project is also
examining other factors that affect their bioavailability to the
environment (for example, in sites that are mined verses unmined;
vegetated verses barren; saturated (permafrost) verses drained; forested
verses muskeg) {Crock, Larison and Gough, 2000; Gough and Crock, 1999;
Gough and others, 2001}.

![](media/image3.png){width="8.058333333333334in"
height="5.716666666666667in"}

Figure 2. Study site locations for water, soil, vegetation, and sediment
samples, Fortymile River watershed.

## Geologic and Hydrologic Setting

Bedrock and alluvium control the minerals and chemical elements
available to enter the hydrologic and biologic systems. Therefore,
understanding the geologic framework of the area is the first step in
assessing the effect of past and present mining operations on the
Fortymile River. One of the goals of this project is to chemically
characterize the bedrock of the area in order to understand its role in
determining the composition of the region's rivers and streams (Day and
others, 2000; Gamble and others, 2001). These waters, in turn, flow into
the Fortymile River drainage and form the "background" necessary to
evaluate the effect of the mining operations on the water chemistry and
turbidity (Wanty and others, 2000).

The bedrock of the Fortymile Mining District is composed of volcanic and
sedimentary rocks of Paleozoic (?) age that have been intruded by
younger granitic rocks (Day and others, 2000; Dusel-Bacon and others,
1995; Foster and Keith, 1969; Foster and others, 1994). The volcanic
rocks were originally basalt similar to that formed in modern marine
environments. The original sedimentary rocks were variable in
composition and are also similar to those seen in modern marine
environments. This entire package of rocks experienced regional
mountain-building event(s) during Jurassic time in which the rocks were
metamorphosed, deformed, and invaded by granite. The regional tectonic
mountain-building event(s) caused several periods of folding of the
rocks, the latest of which produced regional north-northeast oriented
anticlines and synclines (Day and others, 2000; Yeend, 1996).

Recent geologic mapping has outlined several distinct types of alluvial
deposits that range in age from Tertiary to Recent. During the Tertiary
Epoch, numerous benches were cut into the bedrock by the forces of
erosion. These benches have Tertiary-to Quaternary-age gravel deposits
upon them, which locally host placer gold (Yeend, 1996). Along the banks
of the Fortymile River, Quaternary alluvial gravel, sand, and silt
deposits have been the main source of the placer gold mined to date and
are the principal target for the dredge mining operations along the
river.

The Fortymile River drains mostly subarctic forest and muskeg with
discontinuous permafrost. Even the regions that are not underlain by
permafrost are commonly frozen to various depths during the growing
season. Discharge is highly variable (Kostohrys and others, 1999) and
reflects (1) a rapid spring ice-break-up period (April), (2) runoff from
storm events (the frozen nature of the terrain accentuates the runoff
potential), (3) periodic summer dry periods, and (4) freeze-up
(October).

## STUDY METHODS

##### Study Design and Sample Collection

Field sampling was conducted June 17 through June 24, 1998. All sites
where water, rock, soil, stream sediment, and vegetation material were
collected were located on 1:63,360-scale topographic maps, GPS
coordinates recorded, and often photographs were taken.

### Geology

In order to meet the objectives of this study, a structural geologic
basemap has been compiled (Day and others, 2000). This effort is an
extension of the work of Foster and Keith (1969), Foster (1976), Foster
and others (1994), and Dusel-Bacon and others (1995). Extensive
vegetative cover in the Yukon-Tanana Upland makes outcrop examination
difficult; however, both helicopter and river boat support allowed
access to ridges, roadcuts, and stream banks and channels. Rock samples
were collected for geochemical, thin-section, and petrographic analysis
(Gamble and others, 2001). The rock-sampling program was designed to
address two specific issues: 1) the need to characterize regional
lithologic units that underlie the study area; and 2) the need to
characterize any possible mineralized and (or) altered zones that might
occur in the study area. Sample sites and sample descriptions for the
rock samples are listed in Table 4, and analytical results are listed in
Tables 8, 9, and 10. Samples from regional lithologic units were
collected at sites thought to best typify the unit being examined. In
order to minimize small-scale compositional variations, three to five
separate pieces of the rock were collected over a surface exposure of
approximately twenty-five square meters. Similarly, altered and (or)
mineralized rock samples also consist of multiple pieces of material,
but the size of the area sampled was often more restricted due to the
smaller size of the target zone.

### Hydrology

The hydrology and hydrogeochemistry of the region is being constructed
through the examination of integrated flow and chemistry measurements on
the mainstem of the Fortymile River and its tributaries (fig. 2).
Tributaries were selected for study based on (1) watershed area, (2)
geologic terrain, (3) results of past geochemical sampling (Foster and
Clark, 1970), (4) results of a reanalysis of archived NURE (National
Uranium Resource Evaluation) samples (Hoffman and Buttleman, 1996), and
(4) current and past mining activity. Tributaries draining watersheds
that met these criteria were then sampled just above their confluence
with the Fortymile River. The location, description, and geochemistry of
water samples are given in Tables 3, 6, and 7. Also listed in Table 2a
and 2b are the references for water sampling protocols used in the
study.

[Soils, vegetation, and stream sediments]{.underline}

The collection of soils, vegetation, and stream sediments was based on
the geologic and hydrologic framework being constructed. Tables 5
(description and location), 11a, 11b (soil), 12a, 12b (green alder),
13a, 13b (grayleaf willow), 14a, 14b (feather moss), 15a, 15b (green dog
lichen), 16a, and 16b (white spruce) list the location, description, and
analytical results of soil and vegetation samples. Soil and vegetation
sampling locations were upslope of the area in the stream where the
hydrogeochemical parameters were measured. Selection of the area was
based on geology, aspect (south-exposures being preferred), and
vegetation community and was usually less than 10 vertical meters above
the stream. Vegetation and soil sites were upland conifer stands,
usually dominated by white spruce and birch, with an understory of mixed
shrubs and a dense ground cover of mosses and scattered lichens. Obvious
floodplain and debris flow areas were avoided. Soil pits were dug to the
C-horizon or to a depth dictated by the presence of frozen ground. At
each site, approximately 1 kg of Oa (surficial organic layer), A1-, B-,
and C-soil horizons were collected from the pits and placed in
soil-sample paper bags. Vegetation samples (approximately 200 g, dry
weight) consisted of the leaf and stem material of the young, growing
branches (approximately the terminal-most 10-cm) of *Salix glauca*
(grayleaf willow) and *Alnus crispa* (green alder). Samples are a
composite of the branches from several small individuals in the
immediate vicinity of the soil pit. The material was clipped using
stainless steel shears, placed in Hubco® bags, and labeled. In addition,
a large, integrated sample each of the ubiquitous feather moss
(*Hylocomium splendens*) and green dog lichen (*Peltigera aphthosa*) as
well as a composite sample of the last two year's growth of white spruce
(*Picea glauca*) twigs and needles was collected. To help assess the
local chemical variability, at four sites duplicate stream sediment,
soil, and vegetation samples were collected. In the following data
tables, these site duplicate samples are designated with an "X" as a
suffix to the sample number. Also laboratory-prepared analytical splits
are designated in all the tables with a "Y" as a suffix to the sample
number.

Stream sediment samples were collected at most of the hydrogeochemical
sampling sites (Table 5) and the analytical results for these samples
are presented in Table 17. When a stream sediment sample was collected
on both the tributary and the main river upstream from the tributary,
the sample suffix is "SS1" for the tributary and "SS2" for the upstream
main river sample.

##### Sample Preparation and Analysis

All samples were shipped to the Denver Laboratories of the USGS for
analysis. Methods of sample storage, shipping, preservation, drying,
preparation for analysis, and analysis are described elsewhere and
follow the procedures outlined in Crock and others (1993), Arbogast
(1996), Curry (1996), Lichte and others (1986), Gough and Crock (1997),
Briggs and Meier (1999), and Lamothe and others (1999). Table 1a lists
the concentration ranges for major-element-oxide analysis in rocks by
wavelength dispersive x-ray fluorescence spectrometry. Tables 1b and 1c
list the lower limits of determination (LLD) for the other methods used
in the analyses of the solid samples. Tables 2a and 2b list the LLD's
for both field and laboratory methods used for the analyses of the water
samples. The vegetation and soil samples were ashed at 500^o^C in a
muffle furnace in porcelain dishes prior to the determination of most
elements. Except for the determination of gold and FeO% in rock samples
(Tables 10) and gold in stream sediments (Table 17), all analytical
results reported herein were performed at the Denver, Colorado
laboratories of the USGS. Methods used by the contract laboratory are
described in Arbogast (1996) -- gold by graphite furnace-atomic
absorption spectrometry and FeO% by colorimetry. National Institute of
Standards and Technology (NIST) and internal USGS reference materials
and laboratory-made duplicate sample (designated in the data tables with
a suffix of "Y" to the sample number) were submitted to the laboratories
as part of each suite of samples. The results are presented for the
duplicate samples in the respective data tables. Quality assurance (QA)
and control (QC) practices, for most of the analysis methods used, are
provided in more detail in Arbogast (1996).

**ANALYTICAL RESULTS**

The tables in this report list all chemical analysis results for the
samples of water, rock, soil, stream sediment, and vegetation collected
in 1998 at the Fortymile River study area. The purpose of this report is
the release of these data and the report is not meant to be
interpretative. Analytical results for anions and major and minor
elements are presented in Tables 6 and 7 for the water samples. Table 8
presents the major element determinations of selected rock samples.
Table 9 presents the rare earth element and other selected trace
elements for selected rock samples as determined by the sodium peroxide
method (Lichte and others, 1986). Table 10 presents the remaining
elemental determinations for the rock samples measured by various
methods. Due to convention, many of the analyses for soils and
vegetation have been converted from a measured ash-weight basis to a
dry-weight basis. The data as measured on the samples of vegetation ash
and soil ash and raw material are given in Tables 11a (soils), 12a
(green alder), 13a (grayleaf willow), 14a (feather moss), 15a (green dog
lichen), and 16a (white spruce). The data converted to a dry-weight
basis for all the samples of vegetation and soil are given in Tables 11
(soils), 12 (green alder), 13 (grayleaf willow), 14 (feather moss), 15
(green dog lichen), and 16 (white spruce).All data as measured are also
presented in Tables 11a (soils), 12a (green alder), 13a (grayleaf
willow), 14a (feather moss), 15a (green dog lichen), and 16a (white
spruce) for those media where the measured data were converted from an
ash-weight basis to a dry weight basis.

#### 

#### ACKNOWLEDGEMENTS

We wish to thank the logistical assistance of Jim Vohden, Alaska
Department of Natural Resources, Division of Mining and Water
Management, Fairbanks. We are especially grateful to Larry and June
Taylor of Eagle, Alaska, for their hospitality and for sharing their
knowledge of the river and the region.

## 

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