![](media/image1.png){width="2.325in" height="0.8729166666666667in"}

**Bedrock and soil geochemistry from Voyageurs National Park,
Minnesota**

***By* Laurel G. Woodruff^1^, William F. Cannon^2^, Connie L. Dicken^2^
and Shana Pimley^2^**

**Open-File Report 02-196**

**2002**

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

**\
**

**U.S. DEPARTMENT OF THE INTERIOR**

**U.S. GEOLOGICAL SURVEY**

^1^ U.S. Geological Survey, 2280 Woodale Drive, Mounds View, MN 55112

^2^ U.S. Geological Survey, MS 954, Reston, VA 20192

**Table of Contents**

**[Section Page Number]{.underline}**

**Introduction** **1**

**Bedrock Geology** **1**

**Glacial Geology** **1**

**Methods of Study** **2**

**Description of Data Files** **4**

**References** **6**

**Table 1.** Lower detection limits for ICP-AES methods. **7**

**Table 2.** Lower detection limits for ICP-MS methods **8**

**Introduction**

Bedrock, forest floor, and mineral soil sampling in Voyageurs National
Park (VNP), Minnesota in 2000 and 2001 is part of a multidisciplinary
project that includes the U. S. Geological Survey, ,National Park
Service, University of Wisconsin -- La Crosse, Minnesota Pollution
Control Agency, and the Minnesota Department of Natural Resources. The
joint project is examining the distribution of mercury in age-1 perch,
lake water, bedrock and soils for eighteen watersheds in the interior of
VNP. The purpose of the project was to establish the background and
baseline geochemistry for bedrock and soil in the region, and to
determine terrestrial mercury sources and sinks in VNP.

**Bedrock Geology**

Bedrock in VNP consists of Late Archean age rocks of the Superior
Province. The Rainy Lake-Seine River fault occurs in the very northern
part of the Park, separating the Wabagoon subprovince on the north from
the Quetico subprovince on the south (Day and others, 1990). Minor gold
mineralization is found on several small islands in Rainy Lake along the
tectonized margin of the fault. The host rock is mylonitic schist (Day,
1990), and gold typically is found in quartz, associated with pyrite,
arsenopyrite, and ankerite. A short-lived gold rush in the late 1890's
resulted in numerous small excavations and the building of a stamp mill
on the mainland near the largest deposit on Little America Island.
Mercury was used in the processing of ore in the stamp mill, and
tailings were released into Rainy Lake, just outside Park boundaries.

Rocks of the Quetico subprovince in the northern part of the Park are
fine- to medium grained schist and graywackes (Day and others, 1990).
Several small leucogranite and dioritic intrusions cut the
metasediments. In the southern and eastern part of the Park
metasediments grade into schist-rich migmatites and then into more
granite-rich migmatite. Large areas of pink to gray biotitic, massive to
weakly foliated Lac La Croix granite are predominant in the eastern end
of the Park (Day and others, 1990). Rocks correlative with bedrock in
the Park have been dated from 2750 to 2500 Ma (Goldich and Peterman,
1980).

**GLACIAL Geology**

Multiple episodes of glaciation have covered northern Minnesota.
Following retreat of the last ice sheets, the area was inundated by
Glacial Lake Agassiz, which probably last drained out of the VNP region
by 9700 B.P. (Clayton and Moran, 1982). Deposits of Lake Agassiz lake
clay and glacial till and outwash from two disparate Late Wisconsin
glacial lobes derived from two different ice centers are found in VNP
(Sado and others, 1995). Bedrock in the western third of the Park is
covered by ground moraine that is part of the Erskine moraine of the Des
Moines lobe (Hobbs and Goebel, 1982). Des Moines lobe tills were derived
from shales and limestones in the lowlands of Manitoba, and are
generally clayey and carbonate-rich, occasionally with limestone clasts.
Overlying bedrock in the eastern two-thirds of the Park are thin glacial
deposits of the Vermillion moraine that is part of the Rainy lobe. The
Rainy lobe is derived from rocks of the Superior Province, a
greenstone-granite terrane. As a result, glacial deposits in the
Vermillion moraine are sandy and stony with little clay (Hobbs and
Goebel, 1982).

**mETHODS OF STUDY**

**Sample Collection**

Geochemical sample media include rocks and different soil horizons
([Figure 1](../Figure_1.pdf)). Rock samples were collected from outcrop
and from the gold mine dump on Little America Island. Rock samples were
typically composite chip samples or single grab samples collected at
each site. Rock descriptions were recorded in the field and are included
in the rock data file.

Soil sample sites were selected for different criteria. Most samples
were collected within the watersheds of the lakes investigated in the
multidisciplinary study. Within each watershed, attempts were made to
collect from both upland and lowland (but not wetland) sites. Several
sites outside of the studied watersheds were collected to extend the
sampling area to include all available bedrock types and deposits from
the two glacial lobes. Additional soil samples were collected from areas
that had been burned recently by either prescribed or natural fires.

Soil samples were collected from soil pits hand dug with a shovel and
extended with a hand auger. Sample pits were completed to the C-horizon
or to a depth dictated by the presence of impenetrable rock. From each
soil pit, soil from different horizons, including O-, A-, E- or
C-horizons, was collected so that each sample site has multiple
geochemical analyses, each representing a different soil layer.

The O-horizon is the organic matter that lies on top of a mineral soil.
The organic layer is divided into Oi (forest litter), Oe (forest duff)
and Oa (humus) horizons. Forest litter is undecomposed, identifiable
dead plant material. Forest duff is partially decomposed organic
material that may underlie the litter layer. Humus is completely
decomposed, non-identifiable organic material. At each soil sample site,
Oe-horizon material was collected, if available. Field descriptions
discriminate between undecomposed forest litter and more decomposed
forest duff, but do not attempt to distinguish duff from humus. Forest
litter was collected at only five sites. Samples from Oe-horizons
typically were grab samples collected from the soil plug removed from
the sample pit. Litter material, when collected, was composited from
material in the area of the sample site.

The A-horizon is the upper layer of mineral soil. Typically the
A-horizon has accumulated organic carbon and is distinguished from
underlying soil horizons by a change in color. An E-horizon is a zone of
eluviation, which is easily distinguished by its light, buff or gray
color. A-horizon soils were collected at each sample site, with material
composited from the entire thickness of the horizon. A limited number of
E-horizon samples were also collected from sample sites.

Subsoil samples collected from the C-horizon typically were composed of
weathered parent material, which, in VNP, is either bedrock or thin
glacial deposits on bedrock. The depth of collection was typically
constrained by the depth to bedrock.

**Sample Preparation**

All samples were shipped to the USGS analytical laboratories in Denver,
CO for sample preparation. Methods for sample preparation for analysis
are described here and in more detail in Arbogast (1996).

***Rocks***

Rocks were crushed to 0.5 cm fragments in a jaw crusher and fed into a
ceramic plate pulverizer where fragments were reduced to approximately
minus 100-mesh. Each pulverized sample was split, with a portion
submitted for geochemical analysis and a portion archived. Clean quartz
rock and sand was crushed and pulverized between samples to eliminate
cross-contamination.

## Soils

O-horizon soils were air-dried and milled. Samples were split with one
portion set aside for mercury analysis and the remainder of the sample
ashed at 500 °C and submitted for analysis. Percent ash is calculated
as:

\% ash = (ashed sample weight/unashed sample weight) x 100

A- and C-horizon soils were air-dried, disaggregated if necessary, and
sieved to \<63 microns.

**Analytical Techniques**

A large number of chemical elements were determined, using a variety of
quantitative analytical techniques. XRAL Laboratories, Toronto, Canada,
did all rock and A- and C-horizon analyses on contract to the USGS.
O-horizon samples were analyzed in laboratories of the USGS in Denver,
CO, following protocols described in Arbogast (1996). USGS analysts who
provided laboratory assistance with organic samples are Paul Briggs, Zoe
Brown, and Monique Adams. Analytical duplicate samples comprised about
10 percent of the total number of samples submitted. These duplicates
are not retained in the accompanying data files. A description for each
analytical technique and the laboratory where it was completed is given
below.

## Inductively Coupled Plasma-Atomic Emission Spectroscopy

Forty major, minor, and trace elements were determined in rocks and soil
by inductively coupled plasma-atomic emission spectrometry. Each sample
was decomposed using a mixture of hydrochloric, nitric, perchloric, and
hydrofluoric acids at low temperature. The digested sample was aspirated
into the ICP-AES. Analyzed elements and lower detection limits are given
in Table 1. USGS/XRAL

***Inductively Coupled Plasma-Mass Spectrometry***

Ashed O-horizon samples collected in 2000 were digested in a multi-acid
mixture (hydrochloric, nitric, perchloric, and hydrofluoric acids) and
analyzed for 42 major, minor and trace elements by ICP-MS. Analyzed
elements and detection limits are given in Table 2. USGS

***Atomic Absorption Spectrophotometry***

Mercury was measured in rocks and soils using the cold-vapor AAS
technique. Samples were decomposed in a mixture of nitric and
hydrochloric acids. Potassium permanganate, sulfuric acid and potassium
persulphate were added to the solution, followed by a NaCl-hydroxylamine
solution and then transferred to a cold-vapor atomic absorption mercury
analyzer. The lower detection limit for mercury is 0.02 ppm. USGS/XRAL

For arsenic analyses, sample material was mixed with sodium peroxide and
heated in a muffle furnace set at 750 °C for four minutes. The resulting
sample mixture was cooled and diluted with 15 ml of water and 5 ml of
concentrated hydrochloric acid. Ascorbic acid KI solution and
hydrochloric acid were added to the mixture before being introduction to
the AAS. The lower detection limit for arsenic is 0.6 ppm. USGS/XRAL

For selenium analyses, samples were mixed with nitric, hydrofluoric and
perchloric acids and heated. After the solution cooled hydrochloric and
nitric were added, and the mixture heated again and cooled prior to
analysis by AAS. The lower detection limit for selenium is 0.2 ppm.
USGS/XRAL

Two samples of rock collected from mine dumps and adits were analyzed
for gold by AAS after collection by fire assay. The lower reporting
limit for gold is 5 ppb. XRAL

***Automated Carbon Analyzer***

A-horizon soil samples were analyzed for total carbon by combustion in
an oxygen atmosphere at 1370°C to oxidize carbon to carbon dioxide.
Moisture and dust were removed and a solid-state infrared carbon
detector measured the carbon dioxide gas. The lower reporting limit is
0.05%. XRAL

***Columetric Titration***

A-horizon soils were analyzed for carbonate carbon by coulometric
titration. The samples were treated with hot 2N perchloric acid and the
evolved carbon dioxide passed into a cell containing a solution of
monoethanolamine. The carbon dioxide, quantitatively absorbed by the
monoethanolamine, was coulometrically titrated using platinum and
silver/potassium-iodide electrodes. The lower reporting limit is 0.01%.
XRAL

***Automated Sulfur Analyzer***

Total sulfur was measured in A-horizon samples by mixing the soil with
iron chips and LECOCEL. The mixture was heated in a combustion tube in a
stream of oxygen at high temperature, oxidizing sulfur to sulfur
dioxide, which was then measured by an infrared sulfur detector. The
lower reporting limit for sulfur is 0.05%. XRAL

**dESCRIPTION OF DATA FILES**

The analytical data files are provided as separate Microsoft Excel
2000.xls files. The samples are organized into media type with
individual files for soils horizons and rocks samples. Five individual
data files are included in this Open File. These are:

1\) **Bedrock.xls** Bedrock geochemical data

2\) **O_2000.xls** Analyses of organic O-horizon samples collected in
2000. All elements except Hg have been converted from a measured
ash-weight basis to a dry-weight basis. Hg values, which were determined
from unashed sample, are not corrected for ash content.

3\) **O_2001.xls** Analyses of organic O-horizon samples collected in
2001. All elements except Hg have been converted from a measured
ash-weight basis to a dry-weight basis. Hg values, which were determined
from unashed sample, are not corrected for ash content.

4\) **All_A.xls** Analyses of A-horizon and E-horizon samples collected
in both 2000 and 2001.

5\) **All_C.xls** Analyses of C-horizon soil samples collected in both
2000 and 2001.

**Common Data Fields**

***Field_No.***

Field numbers for soils indicate the site label, the year of sampling,
and the soil horizon. V-00-xx soil samples were collected in 2000, and
V-01-xx soil samples were collected in 2001. VOYA- soil samples were
collected in 2000 for a study on the impact of fire on soils. VR-x rock
samples were collected in 2000. V-01- x rock samples were collected in
2001.

***Coordinates***

Latitude and longitude for sample site locations are given in the data
tables as decimal degrees. The coordinates were determined by GPS during
sample collection. The datum was 1927 CONUS and the spheroid was Clarke
1866.

***Geochemical Analyses***

All geochemical data are given in the following format. Field
identifiers consist of three lines. The first line gives the chemical
element symbol and unit of measurement. The second line is an
abbreviated code for the analytical technique used for the element in
that particular column. Reporting units are percent (%), parts per
million (ppm), and parts per billion (ppb). The analytical methods codes
are:

**ACA** automated carbon analyzer

**ASA** automated sulfur analyzer

**AAS** atomic absorption spectrophotometry

**ICP_AES** inductively coupled plasma-atomic emission spectroscopy

**CT** columetric titration

**CV** cold-vapor atomic absorption spectrophotometry for mercury

**ICP_MS** inductively coupled plasma-mass spectrometry

For all geochemical data the symbol '\<' indicates that an element was
not detected at the lower limit of detection. A blank entry indicates
that the samples were not analyzed for that particular element. The
third line lists the laboratory (XRAL or USGS) where elemental analyses
were done.

**Unique Data Fields**

Individual data files have several unique fields.

**Bedrock.xls**

> ***Rock_Description*** description of the rock type, based on field
> observations

**O_2000.xls and O_2001.xls**

***Soil_Horizon*** Oi (forest litter) or Oe (forest duff)

***Horizon_Thickness*** estimated thickness of O-horizon

***ASH\_%*** percent ash as calculated from formula given above

**All_A.xls**

***Soil_Horizon*** A- or E-horizon

***Horizon_Thickness*** estimated thickness of soil horizon

**All_C.xls**

***Depth*** depth at which the sample was collected

**rEFERENCES**

Arbogast, B.F., editor, 1996, Analytical methods manual for the Mineral
Resource Surveys Program, U.S. Geological Survey: U.S. Geological Survey
Open-File Report 96-525, 248 p.

Clayton, Lee and Moran, S.R., 1982, Geochronology of Late Wisconsin
glaciation in middle North America: Quaternary Science Reviews, v. 1, p.
55-82.

Day, W.C., 1990, Bedrock geologic map of the Rainy Lake area, northern
Minnesota: U.S. Geological Survey Miscellaneous Investigations Map
I-1927, scale 1:50,000.

Day, W.C., Southwick, D.L., Schulz, K.J. and Klein, T.L., 1990, Bedrock
geologic map of the International Falls 1° x 2° quadrangle, Minnesota,
United States and Ontario, Canada: U.S. Geological Survey Miscellaneous
Investigations Map I-1965-B, scale 1:250,000.

Goldich, S.S. and Peterman, Z.E., 1980, Geology and geochemistry of the
Rainy Lake area: Precambrian Research, v. 11, p. 307-327.

Hobbs, H.C., Goebel, J.E., 1982, Geologic map of Minnesota: Quaternary
geology: University of Minnesota, Minnesota Geological Survey, scale
1:500,000.

Sado, E.V., Fulllerton, D.S., Goebel, J.E., and Ringrose, S.M., 1995,
Quaternary geologic map of the Lake of the Woods 4° x 6° Quadrangle,
United States and Canada: U.S. Geological Survey Miscellaneous
Investigations Map I-1420 (NM-15), scale 1:1,000,000

Table 1. Lower detection limits for ICP-AES method (USGS and XRAL).

+-------------------------+--------------------------------------------+
| **Element**             | #### Lower detection limit                 |
+-------------------------+--------------------------------------------+
| Aluminum, Al            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Calcium, Ca             | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Iron, Fe                | 0.02 %                                     |
+-------------------------+--------------------------------------------+
| Potassium, K            | 0.01 %                                     |
+-------------------------+--------------------------------------------+
| Magnesium, Mg           | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Sodium, Na              | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Phosphorous, P          | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Titanium, Ti            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Silver, Ag              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Arsenic, As             | 10 ppm                                     |
+-------------------------+--------------------------------------------+
| Gold, Au                | 8 ppm                                      |
+-------------------------+--------------------------------------------+
| Barium, Ba              | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Beryllium, Be           | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Bismuth, Bi             | 10 ppm                                     |
+-------------------------+--------------------------------------------+
| Cadmium, Cd             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Cerium, Ce              | 5 ppm                                      |
+-------------------------+--------------------------------------------+
| Cobalt, Co              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Chromium, Cr            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Copper, Cu              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Europium, Eu            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Gallium, Ga             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Holmium, Ho             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Lanthanum, La           | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Lithium, Li             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Manganese, Mn           | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Molybdenum, Mo          | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Niobium, Nb             | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Neodymium, Nd           | 9 ppm                                      |
+-------------------------+--------------------------------------------+
| Nickel, Ni              | 3 ppm                                      |
+-------------------------+--------------------------------------------+
| Lead, Pb                | 4 ppm                                      |
+-------------------------+--------------------------------------------+
| Scandium, Sc            | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Tin, Sn                 | 5 ppm                                      |
+-------------------------+--------------------------------------------+
| Strontium, Sr           | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Tantalum, Ta            | 40 ppm                                     |
+-------------------------+--------------------------------------------+
| Thorium, Th             | 6 ppm                                      |
+-------------------------+--------------------------------------------+
| Uranium, U              | 100 ppm                                    |
+-------------------------+--------------------------------------------+
| Vanadium, V             | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Yttrium, Y              | 2 ppm                                      |
+-------------------------+--------------------------------------------+
| Ytterbium, Yb           | 1 ppm                                      |
+-------------------------+--------------------------------------------+
| Zinc, Zn                | 2 ppm                                      |
+-------------------------+--------------------------------------------+

Table 2. Lower detection limits for samples analyzed by ICP-MS (USGS).

+-------------------------+--------------------------------------------+
| **Element**             | #### Lower detection limit                 |
+-------------------------+--------------------------------------------+
| Aluminum, Al            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Calcium, Ca             | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Iron, Fe                | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Potassium, K            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Magnesium, Mg           | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Sodium, Na              | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Phosphorous, P          | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Titanium, Ti            | 0.005 %                                    |
+-------------------------+--------------------------------------------+
| Silver, Ag              | 0.5 ppm                                    |
+-------------------------+--------------------------------------------+
| Arsenic, As             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Gold, Au                | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Barium, Ba              | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Beryllium, Be           | 0.1 ppm                                    |
+-------------------------+--------------------------------------------+
| Bismuth, Bi             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Cadmium, Cd             | 0.1 ppm                                    |
+-------------------------+--------------------------------------------+
| Cerium, Ce              | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Cobalt, Co              | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Chromium, Cr            | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Copper, Cu              | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Europium, Eu            | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Gallium, Ga             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Holmium, Ho             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Lanthanum, La           | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Lithium, Li             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Manganese, Mn           | 4.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Molybdenum, Mo          | 0.5 ppm                                    |
+-------------------------+--------------------------------------------+
| Niobium, Nb             | 4.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Neodymium, Nd           | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Nickel, Ni              | 2.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Lead, Pb                | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Antimony, Sb            | 0.1 ppm                                    |
+-------------------------+--------------------------------------------+
| Scandium, Sc            | 2.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Tin, Sn                 | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Strontium, Sr           | 2.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Tantalum, Ta            | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Thorium, Th             | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Thallium, Tl            | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Uranium, U              | 0.1 ppm                                    |
+-------------------------+--------------------------------------------+
| Vanadium, V             | 2.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Yttrium, Y              | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Ytterbium, Yb           | 1.0 ppm                                    |
+-------------------------+--------------------------------------------+
| Zinc, Zn                | 2.0 ppm                                    |
+-------------------------+--------------------------------------------+