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**Geochemistry of bedrock and glacial deposits in the vicinity of the
Bend massive sulfide deposit, north central Wisconsin**

***By* Laurel G. Woodruff^1^, John W. Attig^2^, William F. Cannon^3^,
Suzanne W. Nicholson^3^ and Klaus Schulz^3^**

**Open-File Report 03-353**

**2003**

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^ Wisconsin Geological and Natural History Survey, Madison, WI 53711

^3^ U.S. Geological Survey, MS 954, Reston, VA 20192

**Introduction**

In 1998 the U.S. Geological Survey (USGS) initiated a study to examine
the natural regional environmental impact of sulfide mineralization
exposed to episodic weathering and glaciation. The study focused on the
Bend copper-gold massive sulfide deposit located in the Medford District
of the Chequamegon National Forest in north central Wisconsin. The Bend
massive sulfide deposit is a small, metal-rich sulfide body hosted by
Paleoproterozoic metavolcanics. The mineralized horizon subcrops beneath
100-120 feet of glacial cover, and consists of massive pyrite and other
sulfides. Bedrock and ore geochemistry are well characterized by
analyses of diamond drill core provided to the USGS by Sharpe Energy and
Resources.

In July 1999, five rotosonic drillholes were completed through the
unconsolidated Quaternary sediment, averaging about 100 feet thick, on a
transect across the Bend deposit. Nearly continuous core was recovered
from the surficial material along with several feet of the underlying
bedrock. Samples representing the entire section were analyzed by the
USGS to give a two-dimensional representation of element dispersal from
the unmineralized bedrock. In addition, one hundred regional till
samples were subsampled from the archives of the Quaternary Sediment
Laboratory in the University of Wisconsin-Madison Department of Geology
and Geophysics. These regional samples were collected mainly from Taylor
County, where the Bend deposit is located, as well as contiguous parts
of Clark and Marathon Counties.

This open file report presents all of the geochemical data collected for
this study. Additional publications describing the data in more detail
are being completed.

**Bedrock and Glacial geology**

The Bend deposit is one of a number of undeveloped massive sulfide
deposits located within the Paleoproterozoic (1889 to 1835 Ma)
Ladysmith-Rhinelander metavolcanic complex. The complex is a group of
rocks that occur across much of north central and northeastern Wisconsin
(Figure 1). The Ladysmith-Rhinelander metavolcanic complex and related
rocks are interpreted to have formed in an island arc-back arc setting
(Sims and others, 1989). In the area of the Bend massive sulfide
deposit, regional bedrock is a steeply dipping, interbedded sequence of
schistose rhyolite and rhyodacite lava flows, and quartz-crystal tuffs
that were regionally metamorphosed to lower greenschist and amphibolite
grade.

Sulfide mineralization and associated alteration (sericitization and
silicification) at the Bend deposit resulted from multiple hydrofluid
discharges onto the sea floor as well as subsurface replacements within
a fossil fumarole system. The identified deposit consists of a series of
steeply dipping, stacked massive to semi-massive, copper-gold-bearing
pyritic sulfide lens. Ore minerals include variable amounts of
chalcopyrite and lesser tetrahedrite-tennantite, bornite and gold-silver
tellurides. Geochemistry for this suite of sulfide minerals is similar
to many other gold-rich "Cu type" volcanogenic massive sulfide deposits
in the world, with high values of arsenic, bismuth, mercury, tellurium,
thallium, and antimony in the mineralization (DeMatties, 1994). Gossan
and mineralized saprolite have developed along the approximately
1000-foot strike length of the mineralization where it approaches and
intersects the bedrock subcrop surface.

The area of Wisconsin around the Bend deposit has been glaciated several
times during the Quaternary, most recently during the Wisconsin
Glaciation. Ice last wasted from the region 15,000 years ago (Attig,
1993). Surficial glacial sediments across much of northern Wisconsin
belong to the Copper Falls Formation, which had it source in the Lake
Superior region. In much of Taylor County, which includes the Bend
deposit, the Copper Falls Formation overlies deposits of the older,
pre-Wisconsin Marathon Formation, which had a source in the shale and
limestone bedrock of central Canada (Attig, 1993) (Figure 1). In the
immediate vicinity of the Bend deposit, core from the five rotasonic
boreholes (Figure 2) reveal a complex glacial stratigraphy with numerous
intervals of till, outwash and lake deposits.

**mETHODS OF STUDY**

**Sample Collection and Preparation**

Geochemical sample media analyzed for this study include nonmineralized
bedrock, mineralized bedrock, massive sulfide and glacial materials. All
rock and glacial 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
Taggert (2002).

***Rocks***

Rock and massive sulfide samples were collected from available drill
core. Between 1976 and 1994 diamond drilling was conducted on the Bend
deposit by a consortium of exploration companies that formed the Jump
River Venture; by 1994 only Sharpe Energy and Resources remained in the
Venture. Core logs provided by Sharpe were used to select regional, and
mineralized as well as altered rock samples collected for most
lithologies present to characterize mineralization and surrounding host
rocks.

Sample splits from the diamond drill core 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 were crushed and
pulverized between samples to minimize cross-contamination.

## Glacial Materials

Regional till samples were collected as part of a study of the
Pleistocene geology of Taylor County, Wisconsin (Attig, 1993). Till
samples were taken from splits stored in a repository at the Quaternary
Laboratory in the Department of Geology and Geophysics at the University
of Wisconsin-Madison. Samples were collected from outcrops and from the
bit of a solid-stem auger or from split-spoon corers advanced ahead of a
hollow-stem auger. Multiple samples often were collected from a single
borehole. Samples were described in the field and then analyzed in the
Quaternary Laboratory. Grain-size distribution of the less-than-2mm
fraction was determined using dry sieve and hydrometer techniques.
Munsell color and magnetic susceptibility were also determined in the
laboratory using standard techniques.

Core samples of the unconsolidated deposits overlying bedrock in the
immediate vicinity of the Bend massive sulfide deposit were collected
from five rotasonic boreholes (Figure 2) drilled for this project. The
locations for the rotasonic boreholes were constrained by access along
Forest Road 112, but were selected to be both up-ice (Borehole Ta-1) and
down-ice (Boreholes Ta-3, -4, and --5) from the subcrop trace of
mineralization), as well as directly over the area of mineralization
(Borehole Ta-2) (Figure 2). Core was extracted from the holes in 10-foot
intervals and transported in plastic bags to a nearby core storage
facility where the core was split and logged. Sampling intervals were
determined by changes in the nature of the glacial deposits. Samples
collected for grain-size distribution of the less-than-2mm fraction,
Munsell color and magnetic susceptibility were analyzed at the
Quaternary Laboratory at the University of Wisconsin using standard
techniques. Samples collected for geochemical analysis typically were
composited from continuous intervals of similar material and sent the
U.S. Geological Survey Laboratories in Denver, CO for processing.

**Geochemical Analytical Techniques**

A large number of chemical elements were determined using a variety of
quantitative analytical techniques. All geochemical analyses were done
at the USGS contract analytical laboratory, XRAL Laboratories, Don
Mills, Ontario, Canada. Quality assurance/quality control (QA/QC)
concerns were addressed through the use of internal reference standards
and analytical duplicates for all samples processed by the USGS.
Standard procedures require that QA/QC samples comprise about 10 percent
of the total number of samples analyzed. Reference standards were
interspersed with each batch of samples submitted for analysis. Values
for the reference standards were checked to assure that reported values
are within +/-20 percent of the accepted standard values. Analytical
duplicates were included with each batch of samples. Duplicate analyses
were checked to assure that the relative percent difference between
duplicates was no greater than 20% for individual elements.

Each of the techniques used by XRAL is described in detail in Taggert
(2002).

### Summary of XRAL Geochemical Techniques 

***Atomic Absorption Spectrophotometry (AAS)***

Antimony (Sb), arsenic (As), selenium (Se), tellurium (Te) and thallium
(Tl) were all analyzed by hydride generation atomic absorption
spectrophotometric techniques. For arsenic and antimony, samples are
mixed with sodium peroxide and heated in a muffle furnace set at 750°C
for four minutes. The sample is cooled then 15 ml of water and 5 ml of
concentrated HCl is added. The mixture is shaken and 0.25 ml of an
ascorbic acid KI solution is added then diluted with 20% HCl and let to
stand overnight. The lower detection limit for both As and Sb is 0.6
ppm.

Selenium and tellurium are determined by adding the sample to a mixture
of nitric, hydrofluoric and perchloric acids and heating. After the
solution is cooled hydrochloric and nitric are added, heated again and
cooled, after which the sample is analyzed. The lower detection limit
for Se is 0.2 ppm and for Te is 0.1 ppm.

Thallium is determined by weighing 0.1g of sample into a zirconium
crucible. Approximately 0.75g of sodium peroxide is added and mixed. The
mixture is heated in a muffle furnace set at 750°C for four minutes. The
sample is cooled then 15 ml of water and 5 ml of concentrated HCl is
added. The mixture is shaken and 0.25 ml of an ascorbic acid KI solution
is added then diluted with 20% HCl and let to stand overnight before
analysis. The lower detection limit for Tl is 0.1 ppm.

***Automated Sulfur Analyzer (ASA)***

Total sulfur (S) was determined using an automated sulfur analyzer.
Approximately 0.25 g sample is weighed and mixed with 1 g vanadium
pentoxide flux. The sample is combusted in an oxygen atmosphere at
1350°C where the sulfur oxidizes to sulfur dioxide. Moisture and dust
are removed and a solid-state infrared detector then measures the sulfur
dioxide gas. The lower reporting limit for S is 0.05%.

***Columetric Titration***

Samples were analyzed for carbonate carbon by coulometric titration. The
sample is treated with hot 2 *N* perchloric acid and the evolved CO~2~
is passed into a cell containing a solution of monoethanolamine. The
CO~2~, quantitatively absorbed by the monoethanolamine, is
coulometrically titrated using platinum and silver/potassium iodide
electrodes. The lower reporting limit is 0.01%.

Some rock samples were analyzed for ferrous oxide (FeO) by digesting the
powdered rock with with a mixture of sulfuric, hydrofluoric, and
hydrochloric acids. The solution is titrated with potassium dichromate
using sodium diphenylanime sulphonate indicator. The lower detection
limit is 0.01%.

***Continuous Flow-Cold Vapor Atomic Absorption Spectrometry***

For mercury (Hg) analyses, samples were digested with nitric acid and
sodium dichromate in a disposable test tube and diluted with water.
Samples are then mixed with air and a sodium chloride-hydroxylamine
hydrochloride-sulfuric acid solution and Hg (II) is reduced to Hg° with
stannous chloride in a continuous flow manifold. The mercury vapor is
separated and measured using continuous-flow cold vapor-atomic
absorption spectrometry. The lower detection limit for Hg is 0.02 ppm

***Essential and Nonessential Water***

Essential water (H~2~O^+^) is determined by drying the sample for 1 hour
at 105 ± 5°C to remove H~2~O­ (hydroscopic water). Then the sample is
heated at 950°C by using a tube furnace. The H~2~O^+^ is absorbed by
magnesium perchlorate. From its gain of weight the amount of combined
water is calculated. Non-essential water (H~2~O^-^) is determined by
drying the sample for 2 hours at 105 ±5°C, from the loss in weight,
non-essential water, in percent, is calculated. The lower reporting
limit is 0.05% for both forms of water. Total water is the sum of the
two constituents.

***Fire*** ***Assay***

Gold (Au) was determined by atomic absorption spectrophotometry after
collection by fire assay. An assay fusion consists of heating a mixture
of the finely pulverized sample with about three parts of a flux until
the product is molten. One of the ingredients of the flux is a lead
compound which is reduced by other constituents of the flux or sample to
metallic lead. The latter collects all the gold, together with silver,
platinum metals, and small quantities of certain base metals present in
the sample and falls to the bottom of the crucible to form a lead
button. The gangue of the ore is converted by the flux into a slag
sufficiently fluid so that all particles of lead may fall readily
through the molten mass. The choice of a suitable flux depends on the
character of the ore. The lead button is cupelled to oxidize the lead
leaving behind a dore bead containing the precious metals. The dore bead
is then transferred to a test tube, dissolved with aqua regia, diluted
to a specific volume and determined by atomic absorption
spectrophotometry. The lower detection limit for Au is 5 ppb.

## Inductively Coupled Plasma-Atomic Emission Spectroscopy

Forty major, minor, and trace elements were determined in rocks and
mineral soils by inductively coupled plasma-atomic emission
spectrometry. Each sample was digested 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.

**dESCRIPTION OF DATA FILES**

The analytical data files are provided as five separate Microsoft Excel
2000.xls files. The five files are:

1)  **Bend_regional.xls** Analyses of rock samples taken from diamond
    drill core. Samples are representative of the Ladysmith-Rhinelander
    metavolcanic country rock in the vicinity of the Bend massive
    sulfide deposit.

2)  **Bend_deposit.xls** Analyses of mineralized and altered rock
    associated with massive sulfide mineralization at the Bend deposit.

> 3\) **Bend_massive_sulfide.xls** Analyses massive sulfide from the
> Bend deposit.
>
> 4\) **Regional_till.xls** Analyses of till samples collected in the
> region around the Bend massive sulfide deposit, including samples from
> Taylor, Marathon and Clark counties.
>
> 5\) **Rotasonic_core.xls** Analyses of unconsolidated glacial material
> and regolith collected from five rotasonic boreholes drilled in the
> immediate vicinity of the Bend massive sulfide deposit. Included are
> geochemical analyses on samples collected by the USGS and physical
> characteristics determined from separate, but comparable samples
> collected by John Attig of the Wisconsin Geological and Natural
> History Survey (WGHNS).

### Common Data Fields

In all data tables the following abbreviations are used as needed: ins.
= insufficient sample for analysis; dup. = duplicate sample.

***Field Number***

Field numbers are given for all bedrock, mineralized rock, and glacial
samples. For samples taken from diamond drill core the **Field Number**
consists of the drill hole number and the footage (down hole) where the
sample was collected. For the regional till samples the first letters in
the **Field Number** indicates the county where the sample was collected
(Cl = Clark, Ma = Marathon, and Ta = Taylor) and the final two numbers
show the year the sample was collected. For the rotasonic core the
**Field Number** indicates the borehole number (Ta-1 through Ta-5).

***Coordinates***

Latitude and longitude for sample site locations are given in the data
tables as decimal degrees. The coordinates for the diamond drill core
samples are for the location of the drill hole collar. Coordinates for
the rotasonic holes were determined by GPS and all holes were vertical.

***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 weight percent (wt. %) or
parts per million (ppm). The analytical methods codes are:

**AAS** atomic absorption spectrophotometry

**ASA** automated sulfur analyzer

**CT** columetric titration

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

**FA** gold by fire assay and atomic absorption spectrophotometry

**ICP-AES** inductively coupled plasma-atomic emission spectroscopy

The third line lists the laboratory (**XRAL** or **WGHNS**) where the
analyses were done.

**Unique Data Fields**

Individual data files have several unique fields.

**Bend_regional.xls**

> ***Rock Description*** rock lithology determined from drill logs and
> field notes
>
> **Bend_deposit.xls**
>
> ***Rock Description*** rock lithology determined from drill logs and
> field notes
>
> **Bend_massive_sulfide.xls**
>
> ***Rock Description*** ore description

**Regional_till.xls**

> ***Sample Depth (feet)*** estimated depth from which sample was
> collected in auger hole
>
> ***Glacial Deposit Designation*** the name of the glacial formation
> and member (if known) for each sample -- descriptions of each unit are
> given in Attig (1993)

**Rotasonic_core.xls**

> ***Depth Interval*** depth from which the sample was collected --
> samples typically were composited over the entire interval given
>
> ***Field Description*** nature of glacial material or bedrock as
> determined from core logging in the field
>
> ***Glacial Formation*** name of the glacial formation determined from
> core logging in the field, based on observable characteristics

**acknowledgements**

Sharpe Energy and Resources provided diamond drill core, drill logs, and
additional information on the Bend massive sulfide deposit through the
auspices of Ted DeMatties. Randy Rabideaux and Greg Knight of the USDA
Forest Service provided assistance for National Forest access and
rotasonic drilling permitting. Doug Ottke, formerly of the USGS,
provided able field assistance. Connie Dicken and Art Schultz of the
USGS and Ted DeMatties provided reviews of text and tables.

**rEFERENCES**

Attig, J.W., 1993, Pleistocene geology of Taylor County, Wisconsin.
Wisconsin Geological and Natural History Survey Bulletin 90.

DeMatties, T.A., 1989, A proposed geologic framework for massive sulfide
deposits in the Wisconsin Penokean volcanic belt. Economic Geology, v.
84, p. 946-952.

Sims, P.K., Van Schmus, W.R., Schulz, K.J. and Peterman, Z.E., 1989,
Tectonic-stratigraphic evolution of the early Proterozoic Wisconsin
magmatic terranes of the Penokean Orogen. Canadian Journal of Earth
Science, v. 26, p. 2145-2158.

Taggert, J.E., Jr., 2002, Analytical methods for chemical analysis of
geologic and other materials, U.S. Geological Survey: U.S. Geological
Survey Open-File Report 02-0223.

Table 1. Lower detection limits for 40-element ICP-AES method.

+-------------------------+--------------------------------------------+
| **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                                      |
+-------------------------+--------------------------------------------+