U.S. Department of the Interior

U.S. Geological Survey

Geochemistry of Mine Waste and Mill Tailings,

Meadow Deposits, and Stream Bed Sediment

and the General Hydrology and Water Quality

of the Frohner Meadows Area, Upper Lump Gulch,

Jefferson County, Montana

Geochemistry of Mine Waste and Mill Tailings,

Meadow Deposits, and Stream Bed Sediment

and the General Hydrology and Water Quality

of the Frohner Meadows Area, Upper Lump Gulch,

Jefferson County, Montana

Scientific Investigations Report 2005–5265
Geochemistry of Mine Waste and Mill Tailings, 

Meadow Deposits, and Stream Bed Sediment

and the General Hydrology and Water Quality

of the Frohner Meadows Area, Upper Lump Gulch, 

Jefferson County, Montana

By Terry L. Klein, Michael R. Cannon, and David L. Fey

Prepared in cooperation with the U.S. Department of Agriculture Forest Service

Scientific Investigations Report 2005–5265

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

Posted online March 2006

Version 1.0

This publication is available only online at

http://www.usgs.gov/sir/2005/5265

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natural hazards, and the environment:

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Klein, T.L., Cannon, M.R., and Fey, D.L., 2006, Geochemistry of mine waste and mill tailings, meadow deposits, and 

stream bed sediment and the general hydrology and water quality of the Frohner Meadows area, upper Lump Gulch, 

Jefferson County, Montana: U.S. Geological Survey Scientific Investigations Report 2005–5265, 50 p.
iii

Contents

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

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

Purpose and Objectives.......................................................................................................................3

Description of Study Area ...................................................................................................................3

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and

Stream Bed Sediment......................................................................................................................4

Field Methods and Sample Preparation ...........................................................................................6

Laboratory Methods.............................................................................................................................6

Mine Waste and Mill Tailings .............................................................................................................6

Downstream Distribution and Metal Content of Mine Waste and Mill Tailings................6

Acid-Generating Capacity and Leachability of Mine Waste and Mill Tailings..................8

Meadow Deposits...............................................................................................................................11

Premining Metal Concentrations in Frohner Meadows......................................................11

Postdepositional Metal Migration ..........................................................................................12

Area A—Upper Frohner Meadows ........................................................................................17

Area B—Upper Frohner Meadows ........................................................................................19

Area C—Lower Frohner Meadows ........................................................................................22

Upper Lump Gulch .....................................................................................................................22

Panama Mine Meadows ..........................................................................................................28

Thickness-Weighted Average Concentrations of Ore-Related Metal in

Core Samples................................................................................................................28

Stream Bed Sediment ........................................................................................................................28

Regional Background-Metal Concentrations in Stream Bed Sediment...........................29

Stream Bed–Sediment Consensus-Based Probable-Effect Concentrations ..................29

Metal Concentrations in Frohner Meadows Compared with Background 

Concentrations and CBPEC Standards.....................................................................30

Downstream-Concentration Plots of Ore-Related Metals..................................................30

Arsenic................................................................................................................................30

Cadmium.............................................................................................................................31

Copper.................................................................................................................................34

Lead.....................................................................................................................................34

Zinc......................................................................................................................................35

Hydrology ......................................................................................................................................................35

Methods of Investigation...................................................................................................................37

Ground Water......................................................................................................................................37

Surface Water.....................................................................................................................................38

Water Budget ......................................................................................................................................38

Water Quality................................................................................................................................................40

Ground Water......................................................................................................................................40

Surface Water.....................................................................................................................................41

Trace-Metal Loads..............................................................................................................................41

Conclusions...................................................................................................................................................44

Summary........................................................................................................................................................45
iv

Mine Waste and Mill Tailings ...........................................................................................................45

Area A—Upper Frohner Meadows ........................................................................................45

Area B—Upper Frohner Meadows ........................................................................................46

Area C—Lower Frohner Meadows ........................................................................................46

Upper Lump Gulch .....................................................................................................................46

Panama Mine Meadows ..........................................................................................................47

Stream Bed Sediment ........................................................................................................................47

Hydrology .............................................................................................................................................47

Ground-Water Quality ........................................................................................................................48

Surface-Water Quality .......................................................................................................................48

References Cited..........................................................................................................................................48

Figures

1–3. Maps showing location of:

 1. Frohner Meadows study area within upper Prickly Pear Creek watershed,

Montana..................................................................................................................................2

 2. Frohner Meadows study area and geographic features................................................3

 3. Stream bed–sediment, individual core, and composite mill-tailings sample sites

and core lines in Frohner Meadows and upper Lump Gulch.........................................5

4. Ternary plot of total concentrations of arsenic, lead, and zinc in mine waste,

unprocessed ore, and mill tailings from Frohner Meadows area ........................................7

5. Diagram showing acid-generating capacity and yields of ore-related metal in mine

waste and mill tailings from Frohner Meadows area and two other mine sites..............10

6. Composite image and geochemical profile of core 1–150...................................................13

7. Composite image and geochemical profile of core 3–250...................................................14

8. Map of upper mill tailings area (area A) showing thickness of metal-enriched material

and depth to bottom of enriched interval ...............................................................................15

9. Map of main mill tailings area (area B) showing thickness of enriched material and

depth to bottom of enriched interval .......................................................................................16

10. Photograph of trench showing cross section of mill-tailings debris fan along Frohner

Meadows creek ..........................................................................................................................18

11. Map of upper mill tailings area (area A) showing thickness of enriched material and

thickness-weighted averages of metal concentrations in enriched interval...................20

12. Photograph of mill tailings exposed along Frohner Meadows creek in main

mill-tailings impoundment (area B)..........................................................................................21

13–16. Maps of:

 13. Main mill-tailings area (area B) showing thickness of enriched material and

thickness-weighted averages of metal concentrations ...............................................23

 14. Frohner Meadows showing location of sampling sites ................................................24

 15. Lower Frohner Meadows (area C) showing thickness of enriched material and

depth to bottom of enriched interval................................................................................26

 16. Lower Frohner Meadows (area C) showing thickness of enriched material and

thickness-weighted averages of metal concentrations in enriched interval ...........27

17–22. Downstream-concentration plots of metals in stream bed sediment:

 17. Arsenic ..................................................................................................................................32
v

18. Cadmium.......................................................................................................................................33

19. Iron and manganese ..................................................................................................................33

20. Copper ..........................................................................................................................................34

21. Lead...............................................................................................................................................36

22. Zinc................................................................................................................................................36

23–27. Histograms showing instantaneous loads of total recoverable metals:

 23. Arsenic ..................................................................................................................................42

 24. Cadmium ...............................................................................................................................42

 25. Copper...................................................................................................................................43

 26. Lead .......................................................................................................................................43

 27. Zinc ........................................................................................................................................44

Tables

1. Net acid-producing capacity of mine waste and mill tailings...............................................9

2. Means and standard deviations of ore related–metal concentrations in core samples 

used to define premining conditions in study area...............................................................12

3. Concentrations and instantaneous loads of total recoverable trace metals in

Frohner Meadows area .............................................................................................................25

4. Weighted-average concentration of contaminated material in core samples,

by area..........................................................................................................................................29

5. Median trace-metal concentrations of regional-background stream

bed–sediment samples in upper Prickly Pear Creek watershed and in

Frohner Meadows study area ..................................................................................................31

6. Summary of consensus-based probable-effect concentrations of

ore-related metals in stream bed sediment...........................................................................31

7. Water levels in wells and at surface-water sample sites in Frohner Meadows .............39

8. Calculated mean monthly discharge and annual discharge of

Frohner Meadows creek ...........................................................................................................40

9. Summary of annual water budget of Frohner Basin.............................................................41

Conversion Factors, Abbreviations, and Symbols

Multiply By To obtain

cubic foot per second (ft3/s) 0.028317 cubic meter per second (m3/s)

foot (ft) 0.3048 meter (m)

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

Temperature can be converted to degrees Celsius (°C) or degrees Fahrenheit (°F) by the 

following equations: 

°C = 5/9 (°F – 32)

°F = 9/5 °C + 32
vi

Abbreviated units used in this report:

μg/L micrograms per liter

μL microliter, microliters

μm micrometer, micrometers (micron, microns)

μS/cm microsiemens per centimeter at 25 degrees Celsius

acre-ft acre-foot, acre-feet

acre-ft/yr acre-feet per year

in. inch, inches

in./yr inches per year

ft foot, feet

ft3/s cubic feet per second

L liter, liters

lb pound, pounds

m meter, meters

meq/L milliequivalents per liter

mg/L milligrams per liter

mm millimeter, millimeters

nm nanometer, nanometers

oz ounce, ounces

ppm parts per million 

yr year, years

Abbreviations used in this report:

r 2 correlation coefficient

CBPEC consensus-based probable-effect concentration

EPA U.S. Environmental Protection Agency

HCl hydrochloric acid

HClO4 perchloric acid

HF hydrofluoric acid

HNO3 nitric acid

NAP net acid production

NGVD National Geodetic Vertical Datum

SPLP synthetic precipitation leach procedure
Abstract

Frohner Meadows is an area of subalpine ponds and 

wetlands in glaciated terrane having a low topographic 

gradient near the headwaters of Lump Gulch (a tributary 

of Prickly Pear Creek); it is located about 15 miles west of 

the town of Clancy, Mont., in the Helena National Forest. 

During the last 120 years, ore was extracted at two sites (the 

Frohner mine and the Nellie Grant mine) upstream from 

Frohner Meadows. Lead-zinc-silver veins in granitic rocks 

of the Boulder batholith were mined, and the ore was treated 

nearby. As a result, accumulations of mine waste and mill 

tailings were distributed downslope and downstream by 

anthropogenic and by natural processes.

This report presents the results of an investigation of the 

geochemistry of the wetlands, streams, and unconsolidated sediment deposits and of the hydrology, hydrogeology, and water 

quality of the area affected by these sources of ore-related 

metals. Ground-water samples from most shallow wells in 

the meadows contained high concentrations of arsenic, which 

exceeded the Montana numeric water-quality standard for 

human health. Transport of cadmium and zinc in ground water 

was indicated at one site near Nellie Grant creek (this informal 

name is applied for convenience to an unnamed tributary) on 

the basis of water-quality data from one well near the creek. 

Mill tailings deposited in upper Frohner Meadows contribute 

large arsenic loads to Frohner Meadows creek (also an informal 

name); Nellie Grant creek contributes large arsenic, cadmium, 

and zinc loads to upper Frohner Meadows. Concentrations 

of total recoverable cadmium, copper, lead, and zinc in most 

surface-water sites downstream from the Nellie Grant mine 

exceeded Montana aquatic-life standards. The pH of nearly 

all samples of surface water and ground water was neutral to 

slightly alkaline.

Concentrations of arsenic, cadmium, lead, and zinc 

in stream bed sediment in the entire meadow below accumulations of mine waste and mill tailings are much higher 

than background concentrations in the regional watershed, 

and the meadow concentrations exceed consensus-based, 

probable-effect concentrations for stream bed sediment at most 

sites. Cadmium, copper, and zinc typically are adsorbed onto 

the surface coatings of grains in stream bed sediment. Mine 

waste and mill tailings contain high concentrations of arsenic, 

cadmium, copper, lead, and zinc in a quartz-rich matrix. Most 

of the waste sites that were sampled had low acid-generating 

capacity, although one site (fine-grained mill tailings from the 

Nellie Grant mine deposited in the upper part of lower Frohner 

Meadows) had extremely high acid-generating potential probably because of abundant fine-grained pyrite. Two distinct 

sites were identified as metal sources on the basis of stream 

bed–sediment samples, the meadow substrate, and mine and 

mill-tailings samples. The Frohner mine and mill site contribute material rich in arsenic and lead; similar material from the 

Nellie Grant mine and mill site is rich in cadmium and zinc.

Introduction

Frohner Meadows is an area of subalpine ponds and 

wetlands having a low topographic gradient about 15 miles 

(mi) west of the town of Clancy, Mont., in the Helena National 

Forest (fig. 1). Frohner Meadows is located in Frohner Basin, 

which is in the headwaters of Lump Gulch in the western part 

of the upper Prickly Pear Creek watershed. Two historical 

mines, the Frohner and Nellie Grant mines, are located 

within the Frohner Basin (fig. 2) and upstream from Frohner 

Meadows. Mill tailings, unprocessed ore, and mine-waste 

dumps at these mines have been eroded, washed downstream, 

and deposited in Frohner Meadows on lands administered by 

the Helena National Forest. A mixture of mill tailings and 

unprocessed ore in Frohner Meadows covers an area of about 8 

acres, mostly in the northern or upstream part of the meadows 

(Metesh and others, 1998). Parts of the meadow covered by this 

waste lack vegetation or are covered with dead vegetation.

Previous investigations have shown that water containing high concentrations of dissolved trace metals leaves 

areas disturbed by mining and enters the ponds and wetlands. 

Water within Frohner Meadows and runoff from the wetlands 

Geochemistry of Mine Waste and Mill Tailings, Meadow 

Deposits, and Stream Bed Sediment and the General 

Hydrology and Water Quality of the Frohner Meadows 

Area, Upper Lump Gulch, Jefferson County, Montana

By Terry L. Klein, Michael R. Cannon, and David L. Fey
HELENA

NATIONAL

FOREST

HELENA

NATIONAL

FOREST

Upper Prickly

Pear Creek

Watershed

boundary

Boulder River

Watershed 

Boulder River

Watershed 

Boulder River

Watershed

R. 5 W. R. 4 W. R. 3 W. R. 2 W.

T. 7 N.

T. 8 N.

T. 9 N.

0 1 2 MILES

0 1 2 KILOMETERS

Frohner Meadows

 study area

Helena

M O N T A N A

Map area

Jackson Cr

Quartz Cr

Bualo Cr

Travis Cr

Corral Gl

North Fork Quartz Cr

Roe Gl

McCauley Gl

Kelly Gl

Browns Gl

Lump Gulch

Clancy Cr

Prickly Pear Cr

Westover Gl

Corbin Cr

Comet C

S

r

pring Gl

Wood Chute Cr

Beavertown Cr

Golconda Cr

Anderson Gl

Black Canyon

Dutchman Cr

Warm Springs Cr South Fork

Middle Fork

Curtain Gl

Spring Cr

North Fork

South Fork Quartz Cr.

Bualo Cr

Little Corral Gl

Morgan Gl

Clancy Cr

Stagecoach Gl

Beavertown Cr

Troy Cr

Weimer Cr

Rabbit Gl

Hogan Cr Browns Gl

Badger Cr

Kady Gl

Helena National Forest

(unshaded areas within forest

boundary represent non-forest

parcels)

Little

Bualo Gulch

Lump Gulch

Wickes

Corbin

Clancy

Alhambra

Jeerson City

Park Lake

EXPLANATION

112o07'30" 112o

46o22'30"

46o30'

111o52'30"

Water quality

Stream bed sediment

Base modied from U.S. Department of Agriculture 

Forest Service. Digital line graphs, 1:24,000, 2000. 

Horizontal coordinate information is referenced to 

North American Datum of 1927 (NAD 27) 

Watershed sampling sites of 

Klein, Cannon, and Fey (2003) and

Klein, Thamke, and Farag (2001)

Crow Creek

Watershed

McClellan Creek

Watershed

Tenmile Creek

Watershed

Tenmile Creek

Watershed

Figure 1. Location of Frohner Meadows study area within upper Prickly Pear Creek watershed, Montana.

 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
contain concentrations of trace metals that exceed Montana 

aquatic-life and Montana numeric water-quality standards 

for human health. Dissolved trace-element concentrations in 

mine runoff are attenuated by the wetlands; however, water 

and stream bed sediment downstream from Frohner Meadows contain cadmium and zinc in concentrations that exceed 

Montana aquatic-life standards for water and consensusbased, probable-effect concentrations (CBPECs) for stream 

bed sediment (Klein and others, 2001). Stream bed sediment 

in Frohner Meadows also contains concentrations of arsenic, 

copper, and lead that exceed consensus-based, probable-effect 

concentrations (MacDonald and others, 2000).

The U.S. Department of Agriculture Forest Service 

(USDA Forest Service) identified public lands within the 

Frohner Meadows area that have been degraded by historical 

mining and are in need of remediation. To develop effective 

remediation plans for the wetlands and downstream riparian 

areas, the USDA Forest Service needed additional information about the distribution of metals in mill tailings, meadow 

deposits, and stream bed sediment and about the hydrology, 

hydrogeology, and water quality of the wetlands.

Purpose and Objectives

This report presents data and interpretations derived from 

a comprehensive study of the geochemistry of mill tailings, 

mine waste, meadow deposits, and stream bed sediment and of 

the hydrology and water quality in the Frohner Meadows area. 

The U.S. Geological Survey, in cooperation with USDA Forest 

Service, conducted this study during 2001 and 2002.

Objectives of the study were to (1) characterize physical 

and chemical properties of mill tailings and transported mine 

waste in the meadows, (2) characterize the geochemistry of 

stream-bed sediment and core samples in the wetlands and 

waterways of Frohner Meadows and upper Lump Gulch, (3) 

characterize ground-water flow and quality in the Frohner 

Meadows area, (4) characterize stream discharge and surfacewater quality in Frohner Meadows and upper Lump Gulch, 

and (5) identify sources of trace metals and quantify loads of 

trace metals entering and leaving the meadows. The scope of 

the study was limited to public lands in Frohner Meadows and 

upper Lump Gulch that are adjacent to or downstream from 

the Frohner and Nellie Grant mines.

Description of Study Area

Frohner Meadows consists of two large wetland areas that 

are referred to in this report as “upper” and “lower” Frohner 

Meadows (fig. 2). A small perennial stream connects the two 

wetlands. The wetland of upper Frohner Meadows occupies 

an area of about 14.2 acres, is about 1,670 feet (ft) long from 

north to south, and is at an altitude of about 6,600–6,570 ft. 

The wetland of lower Frohner Meadows occupies an area of 

about 15.5 acres, is about 1,750 ft long from west to east, and 

is at an altitude of about 6,540–6,510 ft. Both wetlands contain 

several inactive beaver ponds that hold water throughout the 

0 0.5 MILES

Figure 2. Location of Frohner Meadows study area and geographic features. Base map from U.S. Geological 

Survey Chessman Reservoir 71⁄2 minute topographic quadrangle.

Introduction 
year. Upper Frohner Meadows receives surface water from 

several small tributaries. The largest tributary drains into the 

northwestern part of the upper meadows and informally is 

named “Frohner Meadows creek.” A smaller tributary enters 

the western part of the upper meadows and is informally 

named “Nellie Grant creek” (fig. 3). Several tributaries from 

unmined areas drain from the northern and eastern parts of 

Frohner Basin into upper Frohner Meadows.

The study area is underlain by granitic rocks of the Boulder batholith (Becraft and others, 1963), which is a very large, 

composite, Late Cretaceous (80–70 Ma), igneous intrusion 

that is exposed throughout an area approximately 30 by 60 

mi. Near Frohner Meadows, the rocks of the batholith range 

in composition from quartz monzonite to granodiorite and 

contain some small, late-stage aplite or alaskite bodies. Rocks 

of the Elkhorn Mountains Volcanics, which are approximately 

the same age (81–76 Ma) as rocks in the Boulder batholith, 

are exposed about 4 mi southeast of the study area. Small 

rhyolite intrusions and flow remnants are found throughout 

the northeastern part of the batholith; the nearest exposure is 

about 1 mi northwest of the study area. Similar intrusive bodies in this part of Montana probably are Eocene or Oligocene 

in age (40–37 Ma) (Ispolatov, 1997). Rhyolite of the Eocene 

Lowland Creek Volcanics (53–48 Ma) unconformably overlie 

exposures of the Elkhorn Mountains Volcanics about 5 mi 

southeast of Frohner Meadows.

Most historical mining activity in the Frohner Meadows 

area took place near Frohner Meadows creek and Nellie Grant 

creek (fig. 2). Mining for base and precious metals was confined to two principal mines, the Frohner mine and the Nellie 

Grant mine. The mined deposits lie in secs. 14 and 15, T. 8 

N., R. 5 W. along a 5- to 40-ft-wide, east-west-trending zone 

(N. 70° W., 70°–83° S.) of quartz and chalcedony veins and 

hydrothermally altered granitic rocks that is more than 0.5 mi 

long (Becraft and others, 1963). Moderately intense sericitic 

alteration accompanies mineralization; some clay alteration is 

present and may be, in part, the result of weathering. Various 

amounts of calcite are disseminated in altered rocks and in 

veinlets in the ore zone.

Ore mineralogy differs in these mines. Ore from the 

Frohner mine contains a variable but significant amount of 

galena, sphalerite, and arsenopyrite and a subordinate amount 

of pyrite. Pyrite is the most abundant sulfide mineral in the ore 

from the Nellie Grant mine, which also contains significant 

galena and sphalerite and subordinate amounts of chalcopyrite; 

arsenopyrite was not observed (Becraft and others, 1963).

The Frohner mine was active from the late 1880s to 

1954, whereas the Nellie Grant mine was active in the late 

1880s through the 1950s and from 1978 to 1982 (Roby and 

others, 1960; Pioneer Technical Services, 1996). The Frohner 

mine consists of at least 2,000 ft of tunnels. The extent of 

underground workings at the Nellie Grant mine is not known. 

Incomplete estimates for the Frohner mine (1928–54) indicated production of 161 troy ounces (oz) of gold, 7,329 troy 

oz of silver, 2,305 pounds (lb) of copper, 91,503 lb of lead, 

and 26,000 lb of zinc from 1,917 tons of ore. The Nellie Grant 

mine is reported to have produced 293 troy oz of gold, 10,279 

troy oz of silver, 3,481 lb of copper, 216,242 lb of lead, and 

47,156 lb of zinc from 1,057 tons of ore between 1948 and 

1957 (Roby and others, 1960).

Two reduction and concentration mill sites are adjacent to 

the Frohner and Nellie Grant mines (fig. 2). The Frohner mill 

originally used gravity concentration, probably with a stamp 

mill for crushing; the gravity concentration system later was 

replaced by flotation (Roby and others, 1960). Mill tailings 

and unprocessed ore from this operation were deposited along 

the adjacent Frohner Meadows creek in stream terraces, in a 

debris fan in the northwest corner of upper Frohner Meadows, 

and in a large area in the central part of upper Frohner Meadows more than 0.5 mi downstream from the mill. Ore from the 

most recent milling at the Nellie Grant mine (1978–82) was 

crushed in a ball mill and concentrated by flotation. No information on early ore processing at the Nellie Grant is available. 

Mill tailings from the Nellie Grant mill are impounded by 

a small dam on the hillside north of the mill site, are buried 

on the hillside east of the mill site, are impounded in a large 

area in the central part of upper Frohner Meadows, and are 

deposited in a small pond at the west end of lower Frohner 

Meadows (fig. 3). Reclamation of the Nellie Grant mine site 

during 1981–83 and in 1993 consisted mostly of recontouring mine waste and mill tailings, controlling ground-water 

flow to mill tailings, revegetation of mine waste, mill tailings, 

and reclaimed areas, and erosion control (Pioneer Technical 

Services, 1996).

Background data for the Frohner Meadows area were 

obtained from an inventory of abandoned or inactive mines 

in the Helena National Forest (Metesh and others, 1998) and 

from records on file at the Montana Department of Environmental Quality, Helena, Mont. Additional information about 

site characteristics and reclamation activities at the Nellie 

Grant and Frohner mines was obtained from reports prepared 

by Pioneer Technical Services, Inc. (Pioneer Technical Services, 1996, 2000).

Geochemistry of Mine Waste and 

Mill Tailings, Meadow Deposits, and 

Stream Bed Sediment

Frohner Basin has been the site of several periods of 

mining during more than a century; activity focused in the 

area west of upper Frohner Meadows at the Nellie Grant and 

Frohner mines. Geochemical investigations were undertaken 

during this study to (1) describe the chemical and physical 

character of the mine waste, mill tailings, and unprocessed 

ore that has accumulated in Frohner Meadows downstream 

from the mine areas (fig. 3) and (2) understand the effects 

of the fluvially transported, ore-related trace metals from 

these mining wastes on the chemistry of stream bed sediment 

throughout Frohner Meadows.

 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
112o11'40'' 112o11'20''

46o26'20''46o26'10''46o26'00''46o25'50''

Frohner Meadows cr.

Nellie Grant cr.

112o12'20'' 112o12'00''

 Lump Gulch Roa

Nellie Grant mine

Nellie Grant mill site

Frohner mine

Frohnermill site

Lower Frohner 

Meadows

Upper Frohner

Meadows

LG

LG

LGFR 

Reclaimed tailings pond

Panama mine meadows

Frohner Meadows cr.

46o26'30''

0

0 500 1,000

500 METERS

1,500 FEET

250

L-162

L-163

L-164

L-165

L-166 L-167

L-1

L-159

L-2

L-3b L-1

L-150

L-151

L-100

L-168

L-161

Core line 1

Core line 2

Core line 3

Core line 4

Core line 5

Core line 6

UFM 2

UFM 3

UFM 1

UFM 4

LFM 1

LFMC 1

PMC 2

PMC 1

PMC 3 

UFMC 1

FMB 1

FMB 2

Core line 250

Area C

Area B

Area A

Dam

Pond, dry pond, or sediment-filled pond

Road

Stream

Approximate outline of meadow areas

Minimum extent of exposed mill tailings

Mine site

Mill site

2001 stream bed sediment sample site

2000 stream bed sediment sample site 

(resampled 2001)

2000 stream bed sediment sample site

Core lineCore siteComposite mill tailings sample site

Area boundary

EXPLANATION

Panama mine meadows triburary

Figure 3. Location of stream bed–sediment, individual core, and composite mill-tailings sample sites and core lines in Frohner Meadupper Lump Gulch.
Field Methods and Sample Preparation

Stream bed sediment was systematically sampled 

throughout Frohner Meadows to determine the sources of 

metals in stream bed sediment at the outlet of the meadows 

(high concentrations of metal in stream bed sediment had 

been found during previous regional investigations (Klein and 

others, 2001)). We also sought to understand the processes 

that alter metal concentrations in stream bed sediment downstream from the mine area and to determine the contribution of 

metals in sediment to the metal budget of the meadow system. 

Most sites were sampled within a 3-day period during July 

2001. This short sampling period minimized any seasonal 

effects on element concentrations owing to changes in stream 

discharge or water chemistry. Two sites (L–1 and L–2, fig. 

3) were sampled in September 2000 when stream discharge 

was somewhat lower than it was in July 2001. Methods of 

sampling and of preparing samples of stream bed sediment are 

described in Klein, Thamke, and others (2003).

Samples of mine waste and mill tailings samples were 

collected to determine their bulk chemical composition and 

acid-producing potential. Surface composite samples were 

collected at five sites (all but one of the major mill tailings 

accumulations); samples contained mill tailings mixed with 

other mine waste (fig. 3). Reclaimed mill tailings at the Nellie 

Grant mill site were not sampled. Crushed but unconcentrated 

ore was sampled at two sites (FMB 1 and FMB 2, fig. 3). 

Material from all sites was collected to a depth of about 3 

in. and was composited from 30 or more randomly selected 

cells throughout the collection site. Sampling methods are 

described in Klein, Thamke, and others (2003). Data from 

previous studies of the Frohner and Nellie Grant mine sites 

(Metesh and others, 1998; Pioneer Technical Services, 1996, 

2000) were used to supplement mine-waste and mill-tailings 

data from this study.

Vertical profiles of mill tailings and mine waste accumulations and meadow deposits obtained from cores in wetland 

areas were used to help determine the thickness and extent 

of mill tailings and the stratigraphy, physical character, and 

chemistry of the mill tailings and meadow deposits. Most 

cores were 2–5 ft deep and were collected along lines at intervals of 50–100 ft. The locations of profile lines and individual 

sample sites are shown in figure 3. The sampling and sample 

preparation methods used for cores are described in Klein, 

Thamke, and others (2003).

Laboratory Methods

Geochemical samples were analyzed by three digestion methods that are described in Klein, Thamke, and others 

(2003). Resulting solutions were analyzed for 40 elements by 

inductively coupled plasma–atomic emission spectroscopy 

(Briggs, 1996). In addition, a fourth digestion method was 

used to measure net acid-generation potential.

Stream bed sediments, composite samples of surface 

mine waste and mill tailings, and samples from cores were 

digested in a mixed four-acid medium of HCl, HNO3, HClO4, 

and HF. This mixed-acid medium dissolves most silicates, 

oxides, and sulfides; resistant or refractory minerals such 

as zircon, chromite, and some tin oxides are only partially 

dissolved. This procedure, referred to as a total digestion, 

releases the bulk of each major and trace element contained in 

a sample. Quality-assurance and quality-control data for totaldigestion analyses are summarized in Klein, Thamke, and 

others (2003, appendix tables 2a–2c).

Stream bed–sediment samples also were analyzed by 

use of a dilute HCl and 1 percent hydrogen peroxide partial 

digestion (dilute-acid partial digestion), which allows the 

selective determination of trace-metal concentrations bound 

within certain specific mineral phases. This digestion releases 

water-soluble and ion-exchangeable metal species from several potentially accumulating phases: hydrous amorphous iron, 

manganese, and aluminum oxide minerals; some crystalline 

iron and manganese oxyhydroxides (Church and others, 1993); 

and water-soluble, ion-exchangeable carbonates. Qualityassurance and quality-control data for this partial digestion by 

dilute acid is summarized in Klein, Thamke, and others (2003, 

appendix table 2d).

Composite samples containing surface mine waste and 

mill tailings were analyzed by the EPA–1312 acidic leach 

method (U.S. Environmental Protection Agency, 1986) and 

by a procedure that determines a sample’s net acid-generation potential (Lapakko and Lawrence, 1993). Results of this 

latter method also simulate the net long-term or total potential 

of a material to produce acid during an unspecified period 

of weathering. The laboratory procedures for these analyses 

and the quality-assurance and quality-control data for the 

EPA–1312 leach are summarized in Klein, Thamke, and others 

(2003, appendix table 2e).

Mine Waste and Mill Tailings

Downstream Distribution and Metal Content of 

Mine Waste and Mill Tailings

The Frohner and Nellie Grant mine areas are the principal 

sources of mine waste and mill tailings in Frohner Meadows. 

A mill was located near each mine (fig. 3), and each mill produced tailings that have accumulated along Frohner Meadows 

and Nellie Grant creeks. Previous studies found that mine 

waste and mill tailings at the Nellie Grant and Frohner mines 

are enriched in potentially toxic metals—arsenic, cadmium, 

copper, iron, lead, manganese, and zinc (Pioneer Technical 

Services, 1996, 2000).

Between the Frohner mill and upper Frohner Meadows, 

tailings were deposited in small stream terraces along Frohner 

Meadows creek and in a mill-tailings debris fan at the change 

in slope where the stream enters upper Frohner Meadows. 

Below this debris fan, the creek has distributed mill tailings 

widely (fig. 3, area A) in the upper part of upper Frohner 

Meadows. The creek also transported a substantial amount of 

 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
mill tailings to a mill-tailings impoundment in the middle of 

upper Frohner Meadows (fig. 3, area B).

Most mill tailings from the Nellie Grant mine were 

impounded in a tailings pond (fig. 3) on the hillslope above 

upper Frohner Meadows, but some were transported into upper 

Frohner Meadows by Nellie Grant creek. Some mill tailings 

from the Nellie Grant mine also were discharged into a beaver 

pond in lower Frohner Meadows (Pioneer Technical Services, 

1996) during the latest period of mining (1979–82).

Seven composite surface samples from mill-tailings 

accumulations in upper and lower Frohner Meadows were 

collected to determine the chemical composition and acidproducing potential of the tailings. These samples were 

collected from each of the three major mill-tailings accumulations: at the west edge of the Frohner mill-tailings debris 

fan (area A), at the main mill-tailings impoundment (area B), 

and at the mill-tailings delta in the western margin of lower 

Frohner Meadows (fig. 3). In addition, shallow cores were 

drilled in these areas (Klein, Thamke, and others, 2003, and 

described in the following section, “Meadow Deposits”), 

and chemical analyses of mill tailings in the cores were used 

to investigate chemical differences among different sources 

of mill tailings. Two samples were also collected from 

dispersed untreated ore at the Frohner mill site (fig. 3, area 

A). Data from previous studies of the Frohner and Nellie 

Grant mine sites (Metesh and others, 1998; Pioneer Technical Services, 1996, 2000) were used to supplement chemical 

analyses of mill tailings and mine waste obtained during this 

study. Selected analyses from the previous studies, as well 

as the results of the total-digestion analyses of the composite 

samples from this study, are summarized in Klein, Thamke, 

and others (2003).

Some variation in composition of mill tailings and mine 

waste at these two mine sites is apparent. A ternary diagram 

of arsenic, lead, and zinc concentrations that uses data from 

surface mine waste and mill tailings and the mill tailings collected in cores (tables 6 and 7 of Klein, Thamke, and others, 

2003) illustrates the compositional variability of mine waste 

and mill tailings (fig. 4). The position of each point on the 

diagram marks the proportion of each metal to the total concentration of the three metals; the position is found by dividing 

the concentration of each metal by the total concentration of 

0.0

0.2

0.4

0.6

0.8

0.0 1.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Frohner mine unprocessed ore

Area A mill tailings

Nellie Grant mine waste

Nellie Grant mill tailings

Area B mill tailings 

As Zn

Pb Mine waste and ore

Mill tailings

EXPLANATION

Figure 4. Total concentrations of arsenic, lead, and zinc in mine waste, 

unprocessed ore, and mill tailings from Frohner Meadows area. Areas 

referred to are shown in figure 3.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 
the three metals. These three ore-related metals are sufficient 

to illustrate the variability, because copper is a minor constituent at the Frohner and Nellie Grant mines and because the 

chemical behavior of cadmium is nearly identical to that of 

zinc. Stream bed sediment in Frohner Meadows and upper 

Lump Gulch is also highly enriched in arsenic, lead, and zinc. 

Unprocessed ore and mine waste from the Frohner mill are 

distributed near the lead axis; arsenic/(lead + arsenic) values 

range from 0.25 to about 0.75. The proportion of zinc to the 

total of the three metals in these samples was very low (0.05 

or less). Waste rock from the Nellie Grant mine had a lower 

arsenic/(lead + arsenic + zinc) value than that of most of the 

unprocessed ore samples from the Frohner mill and waste rock 

from the Frohner mine; that value ranged from approximately 

0.05 to 0.25. The proportion of zinc to total metal content in 

samples of Nellie Grant mine waste was similar to that found 

in unprocessed ore and mine waste from the Frohner mill and 

mine. The area labeled “mine waste and ore” in figure 4 is 

defined by these samples.

Many samples from area A below the Frohner mine and 

mill (fig. 3) plotted within the mine waste and ore field (fig. 

4); this distribution suggests that the samples were predominantly transported mine waste and unprocessed ore (fig. 4). 

Approximately 30 percent of the samples from area A showed 

a high but variable proportion of zinc. These samples were 

from cores in the most distal part of deposits that were sampled in area A; points plotted for these samples form a group 

that trends toward the zinc corner of the ternary diagram. 

These samples were composed of sand- and silt-size mill tailings, and their enrichment in zinc probably is due to entrainment of zinc in mill effluent during gravity ore processing at 

the Frohner mill. Samples of mill tailings in area B plotted 

in the same part of the diagram as did mill tailings from area 

A. Most of the samples of mill tailings from the Nellie Grant 

mill on the west side of area B (fig. 3), from the Nellie Grant 

mill tailings pond (now reclaimed), and from lower Frohner 

Meadows (one sample) were similar to most samples of mill 

tailings from other accumulations in Frohner Meadows (fig. 

4). One sample plotted with those that form the mine waste 

and ore field and probably was waste deposited with tailings. 

The mill-tailings field is defined by these samples where they 

take proportions less than the maximum zinc proportion found 

in ore samples and mine waste (fig. 4).

As compared with mine waste and unprocessed ore 

samples, many surface and core samples from Frohner Meadows were enriched in zinc. This enrichment was most likely 

due to the recovery, during the extraction process, of lead and 

silver from galena (PbS) and of arsenic from either arsenian 

pyrite (FeS2) or arsenopyrite (FeAsS). Early milling processes 

enriched tailings in zinc (from sphalerite, ZnS), because zinc 

was not recovered efficiently in gravity separation mills such 

as the Frohner mill. Zinc was recovered only later by mills that 

used flotation. However, as late as 1982 zinc was still poorly 

recovered. Mill tailings continued to be enriched in zinc, even 

though flotation was used at the Nellie Grant mill, which 

produced the youngest mill tailings in lower Frohner Meadows 

(Pioneer Technical Services, 1996).

The ternary diagram that shows concentrations of arsenic, 

lead, and zinc (fig. 4) is useful in defining the provenance of 

the surface and subsurface samples from Frohner Meadows. 

Determining whether a sample is predominantly ore and mine 

waste or whether it is mill tailings is useful in predicting 

which metals are most likely to be contributed to surface or 

ground water and stream bed sediment in a given area.

Acid-Generating Capacity and Leachability of 

Mine Waste and Mill Tailings

Two important characteristics of mine waste are its ability 

to produce acid and to release soluble metals. The composite 

mine-waste samples were tested to determine both. In the 

procedure used to determine the potential net acid production 

(NAP) (described in Klein, Thamke, and others, 2003), an 

aliquot of each sample was exposed to a strong (30 percent) 

solution of hydrogen peroxide. Sulfide minerals (typically 

pyrite, FeS2) in the sample were oxidized during the digestion and produced sulfuric acid. The results are expressed in 

terms of the concentration of calcium carbonate (CaCO3) in 

kilograms per metric ton that would be required to neutralize 

the resultant acid. The result is a net estimate of the total acid 

that the sample could produce during an unspecified period 

of time, because it takes into account potential neutralization 

by acid-consuming minerals and the continuous generation of 

acid as weathering and transport remove previously generated 

acid. The NAP of a material is the simple difference between 

its acid-producing potential and its acid-neutralizing potential. 

This difference can be determined by separately measuring 

each attribute in the laboratory and taking the difference or by 

measuring one solution in which acid is both produced and 

neutralized by the sample itself, as was done for this study.

Results of the NAP test showed a range of values from 2 

to 250 kg/ton (table 1). Other studies applied this procedure to 

mine-waste material from the Boulder River watershed west 

of Frohner Meadows and to material from the Animas River 

watershed in southwestern Colorado (Fey, Desborough, and 

Finney, 2000; Fey, Nash, and others, 2000). Results from 19 

samples from the Boulder River watershed ranged from 0 to 

34 kg/ton, and results from 110 samples from the Animas 

River watershed, Colorado, ranged from 0 to 167 kg/ton. By 

comparison, the fine-grained sample from the mill-tailings 

delta at the west end of lower Frohner Meadows (sample LFM 

1 NGS) had an extremely high NAP. Another measure of the 

acid-producing qualities of a mine-waste material is known 

as the “neutralization potential ratio,” which is the ratio of the 

neutralization potential to the acid-producing potential, where 

again each potential is measured separately. There are several 

classification schemes for the neutralization potential ratio, 

and a given mine-waste material can be placed into various 

categories. According to one classification scheme by Price 

and others (1997), four categories can be used to relate the 

neutralization potential ratio to the likelihood that a waste 

 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
material will produce acid. These categories are as follows: 

ratio <1, acid production likely; ratio between 1 and 2, acid 

production possible; ratio between 2 and 4, acid-production 

potential low; and ratio >4, no acid-production potential. The 

fourth category can be obtained by mixing four parts of limestone with one part of mine waste (a 4:1 ratio). For example, 

to remediate a sample with a NAP of 10 kg/ton would require 

mixing in 40 kg/ton CaCO3 into the material, or about 170 

lb of limestone per cubic yard of waste. Samples FMB 1 and 

LFM 1 NGS (table 1) had NAP values high enough to make it 

impractical to apply and mix limestone on-site: LFM 1 NGS 

would require more than 4,000 lb of limestone per cubic yard 

(about a 50 percent mix of limestone with waste). In addition, 

this site is under water, which makes it exceedingly impractical to remediate.

All other samples except UFM 2 had relatively low 

NAP values. Three splits of sample UFM 2 were analyzed for 

acidity—a >2-mm fraction, a <2-mm fraction, and a combined 

bulk fraction. Most geochemical studies find that the finer 

fractions contain more of the constituents of interest (Horowitz, 

1991). Such was not the case for acidity in UFM 2. The >2-mm 

fraction yielded an NAP value more than 10 times that of the 

<2-mm fraction and more than twice that of the bulk fraction. 

This sample contained coarse, angular quartz chips that we 

interpret to be coarsely ground ore material from which pyrite 

and other sulfide minerals were not fully liberated.

However, the sample preparation process for this study 

(grinding to <200 mesh) allowed all pyrite to be available for 

reaction in the acidity determinations. Thus, the NAP value 

obtained from the >2-mm fraction was a high estimate of the 

total potential of the >2-mm fraction to create acid. The value 

obtained from the <2-mm fraction, only 2 kg/ton, indicates 

few acid-storing soluble salts or pyrite in the fine fraction. 

The bulk sample yielded a value (12.8 kg/ton) between that 

of the <2-mm and the >2-mm fractions. All three fractions, 

when subjected to the EPA–1312 leach (see below), produced 

leachates having a pH between 3.5 and 3.7. The pH of the 

leach solutions represents a snapshot of the hydronium-ion 

activity, whereas the NAP represents the long-term potential 

for generation of acid.

The leachability of various constituents from the composite mine waste and mill tailings samples was determined by 

the EPA–1312 synthetic precipitation leach procedure (SPLP) 

described in Klein, Thamke, and others (2003). This procedure 

simulates the effect of rainfall or runoff on a dump surface. 

Note that in the discussion that follows, the term “leachable” 

applies to constituents liberated by the SPLP test solution, 

which is deionized water acidified to pH 4.2, and not to those 

liberated by the dilute-acid partial digestion that was applied 

to stream bed sediment. The leachate was analyzed for the 

ore-related metals arsenic, cadmium, copper, lead, and zinc. 

The sum of the concentrations of these five metals in the leach 

solution is plotted against the NAP value obtained from the 

acidity test shown in figure 5. This plot provides a geochemical rank for each waste and tailings source. This rank should 

be considered, along with factors such as amount of material, 

proximity to flowing water, permeability of the substrate, and 

slope aspect, to determine appropriate remediation actions.

The diagram in figure 5 is divided into four geochemical 

classes that are based on the classification of Fey, Desborough, 

Sample

number Description Acid-producing 

capacity 

FMB 1 

Frohner mill 

 Composite ore sample 38

FMB 2 Composite ore sample 7.2

LFM 1 NGS 

Lower Frohner Meadows 

 Nellie Grant mill-tailings delta 250

UFM 1 

Upper Frohner Meadows 

 Mill-tailings debris fan 

 Eastern part, bulk sample 3.1

UFM 2 (bulk) Western part, bulk sample 12.8

UFM 2 (>2-mm fraction) Western part, >2-mm fraction 35

UFM 2 (<2-mm fraction) Western part, <2-mm fraction 2

UFM 3 Main mill-tailings area 4.3

UFM 4 Nellie Grant mill-tailings fan 2.8

Table 1. Net acid-producing capacity of mine waste and mill tailings (kilograms per 

ton CaCO3).

[<, less than; >, more than]

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 
and Church (2000). Class 1 contains material that generates 

little acid (<10 kg/ton CaCO3) and low concentrations of total 

leachable metals (<1,000 μg/L total metals). Class 2 contains 

material that generates little acid and moderate total leachable 

metals. Class 3 contains material that generates little acid but 

high concentrations of total leachable metals. Class 4 contains 

material that generates large amounts of acid and high concentrations of total leachable metals (>10 kg/ton CaCO3 and 

>5,000 μg/L total leachable metals). If other factors are equal, 

class 4 materials then are of highest concern, whereas class 1 

materials are of lowest concern.

Two composite unprocessed crushed-ore samples were 

collected at the Frohner mill site (fig. 3). Sample FMB 1 was 

collected from the ground below the mill, and sample FMB 

2 was collected from an above-ground bin. Both samples 

yielded SPLP leachates with geochemistry similar to each 

other (Klein, Thamke, and others, 2003); lead dominated 

the total dissolved-metal concentrations (13,000 and 19,000 

μg/L total leachable metals, respectively). However, the NAP 

values obtained from the two samples were different. Sample 

FMB 1 had an NAP value of 38 kg/ton CaCO3, whereas 

sample FMB 2 had an NAP value of 7 kg/ton CaCO3. This 

difference may relate to the composition of source material or to differences in the response of source materials to 

weathering. Regardless of the acidities, both unprocessed ore 

samples produced leachates having high concentrations of 

dissolved metals.

Sample UFM 1 was collected at the upper (western) end 

of fluvial mill tailings deposited in Frohner Meadows creek 

as it entered upper Frohner Meadows (fig. 3). This sample 

produced a moderate 2,700 μg/L total leachable metals. The 

low NAP value (3.1 kg/ton CaCO3) indicates that little pyrite 

was present to produce acid.

Sample UFM 2 was collected in upper Frohner Meadows 

(fig. 3, area A) and was separated into three size categories as 

described previously. The different size fractions responded 

quite differently to acidity and SPLP tests. The bulk sample 

and the >2-mm fraction plotted in class 4 (fig. 5). The <2-mm 

fraction, however, plotted in class 2. These mill tailings, which 

probably had been processed by an early stamp mill, still contained many coarsely crushed quartz chips. Despite its coarse 

grain size, the coarse fraction produced a high concentration 

of lead (17,000 μg/L) and a low concentration of zinc (330 

μg/L). The sample of <2-mm material produced only 1,300 

μg/L lead but a slightly higher zinc concentration of 570 μg/L, 

which indicates that the coarse fraction of the mill tailings was 

the source of the high concentrations of metals and high acid 

concentration in the bulk sample.

10

100

1,000

10,000

100,000

1 10 100

Frohner Meadows

Boulder watershed (Fey, Desborough, and Church, 2000)

Animas watershed (Fey, Desborough, and Finney, 2000)

Class 3

Class 1

Class 2

Class 4

POTENTIAL NET ACID PRODUCTION (NAP), IN KILOGRAMS PER TON CaCO3

 ARSENIC + CADMIUM + COPPER + LEAD + ZINC,

IN MICROGRAMS PER LITER

FMB 2

FMB 1

UFM 1

UFM 4

UFM 3

UFM 2<2mm

UFM 2

UFM 2 >2mm

LFM 1

EXPLANATION

Figure 5. Acid-generating capacity and yields of ore-related metal in mine waste and mill tailings 

from Frohner Meadows area and from two other mine sites.

10 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
Composite sample UFM 3 contained some fluvial mill 

tailings similar to the coarse-grained material in sample UFM 

2. It was collected in upper Frohner Meadows throughout the 

relatively large main mill tailings area upstream from UFM 

2 in (fig. 3, area A); tailings samples were collected from 

overbank material that had been transported down Frohner 

Meadows creek. The total dissolved metals (6,500 μg/L, 

dominated by zinc) placed this sample in class 3. This sample 

also produced the second-highest concentration of dissolved 

cadmium (73 μg/L).

Sample UFM 4, collected from the mill tailings debris 

fan on Nellie Grant creek (which drains the Nellie Grant mine 

area) on the west side of upper Frohner Meadows, produced 

a leachate having the lowest pH and highest specific conductance of all the samples. However, the amount of total 

dissolved metals was moderate (3,200 μg/L, dominated by 

zinc), and the net acid production was the second lowest. This 

material probably has a higher proportion of soluble salts and 

a lower concentration of pyrite than the others.

Sample LFM 1, taken from the fine-grained mill tailings 

in the delta of the pond in lower Frohner Meadows (fig. 3, area 

C), produced a leachate with the highest arsenic, cadmium, 

and zinc concentrations (900, 170, and 9,100 μg/L, respectively) of the samples from the study area. This material is 

probably a source of some of the solution-transported arsenic 

that enriches stream bed sediment downstream at site L–159 

(see below).

Meadow Deposits

Frohner Meadows is covered by thick vegetation, many 

shallow beaver ponds, and fine-grained pond-fill deposits that 

now are exposed in breached beaver ponds. Mill tailings have 

been impounded behind several beaver ponds, and many areas 

that contain a substantial thickness of mill tailings are obvious 

from their lack of vegetation. However, in other areas mill 

tailings may be covered by thick vegetation. In these areas, 

mill tailings commonly are concealed by thin, organic-rich 

soil and are difficult to identify. In some ponds where water 

levels have decreased owing to breaches in inactive beaver 

dams or low water flow, fine-grained pond-bottom deposits 

commonly are difficult to distinguish from transported finegrained mill tailings.

A reconnaissance coring program was undertaken 

throughout Frohner Meadows to determine (1) the stratigraphy 

of the meadow deposits including exposed tailings, (2) the 

extent, thickness, and chemical composition of buried mill 

tailings, and (3) the degree of subsurface metal migration 

after deposition. Twenty-seven cores were collected in upper 

Frohner Meadows and nine were collected in lower Frohner 

Meadows. Three cores were also taken in meadow deposits in 

a nearby valley, referred to informally as the “Panama mine 

meadows” (fig. 3). This area has no obvious significant mining 

or milling activity; it was sampled to help establish background concentrations for the study area and to determine the 

origin of the deposits filling an abandoned reservoir in Panama 

mine meadows. Cores were obtained July 16–19, 2001; core 

lengths were 33–133 cm. Sampling methods and data from 

these core samples are discussed in Klein, Thamke, and others 

(2003); geographic locations and other site data are presented 

in appendix 1a of that report, core descriptions and location 

of intervals sampled for chemistry are presented in appendix 

1b of that report, and the results of chemical analyses of 

the sampled intervals, obtained by use of the total-digestion 

method, are listed in table 7 of that report.

Premining Metal Concentrations in

Frohner Meadows

Frohner Meadows has been formed from fill material, 

some of which certainly is derived locally. Part of this mostly 

alluvial fill may have been derived from stream bed sediments 

that were shed by metal-bearing natural exposures of the 

Frohner–Nellie Grant vein system and by weakly mineralized 

rocks that typically surround these vein systems. This stream 

bed sediment likely would have contained higher concentrations of ore-related elements than stream bed sediment from 

sites in drainage basins that have been affected little (or not at 

all) by mining or by natural exposures of mineral deposits.

Establishment of local, premining concentrations of 

ore-related elements allows the determination of the degree 

to which postmining stream bed and pond-fill deposits are 

enriched in metals; such a baseline is necessary to establish 

baseline concentrations that are relevant to remediation 

goals. The area of concern in this study is the area drained 

by Frohner Meadows creek, the upper part of Lump Gulch 

Creek, and Panama mine meadows. To estimate premining 

concentrations, samples were selected from cored intervals 

that appeared to be geologically or geographically isolated 

from mining-derived deposits. These samples were chosen 

from areas that contain no physical signs of previous mining 

activity (Panama mine meadows) or from core intervals that 

are separated from overlying mine waste and mill tailings by 

thick clay layers. The samples used to define the premining 

metal concentrations in Frohner Meadows and their chemical 

analyses are tabulated in Klein, Thamke, and others (2003).

Cores from Frohner meadows contained clay-rich 

deposits and coarse clastic deposits. Clay-rich deposits formed 

during sedimentation that filled in shallow ponds and marshes. 

Sandy or coarse alluvium formed in stream channels or as 

overbank deposits along ancient stream channels. The postdepositional environment of these two types of deposits may 

differ geochemically because of their different physical and 

hydrological characters. In order to determine if background 

concentrations differ in these two environments, metal concentrations determined in clay-rich samples were compared 

statistically with those in coarse clastic deposits.

The population distribution of the metals arsenic, cadmium, copper, lead, and zinc were compared with calculated 

normal distribution curves. Zinc populations were normally 

distributed, but populations of the other four metals were 

not. The nonparametric Mann-Whitney U test was used to 

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 11
compare the metal populations in samples of these two deposit 

types (clay rich and coarse clastic). This test equally rigorously compares two normally distributed or two nonnormally 

distributed populations. The results of this test indicate that the 

metals concentrations of both groups were statistically similar 

(p <0.05) and can be combined to estimate premining concentration levels. A summary of the descriptive statistics for 

background samples from the two groups is shown in table 2.

Trace-element chemistry of stream bed sediment and 

other geologic materials was investigated in the nearby Boulder River watershed (Church and others, 2004). The Boulder 

River watershed lies immediately west of the upper Prickly 

Pear Creek watershed, which contains the Frohner Meadows 

study area. The Boulder River and Prickly Pear Creek watersheds have similar bedrock geology and glacial history, and 

they contain similar types of mineral deposits.

As part of the Boulder River watershed study, 16 sites 

were sampled to determine premining metal concentrations in 

stream bed sediment and terrace deposits downstream from 

areas that were mined or mineralized. Means and standard 

deviations of the Boulder River data are shown in table 2, as 

are similar data for core samples of meadow-fill deposits in 

Frohner Meadows. Concentrations of lead and zinc were substantially higher in premining samples from Frohner Meadows 

than in premining samples from the Boulder River watershed or 

mean global soil and sediment concentrations. However, arsenic and copper concentrations in premining samples from Frohner Meadows were similar to concentrations of those elements 

in the Boulder River watershed and were substantially higher 

than mean global soil and sediment concentrations. Premining 

samples from Frohner Meadows and Boulder River watershed 

contained, as shown by the Mann-Whitney U test, similar arsenic, cadmium, and copper concentrations but different lead and 

zinc concentrations (p <0.05). These results strongly suggest 

that locally derived premining metal concentrations should be 

used as baseline values for the Frohner Basin. Arsenic concentrations in these samples were high relative to global-mean 

sediment and soil concentrations but were similar to premining 

background concentrations in the Boulder River watershed, a 

relationship that suggests that both watersheds possess regional 

high background concentrations of arsenic.

Calculation of geochemical threshold concentrations is a 

technique commonly used in exploration geochemistry to identify anomalous samples. Geochemical threshold concentrations 

presented in table 2 were calculated from the cores by using the 

mean concentration of each metal plus two standard deviation 

concentrations, a widely accepted method (Rose and others, 

1979). These threshold values are used to identify sample intervals in Frohner Meadows cores that had metal concentrations 

likely to be truly anomalous (the core interval was enriched) 

and not merely in the upper range of normal values.

Postdepositional Metal Migration

Vertical chemical profiles were plotted for several cores 

to investigate the vertical variation in concentration of metals 

and related elements. From each core, six samples were taken 

between 5 and 85 cm depth and were analyzed to provide data 

for these plots. These plots reveal two types of profiles. The 

first is illustrated by a core from site 1–150 (fig. 6) in and the 

second is illustrated by a core from site 3–250 (fig. 7). These 

samples are located the western part of core line 1 (fig. 8) and 

the central part of core line 3 (fig. 9), respectively.

The upper part of the core from site 1–150 was a coarse 

mixture of oxidized fluvial mill tailings, unprocessed ore or 

mine waste, and transported colluvial granitic material (slope 

wash) that overlay a thin meadow soil of interfingered peat, 

silt, and fine tailings. The lower part of the core was an interval of interlayered alluvial deposits and transported granitic 

alluvial and colluvial deposits (fig. 10). The chemical profile 

of this core showed high concentrations of one group of metals (arsenic, copper, iron, and lead) in the upper two samples 

(mill tailings and mine waste); concentrations were lower 

and declined in the underlying transported colluvial material, 

meadow soil, and the mixed layer of transported colluvium 

and alluvium (fig. 6). The highest concentrations of this first 

Metal

Frohner 

Meadows 

premining 

concentration 

Frohner 

Meadows 

geochemical 

threshold 

concentration 

Boulder River 

watershed 

premining 

concentration 

Mean global 

sediment 

concentration 

Mean global 

soil

concentration 

Arsenic 58 (32) 122 58 (57) 8 6

Cadmium 2.2 (1) 4.2 <2 (-) 0.05 0.35

Copper 42 (21) 84 59 (32) 33 30

Lead 114 (86) 286 79 (55) 19 35

Zinc 232 (67) 366 159 (52) 95 90

Table 2. Means and standard deviations of ore related–metal concentrations in core samples used to define premining 

conditions in study area.

[All concentrations are total. Frohner Meadows geochemical threshold is premining concentration plus two standard deviations. Mean global sediment and soil concentrations are from Bowen (1979). Boulder River concentrations are from Church and others (2004). Cadmium concentrations 

below detection limit (2 ppm) in Frohner Meadows were assigned a concentration of 1 ppm for calculating the mean. All concentrations are in parts 

per million; standard deviations are in parentheses; <, less than; (-), below detection limit]

12  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
EXPLANATION

DEPTH, IN CENTEMETERS

PARTS PER MILLION OR WEIGHT PERCENT

wt %

s

Figure 6. Composite image and geochemical profile of core 1–150 showing relation between 

stratigraphy and chemistry. Depths not corrected for compaction. ppm, parts per million; wt %, weight 

percent.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 13
EXPLANATION

PARTS PER MILLION OR WEIGHT PERCENT

DEPTH, IN CENTEMETERS

wt %

Figure 7. Composite image and geochemical profile of core 3–250 showing relation between 

stratigraphy and chemistry. Depths not corrected for compaction. ppm, parts per million; wt %, weight 

percent.

14  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
N

v

Minimum extent of exposed mill tailings

111+

1-150

(111)

Sampled core site—Site number in black, thickness

of sampled enriched material in red, and depth

of bottom of enriched interval in parentheses

(depth and thickness in centimeters); +, bottom

of enriched interval not encountered

Core site (not sampled)

Stream bed sediment sample site

Pond

Stream

Dam

EXPLANATION

0 100 FEET

L-164

L-165

1-0

1-40

1-100

1-150

1-200 1-300

1-350

1-500

1-600 1-700

2-0

2-60

2-130

1-250

L-163

52+

35

111+

51

48

40

35

55

78+

9+

(102+)

(52)

(59)

(48)

1-400

57

(76)

(44)

(40)

(65) (86)

(26)

(111)

Figure 8. Upper mill-tailings area (fig. 3, area A, upper Frohner Meadows) showing thickness of metalenriched material and depth to bottom of enriched interval.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 15
3-0 3-100

UFM 1

3-200

3-250

3-300

3-390

4-0 4-100

L-166

250-75

250-200

134+

55+

38

56

112

84

63.5

107+

62+ 0

(38)

(56)

(125)

(84)

(131)

(73+)

(134+) (131+)

Approximate extent of Nellie Grant tailings debris fan

0 100 FEET

N

v

Minimum extent of exposed mill tailings

134+

3-0

(134+)

Sampled core site—Site number in black, thickness

of sampled enriched material in red, and depth

of bottom of enriched interval in parentheses

(depth and thickness in centimeters); +, bottom

of enriched interval not encountered

Core site (not sampled)

Stream bed sediment sample site

Pond

Stream

Dam

EXPLANATION

(82.5+)

Figure 9. Main mill tailings area (fig. 3, area B, upper Frohner Meadows) showing 

thickness of enriched material and depth to bottom of enriched interval.

16  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
group of metals (arsenic, copper, iron, and lead) were similar 

to concentrations of these metals in ore from the Frohner 

mine. Concentrations of a second group of metals (cadmium, 

manganese, and zinc) were lowest in the upper two samples; 

the concentrations of these metals generally increased with 

depth between 26.5 cm and approximately 64 cm. Cadmium, 

manganese, and zinc concentrations also were typically high 

in local unprocessed ore and mine waste and would, therefore, be expected to be high in mill tailings (as in fact was 

seen in bulk samples from the study area; Klein, Thamke, and 

others, 2003, table 6). However, the concentrations of these 

three metals generally were lower in the mill tailings in the 

upper part of this profile than in the underlying deposits. The 

difference in the profiles of these two groups of metals can 

be explained by their chemical behavior during weathering 

and by the mixing of ore-related material (mill tailings, ore, 

and mine waste) with eroded sediments that contain lower 

background concentrations of metals.

Geochemically, arsenic, iron, and lead are relatively 

immobile after weathering and oxidation of the sulfide ore 

minerals, and the abundance of these elements in the profile 

is related to their original concentrations in the mill tailings. 

Reduction in their concentrations can be attributed primarily 

to mixing with geologic material having lower concentrations 

of background metals. In contrast, cadmium and zinc are 

geochemically mobile in oxidizing environments; their concentrations are moderate at the top of this profile and increase 

with depth. This distribution probably reflects oxidation of 

sulfide minerals in mill tailings and mine waste, dissolution 

of cadmium and zinc in the upper parts of the profile during 

weathering and subsequent deposition, and their concentration at deeper levels by precipitation or sorption. The metals 

might be carried in downward percolating water or be laterally 

transported by water in permeable subsurface material. Copper 

shows relatively little change through the profile. Concentrations of all of these metals were markedly reduced in the slope 

wash (28 cm depth) probably because they were diluted by a 

large amount of transported granitic colluvium.

Contrasting geochemical behavior was shown in the core 

from site 3–250 near the middle of core line 3 (fig. 3). This 

core consisted of oxidized fluvial mill tailings that overlay 

a relatively thin layer of reduced, bedded, fine-grained mill 

tailings (fig. 7). These fine-grained mill tailings in turn overlay 

clay-rich, highly organic premining pond-fill deposits and 

fluvial deposits. The highest concentrations of arsenic, cadmium, copper, lead, and zinc were present in the reduced mill 

tailings (fig. 7). The later addition of fluvial material having 

only background concentrations of metals diluted the reduced 

mill tailings and produced lower concentrations of arsenic, 

cadmium, copper, lead, and zinc in the uppermost sample 

interval that generally contains high concentrations of these 

metals (Klein, Thamke, and others, 2003). Below the reduced 

mill tailings in sample 3–250, concentrations of all metals 

were substantially lower in the deep fluvial deposits, and there 

was no apparent postdepositional mobility of any metals, such 

as cadmium, copper, manganese, or zinc, as was observed in 

core 1–150 (fig. 6).

The contrasting behavior of cadmium, copper, and 

zinc at these two sites was probably due to the difference in 

oxidation-reduction characteristics as seen in the upper parts 

of the two cores. As shown by core 1–150, downward percolating or laterally flowing surface water is thought to have 

substantially oxidized the tailings during weathering and to 

have mobilized cadmium, copper, and zinc.

The solubility of the geochemically mobile metals (cadmium, copper, and zinc) is highest under oxidizing conditions, 

which promote their migration into underlying material. These 

effects of weathering are enhanced by the porous nature of the 

underlying material, which allows rapid percolation of surface 

water through the mill tailings, and by the position of the mill 

tailings well above the local ground water. As shown by core 

3–250, the upper parts of the deposits are mostly oxidized, 

fluvially transported, mixed mill tailings and mine waste. 

These materials probably had the same source as the deposits crossed by line 1 (fig. 3), as suggested by the abundance 

of coarse quartz chips. These quartz chips are mixed with 

a small amount of silty, reduced mill tailings that probably 

were locally derived. The similarity of profiles of the three 

mobile metals (cadmium, copper, and zinc) to those of the 

relatively immobile metals (arsenic and lead) suggests little 

postdepositional migration. The conditions in this area differ 

substantially from those at site 1–150. Shallow ground water 

in this area produces near-surface reducing conditions that do 

not promote the solubility of cadmium, copper, or zinc. Lowpermeability material underlying clay-rich pond fill and the 

organic-rich pond fill deposits also may form a physical and 

chemical barrier to metal migration.

Area A—Upper Frohner Meadows

Mill tailings are concentrated in two areas in upper 

Frohner Meadows: a debris fan of fluvial material and mill tailings where Frohner Meadows creek enters the meadow (area A, 

fig. 3) and a large impoundment behind a sinuous beaver dam 

in area B, directly east of the Nellie Grant mine area.

The debris fan and the part of the meadow that lies east of 

the fan were sampled along a longitudinal core line at intervals of 

40–100 ft (fig. 8). Sites and samples along this line are designated with the prefix “1.” Along the line 12 sites were cored; 8 

cores were chosen for chemical analysis (fig. 8), and from those 

8 cores, 31 intervals were sampled. Descriptions of the core 

samples and their geochemistry are contained in Klein, Thamke, 

and others (2003). A typical cross section is exposed in the bank 

of Frohner Meadows creek where it has cut through the western part of the debris fan (fig. 10). Mill tailings and associated 

coarse-grained quartz fragments overlie a thin layer of clay-rich, 

fine-grained mill tailings, which in turn overlie a sequence of 

fine- to medium-grained stream deposits and thin organic-rich 

clay layers that probably were formed in shallow ponds or wetlands. Klein, Thamke, and others (2003) reported total-digestion 

chemical analyses of sampled intervals in table 7 of that report.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 17
Figure 10. Trench showing cross section of mill-tailings debris fan along Frohner Meadows creek (fig. 3, area A, upper Frohner Meadows

units are labeled.
On the basis of those chemical analyses, core samples 

that exceeded the geochemical threshold (table 2) for any 

of the five metals are referred to in the following sections 

as “enriched” material. The mean minimum thickness of 

enriched material in the sampled cores taken along line 1 

was 64 cm; the greatest thickness was at site 1–150, where 

enriched material was greater than 111 cm thick (fig. 8). The 

thickness of enriched material was greater than that of actual 

mill tailings at many sites. Adjacent deposits that are not tailings likely were enriched as infiltrating surface water redistributed metals from the mill tailings during weathering. Thin 

soils (less than 8 cm thick) typically overlay these deposits. 

The stratigraphy of the cored material changes between sites 

1–250 and 1–300, where fine-grained mill tailings were 

deposited directly over clay-rich pond deposits rather than 

over alluvium; similar relations were observed in all cores 

taken east of that site. In several cores, several sequences 

of pond deposits were interlayered with medium- to coarsegrained alluvium. Enriched material at site 1–600 was 35 cm 

thick; no coarse-grained mill tailings were observed at sites 

1–600 or 1–700.

Core line 2 is located 300 ft downstream from line 1 (fig. 

3). Three sites were cored perpendicular to the long axis of the 

meadow, and nine intervals were sampled. Enriched intervals 

at sites 2–0 and 2–60 (fig. 8) were 55 and 78 cm thick, respectively, but the enriched layer thinned between site 2–60 and 

2–130 to only 9 cm. Enrichment at site 2–130 was marginal; 

zinc concentration was 380 ppm, only slightly higher than the 

enrichment threshold value of 340 ppm. Enriched intervals in 

this area directly overlay pond deposits at all sites. Soils were 

from 8 to 17 cm thick along this core line.

Because concentrations of ore-derived metals were highly 

variable within individual cores, the geochemical data in each 

core were vertically integrated by calculating a weighted 

average based on the thickness of the analyzed intervals. This 

weighted average allows comparison of the bulk compositions 

of enriched material among sites. Each sample was assumed 

to represent the composition of the entire stratigraphic unit in 

which it was found. The weighted-average concentration used 

to integrate the metal concentrations was calculated from the 

following equation:

Weighted-average concentration = 

∑ (thickness of sampled interval × metal concentration 

of interval) /

∑ thickness of sampled intervals

(1)

The weighted-average concentration calculated for the 

ore-derived metals from cores in area A (fig. 3) is shown in 

figure 11. In the following discussion, sampled intervals were 

considered slightly enriched if they contained 1–5 times the 

premining background concentration of each metal, moderately enriched if they contained >5 and ≤10 times the premining background concentration for each metal, and highly 

enriched if they contained >10 times the premining background value of each metal.

All cores in line 1, from 1–0 to 1–500 inclusive, and core 

2–0 showed high weighted-average concentrations of arsenic, cadmium, and lead. Weighted-average concentrations of 

zinc and copper were moderate. Samples from cores 1–600, 

2–60 and 2–130 were only slightly enriched in most metals 

or contained concentrations near the premining background 

concentrations, although sample 2–60 was highly enriched in 

cadmium. The lower weighted-average concentrations for all 

metals from samples at sites 1–600 and 2–130 are probably 

due to dilution by material having lower metal concentrations 

from sources east and north of the meadow.

Area B—Upper Frohner Meadows

In upper Frohner Meadows directly east of the Nellie 

Grant mine, a large volume of mill tailings is exposed (area B, 

fig. 3). Samples were taken along two core lines in this area 

of mill tailings; line 3 is perpendicular to the length of the 

meadow, and line 250 is located along a line with a bearing 

of N. 12° E. from sample site 250 on line 3, roughly parallel 

to the length of the meadow (fig. 9). Along line 3, six sites 

were sampled at 50–100 ft intervals, and two samples were 

taken along line 250, at 75 ft and 200 ft north of line 3. An 

additional sample site (UFM 1) lies southeast of site 3–0 near 

the toe of a debris fan at the outlet of Nellie Grant creek. The 

thickness of enriched material ranged from 33 to 88 cm; the 

mean was 62 cm. Mill tailings exposed in a shallow incised 

channel in the center of the meadow contain interlayered 

oxidized silt and fine sand-size mill tailings and coarse quartz 

chips (fig. 12), similar to the material observed along line 1 

(fig. 10). The character of the surface mill tailings changes 

from the middle of this area, where coarse-grained and finegrained tailings interfinger, to the margins of the meadow, 

where tailings are fine- and medium-grained well-sorted sand. 

Samples from sites 3–0, 3–100, and 3–300 (fig. 9) contained 

the greatest thickness of the metal-enriched material. Mill 

tailings at sites 3–100 and 3–200 were mostly silt and clay, 

whereas at sites UFM 1, 3–250, 3–300, 250–75, and 250–200 

sand-size mill tailings of various thicknesses overlay silt or 

clay tailings or mixed fine-grained mill tailings and pond 

sediment. Samples from site 3–390 did not contain identifiable 

mill tailings. Pond-fill sediment overlay the Mazama ash and 

coarse-grained alluvium at sites 3–200, 3–300, and 250–200.

The depositional history of the mill tailings here is complex. Frohner Meadows creek transported mill tailings from 

area A (fig. 3) to the main mill tailings deposits in area B and 

then deposited them in a natural pond behind a beaver dam. 

On the basis of features observed in cores UFM 1 and 3–0, we 

conclude that a second source of mill tailings probably was 

fine-grained mill tailings from the Nellie Grant mill that were 

released into Nellie Grant creek and entered the pond to form a 

delta. These fine-grained tailings also dispersed into the center 

of the meadow. Later, coarse-grained mill tailings, probably also 

from the Nellie Grant mill, were released and covered the earlier 

fine-grained mill tailings; later yet they were partially removed 

by erosion and dispersed into the center of the meadow.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment 19
L-164

L-165

L-163

1-0

35

As 4,720

Cd 14

Cu 255

Pb 8,010

Zn 1,080

1-40

52+

As 9,120

Cd 8.0

Cu 329

Pb 9,580

Zn 913

1-150

82

As 7,550

Cd 11

Cu 378

Pb 8,030

Zn 1,620

1-250

51

As 7,210

Cd 4

Cu 179

Pb 7,740

Zn 337

1-350

48

As 7,990

Cd 18

Cu 676

Pb 3,900

Zn 1,120

1-400

76

As 1,950

Cd 17

 Cu 197

Pb 1,970

Zn 1,200

1-500

40

As 3,600

Cd 39

Cu 535

Pb 3,490

Zn 5,570

1-600

35

As 400

Cd 6

Cu 180

Pb 950

Zn 690 

2-0

55

As 1,300

Cd 7

Cu 161

Pb 880

Zn 938

2-60

78

As 283

Cd 11

Cu 184

Zn 833

2-130

9+

Cd 5.0

Zn 380

N

v

0 100 FEET

Minimum extent of exposed mill tailings

9+

2-130

Cd 5.0

Zn 380

Sampled core site—Site number in black, thickness of

sampled enriched material in red, and weighted average

of metal concentrations for enriched interval (depth and

thickness in centimeters, concentrations in parts per million);

+, bottom of enriched interval not encountered

Core site (not sampled)

Stream bed sediment sample site

Pond

Stream

Dam

EXPLANATION

Figure 11. Upper mill-tailings area (fig. 3, area A, upper Frohner Meadows) showing thickness of enriched material 

and thickness-weighted averages of metal concentrations in enriched interval.

20 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
Two sites (4–0 and 4–100) that lie immediately below 

the main mill tailings impoundment (fig. 9) were sampled 

to determine the extent to which mill tailings had been 

transported downstream into the meadow and pond system. 

At site 4–0, an 11-cm-thick clay- and vegetation-rich layer 

overlay clay-rich pond deposits. These 14-cm-thick deposits 

were a mixture of silt- and clay-sized pond-fill deposits and 

transported clay or silt-size mill tailings. Fine-grained alluvial 

sand, older pond deposits, and Mazama ash underlie these 

pond-fill deposits and transported mill tailings. Enriched 

material, found only at site 4–0, is greater than 62 cm thick. 

The stratigraphy at site 4–100 is similar to that at site 4–0 

except that Mazama ash is not present.

The weighted-average concentrations of metals calculated 

for cores from area B are shown in figure 13. Mill tailings and 

underlying fine-grained, pond-fill deposits in all cores from 

sites 3–0 to 3–300 inclusive and from sites 250–75 and 250–

200 were highly enriched in cadmium. All sites were highly 

enriched in zinc, but zinc was highly variable; overall the 

weighted-average concentrations are about twice those of area 

A (fig. 11). Core material was variably enriched in arsenic and 

lead; arsenic and lead concentrations were much higher than 

geochemical threshold metal concentrations. Compared with 

the enrichment of material in cores from area A, material from 

cores in area B was enriched at most only by half and in some 

cores not at all (that is, it contained only background concentrations). The weighted-average concentrations of copper were 

higher than those concentrations in cores from area A but were 

only slightly above threshold concentrations. Weighted-average 

concentrations of all metals (except cadmium) in the silt- and 

clay-rich deposits in core 4–0 were lower than concentrations 

in samples from the mill tailings impoundment immediately 

upstream. Near-surface samples from core 4–100 were not 

chemically analyzed; the fine-grained sand that underlies the 

upper pond sequence showed no significant enrichment in any 

metal. The weighted-average concentrations of cadmium and 

zinc in UFM 1 were similar to those in other cores in area B. 

However, the weighted-average concentrations of arsenic and 

lead were much lower. This core sampled an artesian outflow 

zone. The artesian water is derived from Nellie Grant creek, 

and a metal-contaminated ground-water plume may have more 

greatly enriched the tailings sediments in zinc and cadmium 

than in lead and arsenic. This interpretation is supported by 

the high concentrations of zinc and cadmium that are found 

in surface water in Nellie Grant creek and in ground water in 

monitoring well MW–1 (fig. 14, table 3).

Figure 12. Mill tailings exposed along Frohner Meadows creek in main mill-tailings impoundment (fig. 3, area B, 

upper Frohner Meadows). Coarse quartz chips form a lag deposit overlying fine-grained oxidized mill tailings.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  21
Area C—Lower Frohner Meadows

Lower Frohner Meadows (area C, fig. 3) contains several 

water-filled abandoned beaver ponds and many dry ponds with 

breached dams (fig. 15). In most of the breached beaver ponds, 

streams are eroding the highly organic and clay-rich pond-fill 

deposits and incising stream channels. The ponds (both wet 

and dry) are separated by relatively dry meadowlands in the 

upper part of the meadow system and by wetlands in the lower 

part, near the meadow outlet. The most recent mining activity 

at the Nellie Grant mine created a small delta of mill tailings 

in the southwest corner of the uppermost pond (which is water 

filled) (Jack Yates, Montana Department of Environmental 

Quality, oral commun., 2001).

The minimum extent of the mill-tailings delta, as judged 

visually, is shown in figure 15. The delta was characterized by 

one 125-cm core at site LFMC 1. Enriched mill tailings of finesand-size material grades downward into clay-rich pond deposits; the tailings are approximately 40 cm thick. Fine-grained 

pyrite is abundant, and partially oxidized pyrite is present to 

about 30 cm depth. The mill tailings are water saturated and 

form a marshy area near the high-water level of the pond.

Core line 5 is about 300 ft downstream from the milltailings delta in a relatively flat dry meadow. Five cores, ranging 

in depth from 73 to 137 cm, were taken at 100 ft intervals along 

line 5. Pond-fill deposits 35 to 96 cm thick overlie Mazama ash, 

periglacial fluvial deposits, or moraine deposits in all cores.

Along core line 6, fine-grained pond-fill deposits in a 

breached beaver pond were sampled. The pond-fill deposits 

range from 19 to 61 cm thick and consist of fine-grained, 

highly organic clay and silt containing abundant woody debris. 

These deposits overlay medium- to fine-grained alluvial 

deposits and periglacial fluvial sediment.

Cores LFMC 1 and 6–0 contained the highest weightedaverage concentrations of metal in area C (fig. 16). Samples 

of mill tailings in LFMC 1, which probably derive from the 

Nellie Grant mine, contained weighted-average concentrations 

of metal similar to those in core 3–0 in area B (fig. 13). The 

enriched material consists of fine-grained mill tailings; some 

underlying clay-rich pond-fill deposits were highly enriched in 

cadmium and zinc and much less enriched in arsenic and lead, 

as is true also in Nellie Grant mine waste and mill tailings. 

Arsenic, cadmium, and zinc concentrations in core 6–0 were 

similar to those concentrations in LFMC 1, but core 6–0 had 

a much higher weighted-average concentration of lead. The 

source of this lead may be clastic grains of lead-rich minerals 

in mill tailings in upper Frohner Meadows, which typically 

contain abundant lead, transported by Frohner Meadows creek 

to lower Frohner Meadows, where mill tailings typically contain less lead. The most enriched material in the upper part of 

fine-grained pond-fill deposits in core 6–0 consisted of organic 

material only; fine-grained alluvium in the lower part (below 

31 cm) was not analyzed.

Sites 5–200 and 5–300 show moderate concentrations of 

ore-related metals in fine-grained pond-fill; the greatest thickness of enriched material is at site 5–300. The horizontal and 

vertical extent of contaminated material along line 5 was not 

adequately defined by sampling. Samples from sites 5–0 and 

5–400 were not analyzed, and at site 5–100, only alluvium lying 

below pond-fill deposits (below 113 cm) was analyzed; its metal 

content was below threshold concentrations (table 2).

As was shown in all core samples from lower Frohner 

Meadows, only the fine-grained upper part of the pond-fill 

deposits was enriched in metals. In some cases, the lower part 

of the fine-grained pond-fill deposits was uncontaminated. In 

all cases, the coarser grained alluvium underlying the finegrained pond deposits was uncontaminated, and this characteristic suggests that deposition of metal from ground water 

is not an important factor in metal accumulation in this area. 

Older buried alluvium was not enriched to a significant degree 

in ore-related metals.

Upper Lump Gulch

Frohner Meadows creek discharges into upper Lump 

Gulch in the southeastern part of the study area. A small 

meadow has formed in a sediment-filled reservoir in upper 

Lump Gulch about 700 ft below the outlet of Frohner Meadows creek (fig. 3). A water-diversion structure here is the 

source of water for Park Lake, which lies about 1 mi to the 

northeast. Stream bed–sediment and water samples taken in 

2000 during a watershed-characterization study identified 

material enriched in ore-related metals at the outlet of Frohner 

Meadows creek (Klein and others, 2001). Metal concentrations decline substantially through the stream reach below this 

reservoir in upper Lump Gulch.

Three cores (LGFR 1, 2, and 3) that ranged from 132 to 

190 cm in depth were taken to determine the mechanism that 

reduces metal concentrations in water and stream bed sediment below the outlet of Frohner Meadows creek. The upper 

20 cm of core LGFR 1 was dark red silt that appeared to be 

oxidized and fine-grained transported mill tailings (Klein, 

Thamke, and others, 2003). The lower part of all cores was 

interbedded thick pond-fill deposits and fine-grained alluvium 

that was as much as 157 cm thick. In cores LGFR 1 and 3, 

which extended deeper than LGFR 2, interbedded pond fill 

and fine-grained alluvium overlay very coarse, poorly sorted 

alluvium that probably was periglacial.

Because these cores were enriched only slightly in 

ore-related metals, and enriched material is vertically discontinuous, weighted-average concentrations of metals were not 

calculated. In LGFR 1, the upper 20 cm, which we interpreted 

to be fine-grained fluvial mill tailings, was highly enriched 

in cadmium and zinc and moderately enriched in arsenic and 

lead relative to the respective threshold concentrations of those 

metals. Near the bottom of this core, between 91 and 152 cm, 

medium- and coarse-grained alluvium that contained abundant grains coated with manganese oxyhydroxide was slightly 

enriched in cadmium and zinc. This interval was slightly 

enriched in arsenic; it contained about twice the premining 

threshold concentration. Clay-rich, highly organic pond-fill 

deposits enclosed this coarse-grained alluvium.

22  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
N

v

L-166

4-100

0

UFM 1

55+

As 837

Cd 33

Cu 150

Pb 972

Zn 3,100 

3-0

134+

As 1,470

Cd 36

Cu 162

Pb 1,830

Zn 2,550

3-100

107+

As 1,790

Cd 78

 Cu 441 

Pb 3,170

Zn 5,030

3-200

63.5

As 3,410

Cd 20

 Cu 343

Pb 3,360

Zn 2,420

250-200

38

As 3,920

Cd 16

Cu 413

Pb 3,770

Zn 1,330

3-250

84

As 4,090

Cd 25

Cu 456

Pb 5,280

Zn 2,370

3-300

116

As 2,435

Cd 24

Cu 357

Pb 3,590

Zn 2,290

250-75

56

As 5,420

Cd 31

Cu 548

Pb 5,470

Zn 2,370

4-0

62+

As 671

Cd 39

Cu 387

Pb 691

Zn 1,410

0 100 FEET

Approximate extent of Nellie Grant tailings debris fan

Minimum extent of exposed mill tailings

116

3-300

Sampled core site—Site number in black, thickness of

sampled enriched material in red, and weighted

average of metal concentrations for enriched interval

(depth and thickness in centimeters, concentration in

parts per million); +, bottom of enriched interval not

encountered

Core site (not sampled)

Stream bed sediment sample site

Pond

Stream

Dam

EXPLANATION

As 2,435

Cd 24

Cu 357

Pb 3,590

Zn 2,290

Figure 13. Main mill tailings area (fig. 3, area B, upper Frohner Meadows) showing 

thickness of enriched material and thickness-weighted averages of metal concentrations in 

enriched interval.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  23
Figure 14. Location of monitoring wells, seismic lines, and surface-water sampling sites in and near Frohner Meadows.

112°11'40'' 112°11'20''

46°26'20''

46°26'30''

46°26'10''

Frohner Meadows cr.

Nellie Grant cr.

00 500 1,000 1,5

250 

112°12'20'' 112°12'00''

 Lump Gulch Roa

Nellie Grant mine

Nellie Grant mill site

Frohner mine

Frohnermill site

Lower Frohner 

Meadows

Upper Frohner

Meadows Reclaimed tailings

 pond

Frohner Meadows cr.

A D

C

FM-5

FM-3

FM-6

FM-2

FM-1

FM-4

FM-7

FM-8

FM-9

MW-1

MW-2

FM-10

B

E

F

G

H

I

J

L-3b

L-3a

Area C

Area B

Area A

FM-5

Dam

Pond, dry pond, or

sediment-filled pond

Road

Stream

Approximate outline of

meadow areas

Minimum extent of

exposed mill tailings

Mine site

Mill site

Surface water site

Seismic line

Monitoring well site

Area boundary

EXPLANATION
Table 3. Concentrations and instantaneous loads of total recoverable trace metals in Frohner Meadows area.

[<, less than; μg/L, micrograms per liter; cfs, cubic feet per second; E, in a cell, estimated; g/day, grams per day; Load (grams per day) = discharge (cubic feet/second) × concentr

Arsenic Cadmium Copper Lead 

Site ID Site

name 

Date Time

Instantaneous 

discharge 

(cfs)

Total 

recoverable 

(μg/L)

Load

(g/day)

Total 

recoverable 

(μg/L)

Load 

(g/day) 

Total 

recoverable 

(μg/L)

Load

(g/day)

Total 

recoverable 

(μg/L)

Lo

(g/d

462638112114201 A 6/25/2001 1255 0.0353 E1 E0.09 E0.03 E0.002 3.2 0.28 <1 <0.09 

8/1/2001 945 0.00353 2 0.02 E0.03 E0.0002 2.2 0.02 <1 <0.00

462636112113801 B 6/25/2001 1340 0.00353 <2 <0.02 0.07 0.001 3.0 0.03 <1 <0.00462637112114401 D 6/26/2001 910 0.0162 3 0.12 0.05 0.002 4.1 0.16 2 0.07

8/1/2001 1020 0.027 9 0.59 0.07 0.005 3.3 0.22 3 0.19

462637112114101 E 6/26/2001 945 0.2066 16 8.09 0.12 0.061 5.1 2.58 4 2.02 

8/1/2001 1050 0.0247 55 3.32 0.13 0.008 5.0 0.30 12 0.72

462635112114401 F 6/26/2001 1005 0.6048 17 25.2 1.40 2.07 7.3 10.8 9 13.3 

8/1/2001 1135 0.138 25 8.44 2.49 0.84 8.0 2.70 11 3.71 

462627112114701 G 6/26/2001 1040 0.063 208 32.1 121 18.7 83.9 12.9 72 11.1 

8/1/2001 1240 0.006 45 0.66 94.0 1.38 15.9 0.23 13 0.19

462626112114301 H 6/26/2001 1115 0.76 39 72.5 7.16 13.3 8.0 14.9 10 18.6 

8/1/2001 1205 0.203 81 40.2 6.23 3.09 8.0 3.97 15 7.45 

10/16/2001 1105 0.09 52 11.5 7.92 1.74 6.4 1.41 9 1.98 

462619112114001 I 6/26/2001 1200 0.86 38 80.0 6.94 14.6 8.9 18.7 8 16.8 

8/1/2001 1350 0.212 71 36.8 6.00 3.11 7.7 3.99 13 6.74 

10/16/2001 1140 0.15 23 8.44 8.96 3.29 5.4 1.98 4 1.47 

462613112114401 C 6/25/2001 1540 0.0671 E1 E0.16 E.03 E0.005 3.0 0.49 <1 <0.16 

8/1/2001 1420 0.01 4 0.10 .06 0.001 2.8 0.07 3 0.07

462612112113001 J 6/26/2001 1300 0.91 34 75.7 6.89 15.3 8.4 18.7 10 22.3 

8/1/2001 1500 0.311 64 48.7 5.66 4.31 7.6 5.78 42 32.0 

462603112112101 L-3a 6/16/2000 1415 0.62 6 9.10 6.31 9.57 7.4 11.2 2 3.03 

10/11/2000 1345 0.0003 10 0.01 9.76 0.01 2.7 <0.001 <1 <0.00

5/10/2001 1100 0.26 7 4.45 6.67 4.24 7.3 4.64 2 1.27 

8/1/2001 1130 0.004 11 0.11 5.21 0.05 6.9 0.07 2 0.02

462612112111501 L-3b 6/16/2000 1445 1.17 15 42.9 13.1 37.5 11.0 31.5 8 22.9 

10/11/2000 1630 0.11 6 1.61 47.1 12.7 5.8 1.56 4 1.08 

3/15/2001 1130 0.06 17 2.50 15.6 2.29 10.3 1.51 9 1.32 5/10/2001 1120 0.78 14 26.7 13.1 25.0 11.4 21.8 7 13.4 

8/1/2001 0950 0.233 33 18.8 4.99 2.84 6.5 3.71 8 4.56 
Figure 15. Lower Frohner Meadows (fig. 3, area C) showing thickness of enriched material and depth to 

bottom of enriched interval. 

5-0

5-400

L-159 LFMC 1

96

(99)

5-300

56

(74)

5-200

14

(35)

5-100

0

(0)

6-100

0

(0)

6-0

31

(31)

6-50

31

(62)

N

v

0 100 FEET

Minimum extent of Nellie Grant tailings delta

14

5-200

(35)

Sampled core site—Site number in black,

thickness of sampled enriched material

in red, and depth of bottom of enriched

interval in parentheses (depth and

thickness in centimeters).

Core site (not sampled)

Stream bed sediment sample site

Pond

Dam

Road

EXPLANATION

26  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
L-159

5-100

0

6-0

31

LFMC 1

96

As 2,290

Cd 50

Cu 239

Pb 1,790

Zn 5,200

5-200

14

As 369

Cd 9.0

Cu 97

Pb 240

Zn 2,400

5-300

96.5

As 258

Cd 19

Cu 379

Pb 999

Zn 1,700

As 2,180

Cd 59

Cu 932

Pb 3,600

Zn 2,530

6-50

32

Cd 11

Zn 1,200 6-100

5-0

0

N

v

0 100 FEET

Minimum extent of exposed mill tailings

32

6-50

Cd 11

Zn 1,200

Sampled core site—Site number in black,

thickness of sampled enriched material

in red, and weighted average of metal 

concentrations for enriched interval

(depth and thickness in centimeters,

concentration in parts per million).

Core site (not sampled)

Stream bed sediment sample site

Pond

EXPLANATION

Dam

Road

Figure 16. Lower Frohner Meadows (fig. 3, area C) showing thickness of enriched material and thicknessweighted averages of metal concentrations in enriched interval.

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  27
Near the surface in core LGFR 2, medium-grained 

alluvium was slightly enriched in arsenic, cadmium, and zinc 

relative to the local geochemical threshold concentration 

(table 2). Near the bottom of the core, interbedded fine sand 

and clay that lay beneath clay-rich pond fill also were slightly 

enriched in cadmium and zinc. In the upper part of core LGFR 

3 coarse-grained alluvium was slightly enriched in cadmium 

and zinc, whereas coarse-grained alluvium in the bottom 30 

cm was slightly enriched in arsenic and lead.

In cores LGFR 1 and 2, buried, permeable, medium- and 

coarse-grained alluvium enriched in cadmium and zinc suggests that these metals may be accumulating in the subsurface 

from metal-enriched ground water. The two deepest samples 

taken from LGFR 1 and the deepest sample taken from LGFR 

2 were below clay layers that may restrict ground-water flow 

into the underlying, more permeable, coarse-grained alluvial 

layers. The most likely source of metal is the highly contaminated surface water that leaves Frohner Meadows near site 

L–3b (fig. 3), immediately upstream from this reservoir site. 

The uppermost samples of these two cores were enriched in 

all ore-related metals, perhaps owing to transport of grains that 

contain arsenic and lead minerals and to solution transport of 

cadmium and zinc by the most recent alluvial material filling 

the reservoir. Coatings of iron and manganese oxyhydroxides 

on stream-transported sediments may themselves be enriched 

in zinc and cadmium and thus contribute zinc and cadmium to 

shallow deposits.

Site LGFR 3 lies along a tributary of the south fork 

of upper Lump Gulch Creek that drains Frohner Meadows 

through site L–150. The near-surface parts of this core were 

slightly enriched in cadmium and zinc, probably because 

surface water that leaves Frohner Meadows upstream from 

L–150 is enriched in cadmium and zinc. The two deepest 

samples in LGFR 3 were slightly enriched in arsenic and 

lead. Arsenic may be transported in ground water under 

reducing conditions, as is noted in some ground-water 

monitoring wells in upper Frohner Meadows, but lead (which 

has a very low solubility in water under all natural conditions) can be transported in significant concentrations only as 

clastic material. Therefore, this enriched material probably 

contains arsenic- and lead-bearing minerals transported early 

in the history of this reservoir, a time that predated the pondfilling sedimentation, which in turn predated construction of 

the impoundment and diversion structure.

Panama Mine Meadows

A large, abandoned, sediment-filled reservoir that lies 

about 1 mi southwest of lower Frohner Meadows was sampled 

to determine the origin of its fill material. The reservoir 

consists of a series of dry and water-filled beaver ponds and 

intervening meadows that have developed behind a breached 

diversion dam (fig. 3). Three cores (PMC 1, 2, and 3), ranging 

in depth from 58 to 80 cm, showed that the deposits that fill 

the reservoir were interbedded pond-fill deposits and medium 

to coarse alluvial sand and gravel consisting largely of granite 

pebbles (Klein, Cannon, and Fey, 2003, appendix 1). These 

coarse clastic deposits are derived locally from the surrounding granitic rocks of the Boulder batholith.

In core PMC 3, one clay-rich pond-fill interval was 

slightly enriched in arsenic and lead relative to premining 

concentrations (Klein, Thamke, and others, 2003). The source 

of the metals and the extent of the enrichment are unknown. 

Background concentrations of metals in water and stream bed 

sediment at site L–1 (fig. 3) (Klein and others, 2001) suggest 

that the active stream system is not the source of this lead 

and arsenic. Samples from PMC 1 showed no unusual metal 

accumulations.

Thickness-Weighted Average Concentrations of 

Ore-Related Metal in Core Samples

For all enriched intervals in cores in each of the three 

areas (A, B, and C in fig. 3), thickness-weighted average concentrations of the five ore-related metals were calculated; the 

calculated concentrations allow comparison of bulk chemistry 

among areas containing enriched material. Materials present in 

different parts of the meadow system and that contain various 

bulk-metal concentrations (table 4) can be compared in terms 

of their potential for contributing metals to ground water, 

surface water, and stream bed sediment. These calculated 

concentrations also serve as an estimate of the metal’s bulk 

concentration in contaminated material. This information may 

be useful during any remediation efforts.

Cores from area A contained the highest bulk concentrations of arsenic and lead, whereas cores from areas B and 

C were highest in cadmium and zinc. This relationship is 

similar to that observed in bulk surface samples of mine and 

mill tailings from the same areas. These average arsenic, 

lead, and cadmium concentrations in cores from areas A, B, 

and C greatly exceeded the geochemical threshold concentrations for each metal (table 2) and showed that sediment 

deposits in the cored areas were highly enriched in these 

metals. In upper Lump Gulch, enriched clastic material in 

cores from the filled reservoir contained weighted-average metal concentrations of arsenic, copper, and lead near 

or below their geochemical threshold concentrations, but 

concentrations of cadmium and zinc were about twice their 

threshold concentrations.

Stream Bed Sediment

Stream bed sediments were sampled to locate stream 

reaches that are enriched in metals owing to natural or human 

causes. Concentrations of chemical elements in stream bed 

sediment present a time-integrated view of chemical input 

from two sources: erosion of underlying bedrock and glacial 

debris upstream from the sample site and erosion of natural 

or cultural point sources such as outcrops of ore deposits or 

mines and mills (either active or abandoned). Downstream 

from natural outcrops of base- and precious-metal deposits 

28  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
and below mine and mill sites, sediment deposits such as 

those in the Frohner Meadows area typically are enriched in 

ore-related trace metals (arsenic, cadmium, copper, lead, and 

zinc). Ore-related metals accumulate in stream bed sediment 

either as detrital grains of the original ore minerals or host 

rock or as secondary minerals formed during weathering of 

ore minerals. The bulk of the secondary minerals is composed of colloidal iron and manganese oxyhydroxides, which 

generally accumulate as coatings on sediment grains. These 

coatings are relatively unstable; they are easily eroded and 

transported during periods of increased stream discharge, are 

easily dissolved by a decrease in oxidation-potential of stream 

water, and may be leached from grain coatings by a decrease 

in the pH of stream water. Other physical variables, such 

as stream velocity, changes in stream gradient, and shallow 

ground-water contributions also can affect the amount of metal 

in stream bed sediment.

The biogeochemical effects of high metal concentrations 

in stream bed sediment on the ecosystem and surface-water 

chemistry are complex. In terms of the local ecosystem, metals 

in stream bed sediment promote the accumulation of metals 

in benthic fauna, which feed on and live in stream bed sediment (MacDonald and others, 2000). Benthic fauna in turn 

is a major food source for many freshwater fish, and metals 

accumulated in benthic fauna may be transferred to fish (Farag 

and others, 2004). The effects on water chemistry of metals 

in stream bed sediment are more complex. The silicate and 

oxide mineral grains that make up most of the stream bed 

sediment are relatively resistant to weathering and release only 

small amounts of metals during a long period of weathering 

(Church and others, 1993). Thus, high concentrations of metals in silicate and oxide grains likely have little effect on water 

chemistry. However, metals found in iron and manganese oxyhydroxide grain coatings can markedly affect water chemistry, 

because relatively large releases of metals into water may be 

induced by relatively small changes in water chemistry, such 

as oxidation potential and pH, or flow conditions during a 

short time period (Horowitz, 1991).

Regional Background-Metal Concentrations in 

Stream Bed Sediment

Regional background-metal concentrations in stream bed 

sediment were determined for the upper Prickly Pear Creek 

watershed (fig. 1 of this report) (Klein and others, 2001). 

Background concentrations of arsenic, cadmium, copper, lead, 

and zinc were determined on samples from sites in streams 

that drain areas having little or no mining history and that are 

underlain by unmineralized granitic bedrock typical of much 

of the watershed. The measured background concentrations 

(determined by total digestion) are much higher than their 

respective mean crustal abundances in granitic rocks. These 

elevated background concentrations may, in part, result from 

the same regional hydrothermal alteration that produced many 

base- and precious-metal deposits in the heavily mineralized northern part of the Boulder batholith. These regionalbackground concentrations in the upper Prickly Pear Creek 

watershed were used to evaluate the degree to which stream 

bed–sediment samples from Frohner Meadows are enriched in 

ore-related metals.

Stream Bed–Sediment Consensus-Based 

Probable-Effect Concentrations 

The health of aquatic organisms is one measure of the 

biological effect of metal contamination in a stream reach. The 

minimum concentrations at which various metals in stream 

bed sediment harm the health of aquatic organisms have not 

been firmly established. Because the mechanisms of metal 

uptake and the effects of metals on an organism’s health are 

poorly understood, no standard has yet been adopted by any 

major environmental agency. Currently, the best alternative to 

such standards is called the “consensus-based probable-effect 

concentration” (CBPEC). These values are based on the protective concentrations of metals as determined by a consensus 

among several methods (MacDonald and others, 2000). A 

CBPEC identifies the contaminant concentration above which 

sediment-dwelling organisms commonly are harmed. CBPEC 

values were derived from the geometric-mean concentration of 

selected published effects-based sediment-quality guidelines. 

The total analysis method of sediment analysis was used to 

establish the CBPEC. These concentrations then were evaluated for reliability by pairing sediment chemistry data with 

toxicity data. The CBPEC values (MacDonald and others, 

2000) are used in this report to relate metal concentrations 

in the stream bed sediment in Frohner Meadows to concentrations of metals that may produce toxic effects on aquatic 

organisms.

Location Arsenic Cadmium Copper Lead Zinc 

Area A—Upper Frohner Meadows 3,520 12 268 3,520 1,190

Area B—Upper Frohner Meadows 1,980 36 293 2,650 2,860

Area C—Lower Frohner Meadows 277 11 189 595 863

Lower Frohner Meadows mill tailings (LFMC 1) 2,290 50 239 1,790 5,200

Upper Lump Gulch filled reservoir 109 9 66 156 648

Table 4. Weighted-average concentration of contaminated material in core samples, by area.

[All concentrations in parts per million]

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  29
Metal Concentrations in Frohner Meadows 

Compared with Background Concentrations

and CBPEC Standards

Stream bed sediment from Frohner Meadows and from 

the upper Prickly Pear Creek watershed was analyzed by total 

digestion and dilute-acid partial digestion of ore-related metals (Klein, Thamke, and others, 2003). Sediment in Frohner 

Meadows creek is highly enriched in ore-related metals as 

compared with median background concentrations in the 

upper Prickly Pear Creek watershed (table 5). On the basis of 

total digestions and dilute-acid partial digestions, metal concentrations at all of the stream bed–sediment sites in stream 

reaches below the mine and mill areas were determined to be 

8–100 times the watershed median-background concentrations 

for arsenic, cadmium, lead, and zinc. Similarly, the median 

copper concentration in the watershed area was determined to 

be 7 times the median-background concentrations produced by 

dilute-acid partial digestion and 4 times the concentration produced by total digestion. Frohner Meadows creek is similarly 

enriched in comparison with the mean crustal abundance of 

these elements in granitic rocks (table 5). These data illustrate 

that Frohner Meadows creek is enriched in ore-related metals 

relative to their mean crustal abundance and to regional background concentrations.

Comparison of the same data (table 5) with CBPEC 

concentrations (table 6) shows that in Frohner Meadows creek 

median concentrations (determined by total digestion and 

dilute-acid partial digestions) exceed the CBPEC concentrations 

for arsenic, cadmium, lead, and zinc by 5 to nearly 30 times. 

Concentrations of these ore-related metals in this creek at these 

sites—downstream from the mine and mill areas—far exceed 

any stream bed–sediment standard value that attempts to define 

aquatic health. Median copper concentrations in Frohner Meadows creek are similar to the CBPEC for copper, which suggests 

that copper concentrations are a lesser threat to aquatic health in 

Frohner Meadows than are the other ore-related metals.

Downstream-Concentration Plots of

Ore-Related Metals

A type of plot called a downstream-concentration plot 

aids identification of the sources of ore-related metals and 

the interpretation of downstream changes in metal concentrations. In these plots, the measured concentration at a site and 

a constant rate of change in concentration between adjacent 

sites are illustrated with a connecting line. These plots provide 

a graphical tool by which changes in metal concentration can 

be evaluated in terms of sources and chemical and physical 

processes. Concentrations of metals derived from dilute-acid 

partial-digestion analyses were used to construct the plots 

because the metals liberated by dilute-acid digestion are more 

readily available to stream water and to aquatic organisms. 

The chemical analyses of samples treated by this method are 

given in table 8 of Klein, Thamke, and others (2003).

Sites L–152 through 155, L–4, and L–4a are outside the 

study area and lie downstream, in that order, from site L–156 

in upper Lump Gulch (fig. 3). These sites were included in 

the downstream plots to illustrate the downstream effect of 

Frohner Meadows on stream bed sediment in upper Lump 

Gulch. Data for those sites are summarized in Klein, Cannon, 

and Fey (2003).

Changes in dilute-acid partial-digestion concentrations 

of arsenic, cadmium, copper, lead, and zinc in stream bed 

sediment as a function of distance downstream are shown in 

figures 17–22. In each figure, an element’s concentration is 

represented on the vertical axis, and the downstream distance 

is represented on the horizontal axis. Downstream distances 

were measured from an arbitrary starting point; to the left of 

the figure is upstream and to the right is downstream. In each 

plot, a green solid line connects metal-concentration data for 

sites along Frohner Meadows creek, beginning above site L–2 

and continuing downstream through upper and lower Frohner 

Meadows to site L–3b. Lump Gulch begins at site L–158, 

which lies upstream from a small, sediment-filled reservoir. 

Site L–l56 (fig. 3) is at the junction of the tributaries that drain 

the Panama mine meadows (fig. 3) and Frohner Meadows. 

Below this reservoir, the stream in Lump Gulch flows from 

site L–156 to L–4 and beyond. A solid yellow line connects 

metal concentration data for stream bed sediment from the 

Panama mine tributary. A dashed green line connects lower 

Frohner Meadows with the Panama mine meadows tributary. 

Water from lower Frohner Meadows flows from the meadow 

primarily in a channel at the eastern end at site L–3b, as well 

as through a second channel that emerges from the meadow’s 

southern edge and connects with the Panama mine tributary. 

The Panama mine tributary mostly is unaffected by contaminated sediment and appears to dilute the concentrations of orerelated metals in sediment in Frohner Meadows creek below 

their convergence near site L–156.

Arsenic

The dilute-acid partial-digestion arsenic concentration (10 

ppm) above the Frohner mine (site L–2, fig. 17) was near the 

background concentration of 6.6 ppm (table 5). The next site 

downstream, L–162, is just below the historical Frohner mill 

site, where a large volume of crushed-ore material is present 

at the surface and in an old ore bin. Erosion has distributed the 

crushed ore down the relatively steep slope into Frohner Meadows creek. The arsenic concentration in stream bed sediment 

here was higher than 2,000 ppm. Downstream through upper 

and lower Frohner Meadows, arsenic concentrations remained 

variably high relative to the upstream samples. A general trend 

toward lower concentrations downstream between sites L–165 

and L–161 probably reflects dilution by sediment containing 

a lower arsenic concentration. The small increase in arsenic 

concentration in the upstream site (L–159) in lower Frohner 

Meadows probably was due to the addition of arsenic-enriched 

material from mill tailings situated at the western end of the 

lower meadow near bulk sample site LFM–1 (fig. 3).

30 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
At site L–158, the concentration of arsenic sharply 

increases. Manganese and iron concentrations also increase 

markedly, perhaps because those metals, which are dissolved 

in spring water in Frohner Meadows, oxidize and precipitate 

out as spring water enters the creek (between sites L–3b and 

L–158). The increase in arsenic concentration may be linked 

to oxidation of arsenic-rich ground water in lower Frohner 

Meadows. However, the extremely high lead concentration at 

this site (see subsequent section) is evidence against its transport in solution and suggests that lead is transported by detrital 

processes. Arsenic concentration decreases substantially 

between site L–158, just above the sediment-filled reservoir 

in upper Lump Gulch, and the reservoir outlet (site L–156). 

On the basis of field observations such as flood-plain width, 

it is likely that the Panama mine tributary contributes far 

more detrital material to the filled reservoir than does Frohner 

Meadows creek. Field observation above site L–3b suggests 

that little coarse detrital material leaves lower Frohner Meadows because of its numerous dams, ponds, and wetlands. Very 

low arsenic concentrations at sites L–151 and L–157 confirmed that stream bed sediment from the Panama mine tributary likely is not contaminated. The tie line between L–157 

and L–156 (fig. 17) illustrates that stream bed sediment having 

low arsenic concentration from the Panama mine tributary 

dilutes the arsenic concentration in typical Frohner Meadows 

creek concentrations below the junction of these streams.

Cadmium

As with arsenic, the cadmium concentration at site L–2 is 

quite low and equals the median for background sites (figure 

18, table 5). The concentration rises to 16 ppm below the 

Frohner mill site (L–162). Tailings from the mill site were 

not particularly high in cadmium; samples from sites FMB–1 

and 2 contained 9 and 4 ppm, respectively (table 6 of Klein, 

Thamke, and others (2003)), so the mill tailings probably 

contribute little cadmium to the stream bed sediment. However, the cadmium concentration in samples from site L–100 

increased substantially to 46 ppm. Cadmium is quite soluble 

and mobile at the nearly neutral pH of the stream waters 

found throughout Frohner Meadows and, as a result, can be 

transported in solution as well as in detrital mineral grains. 

It also can be removed from solution by sorption on iron or 

manganese oxyhydroxides (Horowitz, 1991). This study found 

strong correlations between dilute-acid partial-digestion concentrations of iron and cadmium in stream bed sediment and 

similarly derived concentrations of manganese and cadmium. 

The r2 (correlation coefficient) for iron and cadmium is 0.85, 

and the r2 for manganese and cadmium is 0.71. The diluteacid partial-digestion concentrations of iron and manganese in 

samples from core L–100 were high—23,000 and 16,000 ppm, 

respectively (table 8 of Klein, Thamke, and others, 2003; fig. 

18, this report). Thus, the large amount of iron and manganese 

oxyhydroxide that coats stream bed sediment at that site may 

scavenge cadmium from the dissolved phase and produce sediment concentrations of cadmium that are much higher than 

those in core L–162. This process—the scavenging, by iron 

Table 5. Median trace metal concentrations of regional-background stream bed–sediment samples in upper Prickly Pear Creek 

watershed (Klein and others, 2001, table 2) and median concentrations in stream bed sediments in Frohner Meadows study area.

[Mean crustal abundances for granitic rocks are total analyses and are from Rose and others (1979). All concentrations in parts per million. Conc., concentration; 

(s.d.), standard deviation; n, number of samples]

Table 6. Summary of consensusbased probable-effect concentrations of 

ore-related metals in stream bed sediment 

(MacDonald and others, 2000).

[CBPEC, consensus-based probable-effect 

concentration; ppm, parts per million]

Metal

Dilute-acid partial digestion Total digestion Mean crustal 

abundance in 

Prickly Pear Creek Frohner Meadows creek Prickly Pear Creek Frohner Meadows creek granitic rocks

Conc. (s.d.) n Conc. (s.d.) n Conc. (s.d.) n Conc. (s.d.) n

Arsenic 6.6 (4.8) 6 720 (711) 18 14 (5) 15 950 (1,196) 18 2

Cadmium 1 (0.3) 6 25 (21) 18 4 (1) 16 33 (27) 18 0.1

Copper 15 (8) 6 115 (59) 18 42 (24) 33 170 (92) 18 12

Lead 12 (7) 6 770 (1,110) 18 25 (9) 30 1,250 (1,620) 18 18

Zinc 80 (33) 6 2,000 (1,420) 18 96 (31) 15 2,500 (1,840) 18 51

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  31

Element CBPEC

Arsenic 33

Cadmium 4.98

Copper 149

Lead 128

Zinc 459

(ppm)
and manganese oxyhydroxides in stream bed sediment, of cadmium dissolved in contaminated surface water—probably is 

responsible for the high concentrations of cadmium in stream 

bed sediment at many sites in the study area.

The concentration of cadmium in stream bed sediment 

decreased overall downstream from site L–100 to site L–164 

(fig. 18), probably from dilution by unenriched stream bed 

sediment. Then, from site L–165 in upper Frohner Meadows, 

concentrations increased downstream through the eastern end 

of lower Frohner Meadows site L–3b.

Cadmium also is transported out the south outlet of 

lower Frohner Meadows, as we infer from the high concentration (40 ppm) in samples from site L–150. Stream bed sediment from the Panama meadows tributary diluted the south 

outlet sediment as seen at site L–157, where the cadmium 

concentration dropped to 3 ppm. However, the cadmium dilution in samples from site L–156 was not as marked as that for 

arsenic, probably because dissolved cadmium continues to 

be transported out of Frohner Meadows and deposited onto 

iron and manganese oxyhydroxide grain coatings, even during 

low-flow conditions when clastic transport is minimal. This 

process is relatively independent of the effects of dilution by 

clastic sediments.

The downstream-concentration plot of iron and manganese (fig. 19) shows that the overall patterns of both metals 

are similar to that of cadmium. This similarity supports the 

hypothesis that dissolved cadmium accumulates in sediment 

by sorption on iron and manganese oxyhydroxide grain coatings. The highest concentrations of iron and manganese are 

at site L–158. Most concentrations of ore-related metal below 

this site decrease sharply, a trend that suggests that some of the 

transported metals (cadmium and zinc) may be removed from 

the streamwater by sorption on manganese and iron grain coatings near this site. Similar effects also may occur in the lower 

part of lower Frohner Meadows above site L–3b.

Concentrations of dissolved arsenic, cadmium, and zinc 

in streamwater varied widely in different seasons at site L–3b. 

In addition, the concentrations of these constituents varied 

widely in stream bed sediments collected in October 2000 and 

July 2001. These large variations may be responses to temporal changes in water chemistry related to solubility reactions 

between surface water and iron and between manganese oxyhydroxide grain coatings on stream bed sediments and surficial 

deposits in this marshy area. Alternatively, some of the variation may be related to sample variation. At site L–3b, which 

is at the outlet of lower Frohner Meadows, and at site L–100, 

we collected a sample in October 2000 and in July 2001. In 

both samples, sediment concentrations of all ore-related trace 

metals were lower in 2001 than in 2000. However, the major 

elements aluminum, calcium, potassium, and sodium, which 

were all higher in 2001, indicate that the sample had a higher 

proportion of lithic material (decomposed, plutonic rock-forming minerals) that diluted the ore-related trace metals. The iron 

and manganese concentrations in the 2001 samples were lower 

than they were in 2000 (58 percent and 33 percent at L–3b, 

respectively). The lower concentrations of these scavenger 

elements generally reduced the concentrations of the other elements. Whether the lower concentrations of iron and manganese were due to temporal differences in water chemistry or to 

the heterogeneity of material at these sites is not known.

Figure 17. Downstream-concentration plot of arsenic in stream bed sediment from Frohner 

Meadows creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion analyses.

1

10

100

1,000

10,000

−5 −4 −3 −2 −1 0

L-2

L-162

L-100

L-163

L-164

L-165

L-166

L-168

L-161

L-159

L-3b

L-158

L-167

L-156

L-155

L-154

L-4a

L-4

L-152

L-153

CBPEC

L-157

L-150

L-151

Other tributary

Panama mine tributary

Frohner Meadows

creek and Lump Gulch

ARSENIC, IN PARTS PER MILLION

DOWNSTREAM MILES

Watershed Background

Consensus-based probable 

effect and watershed 

background concentrations

EXPLANATION

32  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
0.1

1

10

100

1,000

−5 −4 −3 −2 −1 0

CBPEC

Other tributary

Panama mine tributary

Frohner Meadows

creek and Lump Gulch

CADMIUM, IN PARTS PER MILLION

DOWNSTREAM MILES

Watershed Background

Consensus-based probable 

effect and watershed 

background concentrations

EXPLANATION

L-2

L-162

L-100

L-163

L-164

L-165

L-166

L-168

L-161

L-159

L-3b L-158 L-167

L-156

L-155

L-154

L-4a

L-4

L-152

L-153

L-157

L-150

L151

Figure 18. Downstream-concentration plot of cadmium in stream bed sediment from Frohner 

Meadows creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion analyses.

Figure 19. Downstream-concentration plot of iron and manganese in stream bed sediment from 

Frohner Meadows creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion 

analyses.

Manganese concentration

Iron concentration

EXPLANATION

L-2

L-162

L-100

L-163

L-164

L-165

L-166

L-168

L-161

L-159

L-158

L-156

L-155

L-154

L-4a

L-4

L-3b

1,000

10,000

100,000

−5 −4 −3 −2 −1 0

IRON, IN PARTS PER MILLION

DOWNSTREAM MILES

Geochemistry of Mine Waste and Mill Tailings, Meadow Deposits, and Stream Bed Sediment  33
Copper

Copper concentrations in the stream bed sediment 

throughout Frohner Meadows are relatively low because the 

mineralized rock in the Frohner and Nellie Grant deposits 

contains only low concentrations of copper. The CBPEC 

of 149 ppm was exceeded at only three sites (fig. 20). Site 

L–2 had a concentration of 19 ppm, slightly higher than the 

median background copper concentration (15 ppm) in this 

study. Below the Frohner mill site, at sites L–162 and L–100, 

copper concentrations were 120 and 200 ppm, respectively. 

Dilution by streambed sediment reduced the concentration 

to 74 ppm at site L–164. Between sites L–165 and L–166, 

Frohner Meadows creek passes through dispersed mill tailings 

(fig. 3) that increase the concentration of copper in stream bed 

sediment. The addition of unenriched stream bed sediment 

diluted the copper concentration at site L–161, at the lower 

end of upper Frohner Meadows. Samples from site L–159 

contained slightly more copper, possibly from the mill tailings 

impounded at the west end of lower Frohner Meadows (fig. 

3). The r2 correlation coefficients for iron and manganese on 

copper were only 0.48 and 0.50, respectively. Thus, copper is 

more likely transported in detrital weathering products or with 

organic matter to which it readily binds.

The concentration of copper was much greater in samples 

from site L–158 than in those from site L–3b. The cause of 

this increase in copper, and in arsenic, manganese, and iron, 

is not clear. Copper concentrations markedly decline between 

site L–158, just above the filled reservoir, and L–156, the outlet to the reservoir (fig. 20). Dilution by uncontaminated sediment from the Panama meadows tributary apparently reduces 

the dilute-acid extractable copper in Frohner Meadows creek 

sediment to 31 ppm at site L–156. Frohner Meadows stream 

bed sediment that is enriched in copper likely will have only 

minor environmental effects, because copper concentrations 

are only slightly higher than regional background concentrations and crustal-abundance concentrations.

Lead

Of the five ore-related metals discussed here, lead is the 

least soluble and least correlated with iron and manganese. 

The r2 correlation coefficients of iron and manganese with lead 

were only 0.05 and 0.37 respectively. These low correlations 

imply that lead is transported as detrital material. Dilute-acid 

partial-digestion concentrations of lead from the stream bed 

sediment probably represent primary galena (PbS) in the 

samples, because galena was readily soluble in the warm, 

dilute HCl used in the dilute-acid partial digestion.

High concentrations of lead in stream bed sediments of 

Frohner Meadows creek are due to an influx from the Frohner 

mine and mill site (fig. 3). In samples taken above the mine 

(site L–2), the dilute-acid partial-digestion concentration was 

low (20 ppm), close to the median-background concentration 

(12 ppm) and well below the CBPEC (128 ppm) (table 6, fig. 

21). Contributions of tailings material from the Frohner mill 

site (and probably from the Frohner mine, although a sample 

was not taken directly below the mine site) increase the lead 

concentration in stream bed sediment to 3,500 ppm at site 

L–162. Dilution by sediment from other sources produced 

a downstream decrease in the concentration at site L–164 to 

940 ppm. Dispersed mill tailings in the meadow between sites 

Figure 20. Downstream-concentration plot of copper in stream bed sediment from Frohner 

Meadows creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion analyses.

L-2

L-162

L-100

L-163

L-164

L-165

L-166

L-161

L-159

L-3b

L-158

L-167

L-156

L-155

L-154

L-4a

L-4

L-152

L-153

L-157

L-150

L-151

L-168

1

10

100

1,000

−5 −4 −3 −2 −1 0

CBPEC

Other tributary

Panama mine tributary

Frohner Meadows

creek and Lump Gulch

COPPER, IN PARTS PER MILLION

DOWNSTREAM MILES

Watershed Background

Consensus-based probable 

effect and watershed 

background concentrations

EXPLANATION

34  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
L–164 and L–166 contribute additional contaminated material that raises the lead concentration at site L–166 to 1,800 

ppm; dilution by other meadow sediment again lowers the lead 

concentration to 480 ppm at site L–161.

A bulk sample of the fine-grained mill tailings (sample 

LFM 1) from the delta at the west end of lower Frohner Meadows contained 8,100 ppm total lead (table 6, Klein, Thamke, 

and others, 2003). These mill tailings probably contribute to 

the increase in the dilute-acid partial-digestion concentration 

of lead at site L–159 (960 ppm). The dilute-acid partial-digestion lead concentration (220 ppm) in samples from site L–3b 

was much lower, probably because only a small amount of 

detrital galena is transported through lower Frohner Meadows. 

The meadow, with its numerous abandoned beaver ponds, 

other ponds, and marshes, effectively traps detrital sediment 

under most stream-discharge conditions. The dilute-acid 

partial-digestion concentration of lead (1,000 ppm) in samples 

from site L–158 was enigmatically high, because solution 

transport cannot be invoked to explain the large rise. One 

explanation is that a past high-energy flushing event moved 

fine-grained detrital lead through the meadows, and material having high lead concentrations settled out in the stream 

where the slope changes to a more gentle gradient (near site 

L–158). Stream bed sediment of the Panama mine tributary 

dilutes lead concentrations at site L–156 (fig. 21). Between 

sites L–158 and L–156 lead concentration drops by a factor of 

about 14, whereas cadmium concentration drops by a factor of 

only 5 (fig. 18). Because cadmium can be transported in solution as well as by detrital grains, a higher proportion remains 

in stream bed sediment downstream from the junction of the 

two creeks.

Zinc

Zinc and cadmium display isochemical behavior. Cadmium commonly substitutes for zinc in sphalerite, the principle zinc ore mineral in the local ore deposits, and strongly 

covaries with zinc in stream bed sediments in the study area. 

The dilute-acid partial-digestion concentration of zinc in 

stream bed sediment above the Frohner mine and mill sites 

(L–2) was 49 ppm (fig. 22), below the median-background 

concentration of 80 ppm (table 5) and far below the CBPEC 

of 459 ppm (table 6). Below the Frohner mill site (L–162), 

the dilute-acid partial-digestion concentration of zinc in 

stream bed sediment (1,400 ppm) was higher than the total 

zinc concentration in the mill waste material itself (400–1,100 

ppm). Farther downstream at site L–100, the dilute-acid partial-digestion zinc concentration (3,300 ppm) was higher still. 

This spike probably reflects sediments enriched by iron or by 

manganese oxyhydroxides that have successfully scavenged 

dissolved zinc. The r2 correlation coefficients of iron and 

manganese with zinc were 0.86 and 0.71, respectively. Zinc is 

transported in the dissolved phase from the Frohner mine area 

on Frohner Meadows creek and then is trapped by sediment 

grain coatings and concentrated in stream bed sediment above 

site L–100.

As with the metals already discussed, between sites 

L–100 and L–164 zinc concentrations are diluted, likely by 

unenriched stream bed sediment from other sources. Between 

sites L–164 and L–161, zinc concentration increases again, 

probably from an influx of dispersed mill tailings between 

L–165 and L–166 and from the accumulation of zinc scavenged from solution by iron and manganese oxyhydroxides. 

The total zinc concentration of the mill tailings submerged 

at the west end of lower Frohner Meadows was 11,000 ppm 

(Klein, Thamke, and others, 2003, table 6). It is not clear if 

zinc is moved by direct transport to site L–159, because the 

dilute acid partial-digestion concentration of zinc at that site is 

the same as at site L–161, which is upstream from the upper 

end of the meadow. However, because the dilute-acid partialdigestion concentration of zinc increases markedly downstream from site L–159 to higher than 4,600 ppm at site L–3b, 

it is probable that those mill tailings contribute some soluble 

zinc to the meadow that is then scavenged by iron and manganese oxyhydroxides near the east end of the meadow.

The familiar dilution of metal in Frohner Meadows creek 

by sediment from the Panama mine tributary occurs again with 

zinc (fig. 22). Note that the alternative path for the transport of 

dissolved zinc from the south side of lower Frohner Meadows 

through sites L–150 and L–157 is similar to that for cadmium. 

As with cadmium, iron, and manganese, zinc concentration in 

stream bed sediment below site L–158 decreased by a factor 

of only 4 or so, whereas lead decreased by a factor of about 14 

and arsenic decreased by a factor of about 32. These relative 

decreases again point out the difference in behavior between 

the metals that are transported primarily in solution (cadmium, 

copper, and zinc) and those that are transported primarily as 

(or on) clastic debris (arsenic and lead). Dilute-acid partialdigestion concentrations of zinc increase downstream to 

site L–155, where the dilute-acid partial-digestion iron and 

manganese concentrations again are high, a trend that suggests 

that in this area iron- and manganese-rich grain coatings accumulate substantial amounts of zinc and cadmium dissolved in 

streamwater.

Hydrology

The recharge, movement, and discharge of water in the 

Frohner Basin (fig. 2) are influenced by many factors, including the climate, geology, and topography of the area. About 

25 in. of annual average precipitation (U.S. Soil Conservation 

Service, 1977) recharges ground-water flow systems and small 

streams that flow into Frohner Meadows. The steep slopes of 

granitic bedrock that surround Frohner Meadows and the relatively flat areas of unconsolidated sediment in Frohner Meadows form a unique hydrologic system that supports the wetland 

environment of Frohner Meadows. Ground-water and surfacewater components of the hydrologic system were analyzed to 

estimate an annual hydrologic budget for Frohner Meadows 

and to understand the hydrologic regime of the wetlands.

Hydrology  35
L-2

L-162 L-100

L-163

L-164

L-165

L-166

L-168

L-161

L-159

L-3b

L-158

L-167

L-156

L-155

L-154

L-4a L-4

L-152

L-153

L-157

L-150

L-151

1

10

100

1,000

10,000

−5 −4 −3 −2 −1 0

CBPEC

Other tributary

Panama mine tributary

Frohner Meadows

creek and Lump Gulch

LEAD, IN PARTS PER MILLION

DOWNSTREAM MILES

Watershed Background

Consensus-based probable 

effect and watershed 

background concentrations

EXPLANATION

L-2

L-162

L-100

L-163

L-164

L-165

L-166

L-168

L-161

L-159

L-158

L-167

L-156

L-155

L-154

L-4a

L-4

L-152

L-153

L-157

L-150

L-151

L-3b

1

100

1,000

10,000

−5 −4 −3 −2 −1 0

CBPEC

Other tributary

Panama mine tributary

Frohner Meadows

creek and Lump Gulch

ZINC, IN PARTS PER MILLION

DOWNSTREAM MILES

Watershed Background

Consensus-based probable effect and watershed 

background concentrations

EXPLANATION

Figure 21. Downstream-concentration plot of lead in stream bed sediment from Frohner 

Meadows creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion analyses.

Figure 22. Downstream-concentration plot of zinc in stream bed sediment from Frohner Meadows 

creek and Lump Gulch. Concentrations derived by dilute-acid partial-digestion analyses.

36  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
Methods of Investigation

The hydrology of the area was investigated by analysis 

of surface-water flow, ground-water flow, and hydrogeologic 

characteristics of the area. A water budget was developed from 

site-specific measurements of discharge and aquifer characteristics and from regional values of precipitation and monthly 

discharge. Metal loads into and out of the Frohner Meadows 

area were estimated from measured values of stream discharge 

and metal concentrations. Seven shallow wells were installed 

in upper Frohner Meadows and three wells in lower Frohner 

Meadows to measure water levels and water quality. Seismicrefraction studies were completed along six lines across 

the wetland areas of the meadows and analyzed to estimate 

thickness of saturated unconsolidated sediment overlying the 

granitic bedrock.

Water-quality samples were collected from both surfaceand ground-water sources in upper and lower Frohner Meadows. Surface-water samples typically were grab samples 

because discharge was too low to allow the use of a depthintegrating sampler. Surface-water samples were filtered onsite through a 0.45 μm syringe filter. Ground-water samples 

were collected from shallow wells by use of a peristaltic 

pump, and samples were filtered on-site through a 0.45 μm 

capsule filter. All samples were processed according to procedures described in Wilde and others (1998) and were analyzed 

by the U.S. Geological Survey National Water Quality Laboratory in Denver, Colo. Analytical methods are described by 

Faires (1993), Fishman (1993), Fishman and Friedman (1989), 

Garbarino (1999), Garbarino and Struzeski (1998), Hoffman 

and others (1996), and Jones and Garbarino (1999).

Ground Water

The bedrock geology of Frohner Basin, the distribution 

and thickness of unconsolidated deposits, and the hydraulic 

characteristics of the unconsolidated deposits and plutonic 

bedrock that underlie the basin largely control local groundwater flow. Frohner Basin (fig. 2) and the surrounding area are 

underlain entirely by plutonic rocks of the Boulder batholith, 

which typically are quartz monzonite and granodiorite (Becraft 

and others, 1963). Nearly all pore space and permeability in 

the plutonic rocks is produced by near-surface weathering 

along joints. Outcrops of the Boulder batholith generally are 

considerably weathered, and weathering has produced large 

open fractures along the joints. In many areas, joints in the 

rocks have sufficiently weathered to leave large, freestanding, 

rounded boulders. Weathering of the plutonic rocks rapidly 

decreases with depth, which is clearly evident in many road 

cuts, mine workings, excavations, and drill holes. In the areas 

examined, the upper 5 ft of rock typically is highly weathered and has open joints. From about 5 to 50 ft depth, the 

plutonic rock grades from slightly weathered to unaltered 

rock, and most joints become tight and contain clay. Below 

about 50 ft, rocks typically are fractured but most fractures are 

extremely tight, and only a few fracture surfaces are weathered 

(McDougal and others, 2004). Gouge typically accompanies 

even the smallest faults in the batholith (Becraft and others, 

1963). Exceptions to these general characteristics may be found 

along some mineralized zones and large fractures. Hydraulic 

conductivity of the plutonic rocks typically is very low. At two 

core holes drilled west of the study area near the continental 

divide, hydraulic conductivities measured by slug tests were 

0.02 ft/day and 0.04 ft/day (Maxim Technologies, 1999). Both 

slug tests were conducted on fractured or weathered quartz 

monzonite of the Boulder batholith at depths of 18–43 ft below 

the land surface. Because of decreasing hydraulic conductivity 

with depth, most ground-water flow in the Boulder batholith 

occurs in the uppermost, weathered zone.

Unconsolidated deposits in Frohner Basin contain boulder till and colluvium on hillsides, and in the lowland areas 

of Frohner Meadows they contain till, alluvium, volcanic ash, 

and organic deposits. During the Pleistocene Epoch, glacial 

ice covered much of the highland area west of the study area. 

From the center of accumulation near upper Cataract Basin, 

ice moved eastward down Lump Gulch, North Fork Quartz 

Creek, and South Fork Quartz Creek, where the ice was joined 

by small tributary glaciers from poorly developed cirques in 

Frohner Meadows and Park Lake (Becraft and others, 1963). 

Before the Pleistocene Epoch, Frohner Meadows drained 

through the North Fork of Quartz Creek; however, Lump 

Gulch captured this drainage during the Pleistocene (Becraft 

and others, 1963).

Moraines deposited by glacial ice dammed the preglacial 

channel of Frohner Meadows creek and formed shallow ponds 

that subsequently filled with clay, silt, sand, volcanic ash, and 

organic deposits. Seismic-refraction soundings conducted 

along upper and lower Frohner Meadows (fig. 14) indicated 

that till and postglacial sediment overlying bedrock are as 

much as 45 ft thick in upper Frohner Meadows and 25 ft thick 

in lower Frohner Meadows. We conclude that a major part 

of the unconsolidated deposits is till, on the basis of large 

boulders exposed along the margins of the wetlands and from 

rocks and till intersected in two types of drill holes: in auger 

holes drilled in the wetlands for installation of shallow test 

wells and in shallow cores in the meadow. Sediments overlying the till (in ascending order) typically are poorly sorted, 

angular, alluvial sand derived from batholith rocks, volcanic 

ash, organic-rich clay, and peat. Hydraulic conductivity of 

the organic-rich clay and volcanic ash is very low, and these 

materials function as confining layers for ground water in the 

thin underlying zone of alluvial sand.

The volcanic ash, tentatively identified as the Mazama 

ash, is a massive, tan, biotitic, air-fall deposit. The age of the 

Mazama ash, which has been estimated by 14C dating to be 

about 7 Ka (Bacon, 1983), provides an approximate age for 

the beginning of the development of postglacial ponds. This 

unit was observed in six cores in Frohner Meadows, ranged 

in depth from 2 to 4.4 ft below the present surface, and was 

0.1–0.8 ft thick where it was intersected.

Discharge of ground water from unconsolidated 

deposits plays an important role in maintaining the wetland 

Hydrology  37
environment of Frohner Meadows. Ground water flows from 

topographically higher areas within Frohner Basin through 

predominantly thin unconsolidated deposits and the uppermost, weathered zone at the top of bedrock and discharges to 

land surface in wetland areas of Frohner Meadows. Groundwater discharge, in the form of numerous seeps, was observed 

along the west, north, and east margins of upper Frohner 

Meadows and along the west margin of lower Frohner Meadows. By comparing water levels measured in shallow (total 

depths 5–9 ft) test wells on Sept. 26, 2001, with surveyed 

elevations of land surfaces and nearby water surfaces (table 

7), we documented a large upward component of groundwater flow. Ground-water levels were higher than land surface 

at three wells (FM–4, FM–5, and FM–7) and were higher 

than the adjacent pond or stream surface at three other wells 

(FM–1, FM–3, and FM–8). Upward hydraulic gradients were 

as much as 0.33 (1.05 ft/3.0 ft) at well FM–5.

Discharge of ground water to wetlands in Frohner 

Meadows contributes to stream discharge in Frohner Meadows creek. Discharge measurements were made at 12 sites on 

Frohner Meadows creek and its tributaries (fig. 14) several 

times in 2001. Small gains in discharge were measured in the 

downstream part of upper Frohner Meadows. Between measurement sites H and I, discharge on June 26, 2001, increased 

from 0.76 ft3/s to 0.86 ft3/s, and on October 10, 2001, discharge increased from 0.09 ft3

/s to 0.15 ft3/s. Measurements 

made on other dates or at other sites indicated small increases 

or small decreases in discharge through different sections of 

Frohner Meadows. Many of the differences in discharge were 

within the measurement error of the methods used. However, 

ground water likely discharges to Frohner Meadows creek 

throughout much of the length of the wetlands, as is indicated 

by observed flow of seeps toward the stream and by measured 

ground-water levels that generally are higher than stream 

surface or land surface.

Downstream from lower Frohner Meadows, discharge 

of ground water through moraine and bedrock likely is small 

because till and batholith rocks generally have low hydraulic 

conductivities. A likely range of hydraulic conductivity, on 

the basis of measured hydraulic conductivity in the Boulder 

batholith (Maxim Technologies, 1999) and published values 

for till (Bouwer, 1978), is 0.003 to 0.3 ft/day; a median value 

is 0.03 ft/day. We calculated that the flow (Darcy equation, 

see Lohman, 1972) of ground water through till and the upper 

weathered zone of bedrock ranges from 0.0001 to 0.01 ft3/s 

and has a median of 0.001 ft3/s, on the basis of the above values of hydraulic conductivity, a width of 600 ft, a thickness of 

60 ft, and a gradient of 0.1 (80 ft/800 ft).

Surface Water

Frohner Meadows creek drains Frohner Basin into Lump 

Gulch and eventually into Prickly Pear Creek (fig. 3). Frohner 

Meadows creek flows adjacent to the Frohner mine and enters 

the wetlands of upper Frohner Meadows in the northwestern 

part of the meadows. Several small tributaries join Frohner 

Meadows creek, including an unnamed tributary that drains 

from the Nellie Grant mine reclamation area. All water that 

drains from upper Frohner Meadows through Frohner Meadows creek flows into lower Frohner Meadows. In the western 

part of lower Frohner Meadows, a small tributary that drains 

the steep slopes west of the meadows joins Frohner Meadows 

creek. At a beaver pond in the eastern part of lower Frohner 

Meadows, Frohner Meadows creek splits into two separate 

outflow channels. The two channels eventually rejoin in Lump 

Gulch. The drainage area of Frohner Meadows creek at the 

outlet of upper Frohner Meadows is 1.04 mi2. At the outlets 

of lower Frohner Meadows, the creek has a drainage area of 

1.30 mi2. The drainage area of lower Frohner Meadows was 

measured as all drainage area upstream from Jefferson County 

Road 1878, where it crosses Frohner Meadows creek (near 

sites L–3a and L–3b, fig. 14).

Frohner Meadows creek has no gaging station that can 

be used to measure daily, mean monthly, or annual discharge 

values; therefore, regression equations (Parrett and Johnson, 

1989) that relate monthly discharge characteristics to drainage area and mean annual precipitation were used to estimate 

mean monthly and annual discharge. The regression equations yielded a mean annual discharge of 0.98 ft3

/s for Frohner Meadows creek at the outlet of lower Frohner Meadows. 

Calculated mean monthly discharge ranged from 0.19 ft3/s in 

January to 3.8 ft3/s in May (table 8).

Base flow of Frohner Meadows creek, which is derived 

from ground-water discharge, also was estimated from measured discharge in nearby streams that drain the areas underlain 

by the Boulder batholith and flow across geologic substrates 

similar to those in the study area. Base flow of Basin Creek, 

Cataract Creek, and High Ore Creek, determined from winter 

measurements made from 1996 to 2000 (Nimick and Cleasby, 

2000; T.E. Cleasby, unpub. data, 2000), averaged 0.11 ft3/s 

from each square mile of drainage area. If we assume that 

Frohner Meadows creek has similar runoff characteristics, then 

discharge at the outlet of lower Frohner Meadows would be 

about 0.15 ft3/s during base-flow conditions. Actual discharge 

of Frohner Meadows creek measured during base-flow conditions on October 11, 2000, was 0.11 ft3

/s at site L–3 (sites L–3a 

and L–3b combined, fig. 14). On the basis of both calculated 

and measured values of stream discharge, ground-water 

discharge is estimated to contribute about 0.15 ft3/s to Frohner 

Meadows creek during base-flow conditions. A larger volume 

of ground water discharges into Frohner Meadows creek during 

and after large rainfall events and spring snowmelt.

Water Budget

An annual water budget for Frohner Meadows and 

Frohner Basin was developed to evaluate relative volumes 

of water that discharge through surface water, ground water, 

and evapotranspiration. This budget was developed by use of 

published values of long-term precipitation and evaporation 

and of calculated values of stream discharge and ground-water 

flow. Calculations of stream discharge and ground-water flow 

38  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
Site name 

Elevation 

of land 

surface 

Water 

level 

below land 

surface 

Date

measured 

Elevation

of water 

surface 

Well FM–1 6582.13 0.96 9/26/2001 6581.2

Well FM–2 6583.79 1.10 9/26/2001 6582.7

Well FM–3 6587.29 0.79 9/26/2001 6586.5

Well FM–4 6597.89 +0.43 9/26/2001 6598.3

Well FM–5 6595.11 +1.05 9/26/2001 6596.2

Well FM–6 6583.76 1.97 9/26/2001 6581.8

Well FM–7 6576.51 +0.16 9/26/2001 6576.7

Well FM–8 6541.55 0.45 9/26/2001 6541.1

Well FM–9 6530.03 1.10 9/26/2001 6528.9

Well FM–10 6517.50 0.76 9/26/2001 6516.7

Frohner Meadows Creek west of well FM–1 (water surface) NA NA 9/24/2001 6580.7

Beaver pond at well FM–7 NA NA 9/24/2001 6575.9

Beaver pond between wells FM–1 and FM–7 NA NA 9/24/2001 6579.2

Stream west of well FM–6 (water surface) NA NA 9/24/2001 6581.9

Frohner Meadows Creek east of well FM–2 NA NA 9/24/2001 6582.7

Frohner Meadows Creek by well FM–3 NA NA 9/24/2001 6585.3

Frohner Meadows Creek, north of well FM–4 NA NA 9/24/2001 6597.1

Frohner Meadows Creek between wells FM–4 and FM–5 NA NA 9/24/2001 6595.2

Beaver pond at well FM–5 NA NA 9/24/2001 6593.8

Upper beaver pond in Upper Frohner Meadows NA NA 9/24/2001 6600.0

Beaver pond at well FM–8 NA NA 9/24/2001 6540.1

Stream at well FM–9 (water surface) NA NA 9/24/2001 6528.9

Beaver pond between wells FM–9 and FM–10 NA NA 9/24/2001 6526.0

Stream at well FM–10 (water surface) NA NA 9/24/2001 6516.7

Table 7. Water levels in wells and at surface-water sample sites in Frohner Meadows, September 24–26, 2001.

[Relative elevations (in feet) were surveyed from temporary bench marks; bench-mark elevations estimated from 1:24,000-scale topographic 

map, National Geodetic Vertical Datum of 1929. +, water level above land surface; NA, not applicable]

were based on the hydrologic conditions of the study area. 

Frohner Basin is located at the headwaters of Lump Gulch, 

and because of its location at the uppermost part of the drainage, all water entering Frohner Meadows likely originates as 

precipitation within the 1.30 mi2 Frohner Basin.

This annual water budget for the basin assumes that 

long-term changes in storage are zero and that the budget may 

be expressed as a simple mass-balance equation (2) in which 

precipitation is equal to all outflows:

Precipitation = Stream discharge + Ground-water discharge 

+ Evapotranspiration (2)

Average annual precipitation for the area between Frohner Meadows and the basin divide is about 25 in. (U.S. Soil 

Conservation Service, 1977). The average annual volume of 

precipitation that falls on Frohner Basin is about 1,733 acre-ft, 

and this volume of water equals all outflows from the basin. 

The stream-discharge component of the annual budget is 

about 0.98 ft3/s (709 acre-feet per year (acre-ft/yr)), of which 

at least 0.15 ft3/s (108 acre-ft/yr) originates as ground-water 

flow within the basin. Ground water that leaves the basin as 

flow through till and granite is estimated at about 1 acre-ft/yr, 

although it could range from 0.09 to 9 acre-ft/yr. A large volume of water leaves Frohner Basin through evapotranspiration. 

Potential evapotranspiration rates for wetlands are greater than 

those for forest or grassland; therefore, total evapotranspiration for the basin is subdivided into evapotranspiration from 

wetland and evapotranspiration from forest.

Evapotranspiration for the wetland area of Frohner 

Meadows can be calculated as a free-water-surface evaporation and is about 30 in./yr (National Oceanic and Atmospheric 

Administration, 1982). Actual evapotranspiration from the 

wetlands probably is only slightly less than potential evaporation because of the large areas of ponded water, wet soils, and 

vegetation, all of which draw on an unlimited water supply. 

Evapotranspiration of 30 in./yr from the 29.7 acres of wetlands 

Hydrology  39
of Frohner Meadows is equivalent to 74 acre-ft/yr. Evapotranspiration from the 802 acres of forest and grasslands in the 

Frohner Basin can be calculated as a remainder in equation 2. 

Rearranging equation 2 gives the following:

Precipitation – Stream discharge – Ground-water discharge – 

Evapotranspirationwetland = Evapotranspirationforest

(3)

Substituting acre-feet per year values into equation 3: 

1733 – 709 – 1 – 74 = 949 acre-ft/yr.

The 949 acre-ft/yr of evapotranspiration from the 802 

acres of forest or grass is equivalent to a rate of 14 in./yr of 

evapotranspiration throughout that area, or slightly less than 

half the rate for wetlands. The water budget for Frohner Basin 

is summarized in table 9.

Water Quality

Samples of ground water and surface water from 22 

sites in Frohner Basin were analyzed for specific conductance, pH, common ions, and trace metals. Ground-water 

sampling sites were selected to allow analysis of ground 

water flowing (1) into Frohner Meadows from various 

sources, (2) out of upper and lower Frohner Meadows, and 

(3) beneath mill tailings deposits in the wetland areas of 

Frohner Meadows. Surface-water sites were selected to allow 

analysis of all inflows and outflows as well as to measure 

changes in water quality within Frohner Meadows. Traceelement loads through Frohner Meadows were calculated 

from discharge and water-quality data.

Ground Water

Ground water was sampled at 10 wells in upper and lower 

Frohner Meadows (sites FM–1 through FM–10, fig. 14 of this 

report; data are in Klein, Thamke, and others, 2003). Well logs 

containing lithologic descriptions and well-completion information can be found in Klein, Thamke, and others (2003). All 

wells were sampled on July 26, 2001, the day after they were 

purged with a bailer. Four wells (FM–1, FM–3, FM–7, and 

FM–10) were sampled a second time on October 17, 2001.

Specific conductance of ground water measured on-site 

during sampling ranged from 144 μS/cm at well FM–5 to 233 

μS/cm at well FM–8. On-site pH values ranged from 6.0 at 

well FM–6 to 7.6 at well FM–4. Calcium was the predominant 

cation in all well-water samples.

Dissolved arsenic was present in most (10 of 14) water 

samples in concentrations exceeding the Montana numeric 

water-quality standard for human health of 20 μg/L in ground 

water (Montana Department of Environmental Quality, 2002). 

High concentrations of dissolved arsenic were present in water 

samples from wells FM–1, FM–4, FM–7, FM–8, FM–9, and 

FM–10. The highest concentration of arsenic was measured 

in a water sample collected on October 17, 2001, from well 

FM–1 (3,380 μg/L), which was completed in an area of mill 

tailings in the central part of upper Frohner Meadows (area 

A). Water from well FM–4, which was completed in the large 

impoundment of mill tailings where Frohner Meadows creek 

enters the west margin of upper Frohner Meadows, also had a 

high concentration of arsenic (414 μg/L). Water samples collected on July 26, 2001, from wells FM–2, FM–5, and FM–6 

on the west, northeast, and east margins of upper Frohner 

Meadows had the lowest arsenic concentrations; they ranged 

from 1.0 μg/L at FM–5 to 13.2 μg/L at FM–6 (Klein, Thamke, 

and others, 2003).

Concentrations of dissolved cadmium, copper, and lead 

were low in water samples from all wells and were below 

human-health standards established by the Montana Department of Environmental Quality (2002). Dissolved zinc ranged 

from less than 1 μg/L in a sample from well FM–3 to 419 

μg/L in a sample from well FM–9.

Water-quality data are available for two additional wells 

in the area: well MW–1 located just west of the central part 

of upper Frohner Meadows, adjacent to Nellie Grant creek, 

and well MW–2 located on private property near the southwestern part of upper Frohner Meadows (fig. 14). Well MW–1 

reportedly is screened between 13.5 and 25 ft below land 

surface in unconsolidated deposits and weathered bedrock; 

depth to water was about 5 ft below land surface, which is 

deeper than the stream level in this area (Pioneer Technical 

Services, 1996). Well MW–2, completed in granitic bedrock, 

is greater than 100 ft deep, is artesian, and flows about 1–2 

gallons/minute (Pioneer Technical Services, 1996). Five water 

samples collected from MW–1 had very high mean concentrations of cadmium (79 μg/L) and zinc (9,300 μg/L). Mean 

concentrations of arsenic, copper, and lead in well MW–1 

were fairly low (Klein, Thamke, and others, 2003). The high 

Discharge 

interval 

Cubic feet/ 

second Acre-feet 

October 0.39 24

November 0.28 17

December 0.23 14

January 0.19 12

February 0.20 11

March 0.25 16

April 0.97 58

May 3.8 234

June 3.3 197

July 1.0 63

August 0.61 38

September 0.43 25

Annual 0.98 709

Table 8. Calculated mean monthly discharge 

and annual discharge of Frohner Meadows creek.

40 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
concentrations of cadmium and zinc measured for well MW–1 

likely are from infiltration of water from Nellie Grant creek 

(see next section), because the well is near the creek, and 

concentrations of dissolved cadmium and zinc in the stream 

are similar to those in ground water at the well. Water samples 

from the deeper well MW–2 had low concentrations of 

arsenic, cadmium, copper, lead, and zinc.

Surface Water

Surface water was sampled at 12 sites (A through J, L-3a, 

and L-3b) in the Frohner Meadows area (fig. 14). Surfacewater-quality data are reported in Klein, Thamke, and others 

(2003, table 6). Sample sites A, B, C, and D were located on 

small tributaries that flow into the wetlands of Frohner Meadows; these tributaries drain areas that show minimal or no 

disturbance from mining. Sample site F is on Frohner Meadows creek, and site G is on Nellie Grant creek. Sample sites E, 

H, I, and J were selected to show potential changes in quality 

as water moves downstream through Frohner Meadows and 

its mill tailings deposits. Sample sites L–3a and L–3b were 

located on the two outflows from lower Frohner Meadows.

Specific conductance ranged from 33 μS/cm at tributary 

inflow site C to 500 μS/cm at site G on Nellie Grant creek. In 

general, specific conductance of all tributary inflows except 

Nellie Grant creek was less than 100 μS/cm, and specific conductance of water discharging from lower Frohner Meadows 

(sites L–3a and L–3b) ranged from 88 to 483 μS/cm. Field 

measurement of samples indicated mostly neutral pH values; 

both the lowest (6.0) and highest (8.2) values were measured 

in samples collected at site L–3b.

Concentrations of trace metals in tributaries to Frohner 

Meadows vary greatly by source of inflow (table 3). Small 

tributaries sampled at sites A, B, C, and D typically had 

low concentrations of arsenic, cadmium, copper, lead, and 

zinc. Frohner Meadows creek, which drains the area of the 

Frohner mine, had higher concentrations of trace metals than 

the small tributaries. The highest concentrations of trace 

metals were measured in Nellie Grant creek, which drains 

the adits and reclaimed area of the Nellie Grant mine. High 

concentrations of trace metals were measured in Frohner 

Meadows creek in the area between the mill tailings deposits 

in upper Frohner Meadows and the outlets of lower Frohner 

Meadows.

Total recoverable arsenic concentrations ranged from less 

than 2 μg/L in samples from tributaries A and B to 208 μg/L in 

a sample from Nellie Grant creek. The total recoverable arsenic 

concentration measured in a sample from Nellie Grant creek 

exceeds the chronic aquatic-life standard of 150 μg/L (Montana 

Department of Environmental Quality, 2002). Total recoverable cadmium concentrations ranged from about 0.03 μg/L in 

samples from tributary sites A and C to 121 μg/L in a sample 

from Nellie Grant creek. Total recoverable copper concentrations ranged from 2.2 μg/L in a sample from tributary site A to 

83.9 μg/L in a sample from Nellie Grant creek. Total recoverable lead concentrations ranged from <1 μg/L in samples from 

tributary sites A, B, and C to 72 μg/L in a sample from Nellie 

Grant creek. Total recoverable zinc concentrations ranged from 

2 μg/L in a sample from tributary site C to 15,100 μg/L in a 

sample from Nellie Grant creek. At most sites along Frohner 

Meadows creek and areas downstream from Nellie Grant creek, 

concentrations of total recoverable cadmium, copper, lead, and 

zinc exceeded Montana aquatic-life standards (Montana Department of Environmental Quality, 2002).

Trace-Metal Loads

Instantaneous loads of trace metals into and out of 

Frohner Meadows were calculated from instantaneous streamdischarge measurements and from measured concentrations 

of total recoverable trace metals in water samples. Calculated 

loads are reported in grams per day (table 3). Graphs of instantaneous loads of total recoverable arsenic, cadmium, copper, 

lead, and zinc are shown in figures 23–27 for two sampling 

periods. The first set of samples was collected on June 25 and 

26, 2001, at all sites A–J and L except L–3. A sample from 

site L–3 (L–3a and L–3b combined) was collected on May 10, 

2001, when discharge was slightly greater than it was during 

the June sampling. The second set of samples was collected on 

August 1, 2001, at a time of low stream discharge.

Annual inflow 

or outflow Source Volume

(acre-feet) Percent

Precipitation of 25 inches per year on 832 acres +1,733 +100

Discharge from Frohner Meadows creek; drainage area of 1.30 square miles –709 –41

Ground-water flow to Frohner Meadows creek (these values included in stream-discharge 

 volume and percentage) 

(>108) (>6)

Ground-water flow out of basin through till and bedrock –1 <1

Potential evapotranspiration from 29.7 acres of wetland –74 –4

Evapotranspiration from 802 acres of forest and grass –949 –55

Table 9. Summary of annual water budget of Frohner Basin.

[+, inflow; –, outflow; >, greater than; <, less than]

Water Quality  41
0

10

20

30

40

50

60

70

80

90

A B D E F G H I C J L–3

LOAD, IN GRAMS PER DAY

SAMPLE SITE

TOTAL RECOVERABLE ARSENIC

June 25–26, 20011

August 1, 2001

1

Sample at L–3 collected May 10, 2001

Figure 23. Instantaneous loads of total recoverable arsenic.

0

5

10

15

20

25

30

35

A B D E F G H I C J L–3

LOAD, IN GRAMS PER DAY

TOTAL RECOVERABLE CADMIUM

June 25–26, 20011

August 1, 2001

SAMPLE SITE

1

Sample at L–3 collected May 10, 2001

Figure 24. Instantaneous loads of total recoverable cadmium.

42  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
0

5

10

15

20

25

30

A B D E F G H I C J L–3

TOTAL RECOVERABLE COPPER

June 25–26, 20011

August 1, 2001

LOAD, IN GRAMS PER DAY

SAMPLE SITE

1

Sample at L–3 collected May 10, 2001

Figure 25. Instantaneous loads of total recoverable copper. 

0

5

10

15

20

25

30

35

A B D E F G H I C J L–3

TOTAL RECOVERABLE LEAD

June 25–26, 20011

August 1, 2001

LOAD, IN GRAMS PER DAY

SAMPLE SITE

1

Sample at L–3 collected May 10, 2001

Figure 26. Instantaneous loads of total recoverable lead. 

Water Quality  43
Small tributaries sampled at sites A, B, C, and D had 

small loads of trace metals in both the June and August 

samples. The larger tributaries of Frohner Meadows creek, 

where it enters upper Frohner Meadows (site F), and Nellie 

Grant creek (site G) contributed the largest loads of total 

recoverable arsenic, cadmium, copper, lead, and zinc to 

upper Frohner Meadows. Sample site E, which discharges 

from the uppermost beaver pond in upper Frohner Meadows, also contributed small loads of total recoverable 

arsenic, copper, and lead (figs. 23–27). The largest arsenic 

loads were measured in Frohner Meadows creek at sites 

H, I, and J, which are downstream from Nellie Grant creek 

and the mill tailings deposits in the central part of upper 

Frohner Meadows. At sites H and I, arsenic loads greater 

than the sum of arsenic loads in upstream tributaries indicate that additional arsenic is entering Frohner Meadows 

creek from mill tailings and ground water in that area. A 

major part of the total recoverable cadmium load in Frohner Meadows creek was contributed by Nellie Grant creek 

(site G). Cadmium load in Frohner Meadows creek (June 

25 or 26 sample) substantially increased downstream from 

the confluence with Nellie Grant creek and remained high 

downstream in samples collected at sites H, I, and J (fig. 

24). Loads of total recoverable copper, lead, and zinc also 

remained high at downstream sample sites H, I, and J (figs. 

25–27).

Figure 27. Instantaneous loads of total recoverable zinc. 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

A B D E F G H I C J L–3

TOTAL RECOVERABLE ZINC

June 25–26, 20011

August 1, 2001

LOAD, IN GRAMS PER DAY

SAMPLE SITE

1

Sample at L–3 collected May 10, 2001

Conclusions

The mine and mill sites at the Nellie Grant and Frohner 

mines contribute significant amounts of ore-related 

metals to stream bed sediment and surface water in the 

study area.

Most surface-water sites in Frohner Meadows below 

Nellie Grant creek exceed the Montana aquatic-life 

standards for the ore-related metals cadmium, copper, 

lead, and zinc (Montana Department of Environmental 

Quality, 2002).

A plume of ground water, rich in ore-related metals 

that likely are derived from infiltration of contaminated surface water at the outlet of Nellie Grant creek, 

locally transports arsenic, cadmium, and zinc into 

upper Frohner Meadows.

Arsenic is transported in shallow ground water in 

concentrations that exceed the Montana numeric waterquality standard for human health throughout much of 

Frohner Meadows (Montana Department of Environmental Quality, 2002).

Much of the metal-enriched sediment in the meadow 

and wetlands is buried and not identifiable from

•

•

•

•

•

44  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
shown by total-metal concentrations in bulk samples and core 

material downstream from the Frohner mill. Results of the 

EPA–1312 leach procedure (Klein, Thamke, and others, 2003) 

showed that the high summed concentrations of ore-related 

metals are dominated by lead. Analyses of two size fractions 

in mill tailings from area A showed that coarse quartz chips 

(>2 mm), which probably are unprocessed ore, also contained 

high concentrations of lead and relatively low concentrations 

of zinc; the coarse fraction also had a higher acid-generating 

capacity than the finer fraction, probably owing to unweathered 

pyrite in the quartz chips that was not removed during ore processing. Fine-grained material (<2 mm) from area A had a low 

acid-generating capacity (table 1) and lower summed-metal 

concentrations. Bulk mine waste and mill tailings from the 

Nellie Grant mine and mill contained high concentrations of 

cadmium and zinc relative to similar material from the Frohner 

mine and mill, as seen in bulk analyses of the debris fan below 

Nellie Grant creek. Acid-generating capacity is low for all surface samples of mill tailings in area B (fig. 3) and for material 

of mixed sources from the Nellie Grant and Frohner mines.

The acid-generating capacity of material from the milltailings delta in lower Frohner meadows is extremely high 

(table 1) relative to other waste material in the study area and 

elsewhere. Oxidation of this material, which might occur if 

water levels were lowered, would generate acidic, metal-rich 

water. The fine grain size of this unencapsulated material 

makes it more susceptible to weathering. This material is 

likely to contribute metals as dissolved or suspended constituents in surface water and ground water or as adsorbed material 

or colloids in stream bed sediment in lower Frohner Meadows and upper Lump Gulch. On the basis of the EPA–1312 

leach data from surface samples, these mill tailings have large 

concentrations of readily leachable arsenic, cadmium, and 

zinc and probably contribute to the solution-transported load 

of metals in surface water in lower Frohner Meadows. The 

effects of acid generated by oxidation of this material could 

be mitigated by the neutral and mildly alkaline nature of the 

surface water in the study area (see table 4, Klein, Thamke, 

and others, 2003) and the probable high acid-neutralizing 

capacity of the local bedrock. The granitic rocks of the Boulder batholith that underlie the study area have a high capacity 

for neutralizing acid that results in characteristically neutral to 

mildly alkaline pH in surface water and the rapid neutralization of acid produced by anthropogenic and natural sources 

(Desborough and others, 1998).

Area A—Upper Frohner Meadows

In area A (fig. 3), mine waste is present in the debris 

fan at the edge of upper Frohner Meadows and in material 

that has been deposited below the fan in the meadow proper 

near the east end of core line 1 and near core line 2. In most 

cases, mine waste, characterized by coarse quartz lag deposits that probably are untreated ore from the Frohner mill, is 

mixed with fine-grained mill tailings. These mixed deposits 

overlie fine-grained mill tailings that were discharged into 

surface features; enriched sediment extends beyond the 

region of obviously unvegetated areas in upper Frohner 

Meadows.

Lower Frohner Meadows effectively traps ore-related 

metals transported in clastic material.

Mill tailings in the upper parts of lower Frohner 

Meadows have a high acid-producing potential and, if 

oxidized during weathering, could release high concentrations of arsenic, cadmium, and zinc. Removal of this 

material would reduce the potential for release of high 

concentrations of arsenic, cadmium, and zinc.

Estimates of premining background concentrations 

of metals in buried alluvial and pond-fill deposit in 

Frohner Meadows are 2.4–4.6 times the watershed 

background concentrations in active stream sediment 

in the Prickly Pear Creek watershed. The estimated 

premining concentration of arsenic (4.1 times as high), 

lead (4.6 times as high), and zinc (2.4 times as high) 

indicate that the Frohner Meadows area contains higher 

natural (premining) concentrations of these metals 

relative to usual regional concentrations as measured 

in areas of the Prickly Pear Creek watershed underlain 

by unmineralized bedrock. The premining background 

concentrations of arsenic, cadmium, and copper in 

Frohner Meadows are similar to those of premining 

sediment in the adjacent upper Boulder River watershed (Church and others, 2004), whereas concentrations of lead and zinc are substantially higher. These 

high background levels in buried premining material 

need to be taken into account in any remediation plan.

It may be possible to excavate and replace contaminated material in upper Frohner Meadows. However, 

without a reduction in the influx of ore-related metals 

from upstream sources such as adit water and mine and 

mill waste, recontamination of Frohner Meadows is 

likely. The wetlands in lower Frohner Meadows appear 

to reduce the concentrations of ore-related metals that 

are transported downstream by clasts in stream bed 

sediments; the wetlands also, under current conditions, 

reduce by sorption the concentrations of some watertransported ore-related metals. Disturbance of these wetlands could change downstream surface- and groundwater chemistry and hydrology to produce higher 

concentrations of arsenic, cadmium, and zinc in surface 

water in upper Lump Gulch; disturbance might also 

reduce the ability of the wetland to trap clastic particles.

Summary

Mine Waste and Mill Tailings

Frohner mine and mill tailings typically contain the 

highest concentrations of arsenic and lead in the study area, as 

•

•

•

•

Summary  45
or accumulated within premining ponds. The coarse mine 

waste probably was transported downstream during flood 

events after a structural failure at the abandoned Frohner mill. 

Fine-grained mill tailings enriched in ore-related metals were 

redistributed by stream action along Frohner Meadows creek 

between the debris fan and the area of core line 2. Each of the 

eight cores analyzed in this area was enriched in ore-related 

metals relative to local background concentrations.

Weathering in the upper part of the debris fan has leached 

arsenic, cadmium, and zinc from the surface and enriched the 

underlying nontailings material in those metals. This downward migration of metal substantially increased the thickness 

of the enriched intervals. The mean minimum thickness of the 

enriched intervals (mill tailings and underlying contaminated 

material) in this area is 52 cm. The weighted average concentration of these metals in enriched intervals was 3,500 ppm for 

arsenic, 12 ppm for cadmium, 270 ppm for copper, 3,500 ppm 

for lead, and 1,200 ppm for zinc. The concentrations of arsenic 

and lead are relatively high compared with their concentrations in other enriched material in the study area; all concentrations exceed the consensus-based probable-effect concentration (CBPEC) for stream bed sediment (table 6). Mine waste 

in the debris fan contributes little clastic material to stream 

bed sediment downstream during low flow because the creek 

is not actively eroding the debris fan. Mill tailings deposited 

in the meadow are effectively stabilized by heavy vegetation 

and contribute only a small amount of clastic material to the 

stream bed sediment under low-flow conditions.

Area B—Upper Frohner Meadows

Deposits of coarse-grained crushed (but unprocessed) 

ore, probably from the Frohner mill, mix downstream with 

fine-grained mill tailings and fluvial mill tailings from the 

Frohner and Nellie Grant mines. This material is impounded 

behind a large reinforced beaver dam. Typically, quartz-rich, 

fluvial mill tailings mixed with fluvially transported, crushedore material overlie thinly bedded fine-grained mill tailings 

that were deposited in shallow ponds. The calculated mean 

minimum thickness of enriched material in this area is 79 

cm. However, the mean thickness is likely to be somewhat 

greater, because the bottom of the enriched material was not 

reached in cores from the mill tailings fan on the west side 

of upper Frohner Meadows (fig. 13). The enriched material 

contained weighted-average metal concentrations of 2,000 

ppm for arsenic, 36 ppm for cadmium, 290 ppm for copper, 

2,700 ppm for lead, and 2,900 ppm for zinc. The material was 

highly enriched in cadmium and zinc relative to weightedaverage concentrations of material from area A upstream from 

this area. However, this enriched material far exceeds CBPEC 

concentrations for stream bed sediment (table 6) for all five 

ore-related metals. Samples from core line 4 (fig. 3) below the 

impoundment dam contained a moderate thickness of enriched 

material in one of two sites. The core at site 4–0 is was slightly 

enriched in arsenic; the arsenic may have been transported by 

ground water from the main mill-tailings impoundment. It was 

substantially enriched in cadmium and zinc relative to samples 

from core line 3 (fig. 3); surface water from upstream sources 

probably transported these metals in solution.

Area C—Lower Frohner Meadows

The main source of enriched material in lower Frohner 

Meadows is the mill tailings delta in the water-filled pond at 

the west end of the meadow (fig. 16). This delta contains mill 

tailings from the latest production episode at the Nellie Grant 

mine, which ended in the early 1980s. One core (LFMC 1) 

from the southern end of the delta contained 96 cm of contaminated material where it is above water. The thickness of 

contaminated material may increase where the delta is submerged in the pond. The thickness-weighted mean concentrations of 2,300 ppm for arsenic, 50 ppm for cadmium, 240 ppm 

for copper, 1,800 ppm for lead, and 5,200 ppm for zinc were 

about half of the concentrations of those metals found in the 

bulk surface sample from the exposed part of the delta (LFM 

1, fig. 15 of this report; Klein, Thamke, and others, 2003), and 

this difference suggests that these deposits may be stratified. 

The extent of the mill tailings is not well documented, and the 

horizontal extent and thickness of contaminated material in the 

pond were not established.

Core samples from core lines 5 and 6, downstream from 

the mill-tailings delta, contained weighted-average concentrations of 280 ppm for arsenic, 11 ppm for cadmium, 190 

ppm for copper, 600 ppm for lead, and 850 ppm for zinc. 

Enrichment of material in area C is thus relatively minor 

compared with the material upstream in areas A and B, but 

concentrations of all metals exceeded the CBPEC for stream 

bed sediment (table 6). Sampling was not sufficient to determine a mean thickness of the enriched unit, but all samples 

of enriched material came from shallow, buried, fine-grained 

pond-fill deposits or present-day meadow soils. A breached 

beaver pond transected by core line 6 contains high concentrations of arsenic, cadmium, lead, and zinc; these metals are 

in a thin surficial layer of fine-grained, organic-rich pond 

bottom material that is eroding into the active channel during 

periods of high water (fig. 15). Downstream plots of stream 

bed sediment (figs. 17, 18, 20, 21, and 22) suggest that metal 

was added to the stream from the mill-tailings delta at the 

head of the lower meadow.

The wetlands near the outlet of lower Frohner Meadows 

(above site L–3b and L–158, fig. 3) provide a barrier to clasticsediment transport and may be accumulating cadmium and zinc 

from ground and surface water in manganese-oxyhydroxide 

grain coatings of stream bed sediment and buried sediment.

Upper Lump Gulch

Cores from the sediment-filled reservoir in upper Lump 

Gulch (fig. 3) were enriched, in a minor and erratic manner, 

in arsenic, cadmium, lead, and zinc. Small arsenic, cadmium, 

and zinc accumulations are associated with sediments that 

are enriched in manganese. This association suggests that 

46  Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana
arsenic, cadmium, and zinc—which originated in ground 

and surface water flowing from Frohner Meadows into upper 

Lump Gulch—are being deposited in manganese oxyhydroxides. Lead, which enriched the deepest part of core LGFR 

3, probably is present in clastic material that was deposited 

early in the sedimentation history of this site and may have 

existed naturally in the premining environment. Stream bed 

sediment at the northwest side of this reservoir (site L–158) 

contains very high concentrations of arsenic, cadmium, lead, 

and zinc, similar to concentrations of those metals at site L–3b 

immediately upstream. Cleanup of the present-day channel-fill material in the sediment-filled reservoir may prevent 

further movement of some easily transported metal-enriched 

clastic material into upper Lump Gulch. However, removal 

of the deep fill material underlying the reservoir site might 

not be necessary or desirable, because the deep material may 

be absorbing some arsenic, cadmium, and zinc from ground 

and surface water flowing from lower Frohner Meadows into 

upper Lump Gulch.

Panama Mine Meadows 

An unused reservoir in Panama mine meadows (fig. 3) is 

filled with medium- to coarse-grained granitic debris from the 

surrounding bedrock. Samples of fine-grained pond-bottom 

sediment in one core were locally slightly enriched in lead and 

arsenic; the source of the excess lead and arsenic is not clear. 

Two possible sources of lead and arsenic are material transported from several small mines located on the drainage divide 

above the reservoir about 1 mi west of the reservoir (Becraft 

and others, 1963) and material derived from unexploited 

deposits in a poorly exposed vein system above the reservoir. 

Downstream from this reservoir, stream bed sediment was not 

significantly enriched in ore-related metals.

Stream Bed Sediment

Chemical analyses indicate that stream bed sediment 

in the study area downstream from the mine waste and mill 

tailings area is substantially enriched in ore-related metals 

relative to background concentrations in the watershed (table 

5). As compared with the median background concentrations 

in upper Prickly Pear Creek watershed, arsenic typically is 

5–250 times as high, cadmium is 3–75 times as high, copper is 

1.5–10 times as high, lead is 2.5–300 times as high, and zinc 

is 4–75 times as high in 15 of 18 sample sites in the meadow 

area. Concentrations at most sites also exceed the CBPEC 

stream bed–sediment screening concentrations of MacDonald 

and others (2000) for arsenic, cadmium, lead, and zinc.

The highest concentrations of lead are below the Frohner 

mill in Frohner Meadows creek. Decreasing concentrations 

toward the meadow outlet (site L–3b, fig. 3) indicate that 

lead minerals are transported as clastic grains and are diluted 

by less-enriched material. The main mill-tailings pond (area 

B, fig. 3) and the Nellie Grant mill-tailings fan in the lower 

meadow (area C) are minor sources of lead in sediments 

downstream from those sites. Material in the main Frohner 

mill-tailings pond enriches stream bed sediment below the 

pond in arsenic, cadmium, lead, and zinc to a greater degree 

than was measured in sediment below the upper mill tailings 

(area A). The highest concentrations of arsenic, cadmium, and 

zinc in sediment are at the meadow outlet (site L–3b). This 

apparent lack of dilution through the meadow system suggests 

that these metals were transported in dissolved or suspended 

form in surface water and were redeposited, perhaps by 

adsorption on iron and manganese oxyhydroxide grain coatings or in colloidal material, near the meadow outlet.

Site L–158, immediately below the outlet of Frohner 

Basin and upstream from the sediment-filled reservoir in upper 

Lump Gulch (fig. 3), is highly enriched relative to background 

concentrations in the watershed of all ore-related metals 

except copper. Concentrations at this site are similar to those 

at L–3b, located at the outlet to Frohner Basin and immediately upstream from L–158, for all metals except lead; lead is 

markedly higher. These high lead concentrations at the break 

in gradient at the edge of the sediment-filled reservoir may 

have resulted from the local accumulation of metal-rich clastic 

material during a large flood. Substantial decreases in concentrations of all ore-related metals are apparent between sites 

L–158 and L–156 immediately downstream from the outlet of 

the sediment-filled reservoir. These decreases probably are due 

to dilution by water and sediment from an unnamed tributary 

that enters the filled reservoir from the south.

Hydrology

Ground water discharged from unconsolidated deposits 

plays an important role in maintaining the wetland environment of Frohner Meadows. Ground water, moving from topographically higher areas within Frohner Basin, flows predominantly through thin unconsolidated deposits at the uppermost 

weathered zone on top of bedrock and discharges to land 

surface in the wetland areas of Frohner Meadows. Ground 

water discharged in the wetland areas slightly increases stream 

discharge, especially in the downstream part of upper Frohner 

Meadows. Little ground water is discharged through moraine 

and bedrock downstream from lower Frohner Meadows.

Frohner Basin surface water is drained entirely through 

Frohner Meadows creek, which drains into Lump Gulch and 

eventually into Prickly Pear Creek. Frohner Meadows creek 

flows adjacent to the Frohner mine and enters the wetlands 

in the northwestern part of upper Frohner Meadows. An 

unnamed tributary, referred to as “Nellie Grant creek” in 

this report, originates at the Nellie Grant mine and enters the 

wetlands in the west-central part of upper Frohner Meadows. 

Calculated mean annual stream discharge of Frohner Meadows 

creek at the outlet of lower Frohner Meadows is 0.98 ft3/s. Calculated mean monthly stream discharge ranges from 0.19 ft3

/s 

in January to 3.8 ft3/s in May.

Summary  47
An annual water budget for Frohner Basin was developed 

to evaluate relative volumes of water that are lost through 

surface water and ground water discharge and through 

evapotranspiration. Average annual precipitation, about 25 

in., produces about 1,733 acre-ft of recharge to the 1.30 mi2

drainage basin. That volume of water leaves the basin as 

evapotranspiration from forest and grass (55 percent of total), 

stream discharge (41 percent of total), evapotranspiration 

from wetlands (4 percent of total), and groundwater discharge 

through till and bedrock (less than 1 percent of total).

Ground-Water Quality

Dissolved arsenic was present in most (10 of 14) groundwater samples in concentrations exceeding the Montana 

numeric water-quality standard for human health of 20 μg/L in 

ground water (Montana Department of Environmental Quality, 

2002). The highest concentration (3,380 μg/L) was measured 

in a sample collected on October 17, 2001, from well FM–1; 

this well is completed in an area of mill tailings in upper Frohner Meadows (fig. 14). Water from well FM–4, which is completed in an area of fluvial mill tailings derived from the Frohner mine, also had a high concentration of arsenic (414 μg/L). 

Concentrations of dissolved cadmium, copper, and lead were 

low in samples from all wells completed for this study and 

were below the maximum limits of human-health standards 

for drinking water (Montana Department of Environmental 

Quality, 2002). Dissolved zinc concentrations ranged from 

less than 1 μg/L in a sample from well FM–3 to 419 μg/L in 

a sample from well FM–9. High concentrations of cadmium 

and zinc measured in ground water in well MW–1, which was 

completed in a previous study, suggest that these metals may 

be transported locally by infiltration of contaminated surface 

water from Nellie Grant creek into upper Frohner Meadows.

Surface-Water Quality

Concentrations of ore-related trace metals in tributaries 

to Frohner Meadows vary greatly by source of inflow. Small, 

undisturbed tributaries typically have low concentrations of 

arsenic, cadmium, copper, lead, and zinc. Frohner Meadows 

creek, which drains the area that includes the Frohner mine, 

has higher concentrations of trace metals than the small tributaries that are undisturbed by mining. The highest concentrations of all ore-related trace metals were measured in Nellie 

Grant creek, which drains the underground workings and 

reclaimed area of the Nellie Grant mine.

Instantaneous loads of trace metals into and out of 

Frohner Meadows were calculated from instantaneous streamdischarge concentrations and measured concentrations of total 

recoverable trace metals in water samples. Small tributaries 

sampled at sites A, B, C, and D (fig. 14) had small loads of 

trace metals in both the June and August sample sets. The 

larger tributaries of Frohner Meadows creek, where they enter 

upper Frohner Meadows (site F), and Nellie Grant creek (site 

G) contributed the largest loads of total recoverable arsenic, 

cadmium, copper, lead, and zinc to upper Frohner Meadows. 

The largest arsenic loads in surface water were measured in 

Frohner Meadows creek at sites H, I, and J, which are downstream from Nellie Grant creek, and in the main mill-tailings 

deposits in the central part of upper Frohner Meadows. The 

large arsenic loads at these sites indicate that additional arsenic 

is entering Frohner Meadows creek from mill tailings and 

ground water in that area. A major part of the cadmium load in 

Frohner Meadows creek is contributed by Nellie Grant creek, 

which drains the area of the Nellie Grant mine.

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Published in the Central Region, Denver, Colorado

Manuscript approved for publication November 28, 2005

Graphics by author

Photocomposition by Mari L. Kauffmann (Contractor, ATA Services)

Edited by Mary-Margaret Coates (Contractor, ATA Services)

50 Geochemistry of Mine Waste and General Hydrology of Frohner Meadows Area, Jefferson County, Montana