Mine Adits, Mine-Waste Dumps, and Mill 

Tailings as Sources of Contamination

By J. Thomas Nash and David L. Fey

Chapter E6 of

Integrated Investigations of Environmental Effects of Historical 

Mining in the Animas River Watershed, San Juan County, Colorado

Edited by Stanley E. Church, Paul von Guerard, and Susan E. Finger

Professional Paper 1651

U.S. Department of the Interior

U.S. Geological Survey
Contents

Abstract .......................................................................................................................................................315

Introduction.................................................................................................................................................315

Purpose and Scope ..........................................................................................................................316

Field Methods ....................................................................................................................................316

Mineral Deposits Classification and Changes in Mining Technology ...............................................317

Geochemical Characterization of Mining-Related Contamination ....................................................318

Passive Leach Tests and Rankings ................................................................................................318

Geochemistry of Mill Tailings and Tailings Drainage ..................................................................319

Mine-Adit Drainage and Ranking ...................................................................................................322

Metal Concentrations ......................................................................................................................322

Metal Loads .......................................................................................................................................324

Mines on Public Land and in the Animas River Watershed Study Area: Contamination 

Potential from Waste Material and Adit Drainage .................................................................324

Mines on Public Land in the Upper Animas River Basin ............................................................324

Setting .......................................................................................................................................324

Kittimack Mill and Lackawanna Mill Tailings ......................................................................324

North Denver Lake and Ben Butler Mines ..........................................................................327

Little Ida Mine ...........................................................................................................................329

Kittimack Mine..........................................................................................................................329

Site B157 ....................................................................................................................................329

Clipper Mine..............................................................................................................................329

Site B219 ....................................................................................................................................330

Forest Queen.............................................................................................................................330

Mighty Monarch and Last Chance Mines ...........................................................................330

Mines on Public Land in the Cement Creek Basin ......................................................................331

Setting .......................................................................................................................................331

Lark-Henrietta Mine Area ......................................................................................................331

Grand Mogul Mine ...................................................................................................................332

May Day Mine ..........................................................................................................................332

Elk Tunnel ..................................................................................................................................334

Natalie/Occidental and Big Colorado Mines ......................................................................334

Avalanche Mine .......................................................................................................................334

Eveline Mine .............................................................................................................................335

Minnesota Gulch Mines .........................................................................................................335

Monarch Mine ..........................................................................................................................335

Mines on Public Land in the Mineral Creek Basin ......................................................................335

Setting .......................................................................................................................................335

Brooklyn Mine Area.................................................................................................................336

Bandora, Burbank, Imogene, and Ruby Trust Mines .........................................................337

Bandora Mine ...........................................................................................................................337

Burbank Mine Tunnel ..............................................................................................................337

Imogene and Ferricrete Mines, and Unnamed Mine Northwest of Burro Bridge ...........338
Silver Crown Mine ...................................................................................................................338

Ruby Trust Tunnel .....................................................................................................................339

Bonner Mine .............................................................................................................................339

Independence Mine ................................................................................................................340

Paradise Mine Area ................................................................................................................340

Sultan Tunnel ............................................................................................................................341

Discussion and Conclusions ....................................................................................................................341

Comparison with Other Studies of Mine Waste ..........................................................................341

Comparison with Other Studies of Mine-Adit Drainage .............................................................342

Mine Sources in Relation to In-Stream Loads .............................................................................342

Significant Sources for Remediation .............................................................................................343

References Cited........................................................................................................................................343

Figures

 1. Graph showing composition of leachate solutions and classification of 

mine waste .................................................................................................................................319

 2. Map showing location and ranking of mine-waste sites on public land .........................321

 3. Graphs showing composition of mine drainage water as a function of pH ....................323

 4. Map showing location and ranking of mine drainage sites on public land ....................326

 5–20. Photographs showing:

 5. Tailings from the Kittimack Mill (site # 192) ...................................................................327

 6. Yellow and gray tailings from the Lackawanna Mill ....................................................328

 7. Small mine north of Denver Lake ....................................................................................328

 8. Sulfidic mine waste at Ben Butler mine ........................................................................329

 9. Kittimack mine ....................................................................................................................330

 10. Lark mine on flank of Red Mountain # 3 .........................................................................331

 11. Grand Mogul mine in headwaters of Cement Creek ...................................................333

 12. Waste piles of sulfidic rock at May Day mine ..............................................................333

 13. Elk tunnel, west of Cement Creek ...................................................................................334

 14. Collapsed adit of Natalie/Occidental mine ....................................................................335

 15. Drainage from Brooklyn mine ..........................................................................................336

 16. Waste dumps at Bandora mine .......................................................................................337

 17. Flow of water from Burbank mine tunnel ......................................................................338

 18. Ferricrete mine adit ...........................................................................................................339

 19. Lower adit and drainage discharge of Bonner mine ...................................................340

 20. Paradise mine ....................................................................................................................341

Tables

 1. Summary of leachate chemistry for mine waste and mill tailings ....................................318

 2. Ranking of mine-waste sites based on size and passive leach test results ...................320

 3. Summary of mine-adit drainage geochemistry ...................................................................322

 4. Ranking of mine-adit discharge for sites on public land ....................................................325

Abstract

The long history of exploration and mining in the upper 

Animas River basin has produced thousands of prospects and 

now-inactive mines that range in size from small exploration 

pits to large mines with tens of miles of workings and mine 

waste with a corresponding range in size. The recovery of metals required the milling of 18.6 million tons of ore that created 

large volumes of mill tailings, part of which were placed in 

streams, or placed in impoundments after 1935. The high 

precipitation—particularly snowfall—in this area infiltrates 

mine workings, mine-waste dumps, and mill tailings to create 

acidic drainage that in places carries high concentrations of 

metals. To characterize the magnitude of acidic drainage and 

the concentrations of contaminants, we sampled 97 mine-waste 

sites, 18 mill-tailings sites, and 60 mine-adit drainages—the 

most significant ones that we could identify on public lands. 

Detailed descriptions of the geochemical determinations made 

on mine water and mine waste enabled us to rank sites for 

their potential to contaminate the watershed. We utilized three 

scores—acid generation, metal release in leach tests, and size—

to rank waste dumps and mill tailings. For mine-adit water, we 

utilized metal-loading scores for copper and zinc to rank the 

potential to contaminate water and degrade aquatic habitat.

Our geochemical characterization results and rankings 

of sites suggest a wide range in potential to contaminate the 

watershed. Out of the more than 500 identified sites on public 

land, only about 40 sites have sufficient size, adit discharge, 

or waste reactivity to be significant sources of contamination. 

Sites that have high rankings as sources and those identified 

by tracer studies of the main streams deserve attention for 

remediation work.

Introduction

Degraded water quality in streams of the Animas River 

watershed study area is well documented (Church and others, 

1997; J.R. Owen, Unpublished report on water quality and 

sources of metal loading to the upper Animas River Basin, 

Colorado Department of Public Health, Water Quality Control 

Division, 1997; Kimball and others, this volume, Chapter E9; 

Wright, Simon, and others, this volume, Chapter E10), but 

the sources of the contaminants are numerous and difficult to 

quantify. Mining at large and small mines and excavating at 

countless prospects have disturbed millions of tons of mineralized rock in the Silverton area and resulted in chemical 

reactions that release acid and metals to receiving waters in 

the watershed. In this chapter we describe sources of contaminants from inactive mines, mine-waste dumps, and mill 

tailings that are on public land. The larger sources of contaminants from mining on lands administered by the U.S. Bureau 

of Land Management (BLM) and United States Department 

of Agriculture (USDA) Forest Service have been previously 

described by Nash (1999a, 1999b).

Although biologic criteria drive the standards for 

desired water quality in the Animas River watershed study 

area (Besser and others, this volume, Chapter D; Besser 

and Leib, this volume, Chapter E19), chemical methods are 

routinely used to measure water quality relative to biologic 

standards. In this study we used field and laboratory methods 

to obtain chemical analyses of mine-drainage water that can 

be evaluated in the context of water-quality standards. In addition, leach tests of mine waste (Fey, Desborough, and Church, 

2000) provide a measure of potential for acid generation and 

metal release; those test results can be used to evaluate which 

waste materials are most reactive and possibly in need of 

remediation. Whereas leach tests provide reproducible and 

reliable chemical measurements, physical factors at the site 

such as the amount of rain and snowfall and the permeability 

of waste material can affect numerical estimates of potential 

acid or metals sources. The actual water quality measured 

from a mine adit or below a mine-waste dump is emphasized 

in this report because that is a real measure of conditions 

at a site. However, even these determinations are only an 

approximation of the effect on the watershed because they 

do not include processes that may improve or further degrade 

water quality after it leaves the mine adit, mill, or dump site. 

Whereas reactions of mine-adit water with mine-waste materials commonly add acid and metals to water, beneficial reactions with wallrocks and mixing of mine-adit drainage with 

Chapter E6

Mine Adits, Mine-Waste Dumps, and Mill Tailings 

as Sources of Contamination

By J. Thomas Nash and David L. Fey
shallow ground water commonly improve water quality before 

the mine-related water enters a stream (Nash, 2002; Plumlee 

and others, 1999). Water-quality investigations by Kimball 

and others (this volume) indicate that only a few of the sites 

on public land described here provide major contributions of 

mine drainage to the major streams of the study area.

Purpose and Scope

The purpose of this study was to describe the magnitude 

of contamination contributed by mines (mine-adit water), 

mine-waste dumps, and mill tailings on public land.

1. Field observations and sampling were designed to obtain 

representative information for mine sites on public land 

and to compare and rank them as sources of contamination. A limited number of samples were collected at 

private sites, with the owner’s permission. Mines with 

no road access and located more than about 2 mi from 

streams were not sampled because this situation was considered not amenable to remediation.

2. Sites were visited a second time for additional observations and sampling if the initial samples suggested a 

substantial source of contaminants.

3. Mine and mill-tailings sites were evaluated by two classbased ranking methods, rather than by numerical methods, to address uncertainties in field measurements and 

sampling.

Field Methods

Mine-waste and mill-tailings samples were collected with 

a protocol designed to provide a statistically reliable, representative sample of the upper 30 cm of a waste pile by combining 

30 or more subsamples taken at uniform intervals across the 

pile and sieving through a 2-mm screen (Smith, Ramsey, and 

Hageman, 2000). Field studies from 1996 to 2000 included 

one or more visits to more than 300 sites (mines or prospects). 

At some sites we collected replicate samples at the same time, 

by a second sampler, or else during the following year. A 

total of 173 mine-waste dump and mill-tailings samples were 

collected from 97 mine-waste dump sites and 18 mill-tailings 

sites, most of which are on public land. Sites with mine-waste 

dumps smaller than approximately 100 tons generally were 

not sampled. Twenty samples of unmined, altered rock were 

also collected. Representative samples of dump rocks and 

mill tailings from 113 sites were analyzed chemically. A total 

of 193 samples of mine-waste dump material, mill tailings, 

and altered rocks were studied using a passive leach method. 

Laboratory methods used in leach tests of mine waste and 

rock are described by Fey, Desborough, and Church (2000), 

and analytical results are reported in Fey, Nash, and others 

(2000).

Water samples were collected using a simplified 

method described by Ficklin and Mosier (1999); we used a 

disposable 60 mL syringe and 0.45 μm (micrometer) cellulose filter and the addition of ultrapure nitric acid to stabilize 

metals until analysis by inductively coupled plasma–mass 

spectroscopy (ICP-MS) and inductively coupled plasma–

atomic emission spectroscopy (ICP-AES) (Nash, 1999a; 

Nash, 2002). The analytical results for our samples of mineadit drainage water and mineralized surface water are reported 

in the database (Sole and others, this volume, Chapter G). 

All adits on public land known to have flowing mine drainage were sampled, along with a limited number of samples 

from private sites for comparison. All water samples were 

collected in August or September, during low-flow conditions (as defined by von Guerard and others, this volume, 

Chapter B).

Discharge at mine portals, an important parameter in 

metal load calculations, is not easily measured. Discharges 

were measured carefully by Mast and others (2000), but in our 

work were based simply on a visual estimate by Nash. Herron 

and others (Jim Herron, Bruce Stover, and Paul Krabacher, 

Unpublished Lower Animas River reclamation feasibility 

report, Upper Animas River Basin, Colorado Division of 

Mines and Geology, 2000, and similar reports for Mineral 

Creek, Cement Creek, and Upper Animas River reclamation, 

1997, 1998, and 1998) determined mine-adit drainage discharges using a portable weir. Comparison of the estimates by 

Nash with discharges measured by Mast and others (2000) at 

the same sites for similar dates suggests that the differences 

are between about 20 and 50 percent. We emphasize that all 

measurements and estimates at mine portals are minimum 

values, because water commonly is lost into alluvium or into 

fractures in bedrock. This is evident at sites discussed later, 

including Grand Mogul (mine # 35, caved adit, with flow 

through a waste dump on alluvium), the Lark and the Joe and 

Johns (mines # 86 and # 87, with caved adits on alluvium), 

and the Bandora (mine # 332, with caved adit on mine-waste 

dump and talus). Because of the loss of mine water through 

alluvium and bedrock fractures, discharge values used in this 

report may err on the low side by 25–75 percent at some sites. 

The effect of these errors in the calculated loads, discussed 

later, is not easily computed but could be large for the absolute 

values. However, because we use ranked metal-load score 

classes, the relative scores are less affected by erroneous 

discharge values than would be numerical scores. They could 

change the ranking score by as much as one class (for example, “very high” would be “high”).

Site names are those in Church, Mast, and others (this 

volume, Chapter E5) insofar as possible, but many small 

mines and prospects on BLM land do not have accepted 

names. For those sites we use the numeric code employed by 

Hite (Barbara Hite, Unpublished mine land inventory report 

for the U.S. Bureau of Land Management, U.S. Bureau of 

Mines, 1995) with the prefix B, such as B015.

316 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 317

Mineral Deposits Classification 

and Changes in Mining Technology

Mineral deposits of the Animas River watershed study 

area and vicinity can be considered to be of just a few types, or 

they can be split into many subtypes for special purposes such 

as economic geology or mining engineering (Burbank and 

Luedke, 1969; Casadevall and Ohmoto, 1977; Guilbert and 

Park, 1986; Bove and others, this volume, Chapter E3). For the 

purposes of this report, we used a simple three-part classification of deposits.

1. Polymetallic veins, rich in pyrite, and having variable proportions of chalcopyrite, galena, sphalerite, and gold- and 

silver-bearing sulf-arsenide minerals as in the Sunnyside 

mine and the majority of mines and prospects in the 

study area. These deposits tend to be along major faults 

inside and outside the Silverton caldera that have moderate argillic alteration halos of pyrite and clay minerals 

5–10 m wide (Bove and others, this volume). Manganese 

minerals (pyroxmangite and rhodochrosite) are locally 

abundant in some veins, and tungsten (as wolframite, an 

iron-tungsten-oxide) and fluorine (fluorite) are abundant 

in some places.

2. Polymetallic breccia pipes, similar in composition to the 

veins but tending to be richer in sulfide and arsenide minerals, as at the Lark mine (mine # 86, Prospect Gulch) and 

National Belle mine (northwest of the study area, at Red 

Mountain Pass). These deposits are restricted to the caldera fault zone, are highly localized as intense bodies of 

alteration and ore minerals, and are associated with broad 

alteration halos of the acid-sulfate type with disseminated 

pyrite-alunite-clay minerals, as in the Red Mountain 

area (Bove and others, this volume). “Polymetallic” is 

an appropriate descriptor for virtually all of the deposits 

of the Animas River watershed study area because many 

base metals and metalloids (collectively called metals 

for simplicity) are concentrated in these deposits, even if 

miners emphasized silver, gold, copper, lead, or zinc for 

economic reasons.

3. Porphyry deposits containing shattered zones filled by 

copper-molybdenum quartz-sulfide veinlets, as, the peak 

3,792 m and Anvil Mountain areas; these mineralized 

areas, having large vertical and horizontal dimensions, 

have been drilled, but none has been mined in this area. 

Weathering of pyrite in the peripheral alteration halo 

is a source of acidic drainage today (Yager and others, 2000; Bove and others, 2000; Bove and others, this 

volume).

Placer deposits of gold in alluvial gravel were mined in a 

few places such as Arrastra Creek; placer deposits will not be 

mentioned further, as they were small and made only a minor 

contribution to the total production in the watershed. They 

are, however, a reminder that mineralized rocks and veins contributed metals to streams of the area prior to mining activity. 

Studies by Church, Fey, and Unruh (this volume, Chapter E12) 

have shown elevated metal concentrations in premining sediment collected throughout the watershed.

Changes in mining and milling technology through the 

years have had important influences on the materials left 

behind in the mines or placed on mine-waste dumps and milltailings piles (Jones, this volume, Chapter C). In the watershed 

at least two stages of technology can be highlighted:

1. Early (1871–1913), small-volume mining of high-grade 

ore zones, with small associated milling infrastructure. 

The miners lacked powered equipment, created very narrow stopes, and generally brought only hand-picked highgrade ore to the surface. Mine-waste dumps were small 

relative to the amount of ore removed.

2. Later (after 1913), increasingly large scale mining 

of lower grade ores was made possible by consolidation 

of workings, availability of electric- and pneumaticpowered machines, and new milling technology. 

Selective flotation was developed to recover specific 

sulfide minerals. The change in milling style was first 

made at Sunnyside with a new flotation mill built in 

1917. Zinc, one of the toxic metals of prime concern in 

the Animas River (Besser and Brumbaugh, this volume, 

Chapter E18), was not deemed economic and therefore 

not recovered before 1904. Significant amounts of zinc 

are found in all of the ores and mine-waste dumps, and 

zinc-rich materials were intentionally left underground in 

many of the older workings because smelters levied a surcharge if the concentrates contained more than 10 percent 

sphalerite (Ransome, 1901). In this stage, mine tunnels 

became many miles in length (some crossing under natural drainage divides), tramways were used to carry distant 

ore to centralized mills, and large mine-waste dumps and 

mill-tailings piles were made. Tailings handling policies 

changed in 1935 when regulations required that mill tailings be confined to so-called “tailings ponds” rather than 

be allowed to go directly into surface streams (Chase and 

Kentro, 1938). The very large (millions of cubic yards) 

tailings piles of some of the large mills in the region are 

physically stable today (the older ones as at Eureka were 

breached during storm events; Vincent and Elliott, this 

volume, Chapter E22). Their contents remain a matter 

of study and concern, however, because the piles were 

not built on impermeable pads (thus infiltrating water 

can escape through the base into alluvium). This brief 

review of the history and technology of mineral extraction in the study area is a reminder that individual site 

evaluations must consider the mode of mining and milling used at the site before remediation technologies are 

considered.
Geochemical Characterization

of Mining-Related Contamination

Passive Leach Tests and Rankings

Two procedures for determining leachable metals in 

mine waste and other material were applied to samples in 

this study. One of the leaching methods was the EPA-1312 

protocol, which involves mixing mine-waste material with a 

dilute-acid extractant and tumbling for 18 hr. This procedure 

is designed to approximate the effect of rainfall on mine-waste 

material (U.S. Environmental Protection Agency (USEPA), 

1986). Because the EPA-1312 procedure is more labor intensive than the passive leach described in the next section, it 

was not applied to all samples from this study. Results of the 

EPA-1312 method are not described here but are compared 

with results of other methods in Fey, Nash, and others (2000). 

Results for the EPA-1312 leach are in Fey, Nash, and others 

(2000) and in the database (Sole and others, this volume). 

The passive leach method, developed by Desborough and Fey 

(1997), is a simpler approach to determining leachable metals 

and was applied to all samples from sites described here. A 

chemical ranking method utilizing the pH and soluble metals 

derived from the passive leach was described in Desborough 

and Fey (1997) and was applied in this study.

The passive leach method was applied to samples collected in the 1997, 1998, and 1999 field seasons. Selected 

results for some of the more significant sites on public land are 

presented here. In the passive leach tests, a 100-g sample was 

exposed to 2L of laboratory de-ionized water (pH of 5.0±0.2) 

in an open 4L beaker, resulting in a sample/extractant ratio of 

1:20. Samples were left at rest for 1 hr, and then gently stirred 

for 5 s (seconds) to prevent stratification of the leachate. The 

pH of the leachate was measured after 24 hr and then a 60 mL 

sample of the leachate was filtered through a Gelman 0.45-μm 

(micrometer) filter using a disposable 60 mL syringe, acidified with 6 drops of ultra-pure HNO3

, and refrigerated prior to 

analysis by ICP-MS.

Results from the passive leach tests show that the minewaste materials generate a wide range of metal concentrations 

and pH values (table 1; fig. 1). The metal concentrations in 

the leachate solutions are a measure of the mobile metals in 

the sample, and the leachate pH is one measure of the acidity 

generated by the sample. The acidity produced in the passive leach is predominantly from the dissolution of watersoluble acid salts. These salts are mostly hydrous iron sulfate 

salts such as melanterite (FeSO4

•7H2O), copiapite (Fe, Mg)

Fe4(SO4)6(OH)2•20H2O) and jarosite (KFe3(SO4)2(OH)6), 

formed as a result of the oxidation of pyrite (FeS2) and other 

sulfides in the waste material. To characterize and rank the 

waste materials, we utilized the method of Desborough and 

Fey (1997), with slight modification, which assigns scores for 

pH and summed metal concentrations Σ(As+Cd+Cu+Pb+Zn, 

in μg/L). For pH values greater than 6.0, a score of 0 is given; 

for pH between 4.5 and 6.0, the score is 1; for pH between 3.5 

and 4.5, the score is 2; and for pH less than 3.5, the score is 

3. Similarly for summed metal content, scores are assigned as 

follows: less than 500 μg/L, 0; between 500 and 1,000 μg/L, 1; 

between 1,000 and 5,000 μg/L, 2; and greater than 5,000 μg/L, 

3. Because both acid generation and metal release are significant characteristics of mine waste, we added the factors to 

represent the relative chemical potential for waste to adversely 

affect water quality. These chemical score values are shown in 

figure 1. For example, samples plotting in the upper left field 

of figure 1 score a six (three from the low pH, and three from 

the summed metals), and have the most potential for adversely 

affecting water quality. Sum scores of two, three, four, or five 

may result from the different possible combinations of pH and 

summed metal scores. Note that no samples plot in the upper 

three fields on the right hand side of the figure, where the 

high pH limits the concentrations of metals in the leachates. 

Although mine-adit drainage water or leachate solutions with 

high pH can have substantial zinc concentrations, none of 

our waste sample leachates had both high pH and high zinc 

concentrations.

The size of a mine-waste dump is also significant in 

estimation of its potential for contamination and should be 

included in the waste ranking. Size, in (2,000 lb) tons, was 

calculated from field estimates of length, width, and thickness; 

uncertainties in dump geometry and waste density suggest 

that the size value carries an error of roughly ±25 percent. We 

utilized five size categories to cover the large range in dump 

sizes in the study area, ranging from 1 (less than 300 tons) 

Table 1. Summary of leachate chemistry for mine waste and mill tailings.

[pH in standard units; elements in μg/L (micrograms per liter)]

pH Al As Cd Cu Fe Mn Pb Zn

Dump samples (n=150)

Minimum 2.28 0.60 0.04 0.02 0.40 0.20 5.2 0.020 0.50

Median 3.44 150 1.20 5.50 28 500 188 120 300

Maximum 8.13 14,000 3,570 165 6,960 144,000 37,400 30,000 30,900

Mill tailings (n=25)

Minimum 2.57 0.10 0.20 0.02 1.0 30 6.7 0.06 0.70

Median 3.90 11 0.30 14 111 35 405 8,000 1,710

Maximum 7.78 6,400 3.5 95 1,500 55,000 20,000 31,000 25,200

318 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 319

to 5 (greater than 50,000 tons), as shown in table 2. An overall 

mine-waste score is obtained by multiplying the dump size 

score by the chemistry score (sum of the pH and metal scores). 

Not included in the waste score are other factors such as proximity to stream, surface water flowing across waste material, 

draining adit water contacting waste material, proximity to 

ground water, substrate hydrologic conductivity, or other factors that are known to influence mine-related contamination—

these attributes are considered in the verbal site descriptions later in this chapter. Finally, the mine-waste scores are 

converted into five classes that we define as mine-waste rank. 

The five mine-waste ranks, from “low” to “very high,” connote 

the approximate potential to create contamination. Each of 

the three parameters in the waste score carries uncertainty and 

error; a numerical value was not used because it might appear 

to be more precise than its constituent measurements could 

support. The locations and rankings of mine-waste dump sites 

on public land are in figure 2.

Geochemistry of Mill Tailings and 

Tailings Drainage

Mills were numerous in the Animas River watershed 

study area, especially along the upper Animas River where 

waterpower was abundant and railroad transportation available (Jones, this volume). Physical evidence remains for more 

than 50 mills and about 23 mill-tailings sites (Nash, 2000). 

Mills and associated mill-tailings impoundments fall into three 

stages of operation: (1) early stage (pre-1913) relatively small 

stamp mills and unconfined mill tailings that were mostly 

lost to the nearby river (either poured into the river or washed 

away during storms); (2) middle stage (c. 1913–1935), larger 

mills that used flotation to recover zinc and created larger 

mill-tailings impoundments, many of which failed during 

major storm events; and (3) late stage (post-1935), large mills 

that placed tailings into designed impoundments after the 

Executive Order in 1935 instituted regulations on mill-tailings 

disposal; most of these tailings are in place today. Tailings 

from early stage 1 mills are not candidates for remediation 

because they have been dispersed downstream, where they 

contribute to the postmining baseline geochemistry of the 

watershed. Some of the stage 2 tailings pose problems today, 

either in place or as overbank fluvial deposits transported by 

flood water (Vincent and Elliott, this volume; Vincent and 

others, 1999). Some fluvial mill tailings have been reclaimed, 

such as those south of Eureka. Stage 3 mill tailings, notably 

the large tailings impoundments of the Mayflower mill, are 

mostly in place (Jones, this volume).

One estimate of the potential for contamination from mill 

tailings comes from leach tests. In our studies of 20 representative mill-tailings samples, half of the samples created leachate solutions of high acidity (pH <3.6), and these acidic solutions contained high to very high concentrations of cadmium, 

copper, lead, zinc, and other metals (fig. 1).

Samples of water that has reacted with mill tailings are 

difficult to obtain because seeps from tailings impoundments 

are rare in this area. In places one can collect pore water 

from within impounded mill tailings (from an auger hole) or 

water seeping from the sides of an impoundment. Pore water 

samples from two impoundments had pH values of 5.9 and 

4.0, and high to extremely high concentrations of cadmium, 

10

100

1,000

10,000

100,000

2 3 4 5 6 7 8

pH, IN STANDARD UNITS

6

5

4

3 2 1 0

5

4

3 2

3

4

SUMMED METALS (As+Cd+Cu+Pb+Zn),

IN PARTS PER BILLION

chemistry class score

Mill tailings

Mine-waste material

Figure 1. Composition of leachate solutions and classification of mine waste.
Table 2. Ranking of mine-waste sites based on size and passive leach test results.

[Site name and # from Church, Mast, and others (this volume); (3), number of samples in average. Size score, acid score, metal score, and waste score explained 

in text. Waste rank, VH, very high; H, high; M, medium; L, low]

Site name Mine or site 

number Size score Acid score Metal score Waste score Waste rank

Brooklyn (3) 141 5 3 3 30 VH

Kittimack tailings 192 5 2 3 25 VH

B157 4 3 3 24 VH

Grand Mogul (3) 35 4 3 3 24 VH

Lackawanna tailings 287 4 3 3 24 VH

Lark (6) 86 4 3 3 24 VH

Henrietta 700 (2) 85 4 3 2 20 VH

Henrietta 800 505 4 3 2 20 VH

May Day (2) 181 5 3 1 20 VH

Ruby Trust 169 4 3 2 20 VH

Clipper 114 3 3 3 18 VH

Bandora (3) 332 5 1.7 2 18 VH

Brooklyn tailings 3 3 3 18 VH

Monarch 180 3 3 3 18 VH

Ben Butler 9 3 2.7 3 17 H

Minnesota Gulch 144 3 3 2.5 17 H

Little Ida 15 4 3 1 16 H

Kittimack mine 201 4 3 1 16 H

Frisco tunnel 19 3 2 3 15 H

Mammoth tunnel 148 4 3 0.5 14 H

Silver Crown (2) 133 4 3 0.5 14 H

Bonner (3) 172 5 2.7 0 13 H

B237 3 2 2 12 H

Burbank 207 4 2 1 12 H

Joe and Johns 87 2 3 3 12 H

Sultan tunnel 266 4 2.5 0 10 H

Upper Brooklyn 2 3 2 10 H

B213 3 2 1 9 M 

N. Denver Lake 3 2 1 9 M 

Legal Tender 189 3 2.5 0.5 9 M 

Forest Queen (2) 195 3 3 0 9 M 

Henrietta 900 506 3 3 0 9 M 

Imogene (3) 136 4 2.3 0 9 M 

North Star tailings 310 3 1.5 1 9 M 

Paradise West 3 3 0 9 M 

Paradise (3) 168 4 2.3 0 9 M 

Independence 171 3 3 0 9 M 

Early Bird 8 4 2 0 8 M 

Avalanche (2) 149 3 2.5 0 8 M 

Last Chance 289 3 2 0.5 8 M 

Columbine 260 3 2.5 0 8 M 

B021 (2) 1 3 3 6 L

Mighty Monarch 285 3 2 0 6 L 

East Burro bridge 3 2 0 6 L 

Elk tunnel (2) 147 3 2 0 6 L 

Ruby Trust tailings 1 3 3 6 L 

Eveline 91 1 2 3 5 L

Ferricrete mine 137 2 2 0 4 L

Eagle Chief 14 3 1 0 3 L

B183 3 1 0 3 L

B229 3 1 0 3 L

B182 3 0 0 0 L

Highland Mary dump 357 5 0 0 0 L

Highland Mary tailings 351 5 0 0 0 L

320 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 321

Figure 2. Location and ranking of mine-waste materials at sites on public land in the Animas River watershed study area. 

Rank is based on size, metal release, and acid-generating potential described in table 2. Map elevations are in feet, except for 

the prominent peak between Middle and South Forks Mineral Creek, designated as peak 3,792 m (its elevation shown in meters).

Kittimack

Bandora

Grand Mogul

Elk tunnel

Low

 Moderate

High

Very high

B182

Sultan

Little Ida

Clipper

Legal Tender

Mammoth tunnel B157

Streamflow gauging station

Silverton

C O L O R A D O

DENVER

Grand

Junction

Animas River

watershed

study area

A72

M34

A68

CC48

Brooklyn

Lark

May Day

Mine-waste rank 

Henrietta 800

Henrietta 700

Henrietta 900

Ruby Trust tailings

Independence Brooklyn

Ruby Trust

Frisco tunnel

Eagle Chief Early Bird

Ben Butler

N Denver Lk

B237

B213 B229

B183

Joe and Johns

Eveline

B021

Minnesota Gl

E Burro Bridge

Upper

Monarch

Lackawanna Mill

 tailings

Last Chance

Mighty Monarch

Burbank

Paradise

west

Brooklyn

Bonner

Imogene

Ferricrete

Silver Crown

Paradise

North Star 

 Mill tailings

Forest Queen

Highland Mary tailings

Columbine

tailings

EXPLANATION

South Fork

Avalanche

Cement Creek

Middle Fork

Animas River

Mineral Creek

Arrastra Cr

13,800

12,890

13,370

13,488

13,152

13,370 13,068 13,474

Base from U.S. Geological Survey

Silverton, 1:100,000, 1982.

Elevations shown in feet except peak 3,792 m

0

0

1 2 3 MILES

1 2 3 KILOMETERS

Kittimack Mill

tailings

3,792 m

37°48'45"

37°52'30"

107°45' 107°37'30"

Eureka

Howardsville

Highland Mary
copper, lead, and zinc. Springs and diffuse inflows on the west 

bank of the upper Animas River near the Powerhouse (1 mi 

northeast of Silverton) are acidic, highly conductive, and rich 

in metals (Paschke and others, 2005; Kimball and others, 

this volume; J.T. Nash, unpub. data, 2000); these inflows and 

possible relations to mill tailings warrant further investigation. 

Water samples of this type, collected from geologically similar 

mill tailings elsewhere on the Western Slope of Colorado 

(Nash, 2002) also tended to be acidic (pH from 2 to 4), with 

high to extremely high concentrations of base metals.

Mine-Adit Drainage and Ranking

Mine-adit drainage is more common in this area than 

in most mining areas of the United States. The combination 

of high precipitation, extensive fracturing (Yager and Bove, 

this volume, Chapter E1; McDougal and others, this volume, 

Chapter E13), and high relief creates numerous springs and 

drainage from mine tunnels. Mine tunnels are common in the 

study area because they afforded efficient access to deep mine 

workings while also draining water from the mine. Vertical 

mine shafts in the study area are also commonly full of water, 

but this water does not usually flow from the shafts and will 

not be considered further. Mine tunnels, on the other hand, 

discharge from 1 to more than 400 gpm (gallons per minute); 

the water quality is highly variable, and most is degraded 

relative to water-quality standards for drinking water or for 

wildlife use. All observations and sampling were conducted 

in late August or early September of 1997 to 2000, during 

lower flow stages of the hydrograph (von Guerard and others, 

this volume). Repeated measurement and sampling of mineadit drainage show that some adit drainages are relatively 

consistent in discharge or composition, but that others vary 

substantially through the year. Seasonal variations in discharge 

and water quality were studied in detail by Mast and others 

(2000) and are discussed elsewhere in this report (Wright, 

Simon, and others, this volume, Chapter E10; Leib and others, 

this volume, Chapter E11; Mast and others, this volume, 

Chapter E7). Variations in mine-adit discharge estimates and 

measurements may explain some differences in ranking by 

various studies discussed later.

The range in geochemical data from mine-adit drainages is summarized in table 3 and figure 3. Both highly acidic 

and moderately acidic mine-drainage water sampled in this 

investigation contains dissolved metal concentrations that 

could be threats to aquatic life. Based on the percentage of 

sampled water that exceeds chronic aquatic life water-quality 

standards (table 3), the most common problems are with zinc, 

pH, and iron, followed by aluminum, manganese, copper, and 

cadmium; other investigations have found similar tendencies. The concentrations of lead and arsenic are much less 

likely to exceed water-quality standards. Because base-metal 

concentrations generally correlate with acidity (fig. 3; Plumlee 

and others, 1999), drainage water with pH values from 2 to 

4 tend to have highest concentrations of toxic metals such as 

cadmium, copper, and zinc. However, metal loadings in the 

study area tend to be highest from draining adits with water 

having pH values from 4 to 6 with discharges greater than 

about 50 gpm.

Highly acidic water (pH 2.3–3.5 observed, fig. 3) is found 

in 27 percent of mine-adit drainages in this study; some springs 

have pH values in this range (Mast and others, this volume). 

Moderately acidic mine-adit drainage (pH 3.5–5.5) is found 

in 38 percent of mine-adit water in this study; springs flowing 

from altered red rock in the study area also commonly have 

pH values in this range. Near-neutral pH values (5.5–7.9) are 

found in 35 percent of draining mine adits, generally where 

tunnels have cut sedimentary rocks or propylitically altered 

volcanic rocks (Yager and Bove, this volume, pl. 1; Bove and 

others, this volume). Metal concentrations range greatly, but in 

general increase with acidity.

Table 3. Summary of mine-adit drainage geochemistry.

[Elements determined by ICP-MS, in parts per billion (μg/L); 108 samples; 

μS/cm, microsiemens per centimeter]

Minimum Median Maximum

Percent 

exceeding 

ALWQ1

pH 2.3 5.2 7.4 84

Conductivity μS/cm 17 380 >2,000 nc

Al μg/L 1.8 380 52,850 64

As μg/L <0.03 1.1 186 5

Cd μg/L <0.01 2.4 1,600 45

Co μg/L 0.06 9.4 154 nc

Cu μg/L <0.1 15 12,000 51

Fe μg/L 20 4,000 28,800 75

Mn μg/L 1.4 1,030 87,200 53

Ni μg/L 0.1 8.8 105 nc

Pb μg/L <0.1 2.0 2,520 19

Zn μg/L 8 980 76,000 87

1

ALWQ, Aquatic life water quality standard (chronic) of CWQCD (2001) 

for other parts of Colorado; nc, not computed.

Metal Concentrations

Eight metals are generally considered to be potentially 

harmful to aquatic health—aluminum, arsenic, cadmium, 

copper, iron, manganese, lead, and zinc (Manahan, 1994; 

U.S. Environmental Protection Agency, 1999; 2001). For 

aquatic biota of the Animas River watershed study area, the 

two metals of prime concern are copper and zinc (J.R. Owen, 

unpub. report, CDPH, 1997). Besser and Leib (this volume) 

have shown that dissolved zinc and copper have the greatest effect on aquatic biota in the study area. Other potentially 

toxic metals, such as silver, cobalt, mercury, molybdenum, 

nickel, and selenium, were detected at low concentrations 

322 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 323

relative to standards for human and aquatic health; only in a 

few cases of extremely acidic mine-adit drainage water were 

these elements sufficiently concentrated to merit concern. Of 

the potentially toxic metals, some have elevated concentrations more commonly than others. Comparing our analyses 

of 108 water samples at mine portals and mine-waste dumps 

with chronic water-quality standards for aquatic life (table 3; 

CWQCD, 2001; Besser and others, this volume, Chapter D), 

we note that for more than half of the mine sites, water compositions exceeded the standards for aluminum, copper, iron, 

manganese, and zinc, whereas concentrations of arsenic and 

lead rarely exceeded the standards. In the descriptions of mine 

sites later in this chapter, metal concentrations in water will 

be described as “high” or “very high” relative to our analyses 

of mine-adit water (summarized in table 3): “high” denotes 

values greater than the median and “very high” denotes values 

greater than the 80th percentile of our analyzed samples. 

Water measurements termed “very high” are usually substantially in excess of chronic water-quality standards for aquatic 

life.

1

10

100

1,000

10,000

100,000

1,000,000

123456789

pH

0.1

1

10

100

1,000

123456789

pH

0.1

1

10

100

1,000

10,000

100,000

123456789

pH

10

100

1,000

10,000

100,000

123456789

pH

0.1

1

10

100

1,000

10,000

123456789

pH

0.1

1

10

100

1,000

10,000

100,000

123456789

pH

1,000,000 IRON, IN PARTS PER BILLION LEAD, IN PARTS PER BILLION ZINC, IN PARTS PER BILLION

COPPER, IN PARTS PER BILLION ARSENIC, IN PARTS PER BILLION ALUMINUM, IN PARTS PER BILLION

Figure 3. Composition of mine drainage water as a function of pH (standard units).
Metal Loads

Another measure of the degree of contamination from 

mine sites is the magnitude of metal loads. A metal load 

is the product of metal concentration and the discharge of a 

stream or mine adit (Mast and others, this volume; Kimball 

and others, this volume). Although health effects on wildlife 

and humans generally are related to metal concentrations, 

loads provide an alternative way of evaluating metal budgets 

in watersheds. We have calculated metal loads for representative examples of mine-adit drainage where the water 

composition has been determined and the discharge has been 

measured or estimated. Because of the time variability in 

discharge and metal concentrations over the year (Mast and 

others, 2000) and uncertainties in our discharge estimates, 

we have expressed the loads as ranked values (table 4). The 

calculated loads for sites sampled at similar times of the year 

over a 3-year period demonstrate substantial variations, but 

not enough to significantly change the relative rankings. For 

example, the loads calculated for the Grand Mogul mine 

(site # 35) for our three sample events all ranked it among 

the top eight sites.

Metal loads of mine-adit drainage from 49 sites have 

been ranked into four classes, from “very high” to “low” 

(fig. 4). These metal load ranks are an approximate measure 

of probable contamination to the watershed. The mine-adit 

drainage ranking (table 4) reflects the sum of scores for copper 

and zinc loads. The load scores for copper and zinc individually are shown in table 4. The locations and ranks of mine-adit 

drainages are shown in figure 4. Additional metals could be 

included in the ranking system, as was done by Butler, Owen, 

and Simon (Peter Butler, Robert Owen, and William Simon, 

Unpublished report to Colorado Water Quality Control 

Commission, Animas River Stakeholders Group, 2001). 

Arsenic was not included because most drainage water in the 

watershed has low arsenic concentrations relative to waterquality standards.

Mines on Public Land and in the 

Animas River Watershed Study Area: 

Contamination Potential from Waste 

Material and Adit Drainage

The following is an itemized discussion of inactive 

mines located on public land in the Animas River watershed 

study area. The discussion is broken down by basin: the upper 

Animas River basin, the Cement Creek basin, and the Mineral 

Creek basin. For each site, we present both the mine waste 

ranking (where waste material is present) and the mine drainage ranking (where applicable), along with field observations 

and other pertinent information from other reports.

Mines on Public Land in the Upper 

Animas River Basin

Setting

The majority of mine production in the study area was 

from the upper Animas River basin (Animas River upstream 

from Silverton), possibly as much as 80 percent of the total 

(estimated from production records; Nash, 2000). Much of 

this basin is underlain by weakly altered (propylitic) volcanic 

rocks in the central and eastern part of the Silverton caldera 

(Bove and others, this volume). Some of the large vein deposits in this subbasin are in radial faults east of the caldera, in 

weakly altered volcanic rocks; these weakly altered rocks 

provide some acid-neutralizing capacity from minerals such as 

calcite and chlorite. Tailings in several settings—private sites, 

public land, and fluvial deposits—are a significant source of 

contamination in this basin.

Most of the large and famous historical mines of the area, 

such as the Sunnyside (mine # 116), Mayflower (mine # 304), 

and Shenandoah-Dives (mine # 355), are on private land 

(Church, Mast, and others, this volume). Public land in this 

basin is administered by the U.S. Bureau of Land Management 

(BLM); more than 200 small mines and prospects are on BLM 

land, and 11 of these were considered to have waste piles large 

enough in tonnage and of sufficient reactivity to be candidates 

for remediation (Nash, 1999b). Fifteen mines on public land in 

this basin release adit drainage, and they are ranked in table 4. 

More than 30 historical mills were located in this basin, but 

most of these sites have little or no remaining mill tailings, 

because either (1) the tailings were not impounded and were 

lost to the Animas River by fluvial transport, or (2) some 

impounded tailings were removed and reprocessed during 

World War II (Jones, this volume). Fluvial mill tailings are 

still common in and along the upper Animas River, redeposited 

after floods breached mill-tailings impoundments. Fluvial mill 

tailings in the flood plain of the upper Animas River 1–3 mi 

south of Eureka are described in detail elsewhere (Vincent and 

Elliott, this volume).

Kittimack Mill and Lackawanna Mill Tailings

Two mill-tailings sites on (or partly on) BLM land, in 

close proximity to the upper Animas River, are among the 

largest sources of contaminants from public land in this 

basin. These are the Kittimack Mill tailings (site # 192) and 

the Lackawanna Mill tailings (site # 287). The magnitude of 

contamination is difficult to quantify, but geochemical analysis 

of the tailings materials shows them to be reactive and rich in 

metals of concern. Because of the large volume of mill tailings at these sites, they rank as very high sources of contaminants (table 2). Leach tests on one sample from each of these 

mill-tailings piles show similar results: the samples generate acidic leachate solutions with extremely high dissolved 

324 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 325

Table 4. Ranking of mine-adit discharge for sites on public land.

[Site name and mine number from Church, Mast, and others, this volume; (3), samples in average; site names with B from Hite (unpub. report, U.S. Bureau of 

Mines, 1995); Cu R and Zn R, copper and zinc load ranks; MD rank, mine discharge rank; MD class, mine discharge class (VH, very high; H, high; M, medium; 

L, low); Cond., specific conductance in μS/cm (microsiemens per centimeter); Q, adit discharge in liters per minute]

Adit site Mine No. Sample ID Cu R Zn R MD rank MD class pH Cond Q L/m

Grand Mogul (3) 35 NAW 530 1 2 1 VH 3.1 470 100

Natalie/Occidental 153 NAW 551 3 1 2 VH 5.2 498 1,600

Joe and Johns 87 NAW 217 2 4 3 VH 2.7 740 80

Brooklyn (3) 141 NAW 508 5 7 4 VH 3.5 590 80

Big Colorado 150 NAW 552 9 6 5 VH 3.6 960 400

Henrietta 800 (2) 505 NAW 213 4 9 6 VH 2.5 1,651 22

B 219 prospect NAW 713 12 5 7 VH 3.2 1,110 20

Ben Butler (3) 9 NAW 156 8 11 8 VH 3.0 453 11

Kittimack (3) 201 NAW 235 7 14 9 VH 5.8 236 93

Henrietta 700 85 NAW 215 11 10 10 VH 2.5 1,550 20

Bandora (3) 332 NAW 399 21 3 11 VH 6.3 484 93

Bonner (3) 172 NAW 517 13 12 12 VH 2.9 545 53

Monarch 180 NAW 321 6 16 13 H 4.1 270 40

Paradise (3) 168 NAW 520 22 8 14 H 4.7 1,010 533

Lark 86 NAW 204 10 21 15 H 3.2 380 20

Mammoth 148 NAW 227 18 13 16 H 4.7 983 160

Ruby Trust (2) 169 NAW 524 17 15 17 H 6.0 272 1,200

Eveline 91 NAW 201 15 26 18 H 3.1 370 40

N. Denver Lake (3) NAW 161 24 17 19 H 3.6 182 17

Elk tunnel (3) 147 NAW 311 25 19 20 H 6.0 938 400

U.S. Basin 143 NAW 582 14 33 21 H 5.6 807 20

Mogul South 30 NAW 329 23 25 22 H 4.4 380 12

Paradise small NAW 869 32 18 23 H 5.1 605 160

Ferricrete (2) 137 NAW 512 28 22 25 M 5.2 280 140

Avalanche (3) 149 NAW 309 16 36 26 M 3.8 372 40

Early Bird 8 NAW 150 19 34 27 M 3.2 339 6

Little Giant 303 NAW 721 30 23 28 M 5.2 120 20

Burbank (2) 207 NAW 603 26 28 29 M 3.8 388 500

King Solomon 306 NAW 883 20 41 30 M 3.2 40 40

Little Ida 15 NAW 380 27 32 31 M 5.2 90 20

Imogene (3) 136 NAW 511 33 29 32 M 6.6 219 147

NW Burro Bridge NAW 598 34 30 33 M 7.3 201 40

Chattanooga Curve 135 NAW 579 37 31 34 M 7.3 282 40

Sultan tunnel 266 NAW 298 29 39 35 M 5.4 494 100

Legal Tender 189 NAW 396 42 27 36 M 5.3 337 93

Paradise west NAW 868 35 37 37 L 4.9 183 400

Forest Queen (2) 195 NAW 232 46 24 38 L 7.2 990 80

Silver Crown 133 NAW 577 36 38 39 L 5.2 360 40

Mighty Monarch 285 NAW 735 39 40 40 L 5.5 183 200

B015 NAW 412 38 47 41 L 5.2 600 12

Bandora east NAW 647 48 35 42 L 3.2 505 20

Minnesota Gulch 144 NAW 878 40 37 43 L 5.6 264 40

Highland Mary 359 NAW 741 41 45 44 L 2.9 239 40

Chattanooga Moly NAW 872 40 46 45 L 5.8 581 40

Last Chance 289 NAW 064 44 42 46 L 6.7 230 240

East Burro Bridge NAW 597 43 48 47 L 7.2 148 12

Eagle Chief 169 NAW 144 45 44 48 L 4.6 80 20

Mazeba NAW 651 49 43 49 L 5.7 210 20

Picayune prospect NAW 852 47 49 50 L 6.8 164 20
Figure 4. Location and ranking of mine drainage sites on public land, Animas River watershed study area. Ranking explained 

in text and in table 4. Map elevations are in feet, except for the prominent peak between Middle and South Forks Mineral Creek,

designated as peak 3,792 m (elevation shown in meters).

Metal load ranking

No drainage

Medium

High

Very high

Low

EXPLANATION

Streamflow gauging station

Silverton

 Animas River

 watershed

 study area

A72

M34

A68

CC48

Brooklyn

Lark

May Day

Picayune

Mazeba

Grand Mogul

B219

Little Ida

Early Bird Eagle Chief

Ben Butler

N. Denver Lk

south Mogul adit

Little Giant

King Solomon

Highland Mary

Paradise

Burbank

Bandora

Bonner

Sultan Last Chance

Mighty Monarch

Legal Tender

Monarch

Bandora East

Paradise W

Silver Crown

Imogene

Elk Tunnel

US Basin

Chattanooga Curve

3,792 m

Bullion King

B15

Mammoth

Ruby Trust Minnesota Gl

Ferricrete

NW Burro Bridge

E Burro Bridge

Forest Queen

Kittimack

Joe and Johns

Eveline

Big Colorado

Natalie/Occidental

Avalanche

Henrietta 700

Henrietta 800

Chattanooga

Moly

Paradise

small

C O L O R A D O

DENVER

Grand

Junction

South Fork

Cement Creek

Middle Fork

Animas River

Mineral Creek 13,800

12,890

13,370

13,488

13,152

13,370 13,068 13,474

37°48'45"

37°52'30"

107°45' 107°37'30"

Base from U.S. Geological Survey

Silverton, 1:100,000, 1982.

Elevations shown in feet except peak 3,792 m

0

0

1 2 3 MILES

1 2 3 KILOMETERS

Eureka

Howardsville

326 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 327

concentrations of copper, manganese, lead, and zinc. Pore 

water from the Kittimack Mill tailings (site # 192, fig. 5) had a 

pH of 4.0, high cadmium, and very high copper, lead, and zinc 

concentrations. Pore water from the Lackawanna Mill tailings (site # 287, fig. 6) had a pH of 5.9, high copper and lead 

concentrations, and extremely high cadmium, iron, manganese, and zinc concentrations. These chemical results suggest 

a high potential for contamination. Results from a tracer study 

by Kimball and others (this volume) show that downstream 

from the Kittimack Mill tailings, colloidal Fe and dissolved 

Ca, Mg, Mn, Cu, Zn, and SO4

 increase. Their location on 

the flood plain made them vulnerable to erosion in extreme 

storms, and seepage or runoff from these impoundments can 

travel straight into the Animas River with little or no chance 

for natural attenuation. A series of shallow wells is needed to 

test for actual infiltration of contaminated water into alluvium 

beneath the mill tailings and the magnitude of ground-water 

flow toward the river.

Leach tests on one sample from the Lackawanna Mill 

tailings impoundment showed high acid generation and high 

metal release, for a waste rank of very high. Likewise, a leach 

test of one sample from the Kittimack Mill tailings impoundment showed moderate acid generation and high metal 

release; the Kittimack waste ranking is also very high because 

the volume of tailings appears to be larger than that at the 

Lackawanna site.

The Lackawanna Mill tailings, entirely on public land, 

were removed by the BLM in the fall of 2000 and transported 

to a new repository at the May Day mine site (# 181) on 

Cement Creek. Similar removal action or substantial remediation work should be considered for the Kittimack Mill tailings, 

which are partly on BLM land.

North Denver Lake and Ben Butler Mines

Two small mines on BLM land in the northern part of 

the upper Animas River basin are moderate sources of contamination (Nash, 1999b) because the dump materials are highly 

sulfidic and mine workings release acidic water. The adit north 

of Denver Lake (site B233, fig. 7) releases water with a pH of 

3.0 and high to extremely high concentrations of cadmium, 

copper, lead, and zinc; the drainage load ranking is high. The 

open trench at the Ben Butler mine (mine # 9; fig. 8) contains 

water with a pH of 3.5 and very high cadmium, copper, lead, 

and zinc concentrations; the load ranking is very high. The 

acidic drainage from North Denver Lake mine infiltrates alluvium before it reaches wetlands at the headwaters of the upper 

Animas River. The water at the Ben Butler mine trench flows 

only slightly and cannot be traced on the surface to Burrows 

Creek, a tributary to the upper Animas River. Passive leach 

tests show that these sulfidic waste materials generate acidic 

leachate solutions (pH values 3.55 and 2.83) carrying high 

Figure 5. Tailings from Kittimack Mill (site # 192) cover tens of acres in flood plain of upper Animas 

River. Because the mill tailings were piled on alluvial gravels, metals leached from the tailings would 

probably migrate through the permeable gravels to the river.
Figure 6. Yellow and gray tailings from Lackawanna Mill (site # 287) were placed in flood plain of the 

upper Animas River, east of Silverton. Because of evidence that the tailings were releasing contaminants 

to the river, the BLM removed the tailings in 2001 and emplaced them in a repository at the May Day mine.

Figure 7. A small mine north of Denver Lake was the source of the pile of sulfide-rich rocks in 

foreground. A small flow of water from the adit gains acid and metals on the dump, then flows east 

to wetlands at the source of the upper Animas River. Drainage in foreground is about 1⁄2 m across.

328 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 329

concentrations of base metals. More specifically, the sample 

from Ben Butler mine released extremely high concentrations 

of lead and zinc and high concentrations of cadmium and copper. The waste leach ranking for North Denver Lake mine is 

medium and for Ben Butler mine is high (table 2).

Little Ida Mine

Major quartz-sulfide veins under Tuttle Mountain, west 

of the Ben Butler mine, were worked by several major mines. 

Other smaller mines explored parts of the vein system and produced sulfide-rich mine-waste dumps of moderate size. The 

Little Ida mine (site # 15) and a mine adjacent to the Frisco 

tunnel (site # 19) are on public land. Leach tests on mine waste 

from the Little Ida mine showed high acid generation and low 

metal release, for a waste rank of high. The leach test on waste 

from the mine near the Frisco tunnel showed moderate acid 

generation but high metal release, for a waste rank of high.

Kittimack Mine

This mine adit (mine # 201) high above Minnie Gulch 

(fig. 9) releases a moderate discharge of water with a pH of 

5.5, but the metals are sufficiently concentrated to produce a 

load ranking of very high. Leach tests on mine-waste material 

showed high acid generation and relatively low metal release; 

the summary waste rank is very high. The relatively high 

metal loadings rank suggests that the mine-adit drainage merits attention. However, the fact that the rocks and alluvium in 

this area are propylitically altered suggests that natural attenuation of metals may occur as the mine-drainage water flows 

toward the upper Animas River, about 2 mi to the west.

Site B157

West of the Kittimack mine several north-trending adits 

explored sulfide veins. One of the dumps, B157, is of moderate size and highly sulfidic. The collapsed adit at site B157 

does not release mine drainage. Leach tests on waste-dump 

material from B157 showed high acid generation and high 

metal release, for a very high waste score. Because this site is 

relatively dry, it may pose a lower risk of contamination than 

chemically similar waste dumps that are wet.

Clipper Mine

In the alpine Sunnyside Basin the Clipper mine 

(mine # 114) workings are small in comparison with others 

nearby. However, the medium-sized waste dump is highly 

sulfidic and produces a notable kill zone (an area downslope 

Figure 8. Large quartz-sulfide veins that were mined at the Ben Butler mine are exposed in these shallow 

trenches, and sulfidic mine waste covers the adjacent slope. Little water from the trenches flows onto the 

surface, but some may flow into the subsurface. Trench is about 2 m across.
of a dump where vegetation has been killed and cannot be 

reestablished, due to mine drainage or the presence of waste 

material) for several hundred feet downslope, indicating acidic 

runoff. The workings release no mine drainage. Leach tests 

show high acid production and high metal release, for a waste 

rank of very high (table 2).

Site B219

Drainage from a small prospect in California Gulch has 

a drainage load ranking of very high because the small flow 

of water contains especially high metal concentrations. This 

prospect is so small as to be virtually a natural outcropping; a 

small mine tunnel explored a quartz vein 3 ft wide. No mine 

waste was studied because the volume is so small; thus we 

have no waste ranking for site B219.

Forest Queen

The Forest Queen mine (site # 195) was a problem 

because the mine tunnel released a substantial flow of water, 

and it formerly ran over the mine-waste dump into nearby 

wetlands. This site has been studied by several scientists 

(Stanton, Fey, and others, this volume, Chapter E25). Remediation was undertaken by the BLM in 1999 as a technology demonstration project. The mine-adit drainage was not 

unusually acidic, but the water quality was degraded. This 

drainage was measured and sampled at least 21 times by 

Mast and others (2000), who recorded pH values in the range 

of 3.7–6.6 during a 4-year period. In August 1997, the mineadit drainage at the collapsed portal had a pH of 5.1 and high 

concentrations of cadmium, iron, and zinc (concentrations of 

arsenic, copper, and lead were lower than in most mine water). 

Concentrations of dissolved zinc ranged from 355 to 709 ppb 

(Church, Mast, and others, this volume, table 7); the one 

Nash sample contained 435 ppb zinc. The load ranking is low. 

Passive leach studies of two samples yielded similar results, 

a high score for acid generation and a very low score for 

metal release. The mine-waste rankings are medium. A water 

sample collected below the mine-waste dump in 1997 (prior 

to remediation) contained lower metal concentrations than did 

the water at the portal.

Mighty Monarch and Last Chance Mines

Two mine tunnels on Kendall Mountain east of Silverton 

release high flows of near-neutral water that contains only 

slightly elevated metal concentrations. The drainage load rankings are low for the Mighty Monarch (site # 285) and low for 

the Last Chance mine (site # 289). Leach tests on waste from 

the Mighty Monarch mine showed moderate acid generation 

but low metal release; the waste ranking is low. Tests on two 

samples of waste from the Last Chance mine showed moderate 

acid generation and low metal release, for waste rankings of 

medium (table 2).

Figure 9. The Kittimack mine has a dump of modest size and relatively low sulfide content, but water 

flowing from the caved adit (left side of photo) is of concern. Although the pH of the water (5.8) is not highly 

acidic, the water carries substantial amounts of zinc.

330 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 331

Mines on Public Land in the Cement 

Creek Basin

Setting

Mine production from this basin was substantially smaller 

than from the adjacent upper Animas River basin, and only 

seven mills and one smelter were built. Although major production came out of the American tunnel, the ore was hauled to 

the Mayflower Mill on the upper Animas River and very little 

waste was placed nearby. Historical mill tailings impounded at 

Gladstone, prior to use of the American tunnel, were removed 

in 1996. Most of the public land in this basin is administered 

by the BLM. A high percentage of this basin is underlain by 

highly altered volcanic rocks, including parts of the three Red 

Mountains that contain acid-sulfate alteration and abundant 

disseminated pyrite (Bove and others, 2000; Bove and others, 

this volume). The seven mill sites were evaluated for remediation (Nash, 1999a). Fifteen sites in this basin are ranked by 

drainage loads in table 4.

Lark-Henrietta Mine Area

Four problematic sites are adjacent mines in upper 

Prospect Gulch: the Lark, Henrietta, and Joe and Johns mines, 

and the 1970s mine-waste dump from the 800 level of the 

Figure 10. Lark mine on flank of Red Mountain # 3 created a dump of modest size but relatively high 

sulfide content; the dump was reclaimed by BLM in 2002. More complex are springs in the hillslope below 

the mine that are highly acidic and rich in metals; the springs are of uncertain origin despite several 

detailed studies.

Henrietta mine (site # 505). The Lark (site # 86) and the 

Joe and Johns (site # 87) mine workings are connected by a 

crosscut tunnel, and some evidence indicates that this crosscut 

carries mine drainage from the Lark workings to the Joe and 

Johns mine. This may explain why only a small discharge of 

water is released at the lowest level of the Lark mine (Lark 

Number 3 adit). Discharges from the Lark and the Joe and 

Johns adits are relatively small, but an unknown amount infiltrates into alluvium and bedrock fractures behind the collapsed 

portals. Remediation work in 1999 was directed at the discharge from the Joe and Johns adit. Surface water in Prospect 

Gulch has been studied in detail using tracer methods (Wirt 

and others, 1999; 2001) to quantify the sources of contamination. The work by Wirt and others demonstrates a large inflow 

of acidic, metal-rich water into Prospect Gulch creek in the 

vicinity of the Lark-Henrietta mines (fig. 10). However, these 

detailed studies coupled with reconnaissance studies by Nash 

do not provide conclusive evidence for the flow path of the 

acidic water. This area of about 60 acres, including both private 

mining claims and public land, is one of the larger sources 

of contamination in the Prospect Gulch subbasin and is so 

complex that it is difficult to reliably distinguish among many 

possible sources.

Mine-drainage load rankings (table 4) show how the 

drainages in Prospect Gulch compare with others in the study 

area. Drainage water from the Joe and Johns mine and the 

seep from the Henrietta 800-level waste pile are extremely 
high in metals and have load rankings of very high. Mineadit drainage sampled at the portals of the Lark and Henrietta 

700 (site # 85) tunnels has lower metal concentrations and 

load rankings of high and very high, respectively. These rankings do not consider details such as variability through the 

year or possible errors in flow estimates due to infiltration 

into bedrock fractures or alluvium that would lower the load 

values. The seeps in and near the Henrietta 800 waste dump 

are especially complex (Wirt and others, 2001).

Leach tests were made of six samples from the Lark 

mine upper and lower dumps (two levels of site # 86); all 

six samples showed high acid generation. Some variation 

occurred in metal release: high in three samples and medium 

in three samples. Considering the range in composition visible at the dump surface, the differences among samples and 

test results are not surprising. The average waste ranking for 

the Lark site is very high. Leach tests on two samples from 

the Joe and Johns waste dump (site # 87) showed high acid 

generation and high metal release, but the relatively small size 

of the dump makes the waste ranking high, instead of very 

high.

The waste dump between the Lark and Henrietta mines 

contains abundant sulfides and is generally less weathered than 

most dump piles in the area, which is consistent with reports 

that a lessee created this waste while exploring the 800 (deepest) level of the Henrietta mine in the 1970s. This waste pile is 

so close to Prospect Gulch that material slides into the creek, 

and runoff flows directly into the creek. A leach test on waste 

from the 800 mine-waste dump showed high acid generation 

and moderate metal release; the waste ranking is very high. 

Less clear is the nature of very acidic water that flows from 

the long narrow waste pile in several places. One possibility 

is that the acid and associated metals are leached from the 

dump when surface runoff crosses the dumps. However, there 

is also evidence for a series of acidic seeps between the dump 

and the road; these seeps have pH values near 2 and extremely 

high metal concentrations. Surface water, after flowing over 

and through the dump, has lower metal concentrations, but the 

higher flow volumes result in higher loadings. This surface 

water flows into Prospect Gulch, and related acidic, metal-rich 

seeps may enter the creek as diffuse inflows, which would 

explain at least part of the increases measured by Wirt and 

others (1999; 2001). A series of wells would be required to 

document the flow and composition of this shallow ground 

water and its flow path.

The Henrietta 900 tunnel (site # 506) was driven in the 

1970s from a lower elevation in Prospect Gulch with the goal 

of intercepting ore under the Henrietta 700 level. The tunnel is 

dry, which is difficult to explain, and the dump contains sparse 

sulfide minerals, suggesting that the target was not reached (as 

described by Jim Herron, Bruce Stover, and Paul Krabacher, 

Unpublished Cement Creek reclamation feasibility report, 

Upper Animas River Basin, Colorado Division of Mines and 

Geology, 1998). The waste was tested by passive leach and 

found to generate acid, but it released very little metal; the 

waste ranking is medium. Remediation is needed to minimize 

the slumping of waste into Prospect Gulch, but the waste is not 

as problematic as most mine waste in the study.

Grand Mogul Mine

This mine (site # 35) in the northern part of the Cement 

Creek basin is one of the larger sources of contamination 

among all sites on public land. Drainage from the collapsed 

mine tunnel seeps through the sulfidic dump and emerges 

at the edge of Cement Creek (fig. 11). Because the flow is 

diffuse, it was difficult to determine the discharge, suspected 

to be on the order of 10–20 gpm but possibly higher. The 

dump is in the flood plain of the creek and there is no chance 

for natural attenuation before the mine drainage enters the 

stream. The mine drainage was detected as an acidic inflow 

enriched in aluminum, iron, copper, and zinc in the tracer 

studies of Cement Creek (Kimball and others, this volume). 

Three seep samples were collected and analyzed in 1997 and 

1998 (Nash, two; Mast and others, 2000, one). The pH values 

ranged from 2.9 to 3.4, and concentrations of cadmium, copper, iron, manganese, lead, and zinc ranged from very high to 

extremely high. Computed metal loads for the Grand Mogul 

seepage are the highest in this study (load rank very high). 

Loads calculated for several repeat sampling events differ 

by about 20 percent, but they all rank in the very high group.

The Grand Mogul dump is highly sulfidic, and sphalerite and galena are visible. Leach tests on three samples show 

similar results: high acid generation and high metal release. 

The leach solutions were highly acidic (pH values 3.3 and 2.7) 

and carried extremely high concentrations of lead and zinc and 

very high amounts of cadmium and copper. The waste ranking 

is very high. The drainage water carried high concentrations of 

lead but not as high as suggested by the leach tests.

The flow paths of mine-adit drainage and dump seepage 

at the Grand Mogul are not well defined but sufficient to guide 

remediation planning. Ownership of the mine and waste dump 

is in question; the dump itself appears to be on public land.

May Day Mine

This site on lower Cement Creek (site # 181) has a 

relatively large dump that is rich in sulfide minerals (fig. 12; 

Stanton, 2000). The mine adit is dry, but water of uncertain 

origin flows below the dump according to piezometer data 

and geophysical studies (Smith and others, 2000; Wright, 

Kimball, and Runkel, this volume, Chapter E23). No mine-adit 

drainage was sampled by us, thus we have no load ranking for 

comparison with other sites. Leach tests on two samples of 

dump materials from upper and lower levels showed very different compositions, as expected from the visible differences 

in mineralogy. The sample from the upper level yielded an 

acidic solution near pH 3 that carried very high concentrations 

of cadmium and copper, and extremely high concentrations 

of lead and zinc. The second sample from the lower level, 

332 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 333

Figure 11. Grand Mogul mine in headwaters of Cement Creek looks like hundreds of other mine sites, 

but tests show that the waste dump is highly reactive, capable of high acid generation and metal release. 

Of more direct concern is water flowing from the base of the dump, probably related to the mine workings 

northeast (left) of the dump; metal loadings from these seeps are among the highest found in this study.

Figure 12. May Day mine, excavated to explore veins west of Cement Creek, created these large 

waste piles of sulfidic rock. To minimize reactions from snowmelt and rain, the BLM reclaimed the 

dump in 2001 by emplacing a geosynthetic liner and covering with clean soil. Lackawanna Mill tailings 

were also emplaced there at that time.
with low sulfide and jarosite content, yielded much less acid 

and metals. The average of the two waste samples yields a 

mine-waste ranking of very high. In the summer of 2001, this 

site was made into a repository by the BLM for mill tailings 

from the Lackawanna Mill. A geosynthetic clay liner was 

installed and the site covered with clean soil for revegetation 

(Rob Robinson, BLM, oral commun., 2004).

Elk Tunnel

This tunnel on the west side of Cement Creek 

(site # 147) was driven westward to access vein deposits. 

The material on the dump is weakly mineralized, suggesting 

that the target vein was not reached. Today, the adit releases 

a large flow (135–260 gpm; Mast and others, 2000) of water 

that deposits conspicuous orange iron deposits outside the 

mine and down the slope to Cement Creek (fig. 13). The 

dump is relatively small and composed mostly of propylitically altered volcanic rocks with low sulfide content. A leach 

test showed moderate acid generation and very low metal 

release; the waste rank is low. The mine-adit drainage flows 

along the edge of the dump but does not appear to react 

with the waste materials. The mine-adit drainage has been 

sampled many times (10 samples, Church, Mast, and others, 

this volume, table 7; 3 by Nash; and several by Herron and 

others (Unpub. Cement Creek reclamation feasibility report, 

CDMG, 1998)). The pH values ranged from 6.1 to 7.2, and 

analyses show consistently low concentrations of most metals. Iron concentrations are high, ranging from about 2,200 

to 10,000 ppb, possibly because dissolved oxygen content 

is very low. The metal of prime concern, zinc, ranges in 

concentration from about 140 to 210 ppb. The mine-drainage 

load rank of this site is high.

Natalie/Occidental and Big Colorado Mines

These mines on South Fork Cement Creek release large 

quantities of mine-adit drainage (fig. 14) that flow directly 

into the creek. The weakly acidic water carries high iron 

concentrations and substantial concentrations of other metals. 

The loading ranks are among the highest in this study (very 

high), largely due to the high discharge. The dumps at the 

Big Colorado (site # 150) may be contributing metals to the 

drainage, but the dump at the Natalie/Occidental (site # 153) 

does not appear to react much with the mine water. Because 

of uncertainties in property status when we sampled in 1998, 

no waste samples were collected at these sites.

These mines clearly are significant sources of contamination in the Cement Creek basin and rank among the highest loaders in the entire study area. The Natalie/Occidental 

tunnel in particular should be evaluated for remediation. It is 

one of about eight sites in this study that release a large flow 

(>100 gpm) of near-neutral pH water with substantial concentrations of copper and zinc and thus are high copper and zinc 

loaders (table 4).

Avalanche Mine

This small site (# 149), in a canyon east of Cement Creek, 

is of concern chiefly because the adit releases acidic drainage. 

Three samples (Nash, two; Mast and others, 2000, one) show 

pH values ranging from 3.6 to 3.8 and very high concentrations of copper, iron, and zinc. The acidic water flows over 

a small mine-waste dump and into a small tributary east of 

Cement Creek. The drainage load rank is medium, near the 

median for all draining mines on public land. Leach tests on 

two samples produced solutions with pH values of 3.6 and 3.8, 

and low metal concentrations relative to other samples in this 

study. Concentrations of iron and cadmium in the leachates 

were elevated relative to biologic criteria. The average waste 

rank for this site is medium.

Figure 13. Elk tunnel, driven west of Cement Creek, did not 

intersect veins of value but does collect water from deep in the 

mountain. The pH of the water and the metal concentrations 

are not extreme, but because of the high flow, the metal loads 

are high.

334 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 335

Eveline Mine

This very small mine (site # 91) on Dry Gulch, about 

1,000 ft north of the west-flowing reach of Cement Creek, 

releases a small volume of pH 3.1 water carrying high concentrations of metals. Despite the low discharge, the load ranking 

is high. The dump is small, but reacts with mine-adit drainage. 

The leach test on one waste sample shows high metal release 

and moderate acid generation; because the volume of waste 

is small, the waste rank is medium.

This site is atypical in that it creates a high loading from 

a small flow of water. The mine is one of several sites studied 

here that was excavated into a zone of ferricrete. The colocation in and along the ferricrete zone probably indicates 

that this mine is along a natural flow path of mineralized 

water. (See Wirt and others, this volume, Chapter E17.) Partial 

remediation of the low discharge should be feasible, but if the 

metal-rich flow is largely related to unmined altered rocks 

on Red Mountain, then remediation might not achieve the 

intended results.

Minnesota Gulch Mines

Several small mines in Minnesota Gulch (site # 144) 

created small dumps with very high concentrations of sulfide minerals, and one adit creates drainage with a pH of 2.9. 

Although small in size, these mines and dumps create drainage 

that is rich in base metals. The metal load rank of low reflects 

the small discharge. This drainage enters the Minnesota Gulch 

creek at the base of the mine-waste dumps; the creek disappears into the alluvial fan before it can reach Cement Creek, 

but the subsurface flow must eventually enter Cement Creek. 

Minnesota Gulch was determined in a tracer study to add 

substantial loads of aluminum, manganese, copper, and zinc 

to Cement Creek (Kimball and others, this volume).

Leach tests on two samples collected from two adjacent 

and compositionally similar waste dumps show similar results: 

very high acid generation and high to moderate metal release. 

The average waste rank for this site is very high.

Another very small prospect, site B015, just a few meters 

from Cement Creek, also creates a small flow of metal-rich, 

pH 3.2 water that flows into the creek. Due to the small discharge, the drainage load ranking for this site is low.

Monarch Mine

The Monarch mine (site # 180) in Porcupine Gulch was 

the site of relatively recent mining, possibly the 1970s. The 

collapsed lower tunnel releases a small flow of drainage, and 

because of high metal concentrations its drainage rank is high. 

Leach tests on two samples from the Monarch mine-waste 

dumps (upper and lower levels) showed high acid generation 

and high metal release; the average waste ranking for the site 

is very high. Mine-adit drainage and dump runoff from this 

site have ample opportunity to react with propylitically altered 

volcanic rocks before entering Cement Creek. The relatively 

small size of the mine and waste dumps and good road access 

suggest that the site would be amenable to remediation.

Mines on Public Land in the Mineral 

Creek Basin

Setting

Mines in this basin are much smaller than in the central 

part of the study area, and the amount of patented land is less 

than in the basins to the east. The majority of the public land 

in this basin is administered by the USDA Forest Service. The 

geology of this basin is more diverse than the other basins 

as it lies astride the western margin of the Silverton caldera, 

includes several intrusive centers and associated highly altered 

rocks with prominent red colors, and is the only basin with a 

Figure 14. Collapsed adit of Natalie/Occidental mine releases 

one of the larger flows of mine water in the study area. Metal 

concentrations of the pH 6 water are not unusually high, but 

because of the high flow rate, loads of copper and zinc are high. 

Adit is about 11⁄2 m across.
significant amount of sedimentary rock. Seven mills were built 

in this basin, but all were quite small; the largest two mills 

were on Mineral Creek near Silverton, not far from the confluence with the upper Animas River. Mill tailings do not appear 

to be a significant factor in this basin. The metal load rankings 

of 19 sites in this basin are in table 4.

Brooklyn Mine Area

An area of about 100 acres in Browns Gulch in the 

vicinity of the Brooklyn mine (site # 141) is one of the most 

highly disturbed areas in the Mineral Creek basin and clearly 

is degrading the water quality of the creek. This mined area, 

of mixed private and public ownership, has evidently been 

worked by several operators over the years, with more activity in the past 20–40 years than has taken place in most of 

the Animas River watershed study area. The most significant 

problems relate to sulfidic mine-waste dumps, a small mill 

and tailings pond, and drainage from the major mine adit.

Water drains from the adit at about 10–20 gpm; composition of the water at the adit mouth appears to be variable over 

time, as analyses of pH and metals reported by Lovekin and 

others (Jonathan Lovekin, Michael Satre, William Sheriff, 

and Matthew Sares, Unpublished abandoned mine land report 

for San Juan Forest, Columbine Ranger District, Colorado 

Geological Survey, 1997), Mast and others (2000), Herron 

and others (Jim Herron, Bruce Stover, Paul Krabacher, and 

Dave Bucknam, Unpublished Mineral Creek reclamation 

feasibility investigations report, Upper Animas River Basin, 

Colorado Division of Mines and Geology, 1997) and from our 

work differ and show a larger range than for most mine-adit 

drainages. Measured pH values range from 3.2 to 4.8, and 

metal concentrations range from relatively low for mine water 

(near aquatic life standards) to highly degraded (4 to more 

than 20 times the aquatic life standards). The bigger problem 

is what happens to this water after it leaves the adit and reacts 

with sulfidic waste rocks on the long face of a large minewaste dump (fig. 15).The mine-adit drainage reacts with the 

waste to become more acidic, dropping to a pH of 2.9, and 

metal concentrations rise dramatically. Iron, copper, and zinc 

are the most significant contaminants; zinc, at about 150 times 

the aquatic life standard, is possibly most problematic. The 

load ranking for the Brooklyn adit drainage is among the highest in this study (very high), and the loads are even higher after 

the water’s reaction with dump materials.

Leach tests on three waste-dump samples showed consistent results: very high acid generation and moderate to high 

metal release. The averaged waste ranking for this site is very 

high. The ranking for the mill tailings also is very high; the 

tailings behave like the mine waste and release large amounts 

of metal and acid.

The Upper Brooklyn mine dump, north of the Brooklyn 

mine, created waste that is chemically similar to that of the 

Brooklyn mine, and likewise released a high amount of acid 

Figure 15. Drainage from Brooklyn mine flows down over sulfidic waste rocks for more than 

100 m, gaining acid and metals. Water quality degrades considerably between the adit and the 

base of the dumps.

336 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 337

in the leach test. The mine-waste ranking for the upper dump 

site rank is high, but the score is considerably lower than for 

the Brooklyn mine dump because the amount of waste is much 

smaller.

Browns Gulch was noted as a substantial contribution of 

aluminum, manganese, lead, and zinc in the Mineral Creek 

tracer study (Kimball and others, this volume). Multiple 

sources of contamination lie in this subbasin, including mines 

and altered rocks above and below the Brooklyn mine, but the 

mine and dump drainage from the Brooklyn mine area appear 

to be the largest source of contaminants.

Bandora, Burbank, Imogene, and Ruby 

Trust Mines

These four mines are problems chiefly from their release 

of relatively large amounts (approximate range 50–200 gpm) 

of near-neutral-pH but contaminated water; they will be 

discussed together because of their geochemical similarities. 

Median flow volumes include: Bandora, 45 gpm; Burbank, 

39 gpm; Imogene, 75 gpm (Mast and others, 2000); Ruby 

Trust, 100–150 gpm (Nash estimate). Seven samples from 

these four sites were collected by Nash from 1997 to 1999, 

and 15 samples are described by Mast and others (2000). The 

water from these mines has near-neutral pH values (5.4–7.4), 

but zinc concentrations are sufficiently large to create substantial loadings. Most metal concentrations are low, but iron and 

manganese are high, and zinc ranges to more than 15,000 ppb. 

The high iron concentrations are reflected by the red iron 

oxyhydroxides that precipitate from the drainage water. The 

drainage load rankings are as follows: Bandora, very high; 

Ruby Trust, high; Imogene, medium; and Burbank, medium.

Bandora Mine

Leach tests were made on three samples from the 

Bandora mine (site # 332; fig. 16). Two samples yielded similar results—high metal release and moderate acid generation, 

for waste rankings of very high. One of the leachate solutions 

carried the highest lead concentration of this study; however, 

lead concentrations in mine-adit drainage water were relatively 

low in this study. A sample of predominantly gray sedimentary 

rock on one of the lower dumps released little metal and a low 

amount of acid, for a ranking of low. The average waste ranking for the Bandora site is very high.

Burbank Mine Tunnel

The Burbank mine tunnel (site # 207) was excavated 

about 20 years ago to access veins identified higher on the 

mountain, but our examination of the dump rocks suggests that 

little ore was encountered. The tunnel collects a large amount 

of water (fig. 17), and the pH of 6.6–7.4 suggests that much of 

the water had reacted with propylitically altered volcanic rocks 

of the type that crop out at the site. The load rankings for copper and zinc (table 4) were medium, suggesting that this is not 

a major source of those two metals of concern. A leach test on 

one dump sample showed moderate acid generation and low 

metal release, and a waste rank of high.

Figure 16. The Bandora mine created a series of mine-waste dumps that are relatively 

unreactive because they are calcareous sedimentary rocks. However, the mine tunnels collect 

and release water with substantial amounts of zinc, despite the near-neutral pH.
Imogene and Ferricrete Mines, and Unnamed 

Mine Northwest of Burro Bridge

These mines are on the west side of Mineral Creek in 

an area of extensive ferricrete deposits. They release relatively 

large flows (20–100 gpm) of near-neutral-pH water that immediately deposits prominent iron oxhydroxide floc (fig. 18). 

Ferricrete is exposed at the mine portals, suggesting that the 

tunnels were made to explore fracture zones that were premining water pathways. The mine workings appear to be relatively 

small, judging from the small volume of waste at the portals, 

and the mine waste is not highly sulfidic. The concern at these 

sites is for the drainage waters; the drainage load rankings for 

all three mines are medium.

Leach tests on three samples from the Imogene mine 

(site # 136) showed very low metal release and moderate to 

high acid generation. The average waste ranking for this site 

is medium. A sample from the Ferricrete mine (site # 137) 

dump showed moderate acid generation and low metal release, 

for a waste ranking of low. No leach test was made of waste 

from the site northwest of Burro Bridge.

Although metal-enriched water flows from these tunnels, 

the source of metals in these mine waters may be largely from 

unmined altered rocks. Although remediation methods such as 

plugging the tunnels would be expected to reduce metal loads, 

analyses of flow paths and fracture systems are needed to 

design effective seals.

Silver Crown Mine

Near Chattanooga horseshoe curve are several prospects for molybdenum and base metals related to an intrusive 

complex (Bove and others, this volume). The Silver Crown 

mine (site # 133) is in volcanic rocks, like the majority 

Figure 17. The Burbank mine tunnel failed to intersect veins exposed 

higher on the mountain, but it continues to release a large flow of 

water carrying enough zinc at pH 5.4–6 to be a significant loader.

338 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 339

of mines in the study area, but has a mineral assemblage 

that suggests higher temperatures of a contact or skarn-type 

deposit. At the surface, the volcanic rocks are not highly 

altered (propylitic). The predominant green colors on the 

dump do not suggest that acid is being generated by waste 

or mine discharge, but two leach tests show high acid generation; metal release was relatively low. The waste rank is high, 

in part because the site is relatively large. Mine-adit discharge 

is ranked low (table 4) and is clear; it has a pH value of 5.7, 

seemingly buffered by the propylitic rocks. Seepage through 

the dump has essentially the same pH, suggesting little or no 

reaction with the dump waste. The site is close to a tributary of 

Mineral Creek, and mine drainage and dump seepage waters 

flow directly into the tributary.

Ruby Trust Tunnel

The Ruby Trust tunnel (site # 169) was driven northward 

to intersect veins that crop out higher on the mountain. The 

tunnel facilitated haulage of ore to the mill and also served to 

drain water from the mine workings. As with numerous other 

deep tunnels in the area, this one continues to carry a large 

volume of water. Load ranking is high. The pH of 5.5–6.0 and 

the composition of the water suggest that the mine drainage 

reacted with propylitically altered rocks cut by the tunnel. 

Because mine-adit drainage flows over the dump and into 

nearby Middle Fork Mineral Creek, work to minimize reactions with the mine waste may reduce metals loading.

A leach test on one dump sample showed high acid generation and moderate metal release, for a waste ranking of very 

high. A leach test on a sample of mill tailings showed similar 

acid generation but high metal release; only a small volume of 

mill tailings remains at the site.

Bonner Mine

This mine (site # 172) on Middle Fork Mineral Creek had 

workings and dumps on several levels, and drainage is released 

on three levels (fig. 19). Based on 11 water samples collected 

from 1997 to 1999 (Nash, 4; Mast and others, 7), we know 

that the pH values are consistently acidic (from 2.7 to 3.4) 

and concentrations of cadmium, copper, iron, manganese, and 

zinc are high. Concentrations of zinc ranged from about 1,500 

to 3,700 ppb. Concentrations of copper also were very high. 

Remediation work in 2000 was designed to improve water 

quality and water management. Information gained during 

excavation in September 2000 (William Simon, oral commun., 

2000) suggests that the several mine levels were not interconnected, or had become sealed off, because water in the upper 

levels did not drain through the lowest tunnel. Mine water at 

three levels flowed out over mine waste prior to remediation.

Figure 18. The Ferricrete mine adit was driven to explore large outcrops of ferricrete but found no 

ore. The mine water is typical of many in the study area with near-neutral pH but high iron content. 

Although zinc concentration in the water is lower than in many mine-adit waters, high flow volume 

creates a substantial zinc load.
Leach tests on three Bonner mine-waste samples showed 

high acid generation and very low metal release; the average 

waste rank is high. The concentrations of copper and zinc 

in leachates were above the median for the study. Because 

these dumps are close to the creek, runoff can enter the 

creek with little or no attenuation. The dump may also be 

adding acid and metals to the percolating mine-adit drainage 

water.

Independence Mine

Independence mine (mine # 171), west of the Bonner 

mine complex, has a mine-waste dump that is much smaller 

than those at the Bonner, but the mineralogy and host rocks are 

similar. Leach tests show high acid generation, but low metal 

release, similar to waste samples from the Bonner. The waste 

rank is medium.

Paradise Mine Area

Several small adits near the headwaters of Middle Fork 

Mineral Creek release large flows of water (pH 4.7–5.2) that 

create prominent white and red deposits close to the portals. 

The largest of these, the Paradise mine (site # 168), is famous 

for the extremely high aluminum concentration in mine-adit 

drainage and the snow-white precipitate that forms on the 

dump (fig. 20). Mineralogical studies show that the white 

material is the hydrous aluminum-sulfate mineral basaluminite [Al4

(SO4)(OH)10•5H2O]. This mine-adit drainage has a 

metal-load ranking of high. Load ranking for aluminum is the 

highest of mine-adit waters in this study, but zinc and copper 

loads are not as high. Load ranking for the Paradise adit is 

high. Nearby adit drainages (informally here named Paradise 

small and Paradise west) have similar compositions but lower 

flow. Paradise west had lower metal load rankings.

Figure 19. Lower adit of Bonner mine, and drainage discharge that flows 

to Middle Fork Mineral Creek.

340 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 341

Leach tests were made on three samples from the Paradise 

waste dump and one sample from the smaller dump to the west. 

The tests of dump waste showed moderate acid generation and 

low metal release; the average mine-waste rank for this site is 

medium. One sample of red iron floc on the Paradise minewaste dump showed high acid generation but low metal release. 

A sample of the white aluminum-rich precipitate showed moderate acid generation and low metal release.

The Paradise mine workings are relatively small, judging from the size of the dumps, and the pH of the water (5.1) 

is relatively high. Arguments were made (Nash, 1999a; Mast, 

Verplanck, and others, 2000) that most of the water has reacted 

with unmined, altered rocks of peak 3,792 m. Steep topography and the large volume of altered rocks that make up that 

peak (Bove and others, this volume) produce metal-enriched 

shallow ground water that can flow into the mine workings or 

fractures. One remediation option, sealing the tunnel, would 

minimize water contact with mineralized rocks in the workings, but we suspect that water of similar character would be 

released along other fractures and that the net improvement in 

water quality in Middle Fork Mineral Creek would be small.

Sultan Tunnel

This site (# 266) is unusual for the study area in that 

the tunnel and mine workings are in a stock of granitic rock 

(Yager and Bove, this volume). The waste dump contains 

abundant pyrite, but few base-metal sulfide minerals were 

visible. A leach test showed high acid generation, but low 

release of copper and zinc; the waste rank is high because of 

the large dump size and high acidity. Mine drainage from the 

adit has substantial flow, a pH value of 6.2 (quite high), and 

moderate copper and zinc concentrations. The mine drainage 

is diverted into a simple ditch, which to some extent minimizes the interaction of mine drainage with the dump waste.

Discussion and Conclusions

Comparison with Other Studies of Mine Waste

The study of mines and their waste dumps in the Animas 

River watershed study area by Herron and others (Jim Herron, 

Bruce Stover, and Paul Krabacher, Unpublished Lower 

Animas River reclamation feasibility report, Upper Animas 

River Basin, Colorado Division of Mines and Geology, 2000) 

included leach analyses of waste materials from more than 

130 sites in which leachate solution pH, metal concentrations, 

and total acidity were determined. The waste characterization 

studies by Herron and others are similar to our studies, and 

the rankings are generally similar. Comparison of rankings for 

32 sites that both groups studied showed most to be similar, 

but rankings were substantially different for some sites. The 

discrepancies may reflect differences in sampling or leach 

protocols. If the discrepancies influence remediation planning, 

Figure 20. The white color and high flow from the Paradise mine make it famous. Several research 

investigations have documented the very high aluminum concentration in this water; the bright white 

material is an aluminum oxyhydroxide phase (basaluminite) that precipitates from the mine water.
further studies should be made to resolve the rankings in 

question. Herron and others (Unpub. Mineral Creek feasibility 

investigation report, 1997; Unpub. Cement Creek reclamation 

feasibility report, 1998; Unpub. Upper Animas River reclamation feasibility report, 1999; Unpub. Lower Animas River 

reclamation feasibility report, 2000 ) are the sole source of 

information for mine-waste sites that are on private land.

Mine waste from representative mines and mill tailings 

in 22 adjoining mining districts on the Colorado Western 

Slope were studied by the same techniques as used here (Nash, 

2002). Passive leach results for 116 samples from those mining 

areas span a larger range than reported here, including more 

values that would rank as low in the scale used here. That 

study supplements the results described here, and suggests that 

release of acid and high concentrations of heavy metals is characteristic of polymetallic mine-waste dumps in the region.

Comparison with Other Studies of 

Mine-Adit Drainage

Previous studies of mines on BLM land (Barbara Hite, 

unpublished mine land inventory report for the U.S. Bureau 

of Land Management, U.S. Bureau of Mines, 1995) and on 

USDA Forest Service land (Unpub. abandoned mine land 

inventory report, San Juan Forest, Columbine district, CGS, 

1997) provide additional descriptions, hydrogeochemical data, 

and interpretations that are generally similar to those of this 

study. Differences of data or opinion for some specific sites 

have been discussed elsewhere (Nash, 1999a, 1999b). Some 

of those differences are matters of emphasis placed on metal 

concentrations rather than metal loads; the previous studies 

tended to emphasize problems of some mine-adit drainages 

having high concentrations but discharges of less than 10 L/m, 

whereas we emphasized the importance of sites with higher 

discharges and higher loads.

The metal-load rankings determined (table 4) are 

in fair accord with the results from Herron and others (Unpub. 

Mineral Creek feasibility investigation report, CDMG, 1997; 

Unpub. Cement Creek reclamation feasibility report, CDMG, 

1998; Unpub Upper Animas River reclamation feasibility 

report, CDMG, 1999; Unpub. Lower Animas River reclamation feasibility report, CDMG, 2000), but the rankings for 

some drainage sites differ substantially. Explanations of the 

differences could involve numerous factors, such as time of 

sampling, sampling protocol, or analytical methods. Hydrogeochemical results, discharges, and computed metal loads 

vary in time; thus, no single sampling event should be used to 

determine remediation strategy.

Mine-drainage water in the headwaters of the 

Uncompahgre River and San Miguel River (Nash, 2002), 

just a few miles north and west of the Animas River 

watershed study area, spans a compositional range that is 

similar to the mine-adit drainages described here and includes 

some extremely acidic water that is even more metal-rich 

than any sampled in our study area. The Western Slope study 

(Nash, 2002) included sampling and chemical analysis of 

180 surface-water samples; no loads were calculated. The 

compositional similarities are especially strong for the mineadit drainages in Red Mountain Creek basin, north of Red 

Mountain Pass. This area is geologically continuous in the 

Red Mountain acid-sulfate alteration system (Dalton and others, this volume, Chapter E2; Bove and others, this volume) 

and is characterized by acidic springs and very acidic mineadit drainage that mimic the springs and mine-adit drainages 

of the Prospect Gulch area (Wirt and others, 2001) and the 

Koehler tunnel–Carbon Lakes area (Kimball and others, this 

volume). Iron-rich mine-adit drainages, natural springs, and 

ferricrete deposits continue west from Middle Fork Mineral 

Creek into the Howard Fork of San Miguel River in the Iron 

Springs mining area near Ophir. A regional pattern of acid, 

iron-, copper-, and zinc-rich spring and surface waters radiates 

from the Red Mountain complex.

Mine Sources in Relation to In-Stream Loads

Quantification of the amount of contamination from 

mine-adit drainages and mine-waste dumps that moves into 

streams is difficult. Although great effort was made to sample 

inflows to streams, especially in the vicinity of the area’s 

inactive mines, the tracer studies of Kimball and others (this 

volume) were not able to directly quantify the contributions 

from most mines in the watershed. Even for draining mine 

adits within a few hundred feet of the streams, the contributions of loads are ambiguous because the hydrology and 

chemical reactions that add or attenuate metals in surface and 

shallow subsurface flows are very complex in the setting of 

these mines (Kimball and others, this volume). Most of the 

mines described here are more than a mile from the major 

streams that were characterized by tracer studies, and for them 

the contributions are especially ambiguous.

Out of the 40 or so mine sources that we identify as 

potentially significant, only a few are close enough to streams 

studied by tracer methods to possibly allow quantification of 

their contributions. The substantial discharges of contaminated 

water from mines such as Bandora, Paradise, and Bonner flow 

into the South and Middle Forks of Mineral Creek, streams 

that were not subjected to a tracer study. Two of the sites 

highlighted here (Grand Mogul and Kittimack Mill tailings) 

were among the 24 major sources of loadings detected in the 

tracer studies (Kimball and others, this volume), and eight of 

the mine sites that we ranked high or very high for mine drainage presumably contributed to high loadings on five tributaries 

highlighted by the tracer studies (Prospect Gulch, Minnesota 

Gulch, Browns Gulch, South Fork Cement Creek, and Middle 

Fork Mineral Creek). Three mines close to Cement Creek that 

are highlighted in our rankings (Mammoth tunnel, Elk tunnel, 

and May Day mine) were detected in the 1996 Cement Creek 

tracer study (Kimball and others, 2002). The contributions 

from the Lark, Joe and Johns, Henrietta, Minnesota Gulch, 

Natalie/Occidental, Brooklyn, Bonner, and Paradise mines 

cannot be ascertained at the point of mixing with the major 

342 Environmental Effects of Historical Mining, Animas River Watershed, Colorado
Mine Adits, Waste Dumps, Tailings as Sources of Contamination 343

streams. More detailed studies, possibly utilizing tracers 

injected into underground mine workings, would have to be 

made to quantify the influence of these and similar mines.

Significant Sources for Remediation

The Animas River watershed study area contains hundreds of potential sources of mining-related contamination 

(Church, Mast, and others, this volume, fig. 1), but the majority of the excavated sites shown on topographic maps are 

exploration prospects that disturbed less than about 50 tons 

of rock. The majority of mines with substantial underground 

workings and waste dumps are patented claims, on private 

property. Fewer than 100 mines and prospects on public land 

were of substantial size, with hundreds of meters of workings and hundreds of tons of mine waste. Out of these sites 

on public land, fewer than 40 create mine-adit drainage or are 

situated close enough to major streams to introduce contamination to the watershed that we consider to be significant.

Problematic mining sites on public land were discussed 

by Nash (1999a, 1999b). Two new sites have been added here, 

mill tailings placed on public land from the Lackawanna Mill 

and the Kittimack Mill. Remediation activities at these or 

other sites will be decided when restoration goals are defined. 

Dozens of mine sites in the study area release water that at 

times exceeds water-quality standards set by CWQCD or the 

Clean Water Act—at the point of discharge. However, these 

sources of contamination may not be measurable in major 

streams or at gauging station A72 south of Silverton.

The magnitude of contamination from “dry” sites—those 

with no obvious surface discharge—is difficult to determine. 

The monitor wells and detailed studies of the May Day mine 

(Wright, Kimball, and Runkel, this volume) demonstrate what 

technologies are needed to evaluate subsurface discharge 

from either dry or draining sites. Because reactions take 

place in surface and ground water between the sources and 

the streams, the contamination predicted by mine site water 

samples, or from laboratory leach tests, may not accurately 

reflect what enters the streams. If the abundant geochemical 

information available for sites on public land is insufficient to 

guide remediation decisions, then detailed engineering studies 

will have to be conducted. If required, those studies should 

include the drilling of wells to document shallow ground water 

in the vicinity of mine adits, waste dumps, and mill-tailings 

impoundments. Also, further study is needed on methods 

to identify the flow paths from mine sources to streams and 

the water:rock reactions along those paths that change water 

quality.

This study has addressed issues of mine waste and 

mine-adit drainage on public land administered by the BLM 

or the USDA Forest Service, but the same issues obviously 

exist for mines on private property. Studies of representative 

private sites by Herron and others (Unpub. Mineral Creek 

feasibility investigation report, CDMG, 1997; Unpub. Cement 

Creek reclamation feasibility report, CDMG, 1998; Unpub. 

Upper Animas River reclamation feasibility report, CDMG, 

1999; Unpub. Lower Animas River reclamation feasibility report, CDMG, 2000), using methods similar to those 

described here, provide data for evaluating the private sites. 

Such an evaluation was done by Peter Butler, Robert Owen, 

and William Simon (Unpublished report to Colorado Water 

Quality Control Commission, Animas River Stakeholders 

Group, 2001). Although questions of detail may remain 

about the magnitude or ranking of some individual private or 

public sites, a general trend seems clear: most of the waste or 

mine-adit drainage sites with highest potential for watershed 

contamination (highest loads or leachate concentrations) are 

on private or mixed private-public sites.

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