U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5165

Questa Baseline and Pre-Mining Ground-Water 

Quality Investigation. 19. Leaching Characteristics 

of Composited Materials from Mine Waste-Rock 

Piles and Naturally Altered Areas near Questa, 

New Mexico
Cover: Photograph of the upper bench of the Sugar Shack South waste-rock pile at the 

Questa Mine, New Mexico. Photograph taken by Paul Briggs.
Questa Baseline and Pre-Mining 

Ground-Water Quality Investigation. 19. 

Leaching Characteristics of Composited 

Materials from Mine Waste-Rock Piles 

and Naturally Altered Areas near Questa, 

New Mexico

By Kathleen S. Smith, Philip L. Hageman, Paul H. Briggs, Stephen J. Sutley, 

R. Blaine McCleskey, K. Eric Livo, Philip L. Verplanck, Monique G. Adams, 

and Pamela A. Gemery-Hill

Scientific Investigations Report 2006–5165

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Smith, K.S., Hageman, P.L., Briggs, P.H., Sutley, S.J., McCleskey, R.B., Livo, K.E., Verplanck, P.L., Adams, M.G., and 

Gemery-Hill, P.A., 2007, Questa baseline and pre-mining ground-water quality investigation. 19. Leaching characteristics of composited materials from mine waste-rock piles and naturally altered areas near Questa, New Mexico: U.S. 

Geological Survey Scientific Investigations Report 2006–5165, 49 p.
iii

Contents

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

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

Physical Setting, General Geology and Hydrology, and Mining History...............................................3

Geographic and Physiographic Features .........................................................................................3

Climate and Vegetation........................................................................................................................4

General Geology....................................................................................................................................4

Mining History .......................................................................................................................................5

Waste-Rock Pile History.............................................................................................................5

General Hydrology................................................................................................................................6

Surface Water..............................................................................................................................6

Ground Water and Aqueous Geochemistry ............................................................................6

Methods...........................................................................................................................................................7

Sampling Strategy.................................................................................................................................7

Laboratory Leaching Procedures ......................................................................................................9

Analytical Methods for Solid Samples..............................................................................................9

Analytical Methods for Leachates.....................................................................................................9

Mineralogy Data...........................................................................................................................................10

Bulk Chemistry Data....................................................................................................................................10

Overview of Leaching Study Applications...............................................................................................18

Mine Waste-Rock Leaching Results ........................................................................................................18

Erosional Scar Leaching Results ..............................................................................................................33

Comparison of Waste-Rock and Erosional-Scar Leaching Results ....................................................38

Comparison of Leachate Composition with Scar-Drainage Waters ...................................................41

Comparison with Previous Leaching Studies .........................................................................................42

Summary........................................................................................................................................................42

Acknowledgments.......................................................................................................................................45

References Cited..........................................................................................................................................45

Figures

1. Map of the study area near Questa, New Mexico..................................................................2

2. Photograph of Southwest Hansen Creek (also known as Little Hansen Creek) 

scar showing the high relief and barren nature of the natural erosional scars, 

near Questa, New Mexico ..........................................................................................................3

3. Photograph of Hottentot Creek illustrating a drainage used for a transect 

to sample an erosional scar, near Questa, New Mexico.......................................................8

4. Photograph of Sugar Shack Middle and Old Sulphur Gulch waste-rock 

piles illustrating their size and relief, and showing benches where sampling 

transects were located, Molycorp Questa mine, New Mexico............................................8

5–31. Graphs showing:

 5. Semiquantitative mineralogy for composited mine waste-rock 

pile samples from the Questa Mine, New Mexico.........................................................12
iv

 6. Semiquantitative mineralogy for composited erosional-scar 

samples, a less-altered sample, and a tailings sample near 

Questa, New Mexico ..........................................................................................................12

 7. Bulk major-element chemical analyses for composited mine 

waste-rock pile samples from the Questa Mine, New Mexico ...................................13

 8. Bulk minor- and trace-element chemical analyses for 

composited mine waste-rock pile samples from the Questa Mine, 

New Mexico .........................................................................................................................13

 9. Bulk major-element chemical analyses for composited 

erosional-scar samples, a less-altered sample, and a tailings sample 

near Questa, New Mexico .................................................................................................14

 10. Bulk minor- and trace-element chemical analyses for 

composited erosional-scar samples, a less-altered sample, and a 

tailings sample near Questa, New Mexico .....................................................................14

 11. Leachate pH from the Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited mine waste-rock pile samples and a 

tailings sample from the Questa Mine, New Mexico ....................................................24

 12. Leachate specific conductance, leachate sulfate concentration, 

and leachate pH from the Field Leach Test (FLT) and the 18-hour leaching 

procedure for composited mine waste-rock pile samples from the Questa 

Mine, New Mexico..............................................................................................................24

 13. Leachate silicon (Si) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................26

 14. Leachate titanium (Ti) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................26

 15. Leachate manganese (Mn) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................27

 16. Leachate iron (Fe) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................27

 17. Leachate aluminum (Al) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................28

 18. Leachate copper (Cu) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................28

 19. Leachate beryllium (Be) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................29

 20. Leachate cadmium (Cd) concentration and leachate pH from

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited

mine waste-rock pile samples from the Questa Mine, New Mexico .........................29

 21. Leachate cerium (Ce) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................30
v

 22. Leachate cobalt (Co) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................30

 23. Leachate chromium (Cr) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................31

 24. Leachate zinc (Zn) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................31

 25. Leachate molybdenum (Mo) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................32

 26. Leachate lead (Pb) concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour leaching procedure for composited 

mine waste-rock pile samples from the Questa Mine, New Mexico .........................32

 27. Isotopic composition of leachate sulfate (SO4) from the mine waste-rock 

piles 18-hour leaching procedure for composited mine waste-rock pile 

samples from the Questa Mine, New Mexico ................................................................33

 28. Leachate pH from the Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited erosional-scar samples and a lessaltered sample near Questa, New Mexico .....................................................................38

 29. Leachate specific conductance, leachate sulfate concentration, 

and leachate pH from the Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited erosional-scar samples near 

Questa, New Mexico ..........................................................................................................39

 30. Leachate iron (Fe) concentration and leachate pH from the Field 

Leach Test (FLT) and the 18-hour leaching procedure for composited 

erosional-scar samples near Questa, New Mexico......................................................39

 31. Leachate aluminum (Al) concentration and leachate pH from 

the Field Leach Test (FLT) and the 18-hour leaching procedure for 

composited erosional-scar samples near Questa, New Mexico................................40

32. Box plots for selected leachable major-element concentrations from 

the 18-hour leaching procedure for composited erosional-scar samples 

near Questa, New Mexico, and composited mine waste-rock pile samples 

from the Questa Mine, New Mexico .......................................................................................40

33. Box plots for selected leachable minor- and trace-element concentrations 

from the 18-hour leaching procedure for composited erosional-scar samples 

near Questa, New Mexico, and composited mine waste-rock pile samples 

from the Questa Mine, New Mexico .......................................................................................41

34. Comparison of the concentration of selected leachable major-element 

concentrations from leaching tests and surface-water samples collected 

from Straight Creek, near Questa, New Mexico ...................................................................43

35. Comparison of the concentration of selected leachable minor- and 

trace-element concentrations from leaching tests and surface-water 

samples collected from Straight Creek, near Questa, New Mexico..................................43

36. Calcium (Ca) plotted against sulfate (SO4) concentrations for mine 

waste-rock leachates, erosional-scar leachates, and erosional-scar 

surface-water samples collected in the field from areas near Questa, 

New Mexico ................................................................................................................................44
vi

Tables

1. Semiquantitative mineralogy for composited mine waste-rock pile and 

erosional-scar samples, Questa, New Mexico .....................................................................11

2. Bulk chemical analyses for composited erosional-scar and mine waste-rock pile 

samples, Questa, New Mexico.................................................................................................15

3. Comparison of the geometric means of bulk chemical analyses for 

composited mine waste-rock pile material with the bulk chemical analysis 

of the Straight Creek erosional-scar area, Questa, New Mexico......................................19

4. Leachate chemical analyses for composited mine waste-rock pile 

samples, Questa, New Mexico.................................................................................................20

5. Leachate chemical analyses for composited erosional-scar samples, 

Questa, New Mexico..................................................................................................................34

6. Comparison of the geometric means of leachate chemical analyses for 

composited mine waste-rock pile material with the leachate chemical 

analysis of the Straight Creek erosional-scar area, Questa, New Mexico ......................42

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch 

millimeter (mm) 0.03937 inch

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Volume

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

liter (L) 61.02 cubic inch (in3) 

milliliter (mL) 0.0338 ounce, fluid (fl. oz)

Flow rate

cubic meter per second (m3/s) 70.07 acre-foot per day (acre-ft/d) 

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

cubic meter per second (m3/s) 22.83 million gallons per day (Mgal/d) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)
vii

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Volume

ounce, fluid (fl. oz) 0.02957 liter (L) 

pint (pt) 0.4732 liter (L) 

quart (qt) 0.9464 liter (L) 

gallon (gal) 3.785 liter (L) 

cubic inch (in3) 0.01639 liter (L)

Flow rate

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Mass

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F–32)/1.8

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter 

(mg/L) or micrograms per liter (μg/L).
Abstract

The goal of this study is to compare and contrast the 

leachability of metals and the acidity from individual mine 

waste-rock piles and natural erosional scars in the study area 

near Questa, New Mexico. Surficial multi-increment (composite) samples less than 2 millimeters in diameter from five 

waste-rock piles, nine erosional-scar areas, a less-altered 

site, and a tailings slurry-pipe sample were analyzed for bulk 

chemistry and mineralogy and subjected to two back-to-back 

leaching procedures. The first leaching procedure, the U.S. 

Geological Survey Field Leach Test (FLT), is a short-duration leach (5-minute shaking and 10-minute settling) and 

is intended to leach readily soluble materials. The FLT was 

immediately followed by an 18-hour, end-over-end rotation 

leaching procedure. Comparison of results from the back-toback leaching procedures can provide information about reactions that may take place upon migration of leachates through 

changing geochemical conditions (for example, pH changes), 

both within the waste-rock and scar materials and away from 

the source materials.

For the scar leachates, the concentrations of leachable 

metals varied substantially between the scar areas sampled. 

The scar leachates have low pH (pH 3.2–4.1). Under these 

low-pH conditions, cationic metals are solubilized and mobile, 

but anionic species, such as molybdenum, are less soluble and 

less mobile. Generally, metal concentrations in the waste-rock 

leachates did not exceed the upper range of those metal concentrations in the erosional-scar leachates. One exception is 

molybdenum, which is notably higher in the waste-rock leachates compared with the scar leachates. Most of the waste-rock 

leachates were at least mildly acidic (pH 3.0–6.2). The pH 

values in the waste-rock leachates span a large pH range that 

includes some pH-dependent solubility and metal-attenuation 

reactions. An increase in pH with leaching time and agitation 

indicates that there is pH-buffering capacity in some of the 

waste-rock piles. As pH increased in the waste-pile leachates, 

concentrations of several metals decreased with increasing 

time and agitation. Similar pH-dependent reactions may take 

place upon migration of the leachates in the waste-rock piles.

Bulk chemistry, mineralogy, and leachate sulfur-isotope 

data indicate that the Capulin and Sugar Shack West wasterock piles are compositionally different from the younger 

Sugar Shack South, Sugar Shack Middle, and Old Sulphur 

Gulch piles. The Capulin and Sugar Shack West piles have the 

lowest-pH leachates (pH 3.0–4.1) of the waste-pile samples, 

and the source material for the Capulin and Sugar Shack 

West piles appears to be similar to the source material for the 

erosional-scar areas. Calcite dissolution, in addition to gypsum dissolution, appears to produce the calcium and sulfate 

concentrations in leachates from the Sugar Shack South, Sugar 

Shack Middle, and Old Sulphur Gulch piles.

Introduction

In April 2001, the U.S. Geological Survey (USGS) and 

the New Mexico Environment Department began a cooperative study to infer the pre-mining ground-water chemistry 

at the Molycorp, Inc., Questa molybdenum mine site in the 

Red River Valley of New Mexico (fig. 1; Nordstrom, 2005; 

in press; Nordstrom and others, 2002, 2003). The Molycorp 

mine, which extracts molybdenite (MoS2) ore, has been operating intermittently since the 1920s and has been a large-scale 

mining operation since an open pit was developed in 1965. 

Possible contaminants of concern from the mine include arsenic, cadmium, chromium, cobalt, copper, lead, manganese, silver, and zinc (U.S. Environmental Protection Agency, 2000).

Steep, barren cliffs of hydrothermally altered rocks 

(termed erosional scars) weather and produce areas of mass 

wasting (fig. 2) in the northern portion of the Red River Valley 

between the towns of Questa and Red River, New Mexico. 

These natural erosional scars result from the oxidation of 

pyrite-rich mineralized rock. Regional hydrothermal mineralization and alteration formed both the mineral deposits at the 

Molycorp mine and the scars in the Red River Valley.

Questa Baseline and Pre-Mining Ground-Water Quality 

Investigation. 19. Leaching Characteristics of Composited 

Materials from Mine Waste-Rock Piles and Naturally 

Altered Areas near Questa, New Mexico

By Kathleen S. Smith, Philip L. Hageman, Paul H. Briggs, Stephen J. Sutley, R. Blaine McCleskey, K. Eric Livo, 

Philip L. Verplanck, Monique G. Adams, and Pamela A. Gemery-Hill
Figure 1. Map of the study area near Questa, New Mexico. Dashed lines show sampling transects for waste-rock piles, and solid lines show samtransects for the natural scar areas. (Map prepared by Philip Verplanck.)

June Bug

 Less

Altered

 SWHansen

Hansen

Straight

SE Straight

Hotten

Goat Hill

Goat Hill

West

Capulin WP Sulphur

Gulch

Sugar Shack

West WP

Sugar

Shack

South WP

 Old Sulphur

Gulch WP

Sugar ShackMiddle WP

(old tailings slurry pipe storage area)

Red River

N

0.5 0.5 MILE

0

0

1.0

Alteration scar transect

Waste-rock pile transect

Sttuuddyyaarereaa WP Waste-rock pile

Columbine Terrace

Hwy 38

105o30’

36o42’

105o30’ 105o27’

Base from U.S. Geological Survey Red River and Questa quadrangles, 1:24,000 (1995).

1.0 KILO
Previous studies by Robertson GeoConsultants, Inc., 

have examined the characteristics of the scar areas (Robertson 

GeoConsultants, Inc., 2000a, 2001a; Shaw and others, 2003) 

and the waste-rock piles (PetraScience Consultants, 2001; 

Robertson GeoConsultants, Inc., 2000b, 2000c; Shaw and 

others, 2002; Wels and others, 2002). A previous USGS study 

reported on the chemistry and mineralogy of samples discussed in this report (Briggs and others, 2003). Other USGS 

investigations conducted in the study area report on detailed 

mineralogy and solids chemistry of unmined but altered rock 

from surface samples and drill cuttings (Plumlee and others, 

2005), regional mineralogy (Livo and Clark, 2002a, 2002b; 

Livo and Knepper, 2004), geology (Ludington and others, 

2004), chemical weathering (Plumlee and others, 2006), and 

water composition of the Red River (Ball and others, 2005; 

Kimball and others, 2006; Maest and others, 2004; McCleskey 

and others, 2003; Verplanck and others, 2006).

This report addresses the leaching characteristics of 

surficial samples of composited mine waste-rock material 

and of naturally altered areas. Leaching information can be 

used to evaluate potential metal and acid release to receiving 

streams and shallow ground water. The goals of this study are 

to compare and contrast leachate data from individual mine 

waste-rock piles and natural erosional scars in the study area, 

and to compare the concentration ranges of the solubilized 

metals from the different sources. These data lend insight into 

the chemical differences of waste-rock piles and erosional 

scars in the Questa area.

Physical Setting, General Geology and 

Hydrology, and Mining History

Geographic and Physiographic Features

The study area is in Taos County in the Taos Range of 

the Sangre de Cristo Mountains of north-central New Mexico 

(fig. 1). The Red River drainage basin is a tributary to the Rio 

Grande within the Carson National Forest. The area is a rugged and altered terrain with steep slopes and V-shaped valleys 

(fig. 1). The study reach of the Red River is in the Red River 

Valley between the Questa Ranger Station at 2,280-m elevation at the west end and the town of Red River at 2,646-m 

elevation at the east end. The canyon walls of the Red River 

Valley climb rapidly from 2,400 m to more than 3,000 m at the 

ridge crest on both the north and south sides of the river. Some 

peaks reach nearly 3,500 m. The 600-m difference in elevation 

between the Red River and the adjacent ridge crest can occur 

over a horizontal distance of less than 2,000 m.

The Molycorp, Inc., Questa molybdenum mine, referred 

to as the mine site, is located on the north side of State Highway No. 38 and the Red River, 13 km east of the mountain 

front and mouth of the Red River canyon. The mine site is 

approximately 16 km2 and encompasses three main tributary 

valleys to the Red River: Capulin Canyon, Goat Hill Gulch, 

and Sulphur Gulch, from west to east, respectively (fig. 1).

Mining activities produced extensive underground workings and an open pit of approximately 0.65 km2

 near or in Sulphur Gulch. Waste-rock piles cover steep slopes on the north 

side of the Red River between Capulin Canyon and Spring 

Gulch (a tributary valley of Sulphur Gulch). Hydrothermally 

altered and extensively fractured and faulted areas of bedrock 

are present in Capulin, Goat Hill, Sulphur, Hansen, Straight, 

June Bug, and Hottentot drainages (fig. 1). The latter four 

drainages are examples of unmined drainages. Weathering 

of extensively altered rock along fracture networks and fault 

zones has resulted in steep, highly erosive, sparsely vegetated 

“alteration scars” that are clearly visible from the ground and 

in aerial photographs (Meyer and Leonardson, 1990). Where 

there has been no mining, these scar areas also are important 

natural sources of trace-metal and acid loading to surface and 

ground waters.

Figure 2. Photograph of Southwest Hansen Creek (also 

known as Little Hansen Creek) scar showing the high 

relief and barren nature of the natural erosional scars, 

near Questa, New Mexico. (Photograph taken by 

Paul Briggs.)

Physical Setting, General Geology and Hydrology, and Mining History 3
4 Questa Investigation 19—Leaching Characteristics

Climate and Vegetation

The Red River Valley lies within a semiarid desert that 

receives precipitation throughout the year and sustains moderate biodiversity. Between 1915 and 2002, the average annual 

temperature was 4°C, the average precipitation and snowfall 

were 52 cm and 370 cm, respectively, and the daily temperatures generally fluctuated by 18°C throughout the year (Western Regional Climate Center, written commun., 2005).

Climate and vegetation vary greatly within short distances because of differences in topography, weather, bedrock, 

and sediment composition. Orographic effects of mountainous 

topography lead to precipitation on the windward slopes and 

localized storms within tributary valleys. Major precipitation 

events include summer thunderstorms and winter-spring snowstorms. Thunderstorms lead to mass wasting in hydrothermally 

altered scar areas, producing debris flows that potentially 

affect vegetation, alluvial aquifers, and the Red River. Winter 

snowpack contributes to ground-water recharge through snowmelt infiltration and runoff.

Prevalent vegetation in the Red River Valley is representative of the following altitude zones: piñon-juniper woodland 

(1,800–2,300 m), mixed conifer woodland (2,300–2,740 m), 

and spruce-fir woodland (2,740–3,660 m; Knight, 1990). 

Willows, cottonwoods, shrubs, perennial grasses, and flowering vegetation are common near the banks of the Red River. 

Extending from the river are widely spaced piñon pines and 

junipers. Gains in altitude give rise to an abundance of ponderosa pines and limber pines, whereas Douglas fir and white 

fir can grow at higher altitudes. This typical mountain community, although diverse, is dominated by ponderosa pines (Larry 

Gough, U.S. Geological Survey, oral commun., 2003).

General Geology

The geochemical interaction of water with soil, colluvium, alluvium, and fractured bedrock produces the composition of surface and ground waters that are the overall focus 

of the baseline and pre-mining ground-water quality investigation. Hence, the geology is a fundamental component to 

understanding the hydrology and ground-water chemistry. This 

section briefly summarizes the general geologic framework 

from several studies (Lipman, 1981; Meyer and Leonardson, 

1990, 1997; Rehrig, 1969; Schilling, 1956), in addition to 

observations made by the USGS scientists currently working 

at the site.

The Taos Range is composed of Precambrian metamorphic rocks and granitic intrusive rocks overlain and intruded 

by Tertiary volcanic and plutonic rocks (Lipman and Reed, 

1989). The volcanic rocks are primarily intermediate to felsic 

composition (andesites to rhyolites) and are intruded by late 

Oligocene and early Miocene quartz monzonites and granites 

that provided the source of the hydrothermal fluids and molybdenite mineralization. The hydrothermally altered volcanics 

commonly contain pyrite mineralization (generally 1–3 percent). The Red River Valley is located along the southern edge 

of the Questa volcanic caldera and contains complex structural 

features and extensive hydrothermal alteration associated with 

the evolution of the Rio Grande rift. The mineral deposits in 

the Red River Valley are considered Climax-type deposits that 

are associated with silica- and fluorine-rich rhyolite porphyry 

and granitic intrusives. The three principal alteration zones 

include highly altered quartz-sericite-pyrite (QSP), less-altered 

argillic (dominantly kaolinite) zones, and mildly altered propylitic zones (containing calcite mineralization). QSP alteration, as the name implies, produces a mixture of quartz, pyrite 

(up to 10 percent), and fine-grained mica (sericite) or illite. 

Chlorite, epidote, albite, and calcite typically are present in the 

propylitic assemblages. Ore deposits contain quartz, molybdenite, pyrite, fluorite, calcite, manganiferous calcite, dolomite, and rhodochrosite. Lesser amounts of galena, sphalerite, 

chalcopyrite, magnetite, and hematite also are present. The 

hydrothermal alteration related to mineralization overprints an 

older, regional propylitic alteration. In these areas, rocks can 

contain a mixture of quartz, pyrite, and illite clays replacing 

feldspars, chlorite, carbonates, and epidote. Abundant minerals 

in waste rock produced by mining activities include chlorite, 

gypsum, illite, illite-smectite, jarosite, kaolinite, and muscovite (Gale and Thompson, 2001).

Andesite volcanic and volcaniclastic rocks are present in 

most scar-area bedrock outcrops and are the dominant bedrock 

units in the Straight Creek, Southeast Straight Creek, Sulphur 

Gulch, and Southwest Hansen scars (Ludington and others, 

2004, and fig. 1). Amalia Tuff, a mildly alkaline, rhyolitic 

tuff, is the dominant rock type in the Goat Hill and Hansen 

scars, and quartz latite porphyry is the main rock type in the 

June Bug and Hottentot (southeast side) scars (fig. 1). Rhyolite porphyry is the main rock type in the Hottentot scar, and 

quartz latite and rhyolite porphyries form the hill slopes of 

many scars. Rhyolite porphyry and tuff do not seem to have 

been substantially affected by propylitization. Advanced argillic alteration was identified in the Hansen and Hottentot scars 

and in areas southwest of the Molycorp open pit. Propylitized 

andesite bedrock is present in several drainages that typically 

do not contain alteration scars.

After the Amalia Tuff erupted and the Rio Grande rift 

began to form 26 million years ago, the landscape of the study 

area consisted of a broad, low-relief plateau (Peter Lipman, 

U.S. Geological Survey, written commun., 2005). Rifting has 

caused as much as 7 km of structural relief across the Sangre de Cristo fault system — the eastern structural boundary 

of the rift and the western boundary of the Sangre de Cristo 

mountain block (Grauch and Keller, 2004; Kluth and Schaftenaar, 1994). Tectonically driven uplift caused the Red River to 

incise into the Taos Range, resulting in the development of the 

present rugged terrain (Kirk Vincent, U.S. Geological Survey, 

written commun., 2005). However, more than a million years 

ago the Red River was essentially the headwater of the Rio 

Grande, and it flowed near the level of the top of the sediments 

within the rift basin (Wells and others, 1987). About 700 to 

600 thousand years ago the San Luis Basin was captured 

by the Rio Grande, which strikingly increased discharges, 
increased incision in the Rio Grande and tributary watersheds, 

and relegated the Red River to the status of one of those 

tributaries (Wells and others, 1987). Although thin Pleistocene 

alpine glaciers formed in the highest peaks of the Sangre de 

Cristo Mountains, they likely had little influence on the form 

of the Red River Valley.

During the late Holocene, forested hillslopes eroded at 

about 0.04 mm/yr as compared to the then-exposed alteration 

scars, which eroded at about 3.0 mm/yr (Kirk Vincent, U.S. 

Geological Survey, written commun., 2005). This extremely 

rapid erosion rate caused tributary watersheds containing 

alteration scars to deliver more sediment to the Red River 

than it could transport away, thus developing large debris fans 

to interfinger with alluvial sediments within the valley (Kirk 

Vincent, U.S. Geological Survey, written commun., 2005). 

These hydrothermally and structurally controlled facies relations have resulted in significant heterogeneities within the 

generally high permeability Red River Valley alluvial aquifer 

because the fan deposits have several orders of magnitude 

lower permeability than the alluvial deposits.

Tectonic deformation, in addition to and accompanying 

igneous and exhumation processes from Precambrian through 

Holocene times, has produced a highly complex array of 

folds, fault zones, fractures, and veins. Since the inception 

of the Questa caldera in the Oligocene, the region around the 

Red River Valley has been in a tensional stress regime, which 

has ultimately produced the ancient and modern Rio Grande 

rift previously discussed (Meyer and Foland, 1991). Generally north-northwest- to north-northeast-striking extensional 

fault zones that have been progressively reactivated during 

the coupled development of the caldera, ore mineral system, 

and the eastern rift flank have accommodated approximately 

200-percent extensional strain focused in the caldera (Meyer 

and Foland, 1991). These fault zones show a wide variety of 

internal deformation and structures, degree of mineralization, 

and dip. Numerous fracture networks, joints, and veins pervasively penetrate the entire study area. Collectively, these brittle 

structures form the permeability structure in otherwise generally low permeability crystalline rock in which the modern 

geochemical and ground-water-flow system exists.

Bedrock at the surface and buried under alluvial, colluvial, and anthropogenic deposits shows a variable and complex 

zone of weathering. Samples collected from a bedrock weathering profile in the Straight Creek scar were studied in detail to 

characterize the mineralogic variations in a weathered profile 

(Ludington and others, 2004). Relatively unweathered bedrock 

exposed in the creek bottom is propylitized andesite with a 

QSP overprint. Depending on location within the weathering 

profile, altered rocks contain variable amounts of quartz, illite, 

chlorite, and plagioclase feldspar, with smaller amounts of 

pyrite, gypsum, rutile, jarosite, and goethite (Livo and Clark, 

2002b; Ludington and others, 2004). Calcite, goethite, and 

sericite are widely distributed in the Red River Valley rocks 

and soils, as revealed by Airborne Visible/InfraRed Imaging 

Spectrometry (AVIRIS; Livo and Clark, 2002b). Calcite is an 

important mineral in the Red River Valley because its 

dissolution effectively neutralizes the acid inflows so that pH 

values in the Red River tend to be alkaline (pH 7–8). Gypsum 

is common throughout the Red River Valley and forms as a 

secondary product of acid-sulfate weathering when pyrite 

oxidizes and reacts with calcite. Because gypsum is soluble in 

water, calcium and sulfate are the major ions for most surface 

and ground waters in the Red River Valley.

The major minerals in rock samples collected during mineral exploration and mining are biotite, calcite, chalcopyrite, 

fluorite, galena, molybdenite, pyrite, quartz, rhodochrosite, 

and sphalerite. Mining activities produced roughly 328 million tons of rock overburden in Capulin Canyon and adjacent 

gulches along the north slope of the Red River (URS, 2001). 

The abundant minerals in waste-rock samples include chlorite, 

gypsum, illite, illite-smectite, jarosite, kaolinite, and muscovite (Gale and Thompson, 2001).

Mining History

Before 1916, prospectors discovered outcrops of rich, 

yellow, weathered rock that looked like sulfur (hence the 

name, Sulphur Gulch) and a greasy mineral that looked like 

graphite (fig. 1). The graphitic mineral was identified as 

molybdenite (MoS2) in 1916 and the yellow mineral was ferrimolybdite, the oxidized product derived from the weathering 

of molybdenite (Schilling, 1956). By 1920 the Molybdenum 

Corporation of America had acquired the property to mine the 

deposit, and the company subsequently shortened its name 

to Molycorp, Inc. A mill and flotation plant were set up by 

1923 for production and small-scale underground mining of 

high-grade veins (averaging 4 percent with a maximum of 

35 percent), which continued until 1958. During the 1950s, 

exploration had identified a large, low-grade deposit (about 

0.3 percent) below the high-grade deposit, and the decision 

was made to extract this ore by open-pit methods (Carpenter, 

1968). Extraction of open-pit ore began in 1965, and tailings 

were transported by a 15-km-long pipeline to a tailings facility 

in the Rio Grande Valley just west of Questa. Peak production 

occurred in 1976 with 11.5 million pounds per year. In 1977, 

Molycorp, Inc., became a wholly owned subsidiary of Union 

Oil Company of California.

Open-pit mining ceased in 1983 and underground mining 

restarted. Waste rock was no longer dumped onto piles at the 

mine site, but the amount of tailings increased. Low market 

values for molybdenum have periodically caused the mine to 

shut down (1986–89 and 1992–95). Active mining continues 

at Molycorp’s Questa mine in response to market demand. 

Further history and related information on the Molycorp 

Questa mine is available from Molycorp, Inc., (www.molycorp.

com) and from the U.S. Environmental Protection Agency 

(USEPA) (U.S. Environmental Protection Agency, 2006).

Waste-Rock Pile History

Open-pit mining operations at the Molycorp Questa mine 

occurred between 1965 and 1983. During the open-pit mining 

Physical Setting, General Geology and Hydrology, and Mining History 5
process, waste rock was placed in various piles at the mine 

site. The Sugar Shack West and Capulin waste-rock piles are 

among the oldest piles constructed during open-pit mining. 

Three roadside waste-rock piles (Old Sulphur Gulch, Sugar 

Shack South, and Sugar Shack Middle) were constructed using 

a “wrap around” method. In the early/middle stages of openpit mining, waste rock was dumped from the higher points 

of these rock piles. As the open pit developed, benches were 

wrapped around the front of the existing piles. No additional 

material has been placed on the roadside piles since 1985 

(Bruce Walker, Molycorp, written commun., 2005; Robertson 

GeoConsultants, Inc., 2000d).

General Hydrology

Surface Water

The Red River originates at an altitude of approximately 

3,658 m near Wheeler Peak, the highest peak in New Mexico 

(4,011 m), and flows roughly 55 km to its confluence with the 

Rio Grande at an altitude of 2,012 m. Total basin drainage area 

is 492 km2, and the drainage area upstream from the Questa 

Ranger Station gaging station (at the mouth of the Red River 

Canyon) is 293 km2. Peak streamflow typically occurs from 

late May to mid-June, with snowmelt-related flows beginning in late March and increasing through mid-April. Summer 

thunderstorms are prevalent in July and August. Between 1930 

and 2001, the mean annual discharge of the Red River at the 

Questa Ranger Station gage ranged from 0.36 to 2.92 m3/s, 

and the average daily discharge ranged from 0.07 to 

21.24 m3/s with an average of 1.33 m3/s (U.S. Geological 

Survey, 2004). The main drainages in the vicinity of the mine 

site are Capulin Canyon, Goat Hill Gulch, and Sulphur Gulch 

on the north side of the Red River.

Springs and shallow alluvial ground-water discharge 

into the Red River, rendering it a gaining stream over much 

of its length (Smolka and Tague, 1989). Between the town of 

Red River and the gaging station near Questa, there are many 

ephemeral seeps and springs along the banks of the Red River 

and also intermittent seeps and springs in tributary drainages 

on the north side of the river (South Pass Resources, Inc., 

1995; Steffen, Robertson, and Kirsten, 1995; Robertson GeoConsultants, 2001b). Aluminum hydroxide often precipitates 

from springs downgradient from scar and mined areas on the 

north side of the Red River, affecting the color and turbidity of 

the river (Vail Engineering, Inc., 1989).

Ground Water and Aqueous Geochemistry

Aquifer units in the Red River Valley are highly varied. 

Waste-rock piles and scars with associated debris fans are geochemically reactive and have high porosity and relatively high 

permeability. Alluvial aquifers are localized and have variable compositions. Hillslope soils are thin and composed of 

materials eroded from adjacent upgradient slopes. Debris fans 

are composed of sediments rapidly shed from their respective 

watersheds. Where the tributary watersheds contain erosional 

scars, the debris fans are large and active and contain both 

coarse- and fine-grained, largely unsorted, clay-rich debrisflow sediments, making them heterogeneities in the alluvium 

as discussed previously.

The chemistry of these sediments reflects the chemistry of their source terrains. The rapidly eroding and altered 

erosion scars have source materials that can generate lowpH, trace-metal-rich ground waters. Sediments deposited by 

the Red River, in contrast, generally consist of well-washed, 

rounded sands, gravels, and cobbles and are composed of 

a mix of lithologies present in the entire Red River Valley, 

including carbonates from the uppermost reaches. The largest 

debris fans caused the Red River alluvium to aggrade behind 

the fans during the Quaternary. Thus, ground water flowing 

in the shallow alluvial aquifer passes alternately through Red 

River alluvium and debris fans and may emerge when a relatively low permeability fan is encountered. Both the Red River 

alluvium and the debris fans act as a complex aquifer unit that 

is less than several hundred meters wide and less than 100 m 

thick.

Alluvial ground water is a calcium-sulfate water type, 

with magnesium commonly the second most abundant cation. 

Ground water downgradient from the waste-rock piles and 

scars has acidic pH values and elevated metal concentrations 

compared to ground water upgradient from these altered areas.

The bedrock aquifer is the largest aquifer in the study 

area but probably contains only relatively small amounts of 

ground water below the weathered zone because of its inferred 

low porosity and low permeability, largely controlled by 

fracture networks. Bedrock ground waters are also calciumsulfate type but generally of neutral pH. Most wells developed 

in the Red River Valley were installed to monitor water quality 

downgradient from mining operations (waste-rock dumps 

and tailings piles), scar areas, or both. Wells installed in the 

Straight Creek drainage (fig. 1) during the USGS study were 

developed to measure water levels and collect water-chemistry 

data for a range of environments in the Red River Valley. The 

aim of this work was to identify and interpret water/rock interactions under non-mining baseline conditions as a reference to 

infer pre-mining water/rock interactions for the mine site.

Hydrothermal alteration produced substantial changes in 

mineralogy over relatively short distances, which is a common feature of hydrothermally altered terrains. Hence, both 

the mineralogy and the resultant water chemistry can change 

substantially on a small spatial scale. Such hydrogeochemical environments are described as highly heterogeneous. This 

heterogeneous character makes the estimation of pre-mining 

ground-water chemistry for an area the size of the mine site a 

highly variable function of changing lithology at the mine site.

6 Questa Investigation 19—Leaching Characteristics
Methods

Sampling Strategy

The scar areas and waste-rock piles pose a formidable 

sampling challenge because of their size, steepness, and heterogeneity. The sampling strategy used in this study was modified from Smith and others (2000). Multi-increment (composite) samples of surficial material were obtained by collecting 

multiple increments (that is, subsamples) along transects of the 

scars and waste-rock piles. Subsamples were collected along 

transects because complete sampling of scars and waste-rock 

piles posed safety hazards caused by the steep, “ball bearing” 

nature of the material covering their surfaces.

Multi-increment sampling was used to focus on the average geochemical behavior of a given scar or waste-rock pile 

rather than the amount of geochemical variation within it. Use 

of this multi-increment sampling approach allows differences 

between waste-rock piles or scars to be addressed and makes 

it possible to identify potential sources of contaminants. One 

30-increment sample collected using this sampling strategy 

contains as much information, relative to average value, as 30 

individual grab samples (Smith and others, 2000).

The scars and rock piles likely generate a substantial 

amount of surface runoff because they are steep and devoid 

of vegetation. As this runoff would be in contact with the 

surficial material of the waste-rock piles and scar areas, only 

the surficial material was sampled in this study. The surficial 

material is geochemically dynamic in that it is in contact with 

the atmosphere and is exposed to seasonal variations in temperature and precipitation. During dry cycles, secondary and 

tertiary minerals may precipitate in near-surface areas; during 

wet cycles, these precipitated minerals may be rinsed away. It 

is likely that runoff from the scar areas ultimately infiltrates 

the alluvial fans and shallow ground-water systems downgradient from the scar areas.

The target population for sampling was defined as the 

surficial (less than 15-cm depth) material along one or more 

transects of a given scar or waste-rock pile, dry-sieved to less 

than 2 mm. The subsamples were randomly collected at equal, 

predetermined distances along the transects and consisted 

of a minimum of 30 increments collected with a stainless 

steel trowel and plastic bucket. In the scar areas, subsamples 

of approximately 100 grams were collected at stream level, 

alternating between right and left banks when possible, and 

placed into a 5-gallon plastic bucket. At the waste-rock piles, 

subsamples of approximately 100 grams were collected along 

transects and placed into a 5-gallon plastic bucket. Each subsample was taken randomly every 20 paces along a transect, 

and particles greater than pebble size were not collected. The 

multi-increment samples were brought back to the Denver 

USGS laboratories, air-dried, mixed, and dry-sieved through 

a stainless steel screen to less than 2 mm. Each final <2-mm 

multi-increment sample weighed at least 1 kg.

Scar samples were collected from the following nine 

drainages: Goat Hill, Goat Hill West, Hansen Creek, Hottentot Creek, June Bug, Straight Creek, Sulphur Gulch, Southeast 

Straight Creek, and Southwest Hansen Creek (also known 

as Little Hansen Creek, figs. 1–3; see Ludington and others, 

2004). The Goat Hill West scar was sampled during the same 

sampling trip as the Old Sulphur Gulch, Sugar Shack Middle, 

and Sugar Shack South waste-rock piles. In addition to the 

scar samples, a sample was collected in a less-altered area 

in the unnamed drainage west of Southwest Hansen Creek. 

Mine waste-rock samples were collected from the following 

five piles: Capulin, Old Sulphur Gulch, Sugar Shack Middle, 

Sugar Shack South, and Sugar Shack West (fig. 1, fig. 4). 

These piles represent about three-fourths of the total waste 

rock produced at the Questa mine site.

The waste-rock multi-increment samples were collected 

on two different collection trips, under different weather 

conditions and by different samplers, because of inclement 

weather during the first sampling trip. The samples collected 

from Old Sulphur Gulch, Sugar Shack Middle, and Sugar 

Shack South were collected during wet conditions from three 

transects, including the base and two benches, for each pile. 

The three-transect multi-increment samples for each pile 

were combined to make one composite for the entire pile. The 

multi-increment samples collected from Capulin and Sugar 

Shack West were collected during dry conditions from one 

transect. For Capulin, the transect was 3 to 6 meters below the 

top of the pile, along the length of the pile. For Sugar Shack 

West the transect was along a bench approximately 12 meters 

above the base of the pile. It is not known what effects sampling under wet compared to dry conditions have on the leachate data, but all samples were air dried before any laboratory 

work. In addition to the waste-rock pile samples, a tailings 

sample was collected from an old tailings slurry pipe (fig. 1) 

on Columbine Terrace near the Red River. This grab sample 

was collected from the end of the slurry pipe located along the 

Red River. The slurry pipe was used to transport tailings from 

the milling facility to the tailings ponds.

In designing the sampling strategy, sampling errors were 

addressed in several ways. The fundamental sampling error 

(FSE) results from particles having different compositions 

and generally is the largest single source of sampling error. 

Important factors influencing the FSE include degree of heterogeneity, sample mass, and particle size. The scar areas and 

waste-rock piles have a large degree of heterogeneity (including compositional, spatial, and particle size). The FSE was 

reduced in our sampling strategy by decreasing the particle 

size. The <2-mm particle size was chosen as the cutoff, which 

was found in a previous study (Smith and others, 2000) to 

encompass the most reactive material in mine-waste piles. 

Used in combination with leaching studies, the <2-mm size 

fraction may tend to slightly overestimate the leachability of 

the material as a whole, but this size-fraction cutoff does not 

appear to miss any leachable phases. Therefore, the <2-mm 

size fraction seems a good choice to reduce the FSE. The 

Methods 7
Figure 3. Photograph of Hottentot Creek illustrating a drainage used for a transect to 

sample an erosional scar, near Questa, New Mexico. (Photograph taken by Paul Briggs.)

Figure 4. Photograph of Sugar Shack Middle and Old Sulphur Gulch wasterock piles illustrating their size and relief, and showing benches where sampling 

transects were located, Molycorp Questa mine, New Mexico. These waste-rock 

piles are closest to the Red River. (Photograph taken by Paul Briggs.)

8 Questa Investigation 19—Leaching Characteristics
amount of sample mass collected was determined according to 

the approach of Pitard (1993) and Gy (1998).

Another sampling error that was addressed is the grouping and segregation error (GSE), which occurs because not all 

particles are randomly distributed. The GSE can be minimized 

by collecting random samples and by collecting multiple 

increments (that is, subsamples). In this study, subsamples 

were randomly collected at predetermined distances along a 

transect, and each multi-increment sample consists of at least 

30 increments (subsamples).

Laboratory Leaching Procedures

Leaching procedures were conducted to identify and 

constrain the amounts of soluble constituents that could 

be released from the waste-rock and scar materials during 

rainstorms and snowmelt. After being air-dried, mixed, and 

dry sieved, the <2-mm-size fraction of the multi-increment 

samples collected from the mine waste-rock piles and the 

natural scar areas were subjected to two back-to-back leaching 

procedures. The first procedure is the USGS Field Leach Test 

(FLT) described in Hageman (2005, 2007) and Hageman and 

Briggs (2000). The FLT can be performed in the field or in 

the laboratory. Because of the need for air drying and mixing 

and the use of back-to-back leaching procedures, the FLT was 

performed in the laboratory. The FLT is a simple, short-duration test that addresses the readily soluble material. The FLT 

was followed by an 18-hour end-over-end rotation leaching 

procedure. The 18-hour procedure involves a longer reaction 

period with end-over-end rotation that results in particle-size 

reduction. This 18-hour procedure is similar to the USEPA 

method 1312 (Synthetic Precipitation Leaching Procedure 

[SPLP]; U.S. Environmental Protection Agency, 2004), except 

that deionized water was used as the leaching solution instead 

of a dilute H2SO4/HNO3 solution, and a 0.45-μm nitrocellulose 

filter was used instead of a glass-fiber filter.

In the FLT, 100.0 g of each <2-mm sample was placed 

in a plastic bottle, and 2 L of deionized water was added. The 

solid-to-liquid leaching ratio is 1:20, the same ratio used in the 

USEPA methods 1311 and 1312 (U.S. Environmental Protection Agency, 2004). Each plastic bottle was capped, shaken 

vigorously for 5 minutes, and allowed to settle undisturbed for 

10 minutes. Approximately 100 mL of each leachate was then 

removed for pH and specific-conductance measurements and 

for chemical analysis. Next, the bottles were recapped, placed 

on an end-over-end rotator for 18 hours, removed, and allowed 

to settle. A portion of the leachates was again removed for 

pH and specific-conductance measurements and for chemical analysis. Subsamples for chemical analysis from the two 

leaching procedures were filtered though a 0.45-μm nitrocellulose filter and either acidified with ultrapure nitric acid to 

pH <1 for analysis by inductively coupled plasma-atomic 

emission spectrometry (ICP–AES) and inductively coupled 

plasma-mass spectrometry (ICP–MS) or refrigerated for analysis by ion chromatography (IC).

Analytical Methods for Solid Samples

Prior to laboratory analysis of the bulk material, the 

<2-mm fraction of the samples was pulverized to 100 mesh 

(<0.15 mm) using a Braun vertical pulverizer equipped with 

ceramic plates. A subsample of the 100-mesh material was 

decomposed in a four-acid mixture of hydrochloric, nitric, 

perchloric, and hydrofluoric acids (Crock and others, 1983) 

and analyzed by ICP–AES (Briggs, 2002a). Total sulfur was 

determined on a subsample of the 100-mesh material by combustion in an oxygen atmosphere with infrared detection of 

evolved SO2 (Brown and Curry, 2002).

The Rietveld method was used for semiquantitative 

mineralogical determinations. This method is a refinement of 

“routine” X-ray diffraction (XRD), which is usually based on 

a single peak or small subset of all of the peaks in the diffraction pattern. The Rietveld method uses all of the lines in 

the diffraction pattern, or even the total pattern, including the 

background. This method requires knowledge of the approximate crystal structure of all phases of interest in a mixture. 

The method consists of fitting the complete experimental 

diffraction pattern with calculated profiles and backgrounds 

and obtaining quantitative phase information from the scale 

factors for each phase in a mixture. In this study, samples were 

micronized in a micronizing mill to an average grain size of 

about 5 μm. An internal standard of Al2O3 with an average 

grain size of 1 μm was added (15 percent by weight) to allow 

quantification of amorphous material. The XRD patterns were 

collected on a Scintag X-1 theta-theta diffractometer (Cu 

K-alpha radiation, Peltier counter) with a 2-mm divergence 

slit and 4-mm scatter slit for the tube and a 0.5-mm scatter 

slit and 0.2-mm receiving slit for the detector. Patterns were 

scanned from 4 to 75 degrees 2-theta with a step size of 0.02-

degree 2-theta and a counting time of 2 seconds per step with 

a sample spinner to reduce preferred orientation. The subsequent quantitative refinements were carried out using version 

2.5 of the Siroquant Rietveld full-profile phase quantification 

program (Taylor, 1991). Relative standard deviation is about 

± 3 percent for major phases ranging to ± 30 percent for trace 

phases (≤3 percent). This method is quantitative, but because 

of the presence of clay minerals, numbers are reported as 

semiquantitative.

Analytical Methods for Leachates

Filtered (0.45 μm) acidified leachates were analyzed by 

ICP–AES (Briggs, 2002b) and ICP–MS (Lamothe and others, 

2002). Filtered (0.45 μm) refrigerated leachates were analyzed for sulfate and chloride by IC using a Dionex DX–120 

(Brinton and others, 1995). Fluoride concentrations were 

determined using an ion-selective electrode (ISE).

For analysis of sulfur isotopes in waste-rock leachates, 

soluble sulfate in the filtered (0.45 μm) leachates was precipitated as barium sulfate. Precipitation was accomplished 

by first using a few drops of 6N HCl to adjust the pH of each 

sample to between pH 3 and pH 4. The samples were then 

Methods 9
heated and stirred to near boiling, at which point 10 to 20 mL 

of 0.5 M BaCl2 solution was added to each sample to precipitate BaSO4

. Heating and stirring continued for 30 minutes, then 

the samples sat overnight before filtration. Sulfur-isotope analyses were performed on the precipitated BaSO4

 by combustion 

using continuous-flow methods described by Giesemann and 

others (1994) with a Carlo Erba NC2500 elemental analyzer 

coupled to a Micromass Optima isotope-ratio mass spectrometer. Sulfur-isotope values are reported as normal δ notation 

relative to the standard Canyon Diablo troilite (CDT) with a 

standard deviation of ±0.2 parts per thousand (per mill [‰]).

Mineralogy Data

Semiquantitative mineralogy of samples from the mine 

waste-rock piles and erosional scars is given in table 1 and 

figures 5 and 6. These data also are discussed in Briggs and 

others (2003). The mineralogical data are consistent with 

the findings of Livo and Clark (2002a, 2002b) and Livo and 

Knepper (2004) that a quartz-sericite-pyrite (QSP) alteration 

signature overprinted by a supergene weathering signature 

accounts for most of the surfaces of the mine waste-rock piles 

and erosional-scar areas. The term “sericite” is used in this 

report to refer to various grain sizes of muscovite and illite. 

During supergene weathering, pyrite and other sulfides are 

converted to jarosite and gypsum, and feldspar is converted to 

kaolinite and alunite. The presence of jarosite reflects acidic 

conditions (Dutrizac and Jambor, 2000; Nordstrom and Alpers, 1999; Swayze and others, 2000). As shown in table 1 and 

figures 5 and 6, quartz, mica (likely sericite), and X-ray amorphous material are the most abundant constituents both on the 

waste-rock piles and on the erosional scars. All of the wasterock piles and scars contain jarosite (ranging between 3 and 

8 weight percent) and, with one exception, gypsum (ranging 

between 1 and 12 weight percent; the exception is the Hottentot scar). Kaolinite was not detected in any samples from the 

waste-rock piles but was present in six of nine samples from 

the scars. Pyrite was detected in all of the waste-rock piles but 

in only two of the scars. The absence of pyrite and presence of 

kaolinite in most of the scars indicates that supergene weathering may be more intense at the scar areas compared with 

weathering in the waste-rock piles. The sample from the lessaltered site contains no detectable gypsum, pyrite, or kaolinite 

but does contain detectable jarosite and hematite, with major 

quartz, plagioclase, and mica. The tailings sample is composed 

of quartz, feldspar, and amorphous material with no detectable 

pyrite and jarosite, relatively low mica, and minimal kaolinite.

Three of the mine waste-rock piles (Old Sulphur Gulch, 

Sugar Shack Middle, and Sugar Shack South) contain a 

smectite/mica mixed phase, which could consist of either 

smectite/muscovite or smectite/illite. These three piles also 

contain more pyrite, gypsum, plagioclase, potassium feldspar, 

smectite, and chlorite and less quartz and amorphous material 

than the other two piles. The Old Sulphur Gulch and Sugar 

Shack Middle piles are shown in figure 4. It appears that these 

three piles contain different source material than the Sugar 

Shack West and Capulin piles. Livo and Clark (2002a) noted 

that, during open-pit mining, rock extracted from the top of the 

system would have been dumped topographically high. If that 

is the case, then it is likely that the Capulin and Sugar Shack 

West piles would have received material extracted near the top 

of the system, and Old Sulphur Gulch, Sugar Shack Middle, 

and Sugar Shack South piles would have received material 

extracted lower in the system. This scenario is consistent with 

the mine waste-rock pile history (previously discussed) in that 

the Sugar Shack West and Capulin waste-rock piles are among 

the oldest piles constructed during open-pit mining and are 

older than the three roadside waste-rock piles (Old Sulphur 

Gulch, Sugar Shack Middle, and Sugar Shack South).

The Goat Hill scar (just west of the waste-rock piles; see 

fig. 1) contains the most mica of all the samples, considerable 

jarosite and kaolinite, and no detectable pyrite. These observations are consistent with the observation of Livo and Clark 

(2002b) that the unmined Goat Hill Gulch area appears to be 

more hydrothermally altered than the scars to the east. The 

scar at Hansen Creek also stands out in that it has the lowest 

mica content and highest kaolinite content, which is consistent 

with the observations of Livo and Clark (2002b).

Bulk Chemistry Data

Bulk chemical analyses of samples from the mine wasterock piles and erosional scars are given in table 2 and figures

7, 8, 9, and 10. These data also are discussed in Briggs and 

others (2003). In preparing figures 7–10, less-than (<) values 

shown in table 2 were replaced with 50 percent of their value. 

The geometric means were also calculated using 50 percent 

of the value of less-than data. Comparison of the geometric 

means (table 2) of the bulk chemistry constituents reveals that 

the mine waste-rock piles are ≥20 percent higher than the 

erosional scars in Ca, Na, Ti, S, Ba, Be, Cu, Mn, Mo, Ni, Sr, 

Th, Y, and Zn. The erosional scars have fairly wide concentration ranges for some elements, but their geometric mean 

is ≥20 percent higher than the mine waste-rock piles in iron, 

phosphorus, and lead.

Comparison of the bulk chemical composition of the 

waste-rock piles shown in figures 7 and 8 indicates that the 

Capulin and Sugar Shack West piles are different from the 

other three piles (Old Sulphur Gulch, Sugar Shack Middle, 

and Sugar Shack South). In particular, the Capulin and Sugar 

Shack West piles are lower in Ca, Fe, Mg, Na, P, Ti, and S 

(fig. 7) and lower in Co, Cr, Cu, Li, Mn, Mo, Ni, Sc, Sn, Sr, 

and V (fig. 8). This trend is consistent with the mineralogy 

data discussed previously and indicates that the source material for the Capulin and Sugar Shack West piles is different. 

Hence, both the mineralogical data and the bulk chemistry 

data indicate that it is likely that the Capulin and Sugar Shack 

West piles received material extracted near the top of the 

system, whereas Old Sulphur Gulch, Sugar Shack Middle, and 

Sugar Shack South piles received material extracted lower in 

10 Questa Investigation 19—Leaching Characteristics
Table 1. Semiquantitative mineralogy for composited mine waste-rock pile and erosional-scar samples, Questa, New Mexico.

 [All results are as weight percent; ND, not detected by X-ray diffraction; <, less than]

Mine waste-rock piles Erosional scar sites

Capulin

Sugar 

Shack 

West

Old 

Sulphur 

Gulch

Sugar 

Shack 

Middle

Sugar 

Shack 

South

Goat 

Hill 

West

Goat 

Hill

Sulphur 

Gulch

SW 

Hansen 

Creek

Hansen 

Creek

Straight 

Creek

SE 

Straight 

Creek

Hottentot 

Creek

Quartz 35 40 27 25 32 27 36 24 26 35 34 30 30 

Mica 12 13 11 10 12 10 18 6 10 5 10 13 15 Plagioclase 6 6 9 10 7 5 7 6 9 5 7 10 3 

K-spar 3 4 5 5 6 3 3 ND ND 2 1 ND 1 Pyrite <1 <1 <1 1 1 <1 ND ND ND <1 ND ND ND 

Chlorite 8 3 10 11 8 10 <1 3 9 1 3 8 7 

Kaolinite ND ND ND ND ND ND 4 <1 ND 5 4 ND 1 Smectite3 ND ND 1 2 2 ND 2 8 8 1 2 5 1 Smectite/Mica4 ND ND 2 3 3 ND ND ND ND ND ND ND ND 

Gypsum 5 3 7 8 6 1 2 12 12 10 8 9 ND Jarosite 4 6 6 5 5 8 7 6 5 3 3 5 5 

Hematite ND ND ND ND ND ND ND ND ND ND ND ND ND Amorphous 26 23 21 20 17 34 21 35 21 34 28 20 37 

1 Less-altered drainage west of SW Hansen Creek.2 Columbine Terrace tailings slurry-pipe sample.3 Probably montmorillonite.4 Smectite/muscovite or smectite/illite.
Figure 5. Semiquantitative mineralogy for 

composited mine waste-rock pile samples 

from the Questa Mine, New Mexico.

WEIGHT PERCENT

0

5

10

15

20

25

30

35

40

Quartz

Mica

Plagioclase

Gypsum

Jarosite

K-spar

Pyrite

Kaolinite

Chlorite

Smectite

Smectite/Mica

Hematite

Amorphous

Capulin 

Old Sulphur Gulch 

Sugar Shack Middle 

Sugar Shack South 

Sugar Shack West 

WEIGHT PERCENT

0

5

10

15

20

25

30

35

40

Quartz

Mica

Plagioclase

Gypsum

Jarosite

K-spar

Pyrite

Kaolinite

Chlorite

Smectite

Smectite/Mica

Hematite

Amorphous

Goat Hill 

Goat Hill West 

Hansen Creek 

Hottentot Creek 

June Bug 

Straight Creek 

Sulphur Gulch 

SE Straight Creek 

SW Hansen Creek 

Less-altered 

Tailings

Figure 6. Semiquantitative mineralogy for 

composited erosional-scar samples, a lessaltered sample, and a tailings sample near 

Questa, New Mexico.

12 Questa Investigation 19—Leaching Characteristics
Capulin 

Old Sulphur Gulch 

Sugar Shack Middle 

Sugar Shack South 

Sugar Shack West 

0.01

0.1

1

10

CONCENTRATION, IN PERCENTAGE

Al Ca Fe K Mg Na P Ti S 

Figure 7. Bulk major-element chemical analyses for composited mine waste-rock pile 

samples from the Questa Mine, New Mexico.

Capulin 

Old Sulphur Gulch

Sugar Shack Middle 

Sugar Shack South 

Sugar Shack West 

CONCENTRATION, IN PARTS PER MILLION

0.1

1

10

100

1,000

Ag 

As 

Au 

Ba

Be

Bi 

Cd 

Ce 

Co 

Cr 

Cu 

Eu 

Ga 

Ho 

La 

Li 

Mn 

Mo

Nb 

Nd 

Ni 

Pb 

Sc

Sn 

Sr 

Ta 

Th 

U 

V 

Y 

Yb 

Zn 

EXPLANATION

Figure 8. Bulk minor- and trace-element chemical analyses for composited mine waste-rock 

pile samples from the Questa Mine, New Mexico.

Bulk Chemistry Data 13
Figure 9. Bulk major-element 

chemical analyses for composited 

erosional-scar samples, a less-altered 

sample, and a tailings sample near 

Questa, New Mexico. 

Figure 10. Bulk minor- and trace-element chemical analyses for composited erosional-scar samples, a lessaltered sample, and a tailings sample near Questa, New Mexico.

14 Questa Investigation 19—Leaching Characteristics

Al Ca Fe K Mg P Ti S 

CONCENTRATION, IN PERCENTAGE

0.01

0.1

1

10

Goat Hill 

Goat Hill West 

Hansen Creek 

Hottentot Creek 

June Bug 

Straight Creek 

Sulphur Gulch 

SE Straight Creek 

SW Hansen Creek 

Less-altered 

Tailings 

Na

EXPLANATION

Ag 

As

Au

Ba 

Be 

Bi 

Cd 

Ce

Co

Cr

Cu 

Eu 

Ga

Ho 

La 

Li 

Mn 

Mo 

Nb 

Nd 

Ni 

Pb 

Sc 

Sn 

Sr 

Ta 

Th 

U 

V 

Y 

Yb 

Zn 

CONCENTRATION, IN PARTS PER MILLION

0.1

1

10

100

1,000

Goat Hill 

Goat Hill West 

Hansen Creek 

Hottentot Creek 

June Bug 

Straight Creek 

Sulphur Gulch 

SE Straight Creek 

SW Hansen Creek 

Less-altered 

Tailings

EXPLANATION
Table 2. Bulk chemical analyses for composited erosional-scar and mine waste-rock pile samples, Questa, New Mexico.

[—, not determined; %, percentage; ppm, parts per million; <, less than]

Erosional scar sites

Constituent Geometric 

mean

Goat Hill 

West

Goat

 Hill

Sulphur 

Gulch 

SW Hansen 

Creek

Hansen 

Creek 

Straight 

Creek

SE 

Straight 

Creek

Hottentot 

Creek June Bug 

alt

Al % 6.4 7.1 5.7 6.7 6.4 6.3 6.1 6.4 6.5 6.9 Ca % .35 .13 .14 .82 .93 .62 .57 .53 .05 .56 Fe % 4.4 4.8 4.7 5.6 5.1 3.4 3.6 4.4 3.3 5.0 K % 3.1 3.5 3.6 2.9 2.7 3.0 2.8 2.9 3.3 3.3 Mg % .78 .64 .38 1.0 1.3 .58 .96 1.0 .58 1.1 Na % .52 .60 .38 .84 .88 .41 .49 .79 .19 .52 P % .15 .17 .099 .16 .19 .11 .12 .17 .16 .19 Ti % .15 .20 .12 .19 .15 .23 .12 .15 .11 .13 S % 1.2 1.3 1.3 1.7 1.9 1.4 1.2 1.2 .84 .89 Ag ppm — 2.6 2.0 < 2 < 2 < 2 < 2 < 2 < 2 < 2 As ppm — 32 14 < 10 15 < 10 < 10 < 10 12 < 10 < Au ppm — < 8 < 8 < 8 < 8 < 8 < 8 < 8 < 8 < 8 Ba ppm 380 286 435 258 226 396 336 419 699 585 1,Be ppm 2.2 3.0 2.9 2.2 1.6 2.5 1.9 1.5 2.0 2.6 Bi ppm — < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10 < 10 < Cd ppm — < 2 < 2 < 2 < 2 < 2 < 2 < 2 < 2 < 2 Ce ppm 70 110 89 79 62 82 56 63 63 48 Co ppm 8.5 8.5 6.7 12 9.0 10 7.0 7.1 5.0 15 Cr ppm 53 68 23 83 74 50 58 54 38 61 Cu ppm 49 99 62 100 25 22 42 39 20 160 Eu ppm — < 2 < 2 < 2 < 2 < 2 < 2 < 2 < 2 < 2 Ga ppm 20 22 22 21 18 23 18 20 22 19 Ho ppm — < 4 < 4 < 4 < 4 < 4 < 4 < 4 < 4 < 4 La ppm 38 63 50 42 34 39 32 36 32 23 Li ppm 23 30 18 28 21 21 26 19 19 24 Mn ppm 367 802 261 408 417 299 373 441 152 455 Mo ppm 16 29 27 12 9.7 4.8 16 13 32 31 Nb ppm 15 32 15 11 11 19 12 12 15 12 Nd ppm 29 38 33 36 28 36 22 26 30 20 Ni ppm 15 19 8.0 29 18 22 15 12 7.4 22 Pb ppm 140 420 270 58 72 44 170 210 140 190 Sc ppm 7.4 8.3 5.5 9.7 8.6 6.4 6.4 7.4 6.6 8.4 Sn ppm — < 5 14 5.2 8.1 < 5 6.9 < 5 < 5 < 5 Sr ppm 195 125 101 311 626 199 121 228 99.0 304 Ta ppm — < 40 < 40 < 40 < 40 < 40 < 40 < 40 < 40 < 40 < 
Table 2. Bulk chemical analyses for composited erosional-scar and mine waste-rock pile samples, Questa, New Mexico.—Continued [—, not determined; %, percentage; ppm, parts per million; <, less than] Erosional scar sites Constituent Geometric mean Goat Hill West Goat Hill Sulphur Gulch SW Hansen Creek Hansen Creek Straight Creek SE Straight Creek Hottentot Creek June Bug 

alt

Th ppm 8.4 28 12 6.2 5.4 5.8 7.2 7.7 7.4 7.4 U ppm — < 100 < 100 < 100 < 100 < 100 < 100 < 100 < 100 < 100 < V ppm 74 72 50 95 91 65 66 80 71 85 Y ppm 6.8 12 5.2 8.2 6.3 10 7.0 4.9 5.4 4.9 Yb ppm — 1.8 < 1 < 1 < 1 < 1 < 1 < 1 < 1 < 1 Zn ppm 66 130 40 55 50 72 84 65 35 120 

Mine waste-rock piles Constituent Geometric mean (all) Geometric mean3 Capulin Sugar Shack West Old Sulphur Gulch Sugar Shack Middle Sugar Shack South Al % 7.0 6.8 6.8 6.9 7.1 6.9 7.4

Ca % 1.1 .40 .41 .39 2.1 1.9 2.3Fe % 3.4 2.6 2.9 2.3 3.6 4.3 4.2K % 3.2 3.3 3.2 3.4 3.3 2.8 3.2Mg % .89 .46 .51 .42 1.3 1.5 1.3Na % 1.1 .82 .92 .73 1.3 1.4 1.4P % .10 .05 .055 .046 .15 .16 .16Ti % .19 .14 .16 .12 .25 .23 .22S % 1.5 1.0 .78 1.2 1.8 2.1 2.3Ag ppm — — < 2 < 2 < 2 < 2 < 2As ppm — — < 10 < 10 < 10 < 10 < 10Au ppm — — < 8 < 8 < 8 < 8 < 8Ba ppm 566 421 447 397 680 684 704Be ppm 2.9 2.4 2.5 2.4 3.6 3.2 3.2Bi ppm — — < 10 < 10 < 10 < 10 < 10Cd ppm — — < 2 < 2 < 2 < 2 < 2Ce ppm 76 71 98 52 85 87 67Co ppm 9.9 5.2 6.4 4.2 14 17 15Cr ppm 59 30 29 32 87 100 92Cu ppm 82 37 43 31 150 130 140
Table 2. Bulk chemical analyses for composited erosional-scar and mine waste-rock pile samples, Questa, New 

Mexico.—Continued[—, not determined; %, percentage; ppm, parts per million; <, less than]

Mine waste-rock piles

Constituent Geometric mean (all) Geometric mean3 Capulin Sugar Shack West Old Sulphur Gulch Sugar Shack Middle Sugar Shack South

Eu ppm — — < 2 < 2 < 2 < 2 < 2Ga ppm 17 24 26 23 14 12 13Ho ppm — — < 4 < 4 < 4 < 4 < 4La ppm 42 40 53 30 48 47 37Li ppm 27 16 18 14 38 39 35Mn ppm 588 383 561 261 816 751 781Mo ppm 90 15 18 12 390 210 340Nb ppm 16 33 40 27 10 9.9 11Nd ppm 31 29 38 22 34 38 28Ni ppm 23 10 12 8.3 39 45 41Pb ppm 92 98 140 71 89 67 120Sc ppm 7.9 5.1 4.9 5.4 10 12 10Sn ppm — — < 5 < 5 5.9 5.0 5.0Sr ppm 307 142 142 142 505 477 560Ta ppm — — < 40 < 40 < 40 < 40 < 40Th ppm 10 10 13 8.4 10 8.5 11U ppm — — < 100 < 100 < 100 < 100 < 100V ppm 73 48 44 52 92 100 95Y ppm 18 23 31 17 16 16 14Yb ppm 1.8 2.9 3.7 2.3 1.4 1.3 1.3Zn ppm 80 52 78 35 110 83 120

1 Less-altered drainage west of SW Hansen Creek.2 Columbine Terrace tailings slurry-pipe sample.3 Geometric mean for Capulin and Sugar Shack West mine waste-rock piles only.
18 Questa Investigation 19—Leaching Characteristics

the system. Accordingly, the Capulin and Sugar Shack West 

piles likely are more similar to the scars than are the other 

three piles.

Comparison of the geometric means of the bulk chemistry constituents for only Capulin and Sugar Shack West (see 

table 2) with the geometric means for the scars reveals that 

these two mine waste-rock piles are ≥20 percent higher than 

the erosional scars in Na, Nb, Th, and Y. The erosional scars 

have fairly wide concentration ranges for some elements, but 

their geometric mean is ≥20 percent higher than the Capulin and Sugar Shack West waste-rock piles in Fe, Mg, P, S, 

Co, Cr, Cu, Li, Ni, Sc, Sr, V, and Zn. It appears that the scar 

samples are higher in iron, sulfur, and several base metals than 

are the Capulin and Sugar Shack West piles.

The bulk chemical composition of the scar samples 

shown in figures 9 and 10 displays fairly wide concentration 

ranges but little deviation from the trends. The scars at Hottentot, Goat Hill West, and Goat Hill all have low calcium values 

in comparison with the other scars. The scar at Hottentot also 

stands out in that it has lower cobalt, nickel, and zinc than the 

other scars.

The USGS has chosen the Straight Creek drainage (fig. 1) 

as an analog site to provide information about pre-mining 

geochemical conditions at the Questa Mine. Comparison of 

the geometric means for bulk chemistry of mine waste-rock 

piles with the bulk chemistry of the Straight Creek scar area 

is given in table 3. The mine waste-rock piles are ≥20 percent 

higher than Straight Creek in Ca, Na, Ti, S, Ba, Be, Ce, Co, 

Cu, La, Mn, Mo, Nb, Nd, Ni, Sc, Sr, Th, and Y. Lead is the 

only element in Straight Creek bulk material that exceeds the 

waste-rock piles by ≥20 percent.

Overview of Leaching Study 

Applications

The <2-mm multi-increment samples from the five mine 

waste-rock piles, nine erosional-scar areas, a less-altered site, 

and a tailings slurry-pipe sample were subjected to two backto-back leaching procedures. The first procedure, the FLT, is 

of short duration (5-minute shaking and 10-minute settling) 

and is intended to leach readily soluble materials. The FLT 

was immediately followed by an 18-hour end-over-end rotation leaching procedure, which is similar to the USEPA 1312 

procedure (U.S. Environmental Protection Agency, 2004). 

The end-over-end rotation results in considerable particle-size 

reduction over the course of the procedure. These leaching 

procedures can be used to qualitatively evaluate potential 

metal and acid release to receiving streams and shallow 

ground water. In addition, they can provide qualitative information about the likely chemical composition of porewater 

within the waste-rock piles and erosional scars. Finally, these 

back-to-back procedures can lend insight into reactions that 

may take place upon migration of porewater through changing 

geochemical conditions (for example, pH changes) both within 

the waste-rock and scar materials and away from the source 

materials. However, these (or any) leaching procedures cannot 

provide quantitative concentrations of actual waste-rock or 

scar contributions to surface or ground water. The leaching 

procedures employed in this study use a 1:20 solid-to-water 

ratio. This same ratio is used in the USEPA 1311 and 1312 

tests (U.S. Environmental Protection Agency, 2004) and is 

dilute enough to alleviate most issues with solubility controls 

during the leaching procedures.

Mine Waste-Rock Leaching Results

For preparation of graphs, data points with qualified 

values were replaced with a value equal to 50 percent of the 

detection limit. Table 4 lists chemical analyses for leachates 

from the mine waste-rock piles. The pH of the waste-rock 

leachates vary between 3.0 (Sugar Shack West) and 6.2 (Old 

Sulphur Gulch). With the exception of Sugar Shack West, 

the pH rises between the FLT and the 18-hour test; figure 11

illustrates this trend. It seems that the higher the FLT pH, the 

greater the pH increase during the 18-hour test. Some of the 

pH increases are as much as 1 pH unit. It appears that the 

increased time and increased agitation, which result in particle-size reduction, are able to expose minerals (for example, 

calcite) that can buffer the pH of the leachate solutions. All of 

the mine waste-rock leachates exhibit an increase in specific 

conductance and sulfate concentration between the FLT and 

the 18-hour procedure. These increases are illustrated in figure 

12. There is also an increase in calcium concentration between 

the FLT and the 18-hour procedure (table 4), indicating dissolution of gypsum with increased time and agitation. Robertson 

GeoConsultants, Inc. (2000b), noted a solubility control by 

gypsum for mine waste-rock leachates at a concentration of 

about 2,000 mg/L sulfate (SO4). Sulfate data in this study do 

not exceed 1,500 mg/L SO4, so solubility control by gypsum 

does not appear to be a factor. Also, results from solubility calculations for the leachates using WATEQ4F (Ball and 

Nordstrom, 1991) do not indicate that saturation with respect 

to gypsum occurred in the leachates. Assuming stoichiometric 

dissolution, calculations indicate that nearly all of the sulfate 

in the Old Sulphur Gulch, Sugar Shack Middle, and Sugar 

Shack South piles can be explained by gypsum dissolution. 

For the Capulin and Sugar Shack West piles, 57 percent and 

39 percent, respectively, of the leachate sulfate can be attributed to gypsum dissolution. There is excess calcium concentration in leachates from the three younger roadside piles (Old 

Sulphur Gulch, Sugar Shack Middle, and Sugar Shack South), 

which indicates that calcium dissolution, in addition to gypsum dissolution, is taking place in those three piles.

In the mine waste-rock leachates, some elements 

increased in concentration between the FLT and 18-hour 

procedure, and others decreased. For most samples, the elements that increased over the 18-hour leaching period include 

Ca, Cd, K, Mg, Mn, Mo, Rb, Si, Sr, and Ti. The elements that 
Table 3. Comparison of the geometric means of bulk chemical 

analyses for composited mine waste-rock pile material with the 

bulk chemical analysis of the Straight Creek erosional-scar area, 

Questa, New Mexico.

[—, not determined; %, percentage; ppm, parts per million; <, less than]

Constituent

Geometric mean

 of mine wasterock piles1

Straight 

Creek Ratio

Al % 7.0 6.1 1.2

Ca % 1.1 .57 1.9

Fe % 3.4 3.6 .94

K % 3.2 2.8 1.1

Mg % .89 .96 .92

Na % 1.1 .49 2.3

P % .10 .12 .83

Ti % .19 .12 1.6

S % 1.5 1.2 1.3

Ag ppm — < 2 —

As ppm — < 10 —

Au ppm — < 8 —

Ba ppm 570 340 1.7

Be ppm 2.9 1.9 1.5

Bi ppm — < 10 —

Cd ppm — < 2 —

Ce ppm 76 56 1.4

Co ppm 9.9 7.0 1.4

Cr ppm 59 58 1.0

Cu ppm 82 42 2.0

Eu ppm — < 2 —

Ga ppm 17 18 .93

Ho ppm — < 4 —

La ppm 42 32 1.3

Li ppm 27 26 1.0

Mn ppm 590 370 1.6

Mo ppm 90 16 5.6

Nb ppm 16 12 1.4

Nd ppm 31 22 1.4

Ni ppm 23 15 1.6

Pb ppm 92 170 .53

Sc ppm 7.9 6.4 1.2

Sn ppm — 6.9 —

Sr ppm 310 120 2.5

Ta ppm — < 40 —

Th ppm 10 7.2 1.4

U ppm — < 100 —

V ppm 73 66 1.1

Y ppm 18 7 2.6

Yb ppm 1.8 < 1 —

Zn ppm 80 84 .95

1

 Geometric mean of five mine waste-rock piles listed in table 2.

Mine Waste-Rock Leaching Results 19
20 Questa Investigation 19—Leaching Characteristics

Table 4. Leachate chemical analyses for composited mine waste-rock pile samples, Questa, New 

Mexico.

[Analyzed by ICP–MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, milligrams per liter; %, percentage; <, less than; ‰, parts per 

thousand ]

18-hour test

Property or 

constituent1

Geometric 

mean2 Capulin

Old 

Sulphur 

Gulch

Sugar 

Shack 

Middle

Sugar 

Shack 

South

Sugar 

Shack 

West

Tailings3

pH 4.9 4.1 6.2 5.6 5.7 3.0 7.0

Sp. Cond. μS/cm 1,470 609 1,840 1,770 2,050 1,070 259

Ag μg/L — <3 <3 <3 <3 <3 < 3

Al* mg/L 1.4 1.7 .12 2.2 1.5 9.0 .039

As μg/L — <1 <1 <1 <1 2 < 1

B* mg/L .021 .032 .013 .012 <0.01 .041 —

Ba μg/L 70 80 76 77 46 76 48

Be μg/L .63 3.2 .10 .40 .30 2.6 < 0.05

Ca* mg/L 280 100 510 490 620 110 49

Cd μg/L 2.6 1.4 3.4 4.6 6.2 .77 .47

Ce μg/L 17 50 2.2 12 13 93 .03

Co μg/L 30 12 18 54 60 34 .09

Cr μg/L — <1 <1 <1 <1 17 < 1

Cs μg/L — .03 .04 .04 .05 < 0.02 < 0.01

Cu μg/L 27 100 3.4 14 13 220 2.7

Dy μg/L 1.2 3.4 .12 1.3 1.1 4.2 —

Er μg/L .48 1.2 .05 .53 .51 1.6 —

Eu μg/L .46 .74 .07 .58 .53 1.2 —

Fe μg/L — <50 <50 <50 <50 16,100 < 50

Ga μg/L .31 .82 .06 .20 .22 1.4 .03

Gd μg/L 2.2 5.9 .24 2.1 2.0 8.0 —

Ge μg/L .10 .20 .05 .06 .08 .26 < 0.02

Ho μg/L .20 .53 .02 .23 .22 .66 —

K* mg/L 2.5 1.4 5.4 4.0 3.7 0.8 2.3

La μg/L 8.2 23 1.6 6.6 6.4 25 .02

Li μg/L 15 6.6 14 22 23 18 .90

Mg* mg/L 11 4.1 13 18 19 7.9 .73

Mn μg/L 2,740 2,280 2,460 3,440 4,770 1,680 51.3

Mo μg/L — < 2 420 110 170 < 2 350

Na* mg/L 1.3 1.2 1.6 1.4 1.0 1.3 .48

Nb μg/L — < 0.2 < 0.2 < 0.2 < 0.2 0.21 .06

Nd μg/L 11 30 1.4 7.8 8.8 58 —

Ni μg/L 83 33 68 120 160 90 .90

P mg/L — < 0.01 < 0.01 < 0.01 < 0.01 .04 < 0.01

Pb μg/L .20 .40 <0.05 .20 .10 .20 .52

Pr μg/L 2.6 7.6 0.30 1.8 1.9 14 —

Rb μg/L 4.9 2.9 9.2 8.3 8.2 1.5 2.8

Sb μg/L .60 .44 .88 <0.3 .46 .73 .35
Mine Waste-Rock Leaching Results 21

Table 4. Leachate chemical analyses for composited mine waste-rock pile samples, Questa, New 

Mexico.—Continued

[Analyzed by ICP–MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, milligrams per liter; %, percentage; <, less than; ‰, parts per 

thousand ]

18-hour test

Property or 

constituent1

Geometric 

mean2 Capulin

Old 

Sulphur 

Gulch

Sugar 

Shack 

Middle

Sugar 

Shack 

South

Sugar 

Shack 

West

Tailings3

Sc μg/L — < 0.6 < 0.6 < 0.6 < 0.6 1.7 0.30

Se μg/L — 1.8 < 1 < 1 1.0 1.6 < 1

Si mg/L 1.4 1.6 1.3 1.4 1.4 1.1 .70

Sm μg/L 2.1 6.5 .21 1.7 1.8 11 —

SO4* mg/L 720 260 1,200 1,100 1,400 390 87

Sr μg/L 926 366 2,530 2,460 2,470 121 332

Tb μg/L .26 .76 .030 .24 .24 .97 —

Th μg/L — < 0.2 < 0.2 < 0.2 .35 3.1 .02

Ti μg/L 8.8 3.6 14 13 16 5.4 1.2

Tl μg/L — <0.1 <0.1 <0.1 <0.1 .10 < 0.1

Tm μg/L .050 .12 .006 .053 .050 .17 —

U μg/L .51 .94 .76 .14 .32 1.1 .47

V μg/L — <0.5 <0.5 <0.5 <0.5 <0.5 < 0.1

Y μg/L 7.5 14 1.3 9.0 9.2 16 .03

Yb μg/L .22 .62 .020 .22 .22 .90 —

Zn μg/L 234 326 76.9 251 285 392 7.00

Zr μg/L — < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2

d34S ‰ — –7.9 2.5 1.3 2.0 –5.8 —

F** mg/L 1.3 .27 2.2 4.0 3.0 .49 .75

Cl** mg/L — <0.6 <0.6 <0.6 <0.6 <0.6 <0.6

SO4** mg/L 789 310 1,200 1,180 1,480 470 99.0

C.I.4 % — –13 9.7 9.7 9.5 –8.1 225
22 Questa Investigation 19—Leaching Characteristics

Table 4. Leachate chemical analyses for composited mine waste-rock pile samples, Questa, New 

Mexico.—Continued

[Analyzed by ICP–MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens 

per centimeter; μg/L, micrograms per liter; mg/L, milligrams per liter; %, percentage; <, less than; ‰, parts per thousand ]

Field Leach Test

Property or 

constituent1

Geometric 

mean2 Capulin

Old 

Sulphur 

Gulch

Sugar 

Shack 

Middle

Sugar 

Shack 

South

Sugar 

Shack 

West

Tailings3

pH 4.3 3.7 5.1 4.6 4.7 3.2 7.4

Sp. Cond. μS/cm 1,020 569 1,110 1,190 1,380 862 145

Ag μg/L — <3 <3 <3 <3 <3 < 3

Al* mg/L 3.9 1.6 2.6 5.0 5.4 8.2 .056

As μg/L — <1 <1 <1 <1 <1 < 1

B* mg/L .028 .041 .017 .024 .024 .042 —

Ba μg/L 73 77 70 75 74 69 43

Be μg/L 2.1 2.4 1.3 2.8 2.8 1.6 < 0.05

Ca* mg/L 180 88 260 270 340 92 22

Cd μg/L 2.1 .99 3.5 3.9 4.8 .61 .16

Ce μg/L 20 40 5.5 11 17 71 .11

Co μg/L 31 8.0 33 56 69 28 .05

Cr μg/L — <1 <1 <1 1.6 16 < 1

Cs μg/L .04 .04 .04 .05 .05 < 0.02 .01

Cu μg/L 170 110 110 230 300 170 2.6

Dy μg/L 2.3 2.8 1.0 2.1 3.1 3.5 —

Er μg/L .88 .92 .42 .79 1.3 1.3 —

Eu μg/L .71 .59 .36 .75 1.2 1.0 —

Fe μg/L — 158 <50 <50 <50 15,700 < 50

Ga μg/L .30 .55 .09 .20 .26 1.0 .02

Gd μg/L 3.3 4.9 1.3 2.6 4.0 6.5 —

Ge μg/L — .08 < 0.05 < 0.05 .07 .20 < 0.02

Ho μg/L .38 .42 .17 .36 .55 .54 —

K* mg/L 1.3 .72 3.1 2.5 2.3 .26 1.7

La μg/L 7.4 17 2.5 4.9 6.5 17.4 .06

Li μg/L 15 4.8 17 22 30 15 .60

Mg* mg/L 9.1 3.6 10 15 16 7.4 .48

Mn μg/L 1,810 1,270 1,570 2,460 2,900 1,380 54.0

Mo μg/L — < 2 24 4.4 12 < 2 95

Na* mg/L 1.2 1.2 1.1 1.1 1.4 1.1 .43

Nb μg/L — < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 .04

Nd μg/L 14 25 4.2 8.2 14 46 —

Ni μg/L 73 25 70 110 150 73 .50

P mg/L — < 0.01 < 0.01 .01 .01 .06 < 0.01

Pb μg/L .43 .69 .20 .30 .40 .88 1.0

Pr μg/L 3.2 6.2 .90 1.7 3.0 11 —

Rb μg/L 3.8 2.9 7.2 8.2 6.5 .75 2.0

Sb μg/L — <0.3 .38 <0.3 <0.3 <0.3 .20
Mine Waste-Rock Leaching Results 23

Table 4. Leachate chemical analyses for composited mine waste-rock pile samples, Questa, New 

Mexico.—Continued

[Analyzed by ICP–MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens 

per centimeter; μg/L, micrograms per liter; mg/L, milligrams per liter; %, percentage; <, less than; ‰, parts per thousand ]

Field Leach Test

Property or 

constituent1

Geometric 

mean2 Capulin

Old 

Sulphur 

Gulch

Sugar 

Shack 

Middle

Sugar 

Shack 

South

Sugar 

Shack 

West

Tailings3

Sc μg/L — < 0.6 < 0.6 < 0.6 < 0.6 1.0 < 0.1

Se μg/L — < 1 < 1 < 1 1.0 < 1 < 1

Si mg/L — < 0.2 .30 .20 .30 < 0.2 < 0.2

Sm μg/L 3.4 5.5 1.1 2.2 3.7 9.0 —

SO4* mg/L 480 230 630 650 820 330 45

Sr μg/L 438 233 1,130 1,070 1,180 48.4 91.3

Tb μg/L .44 .60 .18 .37 .57 .76 —

Th μg/L — < 0.2 < 0.2 < 0.2 < 0.2 3.6 .03

Ti μg/L 5.5 2.6 7.5 7.9 9.4 3.6 .60

Tl μg/L — <0.1 <0.1 <0.1 <0.1 <0.1 < 0.1

Tm μg/L .10 .097 .050 .097 .16 .13 —

U μg/L .94 1.2 .48 .84 1.8 .84 .08

V μg/L — <0.5 <0.5 <0.5 <0.5 <0.5 < 0.1

Y μg/L 11 11 5.7 10 16 13 .03

Yb μg/L .51 .48 .25 .49 .82 .72 —

Zn μg/L 315 214 302 374 474 269 2.60

Zr μg/L — < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2

d34S ‰ — — — — — — —

F** mg/L .49 .11 .88 1.2 1.0 .23 .25

Cl** mg/L — <0.6 <0.6 <0.6 <0.6 <0.6 <0.6

SO4** mg/L 524 260 670 710 890 360 53.0

C.I.4 % — -3.9 2.7 6.0 4.2 1.8 5.96

1

 Constituents marked with an asterisk were analyzed by inductively coupled plasma-atomic emission spectroscopy 

(ICP–AES). Constituents marked with two asterisks were analyzed by IC. The pH, specific conductance, and sulfur isotope 

analytical methods are described in the text.

2

 Does not include Columbine Terrace tailings sample. Specific conductance and pH are arithmetic means.

3

 Columbine Terrace tailings slurry-pipe sample.

4

 Charge Imbalance (C.I.) = 100 x (sum cations – sum anions) / [(sum cations + sum anions) / 2], reported as percent difference. Anion data were analyzed by Ion Chromatography.

5

 Includes NO3 = 1.2 mg/L.

6

 Includes NO3 = 1.1 mg/L.
24 Questa Investigation 19—Leaching Characteristics

Figure 11. Leachate pH from the 

Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited 

mine waste-rock pile samples and a 

tailings sample from the Questa Mine, 

New Mexico.

pH - Field Leach Test

pH - 18-hour test

Sp. Cond. - Field Leach Test

Sp. Cond. - 18-hour test

Sulfate - Field Leach Test

Sulfate - 18-hour test

LEACHATE pH

2

3

4

5

6

7

LEACHATE SPECIFIC CONDUCTANCE, IN MICROSIEMENS 

PER CENTIMETER AND LEACHATE SULFATE,

IN MILLIGRAMS PER LITER

0

500

1,000

1,500

2,000

2,500

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

Figure 12. Leachate specific 

conductance, leachate sulfate 

concentration, and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, 

New Mexico. Sp. Cond., specific 

conductance. LEACHATE pH

2

3

4

5

6

7

8

pH - Field Leach Test

pH - 18-hour test

Sugar Shack

West

Capulin Sugar Shack

Middle

Old Sulphur

Gulch

Tailings

(slurry pipe)

Sugar Shack

South
decreased over the 18-hour leaching period include Al, B, Be, 

Cu, Dy, Er, Eu, Gd, Ho, Nd, Pb, Pr, Sm, Tb, Tm, Yb, and Zn. 

Figures 13 to 15 show the increase in concentration between 

the FLT and the 18-hour procedure for silicon, titanium, and 

manganese, respectively. Increases in concentration of these 

elements indicate that further dissolution of rock-forming minerals is taking place during the 18-hour leaching procedure.

In the mine waste-rock leachates, iron and aluminum 

concentrations appear to be controlled by pH-dependent solubility reactions. As seen in figure 16, Sugar Shack West has 

leachate pH values of 3.0 and 3.2 with approximately 16 mg/L 

of iron present in the leachate. However, when the Capulin 

leachate shifts from pH 3.7 in the FLT to 4.1 in the 18-hour 

procedure, iron shifts from 0.2 mg/L to below detection (lessthan values were replaced with 50 percent of the detection 

limit in preparation of the figure). The other leachates have pH 

>3.7, and all have iron <0.05 mg/L (fig. 16). Nordstrom and 

Alpers (1999) state that schwertmannite, or other sulfate-substituted hydrous ferric oxides, are most likely to control ferric 

iron solubility in acid mine drainage. They note that supersaturation of iron occurs at pH values above about 4. The data 

from this study indicate that the pH cutoff for iron solubility 

is about pH 3.7. These pH-dependent solubility reactions 

also can be noted for aluminum. As seen in figure 17, the pH 

increase between the FLT and the 18-hour procedure for Old 

Sulphur Gulch, Sugar Shack Middle, and Sugar Shack South 

all show a corresponding decrease in aluminum concentration. 

In contrast, Sugar Shack West and Capulin, which have lower 

pH values (pH <4.6), do not show a significant change in aluminum concentration between the FLT and 18-hour leaching 

procedure (less-than values were replaced with 50 percent of 

the detection limit in preparation of the figure). Results from 

solubility calculations for the leachates using WATEQ4F (Ball 

and Nordstrom, 1991) show that Sulphur Gulch, Sugar Shack 

Middle, and Sugar Shack South are all saturated with respect 

to gibbsite, whereas Capulin and Sugar Shack West are not. 

Nordstrom and Alpers (1999) discuss the relationship between 

saturation indices for gibbsite as a function of pH. They 

explain that when acid-mine drainage is diluted by neutral-pH 

water, the pH and aluminum concentrations eventually reach 

the gibbsite solubility curve, and aluminum concentrations are 

controlled by the solubility of a solid phase or by a surface 

coating. Furthermore, for acid-mine waters with pH values 

above 5, solubility of dissolved aluminum is controlled by 

microcrystalline to amorphous Al(OH)3. The data in figure 17

are consistent with these pH-dependent solubility reactions 

and indicate solubility control above a pH of about 5.1.

Some of the elements that exhibit pH-dependent concentration reversals between the FLT and 18-hour leaching 

procedure may be undergoing pH-dependent coprecipitation 

or sorption reactions with iron or aluminum. Figures 16 and 

17 show that iron and aluminum appear to be precipitating during the leaching procedures at about pH 3.7 and 5.1, 

respectively. Figure 18 shows a plot for copper, where leachate 

copper concentrations notably decrease above a leachate pH 

of about 6. Sorption of cations, such as copper, increases with 

increasing pH, and pH 6 corresponds to the pH range in which 

substantial copper sorbs onto hydrous iron oxides (Smith, 

1999; Smith and others, 1998). The pH-dependent sorption of 

copper during the 18-hour leaching procedure explains why 

the copper concentration is higher in the 18-hour leachates for 

the lower-pH samples and lower in the 18-hour leachates for 

the higher-pH samples. These types of pH-dependent sorption 

reactions also may be taking place for Be, Cd, Ce, Co, Cr, and 

Zn (shown in figs. 19, 20, 21, 22, 23, and 24, respectively). 

Conversely, figure 25 shows the relationship for molybdenum, 

where molybdenum concentrations increase with increasing leachate pH. This behavior is typical of anion sorption 

reactions, in which sorption of anions, such as molybdenum, 

decreases with increasing pH (Smith, 1999). These types of 

pH-dependent reactions are likely taking place within the 

porewater of the mine waste-rock piles and in water being 

transported away from the piles. Hence, for a given leachable 

metal concentration that is soluble at a given pH, a portion of 

that concentration may be decreased or increased as a result of 

pH-dependent sorption or coprecipitation reactions.

In this study, lead (fig. 26) leachate concentrations are 

always lower in the 18-hour leachates than in the FLT leachates. As seen in figure 12, sulfate concentrations always 

increase between the FLT and 18-hour leaching procedure. 

Hence, it appears that lead concentrations are being controlled 

by anglesite (PbSO4) solubility because the common-ion effect 

is in operation.

The tailings sample from Columbine Terrace generates circumneutral pH leachates and generally lower element 

concentrations than do the mine waste-rock piles. An exception is the molybdenum concentration. The charge imbalance 

is unusually high for the 18-hour leachate. This is likely due 

to the fact that alkalinity measurements were not made on the 

leachates, so alkalinity is not included in the charge-balance 

calculations. The tailings samples from Columbine Terrace also contained measurable nitrate (data not included in 

table 4).

The isotopic composition of sulfate from the 18-hour 

leachates from the mine waste-rock piles is given in table 4 

and figure 27, which shows two distinct groups. Sugar Shack 

West and Capulin δ34S values range from –5.8 to –7.9 parts 

per thousand, respectively. Old Sulphur Gulch, Sugar Shack 

Middle, and Sugar Shack South all have positive δ34S values ranging from 1.3 to 2.5 parts per thousand. Mineralogy 

data (table 1) and bulk-chemistry data (table 2) indicate that 

there are compositional differences between the Capulin and 

Sugar Shack West piles compared to the Old Sulphur Gulch, 

Sugar Shack Middle, and Sugar Shack South piles. If indeed 

the Capulin and Sugar Shack West piles received material extracted near the top of the system, then their leachate 

isotopic signatures should be similar to those of the erosional 

scars. The isotopic composition of sulfate from the 18-hour 

leachate from the Goat Hill West scar was measured as –2.1 

parts per thousand in this study. Tuttle and others (2003) 

measured the isotopic composition of sulfate from Straight 

(–4.2 to –6.8 parts per thousand), Hottentot (–3.9 to –4.6 parts 

Mine Waste-Rock Leaching Results 25
26 Questa Investigation 19—Leaching Characteristics LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

pH - Field Leach Test

pH - 18-hour test

Si - Field Leach Test

Si - 18-hour test

LEACHATE SILICON, IN MILLIGRAMS PER LITER

0

0.5

1.0

1.5

2.0

Old Sulphur

Gulch

Figure 13. Leachate silicon (Si) 

concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited mine 

waste-rock pile samples from the Questa 

Mine, New Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Ti - Field Leach Test

Ti - 18-hour test

LEACHATE TITANIUM, IN MILLIGRAMS PER LITER

0

5

10

15

20

Figure 14. Leachate titanium (Ti) 

concentration and leachate pH from the Field 

Leach Test (FLT) and the 18-hour leaching 

procedure for composited mine waste-rock 

pile samples from the Questa Mine, New 

Mexico.

26
LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Mn - Field Leach Test

Mn - 18-hour test

0

1,000

2,000

3,000

4,000

5,000

LEACHATE MANGANESE,IN MICROGRAMS PER LITER

Figure 15. Leachate manganese 

(Mn) concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Fe - Field Leach Test

Fe - 18-hour test

LEACHATE IRON, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

100

Figure 16. Leachate iron (Fe) 

concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

Mine Waste-Rock Leaching Results 27
28 Questa Investigation 19—Leaching Characteristics LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Al - Field Leach Test

Al - 18-hour test

LEACHATE ALUMINUM, IN MILLIGRAMS PER LITER

0

2

4

6

8

10

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Cu - Field Leach Test

Cu - 18-hour test

0

50

100

150

200

250

300

350

LEACHATE COPPER, IN MICROGRAMS PER LITER

Figure 17. Leachate aluminum (Al) 

concentration and leachate pH from the 

Field Leach Test (FLT) and the 18-hour 

leaching procedure for composited 

mine waste-rock pile samples from the 

Questa Mine, New Mexico.

Figure 18. Leachate copper (Cu) 

concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

28
Mine Waste-Rock Leaching Results 29

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Be - Field Leach Test

Be - 18-hour test

LEACHATE BERYLLIUM, IN MICROGRAMS PER LITER

0

1

2

3

4

Figure 19. Leachate beryllium 

(Be) concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

Figure 20. Leachate cadmium 

(Cd) concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Cd - Field Leach Test

Cd - 18-hour test

0

2

4

6

LEACHATE CADMIUM, IN MICROGRAMS PER LITER
30 Questa Investigation 19—Leaching Characteristics

Figure 21. Leachate cerium (Ce) 

concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

Figure 22. Leachate cobalt 

(Co) concentration and 

leachate pH from the Field 

Leach Test (FLT) and the 18-

hour leaching procedure for 

composited mine waste-rock 

pile samples from the Questa 

Mine, New Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Ce - Field Leach Test

Ce - 18-hour test

0

20

40

60

80

100

LEACHATE CERIUM, IN MICROGRAMS PER LITER

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Co - Field Leach Test

Co - 18-hour test

0

10

20

30

40

50

60

70

LEACHATE COBALT, IN MICROGRAMS PER LITER
Figure 23. Leachate chromium 

(Cr) concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

Figure 24. Leachate zinc (Zn) 

concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, 

New Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Cr - Field Leach Test

Cr - 18-hour test

0

5

10

15

20

LEACHATE CHROMIUM, IN MICROGRAMS PER LITER

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Zn - Field Leach Test

Zn - 18-hour test

LEACHATE ZINC, IN MICROGRAMS PER LITER

0

100

200

300

400

500

Mine Waste-Rock Leaching Results 31
32 Questa Investigation 19—Leaching Characteristics

Figure 25. Leachate molybdenum 

(Mo) concentration and leachate pH 

from the Field Leach Test (FLT) and 

the 18-hour leaching procedure for 

composited mine waste-rock pile 

samples from the Questa Mine, New 

Mexico.

Figure 26. Leachate lead (Pb) 

concentration and leachate 

pH from the Field Leach Test 

(FLT) and the 18-hour leaching 

procedure for composited mine 

waste-rock pile samples from the 

Questa Mine, New Mexico.

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Mo - Field Leach Test

Mo - 18-hour test

LEACHATE MOLYBDENUM, IN MICROGRAMS PER LITER

0

100

200

300

400

500

LEACHATE pH

2

3

4

5

6

7

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

pH - Field Leach Test

pH - 18-hour test

Pb - Field Leach Test

Pb - 18-hour test

LEACHATE LEAD, IN MICROGRAMS PER LITER

0.0

0.2

0.4

0.6

0.8

1.0
Figure 27. Isotopic composition of 

leachate sulfate (SO4) from the mine 

waste-rock piles 18-hour leaching 

procedure for composited mine wasterock pile samples from the Questa 

Mine, New Mexico.

Sugar Shack

West

Capulin Sugar Shack

Middle

Sugar Shack

South

Old Sulphur

Gulch

-10

-8

-6

-4

-2

0

2

4

LEACHATE 34 SULFUR, IN PARTS PER THOUSAND 

per thousand), and June Bug (–3.4 to –4.1 parts per thousand) 

Creeks, and Verplanck and others (2006) measured the isotopic composition of sulfate from water in Goat Hill (–8.7 parts 

per thousand), Hansen (–6.9 to –8.6 parts per thousand), and 

Straight (–3.2 to –6.6 parts per thousand) Creeks. These δ34S 

values are similar to our δ34S values for the Sugar Shack West 

and Capulin leachates (–5.8 to –7.9 parts per thousand, respectively). Hence, the δ34S values for the Sugar Shack West and 

Capulin leachates are more similar to the erosional scars than 

are the δ34S values for the Old Sulphur Gulch, Sugar Shack 

Middle, and Sugar Shack South leachates.

As was discussed in the “Sampling Strategy” section of 

this report, the waste-rock multi-increment samples were collected on two different collection trips, under different weather 

conditions, and by different samplers because of inclement 

weather during the first sampling trip. It is not known what 

effect this sampling difference has on the data. However, it is 

not likely that such sampling differences are responsible for 

the large differences in mineralogical, bulk-chemistry, and 

sulfur-isotope data discussed earlier in this report. Instead, it 

is likely that there are indeed differences in source material 

between the Capulin and Sugar Shack West piles compared to 

the Old Sulphur Gulch, Sugar Shack Middle, and Sugar Shack 

South piles and that the Capulin and Sugar Shack West piles 

received material extracted near the top of the system. This 

depiction is consistent with the knowledge that the Old Sulphur Gulch, Sugar Shack Middle, and Sugar Shack South piles 

are younger than the Capulin and Sugar Shack West piles.

Erosional Scar Leaching Results

The erosional-scar material has not been subjected to disturbance by mining and, as a result, should be more homogeneous than the waste-rock material for a given sample. Table 5

lists chemical analyses for leachates from the erosional scars. 

The pH of the erosional-scar leachates varies between 3.2 

and 4.1, a much narrower range than for the mine waste-rock 

leachates. Figure 28 shows the pH values for the erosional-scar 

leachates for both the FLT and the 18-hour leaching procedure. Unlike the mine waste-rock leachates, the erosional-scar 

leachates exhibit little difference in their pH values between 

the two leaching procedures. Because the pH values are lower 

and more consistent for the erosional-scar leachates, the 

types of pH controls discussed previously for the waste-rock 

leachates generally do not apply. Figure 29 shows the specific 

conductance and sulfate concentrations for the erosional-scar 

leachates for the two leaching procedures. There is an increase 

in the specific conductance and sulfate concentrations between 

the FLT and the 18-hour leaching-procedure results. There is 

also an increase in calcium concentration between the FLT 

and the 18-hour procedure (table 5), indicating dissolution of 

gypsum with increased time and agitation. Assuming stoichiometric dissolution, calculations indicate that nearly all 

of the sulfate in most of the erosional scars can be explained 

by gypsum dissolution. Exceptions are the Goat Hill West 

and Hottentot scar samples for which only 24 percent and 35 

percent, respectively, of the leachate sulfate can be attributed 

Erosional Scar Leaching Results 33
Table 5. Leachate chemical analyses for composited erosional-scar samples, Questa, New Mexico. [Analyzed by ICP-MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, miper liter; <, less than; ‰, parts per thousand] 18-hour test Property or constituent1 Geometric mean2 Goat Hill West Goat Hill Sulphur Gulch SW Hansen Creek Hansen Creek Straight Creek SE Straight Creek Hottentot Creek June Bug pH — 3.7 3.8 3.6 3.2 4.1 3.3 3.8 3.3 4.0 Sp. Cond. μS/cm — 603 401 1,530 1,930 1,210 1,270 817 379 922 Ag μg/L — <3 <3 <3 <3 <3 <3 <3 <3 <3 Al* mg/L 6.5 30 3.0 37 22 11 11 5.1 4.2 4.2 As μg/L — 2 <1 <1 <1 <1 <1 <1 <1 <1 Ba μg/L 49.9 60.3 45.9 35.4 40.6 44.4 42.4 59 64.3 48.1 Be μg/L 1.7 5.1 1.3 6.3 4.2 6.2 3.2 1.4 .90 2.6 Bi μg/L — — .02 0.006 < 0.005 < 0.005 < 0.005 < 0.005 < 0.005 < 0.005 Ca* mg/L 102 38.0 54.0 322 406 268 234 162 8.90 207 Cd μg/L 1.3 5.9 1.1 3.1 1.4 2.4 4.4 2.1 1.7 2.2 Ce μg/L 14 15 4.1 45 58 29 62 8.8 3.9 58 Co μg/L 22 76 11 110 69 73 37 18 15 24 Cr μg/L 5.0 9.4 <1 8.9 11 <1 5.9 <1 3.1 <1 Cs μg/L .054 .12 .020 .050 .040 .040 .080 .040 .10 .040 Cu μg/L 118 630 129 688 121 79.0 303 61.9 114 313 Fe* mg/L .58 .28 .13 .32 6.0 .28 3.3 .24 2.0 .073 Ga μg/L .23 .56 .06 .58 .68 .33 .60 .10 .07 .40 Ge μg/L .08 .20 .03 .22 .20 .10 .20 .04 .02 .10 K mg/L 1.8 1.5 2.0 1.1 0.85 2.3 1.9 2.1 2.0 2.7 La μg/L 4.2 3.1 1.2 9.9 16 6.3 18 2.7 1.2 24 Li μg/L 7.9 27 4.0 46 20 11 13 4.3 4.0 12 Mg* mg/L 7.1 19 2.8 26 29 18 8.4 4.7 3.5 3.5 Mn* mg/L .94 4.0 1.2 3.0 2.2 4.5 1.8 1.2 .48 1.1 Mo μg/L .74 < 2 .49 .30 .35 < 0.2 .23 < 0.2 < 0.2 < 0.2 Na mg/L .58 1.2 .70 .72 .42 .39 .54 .47 .30 .39 Nb μg/L .037 < 0.02 .040 .040 .040 .020 .020 < 0.02 < 0.02 < 0.02 Ni μg/L 51.8 194 21.0 234 162 164 82.6 40.4 32.7 45.9 P mg/L .04 .09 < 0.01 .03 .03 < 0.01 .01 < 0.01 < 0.01 < 0.01 
Table 5. Leachate chemical analyses for composited erosional-scar samples, Questa, New Mexico.—Continued

[Analyzed by ICP-MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, miper liter; <, less than; ‰, parts per thousand]

18-hour test

Property orconstituent1

Geometric 

mean2

Goat 

Hill 

West

Goat 

Hill

Sulphur 

Gulch

SW 

Hansen 

Creek

Hansen 

Creek

Straight 

Creek

SE 

Straight 

Creek

Hottentot 

Creek

June 

Bug

Pb μg/L .3 <0.05 .2 <0.05 .4 .2 .4 .1 .07 1 Rb μg/L 2.9 13 3.9 4.6 1.8 3.3 4.1 2.7 3.9 2.5 Sb μg/L .3 .4 .3 .2 .2 .2 .6 .2 .2 .1 Sc μg/L .7 .6 .4 1 3 .8 2 .5 .4 .6 Se μg/L 1.7 1.5 < 1 2.4 1.7 1.3 1.6 1.2 < 1 2.6 Si mg/L 1.4 1.0 1.0 1.2 1.3 1.5 1.3 1.4 1.0 1.6 SO4 mg/L 278 — 151 903 1,090 657 615 383 80.0 460 Sr μg/L 164 14.2 35.8 576 1,780 500 84.5 89.2 15.2 1160 Ta μg/L .03 — < 0.02 .03 .03 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 Th μg/L .13 < 0.2 .10 .12 1.5 .02 1.5 .05 .10 .03 Ti μg/L 4.9 3.9 1.8 11 13 7.4 7.0 4.4 1.0 5.0 Tl μg/L .07 <0.1 .07 .05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 U μg/L 1.2 24 .83 3.5 3.7 1.8 3.1 .56 1.7 1.3 V μg/L .5 <0.5 <0.1 <0.1 .2 <0.1 <0.1 <0.1 <0.1 <0.1 W μg/L .04 — .06 .09 .04 .04 .04 .02 < 0.02 .02 Y μg/L 8.7 31 3.3 52 39 23 21 5.9 3.5 15 Zn μg/L 222 1,750 235 331 295 522 634 195 200 185 Zr μg/L — < 0.2 .20 < 0.05 < 0.05 < 0.05 < 0.05 .07 < 0.05 < 0.05 d34S ‰ — -2.1 — — — — — — — — F** mg/L — .80 .72 1.2 .81 .78 .92 .54 .14 .84 Cl** mg/L — <0.6 .69 .76 .80 <0.6 <0.6 <0.6 <0.6 .51 SO4** mg/L — 340 170 1,000 1,260 500 690 430 93.0 518 —
Table 5. Leachate chemical analyses for composited erosional-scar samples, Questa, New Mexico.—Continued [Analyzed by ICP-MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, miligrams per liter; <, less than; ‰, parts per thousand ] Field Leach Test Property or constituent1 Geometric mean2 Goat Hill West Goat Hill Sulphur Gulch SW Hansen Creek Hansen Creek Straight Creek SE Straight Creek Hottentot Creek June Bug Le

alte

si

pH — 3.7 3.7 3.6 3.2 3.8 3.3 3.7 3.3 3.8 Sp. Cond. μS/cm — 547 251 993 1,060 743 642 400 324 446 6Ag μg/L — <3 <3 <3 <3 <3 <3 <3 <3 <3 <Al* mg/L 2.9 21 1.2 24 9.3 5.9 3.5 1.2 2.2 .94 As μg/L — <1 <1 <1 <1 <1 <1 <1 <1 <1 <Ba μg/L 35 83 47 32 9.3 8.7 44 93 23 41 16Be μg/L 1.9 3.1 1.0 5.3 3.1 5.6 2.1 0.90 0.60 1.6 <Bi μg/L .02 — .03 .01 < 0.005 < 0.005 < 0.005 < 0.005 < 0.005 < 0.005 Ca* mg/L 46.1 34.0 24.0 144 144 128 79.0 52.0 6.00 75.0 Cd μg/L .91 4.5 .72 2.5 1.0 1.8 2.8 1.2 1.2 1.2 Ce μg/L 6.2 10 1.4 28 25 15 19 1.9 2.3 13 Co μg/L 14 58 6.8 89 53 46 22 9.6 11 8.7 Cr μg/L 7.5 14 <1 16 11 <1 3.8 <1 4.7 <1 <Cs μg/L .076 .14 .020 .070 .090 .080 .12 .070 .19 .060 Cu μg/L 92.6 503 99.5 625 102 78.9 202 45.2 93.2 213 Fe* mg/L .60 .40 .27 .31 3.8 .82 1.7 .31 1.8 .10 Ga μg/L .12 .41 .03 .40 .41 .20 .21 .02 .05 .09 Ge μg/L .05 .20 < 0.02 .10 .06 .06 .03 < 0.02 < 0.02 .02 < K mg/L .80 .73 .71 .50 .20 1.2 .61 1.1 .73 1.0 La μg/L 1.8 1.6 .34 5.6 6.7 3.1 5.3 .52 .64 5.4 Li μg/L 5.9 19 3.3 39 18 6.7 9.7 3.3 3.0 4.6 Mg* mg/L 4.8 16 1.9 21 22 14 5.7 2.7 2.6 2.1 Mn* mg/L .59 2.9 .66 2.4 1.6 2.8 1.1 .58 .33 .44 Mo μg/L .87 < 2 1.2 .36 .34 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 Na mg/L .40 1.3 .63 .53 .14 .18 .54 .70 .070 .34 Nb μg/L .039 < 0.02 .050 .040 .030 .030 .020 < 0.02 < 0.02 < 0.02 Ni μg/L 36.2 156 13.7 198 131 124 51.5 23.5 24.4 24.6 P mg/L .03 .09 .01 .04 .02 .01 < 0.01 .02 < 0.01 < 0.01 Pb μg/L .4 .1 .1 <0.05 .9 .5 .8 .2 .2 1 
Table 5. Leachate chemical analyses for composited erosional-scar samples, Questa, New Mexico.—Continued

[Analyzed by ICP-MS unless otherwise noted; —, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens per centimeter; μg/L, micrograms per liter; mg/L, miligrams per liter; <, less than; ‰, parts per thousand ]

Field Leach Test

Property orconstituent1

Geometric 

mean2

Goat 

Hill 

West

Goat 

Hill

Sulphur 

Gulch

SW 

Hansen 

Creek

Hansen 

Creek

Straight 

Creek

SE 

Straight 

Creek

Hottentot 

Creek

June 

Bug

Le

alte

si

Rb μg/L 2.8 11 2.9 4.8 2.1 4.3 3.8 2.8 3.6 2.2 Sb μg/L .3 .8 .4 .2 .2 .2 .6 .5 .2 .2 Sc μg/L .4 < 0.6 < 0.1 .9 2 .5 .6 .2 < 0.1 .2 Se μg/L 1.6 < 1 < 1 1.6 < 1 < 1 < 1 < 1 < 1 < 1 < Si mg/L — < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 < 0.2 SO4 mg/L 147 — 77.0 509 482 350 213 138 60.0 167 1Sr μg/L 48.9 6.57 10.2 84.0 250 204 20.2 26.1 5.8 271 4Ta μg/L .02 — < 0.02 .02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < Th μg/L .12 .24 .10 .16 1.2 .04 .68 .05 .13 .02 Ti μg/L 2.7 3.0 1.0 6.7 6.7 4.0 2.7 1.8 1.0 1.9 Tl μg/L .10 <0.1 .20 .05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <U μg/L .87 28 .72 3.6 2.5 2.1 1.6 .34 1.4 .73 V μg/L .3 <0.5 <0.1 <0.1 .1 <0.1 <0.1 <0.1 <0.1 <0.1 W μg/L .05 — .07 .09 .04 .04 .03 < 0.02 < 0.02 < 0.02 Y μg/L 4.0 25 1.2 35 18 11 6.3 1.3 2.2 3.2 Zn μg/L 171 1,250 181 290 241 406 462 155 134 122 2Zr μg/L — < 0.2 .20 < 0.05 < 0.05 < 0.05 < 0.05 .08 < 0.05 < 0.05 d34S ‰ — — — — — — — — — — F** mg/L — .69 .30 1.4 1.4 .52 .61 .15 .09 <0.05 Cl** mg/L — <0.6 <0.6 .57 1.2 1.2 <0.6 <0.6 1.2 <0.6 SO4** mg/L — 300 84.0 584 530 380 240 160 73.0 200 2

1 Constituents marked with an asterisk were analyzed by ICP–AES. Constituents marked with two asterisks were analyzed by IC. The pH, specific conductance, and sulfur 

analytical methods are described in the text.

2 Does not include the less-altered site.3 Less-altered drainage west of SW Hansen Creek.
38 Questa Investigation 19—Leaching Characteristics LEACHATE pH

2

3

4

7

pH - Field Leach Test

pH - 18-hour test

Hottentot Cr.

Straight Cr.

SE Straight Cr.

Hansen Cr.

June Bug

Less-altered

Goat Hill 

West

Goat Hill 

Sulphur Gulch

SW Hansen Cr.

Figure 28. Leachate pH from the Field Leach 

Test (FLT) and the 18-hour leaching procedure 

for composited erosional-scar samples and a 

less-altered sample near Questa, New Mexico. 

Cr., Creek.

to gypsum dissolution. The Hansen Creek sample appears to 

have substantial calcite dissolution in addition to gypsum dissolution with increasing time and agitation during the leaching 

tests.

The elemental content of the erosional-scar leachates is 

highly variable between scars, which results in a large range of 

values for several elements. Figure 30 shows the iron concentrations and figure 31 shows the aluminum concentrations 

for the two leaching procedures. With the exception of the 

Southwest Hansen Creek scar leachate, the iron concentrations 

are similar between the two leaching procedures. The leachate 

pH measurements are around the pH 3.7 solubility control pH 

for schwertmannite or other sulfate-substituted hydrous ferric oxides previously described for the waste-rock leachates; 

hence, iron concentrations may be at least partially controlled 

by pH-dependent solubility reactions. For aluminum, the 18-

hour leachates always exhibited higher concentrations than the 

FLT leachates, and all are within or less than a factor of about 

two for a given sample. All the leachate pH measurements are 

below the pH 5.1 solubility control pH for aluminum, so there 

does not appear to be any aluminum solubility control in the 

scar leachates.

Comparison of Waste-Rock and 

Erosional-Scar Leaching Results

Figures 32 and 33 show box plots for 18-hour leachates 

from the mine waste-rock piles and the erosional scars (for 

preparation of graphs, data points with qualified values were 

replaced with a value equal to 50 percent of the detection 

limit). When the elemental concentrations in the waste-rock 

leachates are compared with concentrations in the scar leachates, generally the waste-rock leachates do not exceed the 

upper range of the erosional-scar leachates. One exception 

is molybdenum, which is notably higher in the waste-rock 

leachates than in the scar leachates. Another exception is iron, 

where the elevated concentration of iron in the Sugar Shack 

West leachate is anomalous. The data shown in figures 28, 32, 

and 33 indicate that the erosional-scar areas can contribute 

low-pH waters with elevated metal concentrations. Because 

of the low pH of the scar leachates (pH <4.1), many metals 

can be mobilized and remain in solution, the exception being 

anionic species such as molybdenum, which tend to be less 

mobile under acidic conditions. The source material for the 

Capulin and Sugar Shack West waste-rock piles appears to be 

similar to the source material for the scar areas. The leachate 

pH values for the Capulin (pH 3.7 and 4.1) and Sugar Shack 

West (pH 3.2 and 3.0) waste-rock piles are in the same range 

as those of the erosional scars.

Table 6 gives a comparison of the geometric means 

for leachate chemistry of the mine waste-rock piles with 

the leachate chemistry of the Straight Creek scar area. Most 

crucial to understanding the differences in leachate chemistry 

is the difference in leachate pH values. The pH of the Straight 

Creek leachate is 3.3. This pH is low enough to maintain iron 

and aluminum in solution, which in turn allows for greater 

mobility of many cationic species in the leachate. Elements in 

higher concentration in the Straight Creek leachate include Al, 

Be, Ce, Cu, La, Pb, U, Y, and Zn. Elements generally in higher 

concentration in the waste-rock leachates include Ba, Mn, Na, 

and Sr.
LEACHATE pH

3

4

5

Hottentot Cr.

Straight Cr.

SE Straight Cr.

Hansen Cr.

June Bug

Goat Hill 

West

Goat Hill 

Sulphur Gulch

SW Hansen Cr.

pH - Field Leach Test

pH - 18-hour test

Sp. Cond. - Field Leach Test

Sp. Cond. - 18-hour test

Sulfate - Field Leach Test

Sulfate - 18-hour test

0

500

1,000

1,500

2,000

LEACHATE SPECIFIC CONDUCTANCE, IN 

MICROSIEMENS PER CENTIMETER, 

AND LEACHATE SULFATE, 

IN MILLIGRAMS PER LITER

Figure 29. Leachate specific 

conductance, leachate sulfate 

concentration, and leachate 

pH from the Field Leach Test 

(FLT) and the 18-hour leaching 

procedure for composited 

erosional-scar samples near 

Questa, New Mexico. Cr., 

Creek; Sp. Cond., specific 

conductance.

LEACHATE pH

3

4

5

pH - Field Leach Test

pH - 18-hour test

Fe - Field Leach Test

Fe - 18-hour test

LEACHATE IRON, IN MILLIGRAMS PER LITER

0

2

4

6

Hottentot Cr.

Straight Cr.

SE Straight Cr.

Hansen Cr.

June Bug

Goat Hill 

West

Goat Hill 

Sulphur Gulch

SW Hansen Cr.

Figure 30. Leachate iron (Fe) 

concentration and leachate 

pH from the Field Leach Test 

(FLT) and the 18-hour leaching 

procedure for composited 

erosional-scar samples near 

Questa, New Mexico. Cr., 

Creek.

Erosional Scar Leaching Results 39
40 Questa Investigation 19—Leaching Characteristics

Hottentot Cr.

Straight Cr.

SE Straight Cr.

Hansen Cr.

June Bug

Goat Hill 

West

Goat Hill 

Sulphur Gulch

SW Hansen Cr.

LEACHATE pH

3

4

5

0

10

20

30

40

pH - Field Leach Test

pH - 18-hour test

Al - Field Leach Test

Al - 18-hour test

LEACHATE ALUMINUM, IN MILLIGRAMS PER LITER

Figure 31. Leachate aluminum 

(Al) concentration and leachate 

pH from the Field Leach Test 

(FLT) and the 18-hour leaching 

procedure for composited 

erosional-scar samples near 

Questa, New Mexico. Cr., Creek.

EXPLANATION

Maximum value

75 percent value

Median (50 percent value)

25 percent value

Minimum value

Erosional scars

Waste-rock piles

Al Fe Mn Si SO4

0.01

0.1

1

10

100

1,000

10,000

LEACHATE CONCENTRATION, IN 

MILLIGRAMS PER LITER

Figure 32. Box plots for selected leachable major-element concentrations from the 18-hour leaching procedure 

for composited erosional-scar samples near Questa, New Mexico, and composited mine waste-rock pile samples 

from the Questa Mine, New Mexico.
Comparison of Leachate Composition 

with Scar-Drainage Waters

Figures 34 and 35 provide a comparison of the composition of the FLT (filled triangles) and 18-hour leachates 

(open triangles) with surface waters, stormwater runoff, 

and snowmelt runoff from Straight Creek (for preparation 

of graphs, data points with qualified values were replaced 

with a value equal to 50 percent of the detection limit). The 

box plots represent 10 filtered surface-water samples from 

Straight Creek collected at intervals between October 2000 

and October 2003 (data from Verplanck and others, 2006; 

samples 00WA197, 02WA121, 02WA124, 02N287, 02N288, 

03WA101, 03WA115, 03N072, 03N122, 03WA165). The 

diamonds are data from a storm event in September 2002, 

which was the largest storm event of the season; the filled diamonds are filtered runoff collected on the first day of the storm 

(sample 02WA154), and the open diamonds are filtered runoff 

collected on day 3 (sample 02WA158), still during a time of 

heavy runoff (data from Verplanck and others, 2006). The 

inverted triangles are data from a runoff sample taken a day 

after a spring snowmelt event in 2003 (data from Verplanck 

and others, 2006; sample 03WA110). The pH values of the 

FLT and 18-hour leachates for Straight Creek were both 3.3, 

the drainage waters ranged from pH 2.7 to 3.1, the stormwater 

runoff samples were pH 3.0 for day 1 and 2.8 for day 3, and 

the snowmelt runoff sample was pH 2.9. With the exception of 

molybdenum and lead, the compositions of the natural drainage waters and runoff waters are quite comparable

(figs. 34 and 35). The FLT and 18-hour leachates have substantially lower element concentrations than do the natural 

Straight Creek waters, but the overall trends (that is, signatures 

or fingerprints) between elements are similar. Analogous findings were reported for comparison of the FLT with mine-waste 

seep compositions at the Rattler mine site in Colorado (Hageman and others, 2005). Comparison of these data reinforce the 

earlier statement that these (or any) leaching procedures 

cannot provide quantitative concentrations of actual wasterock or scar contributions to surface or ground water. However, they can provide qualitative information about the likely 

chemical composition of porewater within the waste-rock piles 

and erosional scars.

Figure 36 shows calcium concentrations plotted against 

sulfate concentrations for leachates, Straight Creek surface-water samples (data from Verplanck and others, 2006; 

samples 00WA197, 02WA121, 02WA124, 02N287, 02N288, 

03WA101, 03WA115, 03N072, 03N122, 03WA165), and 

additional erosional-scar filtered surface-water samples collected from the Capulin, Waldo Springs (not shown in fig. 1), 

Southwest Hansen, west of Southwest Hansen, Hansen, June 

Bug, and Hottentot scar areas (data from Verplanck and others, 

2006; samples 04WA102, 04WA103, 01WA163, 01WA162, 

01WA153, 01WA152, 01WA151, 01WA161, 01WA160, 

01WA157, 01WA156). Dissolved calcium concentrations 

are derived from gypsum dissolution with additional calcite 

dissolution for some sites. Dissolved sulfate concentrations originate from gypsum dissolution or byproducts from 

pyrite oxidation. Both the waste-rock pile leachates and the 

erosional-scar leachates exhibit a fairly tight trend and have 

EXPLANATION

Maximum value

75 percent value

Median (50 percent value)

25 percent value

Minimum value

0.01

0.1

1

10

100

1,000

10,000

LEACHATE CONCENTRATION, IN 

MICROGRAMS PER LITER

Erosional scars

Waste-rock piles

Be Cd Ce Co Cr Cu Mo Ni Pb Zn

Figure 33. Box plots for selected leachable minor- and trace-element concentrations from the 18-hour leaching 

procedure for composited erosional-scar samples near Questa, New Mexico, and composited mine waste-rock pile 

samples from the Questa Mine, New Mexico.

Comparison of Leachate Composition with Scar-Drainage Waters 41
42 Questa Investigation 19—Leaching Characteristics

higher calcium-to-sulfate ratios than do the natural 

erosional-scar samples. Also, the natural erosional-scar 

data are much more scattered than the leachate data. It 

appears that either the leachates have a larger contribution of calcium from calcite than do the natural samples, 

or the natural samples have a larger contribution of 

pyrite-oxidation products, such as readily soluble sulfate 

salts. Calcium-to-sulfate ratios range from 0.3 to 0.4 for 

the waste-rock pile leachates and from 0.1 to 0.5 for the 

erosional-scar leachates.

Comparison with Previous Leaching 

Studies

Shaw and others (2002, 2003) used a solid-to-solution leach ratio of 1:3 in contrast to the 1:20 ratio used 

in this study. Consequently, quantitative comparison of 

leachate concentrations between the leaching studies is 

problematic. However, qualitative findings between the 

studies can be compared and generally are consistent. For 

example, Shaw and others (2003) reported on the contaminant loads from erosional scars and concluded that 

the erosional scars contribute significant concentrations 

of sulfate and leachable metals and that the composition 

and concentration of leachable metals vary significantly 

between scars and within a given scar. These conclusions 

generally are consistent with the findings of our study, 

although variation within a given scar was not addressed 

in our study because we chose to collect multi-increment 

samples to represent average geochemical behavior from 

a given site. Our study finds large variation in the composition and concentration of leachable metals between scar 

areas, and the pH of the scar leachates was consistently 

low (<pH 4.1).

Shaw and others (2002) found that the majority of 

the mine waste-rock material is acid generating and that 

oxidation of pyrite in the waste-rock piles has produced 

leachable oxidation products. They also found pH control 

on the concentrations of metals in the leachates. Our 

findings are consistent with Shaw and others (2002), but 

in addition to the acid-generating potential of most of 

the waste-rock material, our study observed pH increases 

with time and agitation in leachates from the waste-rock 

material. Also, our study observed pH-dependent concentrations of several metals in response to the changing pH 

conditions in the leachates.

Summary

This report documents the leaching characteristics 

of surficial samples of composited mine waste-rock 

material and of naturally altered areas. In the bulk <2-

mm samples, quartz, mica (probably sericite), and X-ray 

Table 6. Comparison of the geometric means of leachate 

chemical analyses for composited mine waste-rock pile material 

with the leachate chemical analysis of the Straight Creek 

erosional-scar area, Questa, New Mexico.

[—, not determined; Sp. Cond., specific conductance; μS/cm, microsiemens 

per centimeter; μg/L, micrograms per liter; mg/L, milligrams per liter; <, 

less than]

Property or

constituent

Geometric mean

 of mine 

waste-rock piles1

Straight 

Creek2 Ratio

pH 4.9 3.3 1.5

Sp. Cond. μS/cm 1,470 1,270 1.2

Ag μg/L — <3 —

Al mg/L 1.4 11 .13

As μg/L — <1 —

Ba μg/L 70 42 1.6

Be μg/L .63 3.2 .20

Ca mg/L 280 230 1.2

Cd μg/L 2.6 4.4 .58

Ce μg/L 17 62 .28

Co μg/L 30 37 .81

Cr μg/L — 5.9 —

Cs μg/L — .08 —

Cu μg/L 27 300 .088

Fe μg/L — 3,300 —

Ga μg/L .31 .60 .52

Ge μg/L .10 .20 .52

K mg/L 2.5 1.9 1.3

La μg/L 8.2 18 .46

Li μg/L 15 13 1.2

Mg mg/L 11 8.4 1.3

Mn μg/L 2,740 1,800 1.5

Mo μg/L — .23 —

Na mg/L 1.3 .54 2.4

Nb μg/L — .02 —

Ni μg/L 83 83 1.0

P mg/L — .01 —

Pb μg/L .20 .40 .50

Rb μg/L 4.9 4.1 1.2

Sb μg/L .60 .62 .97

Sc μg/L — 1.7 —

Se μg/L — 1.6 —

Si mg/L 1.4 1.3 1.0

SO4 mg/L 715 615 1.2

Sr μg/L 930 85 11

Th μg/L — 1.5 —

Ti μg/L 8.8 7.0 1.3

Tl μg/L — <0.05 —

U μg/L .51 3.1 .16

V μg/L — <0.1 —

Y μg/L 7.5 21 .36

Zn μg/L 230 630 .37

Zr μg/L — < 0.05 —

1

 Geometric mean of five mine waste-rock piles listed in table 4 for the 

18-hour leaching procedure.

2

 From values listed in table 5 for the 18-hour leaching procedure.
CONCENTRATION, IN MILLIGRAMS PER LITER

0.1

1

10

100

1,000

10,000

Routine field samples

Field Leach Test

18-hour test

Storm - Day 1 

Storm - Day 3 

Snowmelt

Al Fe Mn Si SO4

Figure 34. Comparison of the concentration 

of selected leachable major-element 

concentrations from leaching tests and 

surface-water samples collected from 

Straight Creek, near Questa, New Mexico. 

Field-sample data are from Verplanck and 

others (2006). Field Leach Test (FLT) data are 

shown as filled triangles, and 18-hour test 

data are shown as open triangles. Box plots 

represent 10 filtered drainage samples from 

Straight Creek collected at intervals between 

October 2000 and October 2003, diamonds are 

data from a storm event in September 2002, 

and inverted triangles are data from a runoff 

sample taken a day after a spring snowmelt 

event in 2003.

Routine field samples

Field Leach Test

18-hour test

Storm - Day 1 

Storm - Day 3 

Snowmelt

CONCENTRATION, IN MILLIGRAMS PER LITER

0.0001

0.001

0.01

0.1

1

10

Be Cd Co Cr Cu Mo Ni Pb Zn

Figure 35. Comparison of the 

concentration of selected leachable minorand trace-element concentrations from 

leaching tests and surface-water samples 

collected from Straight Creek, near Questa, 

New Mexico. Field-sample data are from 

Verplanck and others (2006). Field Leach 

Test (FLT) data are shown as filled triangles, 

and 18-hour test data are shown as open 

triangles. Box plots represent 10 filtered 

drainage samples from Straight Creek 

collected at intervals between October 

2000 and October 2003, diamonds are data 

from a storm event in September 2002, and 

inverted triangles are data from a runoff 

sample taken a day after a spring snowmelt 

event in 2003.

Comparison with Previous Leaching Studies 43
44 Questa Investigation 19—Leaching Characteristics

SULFATE, IN MILLIGRAMS PER LITER

0 1,000 2,000 3,000 4,000

CALCIUM, IN MILLIGRAMS PER LITER

0

100

200

300

400

500

600

700

Waste-rock piles 18-hour test

Waste-rock piles Field Leach Test

Erosional scars 18-hour test

Erosional scars Field Leach Test

Straight Creek field samples

Scar field samples

Figure 36. Calcium (Ca) plotted 

against sulfate (SO4) concentrations 

for mine waste-rock leachates, 

erosional-scar leachates, and 

erosional-scar surface-water samples 

collected in the field from areas near 

Questa, New Mexico (field data are 

from Verplanck and others, 2006).

amorphous material are the most abundant minerals both on 

the surface of the waste-rock piles and on the erosional scars. 

Considerable supergene weathering of both the waste-rock and 

scar materials is indicated by the presence of sulfate and clay 

minerals (for example, jarosite, gypsum, kaolinite). Comparison of the geometric means of the bulk-chemistry constituents 

reveals that the mine waste-rock piles are ≥20 percent higher 

than the erosional scars for Ca, Na, Ti, S, Ba, Be, Cu, Mn, Mo, 

Ni, Sr, Th, Y, and Zn. The erosional scars have fairly wide 

concentration ranges for some elements, but their geometric 

mean is ≥20 percent higher than the mine waste-rock piles for 

iron, phosphorus, and lead.

The composited <2-mm size fractions from five mine 

waste-rock piles, nine erosional-scar areas, a less-altered site, 

and a slurry pipe grab sample were subjected to two back-toback leaching procedures. The first procedure, the Field Leach 

Test (FLT), is a short-duration leach (5-minute shaking and 

10-minute settling) and is intended to leach readily soluble 

materials. The FLT was immediately followed by an 18-hour 

end-over-end rotation leaching procedure, which is similar to 

the USEPA 1312 procedure. The end-over-end rotation results 

in considerable particle-size reduction over the course of the 

procedure. These leaching procedures can be used to evaluate 

potential metal release to receiving waters.

The waste-rock material generally is acid generating but 

appears to have pH buffering capability over time. The pH 

of the waste-rock leachates varies between 3.0 (Sugar Shack 

West) and 6.2 (Old Sulphur Gulch). With the exception of 

Sugar Shack West, the pH rises between the FLT and the 18-

hour test. Some elements increase in concentration between 

the FLT and 18-hour procedures, and others decrease. Generally, the elements that increase over the 18-hour period include 

Ca, Cd, K, Mg, Mn, Mo, Rb, Si, Sr, and Ti. Generally, the elements that decrease over the 18-hour period include Al, B, Be, 

Cu, Dy, Er, Eu, Fe, Gd, Ho, Nd, Pb, Pr, Sm, Tb, Tm, Yb, and 

Zn. The decrease in iron and aluminum concentrations over 

the 18-hour period are likely controlled by solubility reactions 

in response to the corresponding increase in pH. Precipitating 

phases of iron and aluminum can control trace-element concentrations by means of coprecipitation and sorption reactions, 

and we see evidence for this mechanism for several of the metals, including Be, Cd, Co, Cr, Cu, and Zn.

The pH of the erosional-scar leachates varies between 3.2 

and 4.1, a much narrower range than for the mine waste-rock 

leachates. Unlike the mine waste-rock leachates, the erosional-scar leachates exhibit little difference in their pH values 

between the two leaching procedures. The elemental content 

of the erosional-scar leachates is highly variable between 

scars, which results in a large range of values for several elements. When the elemental concentrations in the waste-rock 

leachates are compared with concentrations in the erosionalscar leachates, generally the waste-rock leachate concentrations fall at or below the upper concentration range of the 

erosional-scar leachate compositions. One notable exception 

is molybdenum, which is higher in the waste-rock leachates. 

Because of the low pH of the scar leachates (pH <4.1), many 

metals can be mobilized and remain in solution, the exception 

being anionic species, such as molybdenum, which are less 

mobile under acidic conditions.

Comparison of Straight Creek leachate compositions with 

the composition of Straight Creek erosional-scar drainage and 

storm-runoff waters shows that the FLT and 18-hour leachates 

have substantially lower element concentrations. However, 

the overall trends (that is, signatures or fingerprints) between 

elements are similar between the leaching tests and drainage 

samples. This finding illustrates that these (or any) leaching procedures cannot provide quantitative concentrations of 

actual waste-rock or scar contributions to surface or ground 

water. However, they can provide qualitative information 

about the likely chemical composition of porewater within the 

waste-rock piles and erosional scars.
The source material for the Capulin and Sugar Shack 

West waste-rock piles appears to be different from the other 

three waste-rock piles and similar to the source material 

for the erosional-scar areas. The leachate-pH values for the 

Capulin (pH 3.7 and 4.1) and Sugar Shack West (pH 3.2 and 

3.0) waste-rock piles are in the same range as those of the 

erosional scars. In contrast, the leachate pH values for the Old 

Sulphur Gulch, Sugar Shack Middle, and Sugar Shack South 

piles are higher and show some evidence for acid buffering 

with increased leaching contact time and agitation. Leachates 

from these three piles contain more calcium relative to sulfate, 

which indicates that calcite dissolution is taking place in addition to gypsum dissolution. Also, leachate sulfur isotopes for 

the Capulin and Sugar Shack West piles are similar to isotope 

values for sulfate in the scar areas and lighter than the leachate sulfur-isotope values from the Old Sulphur Gulch, Sugar 

Shack Middle, and Sugar Shack South piles. The Capulin and 

Sugar Shack West piles are older than the other three piles and 

reflect the shallow-earth materials removed at the beginning 

of open-pit mining, whereas the younger three piles consist 

of deeper, less-oxidized material with less pyrite and more 

carbonate.

Acknowledgments

This study was prepared in cooperation with the New 

Mexico Environment Department. Laboratory work was 

performed in the Analytical Laboratories of the Mineral 

Resources Program in Denver, Colorado. We would like to 

thank Molycorp, and in particular Bruce Walker, for their 

assistance and for providing us access to the Questa mine. We 

acknowledge Cyndi Kester, who operated the mass spectrometer for the isotope measurements, Zoe Anne Brown and Cyrus 

Berry, who provided sulfur analyses, and Sara LoVetere, who 

helped sample the mine waste-rock piles. We thank Kirk Nordstrom, Geoff Plumlee, and the Questa advisory committee for 

their helpful editorial comments on this manuscript.

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