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Questa Baseline and Premining Ground-Water Quality Investigation 8.

Lake-Sediment Geochemical Record from 

1960 to 2002, Eagle Rock and Fawn Lakes, 

Taos County, New Mexico

By S.E. Church, D.L. Fey, and M.E. Marot

Prepared in cooperation with the New Mexico Environment Department

Scientific Investigations Report 2005-5006

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2005

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Church, S.E., Fey, D.L., and Marot, M.E., 2005, Questa baseline and premining ground-water quality investigation 

8—Lake-sediment geochemical record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico: 

U.S. Geological Survey Scientific Investigations Report 2005-5006, 40 p.

ISBN 1-411-30544-2
Contents

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

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

Geologic Setting.............................................................................................................................................3

History of Mining............................................................................................................................................4

Previous Geochemical Studies ...................................................................................................................4

Methods...........................................................................................................................................................6

Sampling Plan........................................................................................................................................6

Analytical Methods...............................................................................................................................7

Stream Flow Recorded at the Questa Gage..............................................................................................7

Results and Discussion.................................................................................................................................8

Lake Sediment Chronology .................................................................................................................8

Lake Sediment Geochemistry...........................................................................................................11

Element Anomalies....................................................................................................................18

Comparison of the Data from the Two Lake Sediment Cores.............................................19

Element Suites that May Be Related to Mining....................................................................20

REE from the Magmatic Hydrothermal Breccia, Questa Ore Body...................................23

Results from Stream-Sediment Survey...........................................................................................25

Comparison of Lake Sediment Geochemistry with Other Sources ............................................28

Summary and Conclusions.........................................................................................................................37

References Cited..........................................................................................................................................39

Figures

1. Topographic map of study area showing locations of altered areas, debris fans, 

 mineral deposits, and sediment sample localities ..................................................................2

2. Maps of upper Fawn Lake (A) and Eagle Rock Lake (B) showing location of 

 core sites........................................................................................................................................5

3. Photograph of the USGS pontoon boat used to core sediment in upper Fawn 

 and Eagle Rock Lakes ..................................................................................................................6

4. Photographs of cores from Eagle Rock Lake and upper Fawn Lake ...................................7

5. Plot of monthly discharge versus time (1960–2002) at the Questa gage, Taos 

 County, New Mexico..................................................................................................................15

6. Plot of 137Cs concentration versus depth in Eagle Rock Lake and upper 

 Fawn Lake cores.........................................................................................................................18

7. Plot of concentrations of Na2O, K2O, MgO, and CaO versus depth below the 

 sediment interface for cores from upper Fawn and Eagle Rock Lakes.............................19

8. Plot of concentrations of FeO, Al2O3, TiO2, and SiO2 versus depth below the 

 sediment interface for cores from upper Fawn and Eagle Rock Lakes.............................20

9. Plot of concentrations of P2O5, Li, Sr, and Ba versus depth below the sediment 

 interface for cores from upper Fawn and Eagle Rock Lakes ..............................................21

10. Plot of concentrations of F, La, Ce, Nd, and Y versus depth below the sediment 

interface for cores from upper Fawn and Eagle Rock Lakes ..............................................22

iii
11. Plot of concentrations of Co, Cr, Ni, and V versus depth below the sediment interface 

for the cores from upper Fawn and Eagle Rock Lakes.........................................................23

12. Plot of concentrations of Cu, Mo, Pb, and Zn versus depth below the sediment 

interface for cores from upper Fawn and Eagle Rock Lakes ..............................................24

13. Plot of the sedimentation rate used for both the Eagle Rock and upper 

 Fawn Lakes ..................................................................................................................................25

14. Box plot comparing geochemical data:

 A. Major element data (Na2O, MgO, FeO, Al2O3, and TiO2) from the pre-1979 

 and the post-1979 intervals, upper Fawn Lake core......................................................26

 B. Trace element data (Ba, Sr, Cr, V, Cu, and Zn) from the pre-1979 and the 

 post-1979 intervals, upper Fawn Lake core ....................................................................26

 C. Major element data (Na2O, MgO, FeO, Al2O3, and TiO2) from the pre-1979 

 and the post-1979 intervals, Eagle Rock Lake core .......................................................26

 D. Trace element data (Ba, Sr, Cr, V, Cu, and Zn) from the pre-1979 and the 

 post-1979 intervals, Eagle Rock Lake core......................................................................26

 E. Major element data (Na2O, MgO, FeO, Al2O3, and TiO2) from the upper 

 Fawn Lake core and the post-1979 intervals from the Eagle Rock Lake core...........27

 F. Trace element data (Ba, Sr, Cr, V, Cu, and Zn) from the upper Fawn Lake core 

 and the post-1979 intervals from the Eagle Rock Lake core ........................................27

 G. Major element data (Na2O, MgO, FeO, Al2O3, and TiO2) from the upper 

 Fawn Lake core and pre-1979 intervals from the Eagle Rock Lake core ...................27

 H. Trace element data (Ba, Sr, Cr, V, Cu, and Zn) from the upper Fawn Lake core 

 and the pre-1979 intervals from the Eagle Rock Lake core..........................................27

15. Photographs of the 1981 mill tailings spill, Goat Hill Campground showing: 

 A. Tailings spill from the pipeline break................................................................................28

 B. Cleanup by Molycorp.........................................................................................................28

 C. Mill tailings sediment in the Red River............................................................................28

16. Plot of chondrite-normalized REE patterns for: 

 A. Volcanic rocks......................................................................................................................29

 B. Plutonic rocks ......................................................................................................................29

17. Photographs of four fluorite samples from the D ore body:

 A. Coarsely crystalline fluorite...............................................................................................30

 B. Laminated with more calcite than fluorite ......................................................................30

 C. Coarse-grained mixture of calcite, fluorite, and molybdenite with minor 

 amounts of pyrite.................................................................................................................30

 D. Medium- to coarse-grained mixture of calcite, fluorite, and molybdenite with 

 minor amounts of pyrite......................................................................................................30

18. Electron backscatter photomicrograph showing REE-bearing phosphate and 

carbonate minerals as small inclusions in the fluorite from the D ore body, 

 Questa mine.................................................................................................................................30

19. Plot of concentration of REE Ce from cores from upper Fawn and Eagle Rock Lakes 

and F in core from Eagle Rock Lake versus depth ................................................................30

20. Plots of the concentration of trace elements Ba, Sr, Cr, and V in stream sediment from 

the Red River and its tributaries...............................................................................................32

21. Plots of the concentration of trace elements Ce, Mo, Cu, and Zn in stream sediment 

from the Red River and its tributaries......................................................................................33

iv
22. Box plot comparing major and trace element concentrations with data from composite 

samples of sediment from the altered areas:

 A. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2 from 

 the upper Fawn Lake core .................................................................................................36

 B. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the upper 

 Fawn Lake core....................................................................................................................36

 C. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2 from the 

 pre-1979 interval of the Eagle Rock Lake core ...............................................................36

 D. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the pre-1979 

 interval, Eagle Rock Lake core..........................................................................................36

 E. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2 from the 

 post-1979 interval, Eagle Rock Lake core........................................................................37

 F. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the post-1979 

 interval, Eagle Rock Lake core..........................................................................................37

23. Box plot comparing major and trace element concentrations from premining 

 sediment with data from the pre-1979 interval and post-1979 interval of the 

 Eagle Rock Lake core and data from the mine-waste piles:

 A. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2, 

 pre-1979 interval ..................................................................................................................38

 B. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn, pre-1979 interval ...........38

 C. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2 , 

 post-1979 interval ................................................................................................................38

 D. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn, post-1979 interval..........38

Tables

1. Analytical, statistical, and descriptive data from the core from Eagle Rock 

 Lake, lower Red River valley, Taos County, New Mexico ......................................................8

2. Analytical, statistical, and descriptive data from the core from upper Fawn 

 Lake, lower Red River valley, Taos County, New Mexico ....................................................10

3. Analytical data from debris fans, modern and geochemical baseline sediment, 

 and mill tailings samples, lower Red River valley, Taos County, New Mexico.................12

4. Mean daily peak flow at the Questa gage (08265000), lower Red River valley, 

 Taos County, New Mexico.........................................................................................................14

5. Summary of geochemical anomalies from sediment cores, upper Fawn Lake 

 and Eagle Rock Lake, lower Red River valley, Taos County, New Mexico........................16

6. Dates for some trace element anomalies in the sediment core from Eagle 

 Rock Lake, lower Red River valley, Taos County, New Mexico ..........................................25

7. Analytical data from fluorite and carbonate minerals, magmatic hydrothermal 

 breccia, Questa mine area, lower Red River valley Taos County, New Mexico..............31

8. Statistics for post-1979 concentrations of major and trace elements in sediment 

 from Eagle Rock Lake core, lower Red River valley, Taos County, New Mexico.............34

9. Statistics for trace-element concentrations in sediment from upper Fawn Lake

 core, lower Red River valley, Taos County, New Mexico.....................................................35

v
Lake-Sediment Geochemical Record from 1960 to 2002, 

Eagle Rock and Fawn Lakes, Taos County, New Mexico

By S.E. Church, D.L. Fey, and M.E. Marot

Abstract

Geochemical studies of lake sediment from Eagle Rock 

Lake and upper Fawn Lake were conducted to evaluate the 

effect of mining at the Molycorp Questa porphyry molybdenum deposit located immediately north of the Red River. 

Two cores were taken, one from each lake near the outlet 

where the sediment was thinnest, and they were sampled at 

1-cm intervals to provide geochemical data at less than 1-year 

resolution. Samples from the core intervals were digested and 

analyzed for 34 elements using ICP–AES (inductively coupled 

plasma–atomic emission spectrometry). The activity of 137Cs 

has been used to establish the beginning of sedimentation in 

the two lakes. Correlation of the geochemistry of heavy-mineral suites in the cores from both Fawn and Eagle Rock Lakes 

has been used to develop a sedimentation model to date the 

intervals sampled. The core from upper Fawn Lake, located 

upstream of the deposit, provided an annual sedimentary 

record of the geochemical baseline for material being transported in the Red River, whereas the core from Eagle Rock 

Lake, located downstream of the deposit, provided an annual 

record of the effect of mining at the Questa mine on the sediment in the Red River. Abrupt changes in the concentrations 

of many lithophile and deposit-related metals occur in the 

middle of the Eagle Rock Lake core, which we correlate with 

the major flood-of-record recorded at the Questa gage at Eagle 

Rock Lake in 1979. Sediment from the Red River collected 

at low flow in 2002 is a poor match for the geochemical data 

from the sediment core in Eagle Rock Lake. The change in 

sediment geochemistry in Eagle Rock Lake in the post-1979 

interval is dramatic and requires that a new source of sediment 

be identified that has substantially different geochemistry from 

that in the pre-1979 core interval. Loss of mill tailings from 

pipeline breaks are most likely responsible for some of the 

spikes in trace-element concentrations in the Eagle Rock Lake 

core. Enrichment of Al2O3, Cu, and Zn occurred as a result 

of chemical precipitation of these metals from ground water 

upstream in the Red River. Comparisons of the geochemistry 

of the post-1979 sediment core with both mine wastes and 

with premining sediment from the vicinity of the Questa mine 

indicate that both are possible sources for this new component 

of sediment. Existing data have not resolved this enigma. 

Introduction

The Molycorp Questa mine, located in the Taos Range in 

north-central New Mexico, is currently producing molybdenite 

concentrate and is in the process of developing a mine-closure 

plan. This report is one of a series of reports designed to investigate the geochemical baseline and premining ground-water 

quality in the Red River basin, New Mexico, at the site. The 

main objective of these studies is to determine the premining 

ground-water quality at the Questa mine site. The Red River 

flows past the southern side of the Questa porphyry molybdenum 

deposit. Our study focused both on determining the geochemical 

signature in sediment transported by the Red River prior to openpit mining as well as that transported today, and on determining 

the effect of recent mining activity on the sedimentary record in a 

core from Eagle Rock Lake. Upper Fawn Lake was sampled as 

a geochemical baseline site to document the temporal variation 

of metals supplied by erosion in part of the Red River valley, 

upstream of the Questa mine. Both lakes originated as borrow 

pits during road construction and paving of N. Mex. Highway 

38. The borrow pit that became Eagle Rock Lake was created 

sometime after August, 1954, whereas the borrow pits that form 

Fawn Lakes were created in 1960–1961 (Miguel Gabalgon, 

New Mexico Highway Dept., oral commun., Sept. 2003; URS 

Corp., written commun., 2004). A portion of the water from the 

Red River flows through both Fawn Lakes and Eagle Rock Lake. 

Flow is regulated to about 2 cfs by head gates installed by the 

irrigation organization that owns the surface water rights in the 

Red River valley. The head gates serve as baffles that limit inflow 

and thus limit the amount of sediment deposited in the lakes during 

high flow. Fawn Lakes, located on the Red River upstream of 

the Questa mine (fig. 1), are two small lakes covering an area 

of about 1 hectare. The sediment in these lakes provides an annual 

record for the period from about 1960 to the present. Eagle Rock 

Lake, located downstream of the Questa mine (fig. 1), covers 

about 2 hectares and provides an annual sedimentary record of 

material transported away from the Questa mine site as well as 

from sites upstream. A comparison between the sedimentary 

records of the two lakes potentially provides a measure of the 

impact of development of the Questa mine, which began as an 

open-pit operation in 1965, as well as the mine-site geology prior 

to open-pit mining. Although there was mining activity upstream 
Bitter 

 Creek

Mallette Creek

Lower Bitter Creek

Hottentot

SE Hottentot

SE Straight S Straight

Straight

Hansen

 SW Hansen

June Bug

 EJuneBug

 SJuneBug SE

TruckShop 

 STruckShop

Sulphur Gulch

 GoatHill

S Goat Hill

Capulin

WGoat Hill

Eagle Rock

Questa

105 35'0"W

105 35'0"W

105 30'0"W

105 30'0"W

105 25'0"W

105 25'0"W

 36 

40'

0"N

36 40'0"N

36 

45'

0"N

36 45'0"N

0 2 4 6 8 10 1

Kilometers

o

o

o

o o o

oo

o o

Eagle Rock Lake core

110

111

112

113

114

115

Fawn Lake core

116

117

120

124

105

121

106

107 104

103

123

122

108

207 205,

206

204

203 202 201

Questa open pit

208

Goat Hill Campground

Spring Gulch

 Central (GoatHill) underground

Log Cabin

Explanation

Log Cabin

S Straight

Hottentot

Alteration scar,  with labelDebris fanMineral deposit, with label

124

115

Background sediment  localityModern sediment  locality

Figure 1. Topographic map of study area showing locations of altered areas (scars), debris fans, and mineral deposits (after Ludington and others, 2005) and sediment sample localities (tables 1–3). Outline of the open pit at the Questa mine is shown as a dashed line. Map projection is UTM, zone 13N; geographic coordinate system is North American datum 1927. One additional stream-sediment sample (not shown) was collected at the fish hatchery downstream from Questa near the confluence of the Red River with the Rio Grande. Sample localities of mill tailings spills and debris fans are not shown. 

   Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
beginning in the 1860s, the effect of this previous mining activity 

on the geochemistry of sediment in the Red River from 1961 to 

2002 is an integral component of the geochemical baseline 

recorded in the upper Fawn Lake core. 

Geologic Setting

The Questa mine lies along the southern margin of the Questa 

caldera, which is part of the late Oligocene Latir volcanic field in 

north-central New Mexico (Lipman, 1981). The Latir volcanic 

field consists primarily of mildly alkaline intermediate-composition lavas 1- to 2-km thick that overlie Proterozoic crystalline 

basement consisting of metasedimentary and metavolcanic rock 

that is intruded by numerous granitic plutons (Lipman, 1988; Lipman 

and Reed, 1989; Ross and others, 2002). Andesite and quartz latite 

flows predate caldera formation. Volcanism culminated in the 

eruption of the peralkaline Amalia Tuff (Lipman and others, 1986; 

Johnson and Lipman, 1988) and formation of the Questa caldera 

at about 25.7 Ma (Czamanske and others, 1990; Ross and others, 

2002). Ludington and others (2005) provide the geologic framework of the Red River watershed pertinent to this study. 

The Tertiary volcanic rock was subsequently intruded by 

a series of highly evolved, high-silica granites and subvolcanic 

porphyries (Johnson and others, 1989; Ross and others, 2002) 

that are the apparent sources of the hydrothermal fluids that 

formed the molybdenite deposits. The Bear Canyon and Sulfur 

Gulch stocks are associated with the molybdenum mineralization 

and are characterized by high concentrations of Y, Zr, and the 

rare earth elements (REE) and low concentrations of Ba and Sr 

(Johnson and others, 1989; Ludington and others, 2005). These 

granites and porphyries were emplaced after 24.6±0.1 Ma and 

appear along a N.75°E. trend that extends from the Bear Canyon 

stock at the western range front into the Red River intrusive 

complex northeast of the town of Red River. Mineralization in the 

Questa porphyry molybdenum system is dated at 24.1±0.2 Ma 

(Ross and others, 2002) and is comparable with other Climax-type, 

high-silica granitic stockwork molybdenite deposits (Carten 

and others, 1993). An elongate granitic batholith is inferred at 

depth, which served as the parent body to the high-level stocks 

that gave rise to the known mineral deposits. The Questa deposit 

contains molybdenum mineralization in quartz stockwork with 

minor galena, sphalerite, and chalcopyrite along with fluorite 

and carbonate minerals (Carpenter, 1968; Ross and others, 2002). 

Two ore bodies have been mined underground: Goat Hill (1983–

2000) and D (2001–present). Both have quartz-molybdenite-bearing 

veins in molybdenite-bearing late-stage magmatic hydrothermal breccia (Ross and others, 2002). Carbonate and fluorite 

occur in both the magmatic hydrothermal breccia as well as in 

abundant carbonate and fluorite-bearing veins. Ross and others 

(2002) estimate that the volume of the magmatic hydrothermal 

breccia in the Goat Hill ore body was about 80 percent. Several 

generations of brecciation have been identified; fluorite occurs 

in the latest generation of hydrothermal breccias (primarily in 

zones D and E; table 3 and fig. 7 of Ross and others, 2002). 

Hydrothermal alteration related to mineralization processes 

can be found along the entire length of the mineralized trend. The 

upper part of the Questa deposit has been oxidized, and the 

hydrothermal alteration assemblages are exposed at the surface. 

The alteration assemblages, as mapped by airborne visible–infrared 

imaging spectrometer (AVIRIS) (Livo and Clark, 2002), appear 

to be dependent upon the nature of the underlying mineralization 

and the amount of host rock cover over the mineralized porphyries. 

Alteration associated directly with the molybdenite mineralization 

is potassic, and includes assemblages containing hydrothermal 

biotite and orthoclase (Carpenter, 1968; Ross and others, 2002). 

Phyllic or quartz-sericite-pyrite (QSP) alteration overprints the 

potassic alteration and the known mineralized rock. Within 

the open pit at the Questa mine, the QSP mineral assemblage 

is characterized by the presence of sericite, kaolinite, goethite, 

and jarosite (Livo and Clark, 2002). At Questa, as at other Climaxtype molybdenite systems, QSP alteration is peripheral to the 

underlying molybdenite-bearing rock. Distal to QSP alteration, 

both laterally and vertically, widespread propylitic alteration 

(epidote, chlorite, and calcite) is encountered. It is characterized 

in the AVIRIS image by combinations of epidote and epidote 

plus calcite (Livo and Clark, 2002). 

Meyer and Leonardson (1990) identified additional areas 

of hydrothermal alteration exposed upstream from the Questa 

deposit (fig. 1). These areas have also been mapped by AVIRIS 

(Livo and Clark, 2002) and are discussed in detail by Ludington 

and others (2005). These altered areas are subject to rapid erosion 

of hydrothermally altered rock along the N.75°E. trend above 

the inferred batholith. Steep barren drainages are formed by 

mass wasting and rapid erosion of the highly altered rock 

and are the result of landslides, slumps, rock falls, and fluvial 

processes. In the AVIRIS images, the erosional scars are surrounded by propylitic mineral assemblages, but within the scars, 

QSP alteration assemblages contain kaolinite, sericite, jarosite, 

and goethite (Livo and Clark, 2002). Although supergene 

alteration minerals like kaolinite and gypsum are commonly 

observed, exposures of bedrock usually exhibit primary alteration 

assemblages, most commonly QSP. A large proportion of the 

erosion that occurs in these altered areas takes place during 

intense summer thunderstorms as well as during the spring 

snowmelt. At these times, large amounts of sediment-laden 

water runs off the base of the scars and has formed large debris 

aprons at their base. These debris aprons consist of poorly 

sorted material, rich in pyrite and other weathering products, 

that range in size from large blocks with dimensions of tens of 

meters, down to silt- and clay-size material. The aprons generally 

reach the banks of the Red River, and much of this altered material 

enters the river during periods of high runoff. Large-scale mass 

wasting from these altered areas has been suggested as a source 

of metals in sediment in the Red River. These altered areas and 

their geochemistry are discussed in detail in Ludington and 

others (2005). Three of these altered areas, the Hottentot and 

Straight Creek drainages on the north and June Bug on the 

south, are upstream of Fawn Lakes (fig. 1). Thus, the sediment 

contributed by these altered areas is included in the geochemical 

baseline core from upper Fawn Lake.

Geologic Setting 
History of Mining

Recorded mining began in the Red River mining district 

in the late 1800s (Schilling, 1960). The earliest claims were 

based on the discovery of placer gold in Quaternary gravel and 

sediment, but lode claims were also staked in both Tertiary 

and Precambrian rock for gold, copper, lead, and zinc (Jackson 

and others, 2003; McLemore, 2001). The town of Red River 

was established around 1895 in response to the discovery of 

the first lode gold claims in the area, but the town experienced 

its last true ‘boom’ in 1904 (Schilling, 1960; Pearson, 1986). 

The first claims on what is now the Molycorp property were 

filed by the Western Molybdenum Corporation in 1916; the 

R&S Molybdenum Corporation established claims in 1918, 

and both companies were bought in 1920 by the Molybdenum 

Corporation of America, now known as Molycorp (Schilling, 

1960). Between 1919 and 1958, operators produced 18.4 million 

pounds of molybdenite (MoS2) using selective underground 

stope mining methods to recover high-grade (~4 percent MoS2 ) 

molybdenite ore from veins in the upper portion of the Questa 

ore body (Ross and others, 2002, table 2; Schilling, 1960). 

Open-pit mining began at Questa in 1965 (table 2 of Ross 

and others, 2002). From 1965–1983, an estimated 81 Mt (million 

tons) of ore was removed, averaging 0.191 percent MoS2. Initial 

production was 10,000 tons/day with a mill capacity of 15,000 

tons/day (Carpenter, 1968). A total of 350 Mt of subeconomic 

Mo-mineralized and unmineralized overburden was removed 

from the open pit during the stripping and production of this 

ore (D.C. Jacobs, Unocal, written commun., 2003). From 1983 

through 1991 and from late 1996 to 2000, the Goat Hill ore body, 

south and west of the open pit, was mined using underground 

block- and front-cave methods. A total of 21 Mt of ore, averaging 

0.318 percent MoS2, was removed and processed during this 

period. In 2001, Molycorp began production from the D ore body 

using a gravity-block-caving mining method. This orebody is 

expected to average around 0.338 percent MoS2 (B.M. Walker, 

Molycorp, written commun., 2004). 

Previous Geochemical Studies

The general area on either side of the Questa deposit 

was studied and mapped during the U.S. Geological Survey 

(USGS) wilderness assessment studies in the early 1980s. 

The Red River generally follows the southern margin of 

the Questa caldera. Volcanic rock of the caldera is in fault 

contact with Precambrian rock, which is exposed on the 

south side of the Red River. Tributary streams draining north 

from this Precambrian terrane, with the exception of Columbine Creek, are in Precambrian rock and have no base-metal 

anomalies in stream sediment (Sutley and others, 1983). The 

Questa deposit lies in the caldera on the north side of the 

Red River (fig. 1). Stream-sediment samples taken from 

tributaries draining the north side of Cabresto Creek—

drainage north of the Questa block—also had no base-metal 

geochemical anomalies indicative of a Climax-type porphyry 

molybdenum deposit. No data were collected from the area 

between the town of Red River and Cabresto Creek during 

the USGS wilderness assessment studies.

In 1976, the National Uranium Resource Evaluation 

(NURE) project sampled sediment in surface streams in the 

vicinity of the Questa mine. Sediment was sampled in tributaries 

on both sides of the Red River and analyzed by inductively 

coupled plasma–atomic emission spectroscopy (ICP–AES) 

at Oak Ridge National Laboratory (NURE, 1981). These data 

provide a 1976 geochemical baseline during the period when 

the open pit was in operation (fig. 1). 

Allen and others (New Mexico Office of the Natural 

Resource Trustee, written commun., 1999) conducted a study of 

the sediment geochemistry in the Red River and in the two lakes 

discussed here. They sampled sediment from cores in each of the 

two lakes and from seven localities along the Red River between 

the towns of Red River and Questa. Lake cores were taken near 

the inlet and outlet of the lakes (fig. 2). Samples were collected 

and dried. Following digestion, samples were analyzed for Al, 

Fe, Mn, Co, Cu, Mo, Ni, and Zn by atomic absorption. There was 

no absolute age control on these cores. The layers in the delta 

phase of the lakes were counted and related to annual snowmeltrunoff events to estimate the year that the layers were deposited. 

Concentration data were reported from 11 intervals from Eagle 

Rock Lake core ERL-C1 (1.6-m depth), for 12 intervals from 

Eagle Rock Lake core ERL-C2 (0.7-m depth), and from 11 

intervals from the upper Fawn Lake core UFL-C2 (1.4-m depth). 

Allen and others (unpub. data, 1999) reported several aluminumrich layers in the cores that formed subsequent to about 1980 in 

the Eagle Rock Lake cores. In March 2000, Molycorp initiated a 

study of the sediment in the two lakes to investigate further the 

chemistry of these aluminum-rich precipitates and evaluate 

the stratigraphy of the lake sediment (URS Corp., written commun., 2004). In their report, three cores were taken from the two 

lakes (fig.2, SED-1–SED-3) to duplicate the results of Allen and 

others (unpub. data, 1999), to work out the stratigraphy in more 

detail, and to select intervals to be analyzed for a number of 

metals using a partial digestion procedure.

Jackson and others (2003) have recently completed a water 

and stream-sediment study of the Red River watershed upstream 

of Hansen Creek (fig. 1). They collected 16 samples from locations 

immediately downstream of the major tributary confluences. 

Analyses of water and the <63-μm fraction of the stream-sediment 

samples showed significant increases in conductivity and in 

analyte concentrations in water for Na, Mg, Si, SO4, and F and 

a decrease in pH downstream from the confluence with Mallette 

Creek near the town of Red River (fig. 1). Their sediment data 

showed significant increases in S, As, Cu, and Zn downstream 

from Mallette Creek that were attributed to Tertiary acid-sulfate 

alteration. Strong correlations between the Fe, Ti, and V data 

were attributed to the presence of magnetite that was found in 

heavy-mineral concentrates.

 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
0 50 100 200 FEET

0 50 100 200 FEET

Red River

Red River

02QNM101

02QNM102

NM Highway 38

A

B

105 27'00" 105 26'56" o o

o o 105 34'27" 105 34'14"

o 36

42'

14"

o 36

14'

10"

36

42'

20"

o

36

42'

23"

o

SED-2 UFL-C2

SED-1

SED-3

Explanation

UFL-C2, core from study by Allen

and others (1999)

SED-1, core from URS study

conducted for Molycorp

02QNM102, core from this study

ERL-C1

ERL-C2

SED-3 SED-1

SED-2

Figure 2 Figure 2. Maps of (A) Fawn Lakes and (B) Eagle Rock Lake showing location of the core sites. Also shown are localities 

of cores taken by Allen and others (unpub. data, 1999) and by URS (unpub. data, 2004) for Molycorp.

Previous Geochemical Studies 
Methods

Sampling Plan

We used a pontoon boat to sample lake sediment from 

upper Fawn and Eagle Rock Lakes on consecutive days, June 

19 and 20, 2002 (fig. 3). We anchored the boat in the deepest 

part of each lake, away from the inlet, to collect accumulations 

of largely very fine-grained, suspended sediment rather than 

detrital material to minimize the effects of storm deposits on the 

thickness of individual strata in the cores. We sampled the lake 

sediment by driving a 7.6-cm-diameter polycarbonate coring tube 

into the sediment and then extracted it using a hoist attached to 

the A-frame on the boat (fig. 3). The cores were driven to resistate; 

coarse angular monolithic rock fragments were recovered in the 

basal 1-cm section from each core. We recovered the entire lakesediment stratigraphy from both lakes (53-cm core from upper 

Fawn Lake and 55-cm core from Eagle Rock Lake; fig. 4). 

Little evidence of any discernable stratification was visible in 

the lake cores. The upper few centimeters of sediment in each 

core were light tan, but in both cores, sediment color quickly 

changed to black. All material was silt and clay size. The 

core samples were sectioned at approximately 1-cm intervals 

immediately upon collection, placed in plastic bags, sealed, 

and shipped to the USGS geochronological laboratory at St. 

Petersburg, Fla., for radioisotope determinations. To evaluate 

the source of sediment in the lake cores, we sampled modern 

stream sediment from the active alluvium of the Red River and 

premining sediment from preserved terraces along the course 

of the river to determine the modern and premining geochemical baseline. Sampling methods for the premining baseline 

sampling have been previously described in Church and others 

(2000). We also sampled sediment from six creeks draining the 

altered areas upstream of the Questa mine (fig. 1) to determine 

the type of sediment material being supplied by the barren scar 

areas to the Red River, and we collected composite samples of 

ten terrace fans in the study area to evaluate spatial variability. 

At the laboratory, the lake-sediment samples were air 

dried and split prior to geochemical analysis. Fan and streamsediment samples were sieved to minus 80 mesh and ground 

prior to analysis.

Figure 3. Photograph of the USGS pontoon boat used to core sediment in upper Fawn and Eagle Rock Lakes. Anchors were deployed 

from each corner and the core driven through an opening in the deck. Core was then pulled using a hoist attached to the A-frame tower. 

Core was sectioned on site. The samples were placed in plastic bags and shipped to a geochronology laboratory for processing. Photograph taken at Eagle Rock Lake dam, June 19, 2002, by Philip Verplanck. Stan Church (right) and David Fey (left) are on the boat deck. 

   Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
Analytical Methods

The lake-sediment samples were analyzed for loss on 

ignition (LOI) to remove organic material by heating in a 

muffle furnace at 450oC for 6 hours. Selected samples were 

counted using a Canberra intrinsic germanium detector to 

determine the depth of the maximum 137Cs activity. Peak 

activity was assigned a date of 1963, which corresponds to the 

maximum fallout activity from atmospheric nuclear testing. 

The sample descriptions and the radioisotope results are in 

tables 1 and 2. Stream-sediment, lake-sediment, mill tailings, 

and terrace-composite samples collected for this study were 

analyzed using ICP–AES methods following a mixed acid 

total digestion (HCl, HNO3, HF, and HClO4; Briggs, 1996). 

Samples were submitted blind and were randomized prior to 

analysis. Statistical data for results from replicate analyses 

of these standards are documented in Fey and others (1999). 

Geochemical data are in tables 1–3. 

Samples of the magmatic hydrothermal breccia from the 

D ore body were supplied by Meghan Jackson (Molycorp, 

2003) for analysis. Three of the samples, selected on the basis 

of variations in grain size, were disaggregated and separated 

into discrete phases—a light green phase (fluorite) and a white 

phase (carbonate)—for analysis. Samples were hand-ground 

with an agate mortar and pestle. The samples were digested 

in hot HNO3 and the soluble phase dissolved for analysis. The 

residues were digested using mixed-acid total digestion (HCl, 

HNO3, HF, and HClO4; Briggs, 1996), although additional 

HClO4 was added to insure that insoluble REE fluoride 

minerals did not form. 

Stream Flow Recorded at the 

Questa Gage

Daily stream-flow measurements of surface-water discharge have been recorded at the gage at Questa, New Mexico 

(08265000) for 80 years (beginning in Oct., 1924). The stream 

gage is immediately upstream from Eagle Rock Lake (fig. 1) 

(sample site 110). Data show that the flood-of-record occurred 

in 1979 (fig. 5). Runoff exceeded 300 cfs (ft3/s) for 44 days 

and had an average peak daily flow of 557 cfs on June 9, 

1979. Daily stream-flow data (1960 to Sept. 30, 2002), where 

greater than 300 cfs, are in table 4 (http://nm.waterdata.usgs.

gov/nwis). Periods of peak stream flow correlate well with 

changes in the geochemistry of the core from Eagle Rock 

Lake. 

Figure 4. Photographs of cores (A) from Eagle Rock Lake (sample taken on June 19, 2002) and (B) upper Fawn Lake (sample taken on 

June 20, 2002).

A B

Stream Flow Recorded at the Questa Gage 
Results and Discussion

Lake Sediment Chronology

137Cs is a thermonuclear byproduct released by atmospheric nuclear testing. The U.S. atmospheric nuclear testing 

program began in the 1950s and was terminated in 1965. 137Cs 

reached its maximum activity between 1962 and 1964 (90 percent 

of the 137Cs was released between 1962 and1964; http://www.

eml.doe.gov). 137Cs is swept out of the atmosphere by rain and 

captured on clay minerals in the soil, ultimately ending up in 

lakes and oceans. Thus, radioactive decay of 137Cs with a 

half-life of 30.3 years is ideal for dating of sediment in reservoirs 

where the sediment accumulation rate is low. The 137Cs data 

from both lake cores indicates that the 137Cs peak is only a few 

centimeters above the bottom of the core at depths of 49 and 

50 cm below the sediment interface (fig. 6). Given that both 

lakes were constructed prior to peak 137Cs activity (URS Corp., 

written commun., 2004), this setting is ideal for application of 

the 137Cs dating method. The 137Cs ages were calculated assuming that the depth at maximum 137Cs activity occurred at the 

peak of atmospheric nuclear testing activity in 1963 ± 2 years. 

Counting statistics for peak 137Cs activity are about ±7 percent 

and the sampling error is less than the sampling interval. Thus, 

the Eagle Rock Lake core contains a record of sedimentation 

Sample Depth 137Cs Activity Percent Al2O3 CaO FeO K 2O MgO Na2O P2O5 TiO2 SiO2 As Ba B

Field Number Description (cm) (dpm/g) Moisture Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent ppm ppm p

02QNM101La clay and algae, medium tan 1 -- 0.77 22.67 0.83 5.40 2.53 1.43 0.51 0.37 0.20 66.06 16 780 1

02QNM101Lb clay and algae, medium tan 2 -- 0.77 22.67 0.54 6.95 3.85 1.66 0.35 0.41 0.25 63.32 14 300 

02QNM101Lc clay and algae, medium tan 3 -- 0.66 20.78 0.47 7.59 4.46 1.99 0.42 0.46 0.35 63.48 17 200 

02QNM101Ld beginning of black-streaked clay, some 

orange 4 -- 0.58 20.78 0.46 7.20 4.46 1.99 0.47 0.48 0.40 63.76 20 470 

02QNM101Le half black, half tan colored clay 5 -- 0.75 22.67 0.55 5.66 3.25 1.66 0.40 0.41 0.20 65.19 11 820 1

02QNM101Lf mostly tan clay, one third black 6 -- 0.80 22.67 0.54 6.69 3.13 1.51 0.32 0.41 0.18 64.54 12 640 1

02QNM101Lg 90 percent tan, 10 percent black clay 7 -- 0.70 22.67 0.46 7.98 4.10 1.99 0.36 0.46 0.25 61.74 12 250 

02QNM101Lh 90 percent tan, 10 percent black clay,

orange streaking 8 -- 0.62 20.78 0.46 7.46 4.46 1.99 0.35 0.48 0.30 63.72 13 560 

02QNM101Li 80 percent black clay with orange and tan 

streaks 9 -- 0.76 22.67 0.60 6.30 3.37 1.66 0.36 0.44 0.23 64.36 14 800 1

02QNM101Lj medium-brown clay 10 -- 0.82 22.67 0.74 5.66 2.05 1.21 0.36 0.34 0.12 66.85 14 710 1

02QNM101Lk mix of gray, brown-orange clay 11 -- 0.77 20.78 0.72 6.30 2.65 1.49 0.46 0.39 0.18 67.01 17 820 1

02QNM101Ll mix of gray, brown-orange clay 12 -- 0.79 20.78 0.75 6.18 2.65 1.54 0.47 0.37 0.18 67.08 12 790 1

02QNM101Lm darker gray clay 13 -- 0.78 18.90 0.76 5.66 2.41 1.48 0.47 0.37 0.18 69.77 13 720 1

02QNM101Ln gray-black clay 14 -- 0.79 20.78 0.79 6.05 2.53 1.54 0.44 0.41 0.18 67.27 17 780 1

02QNM101Lo darker gray clay 15 -- 0.78 22.67 0.84 6.30 2.65 1.61 0.49 0.41 0.20 64.82 <10 820 1

02QNM101Lp darker gray clay 16 -- 0.79 20.78 0.80 5.53 2.41 1.46 0.44 0.39 0.17 68.01 11 740 1

02QNM101Lr brown-gray clay 18 -- 0.78 22.67 0.76 5.40 2.53 1.39 0.42 0.37 0.18 66.27 17 780 1

02QNM101Ls brown-gray clay 19 -- 0.76 20.78 0.71 5.40 2.89 1.53 0.46 0.37 0.22 67.64 16 810 1

02QNM101Lt olive-brown clay 20 -- 0.76 20.78 0.68 5.27 3.01 1.58 0.42 0.37 0.23 67.65 15 810 1

02QNM101Lu olive-brown to black clay 21 -- 0.77 22.67 0.78 4.89 2.53 1.46 0.40 0.37 0.18 66.72 14 760 1

02QNM101Lv almost black clay 22 -- 0.78 22.67 0.86 4.76 2.29 1.29 0.35 0.34 0.17 67.27 17 510 1

02QNM101Lw black clay 23 -- 0.75 20.78 0.98 6.05 1.81 1.33 0.32 0.32 0.12 68.30 13 280 1

02QNM101Lx black clay 24 -- 0.72 22.67 0.94 5.79 1.81 1.21 0.38 0.37 0.10 66.74 11 500 1

02QNM101Ly black clay 25 -- 0.76 22.67 0.94 4.12 1.93 1.26 0.49 0.37 0.17 68.07 18 670 1

02QNM101Lz darker gray clay 26 -- 0.79 26.45 0.96 3.47 1.69 1.08 0.40 0.32 0.12 65.50 16 650 1

02QNM101Laa black and olive-brown clay 27 -- 0.76 24.56 0.87 4.12 2.05 1.19 0.43 0.34 0.17 66.27 16 680 1

02QNM101Lab black and olive-brown clay, H 2S smell? 28 -- 0.60 22.67 0.67 5.66 3.49 1.82 0.46 0.39 0.30 64.53 10 320 1

02QNM101Lac part of tan band of clay 29 -- 0.64 22.67 0.67 5.15 3.61 1.82 0.66 0.41 0.28 64.72 16 1,000 

02QNM101Lad part of tan band of clay 30 -- 0.60 22.67 0.67 5.15 4.22 1.99 0.54 0.44 0.35 63.98 14 1,100 

02QNM101Lae part of tan band of clay, more black 31 -- 0.53 22.67 0.64 5.79 4.34 2.32 0.54 0.44 0.37 62.89 11 860 

02QNM101Laf mostly black clay 32 -- 0.69 20.78 0.76 7.59 3.25 1.99 0.59 0.55 0.28 64.19 21 200 

02QNM101Lag black clay 33 -- 0.72 18.14 0.88 7.72 1.93 1.82 0.73 0.44 0.27 68.08 20 140 

02QNM101Lah black sticky clay 34 -- 0.65 18.71 0.96 7.72 3.13 2.16 0.96 0.32 0.32 65.73 13 150 

02QNM101Lai black sticky clay 35 -- 0.64 18.90 0.86 7.20 3.25 2.16 0.85 0.32 0.30 66.17 17 140 

02QNM101Laj black sticky clay 36 -- 0.67 18.90 0.87 7.33 2.89 1.82 0.73 0.41 0.23 66.81 <10 140 

02QNM101Lak black sticky clay 37 -- 0.61 18.90 0.96 7.20 3.01 1.99 0.77 0.37 0.27 66.53 <10 140 

02QNM101Lal black sticky clay 38 -- 0.64 18.52 0.96 7.08 3.13 2.32 0.89 0.30 0.32 66.49 <10 130 

02QNM101Lam black sticky clay 39 -- 0.62 18.14 0.92 7.20 3.13 2.32 0.90 0.27 0.30 66.80 13 130 

02QNM101Lan black sticky clay 40 -- 0.53 18.90 0.92 7.20 3.49 2.49 1.04 0.23 0.37 65.36 <10 150 

02QNM101Lao black clay 41 -- 0.56 18.90 0.95 7.72 3.49 2.32 0.90 0.27 0.33 65.11 11 140 

02QNM101Lap black clay 42 -- 0.47 17.76 1.10 6.95 3.25 2.16 0.89 0.23 0.40 67.27 12 180 

02QNM101Laq black clay 43 1.56 0.41 17.38 1.21 6.43 3.25 1.99 0.98 0.21 0.45 68.10 <10 260 

02QNM101Lar black sticky clay 44 -- 0.41 16.25 1.21 6.43 3.13 1.82 1.00 0.18 0.43 69.54 <10 240 

02QNM101Las black sticky clay 45 -- 0.47 16.44 1.23 6.95 3.13 1.66 0.97 0.21 0.42 69.00 <10 210 

02QNM101Lat black sticky clay 46 1.23 0.63 18.90 1.06 8.36 2.65 1.99 0.71 0.32 0.33 65.68 12 150 

02QNM101Lau black sticky clay 47 -- 0.66 20.78 0.91 6.95 3.37 1.99 0.61 0.37 0.25 64.77 <10 140 

02QNM101Lav black sticky clay, H2S smell? 48 1.88 0.59 20.78 0.92 6.43 3.61 2.32 0.77 0.34 0.35 64.46 <10 170 

02QNM101Law black sticky clay, H2S smell? 49 2.55 0.55 20.78 0.92 6.43 3.61 2.49 0.84 0.34 0.38 64.19 <10 180 

02QNM101Lax black sticky clay, a little tan clay 50 2.98 0.57 20.78 0.91 6.18 3.37 2.32 0.82 0.37 0.35 64.90 <10 180 

02QNM101Lay black sticky clay, a little tan clay 51 2.33 0.55 18.90 0.87 5.92 3.37 2.16 0.84 0.34 0.37 67.24 <10 200 

02QNM101Laz almost half-tan clay 52 2.19 0.53 18.90 0.92 6.56 3.37 2.32 0.94 0.32 0.40 66.26 12 230 

02QNM101Lba tan and black clay, gravel bits 53 -- 0.45 18.52 0.78 5.92 3.37 1.99 0.86 0.30 0.33 67.93 <10 180 

02QNM101Lbb black clay, gravel 54 0.55 0.20 14.74 0.51 3.60 3.61 1.31 1.16 0.16 0.30 74.61 <10 580 

02QNM101Lbc black clay, gravel 55 0.36 0.22 14.55 0.50 3.86 3.01 1.23 1.20 0.16 0.28 75.21 <10 210 

Minimum 14.55 0.46 3.47 1.69 1.08 0.32 0.16 0.10 61.74 10 130 

25th percentile 18.90 0.67 5.56 2.56 1.48 0.42 0.32 0.18 64.73 12 180 

Median 20.78 0.84 6.30 3.13 1.82 0.53 0.37 0.28 66.27 14 310 

75th percentile 22.67 0.92 7.17 3.46 1.99 0.85 0.41 0.35 67.27 17 755 1

85th percentile 22.67 0.96 7.34 3.61 2.32 0.91 0.44 0.37 68.07 17 801 1

90th percentile 22.67 0.97 7.59 4.02 2.32 0.97 0.44 0.40 68.24 17 817 1

95th percentile 22.67 1.14 7.72 4.38 2.32 1.01 0.47 0.41 69.62 20 834 1

Maximum 26.45 1.23 8.36 4.46 2.49 1.20 0.55 0.45 75.21 21 1100 1

Table 1. Analytical, statistical, and descriptive data from the core from Eagle Rock Lake, lower Red River valley, Taos County, New Mexico. 

 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
during the entire period of operation of the Questa mine, beginning 

with the development of the open pit mine in 1965, and has a 

resolution of less than 1 year (55 sampling intervals during a 

41-year period).

We used the hydrologic data to interpret the geochemical 

profiles. Stream-flow data indicate that the flood-of-record 

occurred in 1979 (table 4). Hydrologic data indicate that the years 

prior to and immediately following the flood were low-water 

years. Numerous changes in the concentrations of both major 

and minor elements occurred at about the middle of the core 

from upper Fawn Lake (table 2 sample 02QNM102Ly and 

table 5) at a depth of 25 cm. In particular, the concentrations 

of the major elements Na, K, Mg, Al, Fe, and Ti are elevated, 

whereas the major constituent SiO2 is low, and the concentrations 

of trace elements V, Cr, Co, Ni, Li, Be, Sr, Ba, P, and F, excluding 

the base metals, are elevated. Stratigraphic work for Molycorp 

(core SED-CO3 from upper Fawn Lake, fig. 2A; URS Corp., 

written commun., 2004) suggests that the interval represented 

by the 1979 flood may be somewhat deeper. Since both the 

previous and subsequent years were substantially drier (fig. 5), 

we argue that the stream would not mobilize the heavy mineral 

suites seen in this interval prior to or following the 1979 flood 

event. We suspect that the 1979 event may have deposited several centimeters of sediment in upper Fawn Lake. Using these 

TiO2 SiO2 As Ba Be Cd Ce Co Cr Cu Eu F Ho La Li Mn Mo Nd Ni Pb Sr V Y Yb Zn

Wt. percent Wt. percent ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

0.20 66.06 16 780 14 12 280 85 54 530 10 2,080 6 140 49 2,100 26 240 240 130 170 70 170 9 2,700

0.25 63.32 14 300 9 6 170 31 62 300 5 2,380 <4 94 35 2,200 25 130 110 200 240 82 88 5 1,500

0.35 63.48 17 200 5 4 130 14 74 120 2 2,310 <4 76 30 1,100 22 76 56 180 320 99 34 2 610

0.40 63.76 20 470 3 2 110 8 79 62 <2 2,050 <4 65 26 420 16 55 33 150 370 100 16 1 240

0.20 65.19 11 820 10 7 190 55 64 390 6 2,350 <4 99 32 560 17 150 150 160 230 82 110 6 1,800

0.18 64.54 12 640 14 9 230 53 56 500 8 2,430 4 120 37 720 22 200 180 180 220 74 140 8 2,200

0.25 61.74 12 250 7 6 160 37 69 240 4 2,330 <4 87 38 750 27 110 120 220 270 94 62 4 1,300

0.30 63.72 13 560 4 3 120 15 75 130 <2 2,450 <4 74 32 660 25 68 52 250 320 100 29 2 520

0.23 64.36 14 800 10 7 190 49 64 380 6 2,180 <4 98 33 970 24 150 140 190 260 84 100 6 1,800

0.12 66.85 14 710 16 11 260 80 44 660 10 2,450 6 130 40 1,400 22 240 240 120 150 60 180 10 3,000

0.18 67.01 17 820 12 12 230 92 56 500 8 2,060 4 120 48 1,700 23 190 250 150 170 74 130 7 2,600

0.18 67.08 12 790 11 12 220 93 57 480 7 1,980 4 110 49 2,200 22 180 240 150 160 76 130 7 2,600

0.18 69.77 13 720 11 11 220 92 55 480 7 1,990 4 110 47 2,400 21 180 240 140 150 71 130 7 2,600

0.18 67.27 17 780 13 12 240 97 58 550 8 1,990 5 120 48 2,600 23 200 270 140 160 75 140 8 3,000

0.20 64.82 <10 820 13 13 260 100 60 540 9 1,910 5 130 51 2,700 27 210 270 160 170 79 150 8 2,800

0.17 68.01 11 740 13 12 260 94 54 530 9 1,880 5 130 47 2,600 27 210 260 140 150 71 160 9 2,900

0.18 66.27 17 780 14 12 300 77 50 530 11 1,820 6 150 46 2,000 26 250 220 140 180 68 180 10 2,700

0.22 67.64 16 810 10 11 260 71 55 400 8 2,030 5 140 46 1,900 24 200 200 160 190 75 140 7 2,300

0.23 67.65 15 810 10 10 260 65 58 390 8 2,110 5 140 41 2,000 26 200 190 180 200 78 140 7 2,300

0.18 66.72 14 760 13 13 380 100 55 490 10 2,180 6 190 39 1,900 34 280 260 150 160 70 180 10 2,800

0.17 67.27 17 510 14 14 450 140 47 520 11 2,260 7 230 36 1,800 46 340 300 130 140 62 210 11 2,900

0.12 68.30 13 280 15 19 500 220 39 570 12 2,160 8 250 31 2,100 96 360 450 97 110 52 230 12 3,900

0.10 66.74 11 500 18 20 640 220 44 670 14 2,310 10 320 38 2,200 69 450 470 100 110 53 280 14 4,600

0.17 68.07 18 670 17 10 600 74 54 650 13 2,340 9 310 44 2,000 68 420 200 110 130 62 270 13 2,800

0.12 65.50 16 650 19 11 680 64 46 820 15 2,820 12 350 36 2,000 89 490 180 99 120 52 320 15 2,800

0.17 66.27 16 680 17 10 600 76 51 680 13 2,840 9 310 42 1,900 77 430 200 110 120 58 270 13 2,800

0.30 64.53 10 320 10 10 350 90 72 420 7 817 5 200 51 2,000 68 230 230 200 220 89 140 7 2,400

0.28 64.72 16 1,000 8 5 260 51 79 310 5 1,880 <4 150 51 1,800 48 160 150 200 220 96 99 5 1,400

0.35 63.98 14 1,100 6 7 220 38 87 230 4 2,150 <4 130 42 1,700 43 130 100 210 280 110 70 4 1,100

0.37 62.89 11 860 5 4 170 18 94 140 3 2,060 <4 110 35 1,700 40 97 68 190 320 110 47 2 610

0.28 64.19 21 200 8 7 240 77 77 320 5 1,880 <4 150 41 2,000 100 170 160 130 200 89 100 5 1,500

0.27 68.08 20 140 8 9 180 94 65 370 5 1,820 <4 100 44 2,000 150 140 220 100 160 77 89 5 1,700

0.32 65.73 13 150 6 6 140 61 78 310 4 1,790 <4 82 48 2,000 130 100 150 110 180 91 61 4 1,200

0.30 66.17 17 140 7 5 130 44 76 280 3 1,960 <4 74 46 1,800 130 91 110 120 170 88 52 3 930

0.23 66.81 <10 140 8 6 160 58 62 350 4 1,870 <4 88 46 1,800 160 120 130 130 140 75 69 4 1,200

0.27 66.53 <10 140 9 7 160 58 69 370 4 2,280 <4 88 52 2,000 250 120 140 140 150 77 65 4 1,200

0.32 66.49 <10 130 8 6 120 50 79 340 3 2,190 <4 68 56 2,000 360 85 120 170 170 89 50 3 980

0.30 66.80 13 130 6 5 110 47 79 290 3 1,970 <4 64 52 1,800 300 74 120 160 170 90 42 3 890

0.37 65.36 <10 150 5 3 110 25 86 200 2 1,890 <4 65 44 1,600 150 63 68 160 190 100 31 2 550

0.33 65.11 11 140 6 4 130 39 83 280 2 2,080 <4 77 47 1,600 180 77 90 180 200 99 38 3 750

0.40 67.27 12 180 6 3 230 26 80 160 2 1,670 <4 140 40 1,400 88 130 64 140 200 87 60 4 530

0.45 68.10 <10 260 5 3 260 20 81 81 2 1,590 <4 150 37 1,200 42 140 49 120 220 85 63 4 400

0.43 69.54 <10 240 4 2 270 18 72 58 <2 1,380 <4 160 35 1,000 49 140 42 110 190 77 65 4 340

0.42 69.00 <10 210 5 3 290 30 66 95 2 1,350 <4 170 36 930 75 160 61 96 170 72 75 4 490

0.33 65.68 12 150 7 6 170 57 72 270 3 1,870 <4 94 46 1,100 180 100 120 140 170 84 55 4 920

0.25 64.77 <10 140 8 6 130 56 72 340 4 2,010 <4 72 49 980 180 92 140 170 160 87 51 3 1,100

0.35 64.46 <10 170 8 5 130 43 88 320 4 2,020 <4 76 53 960 140 90 120 170 200 99 48 3 970

0.38 64.19 <10 180 8 4 140 32 95 320 4 2,170 <4 79 54 950 130 91 110 160 230 100 48 3 870

0.35 64.90 <10 180 9 4 140 33 89 350 4 2,030 <4 78 54 880 110 100 120 140 220 98 56 4 1,000

0.37 67.24 <10 200 8 4 140 33 85 320 4 2,000 <4 77 52 770 82 97 120 140 210 97 55 4 1,000

0.40 66.26 12 230 8 4 140 37 82 300 4 1,850 <4 76 58 800 62 96 110 130 190 98 58 4 930

0.33 67.93 <10 180 7 3 120 36 72 260 4 1,830 <4 72 49 690 49 89 110 120 180 87 51 4 870

0.30 74.61 <10 580 4 2 80 19 61 110 <2 1,350 <4 50 29 440 27 47 56 84 160 61 24 2 380

0.28 75.21 <10 210 4 2 77 17 53 110 <2 1,400 <4 47 25 410 25 48 52 77 170 62 24 2 360

0.10 61.74 10 130 3 2 77 8 39 58 2 817 4 47 25 410 16 47 33 77 110 52 16 1 240

0.18 64.73 12 180 6 4 140 33 55 263 4 1,873 5 77 36 963 25 93 110 120 160 71 51 3 875

0.28 66.27 14 310 8 6 205 54 68 340 5 2,025 6 110 44 1,750 49 140 140 140 180 82 73 4 1,250

0.35 67.27 17 755 13 11 260 79 79 498 8 2,188 7 148 49 2,000 108 200 220 170 220 93 140 8 2,600

0.37 68.07 17 801 14 12 303 93 82 531 10 2,331 9 171 51 2,100 150 241 241 181 231 99 180 10 2,800

0.40 68.24 17 817 15 12 429 96 86 564 11 2,371 9 221 52 2,200 174 322 260 197 267 100 201 11 2,870

0.41 69.62 20 834 17 13 600 114 88 664 13 2,450 10 310 54 2,470 205 424 281 204 320 100 270 13 3,000

0.45 75.21 21 1100 19 20 680 220 95 820 15 2,840 12 350 58 2,700 360 490 470 250 370 110 320 15 4,600

Results and Discussion

Table 1. Analytical, statistical, and descriptive data from the core from Eagle Rock Lake, lower Red River valley, Taos County, New 

Mexico—Continued. 

   
Sample Depth 137Cs Activity Percent Al2O3 CaO FeO K 2O MgO Na2O P2O5 TiO2 SiO2 As Ba 

Field Number Description (cm) (dpm/g) Moisture Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent ppm ppm 

02QNM102La tan-buff, wet clay 1 0.25 0.64 17.76 0.58 6.82 3.98 1.82 0.53 0.44 0.32 67.77 11 190 

02QNM102Lb tan-buff, wet clay 2 – 0.56 18.90 0.54 7.72 4.46 1.99 0.50 0.50 0.37 65.03 13 190 

02QNM102Lc tan-black mix of clay 3 – 0.54 18.90 0.55 7.33 4.46 2.16 0.55 0.50 0.33 65.22 16 190 

02QNM102Ld tan-black mix of clay, mottled, 

orange 4 – 0.56 18.90 0.62 6.82 4.10 2.16 0.66 0.48 0.38 65.89 14 240 

02QNM102Le tan-black clay, mostly black 5 – 0.45 18.52 0.62 6.56 3.98 2.16 0.69 0.48 0.37 66.64 <10 290 

02QNM102Lf tan-black clay, mostly black 6 – 0.52 18.90 0.56 6.95 4.22 2.32 0.59 0.50 0.40 65.56 <10 260 

02QNM102Lg tan-black clay, mostly black 7 0.21 0.55 18.90 0.55 6.56 4.10 2.16 0.57 0.50 0.40 66.27 11 210 

02QNM102Lh 90 percent black clay 8 – 0.56 17.19 0.80 6.43 3.49 2.16 0.93 0.37 0.33 68.29 10 160 

02QNM102Li 90 percent black clay 9 – 0.51 18.14 0.87 7.20 3.61 2.49 1.08 0.44 0.42 65.75 10 350 

02QNM102Lj 90 percent black clay 10 – 0.52 18.52 0.76 7.20 3.73 2.49 0.92 0.50 0.37 65.51 15 340 

02QNM102Lk 90 percent black clay 11 – 0.61 17.95 0.83 7.33 3.61 2.32 0.85 0.44 0.32 66.35 12 180 

02QNM102Ll 90 percent black clay 12 – 0.67 16.82 0.94 6.95 3.37 1.99 0.81 0.44 0.35 68.34 19 140 

02QNM102Lm 90 percent black clay 13 – 0.71 16.06 1.34 7.20 3.13 1.82 0.78 0.41 0.33 68.91 11 110 

02QNM102Ln 90 percent black clay 14 0.46 0.73 14.36 3.88 7.20 2.65 1.82 0.97 0.41 0.28 68.41 15 120 

02QNM102Lo 90 percent black clay 15 – 0.71 14.36 3.62 7.08 2.53 1.82 1.01 0.44 0.28 68.86 11 120 

02QNM102Lp 90 percent black clay 16 – 0.64 15.68 3.75 6.43 2.89 2.16 1.19 0.30 0.35 67.25 <10 160 

02QNM102Lq 90 percent black clay 17 – 0.62 17.01 4.82 6.56 3.25 2.32 1.23 0.30 0.37 64.15 13 180 

02QNM102Lr 90 percent black clay 18 – 0.65 15.68 6.70 6.18 3.01 2.16 0.94 0.25 0.32 64.77 12 150 

02QNM102Ls 90 percent black clay 19 – 0.60 17.19 3.48 5.79 3.37 2.16 0.96 0.27 0.33 66.44 <10 240 

02QNM102Lt 90 percent black clay 20 – 0.76 17.57 1.47 6.05 3.37 2.16 1.12 0.30 0.38 67.58 <10 250 

02QNM102Lu 90 percent black clay 21 0.40 0.57 20.78 1.87 6.56 4.10 2.49 0.75 0.37 0.37 62.71 <10 230 

02QNM102Lv 90 percent black clay 22 – 0.54 20.78 2.54 6.43 3.98 2.49 0.75 0.39 0.35 62.28 12 320 

02QNM102Lw 90 percent black clay 23 – 0.53 18.71 2.54 6.30 3.61 2.32 0.78 0.37 0.33 65.03 15 330 

02QNM102Lx 90 percent black clay 24 – 0.54 18.33 1.87 6.43 3.61 2.32 0.88 0.34 0.37 65.84 15 430 

02QNM102Ly 90 percent black clay 25 – 0.54 28.34 1.87 10.03 5.54 3.65 1.33 0.55 0.60 48.07 <10 510 

02QNM102Lz 90 percent black clay 26 – 0.51 18.90 1.07 6.82 3.73 2.49 0.88 0.37 0.40 65.35 14 440 

02QNM102Laa 90 percent black clay 27 0.48 0.49 18.90 1.08 6.43 3.73 2.32 0.89 0.34 0.37 65.93 13 350 

02QNM102Lab 90 percent black clay 28 – 0.46 14.55 0.96 4.76 2.89 1.66 0.69 0.27 0.32 73.90 <10 400 

02QNM102Lac 90 percent black clay 29 0.47 0.50 18.71 1.74 6.43 3.73 2.16 1.04 0.34 0.42 65.43 <10 430 

02QNM102Lad 90 percent black clay 30 – 0.53 17.76 2.54 6.69 3.49 2.16 1.00 0.32 0.38 65.65 12 180 

02QNM102Lae 90 percent black clay 31 0.54 0.51 18.71 1.47 6.30 3.85 2.32 0.84 0.34 0.37 65.79 11 230 

02QNM102Laf 90 percent black clay 32 – 0.52 17.76 1.29 6.30 3.61 2.16 0.78 0.30 0.28 67.52 <10 150 

02QNM102Lag 90 percent black clay 33 0.62 0.59 15.87 2.01 6.69 3.13 1.99 0.75 0.27 0.28 68.99 13 120 

02QNM102Lah 90 percent black clay 34 – 0.57 17.57 2.41 7.59 3.49 2.16 0.73 0.25 0.27 65.53 15 130 

02QNM102Lai 90 percent black clay 35 0.72 0.60 17.38 2.01 7.20 3.37 2.16 0.73 0.23 0.27 66.65 13 120 

02QNM102Laj 90 percent black clay 36 – 0.58 17.38 1.61 7.46 3.37 2.16 0.92 0.25 0.30 66.55 <10 140 

02QNM102Lak 90 percent black clay 37 1.02 0.63 16.82 1.61 6.95 3.25 2.32 1.08 0.23 0.32 67.43 12 140 

02QNM102Lal 90 percent black clay 38 – 0.59 17.01 1.47 6.56 3.25 2.32 1.01 0.23 0.33 67.81 10 150 

02QNM102Lam 90 percent black clay 39 1.13 0.56 16.63 1.12 6.30 3.25 2.32 1.04 0.23 0.33 68.77 <10 170 

02QNM102Lan 90 percent black clay 40 – 0.53 16.63 1.10 6.18 3.25 2.16 1.13 0.25 0.37 68.94 <10 180 

02QNM102Lao 90 percent black clay 41 1.13 0.51 16.25 1.03 5.92 3.13 2.16 1.11 0.25 0.37 69.79 11 200 

02QNM102Lap 90 percent black clay 42 – 0.51 17.01 1.04 6.05 3.37 2.32 1.06 0.25 0.38 68.51 <10 200 

02QNM102Laq some bluff clay 43 1.20 0.46 18.14 0.78 6.18 3.73 2.16 0.85 0.30 0.30 67.57 13 240 

02QNM102Lar some bluff clay 44 – 0.37 18.90 0.79 5.79 4.10 2.32 0.90 0.27 0.33 66.60 <10 770 

02QNM102Las some bluff clay 45 1.22 0.40 18.52 0.90 6.43 3.85 2.32 0.88 0.30 0.37 66.44 10 250 

02QNM102Lat almost all buff clay with gray 46 – 0.37 20.78 0.62 6.43 4.46 1.99 0.53 0.34 0.38 64.47 <10 240 

02QNM102Lau almost all buff clay with gray 47 1.10 0.35 18.33 0.60 5.40 3.98 1.99 0.58 0.32 0.33 68.47 <10 320 

02QNM102Lav almost all buff clay with gray 48 1.60 0.43 18.90 0.91 6.30 3.98 2.16 0.89 0.27 0.40 66.19 16 240 

02QNM102Law almost all buff clay with gray 49 2.48 0.45 17.76 1.03 6.18 3.61 2.32 1.08 0.27 0.37 67.38 14 230 

02QNM102Lax gravel on bottom 50 1.76 0.36 16.06 0.82 5.27 3.49 1.82 1.12 0.25 0.30 70.86 <10 250 

Minimum 14.36 0.54 4.76 2.53 1.66 0.50 0.23 0.27 48.07 10 110 

25th percentile 16.86 0.81 6.30 3.28 2.16 0.75 0.27 0.32 65.54 11 160 

Median 17.76 1.09 6.50 3.61 2.16 0.88 0.33 0.35 66.50 13 220 

75th Percentile 18.85 1.87 6.95 3.98 2.32 1.03 0.43 0.37 68.17 14 283 

85th percentile 18.90 2.54 7.20 4.10 2.32 1.08 0.47 0.38 68.68 15 347 

90th percentile 18.90 3.50 7.33 4.11 2.49 1.12 0.50 0.40 68.91 15 403 

95th percentile 20.78 3.82 7.53 4.46 2.49 1.16 0.50 0.41 69.43 16 436 

Maximum 28.34 6.70 10.03 5.54 3.65 1.33 0.55 0.60 73.90 19 770 

same criteria, we identified the 1979 flood event in core from 

Eagle Rock Lake at a depth of 28–31 cm. Concentrations of Ti 

and the trace elements V, Cr, Co, Ni, and Li, excluding the base 

metals, are elevated. Although the Molycorp core from this part 

of Eagle Rock Lake is thicker than our core, this interval matches 

well with that identified by URS Corp. (written commun., 2004; 

fig. 2B) using stratigraphic descriptions of the core intervals. On 

the basis of the stratigraphic work by URS Corp., the thickness of 

the sediment in Eagle Rock Lake appears to be more than a single 

1-cm sampling interval. We would suggest that it may be as much 

as 4- or 5-cm thick given the changes in the geochemistry (tables 

2 and 5). Using these criteria, the sedimentation rate in Eagle Rock 

Lake both prior to and following the 1979 event would be very 

similar. And it would be about the same in the upper part of the 

upper Fawn Lake core. Attempts to match the other peaks in the 

geochemical data with specific changes in the hydrograph (fig. 5) 

would be ad hoc, so we assume that the sedimentation rate was 

approximately uniform in the two lakes during the period of record. 

Table 2. Analytical, statistical, and descriptive data from the core from upper Fawn Lake, lower Red River valley, Taos County, New Mexico.

10 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
iO2 SiO2 As Ba Be Cd Ce Co Cr Cu Eu F Ho La Li Mn Mo Nd Ni Pb Sr V Y Yb Zn

ercent Wt. percent ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

32 67.77 11 190 3 4 89 14 65 180 <2 1,820 <4 58 30 750 21 46 48 240 210 88 21 2 480

37 65.03 13 190 3 3 95 6 70 120 <2 1,890 <4 63 30 560 25 46 31 280 220 96 15 1 280

33 65.22 16 190 3 3 95 7 76 120 <2 2,100 <4 64 30 480 24 45 32 320 220 99 15 1 280

38 65.89 14 240 3 4 97 14 79 180 <2 1,870 <4 64 30 460 24 48 45 280 220 100 20 2 400

37 66.64 <10 290 3 4 93 15 76 210 <2 1,840 <4 62 30 450 20 48 49 270 220 98 22 2 460

40 65.56 <10 260 3 3 95 12 78 190 <2 1,930 <4 63 30 460 24 45 42 310 240 100 18 1 380

40 66.27 11 210 3 4 97 10 78 180 <2 2,000 <4 65 29 450 24 47 39 310 230 100 17 1 350

33 68.29 10 160 3 4 85 19 82 220 <2 1,980 <4 55 30 470 27 46 51 190 200 100 23 2 480

42 65.75 10 350 3 4 90 20 95 260 <2 1,700 <4 58 34 540 24 48 57 190 240 110 25 2 520

37 65.51 15 340 3 3 89 15 99 260 <2 2,150 <4 59 32 500 26 45 51 220 250 110 21 2 440

32 66.35 12 180 3 4 86 27 88 280 <2 1,910 <4 56 31 470 44 46 64 210 220 110 24 2 540

35 68.34 19 140 3 5 86 36 72 290 <2 1,590 <4 53 30 470 38 49 80 170 200 91 31 2 730

33 68.91 11 110 3 6 80 39 66 290 <2 1,530 <4 50 29 470 34 48 89 150 190 86 32 2 780

28 68.41 15 120 3 7 76 67 62 380 2 1,270 <4 47 30 560 22 50 130 110 230 78 41 3 1,100

28 68.86 11 120 3 8 78 72 64 410 2 1,200 <4 48 30 600 18 52 140 100 230 80 45 4 1,200

35 67.25 <10 160 3 4 83 39 76 260 <2 1,340 <4 52 34 620 12 49 80 120 250 94 32 3 640

37 64.15 13 180 2 3 86 28 84 250 <2 1,480 <4 54 35 630 15 48 67 130 280 100 28 2 480

32 64.77 12 150 2 4 82 28 70 230 <2 1,440 <4 51 31 580 21 46 70 150 270 90 26 2 500

33 66.44 <10 240 3 4 86 31 71 210 <2 1,680 <4 56 33 610 14 48 73 190 220 93 28 2 560

38 67.58 <10 250 3 4 93 31 77 210 <2 1,540 <4 61 34 630 16 52 68 190 210 100 29 2 500

37 62.71 <10 230 3 4 100 23 87 220 <2 1,870 <4 70 34 670 18 52 66 310 240 110 24 2 510

35 62.28 12 320 3 4 99 29 88 260 <2 2,020 <4 66 34 700 19 52 72 270 270 110 26 2 600

33 65.03 15 330 3 4 94 30 85 250 <2 1,770 <4 61 32 660 20 49 70 240 250 100 25 2 570

37 65.84 15 430 3 3 92 23 91 240 <2 1,850 <4 59 33 610 19 48 58 210 240 110 24 2 490

60 48.07 <10 510 4 4 150 29 150 350 2 2,120 <4 94 50 880 34 74 81 320 360 170 34 3 650

40 65.35 14 440 3 3 98 17 98 230 <2 1,990 <4 64 33 590 22 50 49 220 250 120 22 2 410

37 65.93 13 350 3 3 94 17 88 200 <2 1,820 <4 60 33 540 22 48 49 220 230 110 21 2 380

32 73.90 <10 400 2 2 72 16 66 140 <2 1,710 <4 46 24 420 17 38 38 170 180 82 16 1 290

42 65.43 <10 430 3 3 96 22 86 200 <2 1,740 <4 61 33 590 25 50 54 200 250 110 23 2 430

38 65.65 12 180 3 3 94 26 82 210 <2 1,650 <4 59 31 600 29 50 60 180 260 100 24 2 480

37 65.79 11 230 3 3 98 19 86 180 <2 1,800 <4 58 32 560 24 47 46 220 220 110 22 2 370

28 67.52 <10 150 3 3 91 20 82 190 <2 1,820 <4 54 31 560 28 44 50 220 200 100 20 2 380

28 68.99 13 120 3 3 83 28 73 200 <2 1,640 <4 48 29 550 39 42 61 180 190 89 23 2 510

27 65.53 15 130 3 4 94 27 74 220 <2 1,690 <4 54 33 580 41 48 63 200 200 93 25 2 540

27 66.65 13 120 3 4 93 31 75 250 <2 1,750 <4 54 33 580 44 48 74 200 190 94 28 2 640

30 66.55 <10 140 3 4 92 34 79 260 <2 1,600 <4 53 34 600 48 49 81 180 190 97 30 2 670

32 67.43 12 140 3 4 93 29 79 260 <2 1,540 <4 54 34 620 41 50 75 180 200 97 30 3 650

33 67.81 10 150 3 4 94 28 86 250 <2 1,530 <4 54 34 610 36 49 71 180 200 100 30 2 610

33 68.77 <10 170 3 3 94 23 86 260 <2 1,580 <4 55 34 590 37 48 64 160 200 100 29 3 570

37 68.94 <10 180 3 3 90 24 84 250 <2 1,530 <4 52 34 560 33 47 60 160 200 100 29 2 540

37 69.79 11 200 3 3 91 19 85 240 <2 1,470 <4 53 33 540 28 46 56 150 200 99 28 2 500

38 68.51 <10 200 3 3 97 20 88 250 <2 1,560 <4 57 34 550 27 49 57 170 210 100 29 2 520

30 67.57 13 240 3 2 96 18 86 190 <2 1,860 <4 57 32 480 21 46 42 210 180 110 20 2 330

33 66.60 <10 770 2 2 94 11 86 120 <2 1,760 <4 56 35 450 15 43 29 230 200 110 17 2 190

37 66.44 10 250 2 2 97 9 88 160 <2 1,930 <4 58 35 480 17 47 29 180 220 110 20 2 220

38 64.47 <10 240 3 <2 100 <1 80 96 <2 2,050 <4 63 31 410 20 48 20 250 230 100 15 1 150

33 68.47 <10 320 2 <2 97 3 72 77 <2 1,890 <4 59 29 420 19 44 23 230 190 95 14 1 140

40 66.19 16 240 3 2 100 15 78 130 <2 1,710 <4 61 36 500 41 50 38 200 190 100 22 2 290

37 67.38 14 230 3 2 96 16 81 140 <2 1,650 <4 58 37 500 29 48 41 160 200 100 24 2 300

30 70.86 <10 250 3 2 79 13 74 150 <2 1,460 <4 47 30 410 22 40 38 130 190 91 20 2 320

27 48.07 10 110 2 2 72 3 62 77 2 1,200 <4 46 24 410 12 38 20 100 180 78 14 1 140

32 65.54 11 160 3 3 87 15 74 180 2 1,565 <4 54 30 473 20 46 43 170 200 94 20 2 373

35 66.50 13 220 3 4 94 22 81 220 2 1,745 <4 58 33 560 24 48 57 200 220 100 24 2 485

37 68.17 14 283 3 4 96 29 86 258 2 1,885 <4 61 34 600 32 49 70 230 240 110 29 2 568

38 68.68 15 347 3 4 97 31 88 260 2 1,963 <4 63 34 620 38 50 75 270 250 110 30 2 640

40 68.91 15 403 3 4 98 34 88 281 2 2,002 <4 64 35 633 41 50 80 283 251 110 31 3 652

41 69.43 16 436 3 6 100 39 97 323 2 2,078 <4 66 36 687 43 52 85 310 270 110 33 3 758

60 73.90 19 770 4 8 150 72 150 410 2 2,150 <4 94 50 880 48 74 140 320 360 170 45 4 1,200

Lake Sediment Geochemistry 

Sedimentation rates in the two lakes are interpreted to be 

approximately constant except for the 1979 event. The resulting model gives a good correlation of peaks in metal concentrations between lakes and highlights the difference between the 

sediment in both cores. Spikes in metal concentrations in both 

lakes may be associated with smaller flood events recorded at 

the Questa gage (table 4). The presence of the head gates that 

limit the inflow to the lakes to approximately 2 cfs has resulted 

in reducing the amount of sediment transported into the lakes at 

high flow. The irrigation company that owns and operates the 

lakes also reportedly reduces the flow during peak runoff (URS 

Corp., written commun., 2004). The distribution of major and 

trace elements in sediment cored from Eagle Rock Lake and 

upper Fawn Lake is shown in figures 7–12, plotted as a function 

of depth. Peak spikes in concentration of the major and trace elements are summarized in table 5. Peaks were defined as elevated 

Results and Discussion

Table 2. Analytical, statistical, and descriptive data from the core from upper Fawn Lake, lower Red River valley, Taos County, New 

Mexico—Continued.

 11
Field Number Sample Description Latitude DD Longitude DD Al2O3 CaO FeO K 2O MgO Na2O P2O5 TiO2 SiO2 

Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent 

Modern streambed sediment samples

Red River

02QNM-116S Sample taken downstream from Hottentot Creek 36.70710 –105.43282 10.96 0.35 3.09 2.65 0.73 0.51 0.16 0.37 81.19 

02QNM-117S Sample taken upstream from confluence with 

Goose Creek 

36.67313 –105.37953 13.79 2.66 5.66 2.65 1.66 2.56 0.27 0.75 70.00 

02QNM-115S Sample taken downstream from SW Hanson Creek 36.69787 –105.47443 12.47 0.48 4.25 3.01 1.08 0.90 0.27 0.40 77.14 

02QNM-114S Sample taken upstream from Columbine Creek 36.68218 –105.51032 12.47 0.45 4.25 2.89 1.09 0.90 0.27 0.43 77.24 

02QNM-112S Sample taken downstream from Columbine Creek 36.68378 –105.5223 12.84 0.49 4.25 3.01 1.09 0.97 0.27 0.47 76.60 

02QNM-111S Sample taken upstream from Goat Hill 

Campground

36.68737 –105.53987 13.03 0.62 3.86 3.01 1.16 1.19 0.25 0.45 76.43 

02QNM-110S Sample taken at stream gauge site 36.70332 –105.5682 13.60 0.50 4.12 3.13 1.09 1.17 0.25 0.40 75.73 

02QNM-118S Sample taken 4 mi downstream from Questa 

Ranger Station at Red River State Fish Hatchery

36.68420 –105.64925 12.84 0.95 3.47 2.89 1.03 2.02 0.18 0.38 76.22 

Tributaries

03QNM201S Hottentot Creek 36.70780 –105.42975 16.24 0.31 4.37 3.85 0.99 0.35 0.30 0.40 73.18 

03QNM202S SE Straight Creek scar tributary 36.70882 –105.4372 17.19 0.92 7.46 3.98 2.82 1.24 0.62 0.50 65.27 

03QNM203S SE Straight Creek scar tributary 36.70843 –105.4409 16.62 0.29 7.46 4.10 1.99 0.75 0.53 0.37 67.89 

03QNM204S Straight Creek 36.70793 –105.44407 13.98 0.49 5.92 3.49 1.46 0.78 0.39 0.38 73.11 

03QNM205S Tributary upstream from Hanson Creek 36.70375 –105.46072 13.41 1.54 5.27 3.25 1.34 1.62 0.37 0.68 72.51 

03QNM206S Hanson Creek 36.70390 –105.46178 16.24 0.50 6.18 3.85 1.13 0.53 0.34 0.52 70.71 

03QNM207S SW Hanson Creek scar tributary 36.70225 –105.46423 15.68 0.91 7.85 3.73 2.16 1.08 0.55 0.50 67.55 

03QNM208S Sediment from catchment basin near Red River 

across road from Molycorp mill

36.69515 –105.4881 18.51 0.49 6.69 4.10 1.66 0.65 0.48 0.42 67.01 

02QNM-113S Columbine Creek sediment sample 36.67712 –105.51517 13.60 2.24 6.18 2.41 1.56 3.50 0.18 0.58 69.75 

Composite talus fan samples

03KVTF10 Mallette Creek tributary fan 36.72503 –105.39968 13.22 1.23 3.47 3.37 0.93 2.29 0.25 0.42 74.81 

03KVTF1 Graveyard Canyon fan 36.71107 –105.42058 13.22 0.80 6.69 2.89 0.93 1.35 0.30 0.48 73.34 

03KVTF2 Hottentot Creek fan 36.70787 –105.42995 17.57 0.10 5.02 4.10 1.08 0.40 0.32 0.42 71.00 

03KVTF3 Straight Creek fan 36.70853 –105.44403 14.36 0.41 6.82 3.61 1.48 0.63 0.41 0.45 71.83 

03KVTF4 Little Hansen Creek fan 36.70227 –105.46378 15.11 1.33 8.23 3.73 2.16 1.05 0.57 0.45 67.36 

03KVTF5 Small fan immediately downstream from Little 

Hanson Creek

36.70175 –105.46722 13.03 1.33 4.12 3.13 1.24 1.75 0.25 0.55 74.59 

03KVTF5b Small fan immediately downstream from Little 

Hanson Creek (duplicate sample)

36.70175 –105.46722 13.03 3.50 4.12 3.13 1.39 1.75 0.30 0.48 72.29 

03KVTF6 Sample from fan remnant of Sulfur Gulch 36.69445 –105.49818 14.92 1.22 7.08 3.61 2.32 1.75 0.44 0.52 68.15 

03KVTF9 Little Goathill fan 36.68520 –105.52717 14.92 1.29 8.23 3.37 1.64 1.75 0.46 0.43 67.90 

03KVTF8 Goathill fan 36.68675 –105.53818 13.03 0.27 6.05 3.85 0.76 0.81 0.23 0.40 74.60 

03KVTF7 Capulin fan 36.69855 –105.54973 15.49 0.87 7.46 3.85 1.24 1.19 0.34 0.43 69.12 

Background sediment sites

03QNMB120 Red River upstream from Goose Creek confluence 36.66387 –105.54973 13.22 2.52 4.63 2.41 1.58 2.02 0.32 0.60 72.70 

03QNMB124 Red River upstream from Fawn Lake Camp 36.70642 –105.54973 12.84 0.97 5.02 2.89 1.49 1.31 0.37 0.38 74.73 

03QNMB121 Red River upstream from Columbine Creek 36.68302 –105.51005 13.98 1.25 7.20 3.13 1.82 1.75 0.44 0.48 69.95 

02QNM-105Ba Composite sample from river deposit 36.68058 –105.51112 14.36 1.09 5.27 3.25 1.82 1.62 0.32 0.47 71.80 

02QNM-105Bb upstream from confluence with 13.22 0.88 4.37 3.13 1.46 1.48 0.23 0.47 74.75 

02QNM-105Bc Columbine Creek 13.41 0.87 4.50 3.01 1.38 1.35 0.23 0.40 74.85 

02QNM-105Bd 12.09 0.90 5.02 2.89 1.26 1.48 0.32 0.43 75.61 

02QNM-106Ba Composite sample from river deposit 36.68155 –105.51768 14.36 0.99 8.62 3.25 1.99 1.62 0.48 0.47 68.22 

02QNM-106Bb downstream from confluence with 13.98 0.92 9.39 3.13 1.99 1.62 0.53 0.48 67.96 

02QNM-106Bc Columbine Creek on pipeline access 13.41 0.95 7.20 3.01 1.99 1.75 0.41 0.52 70.75 

02QNM-106Bd road 12.66 0.98 6.69 3.01 1.54 1.62 0.39 0.43 72.68 

02QNM-107Ba Composite sample from river deposit 36.68433 –105.52565 12.47 1.02 10.16 2.77 1.43 1.35 0.34 0.40 70.06 

02QNM-107Bb downstream from confluence with 12.66 1.23 6.30 3.01 1.43 1.32 0.32 0.40 73.33 

02QNM-107Bc Columbine Creek on pipeline 12.66 1.96 6.95 3.13 1.59 1.35 0.39 0.42 71.56 

02QNM-107Bd access road 13.98 0.84 3.60 3.25 1.39 1.62 0.21 0.42 74.69 

02QNM-107Be 14.17 0.74 4.89 3.13 1.59 1.48 0.27 0.43 73.29 

02QNM-107Bf 13.60 1.09 4.63 2.89 1.58 2.02 0.23 0.42 73.54 

02QNM-107Bg 13.60 1.23 4.76 2.89 1.53 2.29 0.23 0.42 73.05 

02QNM-104Ba Composite sample from tributary fan 36.68483 –105.53405 14.73 1.68 5.02 2.77 1.21 3.10 0.14 0.50 70.85 

02QNM-104Bb on south side of Red River 15.11 1.27 4.37 3.49 0.93 3.37 0.11 0.50 70.84 

02QNM-104Bc downstream from Goat Hill Gulch 14.17 1.11 3.60 3.37 0.85 3.50 0.11 0.35 72.94 

02QNM-104Bd 14.17 1.54 3.73 3.25 0.98 2.97 0.14 0.40 72.83 

02QNM-103Ba Composite sample from Goat Hill 36.68538 –105.53405 14.92 0.06 5.15 4.10 0.81 0.55 0.27 0.33 73.81 

02QNM-103Bb Gulch fan 15.11 0.06 5.15 4.34 0.85 0.54 0.23 0.35 73.39 

02QNM-103Bc 10.77 0.31 14.15 2.53 0.98 1.29 0.99 0.30 68.69 

02QNM-103Bd 13.41 0.06 4.89 3.98 0.71 0.51 0.27 0.33 75.84 

03QNMB123 Upstream from Capulin Canyon 36.69425 –105.54672 14.54 0.97 6.18 3.01 1.82 1.62 0.37 0.42 71.08 

02QNM-108Ba Red River alluvial deposit about 36.70082 –105.55785 14.36 1.27 6.18 2.89 2.16 2.02 0.41 0.63 70.08 

02QNM-108Bb 1 mi upstream from USDA FS 11.71 1.54 12.86 2.41 1.58 1.48 0.44 0.43 67.55 

02QNM-108Bc Ranger Station at Eagle Rock Lake 12.84 1.05 4.89 3.01 1.36 1.35 0.25 0.42 74.83 

03QNMB122 Red River upstream from USDA FS Questa Ranger 

Station

36.70242 –105.56493 13.41 0.78 5.40 2.89 1.61 1.62 0.37 0.45 73.47 

Mill tailings samples

03QNM209T Tailings from area south of highway 38, along 

banks of the Red River and across road from 

Questa mill plant entrance

36.69470 –105.4961 10.39 1.54 8.75 3.49 0.56 1.89 0.18 0.30 72.90 

03QNM101T Tailings from 2 ft inside tailings pipe at Columbine 

Park pipe yard (Molycorp)

36.68347 –105.52455 0.76 0.57 56.61 0.17 0.23 0.13 0.11 0.12 41.30 

03QNMGHCGT Goathill Campground tailings (1981) 36.68935 –105.54152 13.60 1.40 6.05 3.13 1.59 1.89 0.37 0.52 71.46 

03QNMCAPT Tailings from Capulin pipe break site 36.69558 –105.54823 14.36 3.36 2.32 5.30 0.86 1.89 0.30 0.25 71.37 

03QNM210T Tailings from pipe line break (1979?) 36.70082 –105.55922 13.22 1.36 5.02 2.89 1.41 2.02 0.30 0.50 73.28 

03QNM211T Tailings from pipe line break (1979?) 36.70128 –105.55937 14.54 1.25 5.79 3.25 1.62 1.62 0.34 0.48 71.10 

Table 3. Analytical data from debris fans, modern and geochemical baseline sediment, and mill tailings samples, lower Red River valley, Taos County, New Mexico.

12 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
O MgO Na2O P2O5 TiO2 SiO2 As Ba Be Cd Ce Co Cr Cu F La Li Mn Mo Nd Ni Pb Sr V Y Yb Zn 

cent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

5 0.73 0.51 0.16 0.37 81.19 <10 380 2 3 64 12 32 72 -- 33 18 610 6 26 32 61 170 60 12 1 250

5 1.66 2.56 0.27 0.75 70.00 <10 840 2 3 66 21 82 28 -- 34 22 1,300 3 27 39 25 450 110 18 2 110

1 1.08 0.90 0.27 0.40 77.14 10 620 3 3 84 25 49 89 -- 42 23 880 14 40 57 88 210 66 20 2 430

9 1.09 0.90 0.27 0.43 77.24 15 790 3 3 90 26 50 84 -- 45 22 910 10 43 58 76 230 67 21 2 470

1 1.09 0.97 0.27 0.47 76.60 14 970 3 4 92 25 50 81 -- 46 23 1,100 10 44 60 74 240 68 21 2 470

1 1.16 1.19 0.25 0.45 76.43 <10 1,100 3 4 82 19 51 86 -- 43 23 840 13 40 71 74 240 68 24 2 540

3 1.09 1.17 0.25 0.40 75.73 12 1,100 4 4 94 24 54 120 -- 47 24 1,200 11 45 69 72 240 69 25 2 600

9 1.03 2.02 0.18 0.38 76.22 <10 1,000 3 3 77 21 44 74 -- 40 23 870 14 37 58 59 240 63 22 2 520

5 0.99 0.35 0.30 0.40 73.18 13 1,100 2 <2 94 <1 48 20 1,540 50 22 180 23 37 10 150 170 77 13 1 44

8 2.82 1.24 0.62 0.50 65.27 16 790 2 2 89 2 99 46 1,340 53 26 650 21 33 17 340 280 120 8 <1 110

0 1.99 0.75 0.53 0.37 67.89 17 960 2 2 93 5 66 52 1,680 56 29 440 32 33 17 330 230 93 11 1 100

9 1.46 0.78 0.39 0.38 73.11 13 930 2 <2 81 4 58 52 1,470 48 27 380 32 29 15 230 180 79 12 1 90

5 1.34 1.62 0.37 0.68 72.51 14 1,100 3 <2 98 12 71 70 1,090 50 21 500 90 42 25 100 340 88 24 2 130

5 1.13 0.53 0.34 0.52 70.71 18 940 3 2 120 9 68 34 1,480 64 24 310 12 50 24 73 250 84 25 2 81

3 2.16 1.08 0.55 0.50 67.55 20 690 2 2 86 6 88 35 1,430 51 22 420 23 34 23 120 550 110 8 <1 71

0 1.66 0.65 0.48 0.42 67.01 17 1,100 3 2 100 12 74 92 1,580 54 27 530 34 42 31 170 250 100 16 2 160

1 1.56 3.50 0.18 0.58 69.75 <10 840 2 3 64 15 66 27 -- 36 27 750 3 27 24 57 260 97 20 2 150

7 0.93 2.29 0.25 0.42 74.81 <10 830 3 2 120 10 30 50 -- 72 22 1,200 11 53 19 70 270 56 28 2 210

9 0.93 1.35 0.30 0.48 73.34 <10 1,000 2 <2 78 20 58 38 -- 41 17 720 28 37 32 44 270 83 16 1 130

0 1.08 0.40 0.32 0.42 71.00 <10 1,100 2 <2 110 <1 54 22 -- 58 23 180 24 42 10 170 190 84 14 1 41

1 1.48 0.63 0.41 0.45 71.83 18 800 2 <2 96 1 60 47 -- 57 27 330 33 32 13 270 200 81 9 1 74

3 2.16 1.05 0.57 0.45 67.36 17 660 2 2 86 7 88 34 -- 52 21 390 22 33 20 120 630 110 7 <1 60

3 1.24 1.75 0.25 0.55 74.59 <10 950 3 <2 82 15 73 42 -- 44 22 900 71 34 33 71 290 81 19 2 140

3 1.39 1.75 0.30 0.48 72.29 13 950 2 2 88 16 66 44 -- 45 23 1,400 19 35 35 94 350 80 19 2 200

1 2.32 1.75 0.44 0.52 68.15 <10 1,000 4 2 98 8 110 150 -- 57 32 640 460 41 37 98 420 110 17 1 79

7 1.64 1.75 0.46 0.43 67.90 <10 1,200 3 2 110 23 92 150 -- 63 31 910 25 46 36 170 470 110 14 1 140

5 0.76 0.81 0.23 0.40 74.60 14 960 2 <2 86 3 39 41 -- 49 17 250 45 31 10 210 190 66 12 2 37

5 1.24 1.19 0.34 0.43 69.12 21 920 4 2 170 10 64 110 -- 100 31 850 19 81 25 190 220 89 33 2 190

1 1.58 2.02 0.32 0.60 72.70 12 860 2 <2 74 16 67 44 -- 42 30 1,100 6 36 32 21 410 92 28 3 100

9 1.49 1.31 0.37 0.38 74.73 10 940 2 <2 86 14 68 97 -- 43 26 630 26 44 28 110 230 81 19 2 140

3 1.82 1.75 0.44 0.48 69.95 20 1,100 3 2 110 28 110 120 -- 58 29 1,100 140 56 50 90 330 100 28 2 170

5 1.82 1.62 0.32 0.47 71.80 12 1,000 3 4 87 16 72 100 -- 46 29 720 19 38 35 100 300 91 18 2 220

3 1.46 1.48 0.23 0.47 74.75 <10 1,100 2 3 80 13 63 77 -- 43 24 600 16 34 28 84 270 77 16 2 130

1 1.38 1.35 0.23 0.40 74.85 <10 1,200 2 2 76 13 57 70 -- 41 23 550 12 34 27 90 260 76 15 1 120

9 1.26 1.48 0.32 0.43 75.61 12 790 2 2 72 11 63 52 -- 39 20 420 14 29 22 84 260 82 11 1 110

5 1.99 1.62 0.48 0.47 68.22 18 970 3 4 110 27 97 160 -- 59 30 900 85 52 40 100 300 100 22 2 150

3 1.99 1.62 0.53 0.48 67.96 18 960 4 4 120 35 86 170 -- 66 28 1,000 110 60 38 100 290 100 26 2 140

1 1.99 1.75 0.41 0.52 70.75 <10 920 3 3 110 23 88 110 -- 60 26 830 71 47 32 95 310 96 20 2 110

1 1.54 1.62 0.39 0.43 72.68 <10 940 3 3 100 28 73 100 -- 53 22 860 82 44 28 81 280 90 18 2 87

7 1.43 1.35 0.34 0.40 70.06 10 1,300 2 4 90 28 67 70 -- 42 22 1,200 100 40 31 79 270 82 17 2 120

1 1.43 1.32 0.32 0.40 73.33 16 1,100 2 3 84 20 68 95 -- 44 23 1,300 60 41 34 90 260 79 18 2 140

3 1.59 1.35 0.39 0.42 71.56 13 520 3 3 92 19 73 110 -- 49 24 1,000 84 46 37 74 300 86 19 2 130

5 1.39 1.62 0.21 0.42 74.69 <10 1,100 2 2 75 9 62 70 -- 41 24 300 23 31 26 75 290 80 14 1 110

3 1.59 1.48 0.27 0.43 73.29 <10 1,100 2 2 86 14 69 82 -- 46 27 380 20 39 31 100 280 84 17 2 140

9 1.58 2.02 0.23 0.42 73.54 <10 970 2 2 72 9 67 92 -- 39 25 360 15 31 25 76 280 83 15 2 140

9 1.53 2.29 0.23 0.42 73.05 <10 960 2 3 72 13 58 73 -- 41 28 560 28 32 27 67 290 77 17 2 160

7 1.21 3.10 0.14 0.50 70.85 <10 940 4 4 120 24 35 65 -- 65 41 2,200 12 52 20 85 230 61 43 4 280

9 0.93 3.37 0.11 0.50 70.84 <10 790 5 3 94 11 27 35 -- 45 27 1,200 7 30 14 120 210 61 26 3 180

7 0.85 3.50 0.11 0.35 72.94 <10 900 4 2 100 6 24 35 -- 50 26 1,000 5 38 15 96 160 42 28 3 180

5 0.98 2.97 0.14 0.40 72.83 <10 890 3 3 100 9 35 34 -- 55 27 1,100 4 42 17 84 170 49 31 3 200

0 0.81 0.55 0.27 0.33 73.81 14 500 2 2 130 3 41 38 -- 71 16 220 31 48 8 240 310 66 7 <1 47

4 0.85 0.54 0.23 0.35 73.39 <10 670 2 2 110 2 37 34 -- 61 15 180 19 42 7 220 240 64 8 <1 35

3 0.98 1.29 0.99 0.30 68.69 16 880 3 5 44 17 60 85 -- 26 16 260 100 24 16 58 210 73 7 1 56

8 0.71 0.51 0.27 0.33 75.84 10 520 2 2 97 1 37 37 -- 53 14 170 22 37 6 200 160 59 8 <1 28

1 1.82 1.62 0.37 0.42 71.08 10 920 3 <2 100 36 82 170 -- 50 32 1,400 64 51 36 97 310 95 21 2 150

9 2.16 2.02 0.41 0.63 70.08 13 1,400 3 3 100 19 93 84 -- 51 30 590 35 46 40 77 370 100 20 2 170

1 1.58 1.48 0.44 0.43 67.55 16 900 4 5 94 42 62 110 -- 46 23 2,500 130 52 46 58 290 84 24 2 190

1 1.36 1.35 0.25 0.42 74.83 <10 1,300 3 3 82 17 62 76 -- 44 24 760 29 36 31 83 280 80 16 2 170

9 1.61 1.62 0.37 0.45 73.47 14 840 3 <2 87 15 81 120 -- 48 26 690 64 44 32 74 290 89 20 2 110

9 0.56 1.89 0.18 0.30 72.90 10 310 5 2 47 22 44 92 -- 31 19 310 1,100 20 25 180 220 41 7 <1 99

7 0.23 0.13 0.11 0.12 41.30 80 640 <1 14 62 820 <1 1,200 -- 35 4 360 1,600 53 630 1,600 640 80 6 <1 850

3 1.59 1.89 0.37 0.52 71.46 <10 1,300 3 2 88 18 81 84 -- 48 26 890 130 40 35 89 310 100 21 2 160

0 0.86 1.89 0.30 0.25 71.37 <10 700 4 2 64 2 31 140 -- 40 24 860 370 22 20 200 400 53 17 2 210

9 1.41 2.02 0.30 0.50 73.28 13 930 3 2 90 14 67 69 -- 50 28 870 52 40 30 71 280 85 23 2 170

5 1.62 1.62 0.34 0.48 71.10 <10 1,200 3 2 99 22 83 86 -- 54 29 990 53 45 38 80 330 98 22 2 200

Results and Discussion

Table 3. Analytical data from debris fans, modern and geochemical baseline sediment, and mill tailings samples, lower Red River valley, Taos County, New Mexico—Continued.

 13
concentrations of individual elements that generally occur during 

a short period of time relative to the time frame of the record in 

the core. We have grouped the elements in terms of their primary 

mineralogical residence sites in silicic rock that occurs in the 

study area.

The sedimentary record cored in upper Fawn Lake 

differs markedly from that cored in Eagle Rock Lake (table 

5, figs. 7–12). For the most part, the geochemical data from 

sediment from upper Fawn Lake show minor variations 

throughout the period sampled. The single most striking feature of the geochemical data from the upper Fawn Lake core 

is the large number of trace elements that were concentrated 

during what we interpret as the 1979 flood event. Many of 

the trace elements enriched at this depth in the core occur 

primarily or exclusively in heavy-mineral phases that would 

be mobilized during high flow (tables 2 and 5). Minerals 

identified by x-ray defraction in the upper Fawn Lake core 

sample (02QNM102Ly, depth of 25 cm, and within the interval identified as the 1979 flood event) included quartz with 

minor amounts of montmorillonite, muscovite (illite or sericite), kaolinite, and potassium feldspar (R. Driscoll, written 

commun., 2003). In contrast, data from sediment from Eagle 

Rock Lake are substantially different. Plots of three groups 

of elements, the large-ion-lithophile (LIL) elements (figs. 9 

and 10), the major and minor elements (figs. 7 and 8), and 

the deposit-related metals (fig. 12) generally show markedly 

different geochemical behavior in the sediment from Eagle 

Rock Lake before and after the flood-of-record in 1979 (table 

5). Many elements show marked changes in the baseline geochemical concentrations after the 1979 flood event (shown 

by the gray bands on figs. 7–12). Many of the elements in 

the heavy-mineral phases (Mo, Cu, Zn, Cd, Ba, and Be) had 

peak concentrations during the 1979 flood event and concentrations of the REE were increasing. Minerals were identified 

by x-ray defraction in two samples from Eagle Rock Lake. 

Sample 02QNM101Lax (depth of 50 cm and below the depth 

of the 1979 flood record) contained quartz, muscovite (illite or 

sericite), and minor clinochlore. Sample 02QMN101Lz (depth 

of 26 cm; contained highest concentration of Ce) included 

quartz and minor amounts of montmorillonite like that found 

in upper Fawn Lake. Fluorite and REE-bearing minerals were 

not found at concentrations sufficient to identify by X-ray 

diffraction (about 1 percent by volume). No pyrite or molybdenite was identified and no iron oxide minerals that might be 

carriers of REE, Nb, and Y were identified (R. Driscoll, written commun., 2003). Correlation of peak concentrations of the 

elements associated with heavy-mineral phases and the abrupt 

change in geochemical baselines in this interval (figs. 7–12) 

is the basis of the calibration of the geochronology of the two 

cores in the 1979 flood record. Using these calibration points 

and assuming a uniform sedimentation rate, the data form the 

sedimentation model shown in figure 13. This model indicates 

a slightly higher rate of sedimentation at the core site in upper 

Fawn Lake prior to the 1979 flood and a slightly higher rate 

of sedimentation at the core site in Eagle Rock Lake following 

the 1979 flood event. However, the sedimentation rate, as 

shown by the work of Allen and others (unpub. data, 1999) 

and by URS Corp. (written commun., 2004), varies significantly within the lake, from the inlet to the outlet, and, as 

pointed out by URS Corp. (written commun., 2004), probably 

has varied during the period of record in the lake. 

Table 4. Mean daily peak flow at the Questa gage (08265000), lower Red River valley, Taos 

County, New Mexico

[Flow expressed in cubic ft per second (cfs)]

Year Period

Mean daily 

peak-flow rate

(cfs)

Number of days 

flow exceeded 

300 cfs

1965 June 18–20 320 3

1973 June 14–15 314 2

1979 May 20–July 3 557 44

1983 May 30–June 2 332 4

1984 May 23–May 28 372 6

1985 May 10–11 319 2

1985 June 9–June 13 322 5

1986 June 8–June 9 325 2

1991 May 21–May 24 469 4

1993 May 28 301 1

1994 May 16–June 8 399 21

1995 June 14–June 23 359 10

1997 June 2–June 8 347 7

14  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
Results and Discussion

1960

1965

1970

1975

1980

1985

1990

1995

2000

0 50 100 150 200 250 300 350 400 450

Average monthly discharge (in cfs)

9EAR

Figure 5. Plot of monthly discharge (cfs) versus time (1960–2002) at the gage (08265000) at Questa, New Mexico 

(http://nm.waterdata.usgs.gov/nwis). The flood-of-record occurred in spring, 1979 (table 4). 

 15
Upper Fawn Lake 

Silicates Oxides Sulfides Accessory minerals

Depth (cm) Year Na K Mg Ca Al Si Fe Mn Ti V Cr Pb Co Ni Mo Cu Zn Cd Li Be Sr Ba P F La Ce Nd Yb Y

1 2002

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25 1979 .

26 1979

27 1979

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49 1964

50

51

52

53

54

55

Table 5. Summary of the geochemical data from cores from upper Fawn Lake and Eagle Rock Lake, Red River valley, Taos County, 

New Mexico.

16 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
Eagle Rock Lake

Silicates Oxides Sulfides Accessory minerals

Depth (cm) Year Na K Mg Ca Al Si Fe Mn Ti V Cr Pb Co Ni Mo Cu Zn Cd Li Be Sr Ba P F La Ce Nd Yb Y

1 2002

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28 1979

29 1979

30 1979

31 1979

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50 1964

51

52

53

54

55

Table 5. Summary of the geochemical data from cores from upper Fawn Lake and Eagle Rock Lake, Red River valley, Taos County, 

New Mexico—Continued.

Results and Discussion 17
Figure 6. Plot of 137Cs concentration versus depth (cm) in the 

Eagle Rock Lake and upper Fawn Lake cores. Well-defined peaks 

in 137Cs activity occur at slightly different depths in the two lakes, 

but both are quite close to the bottom of the core where we 

encountered fragmented bedrock. Since the lakes originated as 

borrow pits dug to complete the paving of N. Mex. Highway 38 

from Questa to the town of Red River, the differences in sedimentation at the bottom of the core reflects the fact that roadwork 

began at Questa in the mid-1950s and was completed at the town 

of Red River in 1961. Head gates were installed by the local irrigation organization, which subsequently limited flow through and 

thus sediment accumulation in the two lakes. 

Element Anomalies

Sediment in upper Fawn Lake is characterized by 

occasional peaks in element concentrations above the general 

geochemical baseline recorded in the sediment core (table 5). 

Enrichment of different suites of elements occur throughout 

the core. The element suites K, Fe, Pb, P, and Ti and V, Cr, 

and Pb have peaks that occur at some intervals, whereas the 

suite Na, Ca, Fe, Ni, Cu, Zn, and Cd peaks occur at other 

depths in the core (table 5 and figs. 7–12). The two primary 

sources for sediment for upper Fawn Lake are Precambrian 

rock upstream of the town of Red River (Jackson and others, 

2003) and the altered areas that occur between Red River 

and upper Fawn Lake (fig. 1). Ludington and others (2005) 

document the high erosion rates that occur in the altered 

areas during summer rainstorms. The element suites formed 

during wet years (Fe, V, Cr, and Pb) contain many of the 

elements enriched in sediment from the scar areas (table 3). 

Finally, there is a pronounced Ca and Sr peak in the core 

from 14- to 18-cm depth, which we interpret as an 

anthropogenic source—probably concrete associated with 

building activity in the floodplain in the town of Red River 

or vicinity.

Peak concentrations in the Eagle Rock Lake core are 

much more varied and frequent. We identify several periods 

where different trace-element suites appear in the Eagle 

Rock Lake core. Examination of the elemental associations 

prior to the 1979 flood shows that the element suite 

Al, Ti, V, Cr, Cu, Zn, Li, and F peaked in the interval 

between 48 to 52 cm, and that the element suite K, Mg, 

V, Cr, Pb, Mo, and Li peaked in the interval from 40 to 41 

cm (tables 5 and 6 and figs. 7–12). The rare earth element 

anomalies begin to appear in the core from Eagle Rock 

Lake periodically at a depth of 45 cm, after excavation 

of the open pit. However, at the 1979 flood event, there 

were abrupt changes in the concentrations of many of the 

major elements (figs. 7 and 8). These fundamental changes 

indicate that a new source of sediment was introduced into 

the Red River floodplain downstream from Fawn Lakes 

following the 1979 flood event (shown as gray bands on 

figs. 7–12). Following the 1979 flood event, there was a 

dramatic increase in the concentration of Al, Ba, Co, and 

Ni and a dramatic decrease in the concentrations of Na, K, 

Mg, Fe, Ti, Cr, and V in the sediment cored at Eagle Rock 

Lake. The REE and F peaks (fig. 10) lag somewhat behind 

the 1979 flood event in the Eagle Rock Lake core but 

correspond with the 1979 flood event in the upper Fawn 

Lake core. Note also that the REE anomalies in the Eagle 

Rock Lake core greatly exceed those in the upper Fawn 

Lake core.

18  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
   

   

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.4 0.6 0.8 1.0 1.2

CaO, in weight percent 

-60

-50

-40

-30

-20

-10

0

0 1 2 3 4 5 6 7

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.3 0.5 0.7 0.9 1.1 1.3

Na O, in weight percent 

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.3 0.5 0.7 0.9 1.1 1.3

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

1.5 2.5 3.5 4.5

K O, in weight percent 

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

1.5 2.5 3.5 4.5 5.5

Depth below sediment interface, in centimeters

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

1.0 1.5 2.0 2.5

MgO, in weight percent 

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

1.0 2.0 3.0 4.0

2 Na O, in weight percent 2

MgO, in weight percent CaO, in weight percent 

2 K O, in weight percent 2

Figure 7. Plot of concentrations of Na2O, K2O, MgO, and CaO, expressed as oxides, versus depth below the sediment interface for the 

cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we interpret the geochemical and stratigraphic 

data to indicate the sediment deposited by the 1979 flood-of-record. 

Comparison of the Data from the 

Two Lake-Sediment Cores

Comparisons of the sediment geochemical data from the 

two lake cores are in figure 14. Five major elements, Na2O, 

MgO, FeO, Al2O3, and TiO2, and six trace elements, Ba, Sr, Cr, 

V, Cu, and Zn, are presented as box plots to show the difference between sediment deposited in the two lakes before and 

after 1979. The 1979 core intervals plotted are shown in table 

5. The range of values between the 25th and 75th percentiles 

is remarkably small for many elements. Figures 14A and 

14B compare element concentrations in sediment from upper 

Fawn Lake prior to and subsequent to the 1979 flood. The 

small ranges and median concentrations from pre-1979 and 

post-1979 sediment are very similar indicating no change in 

the source of sediment following the 1979 flood. In contrast, 

the geochemical data from Eagle Rock Lake (figs. 14C and 

14D) show the marked contrast between sediment deposited 

prior and subsequent to the 1979 flood with only Sr, V, and Cr 

showing little change with time. Those changes are also shown 

relative to the data from upper Fawn Lake in figures 14E

and 14F. All five of the major elements showed substantial 

changes in concentration indicating a new source of sediment 

following the 1979 flood. In fact, the concentration ranges of 

the major elements Na2O, MgO, FeO, Al2O3 and TiO2 do not 

even overlap between the 25th and 75th percentiles. In figures 

14G and 14H, we compare the geochemical data from sediment 

in Eagle Rock Lake from pre-1979 with all of the data from 

the sediment core from upper Fawn Lake. Only concentrations 

of Cu and Zn are elevated in the pre-1979 sediment from Eagle 

Rock Lake relative to that in sediment from upper Fawn Lake.

Results and Discussion 19
   

   

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

14 16 18 20 22 24 26 28

Al O , in weight percent

-50

-40

-30

-20

-10

0

14 16 18 20 22 24 26 28 30

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

3 4 5 6 7 8 9 10 11

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

3 4 5 6 7 8 9

FeO, in weight percent

Depth below sediment interface, in centimeters

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.05 0.15 0.25 0.35 0.45

TiO , in weight percent

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.05 0.25 0.45 0.65

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

60 62 64 66 68 70 72 74 76

SiO , in weight percent

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

45 50 55 60 65 70 75

FeO, in weight percent 2 3 Al O , in weight percent 2 3

2 2 SiO , in weight percent 2 TiO , in weight percent 2

Figure 8. Plot of concentrations of FeO, Al2O3, TiO2, and SiO2, expressed as oxides, versus depth below the sediment interface for the 

cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we interpret the geochemical and stratigraphic 

data to indicate the sediment deposited by the 1979 flood-of-record. Concentrations of SiO2 were determined by subtracting the sum of 

the major element concentrations from 100. 

Element Suites that May Be Related to Mining

Different element suites can be associated directly with 

the mining and processing of ore at the Questa mine (table 

6). There is a pattern of molybdenum enrichment in the 

Eagle Rock Lake core from the early 1960s (fig. 12). There 

are also increases in concentrations of Cu, Zn, Co, and Ni 

(figs. 11 and 12), all of which are associated with porphyry 

molybdenum deposits (see for example Carten and others, 

1993). We interpret this progressive enrichment with time of 

this suite of elements to indicate that the beginning of development of open-pit mining at Questa, which began in 1965, 

was having an increasing effect on the availability of this 

suite of elements to erosion and transport by the Red River. 

Concentrations of elements present in the Precambrian rock 

in the pyroxene/amphibole suite were reduced with time, 

and concentrations of elements associated with sulfide mineral phases associated with the Questa ore body increased. 

The most direct and compelling evidence of this hypothesis 

is the increase of the size of the molybdenum peak with 

the continued development of the open pit (1963–1967; 

table 6 and fig. 12). The Mo peak begins to increase prior 

to the development of the open pit because the mine waste 

from the underground vein mining that occurred from 1921 

to 1958 at the site would have had to be removed prior to 

open-pit development. 

A second peak of Mo enrichment, which occurs between 

36 and 40 cm (1970–1978, table 6), does not have any other 

20 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
   

  



&IGURE

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.15 0.25 0.35 0.45 0.55

P2O5, in weight percent 

-60

-50

-40

-30

-20

-10

0

0 400 800 1200

Ba, in parts per million 

Depth below sediment interface, in centimeters

-60

-50

-40

-30

-20

-10

0

20 25 30 35 40 45 50 55 60

Li, in parts per million 

Depth below sediment interface, in centimeters

-60

-50

-40

-30

-20

-10

0

100 150 200 250 300 350 400

Sr, in parts per million 

Depth below sediment interface, in centimeters

-60

-50

-40

-30

-20

-10

0

Depth below sediment interface, in centimeters

0.15 0.25 0.35 0.45 0.55

P2O5, in weight percent 

-60

-50

-40

-30

-20

-10

0

20 25 30 35 40 45 50 55 60

Li, in parts per million

Depth below sediment interface, in centimeters

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-10

0

100 150 200 250 300 350 400

Sr, in parts per million

Depth below sediment interface, in centimeters

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0

0 400 800 1200

Ba, in parts per million

Depth below sediment interface, in centimeters

Figure 9. Plot of concentrations of P2O5, expressed in weight percent, and Li, Sr, and Ba, expressed in parts per million (ppm), versus 

depth below the sediment interface for the cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we 

interpret the geochemical and stratigraphic data to indicate the sediment deposited by the 1979 flood-of-record. Crustal abundance 

values (Fortescue, 1992) of these elements are: P (1,120 ppm), Li (18 ppm), Sr (384 ppm), and Ba (390 ppm). 

deposit-related metals associated with this buildup (fig. 12). We 

interpret this prominent peak at 38-cm depth as either a product 

spill (truck accident) or perhaps a buildup of Mo in the lake 

sediment following a period of high ore production at the Questa 

mine. The peak concentration of Mo tailed off quickly suggesting 

that the peak may have been the result of changes in mill operation 

that reduced the air pollution from the mill. A similar high peak 

concentration of Mo deep in the cores from Eagle Rock Lake 

was also reported by Allen and others (unpub. data, 1999). The 

cause of this peak cannot be determined without access to detailed 

production and maintenance records from the Questa mill, 

which have not been made available by Molycorp.

There are various peaks in concentration of Cu, Zn, Co, 

Ni, and REE that may be explained by breaks in the pipeline 

that carried mill wastes to the repository. The mill-waste 

pipeline parallels N. Mex. Highway 38 from the mill site 

(fig. 1) to a tailings repository west of the town of Questa. 

URS Corp. (written commun., 2003) has documented 

hundreds of pipeline breaks from Molycorp records during 

the life of the Questa mine. The vast majority of these spills 

were small and readily cleaned up by Molycorp (URS Corp., 

written commun., 2003). At the site of the 1981 Goat Hill 

Campground (fig. 1), there is a substantial amount of mill 

tailings dispersed among the trees. The U.S. Department of 

Agriculture (USDA) Forest Service provided photographs of 

this 1981 pipeline break (fig. 15A). The photographs appear 

to indicate that a substantial amount of mill waste was 

lost during this event. Analysis of four mill-waste samples 

Results and Discussion 21
   

   

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Depth below sediment interface, in centimeters

0 150 300 450 600

Ce, in parts per million

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0

Depth below sediment inerface, in centimetersDepth below sediment inerface, in centimetersDepth below sediment inerface, in centimeters

Depth below sediment inerface, in centimetersDepth below sediment inerface, in centimetersDepth below sediment inerface, in centimetersDepth below sediment inerface, in centimeters

40 60 80 100 120 140 160

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1000 1500 2000 2500 3000

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40 50 60 70 80 90 100

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750 1250 1750 2250 2750

F, in parts per million

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0

0 100 200 300 400

La, in parts per million

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0

0 100 200 300 400 500

Nd, in parts per million

-60

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-10

0

0 100 200 300

Y, in parts per million

Ce, in parts per million F, in parts per million

La, in parts per million

Figure 10. Plot of concentrations of Ce, F, La, Nd, and Y, expressed in parts per million (ppm), versus depth below the sediment interface for the cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we interpret the geochemical and 

stratigraphic data to indicate the sediment deposited by the 1979 flood-of-record. Crustal abundance values (Fortescue, 1992) of these 

elements are: F (544 ppm), La (34.6 ppm), Ce (66.4 ppm), Nd (39.6 ppm), and Y (31 ppm). 

collected in 2003 (table 3) along the Red River at the Goat 

Hill, Capulin, and 1979 flood pipeline-break sites have 

remarkably similar compositions and relatively low average 

metal concentrations (Mo, 340 ppm; Cu, 94 ppm; Pb, 120 

ppm; Zn, 170 ppm; Co, 16 ppm; and Ni, 30 ppm), which are 

very similar to those in the mill waste stream analyzed by 

Molycorp (B. Walker, written commun, 2004). However, a 

fifth sample of mill waste (03QNM101T) collected inside 

a piece of pipe in the Molycorp pipeline yard, where it had 

been protected from weathering, gave higher concentrations 

of the metals listed in table 3 (Mo, 1,600 ppm; Cu, 1,200 ppm; 

Pb, 1,600 ppm; Zn, 850 ppm; Co, 820 ppm; and Ni, 630 ppm). 

Concentrations of As (80 ppm) and Cd (14 ppm) were also 

elevated in this sample of mill waste (table 3). This suite of 

metals reside in the sulfide phases in the Questa ore body 

(Ross and others, 2002), and, with the exception of Mo, they 

are not recovered in the milling process. They appear to be a 

heavy-mineral suite concentrated in the pipe. A sixth sample 

collected from a site on the south side of Highway 38 across 

from the Molycorp mill (03QNM209T, table 3) contains 

elevated concentrations of Mo (1,100 ppm), but concentrations 

of other metals are similar to those found in the mill tailings samples. Concentrations of the REE in the mill tailings 

samples do not approach peak concentrations of REE found in 

the core from Eagle Rock Lake (fig. 10 and table 3).

22 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
   

   

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70 90 110 130 150 170

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Depth below sediment interface , in centimetersDepth below sediment interface , in centimetersDepth below sediment interface , in centimetersDepth below sediment interface , in centimeters

Depth below sediment interface , in centimetersDepth below sediment interface , in centimetersDepth below sediment interface , in centimetersDepth below sediment interface , in centimeters

0 50 100 150 200 250

Co, in parts per million

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-10

0

30 40 50 60 70 80 90 100

Co, in parts per million Cr, in parts per million Cr, in parts per million

Ni, in parts per million V, in parts per million V, in parts per million Ni, in parts per million

Figure 11. Plot of concentrations of Co, Cr, Ni, and V, expressed in parts per million (ppm), versus depth below the sediment interface for the cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we interpret the geochemical and 

stratigraphic data to indicate the sediment deposited by the 1979 flood-of-record. Crustal abundance values (Fortescue, 1992) of these 

elements are: Co (29 ppm), Cr (122 ppm), Ni (99 ppm), and V (136 ppm).

REE from the Magmatic Hydrothermal Breccia, 

Questa Ore Body

Concentrations of REE in rock of the Questa caldera 

are high and enriched in light REE typical of highly evolved 

silicic volcanic rock. Plots of the chondrite-normalized REE 

data from volcanic and plutonic rock from the study area 

(figs. 16A and 16B) show that the median REE concentrations from the upper Fawn Lake core are quite similar to that 

from the Amalia Tuff and some of the granitic plutons. The 

range of REE concentrations in sediment from upper Fawn 

Lake is small when compared to the range from Eagle Rock 

Lake (tables 1 and 2). REE concentrations in sediment from 

the core from Eagle Rock Lake are substantially higher than 

rock typical of the evolved rhyolitic Amalia Tuff (fig. 16A), 

have a small Eu anomaly, and are more enriched than the REE 

concentrations in the peralkaline granite (fig. 16B). Whereas 

Lipman (1983) and Johnson and others (1989) report lavas 

that are somewhat more evolved and have greater REE enrichment than those patterns shown in figure 16A, ranges of REE 

concentrations in the Eagle Rock Lake core far exceed values 

reported for typical volcanic and plutonic rock (fig. 16B) from 

the caldera. Neither the Oligocene volcanic rock of the Latir 

caldera nor the REE present in the mill tailings can account for 

the REE anomalies in the Eagle Rock Lake sediment (fig. 10).

Results and Discussion 23
   





 

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Depth below sediment interface, in centimeters

0 100 200 300 400 500

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Depth below sediment interface, in centimeters

0 200 400 600 800 1000

Cu, in parts per million

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Depth below sediment interface, in centimeters

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Depth below sediment interface, in centimeters

0 50 100 150 200

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Depth below sediment interface, in centimeters

50 100 150 200 250 300 350

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Depth below sediment interface, in centimeters

50 100 150 200 250 300

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Depth below sediment interface, in centimeters

0 1000 2000 3000 4000 5000 -60

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Depth below sediment interface, in centimeters

0 400 800 1200 1600 2000

Cu, in parts per million Mo, in parts per million Mo, in parts per million

Pb, in parts per million Pb, in parts per million Zn, in parts per million Zn, in parts per million

Figure 12. Plot of concentrations of Cu, Mo, Pb, and Zn, expressed in parts per million (ppm), versus depth below the sediment interface for the cores from upper Fawn Lake (blue) and Eagle Rock Lake (red). Bands are shown where we interpret the geochemical and 

stratigraphic data to indicate the sediment deposited by the 1979 flood-of-record. Crustal abundance values (Fortescue, 1992) of these 

elements are: Cu (68 ppm), Mo (1.2 ppm), Pb (13 ppm), and Zn (76 ppm). 

The magmatic hydrothermal breccia associated with 

the D ore body described in Ross and others (2002) contains 

abundant fluorite. Since this is the residual or pegmatitic phase 

from the hydrothermal crystallization process, we requested 

samples of the magmatic hydrothermal breccia from Molycorp 

for chemical analysis to evaluate possible enrichment of the 

REE in this late crystallization phase of the deposit. Meghan 

Jackson (Molycorp) provided about a dozen samples of the 

magmatic hydrothermal breccia from the D ore body and 

one sample of fluorite from veins exposed in Sulfur Gulch 

(QSFG, table 7). We analyzed the Sulfur Gulch fluorite and 

four samples of the magmatic hydrothermal breccia from the 

D ore body (fig. 17). Samples analyzed were selected on the 

basis of their variation in texture. Three of the five samples 

(QF-2, QF-3, and QF-4) were disaggregated, and the white 

and green non-sulfide phases were separated by handpicking 

for analysis. Sample descriptions accompany figure 17 and the 

analytical results are in table 7. The white phase was a carbonate-rich phase that was almost completely dissolved in HNO3

. 

The data from the carbonate phases indicate that they are 

enriched in Mn and Li but were not particularly enriched in 

any of the other trace elements. In contrast, the fluorite phase 

in samples QF-3 and QF-4, which appeared to be equigranular 

with discrete banded layers of fluorite and calcite, contained 

24  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
-60

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0

Plot depth, in centimeters

1955 1965 1975 1985 1995 2005

Estimated age of lake sediment

Upper Fawn Lake

Eagle Rock Lake

elevated REE concentrations. However, the concentrations 

are not sufficient to explain the REE anomalies in the Eagle 

Rock Lake sediment core without some enrichment mechanism. This is in contrast with the data from a more coarsely 

crystalline vein fluorite and carbonate sample (QF-2) where 

both Mn and the REE concentrations are not as enriched 

in either the calcite or fluorite phases in the other two 

samples. This more coarsely crystalline vein material does 

have substantially more Ba in the calcite, however, than the 

other calcite magmatic hydrothermal breccia samples (table 

7). Fluorite from the vein sampled in Sulfur Gulch (QSGF1) contains low concentrations of Mn, Ba, and REE. These 

two samples may represent fluorite veins that formed prior 

to ore deposition.

Electron backscatter photomicrographs taken on the 

SEM by Sharon Diehl (written commun., 2003) show that 

three REE-bearing phases occur as small inclusions in the 

fluorite: a hexagonal mineral identified as synchysite, a 

Ca, REE-rich carbonate, a REE-rich CaSO4, and a REErich Ca phosphate mineral (fig. 18). Geoff Plumlee (oral 

commun., 2003) identified microscopic occurrences of a 

rare-earth carbonate-fluoride mineral, possibly synchysite, 

in bedrock drill cuttings from drill hole SC-5B in Straight 

Creek (Ludington and others, 2005) where they appear to 

be associated with hydrothermal quartz-pyrite-carbonate 

veins and disseminations in the altered rock. The magmatic 

hydrothermal breccia forms a substantial component of 

the ore bodies mined at Questa (B. Walker, Molycorp., 

oral commun., 2003). Analyses of F in both the sediment 

from the altered areas (table 3) and from the Eagle Rock 

Lake core over the interval where the REE anomaly occurs 

(table 1 and fig. 19) indicate that there are increased F 

concentrations (2,840 ppm) coincident with the increase 

in the REE concentrations that is about double the 1,450 

ppm F that could be attributed to erosion from the altered 

areas upstream of the Questa deposit. Spills of mill tailings resulting from pipeline breaks such as the Goat Hill 

Campground spill could account for the REE anomalies 

found in the Eagle Rock Lake core providing some mechanism of REE enrichment could be found. Fluorine concentration data from the core interval where the REE peak 

occurred in the sediment from Eagle Rock Lake indicate 

that peak F enrichment occurred subsequent to the 1979 

flood event. Weathering of the REE from REE-bearing 

carbonate minerals in the fluorite would occur rapidly in 

the locally acidic microenvironment of the tailings deposit 

as a result of weathering of the sulfide minerals present 

in the mill tailings. The REE, which have low solubilities 

in near-neutral SO4

–2 solutions and follow the behavior of 

aluminum (Verplanck and others, 1999), would be immediately precipitated at the pH of the water in the Red River as 

REE2(SO4)3 and transported as colloids to be incorporated 

into the sediment core from Eagle Rock Lake. Although we 

cannot demonstrate that the 1981 Goat Hill Campground 

spill (fig. 15) was responsible for the REE anomaly found 

in the Eagle Rock Lake core, we have found no other 

Figure 13. Plot of the sedimentation rate used for both the Eagle 

Rock Lake and upper Fawn Lake cores. The depth of the 1964 137Cs 

peak and the geochemical data from the 1979 flood-of-record were 

used to constrain the sedimentation model (tables 1, 2, and 5). 

plausible sources of elevated REE and F other than those in 

the fluorite and carbonate magmatic hydrothermal breccia 

that could account for these anomalies .

Results from Stream-Sediment Survey

The geochemical data from the NURE and from our 

sediment study of both premining and modern stream sediment 

are summarized in figures 20 and 21. Distances are plotted as 

river-km measured upstream from the confluence of the Red 

River with the Rio Grande River; the Questa open pit is at 18–22 

Table 6. Dates for some trace element anomalies in the sediment core from 

Eagle Rock Lake, lower Red River valley, Taos County, New Mexico. 

Molybdenum Copper-Zinc Cobalt-Nickel Rare Earth 

Elements

1961–1966 1966–1967

1963–1967

1967–1970

1970–1978

1973–1979

1977

1980–1985

1980–1987 1983–1986 1979–1986

1988–1995 1989–1994

1988–1990

1997–1999 1998–1999 1998–1999

2002 2002

Table 6. Dates for some trace element anomalies in the sediment core from Eagle Rock Lake, lower Red River valley, Taos 

County, New Mexico. 

Results and Discussion 25
0.1

1.0

10.0

Concentration, in weight percent

Na O MgO FeO Al O TiO

10

100

1,000

Concentration, in parts per million

Ba Sr Cr V Cu Zn

Upper Fawn Lake core 

 pre-1979 sediment

2 2 3 2

Upper Fawn Lake core, 

 post-1979 sediment

! "

0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

Eagle Rock Lake core, 

 post-1979 sediment

# $

Eagle Rock Lake core, 

 pre-1979 sediment

Concentration, in weight percent

Na O2 MgO FeO Al O2 3 TiO2

Concentration, in parts per million

Figure 14 (above and facing page). Box plot comparing geochemical data (breaks are as shown in table 5). The median value for each 

element is bracketed by the 25th and 75th percentile of the data forming the box; the 10th and 90th percentiles are indicated by the lines 

above and below the box; and the 5th, 95th, minimum, and maximum values are shown as black dots above and below the 10th and 90th 

percentiles. ERL, Eagle Rock Lake. A. Major element data for Na2O, MgO, FeO, Al2O3, and TiO2 from the pre-1979 (n=23) and the post-1979 

(n=24) intervals from upper Fawn Lake core (table 2). B. Trace element data for Ba, Sr, Cr, V, Cu, and Zn from the pre-1979 (n=23) and the 

post-1979 (n=24) intervals from upper Fawn Lake core (table 2). C. Major element data for Na2O, MgO, FeO, Al2O3, and TiO2 from the pre1979 (n=24; ERL pre-1979) and the post-1979 (n=26; ERL post-1979) intervals from Eagle Rock Lake core (table 1). D. Trace element data 

for Ba, Sr, Cr, V, Cu, and Zn from the pre-1979 (n=24; ERL pre-1979) and the post-1979 (n=26; ERL post-1979) intervals from Eagle Rock 

Lake core (table 1). 

26 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

% &

' (

Concentration, in weight percent Concentration, in weight percent

Concentration, in parts per million Concentration, in parts per million

Na O2 MgO FeO Al O2 3 TiO2

Na O2 MgO FeO Al O2 3 TiO2

Upper Fawn Lake sediment

Upper Fawn Lake sediment

Eagle Rock Lake core, 

 post-1979 sediment

Eagle Rock Lake core, 

 pre-1979 sediment

Figure 14 (continued). Box plot comparing geochemical data (breaks are as shown in table 5). The median value for each element is 

bracketed by the 25th and 75th percentile of the data forming the box; the 10th and 90th percentiles are indicated by the lines above and 

below the box; and the 5th, 95th, minimum, and maximum values are shown as black dots above and below the 10th and 90th percentiles. ERL, Eagle Rock Lake. E. Major element data for Na2

O, MgO, FeO, Al2O3, and TiO2 from upper Fawn Lake core (table 2, n=50) and the 

post-1979 (table 1, n=26) intervals from Eagle Rock Lake core. F. Trace element data for Ba, Sr, Cr, V, Cu, and Zn from upper Fawn Lake 

core (table 2, n=50) and the post-1979 (table 1, n=26) intervals from Eagle Rock Lake core. G. Major element data for Na2O, MgO, FeO, 

Al2O3, and TiO2 from upper Fawn Lake core (table 2, n=50) and the pre-1979 (table 1, n=24) intervals from Eagle Rock Lake core. H. Trace 

element data for Ba, Sr, Cr, V, Cu, and Zn from upper Fawn Lake core (table 2, n=50) and the pre-1979 (table 1, n=24) intervals from Eagle 

Rock Lake core.

Results and Discussion 27
Figure 15. Photographs of the 1981 mill tailings spill at the USDA 

Forest Service Goat Hill Campground showing the tailings spill 

from the pipeline break (A), the cleanup by Molycorp (B), and 

(C) mill tailings sediment in the Red River, winter of 1981. (Photos 

from USDA Forest Service files provided by George Long, Questa 

Ranger Station, N. Mex., 2003). 

river-km. The variation of Sr, Cr, V, and Mo in the Red River 

sediment is small relative to source areas, whereas Ba, Ce, and Cu 

show an increase downstream of the Questa deposit. Zinc shows a 

broad zone of enrichment in the Red River sediment downstream 

of the altered areas as well. Concentrations of all metals shown 

are generally higher in the altered areas and in the south-flowing 

tributaries in the NURE data, except for Zn, than in the Red River 

sediment (2002). Many of the north-flowing tributaries, which 

in part drain unaltered Precambrian rock south of the Red River, 

have metal concentrations near that in the Red River sediment or 

have concentrations lower than the altered areas. Median sediment values from upper Fawn Lake match well for Sr, are lower 

than the Red River sediment for Ba, and elevated for the other six 

elements shown (figs. 20 and 21, table 9)—plotting in the field 

defined by data from the tributaries. Concentrations of Cu (220 

ppm) plot above the range shown in fig. 21. Relative to the concentrations found in the Red River sediment, median values in the 

post-1979 sediment of Eagle Rock Lake for Cr and V match well 

(fig. 20 and table 8), but values for Ba and Sr are lower. Median 

concentrations in the sediment core of Eagle Rock Lake after 

1979 (table 8) are twice that in the Red River sediment for Mo, 

but median concentrations for Ce (260 ppm), Cu (500 ppm), and 

Zn (2,650 ppm) plot above the upper boundary of the diagram for 

these elements (fig. 21). We conclude that sediment supplied by 

the Red River at low flow in 2002 is not the same source of sediment in the post-1979 core from Eagle Rock Lake.

Comparison of Lake Sediment Geochemistry with 

Other Sources

Sediment from upper Fawn Lake is not dominated by 

material eroded from the altered areas such as were sampled 

in Hottentot and Straight Creeks (fig. 1), but the contribution 

from the altered areas to the trace-element suite is significant 

(fig. 22). Comparison of the sediment data from the altered 

areas with upper Fawn Lake sediment (figs. 22A and 22B) 

shows higher concentrations of MgO, Al2O3, Cr, V, Cu, and 

Zn and lower concentrations of Ba in sediment of upper Fawn 

Lake than in sediment from the altered areas. The sediment 

composition of the core from upper Fawn Lake is interpreted 

as a mixture of sedimentary material from the basin upstream 

of upper Fawn Lake (Jackson and others, 2003) and the altered 

scar areas. Comparison with the pre-1979 sediment from Eagle 

Rock Lake with the altered areas shows identical patterns for 

this selected element suite (figs. 22C and 22D).

Comparison of the geochemical data from the post1979 sediment from Eagle Rock Lake with the altered areas 

shows a different trend (figs. 22E and 22F). Concentrations 

of Al2O3, Cu, and Zn are elevated and Na2O and TiO2 are 

lower in post-1979 sediment from Eagle Rock Lake than 

those found in the sediment from the altered scar areas. Allen 

and others (unpub. data, 1999) document the presence of an 

aluminum precipitate in the sediment of Eagle Rock Lake in 

the core sampled near the inlet. All three of these elements 

(Al2O3, Cu, and Zn) show enrichment in the lake sediment 

28  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
1

10

100

1,000

Quartz latite

Pre-caldera andesite

Pre-caldera rhyolite

Amalia Tuff

Fawn Lake 

Eagle Rock Lake

Eagle Rock Lake

1

10

100

1,000

Red River pluton

Rio Hondo pluton

Rio Hondo pluton

Sulfur Gulch pluton

Bear Creek pluton

Peralkaline granite

Fawn Lake 

Eagle Rock Lake

Eagle Rock Lake

#HONDRITENORMALIZEDABUNDANCE #HONDRITENORMALIZEDABUNDANCE

,A #E .D 3M %U 'D $Y %R 9B ,U

,A #E .D 3M %U 'D $Y %R 9B ,U

!

"

Figure 16. Plot of chondrite-normalized REE patterns for volcanic (A) and plutonic (B) rocks from 

the study area. REE data from Eagle Rock Lake are the minimum and maximum values recovered from 

the sediment core (table 1), whereas the REE data from upper Fawn Lake is from the sample with the 

median value for cerium (table 2). REE data for the igneous and volcanic rocks are from Lipman and others (1982) and from Johnson and others (1989). 

Results and Discussion 29
!

#

$

"

Figure 17. Photographs of four fluorite samples from the D 

ore body (samples supplied by Meghan Jackson, Molycorp, 

2003). Analytical data are in table 7. A. Sample QF-2 is a 

coarsely crystalline fluorite sample, possibly from a vein. Green 

mineral is fluorite, white mineral is calcite, and minor amounts 

of molybdenite were visible in the specimen. Calcite and fluorite separates were handpicked and analyzed from this sample. 

B. Sample QF-3 is laminated with more calcite (white) than 

fluorite (green). Minor amounts of molybdenite were visible in 

the specimen. Grain size ranged from 2–4 mm. Calcite and fluorite separates were handpicked and analyzed. C. Sample QF-4 

is a coarse-grained mixture of calcite (white), fluorite (green), 

and molybdenite (gray) with minor amounts of pyrite (brass 

color). Fluorite accumulations range in size from about 2 mm to 

1 cm. Calcite and fluorite separates were handpicked and analyzed. D. Sample QF-5 is a medium- to coarse-grained mixture 

of calcite (white), fluorite (green) and molybdenite (gray) with 

minor amounts of pyrite (brass color). Fluorite accumulations 

range in size from about 2 mm to 1 cm. Sample contains wall 

rock inclusion on the lower right. No mineral separates were 

picked from this sample.

&LUORITE

0HOSPHATE

#ARBONATES

MICRONS

Figure 18. Electron backscatter photomicrograph showing REEbearing phosphate and carbonate minerals identified as small 

inclusions in the fluorite from the D ore body, Questa mine (Sharon 

Diehl, analyst, 2003). 

-60

-50

-40

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-10

0

Depth below sediment intervace, in centimeters

0 100 200 300 400 500 600 700

Cerium, in parts per million

Cerium in sediment, 

 upper Fawn Lake

Cerium in sediment,

 Eagle Rock Lake

0 500 1,000 1,500 2,000 2,500

Fluorine, in parts per million

Fluorine in sediment, 

 Eagle Rock Lake

3,000

Figure 19. Plot of concentration of REE Ce from cores from upper 

Fawn Lake and Eagle Rock Lake and F in sediment core from Eagle 

Rock Lake (table 1) versus depth below the sediment interface. 

Note the coincidence between the F peak and the beginning of 

the Ce peak. The Ce peak decays more slowly than the F peak 

indicating a longer time is required for the REE-bearing minerals 

to weather and release the REE to the environment.

30 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
that may be explained by in-stream addition of metals by low 

pH ground water. Water-quality data (McCleskey and others, 

2003) indicate that dissolved metals enter the Red River at 

several places downstream from Sulfur Gulch. They document 

a large inflow of such ground water downstream of Bear Creek 

(just upstream of site 108, fig. 1). 

Data from the composite sampling of the mine-waste 

dumps around the open pit (Briggs and others, 2003) and from 

premining sediment from talus debris near and downstream of 

the Questa deposit (table 3) were examined as possible sources 

of sediment to account for the observed anomalies in the post1979 sediment data in Eagle Rock Lake (figs. 23C and 23D). 

Comparison of the Na2O and TiO2 concentrations in pre- and 

post-1979 sediment (figs. 23A and 23C) shows that the concentration of these elements decreased in the post-1979 sediment, 

whereas addition of sediment from either source would require 

an increase in these two constituents if they were responsible for 

the changes observed in the post-1979 Eagle Rock Lake geochemistry. Concentrations of MgO and FeO, however, change in 

the right direction for additional contributions from these new 

sources to account for the observed changes, and concentrations 

of Cr and V (figs. 23B and 23D) match well with both the altered 

areas and the mine-waste-pile data. Concentrations of Ba and Sr 

match well only with the mine-waste-pile data implicating them 

as a plausible source of sediment found in the post-1979 core 

interval in Eagle Rock Lake. The most plausible explanation for 

the change in the geochemistry of the fine-grained and suspended 

sediment in Eagle Rock Lake is that these geochemical changes 

can be accounted for by the addition of mill-tailings material to 

the Red River during the mill-tailings pipeline breaks. Whereas the 

change in the sedimentary record has been substantial, the actual 

tonnage of material needed to cause these geochemical changes 

may not be large. Concentrations of Al2O3, Cu, and Zn are higher 

in both the pre- and post-1979 Eagle Rock Lake sediment than 

in either the premining sediment or the mine-waste piles (fig. 23). 

Elevated concentrations of Cu and Zn, which both 

Allen and others (unpub. data, 1999) and URS Corp. (written 

commun., 2004) have shown are related to the chemical 

precipitation of the aluminous gels, are not explained by the 

increased sediment load from these two sources. The argument 

that these are chemical precipitates is also bolstered by 

results from factor analysis of the data presented in URS Corp. 

(written commun., 2004) and by the higher water content of 

the sediment in the upper half of the Eagle Rock Lake core 

(table 1) when compared with the sediment in the upper half 

of the upper Fawn Lake core (table 2).

Table 7. Analyses of fluorite from megabreccia, Questa molybdenum mine area, Red River valley, New Mexico.

Results and Discussion  31
Figure 20. Plots of the concentration of trace elements Ba, Sr, Cr, and V in sediment from the Red River (table 3), sediment from tributary 

streams (table 3), and sediment from the 1976 NURE study (NURE, 1981). Data are plotted from the confluence of the Red River with the Rio 

Grande; downstream is to the left at 0 km, the town of Questa is at about 10 km, and the town of Red River is between 31–32 km. Similar geochemical results were obtained from sediment from the Red River upstream of Fawn Lake by Jackson and others (2003). The concentrations of 

the elements Sr, Cr, and V do not change significantly in sediment of the Red River as it flows past the Questa mine open pit (18–22 km); however, Ba is significantly enriched in Red River sediment downstream of the mine site. These enrichments in Ba are also found in the mine-waste 

composite samples analyzed by Briggs and others (2003).

100

300

500

700

900

1100

1300

1500

Ba concentration (in ppm)

0 5 10 15 20 25 30 35 40

Distance (km)

Tributary sediment, altered 

 scar area, this study 

Red River sediment, this study

NURE sediment, north-flowing

 tributaries

NURE sediment, south-flowing

 tributaries

x Columbine Creek sediment, 

 this study

100

150

200

250

300

350

400

450

500

550

600

Sr concentration (in ppm)

0 5 10 15 20 25 30 35 40

Distance (km)

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

Distance (km)

Cr concentration (in ppm)

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35 40

Distance (km)

V concentration (in ppm)

x

x

x

x

open pit

open pit open pit

open pit

Median concentrations in Fawn Lake and 

 Eagle Rock Lake sediment, this study

32 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
40

60

80

100

120

140

0 5 10 15 20 25 30 35 40

Distance (km)

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35 40

Distance (km)

1

10

100

1000

0 5 10 15 20 25 30 35 40

Distance (km)

10

100

1000

0 5 10 15 20 25 30 35 40

Distance (km)

Ce concentration (in ppm)

Cu concentration (in ppm)

Mo concentration (in ppm)

Zn concentration (in ppm)

Tributary sediment, altered 

 scar area, this study 

Red River sediment, this study

NURE sediment, north-flowing

 tributaries

NURE sediment, south-flowing

 tributaries

x Columbine Creek sediment, 

 this study

x

x

x

x

Median concentrations in Fawn Lake and 

 Eagle Rock Lake sediment, this study

open pit open pit

open pit open pit

Figure 21. Plots of the concentration of trace elements Ce, Mo, Cu, and Zn in sediment from the Red River (table 3), sediment from 

tributary streams (table 3), and sediment from the 1976 NURE study (NURE, 1981). Data are plotted from the confluence of the Red River 

with the Rio Grande; downstream is to the left at 0 km, the town of Questa is at about 10 km, and the town of Red River is between 31 

and 32 km. The concentrations of all four elements are enriched in sediment of the Red River before it reaches the Questa mine open pit 

(18–22 km). Concentrations of these metals in sediment from many of the tributaries are elevated above that of the Red River sediment. 

Results and Discussion  33
Na O K 2 O2 MgO CaO Al O2 3 FeO TiO2 P O2 5 SiO2 Mn V Cr Co Ni Mo

Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent ppm ppm ppm ppm ppm ppm

Pre-1979

Minimum 0.59 1.93 1.23 0.50 14.55 3.60 0.23 0.16 64.19 410 61 53 17 42 25Maximum 1.20 3.61 2.49 1.23 20.78 8.36 0.45 0.55 75.21 2,000 100 95 94 220 360Median 0.88 3.25 2.07 0.92 18.90 6.95 0.33 0.32 66.51 1,150 88 78 38 115 130Mean 0.87 3.20 2.05 0.92 18.51 6.71 0.34 0.31 67.10 1,296 86 76 42 108 131StandardDeviation 0.15 0.36 0.32 0.18 1.73 1.10 0.06 0.09 2.81 536 11 10 19 42 84

Post-1979

Minimum 0.32 1.69 1.08 0.46 18.90 3.47 0.10 0.32 61.74 420 52 39 8 33 16Maximum 0.51 4.46 1.99 0.98 26.45 7.98 0.40 0.48 69.77 2,700 100 79 220 470 96Median 0.42 2.59 1.50 0.76 22.67 5.72 0.18 0.37 66.49 1,950 74 56 77 210 26Mean 0.41 2.83 1.52 0.72 22.02 5.85 0.20 0.39 66.05 1,726 74 57 81 212 36StandardDeviation 0.05 0.84 0.26 0.17 1.51 1.09 0.07 0.05 1.89 679 14 10 51 102 23

Cu Zn Cd Pb As Li Be Sr Ba F La Ce Nd Y

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

Pre-1979

Minimum 58 340 2 77 11 25 4 140 130 1,350 47 77 47 24Maximum 370 1,700 9 180 21 58 9 230 580 2,280 170 290 170 100Median 295 925 4 135 13 47 7 180 175 1,875 78 140 97 55Mean 259 878 5 133 15 46 7 183 190 1,844 92 158 103 55StandardDeviation 100 356 1.8 28 4 8 1.6 23 91 266 35 58 32 18

Post-1979

Minimum 62 240 2 97 11 26 3 110 200 1,820 65 110 55 16Maximum 820 4,600 20 250 20 51 19 370 820 2,840 350 680 490 320Median 500 2,650 11 150 14 40 13 170 715 2,180 130 260 200 140Mean 466 2,387 10 151 15 40 12 191 640 2,219 157 305 231 153StandardDeviation 182 972 4.2 38 2 7 4.1 69 196 257 84 167 119 78

Table 8. Statistics for pre-1979 and post-1979 concentrations of major and trace elements in sediment from Eagle Rock Lake core, lower Red River valley, Taos County, New Mexico.

34  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
Na O K 2 2O MgO CaO Al O2 3 FeO TiO2 P O2 5 SiO2 Mn V Cr

Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent Wt. percent ppm ppm ppm

Minimum 0.50 2.53 1.66 0.54 14.36 4.76 0.27 0.23 48.07 410 78 62

Maximum 1.33 5.54 3.65 6.70 28.34 10.03 0.60 0.55 73.90 880 170 150

Median 0.88 3.61 2.16 1.09 17.76 6.50 0.35 0.33 66.50 560 100 81

Mean 0.88 3.63 2.21 1.60 17.91 6.62 0.35 0.35 66.47 551 101 81

Standard

Deviation 0.20 0.52 0.28 1.24 2.10 0.77 0.05 0.09 3.32 92 13 13

Co Ni Mo Cu Zn Cd Pb As Li Be Sr Ba

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

Minimum 3 20 12 77 140 2 100 10 24 2 180 110

Maximum 72 140 48 410 1,200 8 320 19 50 4 360 770

Median 22 57 24 220 485 4 200 13 33 3 220 220

Mean 23 58 26 218 487 4 205 13 32 3 222 243

Standard

Deviation 13 23 9 66 200 1.2 55 2 3 0.4 32 122

F La Ce Nd Y

ppm ppm ppm ppm ppm

Minimum 1,200 46 72 38 14

Maximum 2,150 94 150 74 45

Median 1,745 58 94 48 24

Mean 1,732 58 92 48 25

Standard

Deviation 220 8 11 5 6

Table 9. Statistics for concentrations of major and trace elements in sediment from upper Fawn Lake core, lower Red River valley, Taos County, New Mexico.

Results and Discussion  35
0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

Upper Fawn Lake sediment

Sediment from altered areas

Concentration, in weight percent

Concentration, in parts per million

0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

Sediment from altered areas

Eagle Rock Lake core,

 pre-1979 sediment

Concentration, in weight percent

Concentration, in parts per million

Na O2 MgO FeO Al O2 3 TiO2

! "

# $

Na O2 MgO FeO Al O2 3 TiO2

Figure 22 (above and facing page). Box plot comparisons. The median value for each element is bracketed by the 25th and 75th percentile 

of the data forming the box, the 10th and 90th percentiles are indicated by the lines above and below the box, and the 5th, 95th, minimum, 

and maximum values are shown as black dots above and below the 10th and 90th percentiles. A. Major element concentrations of Na2O, 

MgO, FeO, Al2O3, and TiO2 from the upper Fawn Lake core (table 2, n=50) with composite samples of sediment from the altered areas (table 

3, side tributary samples and samples from debris fans, 03KVTF2–03KVTF9, and 9 composite samples from outcrop; Briggs and others, 

2003). B. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the upper Fawn Lake core (table 2, n=50) with composite samples of 

sediment from the altered areas (table 3, side tributary samples and samples from debris fans, 03KVTF2–03KVTF9, and 9 composite samples 

from outcrop; Briggs and others, 2003). C. Major element concentrations of Na2O, MgO, FeO, Al2O3, and TiO2 from the pre-1979 interval of 

the Eagle Rock Lake core (table 1, n=24) with composite samples of sediment from the altered areas (table 3, side tributary samples and 

samples from debris fans, 03KVTF2–03KVTF9, and 9 composite samples from outcrop; Briggs and others, 2003). D. Trace element concentrations Ba, Sr, Cr, V, Cu, and Zn from the pre-1979 interval of the Eagle Rock Lake core (table 1, n=24) with composite samples of sediment 

from the altered areas (table 3, side tributary samples and samples from debris fans, 03KVTF2–03KVTF9, and 9 composite samples from 

outcrop; Briggs and others, 2003). 

36 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

� �

Na O2 MgO FeO Al O2 3 TiO2

Concentration, in weight percent

Concentration, in parts per million

Sediment from altered areas

Eagle Rock Lake core,

 post-1979 sediment

Figure 22 (continued). Box plot comparisons. The median value for each element is bracketed by the 25th and 75th percentile of the 

data forming the box, the 10th and 90th percentiles are indicated by the lines above and below the box, and the 5th, 95th, minimum, and 

maximum values are shown as black dots above and below the 10th and 90th percentiles. E. Major element concentrations of Na2O, 

MgO, FeO, Al2O3, and TiO2 from the post-1979 interval of the Eagle Rock Lake core (table 1, n=26) with composite samples of sediment 

from the altered areas (table 3, side tributary samples and samples from debris fans, 03KVTF2–03KVTF9, and 9 composite samples from 

outcrop; Briggs and others, 2003). F. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the post-1979 interval from the Eagle 

Rock Lake core (table 1, n=26) with composite samples of sediment from the altered areas (table 3, side tributary samples and samples 

from debris fans, 03KVTF2–03KVTF9, and 9 composite samples from outcrop; Briggs and others, 2003). 

Summary and Conclusions

Summary and Conclusions

Geochemical data from the study of cores in Fawn 

and Eagle Rock Lakes has provided a continuous record of 

sedimentation from their inception. Accuracy of radiometric 

dating using 137Cs is confirmed by the historical dates provided 

by the New Mexico Dept. of Highways on the inception of the 

lakes (URS Corp., written commun., 2004). The geochemical 

data from upper Fawn Lake provide a reliable and continuous 

record of the geochemical baseline concentrations during the 

period from 1961 to 2002. The sedimentary record from the 

Eagle Rock Lake core indicates very similar sedimentary history from its inception until 1979. Concentrations of Mo, Co, 

Ni, Cu, and Zn increased during the period from 1963 to 1967, 

which we interpret as the period when the site for the open pit 

at the Questa mine was being prepared and work on the open 

pit began. Other geochemical anomalies shown by REE and 

fluorine concentrations in the sediment core likely correlate 

with breaks in the pipeline that transports mill tailings to the 

repository west of the town of Questa. REE are present in 

carbonate minerals in the magmatic hydrothermal breccia in the 

ore deposit. Enrichment of the REE by accelerated weathering 

of the hydrothermal breccia phase from spilled tailings is 

required to explain the REE anomalies in sediment from 

Eagle Rock Lake. The sedimentary record of Eagle Rock 

Lake changed substantially in 1979 with large increases in 

concentration for many major elements and metals in sediment in Eagle Rock Lake. This change in source material 

was dramatic; it has resulted in a change in the source of 

sediment supplied by the Red River to Eagle Rock Lake for 

more than two decades. We have shown that the addition of 

sediment from the altered areas upstream of the mine and 

the mine-waste piles at the Questa mine are not sufficient to 

explain all of the observed changes in sediment geochemistry 

between the pre- and post-1979 break defined by the 

geochemical data in Eagle Rock Lake (figs. 7–12). Although 

both mine-waste and premining background sediment from 

altered areas around the Questa porphyry Mo deposit have 

the appropriate compositions to be potential sources of this 

new sediment, existing data are not sufficient to implicate or 

refute either one. Given the very large disturbance represented by the mine-waste piles at the open-pit site, erosion 

of the mine wastes must be considered a plausible source of 

this sediment despite the presence of large berms built by 

Molycorp to prevent their erosion. 

  37
0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

Composites of mine-waste piles, Questa mine

Concentration, in weight percent Concentration, in parts per million

Na O2 MgO FeO Al O2 3 TiO2

Eagle Rock Lake core, post-1979 sediment

Premining background sediment

!

"

0.1

1.0

10.0

10

100

1,000

Ba Sr Cr V Cu Zn

Concentration, in parts per million Concentration, in weight percent

Na O2 MgO FeO Al O2 3 TiO2

#

$

Composites of mine-waste piles, Questa mine

Eagle Rock Lake core, pre-1979 sediment

Premining background sediment

Figure 23. Box plot comparisons. The median value for each element is bracketed by the 25th and 75th percentile of the data forming 

the box, the 10th and 90th percentiles are indicated by the lines above and below the box, and the 5th, 95th, minimum, and maximum 

values are shown as black dots above and below the 10th and 90th percentiles. A. Major element concentrations of Na2O, MgO, FeO, 

Al2O3, and TiO2 from premining sediment (table 3, multiple composite samples from 11 sites) with lake sediment from the pre-1979 interval, Eagle Rock Lake core (table 1, n=24) and mine-waste piles (composite samples from 5 different mine-waste piles at the Questa mine 

site; Briggs and others, 2003). B. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from the premining sediment (table 3, multiple 

composite samples from 11 sites) with lake sediment from the pre-1979 interval, Eagle Rock Lake core (table 1, n=24) and mine-waste 

piles (composite samples from 5 different mine-waste piles at the Questa mine site; Briggs and others, 2003). C. Major element concentrations of Na2

O, MgO, FeO, Al2O3, and TiO2 from premining sediment (table 3, multiple composite samples from 11 sites) with lake sediment from the post-1979 interval, Eagle Rock Lake core (table 1, n=26) and mine-waste piles (composite samples from 5 different minewaste piles at the Questa mine site; Briggs and others, 2003). D. Trace element concentrations of Ba, Sr, Cr, V, Cu, and Zn from premining 

sediment (table 3, multiple composite samples from 11 sites) with lake sediment from the post-1979 interval, Eagle Rock Lake core (table 

1, n=26) and mine-waste piles (composite samples from 5 different mine-waste piles at the Questa mine site; Briggs and others, 2003). 

38  Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
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40 Lake-Sediment Geochemical Record from 1960 to 2002, Eagle Rock and Fawn Lakes, Taos County, New Mexico
 

Manuscript approved for publication, January 12, 2005

Photocomposition and design by Adam Redmon and Amber Hess

Edited by Tom Judkins