Compositional Changes Induced by 

Hydrothermaf Alteration at the 

Red MouQtaio Alunite., Deposit, 

Lake City, Colorado 
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Compositional Changes Induced by 

Hydrothermal Alteration at the 

Red Mountain Alunite Deposit, 

Lake City, Colorado 

By DANA J. BOVE and KEN HON 

Sample analysis shows chemical changes in rocks 

from hydrothermal alteration 

U.S. GEOLOGICAL SURVEY BULLETIN 1936 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-In-Publication Data 

Bove, Dana. 

Compositional changes induced by hydrothermal alteration at the Red 

Mountain alunite deposit, Lake City, Colorado I by Dana J. Bove and 

Ken Hon. 

p. cm.-(U.S. Geological Survey bulletin; 1936) 

Includes bibliographical references (p. ). 

Supt. of Docs. no.: I 19.3:1936 

1. Hydrothermal alteration-Colorado-Lake City Region. 

2. Alunite-Colorado-Lake City Region. 3. GeochemistryColorado-Lake City Region. I. Hon, Ken. II. Title. Ill. Series. 

QE75.B9 no. 1936 

[QE390.5] 

557.3 s-dc20 

[549] 90-3629 

CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Methods of analysis 4 

Adjustments and calculations on data 6 

Discussion of results 13 

Alunite alteration zone 14 

Argillic alteration assemblage 17 

Potassic alteration assemblage 18 

Silicification zone 19 

Marginal alteration assemblage 20 

Summary 20 

References cited 20 

FIGURES 

1. Map showing location and generalized geology of the 

2. 

3. 

4. 

5-14. 

Red Mountain Area 2 

Map showing drill-hole localities and topography 3 

Cross section of hydrothermally altered area 4 

Map showing hydrothermally altered area S 

Graphs showing: 

5. Average gains and losses from alunite alteration assemblage 

6. Average gains and losses from argillic alteration assemblage 

16 

16 

7. Average gains and losses from potassic alteration assemblage 

8. Average gains and losses from silicic alteration assemblage 

17 

17 

9. Average gains and losses from marginal alteration assemblage 18 

10. Average relative percent gains and losses from alunite alteration 

assemblage 18 

11. Average relative percent gains and losses from argillic alteration 

assemblage 18 

12. Average relative percent gains and losses from potassic alteration 

assemblage 19 

13. Average relative percent gains and losses from silicic alteration 

assemblage 19 

14. Average relative percent gains and losses from marginal alteration 

assemblage 19 

TABLES 

1. Original geochemical data for samples analyzed for the mass 

balance study 7 

2. Adjusted geochemical data for samples 10 

3. Geochemical data showing gains and losses from major 

alteration zones 13 

Contents Ill 

Compositional Changes Induced by 

Hydrothermal Alteration at the 

Red Mountain Alunite Deposit, 

Lake City, Colorado 

By Dana J. Bove and Ken Han 

Abstract 

The Red Mountain alunite deposit, one of the largest in 

the United States (more than 70 million metric tons of alunite), 

formed on the eastern margin of the 23.1-Ma Lake City 

caldera, in southwestern Colorado. Several texturally and 

temporally distinct high-potassium dacite intrusions cut highpotassium dacite lavas that were erupted along the eastern 

ring fracture of the Lake City caldera after it collapsed. The 

majority of the dacite intrusions and lavas on Red Mountain 

were affected by hydrothermal brecciation and strong hydrothermal alteration, also dated at 23.1 Ma. 

Alunitized rock occurs in two large, roughly conical 

centers with roots extending as much as 820ft (feet) beneath 

the ground surface. The alunitized rock grades outward into 

argillized and weakly altered high-potassium dacitic rock and 

grades downward through argillic, sericitic, silicic, and potassic zones predominantly in dacite intrusions and hydrothermally brecciated rock. 

Thirty-five altered and fresh rock samples from both the 

dacite intrusions and dacite lavas were analyzed for 10 major 

elements, 6 trace elements, sulfur, H20+, H20-, and C02, in 

order to evaluate the chemical changes that took place in the 

major altered zones during hydrothermal alteration. Massbalance calculations indicate that large quantities of sulfur 

were introduced by the hydrothermal system. Sulfur is 

present primarily as S03 within alunitized rocks and as S2 

within pyrite-bearing potassic and argillic altered rocks. Al20 3 

and ~0 were removed during alunitization, and P04 and 

strontium were enriched due to coupled substitution of P04 afor S042

- and Sr + forK+ in the alunite structure. Water was 

added to all of the altered zones as hydrous alteration 

minerals. Both potassium and rubidium were added to the 

potassic zone, and a slight gain in AI203 was observed in 

kaolinite-altered rocks. An average gain of 15 weight percent 

Si02 took place in the zone of silicification. Zirconium, 

Manuscript approved for publication, March 9, 1990. 

niobium, and Ti02 remained relatively immobile in most of 

the alteration assemblages. 

INTRODUCTION 

Red Mountain, on the eastern margin of the 23.1-

Ma Lake City caldera (Hon, 1987), Lake City, Colo. 

(fig. 1 ), hosts one of the largest replacement alunite 

deposits in the western United States (more than 70 

million metric tons of alunite). Chemical analyses of 35 

samples selected from both altered and fresh rocks from 

Red Mountain were analyzed to evaluate chemical 

changes within the major alteration assemblages. This 

paper briefly summarizes the geology of Red Mountain, 

presents the mass-balance data, and discusses the implications of these data with respect to mineralogic changes 

within the alteration assemblages. 

Data from a 2,777-ft-deep drill hole and three 

relatively shallow holes (figs. 2, 3) indicate that the 

23.1-Ma alunite deposit (Mehnert and others, 1979) is 

the upper level of a weakly mineralized, moderately high 

fluorine "porphyry-type system" characterized by multiple dacite intrusions, minor molybdenite, and strong 

potassic alteration (Bove, 1988; Bove and others, 1988). 

Several temporally and texturally distinct highpotassium dacite intrusions (dacite porphyry of Red 

Mountain) cut older high-potassium dacite lavas (dacite 

lavas of Grassy Mountain) on Red Mountain that 

erupted after collapse of the Lake City caldera. Surface 

exposures of several irregular dacite porphyry intrusions 

are interpreted to be high-level apophyses either 

emplaced prior to, or were possibly fed from, a larger 

stock intercepted by a drill hole about 2,460 ft beneath 

the present ground surface (Bove, 1988; Bove and others, 

1988). 

Introduction 
COLORADO 

• Maparea 

5 MILES 

I 

I 

8 KILOMETERS 

EXPlANATION 

Dacite porphyry dikes; dacite 

porphyry of Red Mountain (Miocene) 

Dacite porphyry Intrusions; dacHe porphyry 

of Red Mountain (Miocene) 

Post-collapse dacite lavas; dacite lavas of 

Grassy Mountain (Miocene) 

Sunshine Peak Tuff (Miocene) 

and resurgent intrusions 

Figure 1. Generalized geology of the Red Mountain area, Lake City, Colo. 

Alunitized rock occurs in two large, nearly conical 

centers whose roots extend as much as 820ft below the 

surface (fig. 3) at Red Mountain. The alunite approaches 

end-member potassic composition. The alunite alteration assemblage is defined by the presence of alunite, 

quartz, and pyrite, with minor amounts of topaz, fluorite, 

pyrophyllite, and gypsum. Paragenetic relations within 

alunitized rock are complex; multiple stages of alunite 

include (1) early fine-grained alunite replacement of 

feldspar phenocrysts and quartz-pyrite-alunite alteration 

of the groundmass, (2) irregular alunite flooding of 

both groundmass and previously altered phenocrysts, 

(3) fine-grained, fracture-controlled alunite veinlets, and 

( 4) localized veinlets of medium to coarse-grained translucent alunite. 

Alunitized rocks grade outward into argillized (kaolinite predominant, plus sericite1

, pyrite and (or) minor 

smectite) and marginally altered rocks2 and grade 

downward through argillic (kaolinite predominant and 

(or) sericite and (or) minor smectite), sericitic (sericitepyrite predominant and (or) kaolinite and (or) minor 

smectite) and potassic (secondary potassium feldspar 

and biotite) altered zones (figs. 3, 4). The top part of the 

potassic alteration zone contains a silicification zone 

1

A term referring to a fine-grained (typically less than 10 

micrometers), highly birefringent micaceous mineral. X-ray diffraction, 

electron microprobe, and geochemical data (Bove, 1988) indicate that 

sericite at Red Mountain is very fine grained high-magnesium 

muscovite or phengite (Srodon and Eberl, 1984). 2

Rocks distinguished by the presence of smectite and sericite 

and containing relatively unaltered phenocrysts of sanidine and biotite. 

Some local variants of this assemblage resemble a typical propylitic 

assemblage. Marginal alteration occurs throughout most of the rocks 

on the periphery of Red Mountain. 

2 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
1on2·3o" 1 07"20" 

38°00' ~::::----,;-;c--.-;,--~~~-,...,.-~,----~~~-,---..,.----,~--,-~....,......,~~--,--,-,..---,,.,---~"'~~-,--;:-:-;-,-----,-,-.,------, 

R5W R4W 

1 MILE 

1 KILOMETER 

Figure 2. Drill-hole localities and topography, Red Mountain area. Dots are drill-hole localities with hole 

numbers. 

characterized in drill core by intervals of microcrystalline 

quartz flooding and later stockwork veinlets of microcrystalline quartz. This drill core shows that argillic 

alteration overprinted earlier sericitic alteration, and the 

potassic zone was superimposed by sericitic and argillic 

alteration near the top of the zone (Bove, 1988; Bove and 

others, 1988) (fig. 3). Although the lateral and vertical 

transition from alunite altered rock into argillic and (or) 

sericitic altered rock was not directly observed, geologic 

data, which include potassium-argon dates on alunite and 

the fresh dacite lavas (Mehnert and others, 1973, 1979; 

Hon, 1987), detailed paragenetic studies, and stable 

isotope studies (Bove, 1988; Bove and others, 1988), 

indicate that the timing of alunitization was closely 

associated with stages of potassic and sericitic alteration. 

Hydrogen-, oxygen-, and sulfur-isotope studies 

constrain the origin of alunite and the source of the fluids 

and sulfur (Bove, 1988; Bove and others, 1988). Each 

stage of alunite has distinctly different isotopic compositions, as do different generations of pyrite. Isotopic data 

suggest that sulfur in stages 1 and 2 alunite was derived 

from sulfate having a magmatic source at temperatures 

of350 °C±25 oc and 200 °C±25 °C, respectively. Stage 3 

and 4 alunite was formed from the local oxidation of H2S 

from the magmatically derived hydrothermal plume as 

atmospheric oxygen was drawn into the upper levels of 

the late-stage hydrothermal system. 

From detailed mineralogic, petrographic, and 

stable-isotope studies, alunite at Red Mountain was 

proposed (Bove and others, 1988) to have formed from a 

bouyant magmatic vapor plume that rose above the level 

of the meteoric-water-dominated fringe of a weakly 

mineralized molybdenum -porphyry hydrothermal system 

Introduction 3 
A------------------------------------------------------------A' 

ELEVATION 

IN FEET 

13,000 

12,500 

12,000 

11,500 

ARGILLIC ALTERATION 

COMPLETELY OVERPRINTS 

11,000 POTASSIC ALTERATION 

10,500 

10,000 

IN THIS AREA 

L____j 

500 FEET 

ARGILLIC ALTERATION 

I I 

(KAOLINITE PREDOMINANT) 

Hole 

LC-1 

(SERICITE PREDOMINANT) 

POTASSIC ITERATION 

? 

Figure 3. Cross section of hydrothermally altered area at Red Mountain, Lake City caldera, showing the profile 

of Red Mountain and the lower 12,601-ft peak. Cross section line A-A' is shown in figure 4. 

Sulfur-isotope studies of the successive stages of alunite 

indicate a respective decrease in the oxidation state of the 

underlying magmas. 

METHODS OF ANALYSIS 

Thirty-five samples from the two predominant rock 

types at Red Mountain-the dacite lavas of Grassy 

Mountain and the dacite porphyry of Red Mountain 

(fig. 1)-were selected for a mass-balance study. Samples 

were analyzed for 10 major elements, 6 trace elements, 

sulfur, H20+, H20-, and C02. Major elements were 

analyzed for by wavelength-dispersive X-ray fluorescence 

(Taggart and others, 1987). Rubidium, strontium, zirconium, yttrium, niobium, and molybdenum were analyzed 

for by utilizing energy-dispersive X-ray fluorescence with 

an accuracy of + 5-10 percent (Ludington, 1981). Total 

sulfur was determined using a Leco SR132 automated S 

analyser. One split (0.25 gram) of a sample was combusted with infrared detection of evolved S02 (Jackson 

and others, 1987). Total H20 was calculated by combustion at 950 oc with Karl Fisher titration (Jackson and 

others, 1987) of H20; H20- (moisture) was determined 

by the same procedure at 110 °C, and H20+ was 

determined by difference (Jackson and others, 1987). 

Determination of carbonate carbon was by coulometric 

titration of acid-evolved C02 (Jackson and others, 1987). 

In order to compare actual gains and losses of 

elements during alteration, the bulk rock density for each 

sample was determined by dividing the weight of the dry 

sample by its volume. As a result, the chemical compositions of the altered samples could be recalculated 

and compared to the equivalent fresh rock on the basis of 

weight per unit volume of rock (Gresens, 1966). Massbalance calculations were made assuming constant 

volume, as indicated by the absence of phenocryst 

4 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
37° 

57' 

30" 

0 1 KILOMETER 

EXPLANATION 

---- Contact 

Quartz-alunite alteration 

Intermediate argillic alteration 

~ ~ Weak argillic 

alteration 

- Marginal alteration 

1 MILE 

Figure 4. Plan view of hydrothermally altered area at Red Mountain. Cross section along line A-A' is 

shown in figure 3. Queried where extent of alteration is uncertain. Topographic base from U.S. Geological 

Survey Lake San Cristobal, scale 1 :24,000. Contour interval 200 ft. 

Methods of Analysis 5 
deformation, similarity in the volume percent of phenocrysts in fresh and altered rocks, and the preservation of 

the original rock texture. 

Only samples of the dacite porphyry (rock unit 

Tdrp, tables 1-3) and the dacite lavas (unit Tldg) were 

included in the mass-balance study. This decision was 

made because of the abundance of these units both at the 

surface and in drill cores, the relative ease of differentiation of even the most altered of these rocks, and the 

availability of fresh samples of these rocks. Five fresh 

samples of the dacite lavas (1 Tldg, 2Tldg, 3Tldg, 3aTldg, 

4Tldg, tables 1 and 2) were collected from outcrops 

around the periphery of Red Mountain, and two fresh 

samples of dacite porphyry (1 Tdrp and 2Tdrp, tables 1 

and 2) were collected from dikes on the northeast and 

southeast flanks of Red Mountain (fig. 1). Two samples 

were collected from the marginal alteration assemblage 

(1TldgM and 2TldgM, tables 1 and 2), and two were 

collected from the quartz alunite zone (1aTldgA and 

1bTldgA). All other samples were collected from drill 

holes LC1 through LC4 (figs. 2, 3). All of the fresh dacite 

lavas (unit Tldg, table 1) analyzed have essentially the 

same composition. Therefore, the most pristine of these 

samples, a vitrophyre, sample 3Tldg, was used as the 

reference fresh-rock sample to which altered samples of 

the dacite lavas were compared. Only two samples of 

fresh dacite porphyry (unit Tdrp) were analyzed. Both 

analyses were also quite similar and, having no geologic 

reason to prefer one sample over the other, we used the 

average of the two analyses as a reference to assess 

changes within altered dacite porphyry samples. 

The increase or decrease of each component of the 

altered rocks compared with that of the parent rock 

(gains and losses), and the average relative percent of 

gain-loss (weight gain or loss of component (x) divided by 

the weight-percent component (y) of fresh rock) are 

illustrated in figures 5-14 and in table 3. Components are 

considered to be relatively immobile if the percent of a 

component gained or lost is within the range of variation 

of the fresh rock (table 2) or within the limits of experimental error of the related analytical technique. 

The original geochemical data were adjusted 

during this study. Several nonstandard components such 

as FeS2, S03, total sulfur (S TOT), and total iron (Fe 

TOT) were calculated (table 2). The derivation and 

meaning of these components, and all other manipulations and adjustments that were made to the samples, 

are documented below. All calculations are presented in 

the sequence in which they were made. 

Adjustments and Calculations on Data 

1. Petrographic data were used to characterize 

the mineralogy of the samples, allowing appropriate 

partitioning of sulfur and iron. 

Sulfur in all alunitized samples devoid of pyrite was 

calculated as S03. Iron, which occurs predominantly in 

these samples as hematite, was calculated as Fe203. 

Alunite-bearing unoxidized samples containing 

pyrite were treated as follows: Reduced sulfur was determined by a chromic ion treatment (Zhabina and Volkov, 

1978; Westgate and Anderson, 1982) with all reduced 

sulfur calculated as FeS2. Any remaining sulfur was 

calculated as S03. Excess iron was calculated as FeO. 

Pyritized (alunite-free) samples were recalculated 

in the following manner: Initially, all sulfur was considered to be contained in FeS2. If excess FeO was 

present (moles FeO more than one-half the moles of 

sulfur), the excess FeO was assigned to FeO or Fe203 

depending on petrographic observations. Conversely, if 

one-half the moles of sulfur exceeded the moles of FeO, 

FeS2 was calculated on the basis of analyzed FeO 

content, and excess sulfur was reported as sulfur. 

Therefore, all sulfur shown in tables 2 and 3 represents 

excess sulfur. 

2. FeS2-adjusted analyses were retotaled and normalized to totals before FeS2 adjustment (original totals), 

correcting for a loss of one oxygen molecule during 

conversion from FeO to FeS2. All analyses were normalized to 100 percent after the above adjustments were 

made. 

3. Fe TOT (tables 2, 3) is total iron expressed as 

elemental iron and equals 0.699 x Fe203 + 0.777 x FeO 

+0.465 x FeS2. S TOT (tables 2, 3) is total sulfur 

expressed as elemental sulfur and equals S03 X 0.40 

+ FeS2 x 0.27 + S (excess sulfur). 

4. Adjustments were made to fresh-rock analyses as 

follows: H20+ (probably present in hydrated glass), 

Hao- (moisture), and C02 were subtracted from the 

fresh-rock analyses, as none of these components are 

present within the primary minerals. H20+ in biotite is 

negligible and therefore was not considered (Bove, 

1988). 

First, H2 0+ and H20- were subtracted from the 

analyses of fresh rock samples, and analyses were normalized to 100 percent. The fresh-rock bulk densities 

were subsequently readjusted due to the loss of H2 0 + 

and H20- according to the following equation: 

Twt. org Twt. DH o D xD - X 2 adj = Twt.-wt.H20 Twt.-wt.H20 

where 

Dadj = bulk density adjusted, 

Twt. =total weight of sample, 

norg =original bulk density, 

wt.H20 =weight percent total H20 in sample, 

DH2o =density of H20 (1.00 gram per cubic 

centimeter). 

6 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
T~ble 1. Original geochemical data for samples analyzed for the mass balance study, Red Mountain alunite deposit, Lake 

C1ty, Colorado 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Rb, Sr, Zr, Y, Nb, and Mo are reported in parts per million; density is 

reported in grams/cm8

; remainder of analyses are in weight percent] 

Sample No. Elevation 

(feet) 

Si02 Al2o3 Fe2o3 FeO MgO CaO Na2o K20 

1 Tldg1 NA 60.60 16.90 2.43 1.51 1.90 3.00 3.60 s.oo 

2Tldg1 NA 63.50 15.50 2.48 1.89 1.78 2.23 3.36 5.03 

3aTldy1 NA 62.60 15.80 2.64 1.78 1.46 3.08 3.94 4.74 

3Tldg NA 63.00 15.90 2.44 .92 1.19 2.66 3.13 5.24 

4Tldg1 NA 63.00 16.10 2.54 1.87 1.29 2.74 3.92 5.23 

1Tdrp2 NA 62.20 15.10 2.47 1.70 1.65 3.04 3.34 4.40 

2Tdrp2 NA 60.70 15.50 3.84 1.89 2.23 2.46 4.12 4.66 

1TldgM NA 66.20 15.20 1.93 .86 .83 .79 2.68 5.94 

2TldgM NA 67.10 14.80 2.37 2.06 .86 .63 2.91 5.56 

1aTldgA NA 57.80 15.10 .36 0 .10 .10 .15 4.09 

1bTldgA NA 60.01 14.00 .32 0 .10 .17 .63 3.07 

1TldgA 12,703 61.80 15.70 .18 0 .10 .10 .25 2.97 

2TldgA 12,543 63.70 12.10 .99 0 .10 .02 .20 3.37 

3TldgA 12,472 35.90 22.70 .64 0 .10 .os .42 6.02 

4TldgA 12,339 55.80 12.80 7.03 0 .10 .02 .34 3.32 

STldgA 12,318 54.70 14.50 1.86 0 .10 .10 .48 3.87 

6TldgA3 12,168 so.oo 15.60 3.56 .10 .08 .ss 3.84 

7TldgA 12' 140 67.60 5.94 10.39 0 .10 .47 .15 1.62 

8TldgA3 12,013 62. 50_ 12.90 4.68 0 .10 .15 .15 1.29 

lTdrpC 12,000 61.10 18.60 0 4.26 .33 .08 .67 4.22 

2TdrpC 11,862 64.10 16.00 0 4.24 .63 .27 2.32 5.26 

3TdrpC 11 '190 60.60 20.40 0 4.71 .34 .02 .15 .84 

4Tdrpc 11,140 60.10 21.80 0 3.64 .38 .02 .15 1.39 

STdrpC 11 '106 67.70 16.60 0 3.52 .so .04 .15 1.99 

6TdrpC 11,090 59.40 24.50 0 1.63 .41 .04 .24 1.22 

1TdrpK 10,494 63.10 15.10 0 3.90 1.49 .60 1.88 6.93 

2TdrpK 10,450 62.40 13.10 0 3.41 5.25 .06 .95 8.96 

3~rpK 10,430 66.10 14.50 0 3.58 .19 .10 1.04 8.29 

4T rpK 10,210 66.80 13.50 0 1.40 2.68 .40 .95 9.77 

STdrpK 10,205 61.10 15.40 0 3.32 2.34 .59 1.27 10.60 

6TdrpK 10,180 63.30 13.20 0 5.17 1.50 .44 1.08 9.01 

7TdrpK 9,874 58.90 16.70 2.55 .87 2.93 .41 1.65 9.78 

8TdrpK 9,774 62.30 14.50 2.31 2.11 1.90 1.94 2.70 7.99 

1TdrpS NA 89.40 1.81 0 3.87 .12 .08 .15 .34 

2TdrpS NA 73.10 11.50 0 2.39 1.44 .09 .79 5.98 

1unaltered dacite lavas of Grassy Mountain. 

2unaltered dacite porphyry. 

3High totals are related to high sulfur determinations. Replicate analyses yielded similar 

high values. However, due to the large variations in chemical analyses for samples from the 

alunite zone, these samples do not significantly affect the average sample analyses and therefore 

were retained in the data set. 

Methods of Analysis 7 
Table 1. Original geochemical data for samples analyzed for the mass balance study, Red Mountain alunite deposit, Lake 

City, Colorado-Continued 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Rb, Sr, Zr, Y, Nb, and Mo are reported in parts per million; density is 

reported in grams/cm3; remainder of analyses are in weight percent] 

Sample No. Elevation H20 Tio2 P2o5 

(feet) 

MnO co2 so3 S· H2o- Total 

1Tldg NA 1.30 0.93 0.51 0.07 0.52 0 0 1. 70 99.97 

2Tldg NA 1.03 .98 .30 .08 .28 0 0 .96 99.40 

3aTldg NA 1.26 1.02 .33 .11 .01 0 0 .54 99.31 

3Tldg NA 2.49 .94 .32 .06 .01 0 0 .14 98.43 

4Tldg NA .64 1.04 .29 .09 .66 0 0 .16 99.57 

1Tdrp NA 1.28 .97 .37 .09 .91 0 0 .63 98.15 

2Tdrp NA 1.43 1.26 .43 .14 .23 0 0 .64 99.53 

1TldgM NA 1.34 .99 .18 .02 0 0 0 1.48 98.44 

2TldgM NA 1.31 .87 .30 .10 0 0 0 .37 99.24 

1aTldgA NA 5.31 .75 .28 .02 .01 18.33 0 .28 102.68 

1bTldgA NA 5.23 .78 .37 .02 .01 17.70 0 .15 102.56 

1TldgA 12,703 4.42 .99 .39 .02 0 12.38 0 .06 99.36 

2TldgA 12,543 4.80 1.00 .12 .02 0 14.48 0 .08 100.98 

3TldgA 12,472 8.13 .87 .48 .02 0 25.28 0 .08 100.69 

4TldgA 12,339 4.87 1.12 .38 .02 0 15.30 0 .14 101.24 

5TldgA 12,318 5.81 .92 .39 .02 0 17.89 0 .07 100.71 

6TldgA 12,168 5.70 .63 .38 .02 0 21.80 2.90 .17 3_105. 33 

7TldgA 12' 140 3.74 2.35 1.00 .02 0 6.48 0 .23 100.09 

8TldgA 12,013 5.36 1.28 .39 .02 0 15.77 0 1.45 3106.04 

1TdrpC 12,000 4.46 1.01 .18 .02 0 0 4.21 .56 99.70 

2TdrpC 11,862 1.70 .88 .20 .02 0 0 3.68 .27 99.57 

3TdrpC 11' 190 6.71 .97 .22 .02 0 0 4.66 .34 99.98 

4Tdrpc 11 '140 6.98 .87 .28 .02 0 0 3.76 .20 99.59 

5TdrpC 11' 106 4.60 .96 .18 .02 0 0 3.26 .27 99.79 

6TdrpC 11,090 7.88 .9 5 .21 .02 0 0 1.89 .21 98.60 

1TdrpK 10,494 1.44 .85 .32 .02 0 0 3.18 .52 99.33 

2TdrpK 10,450 .63 .77 .20 .02 .82 0 2.78 .26 99.61 

3TdrpK 10,430 1.37 .82 .22 .02 0 0 3.39 .26 99.88 

4TdrpK 10,210 .52 .77 .29 .03 0 0 .90 .06 98.07 

5TdrpK 10,205 .64 .93 .40 .02 0 0 2.77 .08 99.46 

6TdrpK 10,180 .80 .84 .32 .14 0 0 2.38 .26 98.44 

7TdrpK 9,874 1.54 1.05 .25 .07 .39 0 .85 .67 98.61 

8TdrpK 9,774 .47 .81 .33 .30 .97 0 .45 .17 99.25 

1TdrpS NA .52 .87 .23 .02 .01 0 3.22 .06 100.70 

2TdrpS NA 1.54 .87 .20 .02 .02 0 1.63 .26 99.83 

After bulk densities were adjusted for H2 0 sub- where 

traction, C02 was removed from the H20-adjusted Dadj =bulk density adjusted, 

samples, and analyses were normalized to 100 percent. Twt. =total weight of sample (100 grams), 

Bulk densities were then recalculated to reflect C02 norg =original bulk density' 

subtraction by using an equation similar to that above: wt.C02 =weight percent C02 in sample, 

Dc02 =density of C02 (2.07 grams per cubic centiTwt. norg Twt. 

meter). 

Dadj X - xnco2 5. Adjustments were made to altered rock analyses as 

Twt.-wt.C02 Twt.-wt.C02 follows: H20- and C02 were removed from the analyses 

8 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
Table 1. Original geochemical data for samples analyzed for the mass balance study, Red Mountain alunite deposit, Lake 

City, Colorado-Continued 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Rb, Sr, Zr, Y, Nb, and Mo are reported in parts per million; density is 

reported in grams/cm5; remainder of analyses are in weight percent] 

Sample No. Elevation Rb Sr 

(feet) 

1Tldg NA 148 491 

2Tldg NA 165 406 

3aTldg NA 190 485 

3Tldg NA 209 497 

4Tldg NA 157 494 

1Tdrp NA 147 490 

2Tdrp NA 142 543 

1TldgM NA 187 337 

2TldgM NA 179 335 

1aTldgA NA 10 545 

1bTldgA NA 0 0 

1TldgA 12,703 0 706 

2TldgA 12,543 0 273 

3TldgA 12,472 7 1,740 

4TldgA 12,339 0 623 

5TldgA 12,318 0 679 

6TldgA 12,168 9 590 

7TldgA 12,140 0 1,270 

8TldgA 12,013 0 553 

1TdrpC 12,000 133 313 

2TdrpC 11,862 207 388 

3TdrpC 11, 190 48 193 

4TdrpC 11,140 65 452 

5TdrpC 11,106 104 276 

6TdrpC 11,090 70 305 

1TdrpK 10,494 283 219 

2TdrpK 10,450 464 235 

3TdrpK 10,430 283 408 

4TdrpK 10,210 398 225 

5TdrpK 10,205 408 203 

6TdrpK 10,180 307 234 

7TdrpK 9,874 435 330 

8TdrpK 9,774 305 371 

1TdrpS 10,350 5 371 

2TdrpS 10,115 208 228 

of the altered samples, the analyses were normalized to 

100 percent, and the bulk densities were adjusted, as 

described in step 4. H20 + was not subtracted from these 

samples because it is a structural component of many of 

the alteration minerals. 

6. A volume factor was used to allow comparison of 

fresh and altered samples. Assuming constant volume 

(discussed previously), this factor indicates proportions 

Zr y Nb Mo Density 

310 27 28 0 2.46 

265 25 35 0 2.50 

315 42 38 0 2.46 

271 56 32 0 2.46 

352 28 41 0 2.62 

278 32 33 0 2.56 

288 27 36 0 2.55 

287 16 36 0 2.12 

299 27 37 0 2.21 

262 16 33 1 2.59 

0 0 0 0 0 

313 20 37 0 2.47 

338 0 34 0 2.49 

295 0 37 0 2.67 

317 6 38 0 2.27 

265 16 33 0 2.65 

252 12 0 0 2.67 

369 43 55 0 1.70 

436 62 54 0 1.72 

301 26 40 0 2.34 

305 46 37 5 2.41 

358 30 37 76 2.09 

289 41 37 103 2.18 

309 44 44 130 2.43 

307 43 35 17 1.97 

303 31 39 134 2.55 

231 39 23 260 2.47 

293 62 42 157 2.37 

263 18 36 645 2.43 

315 24 41 146 2.51 

263 22 35 112 2.44 

369 19 43 73 2.50 

290 30 35 47 2.63 

303 11 42 238 2.55 

267 38 36 87 2.48 

of material lost during alteration and is defined as the 

density of the altered sample divided by the density of the 

fresh sample. Chemical components of the altered rock 

were multiplied by this volume factor (V) to normalize 

for the loss or gain of mass, thus allowing the fresh and 

altered samples to be compared directly. For example, it 

would be erroneous to compare weight percent Si02 in 

100 grams of an altered, relatively low density sample to 

Methods of Analysis 9 
Table 2. Adjusted geochemical data for samples from the Red Mountain alunite deposit, Lake City, Colorado 

[Elevation values are for samples obtained from drill core. Adjustments to data are described in the section on "Methods" in the text. NA, not 

applicable; Std, one standard deviation; Avg, average of number of samples shown. Letters at end of sample numbers indicate: A, alunite zone; 

Sample No. Elevation SiOz Al 2o3 Fe2o3 FeO Fes2 Fe TOT MgO GaO 

(feet) 

1Tldg1 NA 62.83 17.52 2.52 1.57 0 2.98 1.97 3.11 

2Tldg 1 NA 65.38 15.96 2.55 1.95 0 3.30 1.83 2.30 

3aTldT1 NA 64.21 16.21 2. 71 1.83 0 3.31 1.50 3.16 

3Tldg NA 65.76 16.60 2.55 .96 0 2.53 1.24 2.78 

4Tldg 1 NA 64.21 16.41 2.59 1.91 0 3.29 1.31 2.79 

Avg-Tldg NA 64.48 16.54 2.58 1.64 0 2.92 1.57 2.83 

Std NA 1.03 .54 .07 .37 0 .39 .29 .31 

1Tdrp2 NA 65.25 15.84 2.59 1.78 0 3.20 1.73 3.19 

2Tdrp2 NA 62.45 15.95 3.91 1.94 0 4.24 2.29 2.53 

Avg-Tdrp NA 63.85 15.89 3.25 1.86 0 3.72 2.01 2.86 

Std NA 1.40 .05 .66 .08 0 .52 .28 .33 

lTldgM NA 68.23 15.67 1.94 .85 .15 2.09 .86 .81 

2TldgM NA 67.87 14.97 2.40 2.08 0 3.29 .87 .64 

Avg-2 NA 68.05 15.32 2.17 1.47 .08 2.69 .86 .73 

Std NA .18 .35 .23 .62 .08 .60 .01 .09 

laTldgA NA 56.45 14.65 .35 0 0 .25 .10 .10 

lTldgA 12,703 62.24 15.81 .18 0 0 .13 .10 .10 

2TldgA 12,543 63.13 11.99 .98 0 0 .69 .10 .02 

3TldgA 12,472 35.68 22.56 .64 0 0 .44 .10 .05 

4TldgA 12,339 55.19 12.66 6.95 0 0 4.86 .10 .02 

5TldgA 12,318 54.35 14.41 1.85 0 0 1.29 .10 .10 

6TldgA 12,168 47.88 14.94 0 .30 5.20 2.65 .10 .08 

7TldgA 12,140 67.69 5.95 10.40 0 0 7.27 .10 0 47 

8TldgA 12,013 59.76 12.33 4.47 0 0 3.13 .10 .14 

Avg-9 NA 55.82 13.92 2.87 .03 0.58 2.30 .10 .12 

Std NA 8.96 4.10 3.45 .09 1.63 2.31 0 .13 

lTdrpC 12,000 62.23 18.94 0 0 7.25 3.37 .34 .08 

2TdrpC 11,862 65.14 16.25 0 .14 7.00 3.36 .64 .27 

3TdrpC 11,190 61.47 20.69 0 0 7.98 3. 71 .34 .02 

4Tdrpc 11,140 60.97 22.11 0 0 6.17 2.87 .39 .02 

5TdrpC 11, 106 68.57 16.81 0 0 5.95 2 0 77 .so .04 

6TdrpC 11,090 60.59 24.99 0 0 2.78 1.29 .42 .04 

Avg-6 NA 63.35 20.17 0 .03 5.98 2.80 .46 .08 

Std NA 2.84 3.03 0 .05 1.67 .78 .11 .09 

2TdrpK 10,450 63.79 13.39 0 .29 5.32 2.70 5.37 .06 

3TdrpK 10,430 66.89 14.67 0 0 6.05 2.81 .19 .10 

4TdrpK 10,210 68.34 13.81 0 .37 1. 72 1.09 2.74 .41 

5TdrpK 10,205 61.91 15.60 0 .22 5.25 2.61 2.37 .60 

6TdrpK 10,180 64.74 13.50 1.92 .85 4.55 4.12 1.54 .43 

7TdrpK 9,874 60.54 17.12 2.52 0 1.64 2.52 3.01 .42 

8TdrpK 9,774 63.43 14.77 4.16 0 .86 3.31 1.95 1.98 

Avg-7 NA 64.23 14.69 1.23 .25 3.63 2.74 2.45 .57 

Std NA 2.51 1.23 1.55 .28 1.98 .85 1.47 .60 

lTdrpS 10,350 89.56 1.81 0 .26 6.03 3.01 .12 .08 

2TdrpS 10,115 73.73 11.60 0 .57 3.08 1.87 1.45 .09 

Avg-2 NA 81.64 6.71 0 .42 4.56 2.44 0 79 .09 

Std NA 7.91 4.89 0 .15 1.48 .57 .67 .01 

1unaltered dacite lavas of Grassy Mountain. 

2unaltered dacite porphyry. 

3Excess sulfur (described in the section on "Methods" in the text). 

10 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
M, marginal alteration zone; C, argillic zone; K, potassic zone; and S, silicified zone. Rb, Sr, Zr, Y, Nb, and Mo are reported in parts per million; 

adjusted density (see the section on "Methods of Analysis" in text) is reported in grams/cm8; remainder of analyses are in weight percent] 

Sample No. Elevation Na2o KzO HzO 

(feet) 

TiOz Pzo5 MnO 3s so3 3s TOT 

lTldg NA 3.73 5.18 0 0.96 0.53 0.07 0 0 0 

3aTldg NA 4.04 4.86 0 1.05 .34 .11 0 0 0 

3Tldg NA 3.27 5.47 0 .98 .33 .06 0 0 0 

4Tldg NA 4.00 5.33 0 1.06 .30 .09 0 0 0 

Avg-Tldg NA 3.70 5.20 0 1.01 .36 .08 0 0 0 

Std NA .30 .20 0 .04 .09 .02 0 0 0 

lTdrp NA 3.50 4.62 0 1.02 .39 .09 0 0 0 

2Tdrp NA 4.24 4.79 0 1.30 .44 .14 0 0 0 

Avg-Tdrp NA 3.87 4.71 0 1.16 .42 .12 0 0 0 

Std NA .37 .09 0 .14 .03 .02 0 0 0 

lTldgM NA 2.76 6.13 1.38 1.02 .18 .02 0 0 .83 

2TldgM NA 2.94 5.62 1.32 .88 .30 .10 0 0 0 

Avg-2 NA 2.85 5.87 1.35 .95 .24 .06 0 0 0 

Std NA .09 .25 .03 .07 .06 .04 0 0 0 

laTldgA NA .25 3.99 5.19 .73 .27 .02 0 17.90 7.17 

lTldgA 12,703 .25 2.99 4.45 1.00 .39 .02 0 12.47 5.11 

2TldgA 12,543 .20 3.34 4.76 .99 .12 .02 0 14.35 5. 75 

3TldgA 12,472 .42 5.98 8.08 .86 .48 .02 0 25.13 10.06 

4TldgA 12,339 .34 3.28 4.82 1.11 .38 .02 0 15.13 6.b6 

5TldgA 12,318 .48 3.85 5.77 .91 .39 .02 0 17.78 7.12 

6TldgA 12,168 .53 3.68 5.46 .60 .36 .02 0 20.86 11.13 

7TldgA 12,140 .15 1.62 3.75 2.35 1.00 .02 0 6.49 2.60 

8TldgA 12,013 .14 1.23 5.12 1.22 .37 .02 0 15.08 6.04 

Avg-9 NA .31 3.33 5.27 1.09 .42 .02 0 16.13 6.78 

Std NA .13 1.30 1.14 .48 .23 0 0 4.95 2.41 

lTdrpC 12,000 .68 4.30 4.54 1.03 .18 .02 .41 0 4.29 

2TdrpC 11 ,862 2.36 5.35 1.73 .89 .20 .02 0 0 3.74 

3TdrpC 11 '190 .15 .85 6.81 .98 .22 .02 .46 0 4.73 

4Tdrpc 11,140 .15 1.41 7.08 .88 .28 .02 .51 0 3.82 

5TdrpC 11,106 .15 2.02 4.66 .97 .18 .02 .12 0 3.31 

6TdrpC 11,090 .24 1.24 8.04 .97 .21 .02 .45 0 1.94 

Avg-6 NA .61 2.17 5.66 .94 .22 .02 .31 0 3.64 

Std NA .80 1.69 2.10 .05 .03 0 .19 0 .88 

2TdrpK 10,450 .97 9.16 .64 .79 .20 .02 0 0 2.85 

3TdrpK 10,430 1.05 8.39 1.39 .83 .22 .02 .20 0 3.44 

4TdrpK 10,210 .97 9.99 .53 .79 .30 .03 0 0 .92 

5TdrpK 10,205 1.29 10.74 .65 .94 .41 .02 0 0 2.81 

6TdrpK 10,180 1.11 9.21 .82 .86 .33 .14 0 0 2.44 

7TdrpK 9,874 1.69 10.06 1.59 1.08 .26 .07 0 0 .88 

8TdrpK 9,774 2.76 8.14 .48 .83 .34 .31 0 0 .46 

Avg-7 NA 1.41 9.39 .87 .87 .29 .09 .03 0 2.03 

Std NA .60 .87 .41 .10 .07 .10 .07 0 1.03 

lTdrpS 10,350 .15 .34 .52 .87 .23 .02 0 0 3.23 

2TdrpS 10,115 .80 6.03 1.55 .88 .20 .02 0 0 1.65 

Avg-2 NA .47 3.19 1.04 .87 .22 .02 0 0 2.44 

Std NA .32 2.85 .52 0 .01 0 0 0 .79 

Methods of Analysis 11 
Table 2. Adjusted geochemical data for samples from the Red Mountain alunite deposit, Lake City, Colorado-Continued 

[Elevation values are for samples obtained from drill core. Adjustments to data are described in the section on "Methods" in the text. NA, not 

applicable; Std, one standard deviation; Avg, average of number of samples shown. Letters at end of sample numbers indicate: A, alunite zone; 

M, marginal alteration zone; C, argillic zone; K, potassic zone; and S, silicified zone. Rb, Sr, Zr, Y, Nb, and Mo are reported in parts per million; 

adjusted density (see the section on "Methods of Analysis" in text) is reported in grams/cm8

; remainder of analyses are in weight percent] 

Sample No. Elevation Rb Sr Zr y Nb Mo Density adj 

(feet) 

1Tldg NA 148 491 310 27 28 0 2.51 

2Tldg NA 165 406 265 25 35 0 2.54 

3aTldg NA 190 485 315 42 38 0 2.58 

3Tldg NA 209 497 271 56 32 0 2.50 

4Tldg NA 157 494 352 28 41 0 2.63 

Avg-Tldg NA 174 475 303 36 35 0 2.55 

Std NA 22 34 31 11 4 0 0 

1Tdrp NA 147 490 278 32 33 0 2.59 

2Tdrp NA 142 543 288 27 36 0 2.58 

Avg-Tdrp NA 145 517 283 30 35 0 2.59 

Std NA 2 26 5 2 1 0 0 

1TldgM NA 187 337 287 16 36 0 2.14 

2TldgM NA 179 335 299 27 37 0 2.21 

Avg-2 NA 183 336 293 22 37 0 2.18 

Std NA 4 1 6 5 0 0 0 

1aTldgA NA 10 45 262 16 33 1 2.59 

1TldgA 12,703 0 706 313 20 37 0 2.47 

2TldgA 12,543 0 273 338 0 34 0 2.49 

3TldgA 12,472 7 1,740 295 0 37 0 2.67 

4TldgA 12,339 0 623 317 6 38 0 2.27 

5TldgA 12,318 0 679 265 16 33 0 2.65 

6TldgA 12,168 9 590 252 12 0 0 2.67 

7TldgA 12,140 0 1,270 369 43 55 0 1.70 

8TldgA 12,013 0 553 436 62 54 0 1. 73 

Avg-9 NA 2 804 323 20 36 0 2.36 

Std NA 4 477 55 19 14 0 0 

1TdrpC 12,000 133 313 301 26 40 0 2.35 

2TdrpC 11,862 207 388 305 46 37 5 2.41 

3TdrpC 11,190 48 193 358 30 37 76 2.09 

4Tdrpc 11,140 65 452 289 41 37 103 2.18 

5TdrpC 11,106 104 276 309 44 44 130 2.43 

6TdrpC 11,090 70 305 307 43 35 17 1.97 

Avg-6 NA 99 323 314 41 38 66 2.22 

Std NA 53 82 21 7 2 so 0 

2TdrpK 10,450 464 235 231 39 23 260 2.47 

3TdrpK 10,430 283 408 293 62 42 157 2.37 

4TdrpK 10,210 398 225 263 18 36 645 2.43 

STdrpK 10,205 408 203 315 24 41 146 2.51 

6TdrpK 10,180 307 234 263 22 35 112 2.44 

7TdrpK 9,874 435 330 369 19 43 73 2.51 

8TdrpK 9,774 305 371 290 30 35 47 2.63 

Avg-7 NA 371 287 289 31 36 206 2.48 

Std NA 66 75 41 14 6 190 0 

1TdrpS 10,350 5 371 303 11 42 238 2.55 

2TdrpS 10,115 208 228 267 38 36 87 2.49 

Avg-2 NA 107 300 285 25 39 163 2.52 

Std NA 101 71 18 13 3 75 0 

12 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
Table3. Geochemical data showing gains and losses from major alteration zones, Red Mountain alunite deposit, lake City, 

Colorado 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Tldg represents samples of dacite lavas of Grassy Mountain. Tdrp represents 

samples of dacite porphyry. Note that S represents excess sulfur (see "Methods" section in the text); n.m., not a meaningful value. Rb, Sr, Zr, Y, 

Nb, and Mo are reported in parts per million; density is reported in grams/cm3; remainder of analyses are in weight percent] 

Sample No. Elevation Si02 Al203 Fe2o3 (feet) 

1TldgM NA -7.36 -3.19 -0.89 

2TldgM NA -5.77 -3.36 -.43 

Avg-2 NA -6.56 -3.27 -.66 

Avg Rel1 NA -9.98 -19.71 -25.94 

1aTldgA NA -7.28 -1.42 -2.18 

1TldgA 12,703 -4.27 -.98 -2.37 

2TldgA 12,543 -2.88 -4.65 -1.57 

3TldgA 12,472 -27.65 7.50 -1.87 

4TldgA 12,339 -15.65 -5.10 3.77 

5TldgA 12,318 -8.15 -1.32 -.59 

6TldgA 12,168 -14.62 -.65 -2.55 

7TldgA 12' 140 -19.73 -12.55 4.53 

8TldgA 12,013 -24.41 -8.06 .55 

Avg-9 NA -13.07 -3.45 .16 

Avg Rel NA -19.87 -20.81 6.38 

1TdrpC 12,000 -7.28 1.33 -3.25 

2TdrpC 11,862 -3.12 -. 74 -3.25 

3TdrpC 11 '190 -14.16 .84 -3.25 

4Tdrpc 11 '140 -12.44 2.76 -3.25 

5TdrpC 11,106 .60 -.09 -3.25 

6TdrpC 11,090 -17.68 3.15 -3.25 

Avg-6 NA -9.55 1.40 -3.25 

Avg Rel NA -14.95 8.81 -100 

2TdrpK 10,450 -2.90 -3.10 -3.25 

3TdrpK 10,430 -2.53 -2.44 -3.25 

4TdrpK 10,210 .39 -2.92 -3.25 

5TdrpK 10,205 -3.74 -. 74 -3.25 

6TdrpK 10,180 -2.74 -3.16 -1.44 

7TdrpK 9,874 .... 5.07 .73 -.81 

8TdrpK 9,774 .68 -.87 .98 

Avg-7 NA -2.23 -1.80 -2.07 

Avg Rel NA -3.49 -11.30 -63.78 

1TdrpS 10,350 24.49 -14.11 -3.25 

2TdrpS 10,115 7.17 -4.72 -3.25 

Avg-2 NA 15.74 -9.36 -3.25 

Avg Rel NA 24.65 -58.87 -100 

1Avg Rel is average relative percent gained or 

the Si02 content present in 100 grams of its fresh and 

significantly more dense counterpart. Adjusted analyses 

for altered samples were multiplied by the volume factor, 

using the corrected bulk densities derived in steps 4 and 

5, and subtracted from the corresponding densityadjusted fresh-rock analyses, resulting in the weight 

percent gained or lost per unit volume of rock during 

hydrothermal alteration. 

FeO FeS2 Fe TOT MgO CaO 

-0.23 0.13 -0.74 -0.51 -2.08 

.88 0 .39 -.47 -2.21 

.32 .07 -.18 -.49 -2.15 

33.01 n.m. -7.31 -39.56 -77.25 

-.96 0 -2.27 -1.14 -2.68 

-.96 0 -2.40 -1.14 -2.68 

-.96 0 -1.84 -1.14 -2.76 

-.96 0 -2.05 -1.14 -2.72 

-.96 0 1.89 -1.15 -2.76 

-.96 0 -1.16 -1.14 -2.67 

-.64 5.55 .30 -1.13 -2.69 

-.96 0 2.42 -1.17 -2.46 

-.96 0 -.36 -1.18 -2.68 

-.93 .55 -.35 -1.15 -2.66 

-96 0 72 n.m. -14.03 -92.47 -95.91 

-1.86 6.59 -.66 -1.71 -2.79 

-1.73 6.52 -.58 -1.42 -2.60 

-1.86 6.45 -.72 -1.73 -2.84 

-1.86 5.21 -1.30 -1.69 -2.84 

-1.86 5.60 -1.12 -1.54 -2.82 

-1.86 2.12 -2.74 -1.69 -2.83 

-1.84 5.12 -1.32 -1.62 -2.79 

-98.71 n.m. -35.46 -80.49 -97.62 

-1.58 5.08 -1.14 3.11 -2.80 

-1.86 5.55 -1.14 -1.84 -2.77 

-1.52 1.62 -2.70 .56 -2.48 

-1.65 5.10 -1.18 .29 -2.28 

-1.06 4.30 .17 -.56 -2.45 

-1.86 1.59 -1.27 .91 -2.45 

-1.86 .87 -.36 -.03 -.85 

-1.63 3.48 -1.09 .34 -2.31 

-87.24 n.m. -29.41 16.92 -80.83 

-1.60 5.95 -.75 -1.89 -2.78 

-1.32 2.96 -1.92 -.61 -2.77 

-1.46 4.44 -1.34 -1.25 -2.78 

-78.25 n.m. -36.02 -61.91 -97.09 

lost (see "Methods" section in text). 

DISCUSSION OF RESULTS 

Mass-balance data (table 3}, as determined by the 

methods discussed in the previous section of this report, 

are discussed in this section. Average compositional 

gains and losses, and average relative weight percent gain 

or loss within the major alteration zones are graphically 

portrayed in figures 5-14. 

Discussion of Results 13 
Table 3. Geochemical data showing gains and losses from major alteration zones, Red Mountain alunite deposit, Lake City, 

Colorado -Continued 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Tldg represents samples of dacite lavas of Grassy Mountain. Tdrp represents 

samples of dacite porphyry. Note that S represents excess sulfur (see "Methods" section in the text); n.m., not a meaningful value. Rb, Sr, Zr, Y, 

Nb, and Mo are reported in parts per million; density is reported in grams/cm8; remainder of analyses are in weight percent] 

Sample No. Elevation 

(feet) 

Na2o K2o H2o 

1TldgM NA -0.90 -0.23 1.18 

2TldgM NA -.67 -.so 1.17 

Avg-2 NA -.78 -.36 1.18 

Avg Rel NA -24.01 -6.56 n.m. 

1aTldgA NA -3.01 -1.33 5.37 

1TldgA 12,703 -3.02 -2.S1 4.40 

2TldgA 12,543 -3.07 -2.14 4.74 

3TldgA 12,472. -2.82 .92 8.63 

4TldgA 12,339 ·-2.96 -2.49 4.37 

STldgA 12,318 -2.76 -1.39 6.12 

6TldgA 12,168 -2.70 -1.S4 S.83 

7TldgA 12,140 -3.17 -4.37 2.SS 

8TldgA 12,013 -3.17 -4.62 3.SS 

Avg-9 NA -2.98 -2.33 4.97 

Avg Rel NA -91.1S -42.S3 n.m. 

1TdrpC 12,000 -3.2S -.80 2.72 

2TdrpC 11 ,862 -1.67 .28 .20 

3TdrpC 11 '190 -3.75 -4.02 4.10 

4Tdrpc 11 '140 -3.74 -3.S2 4.S6 

5TdrpC 11' 106 -3.73 -2.81 2.97 

6TdrpC 11 ,090 -3.68 -3.76 4.72 

Avg-6 NA -3.35 -2.84 3.4S 

Avg Rel NA -86.4S -60.40 n.m. 

2TdrpK 10,4SO -2.94 4.0S -.79 

3TdrpK 10,430 -2.91 2.99 -.14 

4TdrpK 10,210 -2.96 4.69 -.91 

STdrpK 10,20S -2.62 5.72 -.78 

6TdrpK 10,180 -2.83 3.99 -.63 

7TdrpK 9,874 -2.23 5.06 .13 

8TdrpK 9,774 -1.07 3.S8 -.92 

Avg-7 NA -2.52 4.30 -.57 

Avg Rel NA -65.17 91.36 -100 

1TdrpS 10,350 -3.72 -4.37 -.89 

2TdrpS 10,115 -3.10 1.10 .09 

Avg-2 NA -3.41 -1.60 -.40 

Avg Rel NA -88.08 -33.99 n.m. 

Alunite Alteration Zone 

Average gains and losses and average relative 

weight percent gains and losses within alunitized samples 

are shown in figures 5 and 10, respectively. Mass-balance 

data from individual samples from the alunite zone are 

presented in table 3. 

Mass-balance calculations show large additions of 

sulfur, which is present primarily as so3, to the alunitized 

rocks (table 3, fig. 5). Additions ofS03 average 15 weight 

Ti02 P2os MnO s so3 S TOT 

-0.11 -0.18 -0.04 0 0 0.08 

-.20 -.07 .03 0 0 .oo 

-.15 -.12 -.01 0 0 .04 

-15.72 -36.69 -15.42 n.m. n.m. n.m. 

-.22 -.OS -.04 0 18.S4 7.43 

.oo .os -.04 0 12.32 s.os 

.01 -.22 -.04 0 14.29 S.73 

-.06 .18 -.04 0 26.84 10.74 

.02 .01 -.04 0 13.74 s.ss 

-.01 .08 -.04 0 18.84 7.SS 

-.34 .os -.04 0 22.27 11.89 

.62 .35 -.os 0 4.41 1.77 

-.13 -.08 -.OS 0 10.43 4.18 

.os .06 -.04 0 1S.23 6.6S 

4.60 18 -70.13 n.m. n.m. n.m. 

-.22 -.2S -.10 .37 0 3.89 

-.32 -.23 -.10 0 0 3.48 

-.36 -.23 -.10 .37 0 3.82 

-.41 -.18 -.10 .43 0 3.22 

-.24 -.24 -.10 .11 0 3.11 

-.42 -.2S -.10 .34 0 1.48 

-.3S -.23 -.10 .26 0 3.17 

-30.31 -S4.30 -8S.40 n.m. n.m. n.m. 

-.40 -.22 -.10 0 0 2.72 

-.40 -.21 -.10 0.18 0 3.1S 

-.42 -.14 -.09 0 0 .86 

-.24 -.02 -.10 0 0 2.72 

-.34 -.11 .02 0 0 2.30 

-.11 -.17 -.os 0 0 .85 

-.32 -.07 .19 0 0 .47 

-.32 -.13 -.04 .03 0 1.87 

-27.59 -32.33 -29.52 n.m. n.m. n.m. 

-.30 -.19 -.10 0 0 3.18 

-.31 -.22 -.10 0 0 1.59 

-.30 -.20 -.10 0 0 2.39 

-26.31 -49.28 -83.S6 n.m. n.m. n.m. 

percent and range from 4 to 27 percent. Pyrite (reported 

as FeS2 in tables 2 and 3), which is unoxidized in the 

deeper levels of the alunite zone, shows an addition of 5.2 

percent sulfur in the only alunitized and pyrite-bearing 

sample analyzed (6TldgA). Alunite alteration produced 

average gains of roughly 5 percent H20+ and 262 ppm 

(parts per million) strontium (53 relative percent 

strontium enrichment). In addition, all samples enriched 

in strontium correspondingly gained P20s. The 

correlative enrichment of P20s and strontium within 

14 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
Table 3. Geochemical data showing gains and losses from major alteration zones, Red Mountain alunite deposit, Lake City, 

Colorado-Continued 

[Elevation values are for samples obtained from drill core. Letters at end of sample numbers indicate: A, alunite zone; M, marginal alteration zone; 

C, argillic zone; K, potassic zone; S, silicified zone. NA, not applicable. Tldg represents samples of dacite lavas of Grassy Mountain. Tdrp represents 

samples of dacite porphycy. Note that S represents excess sulfur (see "Methods" section in the text); n.m., not a meaningful value. Rb, Sr, Zr, Y, 

Nb, and Mo are reported in parts per million; density is reported in grams/cm8; remainder of analyses are in weight percent] 

Sample No. Elevation Rb Sr Zr y Nb Mo 

(feet) 

lTldgM NA -49 -209 -25 -42 -1 0 

2TldgM NA -51 -201 -7 -32 1 0 

Avg-2 NA -so -205 -16 -37 0 0 

Avg Rel NA -23.82 -41.18 -5.94 -66.60 -.77 n.m. 

laTldgA NA -199 -450 0 -39 2 1 

lTldgA 12,703 -209 201 38 -36 5 0 

2TldgA 12,543 -209 -225 66 -56 2 0 

3TldgA 12,472 -202 1361 44 -56 8 0 

4TldgA 12,339 -209 69 17 -51 3 0 

STldgA 12,318 -209 223 10 -39 3 0 

6TldgA 12,168 -199 133 -2 -43 -32 0 

7TldgA 12' 140 -209 367 -20 -27 5 0 

8TldgA 12,013 -209 -114 31 -13 5 0 

Avg-9 NA -207 262 34 -37 2 0 

Avg Rel NA -99.10 52.76 12.56 -66.50 6.20 n.m. 

1TdrpC 12,000 -26 -205 -4 -8 3 0 

2TdrpC 11 ,862 46 -128 6 11 1 5 

3TdrpC 11,190 -108 -334 11 -8 -3 61 

4Tdrpc 11,140 -92 -109 -34 3 -2 87 

STdrpC 11,106 -49 -231 12 9 8 122 

6TdrpC 11 ,090 -94 -258 -44 1 -6 13 

Avg-6 NA -62 -213 -9 3 0 57 

Avg Rel NA -43.12 -41.29 -3.24 10.09 -1.23 n.m. 

2TdrpK 10,450 296 -265 -57 5 -11 248 

3TdrpK 10,430 112 -116 -9 25 6 144 

4TdrpK 10,210 227 -278 -31 -15 1 606 

STdrpK 10,205 249 -293 28 -9 7 142 

6TdrpK 10,180 143 -269 -30 -11 0 106 

7TdrpK 9,874 275 -170 80 -14 9 71 

8TdrpK 9,774 163 -113 17 -1 3 48 

Avg-7 NA 209 -215 -1 -3 2 197 

Avg Rel NA 144.87 -41.64 -. 21 -9.05 5.65 n.m. 

1TdrpS 10,350 -142 -124 21 -21 8 235 

2TdrpS 10,115 53 -270 -21 5 2 84 

Avg-2 NA -43 -198 0 -8 5 158 

Avg Rel NA -29.88 -38.34 -.06 -27.51 14.55 n.m. 

alunitized rocks can be explained by replacement of fregen, 1985; Stoffregen and Alpers, 1987). Substitution 

(So4r2 in alunite by trivalent (Po4r3

; this replacement of P20s and strontium in alunite is probably the result of 

was accompanied by substitution of divalent strontium the destruction of primary apatite, which releases H3P04 

cations for monovalent potassium in alunite, which off- into solution, and the liberation of strontium from the 

sets the charge imbalance (Scott, 1987; Botinelly, 1976; alteration of primary plagioclase (Stoffregen and Alpers, 

Stoffregen and Alpers, 1987). Electron microprobe and 1987). 

SEM (scanning electron microscope) analyses of samples With the exception of zirconium, titanium, and 

enriched in P20s and strontium show no evidence of a niobium, which remained relatively immobile, substantial 

discrete mineral phase such as svanbergite [(Sr,Ca) amounts of most other components, including Si02 

AI3(S0)4(P0)4(0H)6], which is common in the alunite (average 13 percent, 20 relative percent), Ah03 (average 

assemblage at Summitville, Colo., and elsewhere (Stof- 3.5 percent, 21 relative percent), K20 (average 2.3 perDiscussion of Results 15 
STOT,::: ••• S03-

s 

-15 -10 -5 0 5 10 15 

LOSS WEIGHT PERCENT GAIN 

-200 

LOSS 

-100 

Mo 

Nb 

0 100 200 

PARTS PER MILLION 

300 

GAIN 

Figure 5. Average gains and losses from alunite alteration assemblage, Red Mountain. S TOT is total sulfur 

calculated as S, and Fe TOT is total Fe calculated as Fe. 

S is excess sulfur. 

cent, 42.5 relative percent), and almost all rubidium, 

were leached from the alunitized rocks. 

In general, most gains and losses of elements can 

be attributed to acid-sulfate alteration (Hemley and 

others, 1969), which is indicated by the breakdown of all 

the primary mineral constituents, except for zircon, and 

the replacement by alunite of predominantly feldspar. 

As shown in table 3, Ah03 has been depleted in all 

but one sample (6TldgA), with losses ranging from 0.7 to 

12.6 percent and averaging 3.5 percent. However, upon 

close inspection of these data, a direct correlation was 

noted between the stage of alunite predominant in a 

sample and the extent of Ah03 depletion; minor to 

insignificant losses of Ah03 were from samples containing predominantly stage 1 alunite (1aTldgA, 1 TldgA, 

and 6TldgA), and appreciably higher depletions were 

from samples in which stage 2 alunite predominates. 

These variations are consistent with petrographic data, 

which show that partial dissolution of stage 1 alunite took 

STOT-· 

so3 

s 

MnO 

P205 

-10 -7.5 -5 -2.5 0 2.5 5 7.5 10 

LOSS WEIGHT PERCENT GAIN 

-200 

LOSS 

-100 0 100 

PARTS PER MILLION 

200 

GAIN 

Figure 6. Average gains and losses from argillic alteration assemblage, Red Mountain. S TOT 

is total sulfur calculated asS, and Fe TOT is total 

Fe calculated as Fe. S is excess sulfur. 

place prior to stage 2 alunite crystallization. Stage 1 is 

composed of dense, fine-grained alunite pseudomorphous after feldspar, whereas stage 2 alunite, which is 

characterized by low crystal density and moderate microporosity, occurs in intricately connected microfractures 

and in microscopic void space created by the dissolution 

of stage 1 alunite. Leaching of stage 1 alunite prior to 

stage 2 would account for the greater Ah03 loss in stage 

2 relative to stage 1 samples. Containment of alunitesaturated fluids within a relatively closed system (at the 

scale of the whole alunite zone) after interim stage 1 and 

2 dissolution, and nonhomogeneous reprecipitation, 

could explain the extreme variations in Ah03 mobility in 

stage 2 samples (2TldgA, 3TidgA, 4TidgA, 5TidgA, 

7TldgA, and 8TldgA, table 3). 

Considering the mobility of iron, all but two 

samples, one of which contained unoxidized pyrite 

(6TldgA), showed either substantial enrichment (1.9-

2.4 percent) or depletion (-1.2-2.4 percent) in total iron 

16 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
Fe TOT 

FeO 

Fe203 

AI203 

Si03 

STOT 

so3 

s 

MnO 

-4 -3 -2 -1 0 1 2 

LOSS WEIGHT PERCENT 

3 4 

GAIN 

M o j~j~j~j~jlj~j~j~j~j~j~j~j~j;j~j~j;j;j;j~j;j~j;j;j;jt;jtj!j!jtij!@ 

Nb 

y 

Zr 

sr !j;j;j~j;jM;;;j;j;j;j;j;j;j;j;j~j;n;;;;l;j;j;j;j;!~;j;j~;j;j;j;j;j;j;;;j;l;j~l· 

Rb ;j;j;j;j;j;~;;;;~mtltl~;~j~;j~;;;j;~;l~ll!l~t;;~~l~ 

-200 

LOSS 

-100 0 100 

PARTS PER MILLION 

200 

GAIN 

Figure 7. Average gains and losses from 

potassic alteration assemblage, Red Mountain. 

S TOT is total sulfur calculated as S, and Fe TOT 

is total Fe calculated as Fe. S is excess sulfur. 

(Fe TOT, table 3). The relative immobility of Fe TOT, as 

noted in pyrite-bearing sample 6TldgA, may indicate that 

Fe TOT was relatively constant in all alunitized rocks 

prior to supergene alteration of pyrite. Hematite and (or) 

limonite, which formed during this alteration of pyrite, 

is present in the group of samples where Fe TOT 

fluctuates. 

Argillic Alteration Assemblage 

Compositional gains and losses and relative 

percent gains and losses for argillized samples are shown 

in table 3. Figure 6 portrays average gains and losses, 

whereas average relative percent gains and losses from 

argillic altered samples are illustrated in figure 11. 

The argillic alteration assemblage is characterized 

by substantial gains in sulfur present primarily as FeS2 

(average 5.1 percent), H20+ (average 3.4 percent), 

STOT 

so3 

s 

MnO 

P20s 

-16 -12 -8 -4 0 4 8 12 16 

LOSS WEIGHT PERCENT GAIN 

-200 

LOSS 

-100 0 100 

PARTS PER MILLION 

200 

GAIN 

Figure 8. Average gains and losses from 

silicic alteration assemblage, Red Mountain. S 

TOT is total sulfur calculated as S, and Fe TOT 

is total Fe calculated as Fe. S is excess sulfur. 

molybdenum (average 57 ppm), and relatively minor 

additions of Ah03 (average 1.4 percent) (table 3, fig. 6). 

The most substantial losses were of MgO (average 1.6 

percent), CaO (average 2.8 percent), and Na20 (average 

3.4 percent), for which average relative losses amount to 

80-98 percent of the equivalent fresh-rock abundances. 

Lesser, though still significant, losses (less than or equal 

to 60 percent relative loss) were in Si02 (average 9.5 

percent), total iron (Fe TOT) (average 1.32 percent), 

K20 (0-4 percent), Ti02 (average 0.35 percent), P20s 

(average 0.23 percent), and rubidium and strontium 

(average 62 and 213 ppm, respectively). Apparent 

mobility of zirconium, yttrium, and niobium was 

probably insignificant and may indicate anomalous traceelement homogeneity in the two fresh samples analyzed 

(table 2). Enrichment of FeS2, H20+, Ah03, and 

molybdenum in the argillic alteration zone is easily 

explained by the presence of as much as 5 volume 

percent pyrite, an abundance of clay minerals (preDiscussion of Results 17 
STOT 

503 

s 

-7 -6 -5 -4 -3 -2 -1 

LOSS WEIGHT PERCENT 

Mo 

Nb 

s d~~~~~~~j~~~~j~j~j~j~jj~j~~~j~j~~j~~tj~jj~~j~jj~~j~j~~~j~jj~~j~j~~~~~~j~~~~~~~jtt@~l1~1tjjjj~~j~j~~~j~j~~~j~~~~~j~~~~~j~j~~~~~~~t~~~~~~~~~~~~~ 

R b ~~~tt~j~j~~~j~~~~~~11~~1j~1j~11I1%1 r 

0 

-200 -150 -100 -50 0 

LOSS PARTS PER MILLION 

2 

GAIN 

I 

50 

GAIN 

Figure 9. Average gains and losses from marginal 

alteration assemblage, Red Mountain. S TOT is total 

sulfur calculated asS, and Fe TOT is total Fe calculated 

as Fe. S is excess sulfur. 

dominantly kaolinite) that account for gains in H20+ 

and Ah03, and sporadic late pyrite-sericite and (or) 

molybdenite-bearing fracture fillings. Variable alteration 

of feldspars and biotite, and complete destruction of 

clinopyroxene, primary opaque minerals, and apatite 

account for the observed losses in the elements discussed 

above. Loss of Ti02, which is considered relatively 

immobile in most hydrothermal environments ( Gresens, 

1966), is substantiated by the presence of leucoxene 

within local pyrite-sericite and (or) quartz veinlets. As in 

the alunitized rocks, zircon appears unaltered, which 

substantiates zirconium immobility. 

Potassic Alteration Assemblage 

Average gains and losses and average relative 

weight percent gains and losses within potassically 

altered samples are shown in figures 7 and 12, respecNb 

y ........ llli 

Zr 

Rb ~~~~~~~~~~~~~~~~~~~~s~rr-llllllllllll MnO 

-100 -80 -60 -40 -20 0 20 40 60 

LOSS RELATIVE WEIGHT PERCENT GAIN 

Figure 10. Average relative percent gains and losses from 

alunite alteration assemblage, Red Mountain. Note gains in 

803 , S TOT, and H20 + in figure 5. 

Nb 

Zr 

Sr 

Rb 

MnO 

P:Ps 

Ti02 

K20 

Na20 

CaO 

MgO 

Fe TOT 

Si02 

-100 -80 -60 -40 -20 0 20 40 60 

LOSS RELATIVE WEIGHT PERCENT GAIN 

Figure 11. Average relative percent gains and losses from 

argillic alteration assemblage, Red Mountain. Gains in S 

TOT, H20+, and FeS2 are shown in figure 6 .. 

tively. Gains and losses and relative enrichment or 

depletions within individual samples are shown in table 3. 

Potassically altered rocks show greater than 80 

percent (197 ppm average gain) average relative enrichment in FeS2 (3.5 percent average gain), K20 

(4.3 percent average gain), rubidium (209 ppm average 

gain), and molybdenum (table 3, fig. 7). Less significant 

amounts of MgO (average 17 relative percent) were 

added to the rocks, resulting in an average gain of 

0.34 percent but as much as 3 percent in one sample. 

18 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
CaO 

-100 -80 

LOSS 

-60 

Sr 

MnO 

P~s 

Ti02 

-40 -20 

Rb 

0 20 

RELATIVE WEIGHT PERCENT 

~99 percent 

~144 percent 

40 60 

GAIN 

Figure 12. Average relative percent gains and losses from 

potassic alteration assemblage, Red Mountain. Gains in S 

TOT, ~0, and FeS2 are shown in figure 7. 

Nb 

y 

Sr 

Rb 

MnO 

MgO 

Fe TOT 

-100 -80 -60 -40 -20 0 20 40 60 

LOSS RELATIVE WEIGHT PERCENT GAIN 

Figure 13. Average relative percent gains and losses from 

silicic alteration assemblage, Red Mountain. Note that gains 

inS TOT, Si02, and FeS2 are shown in figure 8. 

The components most substantially depleted are CaO 

(2.3 percent average loss) and Na20 (2.5 percent average 

loss), with average relative losses greater than 65 percent. 

Total iron (Fe TOT), Ti02, P20s, strontium, and MnO 

were removed from the rocks, resulting in an average 

relative loss ranging from 28 to 42 percent, whereas 

losses in Ah03 are less significant, averaging 11 relative 

percent. As in the argillic alteration zone, zirconium, 

niobium, and yttrium appear to have been slightly 

mobile; however, this apparent mobility may reflect the 

extreme similarity in the trace-element content of the two 

fresh rocks sampled (table 2). 

-100 -80 -60 -40 -20 0 20 40 60 

LOSS RELATIVE WEIGHT PERCENT GAIN 

Figure 14. Average relative percent gains and losses from 

marginal alteration assemblage, Red Mountain. Gain in 

H20 + is shown in figure 9. 

K20 and rubidium enrichment and substantially 

lower potassium-rubidium ratios in altered (potassium: 

rubidium 215) versus fresh rocks (potassium:rubidium 

330) are characteristic of rocks that have undergone 

potassium metasomatism (Scherkenbach and Noble, 

1984). The presence of anomalous molybdenum (occurring as minor molybdenite), averaging about 350 ppm in 

a 900-ft interval in the potassic zone (Bove and others, 

1990), accounts for the observed molybdenum enrichment. The presence of secondary potassium feldspar and 

biotite adequately explains anomalous potassium and 

rubidium enrichments, whereas the high phlogopitic 

component of the secondary biotites (as much as 23 

percent MgO) (Bove, 1988) undoubtedly is the source of 

MgO enrichment. 

The amount of pyrite (FeS2) added to potassically 

altered rocks (average 3.5 percent) is similar to the 

enrichment in all of the altered zones, excepting the 

marginal alteration assemblage, which contains no pyrite. 

As noted in the "Introduction," pyrite in potassically 

altered rocks is paragenetically related to postpotassic 

sericite and (or) quartz alteration. 

Silicification Zone 

Compositional gains and losses and relative percent gains and losses for silicic altered samples are shown 

in table 3. Figure 8 portrays average gains and losses 

within silicic altered samples, whereas average relative 

percent gains and losses are illustrated in figure 13. 

Discussion of Results 19 
Analyses of the two silicified dacite porphyry 

samples are considered to represent high (sample 

1 TdrpS) and low (sample 2TdrpS) ranges of silicification. 

Both samples show gains of Si02 (7 .2 and 24.5 percent), 

averaging 15.7 percent, which equates to 24.7 relative 

percent Si02. Aside from large gains in Si02 (25 

percent), FeS2 (6 percent), and molybdenum (235 ppm), 

most components of sample 1 TdrpS (high-range silicification) have been removed. 

In contrast to sample 1 TdrpS (high-range silicification), sample 2TdrpS contained a significantly greater 

proportion of sericitized secondary potassium feldspar 

relative to microcrystalline quartz. A smaller net gain in 

Si02 (7.2 percent), coupled with enrichment in K20 

(1.1 percent) and rubidium (53 ppm), reflects the mineralogical differences between these samples. Enrichment in 

FeS2 (3 percent) and molybdenum (84 ppm) is considerably less in sample 2TdrpS than in sample 1 TdrpS 

(6 percent FeS2, 235 ppm molybdenum). This difference 

appears to be related to higher fracture densities within 

rocks containing abundant fracture-filling quartz veinlets, which would allow greater infiltration of sulfidebearing hydrothermal fluids. 

Relatively small losses of Ti02 (0.3 percent or 26 

relative percent) occurred in the average silicified sample 

(Avg-2); the losses are consistent with Ti02 mobility 

within argillic and potassic altered rocks. Apparent losses 

in zirconium, yttrium, and niobium may be insignificant 

and may result from anomalous trace-element homogeneity in the two fresh samples analyzed (table 2). 

Marginal Alteration Assemblage 

Of the 23 analyzed components of rocks from the 

marginal alteration assemblage, 15 were relatively immobile during alteration (table 3, figs. 9, 14). Of the eight 

mobile components of these rocks, only H20+ was 

gained (average 1.2 percent) (table 3, fig. 9). Losses, 

for the most part, were relatively minor compared to the 

alteration assemblages previously discussed and include 

depletions in Si02 (average 6.6 percent or 10 relative 

percent), Ah03 (average 3.3 percent or 20 relative 

percent), CaO (average 2.2 percent or 77 relative percent), Na20 (average 0.8 percent or 24 relative percent), 

strontium (average 205 ppm or 41 relative percent), and 

yttrium (average 37 ppm or 67 relative percent) (table 3, 

figs. 9, 14). The losses primarily represent alteration of 

plagioclase and clinopyroxene, whereas H20+ was incorporated primarily in kaolinite, smectite, and sericite. 

Rubidium, zirconium, and niobium were relatively 

immobile (table 3, figs. 9 and 14). 

SUMMARY 

Seven major alteration assemblages from the 23.1-

Ma Red Mountain alunite deposit were studied to assess 

geochemical and accompanying mineralogical changes 

that occurred during hydrothermal alteration. Thirty-five 

samples selected from both altered and fresh rocks were 

analyzed for 10 major elements, 6 trace elements, sulfur, 

C02, H20 + , and H2o-. Mass-balance calculations show 

large additions of sulfur, which was derived from the 

hydrothermal system. This sulfur is present primarily as 

S03 within alunitized rocks and FeS2 within the potassic 

and argillic alteration zones. Ah03 and K20 were 

removed during alunitization, and P04 and strontium 

were enriched due to coupled substitution of Po~- for 

SO/- and Sr2+ forK+ in the alunite structure. Water 

was added to all of the altered zones as secondary 

hydrous alteration minerals. Both potassium and rubidium were added to the potassic zone, and a slight gain in 

Ah03 was observed in kaolinite-altered rocks. An 

average gain of 15 weight percent Si02 took place in the 

silicification zone. Zirconium, niobium, and Ti02 

remained relatively immobile in most of the alteration 

assemblages. 

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Bove, Dana, Rye, R.O., and Hon, Ken, 1988, Evolution of the 

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20 Hydrothermal Alteration, Red Mountain Alunite Deposit, Lake City, Colorado 
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~U.S. GOVERNMENT PRINTING OFFICE: 199~573-()49/26,008 REGION NO. 

Stoffregen, R.E., and Alpers, C.N., 1987, Svanbergite and 

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References Cited 21 



SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Repons 

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic. 

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or 

geographic coverage than Professional Papers. They include the results 

of resource studies and of geologic and topographic investigations; as well 

as collections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water. 

CIJ'culars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public. Information is usually of short-term interest. 

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reproduced on request unlike formal USGS 

publications, and they are also available for public inspection at 

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Open-File Reports include unpublished manuscript reports, maps, 

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Maps 

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Geophysical Investigations Maps are on topographic or planimetric 

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Many maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

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environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensivelistings of U.S. Geological Survey publications are available under 

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