U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5117

Comparison of ASTER- and AVIRIS-Derived Mineral 

and Vegetation Maps of the White Horse Replacement 

Alunite Deposit and Surrounding Area, Marysvale 

Volcanic Field, Utah
FRONT COVER: View of the White Horse mine (bright rocks at center) from the Sevier River flood plain with Marysvale Peak on the skyline, looking towar

dozer cuts above and behind the mine mark the White Hills alunite deposit. The summit of Marysvale Peak is underlain by another alunite deposit. The brighare an exposure of hydrothermally altered volcaniclastic sedimentary rocks and related flows (unit Tmps) that are discussed in the text. Argillically altered roprospect are visible at extreme right center within the northern Bullion Hills. The entire area visible in the photograph lies within the inferred boundary of the 
Comparison of ASTER- and AVIRIS-Derived 

Mineral and Vegetation Maps of the 

White Horse Replacement Alunite Deposit 

and Surrounding Area, Marysvale Volcanic 

Field, Utah

By Barnaby W. Rockwell

Scientific Investigations Report 2009–5117

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Rockwell, B.W., 2009, Comparison of ASTER- and AVIRIS-derived mineral and vegetation maps of the White Horse 

replacement alunite deposit and surrounding area, Marysvale volcanic field, Utah: U.S. Geological Survey Scientific 

Investigations Report 2009–5117, 31 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Geographic and Geologic Setting of the White Horse Mine and Surrounding Area ...................................2

Mineral and Vegetation Maps Derived from AVIRIS data ......................................................................6

Processing and Analysis of ASTER Data.................................................................................................10

Mineral and Vegetation Maps Derived from ASTER Data ....................................................................12

False-Color Composite Image—Vegetation, Snow, and Surface Albedo.................................12

Visible and Near-Infrared Mapping—Iron Minerals ....................................................................12

Vegetation ............................................................................................................................................16

Shortwave-Infrared Mapping and Detector “Scratch” ...............................................................16

Advanced Argillic Alteration and Areal Mixing.............................................................................19

Phyllic Alteration and Pyrophyllite...................................................................................................19

Carbonate.............................................................................................................................................20

Epidote..................................................................................................................................................20

Sericites................................................................................................................................................21

Argillic Alteration in Quartz Arenites...............................................................................................21

Kandite Clay Differentiation ..............................................................................................................22

Comparison of AVIRIS- and ASTER-Derived Mineral Maps.................................................................25

Conclusions...................................................................................................................................................29

Acknowledgments.......................................................................................................................................29

References....................................................................................................................................................29

Figures

1. Index map of study area showing footprints of ASTER data, high-altitude 

AVIRIS data, low-altitude AVIRIS data, and geologic map shown in figure 3....................3

2. Perspective view of the Antelope Range area looking toward the northeast ..................4

3. Geologic map of southern Antelope Range and surrounding area......................................5

4. True-color composite of AVIRIS flightline over White Horse deposit..................................7

5. Map of iron-bearing minerals and water generated from AVIRIS data 

in the 0.35–1.35-micrometer region ...........................................................................................8

6. Map of clay, sulfate, mica, carbonate, and Mg-OH minerals generated 

from AVIRIS data in the 1.45–2.50-micrometer region............................................................9

7. Averaged AVIRIS spectra of vegetation classes ..................................................................10

8. Map of vegetation vigor and dryness generated from AVIRIS data ..................................11

9. Map showing ASTER 431/RGB false-color composite image of the 

Marysvale region........................................................................................................................13

10. Plot of selected convolved laboratory spectra of iron-bearing 

minerals, vegetation, and water (on left) used as references for 

analysis of ASTER data..............................................................................................................14

11. Map of iron-bearing minerals, vegetation, and water derived from spectral 

analysis of ASTER data..............................................................................................................15
iv

12. Plot of selected convolved laboratory spectra of clay, sulfate, mica, carbonate, 

and sorosilicate (epidote) minerals and mineral mixtures having diagnostic 

SWIR absorption features used as references for analysis of ASTER data.....................17

13. Map of clay, sulfate, mica, hydrous quartz, carbonate, and Mg-OH minerals 

derived from spectral analysis of ASTER shortwave infrared (SWIR) data .....................18

14. Shortwave infrared spectral plots of dickite and well-crystallized kaolinite 

from Clark and others (2003b) convolved to ASTER spectral resolution...........................22

15. Map of clay, sulfate, mica, hydrous quartz, carbonate, and Mg-OH minerals 

derived from spectral analysis of ASTER shortwave infrared (SWIR) data 

with dickite added as a reference spectrum.........................................................................23

16. Results of ASTER band depth analysis of mineral identification results 

shown in figure 13 over the Yellow Jacket and Al Kee Mee replacement 

alunite deposits in the Antelope Range ..................................................................................24

17. Map of alunites and kandite clay minerals derived from spectral analysis 

of ASTER shortwave infrared (SWIR) data.............................................................................26

18. Mineral map from figure 13 merged with results of kandite clay differentiation 

based on band-depth analysis .................................................................................................27

19. Comparison of shortwave infrared (SWIR) mineral maps derived from AVIRIS 

and ASTER data ..........................................................................................................................28

Table

1. Measured spectral performance of ASTER VIS, NIR, and SWIR bands. ..........................12
Abstract

This report presents and compares mineral and vegetation 

maps of parts of the Marysvale volcanic field in west-central 

Utah that were published in a recent paper describing the 

White Horse replacement alunite deposit. Detailed, fieldverified maps of the deposit were produced from Airborne 

Visible/Infrared Imaging Spectrometer (AVIRIS) data acquired 

from a low-altitude Twin Otter turboprop airborne platform. 

Reconnaissance-level maps of surrounding areas including the 

central and northern Tushar Mountains, Pahvant Range, and 

portions of the Sevier Plateau to the east were produced from 

visible, near-infrared, and shortwave-infrared data acquired by 

the Advanced Spaceborne Thermal Emission and Reflection 

Radiometer (ASTER) sensor carried aboard the Terra satellite 

platform. These maps are also compared to a previously published mineral map of the same area generated from AVIRIS 

data acquired from the high-altitude NASA ER–2 jet platform. 

All of the maps were generated by similar analysis methods, 

enabling the direct comparison of the spatial scale and mineral 

composition of surface geologic features that can be identified 

using the three types of remote sensing data.

The high spatial (2–17 meters) and spectral (224 bands) 

resolution AVIRIS data can be used to generate detailed 

mineral and vegetation maps suitable for geologic and 

geoenvironmental studies of individual deposits, mines, 

and smelters. The lower spatial (15–30 meters) and spectral 

(9 bands) resolution ASTER data are better suited to less 

detailed mineralogical studies of lithology and alteration 

across entire hydrothermal systems and mining districts, 

including regional mineral resource and geoenvironmental 

assessments. The results presented here demonstrate that 

minerals and mineral mixtures can be directly identified 

using AVIRIS and ASTER data to elucidate spatial patterns 

of mineralogic zonation; AVIRIS data can enable the generation of maps with significantly greater detail and accuracy. 

The vegetation mapping results suggest that ASTER data may 

provide an efficient alternative to spectroscopic data for studies of burn severity after wildland fires.

The AVIRIS-derived maps were produced through the 

quantitative comparison of continuum-removed image spectra 

and laboratory reference spectra by using previously described 

least-squares curve-fitting techniques. The ASTER-derived 

maps presented here were produced by a similar methodology 

adapted for analysis of ASTER multispectral data. This semiautomated methodology is currently being applied to ASTER 

data coverage of large areas for regional assessments of 

mineral-resource potential and mineral-environmental effects. 

While legacy multispectral data such as those acquired by 

the spaceborne Landsat Thematic Mapper sensor can detect 

large hydrothermally altered areas, ASTER data can further 

characterize the alteration in those areas by discriminating 

specific minerals such as sericite, kaolinite, smectite, alunite, 

gypsum, calcite, dolomite, epidote, hydrous quartz (opal or 

chalcedony), ferrous iron minerals, ferric iron minerals including spectrally pure jarosite and copiapite, and certain mixtures 

of these minerals. Compared to spectroscopic remote sensing 

data, however, the large pixels and multispectral nature of 

ASTER data necessarily increase the effects of areal mixing 

of materials within a pixel and reduce the uniqueness of image 

spectra when materials with overlapping absorption features 

coexist within a pixel. Both of these effects result in a lower 

confidence level for spectral identifications derived from 

ASTER data.

In the replacement alunite deposits, the AVIRIS data 

were used to identify halos of argillically altered rocks 

containing quartz + dickite ± kaolinite ± alumino-phosphatesulfate minerals around central cores of alunite ± kaolinite. 

A methodology for the discrimination of these halos using 

ASTER data based on the greater band depth of dickite relative to that of kaolinite is proposed that can identify areas of 

high-grade argillic alteration.

The mineral maps of the White Horse deposit generated 

from low-altitude AVIRIS data have been demonstrated to 

accurately portray the primary geologic features of the deposit. 

The 3-meter pixel size of these data is well suited for delineating most surface features of the deposit, including the fracturecontrolled argillic selvages, which are typically 2–3 meters wide. 

Comparison of ASTER- and AVIRIS-Derived Mineral 

and Vegetation Maps of the White Horse Replacement 

Alunite Deposit and Surrounding Area, Marysvale 

Volcanic Field, Utah

Barnaby W. Rockwell
2 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

The high-altitude AVIRIS data with 17-meter pixel size are 

capable of delineating the central alunite zone and surrounding 

alunite + kaolinite transition and dickite-bearing argillic zones, 

the pyritic “proximal” propylitic/phyllic zone, which underlies 

and surrounds the argillic zones, and “distal” propylitically altered 

volcanic rocks containing calcite and possible chlorite. However, 

when compared to the map derived from the low-altitude AVIRIS 

data, the occurrence of dickite is overestimated at the expense 

of areal and intimate mixtures of kaolinite ± alunite in low 

abundance; thus, pixels matched to dickite had been labeled as a 

mineralogically mixed map unit. If the high-grade argillic alteration detected using the band-depth analysis is merged with the 

standard shortwave-infrared mineral mapping, the ASTER data 

(30-meter pixel size) are also capable of delineating most primary 

deposit features and zoning, but the clay-free central alunite zone 

(30–32 meters wide) cannot be discriminated from the surrounding alunite + kaolinite transition zone because of areal mixing 

effects. In addition, areal mixing of alunite, clay minerals, and dry 

vegetation having leaf biochemical absorptions overlapping with 

the primary sulfate feature of alunite resulted in an overdetection 

of alunite-bearing mineral assemblages at the expense of clay 

minerals, mainly kaolinite.

All maps are presented in a variety of digital formats, 

including jpeg, pdf, and ERDAS Imagine (.img). The Imagine 

format files are georeferenced and suitable for viewing with 

other geospatial data in Imagine, ArcGIS, and ENVI. The 

mineral and vegetation maps are attributed so that the material 

identified for a pixel can be determined easily in ArcMap by 

using the Identify tool and in Imagine by using the Inquire 

Cursor tool.

Introduction

High-resolution spectroscopic image data collected on 

October 17, 1999, by the Airborne Visible/Infrared Imaging 

Spectrometer (AVIRIS) sensor from a low-altitude Twin 

Otter turboprop platform (AVIRIS flightline metadata) were 

analyzed for a detailed study of the surface mineralogy of 

a Miocene epithermal replacement alunite deposit several 

kilometers north of the town of Marysvale, Utah, along the 

southeastern edge of the Antelope Range (Rockwell and 

others, 2006). Multispectral image data collected by the 

Advanced Spaceborne Thermal Emission and Reflection 

Radiometer (ASTER) sensor carried aboard the Terra satellite 

platform orbiting the Earth at 705-kilometer (km) altitude 

were analyzed to show the distribution of hydrothermal 

alteration throughout the Antelope Range and surrounding 

area. This report presents digital versions of the mineral and 

vegetation maps produced from the AVIRIS and ASTER data 

in both Portable Document Format (.pdf), ERDAS Imagine 

format (.img), and JPEG format (.jpg). The methodologies 

used to process and analyze the ASTER data are described. 

The PDF and JPEG format maps are useful for printing and 

detailed viewing through zooming. The Imagine format files 

are useful for integrating the maps with other geospatial data 

in a geographic information system (GIS) and have been fully 

attributed with material identification information, so that the 

material(s) identified in a pixel can be queried using software 

tools such as the Inquire Cursor Tool in Imagine and the Identify Tool in ArcMap.

Geographic and Geologic Setting 

of the White Horse Mine and 

Surrounding Area

The White Horse mine is located at 1,982 meters (m) 

above sea level on undulating terrain that slopes gently 

downward toward the Sevier River, 3 km to the west at 1,771-m 

elevation (fig. 1). Precipitation increases with elevation, and the 

Sevier River valley receives on average about 25 centimeters 

(cm) annually and the lower slopes of the valley as much 

as 30 cm (Daly and others, 1994, 1997). The high Tushar 

Mountains (3,710-m maximum elevation) to the west receive 

as much as 125 cm annually, and the Sevier Plateau to the east 

(3,422-m maximum elevation) as much as 90 cm. The area 

surrounding the mine is covered with sparse sagebrush and 

grasses, with piñon and juniper becoming more abundant with 

increased elevation and precipitation east of the mine. Figure 2 

is a perspective view of the Antelope Range area that shows the 

location of the White Horse mine in relation to other mines and 

important geographic and geologic features. In figure 2, green 

vegetation (shown in hues of green) can be seen to increase in 

density with increasing elevation and rainfall.

The geologic setting of the study area is described by 

Rockwell and others (2006, and references therein). The 

geology and structure of the Antelope Range area are shown 

in figure 3. The area is underlain by eroded stratovolcanoes 

and related calc-alkaline volcanic rocks of the Bullion Canyon 

Volcanics (30–22 Ma, fig. 3) that intruded and covered a 

sequence of Paleozoic and Mesozoic sedimentary rocks. Cores 

of these volcanoes and several monzonite porphyry intrusions 

including the Hoover pluton (HP in fig. 2, Tbci in fig. 3) that 

have been interpreted as the solidified magma sources of some 

of the younger Bullion Canyon Volcanics (Rowley and others, 

2002) are exposed along Marysvale Canyon (fig. 2). The 

Three Creeks Tuff Member (≈27 Ma) of the Bullion Canyon 

Volcanics exposed in the central Tushar Mountains (including Alunite Ridge) is derived from the Three Creeks caldera 

in the southern Pahvant Range (fig. 1). Most of the Antelope 

Range lies within the inferred boundary of the Monroe Peak 

caldera (fig. 3), which erupted near 23 Ma and produced the 

Osiris Tuff, which has been altered at the White Horse deposit. 

The central intrusion (≈23 Ma, unit Tci in fig. 3), a composite 

intracaldera intrusion of quartz monzonite stocks thought to 
Geographic and Geologic Setting of the White Horse Mine and Surrounding Area 3

Figure 1. Index map of study area showing footprints of ASTER data (cyan), high-altitude AVIRIS data (gold), low-altitude AVIRIS data 

(red), and geologic map shown in figure 3 (green). The large orange arrow indicates the viewing direction of the perspective image 

shown in figure 2. Background is shaded relief produced from 1/3 arc second digital elevation data from the National Elevation Dataset 

(NED). Selected deposits, mines, and geologic features (magenta): AKM = Al Kee Mee natroalunite deposit; BS = Big Star natroalunite 

deposit; HP = Hoover pluton; JLT = Joe Lott Tuff Member of Mount Belknap Volcanics; RHC = Red Hills caldera; U = Jungfrau Peak and 

uranium mining area; W = White Hills alunite deposit; WH = White Horse alunite deposit; WK = Winkleman alunite deposit; YC = Yellow 

Cougar gold mine; YJ = Yellow Jacket alunite deposit. Geographic features (yellow): SF = Sage Flat. Larger image is available HERE. 

PDF version of figure is available HERE.
Figure 2. Perspective view of the Antelope Range area looking toward the northeast. Orange arrow in figure 1 shows direction of view. composite (741/RGB) of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data. The approximate horizontal distance between the Whitcenter of the Red Hills caldera (RHC) is 3.7 kilometers. Cultivated fields and riparian vegetation in the Sevier River flood plain at the north visible in bright green at right center. Geographic features: LV = Long Valley; MC = Marysvale Canyon and Sevier River; PF = Poverty Flat; small exposure of pyrophyllite (Rockwell and others, 2005). Geologic features: FG = Fine-grained granite (21–20 Ma, unit Tmf in fig. 3); JLT Mount Belknap Volcanics, dipping to the east and northeast away from the viewer; RHC = Red Hills caldera surrounded by hematite-beathe Mount Belknap Volcanics (unit Tmr in fig. 3). Alunite deposits: BRCM = Big Rock Candy Mountain; ML = Mary’s Lamb mine in southeadeposit (the “Silica Hills” of Kerr and others, 1957) adjacent to highly silicified rocks bearing dickite and local topaz (Rockwell and others, WH = White Horse; WK = Winkleman; YJ = Yellow Jacket, which contains a small but rich deposit of hematite (associated with natroalunfragments) exploited by the Iron Cap mine located at high levels in the Yellow Jacket deposit immediately beneath and partially within a rcap (Callaghan, 1973; Cunningham and others, 1984a). Natroalunite deposits: AKM = Al Kee Mee; BS = Big Star. Copper, gold, and gold-si(gold, silver); T = Trinity (copper), a skarn deposit developed in a faulted slice of Permian limestones immediately adjacent to the Hoover p(gold). U = Jungfrau Peak and uranium mining area. 
Geographic and Geologic Setting of the White Horse Mine and Surrounding Area 5

Figure 3. Geologic map of southern Antelope Range and surrounding area. The white rectangle indicates approximate 

coverage of 1999 low-altitude AVIRIS data over the White Horse deposit. Larger image is available HERE. PDF version of 

figure is available HERE. Modified from Rowley and others (2002).
6 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

be the source of hydrothermal activity that formed surrounding small deposits of copper, gold, and silver (for example, 

Antelope, Yellow Cougar, and Trinity, fig. 2) and replacement 

alunite of similar age, is centered about 1 km northeast of the 

uranium mining area in the Antelope Range (figs. 2 and 3). 

The Big John caldera also formed at or just before this time in 

the south-central Tushar Mountains, erupting the Delano Peak 

Tuff Member of the Bullion Canyon Volcanics. With the onset 

of tectonic extension and Basin and Range faulting around 

23–22 mega-annum (Ma), volcanism changed to bimodal 

composition. The Mount Belknap Volcanics (21–12 Ma) are 

present throughout the study area and emanated from several 

caldera and volcano eruptive centers including the Mount 

Belknap (north-central Tushar Mountains) and Red Hills 

(fig. 2) calderas, which erupted close to 19 Ma, producing the 

Joe Lott and Red Hills Tuff Members, respectively. Exposed 

and concealed intrusions of granitic (fine-grained granite, 

fig. 2) to rhyolitic composition with related domes, flows, and 

tuffs lie along a southwest-trending belt extending from the 

Antelope Range to Alunite Ridge (fig. 1) with age decreasing toward the southwest. These intrusions are thought to be 

the source of uranium mineralization in the Antelope Range 

(fig. 2), polymetallic mineralization in the eastern Tushar 

Mountains near Copper Belt Peak (fig. 1), along Bullion 

Canyon, and at the Deer Trail mine, as well as the ≈14-Ma 

magmatic steam alunite deposits on Alunite Ridge that could 

be related to porphyry molybdenum mineralization (fig. 1). 

Basin and Range faulting accelerated between 8 and 5 Ma, initiating the formation of Marysvale Canyon by the downcutting 

of the Sevier River along entrenched meanders and deforming basin-fill sediments such as the Sevier River Formation 

(22–7 Ma). Bimodal volcanic activity in the area continued 

until the Pleistocene.

Mineral and Vegetation Maps 

Derived from AVIRIS data

The low-altitude AVIRIS data and the techniques used 

to analyze them are described by Rockwell and others (2006). 

Mineral maps produced from high-altitude AVIRIS data of 

the White Horse deposit, the Antelope Range, and the eastern Tushar Mountains are shown in Rockwell and others 

(2000, 2005). The footprints of the low- and high-altitude 

AVIRIS data are shown in figure 1. Both the high- and lowaltitude AVIRIS data were analyzed using a modified version (Rockwell, 2002) of an expert system (Clark and others, 

2003a) that quantitatively compares continuum-removed 

image spectra and laboratory reference spectra using leastsquares curve-fitting techniques. Figure 4 shows a true-color 

composite image of the AVIRIS flightline covering the White 

Horse deposit. Areas in which ferric iron minerals are abundant on the surface appear in red to brown hues in this image. 

Vegetation appears in hues of green. Spectral analysis of the 

AVIRIS data produced a map of iron-bearing minerals and 

water (fig. 5) and a map of clay, sulfate, mica, carbonate, 

and Mg-OH minerals (fig. 6).

Eroded remnants of what could be another hydrothermal 

system are exposed 2 km west-northwest of the White Horse 

mine adjacent to the Sevier River flood plain (fig. 5). In this 

area, the Osiris Tuff contains abundant jarosite, local hematite, 

and mixtures of kaolinite and illite/muscovite (figs. 3, 5, and 

6). The assemblage of jarosite, kaolinite, and illite/muscovite 

is indicative of the pyrite-bearing, “proximal” propylitic (or 

phyllic) alteration of a feeder system (Cunningham and others, 

2005; Rockwell and others, 2005, 2006). The hematite may be 

the only remnant of the overlying advanced argillic assemblage. The lack of any residual alunite and the relatively small 

size of this altered area relative to other replacement alunite 

deposits in the Antelope Range suggest that this hydrothermal 

system was only weakly developed. The east-northeast elongation of the alteration suggests it was controlled primarily by 

faults and (or) fractures as opposed to volcanic stratigraphy 

or massive replacement above an upwelling fluid plume. 

The deposit is situated on the southern, upthrown side of a 

west-northwest-trending, high-angle fault that passes immediately to the north (fig. 3). The southern edge of the deposit is 

aligned with a northeast-southwest-trending fault mapped less 

than a kilometer to the east.

To examine the spatial relationships between mineralogical variations and vegetation, the AVIRIS data were analyzed 

to determine vegetation distribution and vigor. Vegetation 

identified with the AVIRIS data was classified into four broad 

classes based on spectral absorptions related to chlorophyll 

(0.67 micrometer [μm]), leaf water content (0.98 and 1.18 μm), 

and (or) the leaf biochemicals such as lignin and cellulose 

(~2.10 and 2.33 μm) that cause very strong absorptions in dry, 

senescing vegetation (Clark and others, 2003a, and references 

therein). Figure 7 shows averaged AVIRIS spectra sampled randomly from high fit × depth pixels of each class (Rockwell and 

others, 2005, 2006). Principal absorption features are labeled, 

and the pigments or biochemicals responsible for the absorptions are indicated. Prominent absorption features related to 

carotenoid pigments, chlorophyll, and leaf water, but very weak 

to nonexistent leaf biochemical features, characterize the spectrum of dense, moist, green vegetation. With increasing dryness 

and (or) decreasing per-pixel vegetation density (top to bottom), 

the chlorophyll and leaf water features are seen to decrease in 

depth while the leaf biochemical features increase in depth.

Figure 8 shows the distribution of the four vegetation 

classes in the White Horse area. The class “green, moist vegetation” represents a spectral match to the chlorophyll and leaf 

water features of a green lawn grass and corresponds to green 

grasses in the Sevier River flood plain and to piñon/juniper 

at higher elevations to the east of the White Horse mine. The 

weak/sparse green vegetation class represents a match to the 

chlorophyll and leaf water features of an areal mixture of soil 

and sparse green grasses. This class corresponds to either 
Figure 4. True-color composite of AVIRIS flightline over White Horse deposit (red = band 36, 0.682790 micrometer; green = band 19, 0.547320 micrometer; blumeter). Mineralogy and geochemistry of the samples from the locations shown in red are described by Rockwell and others (2006). Larger image is available His available HERE. ERDAS Imagine format data are available HERE.
Figure 5. Map of iron-bearing minerals and water generated from AVIRIS data in the 0.35–1.35-micrometer region. G = gradational stretch appliea gradational stretch show bright colors where the identification had high fit × depth (least-squares fit of reference to image spectrum times deptfeature), and darker color brightness with successively lower fit × depth values (Rockwell and others, 2005, 2006). Sample collection locations are circles. “Red Hills Tuff” indicates exposures of the Red Hills Tuff Member of the Mount Belknap Volcanics. Larger image is available HERE. PDF veHERE. A similar map covering this area that was produced from high-altitude 1998 AVIRIS data is available HERE (Rockwell and others, 2005). ERDare available HERE with material identifications attributed for use in a GIS.
Figure 6. Map of clay, sulfate, mica, carbonate, and Mg-OH minerals generated from AVIRIS data in the 1.45–2.50-micrometer region. “Tmps” indicsedimentary unit (fig. 3) that preferentially alters to kaolinite with local dickite and alunite (Rockwell and others, 2006). G = gradational stretch appliedare indicated with white circles. Larger image is available HERE. PDF version of figure is available HERE. A similar map covering this area that was pr

1998 AVIRIS data is available HERE (Rockwell and others, 2005). ERDAS Imagine format data are available HERE with material identifications attribute
10 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

Figure 7. Averaged AVIRIS spectra of vegetation classes. Spectra 

were sampled randomly from high fit × depth pixels of each mapped 

class. Chlorophyll content decreases and dryness increases from 

top to bottom, expressed by the decrease in band depth of the 

chlorophyll absorption band at 0.68 μm (micrometer) and the increase 

in depth of the leaf biochemical bands at 1.73 μm, 2.09–2.14 μm 

and 2.28–2.34 μm. Principal absorption features are marked with 

plant components responsible for the absorption. CP = carotenoid 

pigments. CHL = chlorophyll. LW = leaf water. LB = leaf biochemicals 

(for example, lignin, cellulose). μm, micrometers. PDF version of figure 

is available HERE.

sparse green grasses in the flood plain or to areal mixtures 

of piñon/juniper, soil, and (or) sparse dry grasses that occur 

mainly on the more shaded north-facing slopes of the hills and 

drainages surrounding the White Horse deposit. These areas 

are underlain by unaltered to weakly altered rocks and soils. 

The dry, green vegetation class represents a match to chlorophyll, leaf water, and leaf biochemical features of an areal mix 

of dry and green vegetation, and the dry, nonphotosynthetic 

vegetation (DNPV) class matches only the leaf biochemical 

absorption features in a reference spectrum of dry, long 

grasses. The dry vegetation classes map primarily in the flood 

plain. The dry, green vegetation class occurs around pixels of 

DNPV and represents a transition between very dry, senesced 

DNPV grasses and moister green grasses.

A comparison of the AVIRIS-derived mineral (figs. 5 and 

6) and vegetation maps (fig. 8) shows that little to no vegetation other than very sparse grasses and sage grow on areas 

underlain by altered rocks, or by the Red Hills Tuff Member 

along the northwestern edge of the AVIRIS flightline. Most 

of the grasses were completely senesced at the time of the 

October AVIRIS overflight. Very little vegetation of any kind 

typically grows on the altered, pyritic rocks of the propylitic 

feeder zones of the hydrothermal systems in the Antelope 

Range area. In addition to mapping surface mineralogy, imaging spectroscopy provides a means for the rapid characterization of vegetation at prospects, mines, or mill sites and can 

reveal geobotanical relationships for enhanced understanding of local lithology and alteration. Also, it can be used to 

identify vegetation that has been stressed due the presence 

of metals or acid soil conditions.

Processing and Analysis 

of ASTER Data

ASTER Level 1B (L1B, Registered Radiance At Sensor) 

data acquired on June 12, 2002, were analyzed to obtain a 

synoptic, regional overview of exposed hydrothermal alteration in the area surrounding Marysvale. Analysis of ASTER 

data is an efficient and cost-effective method of generating 

regional alteration maps, which traditionally have been compiled through extensive field work and sampling (Cunningham 

and others, 1984b).

ASTER scenes can be acquired with either nadir or 

off-nadir viewing geometries. When scenes are acquired with 

pointing angles greater than 6 degrees from nadir, horizontal 

positional errors in the ephemeris data can be severe (up to 

400 m) (Rockwell and Hofstra, 2008). The pointing angle of 

the Marysvale ASTER scene is –8.5 degrees (ASTER scene

metadata). In such significantly off-nadir scenes, and in areas 

with significant topographic relief, orthocorrection is important when integrating ASTER-derived mapping products 

with other geospatial data. For nonorthocorrected Level 1B 

data that has geometric coefficients applied, ephemeris-based 

orthocorrection is impossible. However, projective transforms 

using ground control points and a digital elevation model 

(DEM) with spatial resolutions similar to that of the ASTER 

data (for example, USGS 1/3 arc second DEM data with 10-m 

resolution from National Elevation Dataset) are very useful for geometric modeling of the ASTER data and can yield 

very low positional error. Such a transform was applied to the 

Marysvale ASTER scene.

ASTER data from the visible (VIS), near-infrared (NIR), 

and shortwave infrared (SWIR) spectral regions (table 1) 

were converted to radiance units (λ/m2/sr/μm) through multiplication by gain settings in the metadata after subtracting 

minimum, nonzero digital number (DN) values from the 

SWIR data on a band-by-band basis to reduce effects of stray 

light referred to as “crosstalk” (Iwasaki and Tonooka, 2005; 

Iwasaki and Oyama, 2005). The SWIR data were resampled to 

15-m spatial resolution to match the ground instantaneous field 

of view (GIFOV) of the VIS and NIR data (table 1).

To calibrate the ASTER radiance data to unitless relative reflectance format in preparation for comparison with 

reference reflectance spectra, the radiance spectrum of each 

ASTER pixel was divided by the average radiance spectrum 

of a calibration site covered by the ASTER data in which 

no prominent absorption features are present (“Flat Field” 
Figure 8. Map of vegetation vigor and dryness generated from AVIRIS data. G = gradational stretch applied. Sample collection locations are indicateimage is available HERE. PDF version of figure is available HERE. ERDAS Imagine format data are available HERE with material identifications attribute
12 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

method). Although this calibration technique introduces 

error in the overall shape, or hull, of the data by assuming a flat calibration-site spectrum when few surfaces are 

truly spectrally flat, the technique is ideal for use in frontier 

areas for which no field spectral data of a calibration site 

are available. In general, empirical line calibrations (for 

example, Rockwell and others, 2002, 2005, 2006) using 

reflectance data of a field surface as a reference source 

yield more accurate results. However, if continuum removal 

techniques are used to remove the spectral hull prior to data 

analysis, shape errors in the hull caused by Flat Field calibration have not been found to significantly affect accurate 

material identification.

The ASTER reflectance data were analyzed for mineral 

and vegetation content using an approach based on the principles of imaging spectroscopy that identifies spectral absorption features in the ASTER spectra and is similar to that used 

for the AVIRIS data in this study. This approach was originally 

developed for analysis of high spectral resolution, or spectroscopic, data (Clark and others, 2003a) and was adapted by the 

author for analysis of full scenes of ASTER multispectral data. 

The semiautomated approach involves continuum removal 

and least-squares curve fitting of ASTER spectra to selected 

laboratory reference spectra over spectral intervals characterized by diagnostic absorption features in the reference spectra. 

Reference spectra (Clark and others, 2003b) were convolved 

to ASTER spectral resolution (table 1) prior to analysis. 

Reference materials and material mixtures were selected for 

analysis of the ASTER data if they occur abundantly on the 

Earth’s surface in a wide variety of geologic and climatic 

environments and have absorption features that are diagnostic 

and unique at ASTER spectral resolution. Care was taken to 

include mineral assemblages that occur within hydrothermal 

alteration systems so that patterns of mineralogic zonation 

could be identified and mapped. This analysis methodology is 

currently being applied to an ASTER-based regional mineral 

resource and geoenvironmental assessment of the Central 

Colorado Mineral Belt (Church and others, 2008) and to a 

regional mineral resource assessment in southwestern Utah 

(Rockwell and Hofstra, 2009).

Mineral and Vegetation Maps 

Derived from ASTER Data

False-Color Composite Image—

Vegetation, Snow, and Surface Albedo

Figure 9 shows a false-color composite image produced 

from edge-enhanced ASTER radiance data (bands 431/RGB). 

Green vegetation is displayed in hues of green, and the brightness of the green color is proportional to chlorophyll content. 

Irrigated agricultural vegetation is visible in bright green, moist 

riparian vegetation and deciduous regrowth are shown in bright to 

medium green, and forest vegetation in dark green. Unvegetated, 

high albedo areas, which in the high Tushar Mountains and 

Antelope Range often represent altered volcanic rocks, are 

shown in white to light blue colors. In the Tushar Mountains, 

the bright areas correspond with volcanic rocks of the Mount 

Belknap and Big John calderas that have undergone regional 

propylitic (sericite and chlorite, Callaghan, 1973) to low-grade 

argillic alteration. In the Antelope Range, the bright areas mainly 

correspond to pyritic, “proximal propylitic” (or phyllic) alteration 

in the feeder zones of the replacement alunite deposits, or locally 

correspond to mined, argillically altered areas of these deposits. 

Unaltered to propylitically altered (“distal” type with calcite, 

chlorite and (or) epidote) igneous rocks with low albedo are 

visible in dark blue, especially within Marysvale Canyon along 

the western edge of the Antelope Range (fig. 2). Snow is visible 

in shades of cyan because of intense infrared absorption and is 

limited to the high Tushar Mountains.

Visible and Near-Infrared Mapping—

Iron Minerals

Reference spectra of iron-bearing minerals, vegetation, and 

water used for analysis of the ASTER data with key absorption 

features labeled, and representative examples of ASTER spectra 

of pixels identified as specific materials based on spectral similarity with the reference spectra, are shown in figure 10. Figure 11 

shows a map these materials produced from the ASTER data. 

Note that some of the identified materials are depicted using 

a gradational stretch to show variation in the fit × depth of the 

diagnostic absorption feature(s) used for analysis of that material 

(see map explanation and fig. 5). Fit × depth is proportional to 

both the least-squares fit of ASTER spectra to laboratory reference spectra and the depth of the diagnostic absorption feature(s) 

in the ASTER spectra. Low feature depths may indicate lower 

abundance of the mineral type in the pixel, given a constant grain 

size. For green vegetation, low feature depths (darker shades of 

green) may indicate decreased areal abundance and (or) chlorophyll content. Pixels identified as dry vegetation (shown in yellow 

in fig. 11) may also include carbonate, chlorite, and (or) epidote in 

low abundance.

The most important mineralogical feature of the map 

(fig. 11) is the discrimination of reddish soils and rocks bearing hematite and goethite, shown in orange hues on the map, 

Table 1. Measured spectral performance of ASTER VIS, NIR, 

and SWIR bands.

[N, nadir viewing geometry; μm, micrometer; m, meter. Data from ASTER 

User’s Guide (Earth Remote Sensing Data Analysis Center, 2005)]

ASTER

Band

Central

wavelength

(μm)

Bandwidth

(μm)

GIFOV

(ground

pixel size)

1 0.556 0.09 15 m

2 0.661 0.06 15 m

3 (N) 0.807 0.10 15 m

4 1.656 0.092 30 m

5 2.167 0.035 30 m

6 2.208 0.040 30 m

7 2.266 0.047 30 m

8 2.336 0.070 30 m

9 2.400 0.068 30 m
Mineral and Vegetation Maps Derived from ASTER Data 13

from high concentrations of ferric iron sulfates, hydroxides, 

and local oxides (shown in hues of red on map) that have 

more yellowish to orange color in outcrop and correspond 

mainly to hydrothermally altered rock, including phyllic 

alteration that is overprinted by supergene alteration caused by 

the weathering of pyrite. The reddish rocks and soils bearing 

hematite and (or) goethite shown in orange are characterized by a broad, convex-up hull in the VIS–NIR with deep 

absorption in the shortest ASTER wavelengths caused by 

iron absorption features in the ultraviolet and are spectrally 

similar to nanohematite at ASTER spectral resolution (fig. 10). 

The spectra of these rocks are not characterized by significant electronic crystal field absorptions near 1.0 μm typical of ferric iron minerals (Rockwell, 2004, and references 

therein). Rocks with these VIS–NIR spectral characteristics 

include the upper and middle red members of the Flagstaff 

Formation (Paleocene and Eocene; reddish-brown, interbedded calcareous mudstone, siltstone, and sandstone), the Crazy 

Hollow Formation (Oligocene; brownish-orange to brownishred fine-grained sandstone, siltstone, and mudstone), both 

well-exposed west and north of Richfield (Hintze and others, 

2003), the Red Hills Tuff Member of the Mount Belknap 

Figure 9. Map showing ASTER 431/RGB false-color composite image of the Marysvale region. Larger image is available HERE. PDF 

version of figure is available HERE. Edge-enhanced radiance data of bands 1–4, 6, and 8 are available HERE in ERDAS Imagine format.
Figure 10. Plot of selected convolved laboratory spectra of iron-bearing minerals, vegetation, and water (on left) used as referencedata. The mapped results of the analysis are shown in figure 11. Except for chlorite + muscovite, dry/green grass, and dry grass, mosfor these materials are in the VIS and NIR spectral regions. Reference spectra of additional minerals and materials (for example, copcummingtonite for generic ferrous iron) included in the VIS–NIR image analysis are not shown. Representative ASTER image spectrspecific materials based on spectral similarity with the reference spectra are shown at right with sampling locations, surface featurASTER spectrum selected from a pixel in which no materials were detected is shown in purple at top right. White arrows indicate diused in analysis. Note that emission features are also analyzed (upward-pointing arrows). Color of the spectra match the colors assimaterials in figure 11. BRCM = Big Rock Candy Mountain. Larger image is available HERE. PDF version of figure is available HERE.
Mineral and Vegetation Maps Derived from ASTER Data 15

Volcanics (Miocene, figs. 2 and 3) several kilometers north of 

Marysvale, and locally in altered rocks in the Antelope Range 

and Tushar Mountains, including Alunite Ridge and the Red 

Narrows kaolinite deposits on the northern slopes of the 

Tushar Mountains 3 km north of the Kimberly mining district 

(Rockwell and others, 2005). The basal section of the middle 

white member of the Flagstaff Formation contains reddish 

sandstone layers interbedded with limestone and gypsiferous 

mudstone (Hintze and others, 2003) that give the member 

similar spectral characteristics but with lesser fit × depth 

values (a more subdued convex shape) and thus is shown in 

slightly darker shades of orange in figure 11. Northeast of 

Richfield, alluvial soils in fallow fields derived from the red 

rocks of the Flagstaff and Crazy Hollow Formations show 

high fit × depth values (brightest orange) similar to those of 

the sedimentary rocks from which they are derived. South 

of Richfield, the ferric iron content of the soils in fallow 

fields decreases as the bedrock sources of the soils switch to 

Figure 11. Map of iron-bearing minerals, vegetation, and water derived from spectral analysis of ASTER data. Larger image is available 

HERE. PDF version of figure is available HERE. ERDAS Imagine format data are available HERE with material identifications attributed for 

use in a GIS.
16 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

unaltered volcanic rocks. Ferric iron with low to moderate 

fit × depth values (dark orange in fig. 11) was detected 

in goethitic (Rockwell and others, 2005) tailings deposits 

from the Old Deer Trail mine 2.2 km northwest of the old 

Alunite townsite (site of a loading and processing facility for 

alunite mined from Alunite Ridge in the middle 20th century 

and the current site of the mill for the Deer Trail mine). As 

the base metal mantos under Deer Trail Mountain are highly 

pyritic (Beaty and others, 1986), it is likely that most pyrite in 

the tailings has oxidized, and most of the resultant jarosite has 

weathered to goethite.

Rocks with abundant ferric iron minerals (shown in 

red in fig. 11) that were a spectral match to jarosite in the 

VIS–NIR (fig. 10) have significant ferric iron absorptions near 

1.0 μm (ASTER band 3) and can be considered to have higher 

concentrations of ferric iron than the areas shown in orange 

and discussed herein that were a spectral match to nanohematite. Areas with these spectral features include intense argillic 

and advanced argillic alteration in the Antelope Range, Tushar 

Mountains, and Sevier Plateau, supergene weathering of 

phyllic alteration at Big Rock Candy Mountain and the nearby 

Big Star alunite deposit, and alluvial fan deposits along the 

west bank of the Sevier River containing abundant alunite and 

kaolinite derived from the erosion of the 14 Ma alteration on 

Alunite Ridge and Deer Trail Mountain (Rockwell and others, 

2005). Altered rocks with similar spectral features were also 

identified locally in basin fill of the Sevier River Formation 

(Miocene and Pliocene) west and northwest of Marysvale, 

and in intracaldera fill of the Mount Belknap caldera in the 

high Tushar Mountains that has undergone regional propylitic 

(Callaghan, 1973) and local argillic alteration. Concentrations 

of ferric iron having absorption near ASTER band 3 and high 

fit × depth values (bright to medium red in fig. 11) are important targets for field sampling of hydrothermally altered and 

potentially mineralized rocks.

Several pixels with VIS–NIR–SWIR spectral characteristics of the ferric iron sulfate-hydrate mineral copiapite 

(Clark and others, 2003b, http://pubs.usgs.gov/of/2003/

ofr-03-395/PLOTS/M/copiapite_gds21.2201.gif) were identified on the flanks of Big Rock Candy Mountain (shown in 

magenta in fig. 11). Copiapite, in addition to alunogen and 

epsomite, occur in this highly pyritic phyllic alteration zone 

as precipitates from acidic fluids in drainage channels after 

rainfall (Cunningham and others, 2005). Although melting 

snow (Clark and others, 2003b, http://pubs.usgs.gov/of/2003/

ofr-03-395/PLOTS/L/melting_snow_1-16.9366.gif ) is used 

as a reference material, several pixels of melting snow in 

the high Tushar Mountains were misidentified as copiapite 

because they have absorptions of unknown origin near 1.0 μm 

like those of copiapite. Both melting snow and copiapite show 

marked decreases in reflectance from the NIR to the SWIR; 

thus, some confusion between these materials can be expected 

when mapping at ASTER spectral resolution. Most thick melting snow was correctly identified (light purple in fig. 11).

Vegetation

Green vegetation with pronounced chlorophyll absorption at ASTER band 2 (table 1) was detected at low to moderate elevations in the Tushar Mountains, Pahvant Range, and 

Sevier Plateau. Abundant and moist green vegetation with 

the highest chlorophyll content per pixel (brightest green in 

fig. 11) was detected in agricultural fields and riparian environments including spring-fed drainages in the mountains. Green 

vegetation on north-facing slopes is typically characterized by 

greater chlorophyll abundance per pixel (deeper chlorophyll 

absorptions shown in brighter tones of green in fig. 11) than 

green vegetation on more exposed southern slopes. Dry and 

green vegetation with both chlorophyll and lignin/cellulose 

SWIR absorptions were detected mainly on surfaces with low 

relief, both along the fringes of the green vegetation in the 

mountainous areas and in high plateaus above treeline. The 

dry and (or) green vegetation detected at lower elevations 

(and concomitant lower annual precipitation) surrounding the 

mountainous areas represents transitional vegetation communities between upland pine, aspen, and (or) maple forest with 

significant chlorophyll and relatively dry lowland vegetation 

including piñon, juniper, and sage. The mapping of such variations in vegetation dryness and greenness suggest that ASTER 

data may provide an efficient alternative to spectroscopic data 

for studies of burn severity after forest and rangeland fires for 

which the analysis of AVIRIS data has been proven to be useful (Kokaly and others, 2006).

Shortwave-Infrared Mapping 

and Detector “Scratch”

Selected reference spectra used in the analysis of the 

ASTER SWIR data are shown in figure 12, along with representative ASTER spectra of pixels identified as the reference materials based on spectral similarity. Figure 13 shows a 

map these materials produced from the ASTER data, a subset 

of which was published by Rockwell and others (2006). An 

important feature of figure 13 is the region of erroneous mineral 

detections indicated by the magenta rectangle that is oriented 

parallel to the satellite path approximately 20 km from the western edge of the ASTER scene (one-third of the image swath). 

This area of corrupted SWIR spectral response is present in 

all ASTER scenes and is related to a physical defect (detector 

“scratch”) in the SWIR detectors (Iwasaki and Oyama, 2005; 

Iwasaki and Tonooka, 2005). The SWIR data in this image 

region are characterized by a false and uneven reduction in the 

response of band 5 (table 1), resulting in erroneous detections 

of materials having absorptions in those wavelengths, including 

alunite, pyrophyllite, and kaolinite. Kaolinite in this region may 

appear spectrally similar to alunite and may be falsely identified as such. A polygon shapefile indicating the region affected 

by the SWIR detector “scratch” is provided with this report. 

Although difficult to recognize in figure 13, another parallel 
Figure 12. Plot of selected convolved laboratory spectra of clay, sulfate, mica, carbonate, and sorosilicate (epidote) minerahaving diagnostic SWIR absorption features (on left) used as references for analysis of ASTER data. The mapped results of thfigure 13. Reference spectra of additional minerals (for example, chlorite, chalcedony, and jarosite) included in the SWIR imaRepresentative ASTER image spectra of pixels identified as specific materials based on spectral similarity with the reference with their sampling locations, surface features, or lithologic unit. White arrows indicate selected diagnostic absorption featuthat emission features are also analyzed (upward-pointing arrow). Color of the spectra match the colors assigned to the identBRCM = Big Rock Candy Mountain. wxl = well-crystallized. Larger image is available HERE. PDF version of figure is available 
18 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

Figure 13. Map of clay, sulfate, mica, hydrous quartz, carbonate, and Mg-OH minerals derived from spectral analysis of ASTER 

shortwave infrared (SWIR) data. Larger image is available HERE. PDF version of figure is available HERE. ERDAS Imagine format data 

are available HERE with material identifications attributed for use in a GIS. Indurated sedimentary rocks from Rowley and others (2002) 

are also shown as colored polygons.
Mineral and Vegetation Maps Derived from ASTER Data 19

but less pronounced defect exists immediately to the east of 

the region affected by the primary detector scratch. The SWIR 

data affected by this secondary defect are characterized by false 

reductions in the response of band 7, resulting in erroneous 

detections of carbonate minerals, chlorite, and epidote. Calcite 

in this region may appear spectrally similar to dolomite or 

epidote. Jarosite and hydrous quartz (for example, chalcedony) 

also have diagnostic absorptions near band 7 and thus may also 

be incorrectly identified. For example, jarosite detected using 

the ASTER SWIR data (magenta in fig. 13) within argillized Joe 

Lott Tuff Member of the Mount Belknap Volcanics (unit Tmj of 

Rowley and others, 2002) on Copper Belt Peak (fig. 1) 10.4 km 

west of the town of Marysvale above the Copper Belt mine lies 

within the region affected by the secondary defect and is most 

likely incorrect. However, abundant ferric iron minerals were 

detected in that area by using the ASTER VIS–NIR data (red in 

fig. 11), and goethite (+ kaolinite + sericite, surrounding hematite + smectite on peak 10962 closest to the mine) was detected 

using high-altitude AVIRIS data (figs. 48 and 49 in Rockwell 

and others, 2005).

Advanced Argillic Alteration 

and Areal Mixing

In figure 13, advanced argillic alteration associated with the 

primarily steam-heated alunite deposits surrounding 23–21 Ma 

intrusive rocks are clearly visible in the Antelope Range north 

of the town of Marysvale. Alunite related to higher-temperature 

magmatic steam deposits was detected in the east-central Tushar 

Mountains, including along Alunite Ridge, at the small L & N 

deposit 1 km to the west, and at the Close In colluvial alunite 

deposit in the Sevier River valley. Alunite and kaolinite were also 

detected at the foot of the mountains along Gold Gulch 2.5 km 

south-southeast of the Alunite townsite within Quaternary basin 

fill (unit QTs of Rowley and others, 2002) adjacent to outcrops 

of volcanic rocks erupted from both the Mount Belknap and 

Monroe Peak calderas. The identified alunite and kaolinite in 

these deposits correlate well with the distributions of these and 

related minerals mapped by AVIRIS data (fig. 6 and figs. 49, 

51, and 53 of Rockwell and others, 2005). Alunite was also 

detected at the Sheeprock alunite deposit on the southwestern 

edge of the Tushar Mountains and in several locations on the 

Sevier Plateau, including southeast of Monroe (mainly 1.2 km 

south and 2 km south-southeast of the Monroe hot spring), the 

Marysvale Peak and Aluminum Queen alunite deposits within the 

Monroe Peak caldera, and on the eastern side of the plateau along 

Greenwich Creek 5 km northeast of the Box Creek kaolinite 

deposit (Callaghan, 1973). Primarily kaolinite was identified at 

the Box Creek deposit.

Because of the 30-m GIFOV of the ASTER SWIR data, 

areal mixing of materials has an increased effect on spectral shape 

than in remote sensing data with smaller GIFOV such as AVIRIS 

data. For example, areal mixtures of kaolinite (Al-OH vibrational 

absorptions at bands 5 and 6) and dry vegetation (lignin/cellulose 

absorptions at bands 5 and 8, fig. 7 and table 1) can result in a 

spectrum similar to that of alunite characterized by deep absorption at band 5 and moderate absorption at band 6. Such spectral 

mixing results in a general overdetection of alunite throughout the 

ASTER scene, especially where abundant dry vegetation is present adjacent to argillically altered rocks.

Natroalunite was identified using the ASTER SWIR 

data at the Big Star and Al Kee Mee natroalunite deposits, 

and in wall-rock alteration surrounding the alunite veins on 

Alunite Ridge (figs. 12 and 13). The natroalunite (+ quartz + 

kaolinite + pyrite ± dickite) on Alunite Ridge was also identified 

using AVIRIS data (Rockwell and others, 2005) and confirmed 

in the laboratory (Rockwell, 2002). However, pixels with spectral features similar to that of natroalunite at ASTER spectral 

resolution were also identified at the White Horse deposit, 

where none was found using AVIRIS data (fig. 6) and field 

sampling. Mixtures of alunite with minor kaolinite have SWIR 

spectral features similar to those of natroalunite at ASTER spectral resolution, and thus pixels matched to natroalunite using 

ASTER data were classified on the map explanation of figure 13 

either as natroalunite or mixtures of alunite and minor kaolinite. 

ASTER SWIR data do not have sufficient spectral resolution 

to accurately discriminate natroalunite from mixtures of alunite 

and kaolinite, but pixels matched to natroalunite can be considered to be transitional in alunite content between pure alunite 

and mixtures of alunite with major kaolinite (fig. 12), which 

can be used to identify zones of maximum hydrothermal fluid 

conductivity, acidity, and temperature.

The replacement alunite deposits in the Antelope Range 

are capped by titanium-bearing, hydrofractured, subsinter silica 

consisting of opal and chalcedony (Rockwell and others, 2006, 

and references therein). These silica caps have been mostly 

eroded away and are best exposed at the uppermost levels of the 

Yellow Jacket deposit and in one boulder at the White Horse 

deposit. Because of the small size of the remnant caps and the 

presence of grasses and sage, only six pixels of hydrous quartz 

(spectral match to chalcedony) were identified using AVIRIS data 

with 17-m GIFOV in the Antelope Range, in colluvial blocks 

located in the central Yellow Jacket deposit (Rockwell and others, 

2005). No significant, field-verified hydrous quartz associated 

with alunite deposits was detected in the study area using the 

ASTER SWIR data, although several pixels were identified in 

colluvium derived from altered Navajo Sandstone (Jurassic, unit 

Jn of Rowley and others, 2002) on the east face of Deer Trail 

Mountain, on Big Rock Candy Mountain, and within argillically 

altered rocks 6.3 km southeast of Monroe.

Phyllic Alteration and Pyrophyllite

Where the Sevier River has exposed the phyllic (or “proximal propylitic”) alteration underlying the alunite at Big Rock 

Candy Mountain (BRCM) along Marysvale Canyon (fig. 2), the 

ASTER data analysis identified kaolinite + smectite, gypsum, 

and local kaolinite + sericite and smectite (montmorillonite) 

(figs. 12 and 13). These assemblages were confirmed through 

field sampling (Rockwell and others, 2005; Cunningham and 
20 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

others, 2005) and are typical of the supergene weathering of 

pyritic rocks, in this case altered volcanic rocks bearing hypogene 

pyrite, illite, and local pyrophyllite. Similar phyllic alteration 

with a supergene overprint is also present in the lower parts of the 

nearby Big Star deposit along the east bank of the Sevier River 

and on the north flank of the White Horse deposit (Rockwell and 

others, 2006). Several pixels of pyrophyllite were detected one 

kilometer north of BRCM that have been verified though field 

checking and AVIRIS data analysis (Rockwell and others, 2005, 

2006; Cunningham and others, 2005). The accurate identification 

of pyrophyllite and its differentiation from alunite are difficult 

using ASTER SWIR data because of the low spectral and spatial 

resolution of the ASTER data and because of the typically small 

exposures in which pyrophyllite occurs. Pixels with SWIR spectral characteristics similar to pyrophyllite were also identified in 

the Sevier Valley several kilometers southeast of Richfield. It is 

unlikely that these identifications of pyrophyllite are correct. They 

most likely represent an areal mixture of more common clay 

minerals and dry vegetation. Two areas with kaolinite, smectite, 

kaolinite + smectite, and several pixels of alunite and alunite + 

kaolinite were also identified in this area, although not at the same 

locations as the pixels with spectral features similar to pyrophyllite. These areas have not been field checked but are most 

likely clay minerals in alluvium derived from the Crazy Hollow 

Formation exposed on the flanks of the Pahvant Range west of 

Richfield. Areal mixtures of alunite and dry vegetation may result 

in spectra resembling that of pyrophyllite, as the dry vegetation will increase spectral response in band 6. Areal mixtures of 

alunite, lichen, and (or) other dry vegetation produced AVIRIS 

spectra similar to mixtures of alunite + pyrophyllite in the Silica 

Hills located in the southern portion of the Yellow Jacket deposit 

(fig. 2, Rockwell and others, 2005). Detections of pyrophyllite in 

the upper Silica Hills using the ASTER data may also have been 

influenced by such mixing effects. However, quartz-topaz-dickite 

assemblages in this area (Rockwell and others, 2000), in addition 

to natroalunite-natrojarosite-dickite-kaolinite assemblages found 

in the lower, southwestern part of the Silica Hills adjacent to 

Sage Flat (figs. 1 and 2, Rockwell and others, 2005) may indicate 

that the alunite in this area is magmatic hydrothermal in origin, 

at least in part, as it appears to be at the White Horse deposit 

(Rockwell and others, 2006). In epithermal environments with 

magmatic hydrothermal alunite such as the Goldfield mining 

district in Nevada (Rockwell, 2000) and Tintic mining district in 

Utah (Rockwell and others, 2005), pyrophyllite and alunite (and 

pyrite) can co-occur intimately; thus, some of the pyrophyllite 

in the Silica Hills may be accurate. Calcite and epidote (“distal 

propylitic” assemblage) were identified 1 km east of the BRCM 

deposit within quartz monzonites of the Hoover pluton (figs. 1 

and 2; 23 Ma, Cunningham and others, 1984a, and references 

therein) that were propylitically altered by the Miocene hydrothermal systems active in the vicinity of BRCM. These minerals 

were also identified there by using AVIRIS data (Rockwell and 

others, 2000, 2005). Calcite and epidote ± sericite were also 

identified within potentially propylitically altered “Potassium-rich 

mafic volcanic rocks” (Miocene, unit Tpm of Rowley and others, 

2002) 8 km southeast of the town of Marysvale.

Mineral assemblages similar to those at BRCM previously 

described were detected in mine waste and exposed bedrock near 

Sulphurdale, 4.6 km south of Cove Fort (fig. 13). Sulphurdale is 

the site of significant acid hydrothermal alteration, geothermal 

wells, and a large sulfur deposit that produced all of the country’s native sulfur in 1893 (Callaghan, 1973). Abundant ferric 

iron minerals were detected there by using the VIS–NIR data 

(red in fig. 11), and jarosite, gypsum, and smectite were detected 

using the SWIR data, in addition to several pixels of alunite surrounded by kaolinite + smectite, although the area has not been 

field checked.

Carbonate

Between Kanosh and Cove Fort in the northwest quadrant 

of the ASTER scene, calcite (bright green in figs. 12 and 13) 

was identified in areas underlain by the Ophir Formation (mixed 

limestones, quartzites, and shales) and the Redwall, Callville, 

and Kaibab Limestones (Rowley and others, 2002; Hintze and 

others, 2003). Dolomite (dark green in figs. 12 and 13) and 

mixtures of dolomite and calcite and (or) dry vegetation (blue 

in figs. 12 and 13) were identified within the Laketown, Fish 

Haven, Sevy, Simonson, Ely Springs, and Pakoon Dolomites. 

Significant calcite was also identified within limestones and 

other calcareous rocks of the Flagstaff (middle white member) 

and Green River Formations west of Richfield, and related 

alluvium, colluvium, and mass-wasting deposits (Hintze and 

others, 2003). Comparison of the mineral identifications from 

the ASTER data and the mapped extent of the lithologic units 

from Rowley and others (2002), also shown in figure 13, 

illustrates how vegetation cover (fig. 11) obscures most of the 

calcite and dolomite in these carbonate units. Calcite was also 

identified in Quaternary hot spring travertine deposits (Hintze 

and others, 2003) 8 km northwest of Kanosh. North and west 

of the travertine, large areas of smectite and kaolinite + smectite 

with local hydrous silica (possibly opal and (or) chalcedony 

derived from hot springs) were mapped in Holocene alluvium.

Epidote

Figure 12 shows that spectral matching to the reference 

spectrum of epidote (blue at left) resulted in identifications of 

both epidote and mixtures of dolomite ± calcite ± dry vegetation 

(both blue at right and in fig. 13). This result can be expected, as 

the SWIR spectral response of epidote is very similar to that of a 

calcite + dolomite mixture. The mineral mapping results should 

be compared to geologic maps to determine the lithology and origin of carbonate, chlorite, epidote, and amphibole identified using 

ASTER data, as these minerals are similar in SWIR response 

at ASTER spectral resolution. In addition, these minerals often 

occur as intimate and areal mixtures with each other, especially 

given the large GIFOV of ASTER SWIR data. The differentiation 

of these minerals is further complicated by areal mixing with dry 

vegetation which is also characterized by absorption at ASTER 

bands 7 and 8 (figs. 7 and 10).
Mineral and Vegetation Maps Derived from ASTER Data 21

Sericites

The analysis of the ASTER SWIR data for sericite (white 

potassium mica) was performed using four reference spectra 

of muscovites having a range of cation substitutions between 

aluminum and iron/magnesium (Clark and others, 2003a). 

Increases in iron or magnesium in the muscovite structure will 

result in a shift of the primary Al-OH vibrational absorption to 

slightly longer wavelengths. In figure 13, pixels shown in cyan 

that are labeled “Al illite/muscovite” are spectral matches to 

either muscovite GDS113 Ruby (medium to high aluminum), 

muscovite CU91–250A (medium aluminum), or muscovite 

CU93–1 (low aluminum) (Clark and others, 2003b). Pixels 

labeled “Al/Fe illite/muscovite” in figure 13 (shown in 

medium blue) were a spectral match to an iron-rich muscovite 

(GDS116 Tanzania) and have spectra characterized by a flatter spectral response between bands 6 and 9 than aluminum 

sericite. Pixels matched to iron-rich muscovite (and other lowaluminum muscovite reference spectra) may represent chlorite 

+ muscovite mixtures, especially where they correspond with 

pixels matched to a reference spectrum of chlorite + muscovite 

(fig. 10) from the VIS–NIR data analysis. This spectral confusion has also been recognized with AVIRIS data (Rockwell 

and others, 2005).

Spectrally pure sericite occurs in both altered and unaltered 

sedimentary and volcanic units. In the replacement alunite deposits of the Antelope Range, aluminum-rich sericite (cyan in fig. 13) 

occurs at deep levels in the Miocene hydrothermal systems distal 

to the phyllic (or “proximal propylitic”) alteration within weakly 

altered volcanic rocks including the Bullion Canyon Volcanics 

adjacent to the BRCM and Big Star deposits (fig. 12) and locally 

in the Osiris Tuff surrounding the White Horse and Yellow 

Jacket deposits. Similar sericite was identified in the high Tushar 

Mountains within regionally propylitized and locally argillically 

altered Bullion Canyon Volcanics and along the west bank of the 

Sevier River within Quaternary basin fill (unit QTs of Rowley 

and others, 2002) derived from the altered rocks on Alunite 

Ridge and Deer Trail Mountain (Rockwell and others, 2005). 

Aluminum sericite along with kaolinite and kaolinite + sericite 

were identified in the Crazy Hollow Formation west of Richfield 

and in related alluvial and colluvial deposits (Hintze and others, 

2003). Aluminum/iron sericite was identified in bentonitic 

siltstones, claystones, and sandstones of the Aurora Formation 

(40–38 Ma, unit Tau of Hintze and others, 2003) immediately 

to the south. Calcite and calcite + sericite were identified in thinto medium-bedded limestone units of the Aurora Formation. 

Twelve kilometers east-northeast of Richfield, aluminum/iron 

sericite (with local smectite or low-abundance sericite without 

a mica absorption at ASTER band 8) was also identified in the 

Twelvemile Canyon Member of the Arapien Shale (Jurassic, unit 

Jatc of Williams and Hackman, 1971) which includes brick-red 

shales, bluish-gray and red gypsiferous shales, and bluish-gray 

calcareous shales with interbedded limestones. This sericite generally corresponds with pixels matched to chlorite + muscovite in 

the VIS–NIR data analysis (cyan in figs. 10 and 11), which most 

likely represent bluish-gray shales with sericite and VIS–NIR 

absorptions similar to the iron-related absorptions of chlorite. 

Calcareous Arapien shales and (or) limestone units are clearly 

differentiated by calcite and calcite + sericite identified using the 

ASTER SWIR data, and red shales are indicated by minor ferric 

iron (orange in fig. 11) identified using the ASTER VIS–NIR 

data. Calcite, epidote, and calcite + sericite were identified in 

undifferentiated latite and basaltic andesite flows (unit Tla of 

Williams and Hackman, 1971) in contact with the Arapien Shale 

in this area, indicating possible propylitic alteration.

Argillic Alteration in Quartz Arenites

As quartzites and quartz arenites are brittle and have little 

to no natural acid-buffering capacity, they fracture easily and 

are excellent hosts for fracture-controlled hydrothermal alteration. As these rocks are erosion resistant, they are typically well 

exposed and are thus ideal targets for remote-sensing-based 

mineral mapping. Therefore, such rocks may serve as important 

surface indicators of concealed mineral deposits in sedimentary 

and metamorphic terranes. Quartzites and undivided sedimentary units that include quartzites and other siliciclastic rocks in 

the Marysvale area are shown in figure 13. Abundant aluminum 

sericite was identified within an exposure of Tintic Quartzite 

(Cambrian) 9–10 km west-southwest of Kanosh. This sericite is 

most likely metamorphosed detrital muscovite in the groundmass 

of the quartzite. In the Tintic mining district of central Utah, the 

Tintic Quartzite was found to host argillic alteration including 

hematite + pyrophyllite, dickite, kaolinite, kaolinite + sericite, 

and local alunite (Rockwell and others, 2005). Kaolinite with possible local alunite was identified in Navajo Sandstone (Hintze and 

others, 2003) 5.5 km southeast of Kanosh along the western foot 

of the Pahvant Range. In the vicinity of Alunite Ridge and Deer 

Trail Mountain in the Tushar Mountains, the Navajo Sandstone is 

locally altered to quartzite and has been found to host significant 

argillic alteration related to the magmatic steam alunite deposits 

and base- and precious-metal manto deposits at the Deer Trail 

mine dated at 14 Ma (Rockwell and others, 2005, and references 

therein). Dickite was identified in Navajo Sandstone by using 

AVIRIS data on the upper north-northeast and south-southwest 

flanks of Deer Trail Mountain, and well-crystallized dickite in 

the groundmass of quartzite in Navajo Sandstone sampled from 

colluvium along the northeastern base of Deer Trail Mountain 

was confirmed in the laboratory. These altered rocks were also 

identified using the ASTER SWIR data (fig. 13). Alunite identified within the Navajo in this area has not been field verified 

and may represent areal mixtures of clay minerals with dry 

vegetation, at least in part. Vein alunite similar to that on Alunite 

Ridge is known to have formed above the present-day summit 

of Deer Trail Mountain (and the dickite in the Navajo) because 

of vein alunite in landslide blocks derived from the altered upper 

parts of the mountain found at the Close In alunite deposit in 

Marysvale Valley. Sericite ± kaolinite were identified in relatively 

weakly altered Navajo Sandstone in this area, especially where 

well exposed on south-facing slopes, including mainly colluvial 

deposits on the southwest and southeast flanks of Deer Trail 

Mountain and along Gold Gulch 5 km to the southeast.
22 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

Kandite Clay Differentiation

The kandite clay minerals dickite ± kaolinite may occur 

with quartz in fracture-controlled selvages in a variety of epithermal ore deposit types, often on the periphery of advanced 

argillic lithocaps (Rockwell and others, 2006, and references 

therein). These argillic selvages were formed by hydrothermal fluids with high silica activities and may be mineralized 

with base and precious metals. The dickite-bearing selvages 

(± alumino phosphate-sulfate minerals) usually occur distal 

to the halo of intimately mixed kaolinite + alunite (fig. 6) that 

surrounds replacement alunite deposits in the Antelope Range 

(Rockwell and others, 2000, 2005; Cunningham and others, 

2005). As the kandite group minerals have diagnostic and 

complex doublet Al-OH absorption features in the SWIR that 

vary in shape with crystallinity (Crowley and Vergo, 1988; 

Pontual and others, 1997; Clark and others, 2003b), they are 

readily identifiable by using spectroscopic sensors such as 

AVIRIS and are thus important targets for remote-sensingbased mineral mapping. Figure 6 shows that dickite, wellcrystallized kaolinite, and poorly crystallized and (or) impure 

kaolinite were differentiated based on spectral shape at the 

White Horse deposit using AVIRIS data. However, reflectance 

spectroscopy of the selvages from the White Horse mine 

indicate that dickite and kaolinite are often intimately mixed 

(Rockwell and others, 2006), and areal mixing of the two minerals will thus present difficulties in the remote discrimination 

of the minerals, especially with the large GIFOV of ASTER 

SWIR data.

A recent study used ASTER SWIR data to differentiate 

between kandite minerals in an epithermal deposit (Ducart 

and others, 2006). As dickite and kaolinite have similar 

SWIR spectral shapes at ASTER spectral resolution (fig. 14), 

dickite is not normally included by the author as a reference 

in the analysis of ASTER SWIR data, and pixels matched to 

a reference spectrum of well-crystallized kaolinite (fig. 10) 

are labeled “kaolinite ± dickite/nacrite” in the map explanation (fig. 13). To demonstrate that spectral shape alone is 

insufficient to accurately discriminate dickite from kaolinite, 

dickite was added as a reference spectrum for the analysis of 

the ASTER SWIR data. Figure 15 shows the results of this 

analysis. Based on comparison with geologic maps and results 

from analyses of AVIRIS and laboratory data (Rockwell 

and others, 2005), the differentiation of dickite and kaolinite 

shown in figure 15 is spurious and inconsistent. For example, 

pixels matched to the dickite reference spectrum occur in 

(1) sedimentary rocks (mainly the Crazy Hollow Formation) 

west of Richfield where no dickite is expected; (2) in the 

weathered phyllic alteration on the flanks of BRCM where 

no dickite is found; (3) in volcaniclastic sedimentary rocks 

(unit Tmps of Rowley and others, 2002) that have been 

found to alter preferentially to kaolinite rather than dickite 

(fig. 6 and Rockwell and others, 2006) 1 km northwest of the 

White Horse mine and in the northeastern part of the Yellow 

Jacket alunite deposit; and (4) in basin fill of the Sevier River 

Formation west of the town of Marysvale where kaolinite was 

mapped using AVIRIS data.

Based on the greater depth of the principal SWIR Al-OH 

absorption feature of the dickite reference spectrum relative 

to that of kaolinite (fig. 14b), the results of the ASTER SWIR 

data analysis shown in figure 13 were reevaluated to examine 

the relationship of band depth and kandite mineral identification. Gradational stretches were applied to the fit × depth 

results of pixels matched to well-crystallized kaolinite, and 

to pixels matched to alunite, alunite + kaolinite, and natroalunite for spatial context (fig. 16a). These stretched results 

Figure 14. Shortwave infrared spectral plots of dickite and well-crystallized kaolinite from Clark and others (2003b) convolved to 

ASTER spectral resolution. (a) Reflectance plot showing that the spectral shapes are similar over this spectral range, suggesting that 

shape alone is insufficient to discriminate the two minerals. (b) Continuum-removed reflectance plot demonstrating that the depth of 

the 2.2-micrometer Al-OH feature of the dickite spectrum is significantly greater than that of the kaolinite spectrum. PDF version of 

figure is available HERE.
Mineral and Vegetation Maps Derived from ASTER Data 23

Figure 15. Map of clay, sulfate, mica, hydrous quartz, carbonate, and Mg-OH minerals derived from spectral analysis of ASTER 

shortwave infrared (SWIR) data with dickite added as a reference spectrum. Larger image is available HERE. PDF version of figure is 

available HERE. ERDAS Imagine format data are available HERE with material identifications attributed for use in a GIS.
Figure 16. Results of ASTER band depth analysis of mineral identification results shown in figure 13 over the Yellow Jacket and Al Kee deposits in the Antelope Range. (a) Gradationally stretched fit × depth results of pixels matched to alunite (shades of red), alunite + kao

natroalunite (shades of purple), and kaolinite (shades of yellow). Larger image is available HERE. ERDAS Imagine format data are availaidentifications attributed for use in a GIS. (b) Results from (a) recoded and recolored to highlight kandite mineral differentiation. Pixels mred, alunite + kaolinite in orange, and natroalunite in purple. Pixels matched to kaolinite reference spectrum with high fit × depth values (a) at left) are shown in yellow and are interpreted to represent dickite or well-crystallized kaolinite. Kaolinite matches with lower fit × dof yellow in (a) at left) are shown in green, and are interpreted as kaolinite, mainly poorly crystallized. Results of (b) covering the entire Afigure 17.
Comparison of AVIRIS- and ASTER-Derived Mineral Maps 25

were recoded and recolored to highlight the kandite mineral 

discrimination based on band depth (fig. 16b). Pixels identified 

as kaolinite with high fit × depth values were colored yellow, 

and those with lower fit × depth values were colored green. 

Figure 17 shows these recolored results over the full ASTER 

scene. Although the kaolinite pixels with high fit × depth values (yellow in fig. 16) generally correspond well with areas in 

which dickite was detected using AVIRIS data (indicated with 

magenta circles), some of these pixels correspond to wellcrystallized kaolinite ± minor alunite (for example, in the eastern Big Star deposit adjacent to the Antelope mine, figs. 1 and 

2). Therefore, these pixels were interpreted as either dickite 

or well-crystallized kaolinite and occur almost exclusively in 

areas of hypogene argillic alteration. At the BRCM and White 

Horse deposits, the dickite and (or) well-crystallized kaolinite 

pixels correspond with the dickite-bearing argillic selvages 

identified using AVIRIS data, and the alunite + kaolinite 

halos around the alunite cores were identified as mixtures of 

alunite + kaolinite (orange in figs. 13 and 17). Dickite detected 

using AVIRIS data in altered Navajo Sandstone on the upper 

northeast and southwest flanks of Deer Trail Mountain, and in 

related colluvium at the eastern mountain base, was also correctly identified as dickite and (or) well-crystallized kaolinite. 

Pixels matched to kaolinite with lesser fit × depth values 

(green in fig. 17) correspond to sedimentary kaolinite in the 

Crazy Hollow Formation west of Richfield and in kaolinitic 

areas associated with the alunite deposits. These areas have 

been interpreted as kaolinite, mainly poorly crystallized and 

(or) impure (low abundance). Although the kandite mineral 

discrimination based on band-depth analysis shows promise, 

substantial errors exist, and the results are useful mainly as 

a guide for field sampling of high-grade argillic alteration. 

In addition, as band depth is proportional to material abundance given a constant grain size (Clark, 1999), dickite in 

low abundance (for example, in alluvium derived from altered 

areas) may be misidentified as poorly crystallized kaolinite. 

Figure 18 shows the results of the kandite clay differentiation 

merged with the standard SWIR mapping results shown in figure 13. Pixels with spectra matched to the reference spectrum 

of well-crystallized kaolinite (fig. 12) shown in figure 13 have 

been substituted with (1) the dickite and (or) well-crystallized 

kaolinite (light pink in fig. 18) and (2) poorly crystallized or 

impure kaolinite (yellow in fig. 18) derived from the banddepth analysis.

Comparison of AVIRIS- and ASTERDerived Mineral Maps

Figure 19 shows mineral maps of the White Horse 

mine area produced from low- and high-altitude AVIRIS data, 

and the ASTER data. The 3-m pixel size of the low-altitude 

AVIRIS data (fig. 19a) is well suited for delineating most mappable surface features of the deposit. These data are capable 

of accurately resolving the clay-free alunite zones at the center 

of the deposit from the surrounding 14–15-m-wide alunite + 

kaolinite zone, the 10–11-m-wide “broken clay zone,” and outer 

alunite + kaolinite ± illite zones, which include mine waste rock 

(Rockwell and others, 2006). These data can also resolve many 

small, fracture-controlled zones of alunite + kaolinite ± illite 

surrounded by well-crystallized kaolinite in peripheral areas of 

the deposit. The typically 2–3-m-wide, fracture-controlled argillic selvages that occur peripheral to the central alunite-bearing 

zones are typically intimate mixtures of quartz, dickite, and 

kaolinite, and the low-altitude data are capable of delineating 

the most dickite-rich zones within the selvages, although pixels 

identified as dickite and kaolinite usually occur in close juxtaposition to each other.

The high-altitude AVIRIS data (fig. 19b) with 17-m 

pixel size are capable of delineating the central alunite zone 

and surrounding alunite + kaolinite transition and argillic 

zones, the pyritic “proximal propylitic” or phyllic zone that 

underlies and surrounds the argillic zones, and the “distal” 

propylitically altered volcanic rocks containing calcite and 

possible chlorite. However, when compared to the map 

derived from the low-altitude AVIRIS data, the occurrence of 

dickite is overestimated at the expense of areal and intimate 

mixtures of kaolinite ± dickite ± trace alunite, and thus pixels 

matched to dickite had been labeled as a mineralogically 

mixed map unit. The 17-m pixel size of the data renders them 

less capable of resolving the intimate mixtures of dickite and 

kaolinite in the argillic zones and results in an underestimation 

of the abundance of kaolinite within them. Nevertheless, 

analysis of the high-altitude AVIRIS data has clearly identified the halos of dickite-bearing, high-grade argillic alteration 

in addition to some of the narrow alunite + kaolinite zones 

surrounded by well-crystallized kaolinite mentioned previously, especially in the volcaniclastic Tmps unit outlined in 

figure 6.

If the high-grade argillic alteration detected using the 

band-depth analysis is merged with the standard shortwaveinfrared mineral mapping (fig. 18), the ASTER data (fig. 19c) 

with 30-m pixel size are also capable of delineating most 

primary deposit features and zoning, but the clay-free central 

alunite zone (30–32 m wide) cannot be accurately discriminated from the surrounding alunite + kaolinite transition zone 

because of areal mixing effects. In addition, areal mixing of 

alunite, clay minerals, and dry vegetation having leaf biochemical absorptions overlapping with the primary sulfate 

feature of alunite resulted in an overestimation of alunitebearing mineral assemblages at the expense of clay minerals, mainly kaolinite (for example, localities labeled “1”, 

fig. 19c). Such apparent misidentification of alunite usually 

occurs at the edges of argillically altered areas where areal 

mixing with surrounding dry vegetation and soils with dry 

plant litter can occur. Sensor noise and (or) subtle errors in 

the reflectance calibration may also contribute to the alunite 

overestimation. Small, peripheral alunite zones detected with 

the AVIRIS data also were detected with the ASTER data 

(locality “2”).
26 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

Figure 17. Map of alunites and kandite clay minerals derived from spectral analysis of ASTER shortwave infrared (SWIR) data. 

Larger image is available HERE. PDF version of figure is available HERE. ERDAS Imagine format data are available HERE with material 

identifications attributed for use in a GIS. Areas where spectrally pure dickite was identified with AVIRIS data analysis and (or) 

laboratory analysis of field samples are indicated with magenta circles.
Comparison of AVIRIS- and ASTER-Derived Mineral Maps 27

Figure 18. Mineral map from figure 13 merged with results of kandite clay differentiation based on band-depth analysis. Pixels 

matched to well-crystallized kaolinite shown in yellow in figure 13 have been substituted with (1) dickite and (or) well-crystallized 

kaolinite (light pink) and (2) poorly crystallized or impure kaolinite (yellow) derived from the band-depth analysis. Larger image is 

available HERE. PDF version of figure is available HERE. ERDAS Imagine format data are available HERE with material identifications 

attributed for use in a GIS.
28 Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah

typically supergene clay assemblage kaolinite + smectite was 

smectite, kaolinite + sericite, sericite, smectite (or low-

“5”) using both the AVIRIS and ASTER data. Low-abundance 

the proposed relict feeder zone developed in Osiris Tuff × depth) kaolinite + sericite in alluvium derived 

from the deposit (dark shades of cyan in gradational stretch, 

which kaolinite + sericite and sericite in addition to ferric 

- was removed from the map for the sake of simplicity.

assemblages associated with the weathered “proximal propy- peripheral to the central alunite-bearing zones (for example, locallitic” or phyllic alteration zone in this area and in other areas ity “6”) and at the Saturday prospect (locality “7”) where dickite 

closer to the center of the White Horse deposit (locality “4”) in and kaolinite were detected using the AVIRIS data. Another 

which gypsum was also locally detected as it was in similarly 

(locality “8”) consisting mainly of kaolinite with local dickite 

Figure 19. Comparison of shortwave infrared (SWIR) mineral maps derived from AVIRIS and ASTER data. (a) Low-altitude AVIRIS 

mapping results from figure 6. (b) High-altitude AVIRIS mapping results. PDF version of map with full explanation is available HERE

(Rockwell and others, 2005). (c) Subset of ASTER mapping results from figure 18. See text for explanation of labeled sites. Larger 

image is available HERE. PDF version of figure is available HERE.
References 29

was identified as containing poorly crystallized kaolinite (yellow 

in fig. 19c) with local dickite or well-crystallized kaolinite (pink) 

using the ASTER data. Several pixels with spectra matching the 

alunite (red) and alunite + kaolinite (orange) reference spectra 

were also identified in this area using the ASTER data, although 

no alunite was detected there with the AVIRIS data.

Sericite (cyan in fig. 19c) and local kaolinite + sericite were 

identified in weakly altered undivided intracaldera intrusions (unit 

Tmpi, fig. 3) and locally in Osiris Tuff using both the AVIRIS 

and ASTER data (for example, locality “9”). Calcite and calcite 

+ sericite (muscovite) were identified using all three data types 

in outlying, propylitically altered areas of these intrusions and in 

lava flows of Monkey Flat Ridge (unit Tmpf, fig. 3) to the south 

of the mine (locality “10”).

Conclusions

This study demonstrates that methodologies for remote 

material identification involving continuum removal and leastsquares curve fitting designed for analysis of high spectral 

resolution data can be applied to ASTER multispectral data to 

efficiently generate maps of surface mineralogy and vegetation 

groups that are useful for regional hydrothermal alteration 

detection and characterization and the verification and updating 

of geologic maps (especially in well-exposed sedimentary terranes). These maps are highly applicable to regional mineral 

resource assessments and correlate well with more detailed 

maps generated from analysis of low-altitude AVIRIS data that 

were used for deposit-scale mapping of mineral zonation related 

to Miocene advanced argillic alteration and with maps generated from high-altitude AVIRIS data used for a district-scale 

geoenvironmental study. Concentrations of iron-, clay-, and (or) 

sulfate-bearing (gypsum and jarosite) minerals formed by supergene weathering of pyritic rocks associated with phyllic alteration 

(for example, at Big Rock Candy Mountain), alteration associated 

with Pleistocene to recent hydrothermal activity (for example, 

Sulphurdale), and pyritic tailings deposits (old Deer Trail mine) 

were identified using the ASTER data, demonstrating the applicability of ASTER data for regional geoenvironmental assessments.

Acknowledgments

The author thanks the USGS Land Processes Distributed 

Active Archive Center (LP DAAC), the NASA Earth Observing 

System Data and Information System (EOSDIS), and the Earth 

Remote Sensing Data Analysis Center (ERSDAC) of Japan for 

providing the ASTER data analyzed for this report, and NASA 

Jet Propulsion Laboratory for providing the AVIRIS data. Thanks 

also to Albert H. Hofstra and Eric D. Anderson of the USGS for 

their helpful reviews of this manuscript.

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References 31

Publishing support provided by:

Denver Publishing Service Center, Denver, Colorado

Manuscript approved for publication, May 29, 2009

Edited by Mary A. Kidd

Layout by Joy Monson

For more information concerning this publication, contact:

Team Chief Scientist, USGS Central Mineral Resources

Box 25046, Mail Stop 973

Denver, CO 80225

(303) 236-1562

Or visit the Central Mineral Resources Team Web site at:

http://minerals.cr.usgs.gov/

This publication is available online only at:

http://pubs.usgs.gov/sir/2009/5117/

Rockwell, B.W., Cunningham, C.G., Breit, G.N., and Rye, 

R.O., 2006, Spectroscopic mapping of the White Horse alunite deposit, Marysvale volcanic field, Utah: Evidence of a 

magmatic component: Economic Geology, v. 101, no. 7, 

p. 1377–1395.

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and carbonate minerals across northern Nevada using ASTER 

thermal infrared emissivity data—Implications for geologic 

mapping and mineral resource investigations in well-studied 

and frontier areas: Geosphere, v. 4, no. 1, p. 218–246, doi: 

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quadrangle, southwestern Utah, using ASTER satellite 

data, in Abstracts with Programs, Geological Society of 

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Rockwell, B.W.—Comparison of ASTER- and AVIRIS-Derived Mineral and Vegetation Maps of the Marysvale Volcanic Field, Utah—SIR 2009–5117