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A 1 C 3,8 D
3
2 1
4
4
5 2
Reflectance (offset for clarity)
87 6 53 Atmospheric absorptions
1m
B 1
4
2 3
4 5

Fe-, Mg-, and 6

5 Al-bearing clay (5)
87 6
Hydrated silica +

minor clay? (4) 7
Calcite (1)

Hydrated silica (6?) 8
Chlorite (7)

1m Epidote (2) 0.5 1.0 1.5 2.0 2.5
Hydrated silica +
Wavelength (μm)
calcite or illite (3,8)

Figure 5. (A) Color composite image approximating true color of an outcrop along Mills Creek imaged with UCIS. (B) Spectral parameter map.
Red is the band depth of a spectral feature at 2.21 µm (BD2210) due to Si-OH and/or Al-OH combination absorptions. Green is the band depth
of a feature at 2.31–2.32 µm (BD2310-20) likely due to Mg-OH combinations. Blue is the band depth of a feature at 2.34–2.35 µm (BD2340-50)
due to either a C-O combination in calcite or Fe-OH combinations in a mineral such as chlorite or epidote (Clark et al., 1990). (C) Schematic
lithostratigraphic section from area outlined in yellow boxes in (A) and (B) with colors corresponding to the colors in (B). Dark green layers have
weak Fe/Mg/Al clay features. Other colors correspond with minerals names under the stratigraphic section. (D) Example spectra of different
units with colors corresponding to (B) and (C). Locations of each spectrum are numbered on both images. Dashed lines are, from left to right, at
2.21, 2.31, and 2.34 µm, corresponding with the positions of spectral features mapped in (B). Spectral regions with terrestrial atmosphere are
removed and covered with light gray boxes.

GSA TODAY | DECEMBER 2015 similar areas are compositionally quite variable. VSWIR micro- whereas the float rocks to the right are more similar composition-
images acquired in minutes quickly map distributions of mafic ally to the exposed layered outcrop.
and altered phases while highlighting key compositional varia-
tions, allowing investigators to zero-in on sample locations of CONCLUSIONS
highest interest for more accurate but time-consuming instru-
mental techniques such as electron microprobe, transmission Imaging spectroscopy of samples and outcrops enables new
electron microscopy, or NanoSIMS analyses. science investigations and yields novel or unexpected mineralogic
and petrologic insights into a variety of geological processes
EXAMPLE 4: MAPPING OF SEDIMENTARY ROCKS EXPOSED (Greenberger, 2015). This technique rapidly and non-destructively
AT MILLS CREEK maps mineralogies with little sample preparation, showing mineral
associations that might not otherwise be apparent and guiding
We imaged an outcrop of sedimentary rocks exposed along further investigations using other, more time-consuming tech-
Mills Creek near Mono Lake, California, with UCIS in field niques. Other investigations have used imaging spectroscopy at
mapping mode (Fig. 5; 0.5–2.5 µm; instantaneous field of view similar scales to find economically viable deposits of minerals
1.35 mrad, 12 nm spectral resolution). Using spectral parameters, (Kruse et al., 2012), map carbonate lithologies (Baissa et al., 2011;
we mapped specific mineral phases present at the site, including Kurz et al., 2012), characterize alteration of basaltic samples from an
hydrated silica (opal A), clays (Fe-, Mg-, and Al-bearing), calcite, impact structure (Yokoyama et al., 2015) and in a cold and arid envi-
illite/muscovite, and epidote (Fig. 5B). From these results, the ronment (Cannon et al., 2015b), quantify the abundances of iron in
stratigraphy of the outcrop lithologies can be inferred (Fig. 5C), a mine wall (Murphy and Monteiro, 2013), map clay layers (Murphy
showing variations in the depths of absorption features related to et al., 2014), and study the Black Beauty meteorite from Mars
hydrated silica (red or orange) and clay mineral (green) contents (Cannon et al., 2015a). These types of studies also aid in preparing
of the sedimentary layers. The float rocks above the outcrop and for imaging spectrometers on future landed planetary missions.
along the creek bed at the bottom of the image have diverse Imaging spectrometers used herein are currently employed in labo-
compositions. Based on the higher proportions of rocks with ratories such as at Brown University, the California Institute of
significant calcite (cyan) and illite (magenta), we infer the likely Technology, and the University of Winnipeg.
presence of calcite- and illite-rich units higher in the stratigraphy
that are not exposed at this outcrop. Much of this calcite- and ACKNOWLEDGMENTS
illite-rich talus is located on the left portion of the outcrop near a
small fan and likely is sourced from above the layered section, We would like to thank Headwall Photonics, Inc., especially David Bannon
and Kwok Wong, for use of their hyperspectral imagers to acquire the images
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