Computer processing of Landsat MSS data was performed using contrast stretching and band-to-band ratioing. A false color ratio composite picture showed color anomalies which coincided with known areas of alteration on and about Red Mountain. A helicopter survey of the study area was undertaken using a portable field reflectance spectrometer. One hundred fifty-six spectra were obtained in the 0.4 to 2.5 micrometer wavelength region. The spectra were digitized, and contour maps for 24 wavelength intervals were produced; no spectral anomalies were evident for the known altered areas. A contour map produced from the 1.6 and 2.2 micrometer ratio generally delineated the alteration areas. The 1.3, 1.6, and 2.2 micrometer wavelength data were canonically transformed using a transformation empirically derived from discriminant function analysis of altered and unaltered materials for the Goldfield, Nevada region, and a contour map was produced for the first canonical variable. The known areas of alteration were clearly defined on the contour map

Abrams, M. J.

Siegal, B. S.

English

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V1
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Technical Memorandum 33-810
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Detection of Alteration Associated With a
Porphyry Copper Deposit in
Southern, Arizona
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JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
PASADENA, CALIFORNIA
February 1, 1977
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Page 1 of 2
TECHNICAL REPORT STANDARD TITLE PAGE
1. Report No.
	 33-814 T2.  Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle 5. Report Daft
February 1, 1977
DETECTION OF ALTARATION ASSOCIATED WITH A
6• hr4wming Organization CodePORPHYRY COPPER DEPOSIT IN SOUTHERN ARIZONA
7. Author(:) 8. Performing Organization Report No.M. J. Abrasss, B. S. Siegal
9. Performing Organization Name and Address 10. Work Unit No.
JET PROPULSION LABORATORY
11. Contract or Grant No.California Institute of Technology
4800 Oak Grove Drive NAS 7-100
13. Type of Report and Period CoveredPasadena, California 91103
Technical Memorandum
12. Sponsoring Agency Name and Address
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 14. Sponsoring Agency Code 
Washington, D.C. 20546
15. Supplementary Notes
16. Abstract
The author has identified the following significant results. 	 Alteration
associated with a known porphyry copper deposit, Red Mountain near Patagonia,
Arizona, has been delineated using spectral reflectance data, acquired by
Landsat, a field spectrometer, and by NASA's Bendix 24-channel Multispectral
Scanner (MSDS).
Computer processing of Landsat MSS data was performed using contrast stretch-
ing and band-to-band ratioing.	 A false color ratio composite picture showed
color anomalies which coincided with known areas of alteration on and about
Red Mountain.	 A helicopter survey of the study area was undertaken using
the Jet Propulsion Laboratory's portable field reflectance spectrometer. 	 One
hundred and fifty-six spectra were obtained in the 0.4 to 2.5 µm wavelength
region.	 The spectra were digitized and contour maps for 24 wavelength inter-
vals were producedi no spectral anomalies were evident for the known altered
areas.
	
A contour map produced from the 1.6 and 2.2 pm ratio generally
delineated the alteration areas. 	 The 1.3, 1.6, and 2.2 µm wavelength data
were canonically transformed using a transformation empirically derived from
discriminant function analysis of altered and unaltered materials for the
Goldfield, Nevada region, and a contour map was produced for the first
canonical variable.
	
The known areas of alteration were clearly defined on
17. Key Words (Selected by Author(s)) 18. Distribution Statement
Geosciences (General) Unclassified -- Unlimited
Earth Resources
19. Security Classif.	 (of this report) 20. Security Clossif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 5
33-810
PREFACE
The work described in this report was performed by the Planetology and
Oceanography Division of the Jet Propulsion Laboratory.
s
iii
33-810
ABSTRACT
The author has identified the following significant results. Alter-
ation associated with a known porphyry copper deposit, Red Mountain near
Patagonia, Arizona, has been delineated using spectral reflectance data,
acquired by Landsat, a field spectrometer, and by NASA's Bendix 24-channel
Multispectral Scanner (MSDS).
Computer processing of Landsat MSS data was performed using contrast
stretching and band-to-band ratioing. A false color ratio composite pic-
ture showed color anomalies which coincided with known areas of alteration
on and about Red Mountain. A helicopter survey of the study area was
undertaken using the Jet Propulsion Laboratory's portable field reflectance
spectrometer. One hundred and fifty-six spectra were obtained in the 0.4
to 2.5 pm wavelength region. The spectra were digitized and contour maps
for 24 wavelength intervals were produced; no spectral anomalies were
evident for the known altered areas. A contour map produced from the 1.6
and 2.2 µm ratio generally delineated the alteration areas. The 1.3, 1.6,
and 2.2 µm wavelength data were canonically transformed using a transfor-
mation empirically derived from discriminant function analysis of altered
and unaltered materials for the Goldfield, Nevada region, and a contour
map was produced for the first canonical variable. The known areas of
alteration were clearly defined on the contour map. Spectral reflectance
imagery in the 0.4 to e.5 µr.. ­94vplength region was obtained with NASA's
Bendix 24-channel MSDS. A false color ratio composite was created using
the following ratios: 1.5/.82, 1.5/.46 and .65/.46, chosen to give the
maximum differences between altered and unaltered rock. The alteration
iv
33-810
areas in and around Red Mountain were identifiable. Good separation was
observed between limonitic alteration centered on Red Mountain and alluvial
fans shed northward, and areas of silicic, non-limonitic alteration to the
east.
V
r33-810
This paper presents the results of a joint Jet Propulsion Laboratory-
Continental Oil Company-Kerr McGee Oil Company project to develop remote
sensing exploration techniques for identifying hydrothermal alteration
zones associated with porphyry copper deposits. The study area centers
around Rei Mountain in Southern Arizona, near the town of Patagonia. Red
Mountain, a 3 x 4 km mountain, consists of hydrothermally altered Tertiary
rhyolitic rocks, and overlies a large unmined porphyry copper deposit.
Tertiary alluvial fans, derived from Red Mountain, extend 2.5 km to the
north. Other lithologies exposed locally include Tertiary and Mesozic
extrusives and intrusives, and Paleozoic sediments.
Three types of data were analyzed in an attempt to delineate the
areas of hydrothermal alteration: 1) Landsat MSS imagery; 2) Helicopter-
acquired reflectance spectra; and 3) MSS imagery acquired with NASA's
Bendix 24-channel scanner. Computer processing algorithms, developed dur-
ing a study of alteration at Goldfield, Nevada, were applied to the data.
Two sets of Landsat MSS computer tapes were acquired for the test
area, E-1156-17280 (December 26, 1972) and E-1678-17210 (June 1, 1974).
Preliminary computer processing of both sets of tapes was performed to
remove noise, correct dropped data lines, and rectify geometric distor-
tions resulting from the Earth's rotation and satellite motion. Pictures
were produced from each set of tapes for the four MSS spectral bands.
Examination of the December pictures indicated excessive seasonal vegeta-
tive cover and extreme shadowing due to low sun angle. These factors
rendered the pictures unsatisfactory for further study.
f
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33-810
Vegetative cover and shadowing were less on the June pictures.
Band-to-band ratios were constructed from the digital data. (Ratio
images remove, to the first order ) variations in brightness due to topo-
graphy, and thus gave a truer picture of the spectral characteristics of
a material.) Three ratio positive transparencies (4/5, 5/6 and 6/7) were combined
on an additive color viewer to produce a false-color composite picture.
Ratio 4/5 was projected as blue, 5/6 as green, and 6/7 as red. A subtle
but noticeable red color anomaly centered on Red Mountain was observed.
Other less obvious red color anomalies observed in the vicinity of Red
Mountain were: 1) an area adjacent to the northwest of Red Mountain,
coinciding with the alluvial fans flanking Red Mountain; 2) an area about
8 km to the northwest; and 3) an area about 5 km east of Red Mountain.
These three areas also correspond to areas of known hydrothermal alteration.
In order to obtain a better understanding of the spectral character-
istics of the alterea socks at Red Mountain, a field reconnaissance of the
test area was undertaken and samples were collected from three sites of
known hydrothermal alteration. Laboratory measurements of the spectral
reflectivity in the 0.5 to 2.5 um wavelength region (see Figure 1) revealed
prominent absorption bands at 0.85 um, 1.4 um, 1.75 um, 1.9 um, and 2.15 um.
The 0.85 um absorption band is associated with ferric iron, a constituent
of limonite, hematite, and goethite, which are minerals characteristic of
alteration. Absorption bands at 1.4 um and 1.9 um are characteristic of
adsorbed water of hydrous minerals such as limonite. The 1.75 um and
2.15 um absorptions are assigned to the 0H stretching of clay minerals,
which are also characteristic of hydrothermal alteration.
2
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i
33-810
In the wavelength region spanned by the Landsat MSS, 0.5 um to 1.1 µm,
only the absorption band at 0-85µ m due to ferric iron can be detected. The
influence of this absorption band is to strongly depress the reflectance
of altered rocks in MSS bands 6 and 7, and is inferred to be the cause of
the color anomaly seen in the false color ratio composite picture.
As part of a broader research program to determine the optimal wave-
length regions for identifying hydrothermal alteration, an aerial survey
of the test area was performed using the Jet Propulsion Laboratory's port-
able reflectance spectrometer. The spectrometer measures reflectivity in
the range of 0.4 to 2.5 µ m. Measurements were acquired by helicopter for a
9 x 10 km area about Red Mountain. One hundred fifty-six spectra, each
covering a 9 x 25 m area, were obtained based on a rectilinear sampling
grid with 80 m spacing. The spectra were digitized at 0.05 Pm intervals
for the wavelength region of 0.4 to 1.0 µm and 0.10 µm intervals there-
after. Contour maps were produced for each of the 24 intervals; no
spectral anomalies were evident for the known alteration areas.
Based on previous analysis of spectra of hydrothermally altered and
unaltered materials in Goldfield, Nevada, a contour map was produced from
the ratio of the 1.6 µm and 2.2 pm wavelength region. High ratio values
are indicative of hydrothermally altered materials. The highest ratio
=	 values on the contour map of Red Mountain delineated, in general, the
known altered areas. The 1.3, 1.6 and 2.2 pm wavelength spectral data for
Red Mountain were canonically transformed using a transformation which was
empirically derived from discriminant function analysis of hydrothermally
altered and unaltered materials in the Goldfield, Nevada region. A contour
map was produced for the first canonical variable data. In general, the
i
3
33-810
contour map delineated the altered zones within the test area.
Multispectral reflectance imagery for the test area were obtained
by NASA's 24-channel MSDS in the wavelength region of 0.4 to 12.5 µm. A
false color ratio composite was produced by projecting the ratios 1.5.82,
1.5.46, .65.46 in blue, green and red, respectively. These ratios were
chosen after analysis of the field spectra, in order to provide the maximum
differences between altered and unaltered materials. (Due to sensor mal-
function, the 2.2 µm image was not available.)
Due to the heavy vegetation cover, Red Mountain appears green and
yellow. Limonitic alteration on Red Mountain appears yellow in those
areas which are less heavily vegetated. The northward shed alluvial fan
composed of limonitically•altered debris appears red on the imagery. The
non-limonitic, silicically altered areas to the east of Red Mountain appear
blue. All the altered areas are distinct in color with respect to both the
unaltered areas and the heavily vegetated areas.
4
33-810
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Detection of alteration associated with a porphyry copper deposit in southern Arizona

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