EPS-109 Earth Resources and the Environment
Lab 8: Geologic Mapping with Remote Sensing Data / LandsatTM
Week of April 20-24, 2009
In this lab you will interpret a LandsatTM image from the Andes in northwest Argentina using
Erdas Imagine software.
Basic steps include:
1) displaying the image;
2) identifying features (landforms, strata, structures) using various spectral band combinations;
3) identifying and mapping lithologic units; and
4) locating ore deposits.
Please hand in the interpreted image in addition to answers to the questions included in this lab
hand-out. The best way to do this will be to open a copy of the image in another program (e.g.,
Powerpoint) and to annotate it there, while using Erdas to find the relevant locations using the
different bands and zoom options. We provide copies of the image in pdf (high quality),
powerpoint (relatively high quality) and jpg (medium quality). You may want to show several
insets of the image zoomed in on different areas to show smaller features.
In the Imagine Toolbar click VIEWER. Enlarge the new Viewer window by dragging its lower
right-hand corner to the limits of your screen.
1) In the Viewer toolbar click on the “Open folder” icon and select the file puna_rc1.img under
Courses/EPS109/lab8. You are working with a rectified, full-resolution LandsatTM image with
all seven spectral bands, about a 350MB file. Place the bands in the RGB channels to produce the
closest approximation of an image in the visible spectrum.
What bands should you use? _____________
In the Viewer Menu, select RASTER/BAND COMBINATION, and change the band displayed in
the red channel to one that should help distinguish vegetation from rock outcrop. Click APPLY
and CLOSE. Zoom and pan in the image using tools in the Viewer toolbar.
Q: Is this a wet or dry region? How is vegetation distributed across the image? What
part of the electromagnetic spectrum (and LandsatTM bands) should help to distinguish
vegetation from rock outcrop?
2) In RASTER/BAND COMBINATION return the image to a visible spectra display by restoring
the band displayed in the red channel.
Concentrating on the western half of the image, and adjusting the displayed bands freely, try to
identify:
• standing water
• roads/man-made features
• aeolian deposits
• alluvial deposits
• folded strata
• other??
(an example of each should be annotated on your final image)
3) In RASTER/BAND COMBINATION return the image to a visible spectra display.
Q: What is the geological environment of the region where you identified standing water?
What kind of rocks form there? Name three elements that we mine these deposits for,
and an important use for each.
4) Locate the Tres Cruces structure (the funny “W” shaped fold) in the center of the western half
of the image. Based on the stratigraphic description provided on the attached pages, try to identify
the strata folded in the structure. Adjust the displayed band combinations to accentuate these
strata and increase the “sharpness” of the image. We provide hand samples of rocks to show what
each of these rock units look like – come to the front of the room and examine them.
Q: What geologic strata are folded in the structure? What bands display this best? Is this
an anticline or syncline? Why does changing the displayed bands affect the “sharpness”
of the image?
Q: Draw a schematic cross-section going approximately east-west through the “W” (like
“W”). To do this, imagine that you are slicing vertically through the earth. We want to
visualize what the strata look like underground. Mark where your strata are exposed at
the surface and then connect them by drawing anticlines and synclines. Label the strata
depending on how you identified them.
To the south of the Tres Cruces structure, locate other outcrops of these distinctive strata and
label them on your map. Identify anticlines and synclines. Mark a couple on your map.
5) Significant lead-zinc-silver ore deposits occur in this area where Cretaceous granitic plutons
intrude and alter Ordovician sedimentary rocks. The skarns contain massive deposits of
marmatite-sphalerite, galena, pyrite, pyrrhotite, and chalcopyrite.
Based on your knowledge of the stratigraphy and using different band combinations, locate
exposures of the Ordovician rocks on the western portion of the image. The ore deposits occur
where these rocks come in contact with the Cretaceous granites, which in a 4-3-2 band
combination will appear white/light tan. Note that the intrusives typically cut across stratigraphic
contacts. Locate the granite outcrops and identify areas where the granites come in contact with
the Ordovician rocks. (Mark these on your map.)
Can you identify any alteration zones (mark them on your map)? What band combinations show
this best?
The Minera Aguilar is located along one of these contact regions. Identify the mine and
associated features (roads, living quarters, etc.). Can you locate the mine tailings? How have they
been distributed? Do they have a unique spectral signature? Label these features on your image.