er 
he 
ity 
ds 
he 
he 
nd 
th 
ds 
ng 
1al 
tra 
be 
ed 
on 
he 
In 
tra 
ith 
all 
ils 
ca, 
yh- 
xel 
3x3 meters). Forward and reverse intensity, hue, 
and saturation (IHS) transforms (Haydn et al., 
1982) were applied to the TM color composite. In 
the reverse transform to the RGB (red, green, and 
blue) domain, the intensity and the saturation 
channels were replaced by the aerial photograph 
and by the TM-1 band, respectively. The objective 
of such procedure was to generate an image with 
high spatial resolution and spectral information 
retained from the TM bands. The replacement of 
the saturation channel by the TM-1 band was to 
enhance the areas of hydrothermal alteration, 
because this band presents the best contrast 
between altered and unaltered materials (Figure 
2). The resulting hybrid product with the spatial 
resolution of the aerial photograph and the 
spectral information derived from the Landsat 
TM bands facilitated the identification of the 
areas of hydrothermally altered materials, and the 
mapping of the main faults that cut across the 
study area. 
In order to produce a generalized map showing 
the main lithological/physiographical domains 
present in the study area, a segmentation 
technique that uses a region growing method was 
applied to the hybrid images. A segmented image 
was obtained which showed a number of 
homogeneous regions whose pixels can be 
assumed to belong to the same class. The 
segmented image was classified using a 
supervised region  classifier method which 
identified four different classes of homogeneous 
regions. Field data were used to identify each 
classified region. Based on the classified image a 
map of the study area was produced (Figure 3) 
which showed a very accurate delineation of the 
areas of hydrothermally altered materials. 
S. CONCLUSIONS 
The results showed that a simulated 
natural color composite of Landsat-TM images 
was a very efficient tool to map hydrothermally 
altered materials in vegetated terrains. For the 
natural conditions of the study area, target areas 
were discriminated even when vegetation covered 
up to 60% of the terrain surface. 
9 
ACKNOWLEDGMENTS 
This research was supported by a FAPESP grant 
3822-8-88. The authors also thank Oriente Novo 
Mining Co. for providing support for field work. 
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