A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ

3.2.3 Separation of alteration zones
associated with gold mineralization
Separation and detection of hydrothermal
alterations is important Privileges of satellite
images. Provided, the effects of them be seen
in the surface of the earth. Hydrothermal
alterations are complex process involving
changes in mineralogy, texture and chemical
reaction that occur from reactions between
the hydrothermal fluids with different origin
(atmospheric or magmatic) and rocks.The
most important minerals formed during
alteration, are iron oxides and clay minerals
with OH that if appears at ground surface,
can be detected by satellite images.
Obviously, introduced area must be
controlled by field operations in order to
confirm the presence or absence of
mineralization.
The purpose of ASTER image processing,
in this part is identified different alteration
zones such as argillic or clay and iron oxide
alterations. For this aim, will be an
unsupervised classification to inform of
spectral classes images (find End member).
It is done in Envi4.2 software with
SMACC algorithm (Sequential maximum
Angle Convex Cone). Likewise determining
end of member, the frequency of each
spectral class in the image is determined.
These classes can be associated with one of
the alteration that these are compared as
visually in image or through the spectral
library. Spectrum associated with alteration
minerals that we are following them is stored
from USGS spectral library separately (Fig
4).
Then, extracted End member from the
image be correlated with mineral spectra in
the library. With identification each
mineral´s absorption and reflection point, can
use different methods in ENVI software for
spectral data analysis.
One of these methods is MATCH
FILTERING. In this way, the reflecting
digital value of each pixel is compared with
reference values of minerals. In other
methods-SAM (Spectral Angle Mapping) -
the nearest spectral angle of the minerals, as
standard, with the nearest spectral angle of
pixels of the image are compared.
Figure 4. Overview of the spectral library in
ENVI software
Finally, the probability distribution of
alteration is obtained. Then with the help of
remote sensing interpretation and geological
maps, are correct and finalized.Extracting
information from satellite images in this
section include: Extraction and detection of
Kaolinitic – Alunite alteration, Illite –
Sericitic alteration, advanced argillic
alteration (with using separation Pyrophillit
mineral), iron oxide, and silica alteration.
Multivariate analysis LS-Fit (Linear Band
Prediction) is another method that was
used.In processing the images in this way,
the bond that have objections with other
types of spectral bands are analyzed.The
results of this method as compared to the
mentioned methods, have a higher accuracy
And the noise is much less.
3.2.1.1 Extraction of iron oxide alterations
The main alterations observed in ASTER
image of studied area is iron oxide
alterations, which with band combination
1,2,3 (ie visible wavelengths) are clearly
separated.As seen in Figure 5, the main
alterations of iron oxide aligned with the NE
– SW tectonic trend .These alterations must
be investigated with field operations until to
be confirmed probable mineralization with
them.
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