Hydrothermal Alteration Mapping using Landsat 8 data in

Hydrothermal Mineral Alteration Mapping in parts of
Northwestern Tamil Nadu, India – using Geospatial
Technology
By
M . Ar u n a c h a l a m
B . Te c h
C e n t e r f o r R e mo t e S e n s i n g
Bharathidasan University
Tiruchirapalli -620023
Introduction
• The understanding of structure and tectonics in an area is
important as it sheds light on the magmatism, metallogeny,
groundwater, seismicity, geothermal and hydrothermal resources.
• The Precambrian-Archaean rocks of Southern Peninsular India
exhibit polyphase metamorphism, multiple deformation, repetitive
folding and fracturing.
• The highly fragmented and widely disseminated rock types show
contrasting fold styles, multivariate linear and planar features.
These linear and planar features have controlled localization of
minerals, ore bodies, ultra basics and alteration products at several
places.
• Alteration can produce distinctive assemblages of minerals that
vary according to the location, degree and longevity of those flow
processes.
Aim and Objective
The main aim and objective of the study is
• To understand the structure and tectonics of the study area.
• To prepare various thematic maps such as
• Lithology map and their anomalies,
• Structural Trend Line map and their anomalies,
• Lineament map and their anomalies,
• To interpret and analyze geophysical data (Gravity) and
their anomalies for basement or deep seated structures.
• And to carry out various Digital Image Processing
techniques such as Band Combination, Band Ratio, Least
Square Fit (LS-Fit) and Crosta methods to identify the
hydrothermal mineral alteration zones in the study area.
• Integrating by using the above data sets in the GIS
environment to map the potential Hydrothermal mineral
alteration zones.
Study Area
Fig 1: Location Map of The Study Area
Methodology adopted for the present study
LANDSAT 8, SRTM
GEOPHYSICAL
DATA
THEMATIC
MAP
GENERATION
IMAGE PROCESSING
TECHNIQUES
BAND
RATIO
COLOUR
COMPOSITE
LS FIT
CROSTA
LINEAMENT
STRUCTURAL
TRENDS
DETECTION OF HYDROTHERMAL
ALTERATION ZONE
GEOMORPHOLOGY
ANOMALIES
SUPERVISED
CLASSIFICATION
GIS ANALYSIS AND
INTEGRATION
Identification of Prospect Zones for
Hydrothermal Alteration Minerals
Fig 2: Methodology of the Study
GRAVITY
Data Analysis and Interpretation
Generation of Thematic Maps
JAVADI
KALRAYAN
Fig 3: Base Map
Geological Setting & Tectonic Framework
Study
area
Fig 4: Simplified Geology Map of South India
(after Drury et al, 1984 & Chardon et al, 2008)
Study
Area
Fig 5: Generalized Tectonic Map of South India
(after Drury et al, 1984; T. Harinarayna et al, 2005)
Fig 6 : Lithology Map
Source: Geological survey of India, 2006)

Charnockite Gneiss and
Pyroxene Granulites

Sathyamangalam Complex

Charnockite Group
Khondalite Group
Peninsular Gneissic Complex
–I

Migmatites; Granites



Metavolcanics with
metasediments
Granitoid and Gneiss


Eastern Greenstone
Peninsular Gneissic Complex II

Alkaline Complex



ARCHAEAN
PROTEROZOIC
PALAEOCENE
TO
EOCENE
Uttatur, Ariyalur and
Tiruchirrapalli
Formations
Cuddalore Formation
MIO-PLIOCENE

Recent Sediments &
Alluvium
QUATERNARY
Table 1: Lithological Succession of The Study Area
(Recent)
Fig 7 : Lithological Contact Map
Fig 8: Structural Trend Line Map
Fig 9: Structural Trend Line Anomaly
Zones And Axes Map
Fig 10: Lineament Map
Fig 11 : Geomorphology Map
Fig 12 : Gravity Data
Fig 13 : Gravity Anomaly Map
Alteration Mapping by Using Remote Sensing
• Remote sensing provides information on the properties of the
surface of exploration targets that is potentially of value in
mapping alteration zones and lithological units.
• The importance of the recognition of such spatial patterns of
alteration makes the ‘Remote Sensing Technique’ one of the
standard procedures in exploration geology, due to its high
efficiency and low cost (Yetkin 2003).
• One of the key idea of remote sensing techniques in exploration
geology is that it is applied to rocks, minerals, and structures
associated with a particular ore, and not the ore itself.
• Previous studies explained the fact that certain minerals associated
with hydrothermal processes, such as iron-bearing minerals (e.g.,
goethite, hematite, jarosite and limonite) and hydroxyl bearing or
clay minerals (e.g., kaolinite and K-micas) show diagnostic
spectral features that allow their remote identification (Hunt
1980).
Contd.,
• Here in this study we have considered the hydroxyl (OH) or clay
minerals to map the hydrothermal alteration zones, because,
Hydroxyl-bearing minerals form the most widespread product of
alteration.
Present Techniques in Alteration Mapping:
• Remote Sensing techniques have been applied for years and new
methodological perspectives are still being developed by using
this high technology.
• Band Rationing,
• Least Squares Fitting and
• Crosta Techniques
• are the well known and practiced conventional methods used in
this study for mapping hydrothermal mineral alteration zones.
Band Rationing
Here we have used various bands of Landsat 8 satellite imagery for Band Ratio.
Band Ratio’s such as 4/2, 5/6, and 6/7 are used to discriminate clay mineral
alterations. Clay minerals have absorption in band 7 and have high reflectance in
band 6, therefore clay minerals are displayed in dark pixels in band ratio image 6/7
and bright pixels in band ratio image 5/6.
Fig 18: Band Ratio Image
(B4/B2)
Fig 19: Band Ratio Image
(B6/B7)
Fig 20: Band Ratio Image
(B5/B6)
Fig 19: Band Ratio Image
(B6/B7)
Abdelhamid and Rabba Ratio (1994)
Fig. 21 is the Color composite image
derived from above band ratios
(R[4/2]:G[6/7]:B[5/6]), were use to
map clay mineral alterations zones
(Abdelhamid & Rebba, 1994). Clay
minerals alteration areas are displayed
in dark blue to violet blue pixels
Fig 21: Abdelhamid & Rabba Ratio
R(4/2):G(6/7):B(5/6)
Least Square Fitting
Using LS-Fit outputs (residual band 4, residual band 7 and residual band 2) we
can map hematite (Fig. 23), clay (Fig. 24) and goethite (Fig. 25). The dark
pixels indicate abovementioned minerals in these residual bands (Yetkin et al.
2004).
Fig 23: LS-Fit Residual Band 4
Fig 24: LS-Fit Residual Band 7
Fig 25: LS-Fit Residual Band 2
• Fig.26 is the color composite image of
the residual band 4, residual band 7 and
residual band 2 respectively in RGB
display we interpret the followings:
•
•
•
•
•
•
•
Fig 26: LS-Fit Color Composite Image
R(ResidualB4):G(ResidualB7):B(ResidualB2)
White : Goethite + Hematite + Clay
Orange : Hematite + Clay
Cyan : Goethite + Clay
Purple: Hematite + Goethite
Red : Hematite
Green : Clay
Blue : Goethite
CROSTA (Mapping of Hydroxyl bearing
minerals through PCA)
• The analysis showed that the albedo
(reflectance) is mapped by PC1, and the
spectral difference between shortwaveinfrared and visible ranges is mapped by
PC2.
• PC3 is found to be responsible for displaying
the vegetation and PC4 highlights hydroxylbearing minerals as bright pixels in the PC
image and called Crosta hydroxyl (H) image
(Loughlin, 1991) (Fig. 37) .
Fig 27: PC4 image displaying OH
minerals in bright pixels
Results and Validation
• Finally, accuracy of the outcomes (Results) of above
mentioned methods were checked and supervised
classification has been carried out for better
classification of altered mineral deposits, and
compared with the other anomalies such as
lineaments, Deep seated Faults, Gravity anomalies
such as Gravity highs, Gravity lows and Gravity
breaks, Trend line Anomaly zones and axes and
Lithological contats to map the hydrothermal
alteration zones in the study area.
Fig 28: Flow Chart for Mapping Hydrothermal Alteration
Mineral Prospect Zones
Fig 29: Supervised Classified Band Ratio Image of
6/7
Fig 30 : Supervised Classified Band Ratio Image of
Abdelhamid & Rebba Ratio
Fig 31 : Supervised Classified Image of LS – Fit
Composite Image
Fig 32 : Supervised Classified Image of PC4
Fig 33 : Lineament Controlled Clay Mineral
Alteration Zones Over LS - Classified Image
Fig 34 : Trend Line Anomaly Axes Controlled Clay
Mineral Alteration Zones Over LS – Fit Classified
Image
Fig 35 : Deep Seated Faults Controlled Clay Mineral
Alteration Zones Over LS – Fit Classified Image
Fig 36 : Lithological Contacts Controlled Clay
Mineral Alteration Zones Over LS – Fit Classified
Image
GIS Integration
Fig 37 : Integrated Hydrothermal Alteration Zone
Map Through LS - Fir
Fig 38 : Integ Hydrothermal Alteration
Map Through Band Ratio 6/7
Fig 39 : Integ Hydrothermal Alteration
Map Through PC4 Image
Fig 40 : Integ Hydrothermal Alteration
Map Through Abdelhamid & Rebba Ratio
GIS Integration
Fig 41 : Potential Hydrothermal Mineral
Alteration Zone Map
Fig 42: Probable Conduits for
Hydrothermal Alteration
Fig 43: Mineral Resource Map of The Study Area
Source: Geology and Mineral Resource Map, GSI, 2006
Fig 44: Hydrothermal Mineral Prospect
Zones Map
Conclusion & Recommendation
• From the final integrated map, the high weightages
zones where buffered out as most favourable zone
for the mineral exploration related to hydro thermal
activities.
• Further, in order to validate the potential zones
identified through the above various techniques was
overlaid with the already existing mineral
occurrence map of this region.
• The validation shows that there are nearly 90-95%
of coincidences between the existing mineral
occurrences and mineral potential zone derived
from the present study.
• Further detailed warranted along the potential zones
identified from the present study.
THANK YOU

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