CHAPTER 1 INTRODUCTION

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CHAPTER – 1

INTRODUCTION

1.1 MOTIVATION AND OVERVIEW

The economy of several countries around the world depends mainly on the

presence of natural minerals, which are associated with hydrothermal alteration zones.

The geological features of Yemen is accomplished by large outcrops of Archean-

Proterozoic metamorphic basement blocks belonging to the Arabian Shield, covered by

rocks of Cambro-Ordovician, Permian, Jurassic, Cretaceous, Tertiary and Quaternary age

(Beydoun, 1964; Beydoun, 1966; Greenwood and Blackley, 1967; Robertson Group,

1992, Mattash, 1994; Menzies et al., 1994; Beydoun et al., 1998; Wanas and Abdel-

Maguid, 2006). That makes it very significant in the field of economic geology.

The study area is composed of an active and dynamic geological setting with

prospects of many different kinds of ore deposits, including shear zones bearing valuable

mineral deposits such as gold, copper, and nickel in Precambrian basement rocks. In the

last ten years the Mineral Resources Exploration Sector, which is represented by the

Geological Survey of Yemen and Mineral Resources Board (GSMRB) drew the attention

of several international and local companies, some of which have already started to work

in this field.

Application of remote sensing and Geographical Information System (GIS) based

on spatial data integration for mapping of hydrothermal alteration zones is still not fully

employed in the activities of the Geological Survey of Yemen. Due to the prevalence of

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roughness of the topography, the application of recent techniques to conduct the

geological survey becomes necessary.

Application of remote sensing and GIS techniques in the field of mapping

hydrothermal alteration zones, which are the sources of valuable minerals is considered

as the first academic study in Yemen. This research work provides a case study to

demonstrate the usefulness of the Enhanced Thematic Mapper Plus (ETM+) and

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for

mapping the hydrothermal alteration zones.

Geological applications of remote sensing and GIS community have attracted

attention since the early stage of their development (Sabins, 1997; Lillesand and Kiefer,

2000; Gupta, 2003; Quattrochi and Luvall, 2004). The earliest use of satellite geological

remote sensing was for the purpose of mineral exploration in the 1970s (Vincent, 1997).

Remote sensing technique has opened up a new era in the mapping of altered and

unaltered litho units. It provides useful information on hydrothermal alteration zones,

which is not otherwise available by other means especially in some areas where the

topography is complicated.

Remote sensing can also identify the hydrothermal alteration zones and rock units

even before conducting geological field survey because their reflectance spectra differ

from those of the unaltered rocks. Hydrothermal alteration zone mapping is one of the

most common applications of remote sensing for mineral exploration, in which the spatial

distribution of hydrothermally altered rocks is a key to locating the main outflow zones of

hydrothermal systems, which may lead to the recognition of mineral deposits (Lowell,

1991; Sabins, 1999).

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The principal aim of reconnaissance mineral exploration is thus to map zones of

hydrothermally altered rocks (Carranza and Hale, 2002). Remote sensing images are

useful for mineral exploration in the following four applications, i) mapping regional

lineaments, ii) mapping local fracture patterns that may control individual ore deposits,

iii) detecting hydro-thermally altered rocks associated with ore deposits, and iv)

providing basic geological data (Sabins, 1997; 1999). Mapping of hydrothermally altered

minerals and understanding the characteristics of hydrothermal alteration zones have

progressively become possible by the use of field and laboratory reflectance

spectroscopy. Geological and hydrothermal alteration zones studies require huge

investment, extended time, and tremendous human labour particularly in areas that are

not easily accessible. In contrast, the low cost and high efficiency of remote sensing in

initial exploration makes it an attractive method (Drury, 2001) because of the focusing

attention on more detailed ground based studies in areas that show more promise.

The application of GIS technique in predicting areas having mineral potential

(altered areas) has provided geologists with a powerful tool to help analyse data much

more efficiently than before (Bonham-Carter et al., 1988; Bonham-Carter, 1994; Rencz et

al., 1994) and also helped in land-use planning and management (Madigan et al., 1988).

Based on preliminary studies carried out by the Administration of Minerals and

Rocks in GSMRB, primary analysis of satellite imagery, and geological map, the study

area has selected. Nabitah belt, which represents a unique site for economic mineral, is

also extends into this area.

To ensure the long term viability of the mineral sector, the government of Yemen

has allotted a portion of the revenues from mineral development, such as taxes and

royalties, towards exploration in frontier areas, new resources and new deposit types. The

government has also collaborated with the private sector to minimize the dislocations of

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community, and facilitate the social and economic adjustments that occur upon the

closure of mining operations. All these facilities have helped to attract many companies

(national and international) to investigate in the mineral sector.

1.2 HYDROTHERMAL ALTERATION

Hydrothermal alteration is defined as the reflection and response of pre-existing

rock-forming minerals that have physical and chemical conditions different from those,

under which were originally formed, especially by the action of hydrothermal fluids

(Beane, 1982; Nehal, 2006). Ore deposits are often produced by fluid flow processes that

alter the mineralogy and chemistry of the country rock. The nature of the altered products

is influenced by 1) the character of the wall rock, 2) the character of the invading fluid,

which defines such factors as Eh, pH, vapor pressure of various volatile species, anion-

cation composition, and degree of hydrolysis, and 3) the temperature and pressure at

which the reactions take place (Guilbert and Park, 1986). This alteration can produce

distinctive assemblages of secondary minerals, which replace the original minerals and

these vary according to the location, and the length of time over which the flow processes

operate (Ferrier and Wadge, 1996; Sabins, 1997; Ferrier et al., 2002; Moghtaderi, et al.,

2007). The alteration minerals commonly occur in the zone of hydrothermal alteration,

processing characteristics relative to the ore body and the style and extent of the

alteration and also reflect the type of mineral deposit (Rajesh, 2004). All alterations are

associated with the ore bodies, but not all ore bodies are accompanied by the alteration,

and the presence of altered rocks is a valuable indicator of possible deposits (Sabins,

1999). Hydrothermally altered zones are the results of change in temperature, pressure,

and chemistry of the hydrothermal solutions. Sources of hydrothermal fluids are not well

understood, however, there are three main possibilities that exist. One source can be the

magmatic rocks themselves, which exsolve water (called “juvenile” water) during the

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final stages of cooling. In metamorphic terrains, a potential source of the fluids is the

dehydration reactions which take place during the metamorphic event. With increasing

temperature under metamorphism, early, low temperature, hydrous minerals recrystallize

into new, higher temperature, anhydrous minerals. The excess water circulates through

the surrounding rocks and may scavenge and transport metals to sites where they can be

precipitated as ore minerals. Near the surface, groundwater is another source of water

(called “meteoric” water). Evidences from some ore deposits suggest that meteoric waters

may mix with juvenile or metamorphic waters during late stages of mineralization.

Hydrothermal alteration zones in the present study area have resulted from the

intrusive tectonic events such as invasion of a variety of syn and post-tectonic pan

African granites, mafic and ultramafic dykes, and movement of Arabian plate away from

the African plate. The various important hydrothermal alteration zones include:

silicification, carbonatization, sericitization, serpentinization, clay mineral, and

oxidiation.

Silicification

These zones are associated with shear zones and are occur as bands and layers

involving high replacement of silica. In most of the cases they are hosted in metarhyolite,

amphibolite schist, carbonate amphibolite biotite schist and graphite schist. These layers

and bands are rich in massive and disseminated sulfide materials (pyrite and

arseonpyrite).

Oxidation

This type of alteration occurred in places where oxygenated groundwater flowed

through the rock and resulted in overall oxidation of the original rock (Arehart and

Hulston, 1998). These zones are wide spread in the entire study area with varying

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thickness and width, and they are highly weathered. They are concentrated in shear zone

and are characterized by massive and compact shape in most places. Quartz with the

boxwork textures is associated with these zones. Most of rock samples collected from this

type of alteration and rich in quartz veins show anomalies of gold. Gossans formed from

weathering such as gossans of western Wadi Sharis does not show any anomaly of gold

but it shows anomalies of Co, Cu and Ni.

Carbonatization

Carbonatization is a general term for the addition of any type of carbonate

mineral. Carbonatised zones are represented in the study area by dolomtic marbles, talc-

serpentinite, carbonate, dolomitic limestone, and carbonate-amphibolite schist. These

zones occur as scattered associated with veins of quartz and gossans in the study area.

Sericiticization

This alteration is typically formed by the decomposition of feldspars and can be

detected by its softness, easily stretchable, greasy feel (when present in abundance), and

its distinctive colours include: white, yellowish, golden brown or greenish. Sericitic

alteration implies low pH (acidic) conditions. Alteration zones consis of sericite and

quartz are called “phyllic” alteration. Phyllic alteration is associated with porphyry

copper deposits and may contain appreciable quantities of fine-grained, disseminated

pyrite, which is directly associated with the alteration event. This type of alteration is

very widely spread in the study area; it also contains high anomalies of gold and other

trace elements.

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Argillitic (Clay Minerals)

Argillitic alteration is characterized by the formation of the clay minerals by

extreme base leaching of alumino-silicates. Different image processing techniques

revealed that this type is widely spread in the study area. It is resulting from leached

feldspars and altered to sericite. The presence of this assemblage suggests low pH

(highly acidic) conditions. In rocks intensely affected by argillic alteration, the clay

minerals completely replace the components of the rock.

Serpentinization

Serpentinization is a descriptive term that denotes many processes involved in

producing serpentine group minerals at the expense of anhydrous or less-hydrous Mg-

rich minerals, such as olivine, orthopyroxene, clinopyroxene, and amphibole (O’Hanley,

1996). This type of alteration is common only when the host rocks are mafic to ultramafic

in composition. The highest anomalies of Co, Cu and Ni are found in this type of

alteration. This type of alteration reflects progressive hydrothermal alteration process

taking place in the study area.

1.3 REMOTE SENSING BACKGROUND

Remote sensing is based on the measurement of Electromagnetic (EM) energy.

EM energy can take several different forms. The most obvious form of EM energy that is

experienced is light. All forms of electromagnetic radiation, including light, behave both

as waves and as particles (Drury, 1987; 2001; AL-Daghastani, 2003). EM energy travels

at the speed of light (3×108 m/sec). It is commonly treated as a wave with both electric

and magnetic fields, which are perpendicular to the propagation direction (Fig. 1.1)

(Hunt, 1980; Harris and Bertolucci, 1989).

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The equation of Planck’s Law, defined the EM energy as a photon:

E=hν = h.c/λ (1:1)

Where, E is the photon energy in joules, h is Planck’s constant (6.6256×10-34 JS)

and ν is frequency (Hz) (Harris and Bertolucci, 1989). The EM spectrum extends from

gamma rays to radio waves and the remote sensing operates in several regions of EM

(Table 1.1) (Fig, 1.2). The visible portion of the spectrum has an extremely narrow range

of wavelengths. It extends from 0.4 to 0.7µ m (blue to red). The Ultraviolet (UV) region

has the shortest wavelengths. Thermal infrared and microwave regions have longer

wavelengths used for remote sensing. The EM energy emitted by the sun is reflected,

absorbed, scattered or transmitted by different materials on the earth’s surface (Elachi,

1987; Jensen, 2005).

This study deals only with the visible, near-infrared, short wave infrared and

thermal regions. The Advanced Space-borne Thermal Emission and Reflection

Radiometer (ASTER) measures reflects radiation in 3 bands between 0.45 and 0.86µ m

[Visible and Near-Infrared (VNIR)], in 6 bands from1.6 to 2.43 µ m [Shortwave Infrared

(SWIR)]; and emitted radiation [Thermal Infra Red (TIR)] in 5 bands in the 8.125 to

11.65µ m. Enhancement Thematic Mapper Plus (ETM+) measures reflected radiation in

6 bands between 0.45 and 2.35µ m (VNIR and SWIR), and emittes radiation in one band

in the 10.40-12.50 µ m range (Table 2.1).

The technical term “remote sensing” was first used in the United States in the

1960s, and encompasses photogrammetry, photo-interpretation, and photo-geology.

Remote sensing technique is the science and art of acquiring information (spectral, spatial

and temporal) about material objects, areas, or phenomenoa, without coming into

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physical contact with the objects, or area, or phenomena under investigation (Campbell,

1996; Buhe et al., 2007). The American Society for Photogrammetry and Remote Sensing

(ASPRS) formally defines remote sensing as “the art, science, and technology of

obtaining reliable information about physical objects and the environment through the

process of recording, measuring, and interpreting imagery and digital representations of

energy patterns derived from non-contact sensor systems” (Colwell, 1997).

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Fig. 1.2 Electromagnetic spectrum

Fig. 1.1 An electromagnetic wave is composed of both electric and magnetic vectors (Jensen, 2005)

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Table 1.1 Electromagnetic spectral regions (Sabins, 1997)

Region Wavelength

Remarks

Gamma ray <0,03 nm Incoming radiation is completely absorbed by the upper atmosphere and not available for remote sensing.

X-ray 0.03 to 3.0

nm Completely absorbed by the atmosphere. Not employed in remote sensing.

Ultraviolet 0.03 to 0.4

µm Incoming wavelengths less than 0.3µm are completely absorbed by ozone in the upper atmosphere.

Photographic UV band

0.3 to 0.4µm

Transmitted through atmosphere. Detectable with film and photo detectors, but atmospheric scattering is severe.

Visible 0.4 to 0.7µm

Imaged with film and photodetectors. Includes reflected energy peak of earth at 0.5µm.

Infrared 0.7 to 100µm

Interaction with matter varies with wavelength. Atmospheric transmission windows are separated by absorption bands.

Reflected IR band

0.7 to 3.0µm

Reflected solar radiation that contains no information about thermal properties of materials. The band from 0.7 to 0.9 µm is detectable with film and is called the photographic IR band.

Thermal IR and

3 to 5 µm, 8 to 14 µm

Principal atmospheric windows in the thermal region. Images at these wavelengths are acquired by optical-mechanical scanners and special vidicon systems but not by film.

Microwave 0.100 cm Longer wavelengths can penetrate clouds, fog, and rain, images may be acquired in the active or passive mode.

Radar 0.1 to 100

cm Active form of microwave remote sensing. Radar images are acquired at various wavelength bands.

Radio >100 cm Longest wavelength portion of electromagnetic spectrum. Some classified radars with very long wavelength operate in this region.

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A more modern definition describes remote sensing as the measurement of EM

energy by aircraft or space-borne-mounted sensor for the interpretation of surface and

subsurface features. Based on the type of energy resources, there are two types of remote

sensing, 1) Active remote sensing, in which sensor provides its own illumination and

measures what comes back from the objectives (Laser and Radar). 2) Passive remote

sensing, which relies on naturally reflected or emitted energy of the imaged surface. Most

of the remote sensing instruments fall into the latter category, obtaining pictures of

visible, near-infrared and thermal infrared energy.

1.4 GEOGRAPHICAL INFORMATION SYSTEM (GIS)

GIS technology was developed in Canada during the later part of 1960s for the

Ministry of Natural Resources of Canada. It is a powerful tool for geological application

because it has the integration of many spatial data sets for visual display and analysis. A

GIS can generate two-or three-dimensional images of an area, showing such natural

features as hills and rivers with man made features such as roads and power lines. De By

et al. (2000) defines GIS as a computerized system that facilitates the phases of data

entry, data analysis and data presentation especially in cases dealing with georeferenced

data. GIS is the software package that can generically be applied to many different

applications. A GIS is designed to accept geographic data from a variety of sources,

including maps, satellite photographs, printed texts and statistics. GIS sensors can scan

some of these data directly: for example, a computer operator may feed a map or

photograph into the scanner, and the computer "reads" the information contained in it.

GIS can be regarded as a set of tools to analyze spatial data - meaning the space

around us, where there is live and function. Specifically, a GIS is an automated system

that can capture, store, retrieve, analyze, and display spatial data from actual surrounding

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for a particular objective (Burrough and McDonnell, 1998). GIS is often described as

integration of data, hardware, and software designed for management, processing,

analysis and visualization of georeferenced data (Neteler and Mitasova, 2007). Remote

sensing played a part in the development of GIS, as a source of technology as well as a

source of data (Paul et al., 2005). GIS is widely used to manage data that have a special

component. A digital GIS offers more viewing flexibility than a simple paper map, and

also has tools to enable data analysis. Remotely sensed data from the earth observation

satellites is particularly well suited for use in GIS since satellite imagery is already in a

digital form. The imagery may be included with minimum processing such as geo-

referencing to form a digital orthomap, or used to create other data layer such as land

cover through analysis of its spectral response patterns.

A key concern in geographical information science is how to process geospatial

data to extract features and visualize spatial patterns. Visualization and other GIS tools

for geological and mineral data can aid the analysis of remote sensing data and the

interpretation of various types of information for mineral exploration (Harris et al., 2001).

Although commercial GIS systems, such as ArcGIS, provide an excellent graphic

user interface for visualizing geospatial data, the complexity of geospatial data and some

specific applications such as visualization of subpixel mineral abundance images,

nevertheless call for new visualization techniques.

1.5 INTEGRATION OF REMOTE SENSING AND GIS FOR

MAPPING THE HYDROTHERMAL ALTERATION ZONES

Mapping of hydrothermal alteration zones is one of the most successful

applications of remote sensing in the mineral exploration (Sabins, 1997; Sun et al., 2001;

Carranza and Hale, 2002; Torres-Vera1 and Prol-Ledesma, 2003; Tommaso and

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Rubinstein, 2007). This is because many of the minerals found in hydrothermal altered

rocks have diagnostic from spectral absorption features caused by presence of OH, and

other hydroxyl bonds like Mg Fe-OH and Al-OH (Hunt, 1977). Multispectral image data

have been successfully used for mapping hydrothermal alteration zones since the launch

of Landsat MSS in 1972. With the launch of landsat ETM+ and ASTER and

hyperspectral imagery the capabilities for mapping hydrothermal alteration zones

significantly increased due to increase in SWIR bands. In the SWIR region most of the

altered mineral features could be diagnostic.

The aggressive physical weathering occurs and hence no soil profile has

developed to enhance the suitability of remote sensing to identify and map the

hydrothermal alteration zones. The study area is an example of the successful application

of remote sensing in mapping of hydrothermal alteration zones. The effect of erosion to

remote sensing of alteration areas can be both positive and negative. The positive effects

of erosion emphasize and highlight the resistant structures, such as quartz veins or

silicified outcrops, exposing the central portions of the hydrothermal alteration process.

The negative effects of erosion are primarily characterized by be removal of geological

evidences.

Remote sensing and GIS have been more widely used as an important tool for

analysis in the areas of mineral exploration. They have become an important tool for

locating mineral deposits, in their own right, when the primary and secondary processes

of mineralization result in the formation of spectral anomalies. Additionally, some factors

can be mitigated with ground support during over flights and field validation to improve

statistical mapping methods. High resolution data are available, which can help in

detecting small objects.

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The introduction of GIS to the geological sciences has provided powerful tools to

help geologists to manage and analyse geological data much more efficiently than ever

before. Several examples exist of GIS applications in the geosciences where multiple data

sets are integrated to provide new information to users. Some of these studies used GIS

for prospecting areas of mineral potential (Bonham-carter et al., 1988; Bonham-carter,

1994; Rencz et al., 1994) and land-use planning and management (Madigan et al., 1988).

GIS offers as a potential tool for accomplishing the archiving, managing, analyzing,

integrating and visualizing of the large volumes of geosciences data collected from a

variety of sources (Harris et al., 2001). Hydrothermal alteration potential is a complex

analytical procedure, which requires simultaneous consideration of spatial evidences such

as geological, geomorphological, geochemical and geophysical. The capability of GIS to

manipulate such classified spatial information through amalgamated layers makes it a

unique tool for delineation of potential locales (Mukhapadhyay et al., 2002).

1.6 LIMITATIONS OF REMOTE SENSING AND GIS

Remote sensing is not a panacea that will provide all the information which we

need. It has several challenges in obtaining precise, remotely sensed measurements from

the surface (Jensen, 2005). Some of the main obstacles are the atmosphere, mixtures and

vegetative cover. Even though some of the factors limiting the efficiency of remotely

sensed data are beyond control, proper planning in the data acquisition process may allow

for their mitigation.

In geological remote sensing, there are special limitations such as the existence of

vegetation cover, which makes the application of remote sensing ineffective. So the issue

of vegetation cover is very important because vegetation tends to obscure the rock, and

soil surfaces (Siegal, 1983). It is also difficult to discriminate between vegetation cover

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and some altered rocks in certain image processing because both are enhanced with the

same brightness - one example in the percent work is the band ratio of 5/7, which is very

sensitive to the vegetation so that altered clay and vegetation cover appeared with the

same brightness. Spectral region between 0.68 to 1.3µ m is more influenced by the

chlorophyll absorption of green plants but dry vegetation cover has minor effect (Ustin et

al., 1999).

Remote sensing involves the high cost of purchasing the images such as

Quickbird and IKONOS. Another limitation is the cost of the equipment used for

processing the image. In areas around the equator, cloud cover is a major problem for

spectral scanners but this can be overcome by using radar, although data from radar

scanners are not collected as frequently as spectral scanners. Ability to penetrate the

ground surface is very limited, which means that it only reflects the spectra of surface

materials.

However, GIS has many beneficial applications just like other technological

systems, there are limitations for its use. For example, data for a specific area may lack

spatial or temporal continuity. Additionally, privacy issues can sometimes limit

distribution of data. GIS data may also be subject to misuse or misinterpretation. GIS

professionals can avoid possible misinterpretation of data by clearly stating the purpose

and limitations of the data set in the metadata file when developing GIS data, and also by

using GIS data from other sources responsibly. Data are expensive; learning process on

GIS software can be long and shows only special relationships but does not provide

absolute solutions.

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1.7 RESEARCH OBJECTIVES

The main objectives of the present research study include:

1. To apply the recent techniques of Remote Sensing and GIS for mapping the

hydrothermal alteration zones in North East of Hajjah, Yemen.

2. To study the utility of spectral reflectance of VNIR and SWIR regions for

mapping of altered zones and calibration of the satellite imagery (ASTER and

ETM+).

3. To delineate the lineaments and their analysis.

1.8 LOCATION OF THE STUDY AREA

Republic of Yemen is located at the south-southwestern edge of Arabian

Peninsula. It extends between 12° and 19° north of the equator and between 42° and 55°

east of Greenwich. Apart from the mainland, it includes more than 100 islands, the

largest of which is Socotra in the Arabian Sea. The total area of the country is

approximately 550,000 km², bordered by Saudi Arabia to the north, Sultanate Oman to

the east, the Arabian Sea and Gulf of Aden to the south, and the Red Sea to the west.

Yemen has a strategic location on Bab El-Mandeb, the strait that links the Red Sea with

the Gulf of Aden, one of world's most active shipping lanes.

The study area is located in the North East of Hajjah city, between 43° 36' 47"

and 43° 40' 24" longitudes and 15° 42' 18" and 15° 50' 09" latitudes, the UTM between

351476.25 and 357860.25 E and from 1736760.00 to 1751268.00 N. Generally the relief

of the area is mountainous with moderate to steep slopes and sharp-ridges (Fig. 1.3).

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1.9 CLIMATE OF YEMEN

The climate of Yemen is diverse and varies from one place to another depending

on the altitudes of the regions. Hot and humid on the coastal, moderate on the mountains,

and hot climate in the desert areas. Yemen has a predominantly semi-arid to arid climate,

with rainy seasons during spring and summer, and with high temperature prevailing

throughout the year in low-altitude zone. The climate in Yemen is affected by the Red

Sea, the Indian Ocean (which includes the Gulf of Aden and the Arabian Sea), and the

Mediterranean Sea. They are the sources of moisture for the passing air masses, and they

have their impact on general atmospheric circulation. Yemen is positively influenced by

its mountainous relief, causing orographic rainfall on the windward side. The annual

rainfall reaches a peak of more than 1000 mm/a in the southern mountain near Ibb and

plunges rapidly at the eastern slopes to less than 50 mm/a (Ramlat As Sabatayn, Ar- Rub-

AL-Khali, and Jawl).

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Fig.1.3 Location and Physiographical map of the study area

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1.10 METHODOLOGY

To achieve the research objectives, studies were undertaken in several stages

which are as follows:

• First stage

This stage includes collating the satellite image data [ETM+, ASTER, and

Quickbird Shuttle Radar Topography Mission (SRTM)] and relevant maps (topographical

and geological). Literature review related to this study was carried out. All data used in

this study were geo-references in the Universal Transverse Mercator (UTM) coordinate

system as the map projection and World Geodetic System (WGS 1984) datum, zone 38

north and to the geographical latitude and longitude. Preliminary analysis of different

data was carried out in order to have an insight into the field work that would be required

prior to actual field study that helped the researcher to conduct the field survey by

pinpointing the potential area.

• Second stage

This stage involves field studies such as lithology, and tectonics and their proper

interpretations. Samples were collected with the coordinates using Global Position

System (GPS) for chemical analysis, petrography and spectral reflectance measurements.

The results such as band ratio, PCA and OIF of primary analysis obtained from satellite

images and field study were compared.

• Third stage

This stage consists of three parts: 1) Chemical analysis, petrographical study and

spectral reflectance measurements. 2) Remote sensing data processing. 3) Integration of

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GIS, remote sensing data and field studies for mapping the hydrothermal alteration zones

of the study area. Finally, this stage included field visits for comparing the above results

with the field investigation results.

• Fourth stage

The data collected have been used to pen down the research by organizing the

related information in the study area, its classification and correlation in an orderly

manner according to the changes that took place and the results of those changes. Finally,

the edited version of the results and recommendations of the research have been

presented.

1.11 OVERVIEW OF THE THESIS

The present research work has been presented in eight chapters: First chapter

introduces the general information about hydrothermal alteration, remote sensing and

GIS techniques and their application in mapping the hydrothermal alteration zones.

Location, physiography of the study area, objectives and literature review are presented.

Methodology adopted is also broadly highlighted.

Second chapter deals with the investigation of the satellite imagery (ASTER,

ETM+, SRTM and Google Earth). It also gives a brief description of the programmes and

instruments which were used.

Third chapter is about the geology of Yemen and the study area, which comprises

of different rock units, classification, structures and stratigraphy. Petrography and

geochemical analysis results are presented.

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Chapter four represents the calibration of both satellite data ASTER and ETM+

using the empirical line method. The laboratory spectral reflectance of selected rocks are

measured, analysed and compared with the USGS and ASTER spectral library.

Application of the OIF for selecting the suitable band colour combination as Red

Green Blue (R-G-B) from multispectral data (ASTER and ETM+) for mapping the

different rock units is presented in chapter five.

In chapter six, the utility of PCA and band ratio techniques for mapping of the

altered, unaltered zones and vegetation cover are presented.

Chapter seven is on creating, analysing and comparing of Digital Elevation

Models (DEMs) from digitizing contour lines and from SRTM data. It also presents the

manual digitizing of the lineaments from the Google Earth, panchromatic band of ETM+

and DEMs, and also automatic extraction of the lineaments from some bands of ETM+

and ASTER data.

In chapter eight, the outcome of this research work are pinpointed, and

summarized. Recommendations for further study are also presented.

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Fig.1.3 Location and Physiographical map of the study area