Gold prospecting using Remote Sensing ‘A case study of Sudan’

International Journal of Engineering Research and Development
e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com
Volume 11, Issue 09 (September 2015), PP.01-05
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Gold prospecting using Remote Sensing ‘A case study of Sudan’
Sohieb Ghazali1
Syed Aasif Ahmad Farooqi 2
Vakeel Ahmad Shah 2
Muzafar N.Teli 3
Mudasir A. Dada3
State Remote Sensing Centre J&k Government
Abstract:- Gold has been extracted from northeast Africa for more than 5000 years, and this may be the first
place where the metal was extracted. The Arabian-Nubian Shield (ANS) is an exposure of Precambrian
crystalline rocks on the flanks of the Red Sea. The crystalline rocks are mostly Neoproterozoic in age. ANS
includes the nations of Israel, Jordan. Egypt, Saudi Arabia, Sudan, Eritrea, Ethiopia, Yemen, and Somalia.
Arabian Nubian Shield Consists of juvenile continental crest that formed between 900 550 Ma, when intra
oceanic arc welded together along ophiolite decorated arc. Primary Au mineralization probably developed in
association with the growth of intra oceanic arc and evolution of back arc. Multiple episodes of deformation
have obscured the primary metallogenic setting, but at least some of the deposits preserve evidence that they
originate as sea floor massive sulphide deposits.
The Red Sea Hills Region is a vast span of rugged, harsh and inhospitable sector of the Earth with
inimical moon-like terrain, nevertheless since ancient times it is famed to be an abode of gold and was a major
source of wealth for the Pharaohs of ancient Egypt. The Pharaohs old workings have been periodically
rediscovered through time. Recent endeavours by the Geological Research Authority of Sudan led to the
discovery of a score of occurrences with gold and massive sulphide mineralizations. In the nineties of the
previous century the Geological Research Authority of Sudan (GRAS) in cooperation with BRGM utilized
satellite data of Landsat TM using spectral ratio technique to map possible mineralized zones in the Red Sea
Hills of Sudan. The outcome of the study mapped a gossan type gold mineralization. Band ratio technique was
applied to Arbaat area and a signature of alteration zone was detected. The alteration zones are commonly
associated with mineralization. The alteration zones are commonly associated with mineralization. A filed check
confirmed the existence of stock work of gold bearing quartz in the alteration zone. Another type of gold
mineralization that was discovered using remote sensing is the gold associated with metachert in the Atmur
Desert.
As knowledge of geology and mineralization of the Red Sea Hills improved, it became increasingly
apparent that mineral deposits are located along linear structures trending NE-SW and are associated with acid
volcanicity. Hydrothermal alterations and weathering processes of the sulphide mineralization produce spectral
anomalies that extend beyond the ore body itself. To this end satellite images provide a superb synoptic view of
the structural features and the spectral anomalies. Special interest was focused on ratio image processing
techniques, whereby false colour composite images were produced using combination of bands in Red, Green
and Blue, that rendered maps of alteration zones. Ground-truthing of the outlined areas disclosed the existence
of stockworks that contain gold and sulphide mineralization.
I. INTRODUCTION
In the recent years remote sensing was used extensively in many applications such as geological
mapping, agriculture mapping, hydrogeological investigation and prospecting for mineral deposits The
increasing living standard of the underdeveloped countries entails the search for more resources to meet the
demands of minerals.
Therefore, new exploration techniques must be utilized to discover previously unknown reserves.
Remote Sensing can map and analyze rocks over hundreds of square miles in a single imagery. This geological
mapping may indicate particular areas of interest that can then be investigated in detail on the ground. Improved
geological understanding leads to looking for new resources in previously overlooked areas. The main elements
of geology in Sudan include high‐grade gneisses; low‐grade green schist island‐arc assemblage of
metasediments, metavolcanics and ophiolitic tectonic mélanges. The layered sequences intruded by
syn‐orogenic and post‐orogenic granites; and are separated by structural contacts. The basement rocks are
overlain by Nubian Super Group sedimentary cover followed by Tertiary volcanics and blanketed by Quaternary
to Recent deposits. Gold exploration and exploitation in Sudan dates back to the Farah and Turkish eras. Gold
used to be explored by use of traditional methods at Nahral-Neel, Blue Nile and northern Sudan. The ancient
sites discovered at those areas were about twelve sites.
The most common type of alteration is the breakdown of feldspars and ferromagnesian minerals to a
variety of clays and other hydroxyl bearing minerals. Such minerals can be detected by remote sensing

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techniques since the short wave infrared (SWIR) range of their spectra exhibit absorption (Drury 1993). Besides,
a considerable number of ore occurrences contain sulphide minerals particularly pyrite (FeS2) which undergo
breakdown to sulphuric acid and a number of ferric hydroxides and complex sulphates which are both strongly
coloured and possess crystal field absorption in the visible and near infrared range (VNIR) (Drury, 1993;
Lillesand & Kiefer, 1994; Sabins, 1978). This suite of alteration features proved to be extremely useful in
delineating a variety of hydrothermal ore deposits (Drury, 1993). It has been well established that ferric iron
exhibits pronounced absorption features at around 0.82 μm and 0.35μm, whereas ferrous iron has absorption at
1.0, 4.8-2.0 and 0.55-0.45. Hydroxyl – bearing minerals like clays have a major absorption feature around 1.9,
2.35 and 2.5 (Gupta, 1991). Detection of the above mentioned minerals has been used as prospecting guide for
ore deposits. Ratio images are known for enhancement of spectral contrasts among the bands considered in the
rationing and have successfully been used in mapping alteration zones (Segal, 1983; Kenea, 1994).
Gold is found at al-Mazroub area where Gossanic evidences containing gold ore and other related
mineral have been discovered. These studies have proved presence of extensions of Gossanic evidences in
depths that are estimated at 150 meters inside the ground. Gold ore and other related minerals have also been
discovered in northeastern Sudan between latitudes (20-00, 21-00 degrees) and longitudes (15-35, 30-34
degrees) east. Geological studies and researches have also proved existence of gold at many places in the
country including the Red Sea Mountains, south of Blue Nile, north Sudan (from Halfa northwards until Atbara
on east and west of the Nile), North and South Kordufan State, South Darfur State and others.
The overall objective of the present work is to discuss Sudan experiments in using remote sensing to
prospect for different types of mineralization and to demonstrate the viability of this technique in such studies.
II. STUDY AREA
The present area that was adapted for studying the mineral deposits using Geo-informatics in Sudan
The Bayuda city of Sudan lies in between 18 19 47.62 N 32 40 56.92 E. The total area of study area is
1,535.828296 Square Kilometers. (ETM) image of Landsat 7 satellite are used throughout the analysis. The area
of interest is included within the image 174/47. The Bayuda volcanic field is located in the Bayuda Desert of NE
Sudan, south of the major Abu Hamed bend of the Nile River about 300 km north of capital city of Khartoum.
More than 90 eruptive centers along a WNW-ESE line were constructed over Precambrian and Paleozoic
granitic rocks near the center of the Bayuda Desert. Most vents of the Bayuda field are cinder cones that
produced lava flows which breached the cones. About 10% of vents in the field are explosion craters, the largest
of which, named Hosh ed Dalam, is 1.3 km wide and up to 500 m deep. The youngest basalts of the Bayuda
volcanic field appear to post-date the last period of moist climate in Sudan, which ended as recently as about
5000 years ago. One of the least eroded lava flows at Bayuda was dated at about 1100 years ago.
Figure 1. Shows the Location map of Study area

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III. MATERIALS AND METHOD
Dataset Used
2. Data type:
Remotely sensed data used in this study are shown in the following table:
During the analysis a simple to complex step-wise path is followed. Each analysis result is compared
with the previous one. Conventional methods like color composites, several band rationing techniques, are
applied to the original unregistered raw data.The resulting images are considered to be the potential alteration
maps. If the results display any convergence with the data acquired from previous works then the final
(combination) map of all techniques is registered and processed and prepared for the ground truth. The geology
of the area is gathered from the published maps and mostly forms the basis of the ground truth data
2.1.2 Band Rationing: The band ratio is a technique that has been used for many years in remote sensing to
display spectral variations effectively (Elsayed Zeinelabdein, K.A. (2008).
It is based on highlighting the spectral differences that are unique to the materials being mapped.
Identical surface materials can give different brightness values because of the topographic slope and aspect,
shadows, or seasonal changes in sunlight illumination angle and intensity. These variances affect the viewer’s
interpretations and may lead to misguided results. Therefore, the band ratio operation could be able to transform
the data without reducing the effects of such environmental condition. In addition, ratio operation may also
provide unique information that is not available in any single band which is very useful for disintegrating the
surface materials (Jensen 1996). The band ratio images are known for enhancement of spectral contrasts among
the bands considered in the ratio operation and have successfully been used in mapping of alteration zones
(Segal 1983). From the theoretical knowledge of mineral’s spectral properties, it is well recognized that the
Landsat TM bands ratios of 3/1, 5/7, 5/4 are analyzed for iron oxides, hydroxyl bearing minerals, ferrous oxides,
respectively.
Sensor path Row Date
ETM 174 47 17-04-2005
Table (1): Data types used in this study

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IV. RESULT AND DISCUSSION
Using the theoretical knowledge about the spectral properties of most rocks and minerals, TM bands
3/1 and 5/7 were selected for iron oxides and hydroxyl bearing mineral respectively (see plate 2 and 3). Whereas
band ratio 5/4 has been computed to enhance possible ferrous oxides.
Ratio image obtained using 3/1 band ratio
Ratio Image obtaining using 5/7 band ratio
Ratio Image obtaining using 5/4 band ratio
Based on the above considerations the spectral features of ferric and hydroxyl – bearing mineral, in
which hydrothermally altered rocks are often rich, are used to produce a false colour composite image using
combinations of bands 5/7, 5/4 and 3/1 in R,G and B respectively (see plate 1). The obtained image has mapped
the alteration zone in reddish yellow. This alteration can easily be observed in the lower right corner and right
central part of the image.
Another composite ratio image was produced using bands 5/7, 3/1 and 4/3 in R,G and B respectively
(see plate 2). Although this combination of ratio image appears to be fairly different from the previous one, the
final result remains the same thus lending support to the previous conclusion.
Groundtruthing of the outlined areas of wall rock alterations has disclosed the existence of a quartz stockwork
that contains gold and base metal sulphide mineralization.
Plate (2) Hydrothermal Composite Image 5/7,3/1,4/3

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Ratio image obtained the following band combination: (band 5/ band 7), (band 3/ band 1) and (band 4/ band 3)
assigned to red, green and blue filters, respectively.
Ratio image obtained using the following band combination: (band 5/ band 7), (band 5/ band 4) and (band 3/
band 1) assigned to red, green and blue filters, respectively
However, the performed study should be considered a preliminary step to narrow the search area and paves the
way for more detailed prospecting in the predefined potential sites.
V. CONCLUSION RECOMMENDATION
The gossan type of gold mineralization was successfully mapped in the Red Sea Hills of Sudan making
use of Satellite imagery. The study has demonstrated the application of Remote Sensing as a valuable tool for
assessing the alteration zones. The main aim was to prospect alteration zones and compare the results with the
field records in order to see as to how accurately remote sensing can be used to make alteration assessments in
such a short span of time. This can help as technical alternative which can prospect the alteration zones in very
less time and with moderately good accuracy. Emote Sensing technology gives a fairly good result of
prospecting the minerals with small amount of field survey and has tremendous advantages in terms of
comparatively saving time in prospecting the minerals. The study will go in long way to redress the future
mineral challenges that Sudan will face and will help planners to come out with certain concrete measures and
policies to address the issues.
Band ratio technique was applied and a signature of alteration zone in Yellowish color was detected. A
field check was confirmed the existence of stock work of gold bearing quartz in the alteration zone. Al Ridaa
Mining company now is exploiting gold from such mineralization. The increasing demand for cement in the
current years leads to the construction of several cement factories. These factories used emote sensingin finding
new occurrence for marble.Black sand of magnetite mineralisaton in streams located in northern sudanwas
detected using Quick bird high resolution imagery. This type of mineralization appears as brown hues in images.
Another type of iron ore was found in magnetite rich microgranite, which appears in blue turquoise color in
Landsat images.
REFERENCES
[1]. DRURY, S. A. (1993): Image Interpretation in Geology. 2nd ed.,-271 pp., (Chapman and Hall),
London.
[2]. GUPTA,R.P. (1991): Remote Springer- verlag Geology. – 356 pp., Berlin-Heidelberg (Springer).
[3]. KENEA, N. H. (1997): Digital Enhancement of Landsat Data, Spectral Analysis and GIS Data
Integration for Geological Studies of the Derudeb Area, southern Red Sea Hills, NE Sudan. – 116 pp.,
Berliner Geowiss. Abh., D 14, Berlin.
[4]. SEGAL, D. B. (1983): Use of Landsat Multispectral Scanner Data for Definition of Limonitic
Exposures in Heavily Vegetated Areas. Econ. Geol., 78, pp. 711-722, EL Paso, Texas.
[5]. Kenea, N. H. 1997. Improved geological mapping using Landsat TM data, Southern Red Sea Hills,
Sudan: PC and HIS decorrelation stretching. Intern. Jour. of remote sensing, 18, (12), p. 1233-1244.
[6]. Jensen, R. John, 1996. Introductory Digital Image Processing A Remote Sensing Perspective 2nd
edition, Upper Saddle River, Prentice Hall, New Jersey.
[7]. Elsayed Zeinelabdein, K.A. (2008). Ratio image processing techniques: A prospecting tool for mineral
deposits, Red Sea Hills, NE Sudan. The International Archives of the Photogrammetry, Remote
Sensing and Spatial Information Sciences. Vol. XXXVII. Part B8. Beijing, China
Plate (1):Mineral Composite Image 5/7,5/4,3/1

Gold prospecting using Remote Sensing ‘A case study of Sudan’

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Gold prospecting using Remote Sensing ‘A case study of Sudan’