bul 2004 
COMPARISON OF BAND RATIOING AND SPECTRAL INDICES METHODS FOR 
DETECTING ALUNITE AND KAOLINITE MINERALS USING ASTER DATA 
IN BIGA REGION, TURKEY 
B. T. San, E. O. Sumer, B. Gurcay 
General Directorate of Mineral Research and Exploration, Remote Sensing Center - 06520, Ankara, TURKEY 
tanersan@mta.gov.tr, esumer@mta.gov.tr, boragurcay@mta.gov.tr 
KEY WORDS: Remote Sensing, Geology, Comparison, Detection, Multispectral, Method 
ABSTRACT: 
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) covers a wide spectral region with 14 bands 
from visible to the thermal infrared. The different band ranges can be capable of discriminating and mapping surface rocks 
and predicting pathfinder minerals (i.e. alunite, kaolinite etc.) on alteration assemblages of potential targets. The aim of this 
study is to compare two different discrimination techniques as band ratioing (BR) and spectral indices (SI) applied on Biga — 
Canakkale Area, Turkey. The ground truths were held on 19 locations to compare obtained results. The study area covers 
altered Miocene age acidic volcanic rocks. Alunite and kaolinite are main minerals in hydrothermal alteration zones. During 
the image processing, in order to reduce atmospheric effect on ASTER bands, digital numbers of each image channels are 
converted to relative reflectance for BR and SI techniques. In BR method, two ratios (4/5 and 7/6) were applied to 
discriminate alunite and kaolinite respectively. However, in SI method, 5 SWIR bands (5, 6, 7, 8, and 9) were taken into 
account to detect for alunite and kaolinite presence for each mineral. 19 hydrothermal sites were tested by both methods and 
13 of them were identified as alunite by using SI method. On the other hand, in BR method, kaolinite and alunite were 
discriminated in 11 sites and 8 sites, respectively. As a result, SI and BR techniques can detect alunite and kaolinite minerals. 
SI method gives better results for detecting alunite than that of kaolinite. On the contrary, BR method can be more applicable 
to discriminate kaolinite than alunite. 
1. INTRODUCTION basement is unconformably overlain by Mesozoic 
sedimentary formations and Miocene intermediate 
Advanced Spaceborne Thermal Emission and Reflection volcanic rocks. Silicified and argillized alteration zones 
Radiometer (ASTER) covers a wide spectral region with were identified in some location of the area where 
14 bands from visible to the thermal infrared. The volcanism was active during the Eocene to Miocene, and 
different band ranges can be capable of discriminating andesite, dacite, rhyolite and pyroclastic rocks are 
and mapping surface rocks and predicting pathfinder developed. These are widely distributed in the central 
minerals (i.e. alunite, kaolinite etc.) on alteration part of Biga Peninsula (MTA-JICA-MMAJ, 1990). 
assemblages of potential targets (Ninomiya, 2002). During the beginning of this volcanic period, granodiorite 
intrusions occurred in many parts. There are three major 
volcanic activities aged Eocene, Miocene and post- 
Pliocene. Also, there are two stages of granite activities 
Triassic and Cretaceous to Eocene. Most of iron, copper, 
lead and zinc mineralizations are found associated with 
this type of intrusion. The age of the alteration is inferred 
to be latest Tertiary, and the center of the Tertiary 
: : à volcanic activity is very clearly identified (MTA-JICA- 
Study area, Biga Peninsula, is located on Southern part of MMAJ, 1991.a). 
the Marmara Sea and North-West part of the Anatolia. It 
covers a one ASTER scene, size of which has 60 x 60 km 
area (Figure 1). The study area dominantly consists of 
volcanic rocks such as andesite, rhyolite type. Most of 
andesitic rocks were alterated by hydrothermal effect. 
Kaolinite, alunite type minerals and rocks were derived 
from altered andesite. These kinds of mineral or mineral 
groups indicate the some metalogenic province such as 
lead, zinc and copper deposits. Therefore, these alteration 
minerals are known as indicator minerals for exploration 
of metallic minerals (MTA-JICA-MMAJ, 1990). 
Aim of the study is to compare two different techniques 
for detection of alunite and kaolinite minerals which are 
important mineral to illustrate alteration zones. 
2. STUDY AREA AND GEOLOGY 
2.2. Mining Activity in the Biga Peninsula 
The Biga Peninsula, including the Canakkale Area, is 
considered to be the most important lead-zinc 
metallogenic province of Turkey (MTA-JICA-MMAI, 
1991.a). Also, antimony, gold, silver, mercury, iron and 
other metallic deposits as well as ceramic material 
resources have been found in the peninsula. Thus, this 
peninsula has been the target of geological surveys, 
geochemical prospecting, mining studies and various 
th iects (MTA-JICA-MMAJ, 1991.b). 
2.1. Geology of Biga Peninsula other projects ( ; ) 
The basement of Biga Peninsula consists of pre-Triassic 
metamorphic rocks are called the Kazdag Group. It is 
mainly composed of gneiss, amphibolite and marble. This 
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