Discrimination of iron ore deposits of granulite terrain of Southern Peninsular India using ASTER data Sankaran Rajendran a,⇑ , A. Thirunavukkarasu b , G. Balamurugan c , K. Shankar d a Department of Earth Sciences, Sultan Qaboos University, 123 Al-Khod, Muscat, Oman b Department of Geology, Bharathidasan University, Tiruchirapalli 620 024, Tamil Nadu, India c Centre for Remote Sensing and Geoinformatics, Sathyabama University, Chennai 600 119, Tamil Nadu, India d Department of Earth Sciences, Annamalai University, Annamalai Nagar 608 002, Tamil Nadu, India article info Article history: Received 19 August 2009 Received in revised form 16 November 2010 Accepted 4 January 2011 Available online 1 February 2011 Keywords: Iron ores Lithological mapping Remote sensing ASTER image processing Granulite terrain of Southern India abstract This work describes a new image processing technique for discriminating iron ores (magnetite quartz- ite deposits) and associated lithology in high-grade granulite region of Salem, Southern Peninsular India using visible, near-infrared and short wave infrared reflectance data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite, hornblende biotite gneiss, amphibolite, dunite, and pegmatite have absorption features around spectral bands 1, 3, 5, and 7. ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denom- inator to map iron ores and band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB for associated lithology. The results show that ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in a Red–Green–Blue (RGB) color combination identifies the iron ores much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) is applied to reduce redundant information in highly correlated bands. PCA (3, 2, and 1 for iron ores and 5, 4, 2 for granulite rock) in RGB enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock. Thus, this image processing tech- nique is very much suitable for discriminating the different types of rocks of granulite region. As out- come of the present work, the geology map of Salem region is provided based on the interpretation of ASTER image results and field verification work. It is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of Southern Peninsular India. This work also demonstrates the ability of ASTER’s to provide information on iron ores, which is valuable for mineral prospecting and exploration activities. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The Pre-Cambrian igneous and metamorphic granulite terrains of Southern Peninsular India is engulfed by Arabian Sea on the west and Bay of Bengal on the east side falls parts of Indian Shield. The supracrustal rock groupings recognized in the Pre-Cambrian stra- tigraphy of India are: (1) Ancient supracrustals (Sargur Group rocks of Karnataka; older metamorphic rocks of Bihar and Orissa), (2) Archaean schist belts, and (3) Proterozoic sedimentary basins. The oldest of these three occurs as supracrustal remnants in gneis- sic regions. These are believed to be older than 3400 million years and are well developed in Karnataka, Tamil Nadu and Kerala (Radhakrishna, 1986). These ancient supracrustals consist of shallow-water sediments, mostly psammites, pelites, calc-silicates, ferruginous and manganiferrous sediments. Ferruginous sediments are prominently seen in Salem, Dharmapuri, Tiruchirapalli and Tiruvannamalai regions of Tamil Nadu state, India. The description of the lithology of these older supracrustals and the mineralogical characteristics of iron formations of this group has been presented by Janardhan et al. (1986), Swami Nath and Ramakrishnan (1981), Devaraj and Laajoki (1986), Radhakrishna (1986) and Mahabale- swar (1985). The rocks of this group have been metamorphosed to upper amphibolite facies of metamorphism. The occurrence of ancient supracrustal remnants as enclaves in older tonalitic gneiss indicates that they belong to an earlier sequence. Here, the crudely banded magnetite-quartz rocks and pyroxene granulite rocks are known to occur generally as thin discontinuous intercalations in the charnockite and gneisses terrain. The study area Salem region is located 290 km west of Chennai (the capital of Tamil Nadu state, 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.01.004 ⇑ Corresponding author. Address: Department of Earth Sciences, Annamalai University, Annamalai Nagar 608 002, Tamil Nadu, India. Tel.: +91 9443665737; fax: +91 4144 238080 or 238145. E-mail address: sankaranrajendran@yahoo.com (S. Rajendran). Journal of Asian Earth Sciences 41 (2011) 99–106 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes