Analysis of ETM+ and airborne geophysical data for exploration of porphyry-type deposits in the central Iranian volcanic belt, using fuzzy classification

Abstract

ABSTRACT The area under study is located in the southern part of the Central Iranian Volcanic Sedimentary belt and covers an area of about 488 sq. kms. Sar Cheshmeh and Darreh zar areas with known mineralization and alteration are chosen as control areas. Airborne geophysical data - radiometry and megnetometry – and ETM+ data has been integrated and analysed using fuzzy classification. This type of classification is suggested for remote sensing data, but it can also be used for classification of combined airborne geophysical and satellite data. After defining the training areas(Sar Cheshmeh and Darrehzar areas), the entire region is classified into altered and unaltered areas. This analysis is found useful for exploration of porphyry type deposits in the Central Iranian Volcanic Belt, where most parts of this belt is surveyed by airborne geophysics. Key words: Porphyry type, exploration, ETM+, Airborne geophysics, fuzzy classification 1. INTRODUCTION Many of the known porphyry copper deposits are situated in the Central Iranian volcanic Belt (Fig. 1). This belt has a great potential as far as Tertiary porphyry copper deposits are concerned. Large part of this belt has not been explored in detail. The area under study has an arid climate, mountainous topography and poor veg etation cover (Fig.2).The aim of this study is to propose a method for combination and analysis of the airborne geophysical data and remote sensing data for exploration of porphyry copper deposits in this belt. Remote sensing techniques and spatial data analysis through Geographic Information Systems (GIS) have been jointly applied in a mineral exploration context to identify porphyry rich potential areas in this belt. Results confirm the usefulness of this integrated methodological approach as an effective tool to assess mineral pote ntial in the st udied region Porphyry type deposits are associated with hydrothermal alterations such as phyllic, argillic, potassic and propylitic. Hydroxyl minerals are abundant in the phyllic, argillic and potassic zones. At the same time an oxide zone is developing over many of the porphyry bodies which are rich in iron oxide minerals. The previous studies have shown that the elevated potassium in the sericite zone is often observed around the mineralization areas and also acid sulphate conditions resulting from weathering of near surface sulphides can result in Th mobilization from host rocks and can precipitate with iron in gossan