Spectroscopy of the mineralized tonalite–diorite intrusions, Bulghah gold mine area, Saudi Arabia: Effects of opaques and alteration products on Fieldspec data

Abstract

This paper aims to reveal the spectral characteristics of the mineralized tonalite–diorite intrusions exposed at Bulghah gold mine area, Saudi Arabia, using FieldSpec spectroradiometer and Landsat ETM + data. Gold mineralization at Bulghah gold mine is hosted mainly by Syn- to Late-orogenic tonalite–diorite intrusions aligned in N–S direction and is associated mainly with cataclastic zones and quartz veins. Based on field, petrography and FieldSpec data two main tonalite–diorite groups namely A and B are recognized. Group “A”, recorded at the mine area, is characterized by low flat spectral profiles with overall low reflectance values (~ 10%). These low values are attributed to the presence of high content of trans-opaque phases (hematite and goethite) as indicated by petrographic study. Spectral profiles of group “B”, recorded at Bulghah North area, show high reflectance values (~ 40%) with three main absorption features around the 1.45 μm, 2.20 μm and 2.35 μm wavelength regions. These absorption features are attributed mainly to the presence of clay minerals, sericite, chlorite and carbonate alteration products. To discriminate the above mentioned tonalite–diorite groups, band ratios and Minimum Noise Fraction (MNF) techniques are conducted. Landsat false color composite band ratio image (7/4:R, 4/1:G and 4/5:B) discriminates easily the bluish brick red tonalite–diorite intrusions from the surrounding rock units but failed to distinguish the above mentioned two tonalite–diorite groups. On MNF3 image, the two tonalite–diorite groups can be distinguished easily in which group “A” has white color whereas group “B” has gray color. The present study proved the usefulness of FieldSpec spectral profiles and the processed Landsat ETM + data for discriminating and delineating the mineralized tonalite–diorite intrusions exposed at the study area.