Using air-borne gamma ray spectrometry and remote sensing data for detecting alteration zones around Wadi Saqia area, Central Eastern Desert, Egypt

Abstract

This study presents the air-borne geophysical Gamma Ray Spectrometry data have been used for detecting the alteration zones related to hydrothermal activity. Areas enriched in potassium may indicate the existence of potassic alteration zone that is often associated with hydrothermal alteration accompanied by economic mineral deposits. The radioelements (K (%), eTh (ppm), and eU (ppm)) concentration distribution and the ratios of (K/eTh and K/eU) over the study area were presented. A Potassium Point anomaly map was obtained from the statistical treatment of the K (%), K/eU, and K/eTh spectrometric data. Anomalously High (X+3σ or more) areas were delineated and considered the most preferred areas for potassic alteration. If the maximum values exceed the (X+3σ) threshold, then (X+2σ) or (X+σ) is applied instead. Sixteen areas were delineated and suggested for the presence of potassic alteration. The F-Parameter of Efimov (K*(eU/eTh)) was also implemented as proved approach for delineating the most preferred areas for hydrothermal alteration. The result of the Potassium point anomaly mapping was compared to that of the F-Parameter technique that was used as reference for validating the results. The sixteen anomalous areas revealed from the Potassium point anomaly technique showed perfect correlation with the areas of highly anomalous F-parameter.Remote sensing study supported by field data and laboratory spectral analyses was also implemented in this study as another useful powerful cost-effective approach for alteration mapping. A field study was conducted; samples from the different observed alterations were collected. The spectral signatures of these samples were measured using the “ASD TerraSpec Halo mineral identifier” hand-held spectroradiometer. Spectral analyses were performed to obtain the spectral characteristics of the alteration zones of the study are. The end-members were identified through comparing the measured spectra against the United States Geological Survey (USGS) spectral library in ENVI v.5.1. software. The identified end-members include; Kaolinite, Sericite, Montmorillonite, Chlorite, Epidote and iron oxides. Subpixel Mixture Tuned Matched Filtering (MTMF) mapping technique was finally used for mapping the distribution of these end-members on ASTER nine Visible Near Infra-Red (VNIR) and Short Wave Infra-Red (SWIR) bands. The remote sensing data were validated as Semna gold mine and the identified alterations during the field study were successfully mapped by the remote sensing technique. Finally; Most of the delineated areas using the proposed Potassium point anomaly technique were also evidenced by the approached remote sensing technique. Moreover remote sensing suggested more alteration areas than did the gamma ray spectrometry data.