Utilization of landsat etm + data for mapping gossans and iron rich zones exposed at Bahrah Area, Western Arabian Shield, Saudi Arabia

الملخص EN

Utilization of remote sensing techniques for mapping gossans and iron rich zones exposed at Bahrah area, Western Arabian Shield, Saudi Arabia is the main task of this article.

Spatial dimensions of these gossans are favorable to detect by Landsat ETM+ imagery.

Gossans at the study area occur within the highly foliated, metavolcanic sequence composed mainly of basalts, basaltic andesites, dacites, rhyolites and their tuffs.

Band ratios and density slicing are the main remote sensing techniques used throughout this study to discriminate and map the gossans and iron-rich zones exposed along the NNE-SSW left lateral strike slip faults.

4/5 band ratio image was found to be the most favorable ratio that discriminates the gossans and iron-rich zones.

The gossans have a black image signature on this ratio and this signature is attributed to the absorption feature near band-4 exhibited by pyrite, hematite, goethite and magnetite, the main mineral constituents of gossans.

On 4/5 band ratio image the DN values of gossans were determined (range between 0 and 14) and used by the density slicing technique to slice the gossans and iron rich zones from other rock units exposed at the study area.

Panchromatic Landsat band-8 was prepared for the automatic lineaments extraction using PCI package under the user defined parameters.

The results of lineaments analysis revealed that, the main lineament trends affecting the metavolcanic sequence and the gossans are NE-SW, N-S (NNE-SSW) and NW-SE.

These trends were verified in the field and found to coincide largely with the results of the geophysical studies done by many authors on the study area.

The information extracted from the lineaments analysis, density slicing technique and the field verification were integrated to produce an image map of scale 1:100 000 shows the distribution of gossans and iron rich zones exposed at the study area.