ASTER spectral analysis of ultramafic lamprophyres (carbonatites and aillikites) within the Batain Nappe, northeastern margin of Oman: A proposal developed for spectral absorption

We developed a scientific proposal on spectral absorption in remote sensing and a new image-processing method that is purely based on multispectral satellite image spectra to map ultramafic lamprophyre and carbonatite occurrences. The proposed method provides a simple, yet efficient, tool that will help exploration geologists. In this proposal, in which the spectral absorption is applicable to all satellite images obtained in visible, reflected infrared, and thermal infrared spectral wavelength regions, we found that the carbonatites appear white in colour on a greyscale or RGB thermal infrared image obtained in the thermal infrared wavelength region (3-15 μm) due to molecular emission of thermal energy by such carbonate content, particularly the wavelength recorded by the sensor and that the variation of absorption in spectral bands of an outcrop is due to the differences in percentage of carbonate content or the spectral, spatial, radiometric, or temporal resolution of satellite data or the occurrences of carbonatites to incident energy. The results were confirmed by studying the spectral absorption characteristics of carbonatites in selected world occurrences including parts of Batain Nappe, Oman; Fuerteventura (Canary Islands), Spain; Mount Homa, Kenya; Ol Doinyo Lengai, Tanzania; Mount Weld region, (Laverton), Australia, and Phalaborwa region, South Africa, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper (TM) satellite data. A subsequent study of visible near-infrared (VNIR) and shortwave infrared (SWIR) ASTER spectral bands of Early Cretaceous alkaline ultramafic rocks of Batain Nappe, along the northeastern margin of Oman to map for the occurrences of carbonatite and aillikite (ultramafic lamprophyres) dikes and plugs, showed their detection mainly by the diagnostic CO₃ absorption (2.31-2.33 μm) in ASTER SWIR band 8. The results of image interpretations were verified and confirmed in the field and were validated through the study of laboratory analyses. A few more carbonatite dike occurrences were interpreted directly over the greyscale image of ASTER bands and true-colour interpretations of a Google Earth image along this margin. The carbonatites and aillikite occurrences of the area are rich in apatite, iron oxide, phlogopite, and REE-rich minerals and warrant new exploration projects.