ASTER spectral analysis and lithologic mapping of the Khanneshin carbonatite volcano, Afghanistan

Abstract

Advanced Spaceborne Thermal and Refl ection Radiometer (ASTER) data of the early Quaternary Khanneshin carbonatite volcano located in southern Afghanistan were used to identify carbonate rocks within the volcano and to distinguish them from Neogene ferruginous polymict sandstone and argillite. The carbonatitic rocks are characterized by diagnostic CO 3 absorption near 11.2 μm and 2.31-2.33 μm, whereas the sandstone, argillite, and adjacent alluvial deposits exhibit intense Si-O absorption near 8.7 μm caused mainly by quartz and Al-OH absorption near 2.20 μm due to muscovite and illite.Calcitic carbonatite was distinguished from ankeritic carbonatite in the short wave infrared (SWIR) region of the ASTER data due to a slight shift of the CO 3 absorption feature toward 2.26 μm (ASTER band 7) in the ankeritic carbonatite spectra. Spectral assessment using ASTER SWIR data suggests that the area is covered by extensive carbonatite fl ows that contain calcite, ankerite, and muscovite, though some areas mapped as ankeritic carbonatite on a pre existing geologic map were not identifi ed in the ASTER data. A contact aureole shown on the geologic map was defi ned using an ASTER false color composite image (R = 6, G = 3, B = 1) and a logical operator byte image. The contact aureole rocks exhibit Fe 2+ , Al-OH, and Fe, Mg-OH spectral absorption features at 1.65, 2.2, and 2.33 μm, respectively, which suggest that the contact aureole rocks contain musco vite, epidote, and chlorite. The contact aureole rocks were mapped using an Interactive Data Language (IDL) logical operator.A visible through short wave infrared (VNIR-SWIR) mineral and rock-type map based on matched fi lter, band ratio, and logical operator analysis illustrates: (1) lat-erally extensive calcitic carbonatite that covers most of the crater and areas northeast of the crater; (2) ankeritic carbonatite located southeast and north of the crater and some small deposits located within the crater; (3) agglomerate that primarily covers the inside rim of the crater and a small area west of the crater; (4) a crater rim that consists mostly of epidote-chloritemuscovite-rich metamorphosed argillite and sandstone; and (5) iron (Fe 3+ ) and muscovite-illite-rich rocks and iron-rich eolian sands surrounding the western part of the volcano. The thermal infrared (TIR) rock-type map illustrates laterally extensive carbonatitic and mafi c rocks surrounded by quartz-rich eolian and fl uvial reworked sediments. In addition, the combination of VNIR, SWIR, and TIR data complement one another in that the TIR data illustrate more laterally extensive rock types and the VNIR-SWIR data distinguish more specifi c varieties of rocks and mineral mixtures.

Remote Sensing Exploration of Nb-Ta-LREE-Enriched Carbonatite (Epembe/Namibia)

“…Expert knowledge is often required to get reliable results if the target is rather small [9,10]. However, applications of remote sensing for the exploration of carbonatite were only tested in a few studies ( [9,[11][12][13][14][15][16][17]). Thus, there is a need to improve remote sensing exploration techniques for REEs, Nb and Ta due to an increasing demand during the past few decades and the acceleration of this demand due to their augmenting use in high-tech industry ( [18,19]).…”

A deposit model for carbonatite and peralkaline intrusion-related rare earth element deposits

“…Mars and Rowan (2011) reported that calcic carbonatite could be distinguished from ankeritic carbonatite in the short wave infrared region of ASTER data as indicated by a slight shift in the CO 3 absorption band. Using spectral features, they were also able to map: (1) contact aureole rocks containing muscovite, epidote, and chlorite; (2) the crater rim composed of argillite and sandstone; and (3) iron (Fe 3 + ) and muscovite-illite-rich rocks and iron-rich eolian sands bounding the western side of the volcano.…”

“…More recently, another USGS study (Mars and Rowan, 2011) examined the application of Advanced Spaceborne Thermal and Reflection Radiometer (ASTER) data to map lithologies at the Quaternary-age Khanneshin carbonatite volcano in southern Afghanistan. Mars and Rowan (2011) reported that calcic carbonatite could be distinguished from ankeritic carbonatite in the short wave infrared region of ASTER data as indicated by a slight shift in the CO 3 absorption band.…”

“…Using spectral features, they were also able to map: (1) contact aureole rocks containing muscovite, epidote, and chlorite; (2) the crater rim composed of argillite and sandstone; and (3) iron (Fe 3 + ) and muscovite-illite-rich rocks and iron-rich eolian sands bounding the western side of the volcano. Mars and Rowan (2011) explained in detail how several types of processed ASTER spectral data can be analyzed and used in combination to delineate rock types and mineral mixtures in complex alkaline igneous systems, such as the Khanneshin volcano, which includes carbonatite that varies in composition, along with associated mafic rocks, hornfels, sedimentary rocks, and sediments.…”

Estimation of Supraglacial Dust and Debris Geochemical Composition via Satellite Reflectance and Emissivity

“…Supraglacial tephra found on Hofsjökull translates to very low, featureless SWIR values and conversely, continental supraglacial debris from Lhotse Shar and Imja glaciers display higher VNIR and SWIR reflectance. Although beyond the scope of this study, with atmospheric correction, Hyperion data are theoretically amenable to supraglacial mineralogic differentiation using continuum removal and/or logical operator techniques for discriminating small-scale wavelength and absorption depth-dependent characteristics of glacier surface particulates [70,71]. Component specific absorption features, for example due to silicate-rich dust vs. calcite-rich dust, could be used to attempt a more quantitative assessment of supraglacial composition.…”