Abstract
Reflectance spectra of carbonate minerals in the shortwave infrared (SWIR) and thermal infrared (TIR) wavelength regions contain a number of diagnostic absorption features. The shape of these features depends on various physical and chemical parameters. To accurately identify carbonate minerals or rocks in pure and mixed form, it is necessary to analyze the effects of the parameters on spectral characteristics. In this study, we analyzed spectral absorption feature characteristics of calcite and dolomite in the SWIR (features at 2.3 and 2.5 μm) and TIR (features at 11.5 and 14 μm) wavelength regions, as a function of grain size and carbonate mineral mixtures. Results showed that varying grain sizes and mineral contents in the sample, influence reflectance values and absorption feature characteristics. Absorption band positions of pure and mixed calcite and dolomite in the SWIR and TIR regions for both features were displaced slightly as observed in previous studies. The band positions of calcite and dolomite varied relative to grain size only in the TIR region. These positions shifted to longer wavelengths for the feature at 11.5 μm and to shorter wavelengths for the feature at 14 μm from fine to coarse grain size. The band positions of calcite-dolomite mixtures in the SWIR and TIR regions were determined by the quantity of calcite and dolomite in the sample. These results can be applied for the identification of pure and mixed calcite and dolomite, as well as estimating the relative abundance of both minerals with different grain size and mineral mixtures in a synthetic sample or rock. They can also be used as a preliminary proxy for assessing dolomitization patterns in carbonate rocks.
Highlights
Carbonate rocks, which are recognized as an important natural resource for construction materials and the cement industry [1,2], are sedimentary rocks that mostly consist of calcite (CaCO3) and dolomite (CaMg(CO3)2) [1,2,3,4]
The position of absorption bands for both features in pure powdered calcite and dolomite spectra in the shortwave infrared (SWIR) wavelength region appeared invariant to grain size fraction (Figure 3), confirming results reported by van der Meer [8] and Gaffey [21]
Results of this study indicate that absorption band positions of the two prominent carbonate features in the SWIR and thermal infrared (TIR) wavelength regions are distinctive of carbonate minerals with different grain size and mineral content (Figures 3, 5, 7 and 9)
Summary
Carbonate rocks, which are recognized as an important natural resource for construction materials and the cement industry [1,2], are sedimentary rocks that mostly consist of calcite (CaCO3) and dolomite (CaMg(CO3)2) [1,2,3,4] These carbonate minerals in the form of limestones have an economic interest in terms of petroleum geology, because their porosity is a potential storage reservoir for oil and natural gas [1,2,5,6]. We analyze the spectral absorption feature characteristics of calcite and dolomite in both the SWIR and TIR wavelength regions as a function of grain size and calcite-dolomite mixtures. To accurately identify carbonate minerals in pure and mixed forms, it is necessary to analyze the effects of those parameters that change spectral characteristics
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