Abstract
Numerous reports have successfully detected or differentiated carbonate minerals such as calcite and dolomite by using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). However, there is a need to determine whether existing methods can differentiate magnesite from other carbonate minerals. This study proposes optimal band ratio combinations and new thresholds to distinguish magnesite, dolomite, and calcite using ASTER shortwave-infrared (SWIR) data. These were determined based on the spectral and chemical analysis of rock samples collected from Liaoning, China and Danchon, North Korea and the reflectance values from ASTER images. The results demonstrated that the simultaneous use of thresholds 2.13 and 2.015 for relative absorption band depths (RBDs) of (6 + 8)/7 and (7 + 9)/8, respectively, was the most effective for magnesite differentiation. The use of RBDs and band ratios to discriminate between dolomite and calcite was sufficiently effective. However, talc, tremolite, clay, and their mixtures with dolomite and calcite, which are commonly found in the study area, hampered the classification. The assessment of the ASTER band ratios for magnesite grade according to magnesium oxide content indicated that a band ratio of 5/6 was the most effective for this purpose. Therefore, this study proved that ASTER SWIR data can be effectively utilized for the identification and grade assessment of magnesite on a regional scale.
Highlights
Magnesite (MgCO3 ) is a good refractory and common industrial material, and an important ore that has been utilized for the extraction of magnesium compounds and magnesium metals [1]
We evaluated whether the various ASTER SWIR band ratios proposed for calcite and dolomite in previous studies [8,12] could be applied to magnesite (Table 3)
Magnesite and dolomite were distinguished by a band ratio value of 1.026, while dolomite and calcite were differentiated with a band ratio value of 0.98
Summary
Magnesite (MgCO3 ) is a good refractory and common industrial material, and an important ore that has been utilized for the extraction of magnesium compounds and magnesium metals [1]. Similar to other carbonate minerals such as dolomite (CaMg (CO3 )2 ) and calcite (CaCO3 ), magnesite exhibits spectral absorption features in the shortwave-infrared (SWIR) wavelength range between 1.70 and 2.55 μm, owing to the vibrational processes of its carbonate ions (CO3 −2 ) [2,3] (Figure 1). Strong absorptions of magnesite occur near 2.30 and 2.50 μm, which possess lower wavelengths than those associated with absorption of dolomite (Figure 1). These spectral differences can be utilized as diagnostic features to distinguish magnesite from dolomite and calcite, with less time and cost as compared to those required for chemical analysis. Airborne or satellite remote sensing data can be effectively utilized for mapping or identifying magnesite in well-exposed and extensive areas
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