2026 年 76 巻 1 号 p. 23-41
To establish efficient exploration techniques for LCT pegmatites, exploration activities targeting pegmatites were conducted at the ML 198 concession in the Republic of Namibia and at the Mibra Mine in the Federative Republic of Brazil. In the remote sensing survey conducted at ML 198, direct extraction of lithium-bearing mica, a key mineralization indicator of LCT pegmatites, was performed. In addition, distribution maps of muscovite and kaolinite abundances were generated using a proprietary algorithm developed. Furthermore, supervised classification using an AI-based support vector machine (SVM) was applied to delineate areas interpreted as pegmatite dikes. The results demonstrated that the muscovite abundance map is effective for pegmatite exploration, and suggested that pegmatite dikes with a northeast–southwest trend are distributed over a broad area including the ML 198 region. Geological surveys conducted at ML 198 included surface geochemical line sampling, which revealed characteristic geochemical halos around the Northern Pegmatite and along the southern extension of the ore body. Geophysical surveys at ML 198 were carried out after selecting optimal survey parameters based on prior geophysical simulations. Although the pegmatite bodies were not directly delineated, partial results from the magnetic survey suggest the presence of a structure extending southward from the Northern Pegmatite. Based on the integrated results of these investigations, it is suggested that the Northern Pegmatite may continue southward beneath cover. Consequently, this area is recognized as upside exploration potential. At the Mibra Mine, drone-based surveys indicated that pegmatite bodies exposed within and around the mining pit are characterized by low magnetic anomalies and high potassium (K) values in gamma-ray spectrometry, accompanied by low thorium (Th), high F-parameter values, and reddish tones in RGB imagery. In contrast, small-scale pegmatites distributed in historical mining areas were difficult to directly extract using these geophysical datasets alone. Therefore, it is suggested that evaluating the potential occurrence of pegmatite bodies requires integrated interpretation combining geophysical results with complementary data such as topographic information, aerial photographs, and geological observations. In this study, a technical challenge was undertaken to examine the applicability of geophysical methods to pegmatite exploration, which has traditionally been considered difficult. Although severe constraints remain due to the narrow vein widths of pegmatites and the limited physical property contrasts with host rocks, the results suggest that integrated interpretation combining geological information with individual geophysical datasets can contribute as a supportive approach to pegmatite deposit exploration.
