Preliminary REE Characteristics of Selected Metamorphic and Metasedimentary Rocks from Bayat, Central Java

Abstract

Bayat, Central Java, exposes metamorphic and metasedimentary rocks in the West and East Jiwo Hills, where REE characteristics remain insufficiently documented despite prior work on petrography, mineralogy, structure, and mineralization. This study presents a preliminary evaluation of REE variation in four samples from Gunung Gajah, Gunung Cakaran, Jokotuo, and Sekarbolo, based on megascopic descriptions and whole-rock REE concentrations from La to Lu, compared through total REE (ΣREE) and chondrite-normalized patterns. ΣREE values range from 88.18 to 163.46 ppm, highest in Sekarbolo and lowest in Gunung Gajah, with Gunung Cakaran and Jokotuo intermediate, and the chondrite-normalized patterns generally show LREE enrichment relative to HREE. These differences may reflect variations in siliciclastic input, mica- or clay-rich components, carbonate dilution, source-rock composition, and REE-bearing accessory-mineral abundance, though megascopic and whole-rock data alone cannot determine the specific mineral hosts. By documenting these inter-locality differences, this study contributes the first preliminary REE dataset for the Jiwo Hills metamorphic complex, establishing a geochemical baseline not previously available. The observed variation should nonetheless be regarded as a preliminary signal rather than definitive evidence of REE mineralization or economic potential, requiring further study through additional samples, major and trace element geochemistry, detailed petrography, XRD, SEM-EDS, and mineral chemistry.