Spatial Mineralogical and Geochemical Variations Across Mafic Dike–Country Rock Contacts in the Permian Nam Duk Formation, Thailand

The emplacement of mafic dikes into carbonate-bearing sedimentary successions commonly produces localized mineralogical and geochemical variations in adjacent country rocks. However, the spatial distribution of these variations remains poorly documented in the Permian sedimentary successions of Thailand. The study investigates spatial mineralogical and geochemical variations across intrusive rocks and adjacent sedimentary rocks in the Permian Nam Duk Formation, Phetchabun Province, Thailand. Petrographic observations and whole-rock geochemical analyses (XRF and ICP-MS), supported by qualitative XRD phase identification, were integrated to characterize mineral assemblages and whole-rock geochemistry. The intrusive rocks display porphyritic textures dominated by plagioclase and hornblende, whereas the adjacent country rocks are characterized by quartz, calcite, feldspar, clay minerals, and secondary alteration phases. Spatial variations in mineral assemblages are accompanied by changes in contents of some major oxides (SiO₂, Al₂O₃, Fe₂O₃, MgO, and CaO) and selected trace and rare earth elements. The sedimentary country rocks generally contain higher total REE concentrations, particularly La and Ce, whereas the contact-proximal sample shows values closer to the mafic dike. Site A shows the clearest spatial variations across the exposed mafic dike–country rock contact, whereas site B exhibits compositional variability associated with strongly altered porphyritic andesite and heterogeneous sedimentary rocks. The integrated results document localized mineralogical and geochemical variations across the investigated intrusive–sedimentary rock systems, although primary lithological heterogeneity and secondary alteration may also contribute to these patterns.