Environmentally responsible geological investigation using a multidisciplinary geophysical and geochemical approach

This study presents a multidisciplinary investigation of the Svidnya high-potassium alkaline pluton in the Western Stara Planina Mountains, Bulgaria, combining Electrical Resistivity Tomography (ERT), Induced Polarization (IP), and field X-ray fluorescence (pXRF) to assess their joint potential for exploration. The target rocks of the Svidnya association, represented mainly by melasyenites (shonkinites) and alkaline to quartz syenite dikes, are known from previous studies to be enriched in large-ion lithophile and high-field-strength elements (Ba, Sr, Rb, Zr, Th, U, Nb) and light rare earth elements (La, Ce, Nd), with apatite identified as a principal REE-bearing phase. A geophysical profile crossing the contact between the potassic-alkaline intrusion and Ordovician metasediments reveals two main subsurface domains: a low-resistivity zone corresponding to altered rocks, and a higher-resistivity zone associated with relatively fresh syenite varieties. IP data indicate additional heterogeneities related to variations in lithology and alteration intensity. Field pXRF measurements detected trace concentrations of U, Th, Rb, Sr, Ba, and Nb in slightly altered rocks, confirming the presence of CRM-related elements, although only at qualitative to semi-quantitative levels due to methodological limitations. The results demonstrate that the integrated ERT/IP–pXRF approach is effective for environmentally friendly, non-destructive preliminary delineation of lithological variability and altered zones in prospective alkaline intrusions, and that it also has practical applicability for solving problems in engineering geology, such as the characterization of rock mass heterogeneity, degree of alteration, and subsurface conditions relevant to construction and stability assessments.