This study presents a comprehensive multi-analytical investigation of oil shale and its combustion ash fractions using XRD, XRF, and LA-ICP-MS techniques. The mineralogical composition is characterized by a transition from carbonate-rich phases in raw shale to silicate-dominated assemblages in ash, accompanied by systematic changes in major oxides. Trace elements such as Cr, Pb, As, Ni, and Cd exhibit distinct partitioning patterns across WHB, Cyclone, and ESP ash fractions, with WHB ash showing the highest enrichment for most elements. Matrix-matched calibration ensures reliable quantification of trace elements. The results highlight the role of mineral transformation and ash morphology in governing element mobility during combustion. Notably, potentially hazardous elements tend to accumulate in coarse ash fractions, raising environmental concerns regarding ash disposal and reuse. These findings provide valuable insights into the geochemical behavior of trace elements during oil shale combustion and offer guidance for environmental risk assessment and waste management strategies.