The Hangam bauxite anomaly is located in southern Firouzabad region, Fars Province. This anomaly is developed along the boundary between Sarvak and IIam Formation. According to stratigraphical and sedimentological evidences a sedimentary hiatus has exposed Sarvak limestone to karst weathering, and a layer of argillaceous debris accumulated on its surface and were partly converted to bauxite. Then the bauxite horizon was preserved by deposition of Ham limestone. Microscopic studies of polished-thin sections illustrate to autogenic origin of the Hangam bauxite (Bardossy, 1982). In this study, in order to trace the precursor rock of the Hangam bauxite and mass change calculations during weathering and bauxitization processes, geochemistry of immobile elements are used. Plots of chemical data show that AI, Ti, Zr, Y, Th, Cr and V were immobile during the bauxitization process. Among these elements Ti and AI show the highest correlation coefficient and were used for mass change calculations. Furthermore as Ti02-AI2O, binary diagram shows only one linear trend for all bauxite layers and Sarvak composition plotted along this straight line, it can be concluded that Sarvak limestone is the precursor of Hangam bauxite. Mass change calculations point to net removal of Na, K, Mg and Si from system during bauxitization process. Immobile elements ratios trace the source of the Hangam bauxite to the underlying argillaceous limestone (Sarvak Formation). On the basis of volume change calculations, 113 meters of the Sarvak limestone were converted to Hangam bauxite horizon with about 29 meters thickness.