Abstract: Trend surface analysis of the chemical data on Mortaş bauxite deposit indicates existance of a commonNW-SE axis. AlpOg, iand TiO2 percentage decreases, P^Og and Na percentage increases towards this axis. SiO2 behavesdifferently and decreases radially away from the center of the deposit. Contour maps of the chemical data indicateexistence of a few circular anomalous areas. A12O3 and TiQ, percent decreases and Fe 200 increases towards such anomalous points.Origin of Mortaş bauxite deposit is controversial, magmatic as well as sedimentary origin has been postulated. Ourobservations suggest that Mortaş bauxites may have formed as a weathering product of limestones. The common NW-SEdirection may correspond to the long axis of ia karstic depression. Anomalous points may correspond to limestoneblocks included in bauxite within such depression. The negative correlation between Fe 20 o and Al,O3 as wel as TiO,, andthe independent behavior of SiO may be explained by secondary leaching.