Partitioning of more than 35 elements between coexisting phases in the apatite (Apt)–carbonate (Carb)–H₂O system was studied experimentally at P = 0.5 GPa and T = 1200°C for estimation of the efficiency of fluid transport during the formation of carbonatite in platform alkaline intrusions. The interphase partition coefficients of elements (D) range from n × 10^–2 to 100 and higher, which provides evidence for their effective fractionation in the system. The following elements were distinguished: (1) Apt-compatible (REE, Y, Th, Cu, and W), which are concentrated in apatite; (2) hydrophile (Na, K, Mg, Ba, S, Mn, Pb, U, W, and Re), which are preferably distributed into fluid or the carbonate melt. The high hydrophilicity of alkali metals controls the alkaline character of postmagmatic fluids and related metasomatic rocks, whereas the high D(Fl/Apt) and D(Fl/L_Carb) for S, Zr, W, Re, and U show their high potential in relation to U–W–Re mineralization.