Carbonatites are silica-poor and volatile-rich magmatic rocks that can host some high field strength element and rare earth element (HFSE & REE) deposits. Understanding carbonatite melt compositions is challenging due to their intrusive nature and metasomatic alterations. We use apatite as a geochemical proxy to reconstruct the composition of carbonatite melts. Internally heated pressure vessels (IHPV) and piston cylinder (PC) apparatus are used to define partition coefficients between apatite and alkali-rich carbonatite melts with varying volatile element concentrations (H, F, S, Cl) at 800°C-200 MPa, and at 725-1050°C and 400-800 MPa. The data shows apatite-melt partition coefficients with values ranging from 1 to 6 for Sr, Y, and REE, and <0.5 for HFSE. Apatite-melt partition coefficients for volatiles are DF = 0.97, DCl = 0.14, and DS = 0.031. Temperature, pressure and redox conditions do not significantly influence volatiles, REE and high field strength element (HFSE) partitioning between apatite and carbonatite melt. Over 700 apatite compositions from diverse geodynamic settings reveal that REE contents in coexisting carbonatite melts varies by more than two orders of magnitude, whereas Cl and F contents in melts yield values in the range 0.88-6.01 wt% and 0.04-1.34 wt%, respectively. REE, HFSE, Cl, F contents in carbonatite melts do not correlate indicating that some melts are inherently rich or poor in those elements, possibly reflecting silicate-carbonate immiscibility processes.