Abstract
Carbonatites occur on most continents and are often associated with economic ore deposits. In rare cases, carbonatites are associated with particular Fe and P-rich rocks, the latter of which can also be of economic importance and can form ores for copper, zirconium, or platinum group elements. Here I present some novel experimental constraints in Fe and P-rich carbonate and silicate-rich systems as a starting point to better understand the origin of these rock types. Phase relations in the system CaO-MgO-Fe2O3-P2O5-SiO2-H2O-CO2 were studied at elevated temperatures (1000-1400 °C) and at high pressures (1 GPa). The liquidus of the systems studied varies between 1300 and 1400 °C. Liquidus phases are, depending on bulk composition, olivine or magnetite. Apatite, pyroxenes and calcite were found to generally crystallize at much lower temperatures. Using experimentally determined mineral and melt compositions, melt compositions were calculated for fractional crystallization of Fe- and P-rich carbonate-rich silicate magma.
