Skarns (sensu lato) are carbonate rocks metasomatised by the intrusion of silicate magmas or derived fluids. A process, not studied previously, is the opposite: intrusion and interaction of liquid carbonatites with solid silicate rocks. Carbonatites commonly intrude crustal silicate rocks, and the possible reactions remain unknown. The overall phase assemblage is expected to be similar to skarns because they share the same chemical system. It is thus important to study the reaction of carbonatites with silicate melts in order to understand what is possible in such interactions. This knowledge will then facilitate recognition of natural silicate rocks intruded and metasomatised by carbonatites (“anti-skarns”). Here we show piston cylinder experiments in which a layer of silicate rock was placed on top of a carbonatite layer. We show examples of REE ore deposits (Nolans Bore, NT, Australia and Hoidas Lake, SK, Canada) where carbonatites left behind economic quantities of REE hosted in cumulate fluorapatite.
I will also show some preliminary results from a series of experiments designed to calibrate a thermobarometer using Ca, Mn, Mg and Sr partitioning in apatite and calcite.