The Osongombo Carbonatite Complex in NW Namibia records magmatic differentiation from calcite carbonatite to ferroan dolomite calcite carbonatite and ankerite carbonatite dykes and veins marked by a continuous enrichment of Fe and Mg accompanied by increasing abundance of sulfides and the first appearance of REE-bearing burbankite. This magmatic stage is followed by a carbothermal stage characterized by a distinct mineral assemblage found as vein networks and small patches, which consist of apatite II, baryte, synchysite, parisite and quartz.

The emplacement of these carbonatite dykes/veins produced Fe-rich metasomatic reaction zones of variable thickness (mm to cm) at the contact with Damara marble. Whereas calcite carbonatite exhibits little reaction evidence, apart from a change in grain size, ferroan dolomite calcite carbonatites and ankerite carbonatites show evident compositional and textural changes. Marble-hosted dolomite crystals at the reaction interface exhibit Fe-rich rims. Newly-formed Fe-rich carbonates develop individual crystals and patches in the reaction zone. Marble calcite shows dark orange-to-brown cathodoluminescence colour, overprinted by a brighter orange that reflects calcite formation during carbonatite interaction. Ankerite crystals from the reaction zone are lower in Fe and Mn content than those from the carbonatite. These observations indicate that Fe, Mg and Mn readily migrate towards the marble, Zn shows limited mobility as evidenced by sporadic sphalerite crystallization along the carbonatite-marble contact.

Daqingshanite in the Kamthai REE deposit (India) occurs as two paragenetic types: primary granular coarse grained crystals coexisting with primary carbocernaite, baryte and bastnäsite; and as aligned micro-ovoid globules within clasts of Sr-bearing calcite. Carbocernaite forming trellis-type lamellae in some of these calcite clasts do not represent exsolution and are considered as replacement textures as they formed subsequent to daqingshanite. The origins of the textural relations of the microglobules of daqingshanite to their host Sr-calcite cannot be unambiguously determined, although an exsolution origin is not considered feasible. The textures are similar to those of ‘chalcopyrite disease’ and as such could be interpreted as replacement features formed in a low temperature carbothermal environment which should facilitate replacement. Given that daqingshanite is an early crystallising phase it is also possible that cotectic crystallisation with Sr-calcite occurred, followed by subsolidus re-equilibration with recrystallisation along specific crystallographic planes in the calcite. The Kamthai REE deposit is best described as a low temperature carbothermalite microbreccia consisting of a wide variety of clasts resulting from the autobrecciation of rocks formed during, and after, the magmatic to carbothermal transition of an undetermined parental calcite carbonatite-forming magma. Many clasts have been replaced by late stage La-enriched carbothermal fluids mixed with exogenous water during the final low-temperature stage of evolution of the deposit.