The Miocene Kaiserstuhl volcanic complex in SW-Germany as an eroded stratovolcano is the most prominent carbonatite-bearing occurrence within the province and comprises rocks of two magma series: rather primitive rocks (olivine-nephelinites, olivine-melilitites and nepheline-basanites) that are sodic and are restricted to the small parasitic Limburg volcano (Braunger et al. 2018 and references therein). The Kaiserstuhl itself constitutes more differentiated sodic-potassic rocks, with mostly tephritic and leucite-tephritic lavas intruded by phonolitic satellite intrusions. At two localities, carbonatitic lapilli tuffs, crystal tuffs and a lava occur as part of the pyroclastic series (e.g. Keller 1984 Nature, Schleicher et al., 1990, Wimmenauer, 2003; Walter et al., 2018; Giebel et al., 2019). The subvolcanic central part of the complex consists of phonolites, foid bearing gabbros, polygene diatreme breccias, several different intrusions of calcite carbonatites and various alkali silicate dyke rocks, beforsites and siliciocarbonatites. Phonolites and some of the dike rocks contain xenoliths of ijolite and of sodalite syenite, which was also drilled for scientific purposes in 1970 down to several hundred meters (Bakhashwin, 1971).
Several pyrochlore-rich subvolcanic sövite body and a spatially related polygene diatreme breccia with bulk-rock contents of 0.24 - 1.3% Nb2O5 were mined for Nb from 1949-1952 (Keller, 1984; Wimmenauer et al., 2003). The main ore minerals are pyrochlore and apatite, the abundance of which changes very significantly within the various units. Two shallow boreholes at the western margin of the Kaiserstuhl probed three layers (<1.5m thickness) of carbonatitic lapilli tuffs. In these rocks, pyrochlore is rare but present, with bulk contents of 650 µg/g Nb (Keller 1981; 1990). Moreover, in a geothermal deep-drilling at the Bremgarden airfield south of Kaiserstuhl, carbonatite lapilli were recognized in an nephelinitic tuff layer which is embedded in Eocene sediments and hence significantly older that the Miocene carbonatites of the Kaiserstuhl.
Walter et al., 2018 Pyrochlore as a monitor for magmatic and hydrothermal processes in carbonatites from the Kaiserstuhl volcanic complex (SW Germany) Chemical Geology