Geology and mineralogy of the Sarfartôq carbonatite complex, southern West Greenland

The Sarfartôq carbonatite complex was emplaced in lower Palaeozoic time in a weakness zone within the Precambrian shield. Dolomitic magma intruded in two major stages of activity. In the first stage a steeply dipping conical body of concentric sheets of rauhaugite was formed, while in the second stage several batches of magma were emplaced into the surrounding marginal shock-zone as concentric and radial beforsite dykes and agglomerates. Hydrothermal activity gave rise to several phases of mineralisation in veins and shear zones. The accompanying fenitisation was of the Na-type. The whole complex covers about 90 km². The main rock-forming minerals are dolomite-ankerite, apatite, orange reversely pleochroic phlogopite, richterite-arfvedsonite and magnetite. Important accessories are pyrochlore, zircon and niobian rutile. A complete mineral list is given, together with microprobe data on mineral chemistry. The dolomitic magmas were poor in SiO₂, Al₂O₃ and K₂O in relation to other carbonatites. Nb, U and LREEs are strongly enriched in pyrochloremineralised zones where the Nb content may be up to 40%. Some shear zones are strongly enriched in Th and HREEs (specifically Eu) and lesser Pb and Zn. Niobium, uranium, rare earth elements and phosphorus occur in economically interesting concentrations.