Carbonatite-associated deposits can be subdivided into magmatic types. Magmatic deposits are formed through processes associated with the crystallsation of carbonatites, whereas metasomatic deposits form by the reaction of fluids releases during crystallisation with preexisting or country rocks. Spatially distinct niobium and rare-earth element (REE) mineralisation at the Niobec mine, Québec, are examples of magmatic and metasomatic mineralisation.
The main minerals in the Niobec deposit are carbonates (50%), oxides (magnetite, hematite) (10%), silicates (biotite, chlorite) (10%), apatite (10%), sulfides (1%) as well as fluorite, barite and zircon (1%, collectively).
Niobium minerals in a bipyramidal shape are scattered throughout the carbonatite. These minerals are fine-grained (0.2 mm to 0.8 mm in diameter) and not easily visible to the naked eye. They are commonly associated with geological units with higher content in accessory minerals such as magnetite, biotite and apatite (facies C3b, C3c and C3a).
The ore is analysed in terms of percentage of Nb2O5. The mineralised lenses located on the northern edge of the deposit are characterised with the presence of hematisation, which seems to decrease in intensity with depth. Lenses farther south of the deposit are contained in a more calcitic carbonatite with syenite xenoliths.
The mineralisation mainly includes ferric-pyrochlores, sodic-pyrochlores and columbite as Nb bearing min ........
