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 minerals. The mineralogical characteristics, the alteration and the mineralisation type greatly influence metallurgical recovery, which can vary between 30% and 70%.

The mineralised envelopes vary from 45 m to 185 m in width (north to south), and can reach close to 760 m in length. The areas have a known vertical extension of about 750 m. The deepest completed drillholes (down to block 12, close to a depth of 1,280 metres) show mineralisation at equivalent grade to those of the current mine production. The deposit has a sub-vertical dip.

The average grades of major mineralised envelopes are 0.44% to 0.51% Nb2O5. Considering the block caving method, the definition of high grade mineralised envelopes is no longer necessary because all carbonatite will be mined. Potential mineralised zone remains open at depth.

Niobec has been using the open stope mining method.

The underground mine extracts over 2.3 million tons of ore which, once transformed, produces some 5000 tons of niobium annually.

To break the ore, vertical holes, with a diameter of 17 centimetres (6.5 inches) are drilled off filled with explosives and detonated. The broken-up ore is collected at the base of the open room in a draw point with a loader and transported by truck to the ore pass. After, the ore is crushed underground, and hoisted to the surface to be crushed again prior to being transferred to the concentrator.

Since September 1999, the extraction was performed at depths varying between 100 and 440 metres (300 to 1,450 feet). Today, an 800 metres shaft (2,800 feet) and a ramp provide direct access to the various mine levels, which now cover 730 metres (2,400 feet).

Niobec’s concentration plant uses the one of the most complex ore recovery processes in the world. In order to produce a pyrochlore concentrate (58% niobium pentoxide, Nb2O5), the following steps must occur during the transformation process, which takes place at the plant: milling, sieving, desliming, magnetic separation, three types of flotation, leaching, two-step filtration and concentrate drying. Each ton of ore (1,000 kg) produces in average 2.4 kg of niobium oxide. About 15 different chemicals are used during the concentration process. However, the concentration plant’s waste is pH neutral. In other words, it does not generate acid and is essentially carbonate-bearing.

The crushed ore is deslimed in two stages of cycloning, and the underflow is sent for conditioning prior to carbonate flotation. The carbonate concentrate is sent to the tails. The carbonate flotation rougher and cleaner tails are cycloned in two stages to change the process water and then sent to the py ........