Source and geological context of mineralizations
Niobium is associated with two types of mineralization in igneous rocks: in carbonatites and in certain alkaline or hyperalkaline intrusions, such as syenites.
Mineralizations in carbonatite intrusions
Carbonatites are igneous rocks that contain at least 50% carbonate (calcite, dolomite, ankerite) in association with other minerals such as diopside, amphibole, pyroxene, mica, apatite, magnetite, hematite, sulfides, rare earth minerals, pyrochlore, columbite and tantalite.
They form small intrusive masses (3 to 5 km) within alkaline complexes in the form of sills, dykes or isolated masses of various shapes (circular, elliptical, irregular).
Carbonatite complexes are emplaced in extensional intracontinental geodynamic environments. They are commonly associated with major continental structures ( rift , graben , crustal lineament ) (Jbrak and Marcoux, 2008; Sappin and Beaudoin, 2015).
These rocks are enriched mainly in light rare earths accompanied by niobium , tantalum and phosphorus (Castor, 2008; Jbrak and Marcoux, 2008; Linnen et al ., 2014; Verplanck and Hitzman, 2016).
Examples of niobium mineralization in carbonatites are Mountain Pass, USA, and Araxa, Brazil (Jbrak and Marcoux, 2008).
Mineralizations in syenites and peralkaline granite complexes
Peralkaline igneous rocks ( peralkaline granite , peralkaline granitic pegmatite , syenite ) are emplaced in continental extension zones in association with major crustal structures (graben, rift). They form annular intrusive complexes, pegmatites or massive subvolcanic bodies (Jbrak and Marcoux, 2008; Verplanck and Hitzman, 2016).
Niobium mineralized zones occur as layers rich in niobium minerals (pyrochlore, columbite, tantalite) and rare earth elements in nepheline syenites of large bedded alkaline intrusions, disseminated in hyperalkaline granitic rocks (pegmatites, felsic dykes, minor granitic intrusions) and very finely disseminated in hyperalkaline felsic volcanic rocks ( trachytes , phonolites ). Mineralizations form in large superficial magmatic chambers and are commonly reconcentrated by hydrothermal activity (Jbrak and Marcoux, 2008).
Syenites and peralkaline granite complexes are typically enriched in heavy rare earths accompanied by zirconium, beryllium, niobium and tantalum (Richardson and Birkett, 1996; Jbrak and Marcoux, 2008; Verplanck and Hitzman, 2016).
Examples of niobium mineralized zones in alkaline and peralkaline igneous rocks are Arendal in Norway, Ilimaussaq in Greenland, Lovozero in Russia, Jos in Nigeria, Tamazert in Morocco and Khaldzan-Buregtey in Mongolia (Jbrak and Marcoux, 2008).
Exploration in Quebec
The potential for niobium mineralization is significant in Quebec. Numerous niobium mineralized zones are located in: 1) the Churchill Province , notably in the Labrador Trough and the Mistinibi-Raude Domain near the border with Labrador; 2) the Grenville Geological Province , in Saguenay–Lac-Saint-Jean and Tmiscamingue; and 3) the Superior Province . Other areas have also been identified in the St. Lawrence Platform.
Several projects are underway, some of which are at an advanced stage of exploration. Some work focuses on the evaluation of mineral resources.
The main niobium mineralizations associated with carbonatites are located in the regions:
- from the Labrador Trough, west of Lake Le Moyne (Ashram [Eldor]);
- from Saguenay–Lac-Saint-Jean, north of the city of Saguenay (Niobec mine) and NNW of Lac Saint-Jean (Crevier);
- from Abitibi, north of Lebel-sur-Quvillon ( Montviel Carbonatite );
- from Oka, west of Montreal.
The main niobium mineralizations associated with syenites and peralkaline granite complexes are located in the regions:
- NE of Raude Lake, near the border with Labrador (Crater Lake [Misery Lake] sector);
- from Brisson Lake, near the border with Labrador (Strange Lake – Zone B).
Ashram (Eldor) Mineralized Zone
The Ashram (Eldor) ore zone is Paleoproterozoic in age. It is hosted in a carbonatite belonging to the Le Moyne Carbonatite Complex. Mineralization occurs as a commonly brecciated lens composed mainly of carbonates (calcite, dolomite, ankerite, breunnerite) accompanied by biotite, phlogopite and fluorite. Carbonatite is usually divided into three major phases: early, intermediate and late. The intermediate phase is most closely associated with niobium-tantalum mineralization (pyrochlore, columbite). Grades of 1.14% Nb 2 O 5 , 1.51% Nb 2 O 5 and 2.96% Nb 2 O 5 are notably reported (Commerce Resources, 2014 and 2016). A survey revealed an interval of 0.46% Nb 2 O 5 over 46.88 m, including 0.64% Nb 2 O 5 over 9.90 m (Commerce Resources, 2010).
Crater Lake (Misery Lake) Mineralized Zone
The Crater Lake (Misery Lake) mineralized zone is of Mesoproterozoic age. It is part of the Mistinibi-Raude Domain located in the eastern part of the Churchill Province. Niobium mineralization is accompanied by rare earth elements (REE) and scandium. It is hosted in elongated syenitic units (700 m long by 120 m wide) associated with a peralkaline syenite intrusion (Misery Syenite) characterized by a ring structure. The intervals richest in niobium and REE are generally thin (<1 m) and occur as inclusions or thin dykes. A grade of 0.066% Nb 2 O 5 over 2.05 m is reported in drilling (Rare Minerals Quest, 2014).
Strange Lake Mineralized Zone – Zone B
The Strange Lake – Zone B mineralized zone is of Mesoproterozoic age. It is part of the Mistinibi-Raude Domain located in the eastern part of the Churchill Province. Niobium mineralization is accompanied by rare earth elements (REE) and hosted in lenticular and irregular pegmatite layers (up to 30 m thick). These are associated with a peralkaline granite intrusion (Lac Brisson Pluton) characterized by a ring structure. The pegmatite layers are injected into the dome of the granitic intrusion. Niobium mineralization is disseminated and consists mainly of pyrochlore. Indicated resources are estimated at 277.99 million tonnes grading 0.18% Nb 2 O 5 (Quest Rare Minerals, March 8, 2017).
Crevier mineralized zone
The Crevier mineralized zone is Neoproterozoic in age. It is located ~55 km NNW of Lac Saint-Jean. Niobium and tantalum mineralized zones are hosted in syenite units, locally associated with carbonatite, that belong to the Crevier Alkaline Intrusion. The mineralized zones occur as syenitic and pegmatitic dykes with pyrochlore and megacrystals of nepheline and albite. Niobium and tantalum mineralization is disseminated and consists mainly of pyrochlore. Indicated resources are estimated at 25.8 million tonnes at a grade of 0.186% Nb 2 O 5 (SGS Geostat, 2009).
Mineralized zone of Montviel Carbonatite
The Montviel Carbonatite mineralized zone is of Paleoproterozoic age. It is located north of Lebel-sur-Quvillon, ~13 km east of Lac au Goland. Mineralization is associated with carbonatites of the Montviel Alkaline Intrusion , which is hosted in intrusive rocks of the Abitibi Subprovince. The zones richest in niobium are included in a phase rich in phyllosilicates (biotite, chlorite) and sulfides (pyrite, pyrrhotite, galena, sphalerite and chalcopyrite). Niobium is contained in pyrochlore, a mineral closely related to the phyllosilicate-rich zones in the carbonatite. Pyrochlore occurs as inclusions in biotite. Indicated resources are estimated at 82.4 million tonnes at a grade of 0.17% Nb 2 O 5 (Geomega Resources, June 17, 2015).
Exploitation in Quebec
Only one niobium operation in Quebec, the Niobec mine, is located in Saint-Honor in the Saguenay-Lac-Saint-Jean region. From 8 to 10% of the world's niobium production comes from this mine (Niobec, 2019).
The Niobec mine mineralized zone is hosted in a carbonatite complex (Saint-Honor Carbonatite). The mineralization is disseminated and consists of hematite, maghemite, pyrochlore, columbite, anthraxolite, apatite, magnetite and pyrrhotite. The main niobium-bearing minerals are ferrous and sodium pyrochlore and columbite. The latter are fine-grained (0.2 to 0.8 mm) and are rarely visible to the naked eye. They are associated with accessory minerals such as micas, apatite and magnetite.
The Niobec mine has been in operation since 1976. Production is 5,900 t/year of niobium. Reserves are 416 million tonnes at 0.41% Nb 2 O 5 . Since 1994, the mine has been transforming pyrochlore into ferroniobium following the installation of a converter on the mine site (Niobec, 2019).
Due to ongoing developments (equipment maintenance, process improvements, water management), the increase in mineral resources at depth and the introduction of paste backfill in the operation, the Niobec mine has reserves for several more decades.
The valorization of mining residues from the Niobec mine represents a technical challenge. The typical ore extracted from the mine includes different mineral substances which, if recovered, could be of economic interest.
The Niobec mine has been owned by Magris Resources since January 2015. It is the only underground niobium mine in the world and one of only three in operation.
In the 1960s, a niobium mine known as St-Lawrence Columbium (Main Oka) was operated in the Oka area, west of Montreal. This former mine has about twenty mineralized lenses located within a banded carbonatite with richterite , magnetite and phlogopite belonging to the Oka Hill Carbonatite, of Cretaceous age. This intrusion is part of the Monteregian Suite which intrudes into the sedimentary rocks of the St. Lawrence Platform. The mineralization is disseminated and consists of pyrochlore, latrappite and niocalite accompanied by magnetite , apatite and perovskite . Historical reserves are estimated at 16.69 Mt at 0.44% Nb 2 O 5 (The Northern Miner, May 16, 1974) .
References
CASTOR, SB, 2008. Rare earth deposits of North America. Resource Geology; volume 58, pages 337-347.
JBRAK, M., MARCOUX, ., 2008. Geology of mineral resources. Ministry of Natural Resources and Wildlife; MM 2008-01 , 672 pages.
LINNEN, RL, SAMSON, IM, WILLIAMS-JONES, AE, CHAKHMOURADIAN, AR, 2014. Geochemistry of the rare-earth element, Nb, Ta, Hf, and Zr deposits. In : Treatise on geochemistry (Second Edition), volume 13 (Holland, HD, Turekian, KK, editors). Elsevier; pages 543-568.
RICHARDSON, DG, BIRKETT, TC, 1996. Peralkaline rock-associated rare metals. In : Geology of Canadian mineral deposit types (Eckstrand, OR Sinclair, WD, Thorpe, RI, editors.). Geological Survey of Canada; Geology of Canada No. 8, pages 523-540.
SAPPIN, AA., BEAUDOIN, G., 2015. Classification of the main rare earth element indices in Quebec (Canada): geological context and assessment of their economic interest. Ministry of Energy and Natural Resources, Quebec; MB 2015-10 , 76 pages.
VERPLANCK, PL, HITZMAN, MW, 2016. Rare Earth and Critical Elements in Ore Deposits. Society of Economic Geologists; Reviews in Economic Geology, volume 18, 365 pages.