Buried treasure - rare earths deposit in Canada

Materials World magazine
,
3 Jul 2012

The new discovery of a rare earths deposit in Canada has the potential to revolutionise this restricted market. Could these elements prove not so rare after all? Michael Forrest examines the evidence.

There has been intense interest in rare earth elements (REEs) ever since September 2010, when the Chinese government declared plans to restrict exports. With China producing virtually all of the traded rare earths, the announcement caused grave concern to  manufacturers dependent upon their supply. This challenge to supply a low-volume and to some, obscure, commodity would not normally gain traction in the press, but developments in electronics, permanent magnets, lasers and hybrid autos have rendered some rare earth elements indispensable. Many of these applications have a direct impact on the decarbonisation of energy, for example wind turbines, electric automobiles, and electronics, especially those concerned with defence. 

Ironically, rare earths are not particularly rare, with many deposits identifi ed around the world. Cerium, with a crustal abundance of 68 parts per million, is actually more abundant than copper. Unlike copper, however, there are relatively few economic deposits. Like many other minor metals, in volume terms this limited market allows only rich deposits to corner the market. Take China’s giant, high-grade Bayan Obo deposit, where cerium levels reach 250 times that of crustal averages. 

The majority of deposits contain the light rare earths, with much fewer yielding the heavier elements. The heavy REEs (europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium) are used in liquid-crystal displays and plasma screens, microwave lasers, portable X-ray machines, surgical lasers, oil refi ning, imaging technology, permanent magnets in hard disc drives, and other electronic devices. The light REEs (praseodymium, neodymium, promethium and samarium) are commonly found in polishing agents for glass and computer screens, and in magnets. 

The decision to restrict REE exports instigated intense global activity to find and develop alternative resources, from Australia to Canada. Driven by escalating prices – particularly for the heavy REEs, which command tenfold higher prices – a number of companies either have or are in the process of raising capital. A saturated market leaves little room for all these projects, however, especially for those companies with the more common, light REEs resources as well as those whose smaller resources will inhibit economies of scale. 

Quest for minerals 

REEs, like other rare metals, such as tantalum and niobium, are found in geological settings that enable them to pass through from the mantle where they are enriched, through the crust to the surface. Rifts, illustrated by the geologically modern East Africa rift valley, are a prime location for REEs. Older systems with rifts that have become deformed and overprinted over time may now be seen as shear zones, in which alkali granites or carbonatites can be found. 

One such location is the Tudor Lake shear zone in northeastern Quebec, Canada. The regional feature measures up to 20km wide and can be traced for more than 150km near the Labrador-Newfoundland border. This shear zone aff ects rocks of both the Laporte domain to the west and the De Pas domain to the east. Within this zone lies the Mistatin Batholith, a composite body comprising monzonitic, granitic, granodioritic and rapakivi granitic phases. A small, late-stage peralkaline intrusion called the Strange Lake granite is thought to be related, and lies adjacent to the Mistatin Batholith. 

The Strange Lake deposit is currently being developed by Canadian company Quest Rare Minerals Ltd. ‘It is this late-stage granite that is the focus of our exploration and development,’ says Peter Cashin, Quest President and CEO. The granite is part of a post-tectonic peralkaline granite complex that has intruded along the contact between older gneisses and monzonite at the Churchill province of the Canadian Shield. 

The sub-circular complex consists of generally concentric, high-level granitic intrusions bound by sharp contacts with country rocks. Ring faults at or near the contact of the alkalic complex dip outward at low to moderate angles (20–35°). Within the complex lies a small stock (approximately 1.5km2) of medium grained, generally non-porphyritic ‘exoticrich’ granite, with high overall values of zirconium (Zr), niobium (Nb), yttrium (Y) and REE. Rooted within this medium-grained granite stock are dykes of aplite-pegmatite that also yield signifi cant values of rare metals. 

An airborne survey carried out by Quest in 2009 identified a 2,200x500m radiometric anomaly within the northern part of the Strange Lake alkali granite. Subsequent drilling confirmed what was named zone ‘B’ to contain high grades of more than 1,700m of heavy REE, of good thickness and high proportions. ‘Grab-sampling returned values of 14.4% total rare earths,’ says Cashin. Subsequent drilling in 2010–2011 confirmed inferred resources of 89.6Mt, with a heavy-total REE ratio of 38 at a 0.6% total rare earth cut-off . Raising the cut-off grade to 1.2% total REE, the inferred resources are 2.5Mt with a heavy-total REE ratio of 50, at a grade of 0.76%. 

Strange but true 

Quest is planning to bring these resources into compliant reserves that will make the Strange Lake deposit not only one of the largest in the world, but also one of the highest grades of heavy REE. That said, the project is not without its challenges. With an average annual temperature of 0°C the location is climatically problematic, and a lack of infrastructure in the area restricts access to the exploration camp by means of light aircraft. A saving grace could be Voisey’s Bay nickel mine, which is situated just 125km east. 

‘The initial plan was to transport ore in a slurry pipeline to Voisey’s Bay, where a process plant would upgrade the ore prior to shipment,’ says Cashin. Although feasible, this would require two sets of environmental impact studies and permissions – one for the mine and one for the process plant, as the mined material would pass from Quebec to Labrador and Newfoundland. Quest expects to complete a pre-feasibility study this year, but a preliminary economic assessment on nearsurface mineralisation that could be mined by open pit, has proved encouraging. 

Planning is now focused on building a mill and concentrator at Strange Lake, and trucking the REE concentrate to Voisey’s Bay. Although this will require the construction of an all-weather road, it will allow the entire project to be based in mining-friendly Quebec – complete with advantageous tax rebates. 

Not-so-rare earths? 

With regards to global supply and demand, the Chinese embargo has ignited the market, with a number of players seeking funding for development. However, there will not be enough demand for them all and those with a higher proportion of the scarcer heavy REEs are likely to have the advantage. According to a 2010 US Department of Energy study entitled Critical Materials Strategy, the heavy REEs and neodymium will be in greatest demand for clean energy. 

Although consumers initially saw the Chinese export quotas as an insuperable supply problem, explorers and developers have grasped it as an opportunity to rebalance supply security. Ten large projects regarded as near-term producers will address the balance, although not all will be successful. Encompassing carbonatite and alkali-granites resources, the projects demonstrate that so-called rare earths are in fact not so scarce – they just require significant geological upgrading before they can be regarded as economic deposits.  

Further information

peter.cashin@questrareminerals.com