Nickel - King of the north

Materials World magazine
,
27 Nov 2012

With a global mine production of 1.8 million tonnes, the nickel market is a lucrative one, often perceived as the domain of world-leading companies. Michael Forrest investigates how smaller firms can achieve success in the market.

Since the development in the late 1950s of a high pressure acid leaching technique to extract from nickel-bearing laterites (weathered ultrabasic ocean plate rocks) at Moa Bay in Cuba, production has been moving from traditional magmatic sulphide deposits to lateritic ones. The lateritic weathering of nickel-bearing ultrabasic and basic rocks can result in higher concentrations of nickel. When the price of nickel metals peaked at more than US$52,000 per tonne in 2007, some high grade nickel laterite ores were shipped directly to Chinese blast furnaces for smelting to nickel pig iron used generally for lower priced and lower quality steel products.

However, this is not the norm. Processing laterite deposits is capital intensive, and as a result such projects are usually the domain of world-leading mining companies, as illustrated by the US$4.5 billion Goro hydrometallurgical plant in New Caledonia and the US$5.5 billion Ambatovy mining and processing project in Madagascar. The route to market for smaller companies is with good magmatic nickel sulphide deposits (copper, +/- cobalt +/- platinum group elements) that are much less capital intensive. Nickel sulphide ores can be upgraded by on-site processing to provide a saleable concentrate that, in turn, can be smelted by a regional facility. This is the case for Strongbow Exploration’s Nickel King project in the Northwest Territories of Canada.

The company has a long history of exploration in northern Canada, mostly for base and precious metals, as well as diamonds. When nickel prices began to rise in mid-2006, the company reviewed the nickel potential around the historic Nickel King showing, recognising the area as a prime environment for magmatic sulphide deposits. Magmatic nickel deposits form in ultrabasic and basic rocks derived from magmas deep within Earth. These magmas require a structural setting that will allow their ascent to near-surface crustal levels. At the Nickel King project, two sections of very old, Archean-aged rocks are separated by a major crustal-scale suture – the 2,800km Snowbird tectonic zone (STZ). The STZ has been interpreted variably as a tectonic break between colliding plates, an intercontinental shear zone, or an incipient intra-continental rift within an older orogenic zone. Regardless of its origin, the STZ represents a conduit whereby deep-seated ultrabasic and basic magmas could ascend to shallow crustal levels and potentially form magmatic sulphide deposits anywhere along its entire length.

The deposit is hosted in a norite intrusion that forms two shallow dipping sub-parallel sills stacked upon one another, with mineralisation extending for more than 2,600m. It occurs as nickel-coppercobalt sulphides that are disseminated, net-textured and occasionally semimassive to massive, in zones ranging from 40–110m wide and 2–60m thick. Strongbow actively explored the area between 2006–2008 and completed a 43–101 compliant resource estimate and metallurgical tests in 2009.

The Nickel King area itself has a much longer history, which traces back to 1952 with the Canadian Nickel Company – the forebear of Inco-Vale. However, it was only rarely and intermittently examined between the 1950s and 2006. Nickel, copper and cobalt mineralisation is generally concentrated in the upper margins of both the upper and lower sill, with the best portions enveloped in a broad zone of sulphides ranging from 20–60m true thickness. Drilling by Strongbow has led to the calculation of a geological resource model in the indicated category of 11.1Mt grading 0.4% nickel, 0.10% copper and 0.018% cobalt using a 0.2% nickel cut-off. Inferred resources are 33.1Mt grading 0.36% nickel, 0.09% copper and 0.017% cobalt. Although the Nickel King deposit conforms to the general characteristics of a magmatic sulphide deposit, it is somewhat unique because the mineralisation is hosted solely within the basic rocks (norite) as opposed to ultrabasic rocks. The absence of the silicate mineral olivine in the norite has proved to be very important to the metallurgical characteristics of the deposit because significant portions of nickel can be tightly held in olivine, a common mineral in ultrabasic rocks, and most of this nickel cannot be economically extracted.

Character assessments
In 2009, Strongbow commenced evaluation of the metallurgical characteristics of the Nickel King deposit to determine whether a saleable concentrate could be produced. A 140kg sample of split core was collected from 120–186.5 metres down, and was deemed to be representative of the Main Zone ore grade mineralisation and submitted to testing laboratories. This sample was crushed to coarse size of less than 14mm and blended into a 122kg composite. A 10kg sub-sample was subjected to a finer grind of less than 1.7mm for a head assay to determine whether the coarse composite and the fine fraction returned comparable grades, or if the coarse fraction required dilution to maintain a representative ore grade. Analysis of both the coarse and fine fractions gave similar analytical results, confirming that testing of the coarse fraction would not produce a sampling bias error. A 70kg subsample of the coarse fraction was submitted for calculation of the head grade, flotation tests and a bond ball and rod work index. Flotation is an industry standard technique for the recovery of sulphide minerals. Ten flotation tests on the composite ore sample returned a range of recoveries dependent on the pH, grind size and reagent additions (lime, SIPX collector and CMC depressant). Based on a locked or balanced cycle test (repetitive flotation test until maximum recovery is achieved) of the optimum combination, a concentrate of 16.5% nickel and 4.2% copper was achieved. Strongbow CEO Ken Armstrong explains, ‘This is a saleable concentrate which would be attractive to many domestic and foreign consumers.’

In addition, a test sample was submitted for QEMSCAN and electron microprobe analyses that revealed pyrrhotite, pentlandite and chalcopyrite were the dominant sulphides comprising 12.6%, 1.58% and 0.48% of the total mineral composition of the ore. The total abundance of the minerals identified by QEMSCAN and the mineral analysis confirmed that 88.9% of the nickel is in pentlandite, and that 86% of the nickel can be liberated at a grind size 0.1mm, while 10% of the nickel is found in the pyrrhotite and 88% can be liberated at the same grind size. The absence of olivine in the norite played a major role in achieving relatively high-grade, potentially saleable concentrate from a relatively low-grade deposit.

The Nickel King project has some way to go to improve the resource statement, explore outlying identified targets and finalise the mineralogical test work and process flow sheet. The way forward will include increasing the size of the resource through drilling along the main zone and testing promising nearby targets for potential satellite bodies.

Further information

Ken Armstrong, +44 (1) 604 668 8355