Sudbury, Ont. — It just might be too small for
Ursa holds a 51% stake in the Shakespeare project and is applying for an additional 24%, having spent the required $1.2 million and set aside 200,000 treasury shares in anticipation of the major’s approval. Falco retains a back-in right for 50%, subject to repaying Ursa 2.5-times its expenditures (minus the initial $600,000) and carrying it through to the completion of a bankable feasibility study.
In early 2000, having reorganized itself after a long foray abroad, Ursa was looking for a project closer to home. The company liked what it saw at Shakespeare: an established resource sitting at the intersection of three structural provinces, next door to a renowned nickel camp.
“When we got involved here, this was obviously outside the basin and did not fit the Sudbury story,” said President Richard Sutcliffe. “I was intrigued by the exploration opportunity and originally thought we had a distal Sudbury offset-type deposit, but we did some geochronology early on in the game and determined it was in fact Nipissing in age.
“Now, the significance of that is about 400 million years, and up until what we defined here, nobody had found any significant-scale mineralization [in these older rocks]. There was a lot of smoke, and it was known as a geologically prospective environment for nickel/copper/ platinum-group-metals, but no substantial deposits had been identified in the Nipissing.”
To be sure, initial efforts bore little fruit. Then, in mid-2002, the project began to blossom after hole U3-04 pulled up 89 metres of mineralization some 240 metres east of the historic deposit. The interval averaged 0.57% nickel, 0.64% copper and 0.04% cobalt, plus 0.56 gram platinum, 0.61 gram palladium and 0.32 gram gold per tonne.
Local structures proved troubesome at first but are now better understood. A telling example is a rheomorphic breccia that outcrops on line 700E, near the eastern edge of the new deposit. The structure, which plunges steeply to the south, truncates the surface expression of the zone on that section.
“We see it in both the Nipissing and the ore zone, sometimes at the top and sometimes at the bottom,” Project Geologist Harold Tracanelli told The Northern Miner. “Having looked at most of the rocks here and worked most of the drill holes, when this particular feature crosscuts the zone, I can now tell exactly where the rest of the zone is or whether it has been cut off.”
Added Sutcliffe: “Recognizing that structure has been key for our exploration.”
With that and 24 more holes behind them, last July, consulting firm Micon International pegged the zone’s indicated resource at 4.9 million tonnes grading 0.43% each of nickel and copper, plus 0.03% cobalt, 0.45 gram palladium, 0.41 gram platinum and 0.22 gram gold. Like the original to the west, the new deposit is shallow and remarkably consistent in both mineral continuity and grade.
Ursa’s goal is simple: prove up enough near-surface tonnes to warrant an open-pit operation that trucks run-of-mine ore to Falco’s Strathcona mill. If recent drilling along strike to the east and in the historic deposit is any indication, the junior is poised to make the proverbial leap from explorer to miner.
“Right now we are drilling our holes to 200 metres below surface as a first-level of approximation for a pit,” said Sutcliffe. “But, as we refine the economic model, deeper drilling may become warranted. The other thing is that we are encountering visually higher grades [at the eastern end] that also may warrant deeper drilling.”
Rifting event
The Shakespeare property sits in a 200-km-long arcuate magmatic belt known as Huronian-Nipissing. The belt, which includes the East Bull Lake and River Valley intrusions, is thought to be related to a long-lived (300-million-year) continential rifting event that was centred beneath the Sudbury Basin and spread along the southern margin of the Superior Province.
“If you look globally at magmatic nickel deposits, they often occur along these sorts of geological structures,” said Sutcliffe. “It’s early days, but the environment we are in is somewhat akin to Norilsk [in northern Russia] in that we are dealing with one particular, very small intrusive sequence in a big mafic magmatic event that is carrying a lot of mineralization.”
Mineralization is hosted in a gabbroic sill that thickens to 80 metres and intrudes a quartzite unit of the Huronian Supergroup. Regional tectonism seems to have compressed both into a tight overturned anticline, with bedding dipping steeply to the north.
A cross-section shows quartzite in the hangingwall, followed by layers of quartz diorite gabbro, melagabbro (the mineralized suite), and barren gabbro defined as Nipissing proper. A chilled margin is evident at the base of the melagabbro, clearly indicative of two magmatic pulses.
Sulphide minerals concentrate near the base of the favourable suite and occur in the form of pyrrhotite, chalcopyrite and pentlandite. Nickel seems to be tied up in the pentlandite, which is usually as abundant as chalcopyrite, so metallurgy should be relatively straightforward.
“The issue is how to optimize recovery versus concentrate grade, but I think it’s safe to say there are no significant barriers,” said Sutcliffe.
Ursa has obtained 30% combined nickel-copper grades in cleaner-concentrates, whereas Falconbridge reported recoveries of 80% for nickel and 90% for copper in rougher-concentrates.
Added Sutcliffe: “The issue [in concentrates] is cleaning the pyrrhotite, and the more you do clean that, the more it takes with it.”
EM highs
Geophysics is proving a useful exploration tool: both deposits coincide with electromagnetic highs. Also, on line 900E, which marks the eastern boundary of the resource (it begins on line 100E, and the grid is measured in feet), borehole surveying detected a possible extention to the east and downdip. During the summer, Ursa confirmed this possibility by delineating the favourable horizon about 240 metres beyond the current resource, to line 1700E.
Results are pending for the 10 stepout holes, though some pulled up thick mineralized intersections. For example, hole 30, collared on line 1300E, intersected 60 metres carrying blebby-to-net-textured pyrrhotite and chalcopyrite. (Pentlandite seems to be visible only in polished core.)
By the time of the The Miner’s visit, Ursa had moved the rig back to the historic deposit in the west. The confirmation program will enable the tabulation of a resource to current standards, as historic core and information regarding the method used in the most recent calculation are lost.
In 1985, Falco pegged the Western zone’s global resource at 2.1 million tonnes, between lines 500W and 2000W; within that, to a depth of 30 metres below surface, 1.1 million tonnes graded 0.37% nickel, 0.4% copper, 0.45 gram palladium, 0.41 gram platinum and 0.23 gram gold.
Although a concurrent engineering study came back negative, the author suggested that higher metal prices and the development of an access road on the northern side of Agnew Lake might make an open-pit operation feasible. Logging roads now exist there, and metal prices are considerably higher than those used in the study — $1.80 per lb. nickel, $1 per lb. copper, $750 per oz. platinum, $145 per oz. palladium, and $450 per oz. gold.
Recovery rates were assumed at 76% for nickel, 82% for copper, 76% for platinum, 41% for palladium and 31% for gold.
Results are pending for the five confirmation holes drilled to date. One hole, no. 40, which was being drilled during the Miner’s visit, had pulled up 45 metres of mineralized sill.
“This was actually one of the better-looking intersections we have seen and is the farthest west we’ve been on the property,” said Sutcliffe.
Rugged topography
He also noted that Falconbridge angled its holes from south-to-north, undercutting the zone in places and losing it where cut by the rheomorphic breccia. The decision to drill the holes that way may have been determined by the locally rugged topography — a valley characterizes the less-resistant interior of the intrusion from the outer quartz diorites and quartzites.
“The ridge would locally affect stripping ratios, but it is actually well back for a big part of the zone,” said Sutcliffe. “Nonetheless, it will be a factor.” He added that Ursa’s drilling has intersected the zone deeper than Falconbridge.
A new economic assessment, including an updated resource calculation, is scheduled for completion in the new year. By then, several promising trenches dug in the foldnose and on the southern limb will have been tested as well.
Geological mapping and ground geophysical surveying are under way in an effort to define drill targets further.
Ursa also has increased the size of its wholly owned contiguous property to the east, given that airborne geophysical surveying suggests that the sill continues in that direction for another 12-15 km. Two earlier scout holes collared on individual anomalies pulled up 0.8 metre grading 1.7 grams platinum and 0.7 gram palladium, plus anomalous nickel.
“There still remains a huge opportunity in the Sudbury area for nickel-sulphide mineralization, and we think that we in particular have a new and unique exploration model for a new style of mineralization in an old camp,” said Sutcliffe. “Our exploration focus will be to nail down this strongly mineralized intrusion.”
The property now comprises about 39 sq. km. To acquire 100% in the add-on, Ursa must pay the vendor $162,000, issue 60,000 shares and spend $130,000 on exploration over three years.
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