Fortaleza, Brazil — Some 250 km southwest of this busy port city, structural deformation has transformed one of the world’s largest layered mafic intrusive complexes into a geological puzzle, which, once solved, could create a platinum-palladium-producing district in northeastern Brazil.
Dubbed Pedra Branca, the complex was discovered in the 1960s by local government geologists who were exploring the area for its chromite potential. Five holes were drilled into the Esbarro prospect, and by 1969, an estimated 43,000 tons of material grading 10-28% chromite were established.
The project then sat idle until 1985, when South African-based Gencor and mining powerhouse
Rio Tinto focused on the most northerly chromite occurrence, known as Esbarro 1 and 2. Situated only 15 km from the small village of Capitao Mor, the two showings lie within 400 metres of each other. The major drilled 42 holes over an 800-metre strike length, with 13 of the holes cutting the favourable chromite horizon. Based on a cutoff grade of 1 gram combined platinum-palladium per tonne, the historical holes returned an average of 2.5 grams combined platinum-palladium over 6.1 metres, including a higher-grade section of 6 grams platinum-palladium over 2.1 metres.
Meanwhile, Gencor targeted the central and southern portions of the ultramafic belt. The company carried out trenching and drilled eight holes into the Traipia 1 and Trapia 2 showings, and these holes cut up to 17.8 grams palladium and 2.7 grams platinum over 1.4 metres.
In 1987, with the price of palladium trading at US$100-120 per oz., both these programs were discontinued before the economics of the overall project could be determined.
As the price of palladium started to soar in the late 1990s, Altoro Gold, which recently merged with Denver-based
Covering an impressive 40-by-20-sq.-km area, the ultramafic complex is, in many ways, similar to the largest repository of platinum group metals — the prolific Bushveld complex in South Africa. Initial mapping and sampling by
“World-class belts like this one are so rare that we seized to opportunity to explore it,” says Robert Dickinson, co-chairman of the Hunter-Dickinson (H-D) group of companies, of which Rockwell is one. “There have been a lot of 1-to-3 grams [combined platinum-palladium-gold per tonne] reported in Canada, but the grade here is from 7 to 30 grams, both on surface and in shallow drilling.”
However, unlike its relatively pristine South African counterpart, Pedra Branca has been subject to significant metamorphism and structural impact, making exploration much more challenging.
To solve the structural puzzle, Rockwell tapped some of H-D’s most experienced field staff.
“The idea is to step back a bit and look at the bigger picture,” says Dickinson. “The previous owners lacked the financial resources, but we have the opportunity to do the geological work and then put it all back together.”
The Pedra Branca project covers 998-sq.-km and is underlain by a 100-metre-thick sequence of folded, layered, mafic intrusive rocks. The arcuate belt, representing the limbs of a major syncline, extends for 70 km and is host to one or more platinum-group-element-bearing chromitite horizons.
Rockwell launched a property-wide mapping and sampling program late last year in an attempt to outline drill targets.
“We are now systematically drilling 20 chromite occurrences throughout the belt,” says Rockwell’s exploration manager, Mark Rebagliati. “Four to eight holes will be drilled on each one during the initial pass, and then, as results come in, we can follow them up.”
The first 24-holes of Rockwell’s drill program tested the continuity and down-dip extension of the mineralization at Esbarro. At presstime, assay results from 12 of the holes were in, and, as with the previous drill programs over this area, the lack of mineral continuity appears to limit the size of a potential resource.
Highlights are as follows:
– Hole 1 tested the downdip extension of mineralization hit in Altoro Gold’s drill hole 4 (22.3 metres grading 1.81 grams palladium and 1.08 grams platinum from a down-hole depth of 11 metres) and returned 10.8 metres averaging 1.7 grams palladium and 0.36 gram platinum from 33.2 metres down-hole.
– Moving 50 metres to the east, hole 2 returned 3.8 metres grading 2.24 grams palladium and 0.58 gram platinum from 59.6 metres down-hole.
– Hole 3 was collared 100 metres northeast of hole 2 and returned 0.34 gram palladium and 0.73 gram platinum over 1 metre from 43 metres down-hole.
– Stepping out a further 200 metres to the east, hole 4 tested the mineralization south of Altoro’s hole 8 (6.7 metres grading 2.24 grams palladium and 1.42 grams platinum from 20.6 metres down-hole) and hit two zones. The first returned 2.05 grams palladium and 0.5 gram platinum over 4.9 metres from 22.4 metres down-hole, followed by 13 metres grading 1.49 grams palladium and 0.58 gram platinum from 43 metres down-hole.
– Moving 100 metres north northeast, hole 5 cut five mineralized lenses including 4.14 grams palladium and 4.75 grams platinum over 2.9 metres from surface. The broadest zone cut 1.73 grams palladium and 0.58 gram platinum over 20.1 metres from 14.7 metres down-hole.
– Hole 6 was drilled 100 metres west of hole 4 and hit 0.46 gram palladium and 0.49 gram platinum over 1.3 metres from 77 metres down-hole.
– Holes 7, 8, 9, 10, 12 and 13 were collared along the southwestern margin of the Esbarro zone, covering 450 metres of strike length, but failed to hit the favourable ultramafic horizon.
– Holes 11 and 14 were collared 50 metres northeast and northwest of Altoro hole 8, respectively, and hit wide intervals of the favourable ultramafic horizon. Assay results are pending.
Based on the latest round of drilling, the Esbarro zones cover a 1-km-by-300-to-400-metre-wide continuous mass of ultramafic host rocks. The mineralization could possibly represent a large-scale boudin produced by flattening and structural extension occurring during the main metamorphic event, or it could be a result of irregular intrusive contacts produced by the intrusion of the younger granite body.
“Initial results at Esbarro have been disappointing, but the mineralization may be affected by the adjacent granite,” says Dickinson, “We have now moved the drill to a different target, away from the later-staged body.”
Rockwell intends to define an economic resource over three or four of these pods or troughs throughout the large property.
“Our goal is to find large-scale deposits,” adds Dickinson. “We’re looking all over the world, and here we have the possibility of hitting one. We certainly have unusually high grades.”
Having completed its merger with Altoro Gold, Solitario now holds a 100% interest in a 300-sq.-km area that encompasses the Esbarro and Curiu prospects. Solitario also holds an option to earn 70% of a 120-sq.-km package that hosts the Trapia, Massape and Ipueiras prospects. This option is carried forward from a 1999 agreement between Altoro and
Gold
Rockwell is earning a 60% interest in the property by spending US$7 million over four years and issuing 500,000 shares to Solitario (in five equal allotments of 100,000 shares). Each allotment must have a minimum value of US$100,000.
A firm believer in the future of strong platinum-palladium prices, H-D has also been busy evaluating promising projects from around the globe. In Canada, H-D has inked a deal with
“Our property is roughly the same size as the Thompson belt, which holds 180 million tonnes of better than 2% nickel,” says David Jennings, H-D’s director of property acquisitions.
Lying just south of
“Inco recognized that the Thompson belt and Fox River belt were similar accretionary prisms between the Churchill and Superior Provinces,” says Jennings. “But when Inco hit at Thompson, they walked away without testing Fox River for platinum group metals.”
In the 1990s, Falconbridge picked up where Inco left off and drilled 15 holes into the eastern section of the sill.
“This was not a priority area,” says Jennings. “Logistical reasons forced Falconbridge to start drilling there.”
H-D has its sights set on the PGM potential of the ultramafic body. The sill is known to contain at least two horizons of platinum-palladium-bearing mineralization. At the base of the Upper Central Layered zone, mineralization has been identified over widths of up to 20 metres. Below this, the Lower Central Layered zone grades into a marginal zone that contains disseminated sulphides with platinum-palladium mineralization.
“The exposure is really wretched,” explains Jennings. “It is heavily overburden covered, so we are resorting to geophysics. We see the property as a hugely underexplored belt of incredible size.”
At the western portion of the sill, the Great Falls showing returned grab samples grading 4.4 grams platinum, 4.1 grams palladium and 6.7 grams gold per tonne, plus 1.9% copper and 0.68% nickel. At the nearby KO zone, samples yielded up to 1.3 grams platinum, 3.5 grams palladium, 2.1% copper and 0.94% nickel.
Significantly, the property lies in the heart of the Manitoba diamond play, and although no kimberlites have been identified in the province, a recent till-sampling programs outlined a large diamond indicator mineral train just south of the Fox River property.
“We know that the indicator minerals did not come from massive sulphides,” says Jennings with a smile, “and our property covers a deep-seated crustal feature that has tapped the mantle, where kimberlites come from.”
Several major diamond exploration companies have talked to H-D about a possible joint venture.
“We are there for the PGMs, whereas Falconbridge is there for the nickel,” adds Jennings, “and the diamonds are a pretty good bonus.”
Beginning in June, the company will drill-test 20 targets in a 6,000-metre helicopter-supported program. To earn its interest, the Vancouver-based company must spend $12.5 million over five years.
In April, H-D inked a deal with equal partners
The private company has agreed to spend $2 million on exploration and pay $48,000 in cash to earn its interest. H-D also assumes all the underlying option payments and will act as operator.
The property covers the eastern margin of the Nipigon plate, near Beardmore, and hosts an ultramafic intrusive, dubbed the Eva Kitto cone. The 10-km-in- diameter cone is related to the failed-arm structure, which completes a structural triple junction often associated with major deposits.
Highly anomalous nickel, copper and chromium geochemical values, as well as several geophysical anomalies, mark the intrusion.
H-D will commence prospecting and mapping, followed by geophysics and possibly drilling.
Early to recognize the potential of the area are Inco and Falconbridge. Several geologists have compared the geological setting to that of the prolific Noril’sk mine in Siberia. Noril’sk was a huge find, and, in its heyday, cranked out 2.5 million oz. palladium and 800,000 oz. platinum per year. Output is now falling, as the operation moves from mining massive ore to disseminated and copper-rich ore grades, but the possibility of such a discovery in Canada is attracting attention.
The geological setting of the Nipigon area is marked by a deep-seated regional fault structure where ultramafic intrusions from deep mantle sources are found in contact with abundant sulphur source rocks — favourable locations for hosting continental tholeiite, enriched with platinum group elements.
The area also has impressive platinum group elements and copper-lake-sediment geochemical anomalies that are comparable, and may even be superior, to the anomalies near the Lac des les deposit.
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