Quaterra targets classic platinum play

Ketchikan, Alaska — Some 56 km north-northwest of this regional port city, Vancouver-based Quaterra Resources (QTA-V) and partner International Freegold Mineral Development () are taking platinum exploration back to its historical roots by investigating a classic “Ural-Alaska type” prospect at Union Bay.

Platinum has an extremely high melting temperature (1,769C), and it was not until 1774 that science had advanced enough to melt the precious metal. From then until the discovery of South Africa’s famous Bushveld complex in the early 1900s, more than 92% of the world’s platinum came from deposits found in the Ural Mountains of west-central Russia. (Bushveld, a layered intrusive-type of ultramafic complex, hosts the largest reserves of platinum group elements in the world.)

The largest of these Ural-type platinum deposits occurred in gravel, as small alluvial flakes derived from deeply eroded mafic-to-ultramafic plutonic bodies. The geological setting was recognized as unique, with a concentrically zoned core of dunite, followed by wehrlite, then clinopyroxenite, all of which is surrounded by gabbro. The bedrock occurrences of mineralization appeared to be controlled by magmatic cumulate stratigraphy, with the platinum settling in either thin bands of chromitites hosted in the dunites or magnetite occurring as well-bedded, locally continuous layers intercalated with the clinopyroxenites, or as vein-like bodies of relatively coarse-grained or pegmatoid clinopyroxenites. Copper and nickel content tended to be low, and platinum values far exceeded those of palladium. By the 1920s, the recognition of similar geological bodies in Alaska and northwestern British Columbia led to the classification of “Ural-Alaska type” ultramafic complexes. To date, the limited size and continuity of primary platinum mineralization in these types of bodies have rendered them uneconomic. Only the placer deposits, typically derived from the weathering of chromitites in the dunite cores, have produced economically recoverable platinum.

The Union Bay property is in southeastern Alaska, at the southern end of the 560-km-long-by-40-km-wide Alexander platinum belt, home to 11 known Ural-Alaska-type ultramafic complexes. There is tidewater access west of the property on Cleveland Peninsula, with the only other access limited to either a float plane from Vixen Inlet or helicopter. Topography ranges from flat outwash plains near sea level on the northern portion of the property to rugged peaks hitting 876 metres above sea level at Mt. Burnett in the centre of the claim blocks.

The 5-by-10-km Union Bay complex has zonal features characteristic of a Ural-Alaska complex, with a 1-km dunite core on the southeastern side moving through wehrlite- and magnetite-bearing olivine clinopyroxenites to hornblendite and gabbro on the margins. The complex appears as a lopolith folded along a later-staged west-northwest-trending axis.

Exploration of the property began in 1954, when Columbia Iron Mining targeted magnetite occurrences on the western side of Cleveland Peninsula. Working the project off and on until 1970, the company defined a reserve of 900 million tonnes grading 18-20% iron and 2% titanium. Anaconda Minerals initiated the hunt for platinum group elements at Union Bay in the late 1970s. Following the geological model, the company concentrated its efforts on the chromite occurrences in the dunite core, which are now known to contain little mineralization at Union Bay. The property then sat idle until 1995, when the Alaska Bureau of Mines released pan concentrate data yielding in excess of 1,000 parts per billion platinum from four streams within the Union Bay complex. Follow-up pan concentrates from streams draining magnetite-rich pyroxenite returned as much as 19.4 grams platinum per tonne. Harry Barr-led International Freegold immediately recognized the promise of the complex and acquired the property in May of last year. Limited prospecting led to the discovery of three prospective areas known as the North, Central and Core zones. Of the 187 grab samples collected during the program, nine returned 1.15-17.3 grams platinum-palladium.

Attractive grades

With high platinum prices attracting the attention of many junior explorers, the high-grade values quickly caught the eye of Western Copper Holding‘s (WTC-T) president, Thomas Patton, and its chairman, Dale Corman. An option to acquire half of Union Bay was signed in April through Western Copper’s sister company, Quaterra Resources. The junior can earn its stake by spending US$1 million on exploration and paying US$100,000 in cash over four years. Quaterra also agreed to issue 200,000 shares of its common stock to Freegold — 100,000 shares upon approval of the transaction by the Canadian Venture Exchange and 100,000 shares on May 1, 2002.

“We are looking for a reef, a narrow zone of high-grade platinum that has great lateral extent,” says Quaterra’s president, Thomas Patton.

Earlier this year, Quaterra extended the platinum-palladium mineralization in the North zone and discovered a new zone, dubbed Jaguar.

Based on the latest chip and channel samples, the North zone has been traced over a 400-metre strike length covering a vertical distance of 180 metres. The width of the zone remains in question, but is estimated at 75-125 metres.

A total of 162 chip samples have been collected from the zone with a high value of 17 grams platinum-palladium coming some 100 metres south of the original discovery outcrop (17.3 grams platinum-palladium). Twenty-three of the samples returned values greater than 0.1 gram platinum-palladium, with eight yielding better than 1 gram.

The junior subsequently collected four channel samples (taken with a rock saw) over the zone where previous chip sampling showed high-grade values. Two adjacent 0.3-metre samples yielded 7.9 grams combined platinum-palladium. As expected, the platinum content far exceeds that of palladium.

“The platinum-palladium ratios are quite high,” Quaterra’s project manager, Kurt Freeman, told The Northern Miner on site. “In some cases, its 20-to-1, very platinum-enriched.”

Olivine pyroxenite appears to be the most favourable lithology for mineralization. The presence of magnetite and chromite stringers along narrow, later-staged pyroxenite dykes also seems to have some bearing on the mineralization.

“We don’t know the significance of the dykes, but they occur in greater frequency within the higher-grade zones,” says Freeman.

Moving some 4.8 km to the west on the flanks of Mt. Burnett, Quaterra’s field crews have discovered an extensive zone of magnetite that may mark the extension of the North zone. Several grab samples have been collected, and assay results are pending.

Jaguar zone

The newly discovered Jaguar zone lies 300 metres west of the North zone. So far, chip sampling from this area returned up to 3.34 grams platinum-palladium. Based on field relations and trace element geochemistry, this zone appears to be a distinct parallel zone.

“This zone is a separate animal,” says Freeman. “It has a different chemical make-up than the North zone.”

So far, the partners have traced the Jaguar zone over 275 metres along strike, with the mineralization still open in both directions.

Recognizing the placer potential of “Ural-Alaska type” complexes, including the past-producing Goodnews Bay deposit in northwestern Alaska (600,000 oz. of platinum from 1936 to 1975), Quaterra staked 3.4 sq. km of placer claims that cover a flat-lying plain draining the base of the complex.

With a newly completed $865,000 financing in hand, Quaterra intends to drill-test the North zone with a 1,000-metre program slated to start in August. The company also plans to complete a regional pan concentrate/rock-sampling program over the entire property and test the alluvial potential with auger drilling.

States Patton: “If we can show that the platinum occurs in a discrete zone and that this zone has continuity, then we can greatly expand the program.”

Banking on the promise of Uni
on Bay, Quaterra has staked additional ground 45 km southeast of Ketchikan on Duke Island. This property covers two well-exposed “Ural-Alaska type” complexes that have been interpreted to be parts of the same intrusive at depth. Known as Judd Harbor and Hall Cove, the bodies are 3.2 and 5.6 km in diameter, respectively. Limited sampling earlier this year returned up to 134 parts per billion platinum. Mapping and sampling are planned.

Meanwhile, another of Quaterra’s joint-venture partners, Eastmain Resources (ER-T), is preparing to drill-test targets on its massive sulphide properties in Ontario’s prolific Abitibi greenstone belt. In 1999, Quaterra inked a deal to earn a half-interest in the Abitibi Extension project from Eastmain in return for spending $1.5 million over four years and either issuing 300,000 shares or paying $45,000 in cash. The project consists of four large blocks, named Nette River, Kesagami, North French and Chabbie Lake.

Abitibi Extension occupies the unexplored western extension of the famous belt.

“Owing to the extensive cover, little exploration has been done,” explains Patton. “It has a good risk-to-reward ratio, which suggests that a single drill hole could lead to the discovery of a world-class orebody.”

Quaterra has 30 million fully diluted shares and recently traded in the range of 15 per share.