Tantalum exploration in Northwest Ontario
In the continuing search for the materials that will drive the high-technology industries of the New Economy, tantalum has become one of the most sought-after of all commodities.
Although tantalum is a rare metal that typically occurs in minute concentrations in the Earth’s crust (on average 1 part per million), it finds widespread use in a variety of portable devices that have become today’s essentials. For example, tantalum (in the form of tiny capacitors) is an integral part of cellular phones, pagers, and hand-held and notebook computers: a market that currently soaks up more than 60% of the world supply of this high-tech metal, and which is growing at a rate of around 15% per year.
Such rapidly increasing demand combined with a shortage of supply have sent tantalum prices skyrocketing over the last twelve months. Recent sales of tantalum pentoxide concentrate have surpassed US$400 per pound, in comparison with the average price of US$40-55 per pound under long-term contracts.
Over the last three years a Canadian mineral exploration and development company, Avalon Ventures Ltd., has moved aggressively to identify and secure a number of high-quality tantalum properties in northwest Ontario–action taken in anticipation of the surging demand for the metal by high-tech manufacturers. In so doing the company has discovered significant zones of tantalum mineralization on its Separation Rapids, Raleigh Lake, and Lilypad Lakes properties, suggesting the existence of a new tantalum district in northern Ontario.
From the outset, Avalon’s exploration focus for tantalum has been small pegmatite bodies: rocks that owe their origin to crystallization from the residual liquids of silicate magmas. Although most pegmatites are simply very coarse-grained rocks with compositions similar to normal granites, certain rare types form from strongly fractionated, late-crystallizing granitic liquids: these are extraordinarily enriched in certain elements, notably lithium, beryllium, cesium, niobium, tantalum, rare earth elements, and zirconium. Tantalum minerals such as manganotantalite (MnTa2O6), wodginite (Mn(Sn,Ta)Ta2O8) and microlite [(Na,Ca)2Ta2O6(O,OH,F)] often occur in economic amounts in these rare, strongly fractionated pegmatites, which also contain significant zones of lithium in spodumene or petalite.
Using conventional prospecting methods, in concert with a comprehensive program of lithogeochemistry and ground-based gravity surveys, Avalon has had remarkable success in locating tantalum-bearing zones in pegmatite dykes on all of its rare-metals properties. Amongst these, the Separation Rapids property near Kenora represents the most advanced.
At Separation Rapids, a pre-feasibility study completed in 1999 indicated the presence of a very large petalite and Rb-Kfeldspar deposit (11.6 million tonnes grading 1.34% Li2O and 0.30% Rb2O) hosted in the Big Whopper pegmatite. This deposit is amenable to low-cost, open-pit mining methods and also contains a similar tonnage of low-grade, disseminated tantalum mineralization (0.007-0.010% Ta2O5).
Most recently, exploration has focused on the Lilypad Lakes property. This is located east of Pickle Lake, where at least eight separate pegmatite dykes distributed over an area of 5 km by 2 km all carry high-grade tantalum mineralization (Ta2O5>0.04%), often in association with cesium mineralization in the form of the extremely rare mineral pollucite. Lithogeochemical sampling of individual dykes exposed on surface on the Lilypad Lakes property has yielded assays as high as 0.422% Ta2O5 (i.e., the Double J Dyke). Diamond drilling to depths of around 150 metres has confirmed the presence of wide intersections of economic tantalum mineralization in several of the pegmatites, e.g., 0.061% Ta2O5 over 13.80 metres in the South Dyke, 0.036% Ta2O5 over 34.20 metres in the Rubellite Dyke, and 0.052% Ta2O5 over 10.25 metres in the Pollucite Dyke.
With offices in Toronto and Thunder Bay, Ont., Avalon is well-placed to become an important supplier of this most useful of the rare metals, to major manufacturers both in North America and around the world.
Richard Taylor is a professor of Earth Sciences at Carleton University in Ottawa, Ont., and consults to Avalon Ventures Ltd.