Curator calculates tonnage for Boleo cobalt project

The Boleo project in Baja California Sur, Mexico, is estimated to contain 141 million tonnes grading 2.67% copper and 0.082% cobalt.

The drill-indicated and inferred estimate was recently calculated by International Curator Resources (VSE), which has an option to acquire the project. Meanwhile, Coeur d’Alene Mines (NYSE) can earn half of Curator’s interest by spending US$6 million on exploration and property payments by August, 1997.

The property contains a series of flat-lying, sediment-hosted copper-cobalt beds which were mined from the late 1800s to the mid-1900s. Historic production totals more than 13.6 million tonnes grading 4.81% copper and an estimated 0.12% cobalt.

Curator and Coeur d’Alene are investigating the feasibility of mining two areas — No. 1 Bed and No. 3 Bed — which either did not meet historic cutoff grades or were overlooked by previous operators. The potential also exists for re-mining areas that were backfilled with what was considered waste at the time (based on a cutoff of 3% copper).

The estimate includes a drill-indicated, open-pit resource for No. 3 Bed of 28.6 million tonnes grading 0.79% copper and 0.075% cobalt. The estimate is based on 178 drill holes and a bed thickness of 10.79 metres. A further open-pit, inferred resource for No. 3 Bed is estimated at 62.9 million tonnes grading 0.65% copper and 0.083% cobalt over a bed thickness of 8.79 metres.

Inferred resources occur adjacent to, and between, the drill-indicated blocks, and the joint venture is reasonably confident in the figures based on continuity of the beds as demonstrated by previous operations. Jan Christoffersen, project manager, said the best open-pit potential is in the Saturno area, which contains about 13 million tonnes of the drill-indicated resource at a relatively low stripping ratio of 2-to-1. The balance of the drill-indicated resource is much deeper, with a stripping ratio in the range of 10-to-1 or 8-to-1.

Much of the inferred open-pit resource is deeper still, since property topography consists of a series of ridges and eroded valleys. Christoffersen said there is good chance of outlining shallower reserves below the ridges in the No. 1 and No. 2 Beds, both of which are essentially eroded away in the valleys.

The underground, drill-indicated resource for No. 3 Bed is estimated at 6.4 million tonnes grading 2.88% copper and 0.081% cobalt over an average bed thickness of 1.46 metres. This is based on 15 holes and 802 underground samples — combined into the equivalent 48 drill holes.

A further 30.4 million tonnes grading 2.5% copper and 0.082% cobalt are categorized as inferred in the No. 3 Bed.

Tests completed this year in the San Guillermo area concluded that underground mining would be difficult. That, combined with the sulphide nature of much of the underground material, is prompting the joint venture to concentrate on the project’s open-pit potential.

Preliminary metallurgical testing to date at Boleo is promising. Leaching tests on the Boleo material returned recoveries of up to 91.44% for copper and 54% for cobalt using agglomeration with sulphuric acid and ferric cure.

However, heap leaching would not likely be feasible since a synthetic agglomerator would be required. Agglomeration using cement would not work, as the cement would be broken down by the acid.

“We would like to see a large, aggressive drill program to confirm and expand reserves, as well as provide additional samples for further metallurgical testing,” said Christoffersen. “This is obviously a world-class deposit and I think we’ve only touched the surface.”

Curator and Coeur are now discussing budgets for further work, which should get under way in September.