Metallurgical tests positive at Casposo

Metallurgical tests on drill core from the Casposo gold-silver deposit in Argentina suggest the mineralization may be easy to mill and leach.

Project operator Intrepid Minerals (IAU-V) engaged the Instituto de Investigaciones Mineras, a research body hosted by the National University of San Juan, to do the testing. Composite samples of vein material from Casposo’s Kamila zone, weighing 4-12 kg each, were subjected to 24- and 48-hour bottle-roll tests in sodium cyanide solutions.

Gold recoveries averaged just over 90% for material crushed to 80 mesh (0.18 mm). Recoveries from material ground to 150 mesh (0.1 mm) averaged 91%. Silver recoveries averaged 75% in the coarser material and 79% in the finer material.

Earlier tests had suggested gravity recoveries could reach 25%, so Intrepid management has concluded that acceptable recoveries could be attained without fine milling.

The metallurgical tests are being incorporated into an economic study scheduled to be finished by March 2004.

Verification drilling in June confirmed earlier results obtained by Battle Mountain Gold, now part of Newmont Mining (NEM-N). Battle Mountain held the property from 1998 to 2002. Intrepid’s drill program, 1,800 metres in all, tested depth extensions of the known zones and twinned earlier Battle Mountain drill holes.

From the Intrepid drilling and the Battle Mountain data, outside consultants to Intrepid have developed a resource model for the Kamila zone. The zone, consisting of three mineralized vein structures called Aztec, B-vein, and Inca, is thought to have potential for an open-pit operation, but the consultants made separate estimates for a larger-tonnage resource with lower cutoff grades and for a smaller, higher-grade resource potentially minable from underground.

The preliminary resource, using a cutoff grade of 0.5 gram gold-equivalent per tonne, is 2.75 million tonnes grading 3.7 grams gold and 76.4 grams silver per tonne. Most of that resource is inferred, but the indicated resource is 271,000 tonnes grading 7.1 grams gold and 97.1 grams silver per tonne.

Increasing the cutoff grade to 1 gram per tonne brings the resource down to 2.2 million tonnes and increases the grades to 4.5 grams gold and 89.7 grams silver per tonne. The gold-equivalent cutoff is based on a 90:1 ratio of silver to gold, taking into account both the price ratio and the relative recoveries of the two metals.

For the underground-mine exercise, the consultants calculated a resource of 473,000 tonnes at grades of 12.3 grams gold and 228 grams silver per tonne, based on a cutoff of 5 grams per tonne gold-equivalent.

Drilling is planned for September on the Mercado zone, the northwestern extension of Kamila. Surface mapping of the zone is complete and the area is now being trenched.

Other trenching is under way at Panzon, a showing 500 metres northwest of Mercado, where earlier work by Battle Mountain unearthed a 27-metre-wide vein system that returned average grades of 140 grams silver per tonne. Intrepid has also acquired additional ground surrounding the Casposo concession, which it plans to explore this year.