LATIN AMERICA SPECIAL — Ariel largest producer of gold in

With two mines operating in northwestern Costa Rica, Ariel Resources (TSE) ranks as the country’s largest gold producer.

The mines are centred around Las Juntas near the northern end of the Costa Rican gold belt. A 60-mile-long, northwesterly-trending structure, the gold belt comprises more than 60 known properties.

Known as Tres Hermanos and San Martin, the two operations exist on adjacent properties which, collectively, yield some 300 tons of ore per day. The material is processed in a carbon-in-pulp mill near Matapalo in an area of low relief (which allows for the economic disposal of tailings). The Matapalo mill is 7-9 miles southwest of the mines.

Tres Hermanos is underlain by andesitic ash flow tuffs of the Late Miocene Aguacate Formation. Mineralization occurs in epithermal quartz veins and stockworks. The mineralized zones are typically associated with intersecting, high-angle faults and are genetically and spatially associated with rhyolite dykes and stocks.

The mine is accessible via adits on several levels. The principal vein being mined strikes northeast, measures nearly 6,600 ft. in length and ranges from 3 to 26 ft. in width.

As of Dec. 31, 1994, proven and probable reserves at Tres Hermanos stood at 224,501 tons grading 0.181 oz. per ton. The mine life is expected to range from three to five years, with average production projected at 10,000 oz. per year.

The San Martin mine, which adjoins Tres Hermanos to the east, began shipping surface ore from the Fortuna zone in December, 1993. Earlier this month, open-pit production of mill-grade ore commenced from the San Rafael zone. Last year, the ninth level of the Zopilotillo zone was reconditioned, and it is currently being extended to serve as the main haulage level for the southern portion of the mine. Subsequently, the 4.5 level of the Fortuna vein was reopened for stoping and mining. In addition, a crusher plant, electrical substation and compressor plant were installed below the ninth-level portal, and stopes were prepared above this level. Mining of higher-grade ore from the ninth level began late last fall.

Reserves minable from surface total 3.5 million tons grading 0.0746 oz., while underground reserves are estimated at 320,000 tons grading 0.23 oz. The properties contain significant quantities of lower-grade oxidized ore, which prompted Ariel to begin constructing a 150-ton-per-day (tpd) pilot plant near the San Martin primary crusher. The plant will employ a patented vat leaching technique, an alternative to heap leaching, which was deemed impractical as a result of heavy rainfall at the site.

Last month, by signing a deal to acquire Greenstone Resources’ (TSE) El Recio mine, the company moved one step closer towards its goal of producing 50,000 oz. gold per year. Situated northwest of Tres Hermanos, the mine contains an estimated 120,000 oz. gold grading 0.22 oz.

A feasibility study in 1993 indicated that a 100-tpd underground mine could be established for US$2 million; it would produce 9,000 oz. per year at a cash operating cost of US$189 per oz.

Peripheral to the mining operations, on the Sierra properties, Ariel plans to drill-test several gold-bearing alteration zones. These properties encompass the Boston, Gongolona and Ano Nuevo projects.