Big mines show Mexico’s potential

Newcomers looking for evidence of Mexico’s mineral wealth need only look as far as La Caridad and Real de Angeles.

Not only are they the latest mega-mining projects to be brought into production here, but they also serve as a yardstick for the exploration companies that have become active since the mining laws were changed in 1990. Owned by Jorge Larea’s powerful Industria Minera Mexicana (I.M.M.S.A.) group, La Caridad and its sister copper producer, the Cananea, are in the northwestern state of Sonora where most of the exploration activity in Mexico is centred. Together, they contributed over 87% of the 267,039 tonnes of copper produced in Mexico during 1991. They also helped to make Mexico the world’s fourth largest molybdenum miner with an annual Mexican yield of 4,400 tonnes.

The most recently published reserves at the La Caridad open pit stand at just over one billion tonnes of 0.39% copper and 0.033% molybdenum. At Cananea, reserves are reported at 1.2 billion tonnes of 0.66% copper. While La Caridad or Cananea weren’t on the agenda when The Northern Miner toured Mexico recently, we were fortunate enough to be able to fly to the Real de Angeles mine, Mexico’s largest silver producer.

The open pit operation, which has been in production since 1982, yielded 8.4 million oz. or just over 11% of the silver produced in the Latin American country last year. (Still the world’s biggest silver miner, Mexico churned out 70.7 million oz. 1991, plus 258,654 oz. gold.)

A joint venture between Empresas Frisco and Vancouver-based Placer Dome (TSE), Real de Angeles is also Mexico’s largest source of lead and zinc with 86.8 million lb. and 81.3 million lb. produced respectively in 1991. The complex is situated in semi-desert in the state of Zacatecas where mining activity dates back to 1705.

In an interview with the The Northern Miner, general manager Arturo Zmaudio Guzman said reserves of 85 million tonnes of 40 grams silver, 0.70% lead, and 0.80% zinc can sustain the operation for another 16 years.

Those reserves are hosted in a funnel-like breccia deposit that has been drilled to a depth of 600 metres.

Silver is produced as a byproduct of lead and zinc concentrates. Lead concentrates, consisting of 57% lead, 2.5% zinc and 3.2 grams silver, are shipped to a smelter in Torreon. The zinc concentrates, comprised of 49% zinc, 180 grams silver and 0.9% lead, are refined outside Mexico. Like other Mexican silver producers, including Industrias Penoles’ Las Torres and the Real de Monte mines at Pachuca, Real de Angeles is trying to keep its costs down in the face of low silver prices. At a spot price of US$4.07, Real de Angeles is managing to break even, says plant manager Benjamin Sainz. But in an effort to cut costs, operator Empresas Frisco has spent US$15 million to accelerate mine throughput to a targeted 19,000 from 14,000 tonnes per day. As head grades have also dropped from 64 grams (1.89 oz.) in 1990 to 59 grams (1.75 oz.) in 1991, the company has been trying to increase recoveries by testing new reagents.

Due to a severe shortage of water in Mexico, the huge clouds of dust that are routinely blown out of the crusher and the 240-metre deep open pit may prove to be a problem that mine crews are unable to solve.

At Real de Monte, Mexico’s powerful unions had such a strangle hold on the 4.8 million oz.-per-year operation that the local utility was on the verge of switching off the lights before the mine was privatized in 1990. But officials say, with help from the Washington-based World Bank and the Consejo’s de Recursos Minerales (Mexico’s geological survey), Real de Monte is producing an ounce of silver for about US$4.02.

Located in an area where miners have been active for centuries, the 5-mine complex remains one of the few operations where the process is integrated to such an extent that one can actually buy the finished product a short drive from the mine sites. The complex has produced 826.2 million oz. silver and 6.2 million oz. gold since mining began in 1922.

While touring of Real de Monte’s south mine and refinery, The Northern Miner noted that silver mineralization is mined from narrow veins using manual equipment and cut-and-fill methods. Head grades run at 226 grams.