Mercator Minerals has revised production guidance for its Mineral Park mine in Arizona, USA, which is now expected to produce approximately 89 million copper equivalent lb during 2012. The company previously estimated production of 90 to 100 million copper equivalent lb.

Harder than expected ore reduced mill throughput rates resulted in lower than expected copper production. The updated guidance is based on the concentrator achieving design throughput levels of 50,000 tons per day, with a hard ore blend of up to 40% of total mill feed. The company believes the impact of hard ore on mill throughput has now been resolved.

The 2012 mine plan at the Mineral Park mine includes mining through the transition from supergene enriched copper material into primary hypogene copper mineralization. Mining of the transition zone has encountered a lower percentage of higher grade supergene copper mineralization than expected from the mineral resource model, resulting in a lower copper grade from this material than anticipated, while molybdenum grades are unaffected.

Approximately 20% of the material expected to be processed under the 2012 mine plan is comprised of transition zone ores. Mercator believes that, as mining passes through the transition zone, copper grade and tonnage reconciliation should better correlate with the block model since the copper grades in hypogene mineralization both within and below the transition zone is less subject to the variability associated with secondary enrichment. Overall, the transition zone represents a small percentage of the overall mineral resource and the life-of-mine mineral reserves for the Mineral Park mine.