Preliminary results from an ongoing feasibility study on the Alamo Dorado silver-gold deposit are proving better than expected for
Situated in Mexico’s Sonora state, Alamo Dorado hosts a resource of 79.6 million tonnes grading 45.9 grams silver and 0.18 gram gold per tonne. Within that, open-pit reserves are pegged at 52.5 million tonnes at 63 grams silver and 0.23 gram gold, though a revision is under way to reflect current metal prices and new metallurgical results from the Phase 1 pit.
Material from the starter pit released just over 80% of its silver and 87% of its gold after 379 days of leaching. Recovery rates for the entire deposit are 65% for silver and 75% for gold.
The latest tests also suggest that agglomeration may not be necessary for leaching and that the height of the ore lifts may be inconsequential. Recovery rates were similar for columns 1.5 and 6 metres high, whether agglomerated or not.
Metallurgical testing continues.
Also under way are geotechnical, hydrogeological and condemnation drill programs, as well as environmental studies. The current plan calls for one leach pad with excess capacity to cover any future discoveries.
An earlier prefeasiblity study envisaged Alamo Dorado treating 15,000 tonnes of ore daily to produce an average of 7.1 million oz. silver and 30,300 oz. gold annually over 10 years. Such an operation would cost US$45 million to develop and be repaid in 18 months, assuming a silver price of US$5.28 per oz. and a gold price of US$300 per oz.
Cash costs in the first few years are pegged at US$1.55 per oz.; over the life of the mine, they increase to an average of US$2.96 per oz. The estimates consider byproduct gold credits.
AMEC Simons Mining & Metals is managing the feasibility study, with Metcon Research and Mintec providing assistance in the areas of metallurgy, reserve modelling and mine scheduling. The report is scheduled for completion in the first quarter of 2002.
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