Preliminary metallurgical tests on mineralization from the Ocampo gold-silver properties of
The tests examined composite samples of drill cores from two zones on the property, Plaza de Gallos and Refugio. They were simple column leach tests on crushed core samples.
A 143-day leach of material with 80% smaller than 6.3 mm recovered 88% of the gold and 63% of the silver. Finer grinding, so that the 80% of the material passed a 1.7-mm sieve, allowed recoveries of 91% of the gold and 76% of the silver after 117 days in the column.
Silver recovery is critical, as the metal makes up about 40% of the gross value of the mineralized material. Heap leaching using cyanide recovers around 60% of the silver in a typical gold ore.
Consulting firm Kappes Cassaday & Associates, which did the testing, is recommending that, in future feasibility work, Gammon use a base 85% recovery figure for gold and a 60% figure for silver, or 88% for gold and 73% for silver if the finer crushing is part of the proposed plan.
The tests also showed low reagent consumption, with the coarser material consuming 0.28 kg of sodium cyanide and 1 kg of calcium hydroxide for each tonne of material treated. The finer material is hungrier, consuming 0.69 kg of sodium cyanide, and marginally more caustic.
Gammon’s consultants have identified a suitable area on the property for the leach pad and tailings. An initial, 7-million-tonne pad-and-pond complex should cost about US$1.9 million, and expansion to take another 14 million tonnes would cost a further US$2.4 million.
At last report, the resource at Ocampo stood at 21.7 million tonnes grading 1.44 grams gold and 57 grams silver per tonne in the measured and indicated category, plus 5.8 million inferred tonnes of 1.7 gram gold and 86 grams silver.
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