PT Leigton, a division of Leighton Asia and a part of G-Resources Group, is undertaking the mining activities for a five-year period. The engineering, procurement and construction management (EPCM) contract was awarded to Ausenco in August 2009. By May 2011, around $314m had been invested in the development of the mine. Martabe’s total capital cost is estimated at $576m. Martabe is expected to produce 250,000oz of gold and approximately 2 to 3Moz of silver a year at a cash cost of less than $250/oz of gold. Recoveries are expected to average 76% for gold and 55% for silver. The ore will be treated using 4.5 million tonnes of ore per annum using proven SAG and ball milling, and carbon-in-leach (CIL) technology. Mining of waste will peak after two or three years of operation, reducing the costs in the initial mine life. The plant and infrastructure will be designed to allow for future expansion. The processing facility will be a large-scale ore processing plant.
Mining of the Purnama deposit will be undertaken by conventional open-pit methods with a low average strip ratio of 0.7:1. Two adjacent deposits, Baskari and Pelangi, plus primary gold potential at depth and other virgin targets are expected to provide upside. The most significant and best defined of these is the Purnama deposit, where a resource of 66.7 million tonnes containing 1.74g/t Au and 21.5g/t Ag for a total of 3.7 million ounces of gold and 46 million ounces of silver has been defined by diamond drilling. “Production will be 250,000oz of gold and approximately 2Moz of silver per annum.”
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