The Las Lagunas project is a refractory gold and silver project owned by Panterra Gold Limited. The feed to the project is high grade gold/silver pyritic CIL tailings from prior operation of the Rosario mine in the Dominican Republic. The Las Lagunas tailings dam was constructed in 1991, and was filled with sulphide tailings from open pit operations at the Rosario mine between 1992 and 1999.
Planned production from the project is 65,000 ounces per annum of gold and 600,000 ounces per annum of silver. The project contains significant silver revenue, and the neutral Albion Process™ oxidative leach was chosen for the project, due to the high gold and silver recoveries from the oxidised residue. The process flowsheet was developed by Xstrata Technology with testwork carried out of HRL research facilities in Brisbane in 2004 – 2006.
Construction at the project was completed in the first quarter of 2012, and the project commissioned and operating that year.
The process flowsheet consists of a dredging step to recover 100 tph of tailings from the dam. The dam is also used to re-deposit treated tailings and is mined in cells. Slurry from the dredge is milled to freshen the mineral surfaces prior to flotation. The slurry is then processed through a series 5 x 40m3 of flotation cells to recover a sulphide concentrate grading on average 14 g/t gold and 125 g/t silver, with 16% w/w sulphide sulphur.
The flotation concentrate is produced at a rate of 28 tph. The Albion Process™ plant consists of a M5000 IsaMill™, with an installed power of 1.5MW and a series of five 600 m3 stainless steel Albion Leach Reactors. Each Albion Leach Reactor is fitted with 12 HyperSparge™ supersonic oxygen injection lances, and operates at a pH of 5.5 with continual dosing of limestone slurry. Gold and silver recoveries from the oxidised residue are above 80%.
The oxidative leach plant was sized to oxidise 80 - 85 tonnes per day of sulphide to sulphate. Oxygen is supplied to the Albion Process™ Plant from a 220 tpd VPSA oxygen plant.
Oxidised residue from the Albion Process™ Plant is thickened to approximately 45% w/w and the thickener underflow cooled in a slurry cooling tower to 45°C prior to the cyanide leach.