Las Lagunas Gold Tailings is a retreatment project involving the reprocessing of previously unrecovered gold and silver refractory tailings from the Pueblo Viejo mine.
The project is situated 100km north-west of Santo Domingo, the capital city of Dominican Republic, in the Caribbean. The project is 100% owned and operated by EnviroGold, which was renamed as Panterra Gold in September 2011.
The project is expected to recover a total 435,675oz of gold and 3.9Moz of silver throughout its 6.5 years of mine life production.
Las Lagunas Gold Tailings project history
The Dominican State called for international tenders in 2001 for the evaluation and development of the 600m long Las Lagunas tailings dam. The public bids were received in October 2003. EnviroGold won the tender in March 2004.
The development agreement was signed in April 2004 to reprocess the sulphide tailings stockpiled at the dam through profit sharing with the government. The prefeasibility study was carried out in 2006, and the complete feasibility study report was prepared in 2007. The development of the Las Lagunas project began in 2009.
In January 2012, a 138kV national grid was connected to the processing plant through the 69kV Piedra Blanca-Hatillo line, which runs over the Las Lagunas project area. The process plant was commissioned in June 2012. As of January 2013, the tailings were being fed to the plant at up to 80% of design capacity.
Probable reserves at the Las Lagunas Gold Tailings project stand at 5.2 million tonne (Mt) graded at 3.67g/t Au and 37.6g/t Ag. As of December 2015, the mine was estimated to contain 3.02Mt of indicated resources, at an average grade of 3.76g/t Au and 38.62g/t Ag.
Production of gold from the Dominican Republic mine
The Las Lagunas project produced its first gold / silver doré in July 2012. It produced 32,342oz in 2014, 37,760oz in 2015 and is expected to produce 46,000oz of Au in 2016. The production cost is anticipated to be $350 per oz Au.
Panterra Gold is currently assessing options with prospective suppliers of arsenopyrite concentrates from countries, including Canada, China and Cuba for the Las Lagunas Gold Tailing phase 2 project. Phase 2 will involve the purchase of approximately 100,000tpa of high-grade arsenopyrite concentrate for processing at Las Lagunas facility.
Mining methods and processing at the Pueblo Viejo mine
State-owned Rosario Dominicana acquired the Pueblo Viejo mine in 1969. The run-of-mine (ROM) ore was extracted from the mine through open-pit operations between 1992 and 1999. The recalcitrant quality and metallurgical ramification of the ore resulted in poor gold recoveries. Poor recoveries and decreased gold prices led to the termination of operations of the Pueblo Viejo mine in July 1999.
In an effort to increase the quality of gold recovered from the Pueblo Viejo mine, the tailings were stockpiled in the Las Lagunas tailings dam. Trial mining was carried out at the Las Lagunas project in August 2011.
The tailings stockpiled at the dam are being processed using Xstrata’s Albion oxidation and carbon-in-leach (CIL) techniques. They are retreated through the Albion oxidation process followed by the standard CIL method to produce high grade gold and silver dore bars.
The Albion oxidation processing plant can treat 800,000tpa of ore. It will produce around 85,000oz of Au equivalent during 6.5 years of mine life. The process involves grinding the ore in to small pieces and oxidising it in a leaching circuit at atmospheric pressure. The output of the Albion circuit is further refined in a cyanide leaching circuit to recover the highly graded gold and silver.
The Albion oxidation plant was supplied by Air Products and Chemicals.
Financing Panterra Gold’s Las Lagunas project
EnviroGold signed an agreement with the Macquarie Bank to procure a $37.5m loan, with a guarantee to repay it within 18 months of commissioning of the Las Lagunas project. It also received a $7.5m advance loan against a 3% gold production royalty for the mine lifespan of 6.5 years. Funding began in October 2010.
The capital cost of the Las Lagunas tailings project is estimated at $82.7m, while the operating cost per tonne stands at $30.68.
Macquarie Bank’s outstanding loan to the Las Lagunas project and two royalty streams were assigned to ALCIP Capital in December 2015.