The Veladero Mine
Argentine mining production is concentrated in the Andean region, along the 4,500-kilometer border it shares with Chile. Argentina is positioned to become a major mining force in South America. The last couple of years have witnessed a remarkable increase in the production of gold, copper and other minerals.
The Veladero mine is located in San Juan Province, Argentina, approximately 320 kilometers northwest of the city of San Juan in the highly prospective Frontera District.
The mine commenced operation during the final months of 2005. In 2006, its first full year of production, Veladero produced 511,000 ounces of gold at total cash costs of $168 per ounce. For 2007, the mine is forecast to produce 550,000-575,000 ounces at total cash costs of $350-$365 per ounce.
San Juan province is part of the continental semi-desert. Conditions can be harsh, including -25°C weather during winter months and high winds year round.
The mine is located at elevations of between 4,000 and 4,850 meters above sea level, and comprises two open pits − Filo Federico to the north and Amable to the south.
Gold and Silver Recovery Methods
Gold typically occurs at very low concentrations in rocks – less than 10 grams per ton. At these concentrations, the use of water-based chemical extraction processes is the only economically viable method of extracting gold from ore. Modern mills can recover up to 98% of the gold in ore, using a 0.05% solution of sodium cyanide. Cyanidation remains the most efficient and cost-effective means of dissolving gold from ore.
 |
|
| Haul trucks are loaded with ore at Veladero. |
|
The conventional agitated cyanide leach process consists of grinding ore to less than 0.1mm in size, then adding water to form a slurry of ore and dilute cyanide. Lime is also added to ensure a pH high enough to keep the cyanide dissolved. The slurry is agitated in a series of mixing tanks for several hours to several days, and the cyanide causes the gold to dissolve into solution.
A cost-efficient method for recovering gold from low grade ores is “heap leaching.” This method allows processing of much coarser ore and eliminates the need for agitated tank processes, thus reducing energy use and cost. This process, which is used at Veladero, requires engineering and construction of a “valley” which is lined with an impermeable material, typically high density polyethylene. Ore is piled or “heaped” in the valley, and then dosed with a dilute cyanide solution. As the cyanide leaches through the heap, it absorbs the gold. The impermeable liner protects the surrounding environment and channels the “pregnant” cyanide solution containing gold and silver to a central point for collection and processing. Beneath the liners are leak detection and collection systems to alert personnel to any leaks and to capture cyanide solution and direct it to a central collection area.
|
 |
|
The crushing facilities at Veladero reduce the ore to less than 32 mm before it is transferred to a heap leach facility. |
At Veladero, the ore is crushed to less than 175 mm in a gyrating crusher, and then further reduced to less than 32 mm by cone crushing. Crushed ore is transferred to a heap leach facility at a rate of approximately 40,000 tonnes per day (t/d). Heap leaching generally requires 60 to 90 days for processing ore.
The method employed for gold and silver recovery from pregnant cyanide solutions is Merrill-Crowe zinc precipitation. This involves filtering the solution to remove particulates. Oxygen is then removed from the solution by vacuum. Ultra-fine zinc powder is then added to the solution with a dry chemical feeder. An electrochemical reaction takes place between the zinc metal and the gold and silver, causing both metals to deposit in solid form onto the surface of the zinc particle. The solution, now free of gold and silver, is recycled back to the heap. The recovered gold and silver is smelted into doré on-site and shipped to an outside refinery for processing into bullion.
Environmental Controls
The heap leach facility and the process plant operate in closed circuit. No excess solution is discharged to the environment. Makeup water is added as required to compensate for losses by evaporation. The heap is engineered with redundant systems to prevent contamination of groundwater and surface waters. An extensive monitoring system is in place to ensure that the quality of water in the nearby Río de las Taguas is maintained.
Cyanide, because of its ability to selectively dissolve gold at very low concentrations, remains the most efficient and cost effective means of recovery gold from ore. Barrick adheres to the principles and standards of practice set out in the International Cyanide Management Code for the Manufacture, Transport and Use of Cyanide in Gold Production. Stringent environmental and employee protection systems are in place at Barrick mines and are part of consent conditions to operate. For more details, click here.
|