Aurora rates overall recovery ‘extremely high and effective’
CYANIDE leaching and gravity recovery are the two methods of gold recovery used by Aurora Gold Mine (AGM), which affords it an overall recovery rate of 97%.This is according to Mill Manager Mike Papadakis, who explained that before the recovery of gold can take place, the company is required to crush rocks down “to a certain size”, then place them into the SAG Mill, where steel balls cascade the rocks and grind them so that they look like sugar or even flour when that process is completed.
“Once we grind the rocks down, we have two methods to recover the gold, one is gravity recovery…” Papadakis said last week during a media tour of the facility.
Gravity recovery from grinding circuits is quite common in many operations globally. Effective gravity concentration effort is a function of numerous factors, including the quantity and size of distribution of the Gravity-Recoverable-Gold (GRG) present, downstream processes and water balance, among other things.
“Gold is much heavier than the other minerals, and what we have is a machine that spins extremely fast; like a washing machine on spin cycle,” Papadakis said, adding: “Gold is heavy; it sticks to the side, and the other minerals pass through. We are able to capture the gold that way.”
The second method used to recover gold at Aurora is the cyanide method. Cyanide is added to the large tanks located at the SAG Mill to dissolve the gold. Once dissolved, the company uses activated carbon, a coconut shell about the size of rice crispy. “So we put the three into the tank and we hold the carbon back, and it lets the ground rock pass through,” Papadakis said.
“What happens, is the cyanide molecules stick to the side of the carbon; and we are able to recover the carbon and we are able to reverse that process, and the gold and cyanide molecules unstick and we create a high grade solution which we then send to our refinery,” he added. Papadakis explained that in the refinery, electro-winning is done. Electrowinning, also called electro-extraction, is the electro-deposition of metals from their ores that have been placed in solution via leaching.
“The main difference,” he said, “is that instead of plating a gold sheet, we plate like a gold sludge. We are able to wash that sludge off, we dry it, melt it and we produce… And that’s what we sell on the market.”
Asked which of the two methods has the best recovery rate, Papadakis said gravity recovery will recover approximately 20-30% of gold, but “that recovery is typically governed by the size of the gold. If we get big nuggets of gold, we are going to recover more; if it is extremely fine grain, it is not as effective.”
The Mill Manager said that cyanide leaching is “extremely effective”, with 90-95% gold recovery. The overall recovery of the plant is 97%, “which is extremely high and effective.”
CYANIDE DESTRUCTION
Cyanide leaching, has over the years become quite controversial, as it opens mining pits while releasing many potentially dangerous toxins. Cyanide can have a profound impact on the environment, health and wildlife, but according to Papadakis, Aurora is environmentally conscious and disposes of cyanide in a safe manner.
“We have a process called detoxification; cyanide destruction. We add two chemicals: Sodium metabisulfite and copper sulfate, and we are able to destroy the cyanide down to a very, very low level; we do cyanide destruction,” Papadakis said.
ON TIME AND ON BUDGET
Aurora held its first gold pour at its Cuyuni-Mazaruni location last Tuesday, and the company’s Chief Executive Officer and President of Guyana Gold Fields, Scott Caldwell said the mine was constructed with approximately US$250M. He also said that the project has been completed “on time, and on budget.”
Once fully operational, the plant is expected to produce up to 15,000 ounces of gold monthly, with total gold production estimated at 3.29M ounces in 17 years.
But while the company has touted a 17-year lifespan, Caldwell announced that the lifespan could be increased to 35 years. “It’s going to be around a long, long time, generating some good things for the country,” Caldwell said.
He boasted of the company’s environmental and health consciousness, noting that since work commenced in 1996, it has not lost any of its employees.
Meanwhile, Executive Chairman, Patrick Sheridan said he is extremely proud of the achievement of the company, credit for which goes to the hard-working employees.
“These jobs are going to support a family, pay a mortgage, and develop one’s skills. It is perhaps this legacy that is most important,” he stressed.
Construction of the Aurora mining camp began in 2013, with local and international contractors working together. The company said that a large Peruvian workforce was instrumental in the construction process. Some 1,200 temporary workers were part of the construction process, with 400 expatriates, 700 Guyanese and 100 local contractors.
Guyana Goldfields Inc. is a Canada-based mineral exploration company, primarily focused on the exploration and development of gold deposits in Guyana. The projected Corporate Income Tax is US$509M, Projected Payroll Taxes stand at US$67M and projected Excise Tax is US$43M.
