The Correia Mining Company (CMC) has become one of the first local gold mining companies to adopt mercury-free technology to recover gold and others are being urged to do the same as the shaking tables are being hailed as economically viable and environmentally friendly.
“This is not a demonstration. We are actually now using it in the system and what is most important is that the actual workers of themselves actually like the operation,” said Michael Correia, the company’s owner, at CMC’s Olive Creek mining base on the Middle Mazaruni, Region Seven yesterday.
Minister of Natural Resources and the Environ-ment Robert Persaud, Guyana Geology and Mines Commis-sion (GGMC) head Rickford Vieira, Guyana Gold and Diamond Miners Asso-ciation representatives and GGMC Board members were on hand at the location yesterday to witness the shaking table at work which is said to be the first to be in operation at a commercial level in the country.
Persaud commended the company for leading the way and he noted that the new technology is economically rational, addresses environmental concerns and also comes out of an awareness of what is happening internationally. “Globally…we recognise that the convention will soon be coming in place where you’ll have restriction in the trade of mercury. Access to mercury by our local mining sector will be very difficult and very costly and it is our intention to work with the sector in phasing out the use of mercury and developments such as this will give impetus to that effort,” he said. “We all have to change.”
Mercury is widely used in the gold-mining industry here but concerns have been expressed about how it is employed by miners. The use of mercury, which is toxic to human health and the environment, in gold mining is governed by strict regulations but compliance is another matter.
Mercury is primarily used to create an amalgam with the gold, which is later heated to separate it. In the process of heating, unless a retort is used, the mercury then enters the atmosphere, and precipitates back into the water, from where it enters the ecosystem, and the food chain. A retort is a closed container, which traps and condenses the mercury vapour without releasing it into the atmosphere.
However, some miners use mercury in sluice boxes which eventually leads to the pits being spiked. This system of mercury use is particularly dangerous because it introduces mercury directly into the water system.
Use of the shaking table brings the recovery rate of gold up to 98%, said Charlie De Freitas, the Director of Mining Operations at CMC. According to Vieira, overall recovery rates in the industry are between 36% and 40% and Persaud said that this means that “for every ounce (of gold) that they have mined, two ounces are left back.”
Using the shaking table, it takes about two hours to complete the ‘wash-down’ process of the concentrates obtained after the gold-bearing gravel passes through the sluice box. The water used by the shaking table is recycled.
“So you can get about two times or two and a half times more the amount of gold (obtained) with the current effort,” Persaud said. He added that less land can be utilised without diminishing output. The money being spent on equipment will be reduced while money spent on labour and supplies will remain the same but the operator would be getting two and a half times the amount of gold, he said.
The minister noted that there are also environmental benefits since no mercury is released into the environment and thus, there is no impact on health either. “It makes good money sense, it makes good environmental sense, it makes good health sense,” he said. He expressed hope that other miners would adopt the technology and pointed out that the GGMC will be bringing two shaking tables out of South Africa for demonstrations to miners.
The shaking table used by CMC for its medium-scale mining operation costs US$32,000 but there are smaller, cheaper ones available. Persaud told Stabroek News that tax-free concessions could be obtained on the equipment. De Freitas said that the company chose the model based on the cost, efficiency, operability and the payback period. “This is a viable alternative to mercury,” he said. A generator is used to provide power to the shaking table. “Our table will pay for itself within five years,” De Freitas said but he added that this would also depend on the level of production.
Correia said that the technology requires a little bit of training but the company believes it could be easily implemented. “We believe that it is important that all the people in the mining community, [that] we work with the government to make sure we can do mining in a sustainable way,” he said. He noted that some of the miners would have a problem with the cost, which is approximately $7 million but added that Persaud has some ideas which can assist miners to transition to the technology.
According to Vieira, currently one ounce of mercury is used to produce an ounce of gold. It was noted that a pound of mercury currently costs about $20,000 to $25,000. “The mercury-gold amalgamation system with the mercury is based on the purity of the mercury. When the mercury is used for a period of time, it gets what we call ‘sick’ and is not very effective but the miner don’t know that until he check back his waste, sometimes he see mercury and gold left back. So by having this, you don’t have that problem anymore and the thing with mercury now, after you use it for a period of time, it’s no longer good, most miners either add more or throw that away and get new one, so it’s definitely a benefit in terms of economic, the environment and health,” the GGMC commissioner said.
Correia said that the cost of the recovery equipment is the main reason why miners seem to be reluctant to adopt it. It was noted that the life of a shaking table is about five to eight years but the company is currently only using it for two hours a week.
Persaud suggested that new business opportunities arise out of this technology, saying, for example, that operators could provide processing services to miners for a fee.
