Building Sound Mining Processes

The San Francisco Mine, located 150km north of Hermosillo, is owned and operated by Timmins Gold. The property comprises two open pit mines, though only the San Francisco pit is currently in commercial production, with a rate of between 90,000 and 100,000 tonnes per year and an average ore deposit grade of 0.7 g/t. The La Chicharra pit will begin production at the end of 2013.

The production process starts with the unloading of the material from the trucks, which is then taken to the two grinding systems. After being ground, both bulk materials are mixed together and transported to the lixiviation yard to be processed with cyanide. This process takes around 90 days, acquiring a recovery rate of between 62% and 70% of the mineral in question. When the pad has been irrigated it is then percolated, leaving a liquid solution full of gold. The gold contained in the liquid is fed into two ADR plants in order to be absorbed through activated carbon. The gold-loaded carbon is then isolated in a separate cyanide and caustic soda solution and, after the remnant enters the electrowinning stage, the mineral is refined through electrodeposition. Once the process is complete the gold is then deposited in the form of powder in electrolytic cell cathodes. The powder is left to stand and is later washed, then collected inside an oven, where it is smelted. “I believe Timmins Gold decided this was a good deposit for investment based on production costs,” says Rául Herrera, General Manager of the San Francisco Mine. “Despite high fluctuations in the price of gold the mine has great potential, due to the simplicity of its processes. As a solid operation, in terms of cost management, that helps us to overcome market downturns.”

The mining operation has a high level of automation, with new technologies facilitating the optimization of the design and planning processes, as well as reserve calculations. “This technological advantage has helped us to predict how the pit should be developed, and the zones from which we will be entering the mineralized areas,” Herrera explains. “The network operation center (NOC) for our grinding processes has highly technological systems to control different variables on each piece of equipment. With these systems we know, for example, each machine’s amperage, among other measures, and this allows us to maintain optimal control over the whole mining operation. All data is deployed smartly to operators and supervisors, who require it to evaluate and optimize operations and to be aware of which machines need preventive maintenance.”

Protecting the environment is essential in the operations being carried out at the San Francisco Mine. Water use is an important issue, and is handled efficiently to reduce consumption. Another relevant matter is the use of cyanide. “We put all of our efforts into ensuring that even the slightest superficial discharge does not come into contact with the soil. Our intention is to acquire certification for cyanide use, though in reality it is just a formality because we already comply with all of the standards. Timmins is very committed to protecting the environment,” explains Herrera.