Pogo is an underground mine with a vast network of more than 90 miles of underground roads winding to depths more than 1,000 feet below the surface. The quartz veins of the deposit yield an average of ½ troy ounce of gold per ton of rock, which makes Pogo a high-grade gold mine. Ore is drilled, blasted, loaded onto underground haul trucks and delivered to an underground ore bin. From there, the ore is transported along a 2,500-foot-long conveyor belt to the surface ore bin. The mill pulls ore from the surface ore bin for processing.
Pogo’s underground mining method requires mined-out areas to be backfilled with paste to help provide ground support while the adjacent ore panel is mined. Mill tailings mixed with cement (paste backfill) provide part of the necessary support.
The onsite mill processes up to 3,500 tons of ore daily. Gold is recovered using several unit operations.
Once the ore is delivered to the mill, the grinding circuit reduces the ore to a very fine particle size (about half of the size of a grain of table salt). This is the first step in separating the gold from the rest of the rock.
GRAVITY: Approximately 1/4th of the gold is recovered using gravity methods. Imagine a really big sluice box or gold pan.
FLOTATION: The remaining gold and sulfides are concentrated through flotation. The flotation concentrate is then reground to a powder consistency to expose the finer gold particles.
LEACH CIRCUIT: The exposed gold is extracted using chemistry that makes the gold particles go into solution.
CARBON-IN-PULP: The Carbon-in-Pulp (CIP) process pulls the gold in solution out of the slurry and loads it onto small pieces of carbon. The carbon is then stripped of the gold using a combination of reagents, heat and pressure. Following the CIP, the slurry is detoxified and placed underground as paste backfill to fill the void created during mining.
ELECTROWINNING: The gold in solution is electrodeposited as gold sludge by electrowinning. The gold sludge is then smelted in an onsite induction furnace at temperatures above 2000* F and then poured into large gold bars weighing upwards of 50 pounds.
CYANIDE DESTRUCTION: All materials that have come into contact with cyanide undergo the INCO SO2 process (a chemical process) to destroy the cyanide.
Tailings are what is left once the gold has been removed. The Pogo mill produces two types of tailings. Tailings from the flotation circuit are pressed to remove the moisture with the water recycled back into the milling process. The tailings are then trucked to the surface drystack or they are mixed with the thickened leach/CIP circuit tailings. All of the leach/CIP tailings (post cyanide destruction) are mixed with cement and used to make a paste backfill which is returned to the underground workings.