El Indio’s use of cyanide leach/CIP circuit to scavenge additional gold recovery from flotation plant tailings

Synopsis

Mining and milling of high-grade gold/silver/copper ores at the El Indio mine in Chile commenced in 1981, and continues to be a successful and profitable operation.

Mining of the hydrothermal sub-volcanic quartz and enargite/pyrite veins is performed by open-pit and selective cut-and-fill methods.

The milling plant was constructed based upon initial metallurgical testing of this ore which indicated that the milling process should consist of conventional three-stage crushinq,and crushed product aqueous washing to remove soluble acidic salts, followed by ball-mill grinding and standard flotation to recover about two-thirds of the recoverable gold and silver,ard all the copper minerals. The balance of the recoverable gold and silver would be obtained by treating the flotation tailings by high levels of sodium cyanide, leaching in pachucas, with subsequent extraction of dissolved gold and silver by the carbon-inpulp process.

Soon after the plant start-up it became evident on economic, environmental and metallurgical considerations that almost all the recoverable gold, silver and copper would have to be produced by the flotation circuit with the cyanide leachingC.I.P. plant used only as scavenging operation with low levels of sodium cyanide for additional gold recovery.

This paper shows the metallurgical results which led to the scavenging concept for the leach/C.I.P. plant, the subsequent operational difficulties encountered, how they have been resolved and the improvements in progress.