Crushing & Grinding

The objective of milling gold ores is to extract the gold for the highest financial return. To accomplish this, the ore must be finely ground in order to liberate gold particles.

Each ore has its own gold-liberation characteristics, and wide variables in comminution properties may occur within large gold deposits. Tests and feasibility studies have to define the optimum milling circuit that can deliver adequate mill feed at all times. For the grinding and crushing circuit at Goldstrike, Barrick relies on primary grinding in semi-autogenous grinding (SAG) mills, followed by fine grinding in ball mills.

An autogenous mill is, by definition, a mill that employs coarse ore as the grinding medium while it is itself being ground. In pracice, autogenous grinding has to be changed to semi-autogenous grinding, since lack of adequately hard ore necessitates the addition of large steel balls to maintain the required grinding rate.

Ball mills (as seen above left and below) accomplish the step of fine grinding. Ball mills are high-throughput, closed-circuit grinders with steel balls as the grinding medium. They always operate in closed circuit with classifiers and/or cyclones. All tumbling mills are internally lined; these mill liners, in addition to protecting the mill shell from weark, reduce the slip between the shell and grinding media, and have a significant effect on operating costs.

After crushing and grinding, the slurry proceeds to acidulation.