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.