There has been a great deal of evaluation and discussion on the economics of semi-autogenous grinding versus conventional grinding circuits.

The Henderson Mill, owned and operated by AMAX, Inc., is located 20 miles southeast of Parshall, Colorado. There are minor amounts of galena, chalocopyrite, sphalerite and about 3% pyrite. The major rock type is potassium feldspar-quartz with a Bond Work Index in a fairly uniform range of 12.0 to 13.0

It has been well established chat the primary mechanisms of grind in a semi-autogenous grinding mill are impact breakage, abrasion, and attrition. A particular grind is primarily achieved by changing the balance between the above mentioned mechanisms. This can be accomplished by changing the ball to ore ratio which is done either by changing the volumetric load for a given ball charge or by changing the ball charge for a given volumetric load. The latter requires a longer term to affect.

In the unique case where the mineral demand has exceeded supply and the SAG mill is operating in a limited capacity or is the bottleneck of the process, it must be determined whether the rate of breakage or the rate of transfer through the mill is the limiting factor. Some of the variables affecting both of the above rates are ball to ore ratio, mill slurry density, grate discharge open area, volumetric filling, liner configuration, liner wear, mill speed and feed size. The breakdown of the effect that each variable has on the rate of breakage and rate of transfer is beyond the scope of this paper, but it can be said that the most efficient SAG mill, under reasonably constant conditions, will occur when the rates are in equilibrium with each other.