As discussed in “Autogenous and Semi-Autogenous Mill Selection and Design“, and as demonstrated in other papers presented on this subject, extensive pilot plant testing is generally required to select primary autogenous or partial autogenous circuits because of the magnitude of the problems involved when these circuits are applied to ores not suited to autogenous or partial autogenous grinding.
The size of the property, grade of the ore, and all of the factors associated with these, the time available for testing, cost of obtaining samples and cost of test work, all have a bearing on the extent of test work to be done. After completing metallurgical tests, composite samples made up from drill cores can be used for laboratory Bond Grindability tests needed to select rod mills and ball mills. While not the best approach , primary and cone crushers can be selected by visual observations of the drill cores and using catalog data. Small bulk samples containing ore of pebble size are required to test secondary autogenous (pebble) milling. Bulk samples containing ore in the minus 200mm + 100mm ore are needed for primary autogenous media competency tests. Should pilot plant testing be needed, then bulk samples of from 50 to several hundred tonnes representing the major ore types in the deposit would be required. For primary autogenous and semi-autogenous milling pilot plant testing, a year or more can be required to mine the samples and perform the tests even longer if environmental impact statements are needed to obtain the samples.
Even if it is determined by pilot plant testing that an ore would be a natural for autogenous or partial autogenous grinding, the cost in time and money in some cases could exceed the savings in capital cost by using autogenous grinding.