The first step in minerals beneficiation of an ore is normally crushing which has been defined “as the operations required to reduce run-of-mine ore to grinding feed size”. It would therefore follow that the first metallurgical testing should be conducted on run-of-mine ore but, due to its size, this would be rather impractical. However, there is little need to test large rocks because smaller competent rocks upon examination and under test conditions can show similar characteristics. Good relationships between rock sizes, tonnage rate and equipment sizes have been established in the industry.

Crushing tables supplied by the manufacturer normally can be used directly to size crushing equipment for a given flowsheet. However, if the ore contains a large percentage of primary fines, wet sticky clay or is extremely competent, it may be prudent to conduct crushing tests in the pilot plant on representative samples of the material. These tests will identify crusher power requirements or unusual screen surface area for the ore in question.

It is seldom necessary for the owners of a new mine to invest large sums of money in sophisticated laboratory crushing facilities for the limited number of tests which may be required to prove the crushing characteristics of the ore. All of the major equipment manufacturers have research facilities for determining crushing requirements, their personnel have experience and they welcome the opportunity to work on new ores. They can do crushability tests to determine the work index of the ore and the amount of work required as well as the compressive strength to determine the necessary strength in the crusher. However, the ore dressing research staff must be able to evaluate the results from the crusher manufacturer because, in many instances, they have the final responsibility for flowsheet design and development.

Nevertheless, at least one small jaw crusher and a small cone crusher should be considered standard laboratory equipment for ongoing operations. The jaw crusher procedure should be standardized and may even be calibrated against a “known” ore to compare breaking characteristics.

Following crushing in the laboratory, test sample lots should be riffled, preweighed and the weight adjusted to obtain standard sample lots. One of these lots should be set aside for a comprehensive physical analysis followed by a chemical analysis possibly after the initial grinding test. One should crush no more of an ore than can be satisfactorily tested on the bench scale within one month – particularly when treating high sulphide ores.