The best method in terms of sampling theory is to crush the whole core and then sub sample using a correct method (splitter). However, there is usually a strong push from the geologists to retain half the core as a record of the geology and for other future tests that may be required. Metallurgist in particular will often lay claim to this second half for process testing. Quite frequently half of the remaining half will be sampled as a check assay - but this quarter core sample is only indicative as often different sides of the core can be quite different in terms of composition due to heterogeneity in the geology.

Crushing half-core before pulverizing is usually required - and if the pulverizing equipment cannot accommodate the full lot, then splitting is of the crushed material is required. I would recommend crushing as fine as possible with a jaw crusher than sub sampling with a riffle splitter rather than the cone and quarter method. This latter method is a pretty rough splitting method and prone to bias in sampling.

Cone and quartering is applicable when you have a relatively large amount or coarsely (>30-50 mm) crushed of ore, good homogeneity of mineral of interest in rock, relatively high grade and low importance of segregation. It may work with ferrous metal ores, base metal ores, and should be avoided or used with caution with precious mental ores and some base metal ores.

The best practice is to use splitters. There are different ones to use: types of simple riffle Jones splitter, rotary riffle splitter, spinning splitters, quadrisplittes and so on. They come in various sizes and have different accuracy. Right choice depends on the properties of material you split.

Make sure, you reduce mass on each stage of splitting of the sample according to the size, grade and grain size distribution of mineral of interest. This will allow you to avoid nugget effect and other problems with representativeness. Use Gy’s or Richards-Chechott’s (or Harfeldal’s) formula to find right stages of size and mass reduction.

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