Sampling errors arise both in the initial sample taking (the owner) and by reducing this bulk to a small representative sub-sample (the laboratory analyst) for analysis.

The taking of the original sample is usually not under the analyst’s control, but taking of a representative sub-sample certainly is, and it is important not to introduce unnecessary errors at this point.

In many geological samples and other materials, certain elements (eg P; Cr; Sn or Au) may be present in only a single mineral grain within the sample. For example, if a sample contains 0.10% P₂O₅ which is present entirely as the mineral apatite Ca₃(PO₄)₂, then the total amount of Ca₃(PO₄)₂ in the sample is only 0.22%. So it is important that the sampling technique does not result in loss of this mineral. In general the finer the particle size of the sample the smaller the sampling errors will be for a given mass of sub-sample and given component concentration.

One of the many capabilities of the company laboratory is to provide on-site sample preparation by means of a mobile unit. The mobile unit has been fitted with a range of equipment, including a drying oven, jaw crusher, vibratory feed rotary splitters, sieves for sample sizing, and a vibratory mill. This combination of equipment allows for the processing of samples from borehole drillings or rocks through to the final 50-100g analytical sample that will be routed to either ACT-UIS Laboratórios de Moçambique, Lda. or to UIS Analytical Services (Pty) Ltd in South Africa.

The mobile unit has been fitted with a LM2 mill, originating from Labtech Essa, Australia. This mill differs from traditional mills because of its ability to be fitted with a range of grinding bowls, ranging from 800cc to 2000cc. The useable capacity of each bowl will generally be 60 to 80% of its nominal capacity, allowing the mobile unit flexibility to accommodate different amounts of sample. The LM2 mill will be used for bulk pulverising of ores, minerals and metallurgical samples. Typically samples can be ground to 95% minus 75 micron in approximately 3 minutes depending upon their mass and physical characteristics.