Sampling
The process of taking a small representative portion of a bigger mass is called sampling. The potential value of the bigger mass has the possibility of being determined by analyzing the sample to determine the the metal concentration that it contains.
Grab samples is the name of the first samples taken from a mineral showing. Geological field crews and prospectors grab samples from the outcrops, river beds, road cuts or trenches. These rocks are specifically selected due to the fact that they appear to contain a significant quantity of metal, so they are not considered to be a representative of the road cut or outcrop which the come from.
Grab samples are gathered from the field, the original location of the samples is recorded, labels are placed on each rock and the ones which appear to be more promising are sent to a laboratory for a metal analysis.
Channel sampling may be warranted if significant or worthwhile quantities of metals are present in such grab samples. In this technique of sampling, the badrock from where the sample was taken is exposed as completely as possible, by using some type of earth-moving equipment, a typical equipment which is used for this is the backhoe.
What is done afterwards is that the outcrop is hosed down with water, if by any chance, an area of mineralization is revealed, representative surface samples are taken at regular intervals across the zone which is exposed. These samples are most of the time cut with a portable circular saw which is equipped with a diamond-studded blade, this leaves a linear channel across the outcrop.
The most desirable kind of sample is the surface channel. Most of the time it is cut about 4 inches (10cm) wide and ¾ inch (2 cm) deep across the predicted ore area. The chips of rock removed from it are carefully collected, marked and bagged for further analysis.
The samples of chips are at times taken by the engineer or geologist for a quick approximation of the contained value. A hammer and a chisel are what quickly knock off the random pieces out of the outcrop, an effort is made to take representative amounts of those pieces. The samples of chips should not be completely relied on, so they most of the time do not enter final mathematical calculations of possible reserves.
To space surface channels at regular intervals along the mineralized area is extremely desirable but often it is not practical. This makes one mathematical calculation in the interpretation process obvious.
In some circumstances, particularly when sampling kimberlite rock for diamonds, to collect a bulk sample is very useful, this has the possibility of ranging from a couple hundred kilograms to several tonnes in weight. For a bulk sample, it is important for it to be a representative of the area since this material can be used in the future for definitive metallurgical grades and test work.
