Apr 29 2014
A grab sample is a sample taken from a rock outcrop that is being assessed for the presence of valuable elements. While taking the grab sample, the best looking rock deposit is chosen. The grab sample cannot be taken as a representation of the deposit.
Several types of samples are taken during the mining process - such as grab samples and blast hole samples - and are weighed, according to the tons of the material produced from each sampled area, and averaged. A grab sample is taken from every fifth truck carrying material and sent to the waste dumps. A composite from these samples is made at a 2.5 hour period. The results of these samples are compared with the blast hole samples taken from the same area. Grab sampling takes equal amounts of ore at selected intervals from a mine dump or muck pile. This method is not usually considered a reliable one.
Other mining sampling methods are bulk sampling, channel sampling, and chip sampling. The results of all these methods are combined in order to determine the grade of the ore body. Grab sampling is often a double check on the chip or channel sampling methods.
Apart from ore sampling, grab sampling may also be extended to the air sampling that is done as part of the mine safety measures. A short grab of air is analyzed for the presence of contaminants. This method of sampling is usually applied to indoor air quality evaluations, contaminant analysis, and post-accident clearance sampling.
Sources and Further Reading