Erratic High Values:
The methods used for estimating the values of placer ground rely on the assumption that the value found in a particular sample extends halfway to the next sample. While evaluation of ground having a generally low or fairly uniform average of values can be done using the standard reserve estimation methods, erratic high value samples in a deposit cause problems. Methods for adjusting erratic high values, so an over evaluation of the ground does not occur, include: (1) resampling erratic areas, (2) using the lower value determined, (3) determining what the highest reasonable value should be, and then keeping all sample values within that limit.
Uncased Holes:
The methods used for estimating the values of placer ground rely on the assumption that the value found in a particular sample extends halfway to the next sample. While evaluation of ground having a generally low or fairly uniform average of values can be done using the standard reserve estimation methods, erratic high value samples in a deposit cause problems. Methods for adjusting erratic high values, so an over evaluation of the ground does not occur, include: (1) resampling erratic areas, (2) using the lower value determined, (3) determining what the highest reasonable value should be, and then keeping all sample values within that limit.
Uncased Holes:
The use of uncased drill holes should be discouraged in placer sampling, especially in sampling ground with a high unit value mineral. If uncased holes are used, there is a tendency to unintentionally salt the sample and get overvalued sample results. This problem arises due to the fact that without casing, an excess of material can get into a sample without the evaluator knowing where, within the hole, the material came from. An exception to always casing drill holes is when drilling frozen ground. If the ground being sampled is well frozen, casing is usually not used.
Small Diameter Holes:
Due to the large "nugget effect" associated with sampling ground containing high unit value minerals, the use of small diameter drill holes is not recommended for sampling deposits for gold, platinum, etc. When sampling deposits that have fine-grained material and contain low unit value minerals, small [50 mm (2-in.) diameter] holes may be used.
Small Diameter Holes:
Due to the large "nugget effect" associated with sampling ground containing high unit value minerals, the use of small diameter drill holes is not recommended for sampling deposits for gold, platinum, etc. When sampling deposits that have fine-grained material and contain low unit value minerals, small [50 mm (2-in.) diameter] holes may be used.
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