Geoscience Reference
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where d is the hole radius, length is the sample interval
length, and δ is the density of the material. This slows down 
the drilling process and may be difficult or cumbersome;
however, it is a recommended quality control step.
The actual weight of the sample should be reasonably
close (within 10-15 %) of its theoretical weight. There may
have been sample loss or additions (from cave-ins or down
the hole contamination) that may affect the final sample
weights. In the case of diamond drill core, measuring the
length of the piece(s) recovered allows a % recovery value
to be assigned to each sample. Systematically low recoveries
are generally a cause for concern. It is important to analyze
the relationship between core recovery and grades since bet-
ter grades may occur in intervals with less recovery, such as
fractured rock.
5.1.6
Sample Collection and Preparation
Procedures
Sample collection methods depend on the drill rig used.
Generally, automatic samplers such as the one shown in
Fig. 5.3 are preferred for cuttings since they allow for a more
systematic splitting of the material recovered from the drill
hole. Particular attention should be paid to the potential loss
of fines since they often are high grade material.
A portion of the sampled material should be kept for his-
toric records and future re-checking. Diamond drill cores are
usually split in half with one half being used for preparation
and assaying and the other half stored as a historic record of
the drill hole. The preparation of the sample prior to assay-
ing is a series of size reduction and splitting steps until a fine
powder is obtained for assaying.
Fig. 5.3 AusDrill Blast Hole Sampling System. Courtesy of AusDrill
Ltd
lithology, alteration type and intensity, presence of fractures,
identified minerals, and other relevant comments are regis-
tered, and eventually entered into a computer database.
The geologic information is used to better understand and
predict the mineralization of interest. There are several refer-
ences that describe procedures to map geologic information,
such as the already mentioned Peters ( 1978 ). The geologic
information gathered from drill hole is as important as the
sample grades obtained.
5.1.7
Geologic Mapping and Logging
Procedures
It is important to describe the geologic characteristics of
the rocks at different scales. This is done by geologists in
the field or in the core shack and requires knowledge of the
rock formations, mineralization and alteration types of the
deposit. These observations are made visually with the help
of a hand-lens. There is always a degree of subjectivity in
the geologic descriptions depending on the experience of
the geologists and knowledge of the local geology. A ma-
ture deposit with a large number of drill holes will probably
have well-established procedures for identifying geologic
attributes.
Figure 5.4 shows an example of a logging sheet taken
from one of the early exploration holes of the Escondida
Cu porphyry project, owned at the time by Minera Utah de
Chile, Inc. For each mapped interval, information such as
5.1.8
Sample Preparation and Assaying
Procedures
Sampling heterogeneous materials will incur some error, re-
gardless of the care and technique used to obtain the sample.
It is important to understand the possible impact of these
sampling errors on a resource estimate. Sampling errors are
also related to the distribution of the variable being sampled,
which in some cases is particularly difficult, see Rombouts
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