GUIDELINES FOR SAMPLE COLLECTING AND
ANALYTICAL METHODS USED IN THE U.S. GEOLOGICAL SURVEY FOR
DETERMINING CHEMICAL COMPOSITION OF COAL
By Vernon E. Swanson and
Claude Huffman, Jr.
U.S. GEOLOGICAL SURVEY CIRCULAR
GUIDELINES ON COLLECTING COAL
Specific instructions on the exact type,
number, and distribution of samples to be collected cannot be
given, but some general guidelines should be followed:
- The judgment of the geologist must be
applied toward obtaining samples which will be most
representative of the coal bed.
- Only samples of fresh or unweathered coal
should be submitted for analysis, preferably collected
from a newly exposed mine face or from a drill core. The
samples should be shipped to the laboratory within a few
days after collection to minimize the effect of oxidation
and exposure to air on the moisture content and on the
forms of sulfur.
- The objective should be to obtain a
complete channel sample or core of the minable bed; if
the coal bed is more than 5 feet (1.5 m) thick, a good
rule-of-thumb is to collect one sample of each 5-foot
(1.5-m) interval of coal (for example, four samples of a
bed 20 ft, or 6 m, thick). Special-type samples
(prominent fusain band or pyrite lens, for example) will
also be analyzed at the discretion of the geologist.
- Generally, 4 to 5 pounds (1.8 to 2.3 kg)
of coal should be included in each sample; for rock
samples, 2 pounds (0.9 kg) is sufficient.
- A satisfactory channel sample, for
example, can be obtained from a coal bed in a mine by
first exposing a new, fresh face of the coal, then
chipping an approximately 3-inch by 3-inch (7.5 cm by 7.5
cm) channel downward from the top of the bed with a
chisel or pick-point hammer, producing coal fragments 2
inches (5 cm) or less across. Positioning a horizontal
plastic sheet below the level of channel cutting is
sometimes helpful, particularly if coal accumulates in
excess of the desired sample size, and
cone-and-quartering separation of the coal is needed to
obtain the representative sample.
- Plastic bags (10 ´ 15 in., or 25.4 ´ 38
cm, or larger; thickness 0.006 in. or 0.15 mm) should be
used for the sample, and care should be taken to avoid
contact of the coal with metal during and after
collecting sample (the use of a geologic hammer, of
course, cannot be avoided); sample number, date of
collection, and key description should be written with a
felt-tipped marker pen (permanent ink) on each bag, and
on a label attached to the tie on the bag.
- A rule-of-thumb should be never to collect
just a single sample from one locality--always collect
two samples, or, if a mine face is several hundred yards
(metres) long, collect three channel samples. The main
reasons for collecting two or three samples are that
short-distance compositional changes can be assessed and
that possible analytical errors can be spotted.
- Core samples of coal are better than
samples of weathered coal, but contamination by drilling
fluids generally makes trace-element analysis unreliable.
Name and composition of drilling fluids used should
accompany list of core samples submitted for analysis.
- Shale splits, siltstone partings, or bone
coal less than a few inches (5-10 cm) thick generally
should be included in a channel sample if it is probable
that this material will be included in mined coal.
Special samples of these non-coal materials should also
be collected, based on the judgment of the geologist, to
determine their possible contribution to abnormal element
- If project objectives include the
obtaining of knowledge of coal shipped or of plant feed,
extra care should be taken to collect at least two
representative raw coal, cleaned coal, blend-pile, and
conveyor-belt samples. Such sample sets should include,
where possible, representative samples of the
sink-fraction of washed coal, and of furnace-bottom ash
and fly ash from precipitator and scrubber units.
- Where geochemical data on seatrock or
underclay and overburden rock are desired, representative
samples should be collected, according to the preceding
guidelines. In collecting overburden samples, one of two
methods may be preferable, depending on local conditions:
(a) Channel samples of 5- or 10-foot (1.5- or 3-m)
intervals; or (b) two samples of each lithology, which
can be related to measured sections and assigned weighted
- If permission to sample is obtained from a
company, the offer should be made, and the promise kept,
to provide the company with a copy of the analytical
results as soon as they are completed; where possible,
obtain available analytical data from the company for
comparison with your analyses. It should be made clear to
the company or landowner that the analyses of your
samples will be part of the public record; the collection
of samples which requires a promise to withhold analyses
on a "company confidential" basis should be
done only for compelling scientific purposes.
Created by the EERT WWW Staff.
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