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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 735
1976


GUIDELINES ON COLLECTING COAL SAMPLES

Specific instructions on the exact type, number, and distribution of samples to be collected cannot be given, but some general guidelines should be followed:

  1. The judgment of the geologist must be applied toward obtaining samples which will be most representative of the coal bed.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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 concentrations.
  10. 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.
  11. 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 values.
  12. 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.
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