Coal Terminology
To assess the coal that remains in the earth, standardized methods have been developed. Depending on the level of confidence in geologic assessment and the economic feasability of mining, coal deposits get categorized differently. The specific thresholds (horizontal distances from measurements, and the 6000 foot depth limit) vary regionally, but these apply in Alaska.
This figure is based off of a figure in McKelvey, 1976. Further information was gleaned from Wood et al., 1983. Both these documents are free, but require the DjVu viewer to read.