26 U.S. Code § 613 - Percentage depletion | U.S. Code | US ...
The term "mining" includes not merely the extraction of the ores or minerals from the ground but also the treatment processes considered as mining described in paragraph (4) (and the treatment processes necessary or incidental thereto), and so much of the transportation of ores or minerals (whether or not by common carrier) from the point of extraction from the ground to the plants or ...