1) The fuel used in smelting lead.
When wood had the bark taken off and was dried it became more efficient.1658 Payd … for choping and drying wood for smelting … for getting … chopwood into the kill, Grassington
1709 they keep a gang of horses to carry timber for the mines, to bring oares [ore] and chopwood to the mill, Buckden
1763 granteth them Leive to pill & Chop the Bark, Esholt. An article by Arthur Raistrick has useful information on the process, and further examples of the use of chopwood and chop-kiln. See R&J81-2.