A lode.
1812. Leads (or loads) are the smaller fissures that connect with the larger, which are called by the miners caves.Brackenridge, Views of Louisiana (1814), 148. (N.E.D.)
1817. Although the district of country which contains the present diggings, is considered as comprising the mines, I am of opinion that the lead extends to a very great distance beyond those limits.John Bradbury, Travels, p. 254.