Mineral district
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
A term occasionally used in acts of congress, designating in a general way those portions or regions of the country where valuable minerals are mostly found, or where the business of mining is chiefly carried on, but carrying no very precise meaning and not a known term of the law.
See U. S. v. Smith (C. O.) 11 Fed. 490.