. "Coal mine means an area of land and all structures, facilities, machinery, tools, equipment, shafts, slopes, tunnels, excavations and other property, real or personal, placed upon, under or above the surface of such land by any person, used in, or to be used in, or resulting from, the work of extracting in such area bituminous coal, lignite or anthracite from its natural deposits in the earth by a" . . . . . . .