tommyknockern.

1895 Evening Post (Denver) 26 Aug. 4/4 The legend of Tommy Knocker... This sprite is reputed to put gold and silver in the quartz of the dark prospect holes and is the stanchest friend of the miner.

1901 Salt Lake Tribune 13 Jan. 20/3 We Tommyknockers are what you would call the spirits of departed miners.

1942 Calif. Folklore Q. 1 128 Tales of Tommy Knockers, or Tommy Knackers, as they are properly called, were originally introduced into western mines by the Cornishmen with the development of quartz mining after 1850.

1956 J. Miller Arizona, Grand Canyon State (rev. ed.) i. 164 The belief that mines are inhabited by impish ‘little people’—called kobolds by the Germans, duendes by the Mexicans, and tommyknockers in English.

1992 Western Folklore 51 171 In America, the Tommyknockers became the ghosts of dead miners—an idea less outrageous to American tastes than was the belief in elves.

2010 D. W. Budd Weiser Field Guide Cryptozool. 38 Many miners believed that the Tommyknockers favored them with gifts and good luck.