Tunnel driving methods used at the Ojuela unit of the Compania Minera de Penoles, S.A., Ojuela, Durango, Mexico

Author:	Savage, John P.
Year:	1931
Document Type:	USBI
Issuing Agency:	Dept. of Commerce, U.S. Bureau of Mines,
SUDOC:	C 22.11:6480
Series:	Information circular / Bureau of Mines ;
Report Number:	6480
Subject:	Tunneling--Mexico
Links:	https://hdl.handle.net/2027/txu.059173001324239
	https://hdl.handle.net/2027/mdp.39015077576687