Mining Symposium Duluth, Minn, University of Minnesota, Duluth Branch, American Institute of Mining and Metallurgical Engineers. Minnesota Section, Pfleider, E. P., & Berger, F. E. (1964). Twenty-eighth annual mining symposium and the Fortieth annual meeting of the Minnesota Section, AIME, January 16-18, 1967, Duluth, Minnesota. University of Minnesota.

Mining Symposium Duluth, Minn, Duluth Branch University of Minnesota, American Institute of Mining and Metallurgical Engineers. Minnesota Section, Eugene P. Pfleider, và Frederick E. Berger. Twenty-eighth Annual Mining Symposium and the Fortieth Annual Meeting of the Minnesota Section, AIME, January 16-18, 1967, Duluth, Minnesota. Minneapolis: University of Minnesota, 1964.

Mining Symposium Duluth, Minn, et al. Twenty-eighth Annual Mining Symposium and the Fortieth Annual Meeting of the Minnesota Section, AIME, January 16-18, 1967, Duluth, Minnesota. University of Minnesota, 1964.