TY  - RPRT
TI  - Comments on the "three-step" method for quantification of undiscovered mineral resources
AU  - M.W. Bultman
AU  - E. R. Force
AU  - M. E. Gettings
AU  - F. S. Fisher
PY  - 1993
DO  - 10.3133/ofr9323
UR  - https://pubs.usgs.gov/publication/ofr9323
ID  - ofr9323
ER  -