| Reference | {Deposit:: F1 < HEYL, A. V., AGNEW, A. F., LYONS, E. J., AND BEHRE, C. H., JR., 1959, THE GEOLOGY OF THE UPPER MISSISSIPPI VALLEY ZINC-LEAD DISTRICT: U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 309, 310 P.}{Deposit:: F2 < FLINT, A. E., AND BROWN, C. E., 1955, GEOLOGY AND ZINC-LEAD DEPOSITS IN THE DURANGO AREA, DUBUQUE COUNTY, IOWA: U.S. GEOLOGICAL SURVEY MINERAL INVESTIGATIONS FIELD STUDIES MAP MF 33, 1:12,000.} |