Geology and zinc-lead deposits in the Durango area, Dubuque County, Iowa

Geologic investigations were begun in Iowa to appraise; (1) the possible occurrence of zinc ore in strata that elsewhere in the Upper Mississippi Valley zinc-lead district have been the principal sites of zinc concentration; and (2) lead ore of the type known as "crevice deposits," which were mined so extensively during the 19th century in Dubuque County, Iowa, but have been mined very little since 1910.