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Reconnaissance Sampling of Decomposed Monzonite for Gold Near Flat, Alaska.
The Bureau of Mines in 1967 started an experimental reconnaissance sampling program to find methods for delineating and evaluating lode- gold deposits known to be the sources of stream placer deposits near Flat in the Iditarod Mining District, Alaska. Flat is midway between the Yukon and Kuskokwim Rivers on the northwest flank of the Kuskokwim Mountains. The Iditarod District yielded 1,329,404 fine ounces of placer gold from 1910 to 1966, more than 6 percent of the total placer gold produced in Alaska. The source of almost all the placer gold produced in the Iditarod District is lodes associated with two small bodies of decomposed monzonite, probably Tertiary in age, that have intruded upper Cretaceous sedimentary rocks. Initial work included surface mapping and sampling the monzonites and adjacent rocks. Four hundred fifty samples, taken with a tractor- mounted 4-inch power auger, were supplemented by 149 channel and grab samples and 72 specimens selected for petrographic analyses. Results of the preliminary reconnaissance indicate that the gold is not generally disseminated through the monzonites, but occurs in limited zones. Therefore, current work is directed toward finding methods for delineating such zones and determining the approximate grade.
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division