Genetic model for the Gilman District, based on fluid inclusion, stable isotope, alteration/vein/replacement distribution, and fission-track geochronologic studies
David W. Beaty, C.W. Naeser, C.G. Cunningham, Gary P. Landis, 1988. "Genetic model for the Gilman District, based on fluid inclusion, stable isotope, alteration/vein/replacement distribution, and fission-track geochronologic studies", Geology and Mineralization of the Gilman-Leadville Area, Colorado, T. B. Thompson, David W. Beaty
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A large manto/chimney complex is located at Gilman, Colorado, about 120 km WSW of Denver. The district was discovered in 1879, was consolidated beginning in 1912 by New Jersey Zinc Company as the Eagle mine, and was closed in 1984. Cumulative production of all ore types has been about 11.7 million metric tons with an average grade of 8.5% Zn, 1.5% Pb, 0.7% Cu, 228 gpt (grams per metric ton) Ag, and 1.7 gpt Au (Beaty et al., 1989).
At Gilman, a sequence of Cambrian through Mississippian sedimentary rocks (total stratigraphic thickness-200 m) dip homoclinally eastward at 12-15°. These sedimentary rocks unconformably overlie Precambrian basement (predominantly the Cross Creek batholith), and are in turn overlain by 3000+ m of coarse elastics of the Pennsylvanian Minturn Formation. The sedimentary rocks in the Gilman area are intruded by one exposed igneous mass, the Pando Porphyry, which forms a sill 12–27 m thick in the Belden shale. The Pando Porphyry is a fine-grained quartz latite which crystallized at about 72 Ma (data of Pearson et al., 1962 recalculated by Beaty et al., 1987).