By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Although some prospecting was done in Eagle County in the 1860's it was not until 1879, after the great rush in 1877-78 to the Leadville district about 20 miles to the south (Henderson, 1926, p. 41), that rich oxidized silver-lead carbonate ore was discovered on Battle Mountain in the Gilman district. Many claims were located that year, and in 1880 silver valued at $50,000 was produced (Henderson, 1926, p. 47). In the early 1880's prospectors swarmed over the county and opened small silver and gold mines here and there, but most of these early camps were short lived. Only the Gilman district became a major producer. More than 99 percent of the total metal output credited to Eagle County has come from this district.
The Gilman (Battle Mountain, Red Cliff) district, in southeastern Eagle County on the northeast flank of the Sawatch Range, is between Gilman and Red Cliff, about 20 miles north of Leadville. Gold has been extracted from pyritic gold ores and as a byproduct of base-metal ores.
The initial discovery in 1879 of silver-lead ore in limestone was followed in 1884 by finds of gold ore in the underlying quartzite. The relative importance of the metals mined varied periodically in the history of the district. Before 1905 silver and gold were the major commodities, whereas lead and copper were of minor importance. From 1905 to 1930 zinc was the principal product and from 1931 to 1941 silver-copper ore containing considerable gold was mined. Zinc again regained importance from 1942 through 1959. The total gold production of the district through 1959 was roughly 348,000 ounces.
Precambrian granite, schist, and gneissic diorite are exposed in the bottom of Eagle Canyon and are overlain by thin lower Paleozoic formations that include the Sawatch Quartzite of Cambrian age, the Harding Sandstone of Ordovician age, the Chaffee Formation of Devonian age, and the Leadville Limestone of Mississippian age. Overlying these units is a thick section of Pennsylvanian and Permian (?) sedimentary rocks. A sill of Cretaceous or Tertiary quartz latite appears a few feet above the Leadville Limestone throughout the district. The sedimentary rocks dip about 12Â° NE. and are cut by bedding-plane faults and a few weak high-angle faults (Og-den Tweto and T. S. Lovering, in Vanderwilt and others, 1947, p. 379-381).
Ore bodies occur in (1) veins in Precambrian rocks and in the Sawatch Quartzite and (2) in replacement deposits in quartzite and limestone of Devonian and Mississippian age. Most production has come from replacement bodies in the Leadville Limestone and the Dyer Dolomite Member of the Chaffee Formation. The veins in the Precambrian rocks contain pyritic gold and complex sulfide ores in which sphalerite, chalcopyrite, galena, and pyrite are the chief minerals. The pyrite-gold veins are almost entirely of pyrite with a little gold. Most of the veins terminate or become thin at the base of the Sawatch Quartzite, but those that extend into the quartzite contain scattered pockets of gold-silver tel-lurides, chief among which are petzite and hessite.
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