By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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Gunnison County, in west-central Colorado west of the Continental Divide, produced about 130,000 ounces of gold through 1959. Although the first ore discoveries were placer deposits, most of the gold produced in the county has been a byproduct of silver-lead ore.
Ore was first discovered in 1861 when placer gold was discovered simultaneously along Taylor River in the Tincup district and in Washington Gulch in the northern part of Gunnison County (Henderson, 1926, p. 44, 124). By 1867 placer deposits had been discovered along other gulches. Lode deposits also were known, but little work was done on them until 1872 when silver-bearing rock was discovered in the Elk Mountains. In 1878 discoveries were made in the Gold Brick-Quartz Creek district (Henderson, 1926, p. 125), and the years 1879 and 1880 saw the first rush of miners to southeastern Gunnison County.
Several towns, including Ohio City and Pitkin, were founded between 1878 and 1882. In the fall of 1881 the Denver and Rio Grande Railroad was completed to Gunnison and later to Crested Butte. During the next 4 to 5 years, ore was discovered over a wide area, and several smelters and concentrating mills were built. The most productive years for gold mining were between 1908 and 1913. The period 1934 through 1942 was one of increased activity, but from 1943 through 1959 most of the mines were closed.
The Gold Brick-Quartz Creek district has been the leading gold producer of the county, and the Tincup district is the only other district that has yielded more than 10,000 ounces.
GOLD BRICK-QUARTZ CREEK DISTRICT
The Gold Brick-Quartz Creek district, which includes Box Canyon, is in southeast Gunnison County, 1 to 4 miles north and northeast of Pitkin. Much of the gold mined in this district was a byproduct of lead-silver ores.
After the discovery in 1879 of a boulder of rich silver ore at the mouth of Gold Creek, prospectors flocked to the area and staked many claims in 1879 and 1880. The town of Ohio City was founded in 1881, and the following year the Denver, South Park, and Pacific Railroad reached the new town. Though few of the early claims were successful, lucrative deposits of lead and silver were found later, especially in the 1880's and early 1890's. By 1893 most of the shallow ore bodies were worked out and the price of silver fell at this time; consequently, there was little incentive to keep the mines open (Crawford and Worcester, 1916, p. 12-13).
The district remained virtually deserted until 1934 when the increased price of gold stimulated activity, resulting in considerable gold production from 1934 through 1942. From 1943 through 1959 the district was again dormant.
Early records, though incomplete (Crawford and Worcester, 1916, p. 92-111), indicate that the district produced at least 80,000 ounces of gold through 1959.
The following summary of the geology and ore deposits of the district has been compiled from the reports by Crawford and Worcester (1916) and Dings and Robinson (1957).
The bedrock of the Gold Brick-Quartz Creek district consists of gneiss, schist, and granite of Pre-cambrian age, sedimentary rocks of Paleozoic age, and intrusive rocks of Tertiary age. The Paleozoic rocks range in age from Cambrian to Pennsylvanian. The Tertiary rocks are chiefly intrusive sheets and dikes and range from rhyolite to andesite and diorite porphyry (Crawford and Worcester, 1916, p. 22-68).
The ore deposits are chiefly fissure veins in the Precambrian rocks. Replacement deposits occur in some of the Paleozoic limestone and dolomite, but very little is known about them (Dings and Robinson, 1957, p. 63) and the amount of gold derived from them probably has been very small. The greatest values in the veins have been in silver, gold, and lead, and the lesser values, in copper and zinc. A few veins contain molybdenum and tungsten. Gold and silver vary in relative abundance.
The bulk of the ore produced was limonitic quartz, and only a few mines produced sulfide ore; most mines have not reached a depth below the zone of at least partial oxidation, which extends to a depth of about 1,300 feet. Sulfide minerals found include galena, sphalerite, pyrite, chalcopyrite, arsenopyrite, tetrahedrite, argentite, and ruby silver in a gangue of quartz and local barite. Huebnerite and molybdenite are found in some veins (Crawford and Worcester, 1916, p. 82-83; Dings and Robinson, 1957, p. 62-63).
TINCUP DISTRICT
In the Tincup district in northeastern Gunnison County, about 25 miles northeast of Gunnison, gold has been obtained mainly as a byproduct of silver-lead ores, although a considerable amount has come from placers. Most of the mines are at the head of Willow Creek on the southeast side of Taylor Park.
One of the first reported gold discoveries in the county was in 1861 when a man named Taylor, searching for strayed horses, found good color in what became known as Tincup Gulch. During the next 18 years there was sporadic placer mining in Tincup Gulch. In 1879 the lode source of the placer gold was found, and soon miners streamed into the area. The town of Tincup had a population of nearly 4,000 by the end of 1880. The boom lasted until the price of silver dropped in 1893.
A second period of prosperity began in 1904, which attracted about 2,000 people to the district. This was short lived, and by 1912 the mines were again inactive (God-dard, 1936, p. 552-554). From 1912 through 1959 the district was virtually idle; even the increased price of gold in 1934 did not renew activity.
Total gold production of the district through 1959 was about 16,400 ounces, most of which was produced before 1932.
The rocks exposed in the Tincup district are of three ages: schist and granite gneiss of Precambrian age, sedimentary rocks about 1,000 feet thick of Paleozoic age, and intrusive rocks of Tertiary age. The Paleozoic rocks are chiefly limestone, with some shale and quartzite, and range in age from Cambrian to Pennsylvanian. The Tertiary rocks consist of quartz monzonite porphyry and hornblende diorite porphyry which form dikes, sills, and a stock.
The rocks were folded into a north-trending monocline that dips to the east. Along the east side of the district, the sedimentary rocks are in contact with the Precambrian schist along the Tincup thrust fault that trends about N. 25° W. Another strong thrust of the same trend appears in the southwest part of the district. Numerous small high-angle faults, younger than the thrusts, cut the rocks (Goddard, 1936, p. 557-565).
The most productive ore deposits have been silver-lead-gold blanket deposits and silver-lead-gold veins. Of slight importance are molybdenum-tungsten veins and iron blanket deposits. The metals produced, in the order of their value, are silver, lead, gold, and small amounts of copper. The blanket deposits have been the most productive. These occur at the contacts between limestone and dolomite near intersections with steeply dipping faults or fractures.
The chief primary ore minerals are silver-bearing galena and pyrite and small amounts of chalcopyrite and sphalerite. The gold is probably associated with the pyrite. The chief gangue minerals are quartz and calcite. All the ore of the blanket deposits is at least partly oxidized, and much of the ore consists of cerussite and anglesite, usually associated with some galena, in a limonitic and siliceous gangue. Oxidation of the ore bodies extends to a depth of more than 500 feet.
The vein deposits, which cut the Precambrian granite gneiss and the sedimentary rocks, range from 1 to 6 feet in width and from 600 to 1,000 feet in length. The minerals and character of the ore are similar to those in the blanket deposits (Goddard, 1936, p. 565-569).
