By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Mineral County is in southwestern Colorado near the center of the San Juan Mountains. Mining has been conducted in three general areas in the county, the Creede district, the Spar City district, and the Wagon Wheel Gap fluorspar district, but only the Creede district has had significant production of gold. Ores in the Creede district are valuable chiefly for silver, lead, and zinc, but byproduct gold is important locally. From 1891 through 1959 the district produced about 149,200 ounces of gold.
The Creede and the Cripple Creek districts were the last of the famous mining districts in Colorado to be discovered, and the significant discoveries in both districts were made in 1891. In the 1880's the upper Rio Grande valley was a route of transportation between Wagonwheel Gap and the flourishing mining camps near Silverton and Lake City (Emmons and Larsen, 1923, p. 3-5).
Some of the prospectors traveling this route located promising claims at Sunnyside, about 2 miles west of the present site of Creede, in 1883, and in 1884 a claim was located on the Amethyst or Big vein near Creede. Interest in the area was aroused in 1889 when the Holy Moses vein was discovered on East Willow Creek, and, in 1891, when rich ore was found on the Amethyst vein in the Last Chance, Amethyst, and New York mines. Within a few months, late in 1891 and in 1892, about 10,000 people swarmed into the infant town of Creede (Emmons and Larsen, 1923, p. 4).
In late 1891 the Denver and Rio Grande Railroad was extended from Wagonwheel Gap to Creede, and in 1893 the Creede district had its largest annual production, consisting chiefly of silver but also some lead and gold and having a total value of $4,150,946. Because of the continued drop in the price of silver, production declined sharply in 1894, but there was a fair recovery in 1897, and the district maintained a fairly steady annual output worth about $1 million through 1910. Thereafter production declined and the district was virtually idle between 1930 and 1933.
From 1934 through 1959, annual production of silver, lead, zinc, and gold ranged from less than $300,000 to more than $1 million. Gold production was greatest from 1900 through 1911 when the output was about 92,000 ounces and was valued at $1,899,560 (Emmons and Larsen, 1923, p. 9-10). Total gold production of the district through 1959 was about 149,200 ounces.
The following brief description of the geology of the Creede district has been abstracted from a report by Steven and Ratte (1960a), and the summary of the ore deposits is from a report by Emmons and Larsen (1923).
The bedrock exposed in the Creede district consists of Tertiary volcanic rocks. The ore deposits are localized along faults in a complex graben that extends outward from the Creede caldera, a subcircular subsided mass of volcanic rocks about 10 miles in diameter. Within the caldera, quartz latitic welded tuff at least 6,000 feet thick is exposed. Surrounding the caldera is a mass of volcanic rocks at least 4,000 feet thick which accumulated from several volcanic centers and consists of rhyolitic and quartz latitic welded tuffs, nonwelded pumiceous tuff, and locally interlayered quartz latitic and dacitic lava flows and breccias. Stream and lake sediments and travertine, collectively called the Creede Formation, accumulated along the margin of the caldera.
Known ore deposits of the district occur chiefly as veins along three of the main faults in the graben. A small amount of ore has been mined from disseminated deposits in the basal beds of the Creede Formation where it rests on a highly faulted segment of the caldera margin. The faults in the graben were active many times during caldera subsidence; however, mineralization did not take place until the last main period of movement.
The mines along the Amethyst fault zone produced $55 million worth of metals; all the other veins produced about $2,800,000, and the disseminated deposits in the Creede Formation yielded about $800,000 worth of metals.
The ore deposits in Creede are silver-lead-zinc veins. The unaltered ore is composed mainly of sphalerite, silver-bearing galena, and pyrite in a gangue of amethystine quartz, barite, and chlorite (thuringite). Fluorite, rhodochrosite, chalcopyrite, and native gold are sparingly present. Much of the ore is oxidized, and in some deposits enrichment is pronounced.
Gold as a primary mineral is presumably very finely divided and is probably included in pyrite, galena, sphalerite, and other minerals. The richest gold ore consists of gold in a gangue of manganese oxide in veinlets cutting the older sulfides, and ore with such veinlets may carry as much as 1 or 2 ounces of gold per ton (Emmons and Larsen, 1923, p. 98-103). The gold is not uniformly distributed in the veins; for example, most of the ore mined from the north end of the Amethyst vein contained 0.03 to 0.25 ounce of gold per ton, whereas ore from the south end of the Amethyst lode contained negligible amounts of gold.