Gilpin County Colorado Gold Production
The Central City district is along the southern border of Gilpin County in the vicinity of the towns of Central City and Blackhawk. This district is the northern segment of the rich chain of ore deposits between Central City and Idaho Springs.
Both the mining history and geological setting of Idaho Springs and Central City are so entwined that they are considered an entity and are discussed together in the Clear Creek County section of this report (p. 96).
The production of the Central City district rightfully belongs under the Gilpin County heading. The district is credited with 95 to 99 percent of the $84,114,389 worth of gold mined in the county through 1923 (P. K. Sims, oral commun, 1959). Total gold production through 1959 was about 4,200,000 ounces; all but about 30,000 ounces was from lode mines.
NORTHERN GILPIN DISTRICT
The Northern Gilpin district lies north of North Clear Creek in the central part of the county and extends north to the Boulder County line. The most important mines are just south of Apex and in the vicinity of Gilpin.
Gold was first discovered in the district in June 1859 in Gamble Gulch in the Perigo area, and lodes in both the Dirt and Perigo mines were discovered in 1860 (Bastin and Hill, 1917, p. 68, 197-198). Some of the ore was very rich near the surface, and within a short time 10 or 12 stamp mills were operating (Henderson, 1926, p. 31). However, the rich and easily worked ore was soon exhausted and in 1867 only four or five companies were still operating in the district. After 1868 the camp was almost deserted until 1879 when the Perigo mine again became active and continued activity at least until 1888. The district was revived briefly during the 1930's, but from 1943 through 1959 very little activity was reported.
There was some placer mining near Rollinsville in 1897 (Henderson, 1926, p. 31). Many of the gulches in the district have placer ground, but production was small until 1937-39, when dredging operations along South Boulder Creek recovered 7,724 ounces of gold.
Though the early production is unknown, it was probably small, and the total amount of gold mined in the district through 1959 was probably 35,000 ounces.
The bedrock of the district is a complex of Pre-cambrian rocks, comprising schist of the Idaho Springs Formation and quartz monzonite gneiss, cut by Boulder Creek Granite and by quartz diorite. The Precambrian rocks are intruded by irregular stocks and dikes of quartz monzonite porphyry and dikes of bostonite porphyry of Tertiary age.
The ore deposits are pyritic gold veins in fractures, most of which trend northeast; a few strike west or northwest. The primary ores are in general low grade and contain less than half an ounce of gold and 1 ounce or less of silver to the ton, but some veins have higher grade ore in the supergene-enriched upper parts. Many of the deposits are discontinuous lodes along shear zones that carry pyrite disseminated through several feet of sheared rock; however, fissure fillings are more abundant. Besides pyrite the ore contains variable amounts of chalcopyrite and locally, some galena and sphalerite. Quartz is the common gangue mineral in the veins (Lovering and Goddard, 1950, p. 193-194).