Clear Creek County Colorado Gold Production
The Georgetown-Silver Plume (Griffith) district consists of about 25 square miles centered around the towns of Georgetown and Silver Plume, in western Clear Creek County.
Precious metal lodes were first discovered near Georgetown in 1859, soon after the placer discoveries along Chicago Creek near Idaho Springs. In 1864 when rich silver ores were found in the Argentine district, southwest of Silver Plume, many prospectors were attracted to the region and uncovered significant silver deposits in the Georgetown area. With the successful introduction of smelting at Blackhawk, the sulfide veins were mined after the surface ores were exhausted. As the mines reached greater depths, silver and lead were the main commodities, whereas the surface ores were richer in gold. By 1880, the district was the principal silver producer in Clear Creek County. This trend was maintained, reaching a peak in 1894, after which a gradual decline began (Spurr and others, 1908, p. 173-175). Zinc became a major component of the metal output after 1903, especially during World Wars I and II. Between the two wars the base-metal and silver mines were mostly idle, and most of the sporadic activity was from gold mines. The raise in the price of gold in 1934 failed to effect any marked increase in gold production. From the end of World War II through 1959 the lead-silver mines yielded a few ounces of gold annually.
The total gold output of the district through 1959 was about 145,000 ounces, most of which was mined before 1900.
Bedrock in the Georgetown-Silver Plume district is generally similar to that in the other mining districts in Clear Creek County. Contorted schist of the Idaho Springs Formation is cut by several types of Precambrian igneous rocks, including dikes and sheets of hornblende gneiss, bodies of gneissic quartz monzonite resembling Boulder Creek Granite, and large masses of Silver Plume Granite which makes up about half the bedrock in the district. Stocks and dikes of Tertiary dacite, quartz monzonite porphyry, alaskite porphyry, and granite porphyry were intruded into the Precambrian rocks (Lovering and Goddard, 1950, p. 138-140).
The ore deposits of the district are of two mineralogical types: silver-lead-zinc veins and pyritic gold veins. The rich silver-bearing veins are found chiefly in the very productive area just north of Silver Plume, but some are also found south and northeast of Georgetown. The gold-bearing veins lie in a narrow belt between the two silver belts. North of Silver Plume, the veins carry silver, lead, and zinc, and almost no gold, whereas the gold-bearing veins contain some silver and locally their silver content is higher than gold. The most abundant minerals of the silver-lead-zinc ores are galena, sphalerite, and pyrite. These ores commonly contain less than 0.10 ounce of gold per ton. The chief gangue minerals are quartz and brown carbonates. The principal minerals in the pyritic gold deposits are pyrite, chalcopyrite, gold, small amounts of silver minerals, and quartz gangue. Small amounts of galena and sphalerite are in most of these veins, but where galena is more abundant the veins contain larger amounts of gold and silver. Locally hessite and argentite have been found, and in one mine platinum and iridium were noted (Lovering and Goddard, 1950, p. 141-142).