By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Clear Creek County is in north-central Colorado in the Front Range, west of Denver, and immediately east of the Continental Divide.
Clear Creek County ranks seventh among the gold-producing counties of Colorado with a total of about 2,400,000 ounces through 1959, yet gold is second to silver in the value of minerals mined in the county. Substantial amounts of lead, zinc, and copper are also produced. Most of the precious metals have been recovered from siliceous ores in lodes, but in some deposits they were byproducts of base-metal ores. From 1859 to 1864 gold was almost wholly derived from placer deposits or from the hydraulicking of decomposed outcrops of veins.
Prospecting parties working westward from the first gold discoveries in Colorado near Denver discovered gold in Clear Creek County in early April 1859 along Chicago Creek, just above its junction with Clear Creek near Idaho Springs. Prospectors stampeded to the region, and shortly afterwards the first gold-bearing lodes were discovered and located. Later that year lodes were discovered in the Empire district and as far west as Georgetown. In the middle 1860's discoveries of silver veins in the Argentine and Georgetown-Silver Plume districts drew many mining people to western Clear Creek County (Spurr and others, 1908, p. 173).
When the free-milling oxidized ores were mined out, the mining industry waned until 1868 when the Blackhawk smelter opened and successfully treated the sulfide ores. The ever-widening network of railroads also encouraged mineral exploitation at this time. After 1900 mining activity was accelerated during World War I and in the 1935-41 period.
The country rock in Clear Creek County is a complex of Precambrian metamorphic and igneous rocks cut by Tertiary stocks and numerous dikes of porphyries. The most common porphyries range in composition from quartz monzonite to bostonite and alaskite. The ore deposits are also Tertiary in age and are genetically related to the porphyries.
The following six districts in the county have each produced more than a total of 10,000 ounces of gold: Alice, Empire, Idaho Springs, Freeland-Lamartine, Georgetown-Silver Plume, and Argentine. Of these the Idaho Springs district is the largest producer.
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