By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Jefferson County lies in north-central Colorado immediately west of Denver. The western two-thirds of the county is in the Front Range, and the northeastern third is in the Great Plains. Although placer gold was first discovered along Cherry Creek, east and southeast of Denver, the early prospectors worked along the streams west from there into the mountains, and in 1859 gold placers were discovered along Clear Creek near Golden in what is now Jefferson County (Henderson, 1926, p. 27, 129). No production was recorded from the county until 1885. The county is credited with a production of $32,769 (1,585 ounces) in placer gold during 1885-1905 and with $29,527 (1,428 ounces) in lode gold during 1895-1904 (Henderson, 1926, p. 130). No production was recorded for 1906-31, but a consistent, though small, annual production during 1932-59 totaled 12,478 ounces of placer and 435 ounces of lode gold. Total county gold production through 1959 was about 15,900 ounces.
Lode gold in Jefferson County probably has been derived as a byproduct from several small copper deposits found in Precambrian rocks near Evergreen, notably in the Malachite mine. The deposits are in or very close to amphibolite schists and gneisses, which may be metamorphosed diorite. The deposits probably are Precambrian in age (Lovering and Goddard, 1950, p. 67-68).
Most of the production from Jefferson County has come from the placers along Clear Creek. ImmediÂ¬ately west of Golden, Clear Creek is a narrow stream and the yardage of sand and gravel is limited. East of Golden the gravel is more extensive. In recent years most of the gold production, as in Adams County, has come as a byproduct from sand-and-gravel operations (Vanderwilt, in Vanderwilt and others, 1947, p. 122). It appears reasonable to credit the entire placer production of the county, which was about 14,000 ounces, to this district.
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