Clear Creek County Colorado Gold Production
The Freeland-Lamartine (Trail) district includes about 4 square miles of the Colorado mineral belt and is about 3 miles west of Idaho Springs in central Clear Creek County.
Soon after the discovery of gold placers near the mouth of Chicago Creek in 1859 (Spurr and others, 1908, p. 311), the search for gold spread to the area along Trail Creek, which lies north of Chicago Creek. The first veins were discovered in 1861, but these were not developed until 1868, after the successful smelter operation at Blackhawk. In 1870 railroad facilities became available to the region, and mining activity was stimulated still further. From about 1910 through 1933, mining in the district was intermittent and generally on the decline (Harrison and Wells, 1956, p. 36), but it was revived when the price of gold was increased in 1934. The mines in the district were relatively idle from 1944 through 1959.
Almost all production has come from lode deposits in the Lamartine and Freeland mines. Harrison and Wells (1956, p. 74) estimated that from 1868 to 1905 ore valued at about $5 million was produced, and the output from 1905 to 1953 was valued at $13 million in gold, silver, copper, lead, and zinc. Total gold production through 1959 was about 220,000 ounces, about 100,000 of which was mined from the Lamartine and Freeland mines between 1905 and 1953 (Harrison and Wells, 1956, p. 74).
The country rock in the district consists of the Idaho Springs Formation, which is composed of schist and gneiss of sedimentary origin and is intruded by quartz diorite, granite, and pegmatites, all of Precambrian age. During Tertiary time the Precambrian rocks were intruded by dikes and plugs of porphyries that range in composition from quartz monzonite and bostonite to alaskite. The structure is complex and involves two periods of Precambrian folding and Tertiary arching, fracturing, and faulting (Harrison and Wells, 1956, p. 37-67).
The ore deposits of the district are Tertiary mesothermal fissure veins deposited in fractures near porphyritic intrusive rocks. Two principal varieties of veins are recognized—pyrite-gold and galena-sphalerite. Locally, as observed in the Lamartine tunnel, a transition zone between the two types contains composite ore. The primary minerals of the pyrite-gold veins are pyrite (partly auriferous), chalcopyrite, tetrahedrite-tennantite, and minor galena and sphalerite in a gangue of quartz and carbonate. The galena-sphalerite veins contain galena (partly argentiferous), sphalerite, and pyrite, with subordinate amounts of chalcopyrite and tetrahedrite-tennantite, and quartz-carbonate gangue. Native gold is present in both types (Harrison and Wells, 1956, p. 74, 75).