By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Substantial amounts of gold have been mined from lodes and placers in Trinity County. Mining began in the early 1850's with small-scale placer operations in the Trinity River basin. Later the terrace and channel gravels were worked by hydraulic methods, and huge dragline dredges were used near Junction City and Weaverville. Lode mining has also been successful in the Carrville district.
Total gold production of Trinity County from 1880 through 1959 was 2,036,300 ounces, mostly from placers.
The central part of the county is traversed by a northwest-trending belt of schists belonging to the Abrams Mica Schist and the Salmon Hornblende Schist, both believed to be Precambrian in age, and concordant Paleozoic metasedimentary rocks including quartzites, cherts, slates, limestones and inter-bedded lavas, greenstones, and amphibolite schists (Averill, 1941a, p. 10).
Northeast of this sequence of metasedimentary rocks are large masses of intrusive rocks ranging in composition from granite to serpentine, of probable Late Jurassic age. Sedimentary rocks, possibly equivalent to the Franciscan Group of Jurassic (?) age, are exposed in the southwestern part of the county (Averill, 1941a, p. 10).
The Carrville district is about 5 miles north of Trinity Center, along the Trinity River near its junction with Coffee Creek. Almost its entire production has come from lode deposits, which produced an estimated $1 million in gold through 1910 (MacDonald, 1913, p. 20) ; however, no activity has been reported in recent years.
The country rock consists of schists, of possible Precambrian age, a complex of greenstone of pre-Carboniferous age, and slates and conglomerates that compose the Bragdon Formation of Carboniferous age (MacDonald, 1913, p. 10-14). Intrusive grancdiorite masses of Late Jurassic or Early Cretaceous age cut the foregoing rocks. Large areas of the district are underlain by serpentine believed to be Jurassic in age, and the serpentine is cut by numerous lamprophyre dikes.
The most important ore bodies are replacements of basic dikes in or near granodiorite porphyry masses (MacDonald, 1913, p. 14). The ore is highly oxidized and sheared, and the gold occurs in the oxidized products of pyrite or in the country rock or in the veins in the form of tellurides. Small amounts of silver are present.
TRINITY RIVER BASIN
The Trinity River basin is a large area that includes most of the drainage of the Trinity River, and it extends from Coffee Creek southward through Trinity Center, Dedrick, Helena, Junction City, Weaverville, Lewiston, and Douglas City, and west to the Hay Fork area.
Mining began in this area in the early 1850's and was still active in 1959, though on a much-reduced scale. Placer mining was formerly done on a large scale by hydraulic operations, but large dragline dredges have supplanted the hydraulic giants. The La Grange mine near Weaverville was the largest hydraulic mine in this area (MacDonald, 1910, p. 51). Production of gold from the gravels of the Trinity River basin from 1880 through 1959 was about 1,750,000 ounces.
The gold-bearing gravels of the Trinity basin are related to two cycles of erosion of the Klamath Mountains. The older gravels are partly cemented and locally deformed, whereas the younger gravels occur along the present streams and are undisturbed (Diller, 1914a, p. 14-20). Both types contain workable placers.