By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
The first gold mining in the State was in Jackson County. In 1852, placers along Jackson Creek were worked. Soon afterward placers were discovered along other creeks in the vicinity, and mining of these deposits became a major industry in the county (Oregon Department of Geology and Mineral Industries, 1943, p. 11). Lode deposits were discovered as early as 1859, but the chief gold production has come from the placers. The major districts in the county are Ashland, Gold Hill, Jacksonville, and Upper Applegate.
Much of the gold production from the county was before 1880, when there were no reliable records of the output; however, Winchell (1914b, p. 29), combining estimates and recorded data, reported gold production worth $7,110,333 from 1852 through 1912. From 1904 through 1959 the county produced 35,067 ounces of lode gold, 136,030 ounces of placer gold, and 16,787 ounces undifferentiated as to source. Total gold production from 1852 through 1959, including Winchell's estimates, was about 495,000 ounces.
The geology of Jackson County is given in "Oregon Metal Mines Handbook" (Oregon Department of Geology and Mineral Industries, 1943, p. 13-19). Schists of pre-Mesozoic age underlie the southwest part of the county, and Triassic greenstones and metasedimentary rocks, named the Applegate Group by Wells (1956), underlie its western part. In the northwest part of the county is a small patch of black slate, conglomerate, and tuffaceous sandstone of the Galice Formation, of Jurassic age. The schists, greenstones, and Galice sedimentary rocks were intruded first by masses of peridotite, now altered to serpentine, and later by granitic rocks. In the central part of the county, in Bear Creek and Cottonwood Creek valleys, remnants of the marine Hornbrook Formation of Cretaceous age are present (Wells, 1956). A narrow band of sandstones of the Tertiary Umpqua Formation underline Bear Creek valley, which crosses the county in a northwest direction. Lavas, breccias, and tuffs of Miocene and Pliocene age cover the central one-third of the county; these were intruded by small bodies of basalt and diorite. Pliocene and Pleistocene lavas and cinder conesâ€”the High Cascade Seriesâ€”cover much of the eastern part of the county. The gold deposits are concentrated in the western part of the county and are found in rocks of the Applegate Group and in the granitic and dioritic intrusives.
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