Baker County Oregon Gold Production
By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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The Connor Creek district is along the west drainage of the Snake River between lat 44°21' and 44°44' N. and long 117°03 and 117°18', W.
Placer mining began in this district in the 1860's along Connor Creek, and in 1871 lode gold was discovered at Connor Creek mine. After an estimated maximum production of $2 million in gold (Lindgren, 1901, p. 757), the mine was closed in 1910 and was reopened only briefly in 1915-18 (Gilluly and others, 1933, p. 50). Small amounts of placer gold were produced from the district until 1942. From that time through 1959 there was virtually no production. The district produced about 97,000 ounces of lode gold and about 6,100 ounces of placer gold through 1959.
The following summary of the geology of the district is from Gilluly, Reed, and Park (1933, p. 50). The country rock is dominantly black carbonaceous slate and quartz phyllite and contains small amounts of greenstone, chlorite schist, and limestone. These rocks are of possible Triassic and Jurassic age. The beds dip steeply to the northwest and strike N. 20°-45° E. Granitic rocks have intruded the metasediments west of the district. The gold deposits are in northwest-trending quartz veins that dip steeply southwest. Free gold occurs in the Connor mine with, some argentite and pyrite.
CORNUCOPIA DISTRICT
The Cornucopia district, between lat 44°57' and 45°05' N. and long 117°00' and 117° 15' W., reported very little activity until 1880-85 (Lindgren, 1901, p. 742). Its gold production to 1903 was valued at $1,008,000 (Oregon Department of Geology and Mineral Industries, 1939, p. 25). Production was fairly steady from 1903 through 1941, but it was only a few ounces from 1942 through 1959. Recorded production from 1907 through 1959 was 255,698 ounces of lode gold, 2,441 ounces of placer gold, and 5,800 ounces undifferentiated as to origin.
The oldest rocks in the area are metavolcanics and elastics of the Clover Creek Greenstone, of Permian age (Ross, 1938, p. 21). Other metasedimentary rocks that overlie the Clover Creek Greenstone have obscure stratigraphic relations with one another and are classed as Carboniferous and Triassic. Overlying the Paleozoic rocks are the Martin Bridge Formation and a thick section of younger sediments, all of Late Triassic age. At the close of the Jurassic the rocks were folded and metamorphosed, and in mid-Cretaceous time a granodiorite batholith intruded the series (T. P. Thayer, written commun., 1962). During the closing stages of this igneous activity, the veins were formed, uplift and dissection followed, then the basalt flows of the Columbia River Basalt were poured out on this erosion surface.
The veins occupy shear zones in both the metamorphic and granitic rocks. The larger veins strike N. 40° E. and dip 40° W.; many are offset en echelon. Vein minerals consist of pyrite, sphalerite, chalcopyrite, galena, tetrahedrite, tellurides, and native gold, with quartz as gangue (Goodspeed, 1941, p. 185). Successive stages of microbrecciation and turbid quartz are not noticeable features of these veins.