Baker County Oregon Gold Production
The Lower Burnt River valley district, which includes Weatherby, Gold Hill, Durkee, Chicken Creek, and Pleasant Valley, is between lat 44° 17' and 44°43' N. and long 117° 10' and 117°41' W., along Burnt River in southern Baker County.
The lode mines in this district were worked in the early 1880's, and the placers probably were worked earlier. Small production from the Weatherby area was maintained until 1955; however, most of the production was in early days, when no accurate records were kept. Some of the major lode mines were the Gold Ridge, Gleason, Little Bonanza, and Little Hill. Estimates of early lode production total $928,000 in gold (about 45,000 ounces) (Lindgren, 1901, p. 765; Oregon Department of Geology and Mineral Industries, 1939, p. 67-71). Total production for the district through 1959 was at least 50,000 ounces of lode gold and 3,500 ounces of placer gold. Production data for placers are reliable only for the period since 1932.
Slates, schists, and limestones of possible Triassic age (Lindgren, 1901, pi. 64) are cut by a mass of granodiorite, diorite, and quartz diorite. The sedimentary rocks strike N. 70°-80° E. and dip steeply to the north (Lindgren, 1901, p. 763). Associated with the intrusive masses are discontinuous small quartz veins that are rich in gold.
Nearly all the gulches and streams that drain into the Burnt River in this district contain auriferous placers.
MORMON BASIN DISTRICT
The Mormon Basin (Dixie Creek, Rye Valley, Malheur) district is between lat 44°22' and 44°31' N. and long 117°23' and 117°40' W. in southern Baker County and northern Malheur County.
As early as 1863 placers were mined in the Rye Valley area and were credited with a production of $1 million in gold (Swartley, 1914, p. 228). Although quartz veins were known in the district in the early days, their gold production was not significant until after 1900; it was valued at about $214 million for the period 1906 to 1916 (Oregon Department of Geology and Mineral Industries, 1939, p. 76). About half of this was from the Rainbow, the largest gold mine in the district, and, from 1913 to 1915, the most productive in the State (Gilluly and others, 1933, p. 38). The district reported only small production from 1915 through 1948, and it was idle from 1949 through 1959. Total gold production through 1959 was about 177,500 ounces from lode mines and 56,200 ounces from placer workings.
Gilluly, Reed, and Park (1933, p. 31-49) discussed in some detail the geology and mines of the Mormon Basin area. The oldest rocks exposed are quartzite, quartz schist, slate, greenstone, and chlorite schist of unknown age. These were intruded by masses of gabbro, dunite, pyroxenite, and harzburgite altered for the most part to greenstone, amphibolite, serpentine, and talc. These igneous rocks have been highly sheared and are foliated. A large mass of quartz diorite makes up Pedro Mountain, a prominent landmark, and there are smaller bodies of this same rock throughout the district. The lower parts of the basin are covered by Tertiary stream deposits interbedded with dacite and andesite flows. The gold deposits are in veins in pre-Tertiary rocks near the quartz diorite masses. Vein minerals are quartz, ankerite, and fuchsite as gangue and pyrite, arsenopyrite, galena, sphalerite, polybasite, hessite, tetrahedrite as ore minerals.