By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Gold was first discovered in eastern Oregon in 1861 in Griffin Gulch in the Baker district, Baker County. The town of Auburn was soon established as the first settlement and base for exploration. By about 1870 the richest placers were exhausted, but quartz lodes were discovered and developed, although slowly, and by 1900 were substantially productive in the Cracker Creek, Cornucopia, and Sumpter districts. As placer production decreased, Auburn declined, and Baker became the most important town in the county.
Production data for Baker County before 1880 were not found. From 1880 to 1899, the county produced $8,958,073 (about 434,850 ounces) in gold (Lindgren, 1901, p. 573). From 1904 through 1957, it produced 747,548 ounces of lode gold, 402,490 ounces of placer gold, and 11,626 ounces unidentified as to source. Total recorded gold production through 1959 was about 1,596,500 ounces; from 1954 through 1959 only a few hundred ounces was produced.
Placer mining revived after 1912, and after World War II it was more productive than lode mining. Most of the county's gold production in recent years was from the Sumpter district placer mines, which were closed in 1955.
Lode deposits of Baker County generally are fissure veins that are related to intrusions of granitic, dioritic, and gabbroic rocks (Lindgren, 1901, p. 614). The deposits most commonly are found near contacts of these intrusive rocks with sedimentary or metasedimentary rocks.
Production in the Baker district has been chiefly from the placers in Griffin Gulch but this was in the early years and was unrecorded. After 1900 more than half of the gold produced in the district came from lode mines. Production of gold from 1906 through 1959 was 19,825 ounces from lode mines, 10,890 ounces from placers, and 5,437 ounces undifferentiated, a total of 36,152 ounces.
The oldest rocks of the district are greenstone, phyllite, quartz schist, and limestone composing the Burnt River Schist of probable pre-Carboniferous age (Gilluly, 1937, p. 9-13) and the Elkhorn Ridge Argillite, composed of argillite, tuff, lava, chert, and greenstone, of Permian and Triassic age (Bostwick and Koch, 1962). An unconformity separates these rocks from the superjacent Tertiary andesite and basalt flows. The pre-Tertiary rocks are thrown into strong folds that strike west, but the Tertiary rocks are only gently warped (Gilluly, 1937, p. 8).
The lode deposits are fissure and replacement veins in the pre-Tertiary rocks (Gilluly, 1937, p. 92). Gold, pyrite, chalcopyrite, sphalerite, and locally stibnite and galena occur in a gangue of quartz, sericite, carbonate, and a little clay and scheelite.
Placers have been worked in nearly all the gulches on the south end of Elkhorn Ridge, on Marble Creek, and on Salmon Creek. The most important placers were in Blue Canyon near Auburn, where some of the early discoveries were made.
CONNOR CREEK DISTRICT
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.
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.
CRACKER CREEK DISTRICT
The Cracker Creek district is between lat 44°48' and 44°54' N. and long 118°03' and 118°17' W., north of Sumpter.
The most important lode in this district and in Oregon, the North Pole-Columbia, was discovered in 1887, and it produced about $9 million in gold (Oregon Dept. Geology and Mineral Industries, 1939, p. 34). From 1907 through 1959 a total of 189,389 ounces of gold was recorded from the district.
The country rock in the district is the Elkhorn Ridge Argillite, which probably is of Permian and Late Triassic age. Cutting this argillite is the North Pole-Columbia lode, a vein system that trends northwest to east and continues unbroken for a distance of 5 miles (Lindgren, 1901, p. 658). The vein material consists of quartz, arsenopyrite, pyrite, and some chalcopyrite. Most of the gold occurs in the fine arsenopyrite (Parks and Swartley, 1916, p. 61). Comb structure is common, and some of the earlier minerals are crushed and shattered indicating some movement along the fissure system during deposition.
EAGLE CREEK DISTRICT
The Eagle Creek district is between lat 44°49' and 45°05' N. and long 117°00' and 117°45'- W., in the southern end of the Wallowa Mountains. The boundaries of this district overlap those of the Cornucopia district, and rightly so, for the gold-bearing gravels of the Eagle Creek district were derived from the Cornucopia stock.
Mining began in this district in the early 1860's when placers along Eagle Creek were worked. Those along Paddy Creek were worked also, but most of the gold production was from lodes and some was a byproduct of copper ore. The Sanger mine, the largest producer in the district, yielded an estimated $1.5 million in gold from auriferous quartz veins (Lindgren, 1901, p. 738).
The total early production of the district was estimated at $1,687,400 (about 82,000 ounces) in gold (Lindgren, 1901, p. 738-739). Total recorded production from 1931 through 1951 was 5,782 ounces of lode gold and 69 ounces of placer gold; from 1952 through 1959, no production was recorded.
The country rock of the area is chiefly Triassic greenstone and limestone cut by granitic and diabasic dikes (Gilluly and others, 1933, p. 63). The veins contain pyrite, chalcopyrite, sphalerite, galena, and free gold in a gangue of quartz and some calcite.
The Greenhorn district is between lat 44°33' and 44°44' N. and long 118°25' and 118°32' W. in Baker and Grant Counties.
Both silver and gold veins were mined in the district before 1910. The Bonanza, the chief mine, produced $1.75 million in gold before 1904; it operated only sporadically from 1904 through 1916 (Parks and Swartley, 1916, p. 39). After 1930 the bulk of production was from placers. The total gold production of the district through 1959 was 89,200 ounces from lodes and 10,382 ounces from placers.
The following summary of the geology of the district is taken from "Oregon Metal Mines Handbook" (Oregon Department of Geology and Mineral Industries, 1939, p. 52-53). The district, which is on the eastern lower slopes of Vinegar Hill, is underlain by greenstone, argillite, serpentine, and granodiorite, and is surrounded by younger lava flows of Tertiary age.
The granodiorite was intruded into the greenstone and argillite, and the ore deposits probably were emplaced during the closing stages of the intrusion. The deposits in the Bonanza mine and its vicinity are in argillite; those near the town of Greenhorn are in greenstone. The ores contain mostly gold and silver, but varying amounts of copper and lead are locally present.
Placers near Winterville, Parkerville, and McNamee Gulch were successfully worked. The value of boulders of silicified Tempskya (Cretaceous) "fern wood" in Eocene (?) gravels exceeded the value of the gold (T. P. Thayer, written commun., 1962).
LOWER BURNT RIVER VALLEY DISTRICT
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 $2.25 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.
ROCK CREEK DISTRICT
The Rock Creek district is between lat 44°49' and 45°03' N. and long 118°00' and 118°15' W., 10-15 miles northwest of Baker.
The district, discovered in the late 1880's, was a steady gold producer until 1914, after which activity declined; it was idle in 1959. The principal mine, the Baisley-Elkhorn, produced an estimated $950,000, chiefly in gold (Oregon Department of Geology and Mineral Industries, 1939, p. 85).
Estimated early production of the district was $1 million, mostly in gold (Lindgren, 1901, p. 646). Production from 1934 through 1959 totaled 3,282 ounces of lode gold and 193 ounces of placer gold. A conservative total for the district would be about 51,000 ounces of gold.
The following is summarized from Lindgren's (1901, p. 645-647) description of the geology of the district. The north end of Elkhorn Ridge is composed of granodiorite, the south part is dominantly argillite, and the Rock Creek district is along the contact between them. Diorite dikes cut the argillite near the contact. Near its borders the intrusive is dioritic, becoming granodioritic toward the interior.
Most of the veins are discontinuous but form a zone in the diorite approximately parallel to the argillite-diorite contact. Gangue is quartz with some calcite. Gold occurs in pyrite or as an intergrowth with sphalerite. Other sulfides are galena, chalcopyrite, and locally ruby silver.
The Sparta district is between lat 44°36' and 44°57' N. and long 117°02' and 117°23' W.
Although placer deposits were known in the area at an early date, it was not until 1873, when the Sparta ditch was completed, that enough water was available to exploit the gravel-filled gulches which yielded about $157,000 in gold before 1900 (Lindgren, 1901, p. 737). Quartz veins were discovered a few years after the discovery of the placers, and from 1889 to 1892 they yielded $677,000 in gold (Lindgren, 1901, p. 736). Shortly thereafter the district declined rapidly, and from 1952 through 1959 it was idle.
Total production from the district through 1959 was about 35,200 ounces of lode gold and about 7,700 ounces of placer gold.
The district is underlain by quartz diorite and albite granite of presumable Mesozoic age (Gillully and others, 1933, p. 57-58). These rocks intruded Permian greenstone, only remnants of which remain in the area. Columbia River Basalt unconformably overlies the older rocks. The ore deposits are gold-bearing quartz veins in the diorite and granite. Most of the veins are narrow and cannot be followed for any great distance.
The Sumpter district, between lat 44°37' and 44°48' N. and long 118°00' and 118° 18' W., is predominantly a placer district, but there has been a small gold production from quartz veins that cut argillite. Placer deposits were discovered here in 1862, and production was almost continuous until 1955.
Records of production before 1932 have not been found, but from 1932 through 1955 the district produced 129,004 ounces of placer gold and 2,206 ounces of lode gold. No production was reported from 1955 through 1959.
Terrace gravels along the Powder River and gravels in its tributary gulches, above the town of Sumpter, contain varying amounts of gold. Damming of the Powder River by lavas of the Columbia River Basalt resulted in thick accumulations of gold-bearing gravels in the Sumpter Valley (Lindgren, 1901, p. 655-656). As the river cut through the barrier, lower terraces were created, and these also were worked extensively.
UPPER BURNT RIVER DISTRICT
The Upper Burnt River district, which includes Bridgeport, Bull Run, Unity, and Hereford, is in southern Baker County, between lat 44° 15' and 44°36' N. and long 117°35' and 118°20' W. It is a large district and includes many localities that have produced small amounts of both placer and lode gold. Early production data are scant, but apparently some placers were worked before 1900. Total gold production through 1959 was about 9,300 ounces from all sources.
According to the Oregon Department of Geology and Mineral Industries (1939, p. 97-98), the eastern part of the district is predominantly argillite and contains some limestone and lava flows, and the western part is covered by more recent flows. Auriferous gravels along the Burnt River have been mined.
The Virtue district is between lat 44°43' and 44°57' N. and long 117°22' and 117°45' W.
This is predominantly a lode district; placer operations consisted of small-scale diggings in some of the gulches below the veins. The Virtue mine, discovered in 1862, was one of the largest gold producers in eastern Oregon (Lindgren, 1901, p. 722). Other mines in the district that have produced significant quantities of gold are the Brazos, Flagstaff, Hidden Treasure, and White Swan. The latest production reported from the district was in 1956.
Early production of the district was about $2,500,000 in gold (about 121,000 ounces) ; about $2,200,000 came from the Virtue mine, which had its best years before 1900 (Gilluly, 1937, p. 73). Yearly production data for the district go back only to 1935. The total for the period 1935 through 1957 was 4,837 ounces from lode mines and 288 ounces from placers. Total gold production for the district through 1959 was about 126,000 ounces.
In the northern part of the district a strongly sheared diorite is the predominant country rock, whereas the southern part is underlain by argillite that strikes east-west (Lindgren, 1901, p. 721-722). Most of the more prominent veins strike northwest, and they occur in both the diorite and argillite. Gilluly (1937, p. 94) noted that the veins consist of quartz, calcite, scheelite, and a little sericite. Small amounts of native gold, pyrite, and chalcopyrite are present.