By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Lode and placer gold as well as large amounts of byproduct gold from the West Shasta copper-zinc district have been mined in Shasta County. The major lode districts are the Deadwood-French Gulch, Harrison Gulch, Old Diggings, and Whiskey-town. Placer operations are centered in the Igo disÂ¬trict and along the Roaring River.
Total gold production of Shasta County from 1880 through 1959 was 2,033,000 ounces, mostly of lode and byproduct origin. Output of placer gold from 1905 through 1959 was 375,472 ounces. Most of the foregoing production was before 1940; during 1950-59 less than 1,000 ounces per year was reported.
Precambrian rocks are exposed in the southwestern part of the county (Averill, 1939, p. 110-111). Northeastward the country rock changes successively to the Copley Greenstone of Early (?) Devonian age, then to sedimentary rocks of Devonian, Carboniferous, Permian, Triassic, and Jurassic ages. The southern part of the county is covered with sedimentary rocks of Cretaceous, Tertiary, and Quaternary ages. The east half of the county is blanketed by a series of lava flows extruded during Tertiary and Quaternary time. Lassen Peak, the only active volcano in California, is in the southeast corner of the county.
DEADWOOD-FRENCH GULCH DISTRICT
The Deadwood-French Gulch district is along the central part of the west border of Shasta County. Gold was discovered in this general area in 1848 in the gravels of Clear Creek, and 4 years later gold-bearing veins were producing at the Washington mine (Ferguson, 1914, p. 33). Activity in the district continued at a rather moderate rate until 1941, after which only a few ounces were produced annually. Ferguson (1914, p. 55) reported a production of $1,607,764 (78,000 ounces) through 1911. Production through 1959 was about 128,900 ounces of gold, mostly from lode mines.
The western part of the area is underlain by biotite-hornblende schists of pre-Devonian age, and the eastern part is underlain by a younger rock, the Copley Greenstone, of Early (?) Devonian age, which is overlain by the Bragdon Formation of Mississippian age (Ferguson, 1914, p. 24). These rocks were invaded in Late Jurassic time by a series of granitic and porphyritic rocks.
The gold deposits are in fissure veins that are most numerous in the Bragdon Formation, but some veins occur also in quartz diorite and alaskite porphyry. The vein minerals consist of pyrite, arsenopyrite, sphalerite, galena, native gold, and a minor amount of chalcopyrite in a quartz gangue.
HARRISON GULCH DISTRICT
The Harrison Gulch district is in the southwest corner of Shasta County.
The Midas mine, discovered in 1894, was the major producer in the district and had an output of $3,563,587 in gold until 1914 (Logan, 1926, p. 173-174), when a fire caused it to close. It was reopened the following year under new ownership, and operations continued until 1920. The district was inactive from 1920 through 1959. The total production for the district was about $4 million (Averill, 1939, p. 142). No placer production is recorded in this district.
At the Midas mine, gold occurs in three lenticular quartz veins in a schistose country rock (Logan, 1926, p. 174).
The Igo district is in T. 31 N., R. 6 W., along Clear Creek. The quaternary gravels along Clear Creek near Igo were worked in the early days, but they are only briefly mentioned in the literature (Diller, 1914a, p. 20-21), and no published account of their discovery, development, or early production was found.
The district was revived in 1933 and through 1942 produced more than 113,000 ounces of placer gold, but after 1942 operations were sharply curtailed and the district was dormant in 1959. Total recorded production from 1933 through 1959 was 115,022 ounces; all but a few hundred ounces was from placers.
WEST SHASTA COPPER-ZINC DISTRICT
The West Shasta copper-zinc district, 20 miles northwest of Redding, originally was a gold district, but it later became one of the chief copper producers in the State. Prospectors, drawn to Shasta County by the placer discoveries on Clear Creek in 1848, soon found gold placers in the area west of Redding (Kinkel and others, 1956, p. 76). Copper deposits were also noted at this time, but interest was centered on the gold.
In 1879 considerable excitement was aroused by the discovery of silver in the gossan at the Iron Mountain property in the southern part of the district. Later, in the search for precious metals, large quantities of copper sulfides were found beneath the gossan. In the early 1900's copper was mined on a large scale from the Iron Mountain and Balaklala mines, and gold and silver were obtained as byproducts. Small bodies of high-grade zinc ore were mined at the Mammoth and Iron Mountain mines.
After 1919, production declined, and by 1953 gold was no longer listed in the annual production data for the district. Total gold production through 1959 was about 520,000 ounces.
The oldest rocks of the West Shasta copper-zinc district are basic lava flows, breccias, and tuffs that characterize the Copley Greenstone of Early (?) Devonian age. This is overlain by the Balaklala Rhyolite of Middle Devonian age, and the Balaklala is overlain by the Kennett Formation, which is composed of black cherty shale, tuff, and limestone of Middle Devonian age. Shale, sandstone, and conglomerate of the Bragdon Formation of Mississippian age rests on the Kennett Formation.
In Jurassic time the Paleozoic rocks were invaded first by the Mule Mountain albite granite stock and then by the Shasta Bally biotite-quartz diorite batholith. Deformation accompanied the intrusions, and the Paleozoic formations were folded into a broad anticlinorium. Numerous faults dislocate parts of the arch. In the southern part of the district, elastics of the Chico Formation of Late Cretaceous age and of the Red Bluff Formation of Pleistocene age unconformably overlie the Copley Greenstone (Kinkel and others, 1956, p. 8-9).
The ore deposits, which were emplaced during Late Jurassic or Early Cretaceous time, consist of massive base-metal sulfide replacement bodies in the Balaklala Rhyolite. The ore minerals are pyrite, chalcopyrite, and sphalerite, and small amounts of magnetite, galena, tetrahedrite, pyrrhotite, gold, and silver. The ore controls are believed to be a combination of the anticlinorium structure, favorable lithologic features of the Balaklala Rhyolite, and fissures, which provided access for solutions (Kinkel and others, 1956, p. 79-100).
The Whiskeytown district is along Clear Creek about 5 miles southeast of French Gulch.
The mines are along the edge of a mass of alaskite porphyry of Jurassic or Cretaceous age that cuts the Copley Greenstone of Early (?) Devonian age and lies adjacent to a large mass of quartz diorite and granodiorite of Jurassic or Cretaceous age (Ferguson, 1914, p. 47). The Bragdon Formation, of Mississippian age, is exposed in the northern part of the district.
The Mad Mule mine, which has been the largest producer of the district, is in a diorite porphyry dike that cuts the Bragdon Formation. The ore bodies are small lenses of calcite that occur at irregularities along the contact between the dike and sedimentary rock. Gold occurs most commonly as a thin film on calcite at its junction with the enclosing slate. Gold also is found within the calcite masses along cleavage planes.
Pyrite and manganese-bearing quartz stringers are minor constituents of the calcite lenses (Ferguson, 1914, p. 52-54). Other ore deposits in the district are in quartz veins with minor calcite and with pyrite as the principal sulfide. Gold occurs free in the quartz and in the pyrite.
Production through 1911 was 63,300 ounces ($1,365,000) of gold (Ferguson, 1914, p. 47-55). The district has been inactive for many years.