South Eureka Mine, Sutter Creek, Jackson-Plymouth District, Mother Lode Belt, Amador Co., California, USA
|Latitude & Longitude (WGS84):||38° 22' 49'' North , 120° 47' 42'' West|
|Latitude & Longitude (decimal):||38.38028,-120.79500|
|Köppen climate type:||Csa : Hot-summer Mediterranean climate|
A former lode Au-Ag mine located in secs. 8 & 17. T6N, R11E, MDM, 1.6 km (1.0 mile) SSE of Sutter Creek (town), N of the Amador County airport and E of Sutter Hill, on private land. Discovered before 1891. Holdings were 431 acres. Operated by the South Eureka Mining Co. C/O A. J. Mayman. MRDS database stated accuracy for this location is 100 meters.
The South Eureka Mine is located one-quarter mile east of Sutter Hill in the famous Mother Lode Gold Belt of the Sierra Nevada foothills. While the mine is technically in the smaller Sutter City district, the uniform nature of gold mineralization with neighboring districts has caused some authors to consolidate the smaller neighboring districts into the Jackson - Plymouth district (Clark, 1970).
The South Eureka Mine was originally developed in 1891 and during much of its period of operation was one of the largest producers in the country. Its later discovery was the result of the absence of any quartz outcroppings, the claims being capped by ancient stream gravels. The sinking of the shaft was a speculative venture based on the position of the claims between known producers on the well-defined Mother Lode trend. An inclined shaft was started in black slate which was soft, crushed and heavy (Logan, 1934). It proved to be expensive requiring frequent timbering and realignment. Cross cuts were run to the hanging wall greenstone at 500 foot, 600 foot, and 900 foot inclined depth.
From 1895 to 1908, the property was only a moderate producer from the small ore bodies of the hanging wall vein. This ore ranged for $2 to $6 (period values) a ton in yield and the total output was about $1.2 million (period values) for this period (Logan, 1934). During this time the 2740 level had been reached and 58 assessments had been levied to continue prospecting. A 20-stamp mill was in use part time. In 1908, crosscut to the footwall discovered the foot wall vein system. This ore shoot was subsequently developed by crosscuts from the higher levels, and was stoped up to about the 2000-foot level. The mill was increased to 80 stamps and the property for several years was one of the largest producers in the county employing from 200-250 men (Logan, 1934).
From 1908 until the mine closed in 1917, over 980,000 tons of ore yielding about $4.1 million (period values) was produced (Carlson & Clark, 1954). Total production of the South Eureka was $5.3 million from which about $1 million in dividends was paid (Carlson & Clark, 1954).
The mine closed in 1917 with a total production of $5,300,000 (period values). TIt was under option to the Central Eureka in 1921 and some exploratory work was done but no new ore was found. It is an extension of the Oneida, Kennedy and Argonaut Lead and lies between the Oneida and Central Eureka.
Mineralization is a Au vein deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27), hosted in Late Jurassic slate and greenstone of the Mariposa Formation. The ore body is tabular/pinch and swell in form. Ore Materials: Free milling gold in quartz with auriferous pyrite and arsenopyrite
Disseminated auiferous pyrite and arsenopyrite in greenstone. Controls for ore emplacement include ore shoots within mesothermal gold bearing quartz veins. Local alteration includes hydrothermal alteration of greenstone wall rocks resulting in disseminated auriferous pyrite in large enough bodies to constitute low-grade ore. Local rocks include Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains).
Regional geologic structures include the Bear Mountains Fault zone and the Melones Fault zone. Local structures include the Melones Fault zone.
At the South Eureka Mine, the Mother Lode system occurs in and along a belt of Mariposa slate, which is several hundred feet wide and bounded on both sides by greenstone. Three quartz veins were developed; the hanging wall vein, the foot wall vein, and the "middle vein" (Tucker (1914). A little ore also occurred in hanging wall greenstone.
Form the surface to a depth of 2000 feet, the hanging wall vein is a contact vein on the slate-greenstone contact, below which the vein passes into the greenstone. To a depth of 900 feet, the fissure was filled principally with crushed slate and gouge, containing only a little quartz.. The vein was highly disturbed by faulting with ore occurring in scattered bunches within the slaty gouge filling the fissure. This ore, however, did not turn out to be extensive and was not very profitable (Logan, 1934). On the footwall side of the vein there was also a rich pay streak from 1 to 10 inches wide with heavy sulfides. A crosscut on the 900-foot level also revealed a five-foot wide ore body in mineralized streaks of greenstone within the hanging wall.
In the middle and foot wall veins ore occurs in pockets, in greenstone streaks, and at the junction of the foot wall and middle veins below the 2000-foot level, where they merged into a single ore body. Most of the pay ore in the lower levels is from this ore body.
The foot wall vein was the principal ore body, and was found by following a spur vein from the hanging wall contact vein about 250 feet west until it joined the foot wall vein. It was followed upward from the 2750-foot level to above the 2000-foot level where it split into the foot wall and middle veins. The chief mine production was from ore bodies where the veins split and in the foot wall vein between the 2000-foot and 2750-foot levels (Carlson & Clark, 1954). In winzes and drifts below the bottom of the shaft, the ore body was only 60 feet long on the 2900-foot level where it raked north into the adjoining Central Eureka Mine's 2700-foot level (Logan, 1934).
Ore is free milling gold in quartz with auriferous pyrite, arsenopyrite, and minor amounts of sphalerite and galena. Concentrates formed 1.7% - 2% of the ore and carried form $60 - $72 a ton in gold and 40 to 65 cents in silver (Logan, 1934).
Workings include underground openings comprised of a 2,785 foot inclined shaft with crosscuts, a winze to the 2,900 foot level. Also worked on several of the Central Eureka levels, which were extended into this mine. An 80 stamp mill was erected.
The South Eureka Mine was developed through a 2875-foot inclined (67?) 3-compartment shaft (north shaft), and a 600-foot deep shaft located 880 feet to the southeast (south shaft). Crosscuts were run east and west from the main shaft to the ore bodies. A winze was sunk to the 2900-foot level but no ore was found. When the Central Eureka Mining Company had the property under option they prospected much of the deeper ground between 3500 and 4100 feet by extending several of the deeper levels of the Central Eureka Mine into the South Eureka property. The 3350 south level drift of the Central Eureka Mine was extended to a point 120 north of where the South Eureka shaft would be if continued. A west crosscut from the Central Eureka was run in greenstone near the north end line of the South Eureka on this level. On the 3900-foot level, the drift was run south 1180 feet from the Central Eureka shaft, extending into the South Eureka ground (Logan, 1934). These efforts resulted in the discovery of no new commercial ore bodies.
Ore was milled in an 80-stamp mill with a capacity of 400 tons per day. The ore was crushed, run through a 24-mesh screen, amalgamated, and concentrated on 48 Frue vanners. Mill recovery ranged from 85 to 91 percent. At full production, 200 to 250 men were employed at the mine and mill (Carlson & Clark, 1954).
Commodity Info: Concentrates formed 1.7% - 2% of the ore and carried form $60 - $72 (period values) a ton in gold and 40 to 65 cents (period values) in silver.
Clark (1970) reported that the South Eureka Mine produced $5.3 million.
6 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
145 - 201.3 Ma
|Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains)|
Age: Jurassic (145 - 201.3 Ma)
Stratigraphic Name: Copper Hill Volcanics; Gopher Ridge Volcanics; Logtown Ridge Formation; Mariposa Formation; Monte de Oro Formation; Oregon City Formation; Peaslee Creek Volcanics; Penon Blanco Formation; Brower Creek Volcanic Member; Smartville Complex
Description: Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks.
Comments: Western Sierra Nevada and western Klamath Mountains. Mostly basaltic to andesitic breccias, flows, and tuffs, metamorphosed but with primary volcanic features generally recognizable. Minor associated sandstone and conglomerate. Largely or entirely of marine origin. Includes some rocks interpreted as ophiolites (Smartville complex)
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052.