Delhi - St. Gothard Mine

Site Name

Primary: Delhi - St. Gothard Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Nevada
District: North Columbia District

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Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Nevada County Planning Dept.

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1860
Years of Production:
Organization:
Significant: Y

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular, lens

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Structure

Type: R
Description: Ramshorn Fault, Goodyears Creek Fault

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Alterations

Not available

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Rocks

Name: Slate
Role: Host
Description: black to dark brown, highly siliceous
Age Type: Host Rock
Age Young: Triassic
Age Old: Carboniferous

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Slate
Gangue: Quartz

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Comments

Comment (Development): The date of discovery of the Delhi vein is unknown. The first mention of the mine is in the 1886 report of the State Mineralologist. Prior to 1886, the Delhi Mine was worked by two tunnels. In 1888 there were 6 miles of ditch to bring water to the mine. From 1886 to 1893 the mine was worked continuously and the pay shoot was developed by 4 tunnels; Tunnel No. 4, 83 feet above the river and 900 feet below the outcrop with a length of 1,700 feet; tunnel No. 3, 330 feet above No. 4 was run 1,200 feet; tunnel No. 2, 200 feet above No. 3, and Tunnel No. 1. By 1893 most of the ore had been stoped above Tunnel No. 4; sinking of the shaft below this level was attempted but abandoned because of the excessive amount of water encountered after which the mine was closed. In 1898, the Delhi and neighboring St. Gothard mines were consolidated and reopened as the Consolidated (Delhi) Mine. The No. 4 tunnel was extended to 2,000 feet, as a crosscut for the first 1,000 feet and then along the vein for 1,000 feet. A new 20-stamp mill was also erected. Seventy-five feet above the No. 4 tunnel the vein split on its dip, with an East vein dipping 55? east, and a "West" vein dipping 80? E. A shaft was sunk on the East vein to a depth of 500 feet and a crosscut was driven 400 feet into the footwall before it encountered the West vein. From this shaft, levels averaging 800 feet were run on the east vein at 100 foot intervals. By this time, the main ore shoots of the Delhi vein had been stoped from the bottom of the shaft to the surface - a vertical distance of 1,600 feet. The mine was closed in 1916, reopened and closed again the next year. It was then leased to the Delhi Mines Company, which attempted to reopen it again, but failed due to the excessive water. The mine was finally closed in 1918. At that time the holdings covered about 160 acres including the Last Chance, Yuba River, Yuba River Extension, Helvetia, and St. Gothard patented claims. In 1920, work was begun to use the mine's water for generating electricity to sell to the local power company.

Comment (Economic Factors): The total production for the Delhi-St. Gothard Mine is unknown, but production from 1890 - 1914 was reported to be $1,514,435.

Comment (Commodity): Ore Materials: Free-milling gold-bearing quartz veins

Comment (Commodity): Gangue Materials: Quartz, slate

Comment (Workings): In 1898 the Delhi Mine and neighboring St. Gothard Mine were consolidated into the Delhi-St.Gothard Mine. Prior to this merger, the original Delhi Mine was worked through a series of four tunnels driven southward from the north flank of Grizzly Ridge. Tunnels were 6 x 7 feet and timbered only at the mouth and near the ore shoot. The No. 1 tunnel was the highest, 230 feet long with about 150 feet along the ore shoot. The No.2 tunnel, 200 feet vertically below the No. 1 tunnel, was 1,000 feet long. The No. 3 tunnel, 200 vertical feet below the No. 2 tunnel was 1,200 feet . The fourth (No. 4) tunnel was 330 feet below the No. 3 tunnel and 1,700 feet long. The No. 4 adit was 83 feet above the Middle Fork of the Yuba River and 900 feet below the Delhi vein outcrop. The lower tunnels were crosscut to the vein along the first portion of their length and then run on the vein where it could be economically intersected. The original Delhi Mine ore was treated by wet stamping in an 18-stamp mill, amalgamation in batteries and on plates, and concentration by Frue and Triumph vanners. The mill was powered by water with a 240 foot head and 4 Pelton wheels, one each operating a rock crusher, stamps, hoist, and concentrator. The mill was located at the mouth of Tunnel 1 and the ore had to be hoisted from the lower tunnels from which it was hauled out. The ore was hoisted on a tramway up the steep hillside to a height above the mill where it was dumped on grizzlies. Coarse material was crushed, then dumped in the bin with the material passing the grizzly. From the bin the ore was passed through chutes to the feeders. The original St. Gothard Mine was opened by a 280 foot 5' x 10' vertical timbered shaft and 2 levels on the vein, driven in from the north side of Grizzly Ridge. The shaft connected with an 1,100-foot upper-level drain tunnel at 180 feet. A lower level extended 600 feet to the north and 400 feet east. The mine below the drain tunnel had to be pumped clear of water. A steam plant was used for hoisting ore from the shaft and for pumping. After the Delhi and St. Gothard mines were consolidated, the No. 4 tunnel was extended to 2,000 feet, the first 1,000 feet being a crosscut and the second 1,000 feet along the vein. Since the Delhi vein was found to split 75 feet above the No. 4 tunnel with an East vein dipping 55? east and a West vein dipping 80? east, a shaft was sunk on the east vein to a depth of 500 feet and a crosscut was driven 400 feet into the footwall before it encountered the West vein. From this shaft levels averaging 800 feet long were driven on the East vein at 100 foot intervals.

Comment (Geology): The mine produced from two of three principal fissure-filling mesothermal quartz veins within a group of north-south-trending veins, which outcrop on the north flank of Grizzly Ridge. The largest, or Delhi vein, was mined in the Delhi Mine, and the St. Gothard vein produced in the nearby St. Gothard Mine before these mines were consolidated in 1898. The original St. Gothard Mine was located on the summit of Grizzly Ridge less than a half mile south of the Delhi Mine. A third, smaller vein, the Live Oak, produced in the Live Oak Mine less than a half-mile west of the Delhi-St. Gothard. The Delhi vein strikes N 10? E and dips 75 - 80? east, its outcrop being traceable for about 0.5 mile. The vein ranged from 6 inches to 16 feet wide, but averaged about 5-7 feet wide. The main vein was nearly all quartz and produced gold from an ore shoot reported to be 200 - 400 feet long. Seventy five feet above the lowermost tunnel, the Delhi vein split into an East vein dipping 55? east and a West vein dipping 80? east. Delhi ore was massive banded quartz carrying coarse free gold with auriferous pyrite, chalcopyrite, arsenopyrite, and a small proportion of galena and sphalerite. The ore yielded about 1-4% sulfides assaying $80-$100 per ton. The concentrates were treated by chlorination at the company works adjacent to the mill with 93% of the assay value being recovered. The yield of the quartz ore was generally more than $12/ton. The walls are hard slate with a slight black gauge, but generally they are very smooth. The entire vein, from wall to wall, was mined and milled. The St Gothard vein strikes north-south and dips 80? east. The vein is much thinner than the Delhi vein averaging only 1-2 feet wide. The Gothard outcrop cuts across the contact between the Paleozoic-Mesozoic slate unit and diorite, but in the subsurface the walls are mostly slate.

Comment (Geology): REGIONAL SETTING The northern Sierra Nevada is home to numerous important lode and placer gold deposits. It includes the famous lode districts of Alleghany, Johnsville, Sierra City, Grass Valley, and Nevada City and the famous placer districts of La Porte, North Columbia, Cherokee, Michigan Bluff, Forest Hill, and Dutch Flat to name a few. The geological and historical diversity of most of these deposits and specific mine operations are covered in numerous publications produced over the years by the U.S. Bureau of Mines, U.S. Geological Survey, California Division of Mines and Geology (now California Geological Survey), and others. The most recent geologic mapping covering the area is the 1:250,000-scale Chico Quadrangle compiled by Saucedo and Wagner (1992). The northern Sierra Nevada basement complex has a history of both oceanic and continental margin tectonics recorded in sequences of oceanic, near continental, and continental volcanism. The complex has been divided into four lithotectonic belts; the Western Belt, Central Belt, Feather River Peridotite Belt, and Eastern Belt. The Western Belt is composed of the Smartville Complex, an Upper Jurassic volcanic-arc complex consisting of basaltic to intermediate pillow flows overlain by pyroclastic and volcanoclastic rocks with diabase, metagabbro, and gabbro-diorite intrusives. To the east it is bounded by the Big Bend-Wolf Creek Fault Zone. East of the Big Bend-Wolf Creek Fault Zone is the Central Belt, which is in turn bounded to the east by the Goodyears Creek Fault. This belt is structurally and stratigraphically complex and consists of Permian-Triassic argillite, slate, chert, ophiolite, and greenstone of marine origin. The Feather River Peridotite Belt is also fault-bounded, separating the Central Belt from the rocks of the Eastern Belt for almost 95 miles along the northern Sierra Nevada. It consists largely of Devonian-to-Triassic serpentinized peridotite. The Eastern Belt, or Northern Sierra Terrane, is separated from the Feather River Peridotite Belt by the Melones Fault Zone. The Northern Sierra Terrane is primarily composed of siliciclastic marine metasedimentary rocks of the Lower Paleozoic Shoo Fly Complex overlain by Devonian-to-Jurassic metavolcanic rocks. Farther east are Mesozoic granitic rocks of the Sierra Nevada Batholith. Most Upper Jurassic and younger basement rocks of the northern Sierra Nevada were metamorphosed and deformed during the Jurassic-Cretaceous Nevadan Orogeny. The dominant northwest-trending structural grain is a result of this period of compressive deformation, which produced thrust faults, major northwest-trending folds, and regional greenschist facies metamorphism. This episode also resulted in the intrusions of granitic plutons that formed the Sierra Nevada. LOCAL GEOLOGY The Delhi-St. Gothard Mine is located in the Central Belt lithotectonic unit. Bedrock consists of black to dark brown highly siliceous slate of what was formerly mapped by Lindgren (1900) as the Delhi Formation, a subunit within the metamorphic Calaveras Formation. Saucedo and Wagner (1992) more recently designated this unit as an undifferentiated metasedimentary unit of Paleozoic-Mesozoic age. This unit is intruded by Cretaceous diabase and diorite and by gabbro dikes and intrusions. The main diabase body is exposed as a long, slender lens trending northwesterly through the central portion of the North Columbia District and passing immediately south of the mine. Gabbro occurs along Grizzly Ridge, cutting across the Paleozoic-Mesozoic unit and the diabase.

Comment (Deposit): The Delhi-St. Gothard Mine produced free-milling gold from two of a series of northerly trending mesothermal, fracture filling, low-sulfide gold quartz veins. The larger Delhi vein ranged from 6 inches to 16 feet thick, but averaged 5-7 feet wide. The St. Gothard Vein averaged only 1-2 feet wide. The quartz ores generally yielded more than $12 per ton. The sulfides, which averaged 1-3%, assayed from $80 to $100 per ton.

Comment (Identification): The Delhi-St. Gothard Mine is in the North Columbia District in north-central Nevada County about 9 miles north of Nevada City. While this district is primarily known for its auriferous Tertiary gravels, it included several lode mines; the most important are the Delhi and St. Gothard mines. Originally two independent mines (Delhi and St. Gothard mines), they were consolidated in 1898 and worked until 1916. The mine produced from two north-south- trending mesothermal gold-quartz veins, the Delhi vein and the St. Gothard vein. The more important Delhi vein was mined from the lowest level in the Delhi Mine to its outcrop 900 feet above. Deepening of the mine was prohibited by excessive water. The total production for the Delhi-St. Gothard Mine is unknown, but production from 1890 - 1914 was reported to be $1,514,435.

Comment (Location): Location selected for latitude and longitude is the Delhi-St. Gothard Mine symbol on the USGS 7-1/2-minute Pike quadrangle

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References

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 101-102.

Reference (Deposit): Crawford, J.J., 1896, Nevada County, Delhi Mine: California State Mining Bureau Report 13, p. 241, 266.

Reference (Deposit): Garthwaite, E.M., 1886, Nevada County, Delhi Mine: California State Mining Bureau Report 6, p. 50-51.

Reference (Deposit): Hobson, J.B. and Wiltsee, E.A., 1893, Columbia Hill District, Delhi Mine: California State Mining Bureau Report 11, p. 305-307.

Reference (Deposit): Irelan, W., Jr., 1888, Columbia Hill District, Delhi Mine: California State Mining Bureau Report 8, p. 444-447.

Reference (Deposit): Lindgren, W., 1900, Colfax folio, California: U.S. Geological Survey Atlas of the U.S., Folio 66, 10 p.

Reference (Deposit): Lindgren, W., 1911, Tertiary gravels of the Sierra Nevada, U.S. Geological Survey Professional Paper 73, p. 143-144.

Reference (Deposit): Loyd, R. and Clinkenbeard, J., 1990, Mineral Land Classification of Nevada County, California: California Dept. of Conservation, Division of Mines and Geology, Special Report 164.

Reference (Deposit): MacBoyle, E., 1919, Nevada County, Consolidated (Delhi) Mine: California State Mining Bureau Report 16, p. 147-149.

Reference (Deposit): Saucedo, G. J. and Wagner, D. L., 1992, Geologic map of the Chico Quadrangle: California Division of Mines and Geology Regional Map Series Map No. 7A, scale 1:250,000.

Reference (Deposit): Additional information on the delhi-St. Gothard Mine is contained in File No. 339-3009 (CGS Mineral Resources Files, Sacramento)

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