Church Mine, Logtown, El Dorado Mining District, El Dorado County, California, USAi

Regional Level Types
Church Mine	Mine
Logtown	- not defined -
El Dorado Mining District	Mining District
El Dorado County	County
California	State
USA	Country

A former lode Au occurrence/mine located in the NE¼ sec. 12, T9N, R10E, MDM, 1.8 km (1.1 miles) ENE of Logtown (site), along Deadman Creek at the southern base of Tombstone Mountain (2 miles SE of El Dorado), on private land. Property was 80 acres. Operated by the Madre De Oro Gold Mines Co. Operated in the 1850's, 1860's, 1890's, 1900 to 1907,and 1941 to 1942. MRDS database stated accuracy for this location is 100 meters.

This mine was first worked on a small scale in the 1850's. It was consolidated with the Union Mine in the 1860's but later was worked separately. It was worked extensively in the 1880's and 1890's. It was closed in 1907 but was reopened in 1941 and the recorded production for that year was 169 ounces of Au from 496 tons of ore milled. Idle since 1942. The best ore was from the Kidney vein (middle vein), which was as high in grade as $30 (period values) per ton. The West vein contained only low-grade material. Sulfides formed 1½ to 2¼% of the ore and assayed as high as $140 (period values) per ton. Probably includes the Golden Fleece and El Dorado claims.

The Church Mine lies about 0.5 mile north of the Union Mine. Like the Union Mine, the Church Mine was first worked on a small scale about 1850. During the 1860s, it was consolidated with the Union Mine, but was later worked separately. By 1868, the combined Union and Church properties had produced more than $600,000.

Much information regarding the Church Mine was reportedly destroyed in the 1906 San Francisco fire. However, early annual reports of the California State Mineraloguist indicate that by 1888, the Church Mine was worked through a 315-foot vertical shaft and a tunnel two hundred and forty feet long reaching a vertical depth of 80 feet at 140 feet from the mouth and connected to the surface by a shaft 65 feet deep. At this depth, the mine was producing about 20,000 gallons of water per day. Ore was wet crushed in a stamp mill, amalgamated in a battery, and on outside plates. The mill was powered by a 6 foot Pelton wheel and contained a rock breaker and ten 850 pound stamps capable of crushing 16 ? tons per day. Four thousand pounds of concentrates were produced monthly (Irelan, 1888).

By 1896, the mine had been developed to a depth of 1,200 feet on the main Kidney vein. In 1907, the Church Mine was shut down. At the time of shut down, the property consisted of a three compartment shaft to a vertical depth of 1,350 feet with the vein developed on the 100, 200, 300, 350, 500, 600 700, 850, 1,000, and 1,200-foot levels. On the 1,200 foot level, there was a crosscut from shaft to the vein 670 feet east, from which point a winze was sunk on the vein to a depth of 1,400 feet. The 600 and 1,200 foot levels were run clearv to the property line. The vein was stoped out on ore shoots from 1,200 foot level to the surface (Tucker and Waring, 1916). There was a poor zone between 350 and 500 foot levels, where the ore was replaced by gouge, but ore came in at 500 feet and continued to 1300 feet. Heavy gouge was encountered at the 1,300 foot level and little prospecting was done below that. Ore milled down to 1,300 feet level averaged $17 a ton before heavy gouge was encountered. The gouge was so soft and broken it could be shoveled. It carried a value of about about $4 a ton. On the 1,400 foot level, they drifted 80 feet but the ground ran and swelled overnight and could not be held open. At total depth, the mine was producing 75,000 gallons of water a day.

In 1941, the mine was reopened by the Madre de Oro Mining Company. The shaft was rehabilitated and a new surface plant was built and a 20-stamp mill with flotation erected. Reported production for 1941 indicates that 496 tons of ore were milled from which 169 ounces of gold were recovered. The mine was shut down in 1942 and has been idle ever since. Between 1953-1954, the El Dorado Chrome Company used the mill as a custom Chrome mill, and the North American Tungsten Company used the mill to treat tungsten ore that it trucked in from the Garnet Hill Mine in eastern Calaveras County.

Mineralization is a vein deposit hosted in Mariposa slate. The ore body strikes NNE and dips 74SE at a thickness of 3.05 meters. There are 3 veins at 5 to 10 feet in thickness that strike N to NE and dip steeply. The main vein is the Kidney vein, which strikes N between the surface and the 350 foot level, below that level the strike swings to the NE. From the 350 foot and 500 foot levels, the vein dips 45E, but below the 500 foot level it steepens to 74SE. A number of kidney-shaped ore shoots were developed between the surface and the 500 foot level. The main ore shoot was continuous between the 500 and 1,200 foot levels. Below the 1,200 foot level, the grade decreased greatly. Local rocks include Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains).

The Church Mine developed three veins (West vein, Kidney vein, and East vein) within the Mariposa slates about ? mile north of the Union Mine. Similar to the Union Mine, the veins generally strike NNE-SSW, dip 74? E, and average 5-10 feet wide. The principal and middle Kidney vein was named for a number of kidney shaped ore shoots that were developed between the surface and the 500-foot level. The vein averaged 6 feet wide. While the dip of the Kidney vein was steep near the surface and at depth, it flattened to about 45? E between 350 feet and the 500 foot level where the vein had been largely cut out and replaced by fault gouge. Below the 500 foot level it resumed a dip of 74? SE and its strike trended more NE-SW (Tucker and Waring, 1916). The main ore shoot from the 500 level to the 1,200 level was continuous, but below the 1,200 level, the grade decreased greatly, and at 1,300 feet heavy gouge was encountered and little prospecting was done below that.

The best Kidney vein ore graded as high as $30/ton and was mined during the earliest shallow operations. Ore down to the 1,300 foot level averaged about $17/ ton. Values decreased to about $4/ton or less in the underlying gouge.

Little is recorded about the East and West veins with the exception that the East vein is known to have been worked in the neighboring Union Mine, and the West vein is known to be quite low grade.

Workings include underground openings comprised of a 1,200 foot vertical shaft with crosscuts to the vein. There are 10 levels, a winze, drifts and an extensive surface plant. Levels are at 100, 200, 300, 350, 500, 600, 700, 850, 1000, and 1,200 feet. A 670 foot crosscut extends E to the vein on the 1,200 foot level, from which a winze was sunk on the vein to the 1,400 foot level. On the 600 and 1,200 foot levels, drifts extend N and S to the property line.

Production data are found in: Clark, Wm. B. & D.W. Carlson (1956).

The best ore at $30 (period values) per ton was mined during the earlier operations. Ore milled from as far down as the 1,300 foot level had averaged $17 (period values) per ton. Below that levelit decreased to $4 (period values) per ton, or less. The sulfides assayed as high as $140 (period values) per ton in Au. Considerable amounts of gouge were present, especially in the lower levels. Some of the gouge carried some Au.

Analytical data results: Sulfides comprise 1½ to 2¼% of the ore.

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Link to USGS MRDS:	10092078

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