Garnet Hill Mine (Rheona claim), Garnet Hill, Moore Creek - Mokelumne River confluence area, Calaveras Co., California, USA

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Location
Garnet Hill is a former W-Au-Cu-Mo mine located in secs. 6 & 7, T7N, R16E, MDM, just above the confluence of Moore Creek and the Mokelumne River, on the summit of Garnet Hill. The mine consists of a series of cuts on the summit of the hill.

History
Little is known of the early history of this property, but it may have been prospected for copper during the 1860's. It has long been known as a source of fine garnet and epidote crystals. The property was prospected again during World War I, and during the 1920's and 30's numerous mineral collectors visited the area. During World War II, the area was prospected for tungsten by a number of persons and concerns including the Garnet Hill Tungsten Syndicate, L.A. Smith, and Marsman and Company, but there was no recorded output. Also during this time, the property was briefly examined by the U.S. Geological Survey for the Reconstruction Finance Corporation.


In 1953 and 1954, the mine was operated by the North American Tungsten Mining Company, A.L. Damon, president. Ore was mined in an open pit on the west tactite body and trucked to the mill at the Church gold mine, 5 miles south of Placerville, El Dorado County, where it was treated by flotation. Concentrates were shipped to Bishop for sale. Operations ceased in 1954, and except for annual assessment work, the mine has been idle since.

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Geology
This deposit is at the crest of Garnet Hill, a steep, dome-shaped peak located just south of the Mokelumne River. Scheelite with various amounts of molybdenite and chalcopyrite are scattered sporadically in a series of north-striking parallel tactite bodies. The most extensive tactite body, which is on the west side, is nearly 800 feet long and ranges from 20 to 35 feet in width. Two other major tactite bodies lie to the east on the hill, and there are several smaller bodies as well. Country rock in the vicinity of the tactite consists chiefly of medium-grained gneiss with small amounts of quartz-mica schist and granodiorite. Much of the tactite contains little or no scheelite, but locally it contains scheelite in extremely finely disseminated grains, and in a few places on the surface well formed crystals as much as 2 inches in length have been found.



Chalcopyrite containing minor amounts of gold and fine to coarse-grained molybdenite are irregularly distributed throughout the tactite. The principal scheelite-bearing zone, which is in the west tactite body, is 20 to 25 feet wide and approximately 500 feet long. The ore that was mined in 1953-54 contained from 0.3 to 0.5 percent WO3. The mine is developed by an open pit, several open cuts and an 80-foot adit, now caved, that extends south from the north side of the hill.

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Genesis
Oxidized W-skarn occurs near roof pendant contacts against hornblende biotite granodiorite in the Garnet Hill area of the Sierra Nevada range. Marble lenses were initially transformed to zoned Ca-rich bimetasomatic skarn by reaction with adjacent lithologies. Near igneous contacts, these lenses are replaced by Fe-rich garnet infiltration skarn overprinted by hydrous silicate alteration (GSA Denver Ann. Meeting, 2002, Paper No. 158-2).

Production data are found in: Clark and Lydon (1962).

Mineral List

Actinolite Andradite 'Apatite' 'Axinite Group' 'Biotite' Chalcopyrite

'Chlorite Group' Epidote Ferro-Actinolite 'Garnet' Gold 'Hornblende'

Laumontite Molybdenite 'Mountain Leather' Quartz Riebeckite Scheelite

Stilpnomelane Talc Titanite Tremolite Vesuvianite Zircon

24 entries listed. 17 valid minerals.

References

External Links