O'Brien Mine (S-Bend Mine), Coloma, Coloma Mining District, West Belt, El Dorado County, California, USAi
| Regional Level Types | |
|---|---|
| O'Brien Mine (S-Bend Mine) | Mine |
| Coloma | - not defined - |
| Coloma Mining District | Mining District |
| West Belt | - not defined - |
| El Dorado County | County |
| California | State |
| USA | Country |
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Latitude & Longitude (WGS84):
38° 49' 53'' North , 120° 54' 3'' West
Latitude & Longitude (decimal):
Type:
Köppen climate type:
Nearest Settlements:
| Place | Population | Distance |
|---|---|---|
| Coloma | 529 (2011) | 3.6km |
| Georgetown | 2,367 (2011) | 10.0km |
| Auburn Lake Trails | 3,426 (2011) | 10.2km |
| Cold Springs | 446 (2011) | 10.3km |
| Cool | 4,100 (2017) | 11.6km |
Nearest Clubs:
Local clubs are the best way to get access to collecting localities
Local clubs are the best way to get access to collecting localities
| Club | Location | Distance |
|---|---|---|
| El Dorado County Mineral and Gem Society | Placerville, California | 14km |
| Gold Country Treasure Seekers | Placerville, California | 14km |
| Roseville Rock Rollers | Roseville, California | 35km |
| Fossils for Fun Society, Inc. | North Highlands, California | 44km |
| Sacramento Valley Detecting Buffs | North Highlands, California | 44km |
Mindat Locality ID:
77999
Long-form identifier:
mindat:1:2:77999:0
GUID (UUID V4):
d7124285-9219-46e3-86b9-30acdc8c023e
A former Cr-Fe occurrence/mine located in the SE¼ sec. 7, T11N, R10E, MDM, about 4.65 km (2 miles) NNW of Coloma, on the divide between Indian Creek and Perry Mountain Creek, SW of Perry Mountain (on a steep, SE-facing hillside), on private (patented) land (private lease). Discoverd in 1917. First production occurred in 1918. Owned by Maragret G. Bell (1976) (100%), California (1976). Operated by C. F. Gladwill. Operated by Volo Mining Company (last operator) (1942), California (1976). Operated in 1918 and in 1942. MRDS database stated accuracy for this location is 10 meters.
Mineralization is hosted in rocks of the Amador Group, Logtown (harzburgite, dunite, pyroxenite). The ore body strikes N35W and dips 53S at a thickness of 1 meter, width of 10 meters, and a length of 20 meters. Ore body No. 1 is disseminated, tabular; ore body No. 2 is lenticular; and, ore body No. 3 is irregular. The primary mode of origin was magmatic differentiation. Primary ore control was lithology and the secondary was faulting. Wallrock alteration is intense (carbonitization). Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).
Local geologic structures include: A fault with considerable apparent displacement is exposed in the lower adit and on surface.
Workings include underground openings comprised of 2 adits and a glory hole.
Production data are found in: Cater, F.W., Jr., G.A. Rynearson & D.H. Dow (1951).
The average grade of ore shipped in 1918 was 32 to 34% Cr2O3 (several hundred tons). About 3,000 tons were shipped in 1942 (Volo Mining Co.). Total production was approximately 3,200 to 3,500 tons. Analysis by state agency in 1976 gave the following percentages for disseminated ore: Si02: 03.69%, Cr2O3: 43.85%, FeO: 10.65%, total Fe: 12.87%, Al203: 19.8%, ?: 9.07%, Cr/Fe = 3.00.
Reserve-Resource data are found in: Cater, F.W., Jr., G.A. Rynearson & D.H. Dow (1951).
Reserves and resources: Type: In-situ; estimate year: 1979; inferred: 765 metric tons ore; demonstrated: 254 metric tons of ore; indicated: 254 metric tons of ore. Total resources: 765,000 metric tons of ore at 33% Cr2O3. Very little ore remains.
Select Mineral List Type
Standard Detailed Gallery Strunz Chemical ElementsDetailed Mineral List:
| ⓘ Chromite Formula: Fe2+Cr3+2O4 |
| ⓘ 'Fayalite-Forsterite Series' |
| ⓘ 'Pyroxene Group' Formula: ADSi2O6 |
| ⓘ 'Serpentine Subgroup' Formula: D3[Si2O5](OH)4 |
| ⓘ Talc Formula: Mg3Si4O10(OH)2 |
Gallery:
List of minerals arranged by Strunz 10th Edition classification
| Group 4 - Oxides and Hydroxides | |||
|---|---|---|---|
| ⓘ | Chromite | 4.BB.05 | Fe2+Cr3+2O4 |
| Group 9 - Silicates | |||
| ⓘ | Talc | 9.EC.05 | Mg3Si4O10(OH)2 |
| Unclassified | |||
| ⓘ | 'Fayalite-Forsterite Series' | - | |
| ⓘ | 'Pyroxene Group' | - | ADSi2O6 |
| ⓘ | 'Serpentine Subgroup' | - | D3[Si2O5](OH)4 |
List of minerals for each chemical element
| H | Hydrogen | |
|---|---|---|
| H | ⓘ Talc | Mg3Si4O10(OH)2 |
| H | ⓘ Serpentine Subgroup | D3[Si2O5](OH)4 |
| O | Oxygen | |
| O | ⓘ Chromite | Fe2+Cr23+O4 |
| O | ⓘ Talc | Mg3Si4O10(OH)2 |
| O | ⓘ Pyroxene Group | ADSi2O6 |
| O | ⓘ Serpentine Subgroup | D3[Si2O5](OH)4 |
| Mg | Magnesium | |
| Mg | ⓘ Talc | Mg3Si4O10(OH)2 |
| Si | Silicon | |
| Si | ⓘ Talc | Mg3Si4O10(OH)2 |
| Si | ⓘ Pyroxene Group | ADSi2O6 |
| Si | ⓘ Serpentine Subgroup | D3[Si2O5](OH)4 |
| Cr | Chromium | |
| Cr | ⓘ Chromite | Fe2+Cr23+O4 |
| Fe | Iron | |
| Fe | ⓘ Chromite | Fe2+Cr23+O4 |
Other Databases
| Link to USGS MRDS: | 10029957 |
|---|
Other Regions, Features and Areas containing this locality
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References
(n.d.) Minerals Availability System (MAS), U.S. Bureau of Mines.file #0060170022
