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Oxford Mine (Oxford Mine and mill; Oxford lease and mill; Becky; Case and Myers; Mt. Holly; Gold Bluff; Good Hope; Good Hope Extension No. 2; Jefferson No. 2 claim; Milton claim), Downieville, Downieville Mining District, Sierra County, California, USAi
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Latitude & Longitude (WGS84):
39° 34' 42'' North , 120° 49' 58'' West
Latitude & Longitude (decimal):
Type:
Kรถppen climate type:
Nearest Settlements:
| Place | Population | Distance |
|---|---|---|
| Downieville | 282 (2011) | 2.2km |
| Sierra City | 221 (2011) | 17.1km |
| Pike | 134 (2011) | 21.0km |
| Plumas Eureka (historical) | 339 (2011) | 22.7km |
| Camptonville | 158 (2011) | 23.2km |
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 |
|---|---|---|
| Nevada County Gem & Mineral Society | Grass Valley, California | 44km |
A former Au-Cr-Fe occurrence/mine located in the SEยผ sec. 22, secs. 23, 26 & 27, NWยผ sec. 26, and the NEยผ sec. 27, T20N, R10E, MDM, 2.2 km (1.3 miles) NNW of Downieville, on the divide between the Downie River on the E and Coyote Ravine on the W, on National Forest land. Owned by E. R. C. Zaring, last operator (1941), California. Operated/owned by C. L. Best (1942-1944). MRDS database stated accuracy for this location is 10 meters. This mine is located on a SE-facing slope.
Mineralization is a vein deposit hosted in slate, serpentinite and porphyry (Late Cretaceous-Late Permian dunite of the Calaveras Formation). The deposit occurs in a NW-trending sill-like peridotite body that is a minor, southern extension of a larger mass exposed to the N of the deposit. The ore body strikes N55W and dips 55N at a thickness of 9 meters, width of 1 meter, and a length of 30 meters. Orebody No. 1 is lenticular, disseminated; ore body No. 2 is tabular; and No. 3 is irregular. The primary mode of origin was magmatic differentiation. Primary ore control was lithology and the secondary was fracturing. Wallrock alteration is moderate (carbonitization). Chromite vein is 2 to 7ยฝ feet thick, 50 feet from a slate-serpentine contact, and changes strkike from N15W to N to N15E. The ore is oxidized. The walls are a mixture of slate and soapstone, but the hanging wall on No. 2 extension is porphyry. The deposits occur in 3 zones: 1) The E ore zone strikes N45-55E and dips 60-80N; the W ore zone strikes N20-30W and dips 45SW; the third ore zone strikes E-W and dips 60-70N. An unusual occurrence of high-grade ore containing 58% Cr2O3 was found between the E and W ore zones. The divergence of orientation exhibited by the ore zones within a relatively small area appears to be the result of their distribution within a series of tight, asymmetric folds. Local alteration includes partial serpentinization of host rocks. Local rocks include Paleozoic marine rocks, undivided, unit 4 (Western Sierra Nevada).
Regional geologic structures include the Melones Fault Zone.
Workings include surface and underground openings with an overall length of 1,828.8 meters. The main adit reaches the vein at 650 feet and has 900 feet of drifts. The second adit is 150 feet W with a 50 foot drift. The third adit is 250 feet and cuts the vein 80 feet from the portal and has a 30 foot drift. There was also apparently at least one shaft. Surface workings were comprised of several open pits and shallow cuts. In 1943, several hundred feet of diamond drilling was completed.
About 2,250 long tons of ore had been produced. This included 2,000 tons of grade at 40.60% Cr2O3, 11.76% Fe, 0.22% SiO2 and 0.10% P, with a Cr:Fe ratio of 2.36:1.
Analytical data results: lump ore: 38.59% Cr2O3, Cr to Fe ratio of 2.30:1.
Reserves and resources: Type: in-situ (estimate year = 1975): total resources: 8,000 metric tons of ore at Cr2O3 at 20 weight percent.
Select Mineral List Type
Standard Detailed Gallery Strunz Chemical ElementsDetailed Mineral List:
| โ Formula: Fe2+Cr3+2O4 |
| โ Clinochlore Formula: Mg5Al(AlSi3O10)(OH)8 |
| โ Clinochlore var. Pennine Formula: Mg5Al(AlSi3O10)(OH)8 |
| โ 'Fayalite-Forsterite Series' |
| โ Magnesiochromite Formula: MgCr2O4 |
| โ Native Gold Formula: Au |
| โ Quartz Formula: SiO2 |
| โ 'Serpentine Subgroup' Formula: D3[Si2O5](OH)4 |
| โ Talc Formula: Mg3Si4O10(OH)2 |
| โ Uvarovite Formula: Ca3Cr2(SiO4)3 |
Gallery:
List of minerals arranged by Strunz 10th Edition classification
| Group 1 - Elements | |||
|---|---|---|---|
| โ | Native Gold | 1.AA.05 | Au |
| Group 4 - Oxides and Hydroxides | |||
| โ | Chromite ? | 4.BB.05 | Fe2+Cr3+2O4 |
| โ | Magnesiochromite | 4.BB.05 | MgCr2O4 |
| โ | Quartz | 4.DA.05 | SiO2 |
| Group 9 - Silicates | |||
| โ | Uvarovite | 9.AD.25 | Ca3Cr2(SiO4)3 |
| โ | Talc | 9.EC.05 | Mg3Si4O10(OH)2 |
| โ | Clinochlore | 9.EC.55 | Mg5Al(AlSi3O10)(OH)8 |
| โ | var. Pennine | 9.EC.55 | Mg5Al(AlSi3O10)(OH)8 |
| Unclassified | |||
| โ | 'Fayalite-Forsterite Series' | - | |
| โ | 'Serpentine Subgroup' | - | D3[Si2O5](OH)4 |
List of minerals for each chemical element
Other Databases
| Link to USGS MRDS: | 10086547 |
|---|
Other Regions, Features and Areas containing this locality
North AmericaContinent
North America PlateTectonic Plate
- Calaveras-Baker DomainDomain
- Sierra Nevada BatholithVolcanic Arc
USA
- Sierra NevadaMountain Range
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