Horseshoe Mine (Horseshoe claim; Pedro lease [1918]), Grassely claims (Grassely group; Grassley claims; Grassley group; Lopez lease [1918]; Lopes lease), Peoria Flat, Yosemite Junction, Tuolumne County, California, USAi
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Latitude & Longitude (WGS84):
37° 54' 16'' North , 120° 30' 15'' West
Latitude & Longitude (decimal):
Type:
Köppen climate type:
Nearest Settlements:
| Place | Population | Distance |
|---|---|---|
| Chinese Camp | 126 (2011) | 7.2km |
| Jamestown | 3,433 (2011) | 9.0km |
| Tuttletown | 668 (2011) | 10.4km |
| Sonora | 4,818 (2017) | 13.9km |
| Copperopolis | 3,671 (2011) | 14.8km |
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 |
|---|---|---|
| Calaveras Gem & Mineral Society | Angels Camp, California | 18km |
A former Cr mine located in sec. 25, T1N, R13E, MDM, 0.7 km (2,200 feet) W of Peoria Flat, N of Peoria Pass (on the NW side of a small hill), on private (patented) land. Operated during the period 1914 to 1944. Owned by Eugene Grassley. Operated by George Everhart. MRDS database stated accuracy for this location is 10 meters.
Mineralization is hosted in rocks of the Franciscan Formation (Calaveras Formation ?) (Late Jurassic-Late Permian dunite). The ore bodies are disseminated tabular and lenticular, strikes N15-25W and dips 20W to SW at a thickness of 1 meter, a width of 2 meters, and a length of 15 meters. The primary mode of origin was magmatic differentiation and primary ore control was litholgy. The secondary menas of ore control was folding. Wallrock alteration is intense (Carbonitization and silicification) and serpentization of saxonite. Ore exposed at the shaft collar is 1 meter wide and 15 meters long. The deposit occurs in the northern part of the westernmost of 2 serpentine belts which trend NW-SE across the county. The belt is exposed over an area 30 km by 6 km. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).
Workings include surface and underground openings comprised of an open pit and a 40 foot deep shaft. The mine workings are located in an old placer diggings.
Production data are found in: CDMG Bulletin 134, part 3, chapter 1: 27.
Reserves estimated to be 200 long tons of milling-grade ore averaging 22 to 25% Cr2O3.
Analysis by CDMG in 1976 gave the following results: disseminated ore: SiO2 - 11.70%; Cr2O3 - 38.37%; FeO: 12.08%; Al2O3 - 8.29%; MgO - 15.59%. The Cr:Fe is 2.10
Select Mineral List Type
Standard Detailed Gallery Strunz Chemical ElementsDetailed Mineral List:
| ⓘ Formula: Fe2+Cr3+2O4 |
| ⓘ Magnesiochromite Formula: MgCr2O4 |
Gallery:
List of minerals arranged by Strunz 10th Edition classification
| Group 4 - Oxides and Hydroxides | |||
|---|---|---|---|
| ⓘ | Chromite ? | 4.BB.05 | Fe2+Cr3+2O4 |
| ⓘ | Magnesiochromite | 4.BB.05 | MgCr2O4 |
List of minerals for each chemical element
| O | Oxygen | |
|---|---|---|
| O | ⓘ Chromite | Fe2+Cr23+O4 |
| O | ⓘ Magnesiochromite | MgCr2O4 |
| Mg | Magnesium | |
| Mg | ⓘ Magnesiochromite | MgCr2O4 |
| Cr | Chromium | |
| Cr | ⓘ Chromite | Fe2+Cr23+O4 |
| Cr | ⓘ Magnesiochromite | MgCr2O4 |
| Fe | Iron | |
| Fe | ⓘ Chromite | Fe2+Cr23+O4 |
Other Databases
| Link to USGS MRDS: | 10098575 |
|---|
Other Regions, Features and Areas containing this locality
North AmericaContinent
North America PlateTectonic Plate
- Calaveras-Baker DomainDomain
- Sierra Nevada BatholithVolcanic Arc
USA
- California
- Mother Lode BeltBelt
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