McCormick Mine (McCormick property; Terry and Sell lease [WWI]), Yosemite Junction, Tuolumne Co., California, USA
|Latitude & Longitude (WGS84):||37° 52' 48'' North , 120° 30' 31'' West|
|Latitude & Longitude (decimal):||37.88000,-120.50861|
|Köppen climate type:||Csa : Hot-summer Mediterranean climate|
A former Cr mine located in sec. 2, T1S, R13E, MDM, 2.1 km (7,000 feet) SW of Yosemite Junction, along Mountain Pass Creek, on private land. Discovered in 1875. Operated from 1875 to 1957. Owned by Joseph W. Martin, Sonora, California 95370. Operated by A.E. and A.M. Hemming (North deposit); and by W.R. Williamson (South deposit) (1957-1976). MRDS database stated accuracy for this location is 10 to 100 meters (2 MRDS files).
Mineralization is hosted in the Josephine Ophiolite (dunite). The ore body is lenticular, disseminated & tabular, strikes N30-45W and dips NE (85E) at a thickness of 2.0 meters, a width of 61 meters and a length of 50 meters. The primary mode of origin was magmatic differentiation. Primary ore control was lithology and the secondary control was faulting. Wallrock alteration is intense (carbonitization & bleaching). The deposit consisted of 2 main ore bodies, North & South. Both had about the same strike and dip. The southern body was originally 165 feet long and had an average width of 4 feet and was highly faulted. The northern body was mined to a depth of 100 feet and had an average width of 3 to 6 feet. The deposit occurs in the northern part of the western part of 2 serpentine belts which trend NW-SE across the county. The belt is exposed over an area 30 km by 6 km. Associated rocks include diabase of the Logtown unit. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).
Local structures include the NW-trending Bear Mountain Fault.
Workings include surface and underground openings. Workings of the southern deposit consisted of 3 shafts, 34 to 220 feet deep, and over 700 feet of drifts, crosscuts, raises and winzes. Workings of the northern deposit consisted of shafts and drifts, now caved (1944).
Production data are found in: Stinson (1975), CDMG Mineral Property Report, unpublished.
No more than 615 long tons of ore averaging 46.7% Cr2O3 remained unmined (cited from record 702). The mine was last worked in 1957. 144 long tons of milling grade ore was produced. 53 long tons were shipped. Analysis by the California DMG during 1976 are documented in MRDS file #10190541.
The 1950's production probably came from reworking of the mine dumps.
Analytical data results: Ore averaged 43-49% Cr2O3 and the Cr to Fe ratio was 2.8-3.5:1.
7 valid minerals. 1 erroneous literature entry.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Early Jurassic - Neoproterozoic|
174.1 - 1000 Ma
|Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains)|
Comments: Feather River peridotite, Kings River ophiolite, Kings-Kaweah ophiolite melange. Tectonized ultramafic complexes in western Sierra Nevada and western Klamath Mts., primarily of Ordovician to Early Jurassic age. Characterized in large part by serpentinite-matrix melanges containing blocks and slabs of ultramafic and other rocks
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052.