Plumbago Mine (Marion Mine; Croesus Mine; Standard Extension Mine; Crafts Clute Mine; Enterprise Mine; Hope Mine; Gold Beater Mine), Plumbago, Alleghany District (Forest District), Sierra Co., California, USA
|Latitude & Longitude (WGS84):||39° 27' 10'' North , 120° 48' 42'' West|
|Latitude & Longitude (decimal):||39.45278,-120.81167|
A former lode Au-Pb-Cu occurrence/mine located in the SW¼ sec. 1, & in secs. 2 & 12, T18N, R10E, MDM, 0.5 km (0.3 mile) E of Plumbago, along Buckeye Ravine (about 2 miles SE of Alleghany), on National Forest land. MRDS database stated accuracy for this location is 100 meters.
Mineralization is a vein deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27) hosted in gabbro, schist, serpentinite and basalt. The ore body strikes N49W and dips 38NE at a thickness of 9.14 meters. The quartz vein averages 2 to 4 feet thick with 1 lens 30 feet thick, mostly well-defined, with hornblende schist footwall and a hanging wall of less schistose gabbro than usual for the area. Both walls are well-defined and separated from the quartz by crushed, altered gabbro. Considerable variations in both strike and dip. On the 8 & 9 levels its flatter dip is associated with a great increase of thickness. There are several splits in the parallel veins. The quartz contains gabbro fragments embayed by quartz, suggesting a replaccwemetn of the gabbro. Elsewhere, quartz strands with dark mineral lines suggest thrusting within the vein. A reverse fault displaces schist. The quartz pinches out before meeting a serpentine vein cut, but not distorted, by a basalt intrusion, which may have replaced 60 to 150 feet of quartz. Later quartz veins transverse to major structure & along hanging wall brecciated wall rock is altered to carbonate mariposite and vein quartz, cemented by fine-grained dark quartz. In places gabbro close to the vein contains small arsenopyrite crystals. Vein arsenopyrite occurs in large, bladed clusters. This is the only place in the district where palygorskite is found in tough, felt-like sheets, as filling of small, up to 1 foot, veins. Post-mineralization thrusts occur in places. High-grade ore is associated with coarse arsenopyrite. High-grade ore occurs wherever the vein carries much quartz. Local alteration includes carbonitization. Associated rocks include Late Permian gabbro and basalt. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).
Workings include surface and underground openings with an overall depth of 365.76 meters and an overall length of 609.6 meters and comprised of 4 adits. Adit No. 4 is 500 feet below No. 3, uncaved. Recent work in adit No. 4 extended to the No. 10 level, 800 feet down dip from the No. 4 adit level. There are some 20,000 feet of drifts plus 9,000 feet of raises & winzes.
Production data are found in: Ferguson (1932); McCulloch et al (1964).
Ferguson (1929) estimates return at $86 (period values)/per foot of working in the last 20 years (prior to 1929). The grade of mill rock was $8.40 (period values)/ton. Production of a small amount of Au ore was reported in 1959. Concentrates contain enough Au to warrant being saved, averaging $150 (period values) per ton.
12 valid minerals.
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. 
Ferguson, Henry G. & R.W. Gannett (1929), Gold quartz veins of the Alleghany district, California: A.I.M.E. Technical Publication 211 (class 1 Mining geology 24); […Mining & Metallurgy: 10: 252 (1929)]: 13, 42, 49.
Ferguson, Henry G. & R.W. Gannett (1932), Gold quartz veins of the Alleghany district, California: USGS Professional Paper 172: 48, 129-132, figure 44.
Averill, Charles V. (1942a), Mineral resources of Sierra County: California Journal of Mines and Geology, California Division Mines (Report 38): 38(1): 63.
Carlson, D.W. & W.B. Clark (1956), Lode gold mines of the Alleghany-Downieville area, Sierra County, California: California Journal of Mines and Geology: 52: 237-291.
McCulloch, W.C., Oesterling, W.A., Spurck, W.H., & Tischler, M.S. (1964), Minerals for Industry, Northern California, Southern Pacific Company: Vol. II: 34, 35.
Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 68, 232.
Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193: 19.
Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 33, 137, 171, 399, 442.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10086507 & 10189886.
U.S. Bureau of Mines, Minerals Availability System (MAS) file #0060910114.