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Sunset Mine (Sun Set Chrome Mine; Sugar Pine Chrome Mine), Hughes Mill, Forest Hill Divide area, Placer Co., California, USA

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Latitude & Longitude (WGS84): 39° 6' 15'' North , 120° 46' 48'' West
Latitude & Longitude (decimal): 39.1041679382, -120.779998779
 
A former Cr-Fe occurrence/mine located in sec. 31, T15N, R11E, MDM, 1.5 km (0.9 mile) N of Hughes Mill, along Finning Mill Road and S of Pagge Creek, on private land within a National Forest area. Discovered and first operated in 1881. First production was in 1885 and the last was in 1945. Operatedf by T.C. Green, California (1975). MRDS database stated accuracy for this location is 10 meters. The main workings are approximately 250 feet W of Finning Mill Road and lie SW of a 4-road intersection.

This is one of many Cr deposits/mines placed into a very large area termed the "Forest Hill Divide area" by Rynearson. That area is based on geological and topographic considerations versus mining districts and overlaps several defined districts. Those Cr occurrences within mining districts are listed under their respective districts, the remainder are listed under Rynearson’s "Forest Hill Divide area."

Mineralization is hosted in serpentinite. The ore body strikes N55W and dips 90E at a thickness of 3 meters, a depth-to-top of 15 meters, a width of 30 meters and a length of 150 meters. Ore body No. 1 is disseminated, lenticular. No. 2 is tabular. No. 3 is irregular in form.
The primary mode of origin was magmatic differentiation. Primary ore control was lithology. Wallrock alteration is intense (carbonitization). The ore bodies were localized within a zone 100 feet wide and 500 feet long and were parallel to the local trend of the shear planes, which had the above strike. This deposit occurs in a mass of ultramafic rocks that has intruded a sequence of marine sediments thought to be a part of the Paleozoic Calaveras Group. The eastern edge of the ultramafic mass is co-linear and probably part of the Melones Fault Zone. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains).

Workings include surface and underground openings comprised of a series of shafts, short drifts and numerous shallow surface workings. All workings were completely filled with debris and flooded in 1975.

Production data are found in: Rynearson, Garn Arthur (1953): 202.

Total production through WW2 was 400-500 tons of ore with 54% Cr2O3 with Cr:Fe = 2.99.

Mineral List



5 entries listed. 2 valid minerals.

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References

Bradley, W.W., Huguenin, Emile, Logan, C.A., Tucker, W.B., and Waring, C.A. (1918), Manganese and chromium in California: California Mining Bureau. Bulletin 76, 248 pp.

Rynearson, Garn Arthur (1953), Geological investigations of chromite in California: Chromite deposits in the northern Sierra Nevada, California. California Division of Mines and Geology Bulletin 134, part 3 chapter 5: 202, 221-223, 312, Pl. 14.

U.S. Bureau of Mines Minerals Yearbook for 1953 (1954): 217.

California Journal of Mines and Geology (1955) (Report 51): 51(4) (October): 377.

Chandra, Deb K. (1961) Geology and mineral deposits of the Colfax and Foresthill quadrangles, California. Special Report 67, California Division of Mines: Pls. 1 & 3.

Stinson, Melvin Clarence (1975) California Division of Mining and Geology Mineral Property Report (unpublished).

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10043719, 10077061 & 10237215.

U.S. Bureau of Mines, Minerals Availability System (MAS) file #0060610684.

 
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