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Island Mountain Mine (Dahrman group; Island Mountain Consolidated Mine; Annex; Leach; Merritt Gore; Shotgun), Moose Peak, Island Mountain, Coastal Range, Trinity Co., California, USA

Römerite
Island Mountain Mine, Moose Peak, Island Mountain, Coastal Range, Trinity Co., California, USA

Photo: Rob Lavinsky
Latitude: 40°1'N
Longitude: 123°29'W
A former Cu-Au-Ag-Fe mine located in secs. 9, 10 & 15, T5S, R6E, HM, 0.1 km (200 feet) NNE of Moose Peak (coordinates of record) and 1.2 km (4,000 feet) SSE of Island Mountain (town), on the W bank of the South Fork Eel River, on private land (patented claims). Discovered 1942. Produced 1915-1930. Owned by John Mosier, California (1974). MRDS database stated accuracy for this location is 100 meters.

Mineralization is a Cu-Au deposit hosted in shale and siltstone. The ore body is lenticular at 36. 58 meters wide, 137.16 meters long at a thickness of 42.67 meters. Ore emplacement controls included a shear zone. Andesite is an associated rock. Alteration is local (silicification). The most abundant ore mineral is pyrite. The most important Cu mineral is chalcopyrite. Local rocks include Franciscan Complex, unit 1 (Coast Ranges).

Local geology: Shale and graywacke are members of the Franciscan Formation. Rocks strike N30W and dip steeply NE. Most widespread rock type in the area is the well-bedded graywacke. A zone of graywacke along Pine Creek, below the bridge, consists of alternate layers of fine-grained graywacke and graywacke containing rounded, roughly aligned pebbles of black shale. Most of the prominent ridges are composed of graywacke. The black shale bodies enclosed by the graywacke are narrow and lenticular with an average width of 100 feet. Shale has been silicifeid and re-cemented to form massive boulders in the landslide area near the mine. Other rock types in the vicinity include red and brown chert within graywacke, jagged pinnacles of greenstone, a small body of diabase 1/3 mile SE of the N end of the railroad tunnel, 3 small outcrops of andesite along with a larger mass of andesite farther W and several isolated masses of glaucophane schist.

Local geologic structures include a homocline with beds of shale and graywacke, paralleling the general strike of the graywacke and shale are several notable faults marked by depressions, shear zones and landslides.

Workings include surface and underground openings. The underground workings have a length of 2,721 meters, comprised of 6 adits and 5 shafts with several thousand feet of drifts, crosscuts and raises.

Production data are found in: O'Brien, J.C. (1965): 21.

production information: The principal Cu producer in Trinity County. Huge boulders of float ore contained 5 to 20% Cu, found below the main ore body. Average grade for first 5 years of production was 7% Cu.

Comments on the reserve resource information: About 158,000 tons of ore was estimated to remain in the mine in 1965.

Analyses results: to 1930 (131,600 tons of ore): Cu = 3.3%; Ag = 1.09 ounces/ton; Au = 0.065 ounces/ton.

Mineral List

Aluminocopiapite
Arsenolite
Arsenopyrite
Azurite
Bieberite
Bornite
Calcite
Chalcanthite
Chalcocite
Chalcopyrite
Claudetite
Copiapite
Copper
Coquimbite
Cubanite
Fibroferrite
Goslarite
Gypsum
Halotrichite
Kornelite
Malachite
Melanterite
var: Cuprian Melanterite
Morenosite
Orpiment
Pyrite
Pyrrhotite
Quartz
Römerite
Sphalerite
Szomolnokite


31 entries listed. 29 valid minerals. 1 erroneous literature entry.

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References

Landon, Robert Emmanuel (1927), Roemerite from California: American Mineralogist: 12: 279-283.

Rand, L.H. (1931), The Mines Handbook, Mines Information Bureau: 18, part 1: 588.

Melhase, John (1934), A diversity of many fine minerals available in California for collectors: Oregon Mineralogist: 2(6): 1-2, 4.

Eric, J.C. (1948), Copper in California: California Division of Mines Bulletin 144: 350.

Trask, Parker Davies (1950) Geologic description of the manganese deposits of California. California Division of Mines Bulletin 152, 378 pp.: 314.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 490, 507, 515 & 626.

Stinson, Melvin Clarence (1957a), Geology of the Island Mountain copper mine, Trinity County, California: California Journal of Mines and Geology (Report 53): 53(1&2): 9-33.

O’Brien, J.C. (1965) Mines and mineral resources of Trinity County, California. Caifornia Division of Mines and Geology County Report 4: 125 pp.: 21-22, 62.

Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 85, 95, 104, 112, 128, 130, 134, 151, 156, 186, 205, 214, 258, 274, 283, 290, 312, 324, 357.

Fanfani, L., A. Nunzi, and P.F. Zanazzi (1970) The crystal structure of roemerite. American Mineralogist: 55: 79.

Moore, Lyman (1970), Costing Report for Island Mountain. (Could not find a backup file other than a 12 X 24 accounting sheet with product and reserve data written on it).

Official Railway Guide, The (1975) No. 4, National Railway Location Company, 424 West 33rd Street, New York, NY 1000.

Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 49, 70, 73, 77, 91, 93, 96, 99, 132, 228, 264, 270, 273, 274, 275, 296, 297.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10072353, 10190697 & 10287151.

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0061050029 & 0061050782.

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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