|Quadrangle map, 1:250,000-scale||HG|
|Quadrangle map, 1:63,360-scale||D-6|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||Clara Creek is a west tributary to upper Salmon River. It flows eastward from headwaters on the north end of the Red Mountain ultramafic pluton. The road from Platinum to Goodnews Mining Camp crosses Clara Creek very near its confluence with Salmon River. The map site is at the approximate midpoint of placer mine workings along the creek. This is locality 10 of Cobb (1972 [MF 362]; 1980 [OF 80-909]).|
Clara Creek, a west tributary to upper Salmon River, flows eastward from headwaters on the north end of the Red Mountain ultramafic pluton. It has been placer mined over about 1.4 miles of its 1.5 mile length. Platinum was discovered and placer mining started in 1928. At least some mining took place every year thereafter to 1940 (Fechner, 1988). A dragline was installed in 1935 and larger scale operations exhausted the 200- to 250-foot wide pay streak by 1940 (Mertie, 1969, p. 77).
Gravels in Clara Creek were 10 to 12 feet thick and except for 2 or 3 feet of vegetation-rich material and the upper 2 or 3 feet of gravel, the remainder of the alluvial section was platinum-bearing and mineable (Mertie, 1940). The gravel is subangular, mostly 3 to 4 inches in diameter, and contains cobbles and erratic boulders to 3 or 4 feet across in upper gravel horizons. Higher platinum grades were concentrated on bedrock, in the gravels within a few feet of bedrock, and up to 3 or 4 feet in deeply weathered and fractured bedrock. Mertie (1940) reported that platinum grades were as high as 0.08 ounce per cubic yard but that they were probably generally lower, perhaps averaging 0.02 ounce of platinum per cubic yard. The platinum in Clara Creek is generally fine grained but nuggets up to 2 ounces in size were recovered. Analysis of platinum-bearing concentrate shows 73.29 percent Pt, 5.90 percent Ir, 0.69 percent Os, 0.42 percent Rh, 0.56 percent Pd, 1.01 percent Au, and 18.00 percent impurities (Mertie, 1940, p. 79). The mean of analyses of 6 Pt-rich samples recalculated free of impurities was 88.61 percent Pt, 6.05 percent Ir, 0.97 percent Os, 0.09 percent Ru, 1.01 percent Rh, 0.40 percent Pd, and 2.87 percent Au (Mertie, 1976). Concentrate from one cleanup contained 6.179 ounces gold, 36.098 ounces Ir, 440.421 ounces Pt, 4.221 ounces Os, 0.795 ounce Ru, and 2.569 ounces Rh (Roehm, 1937). A U. S. Bureau of Mines sample from the unmined upper part of the creek contained 0.034 ounce of of PGM per cubic yard; microprobe analysis of this sample showed it to contain 1.6 percent Rh, 0.5 percent Ru, 83 percent Pt, 3.8 percent Ir, 1.0 percent Os, and 8.1 percent Fe (Fechner, 1988, p. 71). Fechner (1988) reported four platinum-bearing phases in this sample: iron-platinum alloy with 8 to 30 percent iron, iron-platinum alloy with minor osmiridium inclusions, hollingsworthite, and sperrylite. The unmined part of upper Clara Creek is estimated to be 900 feet long, 75 feet wide, and 2 feet thick; it contains about 5,000 cubic yards of material having a possible grade of 0.034 ounce of PGM per cubic yard (Fechner, 1988, p. 71).The bedrock of Clara Creek is mostly sheared and deeply weathered chert, quartzite, tuffaceous rocks, and chlorite schist that, in the upper part of the creek are in contact with ultramafic rocks of the Jurassic Red Mountain pluton (Mertie, 1940; Hoare and Coonrad, 1978). The country rocks are included in a regional sedimentary and volcanic assemblage that ranges in age from Paleozoic to Mesozoic (Hoare and Coonrad, 1978).
|Geologic map unit||(-161.712226086619, 58.9592165559639)|
|Mineral deposit model||Placer PGE-Au (Cox and Singer, 1986; model 39b)|
|Mineral deposit model number||39b|
|Age of mineralization||Quaternary.|
|Workings or exploration||Platinum was discovered and small-scale placer mining started in 1928. At least some mining took place every year thereafter to 1940 (Fechner, 1988). A dragline was installed in 1935 and larger scale operations exhausted the 200- to 250-foot wide paystreak by 1940 (Mertie, 1969, p. 77).|
|Indication of production||Yes; small|
|Reserve estimates||The unmined part of upper Clara Creek is estimated to be 900 feet long, 75 feet wide, and 2 feet thick; it contains about 5,000 cubic yards of material having a possible grade of 0.034 ounce of platinum-group metals per cubic yard (Fechner, 1988, p. 71). There are an estimated 500,000 cubic yards of tailings in Clara Creek that contain 0.0080 ounce of PGM per cubic yard (Fechner, 1988, p. 28).|
|Production notes||Fechner (1988) estimates that a total of 3,590 ounces of platinum-group metals were recovered from about 500,000 cubic yards of alluvial material on Clara Creek.|
|MRDS Number||A013207; M045374|
Cobb, E.H., 1972, Metallic mineral resources map of the Hagemeister Island quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-362, 1 sheet, scale 1:250,000.
Cobb, E.H., 1980, Summaries of data and lists of references to metallic and selected nonmetallic mineral deposits in fifteen quadrangles in southwestern and west-central Alaska: U.S. Geological Survey Open-File Report 80-909, 103 p.
Fechner, S.A., 1988, Bureau of Mines mineral investigation of the Goodnews Bay mining district, Alaska: U.S. Bureau of Mines Open-File Report 1-88, 230 p., 3 sheets.
Hoare, J.M., and Coonrad, W.L., 1978, Geologic map of the Goodnews and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-B, 2 sheets, scale 1:250,000.
Mertie, J.B., Jr., 1940, The Goodnews platinum deposits, Alaska: U.S. Geological Survey Bulletin 918, 97 p.
Mertie, J.B., Jr., 1969, Economic geology of platinum minerals: U.S. Geological Survey Professional Paper 630, 120 p.
Mertie, J.B., Jr., 1976, Platinum deposits in the Goodnews Bay district, Alaska: U.S. Geological Survey Professional Paper 938, 42 p.
|Reporters||Travis L. Hudson|
|Last report date||3/18/2001|