|Quadrangle map, 1:250,000-scale||CR|
|Quadrangle map, 1:63,360-scale||C-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Iron King prospects are about 0.4 mile north-northwest of Sunny Hat Point, and about 0.5 mile west-southwest of the northeast corner of section 13, T. 73 S., R. 85 E. The geology and workings at the Iron King prospects are shown on figure 32 of Warner and others (1961).|
The Iron King prospect is in folded and metamorphosed greenstone that is cut by northeast- and north-trending dikes of basalt, andesite, and dacite (Warner and others, 1961). Near the deposit, the greenstone is epidotized. The deposit is an irregular zone about 150 feet long and 10-15 feet wide that trends about N15 E and dips 64NW; it is probably localized along a fault. Magnetite locally makes up 50 percent of the mineralized zone, and chalcopyrite, pyrite, and magnetite are disseminated widely in it. The U.S. Bureau of Mines diamond drilled four holes which did not cut mineralization; their surface sampling indicates that the mineralized zone contains about 2 percent copper. The deposit has been explored by several trenches and prospect pits; most of the area is covered by glacial drift, alluvium, and vegetation. As of early 2011, the Iron King prospect is being developed primarily for its magnetite by Eagle Industrial Minerals (2011). They indicate that the prospect has about 3 million tons of 'good quality magnetite with small but recoverable amounts of copper and gold'.
Recent sampling shows an unusually high gold content in the deposit. Hedderly-Smith (1999 [Inventory]) cites a high-grade sample with over 10 percent copper and 37 percent iron, that contained 19.3 parts per million (ppm) gold, and 79.5 ppm silver. Several other samples across 17 feet of old trench contained 0.246 to to 0.301 ounce of gold per ton and 13.8 to 20.7 ounces of silver per ton. These and other samples contained 2.22 to 3.68 percent copper, and 31.2 to 50.97 percent iron. Hedderly-Smith (1999 [Inventory]) estimates that the deposit has one or more million tons of material that contains 2 to 4 percent copper, one-quarter of an ounce of gold per ton, and more than 35 percent iron.
The Iron King prospect is one of many copper-iron deposits on the Kasaan Peninsula having similar geology and origin (Warner and others, 1961; Eberlein and others, 1983; Brew, 1996). The rocks on the peninsula consist mainly of andesite ('greenstone' in much of the older literature) interbedded with about 25 percent sedimentary rocks comprising approximately equal amounts of limestone or marble, calcareous mudstone and sandstone, and graywacke and conglomerate. These units are part of the Luck Creek Breccia of Silurian and Devonian age, but many of the sedimentary units are similar to and probably grade into rocks of the Silurian and Ordovician, Descon Formation. The bedded rocks are intruded by a profusion of Silurian or Ordovician dikes, sills, and irregular masses of porphyritic gabbro, basalt, andesite, diorite, dacite, and granodiorite. Near some of the deposits, these intrusions may make up 20 percent or more of the outcrop and usually are associated with the development of tactite and alteration of the greenstone. The area subsequently was intruded by several large Silurian or Ordovician plutons; they are mainly granodiorite but locally are diorite and gabbro.
The ore deposits are typically small and of irregular shape; often the ore bodies form lenses or mantos. Some of the deposits conform to the layering in the greenstone and sedimentary rocks. The principal ore minerals are chalcopyrite, pyrite, and magnetite; hematite is often present and a little molybdenite occurs in some deposits. Most of the deposits are associated with tactite or skarn with varying amounts of actinolite, calcite, chlorite, garnet, diopside, epidote, and hornblende. There was significant by-product silver and gold in the ore that was mined in the past, and the gold values in some deposits are high enough to have encouraged exploration in recent years. Marble is more common in the deposits in the western part of the peninsula, where the gold values are generally higher as well (Wright and Wright, 1908; Wright, 1915; Warner and others, 1961; Myers, 1985; Bond, 1993; Maas and others, 1995).
Early interpretations of the ore deposits on the Kasaan Peninsula emphasize their contact metamorphic origin and their probable Mesozoic age (for example, Warner and others, 1961). However, recent radiometric dating and mapping indicate that the deposits formed in a Silurian or Ordovician, arc-related environment characterized by deposition of andesite and submarine sedimentary rocks that were intruded by swarms of dikes of varying composition, mineralized, and then intruded by large granodiorite plutons (Hedderly-Smith, 1999 [Inventory]).The copper deposits of the Kasaan Peninsula were known to the Russians and the first claim was staked in 1867. Most of the production and development occurred from about 1900 to 1918, especially from 1905 to 1907, when copper prices soared and a smelter was built at Hadley on the north side of the Kasaan Peninsula. After World War I, copper supply exceeded demand, prices fell, and there has been no further copper production since 1918 (Wright, 1915; Warner and others, 1961; Roppel, 1991; Maas and others, 1995). However, because of the intense and widespread mineralization on the peninsula, the area has repeatedly been re-examined for copper, iron, and gold, notably during WW II (Warner and others, 1961) and in the last several decades.
|Geologic map unit||(-132.426479522134, 55.5448347777219)|
|Mineral deposit model||Cu-Fe skarn (Cox and Singer, 1986; model 18d).|
|Mineral deposit model number||18d|
|Age of mineralization||The deposit formed in a Silurian or Ordovician, submarine arc-related environment characterized by the deposition of volcanic and sedimentary rocks, the intrusion of swarms of dikes of diverse composition, and the emplacement of several large plutons.|
|Alteration of deposit||Greenstone is altered to epidote. Development of calc-silicate skarn.|
|Workings or exploration||The deposit has been explored by several trenches and prospect pits. During WW II, the U.S. Bureau of mines diamond drilled 4 holes that did not cut mineralization. Recent sampling shows an unusually high gold content in the deposit. As of early 2011, the Iron King prospect is being developed primarily for its magnetite by Eagle Industrial Minerals (2011).|
|Indication of production||None|
|Reserve estimates||Hedderly-Smith (1999 [Inventory]) estimates that the deposit has one or more million tons of material that contains 2 to 4 percent copper, one-quarter of an ounce of gold per ton, and more than 35 percent iron. As of early 2011, the Iron King prospect is being developed primarily for its magnetite by Eagle Industrial Minerals (2011). They indicate that the prospect has about 3 million tons of 'good quality magnetite with small but recoverable amounts of copper and gold'.|
Additional commentsThe Iron King prospects are on or surrounded by land whose subsurface rights are held by the Sealaska Corporation.
Anzman, J.R., 1995, Airborne geophysical survey, Kasaan Peninsula, Alaska, 12 p. (Unpublished report held by Sealaska Corporation, Juneau, Alaska).
Bond, R.W., 1993; The mineralogy and geochemistry of the Kasaan Peninsula, iron-copper-silver-gold skarns, Prince of Wales Island, southeastern Alaska: Salt Lake City, University of Utah, M.Sc. thesis, 130 p.
Brew, D.A., 1996, Geologic map of the Craig, Dixon Entrance, and parts of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2319, 53 p., 1 sheet, scale 1:250,000.
Cobb, E. H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Craig quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-869, 262 p.
Eagle Industrial Minerals, 2011, Current EIMC projects:
Eberlein, G.D., Churkin, Michael, Jr., Carter, Claire, Berg, H.C., and Ovenshine, A. T., 1983, Geology of the Craig quadrangle, Alaska: U.S. Geological Survey Open-File Report 83-91, 52 p.
Hedderly-Smith, D.A., 1997, Report on the 1995 and 1996 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 87 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1998, Report of the 1995-1997 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 130 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1999, Inventory of metallic mineral prospects, showings and anomalies on Sealaska lands, 1988 through 1998: Sealaska Corporation, Juneau, Alaska, 217 p. (internal report held by Sealaska Corporation, Juneau, Alaska).
Hedderly-Smith, D.A., 1999, Results of 1998 work on the Kasaan Peninsula-Sealaska minerals reconnaissance project: Sealaska Corporation, 40 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
http://eagleimc.com/Projects.html (as of Feb 10, 2011)
Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p.
Myers, G.L., 1985, Geology and geochemistry of the iron-copper-gold skarns of Kasaan Peninsula, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 165 p.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Warner, L.A., Goddard, E.N., and others, 1961, Iron and copper deposits of Kasaan Peninsula, Prince of Wales Island, southeastern Alaska: U.S. Geological Survey Bulletin 1090, 136 p.
Wright, C.W., 1915, Geology and ore deposits of Copper Mountain and Kasaan Peninsula, Alaska: U.S. Geological Survey Professional Paper 87, 110 p.
|Reporters||D.J. Grybeck (Contractor, USGS)|
|Last report date||2/28/2011|