|Quadrangle map, 1:250,000-scale||CR|
|Quadrangle map, 1:63,360-scale||C-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This site represents an area of about one-quarter square mile about 1.8 mile south of the town of Klawock. The area covers most of the NW1/4 section 22, T. 73 S., R. 81 E., and the site is in the center of that area.|
This site consists of several small occurrences of similar mineralization in an area of about a quarter square mile; the deposits are exposed along logging roads in an area that is largely covered by forest and surficial deposits. The rocks consist mainly of a thick section of Paleozoic strata (Churkin and Eberlein, 1975). They include the Klawock Formation of Pennsylvanian age, which consists largely of calcareous sandstone, siltstone, and limestone, and the Peratrovich Formation, which at this site consists largely of limestone and cherty limestone.
Several deposits have been identified in the area, some perhaps the same deposit described by different geologists. D.J. Grybeck (unpublished field data, 1991) found pyritiferous sandstone of the Klawock Formation that was bleached and iron stained for about 40 feet along a logging road. The zone contains a lens about 12 inches thick of massive pyrrhotite with minor chalcopyrite and a silicified border zone. A sample of the massive pyrrhotite contained up to 300 parts per million (ppm) silver, 200 ppm arsenic, 150 ppm bismuth, and 3,000 ppm copper Erratic, small patches of calc-silicate minerals with garnet and small, rusty gossan zones occur along the logging road for several hundred yards to the northwest. A grab sample of one of the more prominent gossans contained 7 ppm silver and 700 ppm copper.Hedderly-Smith (1999 [Inventory]) describes several other (or the same) occurrences that were found in 1988 as logging roads were built in the area. Two 1.5-foot-thick stratiform veins or replacement lenses of massive pyrrhotite are separated by 6 feet of ferricrete. Samples contained up to 0.3 percent copper, 1,270 ppm lead, and 3.12 ounces of silver per ton. The deposit strikes about N20E and dips 60W. About 10 feet south of the pyrrhotite lenses, minor galena occurs in a quartz-sulfide vein. About 0.1 mile northwest near a rock pit, samples of mineralized float contained more than 1 percent lead, 1.2 percent zinc, and more than 50 ppm silver. Another sample of chert-carbonate rock adjacent to a felsic dike contained 656 ppm lead, 454 ppm copper, 6.2 ppm silver, 4.66 percent manganese, 16.94 percent iron, 1.38 percent arsenic, and 271 parts per billion gold. Hedderly-Smith indicates that these deposits were first thought to be massive-sulfide deposits but later concluded that they are skarn deposits. There are no intrusions in the immediate area but there may be buried or concealed bodies similar to Permian syenite exposed about a mile to the north that may be the source of these deposits (Churkin and Eberlein, 1975).
|Geologic map unit||(-133.092958343387, 55.5276494688688)|
|Mineral deposit model||Small erratic veins, pyrrhotite lenses, and quartz veins.|
|Age of mineralization||Unclear. These small and erratically distributed deposits are no older than their Mississippian and Pennsylvanian host rocks. There are no intrusions in the immediate area but there may be buried or concealed bodies similar to the Permian syenite exposed about a mile to the north that may be the source of these deposits (Churkin and Eberlein, 1975).|
|Alteration of deposit||Small lenses and masses of skarn developed in limestone; silicification adjacent to pyrrhotite lens; disseminated pyrite in calcareous sandstone.|
|Workings or exploration||Only sampling by government and industry geologists.|
|Indication of production||None|
Additional commentsThe Sealaska Corporation holds the subsurface rights to the land in the vicinity.
Churkin, Michael, Jr., and Eberlein, G.D., 1975, Geologic map of the Craig C-4 quadrangle, Alaska: U.S. Geological Survey Geologic Quadrangle Map GQ-1169, 1 sheet, scale 1:63,360.
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).
|Reporters||D.J. Grybeck (Applied Geology)|
|Last report date||5/1/2004|