Gilpatrick Dike (ARDF #SR136) Ag, Au

Gilpatrick Dike

Mine, Inactive

Alternative names

Sprague and Byers

Commodities and mineralogy

Main commodities	Ag; Au
Other commodities	Cu; Pb; Zn
Ore minerals	arsenopyrite; chalcopyrite; galena; gold; molybdenite; pyrite; pyrrhotite; sphalerite
Gangue minerals	calcite; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale	SR
Quadrangle map, 1:63,360-scale	C-7
Latitude	60.6138
Longitude	-149.575
Nearby scientific data	Find additional scientific data near this location
Location and accuracy	The mine is located in the NE1/4 section 14, T. 6 N., R. 2 W., of the Seward Meridian, on the south side of the divide between Summit and Slate Creeks. There are three adits on the Slate Creek side of the divide at elevations of 2,850, 3,300, and 3,400 feet, along with numerous prospect pits and open cuts. On the Summit Creek side of the divide, there are trenches and prospect pits above 2,400 feet elevation. This is location 29 of Cobb and Richter (1972), location 36 of MacKevett and Holloway (1977), location 54 of Cobb and Tysdal (1980), and location S-253 of Jansons and others (1984). This location is accurate to within a quarter of a mile.

Geologic setting

Geologic description The deposit at the Gilpatrick Dike mine consists of a mineralized Eocene felsic dike (the so-called Gilpatrick dike) and of quartz veins in graywacke and slate of the Valdez Group of Late Cretaceous age adjacent to the dike (Mitchell and others, 1981). The dike contains quartz-filled fractures that carry native metals and sulfides, including gold, arsenopyrite, galena, and sphalerite and some chalcopyrite, molybdenite, and pyrrhotite. These veins and veinlets range in width from a fraction of an inch to 8 or 10 inches (Tuck, 1933). The slate and graywacke 2 to 10 feet from the dike contain quartz veins that are parallel to the dike. The veins are 2 to 12 inches wide and contain the same ore minerals as those in the dike (Tuck, 1933). The dike and adjacent veins are offset by several dextral faults. The presence of gouge on one wall of the dike indicates post-mineralization movement along another fault parallel to the dike. The dike continues for several miles (see Fresno Creek, SR145), but development at this site is restricted to a few thousand feet of its length. The wall rocks near the veins locally display extensive chlorite-sericite alteration. The highest grade of ore coincides with the zones of greatest alteration.
Geologic map unit	(-149.577154575242, 60.6132295134656)
Mineral deposit model	Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number	36a
Age of mineralization	Eocene or younger; the mineralization is in and adjacent to Eocene dike rock.
Alteration of deposit	The dike and the country rocks near the veins display locally intense chlorite-sericite alteration.

Production and reserves

Workings or exploration	There are three levels of adits, at 2,850, 3,300, and 3,400 feet elevation. The lowest adit is 265 feet long, the middle adit has caved in, and the upper adit is 50 feet long. There are also numerous trenches and prospect pits.
Indication of production	Yes; medium
Reserve estimates	Reserves are 2,000 tons of ore at 0.89 ounce of gold per ton and 0.65 ounces of silver per ton (Hoekzema and Sherman, 1983).
Production notes	Most production occurred from about 1937 to 1948. Recorded production was 3,545 ounces of gold and 1,099 ounces of silver from an estimated 3,664 tons of ore (Hoekzema and Sherman, 1983).
Additional comments The location labeled Oracle Mine on the Seward C-7 quadrangle map is the a mill site and is not the location of the working.

References

MRDS Number	A010390
References Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. Brooks, A.H., 1911, The mining industry in 1910, in Brooks, A.K., and others, Mineral resources of Alaska, report on progress of investigations in 1910: U.S. Geological Survey Bulletin 480-B p. 21-43. Brooks, A.H., 1914, Mineral resources of Alaska; report on progress of investigations in 1913: U.S. Geological Survey Bulletin 592, 413 p. Brooks, A.H., 1915, Mineral resources of Alaska; report on progress of investigations in 1914: U.S. Geological Survey Bulletin 622, 380 p. Brooks, A.H., 1916, Mineral resources of Alaska, report on progress of investigations in 1915: U.S. Geological Survey Bulletin 642, 279 p. Brooks, A.H., 1918, Mineral resources of Alaska, 1916: U.S. Geological Survey Bulletin 662, 469 p. Cobb, E.H., and Richter, D.H., 1972, Metallic mineral resources map of the Seward quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-466, 2 sheets, scale 1:250,000. Cobb, E.H., and Tysdal, R.G., 1980, Summaries of data on and list of references to metallic and selected nonmetallic mineral deposits in the Blying Sound and Seward quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-621, 276 p. Grant, U.S., and Higgins, D.F., Jr., 1910, Reconnaissance of the geology and mineral resources of Prince William Sound, Alaska: U.S. Geological Survey Bulletin 443, 89 p. Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p. Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000. Johnson, B.L., 1919, Mining on Prince William Sound: U.S. Geological Survey Bulletin 692-C. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Martin, G.C., Johnson, B.L., and Grant, U.S., 1915, Geology and mineral resources of Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 587, 243 p. Nelson, S.W., Dumoulin, J. A., and Miller, M.L., 1985, Geologic map of the Chugach National Forest, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1645-B, 16 p., 1 sheet, scale 1:250,000. Smith, P.S., 1937, Mineral industry of Alaska in 1935: U.S. Geological Survey Bulletin 880-A, p. 1-95. Smith, P.S., 1941, Mineral industry of Alaska in 1939: U.S. Geological Survey Bulletin 926-A, p. 1-106. Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p. Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1916: U.S. Bureau of Mines Bulletin 153, 89 p. Tuck, Ralph, 1933, The Moose Pass-Hope district, Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 849-I, p. 469-530. Tysdal, R.G., 1978, Mines, prospects, and occurrences map of the Seward and Blying Sound quadrangles, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-880-A, 2 sheets, scale 1:250,000.
Reporters	Jeff A. Huber (Anchorage)
Last report date	3/7/2000