|Quadrangle map, 1:250,000-scale||EA|
|Quadrangle map, 1:63,360-scale||A-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Purdy lode-gold mine is located about 3 miles north-northwest of Chicken at an elevation of about 2,500 feet, on the ridge between Stonehouse Creek and Myers Fork. The mine is in section 18, T. 27 N., R. 18 E., of the Copper River Meridian. The location is accurate within 100 feet. This site is locality 50 of Eberlein and others (1977) and locality 13 of Cobb (1972 [MF-393]).|
The Purdy lode-gold mine is in phyllite within an east-west-trending, fault-bounded block of upper Paleozoic greenschist-facies metasedimentary and metavolcanic rocks (Werdon and others, 2001). South of the Purdy mine, the phyllite is in high-angle fault contact with the down-dropped Chicken basin that preserves a wedge of Tertiary gabbro and sedimentary rocks. North of the Purdy mine, the phyllite is in high-angle fault contact with the Chicken pluton of Jurassic age; hornblende from this pluton gives a 40Ar/39Ar plateau age of 187.8 +/- 0.9 Ma (Layer and others, 2002). The pluton intrudes Paleozoic amphibolite-facies metamorphic rocks. About 1,500 feet northwest of the Purdy mine, the Chicken pluton has been intruded by a porphyritic intrusion of unknown age that is spatially associated with aplite dikes that contain anomalous gold (see EA119) (Szumigala and others, 2000).
Prindle (1905) reported specimen-quality gold in calcite veins that occurs in shale overlying a dark, fine-grained porphyritic rock. He also reported that near the head of Chicken Creek gold occurs in thin calcite veins associated with pyrite-bearing quartz veins in black phyllite (Prindle, 1908). These reports likely refer to the Purdy lode gold mine. Foster (1969 [B 1271-G) described the Purdy deposit as a rich gold-quartz-calcite vein phyllite; it extended to a depth of 6 feet. Fred and Arthur Purdy discovered and mined out the vein(s). Extensive prospecting around the Purdy mine has exposed only a few additional thin, discontinuous calcite veinlets, which contain specks of gold, and abundant bull quartz veins (Foster, 1969 [B 1271-G]). A very high grade sample containing visible coarse-grained gold in quartz-calcite veins within phyllite from the Purdy mine is currently (2002) on display at the University of Alaska Fairbanks museum in Fairbanks, Alaska as part of their permanent collection of historic gold.The Purdy mine consists of two 20-foot-deep trenches that cover an area that extends for about 160 feet east-west by 70 feet north-south. In 1999, the Purdy trenches were mapped by Bryan A. Finseth as part of the Alaska Division of Geological and Geophysical Surveys' Fortymile mining-district geologic mapping project; the following observations are from his unpublished mapping. Two small east-west-trending high-angle faults cut the phyllite and are cut(?) by a 20- to 25-foot-wide north-northwest-trending breccia zone. No igneous rocks are exposed in the trenches. Disseminated pyrite occurs within an iron- and manganese-oxide-stained chert (hornfelsed phyllite?) layer within the phyllite. Along the north wall of the northern trench, both the phyllite and the breccia zone contain pyrite, and the breccia zone contains secondary copper minerals, including malachite and tenorite. Thin calcite coatings are present on some fracture surfaces. A sample of fault gouge with supergene copper minerals contains 1,055 ppb gold, 72.6 ppm silver, 308 ppm arsenic, 73,600 ppm copper, 253 ppm mercury, 2,850 ppm antimony, and 236 ppm zinc (Szumigala and others, 2000). A calcified fault breccia contains 225 ppb gold, 78.6 ppm silver, 134 ppm arsenic, 8 ppm bismuth, 3,100 ppm copper, 148 ppm mercury, 1,610 ppm antimony, and 626 ppm zinc. A whole-rock sample of altered hornfelsed phyllite adjacent to a gold-bearing calcite vein from the Purdy mine has a 40Ar/39Ar plateau age of 182.3 +/-0.9 Ma, probably the age of the gold deposition (Layer and others, 2002).
|Geologic map unit||(-141.949783204191, 64.1156709965017)|
|Mineral deposit model||Possibly epithermal veins (Cox and Singer, 1986; model 25c?).|
|Mineral deposit model number||25c?|
|Age of mineralization||A whole rock sample of altered hornfelsed phyllite adjacent to a gold-bearing calcite vein from the Purdy mine has a 40Ar/39Ar plateau age of 182.3 +/-0.9 Ma, probably the age of the gold deposition (Layer and others, 2002).|
|Alteration of deposit||Hornfelsing of phyllite.|
|Workings or exploration||Fred and Arthur Purdy discovered and mined the vein. Extensive prospecting adjacent to the Purdy mine has exposed only a few additional thin, discontinuous calcite veinlets, which contain specks of gold, and abundant bull quartz veins (Foster, 1969). The deposit was mined out prior to the early 1970s.|
|Indication of production||Yes; small|
Cobb, E.H., 1972, Metallic mineral resources map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-393, 1:250,000 scale, 1 sheet.
Cobb, E.H., 1977, Summary of references to mineral occurrences in the Eagle quadrangle, Alaska: U.S. Geological Survey Open-File Report 77-845, 122 p.
Eberlein, G.D., Chapman, R.M., Foster, H.L., and Gassaway, J.S., 1977, Map and table describing known metalliferous and selected nonmetalliferous mineral deposits in central Alaska: U.S. Geological Survey Open-File Report 77-168-D, 132 p., 1 sheet, scale 1:1,000,000.
Foster, H.L., 1969, Reconnaissance geology of the Eagle A-1 and A-2 quadrangles, Alaska: U.S. Geological Survey Bulletin 1271-G, p. G1-G30.
Foster, H.L., 1976, Geologic map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series, Map 922, 1 sheet, scale 1:250,000.
Foster, H.L., and Clark, S.H.B., 1970, Geochemical and geologic reconnaissance of a part of the Fortymile area, Alaska: U.S. Geological Survey Bulletin 1312-M, p. M1-M29.
Layer, P.W., Drake, J., and Szumigala, D.J., 2002, 40Ar/39Ar dates for mineralization and igneous and metamorphic rocks in a portion of the Fortymile mining district, Eagle quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Preliminary Interpretive Report. [In preparation in 2002]
Mertie, J.B., Jr., 1938, Gold placers of the Fortymile, Eagle, and Circle districts, Alaska: U.S. Geological Survey Bulletin 897-C, p. 133-261.
Prindle, L.M., 1905, The gold placers of the Fortymile, Birch Creek, and Fairbanks regions, Alaska: U.S. Geological Survey Bulletin 251, 89 p.
Prindle, L.M., 1908, The Fortymile gold-placer district, in Brooks, A.H., ed., Mineral Resources of Alaska, Report on progress of investigations in 1907: U.S. Geological Survey Bulletin 345, p. 187-197.
Smith, W.H., 1968, Geochemical investigation of a portion of the Fortymile district, Alaska: Alaska Division of Mines and Minerals Geochemical Report 16, 17 p.
Szumigala, D.J., Newberry, R.J., Werdon, M.B., Finseth, B.A., Pinney, D.S., and Flynn, R.L., 2000, Major-oxide, minor-oxide, trace-element, and geochemical data from rocks collected in a portion of the Fortymile mining district, Alaska, in 1999: Alaska Division of Geological and Geophysical Surveys Raw-Data File 2000-1, 24 p., 2 sheets, scale 1:63,360.
Wasserberg, G.J., Eberlein, G.D., and Lanphere, M.A., 1963, Age of Birch Creek Schist and some batholithic intrusion in Alaska [abs.]: Geological Society of America Special Paper 73, p. 258-259.
|Last report date||5/1/2002|