Mahoney

Mine, Undetermined

Alternative names

Ash
Asche

Commodities and mineralogy

Main commodities Pb; Zn
Other commodities Ag; Au; Cd; Cu
Ore minerals galena; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale B-5
Latitude 55.428
Longitude -131.508
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Mahoney mine is less than 100 feet above sea level on the west shore of George Inlet. It is on the north side of the mouth of the creek draining Mahoney Lake. The site is in section 25, T. 74 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 76 in Elliott and others (1978), and to loc. 293 in Maas and others (1995). The location is accurate within a few hundred feet.
Also see Additional comments.

Geologic setting

Geologic description

The country rocks in this part of Revillagigedo Island are marine, pelitic phyllite and schist that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by a stock and probably related plugs of Tertiary gabbro (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These regionally metamorphosed rocks subsequently were locally contact metamorphosed to hornblende hornfels near the contacts of Cretaceous granodiorite plutons that were emplaced after the regional metamorphism, and then more widely remetamorphosed to hornblende hornfels near the contacts of the Tertiary gabbro. The premetamorphic age range of the pelitic strata is uncertain. Berg and others (1988) assign them a Mesozoic or (Late) Paleozoic age; Brew and Ford (1998) and Crawford and others (2000) assign them to the Gravina belt, of Late Jurassic or Cretaceous age.
The Mahoney deposit consists of a pod or lens 6 inches to 3 feet thick and 350 feet long of massive sphalerite and galena, accompanied by interstitial quartz and calcite. The orebody formed by fracture filling in, and by minor replacement of, dark gray, graphitic, slaty to phyllitic metapelite (Robinson and Twenhofel, 1953; Cobb and Elliott, 1980, p. 71). The metapelite locally is intruded by feldspar-porphyritic dikes or sills.
Maas and others (1995, p. 203-204) note that the deposit has a shallow dip and is slightly discordant to the gently-dipping foliation of the phyllite hostrock. The orebody thickens from west to east and its dip steepens from 17 to 54 degrees. They believe that the deposit was emplaced along a fault, or, more likely, that there has been fault movement along the boundary of the soft sulfides and the relatively hard phyllite. Where the massive sulfides are not present, the fault zone is filled with quartz and crushed phyllite.
The Mahoney deposit was discovered in the early 1900s and originally referred to as the Asche claim (Brooks, 1902, p. 63). The mine was developed mainly in the 1940s and included more than 600 feet of underground workings, along with several surface pits and trenches (Maas and others, 1995, p. 202). From 1947 to 1949, total recovery from about 400-500 tons of ore was 33.1 metric tons (mt) of Zn, 18.1 mt of Pb, 1.27 mt of Cu, 11.6 kg of Ag, and 0.25 kg of Au (Maas and others, 1995, p, 202). Resources are estimated at 2,500 tons of material averaging 6-7% Pb and about 28% Zn (Robinson and Twenhofel, 1953; Cobb and Elliott, 1980, p. 71).
Maas and others (1995, p. 210) collected one-foot-wide samples across the deposit for the first 118 feet of the main adit. These samples averaged 3.2% Pb, 7.6% Zn, and 25.5 ppm Ag. The weighted average of assays of 1.4-foot-long samples along 60 feet of the richest ore was 20.1% Zn, 8.0% Pb, 61 ppm Ag, and 0.69 ppm Au (Maas and others, p. 204). Some samples also contained up to 1200 ppm Cd. Maas and others' sampling showed a direct correlation between high lead and silver values.
Geologic map unit (-131.509688182906, 55.4276508902176)
Mineral deposit model Stratiform, massive-sulfide replacement body

Production and reserves

Workings or exploration
The Mahoney deposit was discovered in the early 1900s and originally referred to as the Asche claim (Brooks, 1902, p. 63). The mine was developed mainly in the 1940s and included more than 600 feet of underground workings, along with several surface pits and trenches (Maas and others, 1995, p. 202). From 1947-49, total recovery from about 400-500 tons of ore was 33.1 metric tons (mt) of Zn, 18.1 mt of Pb, 1.27 mt of Cu, 11.6 kg of Ag, and 0.25 kg of Au (Maas and others, 1995, p, 202).
Maas and others (1995, p. 210) collected one-foot-wide samples across the deposit for the first 118 feet of the main adit. These samples averaged 3.2% Pb, 7.6% Zn, 25.5 ppm Ag. The weighted average of assays of 1.4-foot-long samples along 60 feet of the richest ore was 20.1% Zn, 8.0% Pb, 61 ppm Ag, and 0.69 ppm Au (Maas and others, p. 204). Some samples also contained up to 1200 ppm Cd. Maas and others' sampling showed a direct correlation between high lead and silver values.
Indication of production Yes; small
Reserve estimates Resources are estimated at 2,500 tons of material averaging 6-7% Pb and about 28% Zn (Robinson and Twenhofel, 1953; Cobb and Elliott, 1980, p. 71).
Production notes From 1947 to 1949, total recovery from about 400-500 tons of ore was 33.1 metric tons of Zn, 18.1 mt of Pb, 1.27 mt of Cu, 11.6 kg of Ag, and 0.25 kg of Au (Maas and others, 1995, p, 202). Resources are estimated at 2,500 tons of material averaging 6-7% Pb and about 28% Zn (Cobb and Elliott, 1980, p. 71).

Additional comments

Early reports refer to this property as the Asche, or Ash, claim (Brooks, 1902, p. 63-64; Cobb and Elliott, 1980, p. 71).

References

MRDS Number A012333

References

Reporters H.C. Berg, USGS
Last report date 7/3/1999