Case; Grant Lake Mine, Hope Mining District, Kenai Peninsula Borough, Alaska, USAi

Regional Level Types
Case; Grant Lake Mine	Mine
Hope Mining District	Mining District
Kenai Peninsula Borough	Borough
Alaska	State
USA	Country

There are abundant references to this mine in the literature, but most of them refer only to ongoing work and give no details.
Location: The mine is located in the NE1/4 section 29, T. 5 N., R. 1 E., of the Seward Meridian, on the north side of Grant Lake; the workings extend into the south half of section 20, T. 5 N., R 1 E., in the C-7 quadrangle. The workings are accessible from Moose Pass by the Grant Lake trail that begins either at the railroad bridge on the west shore of Upper Trail Lake or half a mile south of the railroad bridge on the west shore of Upper Trail Lake. (The public is not allowed to walk across to the trail (northern entrance) on the railroad bridge. The southern entrance to the trail is accessed by boat.) The mine camp is at an elevation of 700 feet. The mine workings are about half a mile north-northeast of the camp between elevations of 1,500 and 1,600 feet. This is location 36 of Cobb and Richter (1972), location 45 of MacKevett and Holloway (1977), location 66 of Cobb and Tysdal (1980), and location S-231 of Jansons and others (1984). Cobb and Tysdal (1980) summarized the relevant references under the name Case. This location is accurate to within 300 feet.
Geology: The deposit at this mine consists of quartz veins in interbedded slate and graywacke of the Valdez Group of Late Cretaceous age (Cobb and Tysdal, 1980). The veins occur in three orientations. One set generally parallels the north-northwest strike of the country rock and dips about 70 west. This set of veins contains pods and lenses within a shear zone that follows bedding. The hanging wall of the veins is slate, and the foot wall is graywacke. The veins range from 12 to 36 inches wide and average about 16 inches. The strike length varies, but in the adit at 1,540 feet elevation, this vein was more than 100 feet long. Ore minerals include arsenopyrite, chalcopyrite, galena, and pyrite; gold is also present. The second set of veins strikes roughly east-west and dips 80S. These veins range in width from less than a foot to more than 5 feet. A majority of the material mined came from these veins. They are hosted in graywacke and are truncated on both ends by left lateral faults (Hoekzema and Sherman, 1983). Samples collected by the U.S. Bureau of Mines in 1980 assayed as much as 1.11 ounces of gold per ton (Hoekzema and Sherman, 1983). The third set of veins strikes northwest and dips 65 NE. These veins appear to be discontinuous and barren (Hoekzema and Sherman, 1983).
Workings: The mine workings consist of three adits, at elevations of 1,500,1,540, and 1,600 feet. The 1,500-level adit is 12 feet long and follows a quartz vein that pinches out at the face. The 1,540-level adit is the main working. It is 170 feet long and has two 30- to 40-foot-long crosscuts that follow the east-west-trending veins. The western crosscut is stoped to the surface (Hoekzema and Sherman, 1983). The 1,600-foot adit is about 40 feet long and follows the northwest-trending vein (Hoekzema and Sherman, 1983). Samples collected by the U.S. Bureau of Mines in 1980, assayed as much as 1.11 ounces of gold per ton (Hoekzema and Sherman, 1983). Sampling by the U.S. Forest Service as part of a patent examination showed sporadic gold grade as much as 2.10 ounces per ton, interspersed with barren samples.
Age: Cretaceous or younger; the veins cut rocks of the Valdez Group of Late Cretaceous age.
Production: Production is estimated at 972 ounces of gold and 123 ounces of silver (Jansons and others, 1984).
Reserves: The proven reserves at this mine are reported to be 270 tons of ore having a grade of 0.78 ounce of gold per ton and 0.2 ounce of silver per ton (Hoekzema and Sherman, 1983). The U.S. Bureau of Mines suggested that this deposit has a moderate potential for development as a small mine. The mine was examined both by a private consulting geologist and by a government mineral examiner as part of the patent process. U.S. Government mineral examiners concluded in 1993 that mineralization exposed to that date would not support a small-scale mining operation. The private consulting geologist suggested that further work could define a down-dip extension of the known deposit.

Commodities (Major) - Ag, Au; (Minor) - Cu, Pb
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)

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Link to USGS - Alaska:	SR202

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References