Rich Hill

Mine, Active

Commodities and mineralogy

Main commodities Cu; Fe
Other commodities Ag; Au
Ore minerals chalcopyrite; magnetite; pyrite
Gangue minerals calc-silicate skarn

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale C-2
Latitude 55.52537
Longitude -132.34571
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Rich Hill Mine is shown by name on the USGS 1:63,360-scale topographic map. It is about 0.2 mile east of the center of section 21, T. 73 S., R. 86 E. The geology and workings at the Rich Hill Mine are shown on Plates 26 to 28 of Warner and others (1961).

Geologic setting

Geologic description

The host rocks at the Rich Hill mine are mainly greenstone and interbedded sedimentary rocks that have been pervasively altered to tactite (Warner and others, 1961). These rocks are cut by numerous dikes of varying composition including dacite, diorite, gabbro, basalt, andesite, and diabase, most of which trend north or northwest. The largest dike, up to 50 feet thick, is diorite porphyry that can be traced for more than a quarter-mile. There are several lenses of magnetite nearby.
Most of the mineralization consists of disseminated chalcopyrite, pyrite, and magnetite in tactite, but there are local high-grade pods of chalcopyrite-rich material with little magnetite (Warner and others, 1961). The mineralization appears to be stratabound. Some of the high-grade portions seem to be preferentially aligned along northwest-trending faults and concentrated along chemically more reactive sedimentary rock layers. The main ore body consisted of a mass of chalcopyrite-rich ore along a fault zone that dips N77E and dips 80N to vertical. Warner and others (1961) have defined four zones of mineralization: Zone 1 is about 140 feet wide and exposed for about 500 feet; Zone 2 is about 100 feet wide and about 1,200 feet long; Zone 3 is about 500 feet long and about 160 feet wide; and the size of Zone 4 is indeterminate. Warner and others estimate that about two-thirds of the rock in these zones is waste and the rest contains about 1 percent copper. A block of ore about 100 feet long, 35 feet wide, and 80 feet deep remains; several samples indicate that it runs 1.4 to 2 percent copper.
The workings consist of three adits, many trenches and open cuts, and a small, shallow, glory hole that have developed the mine over a vertical extent of about 120 feet. Granby Consolidated Mining Company shipped a small tonnage of ore in 1917 and 1918 and is reputed to have mined a considerable tonnage of high-grade, chalcopyrite-rich ore in 1928. Maas and others (1995) indicate that the total production was 47 tons of copper, 514 ounces of silver, and 77 ounces of gold. Hedderly-Smith (1999 [Inventory]) cites samples that contained 2 to 3 percent copper and 500 to 1,300 parts per billion (ppb) gold; Maas and others (1995) cite a sample that contained 6.15 percent copper, 12,439 ppb gold and 43.5 parts per million silver.
The Rich Hill Mine is one of many copper-iron deposits on the Kasaan Peninsula having similar geology and origin (Warner and others, 1961; Eberlein and others, 1983; Brew, 1996). The rocks on the peninsula consist mainly of andesite ('greenstone' in much of the older literature) interbedded with about 25 percent sedimentary rocks comprising approximately equal amounts of limestone or marble, calcareous mudstone and sandstone, and graywacke and conglomerate. These units are part of the Luck Creek Breccia of Silurian and Devonian age, but many of the sedimentary units are similar to and probably grade into rocks of the Silurian and Ordovician, Descon Formation. The bedded rocks are intruded by a profusion of Silurian or Ordovician dikes, sills, and irregular masses of porphyritic gabbro, basalt, andesite, diorite, dacite, and granodiorite. Near some of the deposits, these intrusions may make up 20 percent or more of the outcrop and usually are associated with the development of tactite and alteration of the greenstone. The area subsequently was intruded by several large Silurian or Ordovician plutons; they are mainly granodiorite but locally are diorite and gabbro.
The ore deposits are typically small and of irregular shape; often the ore bodies form lenses or mantos. Some of the deposits conform to the layering in the greenstone and sedimentary rocks. The principal ore minerals are chalcopyrite, pyrite, and magnetite; hematite is often present and a little molybdenite occurs in some deposits. Most of the deposits are associated with tactite or skarn with varying amounts of actinolite, calcite, chlorite, garnet, diopside, epidote, and hornblende. There was significant by-product silver and gold in the ore that was mined in the past, and the gold values in some deposits are high enough to have encouraged exploration in recent years. Marble is more common in the deposits in the western part of the peninsula, where the gold values are generally higher as well (Wright and Wright, 1908; Wright, 1915; Warner and others, 1961; Myers, 1985; Bond, 1993; Maas and others, 1995).
Early interpretations of the ore deposits on the Kasaan Peninsula emphasize their contact metamorphic origin and their probable Mesozoic age (for example, Warner and others, 1961). However, recent radiometric dating and mapping indicate that the deposits formed in a Silurian or Ordovician, arc-related environment characterized by deposition of andesite and submarine sedimentary rocks that were intruded by swarms of dikes of varying composition, mineralized, and then intruded by large granodiorite plutons (Hedderly-Smith, 1999 [Inventory]).
The copper deposits of the Kasaan Peninsula were known to the Russians and the first claim was staked in 1867. Most of the production and development occurred from about 1900 to 1918, especially from 1905 to 1907, when copper prices soared and a smelter was built at Hadley on the north side of the Kasaan Peninsula. After World War I, copper supply exceeded demand, prices fell, and there has been no further copper production since 1918 (Wright, 1915; Warner and others, 1961; Roppel, 1991; Maas and others, 1995). However, because of the intense and widespread mineralization on the peninsula, the area has repeatedly been re-examined for copper, iron, and gold, notably during WW II (Warner and others, 1961) and in the last several decades.
Geologic map unit (-132.347392689578, 55.5250076072496)
Mineral deposit model Cu-Fe skarn (Cox and Singer, 1986; model 18d).
Mineral deposit model number 18d
Age of mineralization The deposit formed in a Silurian or Ordovician, submarine arc-related environment characterized by the deposition of volcanic and sedimentary rocks, the intrusion of swarms of dikes of diverse composition, and the emplacement of several large plutons.
Alteration of deposit Pervasive development of tactite in greenstone and sedimentary rocks.

Production and reserves

Workings or exploration The workings consist of three adits, many trenches and open cuts, and a small, shallow, glory hole that have developed the deposit over a vertical extent of about 120 feet.
Indication of production Yes; small
Reserve estimates Warner and others (1961) have defined four zones of mineralization: Zone 1 is about 140 feet wide and exposed for about 500 feet; Zone 2 is about 100 feet wide and about 1,200 feet long; Zone 3 is about 500 feet long and about 160 wide; and the size of Zone 4 is indeterminate. They estimate that about two-thirds of the rock in these zones is waste and the rest contains about 1 percent copper. A block of ore about 100 feet long, 35 feet wide, and 80 feet deep remains; several samples indicate that it contains 1.4 to 2 percent copper.
Production notes Granby Consolidated Mining Company shipped a small tonnage of ore in 1917 and 1918 and is reputed to have mined a considerable tonnage of high-grade chalcopyrite-rich ore in 1928. Maas and others (1995) indicate that the total production was 47 tons of copper, 514 ounces of silver, 77 ounces of gold.

Additional comments

The Rich Hill Mine is on or surrounded by land whose subsurface rights are held by the Sealaska Corporation.

References

MRDS Number A010129

References

Bond, R.W., 1993; The mineralogy and geochemistry of the Kasaan Peninsula, iron-copper-silver-gold skarns, Prince of Wales Island, southeastern Alaska: Salt Lake City, University of Utah, M.Sc. thesis, 130 p.
Hedderly-Smith, D.A., 1997, Report on the 1995 and 1996 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 87 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1998, Report of the 1995-1997 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 130 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
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).
Hedderly-Smith, D.A., 1999, Results of 1998 work on the Kasaan Peninsula-Sealaska minerals reconnaissance project: Sealaska Corporation, 40 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Myers, G.L., 1985, Geology and geochemistry of the iron-copper-gold skarns of Kasaan Peninsula, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 165 p.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004