Reef Ridge

The Reef Ridge is a zinc mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Reef Ridge

Commodity

Primary: Zinc
Secondary: Lead
Secondary: Silver
Secondary: Lead
Secondary: Cadmium
Secondary: Silver
Tertiary: Cadmium

Location

State: Alaska
District: McGrath

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Discovery Year: 1975
Discovery Method: Geochemical Anomaly
Years of Production:
Organization:
Significant: Y

Physiography

Not available

Mineral Deposit Model

Model Name: Mississippi Valley, S.E. Missouri Pb-Zn

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Groundwater has caused all primary metallic minerals to be nearly completely oxidized to secondary minerals; i.e. pyrite has altered to ferricrete; galena has altered to cerussite, and other secondary minerals.

Rocks

Name: Dolomite
Role: Host
Description: vuggy
Age Type: Host Rock
Age Young: Devonian

Analytical Data

Not available

Materials

Ore: Sphalerite
Ore: Smithsonite
Ore: Pyrite
Ore: Hydrozincite
Ore: Galena
Ore: Cerussite
Gangue: Dolomite
Gangue: Pyrite

Comments

Comment (Workings): Workings / Exploration = The Reef Ridge deposit was discovered by WGM Inc. and Patino Ltd. during exploration for base metals in the 1970s on lands selected by Doyon Ltd. (Andrews and Rishel, 1982). From 1976 to 1982, the exploration operator, WGM Inc., completed about 2,000 feet (610 m) of diamond drilling and 1,700 feet (518 m) of trenching on the Reef Ridge property. One drill hole (#8) in the east zone intersected 38 feet (11.5 m) of 7.44 percent zinc, and 19 feet (5.8 m) grading 6.41 percent zinc. One drill hole (#1) in the west zone intersected 56 feet (17 m) grading 10.46 percent zinc. Schmidt (1997) indicates that one hole (not identified) intersected 154 feet (47 m) grading 20 percent zinc at Reef Ridge. Silver and lead values are not given although up to 1,000 ppm cadmium and 1,000 ppm lead were encountered in assay results. No silver values are given. Clautice and others (1993) report assay values of 2.00 percent zinc, and 2,000 ppm cadmium.

Comment (Exploration): Status = Inactive

Comment (Deposit): Other Comments = See also Soda Creek (MD056), Asmyrahha (MD080), Saddle (MD054), Atoll (MD053), Midway (MD046), Big Gate (MD050), Beaver (MD048), Hillside (MD049), and Bear Pass (MD044) Mississippi Valley Type prospects and occurrences in Medfra quadrangle. The Reef Ridge deposit is on land selected or conveyed to Doyon Ltd. For further information contact Doyon Ltd. at 210 1st Ave., Fairbanks, Alaska, 99701.

Comment (Geology): Age = Host lithology is inferred to be Devonian based on fossils at prospect. Age of mineralization is not known.

Comment (Commodity): Gangue = Iron ferricrete

Comment (Geology): Mineralization at the Reef Ridge deposit covers a surface area of about 700 feet (213 m) by 1,200 feet (366 m), and is hosted in the lower portion of the Whirlwind Creek Formation of Latest Silurian to Middle Devonian age (Dutro and Patton, 1982). As subdivided in the prospect area, the Whirlwind Creek Formation that hosts the metallic mineralization at Reef Ridge consists of vuggy dolomite, interbedded laminated Amphipora rich, algal limestone and lime mudstone, a distinctive carbonate conglomerate with black chert pebbles, and a fossiliferous carbonate reef complex. Clautice and others (1993) reported Pb-Pb analyses which are permissive for classification of the Reef Ridge prospect as a classic Mississippi Valley Type deposit. Two major zones have been identified. The eastern zone trends on surface N 20 E and is approximately 450 feet (137 m) long and 60 feet (18 m) wide. Mineralization consisting of secondary smithsonite, with minor flecks of galena and pyrite that have been introduced into tectonic breccias with a distinctive white dolomite gangue. The breccias are introduced along the high angle 'Prospect Fault' (Andrews and Rishel, 1982; Mosher, 1990). The west zone trends N 20 W and is approximately 700 feet (213 m) long and up to 160 feet (49 m) wide. At depth, the west zone deflects to a strike approximately parallel to the east zone decribed above. Mineralization in the west zone is characterized by hydrozincite hosted in strong solution breccias and accompanied by black hydrocarbon residues. Most of the zinc mineralization in the west zone is controlled by a high angle fracture; however, tectonic breccias are not as well developed in the west zone as they are in the east zone. Host lithology is inferred to be Devonian based on fossils at prospect. Age of mineralization is not known.

Comment (Commodity): Gangue = white dolomite

Comment (Reserve-Resource): Reserves = Based on the 1976-1982 subsurface and surface exploration work, an inferred reserve of 1,980,000 tons (1,800,000 tonnes) grading 6.5 percent zinc has been identified at the Reef Ridge deposit (Andrews and Rishel, 1982; Fair and Bright, 1989; Schmidt, 1997).

Comment (Reference): Primary Reference = Andrews and Rishel, 1982

References

Reference (Deposit): Leach, D., Sangster, D., Kelley, K., Large, R.R., Garven, G., Allen, C., Gutzmer, J., and Walters, S., 2005, Sediment-hosted lead-zinc deposits: A global perspective. Economic Geology, 100th Aniversary Volume. pp. 561-607. Also Appendices A, B, C, D, E, and Supplement
Pages: Appendix A, Table A1

Reference (Deposit): Dutro, T.T. Jr., and Patton,W.W. Jr., 1982, New Paleozoic Formations in the northern Kuskokwim Mountains, west-central Alaska: U.S. Geological Survey Bulletin 1529-H, p. H13-H22.

Reference (Deposit): Clautice, K.H., Bowman, N.D., Clough, J.G., Gilbert, W.G., Kline, J.T., Smith, T.E., and Blodgett, R.B., 1993, Land selection Unit 8 (Kantishna River, Ruby, and Medfra quadrangles); References, lead isotope, geochemical and major oxide data: Alaska Division of Geological and Geophysical Surveys, 42 p., 1 sheet, scale 1:250,000.

Reference (Deposit): Schmidt, J.M., 1997, Shale-hosted Zn-Pb-Ag and barite deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska, 1997: Economic Geology Monograph 9, p. 35-65.

Reference (Deposit): Patton, W.W., Jr., Moll, E.J., Dutro, J.T., Jr., Silberman, M.L., and Chapman, R.M., 1980, Preliminary geologic map of Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811-A, 1 sheet, scale l:250,000.

Reference (Deposit): Andrews, Tom, and Rishel, John, 1982, Annual Report for 198, Reef Ridge I-to-XIII Project Areas, Kuskokwim Block, Alaska: Anchorage, Alaska, WGM Inc., Project Report 4, 45 pages, two sheets at 1:63,360 and 1:20,000 scales. (Report held by Doyon, Limited, Fairbanks, Alaska.)

Reference (Deposit): Fair, E.E., and Bright, T.D., 1989, Reef Ridge Project: Pasminco exploration report, Doyon Ltd. Report 89-23, 32 pages (Held by Doyon Ltd., Fairbanks, Alaska.)

Reference (Deposit): Mosher, Greg, 1990, Reef Ridge Project: Pasminco Exploration Ltd., Doyon, Limited Report 92-72, 19 p. (Report held by Doyon, Limited, Fairbanks, Alaska)

Reference (Deposit): Fisher, D.G., and Juilliand, J.D., 1986, Mineral deposit types and their characteristics: U.S. Bureau of Land Management Technical Bulletin 3031-1, 134 pages.

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