Reef Ridge

Prospect in Alaska, United States with commodities Zinc, Lead, Cadmium, Silver, Silver, Cadmium, Lead

Geologic information

Identification information

Deposit ID 10307799
Record type Site
Current site name Reef Ridge

Geographic coordinates

Point of reference Centroid
Geographic coordinates: -154.36695, 63.38349 (WGS84)
Location accuracy 10(meters)
Relative position The Reef Ridge prospect is located on a south-facing spur ridge north of the West Fork of Soda Creek, in the Medfra B-3 quadrangle in Section 26, T. 24 S., R. 23 E., of the Kateel River Meridian, at an elevation of 1840 feet (561 m). Location is precisely known; reporter visited property in 1993 and 1997.
(click for info)

Geographic areas

Country State
United States Alaska


Commodity Importance
Zinc Primary
Lead Secondary
Cadmium Tertiary
Silver Secondary
Silver Secondary
Cadmium Secondary
Lead Secondary

Comments on the commodity information

  • Gangue = Iron ferricrete
  • Gangue = white dolomite

Materials information

Materials Type of material
Cerussite Ore
Galena Ore
Hydrozincite Ore
Pyrite Ore
Smithsonite Ore
Sphalerite Ore
Pyrite Gangue
Dolomite Gangue


  • (Local) 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.

Mineral occurrence model information

Model code 224
USGS model code 32a
BC deposit profile E12
Deposit model name Mississippi Valley, S.E. Missouri Pb-Zn
Mark3 model number 42

Host and associated rocks

  • Host or associated Host
    Rock type Sedimentary Rock > Carbonate > Dolomite
    Rock type qualifier vuggy
    Rock unit name Whirlwind Creek Formation
    Stratigraphic age (youngest) Devonian

Nearby scientific data

Centroid (1) -154.36695, 63.38349

Comments on the geologic information

  • 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.
  • Age = Host lithology is inferred to be Devonian based on fossils at prospect. Age of mineralization is not known.

Economic information

Economic information about the deposit and operations

Development status Prospect
Significant Yes
Discovery year 1975
Discoverer WGM Inc. and Patino Ltd.
Discovery method Geochemical Anomaly

Comments on exploration

  • Status = Inactive

Mining district

District name McGrath

Reserves and resources

  • Type In-situ
    Estimate year 1982
    Inferred 1,800,000mt
    Commodity Subtype Grade units Group Importance Year
    Zinc 6.5 wt-pct Zinc Primary 1982

Comments on the reserve resource information

  • 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).

Comments on the workings information

  • 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.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF MD055

Bibliographic references

  • 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.

  • 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.)

  • 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.

  • 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.

  • 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.)

  • 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.

  • 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.

  • 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

  • Deposit

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

Comments on the references

  • Primary Reference = Andrews and Rishel, 1982

General comments

Subject category Comment text
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.

Reporter information

Type Date Name Affiliation Comment
Reporter 06-MAY-98 Bundtzen, T.K. Pacific Rim Geological Consulting