Reef Ridge

Prospect, Inactive

Commodities and mineralogy

Main commodities Zn
Other commodities Ag; Cd; Pb
Ore minerals cerussite; galena; hydrozincite; pyrite; smithsonite; sphalerite
Gangue minerals iron ferricrete; pyrite; white dolomite

Geographic location

Quadrangle map, 1:250,000-scale MD
Quadrangle map, 1:63,360-scale B-3
Latitude 63.384
Longitude -154.364
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

Geologic description

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.
From 1976 to 1982, WGM Inc., operator for Patino Ltd., 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.
Geologic map unit (-154.366328307396, 63.3834036948658)
Mineral deposit model Southeast Missouri Pb-Zn (Cox and Singer, 1986; model 32a), Fisher and Juilliand, 1886.
Mineral deposit model number 32a
Age of mineralization Host lithology is inferred to be Devonian based on fossils at prospect. Age of mineralization is not known.
Alteration of deposit 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.

Production and reserves

Workings or 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.
Indication of production None
Reserve estimates 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).

Additional 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.

References

MRDS Number 10307799

References

Andrews, Tom, and Rishel, John, 1982, Annual Report for 1981, Reef Ridge I-to-XIII Project Areas, Kuskokwim Block, Alaska: Anchorage, Alaska, WGM Inc., Project Report 4, 45 p., 2 sheets, scales 1:63,360 and 1:20,000. (Report held by Doyon, Limited, Fairbanks, Alaska.)
Fair, E.E., and Bright, T.D., 1989, Reef Ridge Project: Pasminco exploration report, Doyon, Limited Report 89-23, 32 p. (Report held by Doyon, Limited, Fairbanks, Alaska.)
Fisher, D.G., and Juilliand, J.D., 1986, Mineral deposit types and their characteristics: U.S. Bureau of Land Management Technical Reference 3031-1, 153 p.
Mosher, Greg, 1990, Reef Ridge Project: Pasminco Exploration Ltd., Doyon, Limited Report 92-72, 19 p. (Report held by Doyon, Limited, Fairbanks, Alaska)
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.
Reporters Bundtzen, T.K. (Pacific Rim Geological Consulting)
Last report date 5/6/1998