Cub Bear

Prospect, Inactive

Commodities and mineralogy

Main commodities Fe; Mn
Other commodities Ag; Pb; Zn
Ore minerals galena; goethite; hematite; pyrite; pyrolusite; sphalerite
Gangue minerals dolomite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-2
Latitude 64.7114
Longitude -165.7477
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Cub Bear prospect is on the west side of Cripple River, about 4,000 feet northwest of the mouth of Snowshoe Gulch; the prospect is mainly on a steep easterly slope between about 750 and 1,000 feet in elevation in section 18, T. 9 S., R. 35 W., Kateel River Meridian. The location is approximately half-way between two northerly aligned masses of iron minerals (Herreid, 1970; Bundtzen and others, 1994). The prospect is locality 7 of Cobb (1972 [MF 463], 1978 [OFR 78-93]); Cobb's map location (1972 [MF 463]) appears to be about three quarters of a mile north-northeast of the true location.

Geologic setting

Geologic description

The Cub Bear prospect is a ferruginous zone about 3,000 feet long and as much as 200 feet across that strikes north-northwest (Herreid, 1970, figure 6). The prospect contains a mineralized zone near Herreid's samples 1, 2, and 3 that contains anomalous zinc. The main concentration of iron is near Herreid's samples 4, 5, and 6, approximately 1,500 feet north of the zinc-bearing samples. Bedrock exposure is poor at the prospect. According to Herreid (1970, p. 28), the rubble overlying the deposit consists of goethite, dark yellow-brown ferruginous marble, crackled dolomite, medium-grained marble, and fine-grained ferruginous material. Crackled dolomite locally has goethite veinlets, with goethite psuedomorphic after pyrite. Dolomite breccia appears to form a discontinuous envelope around the iron-rich deposit.
The mineralized zone is essentially in marble of the massive marble unit of Bundtzen and others (1994); it occurs along a high-angle fault that separates the massive marble unit to the west from the graphitic schist unit to the east. The mineralized unit is most likely the lowermost massive marble, a unit that Herreid (1970) mapped in thrust contact with underlying mica schist.
The prospect has a small iron resource estimated by Shallit (1942; Mulligan and Hess, 1965, table 3) to be 10,000 long tons with 10 to 20 percent iron and a small tonnage of material containing 30 to 45 percent iron. A sample of goethite collected by Herreid contained 16 percent iron. The prospect also is locally anomalous in zinc. Samples from the south part of the prospect (Herreid's localities 1 to 3) contained as much as 2.4 percent zinc in a 10-foot chip sample. A 100-foot-long sample, collected near Herreid's samples 3 to 6, contained 1,650 ppm zinc. The lead content of these samples did not exceed 67 ppm, and silver content did not exceed 1.3 ppm; no gold was detected.
The iron deposits of the Sinuk River area have generally been interpreted as gossan developed on oxidized sulfide deposits. At the Cub Bear prospect, there is some iron oxide (goethite) psuedomorphic after pyrite, consistent with this mode of origin. Alternatively, the deposits are primarily hypogene iron oxide deposits that are transitional into the carbonate-hosted base metal-fluorite-barite deposits of the area, such as at the Quarry prospect nearby (NM135). The relatively high zinc content of the Cub Bear prospect is consistent with the latter possibility. The age of the deposit is almost certainly post mid-Cretaceous, the age of metamorphism of the host marble. A Late Cretaceous origin was argued for the Quarry prospect by Brobst and others (1971).
Geologic map unit (-165.750337234936, 64.7106362849328)
Mineral deposit model Iron oxide veins and replacement of marble and schist.
Age of mineralization Post mid-Cretaceous, the age of metamorphism of the host schist and marble.
Alteration of deposit Dolomitization peripheral to iron oxide mineralization.

Production and reserves

Workings or exploration The Cub Bear prospect was developed by a series of pits and trenches before 1915 (Eakin, 1915 [B 622-I, p. 361-365]). Mertie (1918 [B 662-I, p. 446]) reported that no recent work was evident in 1916. Cathcart (1922, p. 261), however, reported exploration by 12 trenches, 20 to 30 feet long and about 3 feet deep. The prospect was visited by Shallit (1942) and Mulligan (Mulligan and Hess, 1965) who estimated resources of iron at the prospect. Herreid (1970, figure 6) prepared a map of the prospect at 1:6000 scale. Herreid also assayed samples for gold, silver, copper, lead, and zinc.
Indication of production None
Reserve estimates The prospect has been estimated to contain 100 tons of material with 30 to 45 percent iron and 10,000 tons with 10 to 20 percent iron (Shallit, 1942). There is some manganese oxide.

References

MRDS Number A012783

References

Reporters C.C. Hawley and Travis L. Hudson
Last report date 3/12/2000