Stipek and Kotovic

Prospect, Probably inactive

Alternative names

Bergstrom (Rock Creek)

Commodities and mineralogy

Main commodities Au
Other commodities Ag
Ore minerals arsenopyrite; gold; ilmenite; pyrite
Gangue minerals albite; calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-1
Latitude 64.6088
Longitude -165.4249
Nearby scientific data Find additional scientific data near this location
Location and accuracy This lode prospect is on the southeast side of Rock Creek about 3,000 feet upstream of the Snake River road and 1.85 miles south-southwest of Mount Brynteson. The prospect is at surface elevations of about 200 to 225 feet. The map location is in the NW1/4 section 23, T. 10 S., R. 34 W., Kateel River Meridian, and it is accurate to within 250 feet. This is locality 43 of Cobb (1972 [MF 463], 1978 [OFR 78-93]).

Geologic setting

Geologic description

This prospect was one of two known as Stipek and Kotovic; the second, on the divide between Rock Creek and Glacier Creek, is NM235. he east side of Rock Creek was evidently being prospected by W. Stipek and J. Kotovic in 1916, when it was visited by Mertie (1918 [B 662-I, p. 432-33]). Workings at that time consisted of a 70-foot shaft and 70 feet of crosscuts. The collar of the shaft was at an elevation of about 200 feet. A mineralized zone found in the crosscut was rich in sulfides and reported to strike N5E. Dump material contained 0.4 ounce of gold per ton; stringer sulfide zones without quartz reportedly contained about 7 ounces of gold per ton. A 120-foot-long adit, apparently examined by Mertie (1918), was driven from near the elevation of Rock Creek through the lode. Mertie (1918) reported that a 12-foot vein of shattered white quartz yielded about 250 pounds of concentrate to the ton. Sulfides, especially arsenopyrite, were abundant from the near the vein to the face of the adit. Another adit, 40 feet long, was driven into the lode about 75 feet to the south and apparently encountered the same vein and sulfide zone as the longer adit.
The prospect was inactive when visited by Cathcart in 1920 (Cathcart, 1922, p. 244-245). He reported that tunnels were driven S 75 E and S 25 E and that the quartz-albite vein had a strike of N 65 E and dipped 50 south. Ilmenite occurs on fracture surfaces in the quartz. Wallrock was reported as chlorite-quartz schist, in general agreement with the findings of Bundtzen and others (1994), who mapped the bedrock on Rock Creek as chlorite-rich metaturbidite schist.
The prospect was explored between about 1985 and 1995 by R.V. Bailey, BHP(?), Newmont Mining Company, and Kennecott Exploration Company. This exploration included northwest-trending trenches that exposed stratiform, as well as crosscutting quartz and sulfides and a fault that may cut off the deposit. The trench and drill results show that the deposit is semi-continuous over a northeasterly strike length of about 500 feet, but the grade is low and individual mineral zones are discontinuous. In general, this deposit is similar to those at Reinisch (NM213), Walsh Cut (NM214), and Goodluck Gulch (NM202).
Geologic map unit (-165.427506036554, 64.6080341722836)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Mid-Cretaceous; veins cross cut regionally metamorphosed schist; see NM207.
Alteration of deposit Albitization; extensive sulfidization especially introduction of arsenopyrite.

Production and reserves

Workings or exploration The Stipek and Kotovic prospect on Rock Creek was explored by a 70-foot shaft and about 230 feet of level adit or crosscut workings before 1920. It appears to have been active when visited by Mertie in 1916 (Mertie, 1918 [B 662-I, p. 425-449]). It was inactive in 1920. The prospect was again active between about 1985 and 1995. It was drilled and trenched by several companies including BHP? in 1990, Newmont in 1992, and Kennecott Exploration Company in 1994. Both core and reverse circulation holes were drilled in the appraisal of the prospect.
Indication of production Undetermined
Production notes There possibly was production of minor free gold during milling tests of the ore.