Sophie Gulch (Rock Creek)

Mine, Active

Commodities and mineralogy

Main commodities Au; W
Other commodities Pb
Ore minerals arsenopyrite; galena; gold; hematite; pyrite; scheelite
Gangue minerals albite; calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale NM
Quadrangle map, 1:63,360-scale C-1
Latitude 64.6138
Longitude -165.4157
Nearby scientific data Find additional scientific data near this location
Location and accuracy Sophie Gulch is a small east tributary to Rock Creek that enters Rock Creek at an elevation of about 230 feet and about 0.85 mile northeast of the Rock Creek crossing of the Snake River road. Sophie Gulch was included in localities 43 and 98 of Cobb (1972 [MF 463], 1978 [OFR 78-93]). The location shown as Sophie Gulch by Hummel (1962 [MF 247, location 17]) is the same as the Walsh Cut (NM214) of this report. The Sophie Gulch deposit was covered by U.S. Mineral Survey No. 721 (No. 1 Sophie Gulch Placer). The map location is just inside the north-central border of section 23, T. 10 S., R. 34 W., Kateel River Meridian and it is accurate to within 500 feet.

Geologic setting

Geologic description

Sophie Gulch was placer mined for tungsten (scheelite) in 1916 (Mertie, 1918 [B 662-I, p. 457]); presumably some gold was also recovered. The mine location was about 300 feet above the point where Sophie Gulch enters the flood plain of Rock Creek. The tungsten deposit was a residual placer on mineralized bedrock; the bedrock itself was described as too low grade to be mined. About 4,000 to 5,000 cubic yards of residual placer material were mined and sluiced here that year. Mertie (1918) believed that the Sophie Gulch deposit produced a large percentage of all the scheelite mined in Alaska during 1916, when scheelite was actively sought because of high World War I prices. Scheelite was also reported on the selvages of the northeast-striking sheeted veins. Cathcart (1922, p. 246) visited Sophie Gulch a few years after Mertie. He reported quartz-feldspar and quartz-calcite veins of 'all directions', arsenopyrite, galena, and pyrite in the veins, and abundant arsenopyrite in the schist walls of the veins. Cathcart described the scheelite as yellow-brown and believed that the reddish hematitic alteration of the schist resulted from oxidation of arsenopyrite.
Sophie Gulch closely follows a post-mineral(?), high-angle fault that strikes N 80 W. The fault is generally on the south side of Sophie Gulch; it was exposed and mapped in a trench by Kennecott Exploration Company in 1994. At the mouth of Sophie Gulch, the rocks south of the fault are graphitic quartz schist; the rocks north of the fault are mostly calcareous quartz-mica schist. The schist is cut by northeast-striking sheeted quartz veins. The schist's compositional layering and foliation strike northeast and dip southeast at low to moderate angles.
Locally, the calcareous quartz-mica schist contains albitized zones concordant to the schistosity. The schist unit is succeeded upstream by graphitic mica schist. About 200 feet upstream on the north side, a concordant mineralized zone, locally at least 5 feet thick, was also found in Placer Dome's 1987 trench RT-7-7 (Placer Dome, written communication, 1987). Rocks in this zone contain arsenopyrite, subordinate pyrite, albite, and quartz. This zone dips gently to the southeast and appears to be the tungsten mining location described by Mertie when he visited the prospect in 1916 (Mertie, 1918).
Geologic map unit (-165.418307821022, 64.6130346287679)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a); residual scheelite placer.
Mineral deposit model number 36a
Age of mineralization Mid-Cretaceous; veins cut regionally metamorphosed schist; see NM207.
Alteration of deposit Silicification, albitization, sulfidization, and oxidation of arsenopyrite to hematite.

Production and reserves

Workings or exploration A placer deposit on Sophie Gulch was discovered early in the history of the Nome district. The patent plat issued for No. 1 Sophie Gulch Placer (U.S. Mineral Survey No. 721) shows three cuts in Sophie Gulch itself and a shaft on bedrock north of the gulch. The prospect was developed by shallow underground workings prior to 1916 when it was exploited for tungsten in a hydraulic open cut. Most of the tungsten-rich residual placer was mined then. During World War II, three bulldozer cuts showed very little remaining residual material (Coats, 1944) The area was prospected by R.V. Bailey in the 1980s and was extensively trenched and drilled in 1987 and 1988 by Placer Dome. It was further explored by Newmont in 1992 and by Kennecott Exploration Company in 1994 and 1995. An area that includes Sophie Gulch is being actively explored by Novagold Resources (May, 2000).
Indication of production Yes; small
Production notes Small production at Sophie Gulch began prior to 1916; it was mined extensively in 1916, mainly for tungsten. About 4,000 to 5,000 cubic yards of scheelite-bearing material were processed in 1916 (Mertie, 1918 [B 662-I, p. 425-449]; Coats, 1944; Thorne and others, 1948; Cobb, 1975).

Additional comments

In 1944, the unweathered material was too low grade to mine for tungsten (Coats, 1944, p. 3).