Gossan lode

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Cu
Other commodities Ag; Au; Hg; Mn; Sb; W; Zn
Ore minerals chalcopyrite; hematite; pyrite
Gangue minerals dolomite; manganiferous carbonate; quartz; siderite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale A-6
Latitude 63.194
Longitude -146.94
Nearby scientific data Find additional scientific data near this location
Location and accuracy The map site for the Gossan lode represents a mineralized area about 1 mile north of Coal Creek, east of Clearwater Creek. The area extends from 4,000 to 5,200 feet in elevation and is mainly in the SE1/4 section 10, T. 20 S., R. 4 E., Fairbanks Meridian. The location includes mineral localities 29 to 32 of Clautice and others (1989) and corresponds to locality A39 of Kurtak and others (1992). The location given here is at about the elevations cited in text by Kurtak and others (1992). Their map site (for locality A39), however, seems to be too low in elevation.

Geologic setting

Geologic description

The rocks near the Gossan lode consist of argillite, limestone, dolomite, and schist of probable Paleozoic age (Nokleberg and others, 1982). Minor amounts of andesite are intercalated with the weakly metamorphosed rocks. The strata are intruded by granodiorite of Cretaceous (?) age.
These rocks, particularly the carbonate rocks, have been partly replaced by dolomite, a manganiferous carbonate mineral, siderite, and pyrite. These rocks are variably gossanized on the surface and are stained with hematite, limonite, and manganiferous oxide. The staining is readily visible from the air.
The Gossan lode deposit possibly formed as the result of emplacement of granodiorite (Kurtak and others, 1992, p. 173). Besides the disseminated replacement deposit, quartz-sulfide veins occupy faults and shear zones in pyritized-carbonatized rock. Reported metal values are low. An industry-funded investigation in 1980 determined as much as 1,725 parts per million (ppm) copper (Ellis, 1980), and the U.S. Bureau of Mines found 0.62 percent copper in a quartz-pyrite-chalcopyrite vein (Kurtak and others, 1992, p. 175, sample 1167). This vein also contained 50 parts per billion gold and 1.5 ppm silver. Locally altered argillite, schist, and fault breccia contain anomalous concentrations of copper and zinc (hundreds of parts per million), from 10 to 50 ppm tungsten and from 15 to 85 ppm arsenic, and a fault breccia contains 15 ppm mercury.
Further data are supplied by Clautice and others (1989) in their descriptions of mineral localities 29 to 32 in the Gossan lode area. Locality 29 is altered tuff; it contains 255 ppb gold. Localities 30 and 31 are at the sites of recent spring deposits of calcrete or sinter; the spring deposit at locality 30 contains 3,330 ppm arsenic and 55 ppm antimony. Sample 31, collected adjacent to a modern cold-water spring, contains 6,520 ppm arsenic. Locality 32 is a trench-drill pad location on black gossan that contains 1,370 ppm copper, 345 ppm arsenic, and 726 ppm zinc.
Geologic map unit (-146.94226447645, 63.1935573456879)
Mineral deposit model Affinity to copper skarn or porphyry.
Age of mineralization The main Gossan lode deposit is possibly Cretaceous in age, related to emplacement of granodiorite. Some spring deposits in the area are recent or modern.
Alteration of deposit Introduction of pyrite and iron- and manganese-bearing carbonates.

Production and reserves

Workings or exploration The area was explored by a few trenches. Twenty-two Gossan lode claims were staked in 1973; 12 CM claims were staked in 1981 (Kurtak and others, 1992).
Indication of production None