Unnamed (west of upper Illinois Creek)

Occurrences, Probably inactive

Commodities and mineralogy

Main commodities Ag; Zn
Other commodities Au
Ore minerals malachite; pyrite
Gangue minerals limonite

Geographic location

Quadrangle map, 1:250,000-scale NL
Quadrangle map, 1:63,360-scale A-4
Latitude 64.049
Longitude -157.937
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site consists of two occurrences, informally called Madelyn's gossan and Nate's gossan. Madelyn's gossan is located near the summit of locally-named 'Survey Ridge,' a prominent, east-west-trending ridge about a mile west of upper Illinois Creek. For this record, the site is plotted at an elevation of 1000 feet, near the center of the N1/2 of sec. 5, T. 17 S., R. 5 E., Kateel River Meridian. The location is accurate within 2 miles. Nate's gossan is approximately 1.2 miles east-northeast of Madelyn's gossan.

Geologic setting

Geologic description

Madelyn's gossan consists of sparse, limonitic, quartzite float. Samples contain 10-20% banded limonite after pyrite. Analyses of four rock samples show only slightly anomalous values, including up to 226 ppm zinc, 2.3 ppm silver, and 30 ppb gold (Flanigan, 1998).
Nate's gossan is a small outcrop (10 by 50 meters) of limonitic, brecciated quartzite. The limonite replaces banded and veined sulfides (pyrite?). Traces of malachite occur in nearby graphitic schist. Four rock samples contained up to 80 ppm copper, 308 ppm zinc, 1.0 ppm silver, and 25 ppb gold (Flanigan, 1998).
Geologic map unit (-157.939438027308, 64.0483437978293)
Age of mineralization The nearby Khotol pluton has been dated by K-Ar and Ar/Ar methods at 108-112 Ma (Flanigan, 1998). Flanigan links these occurrences to magmatic fluids from that pluton.
Alteration of deposit Sulfides are oxidized to limonite, and, locally, to malachite (Flanigan, 1998).

Production and reserves

Workings or exploration These occurrences were discovered by Anaconda Minerals Company in 1980; geologic mapping and sampling followed (Flanigan, 1998).
Indication of production None


MRDS Number 10307901


Flanigan, B., 1998, Genesis and mineralization of ore deposits in the Illinois Creek region, west central Alaska: University of Alaska, Fairbanks, M.Sc. thesis, 125 p., 2 plates.
Reporters C.E. Cameron (Northern Associates, Inc.)
Last report date 8/7/2001