Location: The Napoleon prospect consists of several gold-bearing zones within a 3-square-mile area on the ridgeline at the head of Napoleon Creek. The coordinates are the approximate center of the area that was drilled, in section 35, T. 28 N., R. 19 E., of the Copper River Meridian. The location is accurate. Gold showings also occur in sections 31 and 36.
Geology: Rocks in the vicinity of the Napoleon prospect are Paleozoic amphibolite-facies amphibolite, quartzite, paragneiss, marble, orthogneiss, and minor schist (Werdon and others, 2001). These units have been intruded by the weakly to strongly foliated Napoleon hornblende-quartz-monzonite pluton. Hornblende from this pluton gives a 40Ar/39Ar plateau age of 186.5 +/- 1.3 Ma (Layer and others, 2002). The pluton contains small bodies of biotite clinopyroxenite and coarse-grained hornblende gabbro, which may be inclusions, dikes, and/or marginal phases (Werdon and others, 2001). Clinopyroxenite bodies within the Napoleon pluton contain as much as 25 ppb platinum and 6 ppb palladium (Werdon and others, 2000). Biotite clinopyroxenite dikes, which are compositionally and texturally similar in the northeastern Eagle quadrangle, give K-Ar ages of 184-185 Ma (Newberry and others, 1996). The Napoleon pluton and the inclusions/dikes of clinopyroxenite and hornblende gabbro are cut by minor, granite aplite-pegmatite dikes of unknown age. The Napoleon pluton and surrounding country rocks are cut and offset by late high-angle faults. As of 2002, the Napoleon prospect is the most significant lode-gold target in the Fortymile mining district. The Napoleon prospect is primarily a shear-zone-hosted lode gold deposit in the Napoleon pluton. The Napoleon pluton is cut by veins of quartz +/- pyrite +/- hematite +/- epidote +/- carbonate +/- rare visible gold. Vein selvages commonly contain K-feldspar, some of which is slightly replaced by sericite. Sericite-altered K-feldspar from the selvage of a gold + pyrite + quartz vein gives a 40Ar/39Ar isochron age of 127.8 +/- 1.6 Ma (Layer and others, 2002); this is approximately 60 Ma younger than the Napoleon pluton and is tentatively interpreted to reflect the timing of mineralization. A sample of altered, pyrite-bearing Napoleon pluton contains as much as 178.1 ppm gold, 53.2 ppm silver, and 500 ppm tungsten (Werdon and others, 2000). Airborne magnetic and resistivity surveys were flown in the Fortymile Mining district in 1998 (Alaska Division of Geological and Geophysical Surveys and others, 1999). The Alaska Division of Geological and Geophysical Surveys conducted 1:63,360-scale bedrock and surficial geologic mapping in the area from 1999 to 2001. The Napoleon prospect was discovered by Kennecott Exploration in 1997 or 1998as part of their regional exploration program in the area. Kennecott Exploration conducted a detailed soil-sampling program and drilled the Napoleon prospect in 1999. Teck Resources, Inc. conducted a ground geophysical survey on a grid near the Twin Peaks portion of the prospect in 2000, and drilled the Napoleon prospect in 2001.
Workings: Airborne magnetic and resistivity surveys were flown in the Fortymile Mining district in 1998 (Alaska Division of Geological and Geophysical Surveys and others, 1999). The Alaska Division of Geological and Geophysical Surveys conducted 1:63,360-scale bedrock and surficial geologic mapping in the area from 1999 to 2001. The Napoleon prospect was discovered by Kennecott Exploration in 1997 or 1998 as part of their regional exploration program in the area. Kennecott Exploration conducted a detailed soil-sampling program and drilled the Napoleon prospect in 1999. Teck Resources, Inc. conducted a ground geophysical survey on a grid near the Twin Peaks portion of the prospect in 2000, and drilled the Napoleon prospect in 2001.
Age: Sericite-altered K-feldspar from the selvage of a gold + pyrite + quartz vein gives a 40Ar/39Ar isochron age of 127.8 +/- 1.6 Ma (Layer and others, 2002); this is approximately 60 Ma younger than the Napoleon pluton and is tentatively interpreted to reflect the timing of mineralization.
Alteration: K-feldspar adjacent to quartz veins is locally altered to sericite.

Commodities (Major) - Ag, Au, Pd, Pt
Development Status: None
Deposit Model: Shear-zone-hosted gold.

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Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

6 valid minerals.