Main Zone

Prospect, Active

Alternative names

Saddle Zone
Trench 24
Napoleon

Commodities and mineralogy

Main commodities Ag; Au; Pd; Pt
Ore minerals gold; hematite; pyrite
Gangue minerals carbonate; chlorite; epidote; k-feldspar; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale A-2
Latitude 64.1643
Longitude -141.6352
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site consists of 3 discrete but adjacent mineralized zones, the Main Zone, the Saddle Zone, and the Trench 24 zone. These are often combined with the nearby Twin Peaks (EA167) and with the Burnt Ridge (EA168) prospects under the name Napoleon or Napoleon Block/claims. The three zones are near peak 3750 northwest of the head of Napoleon Creek and occupy much of the west half of section 35, T. 28 N., R. 19 E. The location is accurate.

Geologic setting

Geologic description

As described by Eden (2010), this site consists of three discrete but adjacent mineralized zones: the Main Zone, the Saddle Zone, and the Trench 24 zone. All are in the Napoleon pluton which is roughly equidimensional and about 4 miles wide. The pluton is mainly weakly to strongly foliated hornblende, quartz monzonite. Hornblende from this pluton gives a Jurassic 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 form inclusions, dikes, and/or marginal phases (Werdon and others, 2001). Clinopyroxenite bodies in the Napoleon pluton contain as much as 25 parts per billions (ppb) platinum and 6 ppb palladium (Werdon and others, 2000). Biotite clinopyroxenite dikes, which are compositionally and texturally similar to those 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 and aplite dikes of unknown age. The pluton intrudes amphibolite-facies amphibolite, quartzite, paragneiss, marble, orthogneiss, and minor schist (Werdon and others, 2001). The Napoleon pluton and surrounding country rocks are cut and offset by high-angle faults.
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 mineralization was discovered by Kennecott Exploration in 1998 and 1999 by detailed soil and rock sampling and airborne and ground geophysical surveys (Jones and Olson, 1999; Eden, 2010). In 1999, Kennecott drilled 9 holes on the Main Zone, 3 holes on the Saddle Zone, and 2 holes on the Trench 24 zone, and dug 24 trenches that totaled 464 meters. In 2000 and 2001, Tech Resources explored the property with ground and magnetic geophysical surveys and drilled 4 holes on the Main Zone and 3 holes on the Saddle Zone. A large block of claims was staked over the property in 2007 by Millrock Resources Inc., the current owners of the property (Millrock, 2011), and they have done considerable rock and soil sampling.
The mineralization is controlled by a major east-west trending shear zone that has been traced along strike for at least 4 miles (Eden, 2010). As best exposed in the Main Zone, this shear zone is at least 150 feet thick. Along this shear zone, the Napoleon pluton is cut by several discrete concentrations of narrow quartz veins including the three that make up this site. These veins typically strike northwest or north-northeast and dip steeply south. The veins are up to 12 inches thick, and consist of mainly of quartz +/- pyrite +/- hematite +/- epidote +/- carbonate +/- rare visible gold. Samples from the quartz veins assayed as much as 15 ounces of gold per ton and rarely contained less than 0.2 ounces of gold per ton. Vein selvages commonly contain K-feldspar, some of which is partly replaced by sericite. Sericite-altered K-feldspar from the selvage of a gold-quartz vein gives a Cretaceous 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 time of mineralization.
The best exposed mineralization and the focus of most of the exploration has been the Main Zone. The most notable drill intercepts on the Main Zone were two feet that contained 34.71 grams of gold per tonne and 2 feet that contained 17.74 grams of gold per tonne. The drilling at the Saddle Zone and Trench 24 zone tested a strong gold anomalies in soil. The best drill intercepts on the Saddle Zone were 3 meters with 8.49 grams of gold per tonne and 0.5 meters with 14.21 grams of gold per tonne. The best drill intercepts on the Trench 24 zone were 5 feet with 3.90 grams of gold per tonne, and 0.61 meters with 5.566 grams of gold per tonne.
Jones and Olson (1999) classified the prospect as a porphyry gold deposit. More recently, Eden (2010) classified it as a plutonic related gold-quartz vein deposit as defined by Lefebure and Hart (2005).
Geologic map unit (-141.637488383876, 64.163975469995)
Mineral deposit model Plutonic related gold-quartz vein deposit (Lefebure and Hart, 2005).
Age of mineralization Sericite-altered K-feldspar from the selvage of a gold- quartz vein gave a Cretaceous 40Ar/39Ar isochron age of 127.8 +/- 1.6 Ma (Layer and others, 2002); this is tentatively interpreted to reflect the time of mineralization.
Alteration of deposit K-feldspar adjacent to quartz veins is partly altered to sericite.

Production and reserves

Workings or exploration The mineralization was discovered by Kennecott Exploration in 1998 and 1999 by detailed soil and rock sampling and airborne and ground geophysical surveys (Jones and Olson, 1999; Eden, 2010). In 1999, Kennecott drilled 9 holes on the Main Zone, 3 holes on the Saddle Zone, and 2 holes on the Trench 24 zone, and dug 24 trenches that totaled 464 meters. In 2000 and 2001, Tech Resources explored the property with ground and magnetic geophysical surveys and drilled 4 holes on the Main Zone and 3 holes on the Saddle Zone. A large block of claims was staked over the property in 2007 by Millrock Resources Inc., the current owners of the property (Millrock, 2011), and they have done considerable rock and soil sampling.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Eden, Karsten, 2010, Napoleon claim block, Forty Mile mining district, east-central Alaska, April 8, 2010: Unpublished NI43-101 report, 96 p. (posted on www.sedar.com, April 14, 2010).
Jones, S. and Olson, D., 1999, Napoleon Project Report: Kennecott Exploration Company unpublished report, 13 p.
Layer, P.W., Drake, J., and Szumigala, D.J., 2002, 40Ar/39Ar dates for mineralization and igneous and metamorphic rocks in a portion of the Fortymile mining district, Eagle quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Preliminary Interpretive Report.
Lefebure, D.V., and Hart, C., 2005, Plutonic-related Au quartz veins and veinlets, model L02, in Fonseca, A.,and Bradshaw, G., eds., Yukon mineral deposit profiles: Yukon Geological Survey Open File Report 2005-5, p.121-128.
Millrock Resources Inc., 2011, Fortymile: http://www.millrockresources.com/projects/fortymile/ (as of February 6, 2011).
Reporters M.B. Werdon (ADGGS; 2000); D.J. Grybeck (Contractor, USGS)
Last report date 2/28/2011