Burnt Ridge

Prospect, Active

Alternative names

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 64.1554
Longitude -141.6189
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is about 1 mile southeast of peak 3750, about 0.6 mile west of the fork at the head of Napoleon Creek. It is about 0.6 mile north-northeast of the center of section 2, T. 27 N., R.19 E. This prospect is sometimes combined with the nearby Main Zone, Saddle Zone, and Trench 24 prospects (EA115) and with the Twin Peaks (EA167) prospects under the name Napoleon or Napoleon Block/claims.

Geologic setting

Geologic description

The Burnt Ridge prospect like those at the nearby prospects EA115 and EA167 to the north is within the Napoleon pluton, a roughly roughly equidimensional stock 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 within the Napoleon pluton contain as much as 25 parts per billion (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 aplite-pegmatite dikes of unknown age. The Napoleon 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). In 1998 and 1999, Kennecott Exploration did detailed soil- and rock sampling, and airborne and ground geophysical surveys which led to the discovery of the Burnt Ridge mineralization (Jones and Olson, 1999; Eden, 2010). In 1999, they drilled 13 holes on similar mineralization to the north (EA115) and 3 holes on Burnt Ridge. 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 in the area.
While not as well known as the similar mineralization to the north at ARDF site EA115, the Burnt Ridge mineralization is probably related to a major east-west striking shear zone exposed to the north or a similar parallel structure. This shear zone is at least 150 feet thick and contains several swarms of narrow sulfide-bearing quartz veins. The 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. Vein selvages commonly contain K-feldspar, some of which is partly replaced by sericite. Sericite-altered K-feldspar from the selvage of a gold + pyrite + quartz vein gave 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. Samples of the quartz veins contain up to 15 ounces of gold per ton and rarely contain less than 0.2 ounces of gold per ton. The best intercept in the 1999 Burnt Ridge drilling was 35 feet that averaged 1.413 grams of gold per tonne; it included 5 feet that contained 6.56 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 (-141.621187480723, 64.1550760605845)
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 In 1998 and 1999, Kennecott did detailed soil- and rock sampling in the area as well as airborne and ground geophysical surveys which led to the discovery of the Burnt Ridge mineralization (Jones and Olson, 1999; Eden, 2010). In 1999, they drilled 13 holes on similar mineralization to the north (EA115) and 3 hole on Burnt Ridge. The best intercept was 35 feet that averaged 1.413 grams of gold per tonne; it included 5 feet that contained 6.56 grams of gold per ton Teck Resources drilled one hole at the Burnt Ridge prospect in 2001. 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 in the area.
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. [In preparation in 2002]
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