25 Zone

Prospect, Active

Alternative names

25 Gold

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale IL
Quadrangle map, 1:63,360-scale D-7
Latitude 59.8548
Longitude -155.3289
Nearby scientific data Find additional scientific data near this location
Location and accuracy At least 15 holes have been drilled at the 25 Zone prospect; the center of the work is about 1.5 miles southwest of the center of lake 943, locally called Frying Pan Lake. The center is about 0.4 mile south-southeast of the center of section 5, T. 4 S., R. 35 W. The drill sites are scattered over much of the southeast corner of section 5. The location is accurate.

Geologic setting

Geologic description

The 25 Zone prospect is associated with a brecciated intrusive complex that covers about 8 square kilometers (Rebagliati, 2003; Haslinger and others, 2004; Rebagliati and Payne, 2005; Gaunt and others, 2010). The complex consists of pyroxenite and gabbro, intruded by irregular bodies and dike swarms of fine-grained monzonite. The mineralization consists of: 1) polymetallic veins and veinlets with gold, sphalerite, galena, chalcopyrite, and minor disseminated chalcopyrite in the wall rocks; 2) zones with 3-8 percent pyrite associated in some place with quartz-carbonate breccia and in others with strong chlorite-epidote alteration; and 3) quartz veins, replacement patches, and breccia with minor pyrite. The alteration is dominated by a chlorite-epidote-calcite-pyrite propylitic assemblage that occurs as disseminations, phenocryst replacements, and rims around breccia clasts. The rocks locally exhibit silica veining, flooding, and brecciation. Skarn-type alteration occurs along the monzonite dikes. The higher-grade gold intervals in the drill holes are associated with the propylitic and skarn alteration that is ubiquitous in the breccia complex. The mineralization is probably about 90 Ma based on its proximity to the Pebble prospect (IL007),
The prospect and surrounding area has been covered by extensive geologic mapping and sampling, and geochemical and geophysical surveys beginning in about 1986 as part of the exploration of the Pebble block of claims, first by Cominco and then by Northern Dynasty Minerals Ltd., the operator as of early 2011 Northern Dynasty drilled least 15 holes in 2002. Some notable intersects are: 6.10 meters with 28.90 grams of gold per tonne and 0.013 percent copper; 0.31 meter with 260.78 grams of gold per tonne and 0.007 percent copper; and 1.74 meters with 19.27 grams of gold per tonne, 0.20 percent copper, more than 1 percent lead and zinc, and 47.0 parts per million silver. Many intercepts contained 1.0 gram of gold per tonne or more.
Geologic map unit (-155.331091283794, 59.854109052959)
Mineral deposit model Polymetallic quartz veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Probably 90 Ma based on its proximity to the nearby Pebble prospect (IL007).
Alteration of deposit The alteration is dominated by a chlorite-epidote-calcite-pyrite propylitic assemblage that occurs as disseminations, phenocryst replacements, and rims around breccia clasts. The rocks locally exhibit silica veining, flooding, and brecciation. Skarn-type alteration occurs along the monzonite dikes.

Production and reserves

Workings or exploration Covered by extensive geochemical and geophysical surveys beginning in about 1986 as part of the exploration of the Pebble block of claims first by Cominco and as of early 2011 by Northern Dynasty Minerals Ltd. Mapped and sampled at the surface; at least 15 holes drilled by 2002.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

Bouley, B.A., St. George, P., and Wetherbee, P.K., 1995, Geology and discovery at Pebble Copper, a copper-gold porphyry system in southwest Alaska: Canadian Insitute of Mining, Metallurgy, and Petroleum, Special Volume 46, p. 422-435.
Gaunt, J.D., Rebagliati, C.M., Lang, James, Titley, Eric, Melis, Lawrence, Barratt. Derek, and Hodgson, Stephen, 2010, Technical report on the 2009 program and update on metallurgy, Pebble copper-gold-molybdenum project, Iliamna Lake area, southwestern Alaska, U.S.A: Unpublished Technical Report for Northern Dynasty Minerals Ltd., 195 p. (posted on www.sedar.com, Mar. 18, 2010).
Haslinger, R.J., Payne, J.G., Price, S. and Rebagliati, C.M., 2004, 2003 Summary report on the Pebble Porphyry gold-copper project: Unpublished report for Northern Dynasty Minerals Ltd., 119 p. (posted on www.sedar.com, Jun. 30, 2004).
Rebagliati, C.M., 2003, Summary report on the Pebble copper-gold porphyry project; Unpublished report for Northern Dynasty Minerals Ltd., 94 p. (posted on www.sedar.com, Feb. 13, 2003.)
Rebagliati, C.M., and Payne, J.G. 2005, 2004 summary report on the Pebble gold-copper project: Unpublished report for Northern Dynasty Minerals Ltd., 118 p. (posted on www.sedar.com, Apr. 4, 2005).
Rebagliati, C.M., and Payne, J.G., 2007, 2006 summary report on the Pebble gold-copper-molybdenum project: Unpublished report for Northern Dynasty Minerals Ltd., 119 p. (posted on www.sedar.com, Apr. 2, 2007).
Reporters C.C. Hawley, Hawley Resource Group, Anchorage, Alaska; D.J. Grybeck (Contractor, USGS)
Last report date 2/28/2011