37 Skarn

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu
Other commodities As; Pb; Zn
Ore minerals chalcopyrite; galena; gold; magnetite; marcasite; pyrrhotite; sphalerite
Gangue minerals actinolite/tremolite; dolomite; epidote; garnet; quartz

Geographic location

Quadrangle map, 1:250,000-scale IL
Quadrangle map, 1:63,360-scale D-7
Latitude 59.7914
Longitude -155.5116
Nearby scientific data Find additional scientific data near this location
Location and accuracy The 37 Skarn prospect is about 0.5 mile south of the Koktuli River at an elevation of about 1,000 feet. The prospect is about 3.8 miles west-northwest of Sharp Mountain and about 0.4 mile north of the center of section 32, T. 4 S., R. 36 W. The location is accurate.

Geologic setting

Geologic description

Five holes drilled in 2002 by Northern Dynasty Minerals Ltd. on a copper-gold geochemical anomaly found the first skarn mineralization in the Pebble claim block here (Rebagliati, 2003; Haslinger and others, 2004; Rebagliati and Payne, 2005; Gaunt and others, 2010). The host rocks are fine- to medium-grained basalt, basaltic breccias, and minor interbeds of lithic sandstone, siltstone, and mudstone. The basalts and associated rocks are pervasively altered to actinolite/tremolite, epidote, and chlorite. Most of the mineralization is in fracture-controlled veinlets and veins of epidote, dolomite, light-brown garnet, potassium feldspar, pyrrhotite, chalcopyrite, and magnetite. Sphalerite occurs in minor amounts. Some notable intercepts in the 2002 drilling were: 79 meters with 1.0 grams of gold per tonne and 0.40 percent copper; 2.32 meters with 8.19 grams of gold per tonne, 2.460 percent copper, 446 parts per million (ppm) zinc, and 15.6 grams of silver per tonne; 0.43 meters with 14.81 grams of gold per tonne, 4.430 percent copper, 714 ppm zinc, and 33.8 ppm silver; and 1.86 meters with 9.74 grams of gold per tonne, 3.14 percent copper, 692 ppm zinc, and 46.8 ppm silver.
Two more holes were drilled in 2003 on a strong northeast-trending magnetic anomaly (Haslinger and others, 2004). They encountered altered diorite and gabbro. The propylitic alteration suite is characterized by epidote, calcite, chlorite, and magnetite. The mineralization consists of scattered quartz-calcite-chlorite-marcasite veinlets with chalcopyrite, sphalerite, and galena. The best intercepts in the 2003 drilling were 4.7 meters with 0.61 grams of gold per tonne, 0.37 percent copper, 1,802 ppm zinc, and 7.8 ppm silver; and 0.8 meters with 16.50 grams of gold per tonne, 1.00 percent copper, 660 ppm zinc, 10 ppm silver, and 435 ppm arsenic.
Geologic map unit (-155.513789254996, 59.7907044859103)
Mineral deposit model Copper-gold skarn; probably related to porphyry copper-gold deposit (Cox and Singer, 1986; models 18b and 20c).
Mineral deposit model number 18b, 20c
Age of mineralization Probably Late Cretaceous, about 90 Ma, by proximity to the nearby Pebble deposit (IL007).
Alteration of deposit Basalts and associated rocks are pervasively altered to actinolite/tremolite, epidote, and chlorite. Diorite and gabbro are propylitically altered to epidote, calcite, chlorite, and magnetite.

Production and reserves

Workings or exploration The area has been 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 through early 2011 by Northern Dynasty Minerals Ltd. Mapped and sampled at the surface. Five holes drilled in 2002 by Northern Dynasty Minerals Ltd. on a copper-gold geochemical anomaly found the first skarn mineralization in the Pebble claim block. Two more holes were drilled in 2003 on a strong northeast-trending magnetic anomaly.
Indication of production None
Reserve estimates None.
Production notes None.

References

References

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