Sill

Prospect, Active

Commodities and mineralogy

Main commodities Au
Ore minerals gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale IL
Quadrangle map, 1:63,360-scale D-6
Latitude 59.8513
Longitude -155.2074
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Sill prospect is about 9.0 miles northeast of Sharp Mountain near the northeast corner of section 12. T. 4 S. R. 35 W. The location is accurate.

Geologic setting

Geologic description

The Sill deposit is in Tertiary (40 Ma) fine-grained, equigranular to porphyritic latite (Bouley and others, 1995; Haslinger and others, 2004). The mineralization consists of narrow gold-quartz veins and quartz breccias in narrow pyritic alteration envelopes.
The Sill deposit was found in 1988 by Teck Cominco; they drilled 24 holes in 1988 and another 15 holes in 1989 for a total of 3,183 meters. Numerous intercepts contained more than 5 grams of gold per tonne including: 0.61 meters with 22.83 grams of gold per tonne, 0.61 meters with 24.34 grams of gold per tonne, 1.37 meters with 34.29 grams of gold per tonne, 0.49 meters with 26.00 grams of gold per tonne, and 0.30 meters with 25.99 grams of gold per tonne (Haslinger and others, 2004, table 8.0). Although the Sill prospect is in the large Pebble claim block held by Northern Dynasty Minerals Inc. as of early 201, they have done no work on the prospect.
Geologic map unit (-155.209589468342, 59.8506113954183)
Mineral deposit model Low-sulfide gold-quartz veins (Cox and Singer, 1956; model 36a).
Mineral deposit model number 36a
Age of mineralization 40 Ma or younger based on the age of the host rock.
Alteration of deposit Gold-quartz veins are in narrow pyritic alteration envelopes.

Production and reserves

Workings or exploration The Sill deposit was found in 1988 by Teck Cominco; they drilled 24 holes in 1988 and another 15 holes in 1989 for a total of 3,183 meters. Although the Sill prospect is in the large Pebble claim block held by Northern Dynasty Minerals Inc. as of early 201, they have done no work on the prospect.
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).
Reporters D.J. Grybeck (Contractor, USGS)
Last report date 2/28/2011