Pyramid

Prospect, Active

Commodities and mineralogy

Main commodities Cu; Mo
Other commodities Ag; Au; Pb; Sb; Zn
Ore minerals chalcocite; chalcopyrite; covellite; molybdenite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PM
Quadrangle map, 1:63,360-scale C-3
Latitude 55.6298
Longitude -160.6753
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Pyramid prospect is on the south flank of Pyramid Mountain, about 3.3 miles northwest of the mouth of Bishop Creek near the head of Albatross Anchorage. It is centered about 0.3 mile southeast of the center of section 35, T. 53 S., R. 75 W., of the Seward Meridian. The location is accurate to within 1000 feet.

Geologic setting

Geologic description

The Pyramid copper-molybdenum deposit is associated with a quartz diorite pluton that cuts Paleocene to Eocene sedimentary rock of the Tolstoy Formation (Wilson and others, 1995). The stock has been dated at 6 million years (Wilson and others, 1996). The molybdenum mineralization has also been dated at 6 million years by Re-Os methods (Wilkins, 2011).
The prospect is a classic copper-molybdenum deposit having a potassic core surrounded by a phyllic zone and an outer propylitic zone. The central potassic core contains secondary biotite after mafic minerals and 2 to 10 percent magnetite as fracture fillings and disseminated clots and grains. The potassic alteration core in the intrusive, is roughly 800 by 1,700 feet in plan. It is essentially barren with less than 0.25 percent sulfides and copper and molybdenum in the 0.001 to 0.01 percent range (Christie, 1975). The phyllic zone is characterized by sericite, quartz, and andalusite in a zone surrounding the potassic core. It occurs mostly in the intrusive rocks and measures 700 to 2,500 feet in width. The propylitic zone is characterized by chlorite, magnetite, epidote, and calcite.
The highest total sulfide content, 5 to 10 percent, occurs in the inner part of the propylitic zone and outer part of the quartz-sericite zone. Pyrite:chalcopyrite ratios are 50:1 or greater and are associated with copper grades of 0.15 percent or less (Christie, 1975). Toward the inner part of the phyllic zone, pyrite-chalcopyrite ratios decrease and copper grades increase to 0.3 to 0.4 percent; molybdenum grades are 0.03 to 0.04 percent. In the copper-rich part of the system, the sulfides occur as disseminations and thin fracture fillings.
The deposit has been oxidized to depths of 0 to 450 feet and exhibits a supergene blanket of secondary copper enrichment as much as 300 feet thick. The enriched zone contains chalcocite, covellite, and bornite, as well as some chalcopyrite. The best grades of copper, as much as 0.8 percent, occur in the upper 100 feet of the supergene blanket. The thickest enrichment zones are not necessarily associated with the thickest zones of oxidation. Lead, antimony, and zinc are also reported in some assays. The supergene blanket is overlain by a leached capping up to 100 meters thick.
A Quintana-Duval-Aleut joint venture mapped, sampled, and drilled this deposit in 1974 and 1975. They diamond-drilled 19 holes for a total of 5,565 feet. As a result of this work they outlined an estimated resource of 126,000,000 tons of with a grade of 0.403 percent copper and 0.025 percent molybdenum, with potential for another 49 million tons of chalcocite-enriched ore (Christie, 1975).
Pyramid was drilled By Battle Mountain in the late 1980s and they identified gold values that improved the economics of the deposit. Metallica Resources did additional surface sampling in 2005 and 2006 that reinforced the added gold value of Pyramid.
Full Metal Minerals in a joint venture with Antotagasta Minerals S.A. drilled 5 core holes at Pyramid in 2010 to test the lateral and vertical extent of the mineralization (Full Metal Minerals, 2010 and 2011). The mineralization and alteration persisted to the bottom of these holes. Some notable intercepts were: 1) 468 meters that contained 0.272 percent copper, 0.058 gram of gold per tonne, and 0.019 percent molybdenum; 2) 356 meters that contained 0.343 percent copper, 0.078 gram of gold per tonne, and 0.008 percent molybdenum; 3) 289 meters that contained 0.299 percent copper, 0.082 gram of gold per ton, and 0.032 percent molybdenum; and 4) 195 meters that contained 0.63 percent copper, 0.141 gram of gold per tonne, and 0.018 percent molybdenum.
In 2011, the joint venture of Full Metal Minerals of Antofagasta Minerals drilled 12 more core holes that totaled 2,576 meters with results that expanded the mineralization (Wilkins, 2011; Full Metal Minerals, 2012). Including these holes, the mineralization covers an area about 1,100 meters by 900 meters in size and is open in all directions and at depth. The best intercept in the 2011 drilling was 155.9 meters with 0.709 percent copper, 0.024 percent molybdenum, and 0.18 gram of gold per tonne. Most of the drilling through 2011 has been relatively shallow to identify the zone of supergene enrichment and most of the holes have bottomed in mineralized rock.
Geologic map unit (-160.677320514872, 55.6289757311158)
Mineral deposit model Porphyry Cu, Porphyry Cu-Mo-Au (Cox and Singer, 1986; models 17, 21a)
Mineral deposit model number 17, 21a
Age of mineralization The stock that hosts the mineralization has been dated at 6 Ma by K/Ar methods; molybdenite has also been dated at 6 Ma by Re-Os methods (Wilkins, 2011).
Alteration of deposit The alteration consists of a barren, potassically-altered core zone, an intermediate zone characterized by pervasive quartz and sericite, and a propylitic outer zone (Christie, 1975).

Production and reserves

Workings or exploration
In 1975-1975, Quintana-Duval mapped, sampled, and diamond-drilled 19 holes totaling 5,565 feet. The U.S. Geological Survey sampled the deposit in the 1980s. Battle Mountain drilled in the 1980s and Metallica Resources collected surface samples in 2005 and 2006. In 2010, Full Metal Minerals in a joint venture with Antotagasta Minerals S.A. drilled 5 core holes at Pyramid to test the lateral and vertical extent of the mineralization. They drilled 12 more holes in 2011 that totaled 2,576 meters.
In 2012, Full Metal Minerals (FMM) drilled 13 diamond core holes with a total drilled depth of 3,241 meters (Farrow and Arseneau, 2013).
Indication of production None
Reserve estimates In 2013, a 43-101 Technical report, including mineral resource estimate, was published (Full Metal Minerals, 2014). These are: an inferred resource of 94,000,000 tonnes with a grade of 0.092 gram of gold per tonne, 823,000,000 pounds with a grade of 0.40 percent copper, and 40,000,000 pounds with a grade of 0.02 percent molybdenum in the supergene part of deposit, plus an inferred resource of 79,000,000 tonnes with a grade of 0.083 gram of gold per tonne, 515,000,000 pounds with a grade of 0.30 percent copper, and 34,000,000 pounds with a grade of 0.02 percent molybdenum in the hypogene part of the deposit, for a total inferred resource of 173,000,000 tonnes with a grade of 0.088 gram of gold per tonne, 1,338,000,000 pounds with a grade of 0.088 percent copper, and 74,000,000 pounds with a grade of 0.02 percent molybdenum (Farrow and Arseneau, 2013). (Conversion Note: 10,000 pounds = 4.54 tonnes)
Production notes None.

Additional comments

The subsurface of the property is controlled by the Aleut Corporation; the surface is controlled by the Shumigan and the TDX (St Paul) native corporations.

References

MRDS Number A010658; A013224

References

Armstrong, R.L., Harakal, J.E., and Hollister, V.F., 1976, Age determinations of late Cenozoic porphyry copper deposits of the North American Cordillera: Institute of Mining and Metallurgy Transactions, Section B, v. 85, p. 239-244.
Butherus, D. L., Gressitt, E.E., Pray, J., Corner, N.G., Lindberg, P.A., Fankhauser, R.E., 1979, Exploration and evaluation of the Aleut Native Corporation lands: Resource Associates of Alaska Report, 69 p, 90 map sheets, various scales (Held by the Aleut Corporation, Anchorage).
Christie, J.S., 1974, Aleut-Quintana-Duval 1974 joint venture, final report: Unpublished Quintana Minerals Corporation report, 24 p., 3 appendices, 2 maps. (Report held by the Aleut Corporation, Anchorage, Alaska).
Christie, J.S., 1975, Pyramid Project, Aleut-Quintana-Duval joint venture report on 1975 drill program: Quintana Minerals Report, 17 p. (Report held by the Aleut Corporation, Anchorage, Alaska).
Freeport Exploration Company, 1985, 1984 report of activities, Canoe Bay joint venture: Freeport Exploration Company, 25 p. (Report held by the Aleut Corporation, Anchorage, Alaska).
Full Metal Minerals, 2010, Full Metal and Antofagasta Minerals drill 195 meters averaging 0.63% Cu, 0.018% Mo, 0.141g/t Au. or 0.823 Cu equivalent at Pyramid porphyry project, Alaska: http://www.fullmetalminerals.com/s/NewsReleases.asp?ReportID=424115&_Type=News&_Title=Full-Metal-and-Antofagasta-Minerals-Drill-195-meters-Averaging-0.63-Cu-0.01... (News release, Oct. 20, 2010).
Full Metal Minerals, 2011, Pyramid: http://www.fullmetalminerals.com/s/Pyramid.asp (as of Feb 12, 2011).
Full Metal Minerals, 2012, Pyramid: http://www.fullmetalminerals.com/properties/pyramid/ (as of March 18, 2012).
Full Metal Minerals, 2014, The Pyramid Project Overview: http://www.fullmetalminerals.com/properties/pyramid/ (as of July 14, 2014).
Hollister, V.F., 1978, Geology of the porphyry copper deposits of the Western Hemisphere: Society of Mining Engineering, American Institute of Mining, Metallurgy, and Petroleum Engineers Inc., 218 p.
Wilkins, Joey, 2011, Pyramid porphyry Cu-Mo-Au project Alaska Peninsula, Alaska, USA; Full Metal Minerals and Antofagasta Minerals JV: Alaska Miners Association, 2011 Annual Convention, Abstracts, p. 38-39.
Wolfhard, F.H., 1974, Pyramid prospect preliminary evaluation: Quintana Minerals Corporation unpublished report, 9 p., 6 map sheets, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska).
Wolfhard, F.H., 1976, Final report, Pyramid project 1976 work: Quintana Minerals Corporation unpublished report, 2 p. (Report held by the Aleut Corporation, Anchorage, Alaska).
Young, L.E., St. George, P., and Bouley, B., 1997, Porphyry copper deposits in relation to the magmatic history and palinspastic restoration of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 306-333.
Reporters S.H. Pilcher (Anchorage, Alaska); D.J. Grybeck (Contractor, USGS); V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 12/11/2014