Ivanof

Prospect, Active

Alternative names

Kawisgag

Commodities and mineralogy

Main commodities Ag; Au; Cu; Mo
Other commodities As; Pb; Zn
Ore minerals arsenopyrite; bornite; chalcopyrite; covellite; gold; molybdenite; pyrite; pyrrhotite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale SB
Quadrangle map, 1:63,360-scale D-5
Latitude 55.8876
Longitude -159.4223
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Ivanof prospect is on a peninsula between Humpback and Ivanof Bays. It covers an area several miles in diameter, northwest of triangulation station Short. It is at an elevation of about 1,250 feet, at the midpoint of the boundary between secs. 1 and 36, T. 49 and 50 S., R. 65 W, of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

The Ivanof prospect is in sandstone, grits, and conglomerates of the Eocene to Paleocene Tolstoi Formation which is are cut by an intrusive complex (Fields, 1977; Wilson and others, 1995). Biotite from the complex has been dated at 7 million years (Wilson and others, 1994). The sedimentary rock near the complex exhibits intense thermal metamorphism which formed biotite-quartz hornfels.
The intrusive complex, best exposed in two cirque basins, consists of an early diorite porphyry phase and a later, more extensive, quartz porphyry phase. The quartz porphyry intrudes the diorite as well as the Tolstoy Formation. Peripheral sills and dikes similar in composition to the intrusive complex cut the sedimentary units.
Both intrusive phases are mineralized, but only the diorite porphyry contains copper-molybdenum values. The sulfide mineralization, which includes arsenopyrite, pyrite, pyrrhotite, chalcopyrite, bornite, and covellite, covers an area of approximately 2 by 2.5 miles. In the quartz porphyry, pyrite is pervasive as disseminations and fracture fillings as well as in the sedimentary rocks throughout a 3-square-mile area. Two zones of copper-molybdenum-quartz stockwork mineralization were outlined by Bear Creek Mining (Fields, 1977); each extends over an area of approximately 2,000 by 600 feet and occurs in the diorite as well as in the surrounding sedimentary rocks. Base metal values in rock samples collected at the surface were from 500 to 1,700 parts per million (ppm) copper and 20 to 240 ppm molybdenum, with weakly anomalous gold values. Fields describes the pyrite:chalcopyrite ratio as 1:1 to 2:1 in the main mineralized areas and 5:1 to 10:1 in surrounding areas. Rock samples collected by Resource Associates of Alaska in 1979 in the northern cirque contained as much as to 790 parts per million (ppm) copper, 2,400 ppm molybdenum, and 2.4 ppm silver.
Farnstrom (1991) associates the mineralization with two separate, intersecting quartz-sulfide stockworks. The older stockwork consists of quartz-sulfide-chlorite veinlets in the diorite porphyry that are traceable for as much as to 3,000 feet into the sedimentary rocks. These veinlets contain pyrite, pyrrhotite, and chalcopyrite. Pyrite:chalcopyrite ratios exceed 5:1. The younger stockwork consists of veinlets as much as 0.4 inch wide containing pyrite, molybdenite, and only trace amounts of chalcopyrite, covellite, bornite, and malachite. According to Farnstrom (1991), the distribution of the copper-rich stockwork is spotty; the best deposits are at the contact of the diorite porphyry and the sedimentary country rocks.
In 1979, Resource Associates of Alaska discovered quartz veins with gold and arsenopyrite in areas peripheral to the copper-molybdenum mineralization (Moller and others, 1982). Some of these veins are as much as 30 feet wide and can be traced for as much as 2,400 feet along strike. They typically are 5 to 8 feet. wide and contain 0.08 to 0.20 ounce of gold per ton.
Strong secondary biotite is localized in and around the diorite porphyry over an area approximately 1,000 feet in diameter. Widespread sericitic alteration surrounds the biotite zone and coincides with the pyritic halo. Propylitic alteration forms an outer zone of alteration (Fields, 1977).
Farnstrom (1991) described the alteration in and around the diorite porphyry as relatively slight. Mineralized areas, however, are marked by intense bleaching and silicification. According to Farnstrom, chlorite replaces mafic minerals, and also occurs in stockwork veinlets in both intrusive phases. In the diorite, the chlorite is accompanied by epidote. Feldspars in both intrusive phases are altered to sericite, but this type of alteration tends to be more intense in the quartz porphyry. In contrast to Field's (1977) pattern, Farnstrom did not recognize a zonal pattern of alteration. Some of the alteration she describes may be deuteric in origin rather than hydrothermal.
In 2005 and 2006, Metallica Resource Inc. (2008) under an option agreement with Full Metal Minerals that in turn has access to the land under an agreement with several Native corporations, mapped and sampled the prospect and carried out ground geophysical surveys to define targets for future drilling.
Geologic map unit (-159.424303892698, 55.8868004703127)
Mineral deposit model Porphyry Cu, Porphyry Cu-Mo, Porphyry Cu-Au (Cox and Singer, 1986; models 17, 21a, 20c).
Mineral deposit model number 17, 21a, 20c
Age of mineralization Seven million years or younger, based on radiometric dating.
Alteration of deposit According to Fields (1977), the alteration exhibits a zonal pattern with a central potassic core surrounded by a phyllic zone and an outer propylitic zone. Farnstrom (1991) describes sericitic (phyllic) alteration that is related in part to mineralization. The mineralized areas are also marked by intense bleaching and silicification.

Production and reserves

Workings or exploration Bear Creek Mining mapped and sampled this prospect for Bristol Bay Native Corporation in the 1970s (Fields, 1977). Resource Associates of Alaska mapped and sampled the deposit in the mid 1980s, and ran approximately 9 line miles of VLF-EM and magnetic surveys. The U.S. Geological Survey sampled the deposit in the mid-1980s. Cominco mapped and sampled the deposit in 1990 (Farnstrom, 1991). In 2005 and 2006, Metallica Resource Inc. (2008) mapped and sampled the prospect and carried out ground geophysical surveys to define targets for future drilling.
Indication of production None

Additional comments

This prospect is on land interim-conveyed to, or patented by the Bristol Bay Native Corporation.

References

MRDS Number 10308207

References

Farnstrom, H.E., 1991, Ivanof Project, 1990 final report: Cominco Alaska, 12 p. (Report held by Alaska Earth Sciences, Inc., Anchorage, Alaska .)
Fields, E.D., 1977, 1976 Annual report: Alaska search, Chignik area-Bristol Bay region: Bear Creek Mining Company, 44 p., 22 map sheets. (Report held by the Aleut Corporation, Anchorage, Alaska.)
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.
Metallica Resources, Inc., 2008, Exploration- southwest Alaska: http://www.metal-res.com/projects/exploration/southwest_alaska/ (as of May 22, 2008).
Moller, S. A., Bernt, J., Farnstrom, H. E., Toupe, W., Hanneman, Nancy, 1982, Exploration and evaluation of precious metals potential of Bristol Bay Native Corporation lands, SW Alaska, vols. IV and V: Resource Associates of Alaska, Fairbanks, Alaska. (Report on file, Bristol Bay Native 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 (Port Ludlow, WA)
Last report date 6/5/2008