Prospect, Active

Commodities and mineralogy

Main commodities Ag; Au; Ba; Cu; Pb; Zn
Other commodities Co; Sb
Ore minerals acanthite; barite; galena; pyrargyrite; pyrite; sphalerite; tetrahedrite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale SK
Quadrangle map, 1:63,360-scale B-4
Latitude 59.3775
Longitude -136.4185
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Cap prospect is near the north edge of Saksaia Glacier at an elevation of about 3,800 feet. It is approximately 2.1 miles east of Mt. Henry Clay and about 0.6 mile south-southwest of the center of Section 1, T. 29 E., R. 53 E., of the Copper River Meridian. The location is accurate within 500 feet.

Geologic setting

Geologic description

The rocks in the region are part of the Upper Triassic Hyd Group that hosts similar volcanic massive sulfide deposits the length of southeastern Alaska (Newberry and others, 1997). The rocks are predominantly massive and pillow basalts and fragmental basalt and andesite(?), intercalated with siltstone, tuff, and rare rhyolite flows and dikes. They have been subject to greenschist-facies metamorphism; folding and faulting locally repeats the stratigraphy in places, and the rocks are highly altered.
As described by Still (1984) and Still and others (1991), the Cap prospect consists of barite-rich sulfide lenses up to 8 feet thick in a 50-foot-thick, 220-foot-long, iron-stained zone capped by volcanics that outcrop above the Saksaia glacier. The full extent of the prospect is hidden by glacier and surficial material. The barite lenses contain pyrite, sphalerite, galena, and tetrahedrite. Samples contained up to 50 percent barium, 1.1 percent zinc, 0.33 percent lead, 277.7 parts per million (ppm) silver, 1.371 ppm gold, and 100 ppm cobalt.
Rubicon Minerals (1998) cites a 43-foot channel sample that contained 247.6 ppm silver, 0.263 ppm gold, 2,753 ppm zinc, 1,803 ppm lead, and 174 ppm copper. They also report a drill hole with a 76.3-foot-thick intercept that averaged 3.7 ounces of silver per ton. Rubicon (1998) concluded that the Cap prospect lies along a northwest-trending mineral belt that includes the Nunatak (SK058), Cap, and MHC (SK068) prospects. They believe that these deposits are at the same stratigraphic horizon and attribute their distribution to a northwest-trending, shallowly plunging antiform that brings the massive-sulfide horizon close to the surface (Rubicon Minerals, 1998).
As described by Constantine Metal Resources, Ltd., (2007, 2008) and Greig and Giroux (2010), the Cap prospect is a silver-rich, barite-zinc-lead-gold massive-sulfide horizon 7 to 8 meters thick, in a veined and brecciated, amygdaloidal basalt. The deposit is marked by intense quartz-sericite-pyrite alteration. The basalt is capped by a bed of massive pyritic barite. Mineralized seams, veins, and layers up to 4.2 meters thick of massive barite with some chert occur throughout the section of altered basalt. In the core of the altered zone the basalt is completely replaced by quartz, sericite, and pyrite, and only the amygdules remain of the unaltered basalt. The amygdules are filled with quartz, minor barite, and sericite and are locally cored with sphalerite and galena. Veins and the matrix of the breccia in the altered basalt consist mainly of barite, quartz, pyrite, and sericite. The veins commonly have irregular, ‘wormy’ forms and typically are zoned, with pyrite margins and quartz-barite cores. The veins contain pyrite, sphalerite, galena, acanthite, and possibly pyrargyrite. The highest metal values are associated with the barite lenses. Constantine (2007) drilled two holes in 2007 that cut sections 730- and 300-feet thick of altered pyritic rocks. The best intersect was a 25.5-foot interval with 43 grams of silver per tonne, 0.29 gram of gold per tonne, 1.2 percent zinc, and 0.60 percent lead; this interval included a 6.3-foot section that contained 3.75 percent zinc, 1.91 percent lead, 0.18 percent copper, 92.1 grams of silver per tonne, and 0.47 grams of gold per tonne.
There have been several published studies of the mineral deposits in the area by government and academia (MacKevett and others, 1974; Still, 1984, Still and others, 1991; Newberry and others, 1997; Greig and Giroux, 2010) and unpublished studies by industry. The consensus from early on was that they are Late Triassic, stratiform volcanogenic massive-sulfide deposits.
Geologic map unit (-136.420366982544, 59.3771602468731)
Mineral deposit model Kuroko- or Besshi-type volcanogenic massive sulfide (Cox and Singer, 1986; models 28a or 24b)
Mineral deposit model number 28a or 24b
Age of mineralization Late Triassic by analogy with other similar deposits of that age along the length of southeastern Alaska and into Canada (Greig and Giroux, 2010).
Alteration of deposit The deposit is associated with a basalt layer that is intensely altered to quartz, sericite, and pyrite (Constantine Metal Resources, Ltd., 2007, 2008 and Greig and Giroux, 2010).

Production and reserves

Workings or exploration
Mineralization in this area was discovered in 1969 by Merrill Palmer and associates and has been explored by a succession of companies including Alyu Mining in 1976 and 1977; Anaconda Minerals in 1979 and 1980; Southeastern Minerals from 1980 to 1983; Bear Creek Mining from 1983 to 1985; Newmont Exploration from 1987 to 1989; Granges Exploration Ltd. in 1989; Cominco Alaska from 1990 to 1993; Kennecott Minerals from 1993 to 1997, Rubicon Minerals from 1998 to 2000; and Toquima Minerals Corp. in 2004 (Greig and Giroux, 2010). It was also mapped and sampled by the U.S. Geological Survey (MacKevett and others, 1974) and the U.S. Bureau of Mines (Still, 1984), and the Alaska Division of Geological and Geophysical Surveys (Still and others, 1991). In 2006, Constantine Metal Resources acquired the property under a long-term lease and began actively exploring it. Their work has included detailed geologic mapping and sampling, ground geochemical and geophysical surveys (Greig and Giroux, 2010).
The Cap prospect has been explored by a number of companies including Newmont Gold Company and Rubicon Minerals since at least the late 1990s; their work included surface mapping, trenching, and at least three drill holes. As of early 2011, it was actively being explored by Constantine Metal Resources Ltd., who drilled two holes in 2007 (Greig and Giroux, 2010).
In 2014, Constantine reported assay highlights at Cap of 1) 134 grams of silver per tonne over 23.2. meters (3.9 ounces per ton over 75 feet) from drill holes CAP01, and 2) 31 grams of silver per tonne over 90.6 meters (0.9 ounce per ton over 294 feet) (Constantine Metal Resources Ltd., 2014).
Indication of production None
Reserve estimates None.
Production notes None.


MRDS Number A013090


Constantine Metal Resources Ltd., 2008, Cap: (as of April 8, 2008).
Constantine Metal Resources Ltd., 2014, Corporate Presentation February 2014: (as of Sept. 16, 2014).
Greig, C.J., and Giroux, G.H., 2010, Palmer VMS project, southeast Alaska; Mineral resource estimation and exploration update: Technical l report for Constantine Metal Resources Ltd. 82 p. (posted on, Mar. 8, 2010) (as of December 24, 2014).
Newberry, R.J., Crafford, T.C., Newkirk, S.R., Young, L.E., Nelson, S.W., and Duke, N.A., 1997, Volcanogenic massive sulfide deposits of Alaska, in Goldfarb, R.J. and Miller, L. D., eds., Mineral deposits of Alaska: Economic Geology Monograph 9, p. 120-150.
Rubicon Minerals, 1998, Palmer VMS Project, southeast Alaska, Executive Summary: Unpublished report by Rubicon Minerals Corporation, Vancouver, British Columbia, 25 p.
Reporters T.C. Crafford (T. Crafford & Associates, Anchorage); D.J. Grybeck (Contractor, USGS); V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 12/24/2014