Dama

Prospect, Active

Alternative names

Copper Cliff

Commodities and mineralogy

Main commodities Ag; Au; Cu; Zn
Ore minerals chalcopyrite; copper; pyrite

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-1
Latitude 55.05691
Longitude -132.12734
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Dama prospect is at an elevation of about 750 feet, about 0.9 mile east-northeast of hill 2230 and about 0.2 mile west-northwest of the southeast corner of section 34, T. 78 S., R. 88 E.
From the late 1970's to the present (2004), there has been nearly continuous exploration of several geologically similar deposits in an area of about a square mile southeast of the old Niblack Mine (CR216). Those deposits are described separately (CR217-223), but in the recent literature, the Dama prospect and other deposits in the area are commonly grouped together under the name 'Niblack,' or 'Niblack project'.

Geologic setting

Geologic description

There was considerable work on the Dama prospect from 1903 to 1905; the workings included a 250-foot tunnel with about 200 feet of drifts and crosscuts, a 40-foot-deep shaft, and several trenches (Wright and Wright, 1908; Twenhofel and others, 1949). The deposit consists of several mineralized bands up to 125 feet thick in greenschist; one contains more than 50 percent pyrite. Native copper occurs along joint surfaces. A chip sample collected by Twenhofel and others (1949) across 125 feet contained 0.11 percent copper.
Beginning in the mid-70s, a succession of companies, including Cominco-Alaska, Inc., Anaconda Minerals, Noranda Exploration, Houston Oil and Minerals, Long Lac Minerals, and, beginning in 1995, Abacus Minerals, have carried out extensive exploration on several deposits in the Niblack Mine area (CR217-223), testing the now widely accepted theory that they are volcanogenic, stratabound, massive-sulfide deposits. Those deposits are commonly grouped with the old Niblack Mine under the name 'Niblack' or 'Niblack Project'.
The exact location of most of the recent exploration in the Niblack area, including several generations of drilling, is not well documented in the public literature. Anaconda Minerals drilled at least two holes in 1978. Green and others (1989) note that Noranda and Lac Minerals drilled 24,000 feet on the deposits in the Niblack area through 1988, and Abacus Minerals drilled 39,000 feet in 1996 (1997?) (Swainbank and others, 1998). The exploration has been mentioned frequently in the annual reports of the Alaska Division of Geological and Geophysical Surveys since the early 80s. In their most recent annual report (Swainbank, and others, 2002), the deposits are grouped under the name 'Niblack'. The area currently is being explored by Abacus Minerals, and information about their work can be found on their web site (www.amemining.com/properties/niblack_project/; Jan. 26. 2004).
As described by Lac Minerals USA Inc. (1989) and Maas and others (1995), and from a cross-section by Abacus Minerals (www.abacusminerals.com/niblackxsec.htm; April 18, 2000), the area features several large folds that trend west-northwest. The folds consist of a layered sequence of rhyolitic flows and volcaniclastic rocks that host the ore deposits, a hanging wall of mafic flows and sedimentary rocks, and a foot wall of amygdaloidal mafic flows. All of the rocks are regionally metamorphosed to greenschist grade. Maas and others (1991) describe three types of deposits at the Lookout prospect (CR221). It is the best- known deposit and probably typifies the other deposits in the area, including the one at the Niblack Mine. The three types are: 1) volcanogenic massive-sulfide bodies up to 20 feet thick with values of up to 4.9 percent copper, 8.0 percent zinc, 0.265 ounce of gold per ton, and 4.6 ounces of silver per ton; 2) stringer-type sphalerite mineralization in lithic tuffs in the footwalls of the massive sulfide bodies; and 3) auriferous, pyrite-bearing volcaniclastic rocks and polylithic breccias that typically contain about 0.05 ounce of gold per ton, 0.5 to 1.0 ounce of silver per ton, and 1 percent combined copper-zinc across widths of more than 50 feet.
Samples collected by Maas and others (1991) at the Dama prospect contained up to 0.843 part per million (ppm) gold, 20.7 ppm silver, 1.8 percent copper, and 2,203 ppm zinc. Recent work at the Dama prospect by Abacus Mining and Exploration Company indicates that the area is structurally complex. In 1995, they drilled at least one hole that cut a particularly high-grade intercept 51 feet long that contained 6.99 percent copper, 7.60 percent zinc, 0.014 ounce of gold per ton, and 1.80 ounce of silver per ton (www.amemining.com/properties/niblack_project/; Jan. 26. 2004).
The age of the rocks in the area has been variously interpreted. Eberlein and others (1983) mapped the strata as locally metamorphosed graywacke of Silurian or Ordovician age, near a large Paleozoic or Mesozoic granitic intrusion. Gehrels (1992) and Maas and others (1995) mapped them as pre-Ordovician metamorphosed volcanic and sedimentary rocks near a Silurian or Ordovician granitic intrusion. Brew (1996) called them Late Proterozoic and Cambrian Wales Group schist, phyllite, and marble, near a Tertiary granitic intrusion of intermediate composition. Most recently, Slack and others (2002) and S.M. Karl (oral communication, 2003) mapped the strata as Silurian and Ordovician, low-grade, regionally metamorphosed sedimentary and volcanic rocks. Slack and others (2002) also demonstrate that the volcanogenic massive-sulfide deposits in the Niblack area are of Silurian or Ordovician age.
Geologic map unit (-132.128987803574, 55.0565624115454)
Mineral deposit model Besshi-type volcanogenic Ag-Au-Cu massive-sulfide deposit (Cox and Singer, 1986; model 24b).
Mineral deposit model number 24b
Age of mineralization Silurian or Ordovician.
Alteration of deposit Not specifically noted, but probably typical of volcanogenic massive-sulfide deposits.

Production and reserves

Workings or exploration There was considerable work on the Dama prospect from 1903 to 1905; the workings included a 250-foot tunnel with about 200 feet of drifts and crosscuts, a 40-foot-deep shaft, and several trenches. The Dama prospect is within an area about a mile square southeast of the old Niblack Mine (CR216) that has been intermittently active since the 1970s, and currently (2004) is being explored. At least one hole was diamond drilled on the Dama prospect in 1995.
Indication of production None

References

MRDS Number A010036; A010053

References

Brewer, N.H., 1989, Geology of the Niblack massive sulfide property, Prince of Wales Island, Alaska (abs.): Alaska Miners Association, Juneau Branch, Conference Juneau, Abstracts of Professional Papers, p. 34-35.
LAC Minerals (USA) Incorporated, 1989, Niblack Project prospectus, Prince of Wales Island, Alaska: LAC Minerals (USA) Incorporated, 16 p. (Unpublished report held by the Bureau of Land Management, Mineral Information Center, Juneau, Alaska).
Peek, B.C., 1975, Geology and mineral deposits of the Niblack Anchorage area, Prince of Wales Island, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 50 p.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Slack, J.F., Shanks, W.C. III, Karl, S.M., Ridley, W.I., and Bittenbender, P.E., 2002, Geochemical and sulfur isotope compositions of Late Proterezoic and early Paleozoic volcanogenic massive sulfide deposits, Prince of Wales Island and vicinity, southeastern Alaska (abs.): Geological Society of America, Abstracts with Programs, v. 34 (6), p. 113.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004