Trio

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu; Zn
Ore minerals chalcopyrite; pyrite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-1
Latitude 55.05752
Longitude -132.13734
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Trio prospect is about 0.5 mile east-northeast of hill 2230 and about 0.5 mile south of the center of section 34, T. 78 S., R. 88 E. From the late 1970s 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 Trio prospect and other deposits in the area are commonly grouped together under the name 'Niblack' or 'Niblack project' (CR221).

Geologic setting

Geologic description

The deposit on the Trio claims was described by Brooks (1902) as similar to the deposit at the nearby Lookout prospect (CR221); the only workings were a short crosscut that exposed a 10-foot-wide ore body.
Beginning in the mid-1970s, 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 breccia 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.
Maas and others (1992, 1995) collected several samples at the Trio prospect that contained up to 215 parts per billion gold, 1.2 parts per million (ppm) silver, 7,874 ppm copper, and 418 ppm zinc. Abacus Minerals drilled at least one hole on the Trio prospect in 1996 or 1997; 16.1 feet of that hole averaged 0.069 ounce of gold per ton, 1.35 ounce of silver per ton, 6.96 percent copper, and 8.18 percent zinc (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) saw the host rocks as part of the 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. But see the record for the nearby and probably contiguous NIblack deposit (CR221) that has recently been dated as Neoproterozoic, 565 +/- 3 Ma.
As of late 2011, the Trio deposit is often aggregated with the Lookout deposit and referred to as the Niblack deposit (CR221), for instance in the November 2011 estimate of the resources of the Niblack deposit (CR221) (Heatherdale Resources Ltd., 2011).
Geologic map unit (-132.138988364298, 55.0571723543224)
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 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) saw the host rocks as part of the 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. But see the record for the nearby and probably contiguous NIblack deposit (CR221) that has recently been dated as Neoproterozoic, 565 +/- 3 Ma.
Alteration of deposit Not specifically noted, but probably typical of volcanogenic massive-sulfide deposits.

Production and reserves

Workings or exploration A short adit was driven prior to 1902; at least one hole was diamond drilled in 1996 or 1997. As of late 2011, the Trio deposit was being explored as part of the Niblack prospect (CR221). By that time, 343 holes had been drilled on the modern Niblack that mainly consisted of the old Lookout and Trio deposits (Heaterdale Resources Ltd., 2011).
Indication of production None
Reserve estimates The Trio deposit (which is usually aggregated with the Lookout deposits in referring to 'Niblack' (CR221) has an inferred resource of 1.023,000 tonnes of material with a grade of 1.00 percent copper, 1.11 grams of gold per tonne, 1.56 percent zinc, and 16.56 grams of silver per tonne. This Niblack resource estimate is based on 373 drill holes drilled to November 4, 2011. As know then, the Lookout deposit was about 2,200 by 1,700 feet in size with an average thickness of 70 feet; the Trio deposit was about 1,100 by 350 in size with an average thickness of 220 feet.

References

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.
Heatherdale Resources Ltd., 2011, Niblack project overview: http://www.heatherdaleresources.com/hdr/Projects.asp (as of Feb 20, 2011).
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 Proterozoic 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 (Contractor, USGS)
Last report date 4/1/2012