Niblack

Prospect, Active

Alternative names

Lookout
Conundrum
Trio

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-1
Latitude 55.0576
Longitude -132.1461
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The old Lookout prospect is at an elevation of about 1,800 feet, about 0.2 mile northeast of elevation 2230 and about 0.1 mile north-northeast of the southwest corner of section 34, T. 78 S., R. 88 E.
From the late 1970s to the present (late 2011) there has been nearly continuous exploration of several geologically similar deposits in an area of about a square mile southeast of the pre-World War I, Niblack Mine (CR216). Those deposits are described separately (CR217-223). However, the bodies of mineralization that are receiving most of the current (early 2012) attention and are being explored together are near the old Lookout and Trio prospects (CR222). In the recent media and professional publications, the property is generally referred to as the 'Niblack project' or just 'Niblack'.

Geologic setting

Geologic description

The Lookout prospect as described by Brooks (1902) and Wright and Wright (1908) was a mineralized zone up to 300 feet thick in quartz-sericite schist. Within the zone, mineralized bands consist largely of covellite, chalcopyrite, and pyrite. Locally, there are quartz veinlets that have gold values. As of 1908, the workings consisted of two adits, one 160 feet long and the other 60 feet long, and several trenches.
Beginning in the mid-1970s, a succession of companies, including Cominco-Alaska, Inc., Anaconda Minerals, Noranda Exploration, Houston Oil and Minerals, Lac Minerals, Abacus Minerals Corp., Niblack Mining Corp., Committee Bay Resources Ltd., CBR Gold Corporation, and Heatherdale Resources Ltd., the operator in early 2012, have extensively explored the several deposits in the Niblack Mine area (CR217-223), testing the now widely accepted theory that they are volcanogenic, stratabound, massive-sulfide deposits (Ghayemghamian, 2010). Those deposits are commonly grouped with the old Niblack Mine under the name 'Niblack' or 'Niblack Project'. However, most of the work since at least 2005, has been concentrated near the old Lookout prospect described in this record and the Trio prospect (CR222) which now are nearly always referred to as the Niblack project or just Niblack.
From the mid-1970s to 2008, 218 holes were drilled on the Niblack-Lookout deposit from the surface and 28 holes were drilled underground; these total 59,289 meters (Ghayemghamian and others, 2010). There was more drilling in 2009 (but these holes were not included in the 2010 Ghayemghamian resource estimate). In 2008, an 880-meter exploration drift was completed to test the deposit at depth. The various companies have also done considerable surface mapping and sampling and carried out numerous geochemical and geophysical surveys.
In July, 2009, Heatherdale optioned the property from CBR Gold Corporation (Heatherdale Resources Ltd., 2011). A 25,000-foot underground drill program in 2010 expanded the extent of the known mineralization and they had begun a 50,000-foot drill program to test the limits of the ore body.
The rocks in the area are part of the Ordovician to Lower Silurian, Moira Sound unit. At the deposit, the rocks consist of footwall dacite and rhyodacite; the Lookout rhyolite, which hosts the massive-sulfide mineralization; and hanging wall, mafic volcanic and volcaniclastic rocks (Maas and others, 1995; Ghayemghamian and others, 2010). 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. However, the most recent date based on 3 zircon analyses from flows and volcaniclastic rocks immediately above and below the mineralized horizon using CA-TIMS U/Pb techniques is that the mineralization is Neoproterozoic, 565 +/- 3 Ma (Oliver and others, 2011).
The rocks are metamorphosed to greenschist facies. The structure in the area is dominated by several large, north-verging, overturned folds and two major faults. The Lookout body of mineralization is on the overturned limb of a large syncline. Karl and others (2009) interpret the environment of deposition as a rifted, oceanic arc.
The sulfides precipitated on the sea floor in porous, unconsolidated fragmental, volcanic sediments, resulting in zones of semi-massive and massive sulfide bodies up to 20 feet thick. The dominant sulfides are chalcopyrite, pyrite, and sphalerite which generally follow the sedimentary layering (Maas and others, 1995; Ghayemghamian and others, 2010). The massive-sulfide bodies often grade laterally into disseminated, stringer, and replacement sulfides. The main metals of economic significance are copper, zinc, gold, and silver; lead is low, and arsenic, antimony, cadmium, mercury, and selenium values are too low to pose a metallurgical problem.
There have been several increasingly-better estimates of the resources of the Niblack-Lookout deposit as the drilling and exploration has progressed.
As of November 29, 2011, Heatherdale Resources Ltd. (2011) announced that at a cut-off grade of $50, the Lookout deposit has an indicated resource of 5,638,000 tonnes of material with a grade of 0.95 percent copper, 1.75 grams of gold per tonne, 1.73 percent zinc, and 29.52 grams of silver per tonne. The Lookout deposit has an inferred resource of 2,370,000 tonne of material with a grade of 0.73 percent copper, 1.42 grams of gold per tonne, 1.17 percent zinc, and 21.63 grams of silver per tonne. The Trio deposit (which is usually aggregated with the Lookout deposits in referring to 'Niblack' 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 resource estimate is based on 373 holes drilled to November 4, 2011. As then known, 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 feet in size with an average thickness of 220 feet.
Geologic map unit (-132.147748778499, 55.0572523555531)
Mineral deposit model Besshi-type volcanogenic Ag-Au-Cu-Zn 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. However, the most recent date based on 3 zircon analyses from flows and volcaniclastic rocks immediately above and below the mineralized horizon using CA-TIMS U/Pb techniques is that the mineralization is Neoproterozoic, 565 +/- 3 Ma (Oliver and others, 2011).
Alteration of deposit Not specified, but probably typical of volcanogenic massive-sulfide deposits.

Production and reserves

Workings or exploration The Lookout prospect was known before World War I but beginning in the mid-1970s, a succession of companies, including Cominco-Alaska, Inc., Anaconda Minerals, Noranda Exploration, Houston Oil and Minerals, Lac Minerals, Abacus Minerals Corp., Niblack Mining Corp., Committee Bay Resources Ltd., CBR Gold Corporation, and Heatherdale Resources, the operator in early 2011, have extensively explored several deposits in the Niblack Mine area (CR217-223), testing the now widely accepted theory that they are volcanogenic, stratabound, massive-sulfide deposits (Ghayemghamian, 2010). Those deposits are commonly grouped with the old Niblack Mine under the name 'Niblack' or 'Niblack Project'. However, most of the work since at least 2005, has been concentrated on mineralization near the old Lookout prospect described in this record, and it now is the best known of the deposits. In 2008, a 880-meter exploration drift was completed to test the deposit at depth and much of the drilling since then has been from this drift. The various companies have also done considerable surface mapping and sampling and carried out numerous geochemical and geophysical surveys. As of November 4, 2011, 343 holes have been drilled on the Lookout and Trio deposits (Heatherdale Resources Ltd., 2011).
Indication of production None
Reserve estimates There have been several increasingly-better estimates of the resources of the Niblack prospect as the drilling and exploration has progressed. As of November 29, 2011, Heatherdale Resources Ltd. (2011) announced that at a cut-off grade of $50, the Lookout deposit has an indicated resource of 5,638,000 tonnes of material with a grade of 0.95 percent copper, 1.75 grams of gold per tonne, 1.73 percent zinc, and 29.52 grams of silver per tonne. The Lookout deposit has an inferred resource of 2.370 million tonnes with a grade of 0.73 percent copper, 1.42 grams of gold per tonne, 1.17 percent zinc, and 21.63 grams of silver per tonne. The Trio deposit (which is usually aggregated with the Lookout deposits in referring to 'Niblack' has an inferred resource of 1.023 million tonnes 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.
Production notes None.

References

MRDS Number A010000

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.
CBR Gold Corp., 2010, Niblack Au-Cu-Ag-Zn project: http://www.cbrgoldcorp.com/project_areas/united_states/niblack/ (as of February 28, 2010).
Ghayemghamian, Abolfazi, Nowak, Marek, and Kleespies, Peter, 2010, Mineral resource estimation, Niblack polymetallic sulphide project, Alaska, U.S.A.: Technical report for CBR Gold Corp., 177 p. (posted on www.sedar.com, February 5, 2010).
Heatherdale Resources Ltd., 2011, Niblack project overview: http://www.heatherdaleresources.com/hdr/Projects.asp (as of Feb 20, 2011).
Oliver, Jim, Roberts, Keith, and Friedman, Richard, 2011, The Niblack mine: A neoproterezoic precious metals enhanced, volcanic hosted massive sulfide, Prince of Wales Island Alaska. Mineralized zones and mineral resources, structural style, stryatigraphic and U-Pb geochronological relationships Alaska Miners Association, 2011 Annual Convention Abstracts, p. 60-62.
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