Gray Lead

Prospect, Active?

Alternative names

Grey Lead
Hilltop
Rob

Commodities and mineralogy

Main commodities Ag; As; Au; Sb
Other commodities Cu; Pb; Te; W
Ore minerals arsenopyrite; bismuthinite; covellite; digenite; gold; jamesonite; pyrite; stibnite
Gangue minerals quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale BD
Quadrangle map, 1:63,360-scale B-1
Latitude 64.3445
Longitude -144.2523
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Gray Lead prospect is along a ridge at an elevation of about 4,070 feet, about 1.3 mile northwest of the north peak (5080) of Black Mountain. It is about 0.5 mile south of the center of section 31, T. 6 S., R. 18 E., of the Fairbanks Meridian. The location is accurate, though degree of accuracy not reported.

Geologic setting

Geologic description

The Goodpaster region was first explored for placer gold in 1915. In the early 1930s, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. The first underground workings were driven in the winter of 1936. A 450-foot tunnel was driven following a small vein, termed the Blue Lead Extension (BD003). After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the nearby Grizzly Bear Mine (BD018) and a 50-ton mill was constructed. In the summer of 1938, the mill was moved to the Blue Lead Mine and operated for a year and a half until the fall of 1939 (Joesting, 1938). The Gray Lead prospect was also probably discovered about this time. From 1939 to 1941, approximately 1,300 feet of surface and subsurface workings were completed at the Gray Lead prospect (Thomas, 1970). Over 300 feet of the vein was traced at the surface (Joesting, 1938). There was limited exploration reported in the 1970s.
From 1995 to 1999, The Stone Boy Joint Venture (Sumitomo Metal Mining and WGM Inc.) spent more than $1.3 million exploring in the area; they did extensive surface mapping and sampling, surface and airborne geophysics, and 16,215 feet of diamond drilling in 26 holes. The details of the drilling are vague but at least 4 holes were drilled at the Gray Lead prospect. Surface rock samples contained up to 4.93 ounces of gold per ton. The best intercept in the drilling was 13.5 feet that averaged 0.92 ounce of gold per ton (Flanders, 2010).
In 2002, Freegold Ventures Ltd. optioned a large block of claims that covered the Gray Lead land several other nearby deposits that are described separately: the Grizzly Bear (BD018), Michigan Lode (BD025), Wolverine (BD057), Upper Trench, Lower Trench (BD058), and O'Reely (BD059). Freegold has continued the exploration through early 2012 as the Rob project. (Flanders, 2010; Freegold Ventures Ltd., 2012). The work has included extensive geologic mapping, surface sampling, and geochemical and geophysical surveys. In 2004, Freegold commissioned a comprehensive NI 43-101 report (Freeman, 2004) that summarized their and previous work. The 2004 report was updated by Flanders (2010) No ore has been mined from the Gray Lead prospect although 20 holes have been drilled on it since 1995.
As interpreted by Bailey (2001), Freeman (2004), and Flanders (2010), this and the several other similar deposits in the area are near the contact of a large Cretaceous biotite granodiorite stock with a mixed unit of Paleozoic biotite gneiss, feldspar-biotite augen gneiss, and quartzite that form a large gneiss dome. The granodiorite is cut by hornblende, andesite porphyry dikes. The rocks are locally intensely sheared and Grizzly Bear (BD018) and Michigan Lode (BD025) are aligned along the northeast-trending Gray Lead fault. This fault is observed in the underground workings of the Gray Lead prospect and also at the surface where it is marked by pronounced saddle-like depressions across the spurs separating the westward-flowing tributaries of Tibbs Creek.
The lode deposits in the area are gold-bearing quartz veins in shear zones in the metamorphic and igneous rocks. The quartz veins contain gold +/- base metal +/- silver and a variable combination of sulfides, including arsenopyrite, covellite, digenite, jamesonite, pyrite, and stibnite. Typically, the gold content decreases as sulfides increase. Veins are commonly 2 to 3 feet in width but some are as wide as 8 feet (Thomas, 1970). When gold is present, it is usually extremely fine grained. However, veins at the nearby Grizzly Bear mine (BD018) contain relatively coarse gold which is easily visible in hand specimen (Freeman, 2004).
The Gray Lead prospect is on a quartz vein 2 feet in width. In the underground workings, the vein dips steeply west (Joesting, 1938). Freeman (2004) cites numerous grab samples from veins at the Gray Lead prospect that contain up to 2.105 ounces of gold per ton, up to 43.50 parts per million (ppm) silver, more than 1 percent arsenic, up to 1,610 ppm bismuth, up to 415 ppm lead, more than 1 percent antimony, up to 180.50 ppm tellurium, and up to 97.2 ppm tungsten. The many surface samples of veins and altered granite collected in subsequent years varied greatly in their relative and specific metal content but they essentially have the same association of metals. Freeman (2004) classifies the Gray Lead deposit as a quartz vein hosted in gneiss and/or high-grade schist near an intrusion that was the source of the mineralization.
In 2007, Freegold Ventures Ltd. (2007) drilled 8 holes on the Gray Lead vein that totaled 1,529 feet. All of the holes intersected the vein which is in biotite, augen paragneiss. The mineralization consisted of sugary textured quartz with fine-grained bismuthinite and arsenopyrite. The width of the vein varies but probably averages more than 10 feet thick.
Geologic map unit (-144.254626261529, 64.3441346178851)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Genetically related to a nearby Cretaceous granodiorite intrusive.
Alteration of deposit Alteration has been reported as pervasive quartz- sericite- sulfide alteration occurring adjacent to veins and extending for up to one mile from the source structure (Flanders, 2010).

Production and reserves

Workings or exploration
The Goodpaster region was first explored for placer gold in 1915. In the early 1930s, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. The first underground workings were driven in the winter of 1936. A 450-foot tunnel was driven following a small vein, termed the Blue Lead Extension (BD003). After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the nearby Grizzly Bear Mine (BD018) and a 50-ton mill was constructed. In the summer of 1938, the mill was moved to the Blue Lead Mine and operated for a year and a half until the fall of 1939 (Joesting, 1938). The Gray Lead vein was also probably discovered about this time. From 1939 to 1941, approximately 1,300 feet of surface and subsurface workings were completed at the Gray Lead prospect (Thomas, 1970). Over 300 feet of the vein could be traced at the surface (Joesting, 1938). There was limited exploration reported in the 1970s. From 1995 to 1999, The Stone Boy Joint Venture (Sumitomo Metal Mining and WGM) spent more than $1.3 million exploring in the area; they did extensive surface mapping and sampling, surface and airborne geophysics, and 16,215 feet of diamond drilling in 26 holes. The details of the drilling are vague but one or more probably was drilled at the Gray Lead prospect.
In 2002, Freegold Ventures optioned a large block of claims that covered the Gray Lead lode and several other nearby deposits that are described separately: the Grizzly Bear (BD003), Michigan Lode (BD025), Wolverine (BD057), Upper Trench, Lower Trench (BD058) and O'Reely (BD059). Freegold has continued the exploration through early 2012 as the Rob project. (Flanders, 2010; Freegold Ventures Ltd., 2012). The work has included extensive geologic mapping, surface sampling, and geochemical and geophysical surveys. In 2007, Freegold Ventures Ltd. (2007) drilled 8 holes on the Gray Lead prospect that totaled 1,529 feet. Some of the notable intercepts in these holes were: 16.5 feet that contained 0.197 ounce of gold per ton, 13.5 feet that contained 0. 586 ounce of gold per ton, 13.0 feet that contained .841 ounces of gold per ton, 14.0 feet that contained 0.230 ounce of gold per ton, and 6.5 feet that contained 0.677 ounce of gold per ton. In 2008, they drilled 12 more holes that totaled 3,144.2 feet. In addition, 14 grab rock samples were submitted for geochemical analysis, and IP and resistivity surveys were conducted (Flanders, 2010). Highlights of the results of 2008 drilling are 4.5 meters of 18 g/t gold and 2. meters of 62 g/t gold (Freegold Ventures Ltd, 2008).
Indication of production None

References