Gil

Prospect, Active

Commodities and mineralogy

Main commodities Au; Bi; Te
Other commodities Ag; Mo; W
Ore minerals arsenopyrite; pyrite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.0258
Longitude -147.1084
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Gil prospect is on a large block of claims with several areas of mineralization, but most of the the work has been concentrated in a small area targeted as two potential open pit mines. The coordinates are centered there, about 0.9 mile southeast of the mouth of All Gold Creek on Fish Creek. The prospect is about 0.3 mile southeast of the center of section 3, T. 2 N., R. 3 E. of the Fairbanks Meridian.

Geologic setting

Geologic description

The rocks in the area are mainly quartz-mica schist and micaceous quartzite of the lower Paleozoic, Fairbanks Schist. The mineralization at Gil is mostly in the Cleary Sequence, which consists of calc-silicate hornfels, amphibolite, actinolite-white mica schist, felsic schist, and biotite-chlorite schist (Avalon Development Corp., 2005). The Cleary Sequence strikes northeast and dips steeply north. The metamorphic rocks are intruded by several nearby mid-Cretaceous granitic plutons.
Three phases of deformation are recognized at Gil resulting in large-scale asymmetric folds and faults trending northeast with variable dip. The oldest of these faults are low angle reverse faults. Conjugate to the northeast-striking faults are northwest-striking strike-slip faults that dip to the southwest or are vertical. Distinct, close-spaced northwest-striking near vertical joint sets cross cut nearly all lithologies and foliation. These joints are important controls to mineralization (Sims, 2015).
The mineralization at the Main Gil locality is stratabound in calc-silicate hornfels; it consists mainly of auriferous quartz and quartz-calcite veins in shear zones and in limonite-stained fractures. The veins contain 1 to 3 percent sulfides, mainly arsenopyrite. Samples show a strong bismuth-tellurium association, with some molybdenum, arsenic, and tungsten (Avalon Development Corp., 2005). Alteration is seen as an intense retrograde assemblage of calc-silicate minerals (Sims, 2015).
The North Gil locality consists of auriferous quartz veins less then 2 inches thick. The veins are in quartz-white mica schist interlayered with calcareous biotite-white mica schist, felsic schist, and marble. The veins contain less than 1 percent sulfides, mainly pyrite and arsenopyrite (Avalon Development Corp., 2005). Alteration is vein-controlled and consist of sericitc to potassic (secondary biotite) alteration along vein margins (Sims, 2015).
Geologic map unit (-147.110839435821, 65.025383843641)
Mineral deposit model Low-sulfide Au-quartz veins in skarns (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Probably around 92 Ma based on age of mineralization and intrusion of the nearby Fort Knox deposit (Selby and others, 2002).
Alteration of deposit At the Main Gil alteration is seen as an intense retrograde assemblage of calc-silicate minerals. At North Gil alteration is vein-controlled and consist of sericitc to potassic (secondary biotite) alteration along vein margins (Sims, 2015).

Production and reserves

Workings or exploration
The Gil prospect was acquired by Teryl Resources Corp. (Teryl) in 1989 and in 2008 was being explored as a joint venture between Teryl and Kinross Gold Corp. (Kinross) until Kinross acquired Teryl's remaining interest in Gil in 2011 (Teryl Resources Corp., 2008; Sims, 2015).
Since the early 1990s exploration work on the Gil prospect has included soil sampling, geologic mapping, rock sampling, ground magnetic and resistivity surveys, trenching, reverse circulation (RC) drilling, core drilling, airborne magnetic and electromagnetic (EM) surveys, and metallurgical testing (Avalon Development Corp., 2005). Kinross drilled 581 RC holes totaling 52,180 meters and 154 core holes totaling 21,582 meters between 1993 and 2014 (Sims, 2015).
Indication of production None
Reserve estimates
Quandt and others (2008) indicate that the Gil deposit has an indicated mineral resource to modern industry standards of 3.548 million tonnes of material with a grade of 1.03 grams of gold per tonne.
The Gil mineral resource was updated in 2015 with an indicated resource of 29,515.8 million tonnes with a grade of 0.56 grams per tonne (g/t) gold and an inferred resource at 4,026 million tonnes of material with a grade of 0.49 g/t gold. This resource was estimated using a cutoff grade of 0.21 g/t gold based on a gold price of US$1,400 per ounce (Sims, 2015).

References

MRDS Number 10307749

References

Reporters C.J. Freeman, J.R. Guidetti Schaefer (Avalon Development Corporation); D.J. Grybeck (Port Ludlow, WA); N.V. King (Alaska Earth Sciences)
Last report date 2/25/2016