Alder Gulch

Mine, Active

Alternative names

Vinasale

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Bi; PGE; Sb; W
Ore minerals bismuth; gold; ilmenorutile; monazite; scheelite

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale C-6
Latitude 62.696
Longitude -155.71
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Alder Gulch placer mine is located in Alder Gulch, a south flowing tributary that drains the south slope of Vinasale Mountain. The mine workings are at an elevation of 850 feet (259 meters) in the NE 1/4 section 18, T. 30 N., R. 34 W., of the Seward Meridian. T.K. Bundtzen investigated the mine in 1982. The accuracy is within one-quarter mile.

Geologic setting

Geologic description

The Alder Gulch heavy mineral placer deposit consists of auriferous, semi-residual and alluvial, unconsolidated deposits of Quaternary age in a steep gulch on the south flank of Vinasale Mountain. The placer deposit lies down slope and downstream from a mineralized 69.0 Ma granitic pluton that forms most of Vinasale Mountain (Bundtzen, 1986). Alder Gulch has only intermittent water flow and is dry through much of late summer and fall.
The gold and heavy mineral bearing material ranges from 0.5 to 2 meters thick, over stream widths of 12 to 20 meters. Placer gold has been detected for about 2 kilometers below the main workings. The placer deposit begins just below the contact between quartz monzonite and sheared hornfels, which may be a mineralized source for the placer minerals. The stream gradient is very steep and averages about 100 meters/kilometer at the head of Alder Gulch.
Principal heavy minerals identified during mining activities include placer gold that exhibits a fineness of 930, abundant native bismuth and scheelite; minor hastingsite, ilmenite, magnetite, and zircon; trace amounts of monazite, and ilmenorutile; and up to 2.6 ppm PGE (Bundtzen, 1986). The mineralogical source of the PGE is unknown. Sulfide-scheelite-quartz float found in the placer cut contains up to 14.3 grams/tonne gold (Bundtzen, 1986).
In 2010, Freegold completed it's initial drilling on the Vinasale Project; a total of 1,947 meters were drilled in the Central Zone. The results of which were incorporated into Freegold's initial NI-43-101 compliant resource, which was completed in March 2011. The 2011 exploration program included a 13 hole diamond drill program the results of which were incorporated into an updated NI 43-101 compliant resource in March 2012. The addition of 13 drill holes drilled in 2011 and the expansion of the body expanded the tonnage of the resource. During the 2012 exploration season, Freegold completed 13 core drill holes for a total of 11,238 feet (3,425.7 meters). Reconnaissance level rock and soil geochemistry were also completed in the Central Zone, Northeast Zone and in outlying areas (Freegold, 2014).
In March 2013 a new updated NI 43-101 Compliant resource was completed, which incorporated the results of the 2012 drilling. The resource estimate was completed by Giroux Consultants Ltd. of Vancouver, BC. Canada. Indicated resources are 3.41 million tonnes averaging 1.48 grams of gold per tonne for 162,000 ounces, and inferred resources are 53.25 million tonnes averaging 1.05 grams of gold per tonne for 1,799,000 ounces of gold utilizing a cutoff value of 0.5 gram of gold per tonne as a possible open pit cutoff within the total blocks (Abrams and Giroux, 2013).
Geologic map unit (-155.71234538926, 62.6953622554005)
Mineral deposit model Gold heavy mineral placer (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary, based on geomorphic character (in active stream basin) (Bundtzen, 1986).
Alteration of deposit Extensive oxidation of regolith results in grussification of plutonic suite (Bundtzen, 1986).

Production and reserves

Workings or exploration
Surface exploration includes samples collected and processed by mine operator Peter Snow and samples reported by Bundtzen (1986). Sulfide-scheelite-quartz float found in the mine cut contain up to 14.3 grams/tonne gold.
In 2010, Freegold completed it's initial drilling on the Vinasale Project, a total of 1,947 meters were drilled in the Central Zone. The results of which were incorporated into Freegold's initial NI-43-101 compliant resource, which was completed in March 2011. The 2011 exploration program included a 13 hole diamond drill program the results of which were incorporated into an updated NI 43-101 compliant resource in March 2012. The addition of 13 drill holes drilled in 2011 and the expansion of the geologic solid expanded the tonnage of the resource. During the 2012 exploration season, Freegold completed 13 core drill holes for a total of 11,238 feet (3,425.7 meters). Reconnaissance level rock and soil geochemistry were also completed in the Central Zone, Northeast Zone and in outlying areas (Freegold, 2014).
In March 2013, a new updated NI 43-101 Compliant resource was completed, which incorporated the results of the 2012 drilling. The resource estimate was completed by Giroux Consultants Ltd. of Vancouver, BC. Canada. Indicated resources are 3.41 million tonnes averaging 1.48 grams of gold per tonne for 162,000 ounces, and inferred resources are 53.25 million tonnes averaging 1.05 grams of gold per tonne for 1,799,000 ounces of gold utilizing a cutoff value of 0.5 gram of gold per tonne as a possible open pit cutoff within the total blocks (Abrams and Giroux, 2013).
Bundtzen (1986) collected a series of bulk concentrate samples from Peter Snow's 1982 operation, and concluded that up to 68 kilograms of scheelite could be recovered from one tonne of concentrate.
Indication of production Yes; small
Reserve estimates Indicated resources are 3.41 million tonnes averaging 1.48 grams of gold per tonne for 162,000 ounces, and inferred resources are 53.25 million tonnes averaging 1.05 grams of gold per tonne for 1,799,000 ounces of gold utilizing a cutoff value of 0.5 grams of gold per tonne as a possible open pit cutoff within the total blocks (Abrams and Giroux, 2013).
Production notes Between 1930 and 1932, Carl Shutler mined in shallow hand mining cuts and produced 106.5 ounces (3.3 kg) gold and 20.2 ounces (0.6 kg) of byproduct silver Bundtzen, 1986). In 1981 and 1982, Peter Snow produced 16.5 ounces (503 grams) gold and 3.5 ounces (108 grams) of silver from a series of small test pits using a small tractor.

Additional comments

Freegold Ventures Ltd. entered into an Exploration Agreement with an Option to Lease the Vinasale Project from Doyon Limited, an Alaskan Native Regional Corporation, in 2007.

References