Ptarmigan Hill

Prospect, Active?

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Hg; Sb
Ore minerals gold
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale D-2
Latitude 64.9261
Longitude -141.9449
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Ptarmigan Hill gold prospect is located at the north end of the top of the ridge west of Sonickson Creek near hill 2750. The coordinates are the approximate center of the prospect, in the SE1/4 section 12, T. 1 N., R. 28 E., of the Fairbanks Meridian. The location is accurate within 500 feet. The Ptarmigan Hill prospect is located within Doyon, Ltd. selected or conveyed land.

Geologic setting

Geologic description

The Ptarmigan Hill prospect is located at the western end of a linear trend of sediment-hosted epithermal gold prospects informally known as the Crooked Creek trend (Rogers and Bradley, 1998). The Crooked Creek trend includes the Ptarmigan Hill and Mogul Bluff (EA029) prospects and the Ruby and Hudson Coulee gold anomalies defined by soil sampling. At Ptarmigan Hill, a 3- to 30-meter-thick unit of Tertiary conglomerate crops out in the core of a broad northeast-trending anticline (U.S. Bureau of Mines, 1995). The conglomerate contains well-rounded quartz and chert clasts, as well as thin sandstone, siltstone, and shale interbeds (WGM Inc., 1998 [DLR 98-19]). This unit is bounded on the south by Tertiary felsic igneous rocks, and on the north by Paleozoic schist. Tertiary felsic igneous rocks, including quartz-eye rhyolite and quartz-feldspar porphyry, are juxtaposed along regional high-angle faults. Small serpentinite bodies are faulted into the conglomerate by splays of the Tintina fault.
At Ptarmigan Hill, epithermal gold-quartz veinlets are controlled by a steeply dipping, north-trending fracture system that is best developed in silicified conglomerate beds and related rocks (WGM Inc., 1998 [DLR 98-19]). An epithermal event is interpreted to have flooded permeable conglomerates, resulting in weak to moderate silicification (U.S. Bureau of Mines, 1995). Unaltered siltstones seem to have inhibited fluid flow, and higher gold values appear to be concentrated at the siltstone-conglomerate contact. Detrital muscovite from silicified, gold-bearing conglomeratic sandstone at the Ptarmigan Hill prospect gives an average 40Ar/39Ar reset age of 54 Ma; this is considered to be the time of silicification and gold mineralization (Newberry and others, 1996).
Ptarmigan Hill has soil geochemistry anomalies over an area 3,500 feet long (east-west) by 1,000 feet wide (WGM Inc., 1998 [DLR 98-19]). A gold anomaly (greater than 50 ppb) is at least 2,400 feet long in an east-west direction and at least 800 feet wide. Soil assays exceed 1,000 ppb gold, 10 ppm silver, and 800 ppb mercury and are also anomalous in arsenic and antimony. The full extent of the soil anomaly is not known. A Tertiary felsic volcanic(?) rock from the ridge south of Ptarmigan Hill contains 140 ppb gold, 1.4 ppm silver, and 910 ppb mercury; it may be an easterly extension of the Deep Creek trend of volcanic-hosted epithermal gold prospects 15 miles to the west (Rogers and Bradley, 1998).
Drill hole intercepts at Ptarmigan Hill include 20 feet with 0.21 ounce of gold per ton; 22 feet with 0.13 ounce of gold per ton; and 80 feet with 0.055 ounce of gold per ton (WGM Inc., 1998 [DLR 98-19]). American Copper and Nickel Co. defined 3 million tons of material that averages 0.024 ounce of gold per ton. The Ptarmigan Hill and Mogul Bluff (EA029) prospects appear as distinct, resistivity highs due to the silicification of the clastic sedimentary rocks. Additional resistivity highs, coinciding with anomalous gold in soils, occur along the trend east of Mogul Bluff . A nearly continuous, narrow, linear magnetic high that is sub-parallel to the trend of the Tintina Fault, extends westward from Mogul Bluff to Ptarmigan Hill and the rest of the Seventymile gold belt. The magnetic anomalies suggests that an ultramafic(?) body extends beneath the Paleozoic schist and Tertiary sedimentary rocks.
The Crooked Creek trend was explored by American Copper and Nickel Co. (ACNC) from 1987 to 1989 (WGM Inc., 1998 [DLR 98-19]). ACNC drilled 37 holes totaling 13,413 feet at Ptarmigan Hill over an east-west-trending area 2,000 feet long by 400 feet wide. ACNC also conducted ground magnetic, EM, IP, and resistivity surveys at Ptarmigan Hill. In 1996, reconnaissance sampling by WGM Inc. west of Ptarmigan Hill confirmed the presence of gold in the 13-mile-long segment between the Crooked Creek trend and the Flume trend. An airborne EM-magnetic survey was flown over the Flume, Deep Creek, and Crooked Creek trends in 1997 for Ventures Resource Alaska.
Geologic map unit (-141.947227006392, 64.9257799385101)
Mineral deposit model Possibly epithermal veins (Cox and Singer, 1986; model 25c?).
Mineral deposit model number 25c?
Age of mineralization Detrital muscovite from silicified, gold-bearing conglomeratic sandstone at the Ptarmigan Hill prospect have an average 40Ar/39Ar reset age of 54 Ma; this is considered to be the time of silicification and gold mineralization (Newberry and others, 1996).
Alteration of deposit An epithermal system flooded permeable conglomerates with weak to moderate silicification (U.S. Bureau of Mines, 1995). Unaltered siltstones seem to have inhibited fluid flow, and higher gold values appear to be concentrated at the siltstone-conglomerate contact.

Production and reserves

Workings or exploration The Crooked Creek trend was explored by American Copper and Nickel Co. from 1987 to 1989 (WGM Inc., 1998 [DLR 98-19]). American Copper and Nickel Co. drilled 37 holes totaling 13,413 feet at Ptarmigan Hill over an east-west-trending area 2,000 feet long by 400 feet wide. American Copper and Nickel Co. also conducted ground magnetic, EM, IP, and resistivity surveys at Ptarmigan Hill. In 1996, reconnaissance sampling by WGM Inc. west of Ptarmigan Hill confirmed the presence of gold in the 13-mile segment between the Crooked Creek trend and the Flume trend. An airborne EM-magnetic survey was flown over the Flume, Deep Creek, and Crooked Creek trends in 1997 for Ventures Resource Alaska.
Indication of production None
Reserve estimates American Copper and Nickel Co. defined 3 million tons of material with an average grade of 0.024 ounce of gold per ton (WGM Inc., 1998 [DLR 98-19]).

Additional comments

The Ptarmigan Hill prospect is located within Doyon, Ltd. selected or conveyed land. For more information contact Doyon, Ltd., Fairbanks, Alaska.

References

References

Bright, M.J., 1992, Evaluation of Doyon, Ltd.'s Ptarmigan Hill property, northern part of Selection Block 8 (Fortymile): Doyon, Ltd. report, 9 p. (Report held by Doyon, Ltd., Fairbanks, Alaska).
Rogers, Bob, and Bradley, Laura, 1998, Gold deposits of the Seventymile Belt: Extended Abstracts of the 16th Biennial Conference on Alaskan Mining, Second Rush of 98; Alaska Miners Association meeting March 2-7, 1998, Fairbanks, Alaska, p. 22.
WGM Inc., 1998, Ventures Resource Alaska projects, 1997 progress report, Seventymile property exploration, volume 1: Doyon, Ltd. Report 98-19. (Report held by Doyon, Ltd., Fairbanks, Alaska).
Reporters M.B. Werdon; R.L. Flynn
Last report date 5/1/2002