Unnamed (near Horace Mountain)

Prospect, Undetermined

Commodities and mineralogy

Main commodities Ag; As; Au; Cu; Mo; Pb; Zn
Ore minerals arsenopyrite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale CH
Quadrangle map, 1:63,360-scale C-5
Latitude 67.6535
Longitude -149.1799
Nearby scientific data Find additional scientific data near this location
Location and accuracy The center of this prospect is about 1.3 miles north-northeast of the mouth of Sheep Creek on Robert Creek. It is near the center of section 29, T. 33 N., R 7 W. However, similar mineralization is widespread on the north and south side of Horace Mountain. Kurtak and others (2002) include a map showing the regional geology of the area and the location of this and the other deposits of the Chandalar Copper Belt.

Geologic setting

Geologic description

A color and geochemical anomaly that suggested mineralization in this area was first identified in 1983 (Nichol, 1983). In the early 1990s, Central Alaska Gold Company (1992) mapped and sampled the prospect, and Kurtak and others (2002) visited it and collected samples widely on the slopes of Horace Mountain.
A east-northeast-trending, Devonian meta-granodiorite intrusion about 7 miles long and a mile wide makes up most of the central part of Horace Mountain (Dillon and others, 1996; Kurtak and others, 2002). It is flanked by Ordovician quartz-sericite schist, calcareous chlorite schist, felsic schist, and thin-bedded marble. The quartz-sericite schist is thought to be highly-altered metamorphosed intrusive rock.
Red-and-yellow-stained, quartz-sericite schist with zones of 2 to 3 percent pyrite is conspicuous near the meta-granodiorite on both sides of Horace Mountain (Kurtak and others, 2002). This schist probably outcrops continuously along the south side of Horace Mountain. On the west flank of Horace Mountain below peak 5540, samples of quartz-sericite schist with 4 percent pyrite and minor arsenopyrite, and a float sample of siliceous mica schist, averaged 127.5 parts per billion (ppb) gold, 15.7 parts per million (ppm) silver, 1,119 ppm copper, 510 ppm lead, 291 ppm zinc, and 1.16 percent arsenic. On the east flank of Horace Mountain below peak 5192, a 75- to 100-foot-thick outcrop of sericite-quartz schist contains zones of pyrite up to a foot thick. Select samples with 2 to 5 percent pyrite contained up to 62 ppb gold, 1.4 ppm silver, 116 ppm molybdenum, and 134 ppm arsenic.
The mineralization on the flanks of Horace Mountain is probably related to the meta-granodiorite in the center of the mountain and has much the same genesis as the other skarn deposits in the Chandalar Copper Belt (Newberry and others, 1986).
Geologic map unit (-149.182655466723, 67.6531001846612)
Mineral deposit model Mineralized quartz-sericite schist adjacent to a meta-granodiorite pluton.
Age of mineralization Devonian(?) based on Early Devonian Pb/Pb zircon ages from the nearby Baby Creek batholith and Horace Mountain plutons (Dillon and others, 1996).
Alteration of deposit Not noted.

Production and reserves

Workings or exploration Only mapping and sampling by government agencies and industry from 1983 to 2002.
Indication of production None
Reserve estimates None.
Production notes None.

Additional comments

This prospect is on Doyon Ltd. selected lands; for more information, contact Doyon Ltd., Fairbanks, Alaska.
MAS No. 0020310141

References

References

Central Alaska Gold Company, 1990, 1989 annual report to Doyon Ltd. Alaska field operations, v. 1: Unpublished report 90-06A for Doyon Ltd., (on file at Doyon Ltd., Fairbanks, Alaska).
Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Maclean, E.A., 2002, Mineral investigations in the Koyukuk mining district, northern Alaska, 2 vols.: Bureau of Land Management, Alaska Technical Report 50, 845 p.
Newberry, R.J., Allegro, G.L., Cutler, S.E., Hagen-Levelle, D.D., Adams, D.D., Nicholson, L.C., Weglarz, T.B., Bakke, A.A., Clautice, K.H., Coulter, G.A., Ford, M.J., Myers, G.L., and Szumigala, D.J., 1997, Skarn deposits of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 355-395.
Newberry, R.J., Dillon, J.T., and Adams, D.D., 1986, Regionally metamorphosed calc-silicate-hosted deposits of the Brooks Range, northern Alaska: Economic Geology, v. 81, p. 1728-1752.
Nicholson, L.M., 1990, Porphyry copper, copper skarn, and volcanogenic massive sulfide occurrences in the Chandalar copper district, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 164 p.
Nicol, D.L., 1983, Evaluation of the mineral potential of Doyon Ltd.'s Block 5 and 22 (unpublished report 83-04 for Doyon Ltd., (on file at Doyon Ltd., Fairbanks, Alaska).
Reporters D.J. Grybeck (Contractor, U.S. Geological Survey)
Last report date 4/18/2010