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Section 21 Prospect, Goodpaster District, Southeast Fairbanks Borough, Alaska, USA

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The Section 21 prospect is located within Doyon, Ltd. selected or conveyed land. For more information contact Doyon, Ltd., Fairbanks, Alaska.
Location: The Section 21 prospect is at an elevation of 4,700 feet on the southeast side of a ridge that extends south from Mount Harper. The prospect is about 2.5 miles southeast of Mount Harper in the headwaters of the Healy River. The coordinates are the approximate center of the prospect, in section 21, T. 8 S., R. 20 E, of the Fairbanks Meridian. The location is accurate. The Mount Harper area is locality 6 of Cobb (1972 [MF-393]). The Section 21 prospect is located within Doyon, Ltd. selected or conveyed land.
Geology: The Section 21 prospect is in the Mount Harper quartz-monzonite-granodiorite intrusive complex (WGM Inc., 1978). Biotite from the Mount Harper granite gave a 40Ar/39Ar plateau age of 105.8 +/- 0.4 Ma (Newberry and others, 1996). Mineralization and alteration at the Section 21 prospect is associated with a quartz porphyry-aplite plug about 800 meters in diameter (WGM Inc., 1978). A northeast-trending andesitic to dacitic dike complex intrudes both the quartz porphyry and granodiorite. The quartz porphyry-aplite plug contains quartz-molybdenite veining; the quartz veinlets are generally less than 1 millimeter wide. The molybdenite is fine grained, and pyrite is also present. In the quartz porphyry-aplite plug, silicification is the dominant alteration type, with lesser amounts of sericite and clay. Similar alteration is also present in the granodiorite near the quartz porphyry contact. Airborne magnetic surveys detected a magnetic high centered under the altered plug. Samples of vein material in the quartz-porphyry-aplite plug contain as much as 500 ppm molybdenum and 40 ppm tungsten. Samples of milky-quartz, vein material that contains bladed wolframite bordered by scheelite assays as much as 0.4 percent WO3 and 14 ppm silver. Samples collected by the U.S. Bureau of Mines (1995) include a wolframite-bearing quartz vein with 1.7 percent tungsten and 14 ppm silver and aplite and quartz-vein material with 180 ppm molybdenum. Muscovite from a quartz-wolframite vein at the Section 21 prospect gives a 40Ar/39Ar plateau age of 102 +/- 0.4 Ma (Newberry and others, 1998). There are several other molybdenum-tungsten prospects in the MtountHarper area, including VABM Good (EA092), Larsen Ridge (EA091), Quartz-Porphyry (EA094), and Airplane Ridge (EA093). Molybdenite in a quartz vein on the southern slope of Mount Harper was first reported by Chapin (1919). Anomalous tungsten, copper, and molybdenum values were found during stream-sediment reconnaissance in the Mount Harper area by WGM Inc. in 1975; this was followed by geologic mapping and rock sampling in 1976 (Dashevsky and others, 1986). Molybdenum mineralization was discovered at the Section 21 prospect in 1977 (WGM Inc., 1978). WGM Inc. concluded that low grades at surface could not be expected to improve with depth. In 1979, Union Carbide Corp. decided that the property showed features similar to large porphyry molybdenum deposits and that the property warranted drilling (WGM Inc., 1998 [DLR 98-10]). A drill hole by Union Carbide Corp. in 1981 was aborted early without penetrating mineralization (U.S. Bureau of Mines, 1995).
Workings: Molybdenite in a quartz vein on the southern slope of Mount Harper was first reported by Chapin (1919). Anomalous tungsten, copper, and molybdenum values were found during stream-sediment reconnaissance in the Mount Harper area by WGM Inc. in 1975; this was followed by geologic mapping and rock sampling in 1976 (Dashevsky and others, 1986). Molybdenum mineralization was discovered at the Section 21 prospect in 1977 (WGM Inc., 1978). WGM Inc. concluded that low grades at surface could not be expected to improve with depth. In 1979, Union Carbide Corp. decided that the property showed features similar to large porphyry molybdenum deposits and that the property warranted drilling (WGM Inc., 1998 [DLR 98-10]). A drill hole by Union Carbide Corp. in 1981 was aborted early without penetrating mineralization (U.S. Bureau of Mines, 1995).
Age: Muscovite from a quartz-wolframite vein at the Section 21 prospect gives a 40Ar/39Ar plateau age of 102 +/- 0.4 Ma (Newberry and others, 1996).
Alteration: In the quartz porphyry-aplite plug, silicification is the dominant alteration type; there are lesser amounts of sericite and clay. Similar alteration is also present in the granodiorite near the quartz porphyry contact.

Commodities (Major) - Mo, W; (Minor) - Ag
Development Status: None
Deposit Model: Porphyry Mo (Cox and Singer, 1986; model 21b).

Mineral List



5 entries listed. 4 valid minerals.

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References

Burleigh, R.E., and Lear, K.G., 1994, Compilation of data for Phase I of the mineral resource evaluation of the Bureau of Land Management Black River and Fortymile subunits: U.S. Bureau of Mines Open-File Report 48-94, 116 p. Chapin, Theodore, 1919, A molybdenite lode on Healy River: U.S. Geological Survey Bulletin 692, p. 329. Cobb, E.H., 1972, Metallic mineral resources map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-393, 1:250,000 scale, 1 sheet. Dashevsky, S.S., Nicol, D.L., and Bond, J., 1986, Mines, prospects, and geochemical anomalies on Doyon Limited regional overselection lands, Alaska, Blocks 1-8: Doyon, Ltd. Report 86-01a, 300 p. (Report held by Doyon, Ltd., Fairbanks, Alaska). DiMarchi, J.J., Weglarz, T.B., Dickey, C.F., Laux, D.P., Smith, M.T., Toro, J., and Kurtz, J.P., 1991, Central Alaska Gold Co. 1990 annual report, Alaska field operations - Doyon option volume 1: Doyon, Ltd. Report 91-8a. (Report held by Doyon, Ltd., Fairbanks, Alaska). DiMarchi, J.J., Weglarz, T.B., Dickey, C.F., Laux, D.P., Smith, M.T., Toro, J., and Kurtz, J.P., 1991, Central Alaska Gold Co. 1990 annual report, Alaska field operations - Doyon option volume 2, analytical results, geochemical results part A: Doyon, Ltd. Report 91-8b. (Report held by Doyon, Ltd., Fairbanks, Alaska). DiMarchi, J.J., Weglarz, T.B., Dickey, C.F., Laux, D.P., Smith, M.T., Toro, J., and Kurtz, J.P., 1991, Central Alaska Gold Co. 1990 annual report, Alaska field operations - Doyon option volume 2, analytical results, geochemical results part B: Doyon, Ltd. Report 91-8c. (Report held by Doyon, Ltd., Fairbanks, Alaska). DiMarchi, J.J., Weglarz, T.B., Dickey, C.F., Laux, D.P., Smith, M.T., Toro, J., and Kurtz, J.P., 1991, Central Alaska Gold Co. 1990 annual report, Alaska field operations - Doyon option volume 10: Doyon, Ltd. Report 91-8g. (Report held by Doyon, Ltd., Fairbanks, Alaska). Huskey, G.F., 1981, 1981 Lucky 13 project area report: Doyon, Ltd. Report 82-49, 7 p. (Report held by Doyon, Ltd., Fairbanks, Alaska). Jirik, R. Lessman, G., Fernette, G., and Enns, S., 1979, 1978 annual progress report, Doyon Project, Mount Harper area, 21 prospect: Doyon, Ltd. Report 79-08. (Report held by Doyon, Ltd., Fairbanks, Alaska). Newberry, R.J., Layer, P.W., Burleigh, R.E., and Solie, D.N., 1996, New 40Ar/39Ar dates for intrusions and mineral prospects in the eastern Yukon-Tanana terrane, Alaska - Regional patterns and significance, in Gray, J.E., and Riehle, J.R., eds., Geological Studies in Alaska by the U.S. Geological Survey, 1996: U.S. Geological Survey Professional Paper 1595, p. 131-159. Smith, P.S., 1942, Occurrences of molybdenum in Alaska: U.S. Geological Survey Bulletin 926-C, p. 161-210. U.S. Bureau of Mines, 1995, Final report of the mineral resource evaluation of the Bureau of Land Management Black River and Fortymile River Subunits: U.S. Bureau of Mines Open-File Report 79-95, 226 p. WGM Inc., 1998, Veta property, 1997 annual report, volume 1: Doyon, Ltd. Report 98-10, 227 p. (Report held by Doyon, Ltd., Fairbanks, Alaska).

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