Windy Fork Placer Occurrence, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
This page is currently not sponsored. Click here to sponsor this page.
Location: The Windy Fork Placer occurrence is located at the confluence of the Windy Fork of the Kuskokwim River and two unnamed, north flowing tributaries draining the Windy Fork pluton (Gilbert and others, 1988). The occurrence is at an elevation of 2,900 feet (884 m) in the NW1/4 sec. 21, T. 23 N., R. 26 W., of the Seward Meridian. The coordinates given above are in the geographic center of the deposit, which occupies an irregular one square kilometer area. The reporter visited the site in 1988.
Geology: The Windy Fork Placer prospect is a significant accumulation of REE minerals, ilmenite, zircon, and other heavy minerals liberated from the peralkaline Windy Fork composite pluton and concentrated in a high energy glaciofluvial placer deposit (Solie, 1983; Gilbert and others, 1988; Barker, 1991; Bundtzen, Harris, and Gilbert, 1997). Although the Windy Fork pluton contains riebekite granite, biotite granite, and pyroxene syenite phases; it's average chemical composition is that of a peralkaline granite (Solie, 1983). The Windy Fork pluton is radioactive and scintillometer readings taken along traverses across the intrusion range from 650-to-800 cps, about 3 times the average background for granitic rocks. High energy glaciofluvial gravels with significant heavy mineral concentrations have accumulated in an elliptical, one square kilometer area near the confluence of Windy Fork and two second order tributary streams that dissect the Windy Fork pluton (Gilbert and others, 1988). Stream bed and fan deposits contain abundant chevkinite, eudialyte, ilmenite, monazite, tscheffkinite, and zircon and minor to trace allanite, cassiterite, and thorite (Barker, 1991). Natural streaks of black sand rich in magnetite and ilmenite are very common in bedload environments. Monazite and zircon are easily identified in the field. Placer concentrations averaging 7.5 percent titanium, 2.9 percent zirconium, 0.21 percent lanthanum, 0.28 percent cerium, and 460 ppm niobium occur throughout large areas of the placer deposit. Based on systematic bulk sampling, Barker (1991) estimates that the Windy Fork placer deposit contains 13 million cubic meters with an average grade of 9 to 11 kilograms per cubic meter of cerium-enriched, REE heavy minerals.
Workings: Systematic surface sampling of the placer deposit was completed by Barker (1991) during 1988, during a cooperative strategic mineral assessment of the McGrath quadrangle with the Alaska Division of Geological and Geophysical Surveys. Placer concentrations averaging 7.5 percent titanium, 2.9 percent zirconium, 0.21 percent lanthanum, 0.28 percent cerium, and 460 ppm niobium occur throughout large areas of the placer deposit. Based on systematic bulk sampling, Barker (1991) estimates that the Windy fork placer deposit contains 13 million cubic meters that average 9-11 kilograms per cubic meter of cerium-enriched, REE minerals.
Reserves: Barker (1991) estimates that 13 million cubic meters average 9-11 kilograms per cubic meter of cerium-enriched, REE minerals. This inferred resource estimate is considered conservative.
Commodities (Major) - Ce, La, Nb, Ti, Zr; (Minor) - Fe, Sn, Th, U
Development Status: No
Deposit Model: Similar to heavy mineral placer model (Cox and Singer, 1986; model 39d and 39e)
9 entries listed. 6 valid minerals.
The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.
Barker, J.C., 1991, Investigation of rare-earth elements and zirconium in the Windy Fork peralkaline pluton, west-central Alaska: U.S. Bureau of Mines field report, 36 p. Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000. Gilbert, W.G., Solie, D.N., and Kline, J.T., 1988, Geologic map of the McGrath A-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 92, 2 sheets, scale 1:63,360. Solie, D.N., 1983, The Middle Fork plutonic complex, McGrath A-3 quadrangle, southwest Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 83-16, 17 p.