Resources

The areal extent of placer REE-Zr enrichment in the outwash fan is indicated by coloration of sediment; heavy minerals occur in lighter-colored gravel dominantly composed of granite, as shown looking to the southeast in figure 6. Heavy mineral placer deposition continues an unknown distance downstream beyond the limits of present sampling. Based on available information, however, an area of at least 1,670,000 yd2 is mineralized (sub-economic). Assuming an average depth of 10 yds, a total inferred resource of about 17 million yd3 is present. The most abundant heavy mineral grains in the polished sections are ilmenite; titanium is also contained within the rare earth-element-bearing minerals that are present. The second most abundant heavy mineral constituent is zircon, the only zirconium-bearing mineral present in the samples. The most abundant rare-earth-element-bearing mineral is chevkinite (also tscheffkinite), [(Ca,Ce,Th)4(Fe+2,Mg)2(Ti,Fe+3)3 Si4O22]. It is present primarily as liberated grains between 30 and 100 µm in diameter, but is occasionally interlocked with zircon or silicate gangue.

Barker, J.C., 2016, 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.

History

In July 1988, the U.S. Bureau of Mines (USBM) conducted a reconnaissance-level investigation of the northern Windy Fork pluton located in the McGrath A-3 Quadrangle (fig. 1). The pluton extends south into the Lime Hills D-3 and D-4 quadrangles, but due to logistical constraints it was not possible to include the Lime Hills area. The project was performed in cooperation with the Alaska Division of Geological & Geophysical Surveys (DGGS), which provided helicopter support and the geological assistance of D.N. Solie. Ten days were spent in the field for the purpose of determining estimated grade-per-unit-volume values for samples containing niobium, titanium, rare-earth elements (REE), yttrium, zirconium, and other associated lithophile elements.

Barker, J.C., 2016, 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.