Yukon-Tanana REE

Region Alaska, Alaska
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Data-driven prospectivity ranking of watersheds (HUCs; Karl and others, 2016) shows that the focus area includes 52,970 km2 with a total of 112 of 563 HUC's showing high prospectivity; an additional 298 HUCs had medium prospectivity. This belt contains mineralized veins containing allanite, monazite, and thorite associated with mid and Late Cretaceous alkaline syenogranite intrusive complexes. The area of the Roy Creek prospect contains numerous uranium-REE prospects, uraniferous springs, and anomalous streambed sediments.
Identified resources None.
Production None recorded.
Status Limited drilling in Roy Creek area carried out by MAPCO in late 1970s for uranium.
Estimated resources No data.
Geologic maps Approximately 20% of the belt mapped at 1:63,360 scale or better.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Mid and Late Cretaceous alkaline to calc-alkaline syenogranite plutons and extrusive rocks are scattered across the belt. The lithology scores range from 0-1 with an average of 0.87 in the high HUCs. The igneous scores range from 0-4 and have an average of 0.904 in the high HUCs. Alkaline porphyritic biotite syenite and alkali granite plutons in the Roy Creek area; sampled and studied by USGS in 2014-15 but data presently unpublished; no published detailed, systematic geologic mapping around Roy Creek prospect or in surrounding region including possibly correlative igneous units.
Deposits None.
Evidence from mineral occurrences Known ARDF occurrences occur across the focus area associated with alkaline-granite hosted quartz-allanite-monazite veins. ARDF placer occurrences are scattered throughout the alkaline igneous province and contain zircon, xenotime, and monazite. ARDF: LG215. ARDF scores range from 0-2.
Geochemical evidence Sediment scores range from 0-6 with an average of 4.5 points in the high HUC's indicating the focus area is regionally anomalous with respect to REE and associated pathfinders. Burton, 1981 reports up to 15% REE in samples from the Roy Creek ARDF locality.
Geophysical evidence Aeroradiometric scores range from 0-2 with an average of 0.98.
Evidence from other sources No data.
Comments Multiple known magmatic-hydrothermal ore systems including two that are actively mined (Fort Knox and Pogo). Known critical mineral enrichment associated with Fort Knox, but geologic controls are not well understood. Numerous other known base- and precious-metal systems known or suspected in the region that might also have critical mineral enrichment. In the Roy Creek area, fissure veins containing allanite, bastnaesite, monazite, thorianite, thorite, uraninite, and xenotime occur in Cretaceous porphyritic biotite syenite and alkali granite (Burton,1981). The deposit contains significant lanthanum, cadmium, neodymium, praseodymium, ytterbium, and fluorite. Hematitic alteration of wall rock and leaching of magnetite occurs in host rocks. Samples contain up to 0.1% U-238 and 15% REE (Burton, 1981). Commodities include allanite, monazite, thorite, fluorspar, REE (lanthanum, cadmium, neodymium, praseodymium, ytterbium), allanite, bastnaesite, monazite, thorianite, thorite, uraninite, and xenotime.
Cover thickness and description Unknown.
Authors Douglas C. Kreiner, James V. Jones III, Melanie B. Werdon.
New data needs New mapping, geophysics, updated geochemical sampling.
Geologic mapping and modeling needs Systematic detailed geologic mapping of quadrangles containing igneous units such as Tired Pup pluton and Windy Fork pluton that have greatest REE potential. Characterization of hydrothermal alteration and mineral assemblage associated with prospective igneous units. Isotopic data (hafnium, lead) to test crustal character and terrane affinity. Systematic, detailed geologic mapping of quadrangles containing and surrounding Windy Fork pluton and other known Oligocene units in surrounding area of the western Alaska Range.
Geophysical survey and modeling needs Rank 1 or 2 aeromagnetic data to cover the entire belt west/northwest of existing Tanacross survey (Rank 2). Targeted EM where relevant for lithologic and structural mapping under cover.
Digital elevation data needs IfSAR coverage is complete over entire focus area.