Deposits of rare-earth elements (ree) in Alaska can be classified into several groups according to their geologic environment and mineralogical composition, according to this U.S. Bureau of Mines paper. Weathering of silica-rich, late-stage hydrous phases of granitic intrusions produced monazite-xenotime-allanite placers usually associated with tin and tungsten minerals. Additionally, ree in silica-rich intrusions concentrate in greisens, rhyolite porphyry, and radioactive veins. Lithophile element concentrations in some peralkaline complexes and silica-poor intrusions are derived from deeper crustal melts and generally contain higher levels of yttrium subgroup ree. Significant ree resources in polymineralic pegmatite dikes, zoned pegmatites, and epigenetic deposits are associated with peralkaline-alkaline complexes and characterized by multiple ree-cb-u-th mineral phases. About half of the total ree in Alaskan deposits occur in the heavy yttrium subgroup. In contrast to the crustal-related deposits, mantle-derived intrusions, particularly carbonatite and diatreme-breccia pipes, contain the light, cerium subgroup, phosphate and carbonate ree minerals and show a pronounced lack of the yttrium subgroup. The geology and mineral resource potential in much of Alaska is poorly known, particularly as it relates to the occurrence of lithophile elements. However, several definable trends of granites and subalkaline to alkaline and peralkaline rocks provide regional exploration opportunities.
Proc. Symp. on Precious & Rare Metals, Albuquerque, New Mexico, Apr, 1988; Elsevier, 1989, PP. 415-434