Lithologic Period Predicts Yttrium Enrichment in Western United States Stream Sediments

Thomas Alan Woolman 

Screening ground for heavy rare earth prospecting potential at regional scale depends upon archived geochemistry, because favorable intrusive terrain in the western U.S. greatly exceeds what any drilling program could evaluate directly. This research examined whether the lithologic period of intrusive igneous terrain can reliably predict acid-leachable yttrium using only the stream sediment draining it. The author utilized 32,221 reanalyzed NURE-HSSR samples across six western U.S. states, with lithology from the State Geologic Map Compilation and the geological period recovered from the standard geologic map symbol, since the published age field was incomplete outside Arizona. Yttrium served as the HREE precursor proxy, since the eight-coordinated xenotime site preferentially incorporates terbium through lutetium with yttrium. That premise was validated against an independent whole rock compilation, where yttrium tracks the summed heavy lanthanides at a Spearman correlation of 0.900 and the light lanthanides at 0.648. Drainage over Mesoproterozoic intrusive terrain carries a median acid-leachable yttrium concentration 2.03 times that of drainage over intrusive terrain across all other periods. A blocked permutation test, permuting the period label by 150 kilometer blocks within each state, rejected the null hypothesis at an empirical two-sided probability of 0.0246, replicating under a narrower population definition at 1.65 and 0.0359. This signal is magmatic rather than chronological, since a 2,072 sample Belt Supergroup control of comparable age demonstrates no elevation. Enrichment is not monotonic in age, because Archean terrain was the poorest period examined. The distribution peaks at approximately 1.4 Ga, refuting a possible secular mantle cooling explanation.