The Origin of Low-Level Airborne Radiometric Anomalies in the Copper River Basin Region, Alaska Page: 51

                                
exception was the zeolitized rhyolite flows and tuffs near Sanona Creek,
which have been enriched in potassium and depleted in sodium and calcium.
Relionaljrimary uranium deplet ion_(?):   Many of the granitic rock
specimens, which were taken from the outcrops in the study areas, were
relatively fresh and unaltered; yet the analytical data indicate that
they are somewhat depleted in uranium as compared to worldwide averages
for similar rock types. When compared to similar rock types in the
Seward-Selawik-Zane Hills Belt, for example, the Copper River Basin
rocks are indeed uranium-poor, which accents the relatively high uranium-
enrichment factor which characterizes the Seward-Selawik-Zane Hills
suite.
Comparative_ quality of fluorescence versus neutron activation
analyses for uranium:  Figure 13 is a correlation plot of uranium
analyses of replicate sediment and rock samples by the LASL and ADGGS
laboratories, using neutron activation and fluorescence techniques.
Values obtained from the fluorescence technique are consistently lower
than those derived from neutron activation analyses of replicate sam-
ples. Plots of the comparative analyses of rock samples define a curve,
which suggests that there is a systematic error, perhaps instrumental,
in the fluorescence analytical technique. The excellent agreement
between the USGS and LASL-determined values for USGS standard G-2
reinforces the superior quality of neutron activation versus fluores-
cence analysis in homogenous samples.
The three plots showing greatest variance (SU-1, SU-10h, and 3) are
for coarse-grained sediments. In this case, sample heterogeneity
appears to be responsible for the large error in the ADGGS analyses.

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