Discussion/Major Findings

Tuning for Oxides

Results indicate that tuning for oxides is especially important when analyzing REE concentrations. Tuning the instrument to produce an oxide production ratio of around 1% or less CeO/Ce is optimal. Ratios higher than 1% will lead to an increase in the interference of oxides onto the data, and can decrease the actual found concentration after data reduction. Overall, it is important to tune the ICPMS instrument to have low oxide production so that interferences don’t cause too much error in the measured concentrations.

NASC Normalization

REE data is typically normalized to REE standards. One often used standard is the National American Shale Composite (NASC). When normalized to these recorded values, the data show a typical zig-zag REE pattern. Elements with odd atomic numbers have higher concentrations, while even atomic numbers have lower concentrations. The pattern is almost identical between each tune. Carbonates show the lowest concentrations, while whole rocks show the highest concentrations.

The Hammett and Hensel whole rock have the highest normalized concentrations on the graphs. This makes sense because each of these units contain more shale components, so their concentrations will be the most similar to the shale composite. Therefore, the two units plot the highest.

Figures 1 & 2: NASC Normalized REE concentrations for high vs low oxide tuned samples. The numbers on the x axis represent the atomic numbers of the REEs.