To examine the precision and accuracy of our analytical techniques on ultramafic rocks such as ureilites, we analyzed the terrestrial mafic DNC-1 and ultramafic DTS-2 (sometimes listed as DTS-2b) USGS standard reference materials. DTS-2 possesses REE values comparable to those found in Almahata Sitta. Results and comparisons with literature values are presented in Table 2. Where possible, we compare our results with those of the USGS certificates of analysis, but in many cases, compiled values are more complete and recent. Particularly for DTS-2, few literature values are available for comparison for the suite of elements that we present data for here (Table 2).
For the major and minor (Na, Mg, Al, P, K, Ca, Cr, Mn, Fe, and Ni) and REE, our values rarely show deviations greater than 10% from literature values. Some exceptions include Dy and Lu, which are about 15% higher and lower, respectively. While our Eu value for DNC-1 is only 5% lower than accepted values, our Eu value for DTS-2 is half of that compiled from the literature. Perhaps this is due to a paucity of literature data available––only two REE analyses were found for DTS-2 in the literature. Our results for other lithophiles such as Sc, Ti, V, Cu, Sr, Y, Zr, Nb, Ba, Hf, Ta, Th, and U typically have larger deviations from literature values. On average, literature values agree with our own to within 20% for these elements, with the high field strength elements Zr, Nb, Ta showing the largest deviations (up to 50%), especially when compared with the DNC-1 dolerite.
Moderately volatile and thermally labile elements (Zn, Ga, As, Se, Rb, Cd, In, Sn, Sb, Te, Cs, Tl, and Bi) results likewise compare well with prior values with deviations rarely reaching 36% (Te with 30 ng g−1 literature versus 22 ng g−1 for our value for DNC-1). Our lower determined Se value for DNC-1 (0.2 μg g−1 versus 0.55 μg g−1 literature) is another discrepant value. Our thermally labile elements Cd, In, Tl, and Bi data agree extremely well with literature values despite their extremely low concentrations.
Very few analyses exist for siderophile elements in terrestrial ultramafic rocks. However, when compared with available literature values, our siderophile (Co, Mo, Ru, Ag, Pd, W, Re, Ir, and Pt) accuracy is best for Co, Mo, W, and Pt. Larger differences are apparent when considering Ag, Pd, and Pt (Table 2). No literature values are available for Re comparison. The single literature value for Pd in DNC-1, shown for comparison in Table 2, is different than ours by a factor of approximately 10 as is our value for Ir, with comparisons again based on the only literature value available.