School of Engineering and Science - Jacobs University

determinations in carbonate rocks regardless of the acid matrix, concentration
determinations using 62 Ni provide excellent results for samples that are diluted in
HNO 3 , primarily through a reduction in the 25 Mg 37 Cl interference.
Elements that appear to be hosted primarily in refractory mineral phases
resistant to decomposition using the HNO 3 carbonate method include Ti, Rb, Zr, Nb,
Cs, Hf, and Ta, which would be expected for these incompatible elements. Two
elements that may be concentrated in different mineral phases are Ba and Pb (C- and
S-rich minerals?), for which the carbonate decomposition recovers approximately
90% and 80%, respectively, of the concentrations observed for the HF-HClO 4
decomposition method.
As stated above, it appears that the carbonate decomposition provides
satisfactory results for W. However, W is one of three elements apparently ‘lost’
during the analytical recovery test of the carbonate decomposition method, along with
Ta, and to a lesser extent Nb (see Section 6, Fig. 10). The low analytical recovery for
Nb, Ta, and W are attributed to the filtering step of the carbonate decomposition. For
Nb and Ta, the poor analytical recoveries during the carbonate decomposition method
are inconsequential, as regardless, sample dissolution in HNO 3 is not expected to
provide accurate determinations of these elements. In the case of W, the observed loss
during the filtering step is estimated at ~0.002 mg/kg (Fig. 10), which is also
inconsequential when considering the reference concentration of W in the JDo-1
dolomite of ~0.260 mg/kg. It is therefore unlikely that any loss of W during the
filtering step for the carbonate decomposition would significantly affect W
determinations, assuming W is present at concentrations ≥0.050 mg/kg in the sample
powder. This is particularly true when considering the uncertainty in the JUB
measured W data for JDo-1 (~15% RSD).
7.6. Marine ferromanganese nodules and crusts
Samples which comprise a large fraction of the geochemical research
performed with the Geochemistry Lab at JUB are marine ferromanganese nodules and
crusts (referred to collectively as Fe-Mn crusts). These Fe-Mn crusts are typically 13-
15% SiO 2 , 3-5% Al 2 O 3 , ~3% each CaO and MgO, 33-38% MnO, and 8-15% Fe 2 O 3 .
Therefore, the high metal content and interferences from Mn and Fe are expected to
provide the greatest obstacles to accurate trace metal determinations. However, unlike
other metal-rich rocks such as iron-formations, Fe-Mn crusts are highly enriched in
47