The saturation of Zr, P₂O₅ and TiO₂ in felsic to intermediate silicate melts, and the REE partitioning into zircon and other accessory minerals (apatite and sphene) are reviewed in this article.
As discussed in Part I, the latent primitive crust can be characterized by the study of REE in the xenocrystic cores of Archean zircons, such as the 4.2 Ga zircon from Mt Narryer. In order to better understand the geochemistry of the REE, we review the REE partitioning data for zircon, apatite, allanite and sphene in natural felsic to intermediate rock studies and in high pressure experiments.
We also review the experimental results for Zr, P₂O₅ and TiO₂ saturation conditions. The saturation of P₂O₅ and TiO₂ is important for the discussion of the REE partitioning in zircon, because the REE contents in the silicate melt coexisting with zircon is affected by the crystallization of the other REE rich accessory minerals like apatite or sphene.
Based on our reviews, we conclude that REE partitioning cannot be constrained from the studies of natural rocks because the partitioning of the REE is affected by temperature and pressure which we do not know precisely. The SiO₂ content in the silicate melt also affects the partitioning of the REE because it changes the structure of the silicate melt, as briefly reviewed in this article.
In addition, REE partitioning data obtained by conventional “bulk analysis” of zircon is becoming less important. This is because a bulk analysis, especially for LREE, is easily affected by inclusions in zircon, where the LREE are enriched in these inclusions. Only SIMS analyses can eliminate the effect of the inclusions and reveal the actual partitioning of REE in zircon.

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Complete separation of Sr for the isotopic analysis of Mg-rich samples, such as ultramafic rocks and their constituent minerals, was established by adopting a combination of cationexchange chromatography in H⁺ form and pyridinium form with a DCTA complex using extremely small volumes of cation-exchange resin (1ml and 0.5ml respectively), This method made it possible to efficiently separate nanogram sizes of Sr from coexisting large amounts of Mg and Ca with a reduced total elution volume of only 24ml. The method also resulted in the reduction of procedural blanks for Sr and Rb to 32 and 25 pg, respectively.
Applying static multicollection mass spectrometry with Ta-oxide as an ionization activator on a V-shaped W single filament, the isotopic composition of 10 to 20 ng Sr samples separated from 40 to 55mg of ultramafic rock standard (PCC-1) was determined with analytical precision of<0.005% and reproducibility of<0.006%. These precise analyses were performed with a high ⁸⁸Sr⁺ ion beam intensity (>1.5×10^-11 A). Our efficient chemical separation procedure also ensured the absence of Ca and Mg interference to Sr ionization. The Ta-oxide readily eliminated Rb prior to the Sr isotopic analysis in the mass spectrometer. This improved the analytical reliability of isotope dilution mass spectrometry (IDMS) for the simultaneous determination of Sr isotopic composition and concentration. The measured isotopic compositions of spiked PCC-1 agreed within error with those obtained from unspiked measurements, Rb/Sr ratio analyses for PCC-1 using IDMS provided analytical reproducibilities of better than 2%. These achievements indicate that our IDMS technique is capable of yielding trace Rb and Sr concentrations simultaneously with Sr isotopic composition in Mg-rich samples with an analytical reliability similar to that obtained from larger samples ( ?? 1 μg) of common silicate rock samples.

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