Melt extraction volatile elements

Experimental studies show that volatile components such as H2O and CO2 can have profound effects on melting temperature and melt composition (e.g., Kushiro, 1972 Hirose and Kawamoto, 1995 Kawamoto and Holloway, 1997 Dalton and Presnall, 1998 Gaetani and Grove, 1998 Hirschmann et al., 1999a Lee et al., 2000 Asahara and Ohtani, 2001). It has been implicitly assumed in the assessment above that melt extraction occurred in nominally anhydrous mantle. This assumption is most robust in the case of MORE mantle, which has been shown to have a low volatile content (e.g., Michael, 1988 Saal et al., 2002 Chapter 2.07). Inasmuch as off-craton mantle has isotopic characteristics that indicate similar long-term incompatible element depletion to the MORE source, and considering that volatiles are very incompatible elements, a low volatile content at the time of melt extraction from off-craton mantle is implied. Indeed, off-craton mantle may be genetically related to modern MORE mantle. 

The platinum group metals occur jointly as alloys and as mineral compounds in placer deposits of varying compositions. Ru and Os are separated from the PGM mix by distillation of their volatile oxides, whereas platinum, iridium, palladium, and rhodium are separated by repeated solution and precipitation as complex PGM chlorides, or by solvent extraction and thermal decomposition to sponge or powder. PGM scrap is recycled by melting with collector metals (lead, iron, or copper) followed by element-specific extraction. 

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