HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS

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HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS ( handbook-onphysics-and-chemistry-rare-earths )

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REE Mineralogy and Resources Chapter 279 175 TABLE 7 Isostructures of Monazite, Zircon, and Fergusonite (Anthony et al., 1995, 1997, 2000, 2003; Finch and Hanchar, 2003) Monazite (LREEPO4) Huttonite ThSiO4 Rooseveltite BiAsO4 Zircon (ZrSiO4) Hafnon HfSiO4 Thorite ThSiO4 Coffinite USiO4 Xenotime HREEPO4 Pretulite ScPO4 ChromatiteCaCrO4 Behierite (Ta,Nb)BO4 Wakefieldite YVO4 Dreyerute BiVO4 Chermovite YAsO4 Schiavinatoite (Nb,Ta)BO4 Fergusonite (HREENbO4) Formanite HREETaO4 Stolzite PbWO4 Scheelite CaWO4 Powellite CaMoO4 Wulfenite PbMoO4 in carbonatite has chemical composition close to the endmember (ZrSiO4), while zircon in granitic pegmatite, strongly fractionated rock, may contain over 15% REE2O3 (especially HREEs). The high amounts of HREEs are pref- erentially incorporated by xenotime substitution HREE3+ + P5+ $ Zr4+ + Si4+, but a continuous solid solution between the endmembers (zircon and xenotime) is unlikely to exist (eg, F€orster, 2006). Some zircons contain up to 20 wt.% REE2O3 (Tables 6 and 8; Hoshino et al., 2010). Moreover, some zircons from the granitic pegmatite contains high Th and U contents by thorite (Zr4+$Th4+) and coffinite substitutions (Zr4+$U4+). The zircons includes up to 11 wt.% UO2 and a lesser extent ThO2 (up to 7 wt.%) (Table 6; Hoshino et al., 2010). Although zircon grains have a wide variety of the chemical compositions, the four minerals listed in Table 8 are all identified as zircon following the 50% rule. Zircon contains generally less than 1 wt. % REEs and the analyses with significantly higher REE concentrations are attributed to alteration and/or accidental analysis of inclusions (Hoskin and Schaltegger, 2003). However, zircon in silicate rocks contains large amounts of REEs and is one of the valuable REE minerals in Nechalacho alkaline sye- nite deposit, Canada (Hoshino et al., 2013), and Khaldzan Buregtey alkaline granite deposit, Mongolia (Hoshino, unpublished data). Zircon is known to have variable crystallinity in addition to various chemical compositions

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