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Uranium-rich accessory minerals in the peraluminous and perphosphorous Belvís de Monroy pluton (Iberian Variscan belt) Pérez Soba, Cecilia Villaseca González, Carlos Orejana García, David Jeffries, Teresa 552.1 549 Monazite Xenotime Zircon Uranium Peraluminous granites Perphosphorous granites Mineralogía (Geología) Petrología 2506.11 Mineralogía The strongly peraluminous, perphosphorous (<0.85 wt% P2O5) and low-Ca granites from the Belvís de Monroy pluton contain the most U-rich monazite-(Ce) and xenotime known in igneous rocks. Along with these accessory minerals, P-rich zircon occurs, reaching uncommon compositions particularly in the more fractionated units of this zoned pluton. Monazite displays a wide compositional variation of UO2 (<23.13 wt%) and ThO2 (<19.58 wt%), positively correlated with Ca, Si, P, Y and REE. Xenotime shows a high UO2 content (2.37–13.34 wt%) with parallel increases of LREE, Ca and Si. Zircon contains comparatively much lower UO2 (<1.53 wt%) but high P2O5 (<14.91 wt%), Al2O3 (<6.96 wt%), FeO (<2.93 wt%) and CaO (<2.24 wt%) contents. The main mechanism of incorporating large U and Th amounts in studied monazite and U in xenotime is the cheralite-type [(Th,U)4+ + Ca2+ = 2(Y,REE)3+] substitution. Zircon requires several coupled mechanisms to charge balance the P substitution, resulting in non-stoichiometric compositions with low analytical totals. Compositional variations in the studied accessory phases indicate that the substitution mechanisms during crystal growth depend on the availability of non-formula elements. The strong P-rich character of the studied granites increases monazite crystallization, triggering a progressive impoverishment in Th and LREE in the residual melts, and consequently increasing extraordinarily the U content in monazite and xenotime. This is in marked contrast to other peraluminous (I-type or P-poor S-type) granite series. The P-rich and low-Ca peraluminous melt inhibits uraninite crystallization, so contributing to the U availability for monazite and xenotime. Unión Europea. FP7 Ministerio de Economía y Competitividad (MINECO) Universidad Complutense de Madrid Depto. de Mineralogía y Petrología Fac. de Ciencias Geológicas TRUE pub 2023-06-19T13:41:17Z 2023-06-19T13:41:17Z 2014-05-09 journal article https://hdl.handle.net/20.500.14352/34266 0010-7999 ; 1432-0967 10.1007/s00410-014-1008-4 eng SYNTHESYS (226506) CGL2012- 32822 UCM (910492) restricted access application/pdf Springer