RT Journal Article
T1 Uranium-rich accessory minerals in the peraluminous and perphosphorous Belvís de Monroy pluton (Iberian Variscan belt)
A1 Pérez Soba, Cecilia
A1 Villaseca González, Carlos
A1 Orejana García, David
A1 Jeffries, Teresa
AB 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.
PB Springer
SN 0010-7999 ; 1432-0967
YR 2014
FD 2014-05-09
LK https://hdl.handle.net/20.500.14352/34266
UL https://hdl.handle.net/20.500.14352/34266
LA eng
NO Unión Europea. FP7
NO Ministerio de Economía y Competitividad (MINECO)
NO Universidad Complutense de Madrid
DS Docta Complutense
RD 7 may 2024