A precise 232Th-208Pb chronology of fine-grained monazite: Age of the Bayan Obo REE-Fe-Nb ore deposit, China

Zircon from the East Orebody of the Bayan Obo Fe–Nb–REE deposit, China, and SHRIMP ages for carbonatite-related magmatism and REE mineralization events

“…For Kovdor, U is extremely depleted at <1 ppm (rodionov et al 2012). Together with the trace element data of the present study, this bears consistency with the wider context of reported Th/U ratios at Bayan Obo (Chao et al 1992;Wang et al 1994;Chao et al 1997) and with a lithospheric mantle or lower crustal source. rare earth partitioning in zircon-melt systems is discussed by Hanchar and van Westrenen (2007), generally supporting the known preference for Hree in the zircon structure.…”

“…The characteristics of rim zircon growth in terms of compositions, morphology, intergrowths, Cl colours, zoning patterns and radiometric age collectively support a metasomatic secondary growth and fluid alteration explanation, contemporaneous with the main ree-fluorocarbonate mineralization event reported by (Chao et al 1992;Wang et al 1994;Henderson 1997 andKynicky et al 2012), and are indicative of a fluid with significant activity of P. evident from the preservation of volumetrically significant "new" bipyramidal crystal forms outlining rim zircon, it is deduced that there must have been a period in which thick, sub-to euhedral overgrowths, abundantly intergrown with ree (ore) and other minerals, developed around the magmatic cores. The apparent smooth growth transition from core to rim seen in a few places suggests that zircon precipitation (rather than degradation) was dominant at this time, and the promotion of outer crystal-face development suggests growth in an open fluid environment, perhaps analogous to the residual fluids fractionated from a melt as in the model of Harley et al (2007) in their Fig.…”

“…Chao et al 1992;Wang et al 1994;Chao et al 1997). However, it is established that significant ree mineralization (monazite occurrence) was in the late Mesoproterozoic, explained in the review by Smith et al (2014).…”

The Permian–Triassic granitoids in Bayan Obo, North China Craton: A geochemical and geochronological study

“…The large range of zircon ages reported here indicates a longer period of magmatism than previously identified (Fan et al, 2009;IGCAS, 1988;Ling et al, 2013;Wang et al, 1994;Zhang et al, 2003). The ages are clearly later than the ore forming stage constrained from monazite Th-Pb dating by sensitive high-resolution ion microprobe (SHRIMP) (~750-350 Ma) (Ling et al, 2013) or by solution methods (Chao et al, 1992(Chao et al, , 1997Wang et al, 1994), indicating no contribution to formation of the REE deposit. This is also supported by the initial Nd isotopic ratios of the granitoids, which are distinctively different from those of ore-bearing dolomites (Zhang et al, 2003).…”

“…Granitoids are widespread near the Bayan Obo deposit (Fig. 1), which have been studied by several groups (Chao et al, 1997;Fan et al, 2009;Ling et al, 2013;Wang, 1980;Wang et al, 1973Wang et al, , 1994Yang et al, 2000;Yuan et al, 1992). These granitoids were taken by some authors as the key factors that controlled the mineralization (IGCAS, 1988;Wang et al, 1973), while others proposed that the REE deposit has been partially transformed and further metasomatized by the granitoid intrusion (Yuan et al, 1992), but little REE ore-forming material was brought into the orebodies (Yuan et al, 1992).…”