Characterization of Xenotime From Datas (Brazil) as a Potential Reference Material for In Situ U‐Pb Geochronology

Abstract

This study investigates five megacrysts of xenotime (XN01, XN02, XN03, XN04, and XN05) as potential reference materials (RMs) for U‐Pb geochronology. These crystals belong to a 300 g xenotime assortment, collected from alluvial deposits in SE Brazil. Electron microprobe and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS) analyses show that the selected crystals are internally homogeneous for most rare earth element, (REE, except some light REE) but are relatively heterogeneous for U and Th. The xenotime REE patterns are consistent with an origin from hydrothermal quartz veins in the Datas area that cut greenschist‐facies metasediments and that locally contain other accessory phases such as rutile and monazite. High‐precision U‐Pb Isotope Dilution‐Thermal Ionization Mass Spectrometry (ID‐TIMS) analyses showed slight age heterogeneity for the XN01 crystal not observed in the XN02 sample. The two crystals have slightly different average 206Pb/238U ages of 513.4 ± 0.5 Ma (2 s) and 515.4 ± 0.2 Ma (2 s), respectively. In situ U‐Pb isotope data acquired via LA‐(Q,SF,MC)‐ICP‐MS are within the uncertainty of the ID‐TIMS data, showing homogeneity at the 1% precision of the laser ablation (and probably ion microprobe) technique. U‐Pb LA‐(MC, SF)‐ICP‐MS analyses, using XN01 as a primary RM, reproduced the ages of other established RMs within less than 1% deviation. Other Datas crystals (XN03‐05) also display a reproducibility in Pb/U dates better than 1% on LA‐ICP‐MS, making them good candidates for further testing by ID‐TIMS.

A new calibrated strategy for the in situ U–Th–Pb dating of bastnasite by xenotime

“…Xenotime XN01 and XN02 are two loose xenotime crystals collected from the alluvial deposits located near the Datas and Diamantina cities in the southern Espinhaço Range, Brazil. 34 They are probably sourced from quartz veins and show euhedral to subhedral shapes and brown and yellow-brown colors with widths of ∼0.3 cm and lengths of 1 to 2 cm. XN01 and XN02 are both characterized by low common lead and have uniform REE compositions (except La–Ce–Pr), high U concentrations of 433 to 643 and 707 to 1240 ppm, and Th of 1315 to 5079 and 990 to 2431 ppm, respectively.…”

“…XN01 and XN02 have an average ID-TIMS 206 Pb/ 238 U age of 513.4 ± 0.5 and 515.4 ± 0.2 Ma, respectively. 34 XN01 has been verified as a reliable primary standard to calibrate several known standards ( i.e. , MG-1, BS-1, and z6413 xenotimes).…”

Rare earth elements in gneiss regoliths in southern Minas Gerais, Brazil

“…Absolute concentrations of Gd in P3 varied from 11.4 to 19.4 mg kg -1 (Table 1), which may relate to the presence of one or both of the dimorphs monazite and xenotime (Clark, 1984;Ni et al, 1995). These are ubiquitous REE phosphates (general formula REE+Y(PO 4 )) and Vasconcelos et al (2018) sampled 5 xenotime cristals containing from 10800 to 26500 mg kg -1 of Gd, which relate to a 1.2 to 3.0 % Gd 2 O 3 substitution for Y 2 O 3 . Unfortunately, we did not find xenotime crystals in the present samples, as opposed to our previous paper on gnessic profiles in NE Brazil (Santos et al, 2019a).…”

An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO4

“…Xenotime (REPO4; RE = Tb to Lu and Y, Sc) is a commercially important rare-earth mineral and is usually found as accessory inclusions in igneous and metamorphic rocks. [1][2][3][4][5][6][7][8] Natural xenotime minerals are rich in yttrium and also contain variable amounts of heavy rare-earth elements (HREE). [1,[9][10][11] Xenotime mineral crystallizes in the zircon structure type in the tetragonal crystal system with space group: I41/amd (Figure 1).…”