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Journal Article


The Diamantina Monazite: A New Low-Th Reference Material for Microanalysis

Gonçalves, G. O., Lana, C., Scholz, R., Buick, I. S., Gerdes, A., Kamo, S. L., Corfu, F., Rubatto, D., Wiedenbeck, M., Nalini, H. A., Oliveira, L. C. A. (2018): The Diamantina Monazite: A New Low-Th Reference Material for Microanalysis. - Geostandards and Geoanalytical Research, 42, 1, pp. 25—47.
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Gonçalves ,  Guilherme O.

Lana ,  Cristiano

Scholz ,  Ricardo

Buick ,  Ian S.

Gerdes ,  Axel

Kamo ,  Sandra L.

Corfu ,  Fernando

Rubatto ,  Daniela

Wiedenbeck ,  Michael
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Nalini ,  Hermínio A.

Oliveira ,  Luiz Carlos A.

Most monazite reference materials (RMs) for in situ U-Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix-matched RMs, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low-U and low-Th Diamantina monazite from the Espinhaço Range, SE Brazil. It has a U-Pb ID-TIMS weighted mean 207Pb*/235U ratio of 0.62913 ± 0.00079, 206Pb*/238U of 0.079861 ± 0.000088 and 207Pb*/206Pb* of 0.057130 ± 0.000031, yielding a weighted mean 206Pb*/238U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods (LA-(Q, SF, MC)-ICP-MS and SIMS) are within uncertainty of the ID-TIMS data. U-Pb LA-(Q, MC)-ICP-MS runs, using Diamantina as a primary RM, reproduced the ages of other established RMs within < 1% deviation. The LA-MC-ICP-MS analyses yielded homogeneous Sm-Nd isotopic compositions (143Nd/144Nd = 0.511427 ± 23, 2s; 147Sm/144Nd = 0.1177 ± 13, 2s) and εNd(495 Ma) of −18.7 ± 0.5 (2s). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2s), confirming Diamantina's relative homogeneity at test portion masses below 1 ng.