Paper Number: 1423
Discrimination of danburite from different deposits by chemical components: a femtosecond LA-ICP-MS study
Huong, L.T.T.1, Otter, L.M.2, Macholdt, D.S.2, Foerster, M.W.3, Stoll, B.2, Weis, U.2, Jochum, K.P.2
1Faculty of Geology, Vietnam National University Hanoi, 334 Nguyen Trai, Hanoi, Vietnam
2Department of Climate Geochemistry, Max-Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany
3Institute for Geosciences, Johannes Gutenberg University Mainz, J.-J.-Becher-Weg 21, D-55128 Mainz, Germany
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Femtosecond laser ablation-inductively coupled plasma-mass spectrometry was used to determine the concentration of 51 elements, i.e. Li, Be, B, Na, Mg, Al, Si, K, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Ag, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Pt, Au and Tl in 6 danburite samples from 3 deposits in Mexico (2 colourless samples), in Vietnam (2 light yellow samples) and in Tanzania (2 saturated yellow samples). Calcium was determined in a previous study by Huong et al. [1] with electron microprobe analysis and used as internal standard for the current LA-ICP-MS measurements. Femtosecond laser ablation allows non-matrix-matched calibration that is necessary since there is no suitable reference material for danburite [2]. The objective of this study is to characterize the elemental composition of danburite among the three deposits and to preliminarily understand the causes of yellow colour in this mineral.
The results show that the concentrations of REEs in samples from the three deposits differ significantly (Fig. 1). The Tanzanian danburite samples contain extreme high concentration of lanthanide impurities. Total lanthanide content of Tanzanian samples is about 1900 ppm, whereby the concentration of light rare earth elements (LREE: La, Ce, Pr, Nd, Sm, Eu) exceed those of the heavy rare earth elements (HREE: Gd, Tb, Dy, Ho, Er, Er, Tm, Yb, Lu) by a 450-fold enrichment. This result is in good agreement with the investigations of Chadwick and Laurs [3]. The Vietnamese samples are different with a total lanthanide content of ca. 1100 ppm, whereby the concentrations of LREE exceed those of HREE by a 200-fold enrichment. The colourless Mexican danburites appear to be fairly clean from lanthanide with total contents of approx. 1.1 ppm. This finding suggests that REEs content might correlate with the yellow colour in danburite.
The three danburite origins can also be separated from each other by the mass fractions of minor and trace elements i.e. Be, Ti, Mn, Ni, As, Sr and Y. However, the contents of these elements are not related to the colour. In addition, low concentrations of 0.1 – 0.6 ppm of the radioactive element Th are identified in all samples independently from their origins.
References:
[1] Huong et al. (in review) Gems Gemol
[2] Jochum KP et al. (2014) Geostand Geoanal Res 38(3): 265–292.
[3] Chadwick KM and Laurs BM (2008) Gems Gemol 44(2): 169-171