Chao Zhang (1)* , Jinru Lin (2), Yuanming Pan (2), Renfei Feng (3), Renat R. Almeev (1) and
Francois Holtz (1)
(1) Institute of Mineralogy, Leibniz Universit€at Hannover, Hannover, 30167, Germany
(2) Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada
(3) Canadian Light Source, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 0X4, Canada
Abstract: The strong spectral interference between Br- and Al-induced X-ray lines hampers the utilisation of electron probe microanalysis (EPMA) for measuring Br mass fractions in Al-bearing minerals and glasses. Through measuring Br-free Albearing materials, we established an EPMA method to quantify the overlap from AlKα on BrLb, which can be expressed as a linear function of the Al2O3 content. The count rate of the BrLb peak signal was enhanced by high beam currents and long measurement times. Application of this EPMA method to Al- and Br-bearing materials, such as sodalite and scapolite, and to five experimental glasses yielded Br mass fractions (in the range of 250–4000 μg g-1) that are consistent with those measured by microbeam synchrotron X-ray fluorescence (μ-SXRF) spectrometry. The EPMA method has an estimated detection limit of ~ 100–300 μg g-1. We propose that this method is useful for measuring Br mass fractions (hundreds to thousands of μg g-1) in Al-bearing minerals and glasses, including those produced in Br-doped experiments. In addition, the natural marialitic scapolite (ON70) from Mpwapwa (Tanzania) containing homogeneously distributed high mass fractions of Br (2058 ± 56 μg g-1) and Cl (1.98 ± 0.03% m/m) is an ideal reference material for future in situ analyses.
