Bi-concentrations are highest at border of the Cu-rich outer core towards the inner rim of the crystal. The Bi distribution resembles an intense impact at the latest stage of the “neon”-blue growth phase that gradually faded away during further crystal growth (Fig. Par31a). F-concentrations are lowest in the core of the crystal and increase gradually to the mantle of the crystal (Fig. Par31i). They are well correlated with the backscattered image. Darker parts in the BSE-image match with low F-concentrations. Higher F-concentrations correlate with higher concentrations of Mn, Cu and Bi (See Fig. Par28c). Mg, Ti and Zn show a similar distribution like those observed for Mn. They increase towards the mantle of the crystal with very distinct oscillations at certain positions (compare Fig. Par31f, Par31g, Par31h and Par31j). A similar element concentration pattern was measured by LA-ICP-MS. However, the detection capabilities of LA-ICP-MS allowed to expand the analysis of the elemental distribution in “Paraiba”-tourmalines by focusing into other elements at µg/g concentrations that are below the limits of detection of electron microprobe analysis.

LA-ICP-MS ANALYSIS

Laser Ablation-Inductively Coupled Plasma Mass Spectrometry analysis were carried out using a 193 nm ArF Excimer laser ablation system (GeoLasM, Lambda Physik, Göttingen, Germany)

coupled to a DRCII + ICP-MS (Perkin Elmer, Norwalk, USA). A 20 cm3 ablation cell and a 1.5 m tube were used as transport system for the laser-generated aerosols. Helium was used as carrier gas and merged with argon in front of the ICP-MS torch to provide optimum excitation conditions within the ICP. The calibration was carried out using the NIST 610 glass. The element concentrations of NIST 610 were taken from Lit. Par03. The acquisition protocol included always 2 NIST 610 analyses at the beginning and the end of each run and allowed to analyze 16 sample positions in-between. Since tourmaline are heterogeneous systems and consist of a large number of major elements, the normalization procedures for metallic samples (Lit. Par06) and oxides (Lit. Par04) were applied. The analysis and data reduction were carried out following an acquisition, data reduction and quantification protocol (Lit. Par07).

427 individual LA-ICP-MS analysis were carried out on 6 Paraiba tourmalines (Samples 2079*, 2965*, 2972*, 2976.2*, 2976*, 3111-a*) and 260 individual analyses were acquired from 8 Mozambique samples (Samples 2939, 2942, 2942.2, 2943, 3134*, 3138, 3143, 7782* (*traverse). The samples were surface polished prior to the LA-ICP-MS analysis. On each sample, 60 µm craters were place next to each other to provide spatial resolution across different growth zones of the tourmalines.