Lithium and trace-element concentrations in trioctahedral micas from granites of different geochemical types measured via laser ablation ICP-MS

Abstract

The compositions of trioctahedral micas from 51 samples of granitoids with different geochemical affiliations and grades of differentiation from the Bohemian Massif, Central Europe, were analysed using electron microprobe (major elements) and laser ablation inductively coupled plasma mass spectrometry (Li, Sc, Ga, Ge, Nb, In, Sn, Cs, Ta, W, Tl). The micas form a continuous evolutionary series from phlogopite to zinnwaldite. The phlogopites and biotites from the I-type rocks are characterized by 5.5–5.7 Si, 2.4–2.6 Al, <0.1 Li atoms per formula unit [apfu] and Mg/(Mg + Fe) = 0.4–0.8. The biotites from the S-type granites usually contain 5.3–5.7 Si, 3.2–3.6 Al, 0.1–0.3 Li apfu and Mg/(Mg + Fe) = 0.15–0.4. The annites and zinnwaldites from the rare-metal granites contain 5.7–6.8 Si, 3.2–3.8 Al, 0.6–2.6 Li apfu and Mg/(Mg + Fe) < 0.1. The concentrations of F, Rb, Cs and Tl increase from the phlogopites and biotites to zinnwaldites: F 0.1 → 8 wt.%, Rb2O 0.05 → 1.7 wt.%, Tl 2 → 50 ppm and Cs 40 → 2000 ppm. The concentrations of Sn, Nb, Ta and W in phlogopites and biotites from the I- and S-type granitoids generally correlate with those of the parent rocks and reach values of (in ppm) 20–100 Sn, 20–250 Nb, 1–20 Ta and <5 W. The highest concentrations were found in the Li-annites in the relatively early facies of rare-metal granites (in ppm): 250–600 Sn, 400–600 Nb, 60–120 Ta and 50– 120 W. The zinnwaldites in the late rare-metal granites facies are impoverished in these elements, which is explained by contemporaneous crystallization of cassiterite and columbite. Lithium enters the crystal lattice of trioctahedral micas via the exchange vector Li3□Si3Fe–6Al–1up to concentrations of ∼2.5 wt.% Li2O (1.5 apfu Li). At higher Li concentrations, Li is incorporated through the exchange vector Li3Si1□–1Fe–2Al–1.

Atom Probe Tomography Analysis of Mica

“…Empirical relationships between Li 2 O and SiO 2 , Al 2 O 3 , MgO and other minor elements in mica have been used to formulate regression equations enabling the estimation of lithium content from EPMA analysis (Tischendorf et al, 1997; Yavuz, 2001). Most recently, laser-induced breakdown spectroscopy (Fabre et al, 2002), laser ablation inductively coupled plasma mass spectroscopy (Breiter et al, 2017; Rosing-Schow et al, 2018), and SIMS (Ottolini et al, 2010) have been successfully applied for the identification of mica light and trace elements. APT not only provides the estimate of the concentration and isotopic ratios of those elements but, potentially, allows the assessment of their spatial distribution.…”

Can lithium contents in mica be correctly calculated? Tischendorf́s proposal (Mineralogical Magazine 61/1997) 25 years after

“…2000 individual spots where EPMA contents of major elements were obtained. The purpose of the older studies from the Bohemian Massif was to evaluate Li contents in micas to assess the potential of micas as Li resources (Breiter et al, 2017a(Breiter et al, , 2017b. In such cases, 15-20 EPMA spots were combined with 20-25 laser-ablation spots spread over one thin section and resulting means were presented as one sample.…”

“…The datasets evaluated comprise micas from: representative granitoids of the Bohemian Massif, Czech Republic, ranging from phlogopites from ultramafic dykes to zinnwaldites from stanniferous rare-metal granites (RMG) of the Nejdek and Cínovec plutons (Breiter 2017a(Breiter , 2019; muscovites to lepidolites from the Argemela rare-metal granite, Portugal (Breiter et al, 2022); muscovites from the Panasqueira tungsten deposit, Portugal (Breiter et al, 2023a); zinnwaldites to lepidolites from the Beauvoir raremetal granite, France; biotite, muscovite, phengite, zinnwaldite and lepidolite from the Orlovka Ta deposit, Siberia; biotite to zinnwaldite from the Wiborg batholith, Finland; and biotite to lepidolite from the Madeira pluton, Brazil (all in Breiter et al, 2023b). Though the Nejdek, Argemela, Panasqueira and Beauvoir plutons represent strongly peraluminous P-rich granites, the Cínovec, Wiborg and Orlovka plutons represent only slightly peraluminous P-poor post-orogenic granites.…”

“…This paper is based on an extensive set of complex local analyses obtained in our labs in the past years (Breiter et al, 2017a(Breiter et al, , 2019(Breiter et al, , 2022(Breiter et al, , 2023a(Breiter et al, , 2023b. The objectives are to show (1) the bias in Li content estimations according to the Tischendorf´s proposals; and (2) the limits of using estimated values in petrological practice.…”

Refined estimation of Li in mica by a machine learning method

“…Moreover, the simple correlations between Li 2 O and other individual major components are limited to small datasets used in the regression and inconsistent with the complex physico-chemical mechanisms of Li incorporation, which leads to significant errors in their applications (Förster et al 2005;Thiergärtner 2010;Breiter et al 2017b;Breiter et al 2019;Ballouard et al 2020).…”