Author's personal copy Analysis of boron in fluid inclusions by microthermometry, laser ablation ICP-MS, and Raman spectroscopy: Application to the Cryo-Genie Pegmatite, San Diego County, California, USA Mona-Liza C. Sirbescu a, ⁎, Elizabeth G. Krukowski a, 1 , Christian Schmidt b , Rainer Thomas b , Iain M. Samson c , Robert J. Bodnar d a Earth and Atmospheric Sciences, Central Michigan University, Mt. Pleasant, MI 48859, USA b Deutsches GeoForschungsZentrum (GFZ), Section 3.3, Telegrafenberg, 14473 Potsdam, Germany c Department of Earth and Environmental Sciences, University of Windsor, Ontario, Canada d Department of Geosciences, Virginia Polytechnic and State University, Blacksburg, VA 24061, USA abstract article info Article history: Received 12 September 2012 Received in revised form 18 January 2013 Accepted 23 January 2013 Available online 8 February 2013 Editor: D.B. Dingwell Keywords: Raman spectroscopy Microthermometry Laser ablation ICP-MS Boric acid Sassolite Fluid chemistry Boron contents in magmatic fluids are largely unknown, even though B is an important constituent in granitic magmas and, potentially, in ore fluids. Owing to the fact that fluid inclusions from Li-rich pegmatites are typically B, Li, and Na ± F-rich aqueous solutions, salinity derived from microthermometry via the freezing point depression (NaCl eq ) may be inaccurate. In this study, the ratio of the integrated areas of the Raman bands of [B(OH) 3 ] aq 0 at ~878 cm -1 (B [3] \O stretching) and of H 2 O at ~3400 cm -1 (O\H stretching) were used for quantitative analysis of B concentrations in fluid inclusions in quartz. Then, B concentration measured via Raman spectroscopy was used as an internal standard for LA-ICP-MS analysis instead of using Na contents derived from NaCl eq obtained by microthermometry. This study revisits, validates, and optimizes the methodology for analysis of boron in fluid inclusions from granitic pegmatites and from other boron-rich environments by combining results from Raman spectroscopy, LA-ICP-MS and microthermometry. Raman analyses of synthetic solutions that approximate the composition of pegmatitic fluid inclusions were used to evaluate the effects of NaCl (1.1–12 mass%), LiCl (1.5–16), Li 2 CO 3 (0.05–0.6), NaF (0.6–1.7), and LiF (0.006–0.06) on H 3 BO 3 solutions ranging from 0.28 to 2.0 mass% of H 3 BO 3 for the analysis of H 3 BO 3 by Raman spectroscopy. The errors in H 3 BO 3 concentration induced by NaCl, LiCl, and LiF, the most common salts in pegmatitic fluids, were all ≤± 6%. Addition of Li 2 CO 3 in excess of ~ 0.1 Li 2 CO 3 /H 3 BO 3 ratio and addition of NaF in excess of ~ 0.2 NaF/H 3 BO 3 ratio caused a systematic decrease in the intensity of the ν s B [3] \O band at ~878 cm -1 (I 878 ) that resulted in the B concentration being underestimated by as much as 80%. This is relat- ed to an increase of solution pH that decreases the stability of [B(OH) 3 ] aq 0 . The effect of the inclusion-host quartz lattice orientation on the Raman signal was also tested. When the sample is cut perpendicular to the quartz c-axis or if its c-axis is co-planar with the laser polarization plane, the lattice effects on borate calibration become negligible. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Boron is an incompatible element that tends to concentrate in the final crystallization products of highly differentiated granitic magmas, associat- ed fluids, and ore deposits (Dingwell et al., 1996; Thomas et al., 2003; Slack and Trumbull, 2011). However, little is known about boron concen- trations in granitic and pegmatitic fluids. Lithium–cesium–tantalum (LCT) pegmatites are rich in boron, as demonstrated by the presence of tourmaline [Na(Fe, Mg, Li, Al) 3 Al 6 (BO 3 ) 3 (Si 6 O 18 )(OH) 4 ], axinite [Ca 2 (Fe, Mn)Al 2 (BO 3 )(Si 4 O 12 )(OH)], and boromuscovite [KAl 2 (Si 3 B)O 10 (OH) 2 ] (London, 1986; Foord et al., 1991; Clanin, 2004) and tourmaline exomorphic halos (Simmons and Webber, 2008). The fractionation of boron during inward, sequential crystallization of zoned LCT pegmatites and its relatively high solubility in aqueous fluid (Webster et al., 1989; Morgan and London, 1999) typically leads to boron enrichments in the pegmatite inner zones and in the aqueous fluid (London et al., 1996). Elbaite [Na(Li, Al) 3 Al 6 (BO 3 ) 3 (Si 6 O 18 )(OH) 4 ] and other tourmaline-group minerals found in miarolitic cavities of Li-rich pegmatites are thought to be precipitated from exsolved, boron-rich fluids (Samson and Sinclair, 1992; Simmons, 2007). One method to estimate boron concentration in granitic magmas is to analyze bulk compositions of LCT granitic Chemical Geology 342 (2013) 138–150 ⁎ Corresponding author. E-mail address: sirbe1mc@cmich.edu (M.-L.C. Sirbescu). 1 Present Address: Department of Geosciences, Virginia Polytechnic and State Uni- versity, Blacksburg, Virginia 24061, USA. 0009-2541/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.chemgeo.2013.01.014 Contents lists available at SciVerse ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo