First vanadium isotope analyses of V-rich minerals by femtosecond laser ablation and solution-nebulization MC-ICP-MS

Abstract

Vanadium is a redox-sensitive trace metal that occurs in nature as VII, VIII, VIV, and VV, e.g. in a variety of ore-forming minerals like vanadates (hosting VV), sulfides (e.g., patrónite: VIV?S4), silicates (e.g., roscoelite, hosting VIII; cavansite, hosting VIV), and phosphates (e.g., sincosite, hosting VIV). Similar to other redox-sensitive metals (e.g., Fe, Cu, U), the V isotope compositions of V minerals may provide valuable information for source fingerprinting and redox-controlled processes during ore formation. The first in situ V isotope analyses of several natural V minerals (cavansite, descloizite, patrónite, sincosite, vanadinite) were performed in this study employing femtosecond-laser ablation-high resolution-MC-ICP-MS. The δ51V values are determined relative to a V metal (Alfa Aesar, 99.5% V) via standard-sample-standard bracketing, and are recast to the Oxford Alfa Aesar solution value. Mass bias was monitored by addition of an Fe standard to the sample aerosol during analyses. For comparison, aliquots of all mineral specimens were analyzed after chromatographic separation by solution-nebulization MC-ICP-MS. Our laser ablation and solution typically data agree well with each other (within 0.1‰ units), and indicate a significant variation of δ51V values between the analyzed minerals, ranging from −0.5 to +1.3‰ (2 s.e. per analysis typically between 0.04 and 0.06‰). This spread is significantly larger than reported for various reference rocks, and also exceeds the difference for δ51V between the bulk silicate Earth and the chondrite average. The extended range of δ51V values demonstrates that stable V isotope analyses may provide a new proxy for redox-processes in high- and low-temperature studies, including the fingerprinting of redox-induced V mobilization and enrichment processes during the formation of V-rich ores.