Determination of the Li isotopic ratio in spodumene by LA-MC-ICP-MS

Abstract

As a primary lithium-bearing mineral, the in situ microanalysis of lithium isotopic composition in spodumene by LA-MC-ICP-MS provides important insights into the formation of pegmatite-type lithium deposits. This study presents a detailed evaluation of the effects of water vapor addition to the laser carrier gas and potential matrix effects on lithium isotope analysis by LA-MC-ICP-MS. Furthermore, we comprehensively assessed the lithium isotope homogeneity of three natural spodumene megacrysts (SpdLi-N1, SpdLi-N2, and SpdLi-N3) and one synthetic spodumene glass (HPLi-G1). The results indicate that the addition of water vapor did not significantly affect instrumental sensitivity but notably reduced carrier gas consumption. No significant matrix effect was observed between the synthetic glass and natural spodumene samples. LA-MC-ICP-MS analyses revealed homogeneous lithium isotope ratios for SpdLi-N1, SpdLi-N2, SpdLi-N3, and HPLi-G1, with δ⁷Li values of 12.89 ± 0.43‰ (2SD, n = 72), 12.38 ± 0.51‰ (2SD, n = 80), 12.48 ± 0.40‰ (2SD, n = 82), and 4.68 ± 0.49‰ (2SD, n = 18), respectively. These values are consistent with those obtained by solution MC-ICP-MS (12.85 ± 0.31‰, 12.29 ± 0.31‰, 12.37 ± 0.35‰, and 4.74 ± 0.30‰). The homogeneous Li isotopic compositions suggest that all four samples presented in this study can serve as primary reference materials for in situ Li isotope analysis by LA-MC-ICP-MS.