Spodumene reference materials for LA-MC-ICP-MS Li isotopic analysis

Abstract

Lithium isotopes have been widely used in studying the origin of pegmatite-type lithium deposits. However, only a few matrix-matched spodumene reference materials for Li isotope determination are reported in laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analyses, significantly restricting both the measurement accuracy and operational viability of this method. This study investigates four natural spodumenes to examine their potential as spodumene Li isotope reference materials. The results indicate that these spodumenes have identical contents of major elements, but show slightly variations in trace element abundances (e.g., B, Sn, and Ti). A total of six Li isotope analyses on each grain, determined by bulk-rock MC-ICP-MS, yield mean δ⁷Li values of 5.75 ± 0.12‰ (2SD, n = 6), 8.31 ± 0.18‰ (2SD, n = 6), 5.04 ± 0.21‰ (2SD, n = 6), and 12.27 ± 0.26‰ (2SD, n = 6) for SPD-1, SPD-2, SPD-3, and SPD-4, respectively. The average δ⁷Li values of these four spodumenes determined by LA-MC-ICP-MS analyses were 5.69 ± 0.58‰ (2SD, n = 200), 8.33 ± 0.50‰ (2SD, n = 200), 5.06 ± 0.54‰ (2SD, n = 210), and 12.29 ± 0.61‰ (2SD, n = 210). These data indicate that lithium isotope compositions are homogeneous within individual spodumene grains. The large variations in Li isotope compositions among four spodumene grains highlight their suitability as matrix-matched reference materials for in-situ Li isotope analysis of spodumene from diverse pegmatite-type lithium deposits.