The Li isotopic compositions of tourmalines can be used as a powerful geochemical tracer and provide valuable information regarding magma–volatile relationships and the magmatic-hydrothermal evolution of pegmatites. Laser ablation-multiple collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) is the method of choice for in situ Li isotopic analysis. In this study, we investigated the feasibility of Li isotopic analysis in tourmalines by both ns- and fs-LA-MC-ICP-MS with (tourmalines as calibration standards) and without (NIST 610 glass as the calibration standard) matrix-matched calibration. The Li isotopes of tourmalines can be accurately analyzed with matrix-matched calibration by ns- or fs-LA-MC-ICP-MS. However, inaccurate δ⁷Li values were obtained when tourmalines were measured against a non-matrix-matched standard by ns- (∼10.0‰ deviation) and fs-LA-MC-ICP-MS (∼1.5‰ deviation). Wet plasma conditions can significantly reduce the matrix effect in isotopic analysis. Furthermore, the deviation in fs-LA-MC-ICP-MS can be suppressed by water addition after the ablation cell. However, a relatively large deviation (∼4‰) still existed, even though the matrix effect during ns-LA can be largely suppressed by water addition after the ablation cell (∼6‰ deviation was reduced). Fortunately, with the water addition before the ablation cell, an accurate and precise Li isotopic analysis by ns-LA-MC-ICP-MS can be achieved with non-matrix-matched calibration. This study indicated that there was a serious matrix effect in the Li isotopic analysis of tourmalines by ns- and fs-LA-MC-ICP-MS, and water-assisted ns- and fs-LA-MC-ICP-MS were an appealing option for the in situ Li isotope analysis of tourmaline with non-matrix-matched calibration.

Precise constraints on the source and evolution of ore-forming fluids of Carlin-type gold deposits in the Golden Triangle (south China) are of critical importance for a better understanding of the ore genesis and a refined genetic model for gold mineralization. However, constraints on the source of ore fluid components have long been a challenge due to the very fine grained nature of the ore and gangue minerals in the deposits. Here we present He, Ne, and Ar isotope data of fluid inclusion extracts from a variety of ore and gangue minerals (arsenian pyrite, realgar, quartz, calcite, and fluorite) representing the main and late ore stages of three well-characterized major gold deposits (Shuiyindong, Nibao, and Yata) to provide significant new insights into the source and evolution of ore-forming fluids of this important gold province. Measured He isotopes have R/R_A ratios ranging from 0.01 to 0.4 that suggest a maximum of 5% mantle helium with an R/R_A of 8. The Ne and Ar isotope compositions are broadly comparable to air-saturated water, with a few analyses indicating the presence of an external fluid containing nucleogenic ³⁸Ar and radiogenic ⁴⁰Ar. Plotted on the ²⁰Ne/⁴He vs. helium R/R_A and ³He/²⁰Ne vs. ⁴He/²⁰Ne diagrams, the results define two distinct arrays that emanate from a common sedimentary pore fluid or deeply sourced metamorphic fluid end-member containing crustal He. The main ore-stage fluids are interpreted as a mixture of magmatic fluid containing mantle He and sedimentary pore fluid or deeply sourced metamorphic fluid with predominantly crustal He, whereas the late ore-stage fluids are a mixture of sedimentary pore fluid or deeply sourced metamorphic fluid bearing crustal He and shallow meteoric groundwater containing atmospheric He. Results presented here, when combined with independent evidence, support a magmatic origin for the ore-forming fluids. The ascending magmatic fluid mixed with sedimentary pore fluid or deeply sourced metamorphic fluid in the ore stage and subsequently mixed with the meteoric groundwater in the late ore stage, eventually producing the Carlin-type gold deposits in the Golden Triangle.