A potential natural chalcopyrite reference material for in situ copper, iron, and sulfur isotope measurements

Abstract

Chalcopyrite has been extensively utilized for tracing geological processes through its Cu, Fe and S isotopic compositions. However, the matrix-matched reference materials for micro-analysis are lacking. This study focused on assessing the feasibility of a natural chalcopyrite specimen (IGGCcp-1) as a matrix-matched reference material for in situ micro-analysis of Cu, Fe, and S isotopes. Electron probe microanalysis validated the uniform distribution of major elements within chalcopyrite grains, with no evidence of growth zoning. Random spot isotopic measurements using LA-MC-ICP-MS demonstrated remarkable consistency in δ⁶⁵Cu, δ⁵⁶Fe and δ³⁴S. These results indicated that the IGGCcp-1 specimen exhibited its suitability as a reference material. Using SN-MC-ICP-MS technique, the δ⁶⁵Cu value was accurately determined to be 0.43 ± 0.05 ‰ (2S, N = 30). Furthermore, the δ⁵⁶Fe_IRMM-014 and δ⁵⁷Fe_IRMM-014 values were recorded as -0.24 ± 0.04 ‰ (2S, N = 18) and -0.36 ± 0.09 ‰ (2S, N = 18), respectively. Additionally, the δ³⁴S_VCDT measurement, performed with EA-IRMS, yield a value of -0.28 ± 0.60 ‰ (2S, N = 10). These precisely measured isotope ratios established the recommended reference values for the IGGCcp-1 sample in future applications of Cu, Fe, and S isotope micro-analysis.