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Copper sulfide ore is one of the most important sources of Cu in nature. In situ Cu isotope analysis of sulfides is critical for providing useful information on the sources of Cu and tracking the process of sulfide precipitation. The accuracy of in situ Cu isotope analysis relies heavily on matrix-matched reference materials to correct the instrumental mass bias. In this study, a natural chalcopyrite (TQ-Ccp) from the Tianqiao Pb–Zn deposit (Guizhou Province, China) was evaluated as a potential reference material for Cu isotope microanalysis. Major element mapping and determination by electron probe microanalysis (EPMA) demonstrated that there was no internal growth or zonation within the TQ-Ccp chalcopyrite grains. The Cu isotope homogeneity of the chalcopyrite sample was tested by micro-drill sampling and solution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) as well as by laser ablation MC-ICP-MS (LA-MC-ICP-MS). Thirty-two chalcopyrite powders were micro-drilled randomly from the whole hand specimen and from four fragments of chalcopyrite prepared in an epoxy mount, and measured by solution MC-ICP-MS. The dissolved chalcopyrite solutions processed with and without column chromatography yielded a mean δ65CuNIST976 of 0.05 ± 0.03‰ (2SD, n = 20) and 0.04 ± 0.03‰ (2SD, n = 32), respectively, suggesting Cu isotope homogeneity at the whole specimen scale. The Cu isotope homogeneity at the micro-scale was further verified by LA-MC-ICP-MS analyses of the four chalcopyrite fragments in the epoxy mount. In summary, TQ-Ccp chalcopyrite is potentially a suitable reference material for in situ Cu isotope microanalysis, whose recommended δ65CuNIST976 value is 0.04 ± 0.03‰ (2SD, n = 52), as determined by solution MC-ICP-MS analyses. [ABSTRACT FROM AUTHOR]

Origin of low δ 26 Mg basalts is a controversial subject and has been attributed to interaction of isotopically light carbonatitic melts derived from a subducted oceanic slab with the mantle (Yang et al., 2012), or alternatively, to accumulation of isotopically light ilmenite (FeTiO 3 ) in their mantle source (Sedaghatpour et al., 2013). To study the origin of low δ 26 Mg basalts and evaluate whether Mg isotope ratios of basalts can be used to trace deeply recycled carbon, high-precision major and trace element and Mg isotopic analyses on the Cenozoic alkaline and tholeiitic basalts from the South China Block (SCB), eastern China have been carried out in this study. The basalts show light Mg isotopic compositions, with δ 26 Mg ranging from −0.60 to −0.35. The relatively low TiO 2 contents (<2.7 wt.%) of our basalts, roughly positive correlations between δ 26 Mg and Ti/Ti ∗ and their constant Nb/Ta ratios (16.4–20) irrespective of variable TiO 2 contents indicate no significant amounts of isotopically light ilmenite accumulation in their mantle source. Notably, the basalts display negative correlations between δ 26 Mg and the amounts of total alkalis (i.e., Na 2 O + K 2 O) and incompatible trace elements (e.g., Ti, La, Nd, Nb, Th) and trace element abundance ratios (e.g., Sm/Yb, Nb/Y). Generally, with decrease of δ 26 Mg values, their Hf/Hf ∗ and Ti/Ti ∗ ratios decrease, whereas Ca/Al and Zr/Hf ratios increase. These features are consistent with incongruent partial melting of an isotopically light carbonated mantle, suggesting that large variations in Mg isotope ratios occurred during partial melting of such carbonated mantle under high temperatures. The isotopically light carbonated mantle were probably formed by interaction of the mantle with low δ 26 Mg carbonatitic melts derived from the deeply subducted low δ 26 Mg carbonated eclogite transformed from carbonate-bearing oceanic crust during plate subduction. As only the Pacific slab has an influence on both the North China Block (NCB) and SCB, our results together with the study of Yang et al. (2012) demonstrate that the recycled carbonatitic melts might have originated from the stagnant Pacific slab beneath East Asia in the Cretaceous and Cenozoic and that a widespread carbonated upper mantle exists beneath eastern China, which may serve as the main source for the <110 Ma basalts in this area. Thus, our study demonstrates that Mg isotope ratios of basalts are a powerful tool to trace deeply recycled carbon. [ABSTRACT FROM AUTHOR]