Copper Isotope Ratio Measurements of Cu-Dominated Minerals Without Column Chromatography Using MC-ICP-MS

Abstract

This study performed a series of comparable experiments (with or without column chromatography) to evaluate whether non-deviated Cu isotope ratios can be obtained directly by Nu Plasma II multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) using standard-sample bracketing with Ga as internal mass bias correction model (C-SSBIN) without column chromatography. Twelve Cu-dominated minerals (copper plate, native copper, chalcopyrite, bornite, chalcocite, digenite, covellite, tetrahedrite, azurite, malachite, atacamite, and cyanotrichite) displayed little drift in δ 65 Cu values compared with those of minerals with column chromatography, with δ 65 Cu without−with ranging from −0.04 to +0.02‰. This means that Cu isotope ratios in Cu-dominated minerals can be achieved without column chromatography, due to the simple matrix and the stability of the machine by using C-SSBIN mode. The acidity and internal standard concentration mismatch effects, as well as the matrix effect, were strictly assessed by Nu Plasma II MC-ICP-MS in a wet-plasma mode in the State Key Laboratory of Continental Dynamics (SKLCD). Finally, a long-term reproducibility of better than ±0.03‰ [n = 38, 2 standard deviations (2s)] were achieved by repeatedly measuring chalcopyrite without column chromatography over 4 months.

A Potential New Chalcopyrite Reference Material for LA‐MC‐ICP‐MS Copper Isotope Ratio Measurement

“…Recently, Zhang et al . (2020) and Lv et al . (2020) presented a mean chalcopyrite δ 65 Cu ratio of −0.05 ± 0.03‰ and −0.08 ± 0.03‰, respectively, with column chromatography.…”

“…The mass spectrometry analyses followed the procedure established by Zhang et al . (2020) and Bao et al . (2020) and are briefly summarised here.…”

“…One in‐house chalcopyrite (CPY‐1) and one digenite (DIG‐1) were used to monitor the analytical procedure, and their δ 65 Cu values are +0.04 ± 0.02‰ and +0.09 ± 0.03‰ obtained by SN‐MC‐ICP‐MS (Zhang et al . 2020). The SSB method was selected to correct the instrumental mass bias.…”

“…The bulk SN-MC-ICP-MS analyses were conducted at the SKLCD. The sample digestion and column chromatography followed the procedure established by Zhang et al (2020) and are briefly summarised here. Approximate 10 mg of chalcopyrite samples were weighed in the 15 ml pre-cleaned PFA vials and dissolved in a 3:1 (v/v) mixture of high-pure concentrated HCl-HNO 3 at 120°C for 2 h in the capped vial.…”

“…The mass spectrometry analyses followed the procedure established by Zhang et al (2020) and Bao et al (2020) and are briefly summarised here. The δ 65 Cu ratios were determined by using a double-focusing Thermal Scientific ™ Neptune Plus ™ and Nu Plasma 1700 MC-ICP-MS at the SKLCD.…”