Corrigendum to “Volcanic gas composition, metal dispersion and deposition during explosive volcanic eruptions on the Moon” [Geochim. Cosmochim. Acta 206 (2017) 296–311, (S0016703717301503), (10.1016/j.gca.2017.03.012)]

We report an error in the calculation of the bulk composition of the lunar volcanic gas used for Gibbs free energy minimization calculations in our paper from 2017 (Renggli et al., 2017). We thank Matthew Varnam of finding the mistake. Here, we present the corrected lunar volcanic gas composition based on the loss of H, C, Cl, S, and F from a picritic very-low-Ti glass (‘Green #5′) (Saal et al., 2008; Wetzel et al., 2015). The error occurred in the conversion to molar compositions and primarily affects the molar ratios H/S, H/Cl, H/F (Table 1). The composition of the Erta Ale gas composition used for comparison was not affected. The abundances of S, Cl, and F are almost two orders of magnitude lower compared to the original model. In the revised model we excluded N since there are no constraints on the abundance of this element in lunar volcanic gas. We discuss the implications of this difference on the bulk gas speciation (Fig. 1), and the speciation of the metals Zn, Ni, Ga, Pb, Cu, Fe (Fig. 2), and additionally Na (Fig. 3). The relative dominance of H and C in the corrected gas composition is evident in the speciation (Fig. 1), where the gas species CO_(g) and H_2(g) are dominant, both at 1 bar and in the near vacuum at 10^–6 bar into which the lunar pyroclastic eruption plumes expanded. The higher H/S ratio in the corrected model results in a lower abundance of S-species. The S_2(g) species remains the primary S-species at 10⁻⁶ bar and temperatures from 700 to 1300 °C. However, H₂S_(g) is overall relatively more important due to the higher H/S ratio, compared to the model published in 2017. Other S-species (COS, HS, CS₂, etc.) consequently only occur in trace amounts. The H/Cl and H/F ratios are also significantly higher, such that HCl_(g) has an abundance below 10⁻⁴ mol fraction. For this reason, we extend the plotted mol fraction range to 10⁻⁶ (Fig. 1), compared to Fig. 2 in Renggli et al. (2017). In summary, the lunar volcanic gas that drove the pyroclastic eruption of the very-low-Ti melts (sample 15427,41, Saal et al. 2008) was dominated by the gas species CO_(g) and H_2(g), and the primary S gas species were S_2(g) and H₂S_(g). Effect on metal speciation One of the primary outcomes of our study in 2017 was the description of metal (Zn, Ga, Cu, Pb, Ni, Fe) speciation and gas phase transport in the lunar volcanic gas. Since metal transport in the gas phase depends on the gas composition and the abundance of complexing anions S²⁻ and Cl⁻ (Renggli et al., 2017; Renggli and Klemme, 2020) we recalculated the speciation of these metals in the corrected gas model (Fig. 2) and discuss the differences to the published model here. The metals occur as traces in the gas phase, and we added them at a concentration of 0.001 mol% as in our study from 2017. In the corrected gas model, the resulting molar ratios are metal/Cl = 0.27, metal/S = 0.001, metal/F = 0.007, and the complexing anions are in excess of the metal. Consequently, the changes in metal speciation due to the correction of the gas model are very minor and do not affect the overall volatilities relevant to the discussion in the 2017 paper, and Figs. 5 and 6 therein. Here, we describe the differences that we observe in the metal speciation at 10⁻⁶ bar (Fig. 2). In the case of Zn (Fig. 2a), Zn_(g) remains the volatile gas species and ZnS the solid phase below ∼ 720 °C. Changes occur only below 10⁻³ mol fractions, where the model predicts ZnO and Zn as solid phases in the temperature range over which Zn_(g) condenses from the gas phase (620–800 °C). Notably, in the case of Zn, Ni, and Fe (Fig. 2a, b, and f), the solid oxides (ZnO, NiO, FeO) are predicted as trace or minor phases due to the lower abundance of S. The primary Ni gas species remains Ni_(g) and the species NiS_(g), NiCl_(g), and NiF_(g) are less abundant. Due to the lower metal/S ratio in the corrected model Ni is overall more abundant relative to NiS (Fig. 2b). In case of Ga, the abundance of GaCl_(g) is lower in favor of Ga_(g) (Fig. 2c). Similarly, PbS_(g) and PbCl_(g) occur at lower abundances in favor of Pb_(g) (Fig. 2d), and CuCl_(g), CuS_(g), and CuF_(g) have lower abundances in favor of Cu_(g) (Fig. 2e). The low temperature (below 700 °C) abundance of the condensed CuS phase is reduced in favor of Cu in the revised model. Since the publication of our manuscript the outgassing (and in-gassing) of Na in lunar pyroclastic eruptions has received some attention (Ma and Liu, 2019; Liu and Ma, 2022; Su et al., 2023). For this reason, we include a speciation model for Na in the lunar volcanic gas at 10⁻⁶ bar (Fig. 3). Following the speciation calculations of the other metals, Na was added as a trace element to the bulk gas at a concentration of 0.001 mol%. The Na species included in the calculation are Na_(g), Na_2(g), NaCl_(g), NaF_(g), NaH_(g), NaO_(g), Na₂O_(g), NaOH_(g), Na₂SO_4(g), Na, NaCl, NaF, NaH, NaHF₂, NaHSO₄, NaO₂, NaO₃, Na₂O, NaOH, Na₂S, Na₂SO₃, Na₂SO₄, and NaOH*H₂O. At 10⁻⁶ bar Na is volatile at temperatures above 600 °C, forming NaCl_(g) up to 830 °C, and Na_(g) at even higher temperatures. Below ∼600 °C, Na forms NaF and NaCl solids. Condensed metallic Na, as suggested by Ma and Liu (2019), is predicted below 10⁻⁷ mol fraction by the model. Similarly, at the modelled pressure condition of 10⁻⁶ bar Na₂S, suggested as a condensate by Liu and Ma (2022), is predicted at normalized mol fractions below 10⁻⁷, which is below the plotted range (Fig. 3), constituting less than 1 ppm of the overall Na. In comparison with the other metals, the results suggest a volatility trend of Pb ≈ Na > Zn > Ga ≈ Cu > Fe ≈ Ni, based on the speciation model.