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This study provides a zinc and copper stable isotope characterization (δ66Zn, δ68Zn, and δ65Cu) of metalliferous seafloor sediments from the Atlantis II Deep, a hydrothermally influenced brine basin in the Red Sea. Samples collected from box cores that capture the entire stratigraphy in the Deep have δ66Zn and δ65Cu values of −0.31 to 0.34 ‰ (0.02 ‰ median) and − 1.81 to 1.02 ‰ (−0.34 ‰ median) relative to the JMC-Lyon and NIST SRM 976 standards, respectively. These results suggest enrichments of light stable isotopes in sediments compared to the hydrothermal inputs to the basin, which likely overlap the mantle-like isotopic signatures of basalts beneath the Deep. Such shifts to lower δ66Zn and δ65Cu values are consistent with widespread metal sulfide deposition from the brines because sulfide anions preferentially consume the light stable isotopes of zinc and copper. However, this interpretation contrasts with observations in the open ocean, where the fractionation of zinc and copper stable isotopes is strongly influenced by biological utilization and organic matter. Previous studies proposed that metal deposition in the Atlantis II Deep is also driven by adsorption onto iron oxides/hydroxides and their weakly crystalline (Si-)Fe-OOH precursor phases within the brines. However, because this process should accumulate heavy zinc and copper stable isotopes, its influence on isotopic fractionation is likely limited. Controls by metal sulfide precipitation are also indicated by spatial covariations between δ66Zn and concentrations of zinc and copper, that is, δ66Zn values increase whereas metal contents decrease with distance away from hydrothermal venting. Comparable trends are lacking for copper isotopes, perhaps because of additional influence by redox processes or, compared to zinc, a much stronger influence by adsorption onto (Si-)Fe-OOH phases, particularly in areas distal to hydrothermal venting where reduced sulfur could be scarce. Collectively, our results from the Atlantis II Deep indicate that zinc and copper stable isotopes could provide information about base and precious metals deposits from similar paleoenvironments. Firstly, zinc and copper stable isotopes shed light on metal sourcing and accumulation processes. Secondly, mineral precipitation in hydrothermally influenced brine pools produces zinc stable isotope patterns that, at least theoretically, could be of interest in mineral exploration at sub-basin and deposit scales. • Zinc and copper isotope characterization of metalliferous sediments formed by brine pool deposition in the Atlantis II Deep. • Enrichments of light zinc and copper isotopes in sediments when compared to the hydrothermal inputs to the basin. • Isotopic data are consistent with metal sulfide precipitation and lesser adsorption of metals onto Si-Fe-OOH particles. • Increase of δ66Zn with increasing distance from hydrothermal metal release due to uptake of light isotopes by metal sulfides. • Zinc isotope patterns due to metal sulfide precipitation could be of interest in mineral exploration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zinc isotope characterisation of the giant McArthur River Zn-Pb-Ag deposit. • Sulfide ores show invariable whole rock δ66Zn typical for the continental crust. • Only subtle, localized covariation between δ66Zn and relative abundances of Zn, Pb and Ag. • Data indicate rapid Zn precipitation that suppressed (Rayleigh) Zn isotope fractionation. • Discussion of the applicability of Zn isotopes for ore exploration. This study provides a Zn isotope characterization (δ66Zn) of the c. 1,640 Ma clastic-dominated McArthur River Zn-Pb-Ag deposit. Dolomitic, siltstone-hosted sulfide ores were sampled in two separate drill cores. One intersects the stratiform, vertically stacked orebodies at the centre of the deposit, and the other one intersects the south-eastern periphery of the deposit. The analyzed ores show relatively invariable δ66Zn values typical of the continental crust (0.35 ‰ median with 0.05 ‰ standard deviation). This signature is consistent with (near-) quantitative sulfide (sphalerite) precipitation during ore formation, negligible Zn isotope fractionation during fluid transport, and perhaps muted fractionation associated with near-quantitative Zn extraction from the source. Hence, our data show that a pronounced Zn isotope fractionation pattern characterized by lower δ66Zn values closer to the hydrothermal source, as reported from other Zn-Pb deposits, is not developed within the McArthur River deposit. However, across some orebodies, we note a subtle Zn isotope fractionation trend that correlates with the relative abundances of several temperature-sensitive base and trace metals (Zn, Pb, and Ag). This trend can be explained by subtle influence of Rayleigh-type Zn isotope fractionation during fluid evolution and Zn sulfide precipitation. Previous studies have suggested that Zn isotopes may be useful in the exploration for economic mineralization, as these studies observed both a significant Zn isotope halo and δ66Zn values markedly different from the continental crust. However, because both characteristics are not observable at McArthur River, the Zn isotope system may not have been useful in finding this deposit. [ABSTRACT FROM AUTHOR]