| Summary: | Minerals of the Zn-Cd-S-Se system that formed by moderately reduced ~800–850 °C combustion metamorphic (CM) alteration of marly sediments were found in marbles from central Jordan. Their precursor sediments contain Se- and Ni-enriched authigenic pyrite and ZnS modifications with high Cd enrichment (up to ~10 wt%) and elevated concentrations of Cu, Sb, Ag, Mo, and Pb. The marbles are composed of calcite, carbonate-fluorapatite, spurrite, and brownmillerite and characterized by high P, Zn, Cd, U, and elevated Se, Ni, V, and Mo contents. Main accessories are either Zn-bearing oxides or sphalerite, greenockite, and Ca-Fe-Ni-Cu-O-S-Se oxychalcogenides. CM alteration lead to compositional homogenization of metamorphic sphalerite, for which trace-element suites become less diverse than in the authigenic ZnS. The CM sphalerites contain up to ~14 wt% Cd and ~6.7 wt% Se but are poor in Fe (means 1.4–2.2 wt%), and bear 100–250 ppm Co, Ni, and Hg. Sphalerite (Zn,Cd,Fe)(S,O,Se)<sub>cub</sub> is a homogeneous solid solution with a unit cell smaller than in ZnS<sub>cub</sub> as a result of S<sup>2−</sup> → O<sup>2−</sup> substitution (<i>a</i> = 5.40852(12) Å, <i>V</i> = 158.211(6) Å<sup>3</sup>). The amount of lattice-bound oxygen in the CM sphalerite is within the range for synthetic ZnS<sub>1−x</sub>O<sub>x</sub> crystals (0 < <i>x</i> ≤ 0.05) growing at 900 °C.
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