Abstract
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)cub is a homogeneous solid solution with a unit cell smaller than in ZnScub as a result of S2− → O2− substitution (a = 5.40852(12) Å, V = 158.211(6) Å3). The amount of lattice-bound oxygen in the CM sphalerite is within the range for synthetic ZnS1−xOx crystals (0 < x ≤ 0.05) growing at 900 °C.
Highlights
Various aspects of sphalerite geochemistry have received much attention in the literature ([1]and references therein)
This study focuses on high-temperature (800–850 ◦ C) spurrite-fluorapatite combustion metamorphic (CM) marbles from a site in central Jordan locally known as Tulul al Hammam
60 Zn-enriched marble samples from the alTulul showed that approximately one sample per contains different percentages of sphalerite and/or quarries showed that approximately one sample per 10 contains different percentages of sphalerite (Cd,Zn)(S,Se) solid solutions, besides predominant oxygen-bearing primary and secondary minerals
Summary
Various aspects of sphalerite geochemistry have received much attention in the literature ([1]and references therein). The compositions of sulfides may be interesting in terms of impurities and new mineral species: P-T changes and mineral growth in prograde reactions may be responsible for extremely high contents of impurities and rare minerals in high-grade metamorphic assemblages. Under these conditions, sulfides, unlike other rock-forming and accessory minerals, can accommodate chalcophile minor (Cu, Ni, Co, Zn, As) and trace (Cd, Hg, Tl, Sb, Se, Te, Pb, Mo, Bi, Ag, Re) elements. Oxides name of varicolored marbles bear diverse Zn mineralization together with various Ca-U(VI) oxides and [18,19,20,22].
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