Ultrahigh-Temperature Sphalerite from Zn-Cd-Se-Rich Combustion Metamorphic Marbles, Daba Complex, Central Jordan: Paragenesis, Chemistry, and Structure

Minerals of the Zn-Cd-S-Se system that formed by moderately reduced similar to 800-850 degrees 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 similar 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 similar to 14 wt% Cd and similar to 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) angstrom, V = 158.211(6) angstrom(3)). 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 degrees C.