Se-rich tennantite and constraints on p-T-X conditions of selenide mineral formation in the Schlema-Alberoda uranium ore district (western Erzgebirge, Germany)
Förster, H.-J.; Tischendorf, G.
published: Jun 22, 2001
ArtNo. ESP154017602002, Price: 29.00 €
Selenide minerals from the Schlema-Alberoda uranium ore district formed principally during the Jurassic redeposition of the primary pitchblende of Permian age. The selenide assemblage is complex but in general resembles that observed in U deposits of the same type. Geologic observations, mineral stabilities, and thermodynamic calculations suggest the following p-T-X conditions for the main selenide stage at Schlema-Alberoda: 50-100 MPa, 100-150 °C, -55 < fo2< -50, -12< fse2< -15, -26< fs21. Volatile fugacity estimates refer to a temperature of 100 °C and may have changed slightly during the final stage of selenide mineral precipitation. The most interesting mineralogical observation includes zincian tennantite crystals containing up to 14 wt. % Se (corresponding to 2.85 apfu), which represent the most Se-rich members of the fahlore family of minerals known to date. Presence of variable amounts of S in some of the selenides as well as Se in the accompanying sulfides should encourage the measurement of both elements in selenides and sulfides routinely during microprobe analyses, to avoid calculation of inaccurate mineral formulae and to have a better understanding of the geochemistry of Se and S during selenium ore formation.