Distribution of selenium in high-temperature hydrothermal sulfide deposits at 13 degrees North, East Pacific Rise

摘要: "Black smoker" chimneys and Fe-Cu-rich massive sulfides are found on the axial graben off-axis seamounts, respectively, of East Pacific Rise at l3oN. The trace element selenium substitutes for sulfur in solid solution all sulfide minerals. Electron-microprobe analyses were performed under optimal conditions to obtain a minimum detection-limit (MDL) 30 ppm chalcoplrite, with calculated precision ppm. Se content depends physicochemical parameters ore solutions during precipitation. High values occur high-temperature mineral assemblages. highest contents chalcopyrite ( 2500 ppm) euhedral pyrite (= 1500 ppm). For selected samples, lowest mean concentration is 645 These minerals precipitate middle part deposit, equilibrium unmixed hydrothermal waters. On active vents, inferred characteristics fluid are: /(O, 10-35 atm, pH 3-4, /(S, 10-10 T 335oC. outer deposits, where mixi-ng pure waters seawater [/(O) lO-'s 7.8, 2'Cl maximum. S/Se value good agreement that expected or volcanic ores, but range much wider (250 >50,000) This wide variation overlaps S,/Se considered characteristic sedimentary environments, respectively. overlap suggests reconsideration previous inferences made thce deoosits basis value.