Marcasite precipitation from hydrothermal solutions

摘要: Pyrite and marcasite were precipitated by both slow addition of aqueous Fe2+ SiO32− to an H2S solution mixing Na2S4 solutions at 75°C. H2S2 or HS2− H2S4 HS4− formed in the S2O32− experiments, respectively. Marcasite pH < pK1 polysulfide species present (for H2S2, = 5.0; for H2S4, 3.8 25°C). forms when neutral sulfane is dominant polysulfide, whereas pyrite mono-or divalent polysulfides are dominant. In natural where HS2 likely be polysulfides, will form only below 5 all temperatures. The pH-dependent precipitation may caused electrostatic interactions between growth surfaces: protonated ends repelled from sites but not sites. The negative ions S22− strongly attracted positive Masking 1πg* electrons S2 group protons makes isoelectronic with AsS2− As22−, respectively (Tossellet al., 1981). Thus, loellingitederivative structure (marcasite) results protonated. Marcasite occurs abundantly conditions was near site deposition either partial oxidation O2 reaction higher state sulfur that reactive formation e.g., SO42−. temperature as high 240°C (Hannington Scott, 1985), preservation on a multimillion-year scale seems require post-depositional temperatures about 160°C (Rising, 1973; McKibben Elders, 1985).