Marcasite precipitation from hydrothermal solutions

Geochemical implications of subaqueous molten sulfur at Yugama crater lake, Kusatsu-Shirane volcano, Japan.

“…It must be, however, very small in quantity, if any exists. According to Murowchick and Barnes (1986), and Shoonen and Barnes (1991), pyrite is the pre dominant precipitate at pH > 5 whereas marcasite exclusively precipitates from more acidic solutions at temperatures less than 150°C. The pH depen dence of marcasite-pyrite precipitation is strongly related to protonation of polysulfide ions, Sx2 (Murowchick and Barnes, 1986).…”

“…As will be discussed later, molten sulfur from crater lakes dissolves sulfanes (H2SX; x >_ 2) which preferentially precipitate marcasite (Murowchick and Barnes, 1986). In addition, reactions between H2S and SO2 gases in acidic brines at the upper part of the subfloor vent system form polythionates (cf., Komoda, 1987;Maekawa, 1991), which also accelerate the conversion of amorphous iron monosulfide to marcasite (Shoonen and Barnes, 1991).…”

Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites

“…which eventually leads to formation of the thermodynamically favored iron disulfide, pyrite (Rickard and Luther, 1997) or perhaps marcasite if pH is low enough (<~6, Reynolds and Goldhaber, 1983;Murowchick and Barnes, 1986). Thus, the bacteria mediate the geochemical reactions that lead to uranium mineral precipitation and changes in iron mineralogy.…”

Volcanogenic uranium deposits: Geology, geochemical processes, and criteria for resource assessment

“…Some of the best concepts come from some elegant geochemical studies of sandstone-type uranium deposits (Granger and Warren, 1969;Reynolds and Goldhaber, 1983;Goldhaber and others, 1990). Based on experiments on the stability of marcasite (hexagonal FeS 2 ; Murowchick and Barnes, 1986;Schoonen and Barnes, 1991) and metastable sulfur species (Goldhaber, 1983), reduction of uranium by reaction with sulfur should be viable to about 200ºC, which should suffice for many volcanogenic uranium environments. Formation of marcasite infers acidic conditions (below pH 4.5), which may have implications for destabilizing U-complexes, such as bicarbonate-U.…”