FORMATION OF MAGNETITE AND SIDERITE BY THERMOPHILIC FE(III)-REDUCING BACTERIA

Abstract

Possible participation of thermophilic Fe(III)-reducing microorganisms in the formation of Precambrian banded iron formations has been studied using the actualistic approach. The laboratory experiments suggest that the formation of biogenic magnetite or siderite depends on the physical and chemical parameters of the medium. Magnetite is formed under low partial CO2 pressure, excess of amorphous iron hydroxide, and absence of organic colloids. Siderite is formed under high CO 2 partial pressure, limited iron hydroxide, and in the presence of such organic gels as agar, sheaths of iron bacteria, or organic reducing compounds.