Biologically induced iron ore at Gunma iron mine, Japan

Abstract

The mineralogy of sedimentary iron ores from the Gunma iron mine are described to evaluate the role of microorganisms and plants in ore formation. The iron ore is composed of nanocrystalline goethite, well-crystallized jarosite and very small amounts of strengite. The ore characteristically occurs as thick-bands of alternating goethite and jarosite bands, thin-bands of different goethite grain sizes, and fossil-aggregate ore rich in moss and/or leaves. Algal fossils are clearly preserved in the goethite bands in the thick-banded ore. Lattice imaging showed characteristic crystallographic orientations of the goethite nanocrystals. The thin-banded iron ores consist of micrometer-sized chestnut-burr-like goethite aggregates, probably formed by bacterial iron biomineralization. The bands may be attributed to biological or seasonal rhythms. Various products of biomineralization are found in the present-day pH 2-3, Fe 2ϩ -, and SO -rich streams. Bacterial precipitation had var-2Ϫ 4 iations from amorphous Fe-P-(S) precipitates near the outlet of mineral spring to Fe-P-S precipitates and to Fe-S-(P) (schwertmannite-like) precipitates in the midstream. Mosses and green algae are also collecting Fe precipitates in and around the living and dead cells. Comparison of the processes occurring in the present-day streams and the iron-ore specimens supports the interpretation of these ores as the product of biomineralization.

Microbial biomineralization of iron seepage water: Implication for the iron ores formation in intertidal zone of Zhoushan Archipelago, East China Sea

“…BIM processes are characterized by the precipitation on and within cells and the mineral grains have no controlled morphology and size distribution (Akai et al, 1999). The results described above suggest that the iron ores might have resulted from BIM processes.…”

“…Many studies have suggested that minerals forming as a result of microbial activity could present special structures, such as spherical aggregates of different sizes Fortin et al, 1998;Akai et al, 1999;Tazaki, 2000Tazaki, , 2005Williams et al, 2005). The TEM-EDS-SAED pictures of the iron ores showed many fibrous or spherical aggregates of goethite or ferrihydrite, respectively (Figs.…”

“…The formation of iron minerals is generally mediated by the activity of microorganisms, usually bacteria (Ferris et al, 1988;Ghiorse and Ehrlich, 1992;Mann et al, 1992;Akai et al, 1999;Brown et al, 1999;Tazaki, 2000;Ueshima and Tazaki, 2001;Tazaki, 2005), and the bacterial activity may leave some obvious imprints in the ancient minerals. found some fossilized remains of both filamentous and coccoid microoganisms in a stromatolitic grey chert with 2.0 Ga years old from Gunflint Iron Formation, and suggested iron mineral formation was associated with bacteria in the chert.…”

Unique Geochemistry of Sedimentary Iron Deposit Formed by Biologically Induced Mineralization

“…It is likely that the Gunma deposit was formed from one of these acidic spring waters. It is considered that the spring water responsible for the ore deposit was probably ferruginous, cold (less than 30°C), and acidic (pH=2-4) (Shiikawa, 1960;Akai et al, 1999). The iron deposit precipitated on the Pleistocene andesitic lava flows and pyroclastic rocks.…”

“…Among these deposits, the Gunma deposit is the largest sedimentary iron deposit in Japan. A mineralogical study by scanning electron microscopy, X-ray electron microprobe, and transmission electron microscopy was done recently for the deposit and the iron ore was interpreted as a product of biologically induced mineralization (BIM) (Akai et al, 1999).…”