『Abstract
　Fresh and weathered granite from drill cores in Tono, Gifu, Japan, was examined to understand weathering products and the mechanisms of chlorite and biotite weathering under low PO2 conditions. A fresh sample from 365m depth, a slightly weathered light-green sample from 367 m depth, and a nearly fresh sample from 369 m depth (but with brown stains on fractures), were investigated. The XRD, SEM, EMPA, and TEM analysis of green grains present within chlorite, biotite, and plagioclase grains and in veins was found to be Fe²⁺-rich corrensite [about 40 wt％ FeO with Fe/(Fe+Mg)=0.94]. The corrensite is interpreted to have formed from chlorite and biotite via a dissolution-precipitation mechanism. The ＜2 μm fraction of the weathered sample had an Fe²⁺/ΣFe value of 0.69, which, when combined with the presence of amorphous Fe³⁺(hydr)oxides confirmed by TEM, indicates that the Fe²⁺/ΣFe value of corrensite is ＞0.69. These results indicate that on dissolution of chlorite and biotite, Fe²⁺ was transported as Fe²⁺ and precipitated as Fe²⁺-rich corrensite and a part of the dissolved Fe²⁺ was oxidized to amorphous Fe³⁺ (hydr)oxides under low PO2 conditions. The formation of Fe²⁺-rich corrensite and that of Fe²⁺-rich smectite or vermiculite in the laboratory at 1 atm of PCO2 and ≦3×10^-5 atm of PO2 (Murakami et al. 2004) suggest that a possible Fe²⁺-bearing product during Precambrian weathering is Fe²⁺-rich sheet silicates but not siderite.

Keywords: weathering; corrensite; Fe behavior; low O2; atmospheric evolution; granite; TEM』

Introduction
Experimental methods
　Samples
　Analytical methods
Results
Discussion
Timing and mechanism of corrensite formation
Amorphos Fe³⁺ hydroxides and conditions of coexistence of Fe-minerals
Weathering processes under low PO2 conditions
Fe behavior under low PO2 conditions
Implication for Precambrian atmosphere
Acknowledgments
References cited