Alterations in Granodiorite through Experimental Chemical Weathering for a Long Time

Abstract

This study attempts to analyze some initial stages of chemical weathering process by artificially weathering granodiorite of the Paleogene in Akagi-cho, Iishi-gun, Shimane-ken.
In order to conduct the experiment under the condition that will reflect the real surface of the earth as much as possible, we first mixed distilled water with carbon dioxide and with air and then devised a flow system equipment that enables the treated solution to circulate while reacting to the ore. After setting the tempreture of the treated solution at 22°C±2°C, pH4.2-4.4, we continued this experiment for one year at the interval of five-day operation and two-day out of operation. The results of this experiment are as follows.
1. Biotite showed the sharpest reaction: K ion of interlayer was dissolved and decreased. Fe, Mg, Mn ions were gradually removed out of octahedral sheet, while Al ion was added to.
2. The pieces of biotite that were extricated from the rock accepts Ca ion and then changes into nonswelling vermiculite after its K ion of interlayer was partly dissolved.
3. Plasioclase showed the second sharpest reaction: the areas that are rich in Caion and contain inherent fractures or altered minerals were selectively dissolved and disappeared.
4. Altered minerals such as chlorite, apatite, calcite showed a sharp reaction toward the treated solution and influenced greatly the quantity of dissolved ions at the initial stage of weathering process.
5. The dissolved constituents formed a thin film on the rocks and its main ingredients were Al, Si ions. The varieties and the amounts of components were influenced by the dissolved components of the minerals and differed, depending on where the thin film is on the rock.