Showing papers by "Central Geological Survey, MOEA published in 2003"

Hydrothermal alteration of andesite in acid solutions: Experimental study in 0.05 M H2SO4 solution at 110 °C

Abstract: The experimental results indicate that the plagioclase and pyroxenes in the treated samples show micropits and microfractures. Small crystals readily suffered from alteration, as compared with large ones, and the susceptibility of the minerals to the acid solution is decreased in the order of plagioclase, augite, hypersthene and opaque minerals. Plagioclase, which is the most reactive mineral in the experiments, shows an increase of SiO2, but a decrease of Al2O3, CaO and Na2O as the experiments proceeded. The chemical change of the treated andesite, it indicates that the relative amounts of SiO2 ,T iO2, MgO,FeO, MnO and K2O increase, while those of Al2O3, CaO, Na2O and P2O5decrease with an increase of the experimental duration. The relative mobility of chemical elements listed in decreasing order is P, Ca, Al, Na, Si, K, Mg, Fe, Mn and Ti in terms of the Kv alue. It is no wonder that Ca, Al and Na are more mobile than others because these el- ements are readily released into solution from the more reactive plagioclase, while Mg, Fe etc. still stay in the less reactive pyroxenes and opaque minerals.