A detailed analysis of mineral specific porosity : the Charroux-Civray porphyritic granite.

Different experimental methods and image analysis process are performed to study porosity in the Charroux-Civray porphyritic granite. A first assessment of this parameter is given by water porosity. A second is given by autoradiography after impregnation of rock with labeled polymethylmethacrylate (PMMA). This film is a 2D-map of the spatial distribution of porosity. This map may also be used to calculate total or local porosity. The same granite surface used for the autoradiography is stained in order to separate four dominating primary mineral groups: quartz, Fe-Mg minerals (hornblende and biotite), K-feldspars and plagioclase. After digitizing, the petrographical and porosity map are superposed in order to describe the relationships between mineralogy and porosity at the centimeter scale. The results have been checked by Scanning Electron Microscopy (SEM) to study more specifically some zones of the granite (micrometer scale). Moreover, a statistical measure of apertures and density of the microcracks is presented.