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. Several alteration facies of fractured Lipnice granite arestudied in detail on borehole samples by means of mercury intrusion porosimetry,polarized and fluorescent light microscopy, and microprobe chemical analyses. The goal isto describe the granite void space geometry in the vicinity of fractures with alterationhalos and to link specific geometries with simply detectable parameters to facilitatequick estimation of porosity and permeability based on, for example, drill cuttings. Thecore of the study is the results of porosity and throat size distribution analyses on 21specimens representing unique combinations of fracture-related structures within sixdifferent alteration facies basically differing in secondary phyllosilicate chemistry andporosity structure. Based on a simple model to calculate permeability from the measuredporosities and throat size distributions, the difference in permeability between thefresh granite and the most fractured and altered granite is 5 orders of magnitude. Ourobservations suggest that the porosity, the size of connections and the proportion ofcrack porosity increase with fracture density, while precipitation of iron-rich infillsas well as of fine-grained secondary phyllosilicates acts in the opposite way. Differentstyles and intensities of such end-member agents shape the final void space geometry andimply various combinations of storage, transport and retardation capacity for specificstructures. This study also shows the possibility to use standard mercury intrusionporosimetry with advanced experimental settings and data treatment to distinguishimportant differences in void space geometry within a span of a few percent of porosity.

Granite microporosity changes due to fracturing and alteration: secondary mineral phases as proxies for porosity and permeability estimation