Porosity Structures and Capillary Migration in Granites and Limestones Carlos Alves 1 , Carlos Figueiredo 2 , António Maurício 2 and Luís Aires-Barros 2 1. CIG-R, Earth Sciences Department, School of Sciences, University of Minho, Campus de Gualtar, Braga, Portugal 2. Centro de Petrologia e Geoquímica (CEPGIST)/ Centro de Recursos Naturais e Ambiente (CERENA), Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, Lisbon, Portugal Capillary flow is a main process for fluid migration in unsaturated media, being relevant for the study of pollutants and other solutes migration (e.g. salt weathering of stones) and petroleum reservoirs. To characterize the kinetics of the capillary migration (see [1]), two coefficients related to the square root of time can be defined: mass increase per unit area (C w ) and height of rising fringe (C h ). Values of C w can be measured more objectively (with a scale) but are dependent on the porosity of the material accessible by capillarity (all other things being equal, increasing porosity in the capillary range implies higher absorbed mass). For an ideal pore network and water density = 1.00 g/cm 3 , it can be shown (see [1]) that C h = C w x 100/N c (%), where N c (%) represents porosity accessible by capillarity. Porosity after 48 hours immersion under atmospheric pressure (N 48 ) will be considered here as estimator of porosity accessible by capillarity. The coefficient C w x100/N 48 (%) will be used as a parameter for evaluation of capillary migration, represented by C heq (equivalent height of the capillary zone). In this regard, optical and electron microscopy studies have the advantage, in relation to mercury porosimetry or BET, of allowing to relate pore structures to petrographic features, linking the observed macroscopic properties with geological processes and, therefore, the history of the rocks, as well. This research considers two granites and three limestone types from Portugal. The granites (details in [2]) are the Braga granite (biotitic, fine to medium-grained, porphyric) and the Gondizalves granite (two mica, medium-grained). The limestones are two grainstones (commercially designated as Semi-rijo and Moca Creme; details in [3]) and a travertine (details in [4]). Results of the macroscopic tests for C h , C heq and N 48 are presented in Figure 1. Figure 1a shows that, in the specimens where it was possible to assess also C h directly, there is, generally, a good correlation with C heq , with the exception of the travertine specimens. The plot of C heq against N 48 (Figure 1b) shows that the relation of capillary kinetics with porosity depends on the rock type, a feature that can be discussed considering the porosity structures evaluated by optical and scanning electron microscopy. The two granites present clear differences in relation to porosity structures (see a detailed discussion in [2]). Studies by optical microscopy and scanning electron microscopy allow relating the results of porosity and capillarity tests to petrographic features. Braga granite fresh samples show pores inside plagioclase and very thin intra and intercrystal fissures while more weathered samples (Figure 1c) show the development of a network of trans, inter and intragranular (e.g. along cleavage planes of biotite) fissures, as well as a marked development of the porosity inside plagioclase sections (Figure 1c). In the Gondizalves granite, the pore network is mainly related to well-linked fissures that can traverse several sections. The comparison of pore structures explains why Gondizalves granite samples present C heq values similar to the more porous samples of Braga granite. The grainstones (limestones) present clearly lower values of C h and C heq than the granites, in spite of their higher porosity. This is explained by scanning electron microscopic observations showing (Figure 1d) porous micrite aggregates cemented by sparite with thin fissures (affecting the kinetic of capillary migration). Travertine presents the wider dispersion of results and a clear divergence between the direct measurements of C h and the C heq estimations. Travertine results can be attributed to the marked heterogeneity of this rock [4] implying that capillary migration occurs preferentially along some portions of the specimens. Acknowledgements presented in [5]. Microsc. Microanal. 21 (Suppl 5), 2015 © Microscopy Society of America 2015 3 doi:10.1017/S1431927615013823