Influence of fracture system on the exploitation of building stones: the case of the Mondim de Basto granite (north Portugal)

Abstract

The most negative aspects in the exploitation of weathered granites as ornamental stones tend to be heterogenic coloration and fracturing. Therefore, an accurate study is needed for a comprehensive evaluation of the granite resources during an exploration campaign. This paper presents the results of the fracturing evaluation of a region located in north of Portugal, where the Mondim de Basto granite, a stone with a high weathering degree, is exploited. The regional fracturing was evaluated from lineaments in aerial photos and then compared with local jointing in quarries. The jointing in each quarry is characterized according to the strike and dip, joint spacing and volumetric joint count. Two indices were proposed to facilitate the jointing comparison among quarries: the joint space length (Ljs) and joint set spacing (Sjs). Ljs is based on the sum of all the spacing values obtained perpendicularly to the strike direction. Sjs is computed based on the overall mean/median spacing and on the number of joint sets observed in each quarry. The most important joint sets in the subdivision of the rock mass were found not to be in accordance with the regional fracturing patterns, highlighting the necessity of studying the fracturing at all scales.