Granitic dimensional stones in Uruguay: evaluation and assessment of potential resources

Manuela Morales Demarco 0 1 2 Pedro Oyhantcabal 0 1 2 Karl-Jochen Stein 0 1 2 Siegfried Siegesmund 0 1 2 0 K.-J. Stein Natursteininformationsburo, Am Schulzensee 3, OT Waldsee, 17258 Feldberger Seenlandschaft, Germany 1 P. Oyhantcabal Departamento de Geologa , Facultad de Ciencias, Universidad de la Republica , Igua 4225, C.P. 11400 Montevideo, Uruguay 2 M. Morales Demarco (&) S. Siegesmund Geoscience Center of the Georg-August University Gottingen , Goldschmidtstrasse 7, 37077 Gottingen, Germany In Uruguay commercial granite varieties comprise mafic rocks, granitoids, and syenitoids. There is a long tradition in Uruguay, as well as worldwide, of using dimensional stones in architecture and art, specially granitic ones. Some of the present applications of these dimensional stones are as facade cladding, countertops, and outdoor and indoor floor slabs. The color spectrum of the Uruguayan granitic dimensional stones varies from black to light gray, covering a wide variety of red and pink and minor greenish-gray. The decor of these granitic dimensional stones is mainly determined by their fabric, fundamentally the grain size and the color distribution between the different minerals that compose the rocks. In the present research the most important commercial granites were sampled to analyze their petrography and petrophysical properties. A detailed structural analysis has been performed in several deposits, as well as the application of the software 3D Block Expert for modeling the possible raw block size distribution. Other factors controlling the mining viability of the deposits were also studied (e.g., homogeneity/heterogeneity of color and decor) and the possible reserves were calculated. - Terms and standards Granitic dimensional stones are widely used in architecture. Some examples include paving tiles, monuments, interior and exterior wall cladding (Montani 2008) (Figs. 1, 2). Its share of the market of dimensional stones has doubled in the period between 1995 and 2007 (Montani 2008). Due to their durability, granite represents one of the preferred natural materials when deterioration risk is present. Commercially, the term granite is used for dimensional stones consisting of all the hard rocks, even when their lithology strongly differs from that of true granite. In the Earth Sciences, the use is stricter and the name granite only applies to a plutonic rock containing quartz, alkali feldspar, and plagioclase. These rocks plot in a specific field defined by the QAPF classification triangle (Streckeisen 1976). Granitoid is a superordinate category designating a plutonic rock that has between 20 and 60 percent quartz in the QAPF classification (Streckeisen 1976; Le Maitre et al. 2002; Allaby and Allaby 1990; Jackson 1997). It includes the alkali feldspar granites, granites sensu stricto, granodiorites, and tonalites. Syenitoid is a term used for plutonic rocks with a quartz content ranging between 0 and 20 % and a feldspar ratio (alkali feldspar/plagioclase ? alkali feldspar) between 35 and 100 % (Streckeisen 1976; Le Maitre et al. 2002; Allaby and Allaby 1990; Jackson 1997). Gabbroids include all the plutonic rocks showing a feldspar Fig. 1 Uses of Uruguayan commercial granites in the city of Montevideo; a outdoor facade cladding using Moderate Black Dolerite and flooring slabs using Cufre Granite in the Antel Tower; b outdoor sculpture (Vizconde de Maua) using La Paz Granite; c outdoor facade cladding using polished and unpolished slabs of Violeta Imperial Syenite; d outdoor sculpture using Moskart Granite; e different sorts of outdoor flooring slabs using granite; and f outdoor socle and columns using Isla Mala Tonalite in the Central Train Station (Estacion Central AFE) Fig. 2 Global main uses of dimensional stones (in percentage) after Montani (2008) a global uses in 1995 (total finished production: 25 million tons); and b global uses in 2007 (61 million tons) ratio between 0 and 35 % and quartz contents between 0 and 20 % (Streckeisen 1976; Le Maitre et al. 2002; Allaby and Allaby 1990; Jackson 1997). Mafic rock is a term that includes gabbroids but also other igneous rocks (e.g., basalt) composed chiefly by mafic minerals (Jackson 1997). At the beginning of the 21st century, the European countries decided that dimensional rocks must be correctly named according to the petrological description and the standards of international geological terminology (e.g., DIN EN 12407, 2007; DIN EN 12670, 2000; DIN EN 12670, 2001). Outside Europe the American standards are normally used (e.g., ASTM C119 2011). These standards allow the naming of granite as granular igneous rocks, which includes granitoids, syenitoids, and mafic rocks (gabbros, dolerites), but also some granular metamorphic rocks such as gneisses and schists (Quick 2002). In Uruguay, what is commercially known as granite includes a wide variety of lithologies such as granitoids (granodiorite, tonalite, granite s.s.), syenitoids (quartz syenite, alkali feldspar syenite and quartz alkali feldspar syenite), and mafic rocks (gabbro-norite and dolerite) (Table 1). The colored commercial granites include syenitoids and granites s.s., whereas the gray granites comprise granites s.s., granodiorites and tonalites. The rocks that are commercially known as black granites are basically dolerites and gabbro-norites. The mining of dimensional stones in Uruguay began during the first settlements with the construction of fortifications and citadels between the end of the 17th and the beginning of the 18th centuries. Examples are the fortress of Santa Teresa, built from the porphyritic facies of the Santa Teresa Granite and the citadels of Colonia del Sacramento and Montevideo constructed from local granitic and metamorphic rocks. Since the beginning of the 20th century until today, commercial granites have been used for a wide variety of architectural and artistic purposes. The dimensional stone sector had a very important productive phase at the beginning of the 20th century. Syenitoids of the Pan de Azu car-Piriapolis area and granites of La Paz provided material for the construction of the most important cities of the region, especially for Montevideo and the neighboring city of Buenos Aires. The international trend of using commercial granites mainly for decorative purposes and not only for structural ones is a practice used by the architects and construction companies in Uruguay. Commercial granite is used in Uruguay for facade cladding, as paving tiles, for interior floor and wall cladding, countertops, stairs, columns, sculptures, monuments, and precision tables, among other applications (Fig. 1). The dimensional stone market is particularly sensitive to fashion trends and economic constrains. Beginning in the year 2000 the economic crisis in South America led to a severe decline in the construction industry, and thus, in the dimensional stone production. The world production of all types of dimensional s (...truncated)