Black dimensional stones: geology, technical properties and deposit characterization of the dolerites from Uruguay

Abstract

Dimensional stones with a black color occupy a prominent place on the international market. Uruguayan dolerite dikes of andesitic and andesitic-basaltic composition are mined for commercial blocks of black dimensional stones. A total of 16 dikes of both compositions were studied and samples collected for geochemical and petrographical analysis. Color measurements were performed on different black dimensional stones in order to compare them with the Uruguayan dolerites. Samples of the two commercial varieties (Absolute Black and Moderate Black) were obtained for petrophysical analysis (e.g. density, porosity, uniaxial compressive strength, tensile strength, etc.). Detailed structural analyses were performed in several quarries. Geochemistry and petrography determines the intensity of the black color. The Uruguayan dolerite Absolute Black is the darkest black dimensional stone analyzed in this study. The petrophysical properties of Uruguayan dolerites make them one of the highest quality black dimensional stones. Structural analyses show that five joint sets have been recognized: two sub-vertical joints, one horizontal and two diagonal. These joint sets are one of the most important factors that control the deposits, since they control the block size distribution and the amount of waste material.

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

“…Some examples of detailed research in exotic granitic rocks include an investigation on the larvikites of Norway (Heldal et al 2008), on dolerites from Uruguay (Bossi and Campal 1991;Morales Demarco et al 2011), and on a granitic batholith in São Paulo, Brazil (Artur et al 2001).…”

“…In the RPC, a dolerite dike swarm crops out in an area of 20,000 km 2 (Bossi and Campal 1991;Morales Demarco et al 2011). The mined dolerite is commercialized as high quality black granite consisting of two varieties, based on the intensity of their black color: Absolute Black and Moderate Black (Fig.…”

“…The mined dolerite is commercialized as high quality black granite consisting of two varieties, based on the intensity of their black color: Absolute Black and Moderate Black (Fig. 7a, b; Coronel et al 1987;Bossi and Campal 1991;Morales Demarco et al 2011). Absolute Black is mined from dikes that have a fine-grained zone wide enough to produce marketable blocks.…”

“…The mafic rocks in this category all have a tholeitic affinity and their intrusion occurred in an extensional regime (Bossi and Campal 1991;Bossi and Schipilov 2007). The dolerites have been extensively studied by Bossi and Campal (1991) and Morales Demarco et al (2011). Bossi and Campal (1991) determined two geochemical and petrographic groups.…”

“…Bossi and Campal (1991) determined two geochemical and petrographic groups. The rocks of Group A are composed of plagioclase and lower amounts of augite, granophyric intergrowth, amphibole, and opaques; and are characterized by high TiO 2 contents and an andesitic composition (Bossi and Campal 1991;Morales Demarco et al 2011). Group B has a low TiO 2 content and an andesitic-basalt composition.…”