Mineralogische, Petrophysikalische und ökonomische Charakterisierung der Natursteine Uruguays; Implikationen für die Lagerstätteerkundung

Natursteine werden seit dem Altertum als wertvolle mineralische Ressource geschätzt und dienten seitdem zur Errichtung der herausragendsten architektonischen wie künstlerischen Werke, die lange Zeiträume, teilweise Jahrtausende, überdauert haben. Bekannte Beispiele hierfür sind die Pyramiden Ägyptens und die Aphrodite von Milo in Griechenland. Die Wertschätzung als hervorragendes Baumaterial hat auch heute noch Gültigkeit dank ihrer Festigkeit, ihres Farbspektrums und Dekors, sowie ihrer Verwitterungsresistenz. In Uruguay werden vielfältige Typen von Natursteinen gefördert, vermarktet und verwendet. Dolerite von höchster Qualität (kommerziell als schwarze Granite bezeichnet) sind die bedeutendsten und werden deshalb in dieser Studie eingehend untersucht. Ebenso werden die wichtigsten Varietäten von grauen und farbigen Graniten (lithologisch: Granitoide und Synenitoide) hier betrachtet. Auch die dolomitischen Schiefer wurden in die Studie einbezogen, da es sich bei ihnen um einen traditionellen Werkstein aus Uruguay handelt. Die häufigste Verwendung finden Natursteine aus Uruguay als Fassadenverkleidung, Arbeitsplatten und Bodenfliesen im Außen- wie Innenbereich. Die Dolerite können aufgrund ihrer exzellenten petrophysikalischen Eigenschaften auch für spezielle Sonderverwendungen wie Präzisionstische oder lastabtragende Bauteile benutzt werden. Die vorliegende Forschungsarbeit soll helfen die bestehende Lücke an wissenschaftlichen Untersuchungen für diese wichtige mineralische Ressource zu schließen. Das Hauptaugenmerk richtet sich auf die petrographische, petrologische und lagerstättenkundliche Charakterisierung, ferner auf die ökonomischen Aspekte des Natursteinpotentials von Uruguay

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

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

Dolomitic slates from Uruguay: petrophysical and petromechanical characterization and deposit evaluation

Slates are internationally known as roof and façade-cladding material since prehistoric times. The methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones. This has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes. In Uruguay several slates are mined and used in architecture, especially as façade cladding and floor slabs. The most important slates regarding their production and utilization are the dolomitic slates. These dolomitic slates are associated with the Neoproterozoic thrust and fold belt of the Dom Feliciano belt. Representative samples have been geochemically and petrographically characterized, as well as petrophysically and petromechanically analyzed. The petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new European standards, showing values comparable to those registered for internationally known slates. Detailed structural and deposit analysis were carried out in Uruguay in order to evaluate the dolomitic slate deposits. The slates are linked to calc-silicate strata in a greenschist facies volcano-sedimentary sequence and the deposits are located in the limb of a regional fold, where bedding and cleavage are parallel. The main lithotype is a layered and fine-grained dolomitic slate with a quite diverse palette of colors: light and dark green, gray, dark gray, reddish and black. The mined slate is split into slabs 0.5–2 cm thick. In the past, the average production in Uruguay was around 4,000 tons/year and a historical maximum of 13,000 tons was reached in 1993 (Oyhantçabal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity, but our investigation shows a considerable volume of indicated resources and therefore a very good potential

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

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 façade 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 décor 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 décor) and the possible reserves were calculated