Dimensional stones in Uruguay: situation and perspectives

Potential for other Dimensional Stones 

Fuchsite bearing quarzites

The eastern margin of the Nico Perez Terrane is characterized by a lithological association of quarzites and ultramafic metamorphic rocks cropping out for around 200 km (Spoturno et al. 1986; Oyhantçabal & Vaz, 1990). The ultramafic rocks of this association are actinolitites and tremolitites with high Cr and Ni contents (~2000 ppm) suggesting the protoliths are pyroxenites and or peridotites. The accessory minerals of the associated quartzites are muscovite, sillimanite and fuchsite. When the latter is abundant the quartzites have light emerald green colour and may represent an interesting valuable stone.

Conglomerates

Strongly lithified paraconglomerates (Las Ventanas formation, Ediacaran, see location in Fig. 1) are associated with the molasses of the Dom Feliciano belt. The consolidation of these conglomerates is so strong that they usually crop out as rounded boulders similar to granitic rocks and could be apt for saw processing and manufacturing of floor tiles. The variability in colours (grey, reddish, green, etc.) of the rounded pebbles composed of granite, marble, phyllite, rhyolite, etc, makes these conglomerates represent an interesting potential dimensional stone.

Anorthosites

Several mafic intrusions have been identified in the Paleoproterozoic Piedra Alta Terrane. Besides the interest for black stones, some of these plutons contain anorthosite levels that could represent prospects for light coloured (near white) dimensional stones.

Conclusions 

Although small and without long tradition in mining, Uruguay has a complex geology including Archean to Neoproterozoic crystalline rocks belonging to different terranes. This diverse geology offers an assorted variety of dimensional stones. In some cases (granites and marbles) mining has a history of more than a century of supplying natural stones for the metropolis of Buenos Aires and in smaller amounts to Montevideo. The country has also delivered dimensional stones to Europe and Japan during the last decades. An extraordinary case is the black dolerite of Uruguay representing the most valuable black stone of the world. The demand for these dolerites exceeds the supply possibilities, the scarcity of evaluated reserves due to the lack of exploration and mining know-how is the limiting factor for an adequate production. Phyllites and some potential dimensional stones like fuchsite bearing quartzites and conglomerates allow evaluating a promising future for the dimensional stones of Uruguay.