Dimensional stones in Uruguay: situation and perspectives

*(a) Depto. de Geología, Facultad de Ciencias Universidad de la República, Iguá 4225. (11400) Montevideo, Uruguay. E-mail: oyhantca@fcien.edu.uy - Tel: ++598 2 525 86 19. Fax: ++598 2  525 86 17

(b) Geoscience Centre of the University of Gottingen, University Göttingen, 37077 Göttingen, Goldschmidtstr. 3, Germany. E-mail: ssieges@gwdg.de - Tel: +49 +551 39-7929. Fax: +49 +551 39-9700

(c) Natursteininformationsbüro E-mail: Natursteinarchitektur@t-online.de 

Uruguay is a small country in South America (176215 km2) located between Brazil and Argentina and is part of the South American Platform. Its geology is quite diverse and consists of a Precambrian basement cropping out in the south (45%), and Paleozoic to Mesozoic sediments and basaltic flows that are part of the Paraná Basin in the north. This diverse geology offers an assorted variety of dimensional stones. Granites and marbles have a mining history of more than a century producing stones mainly for the regional market. An outstanding case is the black dolerite of Uruguay representing the most valuable black stone of the world with great demand in the international market and prices over 1000 US$/m3. The mentioned resources together with phyllites and some interesting potential dimensional stones like fuchsite bearing quartzites and conglomerates allow evaluating a promising future for the dimensional stone sector of Uruguay. Scarcity of evaluated reserves due to the lack of exploration and mining know-how is the main factor limiting the development of the production.

Introduction 

With a population of 3 millions inhabitants, traditionally agriculture is the main economic activity. The country is highly dependant on the stability of the economy of the neighbouring countries. The regional recession of 1999 and 2002 affected seriously the economy but a gradual recovery is observed since 2003 and the GDP had increased at rates of ca. 6% during 2005 and 2006. Uruguay is a party state of the MERCOSUR agreement, a commercial union with Argentina, Brazil and Paraguay allowing free access to a market made up of 200 million inhabitants. The communications network of medium to high quality pavement is dense and the land has an electrification rate of ca. 95%, therefore opening of new mines should is not problematically.

The country does not have an important mining tradition; the mining sector represents less than 1% of the GDP but in spite of this small incidence, mining of raw materials for the growing metropolis of Buenos Aires during the 20th century represented a flourishing activity during several decades. Marbles, granites and slates were the main rock types mined as dimensional stones, but crushed rock and paving stones were also important products. The oscillations mentioned in the regional economy together with the lack of knowledge about the resources led to the decay of the sector and most of the quarries are currently closed.

Several reviews have considered the situation of the non metallic mineral resources of Uruguay (Bossi, 1978; Coronel, et al., 1987; Oyhantçabal et al., 2000), but published information about the dimensional stones of Uruguay is scarce (Medina, 1990; Bossi and Campal, 1991; Carmignani et al., 1998; Oyhantçabal et al. 2006). An updated revision of the situation and the potential of the dimensional stones sector of Uruguay is presented in this contribution.

Socio-economic importance of the dimensional stones in Uruguay 

The mining activity of Uruguay is based on the exploitation of raw materials for the construction industry, dimensional stones, gold, agate, amethyst, and some industrial minerals like limestone clay for the cement and ceramics industries.

Mining production values ranges between 20 and 50 M dollars (21 M dollars for 2005) and account for around 0.2-0.5% of the GDP. Mining of gold is increasingly important representing in the 2005 ca. 20% of the sector. The sector employs around 2000 workers representing ca. 0.1% of the active population. Export amount average of around 5 Mio dollars per year signifies ca. 0.2% of the total exportations of the country. Gold, dimensional stones (granites), amethyst, agate and sand are the main export commodities. Production data for the period 1997–2005 are presented in Table 1. The impact in the production of dimensional stones of the regional crisis of 1999-2002 is evident as well as a gradual recovery since 2003. The significance of black dolerites in the total production of dimensional stones of Uruguay is also noticeable.

Legal framework 

Mining activity is regulated by law number 15242 (Mining code of 1982) being the Dirección Nacional de Minería y Geología (DINAMIGE) the State agency responsible for the control of the mining activity. The State is the owner of all mineral resources and grants titles to carry out mining activities by private companies. Three different titles are considered in the code: the Prospecting License (up to 3 years), the Exploration License (up to 3 years) and the Concession to exploit (up to 45 years). An environmental authorisation is a pre-requisite before starting of the mining activities.

Overview of the geology of Uruguay

Uruguay is part of the South American Platform and its geology consists of a Precambrian basement cropping out in the south, and Palaeozoic to Mesozoic sediments and basaltic flows that are part of the Paraná Basin in the north (Fig. 1). Two Mesozoic rift basins related to the opening of the Atlantic Ocean are located in the south (Santa Lucía Basin) and east (Laguna Merín Basin).

The Precambrian basement extends over nearly 45% of the country. A first division, proposed by Ferrando & Fernandez (1971), differentiate Paleoproterozoic rocks in the south-west (Transamazonian Cycle: 2.2 - 1.8 Ga), and Neoproterozoic rocks in the east (Brasiliano Cycle: 900 - 550 Ma). Using a plate tectonic approach, Fragoso-Cesar (1980) defined the Río de La Plata Craton in the West (Paleoproterozoic) and the Dom Feliciano Mobile Belt in the East (Neoproterozoic). Recently a tectonostratigraphical terrane approach (Bossi et al. 1993; Basei et al. 2000) has been used to define different terranes in the pre-Brasilano Basement, the Paleoproterozoic Piedra Alta Terrane in the west, the Nico Pérez Terrane in the centre, and the Punta del Este Terrane in the east.