Portuguese ornamental limestones

1. INTRODUCTION
This article talks about the main ornamental limestone producing areas in Portugal. This is not an exhaustive study, but will present the current geological understanding of each of the areas and the fundamental features of the raw materials quarried in them. The regions included here are the Serra de Sicó, Maciço Calcário Estremenho, the region North of Lisbon – Pêro Pinheiro and the Algarve Basin. In all of these regions the limestones quarried for ornamental purposes date from the Mesozoic era. Two distinct zones near Coimbra are also mentioned, one to the north where carbonated rocks from the Mesozoic era occur, and the other to the south where they are of Quaternary age.

Easy quarrying of most Portuguese limestones, plentiful reserves, the size of blocks quarried and their considerable homogeneity in terms of texture and colour, combine to provide a good quality supply at attractive prices, encouraging a high market demand for these stones.

2. LOCATION AND GENERAL FEATURES OF THE MAIN PRODUCING AREAS

2.1. SERRA DE SICÓ
The Serra de Sicó lies in the centre of Portugal between the cities of Tomar and Coimbra. This range of hills is composed mainly of carbonated rocks from the Jurassic era and covers an area of approximately 700 km2. Contrary to the regions described below, in the Serra de Sicó area the quarrying of ornamental limestones is currently sporadic and restricted to the vicinities of Ansião, where the Rosado de Ansião variety is likely to be extracted. However, recent lithostratigraphic studies suggest this region has a high potential for ornamental limestone production.

2.2. MACIÇO CALCÁRIO ESTREMENHO
Together with the region of Évora, where marble is quarried, the Maciço Calcário Estremenho (MCE) shares the leading position in the production of ornamental stones in Portugal. It produced a total of 630,000 tonnes in 1998 (IGM, 2000). The Massif covers an area of 900 km2 in the centre of the country, around 100 km to the north of Lisbon. A large part falls within the Nature Reserve of the Serras de Aire and Candeeiros, one of the entities responsible for planning the mining industry in this region of the country. This Massif is made up of a thick sequence of Mesozoic carbonated rocks which are structurally elevated. Its lithostratigraphy is well known. The productive units of the main ornamental varieties date from Middle-Jurassic, more specifically from the Bathonian and Callovian periods. There are 5 main centres in the Maciço Calcário Estremenho where quarrying is carried out: Pé da Pedreira, Moleanos, Codaçal, Fátima and Alvados.

2.2.1. Pé da Pedreira
Pé da Pedreira, covering around 10 km2, is the main ornamental limestone quarrying centre in Portugal. Moca Creme is the name given to the most common ornamental variety in this region, and it is used mainly for indoor and outdoor facings. Detailed geological studies done in this area by the Instituto Geológico e Mineiro estimate that ornamental limestone potential is around 40 x 106 tonnes (Carvalho, J., 1997). Two other less important quarrying centres, but geologically related to Pé da Pedreira, are Cabeça Veada and Salgueiras (Arrimal). The ornamental varieties found there are known as Semi-Rijo of Cabeça Veada and Semi-Rijo Arrimal, and their uses are similar to those of Moca Creme. Detailed geological studies were done in the Cabeça Veada area and the estimated potential is around 10 x 106 tonnes (Quartau, R., 1998).

2.2.2. Codaçal
Quarrying in Codaçal is restricted to a small area close to the township of the same name. The ornamental limestones from the area are marketed under the name Semi-Rijo Codaçal. They are fairly homogenous and ideal for large sized slabs. The importance of this region for the quarrying industry has been increasing considerably in recent years, because of its potential resources (around 5 x 106 tonnes), the large sized blocks quarried and the very pale colour of the rocks. In addition, although current quarrying is restricted to one particular area, the productive unit stretches over a large area of the Maciço Calcário Estremenho, which gives it enormous potential (Quartau, R., 2000). Within this geological unit there is a small nucleus of quarries at the township of Espinheiro. There the variety Brecha de Santo António is quarried, much used in items of furniture and facings. This is a greyish-brown stone with gold patches, the result of epigenetic phenomena (dolomitization) on limestones in the Codaçal unit.

2.2.3. Moleanos
In the Moleanos area, located on the western edge of the Serra dos Candeeiros, beside National Road 1, the ornamental variety Vidraço de Moleanos is quarried, the best known of the many other types of stone in this area. These are stones with excellent properties for use in works in a wide variety of situations. Although the geologic productive unit of Moleanos – Moleanos Formation – extends widely in the MCE, quarrying is confined to only a small area of around 1 km2 close to the township of Moleanos. This area was the object of a detailed geological survey which estimated its potentials at around 3.75 million tonnes of limestone with good ornamental qualities (Carvalho, J., 1996). However, there are problems due to proximity to the township. The global survey of the whole Moleanos Formation will no doubt suggest an increase in resources and will outline favourable areas in locations where the environmental impact will be less, providing quarrying regulations are correctly pre-defined, and these may even include underground mining. These surveys could also lead to reactivating old quarries such as the ones near the town of Ataíja, where Vidraço de Ataíja was exploited.

Author: Jorge Carvalho, Giuseppe Manuppella and A. Casal Moura (Geologists of the Instituto Geológico e Mineiro – Portugal)
Source: Rochas & Equipamentos