Geoparque Mundial UNESCO

Nº03 – The Phosphorite Mine of la Constanza

Geoparque Villuercas > Nº03 – The Phosphorite Mine of la Constanza

LOCATION AND ACCESS

To access the mining facilities, take the road towards Cañamero and about 500 metres from the centre of Logrosán you will find the site that houses the two galleries of the Costanaza Mine . These can be visited as well as the main facilities, including the Phosphate Interpretation Centre (in the old laboratories) and the Black Room (the old powder magazine), as well as the Vicente Sos Baynat Geominero Museum.

There is a pass through which vehicles can enter the site, as well as a large car park.

ATTRACTIONS OF THE VISIT

The Costanaza Mine was mined intermittently from the end of the 19th century until the middle of the 20th century. When the mine closed in 1944, it was 210 metres deep and had 14 floors.

The set of parallel galleries that make up the mine, in which the Costanaza vein was exploited, giving it its name, is overwhelming, but only the two upper galleries are open to visitors.

Inside we can observe the mineralised phosphorite vein, breccia zones and fault planes, geodes, springs, stalactites, folds, mining support arches and a masonry master shaft.

Outside, we can see installations that still conserve the primitive mining structure in perfect condition, such as the fines factory, the “superfosfato” factory, the pyrite boiler and the mine laboratory, which houses the Phosphate Interpretation Centre.

A tour of the mine explains the details of mining and the method of extraction, known as the «de realce» method because the miners extracted the layers of the seam above their eyesight.

It also explains what the miners were like and their working conditions, the humidity, the very poor equipment, the lamps, initially pico-pata  lamps, and later fuel burners.

Some of these elements can be found decorating the walls of the mine.

You can take a virtual tour here. (Texts in Spanish)

GEOLOGICAL INTERPRETATION

Read Geological Interpretation

The acid magmas that originated the granitic stock of Logrosán, the San Cristóbal hill, caused large fractures as they slowly ascended through the pre-existing rocks (shales and greywackes) of the Ediacaran and other Paleozoic materials, nowadays dismantled by erosion.

The contact between the acid magmas and the Ediacaran bedded rocks, which contain abundant sedimentary calcium and fluorine phosphates, may have favoured the remobilisation and subsequent concentration of these in the seams that today constitute the mine. A fault filled with crystallised magmatic fluids forms a dike or lode when these fluids finally cool and solidify. In this case, the phosphorite vein of the Costanaza mine is one of the most easily recognisable dike deposits in Spain, as it is approximately 5 kilometres long and has a variable width, the maximum being 8 m and the minimum 0.10 m.

In its structure, apatite mineralisation (fluorapatite or phosphorite) alternates with quartz mineralisation, and sometimes carbonates (calcite, siderite and ankerite) also appear. This is a unique mineralogy due to the presence of the fluorapatite discovered in this mine, which makes Logrosán a «Type Locality» for this mineral at world level.

The Logrosán phosphorites were made known by the Irish mining engineer, Mr. William Bowles, who came to work in Spain during the 1750s. The Costanaza mine was mined intermittently from the end of the 19th century until the middle of the 20th century. When the mine closed in 1944, the mine was 210 m deep and had 14 floors, having extracted some 200.000 tonnes of ore for the production of ·superfosfato” fertilisers which were exported to much of Europe.