Erankio

The terrain consists of carbonaceous slate with ferruginous materials, of Palaeozoic age, associated with the Cinco Villas Massif, but it also has inclusions of other minerals. The Palaeozoic slate is close to a contact with Permo-Triassic argillites and Keuper ophites.

Erankio Mina-cueva 1 has 185 metres of gallery development and -20 metres of vertical extent, and has two entrances. Erankio Mina-cueva 2 has 40 metres of development and -4 metres of vertical extent. The greatest interest is presented by cave-mine 1, since apart from its greater development it has an underground river and natural galleries. Mine 2 is almost entirely artificial, with less development of the dark zone and only slight enlargements or modifications due to seepage and collapses.

Erankio Mina-cueva 1 is an artificial mine, abandoned 50 years ago, with several side passages formed by natural processes. Erosive water processes and the removal of fallen materials have enlarged the old mine and have formed small side galleries and other enlargements, forming a cave-mine that is interesting for its rare speleothems. Its development is 185 metres.

The access entrance, 1.5 metres in diameter, gives way to a wider descending gallery that leads into the river gallery, 4 metres wide by 2.5 metres high. Next to the entrance there is a skylight (zero level) that illuminates the entrance area. The walls are generally dark in colour (black, reddish and grey), with lighter areas.

The river gallery, from the fork (level -5), presents a wide horizontal stretch that heads East for 15 metres. Shortly before the terminal chamber (level -4), on the floor and on a wall, there are blocks and white-translucent inclusions of fluorite. If from the fork we follow the river downstream, the gallery narrows and presents stepped cascades, with a floor of fallen blocks. After a 20-metre stretch towards the S-W one reaches another wide fork (level -12). Towards the East a window gives way to another small chamber, which continues in a descending gallery until reaching a flooded sector. The main gallery heads towards the W and crosses a very unstable sector, with a low ceiling, that threatens to collapse. After the unstable stretch the river gallery turns towards the North and has an inverted U section. At level -17 metres it intersects an East side passage of 10 metres through which another water input enters. Downstream the channel loses gradient and has reddish clayey sediments. After another bend the main gallery takes a WNW direction, presenting long straight stretches with an inverted U section. At level -18 metres the water comes to flood the gallery, leaving no banks. The depth of the flooded stretch reaches 60 cm. After 17 metres one arrives below the lower entrance. This is a skylight (pit-sinkhole) of 3 m of vertical extent. At the foot of the vertical there is another fork. The South branch, wide and 15 metres long, is flooded with 1 metre of water. The underground river continues towards the W-N-W through a narrower, flooded gallery with thick sediments. It descends slightly, with traces of periodic flooding and a progressively lower ceiling, which indicates its sumping. The lowest point reached is level -20 metres (final sinkhole).

In the entrance sector there is the greatest number of green-blue and turquoise speleothems forming fine coatings over small areas of the walls. In the stretch of the river gallery there are also drips and on the walls various stalactites and white, ochre and black flowstone. Some of the stalactites have a gel texture; particularly the tip of many white stalactites is a kind of elastic colloid, which moves when the water drops detach.

On the walls of the fork at level -12 there are dark bronze-coloured speleothems of goethite and also some white-cream ones. On the floor there are various grey massive sedimentary deposits, with very disintegrated fragments of marcasite (light brass yellow in colour and metallic lustre) together with others of quartz (white) and fluorite (greenish and yellowish white). On the ceiling and walls of the unstable sector there appear more frequently stalactites, parietal flowstone and coatings of goethite, in bronzed and black metallic tones, dark and shiny. In some niches white-cream speleothems are intercalated, some of them soft, with a gel consistency.

The gallery of the East side passage at level -17 presents stepped gours of clayey materials, soft, in yellowish and reddish tones. At the intersection a large yellowish flowstone forms with gours of different sizes; despite its extremely soft consistency the morphology of the flowstone and gours is similar to those that form in calcite. An enlargement or small chamber is profusely decorated by long stalactites of goethite in black metallic and dark bronze tones. Some of the stalactites measure more than 1 metre in length. In the straight stretches of WNW direction there are smaller speleothems of goethite, bronzed and black. In the terminal sector and in the vicinity of the upper entrance there are some speleothems that form small white, crystalline coatings, in very fine acicular and fibrous aggregates, in some cases with delicate needles up to 1 cm long, probably of epsomite.

Erankio Mina-cueva 1 captures the local infiltration and is currently traversed by a small underground river. The water of the underground course comes from an impracticable internal spring, located at the base of a wall. In the sector of the stepped cascades much water drips from ceiling seepages, increasing the underground flow. At level -17 metres an East side passage of 10 metres provides another water input. At level -18 metres the water comes to flood the gallery, leaving no banks, with a depth of 60 cm. The lower entrance is a skylight (pit-sinkhole) of 3 m of vertical extent through which another water course enters, forming a cascade. The South branch, 15 metres long, is flooded with 1 metre of water. The underground river continues towards the W-N-W through a narrower, flooded gallery with thick sediments, with traces of periodic flooding and a progressively lower ceiling, which indicates its sumping.

The access entrance, 1.5 metres in diameter, gives way to a wider descending gallery that leads into the river gallery. The river gallery, from the fork (level -5), presents a wide horizontal stretch of 15 metres towards the East. If from the fork we follow the river downstream, the gallery narrows and presents stepped cascades, with a floor of fallen blocks; after a 20-metre stretch towards the S-W one reaches another wide fork (level -12). Towards the East a window gives way to another small chamber, which continues in a descending gallery until a flooded sector. The main gallery heads towards the W and crosses a very unstable sector, with a low ceiling; after this stretch it turns towards the North and at level -17 metres intersects an East side passage of 10 metres. After another bend the main gallery takes a WNW direction. At level -18 metres the water floods the gallery and after 17 metres one arrives below the lower entrance, a skylight (pit-sinkhole) of 3 m of vertical extent. At the foot of the vertical there is another fork; the South branch, wide and 15 metres long, is flooded with 1 metre of water. The river continues towards the W-N-W through a narrower, flooded gallery until the lowest point, level -20 metres (final sinkhole).

Interesting and complete study carried out by Carlos Galán of Sociedad de Ciencias Aranzadi, dealing with topics such as Biospeleology, Cave fauna, Geology, Mineralogy and Speleothems.