History
Pozo Monsacro stands at La Foz in the parish of Santa Eulalia, concejo of Morcín, in the Montaña Central comarca of Asturias. The shaft surface installations are on the Morcín side of the boundary with Riosa, but the underground galleries extend beneath Riosa territory. The mountain named Monsacro, which gives the shaft its name, is a historically significant summit in the Asturian landscape.
Coal exploitation in the Riosa-Morcín zone is among the oldest in Asturias. The first documented extraction began on 24 April 1846, with the purpose of supplying fuel to the Fábrica Nacional de Cañones de Trubia. Once that factory secured alternative supply, the state exploitation was privatised; from 1894 different private companies operated the concessions with variable results, dependent on coal market fluctuations. Around 1914 — some sources indicate 1915 — the mines were acquired in a public auction by the Sociedad Hulleras de Riosa. Under Hulleras de Riosa the mountain workings were expanded and a mineral railway was constructed to La Pereda, connecting the extraction zone to the main railway lines of central Asturias.
In 1952 the Empresa Nacional Siderúrgica (ENSIDESA), a state steelmaking company establishing its major works at Avilés, purchased the Hulleras de Riosa mines for 30 million pesetas, recognising the quality of the coal for metallurgical coke production. ENSIDESA then began sinking the vertical shaft, and sinking was completed in 1953. The shaft entered full coal production in 1959. In the same year, 1959, a welded-steel headframe of 40.20 metres in height was installed. The shaft reached a depth of close to 500 metres. The shaft also incorporated a training mine (mina escuela) — a purpose-built underground space used for the instruction of new workers before their assignment to active production workings — as well as a magazine for explosive storage.
On 1 July 1969 the operations and installations of the Sociedad Minas de Riosa, the successor entity, were integrated into HUNOSA, the state coal company established by decree in 1967. Under HUNOSA the shaft continued to operate as one of the company's more productive units, with a workforce of around 586 miners. For some years prior to closure the coal was not raised to the surface at Monsacro itself but transported via underground connection to the neighbouring Pozo Nicolasa at Ablaña in the concejo of Mieres, from which it reached the Batán washing plant. This arrangement followed the closure of the former mineral railway, after which coal had been transported by lorry to the Batán lavadero, and subsequently by conveyor belt from Nicolasa.
Two accidents in 1967 during the ENSIDESA phase killed eight miners from Riosa and Morcín; this tragedy is recorded in local memory.
Pozo Monsacro closed in 2014, during the final phase of Asturian coal mine closures under European Union restructuring policy. The headframe, adit, training mine, and magazine have been listed in the Inventario del Patrimonio Cultural de Asturias as a complex of civil heritage with historical and architectural significance. The former ore-loading tolvas (coal hopper structure) at the mine site have been adapted for a new cultural purpose: they now house the Museo Etnográfico de la Lechería (Ethnographic Museum of the Dairy), part of the Red de Museos Etnográficos de Asturias, which explores the traditional cattle-rearing and cheese-making culture of the Montaña Central alongside the area's mining identity. As of 2023 discussions between the concejo of Morcín, Hunosa, and the concejo of Riosa were ongoing regarding the valorisation of the mining heritage of both concejos for tourism purposes.