[2] Initially, RTM was 75% owned by the Spanish group Unión Explosivos Río Tinto (ERT) and 25% by the British Rio Tinto-Zinc Corporation (RTZ), although the latter increased its shareholding to 49% during the period 1979-1980.

With the creation of Rio Tinto Minera, the ERT group brought all the business lines in the mining basin (copper, gold, silver and pyrites) under the same management.

Rio Tinto Minera, which controlled 27% of SECEM's capital, was one of the actors involved in the formation of the Ibercobre [es] conglomerate in 1978 with the aim of concentrating the Spanish copper industry under a single holding company.

[10] This situation did not last long, as Ercros sold its stake in Rio Tinto Minera to the US company Freeport-McMoRan in 1993, shortly after having declared suspension of payments.

Faced with the situation of constant deficits generated by the Rio Tinto operation, the new owner drew up a viability plan for the business which it presented to the workers.

Negotiations between the two parties were not fruitful, so in 1995 Freerport sold its assets in the Riotinto mining basin to the RTM workers, who became a labour corporation [es].

[Note 1] Rio Tinto Minera even had a Historical Heritage Department in charge of recovering and documenting the archaeological remains found during the course of the mining work.