Site of the former puits N°7 de Monthibert at Trélazé, the last operating shaft of France's last active ardoisière, closed in 2014 and subsequently levelled, with the metal headframe surviving.
The puits N°7 de Monthibert was the last and deepest active shaft of the Ardoisières d'Angers at Trélazé, and the final operating extraction point in France's last underground slate mine. Sunk on the Grands-Carreaux sector, it reached a depth of 520 metres and was equipped in 1976 with a modern metal headframe of 37.5 metres — the most recent headframe in the entire Trélazé basin. The shaft served for both extraction and the descent of all personnel at the Grands-Carreaux site, centralising the entire production of the carrière souterraine.
The Commission des Ardoisières d'Angers, founded 1891 and becoming the Société des Ardoisières d'Angers in 1963, operated the Grands-Carreaux throughout its existence. After the Fresnais quarry closed in 2009, the Grands-Carreaux and the puits N°7 constituted the sole remaining extraction. On 25 November 2013, with the gisement judged exhausted by Imerys, closure was announced.
The plan social was signed 28 March 2014 and effective closure came on 29 March 2014. The carreau was integrally levelled following closure. The metal headframe of the puits N°7 survives among the six remaining chevalements of Trélazé.
The puits N°7 de Monthibert stands on the Grands-Carreaux sector of the ardoisières of Trélazé, the largest and last active slate extraction site in France. The broader history of the Trélazé ardoisières extends from the first recorded quarry at Tire-Poche in 1406 through centuries of open-cast and later underground working. The Commission des Ardoisières d'Angers was formed in 1891 as the consolidated production company and became the Société des Ardoisières d'Angers in 1963.
All open-cast extraction ceased in 1899, and from that point all production was underground. Underground working at Trélazé used the ascending method (en remontant): chambers were opened from a collectrice gallery and worked upward in bands of 2.5 metres, with waste accumulated underfoot. In the 1960s mechanical equipment began to replace hand drilling.
The Grands-Carreaux bassin exploited two principal veins, the Veine Nord and the Veine Sud, with their extreme variants. The puits N°7 de Monthibert was the last shaft sunk in the Trélazé basin. It was equipped in 1976 with a metal headframe of 37.5 metres — the most modern headframe in the basin and the last to be erected — and electric extraction machinery.
The shaft reached 520 metres in depth and served all underground extraction workings to 450 metres. It served as the sole point of descent and ascent for all underground personnel at the Grands-Carreaux. The puits N°3 de Monthibert and the puits N°6 de l'Ermitage provided ventilation and safety backup.
At the end of the 1960s the Ardoisières d'Angers represented 60 per cent of French slate production and operated multiple sites across the north-west, including Bel-Air at Combrée, l'Espérance at La Pouëze, la Rivière at Saint-Saturnin, and the Limet site near Renazé in Mayenne. Production at Trélazé had declined from 80,000 tonnes in 1982 to 40,000 tonnes in 1990 and 25,000 tonnes in 1997. By 2007 the Ardoisières d'Angers employed 220 workers overall, 60 of them underground, with the Grands-Carreaux puits extracting 9,000 tonnes per year and the Fresnais descenderie adding 6,000 tonnes.
When the Fresnais site closed in 2009, the puits N°7 de Monthibert was the sole remaining active extraction point in France. Despite competition from Spanish open-cast slate — cheaper but widely judged inferior in quality — the Ardoisières d'Angers maintained production principally for the restoration of Monuments Historiques, for which the quality of Trélazé ardoise was irreplaceable. On 25 November 2013 the directors of the Ardoisières d'Angers, by then part of the Imerys group, announced closure on the grounds that the gisement was definitively exhausted.
The 153 remaining workers opposed the closure and various options for a takeover were studied without result. The plan social was signed on 28 March 2014 and the definitive closure took effect on 29 March 2014, ending 123 years of continuous activity by the Commission and Société des Ardoisières d'Angers, and closing the last underground slate mine in France. Following closure, the carreau de Monthibert was integrally levelled.
The surface railway lines used for slate transport were dismantled and the majority of industrial buildings razed. The metal headframe of the puits N°7 de Monthibert survives as one of six remaining chevalements from the eight that had stood across the Trélazé basin. The site was classified as a zone naturelle d'intérêt écologique, faunistique et floristique.