The Stephano-Sub-Vosgian coal basin, part of the coalfields of the Vosges and Jura, is located in eastern France and spans the Eastern Haute-Saône, the Territoire de Belfort, and the southern Haut-Rhin. Dating from the Stephanian geological stage, only its central-western section, corresponding to the Ronchamp and Champagney mining area, was extensively mined between the mid-18th and mid-20th centuries due to the quality of its coal seams. Other areas were largely unexploited or minimally developed because of excessive depth (over one kilometer) or the low quality and thickness of the coal seams.

A small coal deposit near the hamlet of Mourière was exploited between 1844 and 1891 on an artisanal scale, characterized by thin and low-quality seams. In the early 20th century, significant coal reserves with sufficiently thick and higher-quality seams were identified near the commune of Saint-Germain. However, the onset of World War I and the subsequent Great Depression delayed potential development. Despite further discussions and proposals during the 1950s, no mining operations were initiated. Between 1757 and 1914, six mining concessions were granted in the region. Three were eventually consolidated (Ronchamp, Champagney, and Éboulet), one remained a small-scale operation (Mourière), and two were never developed (Lomont and Saint-Germain).

Location

The Stephano-Sub-Vosgian coal basin, characterized by a boomerang shape, extends across the eastern Haute-Saône, the northern Territoire de Belfort, and the southern Haut-Rhin. It stretches from Bouhans-lès-Lure, Ronchamp, and Lomont in the west to Wattwiller in the east, with scattered outcrops between Romagny and Habsheim. The basin measures approximately 60 kilometers in length along the Vosges range and up to 20 kilometers in width.

The western portion of the Stephano-Sub-Vosgian coal basin was divided into six concessions: Ronchamp, Champagney, and Éboulet in the northern sector, which were eventually merged along with the operating companies; Mourière, which remained independent; Lomont in the south, which was not developed due to insufficient financial and technical resources for deep mining; and Saint-Germain. The extensive eastern sector did not receive any concessions Nevertheless, it was explored by various companies, including the "." Some limited and short-term artisanal exploration and extraction efforts occurred sporadically across the region.

The nearest coalfields to the Stephano-Sub-Vosgian basin are the to the northeast and the Keuperian coal basin of Haute-Saône, which partially overlaps it to the southwest.

Geology

During the Devonian period, the bedrock of the Belfort region, located along the edge of the Vosges Massif, was formed through detrital sedimentation. In the Carboniferous period, the area was submerged under a sea, leading to marine sedimentation and associated volcanic activity. The coal basin began forming during the Stephanian stage (approximately 307 to 299 million years ago), under layers of fluvio-lacustrine sediments. In the Permian period, the deposit underwent folding and was subsequently overlaid by additional detrital sediments originating from the erosion of the Variscan orogen.

The spoil tips of the Ronchamp and Champagney mining basin contain numerous Carboniferous-period fossils. These include plant species characteristic of both dry, mountainous environments (such as black thorn, ferns, and cordaites) and swampy plains, such as Lepidodendron, Sigillaria, Calamites, and Sphenophyllum. Fossils of freshwater fish have also been found, indicating the presence of a large freshwater body during the period.

The deposit spans the Belfort Gap and the . It comprises several basins, including Mourière and Ronchamp, Saint-Germain, Lomont, Roppe, and Romagny. The Ronchamp and Champagney basins contain the thickest coal seams. In contrast, the seams in the Lomont and Saint-Germain areas, as well as the entire eastern sector, are thin and affected by faulting. The basin dips approximately 20° from north to south and has a structure resembling a ship's hull, reaching depths exceeding one kilometer before rising sharply near the Chagey massif and the Jura massif.

Geologically, the Mourière deposit differs from that of Ronchamp despite being of the same age. The deposits exhibit different inclinations, and in Mourière, the coal seam lies directly on the bedrock. The coal in Mourière is clay-rich and contains pyrite, necessitating washing before sale. Further northwest, the Saint-Germain basin contains coal seams of similar quality to those in Ronchamp. These seams range in thickness from 0.60 to 2.50 meters, with an average just below one meter. The coal-bearing terrain is disrupted by three faults. The first is located south of Saint-Germain, where two drillings spaced 800 meters apart indicate a 42-meter difference in the Permian roof. The second fault lies beneath the Grand Morveau woods, north of Lure, where the dip of the seams becomes too steep. Coal samples from drillings No. 7 and 8 show an average composition of 50% carbon, 27% ash, 23% volatile matter, and a calorific value ranging from 2 to 8 kCAL (8.4 to 33.5 MJ/kg).

East of Saint-Germain, the Ronchamp deposit contains coal seams reaching up to four meters in thickness. It is located along the southern slope of the Vosges massif, with a southeastward dip of approximately 20°, extending toward Lomont, where depths exceed one kilometer. The coal is overlain by a Permian basin composed of red Vosges sandstone and various clay formations. In the Haute-Saône department, coal outcrops are limited to narrow strips north of the Ronchamp deposit, located deep within forested areas, which contributed to their late discovery. Seam thickness in this area varies from a few decimeters to four meters. Further east, the seams are generally of lower quality, appearing as discontinuous, faulted veinlets interspersed with schist. The Stephanian formation also outcrops at Roppe, Anjoutey, and Bourg (three municipalities northeast of Belfort) as well as south of Mélisey, near Lure.

History

The coal basin was discovered around 1744 through outcrops in the hills above Ronchamp and Champagney. Mining operations began in 1757 with the granting of two concessions, which were merged in 1763. The Mourière concession was granted in 1766 but was not exploited until the period between 1844 and 1891. In 1810, the first mine shaft, named Saint-Louis, was sunk. During the same period, small-scale coal extraction also took place near Thann.

In 1820, a departmental company was established in the Haut-Rhin to promote coal exploration and reduce the Alsatian industry's dependence on wood and coal from Ronchamp. Between 1822 and 1832, exploration efforts were conducted, but the initiative was ultimately abandoned due to the limited size and unworkability of the region's coal deposits.

In 1840, the "cuvette de l'étançon" was depleted, and the Ronchamp deposit was considered exhausted by its concession owners. In 1843, coal was rediscovered by two industrialists from Haute-Saône who had acquired the concession. In 1847, the Société des maîtres de forges (Society of Ironmasters) was established and began exploration south of the Ronchamp concession. Both companies competed for a new concession, investing in drilling and exploratory shafts. The Éboulet concession was ultimately granted to the Ironmasters in 1862. Following operational difficulties, the Éboulet concession and its mining company were merged with those of Ronchamp. The consolidated company then entered a period of economic growth that continued until the First World War.

During the late 19th and early 20th centuries, the company managing the Ronchamp mining operations undertook evaluations to assess the remaining coal resources. In 1883 and 1906, the basin was assessed by the General Mining Engineer and geographer Pierre Termier, respectively. Both experts noted the basin's complex geology, including extensive faulting and uplift, the challenging depth of the southern sector, and the unworkable nature of the scattered seams to the east and west. Despite these limitations, they recommended continued exploration in more distant areas where additional deposits might exist. Throughout the 19th century, exploration extended eastward toward Belfort and Mulhouse, conducted by the Ronchamp company and independent operators. However, only small-scale, short-lived mining operations were established in these regions. Industrial coal extraction remained limited to the Ronchamp basin. In the early 20th century, two additional concessions were granted: the Lomont concession (1904) to the south and the Saint-Germain concession (1914) to the west of Ronchamp. The Lomont concession was never exploited due to technical challenges related to deep mining, while exploitation of the Saint-Germain concession was postponed due to World War I and subsequent unfavorable economic and strategic conditions. Both concessions remained unexploited into the early 21st century.

In the 1920s, the Ronchamp coalfields, which had sunk France's deepest mine shaft in 1900 (1,000 meters), entered a period of decline. Despite this, investments continued, and the area experienced an influx of Polish workers. After World War II, the mining operations were transferred to Électricité de France (EDF), which deemed them insufficiently profitable and considered closing them. In response, a mine defense committee was established and extended mining activities by eight years through the renewed extraction of outcrop coal. In 1954, the committee proposed creating the "Charbonnages de Franche-Comté" by exploiting the and the two other concessions in Haute-Saône. This initiative was not implemented. Coal extraction in the basin ceased on May 3, 1958, with the removal of the final coal wagon. The Ronchamp concession, the first granted in the basin, was also the last to be relinquished, in 1961.

Lifespan of the Six ConcessionsThe shafts are colored according to their respective concessions; darker shades indicate periods of coal extraction, while lighter shades indicate other functions or dormant periods.

Concessions

Ronchamp and Champagney

Two coal mining concessions were granted in 1757 following the discovery of coal around 1744: the concession to the lords of Ronchamp at Ronchamp (granted on 11 September 1757) and the concession to the of Lure at Champagney (granted on 21 April 1757). These two concessions were merged on 1 March 1763.

The Ronchamp deposit, which extends into the municipalities of Champagney and Magny-Danigon, was the most extensively exploited in the basin, with an estimated 16 to 17 million tons of coal extracted. It was also the longest-operating site, with industrial activity spanning from the 18th to the 20th century. The deposit significantly influenced the landscape, marked by slag heaps, mining infrastructure, and workers' housing, as well as the region's economy and demographics, including Polish immigration and the development of mining traditions.