By X. Devleeschouwer, E. Goemaere, and C. Mullard

Geological features are superimposed on an aerial photo: the quaternary sediments follow the rivers (blue-green). Note the gallery entrances (blue), shafts (red), and the slate underground workings (maroon).

In 2004, the Geological Survey of Belgium (GSB) launched the first Belgian program of computerized management of mines in the municipality of the Commune of Vielsalm (located in the southeastern part of Belgium in the Province of Luxembourg). Associated partners in this program are the Coticule Museum, the Directorate General of Natural Resources and the Environment of the Walloon region, and the University of Li�ge.

Located in the southern part of the geological formation known as the Caledonian Stavelot-Venn Massif, the Commune of Vielsalm is built upon rocks of the Salm Group (Ordovician age: 465–495 million years old). Rare minerals lie hidden in these metamorphic formations. From the 17th century to the end of the 20th century, Vielsalm was the center of the Belgian mineral extraction industry. Coticule rocks from two deposits were exported across the globe as whetstone (used for honing razors, surgical blades, etc.). The slate deposit is composed of two decametric layers of roofing slate quality, separated by barren slates.

The roofing slate and coticule were initially extracted from open pits and later, starting from the middle of the 19th century, from mines. Approximately 30 concessions of roofing slate and coticule were active in the Commune of Vielsalm. The extraction of coticule from trenches evolved into the mines through the excavation of many shallow shafts from which a superimposed system of sinuous galleries followed the layers of coticule. Then, galleries 150 to 450 meters long were dug into the hillside until they reached the roofing slate layers. The maximum depth of a roofing slate mine could reach 60 to 70 meters because of several superimposed, exploited levels. The lower levels are usually flooded today; the dewatered galleries and their exits are practically unknown.

Schematic above: This is a view of the roofing slate underground workings in the Commune of Vielsalm.

Traditional dwellings and buildings of this area and numerous human traces constitute the last visible signs of this age-old activity. However, this industrial heritage is worthy of interest and deserves greater recognition. Old extraction sites, abandoned without rehabilitation and localized in forest and suburban areas, represent restricted environments for the development of specific fauna and flora. Furthermore, they provide extraordinary mineral sites (to be protected from plundering) and bear witness to the technologies of the past.

Special Nature Protection Zones

Some of these environments are already located in special nature protection zones through the European project Natura 2000 and also partly inside nature reserves. The abandoned mines, which are located on private or public land, are often ignored by the population and represent a real danger to people walking, jogging, or cycling close by, as well as to the surface infrastructures and their owners. This historical and scientific heritage must be preserved, restored, and secured. Its management is a priority but remains difficult because of the high number of mines whose exact locations were unknown prior to the beginning of this program.

Mining plans, administrative and technical archives, old and recent geographic maps (topographic maps, orthophoto plans, geological maps, etc.), and scientific data are dispersed across numerous locations. Until now, this data was not connected, and the different partners involved in this program wanted to acquire a complete and easy-to-use tool for this purpose. As a result, the GSB team created an application with ArcGIS Desktop (ArcView) software with which all the information and available data gathered could be stored in a database and used and managed within an open, dynamic, and visual GIS. ArcGIS was chosen following a detailed product comparison.

Technically, this GIS application is based on the creation of two complementary modules: a relational database management system with Microsoft Access 2000 software for the descriptive data and a cartographic management system with ArcView software for the raster and vector geographic data. The mining plans of Vielsalm, constituting the background documents and starting point of the program, were georeferenced using geographic reference frameworks. This was done through the use of the digital georeferenced and vectorized land register of the Commune of Vielsalm. GPS coordinates were used to enhance precision during the georeferencing procedure of some surface elements represented on the mining plans (shafts, gallery entrances, etc.). The numerous and varied vector layers are associated with the surface and underground extractive industry (galleries, rooms, shafts, waste dumps, etc.), geology (stratigraphic units, structural elements), natural zones (Natura 2000, etc.), land register (parcels, habitations, etc.), and surface infrastructure (roads, castles, etc.).

The slate galleries and exploited rooms close to and behind the Cahay quarter are located in the Commune of Vielsalm, Belgium.

The database and the ArcView software are connected through a geodatabase that avoids double data acquisition and facilitates the management of new information. This tool, containing several Esri scripts, allows users to consult the Access form for each selected vectorized object. In the same way, Internet pages composed of field photographs, schemes, and explanatory text illustrate each object.

The GIS application is a multiuse tool, which highlights the limits of risk zones still unknown by the horizontal projection of the underground galleries at the surface. The observed average density corresponds to one shaft or gallery entrance per hectare in the exploited zones. By cross-checking information via complex requests, this application is able to identify and quantify the geological, biological, and cultural interests of each concession, while concurrently showing the evolution of the landscape modified by man from the end of the 18th century on the basis of available cartographic documents.

Conclusion

The GIS application made by GSB with ArcView is intuitive and easy to use. It is a utility tool for country planners and a management tool for legal authorities of the territory (public administration officials). It could play a great role in the protection, valorization, and preservation of this remarkable heritage, which will help the area's tourism industry. The purpose of the program in the Commune of Vielsalm was to determine medium- and long-term behavior of the mine cavities, assess their surface repercussions, develop methods for monitoring high-risk areas, and, if possible, formulate risk reduction procedures. In the near future, this work will be extended to other Belgian slate basins.

For more information, contact Dr. Xavier Devleeschouwer, geologist of the Geological Survey of Belgium, Royal Belgian Institute of Natural Sciences (e-mail: Xavier.Devleeschouwer@naturalsciences.be, tel.: 32-2-788-76-38).