[LUM#2] Stone Hunters
In the heart of Lozère, the lauziers continue to practice a craft that dates back thousands of years. With the help of geologists and their high-tech tools.
Kneeling in the middle of the quarry, the man hammers away at a rock weighing several hundred pounds. From this giant with brown veins, he extracts sheets a few centimeters thick, slates that will be used to make roofs. An ancestral craft that does not tolerate inaccuracy. Slate can break like glass...
"You have to know the stone, feel it, so you don't break it," explains Roland Jacques. His tools? A simple hammer and a trained ear. "You make the stone ring. You listen to it sing to find out if it has any flaws." His job? Quarryman. A dying profession: in his village of Lachamp, in Lozère, Roland Jacques runs one of the last slate quarries in the region.
Better detection of deposits
"When you dig, you never know what you're going to find," explains Roland Jacques. The jackpot: coming across large sections of intact stone that can be cut into beautiful slates. Unfortunately, quarry workers sometimes have the unpleasant surprise of uncovering broken, unusable rocks."The sedimentary formations identified at Lachamp have been affected by late fracturing, which makes the quality of the extracted stone unpredictable,"explains Cédric Champollion, a geologist at the Montpellier Geosciences Laboratory.
How can we help quarry operators better detect deposits? Romain Duhamel, a master's student in geosciences, took up the challenge. "We sought to identify the least fractured areas using geophysical surveys." Quarry operators make the stone sing? He's going to make it talk. His tools: ground-penetrating radar and electrical sounding.
Radar to the rescue of the hammer
"The ground-penetrating radar sends waves into the ground that propagate differently depending on the nature of the rock. By analyzing how they propagate, we can estimate the condition of the subsoil," explains Romain Duhamel. The same principle applies to electrical surveying: using electrodes, the geologist injects a current which, by measuring the resistivity of the subsoil, makes it possible to detect the presence of any fractures.
"This is the first time such a method has been used," explains Romain Duhamel. And it has beena success: "It produced very consistent results when we compared the profiles obtained with the condition of the rocks visible on the surface, "says the geology student."It helps me know exactly where to start working on my quarry,"says Roland Jacques. "It's simply extraordinary for us lauziers; we would never have had this information otherwise. And if tomorrow a young person wants to open a new quarry, they will need it." To perpetuate an invaluable tradition and expertise and ensure that the inhabitants of Lachamp continue to be known as coperoches, "stone cutters," for a long time to come.
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