2 ore deposits at Chaillac
Although part of the same hydrothermal system, the two deposits are distinct and have been mined by two different companies:
- a vein located in the gneissic basement, mined from 1966 to 2001 by Société Industrielle du Centre SIC, which yielded around 0.9 million tonnes of fluorite
- and impregnation mineralisation in the sandstone sedimentary series (mined by Barytine de Chaillac from 1975 to 2006).
The deposit contained around 2.7 million tonnes of barite at a grade of 33%, making it a world-class deposit. The barite was separated by flotation.
The Rossignol vein is underlain by a basement fault running N10-15°, which can be considered an open zone feeding the hydrothermal system in the Hettangian sandstones above.
In the sandstones, impregnation mineralisation post-dates Hettangian sedimentation. Mineralising fluids used in the aquifer are formed by the pile of detrital sediments (conglomerates and sandstones) beneath the clay formations and fractures affecting already consolidated rocks (banded veins).
The age of the two deposits is a matter of debate. Still, the most reliable recent periods of fluorite mineralisation tend towards events linked to the opening stages of the Atlantic: 180, 150, 130-110 Ma).