Massif Central, France - Carboniferous
The Massif Central
has widespread evidence of Carboniferous volcanism and epithermal
activity. Gold mineralisation in the form of vein systems is associated
with fault systems that form the margins of sedimentary basins in which
coal deposits formed. Chert deposits are also present in the region
(e.g. Grand Croix, Autun, Esnost) and these are world famous for the
permineralised plants and fungi that they contain. Most of the
fossiliferous cherts are considered to have formed as silica-rich fluids
that formed by the dissolution of volcanic ash infiltrated peat
deposits. Relatively recently a number of less richly fossiliferous
chert deposits have been identified and interpreted as hot spring sinter
deposits based on their geological setting, chert textures and major
and trace element concentrations.
The Meillers Autunian hydrothermal chalcedony:
first evidence of a 295 Ma auriferous epithermal sinter in the Frech Massif
Central. Eric Marcoux et al. 2004.
Laminated white sinter apron chert with remnant vuggy porosity.
Beige to grey mottled apron margin chert with cylindrical plant stem.