The metasomatic enrichment of Li in psammopelitic units at San José-Valdeflórez, Central Iberian Zone, Spain: a new type of lithium deposit.

A new type of Li mineralisation in hard rock has been found to occur in the Valdeflórez area (Cáceres, Spain), where there is 111.3 Mt of resources and a mean value of 0.61 wt% of LiO. Lithium is mainly held by very fine-grained micas, important constituents of Ordovician psammopelitic rocks belonging to the Palaeozoic metasedimentary sequence of the Cáceres syncline. The mineralised zone has an elliptical surface shape with a dimension of ~ 700 × 500 m. Lithium-bearing rocks show a characteristic layered appearance, in which light grey quartz-micaceous laminae < 1 mm to some centimetres in thickness, with a variable ratio of quartz to mica, alternate with fine to very fine-grained, dark grey to black tourmalinite laminae parallel to the regional foliation. Subvertical quartz + (montebrasite)-veins that cut the regional foliation at an extremely high angle are also common in this area. Mineralisation and the associated veins are likely to be linked to the intrusion of the nearby Cabeza de Araya pluton. The infiltration of granite-derived Li-, F-, B- and P-rich aqueous fluids into the host rocks through fractures related to shearing processes is considered to be the cause of the formation of Li-rich micas and intense tourmalinisation at the expense of pre-existing phyllosilicates.