LITHIUM-BEARING HYDROTHERMAL ALTERATION PHYLLOSILICATES RELATED TO PORTALET FLUORITE ORE (PYRENEES, HUESCA, SPAIN)

Phyllosilicate associations in hydrothermally altered fluorite ore bod ies are: Li-chlorite +/- pyrophyllite +/- interstratified minerals +/- muscovite +/- kaolinite. Chlorites, the main alteration minerals, are dioctahedral, d060 = 1.489-1.490 angstrom, of la polytype. The struct ural formulae indicate substitution of Al for Si from 0.61-0.78 atoms. The total octahedral occupancy ranges from 4.52-4.71 atoms, with 0.49 -0.69 Li atoms per half cell unit. This composition indicates that the chlorites are intermediate members of the donbassite-cookeite series proposed by Sudo (1978). The mineralogical associations and textural r elations suggest that after intensive silicification which produced al kali alteration under acid conditions, pyrophyllite was produced at th e expense of muscovite and then Li-bearing donbassite formed from the pyrophyllite. The Li needed for the formation of the chlorites could b e genetically related to granitic batholiths which occur close to the fluorite ores.