L ITH IUM-BEARING HYDROTHERMAL ALTERATION PHYLLOSIL ICATES RELATED TO PORTALET FLUORITE ORE (PYRENEES, HUESCA, SPAIN)

ABSTRACT: Phyllosilicate associations in hydrothermally altered fluorite ore bodies are: Li-chlorite + pyrophyllite _+ interstratified minerals _+ muscovite +kaolinite. Chlorites, the main alteration minerals, are dioctahedral, d060 = 1.489-1-490/~,, of Ia polytype. The structural formulae indicate substitution fAI 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 i dicates that the chlorites are intermediate members of the donbassite-cookeite series proposed by Sudo (1978). The mineralogical ssociations and textural relations uggest that after intensive silicification which produced alkali alteration under acid conditions, pyrophyllite was produced at the expense of muscovite and then Li-bearing donbassite formed from the pyrophyllite. The Li needed for the formation of the chlorites could be genetically related to granitic batholiths which occur close to the fluorite ores. Although the most common chlorite species are trioctahedral, there are other Al-bearing species that are di-trioctahedral nd di-dioctahedral. The former have recently been reported occurring in different geological settings such as sedimentary, pegmatitic, hydrothermal and metamorphic environments. The A IPEA Nomenclature Committe