Mineralogía y geoquímica de las micas en las pegmatitas Santa Elena y El Peñón, Provincia Pegmatítica Pampeana, Argentina

GALLISKI, M. A., SAAVEDRA JULIO, MÁRQUEZ MARÍA F.

REVISTA GEOLóGICA DE CHILE

Lugar: Santiago; Año: 1999 vol. 26 p. 125 - 137

0716-0208

Mineralogy and geochemistry of the micas from Santa Elena and El Peñón pegmatites, Pampean Pegmatite Province, northwestern Argentina.  This study describes the physical and optical properties, polytypism, chemical composition and paragenesis of a Li-Al-bearing mica suite from the northernmost pegmatite field of Pampean Pegmatite Province. The micas are from two possible cogenetic rare-element pegmatites: Santa Elena a complex-type, petalite subtype pegmatite, and El Peñón, a beryl-type, beryl-columbite-phosphate subtype pegmatite. The micas are muscovites, lithian muscovites, mixed forms and lepidolites. The muscovites s.l. have 2 M1 structure and chemistry with comparatively low contents of Mn, Li, Rb, Cs, Tl and Y; one specimen could be classified as a 'rose muscovite'. The lepidolites and mixed forms have 2 M2 dominant polytypism with some scarce X-ray reflections of 1 M or 2 M1 polytypes. They are higher in SiO2, MnO, CaO, Li2O, Rb2O, Cs, Tl, Y and P. Li2O ranges between 3,71 and 4,73%, and Rb2O from 0,29 to 2,53%. The geochemical evolution of the micas, illustrated by K/Rb versus lithium, manganese, cesium, thallium and ytrium diagrams, shows a differentiation trend similar to micas from other LCT pegmatite fields. The inferred crystallization path has evolved approximately around 2-3 kbar and 350-400°C, in the stability field of spodumene, in a H2O-saturated environment, under increasing HF, KF and LiF.  Key words: Micas, Pegmatites, Mineralogy, Geochemistry, Argentina.