Distrito pegmatítico Totoral, Sierra de San Luis, Argentina

OYARZÁBAL JULIO CÉSAR; GALLISKI MIGUEL ANGEL

La Plata

Congreso; XVI Congreso Geológico Argentino; 2005

Asociación Geológica Argentina - Universidad Nacional de La Plata

The Totoral pegmatitic field (TPF) is the southernmost pegmatitic field of the Pampean Pegmatite Province. It is located at 32° 53´  - 33° 01´  lat. S and 65° 55´  - 66° 00´  long. W in the San Luis Range, Eastern Pampean Ranges of Argentina. The units of TPF intrude the Pringles Metamorphic Complex formed mainly by a thick psamo-pelitic sequence that undergoes high-T low-P metamorphism in the Lower Paleozoic during the Pampean and Famatinian cycles. The metamorphics are Ms-Qtz-Bt-Alm-Chl-Pl-Mc-Sil-Crd±Tur-Ap-Zrn-Ep-Hem schists formed at ~ 450-500°C and 2-4 kbars that eastward grade to phyllites. The TPF comprises a swarm of rare-element pegmatites of LCT (Li-Cs-Ta) geochemical signature, that forms a 17 Km long submeridional belt, outcropping on the eastern flank of C° La Torre and Paso del Rey granitic intrusives. According to spatial distribution and geochemical links, the TPF has been divided in three pegmatitic groups named: Cerro La Torre, Loma Alta and Paso del Rey. The pegmatites belong to barren-transitional to beryl-type, beryl-columbite-phosphate subtype, complex type with spodumene-subtype and albite type. They carried a rare-element mineralization mined in the middle of the last century by beryl, tantalite, spodumene, and more recently by K-feldspar, albite, quartz and muscovite. Primary phosphate minerals of the series tryphylite-lithiophilite and graftonite-beusite originated a myriad of Mn-Fe-(Al-Ca-Li) secondary phosphates. The field, paragenetic, and especially the trace-element geochemical trends of K-feldspar and muscovite support the statement that the pegmatites were formed by fractional crystallization of strongly differentiated batches of pegmatitic melts derived by differentiation from the peraluminous, fertile S-type granites.