The anatomy of an albite-type granitic pegmatite from the Totoral pegmatite field, San Luis, Argentina

GALLISKI M. A.; MARQUEZ-ZAVALÍA M. F.; CERNÝ P.; OYARZÁBAL J.; MUGAS LOBOS A. C.

Journal of Geosciences

Czech Geological Society

Lugar: Praga; Año: 2015 vol. 60 p. 31 - 44

1802-6222

The Independencia Argentina albite-typegranitic pegmatite is the most distal differentiate in the Cerro La Torrepegmatite group, located in the Eastern Pampean Ranges of Argentina. It is azoned pegmatite formed at two main stages that probably shared the same originbut had separate evolutions. The product of the first stage was apegmatite dominated by albite, quartz and muscovite, with rare K-feldspar and muscovite+ albite pseudomorphs after spodumene, and accessory columbite-group minerals,beryl, fluorapatite as well as garnet. This first-stage pegmatite was emplacedforcefully and crystallized syn-kinematically. Resulting boudinage andnecking-down produced the main body, bulbous in shape and asymmetric in zoning.This pegmatite was subsequentlyintruded by a melt that solidified to a very fine-grained, saccharoidal albiteunit, composed in excess of 97 % by Ab99.1?99.6,with accessory columbite-group minerals and fluorapatite. The normative mineralcomposition of this unit corresponds very well with that of the experimentalproducts of protracted fractionation of rare-element pegmatite melts, with highNa/K ratios and HFSE enrichment. The spatial and temporal association of the twopegmatitic melts, one enriched in H2Oand the other one more evolved, Na-rich, almost alkaline and flux-bearing, stronglysuggests that the two are cogenetic. They probably represent products of arare-element pegmatite magma differentiation at depth that were extracted at differentstages of its crystallization and emplaced at higher crustal levels.