Mineralogy and Origin of the Dumortierite-Bearing Pegmatites of Virorco, San Luis, Argentina

• DOI: 10.3749/canmin.50.4.873
• Publication Date: 2012-10-29T19:19:42Z
• Authors: M. A. Galliski; M. F. Marquez-Zav...; R. Lira; J. Cempirek; R. Skoda
• Keywords: Pegmatite

The Virorco dumortierite-bearing pegmatites, in Sierra de San Luis, Argentina, are a group of thin, steeply dipping dikes one to 10 cm thick. pegmatits symmetrically zoned, with quartz, albite, oligoclase, tourmaline- and dumortierite-group minerals, muscovite kyanite as the major phases; accessory trace minerals include beryl, chrysoberyl, garnet, fluorapatite, columbite-(Mn) tantalite-(Mn), pollucite, gahnite, zircon, uraninite thorite. Holmquistite was found exocontact assemblage. Primary textures magmatic origin were partially disrupted by partial replacements later incipient strong deformation. Five textural compositional types tourmaline-supergroup identified different pegmatitic zones, ranging from dravite-rich compositions rossmanite, passing through schorl Mn-rich elbaite. At least four generations dumortierite-holtite texturally compositionally represented these dikes: earliest dumortierite replaces tourmaline, locally together second generation that grades into As-poor holtite. third is overgrowths or individual crystals As-rich holtite; it commonly overgrown last enriched As. chemical evolution characterized an increase Ta, Nb minor As, followed extensive enrichment As (+ Sb + Bi) along gradual decrease Ta Nb. initial stage comprises crystallization highly evolved boron-rich peraluminous melt. prograde medium-pressure metamorphism, fluid-phase-related episode crystallization. most likely source melt extraction residual almost completely crystallized rare-element parental pegmatite.