Mineralogical characterization of topaz from miarolitic pegmatites and w-bearing greisen in the a-type El Portezuelo granite, Papachacra (Catamarca Province).

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Colombo, Fernando

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En: Revista Asociación Geológica Argentina vol.64, no.2, p.194-200Resumen: The El Portezuelo Granite (Catamarca Province, NW Argentina), probably of Late Devonian or Early Carboniferous age, was emplaced at = 2 kbar and displays the chemical characteristics of an A-type granite. It hosts small miarolitic pegmatites and dikes that belong to the NYF petrogenetic family, miarolitic class, miarolitic-REE subclass, with features more similar to those reported for the gadolinite-fergusonite type. Topaz is widespread both in pegmatites and in a W-bearing greisen genetically related to the granite. In pegmatites it occurs as crystals up to over 15 cm long, showing the forms {120} and {041} (dominant), and also {100}, {010}, {001}, {110}, {130}, {230}, {410}, {150}, {340}, {201}, {203}, {011}, {021}, {031}, {111}, {112}, {221}, {223}, and {445}. Crystals are colorless to pale yellow, more rarely brownish or bluish. Electron-microprobe analyses of gemmy crystals from pegmatites and greisen show that topaz is F-rich (between 19.01 and 20.12 wt. por ciento F, most crystals being slightly zoned) and has very low MgO and TiO2 (= 0.02 wt. por ciento), low FeO (=; 0.03 wt. por ciento), and up to 0.10 wt. por ciento CaO. Refractive indices and unit-cell dimensions reflect the F-rich nature of the studied topaz. This occurrence produces the finest crystals yet known from western South America but probably has no economic potencial as gemstock producer.

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Existencias
Imagen de cubierta	Tipo de ítem	Biblioteca actual	Biblioteca de origen	Colección	Ubicación en estantería	Signatura topográfica	Materiales especificados	Info Vol	URL	Copia número	Estado	Notas	Fecha de vencimiento	Código de barras	Reserva de ítems	Prioridad de la cola de reserva de ejemplar	Reservas para cursos
	Artículo	Biblioteca Instituto de Geología y Mineria "Ing. Carlos F. Stubbe"				C-5 (Navegar estantería(Abre debajo))					Disponible

Relevamiento: 2009.

The El Portezuelo Granite (Catamarca Province, NW Argentina), probably of Late Devonian or Early Carboniferous age, was emplaced at = 2 kbar and displays the chemical characteristics of an A-type granite. It hosts small miarolitic pegmatites and dikes that belong to the NYF petrogenetic family, miarolitic class, miarolitic-REE subclass, with features more similar to those reported for the gadolinite-fergusonite type. Topaz is widespread both in pegmatites and in a W-bearing greisen genetically related to the granite. In pegmatites it occurs as crystals up to over 15 cm long, showing the forms {120} and {041} (dominant), and also {100}, {010}, {001}, {110}, {130}, {230}, {410}, {150}, {340}, {201}, {203}, {011}, {021}, {031}, {111}, {112}, {221}, {223}, and {445}. Crystals are colorless to pale yellow, more rarely brownish or bluish. Electron-microprobe analyses of gemmy crystals from pegmatites and greisen show that topaz is F-rich (between 19.01 and 20.12 wt. por ciento F, most crystals being slightly zoned) and has very low MgO and TiO2 (= 0.02 wt. por ciento), low FeO (=; 0.03 wt. por ciento), and up to 0.10 wt. por ciento CaO. Refractive indices and unit-cell dimensions reflect the F-rich nature of the studied topaz. This occurrence produces the finest crystals yet known from western South America but probably has no economic potencial as gemstock producer.

Artículo en pdf (RAGA 64_2_194.pdf)

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