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Formation of emeralds at pegmatite-ultramafic contacts based on fluid inclusions in Kianjavato emerald, Mananjary deposits, Madagascar

Published online by Cambridge University Press:  05 July 2018

Ye. Vapnik*
Affiliation:
Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel
I. Moroz
Affiliation:
Department of Applied Physics, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel
M. Roth
Affiliation:
Department of Applied Physics, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel
I. Eliezri
Affiliation:
Colgem El 97 Ltd, 52 Bezalel Street, Ramat Gan 52521, Israel
*

Abstract

Kianjavato emerald (Mananjary deposits, East coast of Madagascar) was formed during metasomatic processes at the contact between pegmatites and hornblendites. The metasomatic exchange was related to a Pan-African tectonometamorphic event.

Fluid inclusions in the Kianjavato emerald and quartz were studied by means of microthermometry and Raman probe analysis. Three main types of inclusions were revealed: CO2-rich, CH4-rich and aqueous-rich, with a salinity of ∼2 wt.% NaCl equiv. The inclusions occurred along the same primary and pseudosecondary trails and were considered to be formed simultaneously. Based on fluid-inclusion data, the conditions of emerald growth were 250°C < T < 450°C and P = 1.5 kbar.

The fluid inclusion data for Kianjavato emerald were compared to the data for another Madagascar emerald, Ianapera. The latter is of similar age, but its genesis was determined by a shearing event. Our fluid inclusion data suggested that shearing was also important as a mechanism of introducing CO2-rich fluid for the genesis of the Kianjavato emerald.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

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