| Autor: |
HORN, Adolf Heinrich, PINTEA, Ioan, FUCHS, Yves, GHINESCU, Eduard, LEAL, José Maria, UDUBAŞA, Sorin Silviu |
| Předmět: |
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| Zdroj: |
Romanian Journal of Mineral Deposits; 2020, Vol. 93 Issue 1/2, p15-22, 8p |
| Abstrakt: |
The Capoeirana emerald deposit is located near Nova Era, in the southeastern part of Minas Gerais, Brazil. Two distinct lithologies compose the geology of the zone. One consists of undifferentiated granitoid rocks and the other is formed by volcano-sedimentary rocks, both of them being strongly altered. Emeralds occur in three types of associations. The main one is a meta-ultramafic rock, and the others are quartz- and pegmatitic veins. The mineralization is located at the tectonic contact of the volcano-sedimentary sequence with the gneissic rocks. The best specimen crystallized around quartz fishes in their pressure shadows. Pegmatite veins are the Be source and granitic bodies caused the hydrothermal processes. Chemical investigations on the zoned emeralds show there was an evolution starting with low Cr and very low V concentrations. Micas, picotite, and amphibole microprobe analyses indicate at least two mafic components and a multistage process of formation. The CO2 (±CH4) - H2O - NaCl fluid inclusion type showed the CO2 density between 0.55 - 0.78 g/cm³, the aqueous phase indicated the salinity between 2 - 17 wt.% NaCl eq., the pressure between 0.8 - 2 kb, and the formation temperature between 420° and 690°C. Informally, the CO2 diad based calculation gives 0.479898 g/cm³ density. Sometimes, CO2-rich inclusions show critical homogenization. Complex carbonate/silicate primary and pseudo-secondary inclusions suggest an immiscible process at high temperature trapping conditions. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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