The REE and trace elements potential of the Albeşti Granite, Argeş County, Romania

Abstract

The Albeşti granite, of Early Ordovician age, was formed by crustal anatexis, experienced a medium temperature and medium-to-high pressure metamorphic event and is now hosted by the crystalline formations of the Leaota Mountains (South Carpathians), where it forms stratigraphically concordant lenses. Its most striking feature, similar to other European granites of comparable age and metamorphic history (e.g., the Rumburk granite), is the blue quartz content. It has a peraluminous-calc-alkaline character and its CIPW normative composition plots in the monzogranite field. The purpose of this preliminary study is to determine the REE-bearing mineral content, both for academic and economic purposes, and to contribute to the overall geologic understanding of the Albeşti Granite. Preliminary microscopic observation performed on thin sections has shown the presence, as accessory minerals, of epitaxial rutile on biotite, zircon, monazite and fluorapatite. Monazite is particularly important to the topic of the study because its capacity to incorporate trace and rare earth elements. Biotite crystals present a significant density of pleochroic halos indicative of radioactive mineral inclusions. The heavy mineral fraction was separated using bromoform and then used for polished sections. The sections were then investigated using Micro Raman and SEM. Granite samples have also been analysed for radioactive nuclide content using low-background gamma spectrometry. Based on SEM imaging, SEM-EDS analysis and Raman spectra, the following minerals of interest have been identified: uraninite, xenotime-Y, zircon, monazite-Ce, fluorapatite, thorite, rutile and ilmenite. The SEM imaging has shown monazite alteration halos made up of epidote, allanite and apatite (potential indicator of monazite instability during amphibolite facies metamorphism); uraninite has been observed associated with pyrite and galena. Low-background gamma spectrometry indicates the presence of 212 Pb, 214 Pb, 212 Bi, 214 Bi, 226 Ra, 208 Tl, 228 Ac and 40 K radioactive nuclides. The 212 Pb-212 Bi-208 Tl sequence is consistent with the 232 U decay chain; 214 Pb and 214 Bi are products of 226 Ra, itself a product of 238 U radioactive decay; 228 Ac is a "granddaughter" isotope of 232 Th.

Full text

Goldschmidt2019 Abstract
The REE and trace elements
potential of the Albeşti Granite,
Argeş County, Romania
PANTIA ADRIAN-IULIAN(1), FILIUŢĂ ANDRA-ELENA(1),
LÖRINCZ SAROLTA(1), DUMITRAŞ DELIA-GEORGETA(1),
ION ADRIANA(1), MARINCEA ŞTEFAN(1)
1Geological Institute of Romania, Bucharest, Romania,
012271, e-mail pantia.adrian@gmail.com
The Albeşti granite, of Early Ordovician age, was formed
by crustal anatexis, experienced a medium temperature and
medium-to-high pressure metamorphic event and is now
hosted by the crystalline formations of the Leaota Mountains
(South Carpathians), where it forms stratigraphically
concordant lenses. Its most striking feature, similar to other
European granites of comparable age and metamorphic
history (e.g., the Rumburk granite), is the blue quartz content.
It has a peraluminous-calc-alkaline character and its CIPW
normative composition plots in the monzogranite field. The
purpose of this preliminary study is to determine the REE-
bearing mineral content, both for academic and economic
purposes, and to contribute to the overall geologic
understanding of the Albeşti Granite.
Preliminary microscopic observation performed on thin
sections has shown the presence, as accessory minerals, of
epitaxial rutile on biotite, zircon, monazite and fluorapatite.
Monazite is particularly important to the topic of the study
because its capacity to incorporate trace and rare earth
elements. Biotite crystals present a significant density of
pleochroic halos indicative of radioactive mineral inclusions.
The heavy mineral fraction was separated using bromoform
and then used for polished sections. The sections were then
investigated using Micro Raman and SEM. Granite samples
have also been analysed for radioactive nuclide content using
low-background gamma spectrometry. Based on SEM
imaging, SEM-EDS analysis and Raman spectra, the
following minerals of interest have been identified: uraninite,
xenotime-Y, zircon, monazite–Ce, fluorapatite, thorite, rutile
and ilmenite. The SEM imaging has shown monazite
alteration halos made up of epidote, allanite and apatite
(potential indicator of monazite instability during amphibolite
facies metamorphism); uraninite has been observed
associated with pyrite and galena. Low-background gamma
spectrometry indicates the presence of 212Pb, 214Pb, 212Bi,
214Bi, 226Ra, 208Tl, 228Ac and 40K radioactive nuclides. The
212Pb - 212Bi - 208Tl sequence is consistent with the 232U decay
chain; 214Pb and 214Bi are products of 226Ra, itself a product
of 238U radioactive decay; 228Ac is a “granddaughter” isotope
of 232Th.