Title: Microscopy and Calcite Mineratlizations in Low Rank Coals of Velenje Basin in Slovenia
Speaker: Prof. Mirijam Vrabec (University of Ljubljana, Department of Geology)
Date/Time: September 8, 2015 - 10:30-11:30
Place: MDBF G025
Hunting for diamonds in the Eastern Alps: applying complementary
M. Vrabec1, M. Janák2, N. Froitzheim3, K. Yoshida4, V. Sasinková5, M. Nosko6, T. Kobayashi7
and T. Hirajima4
1 Department of Geology, University of Ljubljana, Ljubljana, Slovenia, firstname.lastname@example.org
4 Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto, Japan
6 Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, Slovak Republic
2 Geological Institute, Slovak Academy of Sciences, Bratislava, Slovak Republic
5 Institute of Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic
7 Faculty of Health & Sports, Nagoya Gakuin University, Aichi, Japan
3 Steinmann-Institut, Universität Bonn, Bonn, Germany
Diamond is a form of elemental carbon stable at very high pressure conditions. Microdiamond grains can
form during the orogenic events responsible for building of high mountain chains, when parts of the Eatrh's crust
are dragged down (subducted) to the realm of the Earth's mantle at depths exceeding 100 km. So far, such
processes were identifyed only in few places on Earth, and as such represent unique opportunity to study the
evolution of Earth’s deep interior.
The latest discovery of diamonds was made in the Pohorje Mountains of Slovenia, where numerous
microdiamonds were found in gneisses as single or polyphase inclusions within host garnet minerals . Their
presence demonstrates that this part of the Eastern Alps was subducted to extreme depths within the Earth's
interior, and was subsequently exhumed back to the Earth's surface without complete breakdown of ultrahigh-
pressure mineral phases, allowing a rear and exceptional opportunity to study them in-situ.
To exclude possible contamination during polishing, specimens from Pohorje were prepared using carbon-
free, i.e. Cr2O3 and/or Al2O3 polishing medium, thus replacing conventionally used diamond polishing paste. In the
final stage of specimen preparation remnants of the polishing material was removed from the surface of thin
sections by using an ultrasonic bath.
To unembigousely determine the presence and type of minerals that contain carbon in these rocks several
micro analytical tecniques were combined, allowing a complete microstrucutral and phase analysis at the sub-
micron scale. Diamond inclusions in garnet minerals were first characterized by optical microscope in plane
polarized transmitted light. Electron probe microanalysis (EPMA) with wavelength-dispersive x-ray spectrometry
Dr. Mirijam Vrabec is an Assistant Professor of Mineralogy, Petrology, and Materials in the Faculty of Natural Sciences and Engineering at University of Ljubljana. Dr. Vrabec received her Ph.D. in Geology and Earth Science from University of Ljubljana.
(WDS) and field-emission scanning microscope (FEG-SEM) equipped with energy-dispersive x-ray spectroscopy
(EDS) were applied for analysis of diamond morphology and detailed elemental analysis of host garnet minerals.
X-ray maps were used to determine the distribution of elements in the sub-micron sized inclusions within
garnets. By Micro-Raman analysis, Raman spectra were obtained from polished thin sections. Diamonds are
characterised by sharp Raman peaks mostly centered between 1332 and 1330 cm-1. The two-dimensional
Raman maps were made to analyse polyphase inclusions of diamond, moissanite, methane and carbon dioxide.
Based on the above listed techniques we managed to undoubtly confirm that diamond inclusions in Pohorje
rocks occur in-situ either as single crystal inclusions or as composed polyphase inclusions of diamond +
moissanite (SiC) and diamond + carbon dioxide + methane. Furthermore, co-existence of diamond and
moissanite as fluid-inclusion daughter minerals implies their crystallization from a supercritical COH-fluid at
reducing conditions . Discovery of diamonds in Pohorje mountains confirms that this unit represents the most
deeply subducted part of the Eastern Alps.
 M. Janák, N. Froitzheim, K. Yoshida, V. Sasinková, M. Nosko, T. Kobayashi, T. Hirajima and M. Vrabec,
Journal of metamorphic geology, 33/5, 495-512, 2015.