Summary:
The present thesis deals with a comparative study in the geochemistry of the
trace and the rare earth elements in tertiary granitoids in central Macedonia,
related or not with known mineralizations and the definition of the geotectonic
environment of the granite magma genesis. The objective of the thesis is the
study of the trace and the rare earth elements’ geochemistry of the Stratoni
granodiorite and the Stratoni – Olympias aplites and pegmatites that are
related with the notorious mass sulfide and precious metal mineralizations, the
Megali Panagia’s granitoids that include the diorite to granite porphyries of
Tsikara and Skouries which is associated with the homonym Cu-Au ore deposit and
the Jerissos’, Mesada’s, Stefanina’s and Mesolakkia’s plutons which are not
related with any known mineralizations. This study aims to give a comprehensive
account on the determination of the granites of the study area, which, even if
are not related with any known ore deposits, they have common geochemical
characteristics of the Large Ion Lithophile Elements (LILE), the High Field
Strength Elements (HFSE) and the Rare Earth Elements (REE) with those that are
related. Specifically, the study is focused on: the definition of the
geochemical characteristics of each pluton, the determination of the
geotectonic environment in which the granite magma has been formed, the
determination of the common geochemical characteristics of the granites that
are associated with known mineralization, the comparison of the above
geochemical characteristics, with those of the granites’ that are not
associated with any known ore deposits. The studied granites presented
petrographic variety, that included diorites, monzodiorites, quartz diorites,
quartz monzodiorites, tonalites granodiorites, granites, pegmatites and
aplites. The Jerissos granite is of Mid Eocene age, which till now It hasn’t
been associated with any mineralization and has the same age with the Sithonia
and Ouranoupolis Plutons in SE Chalkidiki peninsula. It is consisted by
different petrographic types, biotite granite, two mica granite and biotie
granodiorite. The Stratoni plouton is a fine to coarse grained magmatic
intrusion composed by quartz diorite, quartz monzodiorite, tonalite and
granodiorite to granitite petrographic types, but the granodiorite type is the
dominant. In Stratoni – Olympias area there exist a wide network of aplitic and
pegmatitic dykes that usually have been identified as aplite-pegmaties. The
Skouries porphyry close to the Megali Panagia village is a granodiorite to
tonalite porphyry intrusion. South-eastern of the Skouries porphyry, the great
porphyry intusion that occupies the central part of the Tsikara mountain is a
granodioritic to tonalitic porphyry. That porphyry is surrounded by a more
mafic igneous rock, partly porphyritic, mainly of quartz monzodiorite
composition. The Mesolakkia granite is a coarse grained, partly porphyritic
pluton of monzodiorite granodiorite and granite composition. During the
fieldwork, a gossan formation of some tens of square meters, has been
identified in the southern edge of the pluton. The pluton of the Mesada region
is a mid to coarse grained mafic magmatic intrusion of diorite and quartz
diorite to tonalite and granodiorite composition. The Stefanina pluton is a
mid-grained pluton of monzodiorite to diorite composition. Occasionally it is
being crosscut by pegmatite dykes. At the western part of the pluton, close to
the border with the ultrabasic rocks, a highly altered rock with porphyritic
texture, presenting evidence of copper mineralization, has been identified
during the fieldwork. Sampling was carried out during fieldwork, taking care to
include fresh rock samples from any different petrographic types of its pluton.
The bulk rock chemical analyses were implemented by the X-ray Fluorescence
analytical method (XRF) in the Laboratory of the Department of Geology,
University of Leicester, UK. The major elements analyses were performed in
fussed beads while the trace elements analyses’ were performed in pressed
pellets. The chemical analyses of selected samples, for the REE and for the U,
Ta, Hf and Cs as well, were carried out by the instrumental neutron activation
method in the Institute of Nuclear Technology and Radio Safety, National Centre
for Scientific Research “DEMOKRITOS”. The microprobe analyses for the
determination of the mineral chemistry were obtained by E.M.P.A. equipped with
a WD system in the Laboratory of the Department of Geology, University of
Leicester, UK. The variety in petrography presented by the studied plutons
reflects their chemical inhomogeneousness in major elements. In any case, the
Stratoni, Megali Panagia, Mesolakkia Stefanina intrusions the Stratoni –
Olympias aplite-pegmaties and at least parts of Jerissos and Mesada plutons,
have many common geochemical characteristics. They have been formed by
calc-alkaline to high K calc-alkaline to magmas and they are characterized by
high LILE/HFSE και LREE/HREE ratios. Their primitive mantle normalized
spidergrams present negative anomalies at Nb and Ti. These characteristics
indicate that these plutons that have been crystallized from calk-alkaline
magmas, produced in a volcanic arc geotectonic environment, by the partial
melting of crustal, lithospheric mantle and asthenospheric mantle components.
The Stratoni pluton, the Megali Panagia intrusions, the Mesolakkia granitoid,
the granite and granodiorite parts of the Jerissos pluton and the granodiorite
parts of the Mesada pluton, have common geochemical characteristics with the
pre-plate collision granites (that means Volcanic Arc Granites) and with the
post- collision granites (post-COLG). The commonalities in their normalized
trace elements’ spidergrams are so strong that even a common origin for the
granite magma could be suggested. As long the tertiary magmatism is related
with massive sulphide and porphyry copper ore deposits, the Mesolakkia pluton
and the granodiorite parts of the Mesada pluton can be related to
mineralization just similar to the Stratoni and Megali Panagia granitic
intrusions. Moreover, the Stefanina pluton exhibits also common geochemical
characteristics, presenting, high LILE/HFSE and LREE/HREE rations and negative
Nb and Ti anomalies, that indicate a high crust/mantle ratio in the formation
of its parental magma. The geotectonic environment for the magma formation was
a volcanic arc environment. As there is a significant number of common
geochemical characteristics in trace and rare earth elements of the Stefanina
pluton with the above mentioned calk-alkaline plutons the possibility that this
pluton can be related to mineralization, like the above mentioned granitic
intrusions could be suggested. The Stratoni – Olympias aplite-pegmaties and
Stefanina pegmaties are characterized, at least partly, either as
syn-collisional (syn-COLG), or as post collisional (post-COLG), or as volcanic
arc granites (VAG). Whereas the unaltered Stratoni aplite-pegmaties and the
Stefanina granitic pegmatites are presenting geochemical characteristics of
syn-collisonal granites, these characteristics could also be attributed to
their formation during the late stages of a granite magma fractional
crystallization process. The later suggestion is the most favourable as the
Stratoni aplite-pegmaties have been considered, geochemicaly, to be formed at
the latest stages of the granite magma crystallization. Due to the fact that,
Stefanina pegmatites have similar geochemical characteristics with the former,
it is suggested that they could also had been formed at the latest stages of
the magma crystallization process. Different parts of Jerissos granite have
been formed by sequential intrusions of diverse types of granite magmas. Even
though its parts of granite and granodiorite composition have been formed in a
post- collision geotectonic environment, the parts of adamellite composition
have been formed by magma in a syn-collision environment. Moreover, parts of
Mesada pluton have been formed by different types of magmatic intrusions that
have been produced in a diverse geotectonic environments. Those parts of
quartz diorite and tonalite composition have been formed by a “crust dominated”
magma, originated in a within plate environment.
