GEOLOGICA CARPATHICA, 52, 4, BRATISLAVA, AUGUST 2001
239—245
A HEAVY MINERAL ASSOCIATION
AND ITS PALEOGEOGRAPHICAL IMPLICATIONS
IN THE EOCENE BRKINI FLYSCH BASIN (SLOVENIA)
DAVIDE LENAZ
1
, ANTONIO ALBERTI
1
, GIORGIO TUNIS
2
and FRANCESCO PRINCIVALLE
1
1
Dipartimento di Scienze della Terra, via E. Weiss 8, 34127 Trieste, Italy; lenaz@univ.trieste.it
2
Dipartimento di Scienze Geologiche, Ambientali e Marine, via E. Weiss 2, 34127 Trieste, Italy
(Manuscript received January 23, 2001; accepted in revised form June 13, 2001)
Abstract: The heavy mineral assemblages of the Brkini Flysch Basin (Western Slovenia) have been studied in some
detail, and new minerals, hitherto not mentioned in the literature have been found. Among these, Cr-spinels, ilmenites
and one orthopyroxene were recognized. All of them were chemically characterized. Chemical analyses on garnets have
been carried out in order to discriminate between different end-members and they turned out to be similar to those found
in both the Julian (Slovenian) and Istrian basins located to the NW and SE of Brkini, respectively. The chemistry of
Cr-spinels suggests that both peridotitic (type-II and minor type-I peridotites Cr-spinels) and volcanic spinels are present.
This fact suggests that the Outer Dinarides of former Yugoslavia, where type-I peridotites are present, began to be eroded
by Middle Eocene. Moreover, similarities between the minerals of Brkini and those of the Julian and Istrian basins show
that supplies from both the NW and the SE areas are present.
Key words: Brkini, flysch, chemistry of heavy minerals, Cr-spinel.
Introduction
Mineralogy and petrography of flysch formations provide im-
portant information on the composition and role of source
rocks and consequently on the general paleogeography of ba-
sins. In the framework of this type of research, several authors
studied in a first stage the heavy mineral assemblages in order
to define the paleogeography of the different basins (Wildi
1985; Winkler & Ślączka 1992, 1994; Faupl et al. 1998; Von
Eynatten & Gaupp 1999). A second stage of knowledge is the
study of the chemistry of some heavy minerals to better dis-
criminate the source rocks. These studies were performed on
Cr-spinels (Pober & Faupl 1988; Arai & Okada 1991; Cooken-
boo et al. 1997; Sciunnach & Garzanti 1997; Lenaz et al.
2000), garnets (Morton 1985b; Di Giulio et al. 1999; Von
Eynatten et Gaupp 1999), and pyroxenes (Ernst & Shirahata
1996; Schweigl & Neubauer 1996; Acquafredda et al. 1997;
Krawinkel et al. 1998).
In the area of the SE Alps and Outer Dinarides several fly-
sch basins are present: the Claut Basin, the Clauzetto Basin,
the Julian (or Slovenian) Basin, the Vipava Basin, the Brkini
Basin and the Istrian Basin (Fig. 1). The mineralogy of some
of them was studied by Magdalenic (1972: Istrian Basin),
Kuščer et al. (1974: Slovenian Basin), Orehek (1972: Brkini
Basin), Lenaz & Princivalle (1996: Cr-spinel from Istrian Ba-
sin), Lenaz et al. (2000: Cr-spinel from Claut and Julian Ba-
sins).
The Brkini Flysch Basin (Lower—Middle Eocene; Slovenia,
Croatia) covers an area between the Julian Basin (Maastrich-
tian—Middle Eocene; Italy and Slovenia) and the Istrian Basin
(Middle—Upper Eocene; Italy, Slovenia and Croatia). Bios-
tratigraphical, sedimentological, and mineralogical studies
were performed (Piccoli & Proto Decima 1969; Orehek 1972,
1991; Khan et al. 1975; Bonazzi & Tunis 1990; Pavlovec et al.
1991; Bonazzi et al. 1996; Tunis & Venturini 1996).
In this study we will better define the chemistry of the heavy
mineral assemblages of the Brkini sandstones in order to pro-
vide new information on provenance areas. Moreover we will
compare these new data from the Brkini Basin with those from
the Julian and Istrian basins with the aim of establishing
whether supplies are from the SE as suggested by Orehek
(1972, 1991) or from the NW as suggested by Tunis & Ven-
turini (1996).
Geological setting
The Brkini flysch has a synclinal structure and it belongs to
the Rijeka synclinorium sensu lato (Sikic & Plenicar 1975).
The flysch area of Brkini borders with the Cretaceous thrust of
Mt Sneznik in the northeast. At its southern margin, early
Eocene limestone of the Čičarja plateau represents the bound-
ary with the flysch deposits. The contact here may be marked
also by basal grey-brown, sometimes slightly cherty marls and
marly shale (Sikic & Plenicar 1975; Orehek 1991).
In the interior of the syncline, numerous folds and dissected
flysch sections are observed, so, due to strong folding, several
smaller synclines were formed. For this reason and for wide
vegetation cover, the stratigraphic sequence of the flysch of
Brkini has never been described as a whole (Pavlovec et al.
1991). Pavlovec et al. (1991) described its basal part near Ko-
šana, Sv. Trojica and Leskovec. Tunis & Venturini (1996) no-
ticed that the succession continues with siliciclastic turbiditic
strata interbedded with calcarenite, sandy carbonate and marl
followed by thin interbedded sandstones and marlstones inter-
calations. Then, debris flow levels, siliciclastic turbidites and
240 LENAZ et al.
sandy carbonate turbidites occur and, near the top of the se-
quence, coarse quartz sandstones are significant. The succes-
sion is closed by less than one hundred meters of siltites and
fine sandstones presumably representing a molassic facies
(Lutetian and/or post-Lutetian; Tunis & Venturini 1996).
The biostratigraphy of the flysch area of Brkini was investi-
gated by Piccoli & Proto Decima (1969), Khan et al. (1975),
Pavlovec et al. (1991), Tunis & Venturini (1996) who exam-
ined the planktonic foraminifers and the calcareous nanno-
plankton of a few sections. On the basic of the scarce paleon-
tological information, the clastic Eocene deep-sea sediments
belong to the Lower—Middle Eocene and the flysch succession
may have a thickness of about 1000 meters.
The flysch consists mainly of interbedded sandstones and
marlstones: the ratio of marlstone to sandstone bed thickness
changes as do the average thickness of the beds the lithology
and the sedimentary structures, sometimes significantly,
throughout the stratigraphic column. The sandstone beds are
siliciclastic turbidites, the matrix of the usually well sorted
sandstones is carbonate.
The siliciclastic turbidite beds are normally graded with oc-
casional flute casts. Amalgamation can be found, cross bed-
ding, convolute bedding lamination and other sedimentary
structures are usually well developed and also dewatering
structures can be observed in the thickest beds. Plant debris is
frequent especially in the upper part. Some siliciclastic turbid-
ites have layers of plant debris at both their bases and tops.
Orehek (1972, 1991) suggested by studying the flute casts
that the direction of the deposition was from the SE and partly
from the east, and recognized in rocks buried under the Adriat-
ic Sea and in the rocks of Gorski Kotar (Croatia) the source
area of the Brkini flysch. In spite of this, Tunis & Venturini
(1996) recognized some sections measured in the western sec-
tor that the direction of deposition was from the NW as in the
nearby Cormons (Slovenian Basin) and Vipava flysch, sug-
gesting that the Brkini Basin was the eastern prosecution of
the Slovenian trough. Anyway, a direction of deposition from
the SE is very common in the central eastern part of the Brkini
Basin (research in progress). The turbidity currents that deliv-
ered siliciclastic turbidites moved mainly parallel to the
WNW—ESE striking axis of the basin (Orehek 1991), where-
as calciturbidites were delivered from a carbonate paltform
in the S—SW.
Orehek (1972) also studied the mineralogy and petrography
of the Brkini sandstones, reporting that the average content of
sandstone is about 43 % quartz, 5 % feldspar, 28 % calcite,
21 % rock fragments and 3 % micas. As regards the heavy
minerals, Orehek (1972) recognized pyrite (16 %), opaque
minerals (48 %), rutile (7 %), zircon (4 %), tourmaline (3 %),
and garnet (22 %).
Methodology
All the rocks sampled for this study are classified as lithic
graywackes. The main constituents are quartz and calcite; pla-
gioclases, clay minerals and dolomites are minor. K-feld-
spars (microcline) and micas (muscovite, chlorite, biotite) are
very rare.
Sandstones were crushed and divided into different grain
size. Heavy minerals were looked for in the 63—125
µ
m frac-
tion where they are most abundant (Morton 1985a). Succes-
sively they were recognized under the microscope. Some of
them were handpicked, mounted in epoxy resin and analysed
by electron microprobe. About 140 spinel and a few ilmenite
crystals were analysed using a Cameca SX50 electron micro-
probe (15 kV accelerating voltage, 10 nA beam current) at the
University of Tasmania (Australia). Garnet and pyroxene crys-
tals were analysed using the Cameca/Camebax electron micro-
probe (15 kV accelerating voltage, 10 nA beam current) at the
University of Padova (Italy).
X-ray diffraction data of the orthopyroxene crystal were re-
corded on an automated KUMA-KM4 (K-geometry) diffracto-
meter, using MoK
α
radiation, monochromatized by a flat
graphite crystal. The h k l and h -k l reflections were collected
up to 60° of 2
θ
with
ω
—2
σ
scan mode. The peak-base width
was 2.5° 2
θ
and the counting times were variable from 20 to
40 s, as a function of peak
σ
. The intensities were corrected for
absorption according to North et al. (1968). 30 reflections
were accurately centred and used for cell parameter determina-
Fig. 1. Flysch deposits of the SE Alps and Outer Dinarides and
sample locations (numbers).
A HEAVY MINERAL ASSOCIATION IN THE BRKINI FLYSCH BASIN 241
tion (a = 18.3030 (7)
×
10
—1
nm, b = 8.8593 (9)
×
10
—1
nm and
c = 5.2108 (3)
×
10
—1
nm). Structure refinement was performed
by means of SHELX-93 program (Sheldrick 1993). The struc-
ture refinement was carried out assuming fully ionized Mg vs.
Fe
2+
both in M1 and M2 sites, Si
2.5+
for T sites and O
1.5—
for
the six non-equivalent oxygens (Rossi et al. 1983). Reflections
with I > 3 (
σ
I) were considered as observed and were used for
the refinement. All the atoms were treated anisotropically, and
all the parameters were varied simultaneously during the
structure refinement, using the weighting scheme proposed by
the refinement program.
Results and discussion
In this study, besides the minerals identified by Orehek
(1972), as rutile (Fig. 2), zircon (Fig. 2), tourmaline, pyrite and
garnet, new heavy minerals such as Cr-spinel (Fig. 3), il-
menite, and one unique orthopyroxene crystal (Fig. 3) were
recognized and analysed.
Cr-spinel
Cr-spinel is present in all the flysch basins of the SE Alps
and Outer Dinarides, from the Claut and Clauzetto basins
Fig. 3. Above: Cr-spinel crystal, SEM. Below: Orthopyroxene
crystal, SEM.
Fig. 2. Above: Rutile crystal, SEM. Below: Zircon crystal, SEM.
(Lenaz et al. 2000), through the Julian Basin (Lenaz et al.
2000), and the Istrian Basin (Magdalenic 1972; Lenaz & Prin-
civalle 1996; Lenaz 2000). Among heavy minerals, normally
found in sediments, Cr-spinel is particularly useful to basin
analyses. Unlike silicate heavy minerals, such as pyroxene
and olivine, it is resistant to low-grade alteration and mechani-
cal breakdown. In addition, it is a widespread accessory min-
eral in ultramafic and mafic intrusives, cumulates, rocks be-
longing to volcanic suites and some metamorphic rocks.
Therefore, detrital Cr-spinel deriving from mantle peridotites
and volcanic rock types is indicative of igneous and tectonic
activity of the source areas.
In Brkini sandstones Cr-spinels are the most abundant
heavy minerals and show significant compositional variations
of different parameters such as Mg/(Mg + Fe
2+
) (Mg#), Cr/(Cr
+ Al) (Cr#), FeO/Fe
2
O
3
ratios and TiO
2
wt. % content. These
variations suggest different sources related to mantle peridot-
ites and mantle-derived volcanic rocks. According to Lenaz et
al. (2000), Cr-spinels from the Brkini Basin were subdivided
in two major groups on the basis of their TiO
2
content and
FeO/Fe
2
O
3
ratio: the peridotitic group (TiO
2
< 0.2 wt. %;
FeO/Fe
2
O
3
> 3) and the magmatic group (TiO
2
> 0.2 wt. %;
FeO/Fe
2
O
3
< 4).
Peridotitic Cr-spinels predominate over magmatic ones.
Peridotitic Cr-spinels show Cr# number ranging between 30
242 LENAZ et al.
and 86. These compositions mainly correspond to Cr-spinel
from transitional type-II peridotites and in lower extent (about
5 % of spinel population) to type-I peridotites (Dick & Bullen
1984). Only a few magmatic Cr-spinels (Cr# between 35 and
69) were recognized (about 15% of spinel population).
The chemical analyses of the peridotitic (sample 30—1, 30—
61) and volcanic (sample 36—55, 36—69) Cr-spinels having
respectively the highest and the lowest Cr# are shown in Ta-
ble 1.
Cr-spinels are ubiquitous in all the Late Cretaceous—Upper
Eocene flysch basins of the SE Alps and Outer Dinarides. Lenaz
et al. (2000), studying the nearby Julian and Claut flysch basins,
recognized that peridotitic Cr-spinels with harzburgite affinity
are present (Cr# between 50 and 90). To the south, that is in the
Istrian Basin, Lenaz (2000) recognized both type-I and type-II
peridotitic spinels (Cr# between 14 and 72; type-I peridotite Cr-
spinels about 17 % of spinel population). In Fig. 4 the Brkini
peridotitic Cr-spinels are compared with those from the Julian
and Claut basins (Lenaz et al. 2000). Cr-spinels from Brkini are
rather similar to the ones from the Claut and Julian basins, but it
should be noticed that, in Brkini Basin, Cr-spinels with type-I
peridotites affinity, are also present, although they were not rec-
ognized in the Claut and Julian basins.
As regards volcanic Cr-spinels (Fig. 5; fields are from Ka-
menetsky et al. 2001) in the Julian and Claut basins, Lenaz et
al. (2000) found magmatic Cr-spinels with OIB (ocean island
basalts), BABB (back arc basin basalts) and MORB (middle
ocean ridge basalts) affinities. Differences between BABB
and MORB affinities were recognized in the Cr-spinel from
Julian Basin utilizing silicate melt inclusions. Unfortunately,
in Brkini Cr-spinels, melt inclusions are not present, and this
does not allow us to discriminate if they are BABB or MORB-
related. However, by analogy with Julian Basin Cr-spinels, we
suppose that Brkini Cr-spinels with low Al
2
O
3
(15—25 wt. %)
content are related to BABB, while spinels with high Al
2
O
3
(> 25 wt. %) are related to MORB.
Crystal-chemical studies on Cr-spinels from Brkini are cur-
rently in progress.
Ilmenite
Ilmenite grains, sometimes with apatite inclusions, were
recognized only in the molasse sediments (top of the se-
quence). Ilmenite grains were found also in the Istrian Basin
(Lenaz 2000). In both basins ilmenite grains are very scarce.
Ilmenite analyses are reported in Table 2.
Pyroxene
Only one orthopyroxene crystal has been found. It was anal-
ysed by means of single crystal diffractometer in order to rec-
Fig. 5. Al
2
O
3
vs. TiO
2
diagram for volcanic spinels (TiO
2
> 0.2 wt. %;
FeO/Fe
2
O
3
< 4). Full circle: Brkini Basin spinels; open circle: Julian
Basin spinels (Lenaz et al. 2000); open square: Claut Basin spinels
(Lenaz et al. 2000). Arc, OIB, MORB, BABB fields are from Ka-
menetsky et al. (2001).
Fig. 4. Cr# vs. Mg# diagram for peridotitic spinels (TiO
2
< 0.2 wt. %;
FeO/Fe
2
O
3
> 3). Dotted field: Brkini Basin spinels; solid line: Julian
Basin spinels (Lenaz et al. 2000); dashed line: Claut Basin spinels
(Lenaz et al. 2000). Cr# = Cr/(Cr + Al); Mg# = Mg/(Mg + Fe
2+
).
Table 1: Chemical composition and structural formulae of Cr-
spinels. Fe
2
O
3
calculated on the basis of spinel stoichiometry. Cr#
= Cr/(Cr + Al); Mg# = Mg/(Mg + Fe
2+
).
Cr - SPINELS
Peridotitic
Volcanic
Sample
30-1
30-61
36-55
36-69
TiO
2
0.04
0.09
0.44
0.38
Al
2
O
3
6.66
41.32
13.87
37.38
Cr
2
O
3
62.72
26.57
45.35
29.82
Fe
2
O
3
1.87
1.61
8.65
3.84
FeO
20.33
13.79
24.42
12.55
MnO
0.19
0.07
0.29
0.12
MgO
8.26
16.09
6.27
16.93
Total
100.07
99.54
99.29
101.02
Numbers of cations on the basis of 4 oxygens
Ti
0.001
0.002
0.011
0.008
Al
0.266
1.371
0.551
1.239
Cr
1.685
0.591
1.208
0.664
Fe
3+
0.048
0.034
0.219
0.081
Fe
2+
0.577
0.325
0.688
0.295
Mn
0.005
0.002
0.008
0.003
Mg
0.418
0.675
0.315
0.710
Total
3.000
3.000
3.000
3.000
Cr#
86.3
30.1
68.7
34.8
Mg#
40.1
65.3
25.8
65.3
A HEAVY MINERAL ASSOCIATION IN THE BRKINI FLYSCH BASIN 243
ognize the cell parameter (a = 18.3030 (7)
×
10
—1
nm, b =
8.8593 (9)
×
10
—1
nm and c = 5.2108 (3)
×
10
—1
nm) and the
structure. Successively the same crystal was studied by means
of electron microprobe and its chemistry was determined. Its
formula is about En
85
Fs
11
Wo
4
. Chemical and some structural
data are reported in Table 3. Bertolo & Nimis (1993) distin-
guished volcanic, granulitic and high-pressure orthopyroxene
on the basis of their structural data, but the pyroxene of our
study does not plot in any of the fields recognized by them,
therefore, it is not possible to clearly recognize its genesis.
New occurrences of orthopyroxenes and new crystal chemical
studies will yield probably to a better definition of the source.
However, this is the first occurrence of orthopyroxene in the
Brkini Basin and, to our knowledge, in all the basins from the
SE Alps and Outer Dinarides.
Garnet
Garnets were recognized by Orehek (1972), but no chemical
analyses were given in his paper. In this study, garnets were
recognized in the whole sequence but, at present, only a few
garnets from the molasse samples were analysed. Variable
chemistry occurs and the analyses are reported in Table 4. De-
trital garnets analysed in this study are almandine-rich (40—75
mol %), the spessartine component ranges between 0 and 16
mol %, and the pyrope content is particularly high in one grain
(30 mol %). The pyrope-rich garnet is very similar to the gar-
nets from amphibolites associated with the Dinaride ultra-
mafics (Pamic et al. 1973) so that such a kind of source can
be postulated. As regards the other garnets it is not possible
to define a precise source. Some garnets are similar to those
found in the Julian Basin while others are similar to those
found in the Istrian Basin (Lenaz 2000) but more analyses
are necessary.
Conclusions
The study of heavy minerals is important in reconstructing
the history of a sedimentary basin. The occurrence of some
types of heavy minerals is of particular interest, as they are re-
lated to well defined tectonic settings. In the case of the Brkini
Basin new minerals, with respect to published data, have been
identified and analysed, allowing a better knowledge of heavy
mineral assemblages and tectonic evolution of source and dep-
ositional areas.
In the Brkini Basin, Cr-spinels with type-II peridotite and
minor type-I affinities are present. A few volcanic Cr-spinels
are also found. Ophiolites and mafic complexes occur widely
in the Internal and Outer Dinarides of former Yugoslavia.
Table 2: Chemical composition and structural formulae of ilmeni-
tes. Fe
2
O
3
calculated on the basis of ilmenites stoichiometry.
ILMENITES
Sample
36-5
36-4
36-24
36-19
TiO
2
49.92
49.66
49.51
48.96
Al
2
O
3
0.05
0.05
0.08
0.03
Cr
2
O
3
0.00
0.01
0.00
0.00
Fe
2
O
3
5.80
6.16
5.95
6.79
FeO
43.20
42.90
42.57
42.35
MnO
0.55
0.47
0.59
0.55
MgO
0.64
0.72
0.76
0.63
Total
100.16
99.97
99.46
99.31
Number of cations based on the basis of 3 oxygens
Ti
0.944
0.941
0.942
0.934
Al
0.001
0.001
0.002
0.001
Cr
0.000
0.000
0.000
0.000
Fe
3+
0.110
0.117
0.113
0.130
Fe
2+
0.909
0.904
0.901
0.899
Mn
0.012
0.010
0.013
0.012
Mg
0.024
0.027
0.029
0.024
Total
2.000
2.000
2.000
2.000
Table 3: Chemical composition and structural data of BK30 orthopyroxene.
Chemical analyses
Numbers of cations on the basis
of 6 oxygens
Structural parameters
SiO
2
55.08
(0.19)
T site
Si
1.9550
a
0
(nm
× 10)
18.3030
(7)
TiO
2
0.13
(0.04)
Al
IV
0.0450
b
0
(nm
× 10)
8.8593
(9)
Al
2
O
3
1.25
(0.12)
Σ
2.0000
c
0
(nm
× 10)
5.2108
(3)
Cr
2
O
3
0.23
(0.04)
FeO*
10.73
(0.19)
M1 site
Al
VI
0.0056
MgO
29.79
(0.23)
Fe
3+
0.0273
Rsym
2.71
MnO
0.25
(0.07)
Ti
0.0030
N obs. refl.> 3
σ
884
CaO
2.53
(0.11)
Cr
0.0060
R1
2.33
Na
2
O
0.01
(0.01)
Mg
0.9339
wR2
5.86
Total
100.00
Fe
2+
0.0236
GooF
1.255
FeO
9.40
Mn
0.0006
Fe
2
O
3
1.48
Σ
1.0000
Total
100.15
< M1 - O > (nm
× 10)
2.081
(6)
Wo
4.93
M2 site
Ca
0.0952
V M1 (nm
× 1000)
11.884
(8)
En
80.78
Na
0.0000
< M2 - O > (nm
× 10)
2.189
(6)
Fs
14.29
Mg
0.6394
V M2 (nm
× 1000)
12.954
(9)
Fe
2+
0.2592
< TA - O > (nm
× 10)
1.628
(5)
Mn
0.0062
V TA(nm
× 1000)
2.188
(4)
Σ
1.0000
< TB - O > (nm
× 10)
1.641
(5)
V TB (nm
× 1000)
2.254
(4)
244 LENAZ et al.
Lherzolitic peridotites (type-I peridotites) are mainly exposed
in the Outer Dinarides (Karamata et al. 1980), whereas
harzburgites, dunites, gabbroid (type-II peridotites) and volca-
nic rocks are present in the Internal Dinarides (Karamata et
al. 1980).
As regards the nearby Claut and Julian Basin, Lenaz et al.
(2000) suggested that the source area of the type-II spinel
should be located in the Internal Dinarides where harzburgite
rocks outcrop. We suggest that the Brkini Basin was supplied
from both the Internal and Outer Dinarides. This implies that
by Lower-Middle Eocene, not only the Internal, but also the
Outer Dinarides had been eroded and that their material was
supplied to the Brkini flysch.
Ilmenites are present only in the molasse rocks at the top of
the sequence (Lutetian and/or post-Lutetian; Tunis & Venturi-
ni 1996) and in the Istrian Basin (Middle—Upper Eocene) sug-
gesting that an ilmenite-bearing source rock had been eroded
at least by Lutetian times. It is not possible to define its source
even if it possible that its supplies are from the Dinarides.
For the first time, pyroxene has been recognized in the SE
Alps and Outer Dinarides flysch basins. Neither chemistry nor
structural studies permits us to attribute it to a specific rock
source; new occurrences and the related structural studies
could probably yield in the future a better definition of the
source rocks.
The garnets are similar to those found in the Julian Basin
and to those in the Istrian Basin (Lenaz 2000). A pyrope-rich
garnet can be associated with garnets from amphibolites relat-
ed to Dinarides ultramafics. Other garnets cannot be related to
a precise source rock.
Similarities have been recognized to the minerals of both
Julian and Istrian basins (e.g. garnets) so that supplies from
both the NW areas and the SE ones are present, confirming the
paleocurrent data obtained by Tunis & Venturini (1996) and by
Orehek (1972; 1991).
Acknowledgments: DL gratefully acknowledges Dr. V. S.
Kamenetsky and Mr. R. Carampin for assistance in microanal-
yses at the University of Tasmania (Hobart, Australia) and Pa-
dova (Italy), respectively, Dr. E. Cigna for help in sampling
and Mr. L. Furlan for technical assistance. Prof. I. Rojkovič,
Dr. I. Broska and Prof. R. Kryza are acknowledged for their
helpful comments. The financial support of the MURST grant
(Crystal chemistry of mineral species: use of advanced tech-
niques for a modern systematic; Cristallochimica delle specie
minerali: uso di tecniche avanzate per una moderna sistemati-
ca; COFIN ’99; F. Princivalle) is also acknowledged. The Ital-
ian C.N.R. financed the installation and maintenance of the
microprobe laboratory at the University of Padova (Italy).
References
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Table 4: Chemical composition and structural formulae of garnets. Fe
2
O
3
calculated on the basis of garnet stoichiometry.
GARNETS
Sample
NV-a
NV-b
NV-c
NV-d
NV-e
NV-f
SiO
2
36.77
38.72
37.22
37.54
36.37
37.52
Al
2
O
3
20.59
21.52
20.84
20.79
20.60
20.92
Cr
2
O
3
0.01
0.02
0.02
0.05
0.02
0.01
MgO
2.33
8.10
4.51
1.82
2.27
4.62
FeO
30.65
17.73
33.35
29.09
32.93
31.11
Fe
2
O
3
1.13
2.88
1.37
0.70
1.72
0.84
TiO
2
0.01
0.09
0.00
0.08
0.02
0.01
MnO
7.00
0.58
1.84
0.66
5.42
3.42
CaO
1.62
10.63
0.97
9.33
0.81
1.61
Total
100.11
100.25
100.11
100.06
100.16
100.06
Numbers of ions on the basis of 12 oxygens
Si
2.982
2.948
2.977
2.995
2.959
2.990
Al
1.967
1.930
1.964
1.955
1.974
1.966
Cr
0.001
0.001
0.001
0.003
0.001
0.001
Mg
0.282
0.919
0.538
0.216
0.275
0.549
Fe
2+
2.078
1.128
2.230
1.941
2.241
2.074
Fe
3+
0.069
0.164
0.082
0.042
0.105
0.051
Ti
0.001
0.005
0.000
0.005
0.001
0.001
Mn
0.481
0.037
0.125
0.045
0.373
0.231
Ca
0.141
0.867
0.083
0.798
0.071
0.138
Total
8.000
8.000
8.000
8.000
8.000
8.000
Pyrope
9.44
31.13
18.06
7.22
7.57
18.35
Almandine
70.49
40.28
75.95
64.71
77.02
69.68
Spessartine
16.12
-
3.30
1.48
12.62
7.72
Andradite
2.29
5.26
2.61
2.09
2.32
2.00
Grossulare
1.59
23.00
-
24.10
-
2.18
Uvarovite
0.03
0.06
0.06
0.16
-
0.03
Schorlomite
0.03
0.26
0.01
0.24
0.06
0.03
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