554
ISSN 0016-7029, Geochemistry International, 2008, Vol. 46, No. 6, pp. 554–564. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.B. Naumov, V.S. Kamenetsky, R. Thomas, N.N. Kononkova, B.N. Ryzhenko, 2008, published in Geokhimiya, 2008, No. 6, pp. 603–614.
INTRODUCTION
The Inagli deposit of chrome diopside is located
30 km west of the city of Aldan (Yakutia, Russia),
within the Inagli massif of alkaline ultramafic rocks of
the potassic series [1–4]. The massif is situated in the
northwestern margin of the Aldan shield. It is about
20 km
2
in area and is topographically manifested as a
cupola structure with a central caldera. It is nearly iso-
metric in shape and has a concentrically zoned struc-
ture. The central part of the massif is a stock, 16 km
2
in
area, made up of forsterite dunite. The stock is sur-
rounded by alkali gabbroids and pulaskites. The gab-
broids are mainly shonkinites grading into mica-bear-
ing pyroxenites. The pulaskites are accompanied by
alkaline pegmatites, which occur mainly among the
dunites and are less common in the zone of shonkinites.
Sheet intrusions of syenite porphyry occur at the
periphery of the massif within the Cambrian carbonate
sequence.
The structure of the Inagli massif is controlled by a
series of fault systems, the most important among
which are large faults extending beyond the massif, as
well as external and internal ring faults and a system of
conical faults [3]. The external ring fault at the bound-
ary of the dunite stock controls the exposures of shon-
kinite–pulaskite rocks. The fault was active during the
development of the massif. An internal fault is distin-
guished in the western part of the massif on the basis of
Inclusions of Silicate and Sulfate Melts in Chrome Diopside
from the Inagli Deposit, Yakutia, Russia
V. B. Naumov
a
, V. S. Kamenetsky
b
, R. Thomas
c
, N. N. Kononkova
a
, and B. N. Ryzhenko
a
a
Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
ul. Kosygina 19, Moscow, 119991 Russia
e-mail: naumov@geokhi.ru
b
School of Earth Sciences and Centre for Ore Deposit Research, University of Tasmania, Hobart, Australia
e-mail: Dima.Kamenetsky@utas.edu.au
c
GeoForschungsZentrum, Potsdam, Telegrafenberg B120, Potsdam, D-14473, Germany
e-mail: thomas@gfz-potsdam.de
Received April 17, 2007
Abstract
—Melt inclusions were studied in chrome diopside from the Inagli deposit of gemstones in the Inagli
massif of alkaline ultrabasic rocks of potassic affinity in the northwestern Aldan shield, Yakutia, Russia. The
chrome diopside is highly transparent and has an intense green color. Its Cr
2
O
3
content varies from 0.13 to
0.75 wt %. Primary and primary–secondary polyphase inclusions in chrome diopside are dominated by crystal
phases (80–90 vol %) and contain aqueous solution and a gas phase. Using electron microprobe analysis and
Raman spectroscopy, the following crystalline phases were identified. Silicate minerals are represented by
potassium feldspar, pectolite [NaCa
2
Si
3
O
8
(OH)], and phlogopite. The most abundant minerals in the majority
of inclusions are sulfates: glaserite (aphthitalite) [K
3
Na(SO
4
)
2
], glauberite [Na
2
Ca(SO
4
)
2
], aluminum sulfate,
anhydrite (CaSO
4
), gypsum (CaSO
4
×
2H
2
O), barite (BaSO
4
), bloedite [Na
2
Mg(SO
4
)
2
×
4H
2
O], thenardite
(Na
2
SO
4
), polyhalite [K
2
Ca
2
Mg(SO
4
)
4
×
2H
2
O], arcanite (K
2
SO
4
), and celestite (SrSO
4
). In addition, apatite
was detected in some inclusions. Chlorides are probably present among small crystalline phases, because some
analyses of aggregates of silicate and sulfate minerals showed up to 0.19–10.3 wt % Cl. Hydrogen was identi-
fied in the gas phase of polyphase inclusions by Raman spectroscopy. The composition of melt from which the
chrome diopside crystallized was calculated on the basis of the investigation of silicate melt inclusions. This
melt contains 53.5 wt % SiO
2
, considerable amounts of CaO (16.3 wt %), K
2
O (7.9 wt %), Na
2
O (3.5 wt %),
and SO
3
(1.4 wt %) and moderate amounts of Al
2
O
3
(7.5 wt %), MgO (5.8 wt %), FeO (1.1 wt %), and H
2
O
(0.75 wt %). The content of Cr
2
O
3
in the melt was 0.13 wt %. Many inclusions were homogenized at
770
−
850
°
C, when all of the crystals and the gas phase were dissolved. The material of inclusions heated up to
the homogenization temperature became heterogeneous even during very fast quenching (two seconds) produc-
ing numerous small crystals. This fact implies that most of the inclusions contained a salt (rather than silicate)
melt of sulfate-dominated composition. Such inclusions were formed from salt globules (with a density of about
2.5 g/cm
3
) occurring as an emulsion in the denser (2.6 g/cm
3
) silicate melt from which the chrome diopside
crystallized.
DOI:
10.1134/S0016702908060025
GEOCHEMISTRY INTERNATIONAL
Vol. 46
No. 6
2008
INCLUSIONS OF SILICATE AND SULFATE MELTS 555
extensive fracturing, brecciation, and concentration of
vein structures. The fault attenuates in the north and
east.
The major units of the geologic structure of the
deposit are the country dunites and the main sources of
gemstones, pegmatites and feldspar–chrome diopside–
phlogopite metasomatic rocks [3]. The dunites are
characterized by almost horizontal fracture patterns,
which give the appearance of schistosity. The dunites
have the following mineral composition (%):
40
−
85 olivine, 15–60 serpentine, 0.5–3.0 chrome
spinel, 0.3–3.0 chrome diopside, 0.3–3.0 phlogopite,
and 0.1–3.0 magnetite. Fresh dunites from the core of
the massif are composed of forsterite with 2–11% of the
fayalite component and chrome spinel. Serpentinized
varieties contain also serpentine and magnetite. Meta-
somatically altered dunites contain ferromagnesian
micas (mainly phlogopite) and chrome diopside [3].
The dunites host numerous pegmatite veins com-
posed of early chrome diopside-bearing and late
amphibole–feldspar varieties. The pegmatites form
complex branching veins with apophyses and swells.
Their morphology is controlled by the physical proper-
ties of the country rocks: in fractured zones, pegmatite
bodies show abrupt inflections and wedgelike pinching
out of individual branches. The contacts of pegmatites
with the country rocks dip at angles from 30
°
to 60
°
and
flatten with increasing depth to
20°
[3].
The deposit contains ten chrome diopside-bearing
vein zones, among which only one is of economic
importance. The zone consisting of chrome diopside–
phlogopite–orthoclase rocks was tracked and con-
toured by open-cut and underground workings and
explored by drilling to a depth of 50 m. It is about
600 m long, and its thickness ranges from 5 to 115 m
averaging 60 m. The content of chrome diopside in this
zone varies from a few percent to 100%. Chrome diop-
side crystals may be up to 20–50 cm across. They are
divided by fractures into defect-free domains, from a
few millimeters to 2–3 cm across. The chrome diopside
is very transparent and has an intense green color.
Zoned crystals were observed at the contact with the
dunites. They consist of dark brown cores, yellowish
green intermediate zones, and intense green margins.
The chemical compositions of various chrome diopside
crystals are given in Table 1. The content of Cr
2
O
3
in
these crystals is 0.13–0.51 wt % with a maximum value
of 0.75 wt %.
The formation conditions and the chemical compo-
sitions of the parent medium from which chrome diop-
side crystallized are still unknown. The earliest data on
the homogenization temperatures of polyphase (with
numerous crystals) inclusions in diopside were
reported in 1971 [5]. The temperatures appeared to be
fairly high, 770–850
°
C. It was also found that the
homogeneous phase in the heated inclusions did not
remain homogeneous after even very rapid (two-sec-
ond) quenching. The inclusions were always heterog-
enized with the formation of numerous tiny crystals.
These observations suggested that the homogeneous
phase in the inclusions was not a silicate liquid, which
would have produced a quench glass, but a salt melt.
However, no methods were available at that time for the
analysis of crystal phases in the inclusions and estima-
tion of the composition of the mineral-forming
medium. During the following years, local analytical
methods (electron, ion, and proton microprobe; micro-
Raman spectroscopy; etc.) have been developed and
become accessible. This provided an opportunity to
reinvestigate the inclusions in chrome diopside samples
from the Inagli massif by means of various modern
techniques. Such investigations allowed us to reveal the
coexistence of silicate melts and immiscible globules of
Table 1.
Representative analyses (wt %) of chrome diopside from the Inagli deposit
Compo-
nent
123456
core rim core rim core rim core rim core rim core rim
SiO
2
57.00 55.68 55.81 56.35 54.48 56.03 56.04 56.20 56.73 56.05 55.14 54.38
TiO
2
0.07 0.04 0.06 0.07 0.07 0.08 0.05 0.07 0.18 0.21 0.28 0.33
Al
2
O
3
0.18 0.21 0.17 0.14 0.20 0.20 0.16 0.17 0.28 0.27 0.50 0.69
FeO 1.21 1.20 1.12 1.21 1.21 1.25 1.16 1.31 1.92 1.92 2.77 3.39
MnO 0.09 0.10 0.04 0.00 0.06 0.02 0.00 0.04 0.07 0.13 0.05 0.02
MgO 17.92 17.66 18.01 17.78 17.81 18.36 17.85 17.74 17.40 17.32 17.09 16.77
CaO 24.27 24.27 24.14 24.25 23.99 24.15 24.16 23.90 24.05 23.99 24.37 23.92
Na
2
O 0.30 0.30 0.35 0.30 0.29 0.28 0.26 0.27 0.22 0.26 0.24 0.21
Cr
2
O
3
0.27 0.51 0.29 0.40 0.28 0.25 0.21 0.17 0.13 0.13 0.25 0.13
V
2
O
3
0.05 0.02 0.03 0.00 0.00 0.10 0.05 0.03 0.10 0.03 0.03 0.07
Total 101.36 99.98 100.01 100.51 98.39 100.72 99.94 99.89 101.09 100.30 100.70 99.90
Note: (1, 2) Green diopside, (3, 4) bluish green diopside, and (5, 6) brownish green diopside.
556
GEOCHEMISTRY INTERNATIONAL
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NAUMOV et al.
sulfate salt melts, which provided a better insight into
the formation conditions of chrome diopside.
INVESTIGATION OF INCLUSIONS
IN CHROME DIOPSIDE
Methods of the Investigation of Crystal and Gas
Phases in Inclusions
chrome diopside crystals with
polyphase inclusions were polished until the inclusions
were exposed on the surface and then analyzed using
Camebax Microbeam and Cameca SX-100 electron
microprobes (Vernadsky Institute of Geochemistry and
Analytical Chemistry, Russian Academy of Sciences,
Moscow, Russia) under the following conditions: an
accelerating voltage of 15 kV, a beam current of 30 nA,
and rastering over an area of
2
×
2
µ
m. The accuracy of
element analysis was 2% relative at contents of >10 wt %,
5% relative at 5
−
10 wt %, and 10% relative at <5 wt %. In
addition, crystal and gas phases from inclusions were
investigated by Raman spectroscopy at the GeoFors-
chungsZentrum, Potsdam, Germany (Dilor XY Laser
Raman Triple 800 spectrometer operating at a wave-
length of 488 nm and a power of 450 mW).
Results of Inclusion Investigation
as was noted
above, the numerous inclusions in chrome diopside are
polyphase. Their size ranges from a few to 70–100
µ
m,
and the majority of inclusions measure a few tens of
micrometers. The inclusions are composed of numer-
ous crystal phases accounting for 80–90 vol %, intersti-
tial aqueous solution between the crystal phases, and a
gas phase (Fig. 1). Inclusions dominated by the gas
phase were occasionally found. Crystals and aqueous
solution account for a small and variable fraction of the
volume of such inclusions (Fig. 1), which suggests a
heterogeneous state of the mineral-forming medium.
Most of the crystals in the inclusions are unisotropic
and show different birefringence. The inclusions can be
subdivided into two types on the basis of their distribu-
tion in chrome diopside. The first type includes isolated
inclusions not related to any fractures; they can be
50
µ
m50
µ
m
50
µ
m 50
µ
m
20
µ
m 20
µ
m
Fig. 1.
Polyphase melt inclusions in chrome diopside from the Inagli deposit.
GEOCHEMISTRY INTERNATIONAL
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No. 6
2008
INCLUSIONS OF SILICATE AND SULFATE MELTS 557
unambiguously interpreted as primary. Inclusions of
the second type have the same phase and chemical
compositions but occur along healed fractures. We con-
sider them as primary–secondary inclusions (after the
classification of Ermakov [6]). Primary–secondary
inclusions are most common in the chrome diopside.
The visual observation of inclusions in a micro-
scopic heating stage showed that crystal dissolution
begins at low temperatures of
150–200°ë
. A further
increase in temperature (Fig. 2) is accompanied by the
dissolution of most crystals and a decrease in the vol-
ume of the gas phase. In the inclusions shown in Fig. 2,
the gas phase disappeared at
615°ë
, but some crystals
were still present. The cooling of the inclusion resulted
in the reappearance of the gas phase and growth of
small crystals.
The following silicate minerals were identified by
electron microprobe analysis: potassium feldspar, phl-
ogopite, and pectolite. Their chemical compositions are
shown in Table 2. The daughter phlogopite crystals
contain from 0.03 to 0.53 wt % Cr
2
O
3
(averaging
0.31 wt %) and 0.01–0.68 wt % BaO (averaging
0.28 wt %). As the total of analyzed components in
phlogopites was on average 95.7 wt %, it can be sup-
posed that they contain ~4 wt %
ç
2
é
. Among other
volatile components, F (0.20 wt %) and Cl (0.05%)
were determined. Figure 3 shows a photomicrograph of
one of such inclusions. It can be seen that the section
exposed on the surface of chrome diopside and investi-
gated with the electron microprobe is dominated by
potassium feldspar and pectolite. In addition, two apa-
tite crystals and potassium sulfate (arcanite) were
detected in this section.
In addition to silicates, a number of sulfate minerals
were detected in the polyphase inclusions. It should be
noted that many polyphase inclusions contained only
sulfate minerals and were free of silicates. In contrast,
if a silicate mineral was present in an inclusion, sulfate
minerals were also always detected. The electron
microprobe analyses of the sulfate minerals are shown
in Table 3. The potassium–sodium sulfate glaserite
(aphthitalite) [K
3
Na
(
SO
4
)
2
] is widespread; more rare
are the potassium sulfate arcanite (K
2
SO
4
), the sodium
sulfate thenardite (Na
2
SO
4
), the sodium–calcium sul-
fate glauberite [Na
2
Ca
(
SO
4
)
2
], and a calcium–sodium
sulfate (Table 3, analysis 12). The crystals exposed on
the surface are sometimes very small, and the obtained
analyses may reflect the chemical composition of a
mixture of various minerals. Table 3 presents several
examples of such analyses (nos. 13–15), which indicate
the presence of chlorides among the crystal phases,
because the analyses show 0.9–10.3 wt % Cl. In addi-
tion to sulfate minerals, the inclusions contain apatite
with high SrO (8.3–12.7 wt %) and a small admixture
of BaO (0.16–0.41 wt %).
As was noted above, Raman spectroscopy was also
used for the identification of crystal phases in the inclu-
sions. Figure 4 gives examples of Raman spectra for
two sulfate minerals, barite and glauberite. Note that an
important advantage of this method is the possibility of
analyzing inclusion phases without their exposure on
the surface of the host mineral. One of such analyzed
inclusions can be seen in Fig. 5. Thenardite, gypsum
(CaSO
4
·
2
H
2
O), bloedite [Na
2
Mg(SO
4
)
2
· 4H
2
O], and
glauberite were detected in this inclusion. In addition,
anhydrite (CaSO
4
), barite (BaSO
4
), celestite (SrSO
4
),
polyhalite [K
2
Ca
2
Mg(SO
4
)
4
· 2H
2
O], and aluminum
sulfate were identified in other inclusions.
Intriguing results were obtained by the Raman spec-
troscopic analysis of the gas phase from inclusions in
chrome diopside. Hydrogen and water were detected in
all of the analyzed inclusions (11), whereas ëé
2
and N
2
occurred only in trace amounts (<0.005 mol %).
Figure 6 illustrates a positive correlation between the
integrated intensity of hydrogen spectrum in the gas
phase from inclusions in chrome diopside and time.
The point labeled “reverse” in the diagram was
obtained after 600 s of measurement of the ç
2
spec-
25°C 591°C
256°C 615°C
394°C cooling
554°C
508°C cooling
510°C
Fig. 2. Behavior of a polyphase melt inclusion in chrome diop-
side during heating up to 615°ë and subsequent cooling.
558
GEOCHEMISTRY INTERNATIONAL Vol. 46 No. 6 2008
NAUMOV et al.
trum. These results indicate that the hydrogen was not
generated under the influence of the laser beam but was
a real component of the inclusions.
The composition of melt from which the chrome
diopside crystallized was calculated from the visually
estimated volume relationships and occurrence fre-
quency of daughter minerals in the inclusions and the
microprobe analyses of these minerals. The following
volume proportions of phases in the inclusions were
accepted: 33% potassium feldspar, 33% pectolite, 10%
phlogopite, 10% chrome diopside, 3% apatite, 3% sul-
fates, and 8% fluid phase. The estimated melt composi-
tion is given in Table 4. This melt contains 53.5 wt %
SiO
2
; is rich in CaO (16.3 wt %), K
2
O (7.9 wt %), Na
2
O
Table 2. Chemical compositions (wt %) of daughter minerals from silicate–sulfate inclusions in the chrome diopside of the
Inagli deposit
Compo-
nent
123456789101112131415
SiO
2
65.27 65.05 64.08 64.18 43.03 42.93 41.84 42.40 40.96 45.69 40.72 56.13 55.36 56.83 54.56
TiO
2
0.01 0.00 0.03 0.00 1.30 0.61 0.02 1.10 0.55 0.60 0.77 0.03 0.06 0.00 0.09
Al
2
O
3
17.01 17.19 18.87 19.03 11.48 11.28 10.65 12.11 12.52 13.83 12.21 0.12 0.03 0.04 0.00
Cr
2
O
3
––––0.24 0.43 0.19 0.03 0.53 0.32 0.43 ––––
FeO 0.08 0.30 0.14 0.06 5.98 6.20 7.54 8.81 2.04 4.58 6.64 0.28 0.12 0.17 0.06
MnO 0.02 0.00 0.00 0.02 0.09 0.11 0.18 0.13 0.03 0.07 0.19 0.13 0.10 0.19 0.12
MgO 0.08 0.10 0.01 0.00 22.63 23.13 23.90 18.86 26.33 17.12 22.66 0.39 0.16 0.32 0.05
CaO 0.30 0.07 0.09 0.09 0.30 0.17 0.23 0.31 0.13 0.14 0.09 31.93 32.79 32.94 34.67
BaO ––––0.06 0.07 0.01 0.22 0.40 0.68 0.51 ––––
Na
2
O 0.05 0.07 0.03 0.04 0.07 0.06 0.08 0.11 0.07 0.10 0.04 9.22 9.18 9.31 8.54
K
2
O 17.23 17.03 16.56 16.42 11.24 11.19 10.92 10.99 10.89 11.47 10.28 0.18 0.04 0.03 0.01
P
2
O
5
0.11 0.15 – – 0.15 0.16 0.13 0.07 – – – 0.17 0.23 0.08 –
SO
3
0.00 0.00 0.00 0.02 0.07 0.05 0.05 0.10 0.35 0.05 0.08 0.00 0.00 0.00 0.00
Cl 0.00 0.00 0.05 0.00 0.01 0.00 0.12 0.02 0.05 0.09 0.03 0.03 0.02 0.01 0.00
F ––––0.24 0.22 0.17 0.20 0.15 0.18 0.22 ––––
Total 100.16 99.94 99.86 99.86 96.89 96.61 96.03 95.46 95.00 94.92 94.87 98.61 98.09 99.92 98.10
Note: (1–4) Potassium feldspar, (5–11) phlogopite, and (12–15) pectolite; dashes denote not analyzed.
100. µm NaKa 15. kV100. µm BSE2 15. kV
K-sulphste
apatite
K-feldspar
pectolite
Fig. 3. Melt inclusion exposed on the surface of chrome diopside for microprobe analysis. The left panel is the back-scattered elec-
tron image of the inclusions, and the right panel shows the distribution of NaKα.
