ISSN 1028334X, Doklady Earth Sciences, 2013, Vol. 451, Part 1, pp. 766–769. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.I. Alekseev, Yu.B. Marin, 2013, published in Doklady Akademii Nauk, 2013, Vol. 451, No. 3, pp. 314–317.
GEOCHEMISTRY
RareMetal Zircon Rims in Lithium–Fluorine Granites
of the Far East
V. I. Alekseev and Corresponding Member of the RAS Yu. B. Marin
Received February 12, 2013
DOI: 10.1134/S1028334X13070180
Zircon of raremetal lithium–fluorine granites is
characterized by a high concentration of isomorphic
admixtures and rareelement microminerals [1]. We
observed two types of zircon grains in lithium–fluo
rine granites of the Far East: (1) with the core relatively
depleted in admixtures and raremetal rims; (2) with
out a core, with a maximal concentration and spotty
zoned distribution of rare elements [2]. The first type
was formed during crystallization of a melt containing
zircon crystals captured during palingenesis. Transfor
mation of protocrystals was accompanied by over
growth of rims enriched in minor elements and min
eral inclusions (xenotime, uraninite, thorite, mona
zite, and others). Investigation of the composition of
raremetal zircon rims has clarified the history of crys
tallization of the lithium–fluorine granite melt.
BSE and CL images of zircons clearly demonstrate
the presence of a zoned core and two rims: monolithic
inner and fractured and porous outer (Figs. 1, 2). The
compositional peculiarities of these rims were studied
using electron probe microanalysis and secondary ion
mass spectrometry. Electron probe microanalysis
demonstrated poor accumulation of rare elements in
13
BSE
the core (<0.01%), not registered by the energydis
persive detector, except for U and Hf. The adjacent
rim is characterized by a strong increase in the U, Th,
and Y concentrations reaching 6.5, 2.5, and 4.6%,
respectively. The outer rim is depleted in U and
enriched in Hf and Yb with the maximal concentra
tions of 13.2 and 6.3%. Both rims are characterized by
a Zr deficiency and an admixture of incompatible ele
ments, namely Fe, Ca, and Al (Table 1).
Ionic scanning of the zircon core and rims allowed
us to reveal their minorelement composition. Protoc
rystals contain a small admixture of rare elements,
except for Y (1646–10418 ppm) and Hf (6028–
15525 ppm), which provides evidence for poor rare
metal specialization of the protolith (Table 2). Some
times cores contain seed crystals with extremely low
concentrations of minor elements (U < 150 ppm,
Y < 900 ppm, ΣHREE < 460 ppm, P < 100 ppm).
There are cores with higher concentrations of U, Th,
P, Yb, and Nb resulting from mineral inclusions
(Fig. 2, area 3I).
The inner uranium rim of zircon (13 296–23 759
ppm U) is enriched in Th (2688–6781 ppm),
12
II
2III
BSE 2II
CL
2I
11
CL
23
21
22
III
IIII
50 µm
50 µm
1
2
Fig. 1. Raremetal rims of zircon from lithium–fluorine granites of the Verkhneurmiyskii (1) and Severnii (2) plutons of the Far
East; core: 11, 1I, 21, 2I; uranium rim: 12, 1II, 22, 2II; hafnium rim: 13, 1III, 23, 2III. BSE, backscattered electron
images (JSM6460LV, Mining University, Saint Petersburg); CL, cathode luminescence (Camscan MX2500S, Center of Isotope
Investigations, Russian Geological Research Institute). Full circles denote points of electron microprobe analyses (no scale);
empty circles, points of ion microprobe analyses (in scale).
National Mineral Resources University (Mining University), Saint Petersburg, Russia
email: wia59@mail.ru
766
RAREMETAL ZIRCON RIMS IN LITHIUM–FLUORINE GRANITES
BSE 3III
TOF
y
TOF
x
U
x
y
767
TOF
y
x
Y
31
32
33
3I
3II
20 µm
Intensity
120
120
U
Hf
120
Hf
80
80
80
40
40
40
0
x
y
0
x
y
0
Y
x
y
Fig. 2. Raremetal rims of zircon from lithium–fluorine granites of the Verkhneurmiyskii pluton; core: 31, 3I; uranium rim:
32, 3II; hafnium rim: 33, 3III. BSE, backscattered electron images (JSM6460LV, Mining University, resolution 6 nm);
TOF, secondary ions of U, Hf, Y (TOF.SIMS 5, Physical–Technological Institute, Yaroslavl, resolution 0.3 µm); x–y is the
TOF–SIMS profile. See Fig. 1 for other symbols.
P (1262–3553 ppm), and incoherent elements,
namely Ca (on average, 630 ppm), LREE (124 ppm),
Sr (22.8 ppm), H2O (2474 ppm), and F (318 ppm).
The outer hafniumrich rim (10 552–26 587 ppm Hf)
is characterized by the high concentration of Nb
(137–2280 ppm), Ti (5.1–308), and some elements
not typical for zircon, such as Cs (on average,
45 ppm), Ba (14.9 ppm), H2O (3394 ppm), and
F (264 ppm) (Table 2). The distribution of HREEs
between rims is variable, but they are statistically accu
mulated in the uranium zone: 8710–13 877 ppm vs.
3236–10 039 ppm in the hafnium zone. The concen
trations of LREEs in rims are almost the same: 68.5–
206 and 26.9–203 ppm, respectively. The LuN/LaN
ratio ranges from 289 to 9856.
Thus, the concentration of rare elements in rims of
Far East zircon reaches 8.16% (Table 2) exceeding
10% at some points (Table 1). The concentration of
such isomorphic components as Hf, Nb, Ti, Cs, Ba,
Li, F, and H2O sharply increases, and the Th/U ratio
decreases from 1.00 to 0.06 from the core to the outer
rim of the zircon. U, Y, HREEs, Th, P, Ca, and Sr are
accumulated in the intermediate rim. The main role
among the rareearth elements belongs to Yb, Er, and
Dy; the Ce anomaly is smoothed out from core to
periphery (Ce/Ce* changes from 19.0 to 1.5), whereas
Table 1. Chemical composition (wt %) of zoned zircon from lithium–fluorine granites of the Far East
Point
Zone
Al
Si
Ca
Fe
Y
Zr
Yb
Hf
Th
U
O
11
21
31
Core
–
–
–
14.8
15.1
14.9
–
–
–
–
–
–
–
–
–
50.2
49.2
48.4
–
–
–
0.3
0.5
1.3
–
0.1
–
0.3
0.4
1.1
34.5
34.7
34.4
12
22
32
U zone
–
0.6
–
15.1
15.0
14.9
0.9
1.2
–
1.0
1.7
–
1.6
–
–
42.2
39.3
43.5
–
–
–
1.7
0.5
0.6
0.4
1.3
2.0
3.1
6.3
5.3
34.2
34.2
33.7
13
23
33
Hf zone
–
–
–
15.2
16.0
15.8
–
0.1
–
–
0.8
0.8
–
–
–
43.9
41.7
40.7
0.9
0.9
0.4
4.8
4.9
7.6
0.3
0.3
–
1.0
0.7
0.5
33.9
34.5
34.1
Note: Analyses were obtained by electron probe microanalysis, Inca Energy SEM (Mining University). The dash means that the concentra
tion is below the detection limit; totals are normalized by 100%; point nos. are given in Figs. 1 and 2.
DOKLADY EARTH SCIENCES
Vol. 451
Part 1
2013
DOKLADY EARTH SCIENCES
Vol. 451
Part 1
0.3
7.6
0.1
1.9
4.5
0.04
30
163
320
622
115
1135
66
0.23
0.011
9.1
10
1250
La
Ce
Pr
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
H2O
F
Th/U
Eu/Eu*
Ce/Ce*
ΣLREE
ΣHREE
0.76
0.038
5.6
59
1713
1.9
43
1.7
13
16
0.36
55
243
456
835
124
460
98
0.62
471
42
11
1.9
3105
50
0.7
1.1
6957
691
909
2I
0.38
0.019
2.8
339
8255
22
215
16
87
69
0.61
145
625
1781
4938
766
11357
689
15
2580
452
14
12
10418
354
15
11
10706
5523
14 677
3I
0.40
0.003
6.6
69
8710
2.7
55
1.5
10
23
0.06
168
902
2518
4569
552
1971
493
5.2
2690
157
8.1
7.5
15262
316
8.1
1.8
8060
6781
16888
1II
0.24
0.007
1.8
206
9660
13
97
13
83
107
0.45
347
1497
2603
4591
622
2949
343
1.0
1262
1660
53
51
15559
1420
14
8.0
11961
3189
13296
2II
Uranium zone
0.11
0.005
16
97
13877
1.1
83
1.4
11
23
0.10
143
1061
3101
8417
1155
2501
116
3.5
3553
74
6.8
10
17329
473
9.1
3.7
17090
2688
23759
3II
0.06
0.014
1.8
67
10039
3.8
30
4.2
29
40
0.30
106
592
1811
6493
1036
2075
97
2.8
2242
344
28
16
5567
808
8.3
5.0
26587
671
11896
1III
0.35
0.026
1.7
198
9757
16
100
12
70
104
1.4
260
1232
2396
5263
606
19848
1372
5.6
2175
896
106
30
10954
2280
101
90
16130
1913
5536
2III
Hafnium zone
0.19
0.010
1.5
103
7854
8.9
48
6.9
39
48
0.28
147
881
1709
4468
649
5510
391
11
1261
358
82
12
7199
1445
50
15
23012
1313
6923
3III
0.31
0.048
1.6
217
5907
22.7
111
13
70
48.9
1.3
143
713
1227
2742
475
n.d.
n.d.
93
n.d.
n.d.
n.d.
n.d.
7430
72
14
n.d.
15400
2515
8192
mole
zinw
0.33
n.d.
n.d.
85
14658
n.d.
n.d.
85
n.d.
345
n.d.
n.d.
1505
2838
10315
n.d.
n.d.
8400
n.d.
3392
7218
n.d.
n.d.
2225
n.d.
n.d.
n.d.
36400
2293
6972
Analogs
Note: The data of secondary ion mass spectrometry (Cameca IMS4f, Physical–Technological Institute, Yaroslavl). The areas of analyses are shown in Figs. 1 and 2. Analogs denote the
average concentrations of admixtures in zircons from topaz granites calculated by the published data: Mole massif (Australia) [3]; Zinnwald (Germany) [4]; n.d., not determined.
0.5
466
10
4.7
1.2
2168
23
0.5
0.47
8587
259
1143
Li
P
Ca
Ti
Sr
Y
Nb
Cs
Ba
Hf
Th
U
1I
Core
Table 2. Concentration of rare and rareearth elements (ppm) in different zones of zircon from lithium–fluorine granites of the Far East
768
ALEKSEEV, MARIN
2013
RAREMETAL ZIRCON RIMS IN LITHIUM–FLUORINE GRANITES
the Eu anomaly is strengthened (with a minimum of
0.003 in the uranium zone).
Mapping of the zircon cross sections using a mass
analyzer TOFSIMS 5 in the Burst Alignment mode
(high resolution by weight and low resolution by sur
face) and profiles plotted using secondary ion mass
spectrometry confirmed the presence of uranium and
hafnium rims. Yttrium is homogeneously accumulated
in the uranium zone, whereas only local jumps of its
concentrations are observed in the hafnium zone and
core (Fig. 2). TOF spectrometry demonstrated
enrichment of zircon rims in atypical elements
(Ca and Al).
Analysis of published data demonstrates that the
concentration of admixtures in zircon from granites is
usually low: Hf (0.39–3.98%) and Y (0.1–0.5%) are
accompanied by REEs, P, U, Th (up to 0.5%), and
other elements with a total concentration of ~0.0n%
[5]. An exception is provided by zircons from lithium–
fluorine granites of Europe (the Bohemian, Central,
and Carpathian massifs), Australia (New England
Batholith), Asia (Transbaikalia, coastal provinces of
Southeast China), Africa (Arabian Desert), and North
America (Guadalupe Mountains), in which the con
centration of rare elements reaches 10% and more
[1, 6–11]. The zircon described in this paper is of the
same category. In particular, its composition is similar
to that of zircon from raremetal topaz granites from
the Mole (Australia) [3] and Zinnwald (Germany) [4]
massifs (Table 2). It ranks below zircon from Erzge
birge in the concentration of REEs, Th, Bi [7, 8] and
zircon from the Carpathians and Chinese Primor’e, in
the concentration of Hf [6, 9, 10]. However, note that
we reported the data on only one type of this mineral
in Far East granites, which is characterized by a low
concentration of admixtures.
The presence of rims enriched in rare and “nonfor
mula” elements in magmatic zircon is traditionally
interpreted as a result of hydrothermal alterations
[5, 12, 13]. However, they may be explained by mag
matic differentiation as well. An increase in the alumi
num content in a subalkaline granite melt occurs in
magmatic systems with lithium–fluorine differenti
ates accompanied by a decrease in the DHf/DZr ratio to
0.5–0.2 and accumulation of Hf in the residual melt
and outer zones of zircon [1, 14]. The concentration of
rareearth elements in zircons from differentiated
granite complexes also reaches the level typical of
hydrothermal mineralization [3]. We should accept
that the composition of zircon from raremetal gran
ites formed in a fluidsaturated melt is quite similar to
the composition of hydrothermal zircon. In this rela
tion, the high concentrations of water and fluorine in
the rims of Far East zircon are indicative (Table 2).
DOKLADY EARTH SCIENCES
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Part 1
2013
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The general tendency of Hf and U accumulation in
the outer zones of zircon as a result of magmatic dif
ferentiation has been known for the last twenty years
[1], but the presence of uranium and hafnium rims in
zircons from lithium–fluorine granites is observed for
the first time. A similar zoned zircon with stratifica
tion of U and Hf was registered in plumasitic granites
from South China [15]. Raremetal rims in zircons
from Far East granites provide evidence for its forma
tion by overgrowth of relict crystals preserved during
protolith melting. The difference in the composition
of rims may be considered as evidence of the evolution
of the magmatic system towards an increase in rare
metal specialization: U, Y, HREE, P, Th → Hf, Nb,
Ti, Cs, Li, F, H2O.
ACKNOWLEDGMENTS
This study was supported by the Russian Founda
tion for Basic Research (project no. 110500868a)
and the Ministry of Education and Science of the Rus
sian Federation (State contract no. 14.740.11.0192).
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