JOURNAL OF PETROLOGY
VOLUME 38
NUMBER 12
PAGES 1723–1739
1997
Mineralogical Evidence for Two Magmatic
Stages in the Evolution of an Extremely
Fractionated P-rich Rare-metal Granite: the
Podlesı´ Stock, Krusˇne´ Hory, Czech Republic
˘´
´
KAREL BREITER1∗, JIRI FRYDA1, REIMAR SELTMANN2
AND RAINER THOMAS2
´
CZECH GEOLOGICAL SURVEY PRAHA, GEOLOGICKA 6, CZ-15200 PRAHA, CZECH REPUBLIC
1
2
GEOFORSCHUNGSZENTRUM POTSDAM, TELEGRAFENBERG A50, D-14473 POTSDAM, GERMANY
RECEIVED JANUARY 1997; ACCEPTED AUGUST 1997
The Podlesı´ granite stock in the western Krusˇne´ Hory (Erzgebirge)
Mountains, Czech Republic, represents an extremely fractionated,
strongly peraluminous, F- and P-rich, rare-metal granite system of
Late Variscan age. The stock, studied in drill core of 300 m length,
is formed by albite–protolithionite–topaz granite (‘stock granite’,
depth 50–300 m) and shows geochemical and textural zoning. The
stock granite is rich in P (~0·5 wt %), F (0·5–1·2 wt %), Rb
(~1000 ppm), Li (500–1000 ppm) and Cs (100–150 ppm),
and poor in Ti, Mg, Fe, Ca, Sr, Ba, Zr and rare earth elements
(REE). Within the uppermost part of the stock (depth 57–115 m),
the stock granite is intercalated with albite–zinnwaldite–topaz ‘dyke
granite’ layers of 0·5–7 m thickness and a few thin flat dykes of
pegmatite. The dyke granite and pegmatite are even more enriched
in P (~1 wt % P2O5), F (1·0–1·5 wt %) and Rb (up to 3000
ppm), and are also rich in Nb (up to 100 ppm), and Ta (up to
50 ppm). The chemical data for the rock-forming minerals show
distinct differences between the stock granite and the dyke granite
and pegmatite. No chemical zoning of the rock-forming minerals,
either from the upper, rapidly cooled, or from the lower, slowly
cooled parts of the stock granite was observed. These rock-forming
minerals formed during only one stage of crystallization from a
parental melt with moderate contents of P, F, and Li (0·5 wt %
P2O5 in K-feldspar, 5–7 wt % F and 3 wt % Li2O in Li-mica).
In contrast, alkali feldspars and zinnwaldite from the dyke granite
and pegmatite show well-developed chemical zoning. The rims of
K-feldspars are strongly enriched in phosphorus (up to 2 wt %
P2O5), and rims of zinnwaldite grains are enriched in fluorine
(8–9 wt % F). Both zinnwaldite and topaz from the dyke granite
The behaviour of phosphorus in silicic melt and its effect
on melt structure and properties have been the subject
of intensive study during the last two decades (Mysen
et al., 1981; London, 1992; Johannes & Holtz, 1996).
∗Corresponding author. Telephone and fax: 00420-2-5817390. e-mail:
[email protected]
 Oxford University Press 1997
have the OH–F sites fully occupied by fluorine. Also, accessory
phosphates were formed during late magmatic crystallization of the
strongly P, F-enriched residual melt. Thus, the mineralogical data
reflect the presence of two crystallization events within the dyke
granite and pegmatite. The presence of two melts, parental and
residual, the latter strongly enriched in phosphorus, has been also
confirmed by study of melt inclusions in quartz from samples of
the stock granite in its dyke-bearing uppermost part. Mineral, melt
inclusion and whole-rock chemical data from all rock types provide
evidence for two stages of granite evolution, namely crystallization
from parental and residual melts. This means that, in addition to
the granites in Beauvoir (France) and Argemela (Portugal), the
Podlesı´ stock is another well-documented example of a two-stage
evolution of a P-rich granite system.
KEY WORDS:
alkali feldspars; Li-rich micas; granites; Czech Republic
INTRODUCTION
JOURNAL OF PETROLOGY
VOLUME 38
Phosphorus lowers solidus temperature, promotes expansion of the liquidus field of quartz at the expanse of
albite, and increases the solubility of Al and high field
strength elements (HFSE) in melt (London, 1995). Such
enrichment of phosphorus and other volatiles in granitic
melts may result from: (1) fractional crystallization (Yin
et al., 1995; Charoy & Noronha, 1996), (2) liquid immiscibility (liquation) (Roedder, 1984, 1992; Frezotti,
1992; Raimbault et al., 1995; Seltmann et al., 1997;
Zaraisky et al., 1997), (3) filter pressing (London, 1992),
and/or (4) postmagmatic metasomatism with hydrothermal element redistribution (Nova´k et al., 1996). During magma ascent or in situ, the early crystallized minerals
and/or more evolved portion of the melt can be separated
from the primary melt. Both early crystals and segregations of more evolved melt may have undergone
individual evolution paths different from the main portion
of the original magma.
The aim of this study is to assess the potential role for
each of these processes in the generation of an extremely
phosphorus-enriched Variscan rare-metal granite from
Podlesı´ in the western Krusˇne´ Hory (Erzgebirge) Mountains of the Czech Republic. Because only a small number
of such P-rich systems is known world-wide (Kudrin et
al., 1994; Raimbault et al., 1995; Yin et al., 1995; Charoy
& Noronha, 1996) and only limited experimental data
exist (see London, 1995), the Podlesı´ system represents
an excellent, unique case story of magmatic evolution
with only minor alteration. Because of the existence of
a quarry and a number of deep drillholes a complete
geological section is accessible, allowing us to model
magmatic–hydrothermal processes.
GEOLOGICAL SETTING
The Krusˇne´ Hory (Erzgebirge) is one of the classical
metallogenic provinces (Fo¨rster & Tischendorf, 1994;
Breiter & Seltmann, 1995), located near the southern
margin of the Saxothuringian zone at the northwestern
edge of the Bohemian Massif in the Central European
Variscides. Its extent of about 10 000 km2 is determined
partially by Upper Carboniferous plutons that intrude
Upper Proterozoic to Lower Palaeozoic metamorphic
sequences. The plutons are composed of many spatially
subdivided multiphase intrusions. The late rare-metal
enriched intrusions were emplaced into high crustal levels
and are ˇcharacterized by stock-, cupola- and ridge-shaped
apices (Stemprok & Seltmann, 1994). The geochemical
characteristics enable us to distinguish two groups of
highly evolved granites (Breiter et al., 1991; Fo¨rster et al.,
1996): (1) a weakly peraluminous F-rich and P-poor type
related to high-level stocks mostly associated with breccia
pipes (Gottesberg, Altenberg, Sadisdorf, Cı´novec,
Krupka) [A-type granites in the sense of Loiselle & Wones
NUMBER 12
DECEMBER 1997
Fig. 1. Generalized geological map of western Krusˇne´ Hory with
granite distribution.
(1979)], and (2) a strongly peraluminous F- and P-rich type
related to multiple intruded plutons (Ehrenfriedersdorf,
Kra´sno, Podlesı´) ([in the sense of Chappel & White,
1974)]. Tin and tungsten ores (greisen type) are associated
with both types of rare-metal granites and occur mostly
along narrow contact zones with the country rocks.
One of these mineralized areas is the ancient mining
district of Hornı´ Blatna´–Podlesı´, situated in the western
part of the Krusˇne´ Hory Mountains within a pile of
Cambro-Ordovician, mostly pelitic, greenschist-facies
metasediments (Fig. 1). The metasediments are intruded
by a suite of peraluminous granites of the Eibenstock–
Nejdek pluton. The granites are traditionally divided into
the older intrusive complex (‘normal’, OIC), and the
younger intrusive complex (‘tin specialized’, YIC) (Laube,
1876; Breiter & Seltmann, 1995). The youngest, most
fractionated members of the suite are stocks of albite–Limica–topaz granites, e.g. Podlesı´, which typically have
marginal pegmatites (stockscheider) and are commonly
variably greisenized.
GEOLOGY AND PETROGRAPHY OF
´
THE PODLESI STOCK
The Podlesı´ granite system represents the most fractionated part of the S-type Eibenstock–Nejdek pluton.
The Podlesı´ stock (200 m diameter), intrudes phyllites
and biotite granite of the Eibenstock–Nejdek pluton
(Fig. 2). The phyllite envelope of the granite (in the
uppermost 50 m of the studied cores) is strongly altered
to protolithionite–topaz hornfelses and is crosscut by
numerous steep topaz–albite–zinnwaldite–quartz veinlets, accompanied by greisenization and tourmalinization
1724
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
Fig. 2. Geological cross-section of the Podlesı´ granite stock.
of the surrounding rocks. Steep veinlets of silicified aplites
are also abundant. The aureole of hydrothermal alteration (greisens) is limited to regions just outside the
contact with the granite stock.
The internal fabric of the granite cupola has been
studied in three boreholes by the Czech Geological
Survey (Lhotsky´ et al., 1988). The contact of the granite
with the phyllites is sharp, bordered by a marginal
pegmatite zone of 40 cm thickness. The upper part of
the cupola (depth 50–115 m in borehole PTP-1) consists
principally of reddish, medium- to fine-grained albite–
protolithionite–topaz granite (‘stock granite’) with flat
layers of albite–zinnwaldite–topaz granite (‘dyke granite’).
Adjacent to the contacts of both granite types are several
pegmatite dykes (Fig. 3). At greater depth, mediumgrained stock granite has been encountered.
Petrographically, the reddish stock granite is equigranular and fine to medium grained (0·2–1·0 mm). Albite
appears as euhedral lamellar tablets. K-feldspar has
mostly short prismatic subhedral, non-perthitized grains.
Long prisms are twinned and euhedral. Quartz grains
are isometric and anhedral. The mica is protolithionite
[in the sense of Weiss et al. (1993)]. Topaz consists of
euhedral to subhedral grains and makes up 3–4 vol. %
of the rock. Among accessories, apatite prevails (Table 1).
The white dyke granite is fine grained (0·1–0·5 mm).
Quartz, K-feldspar and albite grains are mostly anhedral;
Fig. 3. Pegmatite dykes penetrating along, or near, the contacts of the
stock granite and dyke granite. (Detail from the quarry, thickness of
the pegmatite dykes is exaggerated.)
both feldspars are found also as short subhedral prisms.
Borders of larger feldspar grains have been often leached
and replaced by late quartz, albite and topaz. Grains of
quartz, K-feldspar and topaz are markedly zoned. The
mica is zinnwaldite, and forms subhedral flakes. Large
topaz crystals (0·3–0·5 mm) are subhedral to euhedral;
the small grains are interstitial. Abundance of topaz
1725
JOURNAL OF PETROLOGY
VOLUME 38
NUMBER 12
DECEMBER 1997
Table 1: Modal composition (in vol. %) of granitoids from the Podlesı´ stock (borehole PTP-1)
Sample:
2702
2653
2665
2674
581
Rock:
S
D
S
D
S
Depth (m):
60·5
80·0
89·5
103·5
300·0
Quartz
29·7
33·5
34·3
31·2
32·1
K-feldspar
40·8
33·4
35·3
38·1
30·3
Albite
17·9
17·8
17·7
18·6
26·6
Topaz
3·6
5·8
3·8
3·4
3
Mica
6·8
7·5
7·9
7·9
6·4
Apatite
0·9
0·8
0·7
0·7
0·4
Childrenite
0
0·8
0
0
0
Zircon
0·1
0
0·1
0
0·1
Sericite
0·1
0
0·1
0
0·2
Fluorite
0
0
0
0
0·2
Chlorite
0·1
0·2
0
0
0·1
99·8
99·9
99·9
99·4
Total
100
Rock types: S, stock granite; D, dyke granite.
Remark: Pegmatite is too coarse-grained for modal analysis.
reaches 3·5–6 vol. %. The most common accessory
minerals are phosphates—apatite and childrenite. The
upper contact of the ‘dykes’ is sharp and the lower contact
is often indistinct (diffuse).
The pegmatite consists of relatively large (up to
3 cm × 1 cm) hypidiomorphic columns of partly kaolinitized K-feldspar with a fine-grained granitic groundmass
composed of anhedral quartz, K-feldspar, albite and
zinnwaldite. Topaz is common. Contacts of pegmatite
dykes are in all cases sharp.
The similarity in whole-rock chemistry and mineralogy
of all three above-mentioned rocks suggests that they are
comagmatic at places where melt and exsolved magmatic
vapour phase have been undergoing continuous re-equilibration.
WHOLE-ROCK CHEMISTRY
All granite types from the Podlesı´ cupola are subsolvus,
peraluminous, strongly fractionated alkali feldspar leucogranites.
The stock granite is strongly peraluminous (A/CNK
1·15–1·25). In comparison with common Ca-poor granites (Clarke, 1992), the stock granite is poor in Ca, Fe,
Mg, Sr, Ba, Zr, Sc, V and Pb, and strongly enriched in
incompatible elements such as Li, Rb, Cs, Sn, Nb and
W. The rock is rich in fluorine and phosphorus; it
contains 0·6–1·8 wt % F and 0·4–0·8 wt % P2O5 (Table 2).
The high degree of magmatic fractionation is demonstrated also by low K/Rb and Zr/Hf ratios (22–35
and 12–20, respectively) and high U/Th ratio (4–7). Still
more evolved dyke granite and pegmatite are relatively
depleted in Si, Zr, Sn, W and rare earth elements (REE),
and enriched in Al (A/CNK 1·2–1·4), P (0·6–1·5 wt %
P2O5), F (1·4–2·4 wt %), Na, Rb, Li, Nb and Ta. The
ratios of K/Rb (14–20) and Zr/Hf (9–13) are lower than
in the stock granite.
All rocks are rich in phosphorus, which is mainly
present in the alkali feldspars. P shows a positive correlation with F, Al, Li, Rb, Nb, Ta and peraluminosity
(expressed as A/CNK), and negative correlation with Si,
Zr and Sn (Fig. 4). There is no correlation among P and
Na, K and Sr. High degree of fractionation is documented
also by unusually high concentrations of rare metals. Nb
and Ta are preferentially concentrated in the more
peraluminous dyke granite and pegmatite (50–95 ppm
Nb and 30–55 ppm Ta) compared with the stock granite
(25–50 and 10–25 ppm, respectively). On the other hand,
contents of Sn and W are definitely higher in the stock
granite (10–50 ppm Sn, 20–80 ppm W) than in the dyke
granite and pegmatite (5–20 ppm Sn and 35–60 ppm
W).
The REE contents are generally very low. The chondrite-normalized patterns are relatively flat (Ce/YbCN
4–12) having prominent negative Eu anomalies. Both
dyke granite and pegmatite are even more depleted in
bulk REE, showing remarkably developed lanthanide
tetrad effect (Fig. 5).
The stock granite within the dyke-rich zone (78–120 m
depth in borehole PTP-1) is also enriched relative to its
roof and bottom zones in Al, P, F, Mn, Li, Rb, Cs, Nb
and Ta, and depleted in Si, Zr and REE. Nevertheless,
the differences between the stock granite, the dyke granite
and pegmatite are clearly distinguishable (Fig. 6).
1726
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
Table 2: Geochemical bulk rock data of
representative samples from the Podlesı´ granite
stock (major elements in wt %; trace elements
in ppm)
Sample:
SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Li2O
Na2O
K 2O
P 2 O5
F
H2O+
H2O–
Total
Rb
Cs
Sr
Ba
Zr
Hf
Th
U
Sn
Zn
Pb
Nb
Ta
W
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Y
2708
2361
2360
581
74·05
0·07
14·08
0·66
0·45
0·02
0·05
0·42
0·17
3·99
4·31
0·44
1·14
0·76
0·07
100·20
67·70
0·03
18·37
0·85
0·46
0·04
0·03
0·50
0·35
3·43
5·99
0·91
1·38
0·93
0·08
100·48
69·70
0·02
16·44
0·37
0·67
0·04
0·03
0·48
0·35
4·50
3·51
1·64
1·48
1·32
0·15
100·21
73·13
0·04
13·89
0·10
1·0
0·03
0·05
0·44
0·16
3·74
4·65
0·47
0·64
0·84
0·08
99·04
1203
143
19
7·2
42
2·3
5·9
34
22
37
5·2
33
11
44
2·1
5·4
0·71
2·4
0·96
0·014
1·15
0·30
1·8
0·27
0·62
0·082
0·52
0·069
9·2
3200
180
64
7·2
10
2·4
7·8
21
16
76
2·7
66
49
53
0·25
0·53
0·053
0·16
0·075
0·005
0·12
0·026
0·17
0·028
0·07
0·013
0·09
0·013
1·5
1812
116
375
127
51
7·2
5·8
32
10
84
3·7
124
113
89
0·60
1·2
0·26
1·24
0·38
0·058
0·57
0·093
0·50
0·083
0·20
0·027
0·15
0·023
3·4
1094
107
11
6·6
46
2·1
6·3
33
54
54
9·6
29
9
30
2·9
7·2
0·92
3·2
1·05
0·017
1·18
0·30
1·8
0·28
0·69
0·103
0·63
0·081
9·5
Fig. 4. Correlation of P2O5 with Al, Li (all in wt %), Ta and Sn
(ppm). ×, stock granite; Ε, dyke granite; Μ, pegmatite.
2708, fine-grained stock granite, upper rapidly cooled zone,
borehole PTP-1, depth 55 m; 2361, pegmatite, quarry; 2360,
fine-grained dyke granite, quarry; 581, medium-grained stock
granite, lower part of the stock, borehole PTP-1, depth 300
m.
1727
JOURNAL OF PETROLOGY
VOLUME 38
NUMBER 12
DECEMBER 1997
Fig. 5. Chondrite-normalized REE patterns.
MINERALOGY
Alkali feldspars
All three rock types contain relatively pure end-members
of alkali feldspar: albite with <3% An and K-feldspar
(Kfs) with a maximum of 5% Ab and <1% An. All
structurally studied Kfs are monoclinic (orthoclases). Triclinic microcline (0·65±5) has been found only in the
stock granite immediately above the dyke-rich zone.
High phosphorus content is typical of alkali feldspars
from all studied granite types (Fry´da & Breiter, 1995).
The phosphorus content varies distinctly within the dyke
and stock granite (Fig. 7). The P2O5 content in Kfs in the
dyke granite is very high (between 0·6 and 1·75 wt %);
its distribution shows a distinct zonality (Figs 8 and 9),
whereas in the stock granite the overall content is lower
(0·3–0·7 wt % P2O5) and no zoning has been observed
(Fig. 9). The rubidium content in Kfs, unlike that of
phosphorus, is uniform in both rock types, without any
zoning (0·15–0·25 wt % Rb in the stock granite, 0·35–0·50
wt % Rb in the dyke granite).
The P and Rb contents of albites from all rock types
are lower and more uniform. The P2O5 contents in albite
in the dyke granite are between 0·2 and 1·0 wt %,
Fig. 6. Vertical distribution of selected elements in the Podlesı´ stock:
P2O5, Al2O3, SiO2, F (wt %), Rb and Zr (ppm). ×, stock granite;
Ε, dyke granite; Μ, pegmatite.
whereas concentrations in the stock granite are lower
(0·05–0·7 wt % of P2O5). No zoning in P2O5 has been
observed in albites from the stock granite. Albites from
the dyke granite are zoned, but the rim–core differences
are lower than in K-feldspars. The Rb contents in albite
1728
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
Fig. 7. Histograms of P content-frequency in albite (197 measurements)
and K-feldspars (326 measurements).
are usually <0·1 wt %. The Ba and Sr contents in all
feldspars are below detection limits of electron microprobe analysis (EMPA).
Li-rich micas
In all samples, micas are represented by Li-rich members,
whose chemistry, similar to the K-feldspars, differs
Fig. 9. P2O5 and Rb distribution in orthoclase from the dyke granite
(2360) and stock granite (2647). Scale on each profile represents 0·1 mm.
depending on the host granite type (Table 3). For the
dyke granite and adjacent stock granite, the zinnwaldite
crystals are also distinctly zoned (Fig. 10), with cores
Fig. 8. Cathode-luminescence image of P-rich border zone in Kfs in the dyke granite.
1729
JOURNAL OF PETROLOGY
VOLUME 38
NUMBER 12
DECEMBER 1997
Table 3: Chemical analyses and structural formulae of Li-micas
Sample:
2358
2359
2360
2665
2687
Depth:
quarry
quarry
quarry
90 m
300 m
Rock:
S
P
D
S
S
SiO2
42·9
46·75
48·3
45·0
42·0
TiO2
Al2O3
Fe2O3
FeO
0·75
20·6
0·16
0·29
19·3
20·0
0·17
0·3
11·7
8·2
12·7
1·07
13·2
0
20·7
0·78
21·8
16·9
MnO
0·08
0·19
0·45
0·24
0·18
MgO
0·5
0
0·18
0·43
0·61
CaO
0·13
0·09
0·16
Li2O
2·95
4·2
4·55
3·64
Na2O
0·22
0·25
0·78
0·47
0·34
K 2O
9·34
9·93
8·9
9·91
9·85
1·05
0·72
Rb2O
Cs2O
0·68
n.a.
1·12
1·18
n.a.
n.a.
9·02
8·67
n.a.
n.a.
2·95
0·12
F
7·71
H 2O
0·26
F=O
−3·25
−3·80
−3·65
−3·28
−2·10
Total
97·15
98·95
98·58
98·98
99·11
n.a.
0·25
7·78
0
n.a.
4·98
n.a.
Si
6·361
6·694
6·812
6·477
Al4
1·555
1·288
1·158
1·523
6·301
1·611
Ti
0·084
0·017
0·031
0
0·088
Total Z
8
8
8
8
8
Al6
2·04
1·972
2·162
1·996
2·244
Ti
0
0
0
0
0
Fe3
0·119
0
0·018
0·033
0
Fe2
1·637
1·404
0·971
1·535
2·117
Mn
0·01
0·023
0·054
0·029
0·023
Mg
0·111
0
0·38
0·092
0·136
Li
1·76
2·419
2·58
2·109
1·78
Total Y
5·677
5·818
5·82
5·793
6·3
Ca
0·013
0·014
0·004
0
0
Na
0·063
0·069
0·213
0·131
0·099
K
1·767
1·814
1·6
1·82
1·885
Rb
0·065
0·103
0·107
0·097
0·069
1·908
2
1·925
2·049
2·061
Cs
Total X
O
0·008
20
19·914
20
20
21·453
F
3·616
4·085
3·865
3·544
2·363
OH
0·264
0
0·116
0·424
0·184
2358–2360, wet analyses of mono-mineralic concentrates; 2665 and 2687, EMPA, average of ten points. Li, Rb and Cs by
wet analyses of mono-mineralic concentrates. All in wt %, all analyses at the laboratory of the CGS Praha. Rock types: S,
stock granite; D, dyke granite; P, pegmatite. n.a., not analysed. Recalculation of structural formulae according to Rieder
(1977).
1730
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
Fig. 10. Microprobe profiles across Li-mica crystals from the cooled roof zone of the stock granite (sample 2647) and from the dyke granite
(sample 2360). Contents of all elements are expressed in atoms per formula unit.
1731
JOURNAL OF PETROLOGY
VOLUME 38
being enriched in Fe, Mg and Ti, and rims rich in Si
and Li. Li contents, calculated using the method of Tindle
& Webb (1990), are in overall agreement with analyses
by atomic absorption spectroscopy (AAS) of the mica
separates. Zoning in Si, Fe, Mg and Ti can be explained
by changes of melt chemistry during the zinnwaldite
crystallization. In contrast to the above elements, there
is no zoning in F and Rb (Fig. 10). Fluorine content in
profile across the whole crystals is >8 wt % (Fig. 10),
indicating that F atoms nearly completely occupy the
OH–F sites. If there had been zoning in Rb content, then
it was most probably destroyed by post-crystallization
redistribution of Rb atoms, which are only weakly bound
in inter-layer sites.
Protolithionites [in the sense of Weiss et al. (1993)]
from the stock granite outside the dyke-rich zone are
poorer in Li and Rb, and are also without any distinct
zoning. This character argues for a relatively constant
melt composition during their crystallization. The distribution of Cs in micas within the rock types and also
within single crystals is irregular, but generally the Cs
content is higher in micas from the stock granite, varying
between 0·06 and 0·49 wt %. The Cs content in the
dyke granite varies between 0·05 and 0·26 wt %. No
systematic enrichment or depletion during crystal growth
has been observed.
Zinnwaldites and protolithionites are clearly distinguishable in the Si–Al plot (Fig. 11), where they form
two well-correlated parallel clusters. The Li-rich zinnwaldites are relatively enriched in Al and depleted in Fe;
this corresponds well to the whole-rock chemistry of
parental rocks.
NUMBER 12
DECEMBER 1997
dyke granite have been found. Topaz in the stock granite
contains ~18·5–19·5 wt % F (90–95% of theoretical F
saturation); in the dyke granite, topaz contains 20–21 wt
% F (95–100% of saturation). Some large euhedral
crystals from the dyke zone contain zonally arranged
quartz inclusions, but no zoning in F or Si/Al ratio has
been observed.
Phosphates
Apatite of two generations occurs in all rocks, older Mnpoor euhedral crystals, and younger Mn-rich interstitial
flakes. Both types are poor in Cl (mostly <0·1 wt % Cl)
and moderately F rich (2·5–2·9 wt % F, which represents
~35% of theoretical F saturation).
Childrenite–eosphorite, zwiesselite and triphylite have
also been found in the dyke granite (Table 4). The most
abundant phosphate is the childrenite-rich member of
the childrenite–eosphorite group, which builds euhedral
short prisms 0·02–0·04 mm across. Their texture suggests
primary (late magmatic) origin. Other less abundant
phosphates also seem to be primary. Small euhedral
monazite crystals occur mainly as inclusions in micas;
some of them are surrounded by pleochroic haloes.
Monazite is a main REE host in all rock types. No
amblygonite was found at Podlesı´, although this mineral
is the most common phosphate in Li- and F-rich environments, rare-metal
granites and granitic (LCT-type)
ˇ
pegmatites (Cerny´, 1991; Raimbault et al., 1995).
Other accessories
Quartz
In both stock and dyke granite, quartz occurs in two
forms. The older subhedral grains often contain zonally
arranged albite inclusions. This snowball texture is typical
for highly evolved alkali feldspar granites. The younger
interstitial quartz grains often corrode feldspars. Rhythmical layered textures [e.g. comb quartz layers and other
unidirectional solidification textures (USTs), Carten et al.,
1988; Kirkham & Sinclair, 1988] were not observed in
the Podlesı´ system.
Topaz
Topaz is present in two types (generations). Euhedral to
subhedral isometric crystals are enclosed in all rock types
and are one of the oldest crystallized minerals. The late
interstitial topaz occurs only in the dyke granite and
pegmatite. Both topaz types are rich in fluorine: nearly
all F–OH sites are occupied by F. Only very small
differences in the F content between stock granite and
Relative abundances of accessory minerals are shown in
Table 5. Among them, the Nb,Ta-oxides ˇare the most
important for petrogenetic interpretation (Cerny´, 1991).
Small grains of the most common Nb–Ta rutile are
mainly inherited in mica flakes, sometimes forming
zonally arranged clusters in their inner parts. Columbite,
occurring only in the dyke granite, is partially included
in micas, and partially interstitial. In the pegmatite,
mainly Ta-rich rutile occurs (Breiter & Seltmann, 1995).
Observed textures and conversion of Nb-rich into Tarich minerals during evolution of the system are in
agreement with typical evolution of sodium- (albite-)-rich
ˇ
pegmatitic and granitic environments, as shown by Cerny´
(1991).
MELT INCLUSIONS
The first and essential information which one can obtain
from the melt inclusions is the fact that they exist. In the
case of the samples from Podlesı´ it is important that we
can observe melt inclusions in quartz and topaz, as well
1732
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
Table 5: Distribution of accessory
phases within the granitic rocks of the
Podlesı´ stock
Fig. 11. Si vs Al plot for Li-rich micas (expressed in atoms per formula
unit). Protolithionites from the stock granite (+, top of the stock; Μ,
depth 150 m; ×, depth 300 m) are poorer in Si (and Li) and richer in
Fe than zinnwaldites from the dyke system (Ε, dyke granite; Φ,
pegmatite).
Cassiterite
Columbite
Ilmenorutile
U-tantalite
U-mikrolite
Ixiolite
Wolframite
Huebnerite
Scheelite
Rutile
Ilmenite
Haematite
Pyrite
Bismuthine
Powellite
Roosweltite
Childrenite
Zwiesselite
Triphylite
Stock
Dyke
granite
granite
X
XX
XX
XX
X
Pegmatite
XXX
X
X
X
XX
X
X
X
X
XX
X
X
X
XXX
XX
X
X
X
X
XX
X
X
X, rare; XX, common; XXX, abundant.
Table 4: Chemical analyses (in wt %) and structural formulae of phosphates
Sample:
2651
2360
2669
2669
Mineral:
zwieselite
triphylite
childrenite
eosphorite
udl
20·61
11·02
udl
22·17
udl
9·74
21·74
udl
21·35
31·41
31·54
85·20
84·37
0·65
0·35
0·31
0·70
0·99
0·96
1·01
1·02
5·00
0·65
5·00
0·31
Na2O
CaO
FeO
MnO
MgO
Al2O3
TiO2
P 2 O5
F
Total
Na
Ca
Fe
Mn
Mg
Al
Ti
P
F
O
Fe/(Fe+Mn)
4·24
2·42
36·73
26·06
0·18
32·78
98·16
0·42
34·81
0·42
45·60
10·35
95·85
1·21
0·09
1·10
0·79
0·01
1·00
4·50
0·58
6·04
0·05
5·68
4·82
24·00
All analyses by EMPA at the laboratory of the CGS Praha. udl, under detection limit of EMPA.
1733
JOURNAL OF PETROLOGY
VOLUME 38
NUMBER 12
DECEMBER 1997
Table 6: Examples of electron microprobe results (Cameca SX 50 and SX 100, GFZ Potsdam) on
F- and/or P-rich melt inclusions in quartz of pegmatites and granites from the Podlesı´ stock, Krusˇne´
Hory (Erzgebirge).
Inclusion group:
Rock type:
P-poor, F-rich
´
Podlesı stock granite
P-poor, F-poor
´
Podlesı dyke granite
P-rich
´
Podlesı stock granite
Main group
Ehrenfriedersdorf
granites
Sample:
2358b
2362
2358a
SiO2
66·0±1·4
71·2±1·5
68·2±0·8
TiO2
0·1
0·05
0·1
SnO2
0·02
0·02
n.d.
Al2O3
16·9±0·2
13·8±1·1
17·3±0·2
FeO
1·2±0·1
3·4±1·1
0·8±0·02
MnO
0·1
0·2
0·1
MgO
d.l.
CaO
0·4±0·01
d.l.
0·1
d.l.
0·1±0·01
68·4±1·6
0·03
0·1±0·01
14·6±0·7
0·4±0·04
0·05
d.l.
0·1
Na2O
3·7±0·2
3·2±0·4
2·9±0·2
4·1±0·1
K2O
4·8±0·4
5·0±0·3
4·9±0·4
3·4±0·1
Rb2O∗
0·6±0·08
0·7±0·1
F
8·9±0·3
3·1±0·9
Cl
0·2±0·01
P2O5
Sum
H 2O
0·3±0·05
103·22
(2·8±0·6)†
n.d.
d.l.
0·1
15
11
d K (lm)
25–40
20–60
0·1±0·03
99·5
(1·3±0·4)
n
3·8±0·6
0·2±0·01
2·6±0·4
100·77
0·5±0·04
2·2±0·1
3·0±1·0
98·58
n.d.
n.d.
5
166
25–40
20–100
In the last column is given the average composition of melt inclusions in pegmatite quartz from the tin deposit Ehrenfriedersdorf (Central Erzgebirge) for the purpose of comparison (Thomas et al., in preparation). d.l., below the detection
limit; n.d., not determined; n, number of determinations; d K, diameter of the analysed homogeneous melt inclusions.
∗Calibrated with natural feldspars (from Etyka–Eastern Transbaikalia) and synthetic Rb-feldspars (prepared by St. Melzer,
GFZ Potsdam).
†Five measurements.
as in K-feldspar. Normally, the melt inclusions in feldspar
from the granitic rocks of the Erzgebirge are destroyed
by recrystallization and hydrothermal overprinting.
Therefore, the appearance of melt inclusions in the Kfeldspar is a strong hint that the system was cooled
rapidly, and therefore remained quasi-closed, and that
postmagmatic processes were not important.
From statistical analyses, we obtained from 170 measurements on different samples from Podlesı´ for C W a
value of 7·5±0·8 equiv. wt % water. The extrapolated
solidus temperature (Thomas et al., 1996) for the same
samples is 610±26°C and represents the tendency of
the system towards formation of highly evolved residual
melt. In this paper we confine ourselves to the analytical
determination of the bulk composition of melt inclusions
in the main rock types (Table 6).
The results obtained from melt inclusion studies of the
Podlesı´ samples allow the following interpretation (only
a few inclusions of suitable size could be studied using
EMPA, Table 6).
(1) The stock granite represents the parental system.
The studied melt inclusions in the stock granite (samples
2358a and 2358b) seem, in synthesis with all available
geological, geochemical and mineralogical information,
to reflect the formation of two immiscible liquids (residual
melts enriched extremely in P2O5 plus some F in sample
2358a vs those enriched extremely in F in sample 2358b).
From these two liquids, the parental magmas of the
dyke granite (see rock sample 2362; in sample 2360 no
inclusions of suitable size could be analysed) and
pegmatite (rock samples 2359 and 2361; no EMPA data
from melt inclusions) were generated. We are aware that
the bulk-magma geochemistry may be different from that
of the extremely variable melt inclusion compositions;
however, the latter reflects the general evolution of the
melt system.
1734
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
(2) The melt inclusion group represented by sample
2358a with ~2·6 wt % P2O5 and 2·2 wt % F seems to
represent the liquid producing the dyke granite, whereas
the melt inclusion group represented by sample 2358b
with ~8·9 wt % F seems to reflect the pegmatite melt.
A number of melt inclusions observed in pegmatite and
dyke granite samples characterize melt batches trapped at
complicated pegmatitic to superpegmatitic–hydrothermal
conditions.
DISCUSSION
The ‘ore specialized’ granites [in the sense of Tischendorf
(1977)] of the Krusˇne´ Hory (Erzgebirge) belong to a
group of internationally recognized, strongly fractionated
granite plutons accompanied by Sn–W mineralization.
Several genetic interpretations and models of granite
evolution and granite mineralization have been proposed
during the last 60 years. Most of these interpretations
emphasize the importance of post-magmatic (autometasomatic) overprinting of granites, particularly in
the case of albite–Li-mica–topaz
facies (Teuscher, 1936;
ˇ
Tischendorf, 1977; Stemprok, 1979). The abundance of
the late albite has been explained as being caused by
interaction between primary more potassic granites and
hydrothermal sodium-bearing
fluids (Beus & Zalasˇkova,
ˇ
1962; Tischendorf, 1989; Stemprok, 1993). Nevertheless,
the mineralogy of the Podlesı´ granites suggests a fully
magmatic origin of the specialized granites including the
Krusˇne´ Hory granite plutons. A significant advantage of
the Podlesı´ granite system for the study of fractionation
and crystallization of rare metal-specialized granites is
that greisenization and other types of hydrothermal alteration are nearly absent.
Compared with common stanniferous granites in the
western Krusˇne´ Hory (Breiter et al., 1991; Fo¨rster &
Tischendorf, 1994) and the Cornubian batholith (Manning & Hill, 1990), the Podlesı´ granites are highly enriched
in phosphorus, having >1 wt % P2O5. This makes the
Podlesı´ cupola comparable with the P-rich family of raremetal granites (Beauvoir, Raimbault et al., 1995; Yichun,
Pollard & Taylor, 1991; Yin et al., 1995; Argemela,
Charoy & Noronha, 1991; South Mountain Batholith,
ˇ
Kontak et al., 1996) and LCT-type pegmatites (Cerny´,
1991).
The best-known example of a P-rich granitic suite is
Beauvoir, France. There, superposition of two discrete
units (intrusions) and their contact relations and reactions
have been documented within the stock. According to
the model of Raimbault et al. (1995), fractionation of this
suite occurred at a depth below the emplacement level.
During ascent, the most volatile-enriched part of the melt
moved faster than the rest of the crystal-enriched portion
of the magma. Therefore, the more evolved melt reached
the top of the stock as a true melt before the less evolved
crystal mush. Another example of a P-rich system is
Argemela (central Portugal, Charoy & Noronha, 1991).
There, the ‘initial melt’ is well preserved in feeder channels, and a more evolved rock, containing inherited
crystal cores with more fractionated rims and interstitial
groundmass, forms the upper part of the stock. The
change in melt chemistry between parental and residual
environments was rapid, as documented by sharp zonation of single mica crystals [model presented by Charoy
et al. (1995)]. Unfortunately, the geological relations between feeder channels and more evolved microgranite
within the Argemela stock are unknown.
Many features of the Podlesı´ magmatic system are
similar to that at Argemela. The Podlesı´ system allows
the study of the relations between the parental and
evolved rocks in outcrop. Within the Podlesı´ stock, according to field evidence, three rock types occur: stock
granite, which forms the principal parts of the stock, and
subordinate dyke granite and pegmatite, which are found
as flat layers in the stock’s upper part. The stock granite
in the uppermost peri-contact part of the stock represents
the rapidly cooled portion of initial melt and it preserves
the original chemistry and mineralogy.
Distinct zoning of some Kfs and micas provides mineralogical evidence for two stages of crystallization in
the dyke granite and pegmatite, and only one stage in
the stock granite. The older stage of crystallization of the
dyke granite, represented by Kfs and mica cores, is nearly
the same as that encountered in the stock granite, but
the younger stage of the stock granite evolution, represented by Kfs and mica rims, documents a distinctly
more evolved environment enriched in phosphorus and
fluorine. Theoretically, the younger stage could be magmatic or metasomatic in origin. However, as shown in
the model below, we suggest a magmatic origin also for
the younger stage.
As the melt–fluid K DP is higher than unity (London,
1995), the melt should be richer in P than are coexisting
fluids. On the other hand, reaction of feldspars with
postmagmatic aqueous fluids should produce a decrease
of P content in feldspars and production of secondary
phosphates, expressed by the reaction
P-rich Kfs + zinnwaldite=P-poor Kfs +
muscovite + Fe-phosphates
[as documented by Breiter & Siebel (1995)]. The P-rich
rims of Kfs in dyke granite and pegmatite argue for
principally magmatic crystallization of these rocks from
an evolved residual melt (Fry´da & Breiter, 1995). Thus,
the dyke granite and pegmatite at Podlesı´, in general,
are not a product of metasomatic overprinting of the
stock granite, but are products of crystallization of a
different, more fractionated melt. Thus, mineralogical
1735
JOURNAL OF PETROLOGY
VOLUME 38
data support the existence of two melts within the stock:
parental and residual.
Two main types of melt inclusions (P poor vs P
rich) in quartz from the dyke zone correspond perfectly
to geological observations and mineralogical data. The
first type of melt is nearly identical with the upper, rapidly
cooled zone of the stock granite. The second one is
enriched in Al and P, and depleted in Si and Ca. Both
melts are very rich in fluorine. This corresponds well to
the degree of F abundance in both topaz and mica in
the stock granite and dyke granite (>90 atom. %). The
melt-inclusion data for P-poor melts yield 3–9 wt % of
fluorine, whereas the whole-rock analyses of the stock
granite give only 0·8–1·8% of F; therefore the bulk of
the fluorine from this melt had partitioned into an
aqueous fluid before crystallization ceased. This is in
agreement with experimental melt–fluid K DF p1 ( Johannes & Holtz, 1996). In contrast, the whole-rock F content
in the dyke granite (1·4–2·2 wt %) is nearly the same as
that in the P-rich melt inclusions (~2·2 wt %), meaning
that little fluorine was lost from the P-rich melt of the
dyke granite.
The high concentration of network modifying cations
caused lower viscosity and higher mobility of residual
melt (Mysen, 1987; London, 1995; Johannes & Holtz,
1996). A small volume of evolved melt could be produced
without any observable changes in composition of the
rest of the parental melt.
In Kfs and mica crystals, the ratio of volumes of their
inner cores (which originated from the initial melt) to
their outer rims (which originated from residual melt) is
~1:1. Thus, the actual crystal mush before crystallization
of the dyke granite consisted of roughly one-half crystals
chemically identical to those in stock granite and onehalf residual melt. The present chemistry of the dyke
granite represents an average of these two principal
constituents, with some changes that resulted after fluidadmixing during crystallization.
The formation of two melts may be explained by: (1)
batches or segregations of residual melt trapping crystals
inherited from the parental melt, (2) liquid–liquid immiscibility at depth during magma ascent, or (3) in situ
crystallization within the stock. In the first two cases, the
dyke granite forms true dykes; in the last case it would
be better described as ‘magmatic layers’. The diffuse
character of some foot-wall contacts of the dykes and
lack of steep feeder channels support in situ differentiation
and/or only a short injection of dyke granite magma
into stock granite that was not fully crystallized. The
sharp character of the pegmatite contact with both of
the other rocks argues for interpretation of the pegmatite
as an injection of a small portion of residual, in this case
K-enriched melt.
The processes discussed above operated at a depth
of ~25–70 m below the contact with phyllites (depth
NUMBER 12
DECEMBER 1997
75–120 m in borehole PTP-1). At greater depth, the melt
constitution was stable, nearly like the initial melt, as is
documented by homogeneous Kfs and mica crystals and
whole-rock chemical data in the stock granite of the
deeper part of the stock (120–310 m in borehole PTP1). After the magma in the cupola crystallized, the continuation of fluid flow from deeper parts of the intrusion
caused moderate Li, F and Rb enrichment of the more
permeable stock granite at 93–115 m depth, under the
barrier of the cooled roof and below the thicker dyke
granite layer, as well as some re-mobilization of weakly
bound elements, e.g. Rb and Cs, in mica lattices.
CONCLUSIONS
The crystallization history of the Podlesı´ granite system
can be summarized as follows. The composition of the
initial melt was similar to that of the present stock granite.
The crystallization of this magma started in the outer
upper part of the stock, which cooled quickly and did
not suffer subsequent late- and post-magmatic alteration
(stock granite at depth 50–78 m in the borehole PTP-1).
Here, feldspars and micas show no zoning.
Under the rapidly crystallized carapace, in a practically
closed system, fluids and volatiles became enriched. Mineralogical and melt inclusion data confirm the presence
of three melt types with different crystallization paths:
(1) The stock granite, which is nearly identical to those
mentioned above. (2) The dyke granite, in which major
minerals are strongly zoned, and whole-rock chemistry
suggests enrichment in Al, P, F and Li during crystallization. Rapid change in melt chemistry is documented
in Kfs by P-rich rims; the change in mica compositions
was more gradual. (3) Pegmatite, which is mineralogically
similar to the dyke granite, but enriched in K and
depleted in Si and Na.
Therefore, besides the parental melt, a residual melt
mainly enriched in Na, P, F, Li, Rb and Nb, and a
pegmatitic melt enriched in K, P, F, Li and Rb existed
here. The diffuse character of some foot-wall contacts of
the ‘dykes’ supports in situ differentiation of the residual
melt or only local migration and injection into a stock
granite that was not fully crystallized. The pegmatite
dykes represent injections of a small portion of another
residual, K-enriched melt. At greater depth the homogeneous stock granite crystallized solely from the parental
melt.
ACKNOWLEDGEMENTS
This manuscript was carefully
reviewed by J. Lowenstern,
ˇ
P. Nabelek and M. Stemprok. We thank V. Sixta, P.
Dulski and R. P. Taylor for support with chemical
1736
BREITER et al.
EVOLUTION OF A P-RICH GRANITE
analyses, and V. V. Shatov for modal analyses. We
appreciate the advice and assistance of E. Gantz and P.
Jones during SEM-CL and EMPA studies. The manuscript profited from numerous discussions with T. Jarchovsky´, R. P. Taylor, W. D. Sinclair, D. London, R.
Martin and others, and their helpful comments.
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APPENDIX
Methods for microprobe analysis of
minerals at the Czech Geological Survey
Praha
Minerals were analysed using a CAMSCAN 4-90DV
electron microscope equipped with LINK eXL and Microspec WDX-3PC X-ray analysers. An accelerating
voltage of 15 kV or 20 kV, a beam current of 3 nA, and
a counting time of 100 s were used for the energydispersive analysis (system LINK eXL). This system was
used for analysis of Si, Ti, Al, Fe, Mg, Mn, Ba, Ca, K,
P, Na, Nb, Ta and W, and the detection limits of these
elements are <0·1 wt %. The WDX system was used for
analysis of F (TAP, 10 kV, 100 nA), Cs (PET, 20 kV,
30 nA), and Rb (TAP, 20 kV, 50 nA). The detection
limits for F, Cs and Rb are <0·01 wt %. Natural minerals
were used as standards for Si (quartz), Al (corundum),
Ca (wollastonite), Ba (celsian), K (adularia; orthoclase—
MAC Standard 2726), Na (albite—MAC Standard 2726),
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DECEMBER 1997
P (apatite), Nb (columbite—Standard M42), Ta (columbite—Standard M43), W (wolframite—Standard
M45), Cs (pollucite—Standard M47) and F (CaF2). The
synthetic phases RbAlSiO4 and CsF3 were used as standards for Rb and Cs.
Electron microprobe analyses on melt
inclusions
Samples in the form of small polished thick-section chips
(10 mm × 10 mm × 0·5 mm) were cut from hand
samples and heated in thin-walled quartz glass ampoules
under slightly oxidizing conditions (Ni/NiO + C) for 20
h by rapidly placing the ampoules in the hot zone of a
tubular furnace. For this experiment we used temperatures between 600 and 900°C. However, each sample
was heated only at one temperature and only for one
time. After heating, the sample was quenched in liquid
N2 at about 500°/s to transform the melt in the inclusion
to a more or less homogeneous glass usable for microprobe analysis.
Microprobe analyses were carried out using the Cameca CAMEBAX-SX50 and -SX100 instruments at
the GeoForschungsZentrum Potsdam. The quartz chips
containing melt inclusions were, after heating and
quenching, polished down until the inclusions were exposed on the surface. Analyses were made in the wavelength-dispersive mode with the following conditions: 15
kV acceleration voltage, 10 nA beam current, spot size
of 10–30 lm, 40 s counting time for F using the multilayer
PC1 crystal, 60 s for Sn, 40 s for Rb and P, and 20 s for
other elements. Synthetic oxides and minerals were used
as standards. Rb was calibrated with natural Rb-rich
feldspar (from Etyka–Eastern Transbaikalia; provided by
R. Seltmann) and synthetic Rb-feldspar (prepared by St.
Melzer, GFZ Potsdam). The accuracy of this technique
was verified by analysing chips of synthetic hydrous
glasses (given by F. Holtz and H. Behrens) and Macusani
glass; the agreement between predicted and measured
values is very good.
Microthermometric (thermokinetic)
determination of the volatile contents of
melt inclusions
Primary rock-forming minerals of granites and pegmatites
can trap minute inclusions of the melt from which they are
formed. Melt inclusions provide information on pressure,
temperature and composition of the melt that were
present during geological processes that have long since
ceased. In particular, such inclusions contain information
about the magmatic concentrations of volatile and semivolatile elements in the melt which are obtainable from
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EVOLUTION OF A P-RICH GRANITE
bulk analysis of rock samples. Degassing and recrystallization processes at the final stage of crystallization
and postmagmatic–hydrothermal processes may change
in part the composition of rock samples, whereas inclusions may preserve genetic information. It is widely
accepted that melt inclusions represent trapped samples
of melt, and hence their composition provides constraints
on the original abundance of volatile and fluxing components (H2O, CO2, F, P and B) in the magma. However,
in contrast to extrusive rocks with their glass inclusions,
silicate melt inclusions in intrusive rocks are rarely studied.
This is partly because they are small and mostly crystallized, and are therefore commonly overlooked or misrecognized.
Because the melt inclusions are totally crystallized at
room temperature, we have to homogenize these inclusions to glass before any analyses. This procedure
must be performed so as to avoid or to assess volatile
loss by diffusion. Leakage (i.e. opening of the inclusions)
causes rapid and nearly complete loss of water and other
volatiles. Leaked inclusions generally fail to homogenize
under the experimental conditions (600–1000°C and 20
h). We used a heating–quenching technique that was
first presented by Thomas (1994) and further developed
by Thomas et al. (in preparation).
Using the simple kinetic technique based on the different homogenization behaviour of the crystallized melt
inclusions as a function of volatile content, temperature
and heating duration (Thomas, 1994), we can obtain
values for volatile contents for inclusions within the host
mineral which are situated too deep in the sample or are
too small for ion probe investigations or Fourier transform
IR (FTIR) spectroscopy. The method cannot separate
or distinguish the effect of water from that of other
volatile, semi-volatile or fluxing components. Therefore,
we express the results as ‘equivalent water content’ (C W),
the amount of water which would produce the observed
kinetic effect. In a first approximation, C W is the sum of
H2O, F and P2O5 determined with the electron microprobe. This is analogous to the convention of reporting
salinity in fluid inclusions as equiv. wt % NaCl from
freezing point depression data.
Analysis of whole-rock and mineral
concentrates
Major elements were analysed in the laboratory of the
Czech Geological Survey Praha by standard methods of
wet chemistry with detection limits well under the measured contents and standard deviation (SD) <1% relative.
F was analysed by ion selective electrode, SD <0·13 wt
%; phosphorus by spectrophotometry, SD <5% relative;
Rb, Li and Cs by AAS, SD <5% relative.
Rb, Nb, Sn and Zn were analysed by X-ray fluorescence in the laboratory of the Czech Geological Survey
Praha, with a detection limit of 7 ppm, SD <4% relative
(Rb), SD ~10% relative others.
Ta and W were analysed by the neutron activation
method by Bondar Clegg, Ottawa. Detection limits are
1 ppm (Ta) and 2 ppm (W).
Other trace elements were analysed using inductively
coupled plasma mass spectroscopy at GFZ Potsdam with
the following detection limits: 0·004 ppm (Cs, Pr), 0·006
ppm (La), 0·007 ppm (Ce), 0·008 ppm (Gd, Er), 0·009
ppm (Ho, Lu, Y, U), 0·010 ppm (Sr, Tb, Tm, Yb), 0·011
ppm (Nd, Dy), 0·012 ppm (Eu), 0·014 ppm (Sm), 0·021
ppm (Pb), 0·052 ppm (Ba), 0·13 ppm (Th, Zr), 0·17 ppm
(Hf ).
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