GEOLOGICA CARPATHICA, JUNE 2005, 56, 3, 193204
The role of boron and fluorine in evolved granitic rock
systems (on the example of the Hnilec area,
and IGOR BROSKA
Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. Box 106, 840 05 Bratislava 45, Slovak Republic;
(Manuscript received March 15, 2004; accepted in revised form December 9, 2004)
Abstract: The Hnilec S-type granites show a primary enrichment in the elements Sn, Rb, B, F, Nb, Ta and W which are
hosted in mineral assemblage of cassiterite, tourmaline, fluorite, Ta- and Nb-phase etc. Such an evolved or specialized
character of primary felsic melt was caused by a higher mobility of volatiles (B, F) due to the primary increased contents,
which resulted in depolymerization of melt and consequently the decrease of density and viscosity. The B content in the
granite body increases toward the granite roof-zone and reaches its maximum in the marginal granitic pegmatites and in
the surrounding wall rocks. The greisenized granite parts are generally low in B. Although the F content also increases
towards granitic cupolas and the highest F is in the altered parts (greisens), it is very low in the exocontact wall rocks
compared to boron. Principally, there are not significant differences in boron and fluorine mobility but the observed
assemblage are simply related to precipitation mechanisms, which are very different for the two elements. The main B
carrier is tourmaline, which was formed by primary magmatic and secondary hydrothermal precipitation. The tourma-
line found in the granites is mainly schorl, rarely foitite, whereas, tourmaline with higher dravite molecule is typical of
the granitic exocontact. The schorl with higher dravite molecule also occurs in the cracks and rims of the primary schorl
and formed from post-magmatic volatiles, which circulated between granites and granite host rocks possibly during
mixing of magmatic and meteoric waters. The main concentrators of F are white mica, which trapped fluorine by OH
exchanges, and fluorite. The outline of the greisen formation in the Hnilec region has been interpreted as a process above
the emanation centre in the Hnilec granite cupola at locality Medvedí potok Valley. An emanation spot was a space with
high volatile flux localized above the position of hydromagma which formed beneath a fine-grained granite carapace or
between fine- and coarse-grained granites in the overpressurring regime. If the vapour pressure of the dissolved fluid
exceeded the lithostatic pressure it caused the rupture of the overlying crystalline rocks and the flux of volatiles have
altered rocks and became the source of special mineralization of the Hnilec and Gemer granites.
Key words: Western Carpathians, Gemeric Superunit, greisen, granite, tourmaline, muscovite, boron, fluorine.
Boron and fluorine are widespread volatile elements of crustal
granitic rocks, being found in sedimentary, volcanic, plutonic
and metamorphic environments (Anowitz & Grew 1996). B
concentrations may approach 1 wt. % in some evolved, peralu-
minous tourmaline-bearing granites (Pichavant & Manning
1984), fluorine is generally a minor component in granitic rock,
but may be found highly concentrated in evolved residual melts.
In certain topaz granites or rhyolites it reaches up to 3.2 wt. % F
(Pichavant & Manning 1984; Icenhower & London 1995). The
presence of these volatiles in the felsic melt significantly chang-
es its rheological characteristics such as density or viscosity and
consequently they influence the primary character of the melt
(Dingwell et al. 1993). The decrease of liquidus and solidus
temperature in the felsic melt is further promoted by the in-
crease of water solubility (Manning 1981; Pichavant 1981; Pol-
lard et al. 1987). Along with high P concentration high boron
and fluorine results influence the depolymerization of felsic
melt with following production of higher amounts of residual
melts (Dingwell et al. 1985; Mysen et al. 1981).
Earlier, it was considered that in granitic melts F
forming SiF bonds or it links with Na
and other network
modifiers (Bailey 1977), but precision spectroscopic studies
(Kohn et al. 1991; Schaller et al. 1992) have now shown that a
significant short-range order exists between Na,K+Al and F,
on the one hand, and SiO, on the other hand. Along with re-
moval of Al from bridging AlO
-units, this explains the above
mentioned depolymerization of silicate melts with increasing
F content (Schaler et al. 1992). Moreover formation of
units responds to the liquid immiscibility of F-
rich granitic melts and the silicate component. This is also
shown by experiments in granite-pegmatite melt enriched both
O, B, P and F and consequently in Na
components in residual hydrosaline melt (Veksler & Thomas
2002). Silicate-melt inclusions in topaz-zinnwaldite-granites
from Zinnwald indicate that F can reach up to several percent-
age (6 wt. %) in the differentiated melt (Thomas et al. 2005).
The presence of fluorine in granitic melts might also increase
the solubility of high-field-strength cations by making non-
bridging O atoms available for complexing of these cations,
what is metalogenetically significant.
194 KUBI and BROSKA
The tin prospecting of the Hnilec Granite in the Gemeric
Superunit, which is the uppermost Alpine West-Carpathian
tectonic superunit, during the 1970s revealed the existence of
granites with increased fluorine and boron concentrations en-
riched in rare metal elements as Sn, Nb, Ta and W. These
granites were greisenized and became a source of hydrother-
mal mineralization manifested by the presence of cassiterite,
molybdenite and wolframite occurring in the veins (Grecula &
Drnzík 1995). Underground mining activity, exploration by
drilling and geochemical prospecting has shown the presence
of geological and chemical zonality within the Hnilec granite
body. The analyses of volatile elements, which have been ob-
tained during the prospecting works along granitic profiles,
give the possibility of achieving a better understanding of bo-
ron and fluorine behaviour in granitic magmatic systems. The
aim of this paper is to show the distribution of boron and fluo-
rine within the granitic cupolas and the surrounding wall rock
complexes on the basis B and F analyses gained during pros-
pecting work additionally combined with the technique of mi-
croprobe mineral analyses. Tin distribution will also be dis-
cussed in the framework of B and F spatial variation.
The analysed material consisted of hand-specimen samples.
Sampling was carried out by prospection regularly step by step
in distances of 5 meters. The samples came from a prospecting
gallery from the geochemical profiles and horizontal boreholes.
Boron from crushed rock samples has been analysed by the
AES-ICP (atomic emission spectrometry with inductively cou-
pled plasma) and fluorine by the potentiometrical method (labo-
ratory of the Geological Survey in Spiská Nová Ves). The
whole rock analyses were performed in ACME Laboratory in
Vancouver (Canada) by the ICP-MS analytical procedure which
follows: 1 sintering of a 0.2 g sample aliquot with sodium
peroxide, 2 dissolution of the sinter cake, separation and dis-
solution of the REE hydroxide-bearing precipitate, 3 analy-
sis by ICP-MS using the method of internal standardization to
correct for matrix and drift effects. Natural rocks and pure
quartz reagent (blank) were used as reference standards.
The mineral compositions present in apogranites (tourma-
line, micas etc.) were determined by wave length electron mi-
croprobe Cameca SX 100 at the GÚD laboratory (accelerat-
ing voltage 15 kV, sample current 20 nA, beam diameter
5 µm) with calibrated natural standards.
Geological background characterization of the
The Hnilec Granite is one of the granite bodies within the so
called Spi-Gemer granites or granites occuring in the Gemer-
ic Superunit, which is the highest of the three major Alpine
tectonic units of the Central Western Carpathians (Fig. 1).
This thick-skinned sheet of Upper CambrianSilurian volcan-
ogenic flysch (Gelnica Group) and the Devonian ophiolites
(Rakovec Group) thrusted northward onto the Veporic Supe-
runit during the Paleoalpine (Cretaceous) orogeny is usually
correlated with the Upper Austroalpine units of the Eastern
Alps (e.g. Mahe¾ 1974; Plaienka et al. 1997). During the
Variscan Orogeny the Gemeric Superunit was metamorphosed
in the greenschist and locally the amphibolite facies
(Vozárová & Ivanièka 1996; Faryad 1997; Soták et al. 2000),
whereas the younger Alpine metamorphism reached green-
schist facies conditions (e.g. Krist et al. 1992).
The western Hnilec Granite occurrence with hydrothermal
SnW(NbTa) mineralization forms a granite body 2×1 km
in size with strong zonal structures (Fig. 1). The occurrence
and distribution of elements within the granitic rocks was
studied along three geochemical profiles at the locality
Medvedí potok Valley (Fig. 2). The lower part of this granite
intrusion is composed of two-mica granite represented by
a medium grained rock consisting of subhedral, sericitized
plagioclase (31 vol. %), perthitic K-feldspar (24 vol. %),
quartz (37 vol. %), muscovite (5 vol. %), and small amount of
biotite (1 vol. %). Here the principal accessory minerals are
tourmaline, zircon, apatite, monazite, xenotime, rutile and flu-
orite. The middle part of the Hnilec body consists of medium
grained muscovite granite with similar rock-forming and ac-
cessory mineral proportions, the external part is composed of
fine-grained granite with lower plagioclase (25 vol. %) and K-
feldspar (13 vol. %) contents, and a higher amount of quartz
(45 vol. %) and white mica (17 vol. %). Zircon, monazite,
tourmaline, fluorite, TaNb minerals (columbite groups, Nb
Ta-rutile) are the principal accessory mineral phases in this
part. A fine-grained greisenized granite zone lies directly over
the fine-grained granite and the major constituents are quartz
(52 vol. %), white mica (22 vol. %), plagioclase (14 vol. %)
and K-feldspar (12 vol. %). Accessory minerals include zir-
con, apatite, monazite, cassiterite, pyrite and rare tourmaline
and fluorite. The greisen occurrences are found in the apical
endocontact where they form bodies 100200 m long and lo-
cally 30 m thick usually reaching 12 m. The greisens consist
of quartz (60 vol. %) and white mica (37 vol. %), locally with
plagioclase relicts. Accessories are represented by tourmaline,
increased amount of cassiterite, topaz, apatite, fluorite, molyb-
denite, arsenopyrite and pyrite. The external part of the altered
granitic cupola is locally bordered by a layer of marginal peg-
matite (stockscheider) (Fig. 2). The stockscheider zone is 0.5
up to several meters thick. Generally, the marginal pegmatite
consists of large oriented K-feldspar crystals, with quartz,
white mica, biotite and long prismatic tourmaline crystals. Ac-
cessory minerals are represented by fluorite and cassiterite.
The greisenization caused a zonal arrangement of various
types of metasomatites, appearing in the greisenized parts: 1
the quartz zone (0.21.0 m), 2 the zone of ore-bearing,
quartz-micaceous greisens, 3 the zone of the albitized fine-
grained granite containing lenses of ore-greisens, 4 the
zone of microclinized medium grained granite. The dissemi-
nated SnW(NbTa) mineralization is concentrated mainly
in the greisenized cupola as well as in the hydrothermal cas-
siterite-quartz veins (Drnzík 1982; Grecula & Drnzík 1995).
The geochemistry of the Hnilec granites shows typical fea-
tures of the S-type peraluminous leucogranite suite (Table 1).
The chemical composition of these granites is characterized
by high SiO
contents (75.2 to 76.7 wt. %), relatively high al-
kalies, especially K
O (3.8 to 4.9 wt. %), relatively low MgO
BORON AND FLUORINE IN GRANITIC ROCK SYSTEMS (WESTERN CARPATHIANS) 195
Fig. 1. Position of the Gemeric Superunit in the Western Carpathians mountain system and geological sketch map of the Gemer granite oc-
currences (according to Bajaník et al. 1984). Geological sketch map of the tin deposit in Hnilec-Medvedí potok (modified according to Drn-
(0.06 to 0.28 wt. %) and CaO (0.360.54 wt. %). The REE
normalized patterns of the granites have significant low nega-
tive Eu anomaly (Eu/Eu* ≈ 0.09), and the Rb contents range
from 440 to 868 ppm depending on the differentiation level
(Table 1). The S-type character of the Hnilec granites is also
demonstrated by high initial
Sr ratio (0.710.72; Cam-
bel et al. 1990), ASI index (1.11.2), total REE abundances as
well as elevated P
A Permian age for the Hnilec granites was determined from
monazite (276±13 Ma; Finger & Broska 1999) and single zir-
con grain dating (243±18 Ma; Poller et al. 2002). The Permi-
an age was also confirmed by associated ore mineralization in
granite exocontact on molybdenite by Re-Os dating
(262.2±0.9 Ma; Kohút et al. 2004; Kohút & Stein 2005). Be-
cause the Hnilec granites represent a suite of S-type granitic
bodies primarily enriched in the elements Sn, Rb, Nb, Ta and
W reflecting a special mineral paragenesis, such as cassiterite
and Ta- and Nb-phases, the name specialized S-type granite
suite was accepted for these granites in the Spi-Gemer re-
gion (Uher and Broska; 1996; Broska & Uher 2001).
Fig. 2. Geological map of the prospecting gallery # 2 with marked
the three profiles along the granite roof-zone marked. Sea level
680 m (modified according to Drnzík 1982).
196 KUBI and BROSKA
Boron and fluorine geochemistry of the Hnilec
The boron distribution in the geochemical profiles
(Figs. 2, 3) shows certain regularities. An increased amount of
boron is found in the fine- and medium grained Ms-granites
Table 1: Representative whole-rock chemical analyses of granites
from the Hnilec-Medvedí potok tin deposit (major elements in wt. %
and trace elements in ppm). Analysed by ICP-MS in ACME Labora-
tory (Vancouver, Canada) and B, Sn by OES (Geological Institute of
Slovak Acad. Sci., Bratislava).
(~200 ppm). In spite of the fact that boron is the principal vol-
atile element in these rocks, relatively low B concentrations
were transferred to the altered granite parts and/or to fine-
grained greisenized granite (~15 ppm). On the other hand mar-
ginal pegmatite (stockscheider) from the contact with the wall
rock contains very high B concentrations (~500 ppm), where-
as ore greisens from the inner part are poorer in boron
(~170 ppm). The highest B concentrations (~1000 ppm) were
determined from the exocontact chlorite-sericite phylites
(Drnzík 1982) (Fig. 3).
Fluorine distribution is different in comparison to boron. An
elevated fluorine concentration was observed in the medium
grained Ms-granites (~2500 ppm), but a relatively decreased
fluorine content was found in the upper fine-grained granites
(~1000 ppm) and in fine-grained greisenized granites
(~1300 ppm). A similar concentration of fluorine is found in
the ore greisens (~1500 ppm), a significant increase of fluo-
rine has been observed in marginal pegmatites (stockscheider)
(~3000 ppm), although, on the other hand, lower fluorine
content was found in the exocontact rocks (~1000 ppm; Drn-
zík 1982) (Fig. 3). The statistical parameters of dates from B,
F distributions are presented in Table 2.
The specific boron and fluorine distributions reflect differ-
ences in the precipitation mechanisms of these elements, rath-
er than in their mobility which is similar. Fluorine is transport-
ed as HF and alumino- and siliconhydroxylfluoride complexes
(Tagirov & Schott 2001; Tagirov et al. 2002), whereas boron
forms non-ionic bonds with oxygen, resulting in two types of
oxyanions, trigonal (BO
) or tetrahedral (BO
). More impor-
tant, the precipitation of fluorine compared to boron is dic-
Table 2: Average and ranges of granitic rock compositions from the
Hnilec-Medvedí potok tin deposit (analyses are taken from Drnzík
1982). Averages have been counted from three profiles (see Fig. 2).
Extreme values are omitted.
n = 45
n = 3
n = 24
n = 11
n = 16
n = 27
BORON AND FLUORINE IN GRANITIC ROCK SYSTEMS (WESTERN CARPATHIANS) 197
tated by different compositions of their host minerals (fluorite,
micas vs. tourmaline). In the case of boron, large quantities of
partition material are shifted to the aqueous fluid phase (dur-
ing melt saturation, i.e. the first or second boiling), and it does
not precipitate until the fluid phase reaches a high Mg-Fe
environment (country rock pelites). This explains why most of
the tourmaline (and boron) is located around the contact. On
the other hand, fluorine will not precipitate into abundant fluo-
rite, because of Ca deficiency in the apical part of the cupolas,
and its contents in the fluid are modified by OHF exchanges
with all mineral hydroxyl bearing phases such as micas.
B,F-bearing minerals in the Hnilec granites
Tourmaline is the main boron carrier in the Hnilec granites.
In these granites and the corresponding greisens, it forms eu-
hedral crystals without any rock-forming mineral inclusions
(Fig. 4a,b). Tourmaline is there represented by schorl with
high Fe/(Fe+Mg) = 0.95 to 0.97, locally with elevated F con-
tents (0.64 and 1.17 wt. %). The amount of X-site vacancies
varies in a relatively narrow ranges between 0.260.28 a.p.f.u.
The high ferrous contents determined by Mössbauer spectro-
copy (90 %; Broska et al. 1998) as well as the textural rela-
tionships of tourmaline to the other rock-forming minerals, in-
dicate its primary origin. This tourmaline is identified as
primary mineral phase tourmaline I.
The tourmalines from the greisen part form single crystals
(to 3 cm) or composite aggregates often exhibit zonal texture
(Fig. 4c,d). This schorl probably primary in core (Fe/(Fe+Mg)
= 0.99) is overgrown by secondary Mg-rich schorl (Fe/
(Fe+Mg) = 0.620.73). The schorl with an increased dravite
Fig. 3. Boron and fluorine distribution (in ppm) along the profile # 1 in the prospecting gallery No. 2. (source data, Drnzík 1982). Anoma-
lous values are ecluded from the statistical calculations (points 14, 15).
proportion (Fe/(Fe+Mg) = 0.62 to 0.65) is also typical of the
granite exocontact zone (Figs. 4e, 5; Table 3), where it forms
large black crystals (0.5 mm to 10 cm) in rossete-like as well
as massive globular aggregates with quartz, or discrete quartz-
tourmaline crystals (Broska et al. 1998). This tourmaline rep-
resents a younger post-magmatic phase tourmaline II. Post-
magmatic tourmalines occurred also in the granite but mainly
in its greisenized parts (Fig. 4c,d).
White mica and fluorite due to their abundances are the
most significant fluorine concentrators, other F-mineral phas-
es being apatite and topaz. Although white micas from the me-
dium grained muscovite granite and greisens contain very low
amounts of fluorine (0.010.4 wt.%), higher or moderate fluo-
rine concentrations were determined in white muscovite from
fine-grained granites (1.83.2 wt. %). Howewer, white mica
in greisens also has a low content of F (0.500.70 wt. %). The
compositions of white micas correspond to ferro-aluminocela-
donite (Broska et al. 2002) and they occur as interstitial flakes
(Fig. 4f,g,h, Table 4). Fluorite usually forms small crystals
disseminated in granite, but also thin veinlets or aggregates
along tectonic fissures in granitic rocks. The occurrence of flu-
orine veins is due to post-magmatic or hydrothermal fluid
Discussion and synthesis
Movement of postmagmatic fluids
Boron-bearing fluids easily escape along fractures to coun-
try rocks and form there widespread pervasive tourmaline
mineralization. On the other hand, fluorine accumulates in al-
198 KUBI and BROSKA
tered granites or greisenized near-roof parts, also in medium
grained muscovite granite, but only very slightly in the coun-
try rocks. Similarly to the Gemeric Granite, the strong local
tourmaline precipitation in aureole rocks is known around the
B-rich Cornubian granites in SW England (Jackson et al.
1989; London & Manning 1995), and also from the Podlesí
granite stock in the Kruné hory Mts (Breiter 2002). In con-
trast to it, fluorine aureole is observed around the rare metal
Beauvoir Granite in the French Massif Central (Table 5). The
strong F mobility is there documented by significant decrease
Table 3: Representative microprobe analyses of tourmaline (in wt. %).
of F along Li, Sn and W contents in the last 100 m below the
granite roof (Cuney et al. 1992; Raimbault et al. 1995).
The behaviour of F-rich magmas is different compared to B-
rich ones. The greater mechanical energy produced during
crystallization of B-rich magmas, which is usually related to
the higher content of water, provides a mechanism for breccia
pipe and stockwork formation, while the more passive crystal-
lization of F-rich magmas often results in the formation of dis-
seminated mineralization (Pollard et al. 1987). A breccia pipe
is known from the Hnilec area, although only in a restricted
medium grained muscovite
Atomic proportions based on the sum of T+Z+Y=15 cations
O calculated from ideal stoichiometry
BORON AND FLUORINE IN GRANITIC ROCK SYSTEMS (WESTERN CARPATHIANS) 199
Fig. 4. Microphotographs from granites in the roof zone (a, b) and back-scattered electron (BSE) images of tourmaline and white mica at
the Hnilec-Medvedí potok locality (c, d, e, f). a, b interstitial schorl from the medium grained muscovite granite; c, d schorl
aggregates from greisen; e schorl-quartz from exocontact phyllite; f white mica from medium grained muscovite granite; g
white mica from fine-grained granite; h white mica from greisen. Tur tourmaline, Ms muscovite, Kfs K-feldspar, Cst cas-
siterite, Ap apatite.
200 KUBI and BROSKA
Fig. 5. Quadrilateral Vac.
+Na) vs. Fe/(Fe+Mg) diagram
(atomic proportions) of tourmalines from Hnilec area (Medvedí po-
tok Valley). Black circles medium grained muscovite granite,
grey squares greisen, triangles exocontact phyllite.
Table 4: Representative microprobe analyses of white mica (in wt. %). Total FeO from microprobe analyses has been divided into FeO and
in ratio 50:50.
extent. The common occurrence of B and F in a volatile sys-
tem is not so widespread and is known in detail mainly from
the Cornubian granites. The Hnilec granite system shows a lot
of similarities with this evolution.
Mineralization derived from B and F-rich fluids
Boron-rich magmatic systems result in tourmaline precipita-
tion. Tourmaline in such systems always occurs in the parental
granites as well as in the country host rocks, which indicates a
longer distance of boron migration from granites stopped by
an Fe-Mg environment (London & Manning 1995). The hy-
drothermal tourmaline, schorl or schorl-dravite and dravite
species, in the exocontact aureoles around granitic plutons
usually shows a fine-scale chemical zoning within crystals and
usually preserves the essential chemical characteristics of the
medium grained muscovite granite
Formulae based on 12 oxygens,
O based on the sum of OH+F+Cl=2 a.p.f.u.
BORON AND FLUORINE IN GRANITIC ROCK SYSTEMS (WESTERN CARPATHIANS) 201
Cornubian (SW England)
18112 (Willis-Richards & Jackson 1989)
Beauvior (Massif Central, France)
70448 (Cuney et al. 1992)
Podlesí (Czech Republic)
5196 (Breiter 2002)
Cínovec (Czech Republic)
(Dolej & temprok 2001)
Argamela (Central Portugal)
(Charoy & Noronha 1996)
East Kemptville (Canada)
(Halter & Williams-Jones 1996)
Phuket (SW Thailand)
3531272 2130 (Pollard et al. 1995)
Table 5: Comparison of selected trace elements of highly evolved granites from world localities.
Fig. 7. Sn distribution (in ppm) along the profile # 1 in the prospecting gallery No. 2. For comparison also other rare metals (Mo, W, Nb)
and alkalies (Rb, Cs) distributions are presented (source data, Drnzík 1982).
host rocks (Morgan & London 1987; London et al. 1996). In
southwest England, such tourmaline in host rocks shows a
than in the granites, reflecting a higher oxida-
tion state of the hosts (London & Manning 1995).
The tourmalines of Hnilec and generally in all Gemeric gra-
nitic rocks, including their altered parts are represented by
schorl (Faryad & Jakabská 1997) and schorl-foitite (Broska et
al. 1998). In the Hnilec area, the increased dravite component
was found, except in granite exocontact, only in the rims and
cracks of some primary tourmalines in granite roof zone
(Fig. 4c). Such complex zonality could document a circulation
of volatiles which are derived from granites. These fluids were
contaminated by Mg,Fe-rich country rocks, mixed by meteor-
ic waters, and partly returned back to granite cupolas, where
they caused the formation of a mineral association, including
the above mentioned tourmaline rims. A general scheme of the
evolution of felsic granitic rocks in their apical parts with the
effects of boron emanation on the surrounding rocks is pre-
sented in this sense (Figs. 3, 6).
Fig. 6. General features of roof-zone granite evolution (apogranite)
in the Hnilec area (adapted from Drnzík 1982). Profile AA, see
202 KUBI and BROSKA
The hydraulic rupture of roof-zone (apogranite) with strong
alteration processes in the Hnilec area was also accompanied
by the development of veinlet systems. The quartz veins are
enriched in B, Sn, but also Ta, Nb, Mo, W in the form of cas-
siterite mineralization with low F content. Besides cassiterite,
arsenopyrite, topaz, apatite, columbite and rare fluorite, these
veins contain the higher dravite-schorl type of tourmaline
(Fig. 6). According to the presented data boron can easily be
transported for a long distance to the Fe-Mg-rich exocontact
barrier, but fluorine seems to be stopped earlier by endocon-
tact hydrated minerals such as micas. The different B and F
geochemical behaviour resulted in the different mineral char-
acters of the main B and F concentrators and their stability.
Tin, which generally accompanies the volatile-enriched
granites, typically continually increases in the Gemeric gran-
ites from the internal parts of the granitic body towards the ex-
ternal altered parts with the maximum in the greisens and gre-
isenized granites (Fig. 7). Tin distribution does not correspond
to that of fluorine in granites but in greisen (compare
Figs. 7, 3, Table 2). The deeper medium grained Ms-granites
contain only around 40 ppm Sn, 200 ppm is a characteristic
value for the upper situated fine-grained greisenized granite,
whereas the highest content of Sn was determined in the apical
greisens (~900 ppm). Exocontact aureoles usually have rela-
tively lower contents of Sn (~90 ppm) (Fig. 7). Other rare met-
als, Mo and Nb are slightly enriched in greisen cupola, but on
the other hand, the W content is not (Fig. 7; Drnzík 1982). To
complete the picture of greisen evolution it is necessary to
mention the increased Rb and Cs content in greisen because of
eralier accumulated alkali feldspars in the granite cupola, later
broke down to greisen (Fig. 7).
The Sn transportation in hydrothermal solutions is a func-
tion of a variety of parameters including temperature, pH, ox-
ygen fugacity, bulk salinity and the presence of complexing
ligands (Heinrich 1990; Halter & Williams-Jones1996). Sn
has oxidation states of Sn
in geologically relevant
conditions, and as such its solubility, activity, diffusivity, and
coordination in a silicate liquid may all vary as a function of
. The following precipitation of cassiterite from magmatic
fluids is connected with the decrease of pH of the fluid and
(Halter & Williams-Jones 1996). Sn is generally transport-
ed in the complexes with Cl
Jackson & Helgeson (1985) have also calculated that the rela-
Fig. 8. A hypothetical cartoon of formation of the Hnilec granite
cupola. The overpressuring hydromagma originated under the car-
apace of almost solidified fine-grained granites.
Fig. 9. Probable positions of emanation spots in the Hnilec area indicated by arrows (map background, Bajaník et al. 1984).
BORON AND FLUORINE IN GRANITIC ROCK SYSTEMS (WESTERN CARPATHIANS) 203
tive proportion of fluorine complexes are negligible compared
to chloride complexing, even in F-bearing systems, but ac-
cording to these authors, the most important tin species in so-
lution is SnCl
(Wilson & Eugster 1990; Halter & Williams-
Jones 1996), which is also supposed for the Hnilec area
because Sn does not spatially correlate with F very much
(Figs. 3, 7).
Hypothetical model of the evolution of the Hnilec granite cu-
The observed breccia pipes in the granite cupola are indirect
evidence of an overpressuring regime in the granite cupola at
the Hnilec locality. The hydrothermal breccia described in the
prospecting gallery has been formed from angular fragments
of rocks consisted from topaz granite blocks locally 40 cm in
size cemented by vein mineralization containing cassiterite
and quartz (Drnzík 1982). Unfortunately, the exact position of
the topaz-bearing granites saved as fragments in breccias is
still unknown in the Hnilec locality.
Basically the overpressuring volatile system could originate
on the contact of the solidified fine-grained and underlaying
coarse-grained to porphyric granite in sense that subsolid fine-
grained granite became a carapace for the escape of volatiles
(Jackson et al. 1989; Mark & Foster 2000). Beneath the crys-
tallized granite carapace the upper parts of the magma column
would have been enriched in volatile and lithophile elements
and volatile rich granites or hydrogranites could form
(Fig. 8). In the case when the vapour pressure of the dissolved
fluid in the magma locally exceeds the lithostatic pressure, the
rupture of the overlying crystalline rocks begins, and probably
a catastrophic escape of volatiles occurs as it is supposed in
the Cornubian ore (Jackson et al. 1989). The rupture of the
roof granites and release of volatile-rich fluids, resulted in for-
mation of tourmaline bearing hydrothermal veins and breccias
occurs. The fracture propagation in the granite roof zone has
created an open system for the degassed magmatic-hydrother-
mal fluids which triggered the greisenization of the fine-
grained granite cupola as well as the start of formation of ore
veins in the granite exocontact (Fig. 8). Volatile and metal-en-
riched residual fluids which accumulated beneath the roof rep-
resent probably a possible source of Sn, W and Mo. The greis-
enization and formation of the ore veins in the Hnilec area was
restricted to several small places just above the emanation cen-
tres and in the Hnilec area it is mainly the valley of Medvedí
potok near Su¾ová (Fig. 9).
Boron and fluorine in the Hnilec granites, significantly con-
tributed to the depolymerization of the primary melts. They
show cooperative effect on decreased liquidus and solidus
temperatures and increases of melt quantity. Such a mecha-
nism leads to the formation of a highly evolved and mobile
granitic system, enriched in rare-metal elements. Increased
contents of boron were determined from the deeper medium
grained muscovite granite and fine-grained granite toward the
granite cupolas. Boron concentrations are highest in the exo-
contact country rocks, where it forms a wide contact aureole
around the granitic cupola. Increased boron volumes are also
detected in the marginal pegmatite (stockscheider). Boron is
mainly hosted in a tourmaline, which forms two genetic types:
I. primary magmatic, II. secondary hydrothermal. In contrast,
the highest contents of fluorine typically occur in greisens in
the cupola. Low fluorine concentrations were determined in
the country rocks which make the spatial distributions of B
and F distinctly different. The boron and fluorine distribution
within geochemical profiles indicates the higher geochemical
mobility of boron compared to fluorine. Tin distribution does
not correlate with F and B distribution the tin transportation in
aqueous fluids probably occurs via the chloride complexes.
All data has been used to outline the greisen formation at
the locality Medvedí potok Valley in Hnilec region, which
represents one of several emanation centers within the Gemer
granites. The emanation spot as a room with high volatile flux
was localized above the hydromagmas pools which formed
beneath the fine-grained granite carapace or between fine- and
coarse-grained granites. These hypothetical places were over-
pressured and became sources of special mineralization of the
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