GeolCarp_Vol63_No3_241

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, JUNE 2012, 63, 3, 241—252 doi: 10.2478/v10096-012-0020-8

Geochemistry and electron spin resonance of hydrothermal
dickite (Nowa Ruda, Lower Silesia, Poland): vanadium and

chromium

PAVLE I. PREMOVIĆ

, JUSTYNA CIESIELCZUK

, GRAŻYNA BZOWSKA

and

MILOŠ G. ĐORĐEVIĆ

Laboratory for Geochemistry, Cosmochemistry and Astrochemistry, Department of Chemistry, University of Niš, P.O. Box 224,

18000 Niš, Serbia; pavle.premovic@yahoo.com

Department of General Geology, Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland

(Manuscript received May 7, 2011; accepted in revised form December 7, 2011)

Abstract: Geochemical analyses for trace V and Cr have been done on a representative sample of a typical hydrothermal
dickite/kaolinite filling vein at Nowa Ruda. The mineralogy of the sample is comparatively simple, dickite being the
principal component (ca. 91 % of the total sample). Geochemical fractionation and inductively coupled plasma-optical
emission spectrometry (ICP-OES) indicate that most ( > 90 % of total metal) of the V and Cr reside in the dickite. Electron
Spin Resonance (ESR) shows that most ( > 70 %) of the V in the dickite structure is in the form of vanadyl (VO

) ions. A

high concentration of Cr

is also detected in this structure by ESR. The combination of geochemical and spectroscopic

tools applied to VO

and Cr

allow one to specify the Eh ( > 0.4 V, highly oxidizing) and pH ( 4.0, highly acidic) of the

solution during the formation of dickite from the Nowa Ruda Basin. Substantial proportions of the V and Cr (as well as
VO

and Cr

) in the dickite structure were probably contained in an original hydrothermal acid water. We suggest that

hot hydrothermal waters leached the surrounding varieties of gabbroids enriched in V and Cr for the dickite-forming
solution. The results of this work have shown V and Cr are potentially reliable indicators for geochemical characterization
of the physicochemical conditions of their formation. The bulk-rock V/Cr ratio in hydrothermal dickites and kaolinites
from Nowa Ruda, Sonoma (California, USA), Cigar Lake (Saskatchewan, Canada) and Teslić (Bosnia and Hercegovina)
is also briefly explored here as a potential tracer of redox state during their formation.

Key words: electron spin resonance, kaolinite, dickite, chromium, vanadium.

Introduction

The  kaolinite  group  minerals  include  kaolinite,  dickite,
nacrite  and  halloysite.  Acid  alteration  in  magmatic  hydro-
thermal  systems  is  often  represented  by  minerals  such  as
kaolinite  and  dickite  (Izquierdo  et  al.  2000,  and  references
therein).  Hydrothermal  kaolinite  and  dickite  are  mainly
formed in situ through alteration of source minerals (mainly
K-rich feldspars and other aluminosilicates) by hydrothermal
acid waters.

V and Cr are elements of significance in geochemical cy-

cles as well as important trace elements in biochemistry. The
oxidation states of V in the geosphere correspond to V

, V

and V

. V is present in natural waters, where redox condi-

tions, pH, adsorption and complexation are the main control-
ling parameters of the solubility of this transition metal
element.

In oxygenated natural waters, V is predicted to oc-

cur in the +5 oxidation state, primarily as highly soluble and
mobile vanadate ions: H

n-3

(n = 0 to 4), and as NaHVO

—

(Turner et al. 1981). As a consequence, the V species in-
volved in incorporation processes appear anionic, resulting
in a relatively low affinity for the negatively charged colloi-
dal clay particles (Whitfield & Turner 1987).

Vanadyl ion (VO

) shows a strong tendency to interact

with the surface of Al and other metal hydrous oxides and is

thus capable of becoming specifically bound within the col-
loidal clay particles (Wehrli & Stumm 1989).

Geochemical studies indicate that Cr occurs in natural aquatic

environments in two oxidation states: Cr(III) and Cr(VI). In low
(suboxic/anoxic) Eh natural environments, the main aqueous
Cr(III) species are Cr

and Cr(OH)

. Under oxidizing condi-

tions, aqueous Cr is present in a Cr(VI) anionic form, HCrO

—

and/or CrO

2—

, depending on the pH. Cationic Cr(III) species are

rapidly and strongly adsorbed by colloidal clay particles, but
adsorption of anionic Cr(VI) species onto these particles is
expected to be minimal (Rai et al. 1986, 1987).

Physicochemical conditions during the formation of a non-

hydrothermal  kaolinite  are  usually  deduced  from  field  data
as  well  as  experimental/thermodynamic  data.  The  stability
of this mineral is often expressed in plots using pH and ion
activities.  The  hydrothermal  kaolinites/dickites  are  not  fre-
quently  studied  and  our  knowledge  of  the  physicochemical
conditions necessary for their formation is still limited. One
way to get an objective evaluation of the nature of solutions
during the formation (precipitation) of kaolinites/dickites is
to  examine  components  that  were  undoubtedly  introduced
into  their  lattice  by  these  solutions.  Such  components
certainly include VO

and Cr

ions.

Indeed, VO

and Cr

in natural aquatic environments are

characterized almost entirely by the pH and oxidation reduc-

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tion potential (Eh) of the environment. These two parameters
also have a strong influence on the mobility and complexation
of VO

and Cr

ions. These two ions, therefore, are sensitive

geochemical indicators of the geochemistry of the clay-form-
ing solutions and may provide clues to the origin of the clay
deposits of the past. This has led us to study VO

and Cr

dickite  from  Nowa  Ruda  (NR),  a  hydrothermal  mineral  en-
riched  in  V  and  Cr  (Morawiecki  1956).  After  a  mineral
characterization of the sample using X-ray diffraction, Fourier
transform infrared spectroscopy, differential thermal analysis,
and  scanning  electron  microscopy,  selective  leaching  proce-
dures were performed to establish specific mineral hosts for V
and  Cr  by  inductively  coupled  plasma-optical  emission
spectrometry (ICP-OES). To support the speciation study, we
quantitatively  determined  the  VO

concentration in dickite

using a new experimental calibration with a principle derived
from a previous study of clays (Premović et al. 2011).

Experimental

Geological setting

The Nowa Ruda Basin is located in the Sudetes Mountains

(southwestern  Poland),  near  the  city  of  Wroclaw  (Fig. 1).
The  geology  and  mineralogy  of  this  basin  were  extensively
studied  by  Morawiecki  (1956),  Kowalski  &  Lipiarski
(1973), and Borkowska (1985). The gabbro-diabasic massif
of  the  Nowa  Ruda  Basin,  which  spreads  over  15 km

, is

composed of rocks of probable Proterozoic age (Oberc 1960)
and is represented by olivine gabbros, olivine-free gabbros
with diallage, troctolites and plagioclasites. Most of these
rocks reveal postmagmatic alternation. The upper part of the
gabbroic rocks is weathered.

The regolith covering the gabbroic rocks, composed mainly

of  bauxites,  argillites,  and  gabbros,  breccias  and  conglomer-
ates, is of Carboniferous age (Wiewióra 1967). These forma-
tions are overlain by a thick series of shales of Westphalian A
age,  which  are  followed  by  sandstones  and  carbon-bearing
kaolinitic  shale  of  the  Upper  Carboniferous  formation.  The
Upper Carboniferous is represented by carbon-free sandstones
and conglomerates and is overlain by the clastic formation of
Rotliegendes.  Quaternary  clays,  gravels  and  sands  represent
the youngest rocks. The general stratigraphic succession of the
Nowa Ruda Basin is shown in Fig. 2.

Dickite/kaolinite occurs mainly as veins within the gabbro

weathering  products,  or  is  associated  with  the  dark  grey
kaolinitic shale. The mineral is usually light green or bluish-
green (Fig. 3). Apart from these veins, kaolinite at the Nowa
Ruda  location  also  occurs  in  the  form  of  large  lenses.  Ac-
cording to Kowalski & Lipiarski (1973) kaolinite and dickite
from  the  Nowa  Ruda  Basin  may  have  originated  in  the  hy-
drothermal solutions genetically related to the magmatism of
the Late Carboniferous.

Sample location and description

Kaolinite and dickite are found throughout the abandoned

coal mine Piast near the town of Nowa Ruda. These minerals

Fig. 1. Geographical location of Nowa Ruda.

Fig. 2. General stratigraphic section of the NR region, modified af-
ter Morawiecki (1956) and detailed Geological Map of Sudetes Mts,
1 : 25,000, sheet Nowa Ruda, (Wójcik 1956) and sheet Jugów,
(Gawrónski 1958).

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are generally believed to be the most common product of a hy-
drothermal alteration (Morawiecki 1956). A representative
blue dickite sample (hereafter DS) was collected by L. Stoch
in a vein of kaolinitic shale at the Piast mine. Nine samples of
dickite from Nowa Ruda were also collected by J.C.

Analytical methods

ICP-OES Spectrometry.

V and Cr of the whole-rock sam-

ple and leaching fractions were analysed by ICP-OES. A
Spectroflame ICP-OES instrument was employed and Ar was
used as the plasma gas. Total uncertainty (including accuracy
error) of the analysis ranges from 5 % to 20 % for V and Cr.

For purpose of Cr(VI) detection, DS was digested using

0.28 M Na

/0.5 M NaOH solution heated at 90—95 °C

for 1 h to dissolve Cr

and stabilize it against reduction to

. Subsequently, Cr(VI) could be identified colorimetri-

cally at 540 nm with diphenylcarbazide in acid (pH 2) solu-
tion (Bartlett & James 1979);

1 ppm can be detected.

However, no Cr(VI) could be identified in DS using this
method.

X-ray Diffraction (XRD) Analysis.

XRD patterns were

obtained with the Philips PW 1729 and 3710 diffractometers
using  CoK   radiation  (35  and  45 kV,  30 mA).  Powder  dif-
fractograms were acquired in the 3—90° 2  range, with 7—20 s
counting per 0.01° and 0.04° 2  step. Samples were prepared
using  the  back-loading  procedure  according  to  Moore  &
Reynolds (1989), providing significant disorientation of clay
layers.

Fourier Transform Infrared (FTIR) Spectroscopy.

FTIR

spectra were recorded, in absorbance mode, with a BOMEM
Michelson Series MB FTIR spectrometer. The resolution was
4 cm

—1

in the 400—4000 cm

—1

analysed range. Spectra were

obtained at room temperature from KBr pressed pellets pre-
pared by mixing 1.5 mg of a clay sample with 150 mg of KBr.

Differential Thermal Analysis (DTA).

The DTA curve was

obtained from 20 mg sample in a Pt crucible on a Perkin-
Elmer 7 Series Thermal Analysis System heated at 10 °C min

—1

Scanning Electron Microscope (SEM).

The morphology

and  the  semiquantitative  chemical  analyses  were  performed
by  scanning  electron  microscopy  (scanning  microscope
Philips XL 30 ESEM/TMP) coupled to an energy-dispersive
spectrometer  (EDAX  type  Sapphire).  The  backscattered
electron  (BSE)  mode  was  done  before  microprobing.
Analytical conditions were as follows: accelerating voltage 15
or 20 kV, probe current 60 nA, working distance ca. 10 mm,
counting  time  100 s.  Individual  parameters  are  printed  on
photos:  acceleration  of  electron  beam  and  magnification.
Samples were coated with gold and stuck to a carbon tape.

Electron Spin Resonance (ESR) Spectroscopy.

The ESR

measurements were performed on fine powder samples that
were transferred to an ESR quartz tube. The ESR spectra
were recorded at room temperature using a Bruker ESP 300E
spectrometer at X-band bridges with a standard 100 kHz
field modulation. The measurements were made at 9.3 GHz
utilizing a rectangular TE cavity.

In order to accomplish maximum accuracy and precision it

was necessary to focus attention on the following: a sample
tube was always kept inside the ESR cavity with an approxi-
mate  magnetic  field  uniformity;  and  the  reproducibility  of
the sample positioning was achieved by using the same sam-
ple tube with a fixed holder. Tests verified that all spectra for
the standard measurements were obtained with instrumental
parameters  which  gave  no  instrumental  effects  on  peak
height/shape/width.  Most  of  the  measurements  were  run  at
2 mT  modulation  amplitude,  100 ms  time  constant,  16 min
scan time. The field was scanned on 200 mT when the entire
spectrum  was  desired.  The  instrument  was  carefully  tuned
according to the manufacturer’s directions.

Analysis and fractionation

The fractionation procedure was similar to that used by

Premović (1984). The flow chart in Fig. 4 outlines the major
steps in preparing the four fractions. These are:

Powdered dickite (1 g) was treated (room temperature,

12 h) with acetate buffer: acetic acid/sodium acetate (1 M,
12 h) solution at pH 5.0 to remove most of the carbonates.
This solution also removes other soluble minerals. The soluble
material constitutes the carbonate fraction.

The insoluble residue (I) was demineralized further by re-

peated treatment with cold HCl (6 M). This acid solution re-
moves mostly metal hydroxides and oxides, including
V- and Cr-hydroxides and -oxides. The soluble part consti-
tutes the cold HCl-fraction.

The insoluble residue (II) was demineralized with boiling

HCl (6 M, 80 °C, 12 h). This treatment removes most of the
soluble silicates. The soluble part constitutes the boiling
HCl-fraction.

The insoluble residue (III) was demineralized with boiling

mixture of HF (22 M)/HCl (12 M) (3 : 1 v/v, 80 °C, 12 h).
This acid mixture removes SiO

and A1

. SiO

and Al

removal was checked by FTIR/EDS analyses. The soluble
part constitutes the dickite fraction.

Fig. 3. Example of blue dickite filling the veins within black shales/
slates from the dump of the abandoned coal mine Piast. Sample
size: 7 10 cm.

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Cr (410 ppm), respectively, indicating that the bulk of V and
Cr  reside  primarily  within  the  dickite  structure.  In  addition,
acetate  buffer/cold-HCl  leaching  removed  less  than  1%  of
total V and Cr. This result indicates that a negligible amount
of  V  and  Cr  is  in  the  form  of  hydroxides  and/or  oxides  that
can be specifically adsorbed on the colloidal clay particles or
precipitated (Evans 1978).

XRD analyses

Indicative peaks for distinction between dickite and

kaolinite lie in the range of angles 2 43°—47°, where dickite
generates two main peaks: 2.387 A

and 2.324 A

of intensity

50 and 90, respectively (Joint Committee on Powder Diffrac-
tion Standards (JCPDS) 10—430) whereas kaolinite gives three
peaks: 2.386 A

(intensity I = 25), 2.338 A

(I = 40) and 2.293 A

(I = 35)  (JCPDS  14—164).  We  performed  XRD  analyses  for
nine  representative  samples  of  dickite  from  Nowa  Ruda  to
check  which  mineral  of  the  kaolinite  group  is  dominant.  In
most  of  these  samples  XRD  patterns  show  the  predominant
presence  of  dickite  (Fig. 5A)  which  confirms  the  results  of
Morawiecki  (1956).  Only  a  few  of  them  show  a  minor  pres-
ence of kaolinite-1Tc (Fig. 5B). In almost all the investigated
samples traces of talc [Mg

(OH)

] were noticed.

FTIR analyses

An accurate distinction between kaolinite and dickite can be

achieved by using FTIR, assessing the position and relative
intensities of the OH-stretching bands in the 3600—3700 cm

—1

region (Russel 1987). The FTIR spectrum of DS is shown in
Fig. 6 and is characteristic of dickite. Dickite shows strong
absorption at 3621 cm

—l

and two medium-strong absorption

bands at 3704 and 3654 cm

—1

, whereas absorption bands for

kaolinite are at 3697, 3620, 3669 and 3652 cm

—1

. FTIR analy-

sis  also  showed  that  dickite  is  the  only  kaolinite  mineral
present  in  DS,  confirming  the  XRD  analysis.  Our  XRD  and
FTIR  data  for  DS  are  in  a  good  agreement  with  a  previous
spectroscopic study of DS by Balan et al. (2002).

Differential thermal analysis (DTA)

The DTA curve of DS presents a dehydroxylation peak at

ca. 670 °C and an exothermic peak at about 1000 °C, Fig. 7.
This is in agreement with a typical curve of dickite (Macken-
zie 1970). However, the position of the dehydroxalation peak
towards the high-temperature limit (dehydroxalation peak
generally found in the region 500—700 °C), as well its sharp-
ness, are in accord with a well-ordered dickite structure (Bish
& Duffy 1990).

SEM/EDS analyses

Under the SEM, green or bluish-green DS from Nowa

Ruda have the morphology of well-formed, uniform vermic-
ular  aggregates  of  large  ( 10 µm)  blocky  dickite  crystals
(Fig. 8A,B).  EDS  analyses  show  that  these  crystals  mainly
consist of O, Al and Si (Fig. 8C); minor K, Fe and Ti were
also  detected.  This  elemental  composition  is  indicative  of

Table 1: Geochemical distributions of V [ppm] and Cr [ppm] from
selective leaching experiments of DS from Nowa Ruda.

Fraction

Sediment ( 5 wt. %)

V Cr

Acetate buffer

Cold-HCl

190

Boiling-HCl

340

Dickite

190

435

Insoluble residue

–

Total sample

100 175

410

V/Cr 0.4.

concentration: 160 2 0 ppm

The final residue from (III) is the acid insoluble fraction.

Results

Chemical and ICP-OES analyses

The acetate buffer/HCl demineralizing steps remove only

7 % of DS. This is due to the total dissolution of carbonates
and other soluble minerals [acetate buffer: 3 %], the dissolu-
tion of metal hydroxides and oxides (e.g. V- and Cr-hydroxi-
des and -oxides) [cold-HCl: 1 %] and the destruction of some
silicate minerals [boiling HCl: 3 %] (Table 1). SiO

and

, the dominant constituents of dickite, seem to be unaf-

fected by these demineralization steps. The leaching experi-
ment indicates that more than 97 % of the dickite fraction is
removed by the HF/HCl step, Table 1.

Table l shows the distributions of V and Cr among the four

components of DS. These results show that the HF/HCl frac-
tion contains > 98 % and < 97 % of the total V (175 ppm) and

Fig. 4. Flow chart of fractionation procedure.

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minerals of the kaolinite group. Fig. 8D,E also shows well-
shaped kaolinite crystals.

ESR analyses of VO

Two main sets of transitions can be distinguished in a high

magnetic  field  in  the  total  ESR  spectrum  of  untreated  DS,
around  3400 G  and  in  a  low  magnetic  field  around  1500 G,
corresponding  to  VO

and Cr

, respectively (Balan et al.

2002). In high magnetic fields, the untreated DS shows a mul-
tiline spectrum (Fig. 9A) similar to the spectrum of VO

ions

incorporated into the lattices of some kaolinites (Premović

1984; Muller & Calas 1993). The spectrum shows an aniso-
tropic spectrum signal pattern typical of an axially symmetrical
hyperfine coupling.

The ESR method employed to quantify VO

as previously

described by (Premović et al. 2011) is given by the following
equation:

] = (S

) [C

]

where C is the concentration of VO

, c indicates the clay

sample and st indicates the standard. S is the specific signal
intensity (the integrated area under the corresponding ESR
absorption per g of the sample).

Fig. 8. SEM view of the crystals of the kaolinite group of minerals from Nowa Ruda: vermicular dickite flakes (A, B); EDS spectrum of
dickite (C); and, well-shaped kaolinite crystals (D, E). SEM Photos by Ewa Teper & Justyna Ciesielczuk.

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A glycerol solution was prepared by first dissolving known

amounts of VOSO

· 5H

O in a solution containing 1.5 ml of

concentrated H

+ 0.5 ml of deionized H

O and then dilut-

ing it with glycerol to the desired VO

concentration

(8000 ppm) with thorough agitation. Changes in the loading
Q-factor of the ESR cavity can result in samples with different
dielectric properties. The above glycerol solution has a high
dielectric constant (about 56 D) and cannot be used as a reli-
able comparison of relative VO

concentrations of clays. For

this reason, standards were prepared by mixing / diluting small

Fig. 9. First derivative, room temperature, anisotropic VO

ESR

spectrum of: untreated DS (A); an initial glycerol solution contain-
ing 8000 ppm of VO

(B); and, a standard containing 400 ppm of

in the KGa-2/glycerol mixture (C).

amounts of the glycerol solution with kaolinite to the desired
VO

concentrations. Preparing this mixture has the effect of

maintaining the dielectric medium of standards close to the
clay samples, keeping the Q similar. The standards prepared
in this way covered the range of 50 to 400 ppm of VO

. The

kaolinite used in these standards was KGa-2 (Georgia, USA),
which contains very low amounts of VO

( < 5 ppm).

Figure 9 also illustrates the anisotropic ESR spectrum of:

(B) an initial solution of VOSO

· 5H

O compound dissolved

in H

O and diluted with glycerol and (C) a standard

containing 400 ppm of VO

. These spectra are typical of

those previously reported for VO

in either powder (poly-

crystalline) solids or extremely highly-viscous liquids
(Goodman & Raynor 1970).

Only one line of the VO

anisotropic hyperfine pattern is

considered for obtaining the integrated area. Consequently,
just a narrow part of the VO

spectrum needs to be recorded.

For this purpose, we select the first derivative

V hyperfine

line marked with m

= —5/2|| in the spectra of DS (Fig. 9A) and

the standard (Fig. 9C). This line was chosen in order to keep
the linewidth and lineshape similar and to minimize interfer-
ences from both neighbouring VO

resonance lines and the

lines of other ESR active species present. In addition, from our
continuing study of VO

in various clay materials, we have

found that the anisotropy of the ESR parameters of VO

various clays has little or no effect on linewidth and lineshape
of the —5/2|| line. The area under the —5/2|| line was evaluated
taking into account baseline corrections, multiplying or divid-
ing it by factors required to put the areas of the —5/2|| line of
both the standards and DS on the same setting. A study of the
intensity and width of the —5/2|| line of both the standards and
the DS versus the square root of microwave power showed no
saturation. Consequently, a high power of 100 mW was se-
lected for measurement, ensuring a high absolute intensity of
the —5/2|| line.

We computed the integrated area of the —5/2|| line for five

standard samples containing 400 ppm of VO

prepared on

five different days. Repeatability of results was generally very
good, usually better than ± 5 %.

Although the DS was not collected from freshly exposed

mine faces, repeated ESR analyses over the course of several
months showed no change in its VO

content. Similar ex-

periments on the VO

standards showed that after several

weeks no oxidation had occurred. After six weeks of expo-
sure to air the VO

concentration was virtually unchanged

from its initial value.

If the specific intensities of the —5/2|| lines of the standards

are simply plotted against the VO

concentration a linear

calibration curve is obtained. Fig. 10 shows this plot in the
50—400 ppm range. Using this plot as the calibration curve,
DS was recorded for the VO

spectrum and the specific in-

tensity of the —5/2|| line was determined to obtain the con-
centration of VO

. The vanadyl concentration obtained for

DS is 160 ± 20 ppm, corresponding to more than 70 % total V
(Table 1).

The demineralizing steps with the acetate buffer/HCl do not

affect the concentrations of the VO

ions in DS. However, the

ions disappear (checked by ESR), completely during

HCl/HF demineralization. Therefore it is reasonable to assume

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that these ions are incorporated into the dickite structure. In-
deed, a negligible contribution of dipolar magnetic broaden-
ing arising from interactions between VO

and the

neighbouring VO

and/or other V ions (as expected from

the low V content of dickite, Table l) is consistent with this
notion. The lack of change of the ESR signals attributed to
VO

, even upon prolonged (10 h) laboratory heating of the

dickite at 500 K and in the presence of air, indicates that this
ion is strongly bound to the dickite structure.

ESR analyses of Cr

The representative ESR spectra of Cr

within the dickite

lattice are shown in Fig. 11 in low (A) and high (B) magnetic
fields. According to Balan et al. (2002), these ESR spectra can
be attributed to the isolated Cr

ions in the diamagnetic ma-

trix of the dickite structure. These authors showed that Cr

substitutes for Al

in the octahedral sheet.

In the present study, we show that like VO

, Cr

is com-

pletely removed by HCl/HF demineralization. The corre-
sponding concentration of Cr is 435 ppm. This confirms that
Cr

(like VO

) ions are located within the dickite structure of

DS and are probably present in significant amounts. To quan-
tify Cr

employing a similar method to that described above

would create almost insurmountable experimental problems.

Discussion

Gabbros as a source of V and Cr in NR dickite

As mentioned earlier, the hydrothermal kaolinite and dickite

of the Nowa Ruda Basin are probably related to magmatism of
the Late Carboniferous period. Kraynov & Ryzhenko (1992),
who made a thorough study of Eh/pH in many geochemical
water types, reported that the acidity of the hydrothermal wa-
ters (in areas of contemporary magmatism) is within the pH
range of ca. 0—4 and that the Eh values vary from 0.4—0.8 V.
The field of these waters is marked in Fig. 12 as shaded.

Fig. 10. The glycerol/KGa-2 mixture as a standard for the VO

concentrations range from 50 to 400 ppm.

Fig. 11. First derivative, room temperature, anisotropic ESR spec-
trum of Cr

of untreated DS: in low magnetic field region (A); and,

high magnetic field region (B).

Geochemical data suggest that the geological conditions un-

der which dickite formed must have been relatively rich in V
and Cr (i.e. VO

and Cr

), and they were introduced into dic-

kite during formation aided by an invasive hydrothermal wa-
ter. The fact that  > 95 % of V and Cr (Table l) resides within
the  dickite  structure  indicates  that  most  V  and  Cr  in  dickite-
forming  solution  was  in  a  dissolved  form.  We  suggest  that
most of these two metals were introduced into dickite by this
solution already enriched in V and Cr.

An extensive geochemical study of the gabbro massifs in

Nowa Ruda Basin was carried out by Bialowolska (1973). Ac-
cording to this author, V in gabbroic rocks of the basin occurs
mainly in disseminated form replacing iron and is mostly con-
centrated in pyroxenes (300 ppm) but it is much less abundant
in  olivines  (10 ppm).  Among  the  Nowa  Ruda  gabbros,  the
highest  Cr  content  of  635 ppm  is  concentrated  in  the  olivine
type. Diallage gabbros and troctolites contain about 300 ppm
of  Cr.  Chromium  occurs  in  disseminated  form,  replacing  the
trivalent iron in minerals according to diadochy. It also forms
its  own  minerals,  namely  chromite  and  Cr-spinel  associated
with serpentinized pyroxenes. For this reason, we propose that
hot  hydrothermal  waters  leached  the  surrounding  gabbros,
providing V and Cr for mineralizing solutions.

Initial hydrothermal waters were probably mixed with

groundwaters in the Nowa Ruda Basin, and this probably sig-
nificantly decreased the concentrations of V and Cr. We be-
lieve that the final contents of V and Cr in dickite-forming

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solution depended less on their initial values than on the
degree of subsequent mixing of these two waters.

Morawiecki (1956) carried out geochemical analyses of two

samples of almost pure dickite and one sample of nearly pure
kaolinite  from  NR  veins.  The  dickite  samples  (on  a  whole-
rock  basis)  contained  V  (55  and  80 ppm)  but  Cr  (250 ppm)
was found only in one of these minerals. Such Cr discordance
can  only  be  explained  in  terms  of  the  difference  between  the
dickite-forming solutions. The fact that NR kaolinite studied by
Morawiecki (1956) contained high V (430 ppm) but not Cr is in
line with this interpretation. The variability in V and Cr concen-
trations associated with kaolinite and dickite in the Nowa Ruda
Basin probably represents a difference in dissolved V and Cr
in  their  precipitating  solutions  as  they  were  a  mixture  of  the
original hydrothermal fluid and groundwater at that time.

Conditions of formation of dickite: Eh-pH diagrams

Turekian & Wedepohl (1961) quoted the average contents

of V (130 ppm) and Cr (90 ppm) of ordinary (non-hydrother-
mal) clays. Compared with these clays, DS (see Table l) is
only slightly enriched in V and moderately (4.5 times) en-
riched in Cr.

As mentioned above, most V and Cr in the dickite-forming

solution of DS were in a dissolved form. We assumed that
the concentration of V in this solution was about 5 ppm. This
assumption is based upon a content of about 5 times the V
concentrations typical of natural waters, which means gener-
ally less than 1.2 ppm (Wanty & Goldhaber 1992, and refer-
ences therein).

Fig. 12. Eh-pH diagram for VO

and Cr

at 300 K and 1 atm for

formation of dickite. The assumed total V concentration is 5 ppm.
The shaded area represents Eh/pH region of the hydrothermal waters
defined by Kraynov & Ryzenko (1992). Probable physicochemical
conditions of dickite are represented by the hatched area.

In the case of Cr, a geochemical calculation suggests that all

Cr would be in dissolved form if the total concentrations of Cr
in  the  aquatic  system  at  26.85 °C  are  lower  than  7.5 ppm
(Richard  &  Bourg  1991).  Taking  into  account  that  the  Cr  in
DS  probably  occurs  in  the  form  of  metal  hydroxides  and/or
oxides,  Cr  concentrations  in  dickite-forming  solution  of  DS
were  probably  > 7.5 ppm  (i.e.  > l.5 10

—4

mol · l

—1

); for com-

parison, the concentrations of dissolved Cr typical of natural
waters are < 1 ppb (Richard & Bourg 1991).

We have constructed the stability field of VO

and Cr

as-

suming a total V concentration of 5 ppm in aqueous solution
(Fig. 12)  using  the  FactSage  thermochemical  software/Fact
compound  databases.  For  the  sake  of  simplicity,  we  present
only a part of the diagram. The critical boundary between the
stability  fields  of  VO

and Cr

is not significantly affected

by modifying this value 10-fold in either direction.

The Eh-pH diagram in Fig. 12 is not an accurate representa-

tion of the hydrothermal solution when dickite is formed, and
it is undoubtedly highly variable in its approach to the ideal.
However, because it represents a quantitative estimate based
on the available thermodynamic data, it should be a helpful
tool, if used within its limitations.

Figure 12 only shows the domains of VO

and the solubili-

ty for crystalline VO

or V

. We note that the (hydrous)

V(OH)

is probably more soluble than its anhydrous counter-

part. It is apparent from this figure that the VO

ion is stable

thermodynamically under oxidizing conditions (Eh 0.0V)
only at low pH ( 4). Thus, the presence of a relatively high
concentration of VO

in the dickite of DS indicates that the

oxic dickite-forming solution was probably highly acidic
(pH 4).

The VO

stability field of the diagram is confined by su-

perimposing the Eh-pH field for Cr

for the physicochemical

conditions of dickite-forming solution (Fig. 12). It is apparent
from this figure that for coexistence of VO

and Cr

during

formation of dickite, the Eh values should be > 0.4 V (highly
oxidizing) and pH 4.0. The VO

—Cr

domain is very close

to the Eh-pH domain corresponding to modern hydrothermal
waters in areas of contemporary magmatism, which are within
the pH range of ca. 0—4 and Eh values of 0.4—0.8 V (Kraynov
& Ryzhenko 1992).

In much of the area of interest, the dominant dissolved spe-

cies is Cr

, except above pH 4, where hydroxide complex,

CrOH

, is a major form. A solubility of about 7.5 ppm

( > 1.5 10

—4

mol · l

—1

) for Cr could only be attained if the solid

Cr species in dickite-forming solution was amorphous
Cr(OH)

. The anhydrous crystalline species of Cr

is much

less soluble below about 1 ppb (10

—8

mol · l

—1

). Moreover, the

absence of Cr(VI) in DS implies that the Cr(III) species were
only present during the formation of dickite of Nowa Ruda.
Therefore, the solubility of Cr(OH)

is probably more realistic

for this solution.

Under the deduced oxidizing (Eh > 0.0V) and highly acidic

(pH 4) conditions, the bulk of the Cr in the dickite-forming
solution should be present as Cr

ions, with much smaller

amounts of CrOH

and Cr(OH)

. Indeed, chemical studies

indicate that the Cr

ion is prevalent only at a pH lower than

3.5 and the solubility of Cr

in an aqueous solution decreases

as the solution pH rises above pH 4, with essentially complete

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precipitation as Cr(OH)

occurring at about pH 5.5 (Richard &

Bourg 1991, and references therein). Moreover, according to
reported hydrolysis constants (Rai et al. 1987), Cr

is strongly

hydrolysed in aqueous solutions and the predominant species in
the pH range 6.5—10.5 is Cr(OH)

. Thus, the dissolution of

Cr(III) minerals could only occur in natural acid waters with
pH < 5, giving low, equilibrium controlled, concentrations of
Cr(VI) anions. For this reason, soluble Cr

is usually restricted

to hydrothermal acid waters (DeLaune et al. 1998).

The V/Cr ratio has been used as a paleoenvironmental indi-

cator of sedimentary conditions (Jones & Manning 1994, and
references  therein).  Values  of  V/Cr  4  are  thought  to  repre-
sent  suboxic/anoxic  conditions.  Values  of  V/Cr  4  indicate
slightly  oxidizing  (dysoxic)  conditions,  with  the  correspond-
ing ratio values  2 suggesting oxic conditions within the de-
posit. The V/Cr ratio of dickite is ca. 0.4 (Table l), indicating
that  this  mineral  formed  in  an  oxidizing  environment.  Note
that  one  of  the  NR  dickite  samples  analysed  by  Morawiecki
(1956) has a V/Cr ratio of 0.2.

The abundant association of goethite with NR dickite

(Komusinski  et  al.  1981)  is  consistent  with  its  formation
occurring  under  oxidizing  conditions  as  goethite  occurs  only
in  a  natural  aqueous  milieu  under  oxidizing  conditions  with
Eh  above  0.15 V  (Krumbein  &  Garrels  1952).  In  relation  to
this dickite, it should be noted that: (a) goethite is ultimately
the  most  stable  mineral  phase  associated  with  acid-sulphate
waters (Bigham et al. 1996); (b) the goethite formation becomes
predominant  at  pH > 3  (Davis  et  al.  1988).  Pyrite  trace  was
also detected in DS but not in the dickite samples collected by
J.C. and it is probably of postdiagenetic (secondary) origin.

The findings of highly oxidizing Eh values at low pH are

consistent with the physicochemical characteristics of the hy-
drothermal acid waters. Thus, dickite probably grew from an
O

-enriched acid solution. Laboratory synthesis in a closed

system and under hydrothermal conditions shows that the
optimal pH for kaolinite formation is 3 to 3.5 (Lahodny-Sarc
et al. 1993). The problem is, however, that the hydrothermal
aquatic system of the Nowa Ruda Basin was probably thermo-
dynamically open, so it might not be exactly comparable to a
laboratory autoclave synthesis.

The above Eh-pH diagram is calculated for atmospheric

pressure  and  a  temperature  of  26.85 °C.  A  thermochemical
calculation  indicates  that  no  significant  variations  at  the
scale of our diagram are expected in the thermodynamic pa-
rameters up to 10 bars of atmospheric pressure. This is due
to the fact that pressure only slightly affects the chemistry of
both the ionic species and solids of V and Cr within the O-H
geochemical system. A similar calculation also shows that in
a  hydrothermal  solution  with  temperatures  up  to  ca.
126.85 °C,  the  vertical  line  (as  the  boundary  between  the
VO

solution and the solid VO

stability field) would be

shifted from pH 3.9 to 4.5. On the other hand, the vertical
line, which represents the boundary between Cr

and

CrOH

, would shift from pH 4 to 3.1. Thus, a change in the

temperature up to 126.85 °C would slightly shift the stability
fields of VO

and Cr

in the Eh-pH diagram during forma-

tion of the NR dickite toward a pH lower than 4.

The kaolinite minerals associated with the NR veins are

composed of kaolinite and dickite in variable ratios, although

dickite  was  the  sole  polymorph  identified  in  most  veins
(Kowalski & Lipiarski 1973). The fact that dickite occurs only
in  parts  of  the  Nowa  Ruda  Basin  indicates  that  the  above
physicochemical  conditions  necessary  for  dickite  formation
were reached only locally.

Physicochemical conditions of formation of other hydro-
thermal kaolinites and dickites

In the following, we briefly review relevant geochemical

data (ours and others) for hydrothermal kaolinites and/or dick-
ites from Sonoma (California, USA), Cigar Lake (Saska-
tchewan, Canada) and Teslić (Bosnia and Hercegovina).

Hydrothermal kaolinites from Sonoma

Mosser et al. (1996) examined two V- and Cr-bearing hy-

drothermal kaolinites (named MILO and GEY) that formed in
a  hydrothermal  environment  at  Sonoma  (California,  USA).
The  Cr  and  V  abundances  in  the  MILO  and  GEY  kaolinites
are  presented  in  Table 2.  These  studies  imply  that  Cr

and

ions are present within their structures. Low V/Cr ratios

( 0.1, Table 2) for the MILO and GEY kaolinites indicate an
oxygenic milieu for their formation. The fact that most of the
Fe is localized in small oxide particles associated with the
kaolinites (Mosser et al. 1993) strongly supports this view.

Sample V Cr

V/Cr

Gey

320 23260 0.0

Milo

480

7530

0.1

Cigar Lake

2475

350

7.1

2378

190

4720

0.0

665

310

1780

0.2

664

230

3900

0.1

This work.

concentration: 2700 200 ppm.

Table 2: Geochemical concentrations of V [ppm] and Cr [ppm] (on
the whole-rock basis) in the Gey/Milo/Cigar Lake/Teslić samples.

Hydrothermal kaolinite of Cigar Lake

The U-rich hydrothermal deposit of Cigar Lake consists

predominantly  of  kaolinite  ( > 80 %)  (Mosser  et  al.  1996).
Table 2  lists  the  V  and  Cr  concentrations  of  this  kaolinite.
Mosser  et  al.  (1996)  suggest  that  the  Cigar  Lake  illite  was
hydrothermally  transformed  into  kaolinite  with  V  entering
its structure.

Our ESR analyses show that most ( > 80 %) of the V is

present as VO

ion, and Cr

is below detectable level (Ta-

ble 2). Both the abundant pyrite (1.5 %) associated with this
kaolinite (Mosser et al. 1996) and high V/Cr (7.1, Table 2) in-
dicate strong reducing conditions during the formation of the
Cigar Lake kaolinite.

Hydrothermal dickites and kaolinites near Teslić

Maksimović et al. (1981) investigated three samples (herein

referred as 2378, 664 and 665) of V- and Cr-bearing dickite
and kaolinite from a hydrothermal sulphide vein in ultramafic

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rocks near Teslić (Bosnia). Samples 2378 and 665 contained
predominantly  dickite  and  kaolinite,  respectively,  while  the
third (664) contained equal proportions of both minerals. All
three  samples  exhibited  relatively  high  Cr  and  V  (Table 2).
Maksimović et al. (1981) suggested that the acidity of the hy-
drothermal  solutions  in  which  the  dickite  and  kaolinite  are
formed was between pH 4.1 to 5.3 for a long period of time.
Low V/Cr ratios ( 0.2) (Table 2) and the absence of sulphide
minerals  (e.g.  pyrite)  associated  with  the  Teslić  dickite  and
kaolinite imply an oxygenated hydrothermal milieu.

Conclusion

From the results and considerations given in this paper the

following conclusions can be drawn:

1. High concentrations of V (190 ppm) and Cr (435 ppm)

were found in the dickite of Nowa Ruda;

2. High contents of VO

and Cr

were detected in the dic-

kite of Nowa Ruda by ESR;

3. The V (and VO

) and Cr (Cr

) enrichments of the

dickite of Nowa Ruda occurred during its formation by an
invasive hydrothermal acid water;

4. The ultimate source of V and Cr in the dickite of Nowa

Ruda was probably the surrounding gabbroic rocks of the
gabbro massifs of the Nowa Ruda Basin;

5. V and Cr were leached by initial hydrothermal acid water

before its mixing with a groundwater, forming a dickite-
forming solution;

6. From the geochemistry of VO

and Cr

, it is deduced

that the oxidation potential Eh and pH of the dickite-forming
solution were > 0.4 V and 4, respectively.

Acknowledgments:  Funding  support  from  the  Ministere
francais de l’Education National, del’Enseignement Superieur
et de la Recherche to P.I.P. for his stay at the Institut de Miner-
alogie et Physique des Milieux Condensés (IMPMC), Univer-
sité Pierre et Marie Curie (Paris), is gratefully acknowledged.
The authors are indebted to L. Stoch and T. Allard for making
representative  dickite  sample  available  for  this  study.  We
thank  two  anonymous  reviewers  for  critical  reviews  which
improved the manuscript. Our thanks go to Drs. Jean-Pierre
Girard  and  Adam  Dangić  who  generously  provided  biblio-
graphic material essential for writing this report. The English
editing is done by American Journal Experts.

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