mössbauer investigation of characteristic distribution of iron oxides in sediments from the...

Journal of Radioanalytical and Nuclear Chemistry, Vol. 246, No. 1 (2000) 61�68

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E. Kuzmann,a V. K. Garg,b P. A. de Souza Júnior,c L. A. Schuch,d A.C. de Oliveira,b

Z. Homonnay,a A. Vértesa

aDepartment of Nuclear Chemistry, Eötvös University, Budapest, HungarybDepartment of Physics, University of Brasília, 70910-900 Brasília, D.F., BrazilcDepartment of Physics, Federal University of Espirito Santo, Vitória, ES, Brazil

dDepartment of Physics, Federal University of Santa Maria, Santa Maria, RS, Brazil

(Received May 8, 2000)

Sediments from the Admiralty Bay, King George Island, Antarctica, were investigated by 57Fe Mössbauer spectroscopy, X-ray diffractometry, and

radiometry. Quartz, feldspar, chlorite, calcite, dolomite, mica, kaolinite, hematite and magnetite were identified as constituent minerals in the

sediment samples. The phase composition and the iron distribution among the crystallographic sites of iron-bearing minerals (silicates, magnetite

and hematite) of samples from different location have been derived from the complex Mössbauer spectra. At different locations sediments had

significant characteristic differences in the mineral composition, in the iron distribution among the crystallographic site of silicates, and in the

specific radioactivity of Cs radionuclides. These results indicate differences in the rock formation and alteration by the sediments in this maritime

part of Antarctica. There is a much higher amount of iron oxides in the sediments from south part of the geological fault across the Admiralty Bay

than in the north part. This can be associated with much more alteration in the rocks in the south part compared to the northern one. This finding

can contribute to the question of the history of the formation and alteration of volcanic rocks in the border of Antarctica.

Introduction Controversial statements were given in earlier

works,8,9 based on conventional geological

investigations, whether altered �Jurassic� and unaltered

Tertiary rocks were separated by a major fault which

goes across the Admiralty Bay8 or there are no

differences in the alteration of the rocks located at either

side of the fault.9

Antarctica is known as a continent which is covered

by 3000�4000 m thick ice. Its area is about 7 times of

that of Europe, and Antarctica is uninhabited except a

few observers. It has arctic climate, with extreme by low

temperature with storm wind and with very low

humidity. Less than 2% of the continental area is ice free

which is accessible for the geological and mineralogical

researches. This area is distributed around the periphery

of the Antarctica. Such an area is the King George Island

which is the biggest island of the South Shetland Islands

located parallel to the Antarctic Peninsula to the

direction of South America (Fig. 1).

The aim of our work was to investigate sediment

samples from the Admiralty Bay of King George Island,

Antarctica, from different locations on both sides of the

geological fault. For these studies 57Fe Mössbauer

spectroscopy, which has been successfully applied in

mineralogy and geology10 even for the study of soils

originated from the Antarctica,11 X-ray diffractometry

and radiometry were used as well.In the focus of previous geological researches of

Antarctica, the investigations were related to the

geological history of the Earth dominate.1 WEGENER2

postulated the former existence of a supercontinent

Pangaea (Laurasia and Gondwana). DU TOIT3 placed this

idea on solid geological footing. Paleomagnetism offers

convincing evidence of Gondwana from the late

Precambrian through to early Jurassic time.4 The

separation of continents has occurred about 180 ma ago

at the periphery of Antarctica due to volcanic activity.

The geological faults can be very important from the

point of study of geological occurrences. Such a

geological fault occurs across the Admiralty Bay, King

George Island, as studied in details previously.5�9

Experimental

The samples were obtained near the Brazilian

Antarctic Station called �Comandante Ferraz� (62° 05�

latitude 58° 24� longitude) in the Keller Peninsula in the

King George Island of the South Shetland Islands of

Antarctica (Fig. 2). The marine sediment samples

SEDMAR1-SEDMAR15 were collected from above and

below the geological fault in the Admiralty Bay, in the

King George Island. The sample of SEDMAR1 was

collected from 30 m depth and the sample of SEDMAR2

was collected from 70 m depth, while the other samples

were obtained from 60 m depth.

0236�5731/2000/USD 17.00 Akadémiai Kiadó, Budapest

© 2000 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht

E. KUZMANN et al.: MÖSSBAUER INVESTIGATIONOFCHARACTERISTICDISTRIBUTIONOF IRONOXIDES IN SEDIMENTS

Fig. 1. View of the location of King George Island at Antarctica

Fig. 2. Location of samples in the Admiralty Bay, King George Island, Antarctica

Transmission 57Fe Mössbauer spectra of powdered

samples were recorded with conventional Mössbauer

spectrometers (Wissel, Germany and Ranger, USA) in

the constant acceleration mode. The measurements were

performed between 78 and 300 K in a temperature-

controlled cryostat (Leybold, Germany) with the γ-raysof 1.109 Bq 57Co(Rh) source. Isomer shift values are

given relative to α-Fe. The evaluations of the Mössbauer

spectra were performed with the MOSSWINN

program.12

Conventional gamma-spectroscopy was used to

determine the radioactivity of radionuclides in the soils.

X-ray diffraction patterns were recorded by a computer

controlled DRON-3 powder diffractometer in Bragg-

Brentano geometry with Co Kα radiation and β filter.

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Results and discussion The sextet S1 is associated with hematite, α-Fe2O3,

and the sextets S2 and S3 belong to magnetite, Fe3O4,

when Fe substituted for the tetrahedral A site and the

octahedral B site, respectively 10, 11, 13, 14, 15.

Furthermore, the doublet D1 represents Fe2+ at M2 site,

the doublet D2 represents Fe2+ at M1 site, the doublet

D3 belongs to Fe3+ at M1 site and the doublet D4

represents Fe3+ at M2 site 10, 11, 15, 16. The latter site

assignment is consistent with the occurrence of M1 and

M2 crystallographic sites in the iron-bearing minerals

(chlorite, mica (biotite), kaolinite) which were identified

in the samples.

Figure 3 shows typical X-ray diffraction patterns of

sediment samples. Reflections due to quartz, feldspar,

calcite, dolomite, chlorite, mica, kaoloinite and hematite

can be identified. Table 1 shows the normalized

integrated intensities of the peaks belonging to the

identified main phases, giving the estimated occurrence

of the main minerals of Antarctic sediment samples.

Figure 4 shows the room temperature Mössbauer spectra

of sediment samples. They consist of magnetically split

and paramagnetic components. By taking into

consideration the temperature dependence of Mössbauer

spectra, the optimum spectral decomposition was found

into three sextets and four doublets. The Mössbauer

parameters of these subspectra are shown in Table 2. In

order to distinguish the different micro-environments

more reliably compared to the conventional spectrum

evaluation we have used the quadrupole splitting

distribution method for the evaluation of paramagnetic

spectral part of the Mössbauer spectra of the sediments.

This model-independent method does not require the

apriori knowledge of the number of spectral lines and the

constraints between the Mössbauer parameters.

The quadrupole splitting distributions obtained for the

marine sediment samples are shown in Fig. 5. For the

calculation of distributions, ternary polynomial functions

were used to give the relation between the isomer shift

and the quadrupole splitting values.10,12 The quadrupole

splitting distributions reveal four peaks which can be

associated with four iron micro-environments. The

results of low temperature measurements confirmed

well those obtained at room temperature.

Summary of the site assignment of the spectral

components (Table 2) is as follows:

Fig. 3. X-ray patterns of sediment samples from Antarctica

Table 1. Result of X-ray diffractometry

Sample Quartz Feldspar Chlorite Calcite Dolomite Mica Kaolinite Hematite

SEDMAR1 50 35 4 6 4

SEDMAR2 70 15 10 5

SEDMAR3 75 10 10 2 3

SEDMAR4 50 35 15 5

SEDMAR5 35 63 2

SEDMAR6 60 30 4 6

SEDMAR7 55 30 10 2 2 1

SEDMAR8 65 20 8 2 2

SEDMAR9 17 70 2 2 10

SEDMAR10 55 35 5 2 2 1

SEDMAR11 60 35 1 4

SEDMAR12 10 80 8 2

SEDMAR13 80 15 5

SEDMAR14 70 35 5

SEDMAR15 75 20 5

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Fig. 5. Quadrupole splitting distributions of sediments from Admiralty

Bay, King George Island, Antarctica

Pyroxene andesite or olivine basalt contain phenocrysts

of plagioclase, augite, hypersthene and opaque ore as

well as various amounts of ferromagnesian minerals.5,8,9

Although, the original ferromagnesian minerals have

suffered alteration or have been completely destroyed,

HAWKES5 concluded from the shape of the phenocryst

that the original rocks included olivine basalts,

hypersthene-augite-andesites and augite-andesites.5

It is clearly demonstrated that differences in the

phase composition and in the iron distribution of

sediments located at different sides of the fault. By

comparing the magnetically split subspectra with the

paramagnetic one in Fig. 4, (see the data given in

Table 4) it can be seen that less iron oxide content is

characteristic of the samples (2, 3 and 8) (13�20%) in

the Mackella Inlet at the north part of the Bay. These

samples contain practically no hematite. Another

characteristic group of samples 6, 7, 13, 14, 15 is at the

Keller Peninsula. These samples have iron oxide content

between 23 and 32%. However, on the other side of the

Martel Inlet and on the area of Pt. Hennequin (which is

over the fault), the characteristic iron oxide content (of

samples 1, 5, 11, 12) is 41�48%. Here not only the total

iron content, but the magnetite content also shows a

maximum. Whereas on the other side of the Bay at the

Pt. Thomas the samples (9, 4, 10) have iron oxide of

30�40%.The hematite content looks like to be indicative

either to the locations divided by the main fault below

which hematite is equally distributed in the samples or to

the alteration of the local rocks. The above correlation

can be expressed as a function of silicate content, too.

Fig. 4. Room temperature Mössbauer spectra of sediments from

Admiralty Bay, King George Island, Antarctica

The distribution of Fe2+ and Fe3+ among the

crystallographic sites in the oxides and silicates were

derived from the Mössbauer spectra, as given in Table 3.

More importantly, the results obtained for the iron

distribution and phase composition show a close

correlation with the location of the sediments.

Differences of the phase composition and that of iron

distribution in the samples will indicate the difference in

the formation and alteration of the rocks from which the

sediments originated. Upper Cretaceous-Lower Tertiary

volcanic rocks are below the investigated sediments.5,8

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65


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Table 4. Distribution of iron in the iron containing phases

Sample Fe2O3, % Fe

3O4, % Silicates, %

SEDMAR1 21.7 26.9 51.4

SEDMAR2 3.3 10.1 86.6

SEDMAR3 0.0 14.9 85.1

SEDMAR4 11.7 18.5 69.8

SEDMAR5 10.0 33.3 56.7

SEDMAR6 6.1 15.4 78.5

SEDMAR7 4.0 18.3 77.7

SEDMAR8 0.0 20.8 79.2

SEDMAR9 11.2 28.7 60.1

SEDMAR10 7.2 21.5 71.3

SEDMAR11 13.4 35.9 50.7

SEDMAR12 11.3 29.4 59.3

SEDMAR13 13.0 18.6 68.4

SEDMAR14 5.7 17.0 77.3

SEDMAR15 6.6 16.5 76.9

Table 5. Radiometry results (in Bq.kg�1) in sediments in the King George Island

Sample 137Cs 226Ra 228Ra 40K

SEDMAR1 <1.1 13.6 ± 1.2 12.5 ± 2.9 464 ± 19

SEDMAR2 2.05 ± 0.66 15.9 ± 1.2 17.8 ± 2.4 562 ± 22

SEDMAR3 2.88 ± 0.61 16.2 ± 1.7 11.7 ± 2.2 505 ± 28

SEDMAR4 <1.0 15.9 ± 1.2 10.2 ± 2.6 596 ± 23

SEDMAR5 <0.43 <6.19 12.23 ± 10.85 406.6 ± 50.8

SEDMAR6 <3.34 17.71 ± 3.94 13.91 ± 6.63 333.6 ± 41.9

SEDMAR7 <2.52 <7.53 20.48 ± 9.45 443.1 ± 45.1

SEDMAR8 3.48 ± 1.69 29.99 ± 4.46 41.12 ± 9.55 912.4 ± 76.7

SEDMAR9 <0.58 9.74 ± 1.38 6.47 ± 2.35 324.2 ± 25.0

SEDMAR10 <1.52 5.39 ± 1.95 10.86 ± 3.77 291.9 ± 24.6

SEDMAR11 <0.47 9.66 ± 1.14 11.15 ± 1.78 390.4 ± 28.9

SEDMAR12 <1.43 <3.43 <6.83 184.3 ± 19.5

SEDMAR13 <1.80 10.56 ± 2.12 17.45 ± 4.19 418.5 ± 36.5

SEDMAR14 <0.85 14.35 ± 1.29 17.45 ± 2.19 410.7 ± 29.8

SEDMAR15 <1.72 13.53 ± 2.53 17.32 ± 4.81 127.5 ± 12.9

We have found the correlation between the iron

distribution in the cation sites of silicates and the

mentioned locations. This can be easily seen from the

comparison of quadrupole splitting distribution of the

sediments in Fig. 5. Based upon the characteristic shape

of the distribution curves, it is easy to select the

corresponding samples. The groups samples (2, 3 and 8),

(6, 7, 13, 14, 15), etc. have similar distributions.

Apart from the weathering process the alteration of

the rocks can be associated with the effect of plutonic

intrusions,5 which are characterized by epidote and

pyrite mineralization accompanied by widespread

albitization of plagioclase. Our results show that these

alterations are more pronounced below the south part of

the fault lying along the Enzcurra Inlet-Martel Inlet.

across the Admiralty Bay than in the north part of the

fault.Deviation of the specific radioactivity of 137Cs in

samples 2, 3, and 8 (Table 5) from other samples also

indicates that these samples have a different geological

history. The quartz/feldspar ratio of sediments changes

significantly from north to south direction (see Table 1),

and at the same time the main phase composition of

samples which are on the same side and equidistant on

that side of the horizontal fault is similar. Our

observation supports that both the sides of the fault have

differently altered rocks which is in partially agreement

with the results reported by BARTON.8

Conclusions

Quartz, feldspar, chlorite, calcite, dolomite, mica,

kaolinite, hematite and magnetite were identified as

constituent minerals in the sediment samples from the

Admiralty Bay, King George Island, Antarctica. The iron

distribution among the crystallographic sites of silicates,

magnetite and hematite has been determined by 57Fe

Mössbauer spectroscopy. At different locations

67


sediments had significant differences in the mineral

composition, in the iron distribution among the

crystallographic site of silicates, and in the specific

radioactivity of 137Cs. These results indicate differences

in the rock formation and alteration in this maritime part

of Antarctica. There is a much higher amount of iron

oxide in the sediments from south part of the geological

fault than in the north part. This can be associated with

much more alteration in the rocks in the south part of the

fault compared to the northern one.

4. M. W. MCELHINNY, Paleomagnetism and Plate Tectonics,

Cambridge Univ. Press, Cambridge, 1973.

5. D. D. HAWKES, Sci. Repts Falkl. Isl. Dep. Survey, 26 (1961) 1.

6. K. R. EVERETT, Rep. Inst. Polar. Stud., 58 (1976) 1.

7. W. A. ASCROFT, Sci. Repts Br. Antarc. Survey, 66 (1972) 1.

8. C. M. BARTON, Sci. Repts Br. Antarc. Survey, 44 (1965) 1.

9. J. L. SMELLIE, R. J. PANKHURST, M. R. THOMPSON,

R. E. S. DAVIES, Sci. Repts Br. Antarc. Survey, 87 (1984) 1.

10. E. KUZMANN, S. NAGY, A. VÉRTES, T. G. WEISZBURG,

V. K. GARG, Geological and Mineralogical Application of

Mössbauer Effect, in Nuclear Methods in Geology, A. VÉRTES,

S. NAGY, K. SÜVEGH (Eds), Plenum Press, New York, 1998.

11. E. KUZMANN, L. A. SCHUCH, V. K. GARG, P. A. DE SOUZA Jr.,

E. M. GUIMARÃES, A. C. OLIVEIRA, A. VÉRTES, Brasilian J.

Phys., 28 (1998) 434.*

12. Z. KLENCSÁR, E. KUZMANN, A. VÉRTES, J. Radioanal. Nucl.

Chem., 210 (1996) 105.The work was supported by the Hungarian Scientific Research

Fund (OTKA T029537) and by Brasilian FAP DF (project 104- VKG)

and CNPq (project CNPQ VKG 520414/96-9) projects.13. E. MURAD, J. H. JOHNSTON, Iron oxides and oxihydroxides, in:

Mössbauer Spectroscopy Applied to Inorganic Chemistry,

G. J. LONG (Ed.), Vol. 2, Plenum, New York, London, 1984,

p. 507.References14. E. MURAD, Poorly-crystalline minerals and complex mineral

assemblages, Hyp. Int., 47 (1989) 33.1. G. G. C. CLARIDGE, I. B. CAMPBELL, Physical Geography, Soils,

in: Key Environments Antarctica, Pergamon Press, New York,

Oxford, Toronto, Sydney, Paris, Frankfurt, 1984.

15. J. G. STEVENS, H. POLLAK, Lhi. ZHE, V. E. STEVENS,

R. M. WHITE, J. L. GIBSON, Mineral: Data, Mössbauer Effect

Data Center, Univ. North Carolina, Asheville, 1982, NC 28814.2. A. WEGENER, Die Entstehung der Kontinente, Petermanns

Mittelungen, 1912, p. 185. 16. S. MITRA, Applied Mössbauer Spectroscopy, Physics and

Chemistry of Earth, Vol. 18, Pergamon, Oxford, New York,

Seoul, Tokyo, 1992, p. 197.3. A. L. DU TOIT, Our Wandering Continent, Olivier and Boyd,

Edinburgh, 1937.

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mössbauer investigation of characteristic distribution of iron oxides in sediments from the...

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