MINERALOGIA POLONICA Vol. 32, No 1, 2001 PL ISSSN 0032-6267

Ewa KOSZOWSKA1, Dorota SAŁATA1

MINERALS OF THE GROUP IN METASOMATICALLY ALTERED CARBONATE ROCKS FROM ZAWIERCIE, S POLAND

A b s t a c t . Minerals of the hydrotalcite-manasseite group were identified in samples from two borehols in Zawiercie (ZMZ-9, RK-1). The minerals were found in calciphire bodies (RK-1) and in one small, metasomatic veinlet (ZMZ-9) formed in Middle Devonian dolomites. Alteration of dolomitic sediments was genetically connected with infiltration fluids that caused formation of a gamet-pyroxene skam. Inves­ tigations have revealed the presence of both hydrotalcite and manasseite. Besides, in few places of the veinlet there occurs a mineral, which has been recognized as iowaite.

Key-words: hydrotalcite-manasseite group, calciphires, ska ms, metasomatic veins, Zawiercie, S Poland

INTRODUCTION

The hydrotalcite group minerals belong to a large group of natural and synthetic dihydroxides named also as "layered double hydroxides" or "anionic clays". Their general formula can be written as: M |2XM (0 H)2 (Am“)x/mn H 2 0 (where M+2, M +3 are cations in the hydroxide layers and Am_ is the interlayer anion) and is based on positively charged -like layers with C 03-like anions and water molecules in interlayer positions (Drits et al. 1987) (Fig. la). Within the group, depending on the composition of the octahedral brucite-type cationic layers, three subgroups can be distinguished in which the cations are:

a) M g +2 + Al+3, b) Mg +2 + Fe+3 , c) M g + 2 + C r+3.

In the subgroup of the (Mg,Al) hydroxides the 2H (hexagonal) polytype is ma­ nasseite and the 3R (rhombohedral) is hydrotalcite. In the subgroup of the (Mg,Fe) hydroxides the 2H polytype is sjogrenite and the 3R polytype is pyroaurite. The

1 Jagiellonian University, Institute of Geological Sciences, Department of Mineralogy and Petrography, Oleandry 2a, 30-063 Krakow, Poland; e mail: [email protected]; [email protected] 69 Fig. 1. General structure of minerals of the hydrotalcite group (A) — the scheme of ordered arrangement of atoms in the layer structural elements (Drits et al. 1987) (B) — the structure of a mineral of the hydrotalcite group with the M g/A l ratio 2:1 proposed by Arakcheeva et al. (1996)

corresponding minerals in the subgroup of the (Mg,Cr) hydroxides are and (Arakcheeva et al. 1996). Both hydrotalcite and manasseite are relatively rare in nature. The majority of oc­ currences of the minerals of the hydrotalcite group are associated with serpen tinites, however they were also described from contact rocks (skams) and saline deposits (Ćemy 1963; Scaini et al. 1967). In Poland they have been identified in Kłodawa salt deposit (Wachowiak 1999), in the contact altered carbonate rocks in the Dubie area and in the Dębnik area (Muszyński, Wyszomirski 1998). Minerals of the hydrotalcite-manasseite group were also identified in altered carbonate rocks in Zawiercie (Koszowska, Salata 1997a, b). Although it is almost a rule that hydrotalcite and manasseite form sub- microscopic intergrowths, their separate occurrence is also known (Drits et al. 1987). Hydrotalcite is a scarcely studied mineral, though it plays a significant role in cement production, metal technology, Mg and Al corrosion studies, and is an important acid sorbent and catalyst (Moroz, Arkhipenko 1991; Cavani et al. 1991).

STRUCTURE OF MINERALS OF THE HYDROTALCITE-MANASSEITE GROUP

Both 3R and 2H polytypes of minerals of the hydrotalcite group can have a different M g/A l ratio. The of minerals of the hydrotalcite group with the M g/A l 70 ratio = 2:1, proposed by Arakcheeva et al. (1996), consists of octahedral brucite-type cationic layers in which cations (Mg,Al) are present. Layer 1 is of the brucite type and has the composition [AlMg 2 (OH)6], Layer 2 is a carbonate net of the [C 03] composition, whereas layer 3 is a network of H20 molecules. The layer structural elements along the hexagonal axis form the sequence -2-1-3-1-2- (Fig. lb). All the minerals generally contain only (C03)2- in their interlayers, however varieties containing (S04)2-, CL, (OH)’, (N 03)" and (Cr04)2- anions were also described (Drits et al. 1987). E.g. Koritning and Siisse (1975) described a hydrotalcite containing (OH)- instead of (C03)2- anions in interlayers having the composition: [Mg 6 A l2 (OH ) 1 6 ] + 2 [(0 H ) 2 -4H20 ]-2. Iowaite, a -ferric iron oxychloride having the composition Mg 4 (0 H ) 8F e0 C L H 2 0, was described by Kohls and Rodda (1967) (fide Drits et al. 1987).

SAMPLING AND METHODS OF INVESTIGATIONS

Samples of veinlets and calciphires have been collected from two boreholes ZMZ-9 and RK-1, in Zawiercie (northwest of Kraków, Fig. 2). Minerals from veinlets and calciphires were separated by handpicking under a binocular. Microscopic observations of thin sections were performed with an AMPLIVAL petrographical microscope. X-ray diffraction powder patterns were obtained with a Philips diffractometer using Ni-filtered CuKa radiation. The morphology of minerals and their chemical composition were studied by means of a scanning electron microscope (SEM) JEOL 5410 equipped with an energy dis­ persive spectrometer (EDS) Voyager 3100 (NORAN). Fresh surfaces of rock pieces as well as polished thin sections coated with the carbon film were examined and the contents of cations were evaluated according to the "standardless" procedure of calcu­ lation in Voyager software (i.e. using standards from the software library supplied by the manufacturer). Chemical composition of selected samples of was determined by means of an EDS microprobe ISIS system connected with a JEOL JSM 35 scanning

Fig. 2. Location of the area investigated 71 microscope operating at accelerating voltage of 20 kV and sam ple current of 30 nA with ZAF/FLS corrections. Biotite (for Mg, Si and Fe), chlorite (for Al), almandine (for Ca), rhodonite (for Mn and Zn) were used as calibration standards. The results are given in Table 2 with all the iron recalculated as FeO.

RESULTS

Minerals of the hydrotalcite-manasseite group were found in calciphire bodies, drilled in the borehole RK-1 in Zawiercie and in one small, metasomatic veinlet formed in Middle Devonian dolomites (ZMZ-9, Zawiercie). Both occurrences are genetically connected with metasomatic gamet-pyroxene skarn associated with Cu mineralization. The main compounds of the calciphires are: neomorphic sparitic calcite, euhedral pink or greenish spinel sensu stricto (as disseminated crystals in sparitic calcite), mag- nesioferrite and oval aggregates built mainly of fine-flaky serpentines and small amounts of chlorites, within which occur well-preserved small fragments of forsterite and minerals of the humite group (Koszowska 2001). Reddish-brown veinlets cutting calciphires consist mainly of forsterite and minerals of the humite group. The latter show pleochroism with an absorption scheme: from colourless to yellow and from yellow to orange-yellow and repeated twinning. These minerals in comparison to forsterite are characterized by an admixture of 5.5 wt.% TiC^. Forsterite and minerals of the humite group are preserved in various degrees. They are often altered into serpentine. Minerals of the hydrotalcite group in the calciphires occur in envelopes of spinel crystals (Phot. 1,2,4; Fig. 3) or in spaces among fractures of spinels in association with chlorite, serpentine, and sometimes brucite. Microscopical (optical and electron) investigations allowed to observe the following regularity: minerals of the hydrotalcite group form rims directly around spinel crystals, while outside of the hydrotalcite rims, chlorite and occasionally brucite occur. Hydrotalcite-like minerals were also found as inclusions in magnesioferrite. The metasomatic veinlet cutting dolomites is filled with chlorite, forsterite, mi­ nerals of the humite group, serpentine, dolomite and opaque minerals represented by mag- netite, pyrite and small amounts of chalcopyrite. Chlorite (penninite) occurs in two varieties: a fine-flaky one, about 0 . 0 1 mm in size, forms nests between larger flaky crystals up to 0.2 mm in size. Forsterite and minerals of the humite group undergo alteration into serpentines. Minerals of the hydrotalcite group in the veinlet occur mostly in association with the fine-flaky chlorite. They form "nest" aggregates surrounded by the coarse-flaky chlorite (Phot. 3, 5) and can be present in the "nests" alone, or in association with the fine-flaky chlorite. In both occurrences they form plates up to 20 pm in size, rarely showing weakly visible hexagonal habit (Phot. 6 ). A mineral recognized as iowaite, which appears only in the veinlet, reveals combination of short, hexagonal prism and pinacoid about 10 pm long (Phot. 7; Fig. 4), and is often intergrown with serpentine. 72 4 5 0 0 - o M9

4 0 0 0 -

3500

M C : o 0

Energy (keV)

Fig. 4. Iowaite crystals showing combination of short hexagonal prisms and pinacoid. SEM image. EDS spectrum of iowaite 73 Because it was impossible to separate the monomineral hydrotalcite fraction, further investigations were carried out on polymineral samples. X-ray diffraction patterns from oriented preparations of the investigated veinlet (ZMZ-9 125.7a, b) show two different types of basal reflections (7.84, 3.91-3.87, and 7.66-7.64,3.82-3.81 A, etc.) what indicates the presence of both 3R (hydrotalcite) and 2H (manasseite) polytypes of the hydrotalcite group (Fig. 5). In the patterns of calciphires, mainly reflections of hydrotalcite (7.84-7.76,3.91-3.87 A) were identified. Moreover, an (Mg,Fe)-mineral, whose composition is similar to iowaite, has been identified in the veinlet only on the basis of EDS investigations. This "iowaite" appears there sporadically only in few places. Its reflections in the XRD pattern are difficult to be discriminated because of their coincidence with reflections of other mineral phases, so the presence of this mineral is tentative. Small reflections (10.78 and 11.42 A) which occur in the XRD patterns of the veinlet (Fig. 5) can point to the presence of woodwardite (10.90 A), mountkeithite (11.30 A) or (11.26 A). The latter, described by Rodgers et al. (1977), has mainly an (Mg,Al) hydroxide layer structure with interlayer sulphate and carbonate anions and water molecules. Brindley and Kikkawa (1980) obtained a similar synthetic hydrated sulphate-hydrotalcite phase with a d-spacing of 11.15 A, while Serwicka et al. (1996) synthetised a phase in which a d-spacing of about 1 1 - 1 2 A is connected either with the occurrence of defect layers resulting from partial local dissolution of brucite sheets (due to the intercalation with acidic heteropolyanions), or to the presence of lacunary Keggin species of smaller dimensions. These minerals are structurally relevant to minerals of the hydrotalcite group.

°2© C u K a reflection of hydrotalcite (Hansen, Taylor 1991) reflection of manasseite (PDF 14-0525)

Fig. 5. Fragments of XRD patterns showing difference in the position of hydrotalcite and manasseite, in the veinlet (ZMZ-9) and calciphires (RK-1) Ch — chlorite, S — serpentine 74 TABLE 1

Cations contents of the hydrotalcite-manasseite group minerals from Zawiercie (standardless EDS procedure)

Cations per formula unit calculated on the basis of 4 Mg atoms, bold type — averaged amount of Mg, A1 and Fe. I* — cation composition of iowaite. 7 5 Energy-dispersive spectrometer analyses (EDS) have revealed that the minerals of the hydrotalcite group studied, except Mg and Al, contain Fe and small amounts of Ti, Zn and sporadically Ca. In their structure small quantities of anions such as Cl" (0.03-0.24/4 Mg atom s), (S04)2- (0.01-0.15/4 Mg atoms), (PO 4 )3- (0.01 /4 M g atoms) are also present. The M g/A l ratio oscillates about 2:1 (Table 1). The hydrotalcites studied display the A1/(A1 + M g + Fe) ratio from 0.26 to 0.38 with the average value about 0.33. In comparison the natural hydrotalcite from Kozani has an A l/(Al + Mg + Fe) ratio of 0.37 (Hall, Stamatakis 2000). Brindley and Kikkawa (1979) and Miyata (1980) obtained hydrotalcite with A1/(A1 + Mg) from 0.20 to 0.33, whereas Misra and Perotta (1992) synthesised slightly more Al-rich hydrotalcites with A1/(A1 + Mg) up to 0.38. The phase recognized as iowaite contains in its structure Cl" and (S04)2- (Fig. 4).

DISCUSSION AND CONCLUSIONS

According to the PDF and Drits's (1987) data, manasseite has d-values of basal reflections generally lower than hydrotalcite but these values can be influenced by various factors. One of them could be a presence of large anions such as Cl", Br_, (S04)2- in interlayer positions (Miyata 1983). The minerals investigated contain admixtures of

TABLE 2.

Comparison of the calculated and determined microprobe chemical compositions (wt.%) of the hydrotalcite group minerals

1 — chemical composition of hydrotalcite calculated for ideal formula of 4MgO • A120 3 • C 0 2 • 9H20; 2 — composition of natural hydrotalcites investigateded by Gastuche et al. (1967); 3-7 — hydrotalcite minerals from Zawiercie (RK-1 2023). * Total amount of C 02 + H20 calculated as a difference between the ideal formula (100%) and the total amount of oxides. 76 such anions but only in subordinate amounts. Additionally, proportions of anions fluctuate in various places of a sample and there is no correlation between the value of basal reflections and the amount of the anions. Because of that, the presence of these anions seems to have no impact on the value of basal reflections of the minerals exam in ed. The second factor that could influence the d-value of reflections is the M g/M g + A1 ratio. Investigations of synthetic hydrocarboxides (Gastuche et al. 1967) show that a large value of the ratio shifts main reflections towards higher values. In the samples considered, the M g/M g + Al ratio, because of its variability, seems not to have a signi­ ficant influence on the value of reflections. In X-ray patterns of the samples from the veinlet examined there appear two independent groups of reflections, which are characteristic of both hydrotalcite and manasseite (Table 2). This could suggest that there occurs a mixture of minerals of the hydrotalcite group. In other samples only hydrotalcite is present.

Fig. 6. Fragments of XRD patterns of the investigated samples M — mountkeithite, Mt — motukoreaite, W — woodwardite, Ch — chlorite, C calcite, S serpentine 77 Crystallization of minerals of the hydrotalcite group is mostly connected with secondary process of alteration (Drits et al. 1987; Ramdohr, Strunz 1978). In the calciphires investigated, the minerals of hydrotalcite group seem to be the products of alteration of spinels [similar process was described by Struwe (1958)]. In the veinlet they might form as products of serpentinization of forsterite instead of brucite when Al and Fe are present. The process could be explained on the base of the following reaction (Deer et al. 1963):

2 forsterite + 3 HzO = serpentine + brucite (hydrotalcite)

Acknowledgement. Sincere thanks are due to Dr. K. Bahranowski (Faculty of Geology, Geophysics and Environmental Protections, University of Mining and Metallurgy) for critical reading and Dr. A. Skowroński (University of Mining and Metallurgy) for corrections of the manuscript. Special thanks are directed to MSc. A. Latkiewicz (Institute of Geological Sciences, Jagiellonian University), MSc. J. Faber (Laboratory of Electron Microscopy, Institute of Zoology, Jagiellonian University) and MSc. E. Starnawska (Polish Geological Institute, Warszawa) for help in analyses.

REFERENCES

ARAKCHEEVA A.V., PUSHCHAROVSKII D.Y., RASTSVETAEVA R.K., ATENCIO D., LUBMAN G.U., 1996: Crystal structure and comparative crystal chemistry of A ^M g^O H J^C O jJS^O , a new mineral from the hydrotalcite-manasseite group. Crystallography Reports 47, 6,1024-1034. BRINDLEY G.W., KIKKAWA S., 1979: A crystal chemical study of Mg, Al and Ni, Al hydroxy-perchlorates and hydroxy-carbonates. Am. Mineral. 64, 836-843. BRINDLEY G.W., KIKKAWA S., 1980: Thermal behavior of hydrotalcite and of anion-exchanged forms of hydrotalcite. Clays Clay Miner. 28, 2, 87-91. CAVANI F., TRIFIRO F., VACCARI A., 1991: Hydrotalcite-type anionic clays: preparation, properties and applications. Catalysis Today 11,173-301. ĆERNY P., 1963: Hydrotalkit z Vćźnć na Zapadni Morave. Casop. Moravs. Musea. Acta Musci Moraviae, Vćdy Pfirod. 48, 23-30. DEER W.A., HOWIE R.A., ZUSSMAN J., 1963: Rock-forming minerals. London., v. I-V DRITS V., SOKOLOVA T.N., SOKOLOVA G.V., CHERKASHIN V.l., 1987: New members of the hydrotalcite-manasseite group. Ci/jys Clay Miner. 35, 6, 401-417. GASTUCHE M.C., BROWN G., MORTLAND M.M., 1967: Mixed magnesium- hydroxides. Cla\/ Miner. 7, 177-201. HALL A., STAMATAKIS M., 2000: Hydrotalcite and an amorphous clay mineral in high magnesium mudstones from the Kozani Basin, Greece. Journ. Sedim. Res. 70,3,549-558. H ANSEN H.C.B., TAYLOR R.M., 1991: The use of glycerol intercalates in the exchange of C 0 32- with S 0 42", N 03" or Cl" in pyroaurite-type compounds. Clay Minerals 26, 311-327. KOHLS D.W., RODDA J.L., 1967: lowaite, a new hydrous -ferric oxychloride from the Precambrian of Iowa. Amcr. Miner. 52, 1261-1271. KORITNING S., SÜSSE P., 1975: Meixnerit, Mg6Al2(OH)|fl 4H20, ein neues Magnesium-Aluminium-Hy- droxid-Mineral. Tschcrnt. Mineral. Petr. Mitt. 22, 79-87. KOSZOWSKA E., SAŁATA D., 1997a: Nowe wystąpienia rzadkich minerałów z grupy hydrotalkitu. Prace Specjalne PTMin. 9,110-113 (in Polish). KOSZOWSKA E., SAŁATA D., 1997b: Minerals of the hydrotalcite group — the new occurrence in Poland — preliminary results. Abstracts of Modul'97,1st EMU School and Symposium, Budapest, p. 24. KOSZOWSKA E., 2001: Spinels from calciphires in Zawiercie, Southern Poland. Min. Soc. Pol. Special Papers. 18, in press. 78 MISRA C., PEROTTA A.J., 1992: Composition and properties of synthetic hydrotalcites. Clays Clay Miner. 40, 145-150. MIYATA S., 1980: Physico-chemical properties of synthetic hydrotalcites in relation to composition. Clays Clay Miner. 28, 50-56. MIYATA S., 1983: Anion exchange properties of hydrotalcite-like compounds. Clays Clay Miner. 31, 4, 305-311. MOROZ T.N., ARKHIPENKO D.K., 1991: The crystal-chemical study of natural hydrotalcites. Soviet Gcol. Geopli. 4,52-58. MUSZYŃSKI M., WYSZOMIRSKI P., 1998: Przeobrażenia kontaktowe węglanowych skal dewonu w oko­ licach Dubia kolo Krakowa. Geologia 24, 3,199-217 (in Polish). RAMDOHR P., STRUNZ H., 1978: Klockmanns Lehrbuch der Mineralogie. Stuttgart. RODGERS K.A., CHISHOLM J.E., DAVIS R.J., NELSON C.S., 1977: Motukoreaite, a new hydrated car­ bonate, sulphate, and hydroxide of Mg and Al from Auckland, New Zealand. Mineral. Mag. 41, 389-390. SCAINI G., PASSAGLIA E., CAPEDRI S., 1967: Hydrotalcite di Tonezza (Vicenza). Period. Mineral. 36, 95-102. SERWICKA E.M., BAHRANOWSK1 K„ DULA R., GAWEŁ A., MICHALIK A., NOWAK P., 1996: Synthesis of hydrotalcite-like anionic clays pillared with Keggin-type heteropolymolybdates. Miner. Pol. 27, 1, 77-85. STRUWE H., 1958: Leidsc. Geol. Mededel, 22, p. 237. WACHOWIAK J., 1999: Studium mineralogiczne skal chemicznych i silikoklastycznych złoża solnego Kłodawy. Ph. D. thesis. University of Mining and Metalurgy, Faculty of Geology, Geophysics and Environmental Protections (in Polish).

Ewa KOSZOWSKA, Dorota SAŁATA

MINERAŁY GRUPY HYDROTALKITU Z METASOMATYCZNIE ZMIENIONYCH SKAŁ WĘGLANOWYCH Z ZAWIERCIA

Streszczenie

Minerały z grupy hydrotalkitu-manasseitu zidentyfikowane zostały w próbkach pochodzących z dwu otworów wiertniczych z Zawiercia (ZMZ-9, RK-1). Występują one w kalcyfirach (RK-1) gdzie powstały w wyniku przeobrażenia spineli i w meta- somatycznej żyłce (ZMZ-9), w której ich obecność wiąże się z procesem serpentynizacji forsterytu. Stwierdzono, że w kalcyfirach dominującą fazę stanowi hydrotalkit, pod­ czas gdy w żyłce występuje miesznina hydrotalkitu i manasseitu. Stosunek Mg:Al w badanych minerałach jest zmienny i waha się od 1,4:1 do 2,4:1. Poza glinem i magnezem w minerałach tych występują niewielkie domieszki Fe, Zn, Ca, Ti, Cl', (S 0 4)2-, (PO 4 )3". W metasomatycznej żyłce stwierdzono obecność minerału magne- zowo-żelazowego o składzie odpowiadającym iowaitowi.

79 MINER. POLON. Vol. 32, No. 1, 2001

Phot. 1. Minerals of the hydrotalcite group and chlorites replacing spinel crystal (calciphires, RK-1). Plane polarised light

Phot. 2. Minerals of the hydrotalcite group and chlorites replacing spinel crystal (calciphires, RK-1). Crossed polars

E. KOSZOWSKA, D. SALAT A — Minerals of the hydrotalcite group in metasoma tically altered carbonate rocks from Zawiercie, S Poland 80 MINER. POLON. Vol. 32, No. 1, 2001

Phot. 3. A mixture of a fine-flaky chlorite and minerals of the hydrotalcite group within a coarse-flaky chlorite (the veinlet, ZMZ-9). Crossed polars

Phot. 4. Alteration of spinel into chlorite and hydrotalcite from margins of crystals (calciphires, RK-1). SEM im age

E. KOSZOWSKA, D. SALATA — Minerals of the hydrotalcite group in metasomatically altered carbonate rocks from Zawiercie, S Poland 81 MINER. POLON. Vol. 32, No. 1, 2001

Phot. 5. Hydrotalcite-chlorite aggregates within a coarse-flaky chlorite (the veinlet, ZMZ-9). SEM image

Phot. 6. Fine flakes of hydrotalcite (the veinlet, ZMZ-9). SEM image

E. KOSZOWSKA, D. SALATA — Minerals of the hydrotalcite group in metasomatically altered carbonate rocks from Zawiercie, S Poland

8 2 MINER. POLON. Vol. 32, No. 1, 2001

Phot. 7. Penetration twin of iowaite (the veinlet, ZMZ-9), SEM image

E. KOSZOWSKA, D. SALATA — Minerals of the hydrotalcite group in metasomatically altered carbonate rocks from Zawiercie, S Poland 83