Clay mineralogy of Turkish borate deposits

Chemical Geology, 22 (1978)233-247 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

CLAY MINERALOGY

OF TURKISH

BORATE

233

DEPOSITS

G. ATAMAN and 0. BAYSAL Yerbilimleri Enstitiisii, Hacettepe

oniversitesi, Beytepe,

Ankam (Turkey)

(Received January 3, 1977; accepted for publication April 27, 1977)

ABSTRACT Amman, G. and Baysal, O., 1978. Clay mineralogy of Turkish borate deposits. Chem. Geol., 22: 233-247. Turkish borate deposits, which are considered the largest in the world, have been studied for their clay-fraction mineralogy, the chemistry and the physico-chemistry of their depositional environment. It is found that, in most cases, Mg-montmorillonite, hectorite, vermiculite and mixed layers of 14, -14,, 14,-14, and 14,-14, are the dominant minerals in these deposits with Mgl+ being the principal ion of octahedral sites and K’ being the principal exchangeable ion in phyllosilicates, where Srz+, Caa+ and Li’ appear to be the minor constituents. Na’ and Cal+ occur in borate minerals as co-genetic with the clay minerals. Tt is also found that these deposits contain fifteen different varieties of borate minerals. It is suggested that borate, carbonate and an important part of phyllosilicate minerals were authigenically formed in a relatively warm lacustrine environment with a pH around 9. One of the most interesting aspects of the samples studied from these deposits, is the existence of amorphous fractions of siliceous composition.

INTRODUCTION

Occurrences of authigenic clay minerals formed as a consequence of various geological phenomena, have been studied by many investigators (e.g., Weaver, 1958; Lucas, 1962; EsteouleChoux, 1962; Peterson, 1962; Tardy, 1969; De Segonzac, 1969); Millot (1964) and Erhart (1973a, b) present good summaries of these studies. Although some works have been accumulated on the mineralogy and genesis of borate deposits in general, very little work has been done on the clay minerals associated with these deposits. In this paper, the borate deposits of Turkey (which are known as the largest in the world) are studied not only for their borate minerals but also for their clay mineralogy and the chemical composition of the clay fractions. STUDY AREA AND STRATIGRAPHY

The borate deposits of Turkey are grouped and studied in three principal regions, namely Krrka, Emet and Bigadic-Kestelek, as shown in Fig.1. Stratigraphic columns of these regions are summarized in Fig.2 as four

234

.cr 2

q

5:

0 ._

ID

b

0

235

columns, since the Bigadic-Kestelek and Kestelek.

region is considered separately as Bigadic

STUDY OF CLAY FRXTIONS

A total of about 300 samples was collected from the study area. These samples were taken along certain geologic sections from open-pit and underground workings of each deposit and they are considered as representative of their geological environment. They were crushed and treated for extraction of their clay fractions. * Clay fractions of the Kirka deposits Mineralogical composition. Semi-quantitative clay-mineral analyses of 63 samples were made. The results may be summarized as follows: (a) In all levels, montmorillonite is the dominant clay mineral. (b) Montmorillonite-chlorite (14, -14, ) mixed layers are abundant in samples containing borates. (c) Illite and chlorite are found in a disordered manner, but their occurrences are generally rare. (d) During clay-mineral analyses of the Kirka samples, it has been possible to find some 2-pm fractions that are amorphous in X-ray diffraction. Electron microscope photographs of these particles (Plate I) also show that they do not have any crystalline morphology. Chemical composition. Chemical analyses of the clay fractions of Kirka samples are given in Table I and the results of these analyses may be summarized as follows: (a) Clay minerals are rich in MgO but poor in A1203 and Fe203 contents. (b) KzO content is 2-3 times more important than those of Na,O. (c) One clay sample (K-95), determined to be amorphous in X-ray diffraction, shows a high content of SiOZ and indicates the probable existence of amorphous silica in this sample. As a preliminary conclusion, one can say that in the Ku-ka deposit, clay minerals are principally Mg-montmorillonite (about 80%) with locally Mg-rich (14, -14, ) mixed layers and vermiculite. In some samples, there are also amorphous silica fractions with Mg-rich clays. Clay fractions of the Emet deposits Mineralogical composition. Clay fractions extracted from many samples show a gelatinous aspect and samples of this kind are amorphous in X-ray diffraction. *In this work a detailed study was made, in a semi-quantitative manner, of the clay fractions of 124 samples from Bigadic, 63 samples from Knka and 40 samples from Emet. The results are here only summarized. The details of the mineralogical compositions of all the samples are available from the authors on request.

236

Results of the mineralogical analyses can be summarized as follows: (a) Illite has a continuous distribution within the whole stratigraphy but, with some exceptions, it is only a minor component. It is relatively abundant near or within the horizon of tuffaceous samples. (b) Chlorite and mixed-layered clays are rare and distributed at random. (c) Montmorillonite is the dominant clay mineral. Chemical composition. The chemical composition of the clay fractions of samples from Emet deposits is given in Table II. Results of these analyses can be resumed as follows: (a) Montmorillonites are Al-montmorillonite, Mg-montmorillonite or AlMg-Fe-montmorillonite; the content of Al is significantly high compared with that of the clay fractions from Kvka deposits. (b) Contents of KzO are always higher than those of Na,O and this is particularly visible in sample E-35. (c) In sample E-71, in which illite is the dominant mineral, the content of MgO is specially high. (d) In some samples, amorphous silica is a major component. These samples have a gelatinous aspect when their clay fraction forms a freshly deposited cake. The amorphous state of these fractions is always identified by X-ray diffraction. Clay fractions of the Bigadic deposits Mineralogical composition. In all samples collected from this region, the dominant clay minerals are montmorillonite and vermiculite; in lesser abundance 14, -14,) 14, -14, and 14, -14, mixed layers are determined; 14, -14co mixed layers are characteristic of the Sayakci and Rasih Ihsan mines. In the Kestelek area, illite is present in samples with montmorillonite and chlorite as dominant minerals. As a preliminary conclusion one must say that formerly montmorillonite and vermiculite were the most frequent and abundant minerals. There is also an association of mixed layers that are formed from 14,) 14, and 14, sheets. Chemical composition. The chemical composition of clay fractions is shown in Table III. The most important characteristic of these analyses is the richness in MgO. Sample B-95, quasi-pure montmorillonite, is very rich in MgO.Jn a sample formed principally by amorphous silica (B-64) there is also 7.8% MgO. Only sample B-26, which is a mixture of montmorillonite, illite, vermiculite and 14,-14c mixed layer, has important concentrations of A1203, Fez03 and KzO beside MgO. Sample B-73, specially rich in 14, -14, mixed, layer is also rich in MgO; in this case, Mg’+ is certainly the principal octahedral cation in the atomic structure of this mineral.

l-

KI

RKA

EMET

REGION

v) ;ii

i E LITHOLOGY lo_ .- I

i

.

NAME OF THE UNIT AN0 REMARKS I UPPER

LIMESTONE

(Alternating

UNIT

marl and clay bands at the top. masrif or bre-

cciated at the bare. containing

80% borax. Also ulexlte. cole-

manife. kurnakov~te,

inderborite,

hoffertre,

Inderite.

myoite,

meyer-

tunell~fe. kermte.)

fSome tuffaceour

bands. alternating

layers of marly limestone,

marl and clayey marl from the bottom

to the top.)

IThIn-bedd AlSO “Okxl

LOWER (Thtck

LIMESTONE

and sllicecu

at the fop, pxws

UNIT and slightly riltcified

at the base I

Fig.2. Generalized

stratigraphic

column of the study area.

REG

I ON

1 BiGAD& I ml

I, KE

REGION I

I

IE OF THE UNIT AN0 REMA RKS

NAME OF THE UNIT AND REMARKS

u: g

2,Y R LIMESTONE

UNIT

.UPPER 6lightly

LIMESTONE rlliclfied.

BORATE

UNIT

locally tnterbedded

UNIT

(Interbedded

with clay.)

’

I~mertone. mar,, clay and fuff. Borate ,I present

Only in marly and clayey horizons and consists of coleman~te and ulexite with occasional occurrences of howlee. mite. ~nyolfe, meyerhofferlte

. .. . . . . . *... .:::::::::::-

UNIT :::::::::-:: . . . . . . . VITRIC-TUFF ..‘....... . . ..::.::.. ::..*:..:..:.. m***: *._.:::._.:: :.*;:: (Green, greyirh blue. rhvolmc; normally

marls. tuff. clays and occasionally

I

MARL-LIMESTONE

limestone.

the major cons~sfuent. others. ulexlte. hydro-

IAlternating,

interbedded

pander.

and hydroboraclte.)

graded.)

UNIT hmestone and marls with occasional

sandstone.1

C R y ST A L L 1 N E, terbedded w,fh conglomerate.

red clay, tuff and

(Well-bedded.

fine-grained

T U FF

U N , T

rhyolitic.)

3 volcan~cs of andesttic, dacittc and rhyolific x.1

1 . rj 1 LIMESTONE

UNIT

led. lnterbedded

wth

IICI of and&tic,

dacitic and rhyolitic

I

marl, tuff and clayey lignite.

LOWER fOssillferour,

UNIT

LIMESTONE

(With autocthonour

and allocthonour

rubumtr.

plsol~tic and partly rilicified.

relatively soft, fine-gratned,

First one 1s

Second one is

and lnterbedded

wth

composlfion.1

MARBLE (Alternattng

UNIT with crystalline

[PALEOZOIC] limestone.)

randrtone

I

LI

pp. 237-240

REGION

KESTELEK In

II@

$

I

LITHOLOGY

NAME OF THE UNIT

I

UPPER -

IPoorly

AND REMARKS

CONGLOMERATE

conrolldated,

UNIT

polyqenic with clayey matrix:

towards

the top grader into cross-bedded coarse sandstone, marl and silicified

iimestone.l

BORATE

UNIT

(Alternating limestone

marl and clay with colemanite,

and tuff

MARL-CLAY lAlternatmg tuff

81~0 thin bedded

interleverr.~

UNIT

limestone and marls with lignite bear~nq clay and

bands. Also conqlaeratic

and qlglomeratic

horizons

towards the top.1

)enic, poorly consolidated

with sandy.

into sandstone and marls towards the

IT

rPALEOZOlC1

241

PLATE I

PLATE I. For caption see p. 243.

242

PLATE I (continued)

243

PLATE I (continued)

PLATE

I

Electron photomicrographs

GENESIS

OF CLAY

of samples K-22 and K-14.

MINERALS

AND GEOCHEMICAL

INTERPRETATION

This study was principally oriented to the clay mineralogy of the borate deposits. Where the question of the genesis of the whole series is concerned, however, we must also take into consideration the occurrences of borates and carbonates beside clay minerals. In Neogene time, west Anatolia was covered by many small lakes related to some vertical movements. A set of faults, in relation with these movements, constituted an itinerary for the injection of hydrothermal solutions and volcanic muds into the lake environment. These solutions transported Na+, Ca*+, Sr*‘, Mg*‘, Li’, Si(OH),, HC03- beside borate molecules. Concentrations of these ions and molecules were variable from region to region and in some places hydrothermal solutions also transported As, Sb and S. In the Kuka region, borate deposits formed principally by borax and not by kernite, as stated by Brown and Jones (19’71). For this reason, it is logical to think that in this aqueous environment [B,O,(OH),] *- and Na’ ions were dominant. In the Klrka mines, some spheric kemite bodies ranging from 20 to 50 cm in diameter were also found recently by Baysal and Ataman (1975); this is the first occurrence of kemite in Turkey. In the Emet and Bigadiq mines, the principal mineral is colemanite; ulexite is the next relatively most important mineral here, as it is in the Kirka mine. Other berates such as kumakovite, inderite, inderborite and tunelite, which are Ca, Mg and Sr borates, are found in the Kirka region (Baysal, 1972).

244

TABLE Chemical

I composition

SiO, A’,03 Fe,03 TiO, cao MgO MnO K,O Na,O Ignation 1OS.S

(wt.%)

of the clay fractions

of KIrka region

mines

K-16

K-18

K-22

K-36

K-43

K-90

K-95

57.2 2.40 1.40 0.12 0.60 20.9 0.020 1.19 0.45

56.9 6.67 1.65 0.15 0.42 13.41 0.05 3.61 0.07

60.3 2.40 1.20 0.05 0.30 20.7 0.01 0.78 0.39

51.2 6.58 1.99 0.21 0.69 16.8 0.08 1.28 -

56.7 2.60 0.70 0.22 1.10 19.1 0.026 1.91 0.64

57.7 2.50 1.10 0.21 1.40 23.3 0.021 0.51 0.20

70.2 3.55 0.71 0.09 0.09 7.56 0.03 2.67 0.09

16.4

16.7

11.3

20.6

16.1

13.3

14.9

TABLE

III

1ooo”c TABLE

II

Chemical composition of Emet region mines

SiO, AGo, IWJ, TiO, CaO MgO MnO K,O Na,O Ignation loss loooOc

(wt.%)

of the clay fractions

Chemical composition Biqdiq region mines

E-l

E-5

E-14

E-35

E-71

50.5 12.7 7.67 0.54 0.53 4.23 0.05 0.24 0.18

84.0 5.47 0.87 0.31 0.10 0.93 1.52 0.09

82.3 1.88 0.25 0.10 0.46 0.76 0.47

58.2 13.65 1.10 0.21 0.11 7.89

SiO Al,;),

9.80 0.48

52.3 16.3 6.47 0.51 0.03 5.73 0.02 5.83 0.10

7.15

12.0

10%

22.6

6.03

12.7

Fe,& TiO CaoZ MgO MnO K,O Na,O Ignation

of clay fractions

of

B-26

B-64

B-73

B-95

52.2 12.2 8.90 0.41 0.26 7.10 0.06 3.77 0.66

77.9 0.80 0.22 0.06 0.12 7.84 0.08 0.25

63.9 3.06 1.35 0.13 0.29 12.18 0.08 0.09 0.58

48.8 5.79 1.06 0.16 0.21 22.20 0.03 0.45 0.18

14.25

12.0

17.9

20.5

1ooo3c

An authigenous medium characterized by the existence of colemanite is dominated by Ca2’ and [B304(OH)3] 2- ions (Christ et al., 1958), whereas, the formation of ulexite is controlled by Ca’+, Na2+ cations and [B,O,(OH),] 6polyanions (Clark and Appleman, 1964). On the other side, VaIyashko and Wlassowa (1969), working on the system of Na20-B203-Hz0 at 26°C and changing the B203/Na20 ratio from 1.5 to 2.9 and pH from 11.0 to 8.0, have observed that borax [B,O,(OH),] 2- polyanions, found in borax crystals and also in borax solutions, are stable for B20/Na20 ratios of 2.0-2.3 and for pH = 9.0-8.5. If the B20,/Na20 ratio = 1.5-1.7 and pH = 11-10.5, [B303(OH)5] 2’ polyanions are stable in solution, but the solid precipitated is also borax. Siffert (1962) has demonstrated that it was possible to synthetize sepiolite and Mgmontmorillonite from a solution with a SiO,/MgO ratio = 0.7 and pH = 8.8.

245

These results and conditions of genesis are in perfect concordance with those of a natural paragenesis environment and permit us to determine the pH of the sedimentation medium of borate lakes as 8-9. Colemanite has never been synthetized at normal pressure and temperature. Nikolaev and Chelishcheva (1940) have studied the CaO-Bz03-HZ0 system under normal pressure and observed that colemanite is never formed; they synthetized only inyoite Caz[ B303(OH)5] *G3Hz0. Inan (19’75), studying Ca-borate equilibria in solution at normal conditions, has never synthetized colemanite but meyerhofferite, CaZB303(OH)5.2 HzO. Ataman and Bay& (1973), in a set of heating experiments, have never been successful in transforming inyoite and meyerhofferite to colemanite. Inyoite and meyerhofferite are formed with [ B303(OH)5] 2- polyanions. These ions are stable in a Ca2’ aqueous medium with Bz03/Naz0 = 1.7-1.5, at pH = 10.5-11.0. In these Ca-borate series inyoite is the most hydrous form and it must be in equilibrium with water; however, meyerhofferite seems to be mete&able. Therefore, these two minerals will change to colemanite during diagenesis. The Emet and Bigadic mines, which are very rich in colemanite, also have montmorillonite which is relatively poor in Si. Beside these clayey levels there is a great number of siliceous-gel horizons. The formation of these gels is possible only if the pH of this environment is greater than 9.5. In this case, the solubility of silica increases sharply by the formation of silica anions. A small decrease in pH provokes massive precipitation of silica, producing silicagel horizons. Silicates and specially phyllosilicates formed in this environment, are poorly cyrstallized. This is a general case when crystallization medium solutions are very concentrated. In the Kirka mine, when ulexite, kurnakovite and inderite are formed, there are also silica gels containing Mg in their framework. Kurnakovite and inderite contain [B303(OH)5] 2- polyanions in their structure and their solutions. These polyanions are stable in a solution with a B20,/Na20 ratio between 1.5 and 1.7 and pH = 11.0-10.5. These highly basic aqueous environments are not available for the genesis of phyllosilicates. Among the three borate areas, the Bigadic mines are the richest in ulexite and vermiculite, the latter being the most abundant phyllosilicate. The ionic and molecular materials necessary for borate-phyllosilicate paragenesis are constituted by borate polyanions, Nd, Mg’+, Sr2’, Ca”, K’, Si(OH)4 that are transported in hydrothermal solutions to the lakes in the region. These materials in solution participated in one part in the authigenesis of Mg-montmorillonite, vermiculite and mixed-layer minerals that are formed by 14, -14, and 14, sheets, and in other part in the genesis of many borate minerals. As a result, while Mg” and K’ took place in phyllosilicate formation, Na+, Ca” and Sr” were involved specially in borate minerals. Among the clay minerals, there is an authigenic part as stated earlier, but there is also an aggradated part of the clay minerals. For example, the samples E-l and E-71, which are relatively rich in Fe203, seem to be Fe-beidellite and Fe-illite, respectively. These clay minerals were probably transported to the lakes and aggradated in this environment.

246

CONCLUSIONS

Within the Turkish borate deposits, fifteen kinds of borate minerals were determined. These minerals were formed in an authigenic manner in shallow lakes of Neogene age. Ionic and/or molecular materials entering into the formation of borates, silicates and carbonates were furnished principally by the hydrothermal solutions of volcanic activity. A part of this material has certainly reached the lakes as a volcanic mud. Hydrolysis of this mud increased the ionic concentrations of the lake water constituting the environment of mineral formation. Beside borates, Mg-montmorillonite, hectorite, vermiculite and a set of mixed-layer minerals constituted by 14,) 14, and 14, sheets were formed. Characteristics of the reaction medium may be summarized as follows: The lake water was very rich in alkali, alkali-earth, Ca-borate and borate polyanions with a pH of around 9.

REFERENCES Ataman, G. and Baysal, O., 1973. Bazi bor minerallerinin term% reaksiyonlari ve bunlarin atom yapisina etkisi. Cumhuriyetin 50. Yil Yerbilimleri Kongr. Tebligler Biilt., Ankara, pp. 537-564. Baysal, O., 1972. Borat yataklarinin mineralojik ve jenetik incelenmesi. Hab. Tezi, Hacettepe Univ., Ankara, 157 pp. Baysal, 0. and Ataman, G., 1975. Tiirkiye’de yeni bir bor minerali: Kernit ve olusumunun tarti masi. T&k. Jeol. Kurumu, Biilt., 18(7): 3-10. Brown, \ .W. and Jones, K.D., 1971. Borate deposits of Turkey. In: A.S. Campbell (Editor), Geology and History of Turkey. Petroleum Exploration Society, Libya, Tripoli, pp. 463-492. Christ, C.L., Clark, J.R. and Evans, H.T., 1958. Studies of borate minerals, 3. The crystal structure of colemanite, CaB,O,(OH),*H;O. Acta Crystallogr., 11: 761-770. Clark, J.R. and Appleman, D.E., 1964. Pentaborate polyanion in the crystal of ulexite, NaCaB,O,(OH),*5H,O. Science, 145: 1295-1296. de Segonzac, G.D., 1969. Les mineraux argileux dans la diagenese passage au metamorphisme. MBm. Serv. Carte GBol. Alsace Lorraine, 29: 320 pp. Erhart, H., 1973a. Itinhaires geochimiques et cycle geologique de l’aluminium. Dion, Paris, 253 pp. Erhart, H., 1973b. Itineraires geochimiques et cycle geologique du silicium. Dion, Paris, 271 pp. EsteouleChoux, J., 1962. Etude comparee de la sedimentation argileuse dans les bassins tertiaires de Campbon et Saffre (Loire-Atlantique). ler Coll. Int. Stratigr. Paleogine, Bordeaux, 1962. Inan, K., 1975. Su tapyici bazi bor mineralleri arasmdaki denge iligkileri T.B.T.A.K. 5. Bil. Kongr. (abstr.). Lucas, J., 1962. La transformation des min&aux argileux dans la sedimentation: dtudes sur les argiles du Trias. Mem. Serv. Carte Geol. Alsace Lorraine, 23, 202 pp. Millot, G., 1964. Geologic des argiles. Masson, Paris, 499 pp. Nikolaev, A.V. and Chelishcheva, A.G., 1940. The 25°C isotherm of the system: CaO + B,O, + H,O and MgO + B,O, + H,O. C.R. Acad. Sci. S.S.S.R., 28: 127-130. Gzpeker, I., 1969. Bati Anadolu borat yataklarinm mukayeseli jenetik etudu. Ak Matbaasi, Istanbul, 116 pp.

247

Peterson, M.N.A., 1962. The mineralogy and petrology of Upper Mississippian carbonate rocks of the Cumberland plateau in Tennessee. J. Geol., 70: 1-31. Siffert, B., 1962. Quelques reactions de la silis en solution: la formation des argiles. M8m. Serv. Carte GBol. AlsaGe Lorraine, 21: 86 pp. Tardy, Y., 1969. Geochimie des alterations. Etude des arenes et des eaux de quelques massifs cristallins d’Europe et d’Afrique. Mbm. Serv. Carte GBol. AlsaGe Lorraine, 31: 199 pp. Tardy, Y., Cheverry, C. and Fritz, B., 1974. NQoformation dune argile magnksienne dans les depressions interdunaires du lac Tchad. Application aux domaines de stabilith des phyllosilicates alumineux, magnesiens et ferriferes. C.R. Acad. Sci., Ser. D, 278: 1999-2002. Valyashko, M.G. and Wlassowa, E.W., 1969. IR-Absorptionsspektren von Boraten und borhaltigen wiissrigen LBsungen. Jenaer Rundsch., 1: 3-11. Weaver, C.E., 1958. Geologic interpretation of argillaceous sediments, 1.. Origin and significance of clay minerals in sedimentary rocks; 2. Clay petrology of Upper MississippianLower Pennsylvanian sediments of central United States. Bull. Am. Assoc. Petr. Geol., 42: 254-309.