Mineralogy, geochemistry and genesis of bentonites of the Ordu area, NE Turkey

Mineralogy, geochemistry and genesis of

bentonites of the Ordu area, NE Turkey

E. ABDIÇOGÆ LU AND M. ARSLAN*

Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey

(Received 17 May 2004; revised 4 September 2004)

ABSTRACT: A number of bentonitic clay deposits from the Ordu area (NE Turkey) have been

investigated by optical and electron microscopy, X-ray diffraction and chemical analysis. The clays

are the alteration products of Late Cretaceous trachytic and trachyandesitic pyroclastic rocks. They

contain volcanogenic sanidine, plagioclase, biotite and pumice, along with the diagenetic minerals

opal-CT, cristobalite and rare calcite and zeolite (clinoptilolite). Ca-smectite (montmorillonite) is the

dominant clay mineral. The rare earth element patterns of all the bentonitic clays are generally

similar, although there are variations in the Eu anomaly indicating formation from different types of

pyroclastic rocks. Oxygen and hydrogen stable isotope values suggest that the smectite was formed at

20ÿ40ëC in pore water of mixed meteoric and marine origin during argillization. These features,

together with mass-balance calculations, indicate the enhanced MgO and Sr content of the smectite

resulted from formation at shallow burial depths within a dominantly marine environment.

KEYWORDS: clay, smectite, montmorillonite, bentonite, O and H stable isotopes, marine

alteration, Turkey.

The Eastern Pontides (NE Turkey), a palaeo-island

arc, displays three major volcanic cycles of Liassic,

Upper Cretaceous and Tertiary age (Arslan et al.,

1997). The alteration products of these volcanics,

especially those of Upper Cretaceous age, are very

common. Hydrothermal alteration associated with

volcanogenic massive sulphide deposits is wide-

spread. Clay occurrences (e.g. bentonite, kaolinite

and illite), some of them economic, developed in

the alteration zones of the ore deposits in different

parts of the region.

Since 1978, several researchers, especially from

the General Directorate of Mineral Research and

Exploration of Turkey, have examined the

economic potential of these clay occurrences.

There is, however, little information about the

mineralogical and geochemical characteristics and

origin of the clay deposits (e.g. CË elik et al., 1999;

YalcËõn & GuÈmuÈs° er, 2000; Arslan et al., 2002;

AbdiogÆlu et al., 2004). In the Ordu area, bentonitic

clay deposits are distributed over a 110 km2area

(Fig. 1).

This study describes the bentonitic clay deposits

of the Ordu area, presents systematic analyses of

their mineralogy, geochemistry and stable isotope

signatures, and evaluates the environment of

formation. We demonstrate that despite their

apparent association with hydrothermal ore

deposits, the bentonites are in fact of a low-

temperature origin, formed by the influx of

marine waters.

STRAT IGRAPHY AND LITHOLOGY

The area of our study is located in the west of the

Eastern Pontides, NE Turkey (Fig. 1). Here the

Upper Cretaceous Tirebolu Formation, consisting of

trachyte, trachyandesite, hyalo-trachyte and pyro-

clastics of similar composition, as well as

associated bentonite deposits, make up the base-

ment rocks of the area. The Upper Cretaceous±

Palaeocene Akveren Formation, consisting mainly

of limestone, clayey limestone, tuffite and conglom-

erate, conformably overlies the basement. Both

* E-mail: [email protected]

DOI: 10.1180/0009855054010161

ClayMinerals (2005) 40, 131±151

# 2005 The Mineralogical Society

formations are cut by andesite dykes of Tertiary age

and are uncomformably overlain by terraces and

alluvial deposits of Quaternary age (Fig. 2). Within

the bentonite deposits, there are no marine fossils or

sediments, but the overlying Upper Cretaceous-

Palaeocene Akveren Formation does show evidence

of marine deposition. The age of the bentonites can

be constrained as Upper Cretaceous±Palaeocene, or

older.

Seven separate clay deposits were studied

(Fig. 1), the most extensive located in the

Kavaklar area. The thickness of bentonites in this

area ranges from 0 to 25 m and these have been

exploited from four inactive open pits and one

which is still active. The bentonites range in colour

from white, yellow, pink, yellowish white to

greenish blue. They have a soapy, `popcorn'

texture and are waxy in appearance. Unaltered

biotite, volcanic rock fragments and opal-CT are

commonly observed with the bentonite, and partly

altered ignimbrites characterize the lower part of

the deposits.

Other small bentonite deposits are present in the

areas of Asarkaya, GoÈlcuÈgÆez, YuÈceler, Yedikapõ and

Tavkutlu, which show a range of volcanic-related

features. Flow textures are observed in the Tavkutlu

clay deposit with remnants of ignimbritic tuff, and

volcanic rock fragments characterize the clays in

the Asarkaya and Cevizdere areas in the contrast to

the deposits of the Yedikapõ area formed largely as

alteration products of volcanic agglomerate.

MATER IAL AND METHODS

140 samples were collected from open bentonite

pits of the Tirebolu Formation (Fig. 1). From these,

18 whole-rock and 14 clay-fraction samples were

analysed for major, trace and rare earth element

(REE) analysis. Thirty six samples were selected

for whole rock and oriented X-ray diffraction

(XRD) studies, and six smectite separates were

analysed for oxygen and hydrogen stable isotopes.

Optical microscope studies were carried out on

pyroclastic and partly altered rocks. Scanning

electron microscopy (SEM) studies were conducted

at the Laboratories of Gebze Technology Institute

and Karadeniz Technical University using Philips

XL30 SFEG and Jeol JSM 6400 scanning electron

microscopes.

Selected samples for geochemical and XRD

analyses were ground using an agate mortar and

pestle. In order to obtain clay fractions (<2 mm) for

analysis, chemical treatments (Jackson, 1956) were

carried out to remove carbonates, amorphous silica

FIG. 1. Simplified geological map of the Ordu (UÈ nye-Fatsa) area in NE Turkey showing the location of bentonites

and volcanic rocks across the region.

132 E. AbdiogÆlu and M. Arslan

and free Fe oxides. The samples were further

treated with 1 N acetic acid to remove calcite and

boiled for 2.5 min with 0.5 N NaOH solution to

digest free silica (such as opal-CT). In order to

extract free Fe oxides, the sodium dithionite-citrate

procedure was used (Jackson, 1956; Mehra &

Jackson, 1960; Kunze, 1965). After each chemical

treatment, the samples were washed with distilled

water. For clay mineral analysis, clay fractions

(<2 mm) were separated by sedimentation, followed

by centrifugation of the suspension after overnight

dispersion in distilled water. More complete

dispersion of clay particles was achieved by

ultrasonic treatment for ~15 min. X-ray diffraction

analyses were carried out using a Rigaku DMAX

2200 and a Rigaku DMAXIIC X-ray diffractometer

(Cu-Ka and Ni filter). Semi-quantitative mineral

investigations were performed using the mineral

intensity factors according to an external standard

method (Brindley, 1980). Oriented clay fractions

were analysed in the untreated state (N), after

ethylene glycolation (EG; 60ëC, 16 h) and after

heating (H; 490ëC, 4 h). Mg- and K-saturated

samples were also analysed. The K-saturated clays

were prepared by washing with 20ÿ25 ml of 1 N

KCl, dispersion by ultrasonic vibration, centrifuging

and decanting the supernatant clear solution. This

was repeated twice, first using 1 N K acetate

solution and then with 1 N KCl. The clay fractions

were subsequently washed in alcohol by centrifuga-

tion and then with a mixture of acetone and alcohol.

The supernatant solution was checked for residual

chloride with AgNO3. If chloride was present,

washing with alcohol was repeated. The same

procedure was used to prepare Mg-saturated clays

except MgCl2 and Mg acetate were used. The

FIG. 2. Generalized stratigraphic section of the study area indicating the vertical distribution of bentonite and

volcanic rocks.

Bentonites from Ordu, Turkey 133

K-saturated clays were analysed by XRD in the

untreated state, and after heating at 350ëC and

490ëC. The Mg-saturated clays were analysed in the

untreated state and following glycolation. The di- or

trioctahedral structure of the clays was determined

from the position of the 060 reflection as a measure

of the b dimension using random powder samples

(Velde, 1992). Here, the 211 reflection of quartz

was used as a reference standard. The Green-Kelly

Test (Greene-Kelly, 1953) as modified by Bystrom-

Brusewitz (1976) was used to differentiate between

montmorillonite and beidellite.

Differential thermal analysis (DTA) was carried

out on the clay-sized fraction (<2 mm) using a

Netzch 404 DT Analyser. Analyses were performed

in air atmosphere over the temperature range

20ÿ1100ëC using a heating rate of 5ëC minÿ1.

Chemical analysis of whole-rock and clay

fractions were carried out by ACME Analytical

Laboratories Ltd. (Canada); ICP-AES was used for

the major and trace elements and ICP-MS for the

REE. Samples used for the calculation of mineral

formulae were selected from purified clay samples

containing entirely smectite. Detection limits range

0.01 to 0.1 wt.% for major elements, 0.1 to 5 ppm

for trace elements and 0.01 to 0.5 ppm for the REE.

Six samples of pure montmorillonite (<2 mm)

from open pit 1 in the Kavaklar deposit were

analysed for their O and H isotope values at the

Scottish Universities Environmental Research

Centre (East Kilbride, Scotland). The oxygen

isotopic composition was determined by a modifica-

tion of the laser-fluorination method of Sharp

(1990), which has been described by Macaulay et

al. (2000). Samples were heated at 200ëC under

high vacuum overnight to remove interlayer and

adsorbed surface water. Approximately 1 mg was

reacted with ClF3 whilst heating with a CO2 laser.

The resultant oxygen was purified, converted to

CO2 and the reaction yield determined. The oxygen

isotope composition of the CO2 was measured on

an in-line VG PRISM 3 dual-inlet mass spectro-

meter with a working standard gas calibrated

against international reference materials. The

precision and accuracy of measurement are Ô0.2s

(sigma) for isotopically homogeneous material.

Hydrogen was extracted by heating samples under

vacuum to release bound hydrogen, mostly as water

vapour. Water was then converted to hydrogen by

reaction with hot uranium. Samples were placed

into platinum crucibles that had previously been

heated under vacuum to 1500ëC for >3 h. The

hydrogen produced was delivered to a mercury

manometer by a Toepler pump and the yield

determined by comparing the starting weight of

mineral with micromoles of gas produced. The

extracted hydrogen was analysed using a VG

Micromass 602B mass spectrometer, with a

working standard calibrated against international

standards.

RESULTS AND INTERPRETAT ION

Petrography

The volcanic rocks in the studied area consist of

trachyte, trachyandesite and hyalo-trachyte, and

show microlitic porphyric, hyalo-microlitic

porphyric, glomeroporphyric and flow textures.

FIG. 3. Representative XRD patterns of untreated and

air-dried random powder bulk samples from the Ordu

area bentonites.


Hyalo-trachytes sometimes show perlitic, snowflake

and spherulitic devitrification textures. The rocks

contain phenocrystals of mainly sanidine

(Or55ÿ64Ab32ÿ34An4-8), andesine plagioclase

(Ab55ÿ68An26ÿ42Or4-8), biotite (Mg-number =

0.58ÿ0.61), titanomagnetite, rarely pyrite, horn-

blende and apatite.

The pyroclastic rocks, the precursor materials of

bentonites are agglomerates, crystal tuffs, vitric

crystal tuffs and ignimbrites. Crystal constituents

are sanidine, biotite, rare plagioclase, primary and

secondary quartz, opaque minerals and clay

minerals. Rock fragments are trachytic in composi-

tion. Ignimbrites contain crystals, glass shards,

glassy pumice fragments and some rare rock

fragments. In most cases, eutaxitic fabrics with

intense welding, compaction and alignment of

flattened glassy pumice fragments and elongated-

curved glass shards are very characteristic. Some of

the biotites exhibit deformation textures due to

compaction of the rocks.

Mineralogy and mineral chemistry

In all bentonite samples, smectite is the most

abundant mineral. Other constituents are opal-CT,

cristobalite (opal-C), K-feldspar (sanidine), plagio-

clase and biotite. The terminology used to describe

the silica polymorphs follows Jones & Segnit

(1971). Calcite and zeolite (clinoptilolite) are

scarcely present. Representative XRD patterns of

bulk samples are shown in Fig. 3.

The major smectite mineral is a dioctahedral Ca-

variety; the deposit from Kavaklar is mineralogi-

cally homogeneous and consists almost entirely of

this mineral. The Asarkaya, Cevizdere, YuÈceler,

Yedikapõ locations are also characterized by Ca-

smectites whereas GoÈlcuÈgÆez has a Na-Ca variety.

Although it is difficult to distinguish Ca-smectite

from Mg-smectite because of their similar d values,

chemical analysis of purified clay fractions clearly

indicate that the dominant cation in the interlayer

region is Ca. The basal spacing (001) of the

untreated Ca-smectite is between 14.2 and 15.1 AÊ

and that of Na-Ca smectite ranges between 14.6 and

12.5 AÊ at 54% relative humidity. Second, third,

fourth and fifth order basal spacing can be

identified in the XRD patterns of the untreated

and glycolated samples; in the heated samples only

the first, second and third order spacing are present

(Fig. 4). The glycolation of Mg-saturated samples

caused a shift of the smectite peak from 14.0 to

17 AÊ . The absence of mixed-layer illite-smectite

minerals is inferred from the width of the 17 AÊ

peak (ethylene glycol-solvated) and the existence of

rational d spacing of the remaining basal reflec-

tions. All the treatments such as K and Mg indicate

pure smectites. K saturation and heating at 350 and

490ëC results in a collapsed smectite peak at 12.07

and 9.91 AÊ respectively. The basal d spacing of

FIG. 4. XRD patterns of oriented clay fractions (<2 mm) from the Ordu area bentonites.


12.07 AÊ after heating at 350ëC is due to rehydration

and corresponds to a monolayer of H2O in the

interlayer.

The d060 peak of smectites ranges from 1.488 to

1.500 AÊ (average 1.493 AÊ ) indicating a dioctahedral

layer, typical of montmorillonite and beidellite

(Wilson, 1987).

The Greene-Kelly test indicates that the smectite

is montmorillonite because the basal peak did not

expand after treatment with ethylene glycol

(Fig. 4); it is however acknowledged that this test

does not distinguish between all montmorillonites

and beidellites (Wilson, 1987).

The DTA curves of the samples show three

endothermic peaks (Fig. 5). The first endothermic

peak occurs at 140ÿ170ëC and corresponds to the

loss of adsorbed water. The second peak at

690ÿ720ëC reflects the loss of hydroxyl water,

and the third endothermic peak at 820ÿ900ëC

indicates collapse of the montmorillonite structure.

A sharp exothermic peak at 990ëC is taken to

reflect the crystallization of a new mineral phase,

probably b-quartz (Grim & Kulbicki, 1961). These

DTA curves are similar to those of Cheto-type

montmorillonite described by Grim & Kulbicki

(1961).

When viewed by the SEM, all the clay samples

display honeycomb texture with platy smectite

particles showing edge-to-edge, and edge-to-face

contacts (Fig. 6). Our SEM studies also reveal

information about the alteration process. Alteration

commonly begins perpendicular to micro-fractures

within volcanic glass (Fig. 7a,d), and then rapidly

alters the glass to form a spongy pseudomorphic

texture (Fig. 7b) of smectite and opal-CT (Fig. 7c).

Such alteration textures are common in the

Asarkaya, Tavkutlu, Cevizdere, GoÈ lcuÈ gÆ ez,

Yedikapõ and YuÈceler areas and in the lower parts

of the Kavaklar open pits.

Major, trace and REE concentrations of smectite

(<2 mm) and their structural formulae calculated on

the basis of 11 oxygen atoms (Weaver & Pollard,

1973) are given in Table 1 and Table 2, respec-

tively. The dioctahedral smectites are rich in Al2O3

FIG. 5. Differential thermal analysis curves of smectites from various locations (Is° 1 2/1-3, Kavaklar; Cev,

Cevizdere; As, Asarkaya; 18, Yedikapõ; T, Tavkutlu; Y, YuÈceler).

FIG. 6. Honeycomb texture of the Ordu area smectites

folded and loosely packed.


that ranges between 18 and 21 wt.%. The K2O

content of the clay fractions is 0.68ÿ2.40 wt.% and

K as interlayer cation is 0.03ÿ0.21 per unit

formulae. These values may not be consistent

with general smectite compositions but Tsipursky

& Drits (1984) proposed that smectites close to the

montmorillonite/beidellite boundary could contain

0.27 K atoms. Another possibility is that the

interlayer composition may have been modified by

ion exchange at a later stage, after bentonite

formation.

When the octahedral composition of these

smectites is plotted on a Mg-Al-Fe triangular

diagram (Fig. 8; GuÈven, 1988), Kavaklar samples

plot in the Tatatilla field (TA) of montmorillonite,

whereas smectites from the other locations plot in

the beidellite field. However, based on the

tetrahedral charge/octahedral charge ratio of the

smectites (0.39ÿ0.67) they show more typical

characteristics of montmorillonites (GuÈven, 1988).

Christidis & Dunham (1993) suggested that

bentonites derived from intermediate (dacitic-

andesitic) precursors are extremely heterogeneous,

as far as their composition is concerned, and are in

compositional transition between beidellite and

Tatatilla-type montmorillonite, with probable solid

solution between the two species.

Geochemistry

Volcanic rocks of the study area are generally

medium alkaline to tholeiitic-alkaline transitional in

character and have high K, Rb, Th and light REE

and low Sr, Ba, P, Ti and Eu contents.

FIG. 7. SEM images of the Ordu area bentonite samples; (a) micro-fractured volcanic glass, (b) spongy

pseudomorphic texture in glass shard, (c) spongy glass shards and smectite + opal-CT forming from the glass,

(d) smectite forming along the microfractures in glass.

FIG. 8. Ternary diagram of the main octahedral cations

for the Ordu area smectites (GuÈven, 1988). Key to the

abbreviations: TA = Tatatilla montmorillonite, OT =

Otay montmorillonite, CH = Cheto montmorillonite,

WY = Wyoming montmorillonite, Fe-M = Fe-rich

montmorillonite, BI = beidellite, Fe-BI = Fe-rich

beidellite. The dashed line separates the Fe-rich

smectites.


TABLE 1. Major (wt.%), trace and REE composition of the dioctahedral smectites from the Ordu area, NE Turkey.

Sample Is° 1 2/1 Is° 1 2/2 Is° 1 2/3 Is° 1 2/4 Is° 1 2/5 Is° 1 2/6 Is° 1 2/7 Is° 1 2/8 Is° 1 2/9

location Kavaklar area open pit 1

SiO2 55.76 54.77 55.19 55.68 57.04 54.61 54.86 56.72 54.51

Al2O3 19.27 19.34 18.86 18.94 18.37 20.02 19.67 18.60 18.00

Fe2O3* 1.19 1.14 1.01 1.01 1.17 1.27 1.18 1.30 1.20

MgO 4.39 4.22 3.92 3.91 3.95 4.59 4.53 3.85 4.10

CaO 2.55 2.57 2.51 2.55 2.69 2.68 2.52 2.47 2.90

Na2O 0.34 0.37 0.34 0.36 0.39 0.49 0.46 0.39 0.33

K2O 0.62 0.89 0.83 0.96 0.86 1.07 0.69 0.82 0.67

TiO2 0.11 0.11 0.11 0.12 0.11 0.12 0.12 0.11 0.12

MnO 0.04 0.02 0.03 0.03 0.03 0.03 0.02 0.02 0.11

LOI 17.40 18.10 18.90 18.00 16.80 16.60 17.20 17.40 18.00

Sum 101.66 101.53 101.70 101.56 101.41 101.47 101.24 101.67 99.94

CaO/Na2O 7.50 6.95 7.38 7.08 6.90 5.47 5.48 6.33 8.79

Trace elements (ppm)

Co 0.6 0.7 0.7 0.5 0.6 0.6 0.8 0.7 0.9

Cs 4 4.2 4.2 4.1 4.3 3.5 4.3 3.7 3.8

Ga 14.1 14.1 13.1 12.7 11.5 14.1 13.3 13 11.4

Hf 4.1 4.1 3.2 4.2 3.7 4.3 4 3.6 3.2

Nb 7.2 8.4 6 9.5 7.5 8.2 9.9 9.3 10.4

Rb 42.4 53.3 49.8 52 65.5 54.2 53.3 41.1 45.3

Sn 2 2 2 2 2 2 2 2 2

Sr 102.2 105.6 94.8 110.5 90.4 114.7 112.6 99 119.2

Ta 0.9 1.1 1 1.1 1 1.1 1.2 1.1 1.1

Th 32.6 31.2 27.5 29.8 36.8 32.8 32.5 28.4 25.1

Tl 0.3 0.2 0.2 0.3 0.1 0.1 0.2 0.2 0.4

U 0.5 0.7 0.5 1.1 0.9 1.2 1.2 0.6 1.1

V 12 13 11 9 8 <5 6 7 9

W 2 2 1 2 2 3 3 2 3

Zr 88.6 81.4 68.1 105.2 80.4 96.6 89.5 78.2 76.8

Y 18.9 24.9 14.4 15.3 17.7 18.6 14.2 13.6 21.8

Cu 2 2 1 2 2 1 2 2 1

Pb 15 13 12 11 12 13 13 8 24

Zn 20 14 11 12 12 15 14 11 13

Ni 2 3 1 6 1 1 <1 3 1

Ba 15 6 <5 13 9 7 9 14 11

Sc 1 1 1 2 2 1 2 1 1

REE (ppm)

La 42 41.3 30.5 31.1 50.5 34.9 32.5 29 33.6

Ce 73.5 64.1 56.1 52.4 87 65.5 60 51.6 56.5

Pr 7.3 6.44 4.67 5.21 8.34 5.96 5.68 5.03 5.29

Nd 23 20.7 15.1 16.1 27.2 19.4 17.6 15.2 16.9

Sm 3.8 3.6 2.4 2.9 4.7 3.4 3 2.9 2.8

Eu 0.34 0.38 0.2 0.3 0.49 0.33 0.3 0.31 0.32

Gd 2.8 2.97 1.6 2.16 2.94 2.25 2.07 1.79 2.51

Tb 0.53 0.5 0.27 0.4 0.57 0.41 0.35 0.31 0.43

Dy 3.01 3.57 2.36 2.49 2.86 2.79 2.71 2.06 2.88

Ho 0.62 0.67 0.4 0.49 0.53 0.6 0.45 0.42 0.58

Er 2.16 2.45 1.53 1.55 1.88 2.22 1.78 1.6 1.98

Tm 0.33 0.35 0.22 0.26 0.26 0.33 0.25 0.23 0.31

Yb 2.91 2.92 1.94 2.21 1.92 2.66 1.98 1.84 2.5

Lu 0.48 0.46 0.33 0.33 0.38 0.46 0.33 0.29 0.41


Table 1 (contd.)

Sample Average Cev4 Y1 G6 T1 As 5

location Kavaklar Cevizdere YuÈceler GoÈlcuÈgÆez Tavkutlu Asarkaya

SiO2 55.46 56.91 55.68 56.71 61.01 59.10

Al2O3 19.01 21.00 21.34 20.82 20.16 19.74

Fe2O3* 1.16 1.11 1.50 1.79 1.19 1.02

MgO 4.16 2.76 3.18 2.74 2.09 3.21

CaO 2.60 2.65 2.27 1.02 3.11 1.54

Na2O 0.39 0.66 0.77 1.48 0.83 0.92

K2O 0.82 1.99 1.26 2.40 1.49 0.59

TiO2 0.11 0.13 0.13 0.17 0.13 0.10

MnO 0.04 0.02 0.01 0.03 0.01 <0.01

LOI 17.60 14.00 15.20 12.80 11.90 14.80

Sum 101.35 101.23 101.34 99.97 101.93 101.03

CaO/Na2O 6.88 4.02 2.95 0.69 3.75 1.67


Co 0.68 2.9 3.6 2.9 1.1 < .5

Cs 4.01 5.4 5.3 5.4 5.5 4.1

Ga 13.03 13.2 13.7 13.9 13.2 13.7

Hf 3.82 3.2 3.6 3.3 3.3 3.5

Nb 8.49 34.1 39.1 36.4 13.3 34.9

Rb 50.77 133.5 91.2 220.9 103.2 41.5

Sn 2.00 3 3 3 2 3

Sr 105.44 126.2 103 70.1 234.4 137.4

Ta 1.07 4.3 4.9 4.2 1.3 4.4

Th 30.74 19.9 24.7 26.4 34.5 15.8

Tl 0.22 0.4 0.5 1.5 0.7 0.1

U 0.87 8.6 1.5 5.5 2.4 0.6

V 8.33 10 13 14 6 <5

W 2.22 2 2 4 7 1

Zr 84.98 80.9 74.4 92.9 79.8 65.6

Y 17.71 14.6 18.5 18 11 13.4

Cu 1.67 4 3 4 3 1

Pb 13.44 13 7 6 7 <3

Zn 13.56 7 10 13 7 6

Ni 2.00 2 3 4 1 1

Ba 9.33 36 31 79 15 11

Sc 1.33 1 2 2 1 <1

REE (ppm)

La 36.16 32.3 43.2 38.4 39.2 26

Ce 62.97 53.4 76.1 58.8 81 24.7

Pr 5.99 4.9 6.73 6.13 6.86 3.64

Nd 19.02 15.1 21.8 19.6 22.1 11.2

Sm 3.28 2.6 3.2 3.7 3.3 1.9

Eu 0.33 0.25 0.3 0.34 0.36 0.11

Gd 2.34 2.01 2.58 2.26 2.34 1.86

Tb 0.42 0.37 0.47 0.48 0.38 0.33

Dy 2.75 2.44 3.07 3.16 2.29 2

Ho 0.53 0.49 0.58 0.59 0.34 0.43

Er 1.91 1.62 2.04 1.98 1.13 1.29

Tm 0.28 0.19 0.28 0.28 0.17 0.18

Yb 2.32 1.68 2.25 2.1 1.3 1.61

Lu 0.39 0.29 0.37 0.38 0.22 0.28

All Fe as Fe2O3


Major and trace elements of 18 samples from all

bentonite deposits are shown in Table 3. The loss-

on-ignition for this suite ranges between 8.9 and

15.4 wt.%. The silica contents, representing rocks

of intermediate-acidic composition, range from 62

to 70 wt.% in the Kavaklar area (average

65.3 wt.%) and from 69 to 75 wt.% (average

72.5 wt.%) in the other areas.

As there is evidence for the mobility of major

elements during the argilization of the parent rock,

the chemical discrimination diagram of Winchester

& Floyd (1977) was used, based on the concentra-

tions of immobile elements (Zr/TiO2, Nb/Y)

(Fig. 9).

Samples from the Kavaklar and Yedikapõ areas

plot in the trachyandesite field close to the rhyolite/

trachyandesite boundary, whereas samples from

Cevizdere, Asarkaya, YuÈceler and Tavkutlu plot

entirely in the trachyte field. However, there may

be some bias here towards a more alkaline character

during bentonite formation (e.g. Christidis, 1998)

because Y is known to be more mobile than Nb,

whereas Ti and Al are very immobile elements.

In general, the bentonites have low contents of

Sr, Ba, Ti and P and high contents of K, Rb and Th,

and are therefore similar in composition to the

surrounding volcanics (Fig. 10). The whole-rock

REE contents of the bentonites have been normal-

ized to that of North American Shale Composite

(NASC) (Gromet et al., 1984). The patterns

(Fig. 11) are similar overall but there are notable

differences in the Eu content, with anomalies

suggesting clay formation from a variety of

pyroclastic products. Normalized ratios of Eu/Eu*

TABLE 2. Structural formulae of the dioctahedral smectites from the Ordu area.

Sample Is° 1 2/1 Is° 1 2/2 Is° 1 2/3 Is° 1 2/4 Is° 1 2/5 Is° 1 2/6 Is° 1 2/7 Is° 1 2/8 Is° 1 2/9 cev4 Y1 G6 T1 As 5

no.

Tetrahedral

Si 3.91 3.89 3.93 3.93 3.98 3.82 3.86 3.96 3.93 3.88 3.83 3.88 4.01 4.01IVAl 0.09 0.11 0.07 0.07 0.02 0.18 0.14 0.04 0.07 0.12 0.17 0.12 0.00 0.00

OctahedralVIAl 1.5 1.51 1.51 1.51 1.49 1.47 1.49 1.49 1.46 1.57 1.56 1.56 1.56 1.58

Ti 0.01 0.01 0.01 0.01 0 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Fe3+

0.06 0.06 0.05 0.05 0.06 0.07 0.06 0.07 0.07 0.06 0.08 0.09 0.06 0.05

Mg 0.43 0.42 0.42 0.41 0.41 0.45 0.44 0.4 0.44 0.28 0.33 0.28 0.21 0.33

Mn 0 0 0 0 0 0 0 0 0.01 0 0 0 0 0

TOC 2.00 2.00 1.99 1.98 1.96 2.00 2.00 1.97 1.99 1.92 1.98 1.94 1.84 1.97

OC 0.42 0.41 0.44 0.46 0.53 0.44 0.43 0.48 0.47 0.51 0.38 0.45 0.68 0.41

Interlayer

Mg 0.03 0.03 0.00 0.00 0.00 0.03 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Ca 0.19 0.2 0.18 0.19 0.2 0.2 0.19 0.18 0.22 0.19 0.17 0.07 0.22 0.11

Na 0.05 0.05 0.05 0.05 0.05 0.07 0.06 0.05 0.05 0.09 0.1 0.19 0.1 0.12

K 0.03 0.08 0.08 0.09 0.08 0.1 0.06 0.07 0.06 0.17 0.11 0.21 0.13 0.05

ILC 0.52 0.59 0.49 0.52 0.53 0.63 0.58 0.48 0.55 0.64 0.55 0.54 0.67 0.39

TLC 0.51 0.52 0.51 0.53 0.55 0.62 0.57 0.52 0.54 0.63 0.55 0.57 0.68 0.41

TOC: total octahedral cations, OC: octahedral charge, ILC: interlayer charge, TLC: total layer charge

FIG. 9. Discrimination of the Ordu area smectite-rich

bentonite samples using a Nb/Y-Zr/TiO2 immobile

element diagram (Winchester & Floyd, 1977).


with values of 0.19ÿ0.56 are considered to be

negative anomalies and probably reflect crystal

fractionation of plagioclase during the magmatic

evolution of the precursor rocks.

Any mineral formed in equilibrium with oxic

marine waters is likely to be characterized by a

negative Ce anomaly (Jeans et al., 2000), whereas

under suboxic and anoxic marine conditions, Ce

precipitation is reversed and has little or no

negative anomaly (German & Elderfield, 1990).

As none of the bentonite samples studied here has

negative Ce anomalies the alteration in considered

here to have occurred primarily under poorly

oxygenated marine conditions.

During alteration, some elements are mobile

whereas others are relatively immobile and

become enriched in the residual rock (e.g.

Christidis & Dunham, 1993, 1997; Christidis,

1998). The extent of element mobility during

alteration of pyroclastic/volcanic parent material

of the bentonites can be estimated using the method

of MacLean & Kranidiotis (1987). Although the

method does not take into account either possible

change in the density of the parent and daughter

rock or changes in the rock volume (MacLean,

1990), the mass-balance calculations can be used to

indicate relative gains or losses of elements during

bentonite formation. Zircon is the most immobile

element and shows high correlation coefficients

with the other elements (Table 4). All samples have

been grouped according to their locations and

degree of alteration (Table 5). The parent material

used in the calculations is the anhydrous hyalo-

trachyte Y3. The equation used can be written for

SiO2 as follows (MacLean & Kranidiotis, 1987):

SiO2 �

SiO2�wt:%�

Zr�ppm�(alt. rock)� Zr(ppm. hyl. tr.)

Using the above equation, calculations were

performed for each element and the values subtracted

from sample Y3 concentrations in order to determine

mass gains and losses (Table 6). Figure 12a,b shows

graphically the elemental loss and gain that has

occurred during the alteration of the parent material.

The Si, Na and K have been depleted in almost all

deposits whereas Mg and Ca are enriched. The

increases in Mg and Ca may be relative but the gains

in Mg probably reflect the circulation of seawater

through the precursor material of the bentonites

during its alteration (Fisher & Schmincke, 1984;

Christidis & Dunham, 1997; Christidis, 2001). This is

supported by trace element loss and enrichment in Sr.

For example; dolomites forming in a marine

environment are known to have high Sr content

(Land & Hoops, 1973). At the beginning of the

alteration, K increased and then depleted during more

advanced alteration. Other changes in elemental

concentrations are reflected in the mineral assem-

blage of the samples; the excess silica precipitated as

opal-CT and/or zeolite and the loss of the Rb may be

related to breakdown of biotite (Fig. 12b).

STABLE ISOTOPE GEOCHEMISTRY

OF SMECT ITES

The isotopic compositions of the montmorillonite

clay fractions (<2 mm) from the open pit 1 in the

FIG. 10. Spider diagram of the Ordu area bentonic clay

samples normalized to N-type MORB (the shaded field

represents trace element compositions of the surround-

ing volcanic rocks and bentonites; normalizing values

from Sun & McDonough, 1989).

FIG. 11. REE patterns of the Ordu area bentonite

samples normalized to North American Shale Compo-

site (NASC, Gromet et al., 1984).


TABLE 3. Major (wt.%), trace and REE concentrations of the bentonites from the Ordu area.

Sample Is° 1 2/1 Is° 1 2/2 Is° 1 2/3 Is° 1 2/4 Is° 1 2/5 Is° 1 2/6 Is° 1 2/8 Is° 1 2/9 Is° 1 2/10

location Kavaklar open pits

Open pit 1

SiO2 64.17 65.62 65.55 66.13 64.07 62.08 61.55 62.32 67.56

TiO2 0.12 0.13 0.12 0.13 0.13 0.13 0.14 0.13 0.13

Al2O3 13.76 14.39 13.69 14.2 14.13 14.47 15.39 15.34 14.72

Fe2O3* 1.01 0.76 0.75 0.79 1.02 0.96 0.88 0.89 0.83

MnO 0.07 0.03 0.03 0.08 0.03 0.03 0.03 0.02 0.02

MgO 3.45 2.90 2.70 2.80 2.58 3.42 3.69 3.60 2.94

CaO 1.67 1.71 1.51 1.54 1.52 1.62 1.66 1.65 0.99

Na2O 0.55 0.79 0.72 0.81 0.9 0.77 0.83 0.81 1.34

K2O 0.68 1.48 1.05 1.29 1.43 1.04 0.95 0.78 0.9

P2O5 <0.01 0.01 <0.01 <0.01 <0.01 0.01 0.01 <0.01 0.02

LOI 14.3 12.1 13.7 12.2 14 15.4 14.8 14.3 10.5

Sum 99.78 99.92 99.82 99.97 99.81 99.93 99.93 99.84 99.95


Zr 116.4 115.6 100.4 104 103.4 108.2 129.4 118.3 139.4

Y 21.2 31.6 15.4 16.9 24.3 18 16.6 13.7 22

Sr 139 259.6 177.8 207.4 138.6 145.5 150.2 148.8 153

Rb 50.8 84.6 69.3 77.2 120.2 57.9 54 55.1 68.9

Th 29.4 34.7 29.1 27.2 48.7 30.4 31.3 28.6 31.9

Ta 1.1 1.4 1.7 1.4 1.4 1.2 1.4 1.4 1.3

Zn 9 7 7 7 7 10 9 10 6

Sn 1 2 2 1 2 2 2 2 2

Pb 11 10 10 8 8 9 9 10 8

Co 0.7 0.8 0.7 0.5 0.6 0.6 0.7 0.7 0.9

Cr 100 80 100 90 70 100 70 70 30

Ba 29 22 14 29 17 21 17 15 16

Nb 12.8 21.2 14.4 14.6 15.6 12.6 15.4 14.7 17.4

Y 21.2 31.6 15.4 16.9 24.3 18 16.6 13.7 22

Cs 3.1 4 4.2 4.2 5.5 3.4 3.3 3.5 6.8

Ga 14.2 15.4 13.9 12.8 13.2 14.7 15.5 16.3 16.9

Hf 3.9 3.9 3.6 3.4 3.8 3.7 4 4.2 4

Sc 2 2 2 2 4 2 2 1 2

W 3 4 3 3 5 4 5 5 6

REE (ppm)

La 34.4 48.9 33.9 29.8 81.8 32 27.5 24.8 26.6

Ce 65.8 79.6 60 50.2 138.7 63 55.1 50.6 67.7

Pr 5.89 7.43 4.96 4.73 12.69 5.33 4.82 4.46 4.66

Nd 19 23.9 15.7 15.3 41.2 16.4 14.8 14.3 14.1

Sm 3.1 3.9 2.4 2.5 6.9 2.7 2.3 2.5 2.4

Eu 0.38 0.50 0.35 0.34 0.84 0.38 0.32 0.32 0.36

Gd 2.17 3.28 1.87 1.91 5.15 2.05 1.91 1.62 2.01

Tb 0.38 0.52 0.31 0.32 0.64 0.34 0.32 0.27 0.33

Dy 2.77 3.59 2.06 2.31 3.71 2.38 2.22 1.92 2.57

Ho 0.68 0.86 0.48 0.56 0.76 0.57 0.54 0.47 0.68

Er 2.4 3.04 1.61 1.98 2.26 2.07 1.91 1.59 2.41

Tm 0.4 0.47 0.25 0.33 0.3 0.33 0.3 0.25 0.4

Yb 3.36 3.65 2.06 2.65 2.41 2.76 2.56 2.12 3.11

Lu 0.54 0.59 0.31 0.4 0.36 0.45 0.4 0.33 0.5

La/Lu 6.61 8.60 11.35 7.73 23.59 7.38 7.14 7.80 5.52

(EuN/Eu{) 0.42 0.42 0.49 0.46 0.41 0.47 0.45 0.46 0.49


Table 3 (contd.)

Sample Is° 2.4 Is° 5.2 Is° 4.2 Is° 3.2 Average Y1 T1 As5 18 Cev4

location Kavaklar YuÈceler Tavkutlu Asarkaya Yedikapõ Cevizdere

Pit no: 2 5 4 3

SiO2 66.85 61.67 69.51 66.83 65.28 72.76 73.11 74.51 68.58 73.6

TiO2 0.13 0.14 0.1 0.14 0.13 0.14 0.11 0.09 0.15 0.10

Al2O3 13.42 15.32 11.01 15.53 14.13 11.71 12.23 10.75 12.81 11.67

Fe2O3* 0.83 0.91 0.84 1 0.89 0.99 0.64 0.66 1.2 0.67

MnO 0.02 0.01 0.02 <0.01 0.02 0.01 0.01 <0.01 0.05 0.01

MgO 2.79 3.5 2.8 1.98 2.95 0.88 0.7 1.57 0.95 1.12

CaO 1.14 1.59 1.08 1.41 1.43 1.14 2.13 1.05 0.98 1.12

Na2O 1.15 0.71 0.73 1 0.87 1.38 0.34 1.26 2.27 0.88

K2O 1.1 0.81 0.6 1.72 1.06 1.74 1.53 1.2 3.92 1.87

P2O5 <0.01 0.01 <0.01 <0.01 0.00 <0.01 <0.01 <0.01 <0.01 <0.01

LOI 12.4 15.4 13.3 10.3 13.17 9.2 9 9.4 9 8.9

Sum 99.83 100.07 99.99 99.91 99.92 99.95 99.8 100.49 99.91 99.94


Zr 111.6 120.5 101.7 109 112.86 138.3 117.6 83.2 124.9 111.9

Y 19.4 23.2 14.2 9 18.21 19.3 10.4 14.4 15.7 15.7

Sr 167.9 170.6 134.2 177.1 165.67 113.5 395.7 159.9 101.1 108.3

Rb 56.8 45.7 48.2 63.4 62.21 134.3 114.8 51.6 195.2 185.6

Th 32.3 36.8 20.1 20.9 29.95 30.1 29.9 19.3 35 23.8

Ta 1.6 1.5 1.1 1.3 1.38 4.7 1.2 4.5 1.2 4.9

Zn 7 9 11 7 8.25 4 2 6 8 6

Sn 1 2 1 2 1.64 2 1 2 2 3

Pb 11 7 9 8 8.99 8 6 <3 6 <3

Co 0.7 0.7 0.8 0.9 0.74 3 1.1 0.5 1.9 0.7

Cr 80 110 100 70 84.45 110 110 110 140 130

Ba 33 23 48 40 28. 42 27 16 61 22

Nb 15 17.9 12.9 15.4 15.36 44.6 14.4 44 13.3 45.9

Y 19.4 23.2 14.2 9 18.21 19.3 10.4 14.4 15.7 15.7

Cs 3.6 3.3 4 3.8 3.95 5.4 5.6 4.4 6.9 7.5

Ga 16.1 18 13.6 16.2 15.38 15.3 13.8 15.2 13.6 16.3

Hf 3.5 4.2 3.7 3.7 3.81 4 3.7 3.3 3.7 3.7

Sc 2 1 1 2 1.81 1 1 1 2 1

W 3 4 3 4 3.86 2 6 1 5 1

REE (ppm)

La 44.00 38.30 22.1 30.4 35.72 44.3 32.2 30.6 40.7 28

Ce 80.10 71.80 37.50 50.40 65.01 80.00 68.30 34.10 70.90 42.30

Pr 7.16 6.12 3.82 4.81 5.80 6.96 5.77 4.16 6.36 4.25

Nd 22.3 19.7 11.5 15 18.27 21.7 18.3 12.3 19.4 13.2

Sm 3.50 3.10 2.00 2.40 2.97 3.50 2.80 2.30 2.70 2.30

Eu 0.49 0.44 0.27 0.37 0.41 0.36 0.42 0.13 0.46 0.15

Gd 2.6 2.61 1.57 1.61 2.27 2.75 1.87 1.83 2.2 1.63

Tb 0.41 0.45 0.24 0.25 0.36 0.43 0.28 0.29 0.34 0.3

Dy 2.74 3.08 1.78 1.46 2.44 2.74 1.57 1.99 2.12 1.97

Ho 0.63 0.75 0.41 0.34 0.58 0.61 0.34 0.44 0.51 0.5

Er 2.12 2.61 1.52 1.01 1.98 2.04 1.05 1.39 1.83 1.6

Tm 0.34 0.42 0.24 0.15 0.33 0.32 0.17 0.22 0.3 0.26

Yb 2.7 3.26 1.96 1.31 2.52 2.54 1.33 1.77 2.5 1.97

Lu 0.4 0.49 0.29 0.2 0.39 0.38 0.19 0.29 0.44 0.31

La/Lu 11.42 8.11 7.91 15.78 10.17 12.10 17.59 10.95 9.60 9.38

(EuN/Eu{) 0.48 0.46 0.45 0.54 0.46 0.34 0.53 0.19 0.56 0.22

* All Fe as Fe2O3

Eu{= (SmNGdN)/2


Kavaklar area are given in Table 7. The O and H

isotopic values vary within narrow limits from +22

to +22.4% and ÿ75 to ÿ96%, respectively.

When the isotopic values of the montmorillonites

are plotted in a dD/d18O diagram (Fig. 13), they fall

near the smectite (SM) line, which represents the

isotopic compositions of smectites in equilibrium

with meteoric water at 20ëC. The Ml field

represents the isotopic compositions of the

Archidona montmorillonite Deep Sea Drilling

Project (DSDP) samples described by Andrews

(1980) and Lawrence & Drever (1981), which

formed by seawater-basalt interaction at tempera-

tures between 30 and 55ëC. In Fig. 13, the

TABLE 4. Correlation coefficient of Al, Ti, Hf, Nb, Zr

and Y for the volcanics and bentonite occurrences of

the Ordu area. The shaded fields are meaningful values

at p <0.0500.

Al Ti Hf Nb Zr Y

Al 1.00 0.49 0.56 ÿ0.48 0.53 0.22

Ti 0.49 1.00 0.26 ÿ0.30 0.58 0.11

Hf 0.56 0.26 1.00 ÿ0.20 0.81 0.35

Nb ÿ0.48 ÿ0.30 ÿ0.20 1.00 ÿ0.42 ÿ0.18

Zr 0.53 0.58 0.81 ÿ0.42 1.00 0.33

Y 0.22 0.11 0.35 ÿ0.18 0.33 1.00

TABLE 5. Grouped anhydrous samples based on 100 g from the Ordu area (REE indicate average REE

content).

Fresh rock Partly

(Y3) altered Kavaklar YuÈceler Tavkutlu Asarkaya Cevizdere Yedikapõ

Major oxides (wt.%)

SiO2 79.26 72.52 74.49 80.16 80.50 81.77 80.83 75.42

Al2O3 11.39 14.73 16.77 12.90 13.47 11.80 12.82 14.09

Fe2O3* 0.93 0.97 1.02 1.09 0.70 0.72 0.74 1.32

MgO 0.05 0.39 3.50 0.97 0.77 1.72 1.23 1.04

CaO 0.40 0.53 1.73 1.26 2.35 1.15 1.23 1.08

Na2O 3.51 1.70 1.00 1.52 0.37 1.38 0.97 2.50

K2O 4.31 8.70 1.27 1.92 1.68 1.32 2.05 4.31

TiO2 0.10 0.40 0.15 0.15 0.12 0.10 0.11 0.16

P2O5 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

MnO 0.02 0.03 0.04 0.01 0.01 0.01 0.01 0.05

Cr2O3 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02

Sum 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00


Sc 1.00 4.33 2.00 1.00 1.00 1.00 1.00 1.00

Co 1.20 1.40 0.71 3.00 1.10 0.50 0.70 1.90

Cs 3.90 3.67 4.06 5.40 5.60 4.40 7.50 6.90

Ga 15.40 11.13 15.27 15.30 13.80 15.20 16.30 13.60

Hf 3.30 3.50 3.83 4.00 3.70 3.30 3.70 3.70

Nb 41.50 11.13 15.58 44.60 14.40 44.00 45.90 13.30

Rb 209.90 224.93 66.99 134.30 114.80 51.60 185.60 195.20

Sn 3.00 2.00 1.75 2.00 1.00 2.00 3.00 2.00

Sr 22.20 117.07 169.63 113.50 395.70 159.90 108.30 101.10

Ta 4.90 1.00 1.39 4.70 1.20 4.50 4.90 1.20

Th 28.00 22.30 31.78 30.10 29.90 19.30 23.80 35.00

Tl 1.20 1.33 0.35 1.60 0.80 0.30 0.60 0.50

U 5.50 6.30 2.79 3.80 2.10 0.90 14.70 11.00

W 5.00 4.00 4.08 2.00 6.00 1.00 1.00 5.00

Zr 82.20 125.60 114.68 138.30 117.60 83.20 111.90 124.90

Y 12.90 15.07 19.28 19.30 10.40 14.40 15.70 15.70

Aver. REE 8.92 8.34 10.54 12.05 9.61 6.56 7.05 10.77

* All Fe as Fe2O3


supergene/hypogene (SH) line described by

Sheppard et al. (1969) and the lines for kaolinite

and montmorillonite are from Savin & Epstein

(1970). Sheppard et al. (1969) showed that

hypogene and supergene clays that equilibrated at

surface temperatures can be distinguished from each

other because the isotopic compositions of hypo-

gene clays plot closer to the meteoric water line.

TABLE 6. Mass gains and losses from the Ordu area samples in g and ppm (based on 100 g of

freshest rock Y3 and constant Zr).

Partly Kavaklar YuÈceler Tavkutlu Asarkaya Cevizdere Yedikapõ

altered

Major oxides (g)

SiO2 ÿ31.80 ÿ25.87 ÿ31.62 ÿ22.99 1.53 ÿ19.89 ÿ29.63

Al2O3 ÿ1.76 0.63 ÿ3.73 ÿ1.98 0.26 ÿ1.98 ÿ2.12

Fe2O3* ÿ0.29 ÿ0.20 ÿ0.28 ÿ0.44 ÿ0.21 ÿ0.39 ÿ0.06

MgO 0.21 2.46 0.53 0.49 1.65 0.85 0.64

CaO ÿ0.05 0.84 0.34 1.24 0.73 0.50 0.31

Na2O ÿ2.40 ÿ2.80 ÿ2.61 ÿ3.25 ÿ2.15 ÿ2.80 ÿ1.87

K2O 1.39 ÿ3.40 ÿ3.17 ÿ3.13 ÿ3.01 ÿ2.80 ÿ1.47

TiO2 0.16 0.01 ÿ0.01 ÿ0.02 0.00 ÿ0.02 0.01

P2O5 0.00 0.00 0.00 0.00 0.00 0.00 0.00

MnO 0.00 0.01 ÿ0.01 ÿ0.01 ÿ0.01 ÿ0.01 0.02

Cr2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Sum ÿ34.55 ÿ28.32 ÿ40.56 ÿ30.10 ÿ1.20 ÿ26.54 ÿ34.19


Sc 1.84 0.43 ÿ0.41 ÿ0.30 ÿ0.01 ÿ0.27 ÿ0.34

Co ÿ0.28 ÿ0.69 0.58 ÿ0.43 ÿ0.71 ÿ0.69 0.05

Cs ÿ1.50 ÿ0.99 ÿ0.69 0.01 0.45 1.61 0.64

Ga ÿ8.11 ÿ4.46 ÿ6.31 ÿ5.75 ÿ0.38 ÿ3.43 ÿ6.45

Hf ÿ1.01 ÿ0.56 ÿ0.92 ÿ0.71 ÿ0.04 ÿ0.58 ÿ0.86

Nb ÿ34.21 ÿ30.33 ÿ14.99 ÿ31.43 1.97 ÿ7.78 ÿ32.75

Rb ÿ62.69 ÿ161.88 ÿ130.08 ÿ129.66 ÿ158.92 ÿ73.56 ÿ81.43

Sn ÿ1.69 ÿ1.75 ÿ1.81 ÿ2.30 ÿ1.02 ÿ0.80 ÿ1.68

Sr 54.42 99.38 45.26 254.39 135.78 57.36 44.34

Ta ÿ4.25 ÿ3.90 ÿ2.11 ÿ4.06 ÿ0.45 ÿ1.30 ÿ4.11

Th ÿ13.41 ÿ5.23 ÿ10.11 ÿ7.10 ÿ8.93 ÿ10.52 ÿ4.97

Tl ÿ0.33 ÿ0.95 ÿ0.25 ÿ0.64 ÿ0.90 ÿ0.76 ÿ0.87

U ÿ1.38 ÿ3.50 ÿ3.24 ÿ4.03 ÿ4.61 5.30 1.74

W ÿ2.38 ÿ2.07 ÿ3.81 ÿ0.81 ÿ4.01 ÿ4.27 ÿ1.71

Zr 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Y ÿ3.04 0.92 ÿ1.43 ÿ5.63 1.33 ÿ1.37 ÿ2.57

Aver. REE ÿ3.47 ÿ1.37 ÿ1.77 ÿ2.20 ÿ2.45 ÿ3.74 ÿ1.84

* All Fe as Fe2O3

TABLE 7. Oxygen and hydrogen isotopic composition of smectites from the Kavaklar area

(samples from open pit 1).

Sample Is° 1 2/2 Is° 1 2/3 Is° 1 2/4 Is° 1 2/5 Is° 1 2/6 Is° 1 2/8

d18OV-SMOW (%) 22.0 22.0 22.2 22.4 22.0 22.2

dDV-SMOW (%) ÿ77 ÿ96 ÿ89 ÿ8 ÿ75 ÿ87

Water content (wt.%) 4.5 5.4 4.14 4.86 5.04 4.68


Adopting this approach, the isotopic composition of

the Kavaklar montmorillonite can be observed to

overlap with the field of low-temperature mont-

morillonite (MI) thus indicating formation at low

temperature rather than at higher temperatures

within a hydrothermal environment.

The isotopic composition of clays depends on the

conditions of formation such as temperature, and the

isotopic composition of the fluids responsible for

their formation (e.g. Yui & Chang, 1999). In order to

deduce such conditions of formation, the degree of

isotopic fractionation between the fluid and mineral

phases needs to be known as a function of

temperature (e.g. Yui & Chang, 1999). In this

study, we have determined and plotted (Fig. 14) the

O- and H-isotopic compositions of the fluid, the H-

FIG. 12. (a) Mass change in grams of the major elements, and (b) (facing page) mass change in ppm of the trace

elements during bentonite formation in the studied area.


isotope fractionation relationship between mont-

morillonite and water (Yeh, 1980), and the

O-isotope fraction relationship between smectite and

water (Sheppard & Gilg, 1996). The equation of Yeh

(1980) is valid for formation temperatures between

29 and 120ëC, and was selected here because the

formation temperature of montmorillonite in the

studied area is considered to be low. Assuming the

isotopic compositions of the analysed montmorillo-

nites have retained their isotopic compositions from

the time of formation, the isotopic compositions of

the fluid can be calculated for various temperatures

using the equations mentioned. The results for the

Ordu area bentonites are shown in Fig. 14.

Since the precursor materials of bentonites

formed in shallow marine environments in the

Eastern Pontide volcanic arc, the fluids for mont-

morillonite formation can be considered to have

been seawater and/or meteoric water. The present-

day d18O and dD isotopic compositions of the

Black Sea are ÿ3% and ÿ25%, respectively,

(Balderer, 1999) and of meteoric water, ÿ12.2%

and ÿ13.73% (GuÈltekin, 1999), respectively. If

these two components played an active role in the

formation of the montmorillonites, the calculated

isotopic composition of fluid should lie between

these two extremes. The isotopic relationships of

Fig. 14 indicate that the montmorillonite probably


formed from a mixture of seawater and lesser

amounts of meteoric water at a temperature of

20ÿ40ëC.

These suggestions are based on the assumption

that the water/rock ratio during the water-rock

interaction was high, otherwise O-isotope values

from smectite samples are not indicative of the O

isotope values of ambient fluid (Yui & Chang,

1999).

Water/rock ratio calculations were based upon

the equation proposed by Ohmoto (1986), where

d18Orock

initialwas taken as 6.5Ô1%, which is the

general value for basaltic and andesitic rocks

(Taylor, 1979). As feldspar was thought to be the

best mineral for indicating the isotopic composition

of the water, d18OinitialH2O

was calculated at equili-

brium temperature from 350 to 700ëC using the

feldspar-water equation of O'Neil & Taylor (1967)

proposed for a closed system. For the d18OfinalH2O

value, the smectite-water equation of Savin & Lee

(1988) was used. The result of these calculations

indicate a water/rock ratio of >1 for montmorillon-

ite formation, with temperatures between 20 and

50ëC and an equilibrium temperature between

plagioclase-water of 350ÿ700ëC.

FIG. 13. dD vs. d18O plot showing the isotopic

compositions of the Kavaklar area smectites. MWL,

meteoric water line; the lines for kaolinite and

montmorillonite are from Savin & Epstein (1970);

SH, supergene/hypogene line of Sheppard et al. (1969)

and SM, smectite line representing isotopic composi-

tions of smectite in equilibrium with meteoric waters

at 20ëC. Mh and Ml, isotopic compositional ranges of

high-temperature and low-temperature montmorillon-

ites. Black Sea, the isotopic composition of its present-

day seawater (Balderer, 1999).

FIG. 14. dD vs. d18O plot showing calculated isotopic compositions of fluids in equilibrium with the Kavaklar

smectites at different temperatures. The shaded area represents the isotopic compositions of the present-day meteoric

water of Black Sea region. Equations used in calculations are as follows: 1000 Ina(O)(smectite-water)= +2.55(106/T

2) ±

4.05 (Sheppard & Gilg, 1996) and 1000 Ina(H)(montmorillonite-water)= ÿ19.6(103/T) + 25 (Yeh, 1980).


SUMMARY AND CONCLUS IONS

Earlier researchers (e.g. Kamitani, 1978; CË elik et al.,

1999) considered the bentonitic clays in the Eastern

Pontides to be of hydrothermal origin because of

their association with massive sulphide deposits and

young intrusive rocks. However, the bentonites we

investigated provide evidence of having been formed

by the in situ alteration of pyroclastic materials in a

shallow marine environment.

Our findings are as follows:

(1) The bentonites contain a range of residual

minerals and textures derived from a variety of

pyroclastic parent rocks.

(2) The bentonites are essentially monomineralic

smectite and display no vertical or lateral zoning as

described for hydrothermal alteration (Inoue, 1995).

(3) H and O stable isotope data from the smectite

indicate precipitation from mixed marine/meteoric

waters at 20ÿ40ëC.

(4) Mass-balance calculations on the develop-

ment of the bentonites from their parent pyroclastic

rock show relative enhancement in Mg and Sr,

features that are typical of alteration in a marine

environment.

(5) Lack of zeolites and extensive loss of SiO2

during argillization suggest a well-flushed system of

alteration (e.g. Christidis & Dunham, 1997).

(6) The various bentonite deposits occur within a

formation of volcanics and pyroclastics (Tirebolu

Formation) and were probably deposited subaerially

as there is no evidence of associated marine or

other sediments. However, the pore waters from the

overlying marine sediments (Akveren Formation)

are suggested to have penetrated the underlying

non-marine sediments and to have played an

important role in the formation of bentonites by

argillization of pyroclastic rocks.

ACKNOWLEDGMENTS

This study is partly supported by Karadeniz Technical

University Research Funds (Project 20.112.005.9). The

authors thank Prof. A. E. Fallick at the Scottish

Universities Environmental Research Centre (East

Kilbride, Scotland) for performing stable isotope

analyses and reviewing an earlier version of the

manuscript, and Professor L. Warr for his editorial

comments and suggestions. Comments and helpful

suggestions by C.V. Jeans and an anonymous reviewer

are greatly appreciated.

REFERENCES

AbdiogÆlu E., Arslan M., Kolaylõ H. & Kadir S. (2004)

Mineralogical and geochemical characteristics of the

Tirebolu (Giresun) bentonite deposits, NE Turkey.

Geochimica et Cosmochimica Acta, Goldschmidt

Conference, Copenhagen, A416.

Andrews A.J. (1980) Saponite and celadonite in layer 2

basalts, DSDP Leg 37. Contributions to Mineralogy

and Petrology, 73, 323ÿ340.

Arslan M., TuÈysuÈz N., Korkmaz S. & Kurt H. (1997)

Geochemistry and petrogenesis of the Eastern

Pontide volcanic rocks, Northeast Turkey. Chemie

Der Erde, 57, 157ÿ187.

Arslan M., Kolaylõ H. & AbdiogÆlu E. (2002) Tirebolu

(Giresun) yoÈ resindeki kil yataklarõnõn jeolojik,

mineralojik, jenetik ve ekonomik oÈzelliklerinin

incelenmesi. Karadeniz Technical University

Scientific Research Project: 2002.112.005.4.

(Continuing).

Balderer W. (1999) Application of Isotope Techniques.

Hydrogeology Short Course Notes, Istanbul.

Brindley G.W. (1980) Quantitative X-ray mineral

analysis of clays. Pp. 411ÿ438 in: Crystal

Structures of Clay Minerals and their X-ray

Identification (G. W. Brindley & G. Brown, editors).

Monograph 5, Mineralogical Society, London.

Bystrom-Brusewitz A.M. (1976) Studies on the Li test to

distinguish between beidellite and montmorillonite.

Pp. 419ÿ428 in: Proceedings of the International

Clay Conference, Mexico City (S.W. Bailey, editor).

Applied Publishing Ltd. Wilmettei, Illinois.

CË elik M., Karakaya N. & Temel A. (1999) Clay

minerals in hydrothermally altered volcanic rocks,

Eastern Pontides, Turkey. Clays and Clay Minerals,

47, 708ÿ717.

Christidis G. (1998) Comparative study of the mobility

of major and trace elements during alteration of an

andesite and a rhyolite to bentonite, in the islands of

Milos and Kimolos, Aegean, Greece. Clays and Clay

Minerals, 46, 379ÿ399.

Christidis G. (2001) Formation and growth of smectites

in bentonites: A case study from Kimolos Island,

Aegean, Greece. Clays and Clay Minerals, 49,

204ÿ215.

Christidis G. & Dunham A.C. (1993) Compositional

variations in smectites Part I. Alteration of inter-

mediate volcanic rocks. A case study from Milos

Island, Greece. Clay Minerals, 28, 255ÿ273.

Christidis G. & Dunham A.C. (1997) Compositional

variations in smectites Part II: Alteration of acidic

precursors, a case study from Milos Island, Greece.

Clay Minerals, 32, 253ÿ270.

Fisher R.V. & Schmicke H.U. (1984) Pyroclastic Rocks.

Springer-Verlag, New York, 472 pp.

German C.R. & Elderfield H. (1990) Application of the

Ce anomaly as paleoredox indicator: the ground


rules. Paleoceanography, 5, 823ÿ833.

Greene-Kelly, R. (1953) The identification of montmor-

illonoids in clays. Journal of Soil Sciences, 4,

233ÿ237.

Grim R.E. & Kulbicki G. (1961) Montmorillonites: High

temperature reactions and classifications. American

Mineralogist, 46, 1329ÿ1369.

Gromet L.P., Dymek R.F., Haskin L.A. & Korotev R.L.

(1984) The `North American Shale Composite': its

compilation, major and trace element characteristics.

Geochimica et Cosmochimica Acta, 48, 2469ÿ2482.

GuÈltekin F. (1999) GuÈmuÈs° hane ve Bayburt yoÈresi

mineralli su kaynaklarõnõn hidrokimyasõ ve izotopik

oÈ zell ikleri . PhD thesis, Trabzon, Turkey

(unpublished).

GuÈven N. (1988) Smectites. Pp. 497ÿ559 in: Hydrous

Phyllosilicates (S.W. Bailey, editor). Reviews in

Mineralogy, Vol. 19. Mineralogical Society of

America, Washington, D.C.

Inoue A. (1995) Formation of Clay Minerals in

Hydrothermal Environments. Pp. 268ÿ329 in:

Origin and Mineralogy of Clay Minerals (B.

Velde, editor). Springer-Verlag.

Jackson M.L. (1956) Soil Chemical Analysis ÿ

Advanced Course. Department of Soil Science,

University of Wisconsin, Madison.

Jeans C.V., Wray D.S., Merriman R.J. & Fisher M.J.

(2000) Volcanogenic clays in Jurassic and

Cretaceous strata of England and the North Sea

Basin, Clay Minerals, 35, 25ÿ55.

Jones J.B. & Segnit E.R. (1971) The nature of opal: I.

nomenclature and constituent phases. Journal of the

Geological Society of Australia, 18, 57ÿ68.

Kamitani M. (1978) DogÆu Karadeniz boÈlgesi'ndeki

kaolin, serisit ve montmorillonit kil yataklarõ.

M.T.A. Genel MuÈduÈrluÈgÆuÈ, Ankara (unpublished).

Kunze G.W. (1965) Pretreatments for mineralogical

analysis. Pp. 568ÿ577 in: Methods of Soil Analysis

Part I. Physical and mineralogical properties

including statistics of measurement and sampling

(C.A. Black, editor). Agronomy Society of America

Inc., Madison, Wisconsin.

Land L.S. & Hoops G.K. (1973) Sodium in carbonate

sediments and rocks: A possible index to salinity of

diagenetic solutions, Journal of Sedimentary

Petrology, 43, 614ÿ617.

Lawrence J.R. & Drever J.I. (1981) Evidence for cold

water circulation at DSDP Site 395: Isotopes and

chemistry of alteration products. Journal of

Geophysical Research, 86, 5123ÿ5133.

Macaulay C.I., Fallick A.E., Haszeldine R.S. & Graham

C.M. (2000) Methods of laser based stable isotope

measurement applied to diagenetic cement and

hydrocarbon reservoir quality. Clay Minerals, 35,

313ÿ322.

MacLean W.H. (1990) Mass change calculations in

altered rock series.Mineralium Deposita, 25, 44ÿ49.

MacLean W.H. & Kranidiotis P. (1987) Immobile

elements as monitors of mass transfer in hydro-

thermal alteration: Phelps Dodge massive sulfide

deposits, Matagami, Quebec. Economic Geology, 2,

951ÿ962.

Mehra O.P. & Jackson M.L. (1960) Iron oxide removal

from soils and clays by a dithionite-citrate system

buffered by sodium bicarbonate. Clays and Clay

Minerals, Proceedings of the 7th Conference,

National Academy of Science, National Research

Council Publication, pp. 317ÿ327.

O'Neil J.R. & Taylor H.P. (1967) The oxygen isotope

and cation exchange chemistry of feldspars.

American Mineralogist, 52, 1414ÿ1437.

Ohmoto H. (1986) Stable isotope geochemistry of ore

deposits. Pp. 491ÿ559 in: Stable Isotopes in High

Temperature Geological Processes (J.W. Valley &

J.R. O'Neil, editors). Rewiews in Mineralogy, 16.

Mineralogical Society of America, Washington, D.C.

Savin S.M. & Epstein S. (1970) The oxygen and

hydrogen isotope geochemistry of clay minerals.

Geochimica et Cosmochimica Acta, 34, 25ÿ42.

Savin S.M. & Lee M. (1988) Isotopic studies of

phyllosilicates. Pp. 189ÿ223 in: Hydrous

Phyllosilicates (S.W. Bailey, editor). Rewiews in

Mineralogy, 19. Mineralogical Society of America,

Washington, D.C.

Sharp Z.D. (1990) A laser based microanalytical method

for the in-situ determination of oxygen isotope ratios

of silicates and oxides. Geochimica et Cosmochimica

Acta, 54, 1353ÿ1357.

Sheppard S.M.F. & Gilg H.A. (1996) Stable isotope

geochemistry of clay minerals. Clay Minerals, 31,

1ÿ24.

Sheppard S.M.F., Nielsen R.L. & Taylor H.P. (1969)

Oxygen and hydrogen isotope ratios of clay minerals

from porphyry copper deposits. Economic Geology,

64, 755ÿ777.

Sun S.S. & McDonough W.F. (1989) Chemical and

isotopic systematics of oceanic basalts: implications

for mantle composition and processes. Pp. 313ÿ345

in: Magmatism in Ocean Basins (A.D. Saunders &

M.J. Norry, editors). Special Publication 42,

Geological Society of London.

Taylor H.P. (1979) Oxygen and hydrogen isotope

relationships in hydrothermal mineral deposits. Pp.

236ÿ277 in: Geochemistry of Hydrothermal Ore

Deposits (H.L. Barnes, editor), Wiley Interscience,

New York.

Tsipursky S.I. & Drits V.A. (1984) The distribution of

octahedral cations in the 2:1 layers of dioctahedral

smectites studied by oblique-texture electron diffrac-

tion. Clay Minerals, 19, 177ÿ193.

Velde B. (1992) Introduction to Clay Minerals,

Chemistry, Origins, Uses and Environmental

Significance. Chapman & Hall, London, 198 pp.

Weaver C.E. & Pollard L.D. (1973) The Chemistry of


Clay Minerals. Developments in Sedimentology, 15,

Elsevier Science Publishing Co., Amsterdam,

213 pp.

Wilson M.J. (1987) X-ray powder diffraction methods.

Pp. 26ÿ98 in: A Handbook of Determinative

Methods in Clay Mineralogy (M.J. Wilson, editor).

Blackie and Sons Ltd, Glasgow, UK.

Winchester J.A. & Floyd P.A. (1977) Geochemical

discrimination of different magma series and their

differentiation products using immobile elements.

Chemical Geology, 20, 245ÿ252.

YalcËõn H. & GuÈmuÈs° er G. (2000) Mineralogical and

geochemical characteristics of Late Cretaceous

bentonite deposits of the Kelkit Valley Region,

Northern Turkey. Clay Minerals, 35, 807ÿ825.

Yeh H.W. (1980) D/H ratios and late stage dehydration

of shales dur ing bur ia l . Geochimica et

Cosmochimica Acta, 44, 341ÿ352.

Yui T.F. & Chang S.S. (1999) Formation conditions of

vesicle/fissure-filling smectites in Penghu basalts: a

stable-isotope assessment. Clay Minerals, 34,

381ÿ393.


Mineralogy, geochemistry and genesis of bentonites of the Ordu area, NE Turkey

Documents

Transcript of Mineralogy, geochemistry and genesis of bentonites of the Ordu area, NE Turkey