Canadion Mineralogist
Vol. 30, pp.415-421(1992)
CHERTSIN SILICEOUSSEDIMENTSOVERLYING
MANGANIFEROUS
WESTERNTHESSALY,GREECE
THE KOZIAKASOPHIOLITE,
NIKOS SKARPELIS
Deportmentof Geology,Universityof Athens,Panepistimioupoli,15784Zografou'Athens,Greece
KONSTANTIN HATZIPANAGIOTOU
Departmentof Geology,Universityof Patros,26110Patras'Greece
MICHAEL KAISERLOGLOU
Departmentof Geogrophy,Universityof Edinburgh,EdinburghEH8 gXR' U.K.
ABSTRACT
In the Koziakas range of Greece,manganiferouscherts are hosted within Jurassic siliceoussedimentsthat are
spatially associatedwith ophiolitic basalts. Pyrolusite and minor manganite and barite are found within the
manganiferouscherts.The FelMn ratio is very low (0.005). Mn, Ni, Cu and Zn are positively correlatedwith each
other, whereasa negative correlation exists between Si and these metals. A comparison of the chemistry of the
manganiferouschertswith ocean-floormetalliferoussediments,Fe-Mn crustsand deep-seanodulessuggeststhat they
wereformed as a result of hydrothermaland hydrogenousprecipitationof metals.The closeassociationof the siliceous
sedimentswith the ophiolitic basalts and the geochemicalfeatures of the manganiferouscherts suggestthat the
manganeseoxideswere formed on the flanks of a spreadingridge, away from fields of hydrothermal vents.
Keywords: manganiferouscherts, metalliferous sediments,Jurassicradiolarian chens, ophiolite, Koziakas range,
Creece.
SOMMAIRE
Des cherts manganiferesont 6te d6couvertsdans la chaine de Koziakas, en Grdce; ils font partie d'une sdquence
s6dimentairejurassiqueassoci6ei desbasaltesophiolitiques.Les chertscontiennentpyrolusite et, commeaccessoires,
manganiteet bilyte. Le rapport Fe/Mn est trbs faible (0.005).Mn, Ni, Cu et Zn font preuved'une auto-corr6lation
positive,tandis que Si montre une corrdlation n6gativeavecces6l6ments.D'aprds une comparaisonde la composition
des cherts manganifbresavec celle des s6dimentsm6tallifbreset des nodules des fonds oc6aniques,et des cro0tesa
Fe-Mn, ces s€dimentsr6sulteraient de la pr6cipitation hydrothermale et hydrog6n6tiquedes m€taux. L'6troite
associationde cess6dimentsmanganifbressiliceuxet desbasaltesophiolitiques,aussibien que leurstraits 96ochimiques,
font penserque les oxydesde manganbseont ete precipit6ssur les flancs d'une ride oc6anique,i une certainedistance
des €ventshydrothermaux.
(Traduit par la R6daction)
Mots-cl6s:chertsmanganifbres,s6dimentsm6tallif0res,chertsir radiolairesjurassiques,ophiolite, chainede Koziakas,
Grdce.
authors(Kiskyras1957,Spathi1964,Markopoulos
& Skounakis 1980, Panagos& Varnavas 1980,
Occurrencesof manganeseoxide mineralization 1984,Skounakis& Markopoulos 1981,Varnavas
geneticallyassociatedwith ophiolitesoccur in many & Panagos 1983, 1984, Robertson& Varnavas
localities of continental Greeceand the Pelopon- 1990,Varnavaset al. l99l). Combinedgeological,
nesus. Most of these occurrencesare of small mineralogicaland geochemicalinvestigationsind!
tonnage and low grade. The mineralization is cate that the manganesemineralization is a result
hosted in cherts and radiolarian cherts and forms of hydrothermal processesassociatedwith subpockets or disseminations,mainly of manganese marine volcanic activity in small oceanic basins
oxides.The geology,mineralogyand geochemistry during the Jurassic.
of the Mn depositshave been studied by various
More recently, new geologicaland petrological
4t5
INTRODUcTIoN
4t6
THE CANADIAN MINERALOGIST
findings indicate that parts of a dismembered
ophiolite are exposed in the Koziakas range
(Capedri et ol. 1985, Lekkas 1987). Siliceous
sedimentsare associatedwith the ophiolite. Several
outcrops of manganiferouscherts appear in these
siliceous rocks, near the villages of Genesi,
Mouzaki and Xylopariko (Fig. 1A).
In this paper, geological and geochemicaldata
are discussedin terms of the origin and tectonic
setting of the mineralization.
++N
*1.@
+++
+++
+++
+++
+++
UZAKI
ffis
lTlo ffia
FlTz IITIg
r lLT:.:'-l
2ffi
sffi
rFl
rffi
olrTril
@
Fto. l. A. Geologicalsketch-mapof the area of westernThessaly(Capedri et al.
1985).l. Quaternary,2. Molassicsediments,3. Tertiary flysch of the Pindos
Unit, 4. Western Thessaly Unit, 5. Mesozoic sequenceof Pindos Unit, 6.
Pelagonianunits, 7. Northern Pindos ophiolite, 8. Koziakasophiolite, 9. Orhris
ophiolite and transgressiveCretaceoussediments.B. Simplified generalsection
of the Koziakas range (after Capedri et al. 1985) showing the setting of
manganiferouscherts. l. Tertiary flysch, 2. Upper Cretaceouslimestones,3.
Upper Jurassic- Lower Cretaceousclastic sequence(flysch) rich in ophiolite
detritus,4. Radiolaritesand red pelites,5. Upper Triassic- Jurassiclimestones,
6. Ophiolitic rocks of Koziakasrange.
MANGANIFEROUS CHERTS. KOZIAKAS OPHIOLITE
417
Frc. 2. A. Alternation of parallel-laminatedred cherts Qight) and pelites (dark) in the Genesi area, Kozidkas.
B. Manganiferous massivecherts (dark) in bedded cherts and radiolarites flight). C. Skeletonsof radiolaria
partly replaced by pyrolusite, set in a matrix of fine-grained manganeseoxides and quartz, Xylopariko
(reflectedlight). D. Microcrystalline quartz (ight) with disseminatedgxainsor aggregatesof manganeseoxides
(dark), and radiolaria replacedby pyrolusite, Genesi(transmittedlight).
GsoloclceL SETTING
The Koziakas Mountains consist of a sequence
of Triassic to Eocene carbonates, cherts,
radiolarites and clastic sediments, and Jurassic
ophiolitic rocks. The lower part of the sedimentary
sequencecomprises Triassic to Upper Jurassic
carbonate and siliceousrocks, whereasthe upper
part contains carbonate and clastic rocks of
Jurassic to Eocene age. The ophiolitic rocks of
Koziakas are thrust over the sedimentaryrocks,
and the whole Koziakas Unit is thrust over the
Pindos Unit (Fig. lA). Theseophiolitic rocks occur
along a NW-SE alignment of ophiolite outcrops,
with the Othris and Pindos ophiolites to the
southeastand northwest, respectively.The general
structure of the Koziakasrange and the geological
setting of the manganiferouscherts are shown in
the geological section (Fig. lB). The ultramafic
sectionof the ophiolite comprisesmantle tectonites
ranging from spinel harzburgites to plagioclase
harzburgites.Pillow lavasinterstratifiedwith cherts
show a MORB affinity; variable geochemical
signatures include normal, transitional and enriched MORB (Capedri et al. 1985). Massive
gabbros occur in minor amounts to the northeast
of Mouzaki; scarce dykes of olivine gabbro
cross-cutultramafic rocks.
Sequencesof pillow lava commonly contain
interbedded siliceous sediment. Micropalaeontological data indicate an Upper Jurassic age
(Lekkas 1987). Sections of siliceous sediment
consistof two main alternating lithologies: chert radiolarian chert and pelite (Fig. 2A). Chert beds
are parallel-laminated,reddishbrown to beige,and
5 to 30 cm thick. They are composedof quartz and
minor amounts of clay minerals, chlorite and
hematite. Cherts contain 88-92V0 SiO2, <Wo
F%O:, (1.5%o MnO and 2.5-3.0V0AlrO3 (Skarpelis, unpubl. data). By mode of occurrence,
418
THE CANADIAN MINERALOGIST
mineralogyand chemistry,the chert beds compare
well with the Jurassic bedded cherts overlying
ophiolites in the Northern Appennines (Barrett
1981,1982).Peliticbedsare red to brown and 3 to
5 cm thick. Radiolaria are commonly found in the
chert beds. The stratigrafically lower part of the
siliceous section contains blocks of ophiolitic
basalt, being possibly deposited within the sediments during early stagesof siliceous sedimentation.
Mops or Occunnsxcr
TABLE I. AVERACE CI{EMICAL COMPC'SINON OF KOZIAKAIi MANGANIFROUS
CIIERTS AND DATA ON RICENT MB'TALLIFEROUS DEPOSTN
7
Situ%
M!
F€
Al
Ti
Ca
m96
36'20
0.17
0.ll
0.01
0.ll
Nippo
Co2fd'13
()I4080
7A
51
Ba
l4g7
l. K@iak6 o4fruif€@
1.45
47.ffi
0.66
024
0.m
0.98
124
93
2M
41.m
0.80
55.m
0,n
310
33
rm
180
39
50
4m
cbffi (@fp
mm
ol8 @lls).
68
24,
l.61
0.93
1630
48.m
4.n
1.fi
036
l2J0
r37
16
W
35
2.m
742,ff
2 M@ vrlB
D,.A
l9.m
55ff)
r3m
1480
750
fq mmg@
qid€
mmdr frel( DSDP lr8 70 (Mmby & GII@ fgel).
Am fF Calrpag6 \flo$mal
The manganiferouscherts at Koziakas occur as M3. Ifydntl@sl
c€dq, sdsrc€t@ Pacific (M@by a 41.l9&4). 4,
dsposit d @{Eadidg
massivelensesthat lie concordantly within bedded Hydro$Bdal depositd sFqdnrg @tq, Galapag6 legia (M@ A Vogt ly'O.5. Mogm
ftoo the hydothamrt @!d Add @ &e Cal@fp6 sFrsditrS c€ds (V@8&
rybL
red cherts and radiolarites (Fig. 2B). Maximum @ts
MANoP sitc H, Peift
1980). 6. Fmogrc
dl€s,
dal& aited h P@agps& Vm
thicknessof the lensesranges from 5 cm to I m. (Dj@@d a at. 1984). 7. I{ydog@@s cEt (D:/Edd d al f984).
Commonly, two or more lensesare separatedby
cherts. Pinch-and-swellstructuresare rare. Lenses
ofmanganiferouschertgraduallypasslaterally into hydrothermal deposits(Bonnatti et al. 1972)(Fie.
barren red cherts, suggestingthat the two types of 3). Co is markedly enrichedin the manganiferous
chert were depositedcoevally.
cherts relative to typical hydrothermal deposits,
and showsa slight positivecorrelationwith Fe, Mn
METHODS
and Cu. The Si/Al ratio is low (Fig. 4), and
resemblesvalues in hydrothermal ores like the
Mineralogy was investigated using optical manganiferous chert deposits of the Franciscan
microscopy, X-ray powder diffractometry and ophiolite in California (Crerar et al. 1982). Si is
electron-microprobetechniques. Fe,l(cyradiation negativelycorrelated with all elementsexceptBa,
was used for Mn-rich specimens. Samples of whereas Fe, Mn, Cu, Ni and Zn are positively
manganiferous cherts taken from various lenses correlatedwith eachother (Table 2). Ba is depleted
were analyzed using inductively coupled plasma in the manganiferouscherts relative to ferromanemissionspectrometryat the Institute of Geology ganesenodulesand to manganeseoxide crustsfrom
and Palaeontology, Technical University of the GalapagosHydrothermal Mounds Field (Lee
Braunschweig.Measurementswere carried out on 70). Similar levels of Ba concentrationhave been
dilute solutions following decomposition with reported from the Thessaly, Euboea and some
hydrofluoric-perchloric acid. The analytical Pindos deposits, where it is associatedwith the
precisionwas found to be better than t 5Vo.
Mn-oxide fraction (Varnavas & Panagos 1983,
Varnavaset al, l99l). Co shows a slight positive
MINERALOcY AND GEocHEMISTRY
correlation with the other metals.
The chemical composition of the Koziakas
The main manganeseoxide mineral is pyrolusite. manganiferouschertsis generallycomparablewith
Manganite relics and barite are rare. The man- that of Mn deposits described from Othris,
ganeseoxides are commonly disseminatedwithin Thessalyand Euboea(Panagos& Varnavas1984,
the microcrystallinesiliceousmatrix. Radiolaria are Varnavaset al. 1991),and with manganesedeposits
preservedwithin the manganiferouscherts, with found at the base of the chert section of the
their skeletonscommonly replaced by pyrolusite Northern Appennine ophiolites (Borr\atti et al.
(Figs.2C, D).
t976i..
The manganiferouscherts have low concentrations of all the major elementsexcept for Si and
DIscussIoN
Mn (Table l). They contain between27 and 46 wt9o
Mn, and between 13.4 and 25.7V0 Si. The
concentration of Fe is extremely low. Extreme
The mode of occurrenceof the manganiferous
fractionation of Fe from Mn is indicated by the cherts indicates a synsedimentary deposition,
very low Fe,/Mn value (0.005).The concentrations whereas the geochemical data suggest that
of Ni, Co and Cu are lower than those of modern hydrothermal processesplayed an important role
oceanic hydrogenous sediments and nodules in their formation. The Koziakas samples are
formed by slow precipitation from normal chemically comparable with recent oceanic
seawater,and slightly higher than those of typical hydrothermalMn-rich deposits,and especiallywith
4t9
MANGANIFEROUS CHERTS. KOZIAKAS OPHIOLITE
+ C u) x 1 O
Koziakas
Mn
Fe
FIc.3. Triangular diagram showing Mn - Fe - (Ni+Co+Cu) x 10 for the
manganiferouscherts of Koziakas. Fields for submarineFe-Mn deposils are
given for comparison:hydrothermal depositsand hydrogenoussedimentsafter
Bonnatti et ol. (1972), Franciscandepositsafter Crerar el a/. (1982), Fe-Mn
crusts and ferromanganesenodules after Toth (1980), and East Pacific Rise
metalliferoussedimentsafter Corliss & Dymond (1975).
manganesecrusts from the field of hydrothermal
moundsnearthe Galapagosspreadingcenter(Table
l).
The strong negativecorrelation betweenSi and
all the metals examinedindicatesthat silica acts as
a diluent, as also described for Mn deposits of
Thessalyand Euboea (Varnavaset al. l99l). The
concentration of Ba is negatively correlated with
that of Fe, Mn, Cu, Ni and Zn. Although Ba
enrichment in hydrothermal sediments is well
documented,the positive correlation of Ba with Si
and Co suggeststhat at least some of it is of
hydrogenousorigin. Since Co shows no evidence
of enrichmentin hydrothermal deposits(Moore &
Yogt 1976,Toth 1980),the higher concentrations
detected in the manganiferous cherts suggesta
COEFFICIBNn| BETWEEN ELEMENTS IN TI{E
TABLE Z ro-TION
MANGANIFEROUS CIIERTS OF K@IAKAS
sir
Al wm
Frc. 4. Si versusN diagram (from Crerar et ol, 1982)in
which compositionsof Koziakasmanganiferouscherts
are comparedwith fields of typical marine sediments.
Fo
I\rn
6
Ni
cxi
?^
Ba
-O.48
4.9
-{.91
-{.88
-0.16
4.94
026
I
0.45
0J7
0A
038
054
-0.40
I
0.89
0.87
0.14
0.94
-{25
I
0.89
02A
0.78
4.6
I
4.r2
0.70
4.44
I
0.n
0.2.
I
-{.14
I
420
THE CANADIAN MINERALOGIST
partial hydrogenousorigin. This metal, along with
Ni and Cu, may have been coprecipitated or
adsorbed onto colloidal Mn hydroxides. Strong
hydrogenousinputs are important in areasof slow
rates of sedimentation, which favor the slow
accumulation of Mn oxides typical of deep-sea
manganese
nodules.The strongpositivecorrelation
of Ni, Cu and Zn with Mn (Table 2) suggeststheir
associationwith the Mn oxides.
Lalou (1983) consideredtwo models for the
formation of hydrorhermal and hydrogenous
metalliferous deposits.In model I, the two types
of depositshad independentsourcesof elements,
the metalliferous crusts having a local hydrothermal source,related to submarinevolcanic activity,
and Mn nodules from abyssal plains, having a
hydrogenoussource.In the secondmodel, both the
metalliferous crusts and the nodules received an
input of hydrothermalMn and other metalsderived
from axial or off-axial hydrothermal vents. Most
of the exhaledhydrothermalMn probably accumulatescloseto the parent vent, whereasa fraction is
dispersedin oceanwater. Lalou suggestedthat the
hydrothermal fraction of Mn is transported over
the abyssal plains in the form of hydroxide
particles.As an excellentscavengerfor tracemetals
dissolvedin seawater,it becomesenriched in Ni,
Cu and Co during its transport, and may represent
the main sourceof Mn in ferromanganesenodules.
In the case of the Koziakas manganiferous
cherts,metal depositionmay have occurredon the
flanks of a spreading ridge, where siliceous
sediments were deposited. This conclusion is
supportedby the following points: a. The geological link of the bedded cherts with MORB-type
basaltsof the ophiolite. The manganiferouscherts,
which lie within siliceoussedimentsthat originally
cappedthe ophiolite, wereprobably depositedaway
from the axis of the spreading ridge. b. The
geochemicalfeaturesof the manganiferouscherts
indicate that submarinehydrothermal exhalations
rich in Mn were responsiblefor their formation.
The hydrogenous input of some trace metals
suggeststhat the Mn oxidesaccumulatedrelatively
slowly, which is consistentwith deposition away
from a center of hydrothermal discharge.
ACKNowLEDGEMENTS
We gratefully acknowledgeProf. Dr. S. Varnavas,Universityof Patras,and Dr. T.J. Barrett,
McGill University, for critical reviews of the
manuscript.
REFERENcES
BARnErr, T.J. (1981): Chemistry and mineralogy of
Jurassicbeddedchert overlyingophiolitesin the
Italy. Chem.Geol.34,289-317.
North Apennines,
(1982): Stratigraphyand sedimentologyof
Jurassicbeddedchert overlyingophiolitesin the
North Apennines,Italy. Sedimentology29, 3535t5.
BoNNarrr, E., Knesvrn, T. & RvoBrr, H, (1972):
Classification and genesisof submarine iron-manganese deposits. .In Ferromanganese Deposits on
the Ocean Floor (D. Horn, ed.). National Science
Foundation, Washington (149-166).
Zsnsr, M., KeY, R. & Rvorn, H. (1976):
Metalliferous deposits from the Apennine
ophiolites: Mesozoic equivalents of 'modern
depositsfrom oceanicspreadingcenters. Geol, Soc,
Am. Bull. 87,83-94.
CaeEoru,S., LEm,ls, 8., PeeaNmoLaou,D., SrnnpElrs,N., Vex'runEr-r-r,
G. & Gello, F. (1985):The
ophiolite of the Koziakas range, Western Thessaly
(Greece).Neues Jahrb. Mineral. Abh. 152,45-64.
ConLrss, J.B. & DyvoNo, J. (1975): Nazca Plate
metalliferous sediments. L Elemental distribution
patterns in surface samples. Trans Am, Geophys,
Union 56,445 (abstr.).
CnEnan,D.A., NavsoN, J., Cuyr, M.S., Wrrlnlurs, L.
& FercrNsoN,M.D. (1982): Manganiferouscherts
of the Franciscan assemblage.I. General geology,
ancient and modern analogues, and implications
for hydrothermal convection at oceanic spreading
centers. Econ. Geol. 77, 519-540.
DvnoNo, J., Lvlr, M., FrNNrv, B., Prern, D.2.,
MuneHy, K., CoNneo, R, & Prsras, N. (1984):
Ferromanganesenodules from the MANOP Sites
H, S and R - control of mineralogical and chemical
composition by multiple accretionary processes.
Geochim. Cosmochim. Acta 48, 931-949.
Krsrynns, D. (1957): The Manganese Ores of the
Peloponnese. Peloponnisiaka, B, Athens (in
Greek).
deposits:
Lelou, C. (1983):Genesisof ferromanganese
hydrothermal origin. 1r Hydrothermal Processesat
Seafloor Spreading Centres (P.A. Rona, K.
Bostrdm, L. Laubier & K.L. Smith, Jr., eds.).
Plenum, New York (503-534).
Lrrres,
E. (1987): Geological Structure and
Geodynamic Evolution of the Koziakas Range
(Western Thessaly). Ph.D. thesis, Athens, Greece.
Manropoulos, T. & SrouNerrs,S. (1980):Barium-haltige Manganerzebei Kournovo, Othris. Ann. Geol,
Pays Hel.29, 800-807Moonnv, S.A. & CRoNAN, D.S. (1983): The
geochemistry of hydrothermal and pelagic sedi-
MANGANIFEROUS CHERTS. KOZIAKAS OPHIOLITE
ments from the Galapagos Hydrothermal Mounds
Field, D.S.D.P. Leg 70. Mineral. Mag. 47,
291-300.
-,
& Glasnv, G.P. (1984):Geochemistry
of hydrothermal Mn-oxide deposits from the S.W.
Pacific island arc. Geochim. Cosmochim. Acta 48.
433-Ut.
Moom, W.S. & Vocr, P.R. (1976): Hydrothermal
manganese crusts from two sites near the
Galapagos spreading arts. Earth Planet. Sci. Lett.
29,349-356.
PeNacos,A.G. & VanNaves,S.P. (1980):Preliminary
observations on manganesedepositsin the areasof
Othris and Argolis (eastern Greece). In Proc.
Intern. Symp. Metallogeny of Mafic and
Ultramafic Complexes 2 (S.S. Augustithis, ed.).
Athens (257-280).
(1984): On the genesisof some
& manganese deposits from eastern Greece. /n
Syngenesisand Epigenesis in the Formation of
Mineral Deposits. Springer-Verlag, Heidelberg
(5s3-561).
RorrnmoN, A.H.F. & VenNavas,S.P. (1990):Metalliferous and pelagic sedimentation of the Mesozoic
Pindos ocean, Greece. Fifth Congress, Geol. Soc.
Greece (Thessaloniki), Abst. Vol.
421
Srounerrs, S. & MenroPoulos, T. (1981): Zur
mineralogischen Zusammensetzung der Manganerzknollen bei Spartia, Othrys-Gebirge,
Griechenland. Proc. Acad. Athens 56,375-387.
SearHr, A. (1964): On the Mineralogical Composition
of the Greek Manganese Ores. Ph.D. thesis, Univ.
Thessaloniki, Thessaloniki, Greece.
Toru, J.R. (1980):Depositionof submarinecrustsrich
in manganeseand iron, Geol. Soc.Am. Bull,9l,
M-54.
VanNeves,S.P. & Pe,Na,cos,
A.G. (1983):The use of
trace metalsin elucidating the genesisos someGreek
and Cyprus manganeseand ferromanganesedeposits.
/n The Significance of Trace Elements in Solving
Petrogenetic Problems and Controversies (S.S.
Augustithis, ed.). Theoprastus Publications,
Athens, Greece(819-857).
(1984): Mesozoic metalliferous
& sediments from the ophiolites of Ermioni, Greece;
analogueto recent mid-ocean ridge ferromanganese
deposits.Chem. Geol. 42,227-242.
PHtLLtrerrs, G, (1991):
&
Geochemistryof manganesedepositsfrom Thessaly
and Euboea, Greece. Chem, Geol. (in press).
ReceivedApril 22, 1991,revised manuscript accepted
October 7, 1991.