The origin of hydrothermal metalliferous sediments associated with the early Mesozoic Othris and Pindos ophiolites, mainland Greece

Se~&ncntary (;eoh~*,,),'. 83 (1993) 87~ 113 i-]sevicr Science Publishers B.V., Anlsk~rdam

S7

The origin of hydrothermal metalliferous se Jln" cnl:s associated with the Early Mesozpic Othris and Pindos ophiolites, mainlaritt Greece A . t t . F . R o b c r t s o n " a n d S.P. Varnaw.ls ~' " lhTmrtmenl ~l (;eology amt (;eophysies, Unil'ersio' O[ Edinl~mgh. l f ~ ' s / M a i n s Road, l(dinhurgh, L II? .,',/1t', liK ;' D~Tarl#nent Of (;eology, University Of Patra.s, Patras, Greece ( Received Novemhcr 18. 191,q: revised version acccplcd Jltly 15, Iq921

A t l S T I , ' . A ( ' I'

Robertson, A.II.F. and Varnavas, S.P., 19ql3. The origin of hydrolhcinlal nlclall;fcrl,u,, ,.c.dinlcllls as,-,ocialvd ~silh lhc I all~, Mesozoic ()lhris and Phldos ophioliles, nlalilll;llld (irccce. Sedilllc'lll, (;c~H, H 3 : g 7 II 3. Metallifcm|lS sediments arid sulphides are associated with the .lurassic Olhris and Pind~)s ophi(Hiles, eenlral amd northern Greece. These ophiolites formed at an Early Mesozoic spreading ridge within a small, Pindos ocean basin created by rifting of the northern margin of (hmdwanaland. Ubiquilous lerrigenous hilt was derived from adiacent conlinenial margins, mainly the Pelagonian microcontinent to the east. In the Oihris area, disseminated, massive and vein sulphides occur within and above MORl3-1ype pillow lavas and volcaniclastic sediments. Sulphide was precipitated in tluarlz veins within fault-controlled slockworks. Epidote (with local epidosite) ix locally very abundant in cxirusives innncdiatcly underlying thick Si-Fe-rich hydrothernlal sediments. Massive sulphides were precipitated as small faull-c~mtrollcd hodic~. that are directly overlain by Fe-rich mudstones and Fe-rich cherts, strongly depleted in Mn. Mtidsltules, iclalively enriched in hydrolhermal Fe. Mn. Cu, Zn. Pb, REE and Ba, were ponded into small fault-controlled hl~lh,ws around till: frm,,cs of the sulphide-precipitating field. Elsewhere (e.g. northern Othris), manganese-rich layeP~ in ribbon radilllarih',. ire shongly enriched in Mn and trace-elements. Metal-enriched deposits are also found within slices of mid-~ccan ridge-type l:.lvas associaled wilh melange (Avdella Melange) structurally ilndcrlying lhe Pindos ophiolile, NW Greece. Sulphidcs there arc restricted to tiny massive deposits twcrl~ing pillms lava and sulphide veins within ophiolitic exlrusives. Pilk~w lavas are overlain by v~lcanic talus brcccias. ',hod from submarine fault scarps. Overlying melallifcrous mudslol,~es are enriched in Fe and other hydrothernlal c~ulslilueilts. probahly derived from nearby sulphide precipitating zones and mixed with lilhogenous sediments. The metalliferous deposits presep,'e a variety of hydrothermal deposits ~sithirl an Igarly Mesozoic snmll t)cc;m imshl. The Pindos sediments Jeilcct mixing of ferrnginous hydrothermal constituents with terrigeuous scdimenl, p~,,,,ibly dulint'_ the earlier stages of b~isin opening. The Othris sulphide and ferrnginons oxidc..sedimcnls lecllrd esidcncc el a sniall, high-tcnlpcr;,tltlrc hydrotherillal fiehl, forllled Ilcar Ihc spreading axis whcll Ihe oce;lil ilCalcd tit, iI1;ixilnlllll width. Manganese-rich cherls in the northerll ()lhris area reflect widespread accumulati(m oi h vdiolhcrn3',il colisti{uciits o!i lhc abyssal plain, derived from axial high-temperature hydrtithermal fields and/or related Io low-temperature (oll-.ixb,'?) discharge.

two Early Mesozoic

I n I rod uciion

ophi()litc-rchitcd

units:

ihc

O t h r i s o p h i o l i t e , c e n t r a l G r e e c e , a n d l h c
T h e purpose of this p a p e r is to d o c u m e n t and interpret metalliferdus sediments associated with

melange',

norihwestern

light o f c o m p a r i s o n s modern

oceanic

Greece

(Fig.

wilh similar

deposits.

1). in !he

Teihyan

Metalliferous

and sedi-

m e n t s a s s o c i a t e d w i t h m a s s i v e s u l p h i d c s h a v e a:Correspondence to: A [I.F. Robertson, Department of Geology and Geophysics. University of Edinburgh, West Mains Road, Edinburgh, Ell~J 3JW, UK. 0037-1)738/93/$06J)11

ready been documented

lites,

from a number of

including the Troodos, Cyprus

son and

Hudson,

q, 1993 - Else~ ier Science Publishers B.V. All rights reserved

1973; V a r n a v a s ,

(e.g.

ophio-

Robert-

1981; B o y l e ,

~g

A

t l I" I(()I~l'l( IN()N A N t ) N tL V A R N A V A S

however, rcnlaincd sceptical xhlce massive sub phidcs wcre then virtually unknown in the mod~ ern

I Oph}olm~smmv~,d

from the Pmdoq o co , m

'[.,

[--~[OphIoIIloS d~.~rlvod from --

Vardar (Axio8) oc~nn

Fit,'. I. Outline Iectonostratigl+aphic ZO+iCSof (ire¢c¢ sllowiiI b' the settings of the Olhris and PiIldos ophiolilcs.

1990) and O1nan (Fleet and Robcrtson, 1980; Robertson and Fleet, 1986; Haymon et al., tg89, 1990). Previous reports of metalliferous sediments associated with Greek ophiolitic terranes, e.g. Argolis (Varnavas and Panagos, 1984) and Pindos (Panagos and Varnavas, 1984), have suggested that hydrothermal processes dominated. We investigate this aspecl further here, based on new fiekl and geochemical information. Ocean ridge hydrothermal processes The importance of hydrothermal processes in the oceans began to be appreciatc~l after discovery of fcrromanganifcrous and trace-metal enriched sediments on the flanks of the East Pacific Rise (e.g. Bostr6m and Peterson, 1969). Similar deposits were soon identified overlying onhiolites (e.g. Cyprus umbers: Robertson and Hudson, 1073). Evidence from ophiolites suggested that the metalliferous oxide-sediments and sulphides were both related to hydrothermal activity at spreading ocean ridges (Constantinou and Govett, 1972: Robertstm,, t976). Oceanographers,

oC¢;lllS. M o r e

rccclllly,

however,

[he t o n i -

biued results ot geophysical surveys, water sarnpiing, obsemvalhms wilh sub|l~crsibles and drilling have confirmed lhc ilnporlaiice of hydrothernlal processes Ihrouglloul tile oceans, ill tile Pacific and Atlantic and elsewhere (rcccnt review by V~|u l)amrn, 19,'0 and Klein, 1991). '|'he si|nilar tor|nati|nl of oceanic a||d ophiolitic hydrotherm:" dcposils was generally accepted after bla{ . smoker chimney fragments were identified in the Cyprus massive sulphides (Oudin and Constantiram, 1084). Rccenl exploration has revcak:d :;real diversity in oceanic hydrothernml systems, rang ing from ihosc on sedimenlcd, as opposed to unscdimenled ridges (e.g. !!',asl Pacific P,ise), in rrlarghla[ basins and asso.eiated with seamounts (scc Klein, ]091). The duration of high-temperalure hydrolhcrmaI activity at individual si;e,,, rangcs from tens to thousands of years, as in the case ¢/t' tile Mid-Atlantic Ridge TAG field (Von Datum, 1991)). Ophiolites contribute useful information, as three-dimensional relationships are exposed in a variety of tectonic settings. Most recent marine studies have concentrated on the massive sulphidcs and information on related hydrothermal sedinlcn!s remains limited, l:or examplc, the relalive importance of high-, as opposed to low-temperature hydrothermal systems for the formation of ferruginous and manganiferous hydrothermal sediments remains unclear. Hydrothermal processes (e.g. Nehlig and Juteau, 1988) and metalliferous sediments from Upper Cretaceous Tethyan ophiolites are ah'eady well known (e.g. Oman, Cyprus), but little information is available on hydrothermal deposits associated with Late Triassic-Middle Jurassic ophiolites, extensively developed further west in Greece, Albania and Yugoslavia. Documentation and interpretatkm of these d~:posits arc the objectives of this paper, Regional geological setting The Othris and Pindcs ophiolites are reconstructed as cmplaced remnants of a small Mesozoic ocean basin, termed the Pindos ocean, Io-

()l¢,l(ilN OI + tI"¢I)R()TIIIiRMAI, MI{I+ALI+IFI!ROllS SILI)IMENTS

~¢)

cared along the northern margin of Gondwanahind (Smith, 19'77; Robcrtson and Varnavas, 1990; Robertse " et aL, 1991). This ocean basin was bordcred to the west by Apulia, a large microcontinenl, csscmially part of Gondwanaland, and to the cast b~/ the l'clagonian microcontincnt. The Pindos ocean riHcd in the l,atc Permian--Middle

Triassic and was probably at its maximunl width in Early-Middle Jurassic (Fig. 2). During the mid-Jurassic the Pindos ocean underwent regional compression, leading io the initiation of an intra-oceanic sul~duction zone. The Pindos ophiolitcs are believed to have fl~rmed by spreadint?~ above this subduclion zone (Kostopoulos, 1989;

T

N A~ban,an ophlo$lle f,

Z,, + ,

%#

Kat~lOna

~ 2 ~ 7,4.

/'X

Vourmo~ y,,,.o.

Othr~S

:pc ~/"

~%

ga

%%> \

~

-

~"

\ Ep,davro,~

00%4"

)4 0

F---/)--~ STABLE FORELAND L. . . .

~i---~ CONTINENTAL ~_ ] MARGIN

!~ ~ 3 R J F T E D CARBONATE PLATFORMS

~\

Km

200

SPREADING CENTRE (AB_'/E SUBDUCTIONZONE)

EXTENSIONAL GNABENS

Fig. 2. lnfclr,,:d lotto[lie '-,cttillg ot lilt Phi.do's. ()till*is alld o t h e r G r e e k ophioliles wilhhl the Pim.los ~.~cean in Late Triztssic-[iarb .lura~,~,ic thnc. After Robcrtson el al., 1991

t)(,

A.H.F. ROBERTSONAND S.P. VARNAVAS

Jones and Robertson, 1991; Jones eta[., 1991, fig. 8). Extrusives and sediments are largely absent from these ophiolites, although evidence of hydrothermal processes (e.g. epidosite-rclated alteration and minor sulphide mineralisation) has been identified (Valsami, 1990). The Pindos ocean basin finally closed in thc Early Tertiary relatcd to convergence of Africa and Eurasia, giving |'ise to the traditional pattern of "is,.)pic', or tectonostratigraphic zones in the Greek area (Aubouin ct al., 1970; Fig. 1).

(Valsami, 1990) in the area studied, although other lava types are present elsewhere, particularly in eastern Othris (Nisbet, 1974; Rassios, 1989b; Fig. 3). The metalliferous sediments discussed here formed at or near a spreading ridge within the Pindos ocean. Ribbon radiolarites exposed throughout the central Othris Mountains (Nisbet and Price, 1974; Nisbet, 1974) are pre sumed to have accumulated on the abyssa] plain adjacent to the spreading ridge.

Pin(los ophiolitic melange Othris ophiolite In Othris, metalliferous sediments occur within extrusives of the Sipetorrcma Pilk~w Lava (Mirna Group; Smith et al., 1975). A pre-Middle Jurassic (pre-t69 _+4 Ma) age fl)r the lavas is suggested by radiometric dating of an amphibolite metamorp!-~ic sole (Spray et al.. 1984). Associated radiolarires could not be dated due to rccwstallisation (e.g. FerriEre, 1982). "Immobile' trace-clement analyses suggest that the Othris Sipetorrema Pillow Lava is of mid-ocean ridge (MORB)-type

The metalliferous deposits .,f the F ":k.-~ Mountains occur within slices o~ NTORB-type ~ ~trusivcs and sediments, forming par¢ of a regionally important melange unit (Av;i~i:a Melange), that structurally underlies the Pin&,s ophiolite (Jones and Robcrtson, 1991). The P,ndos ophiolite (Fig. 1) is dated as mid-Jurassic, or earlier, based on radiometric dating of the metamorpl,ic sole (corrected to I65 plus or minus 3 Ma; Spray et al.. 1984). Ophiolitic slices sandwiched between the Pindos ophiolite above and the Avdelta

~ PINDOSZONE "~ ~ Mainly Quaternary z PEL*GO,~*, ~W----[[~[[LCretaceous platform carbonates \ x, )¢&Pmdos~x ~x~"-~ ~PermianU.Jurassic platform carbonates ~ ~ '~O Triassic -- Jurassic rift and passive margin \ t~ia

.:.',vo,oan,c. aoOso,imonts

\

ophiolitic extrusives ~ - ~ and minor intrusives ] ~"~x'5"~ ~ L;i;i:[::.:I Ophiolitic peridotites __.4F---{-~'~ ~.~K,,~...~

a.dgabbros

t. t

,

x ~~@ h r'~'~ '

.

iohs

Ftg. 3. Sirr!p~ificd gcologica! m~p ~f thL" ()thr~, area. silo~ing the localities discussed in the ~cxt. Ba~cd on Smith ¢~ aL, 1975: FerriC:re. !9,":2.

ORIGIN OF HYDROTHERMAt. METALLIFEROUS SI:-I)IMI'.NTS

Melange below show contrasting, volcanic-arc basalt and high-magncsian andesite (boni|dte)type compositions and are interpreted as oceap_;c crust formed above a subduction zone, possibly in a fore-arc setting (Kostopoulos, 1989; Jones and Robertson, 199l; Jones et al., 1991). By contrast, the underlying Avdella Melange includes fragments of oceanic crust, seamounts and continental margin sediments, dated as Late TriassicEarly Jurassic (Jones end Robertson, 1991) and interpreted as a subduction complex formed by accretion of slices of oceanic M O R B - t y p e cru.s* in a trench setting. In summary, both the Othris and Pindos metalliferous deposits formed within several hundred kilometres of each other near a pre-Middle Jurassic spreading ridge in a narrow (less than 500 km wide) ocean basin. Different lc,calities may, therefore, be expected to preser~:e fragments of originally widespread hydrothermal deposits. Previous work The mineralogy of the Othri,, F e / M n deposits was reported by Spathi (1964), Markopoulos and Scounakis (1979) and Scounakis and Markopoulos (1981). Manganese deposits from the Othris ' s h a l e - c h e r t - e p h i o l i t e complex' were studied by Panagos and Varnavas (1984) and Varnavas and Panagos (1986). Mineraliscd sites were recently re-investigated at Limogardion /Rassios, 198%), Ayia Ekaterini (Konstantopoulou et al., 1988), Neohorion and Stirfakas (A. Rassios, pers. commun., 1991: Fig. 3). MassKe, stockwork and disseminated sulphides are known at Limogardion (Rassios, 1989a; Valsami, t990)o Sulphides associated with the Pindos ophiolite were discussed by Maratos (!972), Melidonis and Demou (!979). Bertolani et al. (1981) and Scounakis et al. (1981), including occurrences in the D h i s t r a t o n - A r m a t a area (Konitsa reginni studied here. Othris metalliferous d e o o s i i s ~ f i e l d evidence

Sulphides Stockwork sulphides at Limogardion (Rassios, 198%: Fig. 4~ were interpreted by Valsami (1990)

0l

r--h-~-i--- L T - ~ k-' ~ ~ 5'X

~-~T ..... _J_ NORTHERN j

<2

If IN,

©

J

KE~

~ZiT] U. Cret . . . . . . -~--3

/~--~

limest . . . . . . . . .

so,?,,~,o~

~-L-T:'~:>~>"-',~--

: ....

.? 0

T-: : - 200

lg~4~

'~ v ' ~

--

7 ......... l ...... ~ " [

r £ ~

~- ......

1

F i g 4. Sketch map o f the kim~gard[on ~ulphid,: ,iincra~i,cd arc:L Othris. M a p p i n g simplified after Rassio>

lU,~0"O. [h~: mineral deposits occur within a latcralh di>continmm~ q~ce~ o f ophiolitic Sipetorrcma Pitlo~ Lava. located :4E ~ff Linlog~> rdion vii!age {Stoa valley, ca. 20 km from t . a m i u ) This uld'~ istructurall.,, underlain hy unmineralised purpic. ,,c-::uk, r pillow law,. correh|ted with the Lu~e T~iassic Agrdia la~a-. B~)!h

units are o':eriain b) lateritic sediments and I. pncr ('rctaceous ,.hallo;~-water limestones after lCCWdliC empl~ccmcn[ ,
as evidence of a high-temperature hydrothermal system. A strong .'aructural control on mineralisation is visible there (Rassios, 198%: Fig. 4L For example prominent faults are ma~:,¢d h> the strong shearing of pillow lavas and la~a hrcccias (Fig. 4). Extrusives in :he hanging wa!l of this fault are silicified, and contain abundant epidote and zones of disseminated sulphide (now gossan), uo to 5 m thick. At both Limogardion and Ayia Ekaterini (g_.. 3). massive sulphides are undedain by zones ot disseminated sulphide, up to 30 m by 5 m thick. This material is now mainly oxidised to form a spon~: textured gossan ('porolithos" of Ra,,sios. t989a). Mineralised chert is o,.~mm:::r~]y prc>L-.qt in ti,e imerstices of minera!iaed Mllow h:.,t. Near ~.he suil:K:..dc nii '-~disa~ic, n zoo!ire f~cic,, extrusives are transformed ~,~; a g~ccnschi.,4 f'~cic-, assemblage of quartz, chlorite, sphene, pyrite and

9 ")

A . H ~ " ~ . O B E I R T S O N A N D S.P. V A R N A " / A S

very rare chalcopyrite (Valsami, 1990). The extent of alteration increases stratigraphically downward ,ithin the stockwork mineralised zone. Valsami (1990) inferred an inclined hydrothermal upflow zone, ca. 60 m below the contemporaneous lava surface (S area; Fig. 4). Both mineralisation and alteration decrease laterally and vertically away from this stockwork zone, suggesting that a single large hydrothermal system was active in the Stoa valley (Limogardion, S area; Fig. 4). Alternatively, Rassios (1989a) inferred the existence of small stockworks at different stratigraphical levels. At Limogardion, pillow lavas and lava breecias immediately underlying thick siliceous metalliferous sediments in the 'N area' (Fig. 4) contain abundant epidote, mainly as centimetre-sized clots', often replacing hyaloclastite in the interstices of individual pillow lavas. In addition, rare, large clasts (more than 15 cm across) o ~ pure epidosite are found within pillow breccias. Veins

and vugs within this breccia are lined with calcite, epidote and chalcopyrite and secondary minerals (turqugise, malachite and azurite; A. Rassios, pers. commun. 199 z). The abundant epidote (and local epidosite.~ attests to the upward percolation of hydrothermal solutions (probably at high temperatures) through pillow breccias that accumulated as talus alorg fauk scarps (A. Rassios, pers. commun., 1991). It is unclear if the epidote enrichment (and local epidosite) is related to hydrothermal genesis of tl-,¢~ immediately overlying metalliferous cherts, {~: to hydrothermal processes operating at higher levels of the crust that are not now preserved. Stockwork-type su!~.,.idas are also well exposed within the Sipetorrer~a Pillow Lava at Stirfakas (Fig. 3). Maratos ~#72) repolted the presence of quartz, sulphide, chalcopyrite and secondary minerals at this locality. The mineralisation is concentrated in NW-SE-trending zones of sheared pillow lavas, shot through with numerous

LIMOGARDION

KEY

Transgressive limestone Transgressive bauxite

Colours

E~[~] Fe-chert (jasper)

R Gn Gy BI

"~ Disseminated sulphide ~

Metalliferous mudstone

~

olcaniOastic mudstone

~

Votcaniclastic sandstone

~

Epidosite

~-7

Quartz veins and

Red Green

Grey Black

0

metr~

1

Nodular replacement chert ::] Pillow lava [~] ~

Lava breccia ar,d hydroclastite Sutphide mineralised lava

Gy

--1

Bi .2i. ., :/ ::. .: Gy ... -....-..:..

Gn lm

I

4 5 3 1 2 Fig. 5. Measured logs of extrusivesand .:edimentsin the Limogardionmh~eralisedarea. Othris. See Fig.4 for locationsof logs.

ORIGIN OF HYDROTHERMAL METALLIFHROUS SEDIMENTS

Quartz veins, traceable over 300 m longitudinally. The most prominent shear zone, 5--6 m thick contains numerous quartz veins, up to 1 m wide, with abundant disseminated sulphide, now almost entirely oxidised to gossan. The vein zones become less numerous, discontinuous and thinner (less than 1 m) laterally. The adjacent pillow lavas are unmineralised. Similar, but smaller, zones of quartz veining, with sulphide, arc seen at Neohorion (Fig. 3). Approximately half the host successions there are volcaniclastic and the remainder pillow laves. Quartz veins are steeply inclined and cut the bedding almost at right angles. Individual veins are lenticular, mostly up to 2 m thick by 2 - t 0 m long. Disseminated sulphide impregnates the adjacent lavas and sediments, which are often silici-. fled and largely oxidised to gossan. Massive sutphides are not exposed. Pyrite. chalcopyrite and malachite are present (Maratos, 1972). At Limogardion, sulphide mineralisation is restricted to less than 2 km 2 (Rassios, 1989a; Fig. 3). Massive sulphide, up to 5 m thick, overlies stockwork sulphide; tMs in turn is overlain by hydrothermally altered ;dva, with numerous veins of ferruginous chert ('jasper'), containing disseminated pyrite (Rassios, 1989a). The sulphide mineralogy is mainly pyrite and quartz, with very subordinate epidote, sphalerite, chalcopyrite, barite, pyrrhotite and pentlandite (Mousoulos, 1962; Maratos, 1972; Rassios. I989a). The richest sulphide ore originally contained up to 5% Cu, but values of less th"n 2% Cu are typical (Rassios, 1989a). Smaller massive sulphides are also exposed at Ayia Ekater;ni and elsewhere (Fig. 3).

Metalliferous sedimems Orange, ferruginous oxide-sediment and ferruginous chert ('jasper') occur together in the vicinity of the massive sulphides. The chert is defined as highly siliceous sediment (greater than 95% SlOe). At Limogardion, massive and disseminated sulphides are directly overlain by red oxide-sediment and chert, containing disseminated sulphide (Fig. 5, log 3). Mineralised cherts contain quartz-lined cavities (vugs) and are cut by

93 Bedded Fe- mudstone, now gossan

,m I

~-=

-

-

-

_

Sheared pillow5

--~ ~

Massiv~ !mlphid~ ~nOW O*~idi~,ed

a

.

-

..I-.- --> < , . . . ¢ ~ -_iX,

'Cj ""

/"--------'/

oh. with calcareous partings

b

Metalliferous ribbon chert

F

-Ira L_:

\° }o

/2/-<

° o

° ° o ~

°-° ° ° ° °°/ % ~ o - o-5-/_Wh!te alterea ~ ° %mall piltowff

MA,,i,eroos mudst0ne

C

Fig. 6. Fic,d sketche~, of i a v a - s e d i m c n t relations at A i, Ekaterini. Othris. (a) Hydrothc,"mally altered pillow lava is overlain by oxidised massive sulohidc. (b) R e d ja.,,per and carbonate is interbedded with pillow lavas near the mineratised zones. (c) Intercalation of metalliferous and pelagic s e d i m e n t s ~.ithin altered lava.~. See Fig. 3 for location of Ayia Ekaterini.

quartz veins. Unmineralised pillow lavas and lava breccias in the vicinity are interbedded with en echelon lenses of red chert, both with (Fig. 5, log l) and without (Fig. 5, log 2) disseminated sJlphidc. Individual lenses, up to t m thick, can be traced up to 60 m laterally. At Ayia Ekaterini (Figs. 6a and 6b). several lenses of red chert are exposed within tens of metres of the sulphides. Thin, recrystallised limestones are also interbcdded with chert. At Limogardion. metalliferous mudstones are exposed ca. 500 m north of the more northerly sulphide occurrence (Fig. 4). Unmineratised pillow laves are interbedded with

94

.A.II I-. l~.Ol{[:b',l SON AND S.P. VARNAVAS

iaminatcd, chocolate-brown metalliferous mudstones, 1-2 m thick (Fig. 5, iog 5}_ These scdimeres are located in small hollo-.,':~ in the piiiow lava surface and can be traced up to 10 m laterally. The mudstones are homogeneous, apart from small siliceous segregations. The immediately underlying lavas are pale and highly altered. Metalliferous mudstones also occur at Ayia Ekaterini (Fig. 6), again ponded in hollows in the pillow lavas, away from the immediate mineralisation zones. These mudstones are locally underlain by white, highly altered lava breccias. Elsewhere al Limogardion, epidote-imprcgnatcd lawls in the northern mineraliscd area (Fig. 4) are dcpositionally overlain by 8-10 m of grey chert. Beds are up to 1.5 m thick at the base and generally decrease in thickness upward. The lower part of the succession contains abundant disseminated sulphides, whilst the upper part is encrusted with dark grey metalliferous oxide-sediment (Fig. 5, lot, 4). 1 ne Fe-cherts are unconformably overlain by post-emplacement bauxitic mudstone and Late Cretaceous shallow-water limestone.

5, logs I and 2). Votcaniclastic sandstones there, are locally replaced by black, vitreous nodular chert, assumed to have formed by diagenetic replacement. At Ayia Ekaterini, pelagic sediment near the mineralisatkm is restricted to minor ribbon radiolarite (coated with manganese oxides), overlying metalliferous mudstone (Fig. 6c). Further from the mineralisatiom ribbon radiolarites occur as lenses, up to I0 m thick by 200 m long. Elsewhere, pelagic sediments are commonly interbedded with unmineraliscd lavas and mainly comprise thin-bedded, pink pelagic limestones and ribbon radiolarites. At Neohorion (Fig. 3), sulphide mineralisation is mainly within volcaniclastic sediments, comprising lava breccia, volcaniclastic sandstones, siltstones, siliceous limestone and calcaLous chert: also small lenses (0.3-1.6 m long) of pink, recrystallised limestone (Fig. 7, log 1). The volcaniclastic sediments are brown or green and contain variable amounts of disseminated sulphide. Volcaniclastic sediments away from the mineralised zone include purple volcaniclastic silt, coated with manganese oxide (Fig. 7, log 2). An in-situ sedimentary cover near Neohorion (Fig. 3; A. Rassios, pers. commun., t989) comprises several metres of pink, grey and white siltstone, shale, siliceous shale and b~own finely laminated mudstcne (Fig. 7, log 3), located in a shallow depression in the pillow lava surface. The succession is terminated upward bv a thrust sheet of serpentinite.

A ss'ocia ted sedb neJt ts

At Limogardion, fcrruginous cherts arc commonly interbeddcd with thin (centimetre to dccimctrcs thick) layers of brown, or green volcaniclastic sandstone, siltstone and mudstone (Fig.

I O Metre 8r

Gy

P:.:P I

P0 :ii:i/.:):t

ZSl

Pk

Z\_J

~

Silicified

~

Disseminated pyrite

~

M e t a l h f e r o u s o x i d e sediment

~

Mudstone/shale

~

Vofcaniclastic sandstone

~[-'7

Fe-chert (jasper)

~

Petagie limestone

Z"----t

E-~

Lava breccia

r-~,

~

P~How {ava

1---4 .... <

NEOHOR!ON

KEY

I

INTERLAVA MtNERAUSED

INrERLAVA UNMtNERALISED

SUPRALAVA

1

2

3

R Red Gy Grey P Purpfe Br Brown Pk Pink

Fig. 7. Logs of lhe inter-!ava and supra-tara scdimcm~ at Neohorion. Othri~. Sec Fig. 3 for D,cation of Ncoh~ri~m.

ORt(IIN OF tlYI)ROTttt:RMAL METAl I.|FEROUS SKDIMI.ZNt%

Supr>tava Mn-rich radiolarites In many areas of western and northern Othris, the Sipetorrema kava unit is overlain by ribbon radiolarites, up to several tens of metres thick. The contact is commonly thrusted (A. Rassios. pers. commun., 1989). A succession studied from the northern Othris ophiolite (between the villages of Ekara and Agoriani: Fig. 3) exhibits disrupted pillow lava overlain by red ribbon radiolarite, ca. 15 m thick. Manganese oxide occurs there as coatings and as interbeds of black mudstone, up to 10 cm thick. At this locality, parts of *he succession have experienced severe diagenedc alteration forming discontinuous zones of white recrysiallisea chert, up to several metres thick, Black crystalline manganese oxide occurs as segregations, up to several centimetres in s,~ze. The strong alteration is assumed to relate to tectonic emplacement in Late Jurassic time. In summar$,, the local and regional setting of the Olhris metalliferous deposits is shown in Fig. 8.

Sedimenta~' petrography At Limogardion. sulphide-impregnated, bedded cherts overlying epidote-rich lava (northern

95

pit, Fig. 4) comprise radiolariaa-rich ~c':rig:enous silt, wid~ abundant pyrite framboids. Mcta!!iferous mudstor_,es~ adjacent to the mineraii~,ed zone in the southern pit (Fig. 41 are fcrruginous radiolarites and mudstoncs, with variablc abtmd,~qces of quartz, polycq,stallfi~e quartz, muscovite ~md feldspar, and also numerous small (mil!i,.-netresized) sub-rounded to elliptical mudstonc intraciasts. MiItimetre-thick silt lenses are packed with green, chlorite-rich, angular g:ains. Small pyrite custals were observed within ;ntraclast-rich tnudstone. Diagenetic features include infi!ling and partial replacement by finely cwsiallinc calcite, segregation of chlorite and iron oxide, and quartz overgrowth development. Inter-lava ferruginous mudstones furtner from the massive sulphides {northern pit, Fig. 4) consist of ferruginous mudstone, with clay minerals, small feldspar custats and yew small quartz grains, together with scattered, yew poorly presep,,ed radiolarians, mostly reptaced by chatcedonic quartz. At Neohorion (Fig. 3). mudstones inlerbedded with coarse-grained volcanidastic sediments within the sulphide minera!ised zone are rich in small %ldspar cD~stals and contain rare radiolariarts and sponge spicules, with partia! replacement by fine-grained chatcedonic quarlz. Associated pink inter-lava sediment comprises fine-grained

(a) APULIAN CONTINENTAL MARGIN

PKLAGONIAN C O N T I N E N T A L MARGIN

PINDOS OCEAN

MORE{

Othris ophiolites

reiated

Pindos melange •

Z

Z

,"

LATE TRIASSIC-EARLY JURASSIC (b) Above-subductJon zone related P i n d o s ophio|ite Z

Z

~

:*

"

Z

Z

Z

MID JURASSIC Fig. S. Inferred plate fectonic seltings oi the Othris and Pindos ophio!iles. ~a} Othris ophiolitc and Pindos ophiotitic melange with melMlfferou~ deposit', formed at a mid-ocean ridge. (b) Genesis of the main Pindo,, ophiolile aho~c a subduclion zone. Only deposils re!ated to situalkm (a) are discussed here.

06

volcaniclastic sediment with feldspar, pyroxene, zeolites and scattered pyrite framboids. There are also rare interbedded radiolarites, with well preserved radiolarians in a matrix of fine-grained, ferruginous oxides. However, other interbeds of finely laminated mudstones are of terrigenous origin, with abundant muscovite, quartz, polycrystalline quartz and feldspar. Secondary carbonate largely replaces mudstone with finely crystalline calcite and minor chlorite segregations. Mudstone depositionally overlying the volcanic succession at Neohorion is dominantly terrigenous, with abundant fine-grained muscovite, quartz and opaque iron oxides. Associated cherts are heavily recrystallised and replaced by quartz. At Ayia Ekaterini (Fig. 3), typical gossan (altered sulphide) comprises recrystallised iron oxide with scattered, very small terrigenous grains. Associated radiolarites contain small mudstone intraclasts, The north Othris, Mn-rieh ribbon cherts are densely packed with radiolarians, tests being recrystallised to chalcedonic quartz. Individual radiolarian tests are infilled with Mn oxide and drusy quartz, within local Mn-rich segregations. In summary, ubiquitous fine-grained terrigenous quartzose sediment is assumed to have been derived from the Pelagonian microcontinent to the east, with the addition of minor volcaniclastic silt eroded from subjacent oceanic crusL together with biogenic (i.e. radiolarians) and hydrothermal constituents (see below). Diagenetic features include: early precipitation of euhedral pyrite cry.stats and framboids; later-stage recry,stallisation and infilling of radiolaria; quartz overgrowths; Fe and Mn segregation: chloritisation of volcanic grains (volcanic glass?); and variable replacement by (hydrothermal?) calcite.

X-ray mineralogy of seal"Rents At Limoga,'dion (Table 1), inter-lava Fe-rich cherts contain quartz, pyrite, hematite, calcite, illite and kaolinite. A thick lens of mineralised chert overlying the highest exposed lavas (in the northern pit, Fig. 4) contains quartz, hematite, goethite, pyrite, chlorite, albite and muscovite.

k H.F. ROBERTSON AND S.P. VARNAVAS

Less mineralised sediments further from the sulphides contain quartz, hematite, chlorite, chlorite-smectite and albite. Altered lava talus near sulphide mineralisation at Ayia Ekaterini and Neohorion contain celadonite and locally, montmorillonite. Associated sediments contain variable abundances of quartz, calcite, celadonite, hematite, muscovite, albite and pumpellyite. Altered sulphide at this locality (gossan) comprises goethite, albite and hematite.

Chemical analysis The Othris sediments were analysed by X-ray fluorescence, using the method of Fitton and Dunlop (1985). Twenty-seven were analysed from Limogardion, eight from Ayia Ekaterini and twenty-eight from Neohorion. Eight samples of the north Othris Mn-rich cherts were also analysed. Selected analyses are shown in Table 2. A small number of Late Triassic mudstones that accumulated along the eastern margin of the Pindos ocean (at Anavra) is also included for comparison but not discussed in detail here. At Limogardion, sampling was concentrated on inter-lava sediments exposed at varying distances from the northern and southern su!phide areas (Figs. 9-11). The most iron-rich sediments directly overlie oxidised massive sulphides (gossans) (Table 2, No. 6). Orange oxide-sediments and cherts are very ferruginous (Table 2, No:~. 6, 7). Cherts with the highest SiO~ values occur as lenses, extending up to several tens of metres laterally from the massive sulphides (94.14%; Table 2, No. 9). Sediments with high lithogenous contents (e.g. A1203, MgO, K20, Cr, Zr) commonly overlie Fe-rich mudstones and chert. More distal siliceous sediments, located further from the massive sulphides (northern area; Fig. 3) exhibit the highest MnO values (0.79%; Table 2, No. 24). Trace-elements (Cu, Ni, Zn, Ba) are enriched in inter-lava cherts and mudstones, relative to the lithogenous siltstones. Thick cherts directly overlying the epidote-rich pillow lavas are also metal-rich (i.e. Zn, 548 ppm; Table 2, No. 11). Iron-rich, inter-lava mudstones of the north

97

ORIGIN OF HYDROTHERMAL METALLIFEROUS SEDIMENTS

area exhibit enrichment in K20, MgO, MnO, P205, Cr, V, Cu, Ni, Ba, Pb, La, Ce, Nd, relative to associated lithogenous muds.

At Ayia Ekaterini (Table 2) metalliferous deposits are all relatively depleted in MnO. Most deposits are low in CaO, reflecting the essentially

TABLE 1 Whole-rock X-ray diffraction results of metalliferous sediments from the Othris area (sec Fig. 3 for locations) Limogardion

No.

Major component

Minor component

Trace component

16 18

Otz, Hem Chl-Smect

Chl-Smect

Qtz, Hem

Mudstone near sulphide

27 26

Qtz, Hem Otz

AIb Alb, Hem

Chl Chl

Sulphide mineralised mudstone

34 32 29 28

Qlz Qtz Qtz Qtz

Hem, Goe, Pyr Chl, Pyr Chl Alb. Hem

Hem Mu~;c

2 5 6 7 11 13 1

Qtz, Otz, Qtz Qtz Qtz, Qtz. Qtz,

N O R T H OTHRIS Radiolarian chert

7 17

Qtz QIz, Hem

NEOHORION

35

Qtz

Hem. Musc

Basal mudstones

28

Qtz

Celad, AIb

30 31

Ct, Qtz Qtz

Inter-lava mudslone near sulphide

80

Qtz. Chl

Inter-lava mudstone sulphide away from sulphide

82 82a

Qtz Qtz

Alb, Hem, Ch!, Musc All), I Icm

86

Qtz

Alb. Hem

Musc, Chi Musc

16a 18a 19

Goe Qtz Qtz

Alb. Hem Ct, Hem, Celad Musc, Hem

Alb

23 22 20 21

Qtz Qtz Ct, Qtz Mont

Hem Musc. Hem Celad Qtz

N area

Mudstone away from sulphide

S area

Inter-lava Fe-chert

Crust on lava

Ct, Hem Hem Pyr, I11, Hem. Kaol Kaol, I11 Hem Hem Ct, Hem

Kaol, III

Alb

Musc

AYIA EKATERINI Gossan Inter-lava mudstone

1 m above no. 22 Basal, sediment above lavas Top of lavas Altered lava clasts

Musc, Alb AIb, Pump

Key to minerals: AIb = Albite, Ct = Calcite, Celad = Celadonite, Chl = Chlorite, Hem = Hematite, M u s c = Muscovite, Pump = Pumpellyite, Qtz = Quartz, Kaol = Kaolinite, Mont = Montmorillonite, Goe = Goethite, Pyr = Pyrite, I11 = lllite, Smect = Smectite.

g TABLE 2 Selected analyses of sulphide related sediments (1-13), and of metalliferous and pelagic sediments from the Othris ophiolite

1 GR89-t6A

2 GR89-21

3 GR89-15

4 GR89-18A

5 GR89-22

6 LMN89-1

7 LMN89-14

8 LMN89-5

9 LMN89-13

117 LMN89-7

11 LMN89-29

t2 LMN89-18

13 LMN89-17

SiO~

11.03

55.41

23.27

76.72

78.76

44.97

61.55

94.09

91.33

70.02

85.37

68.70

71.02

AI20 3 Fe,O3

5.20 70.81

18.48 5.83

2.37 17.01

3.62 9,02

7.45 4.77

0.80 43.57

1.07 34.61

0.15 5.80

1.06 6.44

8.15 14.86

3.57 6.98

3.31 23,50

3.06 21.82

MgO

0.63

4.57

1.65

1.66

1.47

*

0.11

*

*

0.32

1.14

1.18

1.06

CaO

0.57

1.46

28.87

2,60

1.112

5.38

0.29

{).05

0,17

{7.30

0.07

0.53

0.50

Na20

0.41

0.45

0.17

0.03

{).30

*

0

0.0,0

004

0.01

0.07

*

0.00

K20

0.{)4

5.45

1.08

2.37

1.97

0.02

0.05

0.01

0.08

~.15~

0.03

0.23

0.21

TiO 2 MnO

0.37 0.04

1.53 0.09

0.11 04!

0.20 0. t3

/).37 1.15

0.06 0.07

0.03 0.96

0.02 0.01

0.06 0.00

0.47 0.02

0.16 0.66

0.15 0.11

0.14 0.10

P2 05

0.06

0.16

3.14

0.14

0.115

0.19

0.14

0.04

0.03

0.07

0.06

0.13

0.12

Total

89.15

93.43

78.09

96.48

97.31

94.93

98.73

1170.07

99.17

95.37

98.10

97.82

98,03

LOI

10.51

7.13

21.44

3.70

2.5,1

4.87

1.00

(7.64

0.68

4.59

1.79

2.04

1.85

Ni

23

90

2(7

22

44

2i

37

12

11

61

38

50

51

Cr V

104 359

498 440

132 412

39 127

33 52

20 135

20 15{)

3 39

25 94

117 649

24 92

134 555

124 458

* 222 87 t8 8 53 5 37 14 * i,'; 5 8 19

Sc

*

50

*

9

9

*

~

*

0

12

2

Cu Zn

3356 409

175 118

168 58

23 23

86 84

11 18

11 35

4 18

3 32

391 149

28 548

Sr

49

54

119

18

39

t2

7

2

13

23

8

Rb

7

106

25

57

73

4

4

*

1

21

0

Zr

26

73

45

39

79

13

11

2

l0

90

44

Nb

0

5

4

3

10

1

1

2

1

7

4

Ba

14

47

29

16

177

75

102

4

84

75

*

Pb Th

* *

14 2

t1 ~

3 !

27 9

3 *

3 *

4 2

6 *

53 4

3 4

La

2

10

24

8

27

9

5

*

7

22

17

Ce

*

14

11

8

49

~

*

0

4

31

!7

Nd

*

20

17

5

2

~

*

0

3

14

13

Y

5

40

69

!9

24

23

I1

1

5

25

24

* 176 86 18 7 49 4 84 16 * 22 4 9 19

o

7~

T A B L E 2 (continued) 14 NE89-76 SiO. A1203 Fe20 3 MgO CaO Na20 K 20 TiO 2 MnO P205 Total LOI

5 15 NE89-82

16 NE89-85

17 NE89-80

18 GR89-26

19 GR89-28

211 GR89-29a

21 GR89-33A

82.31

57.97

61.72

73.79

69.83

65.84

63.53

48.52

4.52 5.93 1.97 3.05 0.02 0.03 0.21 0.t3 0.07

11.49 16.03 5.47 0.53 1.116 1.24 0.58 1.39 0.1 ¢,

12.32 14.53 2.50 0.90 1.35 2.42 0.61 I).75 0.13

6.42 12.09 3.54 0.22 * 0.0 t 0.32 0.33 I).115

7.27 9.89 3.04 2.(P, 0.35 4.45 0.35 0.07 0.04

11.37 6.05 2.56 4.09 2.18 3.48 1.01 0,24 0.60

12.45 6.3,;~ 3.50 158 055 8,43 0.71 0,02 0.14

98.24

95.90

97.22

96.74

97.32

97.42

1.60

4.00

3.29

3.03

3.23

2.57

22 GR89-5

23 GR89-4

24 GR89-8

25 GR89-12

93.84

60.59

53.54

86.33

15.22 9.66 5,90 0,92 4.63 0,13 1.93 t).17 0.24

1.62 0.52 0.04 0.13 0.07 0.26 0.07 L67 0,03

1.82 1.43 0.66 I).79 0.14 0.51 0.08 24.50 0.07

1.84 0.60 0.37 I),66 n08 0.42 0.09 31.37 0~08

4.55 3.8 l 0.77 0.10 0,11 11.77 0.18 11.73 0.03

97,26

96.32

98.26

90.59

89.114

97.38

3.11

2.70

1.41

6.93

7.33

2.31

Ni Cr V

218 30 52

96 63 156

167 77 158

83 :~9 100

44 54 70

68 99 171

30 113 88

124 296 320

42 13 21

598 211 120

2033 20 112

78 33 37

Sc Cu Zn

5; 70 22

10 7 120

13 68 94

5 1771 79

5 43 74

26 i 32 154

13 63 95

42 53 86

2 17 16

0 86 107

* 143 64

7 129 42

Sr Rb Zr Nb Ba Pb Th La Ce Nd Y

171 0 56 6 * 16 4 21 25 17 17

52 41 136 13 210 12 8 51 66 36 47

45 66 139 14 238 17 11 52 53 32 42

5 0 78 8 * 0 3 26 27 21 25

22 162 90 7 86 29 7 17 23 14 18

1115 84 101 8 95 46 9 102 179 112 90

29 174 132 7 147 2(1 14 36 79 51 38

124 1 156 9 4 * * 6 21 16 31

52 9 15 2 33 5 2 7 22 10 10

1174 !1 73 4 746 22 * 29 32 17 60

412 10 43 5 3682 8 * 78 03 48 70

23 32 37 6 107 38 6 13 42 I1 12

l - 5 = Ayia Ekaterini; 6 - 1 3 = Limogardion (see Fig. 3 for location); 14-21 = Neohorion; 22-25 = N Othris. 1 = Gossan; 2 = pale altered basalt below metalliferous m u d s t o n e ; 3 = red siltstone; 4 = Fe-fich chert; 5 = cherty m u d s t o n e above pillow lava; 6 = inter-lava Fe-chert above gossan; 7 = crust on Fe-chert; 8 = Fe-chert; 9 = Fe-chert; 10 = siliceous sediment; 11 = siliceous volcaniclastic sediment; = t2 metalliferous m u d s t o n e ; t3 = metalliferous m u d s t o n e ; 14-18 = inter-lava siltstones; 18-20 = m u d s t o n e s and siltstones above the lavas; 21 = pillow basalt; 2 2 - 2 5 = ribbon radiolarites, ranging from black to white, with variable M n enrichment. Major-elements in wl%; trace-elements in ppm; LOI = loss on ignition.

o

5 O 7~ o ..~ .-~

>

>

o

Z

1()0

A.I-I.f-. ROBI~R'I'SON AND S.P. VARNAVAS

(a)

Si

(b)

~ A y i a

si

Ekaterini

A

O Gossan X Ochre O Mixed silica/volcaniclastJc

+ Alteredbasalt

Fe

. . . . . . . . . . . . . . .

(C)

AI Fe

.

.

.

.

.

.

.

.

(d)

Si z ~

Limogardion

.~k"°, ~ /;,% ~ ~-~ . / ~k /~x-~ + + '~

.

.

O Jasper + Mixed oxide/volcaniclastie X Mudstones a' Ochre

.

.

.

AI

si

Neohorion

~..

O In,~erlava O Supra-lava x Pillow lava

/

• Ribbon chert. Jurassic N. Oihris O Mudstone. above U.Triassic

Or'OO ,- \x

AI F e Z " ,. . . . . . . . . . ' ~ ' . XAi Fe Fig. 9. Ternary Si-Al-Fe plots of analyses. (a) Ayia Ekaterini. {b) Limogardion. (c) Neohorion. (d) N Othris Mn cherts. See Fig. 3 for locations. This diagram highlights the relative contribution of lithogenous (AI), hydrothermal (Fe) and hydrothermal plus biogenic constituen(s (Si). See text for further explanation.

(a)

(b)

si / / ~

Limogardion o Jasper + Mixed oxide / voicaniclastic sediment x Mudstone

Mn /

.

.

.

.

.

.

.

.

.

.

.

,

,,

~

\ Fe

AI

® Mudstone-chert "I O Diageneticallv t. Jurassic

alteredchert jNOthr's/

m Mudstone, UTriassuc

A°av-ab°veaP"'°,a.a, w

/

/~

A /"

~.

"~ ,~

,,

Mn

Fig. 10. Ternary plots of analyses from Lmlogardion (Othris). (a) Si-Mn-Fe. (b) AI-Mn-Fe. See text for explanation.

Fe

ORIGINOFHYDROTHERMAL METAI_LIFEIROUS SEDIMENTS (a)

lO1

(b)

Ni+Cu+ Zn x l O 0 ~

si

:;!! All sulphide-relatedioth rS • Mn-chert N. OthrisJPindos

Mudslone sii'( ~ / k ~ k

Fe cherts and lasper s, L~mogardion "

~ ~

Ochres, Llmogard~on

~

~ ~

Inter- and suoralay3, Neohor~on

/

AI Fig. 11. Terna~, plots. (a) (Ni + Cu + Z n ) × 100-Fe-Mn for all the Othris and Pindos metalliferous sediments. (b) Si-Fe-AI of sediments from N Othris.

non-calcareous nature of the pelagic sedimentation. However, some inter-lava limestone is also present (Table 2, No. 2). Gossan material is rich in Cu and Zn (Cu 3356 ppm; Zn 409 ppm; Table 2, No. 1). Red oxide-sediments overlying the gossans are strongly enriched in Fe (Table 2, No. 3). Many of these samples are seen to contain disseminated sulphide, although Cu values are low (e.g. 175 ppm; Table 2, No. 2). In addition to SiO, and Fe20 3, red chert contains AI (up to 9.02%) and other constituents (i.e. T i O 2 t o 0,37%; Rb to 73 ppm; Zr to 79 ppm) of mainly lithogenous origin (Table 2, Nos. 4, 5). Several

samp!es of red sediments overlying gossan are also relatively rich in P:O 5 (3.14%; Table 2, No. 3) and Y (69 ppm). At Neohorion (Fig. 9c), the inter-lava and supra-lava sediments are essentially identical in composition. Manganese is, however, only locally enriched, re!ative to associated volcaniclastic muds (Tabk 2; 1.39%, No, 15). Several samples of mudstones, within and above the lavas are relatively rich in Ni, V, Cu (e.g. 1771 ppm, No. 17), Zn, St, Ba and Pb. The most manganiferous supra-lava mudstone is relatively rich in P20~ (0.60>(,, La. Ce, Nd and Y.

--'-]Later Tertiary elastics +

+

÷

' ~ " - - ~ . - "~ • - " " o'~.-&.. ;- " ~ k

. . . . 4- + + 4-+,,,% . • ~ ~ ~rma,a 6 + J~. • " - .~.

. P~,dhes

L _ j E a r l y Tertiary Pindos flysch ~Cretaceous limestones f--;.:-:] and flysch

rqPindos o..,o.,o ~ .

~

= . ~,~+

o

rJO~'z,,./;~. : \+Y,~ [, ~, ,~

~/~.,.~%~l~. Z F ~

++ ~

~

b- pm i

m

nge

Mesozoic carbonate platform

Fig. 12. Outline geological map of the Pindos Mountains, NW Greece, shewing the locations of the metalliferous deposits, discussed here. Modified after Jones and Robe rtson (1991).

102

A.H.F. RC'BEf,~TSON AND S.P. VARN/.,,VAS

lau- 5

Serpentinite of peridotite nappe Dismembered metamorphic sole Volcanic-sedimentary tectonic melange

8

5

Cretaceous

Tertiary

(b)

f

deep sea sedimentary

turbiditic

sandstones

rocks

('Pindos flysch')

Ser0entinite Basaltic pillow lava Bedded lava breccia

~.~'~l/')~)~).~~~Overlying hydrothermal mudstenes 0 ARMATA area

~

'l/~

/~Disorganised tectonic melange I"~/

Fig. 13. Field setting of the Pindos metalliferous sediments. (a) Sketch of the overall structural succession in the mineralised area. The sv!,~hides and oxide-sediments occur with extrusives of the highly dismembered Aspropotamos Complex, Pindos Mountains. (b) Sketch cross-section of local mineralised area.

The chemical composition of the manganiferous cherts from north Othris contrasts with the three sulphide-related sediments discussed above, as they are mainly rich in Mn, bt, t deoleted in Fe (Table 2, Nos. 23, 24; Figs. 8d and 9b). The most Mn-rich, Fe-poor sediments are also rich in Ni (2033 ppm, No. 24), Ba and Sr.

range from sparsely, to highly vesicular and are often coated with ferruginous oxide. The pillow lavas are disconformably overlain by lava breccias 0 - 15m of red cherty radiolarian mudstone 0 - 12m of mudstone with volcaniclastic siltstone partings 2 - 10m of fissile brown Fe, Mn mudstone with rare volcaniclas'.~c siltstones

Pindos meta|lifet~us sediments 0 - 70m lava breccia with local interstitial Fe, Mn mudstone

We now go on to discuss the metalliferous deposits of the Pindos area (Fig. 12), at Padhes, Armata, Brisca (near Dhistraton) and Perivoli, areas originally mapped as Diabase Breccia by Brunn (1956; Fig. 12). The mineralised extrusives there consist almost entirely of severely dismembered thrust sheets and tectonic melange (Fig. 13). However, local intact successions, up to 100 m thick, include sulphides and metalliferous sediments (Fig. 14).

Up to lO0m of basaltic pillow lavas, commonly vesicular Disseminated and vein sulphide, reduced, and silicified zones at lava - sediment surface (gossans) just below, or deeper in lava succession

Field evidence 1C [

Up to 80 m-thick successions of basaltic pillow lavas in the mineralised area are dominated by well formed, equant pillows (less than 1 m in size), with a virtual absence of massive flows, or interbedded sediment (Fig. 15, log 1). The lavas

|

metres

0L

COMPOSITE

LOG

Fig. 14. Composite succession of lavas and metalliferous sediments in the Pindos Mountains.

ORIGIN OF HYDROTHVRMAL ME IAI_IJFEROUS SEDIMENTS

103

centimetre.~ :" ok. Adjacent lavas are locally grey-green, silicified and contain minor epidote and disseminated sulphide. Metalliferous sedimcnts are intercalated with the uppermost several metres of lava breccias in the Armata-Dhistration area (Fig. 13, Fig. 15, log 1), usually as lenses of ferruginous mudstones. These sediments are overlain by up to 8 m of finely laminated, soft, fissile, purple-brown metalliferous oxide-sediments. There are also rare occurrences of black manganiferous concretions, less than 4 cm in diameter. Locally, at Brisca (Fig. 15, log 6), basal sediments overlying pillow lavas comprise red siliceous oxide-sediment; above, metalliferous sediments are unusually dark coloured. At Perivoli (Fig. 15, tog 7), basal metalliferou~ sediments, locally overlying a small gossan (see above) contain thin partings of terrigenous siltstone and sandstone and mudstone intraclasts (up to 1 cm in size). Where intact successions are preserved (e.g. near Armata; Fig. 15, logs 2, 3). ferruginous metalliferous oxide-sediments low in the succession pass upward into grey-purple mudstones, interbedded with grey terrigenous siltsmne and fine-grained sandstone. The succession ends with thin-bedded siliceous mudstones, rich in muscovite.

up to 90 m thick (e.g. Fig. 15, logs 2-4). These breccias are crudely stratified to massive and are composed of sub-rounded, broken pillow lavas, up to 0.9 m in size. There is a sparse matrix of poorly sorted, green volcmiclastic silt, mainly derived from devitrified valcanic glass. Individual intact pillows, with chil!ed margins, are present within the lava breccias. Most of the clasts appear to have formed by spalling along cooling cracks. Pyrite and chalcopyri:.e were reported from the Armata area (at Krona and Ethies), whilst pyrite, chalcopyrite, cupranite and azurite wer~ recognised further southwest, at Perivoli and Mikroliradon (Mousoulos, 1962; Maratos, 1972). At Perivoli (Fig. 12), a very small, 0.6 m-thick massive sulphide (now oxidised to gossan) is overlain by laminated metalliferous mudstone (Fig. 15, log 7). Massive sulphide, and red jasper cut by mineralised veins, rich in disseminated sulphide can be recognised. Minor stoclexork-type sulphide is present at one metalliferous sediment !ocality (Armata, Fig. 12). Mineralised zones, several metres wide, extend ca. 60 m downward in the lava succession below the overlying metalliferous sediments (Fig. 15, log 2). MineraliscO lavas are cut by sub-vertical veins of quartz and sulphide, up to several

"_-'-_ =-_-'2["

! ,

&i

S~

PERIVOLI

-.

7

•~ 7 ~ q

ARMATA

!&

5

4 KEY ~

ie>-4

~ed~ect repi,3cemenl chert

~ ~iydrothermalvetoingand altera~don [ L ~ Disseminatedsuipmde ~ Fe-r~cnmudslone

L l O m ~

~

?

LlOm

Massive sulphide(gossa~)

_~-Z]_Me~all,~e~ousmuds*,one I t Volcamclastmsandstoneand sdtstone tOL.~__jLavaconglomerate

PADHES

ARMATA

ARMATA

1

2

3

~

Pil}owlava

BFIISCO 6

Fig. 15. Logs of local successions of extrusives and metalliferous sediments in the Pindos Mountains (see Figs. 1 and 12 for setting}.

104

A.H.F. ROBERTSON AND S.P. VARNAVAS

Petrography and mineralogy of sediments The highest inter-lava sediments, exposed at Padhes to Armata (Fig. 15, logs 1, 2), comprise siltstones, with abundant polycrystalline quartz and muscovite and scattered poorly preserved radiolarians, replaced by chalcedonic quartz. Typical supra-lava mudstones (e.g. at Brisca, Fig. 15, log 5) contain abundant muscovite, polycrystalline quartz, plagioclase and small clasts of basalt. Ferruginous mudstones near the base of the supralava sediment succession (at Armata, Fig. 15, logs 2, 3) contain tiny grains of plagioclase and basalt in a microcrystal[ine matrix, with well presereed radiolarians and scattered sponge spicules. The radiolarians are infilled with tlcanslucent, microcrystalline silica and a few contain ch~:lcedonic quartz. Laminated mudstones towards the top of the succession contain abundant muscovite, polycrystalline and single-crystal quartz, minor plagioclase and scattered patches of secondary chlorite. Poorly preservec~ radiolarians are replaced and infilled with chalcedonic quartz. Some radiolariarts were dissolved, leaving only part of the test preserved as black ferruginous oxide. Metallifer-

ous mudstones at Perivoli (Fig. 15, log 7) are ferruginous~ ~Ath terrigenous quartz, muscovite, plagioclase, and scattered radiolarians, infilled with finely crystalline chalcedonic quartz. Samp!es of Pindos mudstones were subjected to whole-rock X-ray diffraction (Table 3)° Interlava sediments at Padhes contain hematite, quartz, chlorite and albite. Sediments intercalated with overlying lava breccias are mineralogically similar, but contain less feldspar. Fluorapatite is present in one sample (P 21; Table 3), as well as traces of smectite. The supra-lava sediments are compositionally similar, but contain muscovite from the base of the succession upward, together with quartz, hematite, ~U,ite and chlorite. Secondary layers associated ;~ith the Brisca and Perivoli sulphides contain quartz, calcite, hematite, calcic plagioclase, fluorapatite, chlorite and muscovite. In summary, terrigenous constituents are present throughout, especially higher in the supralava succession. Sedimentary structures suggest deposition by dilute turbidity currents. The source of the terrigenous sediment is believed to have been the Pelagonian microcontinent to the east

TALLE 3 Whole-rock X-ray diffraction results from metalliferous sediments associated with the Pindos ophiolite Location

No.

Major component

Minor component

Trace component

Padhes Inter-lava mudstone Inter-breccia mudstoae Inter-breccia mudstone

P-26 P-21 P-22

Hem, Qtz Hem, Qtz Hem, Qtz

('hi, AIb Fluor Chl

AIb. Chl, Smect AIb. Smect

P-33 P-4o P-46

Qtz, Item Qtz, AIb Qtz. Aib

AIh Chi Ch!, Item Chl, Ct. Musc

P-50 P-51 P-56

Qtz QIz Qtz, Ct, Hem

AIb, Hem Hem, Mu.~c

Alb

P-57 P-57

Qtz Ca-albite

Musc, Hem Fluor, Chl

Musc

Armata Basal supra-lawL sediments Mudstone Siltstone

iviusc Musc, Smect

Brisca Supra-lava sediments Supra-lava sediments Secondary. layer Perit 'oli Supra-lava sediment Secondary layer

Key to minerals: Alb = albite, Ct = calcitC Chl = chlorite, Fluor = flaorapatite, Hem = hematite, Musc = muscovite, Pump = pumpellyite, Smect = smectite, Qtz = quartz.

ORIGIN OF HYDROTHERMAL METALLIFEROUS SEDIMENTS

!(}5

(Fig. 9). Minor fine-grained basaltic detritus was eroded from subjacent oceanic crust, as in the Othris area.

pensation depth. Several samples are, however, enriched in CaO, including the higher levels of the terrigenous-dominated mudstones at Armata (to 8.90%), diagenetically altered sediment (e.g. secondary layers at Brisca, 5.83%) and tectonically deformed sediment (i.e. mudstone from a shear zone at Armata, 27.19%). Samples of mudstone from the stratigraphically highest inter-lava sediments (Padhes; Fig. 12) plot in the mixed S i - F e - A I field and exhibit relatively high absolute values of MnO (up to 968 ppm). Zn is also relatively enriched (to 157 ppm).

Chemical analysis The Pindos sediments (Table 4) plot in three fields of the S i - F e - A I diagram (Fig. 16): Si-, Feand Al-rich (the greatest number); Si-Fe-rich (common); and Si-rich (minor). Most of the samples are carbonate-poor (less than 1.5% CaO), suggesting deposition below the carbonate corn-

TABLE 4

Selected analyses of mudstones from the Pindos ophiolite Padhes

SiO ~

Armata

Brisca

28

29

30

31

32

33

34

35

36

37

38

39

2-19

P-21

P-26

P-33

P-36

P~46

P-50a

P-51

P-52

P-58

P-60

P-61

38.72

44,41/

55,12

61.75

57.34

59.44

AI20 3

5.34

5.74

8.53

111,29

11/.57

13,72

Fe20 3 MgO CaO

47.25

40.1/1

24.49

16.31

20.35

4.21

5.05

4.18

3.62

0.57

0.64

0.91

Na 20

0.43

0.31

K~O

0.56

0.39

TiO,

().18

1/.22

MnO

0.51

P205

0.16 97.94

Total

Perivoli

84.9

611,1/9

87.47

77.91

76,59

75.33

2.37

10,74

2.73

9.41

111.29

10.96

9.99

7.66

17,51/

4.02

4.16

4.32

4.59

4.12

5.76

0.58

2,14

1.20

1.211

1/.29

1.3t)

1.05

11.68

0.9fi

1.60

0,47

i).54

0.49

0.30

0.49

1.48

11.92

0.97

1.87

I).87

0.75

0.14

0.32

1.12

0.51

0.48

1.711

1.83

1.61

0.12

3.49

1t.57

2.71

3.07

2.71

0.32

0,41

11.43

11.94

0.07

0.50

0.1(t

0,35

/I.38

11.39

0.67

1.17

0.50

0.39

0.7g

I).113

1.25

0.31

11.17

(L118

0.12

11.17 97.61

0.32 97.115

1t.16 96.72

0.12 96.72

11.1:~ 94.79

1t.!2 97.95

0.12 97.1t2

0.1t6 97.15

11.1t7 96.82

(1.~7 96.52

1t.111 96.51

Ni

13/t

1(14

108

129

123

184

19

154

39

64

51

95

Cr

171

155

93

127

1411

292

6

53

13

47

4"7

69

V

751

669

649

324

356

234

112

135

45

85

75

75

Sc

4

a

9

II

12

23

1

11!

2

8

6

9

Cu

107

175

332

239

93

119

81

154

63

2111

123

273

Zn

12,5

139

157

134

137

125

14

116

115

385

140

t74

Sr

29

25

45

32

34

51

39

61

46

20

22

411

Rb

23

16

19

69

71

64

3

124

21

20

1116

95

Zr

78

78

77

98

97

124

37

156

28

73

81

92

Nb

4

5

5

7

8

8

3

13

3

8

8

1t

Ba

258

| 52

1112

1211

43(1

83

219

365

2119

195

182

151

Pb

96

611

24

36

47

27

9

79

[6

18

18

15

Th

1

1

3

7

6

6

2

9

3

8

7

8

La Ce

34 111

23 9

45 43

38 48

38 42

11 43

4 19

65 9/t

14 13

28 711

31 69

5 86

Nd Y

6 34

4 38

39 31

37 34

16 29

15 3

11 18

53 42

12 14

16 15

14 17

19 19

2 8 - 2 9 = mud.~;tones from top of lava breccia succession, near Padhes; 31 = mudstones from base of metalliferous sediment succession, Armata; 32 = as 31 along strike; 33 = mudstones higher in the supra ophiolite succession, near Aramata: 34 = basal

metalliferous sediment near sulphide, Brisca (near Dhistraton); 35 = same, but higher in the succession; 36 = siliceous lens higher in the succession: 37-39 = mudstone overlying oxidised sulphide (gossan), Perivoli. Major-elements in wtCb; trace-elements in ppm.

H}{;

AH.F.

Si

Pindos

/ : ~

t' Y//

/

X

:~ ~ ~

"~

~

"

~

t-'~ .*

Perwoli

1

0

Kiatrabec

j

+

Kiatrabee-

Inter-

\

J

Fig. !6. S i - F e - A I ternary plot of metalliferous sediments trom lhe Pimh,s ophiolite. See rex! for explanation.

Supra-lava sediments in this area are relatively enriched in Fe:O~ (up to 47.25%; Table 4, Nos. 28-30), also locally in V (to 1036 ppm), Ba (to 258 ppm), Cr (to 201 ppm), Ni (177 ppm), Zn (to 193 ppm)~ Sr (to 57(1 ppm) and Y (to 257 ppm). MnO values are relatively low (up to 0.71%). Most of the mudstones from Armata (ca. 2 km away) are more siliceom, (TaMe 4, Nos. 31-33). Trace-elements are sporadically enriched; e.g. Cr

(a)

YSON

.AND

S.P.

VARNAVAS

(to 921 ppm), Ni (to 616 ppm), Cu (to 239 ppm), Zn (to 142 ppm) and Zr (to 163 ppm). Terfigenous mudstone from near ~he top of the succession at Armata is relatively rich in CaO, Na20, K20, Cr, Ni and Zr. Sediments at Brisca (near Dhistraton) are compositionally varied (Table 4, Nos. 34-36; Fig. 16). The basal sediment immediately above the extrusives is vmT siliceous (84.9% SiO 2, Table 4, No. 34), but Mn-depleted (MnO 0.03%). Samples several tens of metres from a small massive sulphide are ferruginous (17.50~), siliceous (60.09%, Table 4, No. 35) and relative!y enriched in Ba (365 ppm), Rb (124 ppm) and Zr (156 ppm). Diagcneticaily altered siltstone is relatively enriched in AI20 3 (18.40%), N a 2 0 (5.82%), MnO (0.82%) and P205 (1.i3%), Ce (104 ppm), Cr (180 ppm), Ni (164 ppm), Cu (131 ppm), Zn (555 ppm), Rb (1001 ppm), ZI (299 ppm) and Nb (69 ppm). Mudstones from Pcmoii are the most Stand A!-rich (Fig. i6; TaN: 4, Nos. 37-39). Mudstones directly overlying tiny gossans there, are Mn-poor (to 0.17%), not significantly Fe-enriched (up to 5.96%), but show slight Cu (to 273 ppm) and Zn (385 ppm) enrichment. High levels of K , O (up to 3.31%) reflect muscovite content.

(b)

AI

, " ":i

A!

Average deep sen c,{rbonat~

/ pelagic ~ -sedlmenlS ~

mudo~anf's

/' OthH, Mr! cs3ildS#OitI~~>

6

\\

,

N~

Sem,HI

2~-L<

A..........

deoosds

/ "

Bauer Deep sediments

Ct~r,% .I;.u b ,

Ar ,i k ,~OH:~

BntJe,

S Cyprus

\ Olhrl5 Mt~ cherl5

5 I

rroodos~

/~

Avor,lge sh:dc,

~

Cyprua bas.~l umber l n d ~c,:r B,ISSlt umbe,

3,4

'-" .... c h i n I~:

~

/1

/

Aver,lge

,/~

nontrenlto 4 ,OthrlS ,,qd Prndob

",

I1

X \

~

" ,~,,od ~........ bl,,~mount

~/

Average Easl ..~ Pacific Rise crostal sediment

'I

'

,

Average PC]ClflC~ Amph D2sedmounf Sedlrnerll

Fe

2

Fig. 17. Comparisons of ancient with ,nodern ',ediments. (a) A I - M n - F e plot comparing the Greek sediments with other Telhyan

ophiolite-related metalliferous sedh'nents (1. Bonalti el al.. 1976: 2, Robertson and Fleet, 1986: 3, Rohertson and Hudson, 1973: Boyle, ~990; 4, Roberison, 19,.%b; 5. R-)bertson. 1976), (b) A I - M n - F e plot comparing the Greek metalliferous sediments with modern oceanic metalliferous sedimems (1, Bostr6m. 1975; 2, Bonatti and Joensu, 1966; 3, Jenkyns and Hardy, 1975; 4, Corliss et al., 197'7: 5, Turekian and Wedepohl, 1961: 6, Dymond et al., 1976).

O R I G I N OF H Y D R O I ' H E R M A L M E T A L I . I F E R O U S SI-DIMI-,NTS

Comparisons with other Tethyan metalliferous sediments We now compare the Othris and Pindos deposits with counterparts elsewhere in the Mesozoic Tethyan a r e a . The Othris sulphide-?elated sediments are similar to those of the Troodos (Cyprus) and Semail (Oman) ophiolites. Normal faults, as at Limogardion are interpreted as hydrothermal pathways in Cyprus (Adamides, 1980) and Oman (Haymon et al., 1989, 1990). The Othris massive sulphides are similar in size to small massive bodies located at the contact between the lower and upper lava units in Oman (Karpoff et al., 1988; Pflumio, 1988), but are much smaller than the Cyprus and Oman larger orebodies (e.g. Skouriotissa in Cyprus; Lasail in Oman). Epidosites, interpreted as reflecting high-temperature hydrothermal discharge, are at present known only locally as ctasts in talus at Limogardiono but are much widespread, for example, in the sheeted dykes of the Late Cretaceous Troodos ophioIite (Richardson et al.. 1987). Epidosites present in the stockwork zone of the supra-subduction zone Pindos ophiolite (not discussed here; Valsami, 19901 are notably similar to epidesites from Mathiati in Cyprus (Richards et al., 19891. In contrast to Troodos, hox~ever, the Othris sulphide area was overprinted by a high-temperature background assemblage, which Valsami (1990) interprets as a late-stage magmatic event. What is unusual is that the local Othris epidosite~ are present in the extrusives rather than sheeted dykes, suggesting that high-temperature seawater-lava interaction and leaching were taking place in the upper crust close to the seafloor. The Othris Fe-rich oxide-sediments are similar to Late Cretaceous ferruginous oxide-sediments (ochres) in Cyprus (e.g. Skouriotissa; Conslantinou and Govett, 1972; Robertson, 19761, Oman (e.g. Lasail; Haymon et al., 19901 and in the Late Cretaceous Ermioni mining area of Argolis (Fig. 1; Varnavas and Panagos, 1984, 1985, 1989; Robertson et al., 19871. Ferruginous mudstones near sulphides (Limogardion N area) specifically, are similar to mudstones occurring with small massive sulphides in Argolis° The altered mont-

1(}7

morillonite-rich lava talus beneath metalliferous sediment is similar to the alteration zones beneath the Fe-Mn umbers in Cyprus (GiIlis and Robinson, 19901. On the other hand, the Othris sulphide and oxide deposits differ from those of Cyprus, Oman aT,,d Argolis in a number of respects. (1) Metalliferous Fe-cherts are abundant in the lavas surrounding the sulphides. (2) Sediments up to hundreds of metres from the sulphide zones are relatively depleted in Mn and many trace-elements. (3) None of the deposits is as enriched in Mn and trace-metals as typical Troodos or Oman umbers (tLobertson and Hudson, t973; Fleet and Robertson, 1980; Boyle, 19901. (4) Only small massive sulphides are known. The north Othris Mn-rich cherts are similar to cherts reported from a number of Tethyan settings, including Antalya, SW Turkey (Robertson, 19811, Mamonia, SW Cyprus (Robertson and Boyle, 1983), Oman (Robertson, 1986a), north Italy (Bonatti et al., 1976; Barrett, 19811 and the Eastern Alps (Decker, 1990). In Argolis (Greece) Mn-rich cherts commonly occur within inter-lava ribbon radiolarites (Robertson et al., 1987). The northern Apennine Mn-rich cherts mainly occur at the base of the succession overlying the ophiolite (Barrett, 1981). Manganese-rich layers, similar to north Othris, are found within ribbon radiolarites of Upper Jurassic-Lower Cretaceous age, depositionally overlying Late Triassic pillow basalts in the Antatya Complex, SW Turkey (Robertson, 1981). The Pindos metalliferous sediments are similar to volcaniclastic units exposed on a much larger scale within the Sooth Troodos Transform Fault Zone (Arak~:pas fault zone) in Cyprus (Simonian and Gass, 1978). However, the sediments there are interbedded with extrusives, unlike Pindos. Similar lava breccias also occur, on a much smaller scale, infilling small half-grabens beneath metalliferous sediments in the Troodos (e.g. Boyle and Robertson, 1'-184) and Oman ophiolites (Fleet and Robertson, 1980). lnterbeds of volcaniclastic sediment within metalliferous sediments, similar to the Armata area, Pindos, also locally overlie ophiolitic extrusives in Oman (e.g. Wadi Ahin; Fleet and Robertson, 1980) and in the Sakalavite

l()~

A.H.F. ROBERTSON

lava unit of Hatay, S Turkey (Robertson, 1986b). Ophiolite-derived breccias also form part of the sedimentary cover of the Jurassic Apennine ophiolites; however, this commonly contains much plutonic ophiolite-derived material, in contrast to Pindos (e.g. Cortesogno et al., t978). i ' degree of metal enrichment, the Pindos inter-lava and supra-lava mudstones are similar to mudstones overlying the Late Triassic lavas of AntMya (Robertson, 1981) and also stratigraphica;ly higher (less metalliferous) mudstones overlying the Late Cretaceous Oman ophiolite (Robertson and Fleet, 1986). However, the Pindos and Othris metalliferous sediments differ from their Cretaceous counterparts (e.g. Cyprus, Oman) in that terrigenous sediment is abundant. In this respect, they are more similar to the Antalya metalliferous sediments, interpreted as emplaced oceanic crust formed near a Triassic rifted continental margin.

(a)

~

..~.~o..,

o7._

.

K ~ 'E¥ I-=-~

A N D S.P. V A R N A V A S

Discussion: hydrothermal processes in the Pindos ocean

The Othris and Pindos metalliferous sediments were laid down near the axis of the Early Mesozoic spreading ridge in a small ocean basin, while the Mn-rich cherts accumulated much more widely on the adjacent abyssal plain (Fig. 18). The most comparable modern setting is the southern Red Sea and the Gulf of Aden (Cann et al., 1977). The Pindos and Othris ophiolitic units were emplaced eastward onto the Pelagonian microcontinent in the Late Jurassic, while the Apulian passive margin was not deformed until suturing of a remnant Pindos ocean basin in the Early Tertiary. This suggests that the metalliferous deposits associated with both the Othris ophiolite and the Pindos ophiolitic melange formed on the eastern side of the spreading ridge in the preMiddle Jurassic.

-"

~

~

~-

~"

~-"",'-,r'~_ ~""'A'/I/~S -b..4"~ ) ,'N--, ,", )."~" r', ,-'xy'h.#. ge-rich

0

15

Fe-cich chert (jasper)

oxide - sediment

~"-~,'~,'%,'%

I

I

Massive

Metres

sulphide

Epidosde

pi,o~ lava

OTHRIS

DEPOSITS

Lava breccia 7--]

Ocean floor normal fault

\ .

,"x , ~ . ~ , ,"-, ~ , ~ , - ' ,

/

\

,", ,'-z

,-

. ,", ,",,~.

" , ,", ,'x ,a, e.,v. ~ ~ x..,-',Z-x,N '.&F,,,'x,,%,'v-,r-,,'-. :z, )--,%Z.')..,c', ¢x ,-'-,,-¢, "¢,A l~,%,'x"a~'" ""

PtNDOS

DEPOSITS 0

2

I

r

Km Fig. 18. R e c o n s t r u c t e d s e t t i n g s of G r e e k m e t a l l o g e n e s i s . (at O t h r i s ( L i m o g a r d i o n ; A y i a E k a t e r i n i ) . (b) Pindos. See text for expialmtion.

ORIGIN OF HYDROTHkRMAL MIZTALLIFEROUS SEDIMENTS

The ocean floor topography was strongly influenced by faulting in all the sulphide mineralised area, particularly Pindos. Faults controlled the location of stockwork and massive ores (e.g. at Limogardion) and mineralising solutions percolated through talus shed from faults (e.g. Neohorion). Stockworks in Othris and Pindos, dominated by sulphide-bearing quartz vein systems (e.g. Neohorion, Stirfacus), mark the discharge pathways of high-temperature hydrothermal fluids. Disseminated sulphide was also precipitated in lavas adjacent to the hydrothermal upflow zones, particularly close to massive sulphides. These zones are now largely altered and oxidised to a spongy silica-iron rock ('porolithos' of Rassios, 1989a). The massive sulphides were precipitated as small fault-controlled bodies (up to tens of metres across) above the stockworks, similar to the black smokers of modern spreading axes (e.g. Von Damm, 1990; Klein, 1991). The Othris sulphides accumulated on an unsedimented ridge and were buried by further eruptions soon after formation as in some East Pacific Rise examples (Hekinian et al., 1983; Klein, 1991), in contrast, for example, to the much more long-lived, polymetallic sulphides of the Mid-Atlantic Ridge TAG area (Rona et al., 1986). Iron-oxide sediments and Fe-rich cherts, containing variable amounts of fine-grained terrigenous sediment directly overlie the massive sulphides at Limogardion and Ayia Ekaterini. These sediments precipitated as primary ferruginous oxide, silicate a n d / o r sulphide-rich hydrothermal sediment (later oxidised). Similar Fe-rich sediments characterise modern spreading centre hydrothermal fields (e.g. Pacific Ocean: Hekinian and Fouquet, 1985; Atlantic Ocean: Shearme et al., 1983) and are also known, for example, in the Hellenic volcanic arc (Smith and Cronan, 1983; BostrBm and Widenfalk, 1984; Varnavas and Cronan, 1991). The ferruginous cherts ('jaspers') associated with the sulphides are interpreted as hydrothermal solutions released from, or near the sulphide-precipitating vents. In contrast, radiolarian mudstones, mixed with hydrothermal constituents accumulated in small fault-controlled hollows around the fringes of the sulphide-precipitating field. The thickest Fe-cbert lens con-

109

tains abundant disseminated sulphide and accumulated directly above the epidote-rich zone, with local epidosite clasts in volcanic talas (discussed above). Less siliceous metalliferous mudstones accumulated in fault-controlled hollows away (i.e. t00-500 m) from the sulphide mineralised zones. At Ayia Ekaterini, one such fault hollow was infilled with metalliferous mudstone, pillow lava debris, and metalliferous radiolarite. Manganese is not a significant constituent of any of the Othris sulphide-related deposits, in contrast, for example, to the East Pacific Rise crestal sediments (Bostr6m and Petersor~, 1969) and ancient counterparts (Dymond et al., t976). The explanation is probably that Mn was vented from the hydrothermal field and dispersed by currents onto the lavas some distance away (i.e. more than 1 km). In the Pindos area, ocean iloor faulting, possibly parallel to the spreading axis, gave rise to fault scarps, which underwent mass wasting to form submarine talus screes after volcanism ended. Tiny massive sulphides (e.g. at Perivoli) were precipitated at the top of the lavas and directly overlain by Fe-oxide sediments. The stockworks of these small sulphide mineralised zones are represented by underlying quartzsulphide vein systems. Mudstones overlying the lavas and lava breccias contain a subordinate component of hydrothermally derived metalliferotis oxide-sediment. Minor hydrothermal conduits are present in the directly underlying sulphide mineralised lavas. However, it is probable that the oxides were precipitaled from larger-scale hydrothermal discharge zones elsewhere in the vicinity and were then ponded into fault-controlled hollows by currents. The Mn-rich ribbon radiolarites of north Othris are essentially siliceous biogenic sediments. Hydrothermal manganese in these sediments probably drifted frem near the spreading axis and settled on the adjacent abyssal plain. After deposition, these cherts underwent partial recrystallisation and redistribution of Mn, apparently related to deep burial and tectonic deformation. The Mn-rich layers in the cherts are compositionally similar to hydrothermal manganese oxides from the TAG area of the Mid-Atlantic Ridge

] 10

(e.g. Scott et al., 1974). Similar Ba-enrichment is also reported from modern Mn-rich, Fe-poor crusts from the Eratosthenes seamount in the eastern Mediterranean (Varnavas et al., 1988). Conclusions Metalliferous sulphides and related metalliferous and pelagic sediments associated with Greek ophiolites formed at, or near a spreading ridge within a Late Triassic-Early Jurassic small ocean basin. Terrigenous silt is ubiquitous, probably derived from the Pelagonian microcontinent to the east. In Othris, stockwork sulphides are represented by fault-controlled quartz-sulphide vein systems within pillow lavas. Mineralisation is locally found within volcaniclastic sediments. Steeply inclined stockworks (marked by sulphide mineralisation), greenschist facies alteration and qua~tz veining mark zones of high-temperature hydrothermal discharge. Small massive sulphides in Othris were precipitated as small fault-controlled bodies on the ocean floor. Underlying lavas contain disseminated sulphide now oxidised to gossans. In Othris, massive sulphides are directly overlain by ferruginous and siliceous oxide-sediments. The Mn-poor nature of the ferruginous sediments close to the Othris sulphideprecipitating areas reflects high-temperature vent discharge and the dispersal of oxide-sediments away from the spreading axis (where Mn-rich silica sediments accumulated). Silica in the ferruginous cherts ('jaspers') close to the sulphides is interpreted as mainly of hydrothermal origin, while radiolarian sediments accumulated in small hollows around the fringes of the sulphide field. Less siliceous, slightly manganiferous oxide-sediments were ponded into fault-controlled hollows in the lavas away from the main sulphide hydrothermal field (within 500 m). Widespread manganiferous ribbon radiolarites, tectonically overlying the Othris mid-ocean ridge-type lavas, are enriched in hydrothermal Mn and tracemetals and are interpreted as biogenic sediments mixed with Mn oxides derived from high-temperature axial vents a n d / o r off-axis low-temperature vents. Minor disseminated, vein and tiny massive sulphides occur in the Pindos ophiolite near the top

A.H.F. R O B E R T S O N A N D S.P. V A R N A V A S

of the extrusive succession. Sulphide-precipitating zones are recorded by localised, pervasive epidosite development in zeolite and greenschist facies lavas. Volcanic talus was shed from seafloor fault scarps and then overlain by hydrothermal oxide-sediment, mixed with mostly terrigenous silt. Finally, the different deposits record fragments of once extensive hydrothermal deposits, including small high-temperature hydrothermal sulphide fields (e.g. Limogardion), oxide-sediments mixed with terrigenous sediments and ponded along major seafloor fault-controlled depressions (Pindos) and widespread biogenic and manganiferous accumulations on the adjacent abyssal plain (N Othris). Acknowledgements For helpful discussions we thank A. Rassios, G. Jones, E. Valsami, D. Kostopoulos and JoR. Cann. A. Rassios and E. Valsami are particularly thanked for making available unpublished information. The manuscript benefitted from comments by P. Degnan, G. Jones, A. Rassios, E. Nisbet, E. Valsami and an anonymous referee. The work was partly funded by Patras University (to S.V.) and by the Carnegie Trust for the Scottish Universities (to A.H.F.R.). References Adanlides, N.G., 1981!. The form and enviromnent of the Kalavassos ore deposits. In: A. Panayiotou (Editor), Proceedings of International Ophiolite Symposium, Nicosia, Cyprus, pp. 117-129. Aubouin, J., Bonneau, M., Celet, P., Charvet, J., ChSment, B., Degardin, J.M., Dercourt, J., Ferri~re, J., Fleury, J.J., Guernet, C., Maillot, H.. Mania, J.tl., Mansy, J.L., Terry, J., Thi~bault, P.. Tsoflias, P. aed Verriex, J.J., 1970. Contributkm ~.l ia g&)logie des Hellenides: le Gavrovo, le Pinde et la zone ophiolitique subpelagonienne Ann. Soc. gt~ol., Nord., 91): 277-306. Barrett, T.J., 1981. Chemistry and mineralogy of Jurassic bedded chert overlying ophiolites in the North Apennines, Italy. Chem. Geol., 34: 289-317. Bertolani, M., Capedri, S. and Giacobazzi, C., 1981. Sulphide ore deposits in the ophiolite at Mt. Kodra (N. Pindos, Perivoli, Greece). UNESCO. An International Symposium on Metallogeny of Marie and Ultramafic Complexes: The Easlern Mediterranean-Western Asia Area and its Com-

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