Mafic-dominated volcanogenic sulphidedeposits in the Troodos ophiolite, CyprusPart 1–The deposits of the Solea graben

N. G. Adamides*

The Solea graben in the Troodos ophiolite of Cyprus is host to some of the largest and richest

cupriferous sulphide deposits on the island. The graben is oriented in a northwesterly direction

and defined by similarly oriented dykes and faults. The deposits within the graben display a

variety of characteristics which reflect their mode of genesis. They include deposits displaying

classic exhalative genesis, as well as others which formed at some depth below the seafloor, or

by fluids which travelled away from their source to deposit sulphide on the surface of the ocean

floor. A special case is the Phoenix deposit which is the result of supergene enrichment from the

weathering of massive sulphide. A strong control of ore deposition is evident for some of the

deposits by a major structure interpreted as an oceanic detachment fault. Other deposits are

localised at the intersection between axial structures and transfer faults. However, in all cases, an

underlying heat source appears to have played a major role in ore deposition. The location of the

deposits at the top of the volcanic sequence is consistent with an off-axis setting.

Keywords: Troodos ophiolite, Solea graben, Cyprus, VMS deposits, Mineralisation, Copper

IntroductionThe Troodos ophiolite (Moores and Vine, 1971) is afragment of Mesozoic ocean floor formed approximately91 million years ago (Mukasa and Ludden, 1987) andbrought to its present position as a result of the collisionbetween Eurasia and Africa during the Alpine orogeny(Gass and Masson-Smith, 1963). The ophiolite com-prises a complete sequence from ultramafic rocks at thebase, comprising mainly harzburgite and dunite, over-lain by gabbroic rocks, a sheeted dyke complex, and thePillow Lava Series (Fig. 1). This association is inter-preted as the result of partial melting of mantle material,now represented by the harzburgite, resulting in theformation of the overlying cumulates and sheeted dykes,and the extrusion of the lavas on the sea floor.

The sulphide deposits occur at all levels in theextrusive sequence, but are particularly associated withthe Pillow Lavas Series, with the largest and morecopper-rich deposits being associated with the UpperPillow Lavas. Geochemical studies, particularly subse-quent to the Cyprus Crustal Study Project, resulted inthe refinement of the volcanic stratigraphy into a lowerarc tholeiite suite (suite A), a depleted arc tholeiite suite(suite B), and a highly depleted boninitic suite (suite C)(Cameron,1985; Robinson and Malpas, 1990; Robinsonet al., 1983). Suite A roughly corresponds with the

Lower Pillow Lavas, and suites B and C are correlatedwith the Upper Pillow Lavas; however, the geochemicalboundaries rarely coincide with the mapped contactsbetween units, which were based on field criteria.Furthermore, local interbedding between units has beendocumented, suggesting a close spatial and temporalrelationship and a subduction initiation slab edge settinghas been recently proposed for the genesis of theTroodos ophiolite (Pearce and Robinson, 2010).

Formation of the deposits, which are of the Cu–Znmafic type (Barrie and Hannington, 1999) has beenlinked to hydrothermal activity at a spreading axis,similar to that identified and extensively studied atpresent-day equivalent settings such as the East PacificRise (Spiess et al., 1980; Haymon, 1982) and the Mid-Atlantic Ridge (Rona, 2005). Seawater circulation hasbeen invoked for the genesis of the deposits (Spooner,1977; Spooner and Fyfe, 1973) and this hypothesisappears substantiated by isotopic data (Heaton andSheppard, 1997) as well as extensive experimental workof basalt-seawater interaction (Seyfried and Bischoff,1977, 1979, 1981; Mottl, 1978; Mottl and Holland,1979). However, substantial contribution from mag-matic degassing has also been proposed by someworkers (Yang and Scott, 2002). Epidosite zones presentwithin the sheeted dyke complex which underlies thePillow Lavas Series have been proposed as the result ofextreme leaching of elements which formed the sulphidedeposits and overlying polymetallic sediments (Lydonand Jamieson, 1984; Richardson et al., 1987; Bettison-Varga et al., 1995; Jowitt, 2008).

N G Adamides Geological Services Ltd, Astromerites, Nicosia 2722,Cyprus

*Corresponding author, email adamide@logos.cy.net

� 2010 Institute of Materials, Minerals and Mining and The AusIMMPublished by Maney on behalf of the Institute and The AusIMMReceived 30 May 2010; accepted 10 February 2011DOI 10.1179/1743275811Y.0000000001 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2 65

The Solea graben (Varga and Moores, 1985) is aninterpreted north-northwest-trending tectonic featurewhich hosts some of the largest sulphide deposits on theisland. These include the Mavrovouni and Apliki depositsin the western end of the graben (Bear, 1963; Bruce, 1947)(Table 1) and the Skouriotissa group of deposits furthereast (Adamides, 1984, 1987; Constantinou, 1972; Cons-tantinou and Govett, 1973; Hutchinson and Searle, 1971).Although the details of the deposits have been recorded tovarying degrees in the past, there is no compilation ofinformation within the context of their structural settingand mutual relationships. This is the primary purpose ofthis work. In view of the inaccessibility of some of thedeposits, due to the ongoing partial occupation of theisland, information from historical records will be utilisedand compiled and placed in the context of the geologicaland structural setting of the mineralisation.

Historical outlineThe deposits of the Skouriotissa and Mavrovouni region(Fig. 2 and Table 1) have been known and exploited sinceancient times. Archaeological evidence exists for almostcontinuous exploitation for the last 4000 years. Majorslag heaps present at both Skouriotissa and Mavrovounitestify to the extent of ancient mining activity. It was theseslag heaps that attracted the attention of a youngprospector, Charles Godfrey Gunther, who was sent tothe island in 1914 by two American engineers, ColonelSeely Wintersmith Mudd and Philip Wiseman (Lavender,1962). Gunther initially discovered the nearby Skourio-tissa massive sulphide deposit, as a flat-lying lens ofmassive cupriferous pyrite, located directly beneath sedi-mentary rocks. Mavrovouni lay undiscovered for severalyears after initial drilling in 1919 had only returneddisseminated mineralisation giving the erroneous impres-sion that most of the orebody was of the disseminatedtype (Bear, 1963). When Professors Gilbert Cullis and

Broughton Edge visited the island in 1922 for the prepa-ration of their classic report on the cupriferous deposits ofthe island (Cullis and Edge, 1927) the site of the futureMavrovouni deposit was described as an area of extensiveiron staining; however, the intensity of alteration wasthought unpromising. Subsequent exploration by CyprusMines Corporation (CMC) outlined the richest deposityet to be found on Cyprus, comprising 15 million tonnesof massive pyrite assaying 4?5% copper and 48% sulphur,0?4% zinc 0?78 g t21 gold and 7?8 g t21 silver (Bear,1963), excluding the disseminated material surroundingthe deposit.

Strong oxidation at the site of the Apliki deposit, 3 kmsouth of Mavrovouni, attracted the attention of ancientprospectors. Exploration in the early twentieth centurystarted during the gold rush of 1935 and as a result, theunderlying sulphide mineralisation was intersected in 1937(Bruce, 1947). Partial mining of this material took placeat that time; however, the deposit was finally outlined andmined by opencut methods in the 1960s and early 1970s.Part of the oxidised ore, untreatable by flotation, wasstockpiled separately and now represents a valuableresource for hydrometallurgical exploitation. By the cessa-tion of mining in 1973, approximately 1 650 000 t aver-aging 1?8%Cu and 36%S were mined (Adamides, 1982). A

Table 1 Resources in the deposits of the Solea graben

Deposit ’000 tons Cu/% S/% Source

Mavrovouni 15 000 4.5 48.0 Bruce, 1947Mavrovouni 4th grade 11 000 0.30 31.4 CMC recordsEast Lefka 1200 1.60 14.9 CMC recordsApliki 1650 1.80 36.0 HMC recordsWest Apliki 3600 0.34 na HCM estimationPhoukasa 6000 2.25 46.0 Bruce, 1947Phoenix 40 000 0.40 na HCM estimationThree Hills 6174 0.37 na HCM estimation

1 Geological map of the Troodos ophiolite, showing location of major sulphide deposits. Adapted from 1 : 250 000 scale

mapping by the Geological Survey of Cyprus

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66 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

small quantity of low-grade material remains in the northside of the ore zone.

Immediately west of Phoukasa, a large mass of dissemi-nated sulphide mineralisation defines the Phoenix deposit.The orebody was partly developed by CMC as a pressure-leaching operation; however, mining was interruptedfollowing the Turkish invasion in 1974, and is currentlybeing exploited by hydrometallurgical methods.

The smaller deposits of Three Hills and West Apliki(Fig. 2) were discovered by CMC; however, with theexception of some development work, they were notexploited. Three Hills has now been partly mined byHellenic Copper Mines Ltd (HCM) as part of theirhydrometallurgical exploitation of the Phoenix deposit;however, a significant resource still remains.

Structure of the Solea grabenStructural studies of the Troodos ophiolite by Varga andMoores (1985) identified three asymmetrical N–NW-trending graben, defined by opposing, inward-dippingSheeted Dyke Complex domains and correlation withmajor sulphide mineralisation. These were termed fromwest to east, the Solea, Mitsero (or Ayios Epiphanios),and Larnaca graben. The axis of the Solea graben isinferred to coincide with the location of the Skouriotissadeposit, with the Mavrovouni deposit considered tohave formed in an off-axis setting. The extents of theSolea graben are considered to be bounded to the northby the sedimentary rocks, with the southern borderreaching as far as the Arakapas Fault Belt (Hurst et al,1994; Simonian and Gass, 1978).

Palaeomagnetic studies (Allerton and Vine, 1987 and1991) support the model proposed by Varga and Moores(1985) and suggest formation of the Solea graben bylistric faulting adjacent to a spreading ridge. The studyin the shallow intrusive and extrusive section of theSolea graben suggests rotations of up to 78u around axeswhich are parallel to the orientation of the dykes,consistent with the above interpretation. The graben isapparently terminated along an east–west set of faults tothe south, probably indicating the presence of a minortransform fault.

The general structure of the Solea graben, inferredfrom the above studies, is substantiated by extensive fieldwork and evaluation of geophysical data carried out bythe author. A north–northwesterly orientation of thedykes in the area of the Apliki deposits (Fig. 2), cou-pled with a steep northeasterly dip, suggests a similar

3 Stereographic projections (Fisher, equal area, lower

hemisphere) of poles to dykes in the Apliki region (A)

and south of Skouriotissa (B)

2 General geology of the Skouriotissa-Mavrovouni region. Compiled from CMC data (Mavrovouni region) and the author’s

field work (Apliki and Skouriotissa areas)

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Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2 67

orientation of the Solea graben, with the direction of dipof the dykes suggesting location of the axis in the presentnortheasterly direction (Fig. 3A). A slight change inorientation to a more northerly strike and steeper dips ofthe dikes in the area south of the Skouriotissa deposits(Adamides, 2001b) (Fig. 3B) is consistent with blockrotation probably as a result of underlying listric faulting.Such faulting is also inferred from the identificationwithin the Sheeted Complex of narrow shear zonesassociated with minor mineralisation, oriented parallel tothe northwesterly orientation of the graben and markingrotation of the diabase dykes to shallow dips.

The conclusions derived from surface geology aresupported by the magnetic signature of the region(Fig. 4). A system of axis-parallel northwesterly structuresis complemented by lineaments of transverse orientation.Such chequerboard pattern of magnetic lineaments ischaracteristic of the northern part of the Troodos ophiolite(Cooper, 1993), and is correlated with similar pattern onpresent-day spreading axes, such as the Mid-AtlanticRidge (McAllister and Cann, 1996) where the transversestructures are interpreted as transfer faults and generallymake angles of 60–70 with the axis-parallel faults.

The magnetic image also highlights in the area of theMavrovouni and Apliki deposits an extensive region oflow magnetic intensity, which is spatially associated witha major north-trending structure forming the boundarybetween the Sheeted Complex in the west and the pillowlavas in the east. The zone coincides with the northerlyextension of the Troodos Forest Fault (Hurst et al.,1994), which is associated with a steep hydrothermalgradient (Schiffman et al., 1987) and may be directlyrelated to the genesis of the Mavrovouni and Aplikideposits.

Geology of the sulphide deposits

Mavrovouni–Apliki groupMavrovouni

The deposit is presently inaccessible to detailed study, andmost of the information is extracted from the examina-tion of the meticulous records kept by CMC (Adamides,

2004). Geological mapping (Fig. 2) suggests that the siteof the deposit was characterised by extensive chloritisa-tion of the lavas. The deposit was located within theUpper Pillow Lavas, close to the contact with a northerlystructure which brings the Lower Pillow Lavas intostructural juxtaposition. This fault continues southwards,forming the boundary between the Basal Group andLower Pillow Lavas in the area of Apliki (Adamides,1982). The structure was not considered by early workersto be the feeder channel for the Mavrovouni depositbecause disseminated mineralisation continues across itwithout evidence of displacement or focussing of thehydrothermal fluids (Wilson, 1959).

Modelling of mined levels from historical records (Fig. 5)suggests that the deposit was elongate in a north–southdirection, and was locally cross-cut by similarly trendingzones of limonitic oxidation. This suggests that north-trending structures played a role in the channelling ofhydrothermal fluids and later acted as conduits for oxidisingfluids to descend to lower levels in the massive sulphide. Thedeposit was almost totally enclosed within the lavas, with

4 Magnetic signature of the western part of the Solea graben. Positive and negative symbols denote magnetic highs and

lows respectively. Interpreted aeromagnetic lineaments are also shown. The map is a compilation of CMC aeromag-

netic survey (Mavrovouni to Skouriotissa area) and a helicopter-borne survey (Dighem, 1999) for the Apliki area

5 Block model of worked levels of the Mavrovouni

deposit. Constructed from historical CMC data by the

digitisation of mined-out massive sulphide and limonite

ore from the original underground plans. Cell size:

x52 m, y52 m and z51 m

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68 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

only limited portions exposed at the contact with theoverlying sedimentary rocks.

Figure 6 is a north–south section derived from drillholerecords, and depicts the orebody as a series of disconnectedlenses of cupriferous massive pyritic ore enclosed within amass of disseminated low-grade mineralisation. The lavasoverlying the mineralisation are thickening northwards,and vary from fresh to variably altered and oxidised;however, a zone of propylitised and altered lavas inter-venes between the massive ore and the unmineralisedcover. The distribution of copper within the ore zonesuggests an association with high sulphur content, with theenvelope of disseminated mineralisation being generallylow in copper.

No clearly defined stockwork zone is present in theMavrovouni deposit, which is apparently underlain by anextensive layer of weaker mineralisation, with no indica-tion of a specific hydrothermal or structural conduit. Thisis in contrast to other similar deposits, e.g. Skouriotissa,Mathiatis and Limni (Adamides, 1975, 1984; Lydon andGalley, 1986) where the site of egress of the hydrothermalfluids onto the seafloor is generally defined by brecciationand silicification with abundant deposition of quartz andsulphides gradually decreasing in intensity with depth.

The Mavrovouni ore was similar in many respects tomassive ore from elsewhere in Cyprus, e.g. Skouriotissa(Constantinou, 1972), being described as having a frag-mental (conglomeratic) appearance with hard sulphideblocks enclosed in a sandy friable matrix (Bruce, 1947;Wilson, 1959). The texture was attributed to the replace-ment of pillows, initially around pillow margins and laterthrough a system of cracks into the entire pillow resultingin the fragmental appearance. In view of the possible sub-sea floor replacement genesis of this deposit, this inter-pretation may be more appropriate for most part of theMavrovouni deposit, with the exception of the limitedexhalative part where the hydrothermal fluids reached thesea floor.

East Lefka

The deposit is inaccessible to direct study as it is stillunexploited, and all information is derived from archivedCMC data (Adamides, 2004). The orebody is located atthe upper parts of the volcanic pile, beneath recentalluvium, and occurs in the form of disconnected lenses ofore in volcanic breccias which are interbedded with andunderlain by unaltered lavas (Fig. 7), without evidence ofa stockwork zone. The lithology of the ore, as describedin drillhole logs, was mostly in the form of nodulargrains of sulphide coated with sooty chalcocite and

accompanied by bornite and chalcopyrite in the glassymatrix of a volcanic breccia. The mineralised zone wasveined by grey and red pyritic jasper. The glassy lavabeneath the ore zone was commonly zeolitised, andcontained nodular sulphide in a mostly unaltered matrix.

Evidence for a possible transported nature of the EastLefka deposit is the large length/thickness ratio of theore zone, the absence of evidence for a channelway forthe hydrothermal fluids, and the intercalation ofsedimentary units both above and below the mineralisedhorizon. Intercalation between volcano-sedimentary andvolcanic rocks is a common feature of the immediateenvironment of the deposit.

Apliki

Recent mapping of the environs of the Apliki mine(Adamides, 2003a), coupled with the examination of oldCMC records, has brought to light the main features ofthe disposition of this structurally controlled deposit. Onthe eastern wall of the opencut, unmineralised LowerPillow Lavas are associated with hyaloclastic materialand thick columnar-jointed flows. Their contact with themineralised lavas is faulted. The lavas east of the fault areincreasingly chloritised as the contact is approached, andanalcite is joined by quartz as the vesicle-filling mineral inthe hanging wall lavas, suggesting the addition of silica aswell as alkalis in the lavas by the hydrothermal fluids. Onthe western side, fresh, hyaloclastite-rich Lower PillowLavas are exposed, whereas on the north wall, the contactwith the ore zone is defined by satin spar gypsum veiningassociated with leached lava and chloritic breccia, andintense shearing.

The exposed mineralisation is of typical stockworktype, with veins and cavity fillings of pyrite and subor-dinate chalcopyrite in fractured lavas. Jasper is wide-spread in veins in the altered lavas. Examination of the

6 North–south section through the Mavrovouni deposit

7 Geological section through the East Lefka deposit

8 East–west section through the Apliki deposit. Redrawn

from archived CMC data

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Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2 69

CMC records revealed that, in contrast to the picture thatemerges from the present geological associations, massivesulphide originally overlay the stockwork zone and thiswas in turn overlain by Upper Pillow Lavas andtuffaceous sediments (Fig. 8), suggesting that the massivesulphide mineralisation was structurally controlled withina mini graben and owed its preservation to the cover oftuffaceous units and lavas. Historical geological maps ofthe environs of the Apliki deposit prior to miningindicated the presence of limestone overlying the shalesin the area of the opencut, reinforcing the interpretationthat a much younger sequence, now removed by mining,occupied the space between the two bounding faults. Theore zone extends northwards in the form of low-gradedisseminated mineralisation while the southern exten-sions merge into altered ground and are mainly coveredunder waste dumps.

West Apliki

This concentration of predominantly disseminated-stylemineralisation is defined on the surface by an extensivearea of haematitic and limonitic oxidation. The deposit islocated within Lower Pillow Lavas, close to the faultedcontact with the Sheeted Complex (Adamides, 2001c;2003a), (Fig. 2). The mineralisation predominantly com-prises pyrite and chalcopyrite, with the sulphides oxidisedat higher levels into limonite, haematite and goethite. Atlower levels, pyrite is mostly preserved, but chalcopyrite isreplaced by chalcocite, bornite and covellite, with unal-tered chalcopyrite increasing in proportion with depth.

A controlling function in the deposition of themineralisation is played by a well-defined north–north-easterly trending fault which is exposed at various placesin the western end of the oxidation zone. The fault ismarked by strong shearing, and dips steeply to the east–southeast. The highest grades of the mineralisation are

concentrated in the hanging wall side of the structure,although chloritic alteration, silicification and low-grademineralisation locally persist into the footwall side.Furthermore, strong oxidation, which is mainly confinedto the hanging wall side, persists southwards along thefault, suggesting that the fault has acted as a pathway tothe mineralising fluids which replaced suitable lithologies,where more intense fracturing due to fault movementsprepared the ground for deposition of ore fluids. Anortherly trend of the structure is in agreement with asimilar trend and easterly dip of the dykes in the SheetedComplex in this area.

The mineralisation sharply terminates in the northerlydirection against another fault marked by shearing andhaematitic gouge, with unaltered Lower Pillow Lavas in thefootwall side. In the hanging wall side, the mineralisationdecreases in intensity southwards, and the altered chloritisedground beyond the ore zone is characterised by brecciation,widespread quartz and jasper veining and epidotisation.These associations have been interpreted as the result of theinteraction of hydrothermal fluids with oxygenated seawaterduring ore deposition (Adamides, 1984).

The lithological relationships at West Apliki suggest thatore localisation was controlled by the two orthogonalstructures which assisted in the focussing of the hydro-thermal fluids with deposition of the sulphides predomi-nantly in their hanging wall side, with the footwall side beingeither unaltered or chloritised but generally unmineralised.

The Skouriotissa depositsPhoukasa

The Phoukasa deposit (Fig. 9) conforms with the classicstyle of Cyprus-type massive sulphide deposits as initiallystylised by Hutchinson and Searle (1971) from observa-tions at Skouriotissa and North Mathiatis. A laterallyextensive lens of massive sulphide was locally overlain by

9 Geological map of the Skouriotissa area

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70 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

ochre and laterally resting on unaltered pillow lavas. Astockwork zone was implied to underlie the massivesulphide; however, initial exploration did not identify itspresence due to its limited extent compared to theoverlying massive pyritic lens.

Modelling of the Phoukasa deposit by the use of datafrom the work of Cullis and Edge (1927) highlights thelensoidal form of the massive sulphide and the truncatingrole of a north-trending post-mineralisation fault whichdownthrows the western part of the pyritic lens towardsthe west by a distance of 30 m (Fig. 10). The massivesulphide deposit is directly overlain by ochre, followed byumber of the Perapedhi Formation without any inter-vening lavas. The ochre has been extensively studied byConstantinou (1972) and interpreted as the product of thesubmarine oxidation of massive sulphide.

Directly underlying the massive sulphide lens was astockwork zone which comprised an association of quartz,pyrite and chalcopyrite which extends with diminishingintensity to lower levels, merging into the underlyingpervasively altered lavas. A lateral gradation of the stock-work mineralisation into unaltered lavas in the northernside of the deposit was described by Adamides (1984), andwas marked by a change from chlorite-dominated assem-blages in the stockwork zone to the smectite-dominatedunaltered lavas through an intermediate zone of mixed-layerclays. This transition defines a temperature gradient from300–350uC within the central parts of the stockwork pipe tolow-temperature assemblages in the areas away from centre.The Phoukasa massive sulphide was overlain in its easternextensions by a sequence of thin-bedded pyritic cherts,which are interpreted as hydrothermal in origin and similarto the siliceous exhalites in equivalent settings (Juniper andFouquet, 1988; Duhig et al., 1992a).

Phoukasa was separated from Phoenix by a majorstructure, the Skouriotissa Fault (Adamides, 1987), whichbrought the massive sulphide and unaltered olivinebasalts into structural juxtaposition (Fig. 11). Closelyassociated with this structure was an extensive layer ofauriferous leached lava which formed a subhorizontalblanket over the eastern part of Phoenix. This leachedmaterial, which in places consisted entirely of vuggy silicawith veins and disseminations of crystalline jarosite, wasoriginally overlain by the sedimentary units suggestingthat it is probably the result of the oxidation of massivesulphide mineralisation which was initiated at an earlystage in the history of the deposit. The present relation-ships are due to post-mineralisation dextral transcurrentmovements along the Skouriotissa Fault, which resulted

in the uplift and erosion of the western part of thePhoukasa lens, whose eastern extension was preservedunder the cover of umber and ochre.

Phoenix

The deposit (Adamides, 1987) (Fig. 12) is the only onepresently worked, and comprises an extensive body ofdisseminated mineralisation which extends in a westerlydirection almost to the area of Karyotis River (Fig. 9),where the alteration zone is displaced northwards by aconcealed structure. The mineralisation was limited to thenortheast by the Skouriotissa Fault; however, the contactsin all other directions are gradational. Typical examples ofsuch gradations from unaltered olivine basalts to miner-alised lavas are observable in the southeastern part ofPhoenix. In a southwards traverse from the olivine basaltsto the mineralised ground, earthy haematite initiallyappears in interpillow spaces within the unaltered lavas,increasing in abundance as the contact is approached,followed by incipient chloritisation which increases inintensity until it merges into the pervasively altered andmineralised ground.

The mineralisation at Phoenix is mostly representedby veins and disseminations of pyrite in pervasivelychloritised but only weakly silicified pillow lavas. Pillowstructures are discernible in numerous places, but,elsewhere, tectonic movements probably also associatedwith hydraulic fracturing resulted in the obliteration ofpillow structure. Extensive tectonic brecciation is parti-cularly evident in the area close to the SkouriotissaFault, where it is associated with widespread satin sparveining. Non-pillowed flows are locally present withinthe pillow pile, and these are invariably more poorlymineralised than the pillowed units; however, dykes areentirely absent. However, dykes are entirely absent andmineralisation is mainly in the form of replacement ofthe interpillow spaces as veinlets traversing the body ofthe pillows, and as lesser pyritic disseminations insidethe pillows.

Primary chalcopyrite is generally scarce in Phoenix,and has been observed in some quantity only very locally,such as the southern parts of the opencut (Fig. 13A). Themain copper minerals at higher levels in the oxidised zonewere oxides of copper passing at deeper levels intosupergene sulphides, predominantly chalcocite which inthe areas close to the Skouriotissa Fault, immediatelybeneath the blanket of leached lava, occurred commonlyin massive form closely associated with pyrite. Elsewhere,chalcocite-coated pyrite is the main form of copper ore.Atacamite was common in the supergene zone directlybeneath the leached lava and nodular delafossite is

10 Block model of the Phoukasa deposit, constructed

from data of Cullis and Edge (1927) by the digitisation

of original outline of massive sulphide. Cell size: x55,

y55 and z51

11 Geological section through the Phoukasa and Phoenix

deposits

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Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2 71

commonly described in CMC logs to accompany thesupergene assemblage.

At the current deeper levels of the deposit, the coppermineralisation is mainly represented by delafossite asso-ciated with goethite and native copper (Adamides, 2010)(Fig. 13B). An apple-green, sugary-textured mineral,tentatively identified as nontronite is a common associateof the ore minerals. Petrographic evidence suggests that itis paragenetically late, replacing both quartz and earlierchlorite (Fig. 13C). Its genesis may be related to thedownward percolation of iron- and silica-rich fluids undersupergene conditions (Harder, 1978). Its spatial associa-tion with the areas close to the Skouriotissa Fault is consis-tent with this interpretation. However, X-ray diffractionwork on visually similar material returned a natroalunitepattern (H. Prichard, pers. commun., 2010), and furtherwork is required to confirm the nature of the supergeneminerals.

Wall rock alteration is mainly represented by anassociation of quartz and chlorite, typical of most of theCyprus deposits. Chlorite replaces interstitial glass andferromagnesian minerals. Plagioclase crystals are com-monly replaced by a mosaic of smaller quartz crystals. Twogenerations of chlorite are commonly present: matrixchlorite, which is typically green and faintly pleochroicwith non-anomalous birefringence; and chlorite occurringin vesicles and veins, which is well-crystallised, green with abrownish tint, and faintly pleochroic with non-anomalousbirefringence. Previous petrographic work on Phoenix(Nicolaides, 1999) identified this second-generation well-crystallised chlorite as rectorite. In the vesicle paragenesis,chlorite occupies the walls and quartz the inner parts,probably suggesting that chloritisation preceded silicifica-tion. The intensity of alteration varies with lithology andlocation within the ore zone, and the more massive non-pillowed units are less altered than the pillowed lavas. Inthe latter cases, plagioclase is albitised and the matrix ofthe rock is composed of low-birefringence chlorite with

subordinate carbonate replacing plagioclase, which, incontrast to the lavas, is partly preserved.

Epidote is common in the marginal parts of the orezone, and abundantly present in the deeper parts of thedeposit, where it forms euhedral radiating crystalscommonly associated with quartz (Fig. 13D). It variesin colour from shades of pink to pistachio green,reflecting compositional variations. The genesis of themineral is associated with minimum temperatures of theorder of 200–250uC (Arnason and Bird, 1992) andincreased oxygen fugacities, and in the Cyprus hydro-thermal systems, it is commonly present in the marginalparts of the ore zones, as well as in the deeper extensionsof the stockwork zones where hydrothermal epidote maymerge into regional-metamorphic epidote.

Red jasper is widely present in the mineralised lavas,either in the form of veins or as material partly fillinginterpillow space. The jasper is commonly pyritic and locallymay be the product of mineralisation of pre-existinginterpillow sediments (Richards et al., 1989). However, itscommon association with fault zones, and the increasedpresence of jasper at the marginal parts of the ore zonesuggest a genesis related to interaction of the hydrothermalfluids with seawater. In addition to the blood-red haematiticjasper, grey cherty silica veins, probably representing itsreduced equivalent, are also present in the mineralised lavas.Biogenic forms identified in jaspers from Phoenix (Fig. 14)suggest a genesis by low-temperature silica–iron-rich fluidsclose to the area of high-temperature hydrothermal activity,as commonly observed in present-day (Emerson andMoyer, 2002; Little et al., 2004) as well as in ancientanalogous environments (Juniper and Fouquet, 1988;Duhig et al., 1992a, b).

Immediately west of Phoenix beyond the KaryotisRiver, an extensive area of chloritic alteration and jasperveining centred on the Aphisallos Ridge (Fig. 9) is thelateral extension of the Phoenix ore zone. No economicmineralisation has been identified at this locality;

12 Geological map of the Phoenix deposit

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72 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

however, the pervasive chloritisation and widespreadjasper veining suggest the action of low-temperaturehydrothermal fluids, as observed in modern analogoussettings (Rona, 2005).

Three Hills

The deposit is located southeast of Phoukasa (Fig. 9) andwas discovered by CMC, initially referred to as the K-Zone. A gallery was driven into the hillside and wassampled in detail (Fig. 15), the results of the samplinghighlighting the copper-rich nature of the mineralisation.However, no exploitation of the deposit was performeduntil 2003 when HCM exploited part of the deposit byopencut methods. The operations were temporarily inter-rupted during the slump in copper price and a significantresource still awaits exploitation.

The surface expression of the deposit was unimpres-sive, with the conspicuous multicoloured gossan of otheroccurrences, such as West Apliki, being absent, and theground characterised by generally weak iron staining andlocal stronger haematitic oxidation. Similarly to Phoe-nix, the mineralised lithology comprises entirely pillowlavas with local non-pillowed units; dykes are absent(Adamides, 2002). The rocks are pervasively chloritised inthe area around the deposit, and the mineralisation wassurrounded as well as overlain by an alteration envelope.

The ore mineralogy mainly comprised an association ofpyrite and chalcopyrite with local sphalerite (Adamides,2002). Pyrite is the most common sulphide mineral andoccurs in the entire mass of altered lavas either asdisseminations within the body of the rock or as veinscommonly in association with quartz. In the oxidisedzone, the pyrite is replaced by hydroxides of the goethite–lepidocrocite group. In the paragenetic sequence, pyriteappears to be the earliest sulphide to crystallise from the

hydrothermal fluids, generally occupying the walls ofveins, and deposited on quartz which lines the fractures.Although the pyrite is mainly in the form of thin veins ordisseminations, in areas of intense mineralisation, pocketsof massive pyrite form by total replacement of the hostrock. The mineral occurs in well-developed commonlystriated cubes or pyritohedra.

Chalcopyrite is present in many parts of the opencut,although in most cases it is partly or entirely replaced byits secondary minerals. It is intimately intergrown withthe other sulphide minerals in veins, and commonlyshows iridescent blue and red coatings as a result ofincipient oxidation, with widespread interstitial chalco-cite and covellite. In the more intensely oxidised parts ofthe deposit, chalcopyrite is replaced by an association ofcovellite and chalcocite. Paragenetically, the chalcopyr-ite is later than the pyrite, occupying the central parts ofveins often in association with sphalerite. In contrast tothe chalcopyrite which is variably oxidised, the sphaler-ite is entirely fresh, black in colour, with excellentcleavage and a honey-brown resinous lustre.

Quartz is the sole and ubiquitous gangue mineral,occurring in all parts of the deposit in the form of veinsand vesicle fillings. In the chloritised zone, it linesvesicles or forms thin veinlets of euhedral clear crystals.In the mineralised zone, it accompanies the sulphideminerals and generally lines the walls of veins indicatingits early position in the paragenetic sequence. However,the mineral is also intergrown with the sulphide mineralsindicating that its precipitation persisted throughout themineralising episode.

The Three Hills deposit is an ore concentration which isconsidered to have been deposited in a lithologically andstructurally amenable site, with ore deposition taking

13 Mineralogical aspects of the Phoenix deposit: (A) fracture-guided replacement of chalcopyrite by covellite and chalcocite;

(B) association of native copper and delafossite in altered lava; (C) possible supergene nontronite replacing earlier hydro-

thermal quartz and chlorite; (D) hydrothermal deposition of euhedral epidote and quartz in veins at the basal parts of the

Phoenix deposit. Abbreviations: COV5covellite; CPY5chalcopyrite; CU5native copper; DE5delafossite; EP5epidote;

GO5goethite; NO5nontronite; QZ5quartz

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Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2 73

place predominantly beneath the sea floor. Structurally, itis located on the southern extension of the Skouriotissafault, and the controlling structure may have been anoffshoot of this fault. The symmetrical distribution offaults and veins around this structural direction providessupport for this conclusion.

Discussion and conclusionsA description has been provided of the setting of thedeposits in the western part of the Solea graben. Thedeposits vary from the unequivocally exhalative, classicCyprus-type, typified by Phoukasa, to deposits formingin most part within the lavas, e.g. the Three Hills depositwhich probably never had an exhalative component.Subsurface deposition of the latter mineralisation bymixing of the hydrothermal fluids with seawater resultedin extensive chloritisation which characterises the localarea. A structural control for ground preparation andthe deposition of sulphides may have been provided bythe intersection between the southeasterly extension ofthe Skouriotissa fault and northerly structures.

The Mavrovouni deposit probably formed in mostpart within the lavas, as it is surrounded on all sides byaltered and chloritised lavas with a zone of disseminatedmineralisation overlying the more massive pyritic core(Bruce, 1947; Wilson, 1959; Bear, 1963). Locally thehydrothermal fluids may have reached the sea floor,depositing exhalative mineralisation and resulting in theformation of the East Lefka deposit in the form ofdisconnected lenses devoid of associated stockworkzones in the surrounding lavas, probably by movementof the sulphide-laden hydrothermal fluid down the localpaleoslope. A corollary of this inference is that thedensity of the hydrothermal fluids was higher than theambient seawater, resulting in ore deposition in localdepressions on the sea floor and not their dissipationinto the surrounding water, conforming thus to the type1 hydrothermal fluid of Sato (1972).

The genesis of the Phoenix deposit is interpreted to bethe result of supergene processes which were probablyinitiated at an early stage in the history of the deposit. Assuggested from the geological section (Fig. 11), if anoriginally geometrically balanced sulphide lens is assumed,a considerable part of the western extension of this lenswas dextrally translated and uplifted, with relation to theeastern part, along the Skouriotissa Fault. Weathering,initiated under submarine conditions but probably inten-sified after exposure to the subaerial environment, resultedin the generation of copious amounts of sulphuric acid by

breakdown of the massive sulphide (Seward, 1999) leavinga residue of leached auriferous lava composed mainly ofporous silica and jarosite. The gold previously contained inthe massive sulphide remained spatially associated withthis leached material; however, the copper descended insolution to lower levels where it was deposited in the formof chalcocite, using the abundant disseminated and veinpyrite in the Phoenix deposit as the catalyst for itsprecipitation. Iron- and silica-rich supergene fluids simi-larly moved downwards to deposit abundant natroalu-nite and nontronite, particularly in the areas close to theSkouriotissa Fault, replacing the pre-existing alterationassemblage. The deposition of nontronite is favoured bythe presence of abundant iron and silica in solution, as aresult of the oxidation of the massive sulphide, and thechange of physicochemical conditions from oxidising closeto surface to reducing at depth (Harder, 1978).

In the absence of the pyrite, the copper-rich fluidswould have been dissipated and lost from the immediateenvironment. Without this secondary enrichment, thePhoenix deposit would in most part be a vein-typemostly pyritic deposit with only minor local chalcopyriteveining. If the assumption is made that the grade ofPhoenix prior to the supergene enrichment was 0?2%Cu,the present resource which amounts to 40 million tonnesof ore of average grade 0?4%Cu would be produced bythe weathering of approximately 3?5 million tonnes ofmassive sulphide of the average grade of Phoukasa(2?25%Cu). This in turn suggests that the originalPhoukasa massive sulphide deposit was close to 10million tonnes in size.

Controls of ore depositionOne of the more intriguing aspects of the mineralisationin the Solea graben is the absence of unequivocalevidence of a structural control in the deposition ofsome of the ore concentrations. This observation has ledBear (1963) to suggest that an underlying heat sourcemay, in some cases, have been the primary factor for oredeposition. In the case of the Skouriotissa group, theSkouriotissa Fault may have played a role in groundpreparation, as it bisects the massive sulphide lens andits northwesterly orientation suggests that it may havebeen one of the axis-parallel structures, later rejuvenatedas a transcurrent fault. However, the role of thisstructure is local and its trace feathers out into a seriesof minor structures in its southeastern extensions,although northwestwards it may be extending as far asthe environs of Aphisallos ridge (Fig. 9). A more deep-seated cause for the deposition of the Skouriotissa group

14 Textures observed in jaspers of the Phoenix deposit: (A) association of colloform haematite bodies, in places with

central siliceous core, enclosed in microcrystalline, locally recrystallised silica, suggesting a colloidal precursor; (B)

rod-like haematite bodies enclosed in microcrystalline silica (cf. Little et al., 2004; Fig. 3B); (C) tubular haematite

forms of possible organic origin, enclosed in microcrystalline silica

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74 Applied Earth Science (Trans. Inst. Min. Metall. B) 2010 VOL 119 NO 2

may be envisaged by the localisation of the Phoukasamassive sulphide lens at the intersection between anorthwesterly axial structure and a northeasterly trans-fer fault, evident from the magnetic map (Fig. 4);however, an underlying cause, such as a gabbro stock,may be the cause of ore deposition at this location, sincesimilar structural intersections elsewhere are barren ofmineralisation. Hydrothermal circulation induced by alarge shallow intrusive feeder to the Upper Pillow Lavasis suggested for the genesis of the deposits (Bettison-Varga and Varga, 1989) and is generally considered apre-requisite for the generation of sulphide deposits(Large, 1977; Galley and Koski, 1999; Alt, 1999). Theassociation between high-level off-axis magma chambersfeeders to the Upper Pillow Lavas and mineralisationhad also been previously suggested by Adamides (1984)on the basis of observations at the Limni and Kalavasosmining districts.

Evidence for the presence of gabbroic intrusives under-lying the Skouriotissa deposits is suggested from descrip-tion of deep holes in historical CMC logs; however, theirrole in ore genesis cannot be confirmed without furtherevidence. Extensive epidotisation recorded in the rocksdirectly below the Skouriotissa deposits has been cited byJowitt (2008) as possible evidence of intense leaching dueto the passage of large amounts of hydrothermal fluids;however, the mode of occurrence of the quartz–epidoteassemblage mainly as vesicle fillings in the lavas suggests ahydrothermal origin of the epidote as part of the haloaround the areas of more intense sulphide mineralisation,and not as a residual product of hydrothermal leaching.

The role of high-level intrusives in the genesis of theMavrovouni group of deposits may be more substan-tiated than for the Skouriotissa group. As indicatedfrom surface geology (Fig. 2), there are widespreadintrusives in the region between the Mavrovouni andApliki deposits, mainly in the form of medium-graineddolerites concordant with the enclosing lavas, and thesemay be the surface manifestation of an underlyingmagma chamber which has driven circulation.

The northerly trend of the controlling structures forboth the Apliki and the Mavrovouni deposits is oblique tothe northwesterly trend of the Solea graben, and displays aclose association with the structure that forms the contactbetween the Sheeted Complex in the west, and the pillowlavas to the east in the area of Apliki. This structure, theTroodos Forest Fault (Hurst et al., 1994), may be traced

southwards into the Plutonic Complex. A close associationbetween this fault and hydrothermal activity has beennoted by previous workers (Schiffman et al., 1987), and issupported by findings in this work: extensive chloritisationand iron staining characterises the Sheeted Complex in theproximity of this structure, and thin (metre-scale) north-trending epidosite alteration is present in the diabase dykeson the Apliki-Lefka road south of the Apliki deposit. Theintense chloritisation mapped by CMC geologists at thenorthern continuation of the fault, the north-trending longaxis of the Mavrovouni deposit and the control of theApliki deposit by a possible splay of this structure (Hurstet al., 1994) suggest that this was probably the controllingstructure for the deposits of the Apliki–Mavrovounigroup. It is suggested here that this structure is a possibleoceanic detachment fault and its role in the focusing ofhydrothermal fluids is similar to that invoked for similarstructures in the Mid-Atlantic Ridge, e.g. at the TAGhydrothermal field (McCaig et al., 2007).

In conclusion, the deposits of the Solea graben in thearea examined exhibit a variety of modes of genesis, fromthe purely exhalative (Phoukasa, Apliki), to subsurfacereplacement (Mavrovouni, Three Hills) and supergeneenrichment (Phoenix), to deposits devoid of a stockworkzone such as East Lefka which probably formed as a resultof deposition on irregularities of a paleoslope from fluidswhich contemporaneously were forming the Mavrovounideposit. The lack of strict axis-related structural controland their stratigraphic location at the top of the PillowLava Series is consistent with formation in an off-axissetting. Hydrothermal fluids were probably triggered byhigh-level intrusions, and, in the case of Mavrovouni, therole of the major Troodos Forest Fault may have beencritical in controlling ore deposition.

Acknowledgements

Grateful thanks are due to the Management of HCMLtd, and in particular to its Chief Executive Officer MrC. Xydas, for permission to publish this work. Thanksare also extended to two anonymous reviewers forconstructive comments on the manuscript.

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A number of errors in the print version of this paper were corrected before publication of the online version,which should be viewed as definitive. An erratum detailing the changes will appear in the next printed issue of thejournal (Vol. 119, No. 3).

Adamides Mafic-dominated sulphide deposits in the Troodos ophiolite, Cyprus: Part 1

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