Phanerozoic Metallogeny of the Caucasus Region during the...

saqarTvelos mecnierebaTa erovnuli akademiis moambe, t. 10, #3, 2016

BULLETIN OF THE GEORGIAN NATIONAL ACADEMY OF SCIENCES, vol. 10, no. 3, 2016

© 2016 Bull. Georg. Natl. Acad. Sci.

Geology

Phanerozoic Metallogeny of the Caucasus Regionduring the Tethys Ocean Subduction and at thePost-Collision Stage

Vladimer Gugushvili*, Tamar Beridze*, Sophio Khutsishvili*,Ramaz Migineishvili*

* Alexandre Janelidze Institute of Geology, Ivane Javakhishvili Tbilisi State University, Tbilisi

(Presented by Academy Member Irakli Gamkrelidze)

ABSTRACT. The interrelation of geodynamic development, volcanic activity and metallogeny of theCaucasus region is determined by subduction at the pre-collision stage, as well as by synorogenicmagmatic activity at post-collision setting. Pre-collisional development at the normal subduction stageincludes island arc setting, calc-alkaline volcanism and gold-copper-base metal mineralization.Transformation of subducting slab (roll back, break off, detachment and delamination) was related tomantle diapir and spreading revealed in back/inter-arc settings. It resulted in tholeiite-alkali olivinebasalt and shoshonitic volcanic activity and in copper-zinc-pyrite mineralization as well. In the course ofa strengthening the diapir incursion the back-arc transformed into a small ocean basin, where ophiolitevolcanism and copper-pyrite mineralization occurred. Transformation of subducting slab (TSS) tookplace along its dip and laterally as well, which mainly manifested itself in modes of geodynamicdevelopment, volcanism and metallogeny. The post-collisional development commenced after the closureof the ocean and is characterized by high grade of gold and low grade of base metals associated of raremetals (Sb, W, Mo and Hg). The high geochemical background of rare metals is a geochemical indicatorfor post-collision setting, unlike the pre-collision setting. At the same time this association is a prospectingguide to gold mineralization. © 2016 Bull. Georg. Natl. Acad. Sci.

Key words: pre-collision setting, island arc, back-arc, inter-arc, gold-copper, base metals

The Caucasus region has been the part of Eura-sian active margin. Its geodynamic development wasrelated to subduction, collision and closing of theTethys Ocean during ongoing convergence of Eura-sian and Afro-Arabian continents.

In response to pre/post-collisional events the dis-tinct metallogenic episodes occurred that are exam-

ined in detail in V.Gugushviliґs monograph [1] as wellas in a number of publications [2-10].

It is established that at pre-collisional stage, trans-formation of subducted slab (TSS) was responsiblefor specific linkages between geodynamic settings,magmatism, and metallogeny. In the course of normalsubduction (without TSS) the island arc setting, calc-

80 Vladimer Gugushvili, Tamar Beridze, Sophio Khutsishvili, Ramaz Migineishvili

Bull. Georg. Natl. Acad. Sci., vol. 10, no. 3, 2016

alkaline volcanics and gold-copper base metal miner-alization were formed. The TSS resulted in mantlediapir incursion, enrichment of magma with mantlecomponents, spreading, and back/inter-arc rifting. Atthe first stage of rifting, when diapir incursion andmantle influence were comparatively weak, thevolcanism was characterized by shoshonitic-trachyandesitic compositions. Further continuationof these transformations led to the intensification ofdiapir incursion and spreading, which in turn causedtholeiitic, alkaline olivine basaltic and picrite basalticvolcanism as well as formation of zinc-copper sulfidemineralization. At this stage the mantle influence ismore conspicuous by geochemical and petrochemi-cal indicators. The farther intensification of diapirincursion and spreading caused conversion of back-arc in the small ocean setting with ophiolite volcanicactivity, ultramafic dunite-peridotite magmatism andCyprus type copper-pyrite mineralization.

The pre-collisional stage continued until collisionand formation of ophiolite sutures. In the central seg-ment of Eurasian active margin, including Iran, Cau-casus, Turkey and Balkan–Carpathians, the subduc-tion commenced in the Late Proterozoic and contin-ued up to Late Eocene suturing [1]. The closure ofTethys Ocean in the Oligo-Miocene and stressing

African-Arabian continent on the Eurasian initiatedthe stage of post-collisional development. It resultedin formation of the fold-thrust structures as well as insynorogenic intrusive activity. These events con-tributed to the specific metallogenous features char-acterized by high grades of gold and low grades ofcopper-lead-zinc mineralization in close associationof rare metals – Sb, W, Mo, Hg. This association is ageochemical indicator of post-collisional situation,but is unlike to pre-collisional setting [1].

So, the both pre-collisional and post-collisionaldevelopments are tightly related to TSS.

The geodynamic development of the Caucasusis the distinct example of interrelationship betweenpre/post-collisional processes and metallogeny con-trolled by TSS.

In the Caucasus, the island arc setting related tonormal subduction, temporary and spatially alternatedwith the back/inter-arc settings, which were formeddue to TSS and diapir incursion. The TSS took placealong its dip from south to north, as well as laterallyfrom west to east. The pre-collisional stage in theCaucasus started in Paleozoic and lasted until LateEocene, before formation of suture zones.

Normal subduction gave rise to the calc-alkalineandesite-basalt-dacite suite in the Paleozoic Dizi se-

Fig. 1. Schematic map of the main tectonic units of the Caucasus and adjacent areas, after Sh. Adamia

Phanerozoic Metallogeny of the Caucasus Region during ... 81


ries at the southern slope of the Great Caucasus [2].To the north, the TSS and incursion of mantle diapircaused formation of inter-arc rift in the Fore Rangezone of the Great Caucasus. This event resulted information of Paleozoic tholeiitic and rhyolitic volcanismand copper-zinc-sulfide mineralization of the Khudesgroup of deposits (Khudes, Urup, Daud) (Fig. 2-I).According to iron fractionation the tholeiites belongto abyssal tholeiites, whereas by Ti content and K/Rbratio they correspond to island arc tholeiites [11]. Suchgeochemical dualism is typical of basalts of moderninter-arc rifts of New Georgia and Hebrides [11]. Themineralization of Khudes group of deposits does notcontain the lead, so sialic crust material did not partici-pate in the mineralization process. The source of zinchere might be the subducted basaltic slab, as well asbasaltic crust in the process of spreading, but coppermight be derived from the mantle diapir [1].

Fig.2-I presents a relation between volcanism andmetallogeny in normal subduction setting and in theregime of TSS. The normal subduction is responsiblefor calc-alkaline volcanism of andesite-basalt-dacite–rhyolite composition of the Dizi series, but the north-vergent transformation of dipping slab is a key forthe inter-arc rifting with tholeiite volcanic activityand zinc-copper sulfide VMS type mineralization.

In the Caucasus region the northvergent TSS alsooccurred during Early Jurassic time (Fig.2-II). Thenormal-subduction-related calc-alkaline basalt-andesite–dacite volcanics are known in the Loki-Garabakh zone of the Lesser Caucasus [3]. Volcanicactivity here started in the Liassic (Hettangian-Sinemurian) and lasted until Neocomian stage. Tothe north, in the Caucasian intermountain region (theGeorgian Block) the normal-subduction-related calc-alkaline volcanic activity is established in the Liassic(Hettangian-Sinemurian) and lasted until Aalenianage. Here the Paleozoic Loki and Dzirula salients areoverlain by calc-alkaline rhyodacitic volcanic suites[2]. At the same time, the northward-subducting slabsubjected to transformation that manifested itself inincursion of mantle diapir and spreading, as well as

in formation of the back-arc basin (marginal sea),where turbidite sedimentation, tholeiite volcanism andrelated VMS type pyrite-chalcopyrite-sphalerite-pyrhotite mineralization (with minor lead and gold)occurred (at the southern slope of the Great Cauca-sus). This mineralization is represented by Filizchaigroup of deposits (Filizchai, Katsdag, Kizildere,Adange). The bottom of Lower Jurassic marginal seaat the stage of spreading was partly underlain bysialic crust. Its relics on the basaltic crust are fixed upto date [12]. Presumably, this sialic crust was a sourcefor gold and lead of these deposits, whereas copperis probably derived from mantle diapir, and zinc mightbe sourced from subducting slab and/or basaltic crustin the process of spreading [1]. The tholeiites hereare characterized by back-arc geochemical indicators:low REE contents, normal chondrite characteristicsof Ni and Ti [10].

The northvergent transformation of normal sub-duction is fixed as well in the Middle-Upper Jurassic(Fig.2-III). The andesite-basalt-dacite-rhyolite calc-alkaline volcanic series in the Loki-Garabakh zone ofthe Lesser Caucasus formed due to the normal sub-duction processes. Significant gold-copper-basemetal porphyry, epigenetic, and Kuroko-type VMSdeposits (Shamlug, Alaverdi, Gedabek, Karadag,Chovdar etc) are related to these volcanic series. Tothe north, in the Georgian Block, the subducting slabexperienced the transformations to stipulate forma-tion of Upper Jurassic (Kimeridgian, Tithonian) alka-line-olivine basaltic and trachytic suite intersectedby monchiquite and camptonite stocks [13]. On thebase of drilling materials in the Rioni river depressionof the Georgian block, M.Lordkipanidze [14, 15] de-fined a thick (2200m) volcanic series of tholeiitic, high-Ti olivine basaltic and trachytic compositions andinterpreted the series as the products of interplaterifting. We suppose that formation of the back-arcsetting in the Georgian Block was related to TSS,incursion of mantle diapir and spreading.

In the Caucasus similar situation also occurred inCretaceous (Fig. 2, IV). In the Artvin-Bolnisi and



Fig. 2. Precollision and postcollision development and metallogeny excmplified on the Caucasus region. mineralization1. subducted slab, 2. basaltic crust, 3. sialic crust, 4. calc-alkaline volcanic series, 5. shoshonite series, 6. tholeiite andalkali olivine basalt series, 7. VMS mineralization, 8. granodiorite porphyry, 9. fold-trust zone, 10. faults.Precollision mineralization: -Au, Pb, Cu, Zn; - Pb, Zn; - Zn, Cu; - Zn, Cu, Pb;Postcollision mineralization: - Au, Cu, Zn, Pb assocated Sb, W, Mo, Hg; Mo, Cu, Au.



Somkhit-Garabakh zones of the Lesser Caucasus thenormal subduction-related calc-alkaline island-arc-type volcanic activity occurred. In the Bolnisi oredistrict (the eastern part of the Artvin-Bolnisi zone)the Senomanian-Santonian andesite-basalt-rhyodacite volcanics host the gold-copper-base met-als mineralization that are related to porphyry mineralsystem [1]. In Campanian, in response to deforma-tion of this subducting slab, the island arc settingtransformed in the incipient stage of back-arc struc-ture resulted in mantle diapir incursion, as well as information of high-Ti and high-Mg alkali olivinebasalts and trachyandesites of the Shorsholety suite(Fig. 2-IV). This suite has geochemical and petro-chemical characteristics distinctly diagnostic of back-arc setting [1]. According to TiO2 /P2O5 ratios, G.Nadareishvili [16] referred the Shorsholety suite to avolcanic formation of continental rift, which is con-trolled by deep faults.

87Sr/86Sr ratios of normal-subduction-relatedTuronian-Santonian volcanic formations of theBolnisi ore district range from 0.710 to 0.715 and aremore consistent with that of island-arc-type volcanics,and 208Pb/204Pb ratios are around 38. 87Sr/86Sr ratios ofthe Shorsholety suite that is related to CampanianTSS and mantle diapir incursion do not exceed 0.705.

The similar situation was described in thePanagyurishte ore district (Bulgarian Srednegorie),which is also a part of the same Eurasian metallogenicbelt [4]. Here the Upper Cretaceous volcanism andmineralization were also controlled by two stages ofsubduction: (i) calc-alkaline volcanism was related tonormal subduction, whereas (ii) transformations ofsubducted slab (roll back and detachment) led to in-cursion of mantle’s material and transition of islandarc situation to incipient stage of back-arc.

In the Bektakari ore cluster of the Bolnisi ore dis-trict the transformation of subducted slab and diapirincursion are manifested in the hydrothermal altera-tion and metallogeny. At the first stage the alkali-carbonate hydrothermal fluids resulted in the potas-sium feldspar alteration and silicification, as well as

in non-sulfide gold mineralization. The second stageinvolves the intensification of mantle diapir incur-sion and high temperature hydrosulfide fluid activityto generate gold-copper-base metal mineralizationand ore wall rock high temperature epidote-zoisitepropylitization. It is noteworthy, that here sulfide min-eralization cemented quartz-K-feldspar breccias, butthe epidote-zoisite propylitization is superimposedon the quartz-K-feldspar metacomatites [1].

The more intensive transformation of subductedslab occurred in the Georgian Block area (Fig. 2-IV),where the Turonian–Santonian Mtavari suite iscropped out. This suite consists of picrite-basalts,alkali olivine basalts, trachyandesites and trachytes.They are intersected by numerous phonolite ultraalkaline extrusions [13, 17]. The Mtavari suite showsa back-arc-related signature, based on petrochemicaland geochemical data and is characterized by highcontents of TiO2, MgO, P2O5, V, Co, Ni and Cr [17]. Itshould be noticed that in this suite the high tempera-ture epidote-zoisite-actinolite regional-scalepropylitization is recognized, presumably associatedwith mantle diapir incursion.

Transformation of the subducted slab and relatedmantle diapirism continued in Eocene. It is stronglyexemplified in rifting that initiated in Cretaceous inthe Achara-Trialeti zone of the Lesser Caucasus (Fig.2-V). The Cretaceous volcanics are represented hereby calc-alkaline andesite-dacite volcanic series in-cluding shoshonitic volcanics [15]. In the westernpart of Achara-Trialeti zone the Eocene volcanic se-ries of tholeiitic and alkaline olivine basaltic compo-sitions are exposed. The series thickness exceeds5000m. Geochemical and petrochemical peculiaritiesof these rocks are diagnostic of back-arc magmatismthat is governed by slab transformation and mantlediapir incursion [15]. It is known as Chidila suite.Chidila suite is underlain by Nagvarevi suite repre-sented by shoshonites and trachyandesites. By pet-rochemical characteristics they are comparable tomagmatism of the incipient stage of back-arc setting.Chidila suite is overlained by Upper Eocene series



(Adigeni suite) including shoshonites,trachyandesites and dellenites. They differ in somepetrochemical and geochemical features from thenormal-subduction-related calc-alkaline volcanics[14, 15]. We suggest that formation of this UpperEocene series occurred in response to a slackeningof processes of TSS and diapir incursion at the wan-ing stage of late back-arc system.

In the western part of the Achara-Trialeti zoneboth Middle Eocene olivine basalts and Upper Eoceneshoshonites are intersected by granosyenitic andsyenitic-dacitic stocks (Merisi, Namonastrevi andUchamba intrusives). These stocks were the mainfluid flow pathways from deep magmatic chambersand control both porphyry copper-gold and lowsulfidation epithermal gold mineralization.

The deformation of subducted slab caused for-mation of the interarc setting of the Achara-Thrialety.Southern of Achara-Trialety in the Turkish Pontidesand Artvin-Bolnisi zone Cretaceous calcalkaline andEocene shoshonitic volcanic activity occurred. Sohere, also, normal subduction from south to northalternates with TSS.

Besides that the lateral TSS is established to thenorth from the Izmir-Ankara-Erzincan-Sevan suturezone, in the limits of Lesser Caucasus, namely in bothEastern Black Sea-Achara-Trialeti and Talish-SouthCaspian zones (Fig. 1 and 3) [14, 15]. In the biogra-phy of both zones there were distinctly readable lat-eral conversions of back/inter-arc paleorift structureinto small ocean basin: (i) Achara-Trialeti paleorifttransformed to Black Sea small ocean basin to thewest, and (ii) Talish paleorift transformed to CaspianSea small ocean basin to the east. Presumably in ei-ther direction an intensification of the TSS processand diapir incursion took place.

Furthermore, in the western part of the Achara-Trialeti zone (the Achara-Guria region) the MiddleEocene tholeiitic-basaltic volcanic series is laterallychanged eastward to shoshonitic-trachyandesitic-dellenitic series (Akhaltsikhe region) further eastwardto calc-alkaline andesitic-dacitic series (around theAchara-Imereti and Trialeti mountain ridges) [14, 15,

18]. This picture might be determined by a lateralslackening of the processes of TSS and diapir incur-sion, as well as by eastward transformation of back/inter-arc rifting to normal subduction. Consequently,mantle’s influence is gradually decreased to the east.In particular, tholeiitic-basaltic volcanic series ishigher in magnesium and titanium than theshoshonitic-trachyandesitic-dellenitic series. MgOconcentration in tholeiitic-basaltic volcanic series isin the limits of 7-8%, TiO2 mainly varies from 0.6 to0.8% sometimes exceeding 1.5%; SiO2 ranges from 44to 48%; whereas in the shoshonitic series SiO2 is upto 54-70%, MgO is less than 3%, TiO2 varies from 0.2to 0.4%. Besides that Shoshonitic-trachyandesitic-dellenitic series is characterized by high contents ofalkalies: sum of Na2O+K2O is about 10-12%, whereasthat in calc-alkaline andesite-dacites is less than 4%[14, 15, 18].

It is noteworthy that ratio of 87Sr/86Sr in the rocks ofshoshonitic series is 0.7041-0.7045 [19], whereas that incalc-alkaline series is definitely higher - 0.708-0.715.

The interarc tholeiite-basaltic series of the Achara-Thrialety regionally are substituted by high tempera-ture epydote-zoisite-actinolite propylitization [20],whereas the shoshonitic series volcanics are alkali al-tered and substituted by lower temperature chlorite-albite and zeolite propylitization. Thus, intensity of diapirincursion and mantle influence revealed as on the mag-matic trend, so on the character of fluid activity.

Transformation of SN dipping subducted slabresulted in the Tallish backarc formation, which isbordered by Eocene trachyandesite-shoshonite vol-canic series southwards (Fig.3). The latter overliescontrolled by normal subduction Cretaceous calc-alkaline andesite-dacite volcanic suite. During theEocene the subducted slab transformation firstly wasmanifested in the formation of shoshonite volcanicseries. Further strengthening of transformation anddiapir incursion revealed in the formation of Talishbackarc with related alkali olivine basalt-phonoliteseries. Petrochemical and geochemical backgroundof Talish bacark volcanics is similar to those of theAchara-Thrialeti.



In the Talish backarc setting the Middle Eocenebasalts are overlain by Upper Eocene volcanic-sedi-mentary suite, dissected by peridotites, gabro-peridotite and picrite stocks and complex of dikes[21]. It is noteworthy that in the Achara-Thrialetimantle influence is weakening till Upper Eocene andformation of shoshonite series takes place in UpperEocene. On the contrary, in the Talish backarc set-ting the mantle influence strengthening is evidencedby intrusion of ultramafic peridotite stocks.

Thus, in the Caucasus, at precollision stage ofgeodynamic development, magmatism andmetallogeny are controlled by character of subduc-tion and transformation of dipping slab. The normalsubduction revealed in calc-alkaline volcanism andgold-copper base metal mineralization, whereas trans-formation of subducted slab revealed in the forma-tion of backarc-interarc and minor ocean settings.The backarc and inter-arc settings are characterizedby tholeiite and alkali olivine basalt volcanism andmainly by zinc-copper sulfide mineralization, wheregold and lead are known as a traces. The exclusion isthe stage of backarc setting, where sialic crust par-ticipates in the mineralization. Here in ores occursthe subordinate amount of gold and lead (Filiz-chai

group of deposits). In case of slab transformationand diapir incursion strengthening the backarc set-ting transforms into the minor ocean stage of theBlack and Caspian seas basins, so as in the associ-ated Kьre complex represented by ophiolitesultramafic dunite-peridotite intrusive bodies and Cy-prus type copper- pyrite mineralization [1].

The closure of Tethys Ocean and stressing the Afro-Arabian continent on the Eurasian margin led topostcollisional stage of development of the Caucasusregion accompanied by the formation of gold-copperbase metal and lowsulfidation epigenetic gold minerali-zation. The postcollisional metallogeny distinctly dif-fers from precollisional one. It is characterized by highgrade of background gold and the low trend of basemetal mineralization in the proper sulfide ores, whereaslow-and nonsulfide gold mineralization is representedmainly by gold-antimony and gold-sheelite quartz veinsand stockworks. At the same time postcollision propersulfide and low sulfidation gold mineralization coincideswith rare metals (Sb, W, Mo, Hg) association, which isnot characteristic for similar precollision mineralization[1]. Among them the only exclusion is molybdenum,which participates in the precollision island arc ores.The association of rare metals is characterized for

Fig. 3. Schematic map reflects the E-W lateral geodynamic transformation of subducted slab above IAES suture , shownthe character of the Eocene volcanic series in the East Pontides and Lesser Cauacasus. BS-Black Sea, CS-CaspeanSea, GC-Great Caucasus, SSC-Southern Slope of Caucasus, TC- Transcaucasus, AT-Achara-TRialety, LS-LesserCaucasus, EP-East Pontides, BSMO-Black Sea Minor Ocean, T-Talysh 1-ophyolites, 2-alkaline olivine basalts andtholeiites of bakarc settings.3.- Eocene calc- alkaline volcanic series of island arc, 4-Shoshonite series, 5-Creta-ceous calc-alkaline series of island arc.



postcollision setting as in ores, so in ores wall rockaltered zones, so generally in hostrocks.

The investigation of postcollision setting in theEurasian active margin area along the border of Iran,Caucasus, Turkey and Balkans exhibited, thatpostcollision setting commenced in the Oligo-Miocene and everywhere is characterized by abovementioned criteria [1]. The similar situation is evi-denced in postcollision settings of the various agesworldwide [22-24] and is characterized by mentionedrare metals association which represents thegeochemical background of the settings.

It is well known that different settings of theprecollision stage of development are characterizedby distinct geochemical criteria - 87Sr/86Sr, 208Pb/204Pbratios, grades of chondrite and REE etc. On the con-trary the postcollision setting, which comprises vari-ous rocks of the precollision stage, lacks any distinctgeochemical criteria. The geochemical indicators ofthe precollision setting were established in the unal-tered magmatic and volcanic rocks, whereasgeochemical indicators of postcollision setting is rep-resented by rare metals association (Sb, W, Mo, Hg)formed as a result of hydrothermal alteration of thehostrocks. Accordingly this association is generallyregarded as the geochemical indicator forpostcollision settings.

The postcollision development of the Caucasus(the Main Range and Southern Slope) and of theMegri-Ordubad zone of the Lesser Caucasus is shownbelow (Fig. 2, VI).

In the Megri-Ordubad Cenozoic magmatic province,significant gold-molibden mineralization is related to theOligocene-Miocene granodioritic stocks (Kajaran andAgarak deposits) associated with minor Sb, W and Hgquantity. In the Sevano-Akera suture the dacite por-phyry stocks control substantial gold mineralization inquartz-antimony veins and stockworks (Zod andMerhadzor deposits). Ores and orewall rocks are asso-ciated with presense of Sb and W [1].

The postcollision gold mineralization coincideswith Sb, W, Mo and Hg association widespread in

the fold-thrust zone of the Caucasus (Fig.2,VI). Heregold and above mentioned rare metals mineralizationis related to the orogenic stage of postcollision set-ting development. The most significant among themis the Zopkhito deposit, represented by epithermallow sulfidation quartz-antimonite veins and gold-copper base metal mineralization. High gold grade inZopkhito deposit occured on the low trend of basemetals. Synore quartz-sericite zone is goldbearing aswell and is characterized by high grade of antimony.The goldbearing veins cross-cut lower Jurassicshales. The gold grade in the veins is 4.35 ppm, sil-ver-4.15 ppm. The gold resource of the deposit is34.110 t., Sb – 41223 t., silver -39.241 t.

In the fold-thrust belt of the Caucasus are knownnumerous goldbearing rare metals ore manifestationscontrolled by Oligo-Miocene dacite extrusive domesand granodiorite stocks (Avadhara, Akhey, Notsarulaetc.). Another orogenic vein type deposit is theLukhumi where gold-antimonite-arsenopyrite miner-alization is controlled by faults and shear zones. Thedeposit is hosted by Upper Leassic shales and lime-stones and is presented by quartz-antimonite-carbon-ate-realgar-orpiment veins and quartz-carbonate andquartz-sheelite stockworks. The gold grade in the veinsis 5.10 ppm, As-6.7%, Sb-7.37%. The ore reserves483000 t consist of Au-14.04 t, Sb-2580 t, As -1800 t.

Abundant rare metals occurrences are known inthe fold-thrust zone as well: Carobi molybdenum de-posit with Mo grade 9.8% (Mo reserves 50 t.), Notsarasheelite mineralization with grade of W-35%, Au-2.3ppm. Mineralization is controlled by Cenozoic granitoidstocks. Here, also, occur mercury occurrences associ-ated with Sb: Akhey - 0.34% Hg (reserve2564 t.),Avadhara-Hg – 0.29% (1353 t.), Akhahcha Hg- 0.5%(2200 t.). The mineralization is localized in the LowerJurassic shales and controlled by fault zones.

In the Caucasus to the regional fault is relatedHokrila–Achapara ore manifestation. Gold is associ-ated to Sb and W here. The mineralization is hostedby goldbearing quartz- sheelite, quartz-pyrite, quartz-polymetallic and quartz veins. The gold grade in the



ores reaches 3-4 ppm [25].So, postcollision mineralization is characterized

by high grade of gold and low trend of base metals.Gold is associated by the rare metals (Sb, W, Mo, Hg)which represent the prospecting criteria for the goldmineralization. At the same time these rare metalsparticipate in antimonite, sheelite, wolframite andmercury deposits.

The genesis of gold and rare metals inpostcollision settings is related to transformation ofthe subducted slab in the depth and incursion ofhigh temperature fluid flows in the lithosphere. Thefluids were leaching gold and rare metals from thicksialic crust of the orogene and depositing them asporphyry and epigenetic mineralization with the highgrade of gold and rare metals and low trend of basemetals.

Postcollision setting is characterized by highgeochemical background of indicator rare metals (Sb,W, Mo, Hg). Accordingly this complex of rare metalsis the geochemical indicator of the postcollision set-ting and they are absent in precollision situation.

Thus, investigation in the Caucasus region ex-posed following tendencies in the interrelation ofgeodynamic development with magmatism andmetallogeny:

– At the precollision stage of development theisland arc setting spatially and temporary is control-led by normal subduction, evidenced by interrela-tion of calc-alkaline volcanism and gold-copper basemetal mineralization. Transformation of subductedslab and mantle diapir incursion initiated spreadingand therefore backarc-interarc settings revealed inthe olivine basalt tholeiitic and shoshonitic volcanicactivity followed by zinc-copper-pyrite VMS miner-alization. The intensification of slab transformationand diapir incursion caused further transition of thebackarc into Minor Ocean setting accompanied byophiolite volcanism, ultramafic dunite-peridotite mag-matic activity and Cyprus type copper-pyrite miner-alization.

– The metallogeny of the island arcs with gold-

copper base metal mineralization is conditioned byparticipation of the sialic and basaltic crusts and themantle material. The metallogeny of backarc-interarcsettings (without participation of the sialic crust) re-vealed in the zinc-copper-pyrite mineralization. Theoceanic setting, where neither sialic, nor basaltic cruststake part in the mineralization processes, is character-ized by copper-pyrite ores. Thus, the source of goldand lead is the sialic crust, source of zinc - basalticcrust, whereas source of copper is the mantle, whichparticipates in all above mentioned settings.

– On the postcollision stage, during subductionand slab transformation, as along the slab dipping,so laterally, island arc - backarc-interarc transitionoccurred. Reinforcement of diapir incursion andspreading in Minor Ocean setting revealed in coher-ent magmatism and metallogeny.

– The postcollision setting distinctly differs fromprecollision one, as by metallogeny, so bygeochemical indicators. It is characterized by highgrades of gold at the low trend of copper-base met-als, in contrast to precollision settings, here minerali-zation always coincides with association of rare met-als – Sb, W, Mo and Hg spread in the ore wall rocksas well as in the host rocks. Postcollision setting ischaracterized by high background of these rare met-als association which could be regarded as thegeochemical indicator of the postcollision setting.The geochemical characteristics of the precollisionsetting incorporated in the fresh volcanic and mag-matic rocks, whereas the postcollision indicators arethe products of hydrothermal alteration. They wereleached from thick orogenic sialic crust by the pro-tracted high temperature fluids.

Acknowledgment. The exploration was financialsupported by Shota Rustaveli national science foun-dation project FR/81/9-152/14. We sincerely thank A.Tvalchrelidze, who reviewed the paper and T.Chkhotua, R. Chagelishvili and H. Gugushvili for col-laboration and participation in investigation and crea-tion the article.



geologia

kavkasiis regionis fanerozouli metalogeniateTisis okeanis subduqciis procesSi dapostkoliziur etapze

v. guguSvili*, T. beriZe*, s. xuciSvili*, r. migineiSvili*

* ivane javaxiSvilis sax. Tbilisis saxelmwifo universitetis al. janeliZis geologiis instituti,Tbilisi

(warmodgenilia akademiis wevris i. gamyreliZis mier)

geodinamikis urTierTdamokidebuleba vulkanizmTan da metalogeniasTan prekoliziuriganviTarebis etapze ganpirobebulia subduqciiT, xolo postkoliziurze _ orogenezisiTda sinorogenuli magmatizmiT. prekoliziuri ganviTareba normuli subduqciis etapzeukavSirdeba kunZulTa rkalur viTarebas, kirtute vulkanur aqtivobas da oqro-spilenZpolimetalur gamadnebas. subducirebuli filis transformacia mantiuri diapirisSemoWriT spredings ganapirobebs da bekark-interarkul viTarebaSi vlindeba, toleit-bazalturi da SoSonituri vulkanizmiTa da TuTia-spilenZis mineralizaciiT. diapirisSemoWris gaZlierebis Sedegad bekarki Cainacvleba mcire okeanuri viTarebiT ofioliturivulkanizmiT da spilenZ-kolCedanuri gamadnebiT.subducirebuli filis transformaciaxdeba rogorc subducirebuli filis daZirvis mimarTulebiT, ise lateralurad filisdaZirvis mimarT. igi orive mimarTulebiT geodinamikuri viTarebis da magmatizmisa dametalogeniis xasiaTis monacvleobaSi vlindeba.

postkoliziuri ganviTarebis etapi okeanis daxurvas ukavSirdeba. igi xasiaTdebaoqros maRali SemcvelobiT polimetalebis dabali trendis fonze. gamadnebas axlavsiSviaT elementTa - Sb, W, Mo da Hg asociacia. aRniSnul iSviaT metalTa maRaligeoqimiuri foni damaxasiaTebelia postkoliziuri viTarebisaTvis da igi warmoadgens amviTarebis geoqimiur indikators. aRsaniSnavia, rom iSviaT metalTa es kompleqsi araxasiaTebs prekoliziur viTarebas. amave dros igi oqros gamadnebis Zebna- ZiebiT kriteriumswarmoadgens.

Phanerozoic Metallogeny of the Caucasus Region during the...

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