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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/359353039 MoritzGedabekSEGSpecPub24 Article · March 2022 DOI: 10.5382/SP.24.11 CITATIONS READS 0 610 6 authors, including: Robert Moritz Richard Spikings University of Geneva University of Geneva 250 PUBLICATIONS 4,216 CITATIONS 180 PUBLICATIONS 6,020 CITATIONS SEE PROFILE Massimo Chiaradia University of Geneva 341 PUBLICATIONS 9,363 CITATIONS SEE PROFILE All content following this page was uploaded by Robert Moritz on 20 March 2022. The user has requested enhancement of the downloaded file. SEE PROFILE Gold Open Access: This paper is published under the terms of the CC-BY-NC license. ©2021 Society of Economic Geologists, Inc. SEG Special Publications, no. 24, v. 2, pp. 181–203 Chapter 11 Jurassic-Early Cretaceous Magmatic Arc Maturation and Ore Formation of the Central Tethyan Metallogenic Belt: Evidence from the Gedabek Mining District, Lesser Caucasus, Azerbaijan Robert Moritz,1,† Pierre Hemon,1 Alexey Ulianov,2 Richard Spikings,1 Massimo Chiaradia,1 and Vagif Ramazanov3,* 1Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Geneva, Switzerland 2Institut of Earth Sciences, University of Lausanne, Géopolis, 1015 Lausanne, Switzerland 3Geological Department, Baku State University, Z. Khalilov St. 23, Az1145, Baku, Azerbaijan Abstract The Jurassic to Early Cretaceous magmatic and metallogenic evolution of the Lesser Caucasus and Eastern Pontides segment of the Central Tethyan orogenic belt is still poorly understood. This study reports an investigation about the link between ore formation and magmatic evolution in the major Gedabek porphyry-epithermal mining district, which is located in the Somkheto-Karabagh belt, Azerbaijan. Long-lasting magmatic arc evolution of ~50 m.y., from the Middle Jurassic to the Early Cretaceous, is supported by new U-Pb zircon ages between 164.3 ± 0.7 and 125.1 ± 0.5 Ma. Middle Jurassic magmatic rocks have a dominantly tholeiitic to transitional and primitive island-arc composition, whereas Late Jurassic to Early Cretaceous magmatic rocks are calc-alkaline to shoshonitic and have mature island-arc compositions. Radiogenic isotopes document a higher mantle contribution during petrogenesis of the Late Jurassic-Early Cretaceous magmatic rocks. The combined data document progressive magmatic arc maturation and crustal thickening from the Middle Jurassic to the Early Cretaceous, accompanied by slab roll-back and asthenospheric upwelling. This evolution is shared by other areas of the Somkheto-Karabagh belt and its southern extension in the Kapan block, which also host porphyry-epithermal mining districts. Muscovite and K-feldspar from a porphyry Cu-related potassic alteration assemblage at the Gedabek deposit (overprinted by a younger intermediate- to high-sulfidation epithermal system) have yielded 40Ar/39Ar ages between 140.1 ± 1.0 and 136.3 ± 0.9 Ma. Together with a previous Re-Os molybdenite age, they document formation of the porphyry-epithermal systems at the end of the long magmatic arc maturation of the Gedabek district. Although ore-forming events were diachronous along the arc, the relative timing of magmatic evolution and ore formation at Gedabek is shared by the other Late Jurassic to Early Cretaceous mining districts of the Somkheto-Karabagh belt and the Kapan block. Our study demonstrates that long arc maturation and crustal thickening has taken place along the southern Eurasian margin from a Middle Jurassic nascent arc to an Early Cretaceous evolved arc. This evolution is in line with the essential prerequisites for the genesis of porphyry-epithermal systems in orogenic belts. It also provides evidence that Middle Jurassic to Early Cretaceous magmatic fertile systems and porphyry-epithermal centers have been preserved in this belt. Introduction The Western to Central Tethyan metallogenic belt extending from southeastern Europe to Iran hosts a great diversity of porphyry, epithermal, and volcanogenic massive sulfide ore deposits (Richards, 2015; Moritz and Baker, 2019). Most of the studies were focused on Late Cretaceous to Cenozoic systems, which was a very fertile metallogenic time frame during the convergence and subsequent collision of Arabia, Africa, and Gondwana-derived microcontinents with the southern Eurasian margin (Fig. 1; e.g., Von Quadt et al., 2005; Aghazadeh et al., 2015; Delibaş et al., 2017; Menant et al., 2018; Kusçu et al., 2019; Rabayrol et al., 2019; Voudouris et al., †Corresponding author: e-mail, [email protected] *Deceased May 7, 2014. 2019; Zürcher et al., 2019). By contrast, the Jurassic to Early Cretaceous metallogenic evolution of the Western to Central Tethyan metallogenic belt is only poorly known and documented (Richards, 2015; Zürcher et al., 2019). Erosion below preservation levels of porphyry and epithermal deposits has been invoked to account for the relative scarcity of such Jurassic-Early Cretaceous systems (Richards, 2015). It also explains why many mineral exploration programs along the Western and Central Tethyan metallogenic belt are predominantly focused on Late Cretaceous and Cenozoic settings (e.g., Baker, 2019). Nevertheless, northward Tethyan subduction and its tectono-magmatic evolution can be traced back to the Triassic in the Pontides (Okay et al., 2020) and to the Late Carboniferous-Permian in the Lesser Caucasus (Adamia et al., 2011; Rol- Open Access (CC-BY-NC) publication of the Jeremy P. Richards memorial volume was generously supported by BHP Metals Exploration and the Laurentian University Mineral Exploration Research Centre (MERC) and Harquail School of Earth Sciences (HES). Supplementary files are available online at www.segweb.org/SP24-VOL2-Appendices. doi: 10.5382/SP.24.11; 23 p. 181 182 MORITZ ET AL. Gre Black Sea TS RM IAESZ rya Saka Cy TAP EP pru s BM ch tren gr os h- Alb Do su kh Sa ta tur e orz Iranian blocks r na nd aj -S irj an c ne ar zo ic 250 km Za ie at Cenozoic Ur m Late Cretaceous z ag Jurassic-Early Cretaceous Present-day subduction zone Suture zone Caspian Sea Albor m Mediterranean Sea Porphyry-epithermal deposits: s um Arab ia plat n e N su SAB IAESZ PM is suture Bitl ra pla sian te Cau casu s Le sse rC au AS ca AS Z Fig. 2 Sakarya zone CACC TAP an ge arc e A ckh ba nc tre c ni le l He CP zone Eu ater Persian Gulf Fig. 1. Main tectonic, mountain ranges, and porphyry-epithermal deposits of the Central Tethys orogenic belt segment extending from Western Turkey through the Caucasus to Iran. The main tectonic zone outlines, and locations of suture and subduction zones are from Okay and Tüysüz (1999) and Dilek and Altunkaynak (2009). The ore deposit locations and ages are from Richards (2015), Moritz et al. (2016a), Delibaş et al. (2019), Kusçu et al. (2019), and Mederer et al. (2019). The background topographic relief map is from https://maps-for-free.com. Abbreviations: ASASZ = Amasia-Sevan-Akera suture zone, BM = Bitlis massif, CACC = Central Anatolian Crystalline Complex, CP = Central Pontides, EP = Eastern Pontides, IAESZ = Izmir-Ankara-Erzincan suture zone, PM = Pütürge massif, RM = Rhodope massif, SAB = South Armenian block, TAP = Tauride-Anatolian platform, and TS = Timok-Srednegorie zone. land et al., 2011, 2016). Furthermore, several Jurassic to Early Cretaceous ore deposit centers related to the early evolution of the Central Tethyan belt have been reported in both orogenic segments (Fig. 1; e.g., Mederer et al., 2014, 2019; Moritz et al., 2016a; Calder et al., 2019; Delibaş et al., 2019; Günay et al., 2019). This indicates that the early geodynamic evolution of the Central Tethyan orogenic belt must also be considered as a potentially fertile setting, which needs better documentation and requires further studies and regional correlations. In this contribution, we document the ore deposit diversity and the geologic setting of the major Gedabek area (Figs. 2, 3a) located in the Somkheto-Karabagh belt of western Azerbaijan (Babazadeh et al., 1990; İsmayıl et al., 2021b), and which has been recognized as one of the major Jurassic-Early Cretaceous ore deposit segments along the Central Tethyan belt (Zürcher et al., 2019; Figs. 1, 2). This study presents new lithogeochemical, radiogenic isotope, and geochronological data on the Gedabek mining district, Azerbaijan, with a focus on the Gedabek deposit (Fig. 3b). The new data allow us to understand its metallogenic evolution and place it within the Jurassic-Early Cretaceous regional geologic framework and magmatic arc maturation of the southern Eurasian margin (Figs. 1, 2). Together with previous contributions, our study at Gedabek demonstrates that Jurassic to Early Cretaceous magmatic arc construction and maturation were fertile periods during the Tethyan metallogenic belt evolution, and that such Mesozoic arcs must be considered as favorable target zones during mineral exploration. Regional Geologic and Geodynamic Setting The Lesser Caucasus includes three main tectonic zones (Fig. 2; Sosson et al., 2010; Adamia et al., 2011): (1) the Somkheto-Karabakh belt and the Kapan block, which belong to a discontinuous, NW-oriented Jurassic-Cretaceous magmatic arc (Kazmin et al., 1986; Rolland et al., 2011; Mederer et al., 2013); (2) the Jurassic-Cretaceous ophiolite of the Amasia-Sevan-Akera suture zone (ASASZ, Fig. 2), which is correlated with the Izmir-Ankara-Erzincan suture zone in Anatolia (IAESZ, Fig. 2; Hässig et al., 2013); and (3) the Gondwana-derived South Armenian block (SAB, Fig. 2), which consists of a Proterozoic metamorphic basement, Devonian to Paleocene sedimentary and volcanic rocks (Sosson et al., 2010; Hässig et al., 2015), and abundant Cenozoic plutons (Moritz et al., 2016b; Rezeau et al., 2016, 2017). The South Armenian block collided with the Somkheto-Karabagh belt during the late Campanian-early Maastrichtian (~73–71 Ma; Rolland et al., 2009a, b), and it is interpreted as the northeastern extension of the Tauride-Anatolide platform (TAP, 183 GEDABEK MINING DISTRICT, AZERBAIJAN 42° 38° 40° N 42° Black Sea 44° ATB 41° Ordu Eurasia n Rize ASASZ Olur? es Eastern Pontid IspirUlutas 133 130 Ma Z IAES NAF 40° Dambludka? margin ras Turkey ian Bolnisi Georgia Trabzon Eu Tbilisi Batumi Armenia Yerevan Erzurum Ru 46° GC ma ia Az rgi er n Alaverdi-Teghout ss ba 161 - 146 Ma So mk he Le to ss er n 41° Gedabek district Fig. 3a - 183 - 133 Ma Ca Kara uc SAB ija 42° bagh Qizilbulaq Mehmana 154 131 Ma as us be kh 0 100 km 38° 40° 42° Cenozoic magmatic intrusion Paleocene and predominantly Eocene sedimentary and volcanic rocks Cretaceous to Cenozoic magmatic intrusion Middle Jurassic to Cretaceous magmatic intrusion Late Paleozoic to Jurassic magmatic intrusion Late Cretaceous volcanic and sedimentary rocks Cretaceous flysch Jurassic and Early Cretaceous sedimentary and volcanic rocks Middle Jurassic to Early Cretaceous ophiolitic series Undifferentiated Proterozoic to Triassic rocks Lake and Sea he va KB Main types of ore deposits and prospects: Jurassic-Early Cretaceous deposits Late Cretaceous volcanogenic massive sulfide Late Cretaceous porphyry-epithermal systems Cenozoic porphyry-epithermal systems AF AS AS Z Kapan Shikahogh n 44° Oligocene to Quaternary sedimentary and volcanic rocks Major fault and suture zone Iran TAP itc lt Na 46° AF 166 130 Ma 39° Araks fault ASASZ Amasia-Sevan-Akera suture zone ATB Adjara-Trialeti belt (Eurasian margin) GC Greater Caucasus (Eurasian margin) IAESZ KB Izmir-Ankara-Erzincan suture zone Kapan block (Eurasian margin) NAF North Anatolian fault SAB South Armenian block (Gondwana-derived) TAP Tauride-Anatolide platform (Gondwana-derived) Fig. 2. Simplified geology of the Lesser Caucasus (consisting of the Somkheto-Karabagh belt, the Amasia-Sevan-Akera suture zone, the Kapan block, the South Armenian block, and the Adjara-Trialeti belt), the Eastern Pontides, and adjacent tectonic zones (after Moritz et al., 2020), with location of major ore deposits and prospects (after Yiğit, 2009; Moritz et al., 2016a; Delibaş et al., 2019; Kusçu et al., 2019, Mederer et al., 2019; Revan, 2020). Magmatic and ore deposit ages obtained in previous studies are shown only for Jurassic and Early Cretaceous locations. The question marks next to Olur and Dambludka indicate that the absolute ages of ore formation at both prospects is still highly uncertain, and geochronological studies remain to be carried out to test Jurassic-Early Cretaceous ages as discussed in the main body of text. See area of Figure 2 in Figure 1. Fig. 2; Barrier and Vrielynck, 2008; Sosson et al., 2010; Robertson et al., 2013). The Somkheto-Karabagh belt and the Kapan block were formed along the Eurasian margin during long lasting N- to NW-verging Jurassic-Cretaceous subduction of the northern branch of the Neotethys (Kazmin et al., 1986; Adamia et al., 2011; Rolland et al., 2011, 2016; Mederer et al., 2013). The Mesozoic rocks are locally underlain by Proterozoic and Paleozoic crystalline basement rocks (Shengelia et al., 2006; Zakariadze et al., 2007; Rolland et al., 2011), which belong to the Variscan belt of the Black Sea region (Okay and Topuz, 2017). Paleogene and Quaternary sedimentary and volcanic rocks cover the older rock sequences (Sosson et al., 2010; Adamia et al., 2011). The Mesozoic rocks of the Somkheto-Karabagh belt and the Kapan block record progressive magmatic arc construction, evolving from a nascent Middle Jurassic arc with tholeiitic to transitional magmatism to a mature Late Jurassic and Early Cretaceous arc characterized by medium to high-K calc-alkaline magmatism (Mederer et al., 2013, 2019; Calder et al., 2019). Regional exhumation and extensional tectonics at ~167 to 166 Ma is attributed to steepening of the subduction geometry (Rolland et al., 2011). This major Jurassic to Early Cretaceous magmatic activity was abruptly shut off at ~130 Ma, resulting in a ~40-m.y.long magmatic lull (Hässig et al., 2020). It coincided with a significant subduction slowdown along the European margin, extending from the Pontides to the Lesser Caucasus (Rolland et al., 2009b, 2011; Okay et al., 2013; Hässig et al., 2016), and Early Cretaceous uplift and denudation in the Somkheto-Karabagh belt (Sosson et al., 2010) and in the Pontides (Okay et al., 2006). North-verging subduction of the northern Neotethys resumed at ~90 Ma (Okay et al., 2006, 2013; Hässig et al., 2016, 2020; Kandemir et al., 2019). Late Cretaceous subduction-related magmatism was mainly developed along an E-W-oriented belt, extending from the Eastern Pontides to the Bolnisi area at the northern tip of the Lesser Caucasus (Fig. 2), in an extensional tectonic setting (Kandemir et al., 2019; Moritz et al., 2020). By contrast, Late Cretaceous magmatic activity was significantly reduced in the 184 MORITZ ET AL. Gosha 45°30’ 40°45’ 46° Sämkir Djaygir Garadagh Maarif U 133 Ma Gäncä Barum 151-149 Ma* N jan N Gedabek 144140 Ma* Dashkesan 148-138 Ma* Dashkesan 40°30’ 10 km Quaternary sedimentary rocks Bayan 210? Ma* Chovdar Fig. 3b 140- Gedabek 136 Ma** * ai erb Az enia Arm G 45°30’ 40°45’ Kharkhar 133 Ma** B Armenia 40°30’ Gilambir 180?-169 Ma* AtabekSlavayanka 166 Ma* Sha anti mkhor clino rium a Gabahtepe 183?-158 Ma* and 145 Ma* 46° Jurassic-Early Cretaceous intrusions: Main ore deposit types: Eocene volcanic and volcano-sedimentary rocks Granodiorite, granite Porphyry Cu Cretaceous limestone, marl, sandstone, clay, tuff, sandstone Kimmeridgian tuff, volcano-sedimentary rocks, basalt, andesite Quartz diorite, diorite Fe-Co skarn Callovian-Oxfordian limestone and tuff Ma* Bathonian volcano-sedimentary rocks, conglomerate, sandstone, siltstone Precious metal and/or base metal epithermal Plagiogranite Porphyry Cu overprinted by epithermal system U-Pb zircon age Ma** Re-Os molybdenite age Late Bajocian rhyolite and dacite Ma*** Early Bajocian basalt and andesite 40 Ar/ 39Ar muscovite and and K-feldspar age 567600 Sample locations of this study 567400 Town 567000 Gabbro, gabbrodiorite, norite 4492800 02 b 100 m Fault Quaternary sedimentary rocks Supergene oxidation zone Area with semi-massive sulfide bodies 06 Disseminated pyrite Stockwork mineralization type 23 Hydrothermal (?) breccia Gedabek central open mine pit area Sample locations in the Gedabek open pit (see Gedabek location above in Fig. 3a): U: Ugur Potassic alteration zone 27 4492400 G: Gadir Argillic alteration (kaolinite/dickite) 17 05 N: Novogorelovka Late stage carbonate veins 16 04 B: Bittibulakh N U-Pb zircon dating - 40Ar/ 39Ar dating - Dike Quartz-porphyry body Diorite (Gedabek intrusion) Bathonian andesitic tuff affected by propylitic alteration sphalerite microprobe analyses Fig. 3. a. Simplified geologic map of the Somkheto-Karadagh belt in the Gedabek area (after Alizadeh, 2008), with sample locations for the geochronological study (see Fig. 7): sample XX-11-01 at Kharkhar and sample MA-11-02 at Maarif for U-Pb zircon dating; see area of Figure 3a in Figure 2. b. Geologic map of the Gedabek deposit (map provided by the Anglo Asian Mining Company, now Azerbaijan International Mining Company Limited, and additional data from Cukor, 2010; Hemon, 2013; İsmayıl et al., 2021b), with location of samples for the geochronological study (samples GE-11-06 and GE-11-17 for U-Pb zircon dating, and samples GE-11-04B, GE-11-16B, GE-11-23, and GE-11-27 for 40Ar/39Ar dating: Fig. 7) and sphalerite microprobe studies (samples GE-11-02, GE-11-04, and GE-11-05: Fig. 6b). The ages of the intrusions at Gabahtepe, Gilambir, Atabek-Slavayanka, Barum, Bayan, Dashkesan, and Gedabek are from Sadikhov and Shatova (2016, 2017), Sadikhov et al. (2018), and Sadikhov (2019). See Table 1 for summary of the ore deposits and prospects of the Gedabek area. GEDABEK MINING DISTRICT, AZERBAIJAN Somkheto-Karabagh belt and the Kapan block (Hässig et al., 2020). Regional Metallogenic Setting The metallogenic evolution of the Lesser Caucasus can be subdivided in two stages (Moritz et al., 2016a). The first stage was related to NE-verging Jurassic to Cretaceous subduction of the northern Neotethys branch, which resulted in volcanogenic massive sulfide, porphyry, and epithermal ore deposit formation along the Eurasian margin (Fig. 2; Table 1), including the Kapan block (Mederer et al., 2019), the Alaverdi-Teghout districts of the Somkheto-Karabagh belt (Mederer et al., 2014; Calder et al., 2019), and the Bolnisi district in Georgia (Moritz et al., 2020). The ore deposits and prospects of the Gedabek district belong to this first metallogenic stage. The second metallogenic stage started during the Cenozoic, after Late Cretaceous collision of the South Armenian block with the Eurasian margin. Major porphyry and epithermal deposits were formed in the South Armenian block (Fig. 2), first, during N-verging subduction of the southern Neotethys branch beneath the Tauride-Anatolide platform and western Iran, and then during subsequent Arabia-Eurasia collision (Moritz et al., 2016a, b; Rezeau et al., 2016, 2019; Hovakimyan et al., 2019). Geologic Setting of the Gedabek Mining District The Gedabek mining district is located in the central part of the Somkheto-Karabagh belt (Figs. 2, 3a). The predominant rock sequences consist of Bajocian basaltic, andesitic, rhyolitic, and dacitic volcanic rocks, which are overlain by Bathonian volcano-sedimentary rocks, tuff, conglomerate, sandstone, and siltstone. The Bajocian and Bathonian rock sequences are covered by Callovian and Oxfordian tuff, sandstone, and limestone, followed by Kimmeridgian tuff, basalt, andesite, and volcano-sedimentary rocks. The youngest rock sequences include Cretaceous and Quaternary sedimentary rocks (Fig. 3a; Babazadeh et al., 1990). The main structure of the district is the Shamkhor anticlinorium, which has a northwest orientation and is parallel to the Somkheto-Karabagh belt (Fig. 3a). A long magmatic evolution is recorded in the Gedabek district. The oldest intrusions include the Gabahtepe diorite/ quartz diorite, and the Atabek-Slavayanka and Gilambir plagiogranite, with U-Pb SHRIMP zircon ages ranging between 183 ± 4 and 158 ± 2 Ma (Figs. 3a, 4; Sadikhov and Shatova, 2016, 2017; Sadikhov, 2019). A U-Pb SHRIMP zircon age of 210 ± 5 Ma has been yielded by the Bayan diorite/quartz diorite, in the eastern part of the district (Figs. 3a, 4; Sadikhov and Shatova, 2016). However, such a Late Triassic magmatic age is questionable, since the Bayan intrusion is emplaced in younger host rocks mapped as Bathonian (Fig. 3a). The U-Pb SHRIMP zircon ages of 180 ± 1 Ma (i.e., Toarcian; Sadikhov and Shatova, 2016) and 183 ± 4 Ma (i.e., Pliensbachian; Sadikhov and Shatova, 2017) from, respectively, the Gilambir and Gabahtepe intrusions are also at variance with respect to the younger Bathonian age of their host rocks (Fig. 3a). Either the dated zircons were inherited by the intrusions from older rock sequences or the Middle Jurassic stratigraphic age of the immediate host-rock sequences must be revised. The youngest intrusive events include the Gedabek and Barum diorite/ 185 quartz diorite, and the Dashkesan granodiorite/granite, with U-Pb SHRIMP zircon ages ranging between 151 ± 1 and 138 ± 2 Ma (Figs. 3a, 4; Sadikhov and Shatova, 2017; Sadikhov, 2019). Thus, the spatial distribution of U-Pb zircon ages documents a broad north to south migration of intrusive activity in the Gedabek district (Fig. 3a). Late mafic and felsic dikes were emplaced along NW-oriented, and subsidiary NE-, N-, and E-oriented faults (not shown in Fig. 3). Ore Deposits and Prospects of the Gedabek Area The Gedabek district and the adjoining areas of the Azerbaijan segment of the Somkheto-Karabagh belt host a large number of deposits and prospects. The main ore deposit characteristics are summarized in Table 1. A major operating Fe-Co skarn deposit is hosted by Late Jurassic sedimentary rocks intruded by Early Cretaceous gabbro and granite at Dashkesan (Fig. 3a; Mustafabeyli et al., 1962; Kashkai, 1965; Safirova, 2016; Alizadeh et al., 2017). Two major high-sulfidation epithermal deposits are hosted by Middle Jurassic volcanic rocks and tuff at Chovdar and Gosha (Fig. 3a). Mining in the Gedabek district started about 2,000 years ago, with 56,000 tons (t) of copper and 134.16 t of gold-silver doré produced from 1864 to 1917, when mining activity ceased with the start of the Russian Revolution. The porphyry Cu Garadagh, Kharkhar, and Djaygir prospects are located in the northern part of the district and are spatially associated with the Atabek-Slavayanka composite intrusion (Fig. 3a; Babazadeh et al., 1990). The porphyry Cu prospects consist of 700- to 800-m-wide stockwork-type orebodies, which are distributed along a north-south trend over a distance of 1.5 to 2 km. The major part of the porphyry orebodies is hosted by a central quartz-sericite-pyrite alteration zone, which grades outward into quartz-sericite and argillic alteration zones, and a marginal propylitic alteration zone. Potassic alteration is only poorly developed in the mining district (Babazadeh et al., 1990), which indicates that the Garadagh, Kharkhar, and Djaygir prospects represent the apical parts of typical porphyry Cu systems (Sillitoe, 2010). The highest ore grades are located in the apical parts of a quartz diorite porphyry intrusion at the Garadagh and Kharkhar prospects (Babazadeh et al., 1990). Molybdenite from Kharkhar has yielded an Re-Os age of 133.27 ± 0.53 Ma (Moritz et al., 2016a). Several epithermal systems have been reported, mainly in the southern part of the district (Moritz et al., 2016a). Next to Gedabek, Gadir, Bittibulakh, and Novogorelovka are three of the best-known epithermal occurrences (Table 1; Fig. 3a). Bittibulakh is located along a NW-oriented structure at the contact with Bajocian andesite and andesitic tuff and close to the Atabek-Slavayan plagiogranite. The Cu-As-Au prospect is a 60- by 50-m-sized body, including small lenses of pyrite, enargite, chalcopyrite, and barite and subsidiary covellite, sphalerite, and galena. It is surrounded by quartz-pyrite veins and disseminations. Novogorelovka is a Cu-Zn stockwork-type NW-oriented lens-shaped orebody consisting of Fe-rich sphalerite, chalcopyrite, and pyrite. It is hosted by early Bajocian andesite and andesitic tuff crosscut by a Late Jurassic quartz diorite. Directly west of Gedabek (Fig. 3b) sits the recent discovery of Gadir, which has been developed as an underground operation. It consists predominantly of a pyrite-sphalerite-galena assemblage with subsidiary chalcopy- 186 MORITZ ET AL. Table 1. Major Late Jurassic-Early Cretaceous Porphyry-Epithermal-Skarn Ore Deposits and Prospects of the Lesser Caucasus and the Eastern Pontides Deposit name Deposit type Reserves (ore grade) Status Age Host-rock geology Somkheto-Karabagh belt, Gedabek mining district, Gosha prospect, and Chovdar deposit (see Fig. 3, and locations in Fig. 2) Bitti-Bulakh High-sulfidation Past production: 16,000 t @ 2% Closed Early Cretaceous Bajocian andesite and tuff, epithermal Cu; unknown reserves and intruded by plagiogranite resources: 0.53 g/t Au, 0.5 g/t Ag, 1.07% Cu Chovdar High-sulfidation 18.1 Mt @ 2.19 g/t Au, 16.72 g/t In production Uncertain, possibly Bajocian tuff, andesite, dacite, epithermal Ag (probable reserves and indiLate Jurassic or Early and rhyolite cated-inferred resources) Cretaceous Dashkesan Fe-Co skarn 270 Mt @ 35 to 40% Fe In production Early Cretaceous Late Jurassic tuff-bearing carbonate rocks intruded by Early Cretaceous gabbro and granite Djaygir Porphyry Cu 117 Mt @ 0.354% Cu (indicated to Prospect Early Cretaceous Late Jurassic quartz-diorite inferred resources) intruded in Bajocian tonalite, andesitic to rhyodacitic tuff and tuff-sandstone Gadir (Low-sulfidation) 0.8 Mt @ 2.73 g/t Au, 11.89 g/t In production, Early Cretaceous Mainly in quartz porphyry, and epithermal system Ag, 0.17 % Cu (proven-probable underground at contact with hornfels in associated with reserves) mine andesite porphyry Cu Garadagh Porphyry Cu 41.5 Mt @ 0.43% Cu, 0.002% Mo Prospect Early Cretaceous Late Jurassic quartz-diorite (indicated to inferred resources) intruded in Bajocian tonalite Gedabek Porphyry Cu over12.1 Mt @ 0.9 g/t Au, 0.3% Cu, In production, 139.8 ± 0.9 to 136.1 Highly altered quartz porphyry printed by epither8.9 g/t Ag (proven and probable open pit ± 0.9 Ma (40Ar/39Ar (dacite?) intruding Jurassic mal system reserves) K-feldspar and muscoandesitic volcanic and volcanivite ages) clastic rocks Gosha High-sulfidation epithermal 7.4 Mt @ 4.7 g/t Au, 6.33 g/t Ag (proven-probable reserves and indicated-inferred resources) In production Uncertain, possibly Late Jurassic or Early Cretaceous Bajocian andesite intruded by rhyodacitic subvolcanic intrusion Kharkhar Porphyry Cu Novogorelovka Epithermal polymetallic Unknown reserves and resources: Prospect 0.53 g/t Au, 0.5 g/t Ag, 1.07% Cu Early Cretaceous Ugur Epithermal 3.6 Mt @ 1.3 g/t Au, 7.0 g/t Ag (proven-probable reserves) In production, open pit Early Cretaceous Closed 141 ± 5 Ma and 150 ± 5.5 Ma (K-Ar wholerock age of altered host rock) Bajocian subvolcanic quartzdacite, andesite and basalt Closed 135 ± 6 Ma, 142 ± 6 Ma (K-Ar sericite age of altered host rock) Bajocian dacitic tuff and andesitic agglomerate 22.6 Mt @ 0.367% Cu, 0.003% Prospect 133.3 ± 0.5 Ma (Re-Os Late Jurassic quartz-diorite Mo, 0.2 g/t Au, 2-4 g/t Ag (indimolybdenite age) intruded in Bajocian tonalite cated to inferred resources) Maarif 32 Mt @ 0.51-0.72% Cu, 0.01% Prospect Early Cretaceous Bajocian andesitic porphyry Mo, 0.5-2 g/t Au (probable intruded by subvolcanic reserves) rhyodacite Somkheto-Karabagh belt, Gedabek mining district, Gosha prospect, and Chovdar deposit (see Fig. 3, and locations in Fig. 2) Somkheto-Karabagh belt, Alaverdi mining district (see locations in Fig. 2) Akhtala Polymetallic lenses and veins 1.2 Mt @ 0.58% Cu, 1.67% Pb, 4.48% Zn, 1.3 g/t Au, 104 g/t Ag (proven-probable reserves and indicated resources) Alaverdi Cu-pyrite bodies and 1.2 Mt @ 5.6% Cu, 0.12 g/t Au, polymetallic veins 5.8 g/t Ag (indicated-inferred resources) Shamlugh Cu-pyrite bodies and 4 Mt @ 3.53% Cu, 1.70% Pb, Open- pit and polymetallic veins 4.96% Zn, 1.03 g/t Au, 8.1 g/t Ag underground (proven-probable reserves and mining indicated resources) Teghout Porphyry Cu-(Mo) 460 Mt @ 0.34% Cu, 0.01% Mo, 0.01 g/t Au Open-pit mining started in 2015 Early Bajocian andesite and late Jurassic subvolcanic quartz-dacite intrusion Middle Jurassic to Early Cretaceous felsic intrusions in Bajocian rhyolite and dacite, and tuff Maximum age: 155 ± 1 Bajocian basaltic andesitic, Ma (U-Pb zircon age andesitic and dacitic tuff and of altered rhyolite sill); lava breccia, overlain by a rhy142 ± 6 Ma and 161 olite sill (named albitophyre) ± 4 Ma (K-Ar wholerock and sericite ages of altered host rock) 145.5 ± 0.5 Ma and 149 Middle-late Jurassic polyphase ± 3 Ma (K-Ar sericite intrusion, including quartzage) and 145.85 ± 0.59 diorite, biotite-hornblende Ma (Re-Os molybtonalite and leucogranite denite age) 187 GEDABEK MINING DISTRICT, AZERBAIJAN Table 1. (Cont.) Main mineralogy Alteration Orebody geometry References Pyrite, enargite, barite, chalcopyrite, famatinite, subsidiary fahlore, sphalerite, galena, covellite Silicification, sericite, argillic alteration (kaolinite) Disseminated and lenses Butenko (1947) Pyrite, gold, enargite, tennantite-tetrahedrite, barite Silicification; vuggy quartz; argillic alteration (kaolinite) Hornfels (pyroxene, scapolite, plagioclase, amphibole, biotite) Quartz, sericite, pyrite, kaolinite, chlorite Subvertical barite-polymetallic veins, highly silicified subhorizontal horizons Musaev and Shirinov (2002), https://azergold.az/en/projects/ Massive, up to 60 m thick and 100 to 2000 m long lens-shaped bodies Mustafabeyli et al. (1962), Kashkai (1965), Safirova (2016), Alizadeh et al. (2017) https://azergold.az/en/projects/ Pyrite, native gold, hessite, chalcopyrite, sphalerite, galena, arsenopyrite, digenite Quartz, adularia, pyrite, chlorite, epidote, illite, smectite, calcite Hydrothermal breccia, veins and dissemination Veliyev et al. (2018), İsmayıl et al. (2021a), https://www. angloasianmining.com/ Pyrite, chalcopyrite, bornite, covellite, chalcocite, molybdenite Pyrite, chalcopyrite, sphalerite, stephanite, barite, native gold, bornite, chalcocite, covvelite Quartz, sericite, pyrite, kaolinite Silicification, sericite, pyrite, argillic alteration, muscovite, K-feldspar, biotite Disseminated and stockwork Gold with pyrite and tellurides, lesser amounts of chalcopyrite, arsenopyrite, base-metal sulfides and sulfosalts Silicification, disseminated pyrite, kaolinite Pyrite, chalcopyrite, bornite, covellite, chalcocite, molybdenite Quartz, sericite, pyrite, kaolinite Orthogonal system of N-S and E-W subvertical kaolinite-pyrite-quartz veins; better ore grades in crosscutting areas of both structures Disseminated and stockwork Babazadeh et al. (1990), https:// azergold.az/en/projects/ Mamedov (1983), Cukor (2010), Hemon (2013), İsmayıl et al. (2021b), https://www. angloasianmining.com/, this study (including ages) Babazadeh et al. (2003), Cukor (2010), https://www. angloasianmining.com/ Pyrite-chalcopyrite-molybdenite Sliicification, sericite, disseminated pyrite, chlorite Stockwork Fe-rich sphalerite, chalcopyrite, pyrite Silicification, sericite, argillic alteration (kaolinite) Silicification, kaolinite, pyrite Lens-shaped orebody Mamedov (1983) Quartz breccia https://www.angloasianmining.com/ Galena, sphalerite, chalcopyrite, tennantite, tetrahedrite, and subsidiary bornite, chalco cite, marcasite, cassiterite, argentite, electrum, native gold and silver; barite, quartz, sericite, chlorite, calcite, gypsum Chalcopyrite, pyrite, sphalerite, bornite, chalcocite, and subsidiary galena, tennantite, stannite, emplectite, argentite, native gold and silver, electrum, arsenopyrite; quartz, sericite, chlorite, anhydrite, gypsum, calcite, dolomite Chalcopyrite, pyrite, sphalerite, bornite, chalcocite, and subsidiary galena, tennantite, stannite, emplectite, argentite, native gold and silver, electrum, marcasite; quartz, seri cite, chlorite, barite, calcite, gypsum Silicification, sericite, chlorite, carbonate, pyrite, pyrophyllite, dickite Stockwork and subhorizontal, stratiform lenses; intersection of dikes and NE-oriented fractures with NS-oriented faults; EW-oriented veins Paronikyan (1962), Nalbandyan (1968), Zohrabyan and Melkonyan (1999); ages by Bagdasaryan et al. (1969) Silicification, sericite, chlorite, carbonate, pyrite Structurally controlled by NNW- and NNE-oriented faults, and lithologic contacts; subvertical veins in deeper part; stockwork and subhorizontal, stratiform lenses in shallower part Nalbandyan (1968), Khatchaturyan (1977), Zohrabyan and Melkonyan (1999); ages by Bagdasaryan et al. (1969) Silicification, sericite, chlorite, carbonate, pyrite, hematite Structurally controlled by NNW- and NNE-oriented faults, and lithologic contacts; subvertical veins in deeper part; stockwork and subhorizontal, stratiform lenses in shallower part Nalbandyan (1968), Khatchaturyan (1977), Zohrabyan and Melkonyan (1999), Calder et al. (2019) Chalcopyrite, pyrite, molybdenite; subsidiary sphalerite, galena, bornite, tetrahedrite, magnetite, chalcocite, covellite, and rare enargite, luzonite and native gold; quartz, anhydrite, carbonates, sericite Quartz, sericite, pyrite, subsidiary kaolinite Stockwork, disseminated Amiryan et al. (1987), Melkonyan and Ghukasian (2004); ages: Paronikyan and Ghukasian (1974) and Moritz et al. (2016b) Mainly magnetite (up to 90%), sulfides (up to 20%, chalcopyrite, pyrite, chalcocite, subsidiary bornite, sphalerite, arsenopyrite, galena) Pyrite, chalcopyrite, and subsidiary molybdenite Pyrite, chalcopyrite, barite, hematite Disseminated and stockwork Disseminated, vein-type and semimassive to massive pyrite lenses Babazadeh et al. (1990), https:// azergold.az/en/projects/; Age from Moritz et al. (2016a) 188 MORITZ ET AL. Table 1. (Cont.) Deposit name Deposit type Reserves (ore grade) Status Age Somkheto-Karabagh belt, Qizilbulak/Mehmana mining district (see location in Fig. 2) Drmbon/ Cu-Au, epithermal? 3.3 Mt @ 3.9 g/t Au, 5.1 g/t Ag, Closed since 2014 Post-Oxfordian Qizilbulaq 1.3% Cu (indicated-inferred resources) Kapan and Shikahogh districts (see locations in Fig. 2) Centralni East Cu-Au, sulfide Estimated 30,000 t mined since stockwork 1843 @ 1.16% Cu (both Centralni deposits together) Centralni West Cu sulfide-quartz Estimated 30,000 t mined since veins and stock1843 @ 1.16% Cu (both work (VMS-type?) Centralni deposits together) Shahumyan Epithermal polymetallic veins Shikahokh Porphyry Cu 2006–2011: 1.8 Mt @ 1.53 g/t Au, 29.8 g/t Ag, 0.24% Cu and 1.52% Zn; estimated resources in 2017: 15 Mt @ 2.7 g/t Au, 48 g/t Ag, 0.5% Cu Unknown reserves Underground and 144.7 ± 4.2 Ma (Re-Os open pit, abanpyrite isochron) doned in 2004 Underground 161.8 ± 0.8 Ma operation, (40Ar/39Ar sericite closed 2008 ages) Porphyry type Unknown reserves rite in quartz veins and has been interpreted as a low-sulfidation epithermal system associated with porphyry Cu (Veliyev et al., 2018; İsmayıl et al., 2021a). Gedabek Deposit In addition to sampling at the regional scale, much of the sampling for this study has been carried out at the Gedabek deposit (Table 1; Fig. 3). Therefore, this deposit is described in more detail. The Gedabek Au-Ag-Cu deposit has been mined since the 19th century, and since 2008, it has been exploited by the Anglo Asian Mining company as an open-pit mining operation. The Gedabek ore deposit is hosted by a subhorizontal silica-rich lens mapped as a “quartz-porphyry body” by local geologists (Cukor, 2010; Hemon, 2013; İsmayıl et al., 2021b) and is located at the contact between the Gedabek diorite and the overlying Bathonian volcano-sedimentary rocks (Fig. 3b), which are andesitic tuff (Fig. 5a-b). Mafic to felsic dikes with different orientations crosscut the immediate host rocks of the Gedabek deposit (Figs. 3b, 5a, c). North- and W-oriented Bajocian basaltic andesite to dacite Middle Jurassic andesite and quartz-dacite Underground mining Middle Jurassic breccia lava, hyaloclastite, lava flows 156.1 ± 0.8 Ma Middle Jurassic subvolcanic (40Ar/39Ar alunite ages) quartz-dacite Prospect Early Cretaceous Bolnisi district, southern Georgia (location in Fig. 2) Dambludka/ Epithermal Uncertain reserves: 1.87 Mt @ Prospect Unknown Dambludi 1.9 g/t Au -30.1 g/t Ag, 5.3% Zn, 2.7% Pb, 0.8% Cu, 170 g/t In; locally up to 10 g/t Au, 7.1% Cu, 15.6% Pb, 21.8% Zn; Bonanza areas up to 717 g/t Au Southern Eastern Pontides, Turkey (see locations in Fig. 2) İspir-Ulutaş Porphyry Cu-Mo Porphyry: 73.6 Mt @ 0.35% Cu, Feasibility studies 131.0 ± 0.7 Ma (Re-Os (and subsidiary 0.03% Mo; skarn: 3 Mt 1.3% Cu, molybdenite age) skarn) 4.8% Zn, 33 g/t Ag Olur Host-rock geology Prospect Unknown Early Cretaceous granodiorite, monzonite and quartz-monzodiorite intruding Middle Jurassic to Early Cretaceous volcanic and volcano-sedimentary rocks Jurassic to Cretaceous rhyolite-dacite, hornblende quartz porphyry, tuff, tuff breccia, tuff sandstone Porphyritic granite, porphyritic rhyolite-ltite intrusions Jurassic dacitic, andesitic and basaltic volcanic rocks, inter layers of tuff and sandstone, and subvolcanic dacite-rhyodacite (interpreted as Eocene) faults occur to the east of the deposit, and a breccia body is located at the intersection of the two fault systems (Fig. 3b). The immediate host-rock of siliceous lens consists of quartz phenocrysts in a fine-grained matrix composed predominantly of quartz, and variably distributed K-feldspar (identified by staining, XRD, Raman spectroscopy and scanning electron microscopy) and disseminated pyrite (Fig. 5d-e). Locally, pyrite can be very abundant, and it forms semimassive bodies (Fig. 5f). Flaky muscovite is also present in places accompanied by pyrite dissemination (Fig. 5g). Granodiorite and gabbro diorite dikes within the Gedabek open pit are overprinted by biotite, K-feldspar, and sulfide, with biotite present in small veins (Fig. 5h). These observations demonstrate that the immediate host rock of the Gedabek deposit has been overprinted by a potassic alteration assemblage (Fig. 3b). In the eastern part of the ore deposit, an alteration assemblage consisting of sericite, quartz, and pyrite overprints the quartz-Kfeldspar and muscovite alteration assemblage (Fig. 3b), which in turn is overprinted by kaolinite/dickite, and late-stage cal- 189 GEDABEK MINING DISTRICT, AZERBAIJAN Table 1. (Cont.) Main mineralogy Alteration Orebody geometry References Pyrite, chalcopyrite, native gold, hematite, and subsidiary sphalerite, galena, bornite, and tennantite-tetrahedrite Silicification, sericite, carbonate, chlorite, hematite Lens-shaped, stockwork and disseminated Agakishiev et al. (1989), Vardanyan (2008), Mederer et al. (2014), https://www.angloasianmining. com/ Pyrite, chalcopyrite, colusite, tennantitetetrahedrite, and minor luzonite, galena, enargite, covellite, tellurides Chalcopyrite, pyrite, and minor sphalerite, galena and tennatite-tetrahedrite; gangue: quartz and carbonates Argillic alteration and silicification, diaspore, dickite Chlorite, quartz, epidote and carbonate alteration; sericite close to ore Phyllic alteration, and advanced argillic (alunite), and hematite in uppermost part Stockwork in upper part of the deposit, EW-oriented veins at depth Achikgiozyan et al. (1987), Mederer et al. (2019) EW-oriented veins Achikgiozyan et al. (1987), Mederer et al. (2019) Subvertical EW-oriented veins Achikgiozyan et al. (1987), Matvev et al. (2006), Mederer et al. (2019) Stockwork Achikgiozyan et al. (1987), Mederer et al. (2013, 2019), Melkonyan et al. (2018) Pyrite, chalcopyrite, sphalerite, galena, fahlore, tellurides, enargite, digenite, bornite, chalcocite, native gold and silver; gangue: quartz, carbonate, anhydrite, sericite and kaolinite Pyrite, chalcopyrite, bornite, magnetite Sulfides Quartz, sericite, chlorite ENE-oriented, about 0.5 km2 area of quartz vein swarm Georgian Mining Corporation (2018, 2019), Tvalchrelidze (2003) Pyrite, chalcopyrite, molybdenite, sphalerite, hematite, covellite Sericitic, argillic and porphyryitic alteration, distal propylitic alteration Advanced argillic, argillic, sericitic, propylitic alteration Stockwork, and isolated NW-oriented quartz veins Delibaş et al. (2016, 2019) Disseminated, stockwork, vein type Önal et al. (2017) Pyrite, chalcopyrite, sphalerite, galena, pyrrhotite, quartz, calcite, barite cite veins (Hemon, 2013). Supergene oxidation affects the altered rocks in different parts of the open pit (Fig. 3b). In distal locations, the alteration assemblage consists of epidote and chlorite, with selective replacement of some tuff beds of the Bathonian host rocks (Fig. 5b). The predominant ore minerals of the early mineralization stage consist of chalcopyrite and sphalerite, as disseminations and veins (Fig. 5f, j) in the quartz-K-feldspar-pyrite alteration zone (Fig. 5d-f). Stockwork-type orebodies are present in the eastern part of the deposit (Fig. 3b) and were intersected by drilling (Fig. 5i). Sphalerite of this early mineralization stage is typically dark colored. Chalcopyrite contains inclusions of pyrrhotite, marcasite, arsenopyrite, tennantite, and galena (Hemon, 2013). Subdsidiary barite is associated with this mineralization type. Late-stage chalcocite, covellite, and enargite replace chalcopyrite and represent a second mineralization stage (Fig. 5k). A separate mineralization type consists of disseminations with mainly galena and tennantite, and subsidiary chalcopyrite, sphalerite, arsenopyrite, pyrite, iron oxides (including magnetite, hematite, and ilmenite intergrown with chalcopyrite), and rare telluride minerals. This mineralization type contains a free gold-bearing phase in the form of electrum (Fig. 5l). Native gold and electrum have also been described by İsmayıl et al. (2021b) in association with chalcopyrite and petzite. Based on whole-rock analyses, the galena-tennantite-electrum-hessite assemblage is associated with the highest gold and silver grades (Fig. 6a; Hemon, 2013). High gold and silver grades were also yielded by ore samples with high abundances of chalcopyrite and dark-colored sphalerite (Fig. 6a). No crosscutting nor any genetic relationship could be defined for the galena-tennantite-electrum-telluride mineralization type with respect to the early chalcopyrite-sphalerite vein and dissemination stage and the late-stage chalcocite-covellite-enargite overprint. The alteration and opaque mineral characteristics, pattern, and sequence at the Gedabek deposit are consistent with a dominant potassic alteration zone (K-feldspar, flaky muscovite, and biotite; Fig. 5d-h) in a porphyry Cu system, 190 MORITZ ET AL. NW NW to SE younging of ore-related magmatism and ore deposit/prospect ages Somkheto-Karabagh belt and Kapan block: Along arc, NW to SE increase of mantle component in magma sources of Late Jurassic-Early Cretaceous intrusions 190 SE 170 180 160 6 Alaverdi district and Teghout 7 Time (Ma) 150 7 (northern Armenia, Somkheto-Karabagh) 8 7 7 140 130 120 U-Pb zircon age Rb-Sr isochron age Re-Os age 7 40Ar/ 39Ar mineral age 40Ar/ 39Ar whole-rock age 8 7 7 7 7 7 7 7 5 Teghout porphyry Cu Ga,1, ? Ga, 3 Gi, 2, ? Dated intrusions of the Gedabek district (see Fig. 2): A = Atabek-Slavayanka, B = Barum, D = Dashkesan, Ga = Gabahtepe, Ge = Gedabek, Gi = Gilambir, ? = questionable age, because host rocks are mapped as Middle Jurassic Ga, 3 Gi, 2 Ga, 2 A, 3 Ga, 2 B, 3 Gedabek district B, 2 D, 3 (Azerbaijan, Somkheto-Karabagh) Gedabek open pit 9 D, 3 Granodiorite dike (GE-11-06, Gedabek open pit) this study 10 Granodiorite (MA-11-02, Maarif) Muscovite (GE-11-23) K-feldspar (GE-11-27) K-feldspar (GE-11-16B) K-feldspar (GE-11-04B) Granodiorite dike (XX-11-01, Kharkhar) 5 Kharkhar porphyry Cu Centralni West: muscovite 10 Shahumyan: alunite (southern Armenia, Kapan block) 9 9 9 Shikahogh porphyry prospect 9 11 11 11 12 İspir-Ulutaş 12 İspir-Ulutaş porphyry Cu (Turkey, Eastern Pontides) Early Jurassic Ge, 4 D, 3 D, 3 Gabbroic diorite dike (GE-11-17, Gedabek open pit) Kapan and Shikahogh districts Ga, 2 Middle Jur. Late Jurassic 13 14 14 Early Cretaceous Fig. 4. Summary of Jurassic and Early Cretaceous igneous, ore-forming, and hydrothermal events in the Somkheto-Kabaragh belt, the Kapan block, and the Eastern Pontides. See location of samples of this geochronological study in Figure 3. References: 1 = Sadikhov and Shatova (2017), 2 = Sadikhov and Shatova (2016), 3 = Sadikhov (2019), 4 = Sadikov et al. (2018), 5 = Moritz et al. (2016a), 6 = Melkonyan et al. (2014), 7 = Hässig et al. (2020), 8 = Calder et al. (2019), 9 = Mederer et al. (2013), 10 = Mederer et al. (2019), 11 = Melkonyan et al. (2016), 12 = Delibaş et al. (2016), 13 = Delibaş et al. (2019), 14 = Karsli et al. (2021). bordered by a marginal propylitic alteration assemblage consisting of epidote and chlorite (Fig. 5b; Sillitoe, 2010; Runyon et al., 2019). The overprinting sericite-quartz-pyrite, and subsequent kaolinite/dickite and chalcocite, covellite, and enargite (Fig. 5k) assemblages document increasing acidity and sulfidation state of the hydrothermal fluids during the overprint by a shallow epithermal system (Einaudi et al., 2003; Sillitoe, 2010). The decreasing iron concentration in sphalerite throughout the paragenetic sequence, from the early chalcopyrite dark-colored sphalerite assemblage to latestage light-colored sphalerite, associated with covellite and chalcocite, is also in line with an increasing sulfidation state of the hydrothermal fluids at Gedabek (Fig. 6b; Hemon, 2013). Pyrophyllite and alunite described by İsmayıl et al. (2021b) are additional evidence for the late-stage increase in reactivity of the hydrothermal fluids at Gedabek. This sequence of hydrothermal and ore-forming events, documenting an epithermal overprint on a porphyry Cu deposit at Gedabek is consistent with the Early Cretaceous uplift and denudation evolution described at the regional scale in the Somkheto-Karabagh belt by Sosson et al. (2010). Results Geochronology Both LA-ICP-MS U-Pb zircon geochronology and 40Ar/39Ar incremental-heating experiments were applied to constrain GEDABEK MINING DISTRICT, AZERBAIJAN Fig. 5. a. Middle Jurassic gabbro dioritic dike (sample GE-11-17 dated at 164.3 ± 0.7 Ma by U-Pb zircon geochronology, see Figs. 3b, 7a), overprinted by hydrothermal alteration and crosscutting silicified Bathonian andesitic tuff in the Gedabek open pit. b. Bathonian andesitic tuff, to the south of the Gedabek open pit, with an epidote-chlorite alteration assemblage replacing preferentially distinct tuff layers. c. Granodioritic dike (sample GE-11-06 dated at 140.3 ± 0.9 Ma by U-Pb zircon geochronology, see Figs. 3b, 7b), overprinted by potassic alteration. d. Main host rock of the Gedabek deposit affected by potassic alteration, including quartz-K-feldspar-pyrite (sample GE-11-27 dated at 138.5 ± 1.1 Ma by 40Ar/39Ar K-feldspar geochronology, see Figs. 3b, 7f), with quartz phenocrysts and crosscut by quartz-sulfide veins. e. Scanning electron microscopy, backscattered imagery of the quartz-K-feldspar-pyrite alteration assemblage with subsidiary barite characteristic of the main host rock of the Gedabek deposit (Fig. 3b). f. Main host rock of the Gedabek deposit affected by quartz-K-feldspar-pyrite alteration, with a high abundance of pyrite (semimassive pyrite body), crosscut by dark-colored sphalerite and chalcopyrite veins (sample GE-11-04B dated at 136.1 ± 0.9 Ma by 40Ar/39Ar K-feldspar geochronology, see Figs. 3b, 7g). g. Potassic alteration of the Gedabek ore deposit host rocks overprinted by sericitic alteration (transmitted light, crossed polarizers; sample GE-11-23 dated at 139.8 ± 0.9 Ma by 40Ar/39Ar muscovite geochronology, see Figs. 3b, 7e). h. Green biotite vein in a host rock affected by pervasive potassic alteration, including fine-grained biotite, sulfide minerals, quartz, and K-feldspar (transmitted plain light). i. Drill core sample from the stockwork-type mineralization (drill hole SGS DD 99, depth 155 m). j. Typical predominant ore mineral assemblage (pyrite, chalcopyrite, sphalerite) hosted by the potassic alteration zone, including quartz-K-feldsparpyrite alteration (dark inclusions; see Fig. 3b; reflected light microscopy). k. Late-stage covellite and enargite replacing and rimming chalcopyrite in a silicified host rock (reflected light microscopy). l. Scanning electron microscopy, backscattered imagery of the galena-tennantite-dominated ore with subsidiary hessite, arsenopyrite, chalcopyrite, and electrum (Au/Ag = 3). Mineral abbreviations: apy = arsenopyrite, brt = barite; ccp = chalcopyrite, chl = chlorite; cv = covellite, el = electrum, eng = enargite; ep = epidote, gn = galena, hes = hessite, kfs = K-feldspar, ms = muscovite, py = pyrite, qz = quartz, ser = sericite, sp = sphalerite, tnt = tennantite. 191 192 MORITZ ET AL. 1000 a Ag (ppm) 100 10 1 0.1 0.01 0.1 1 Au (ppm) 10 100 Galena-tennantite assemblage (disseminated) Chalcopyrite-dark colored sphalerite (vein in semi-massive pyrite body) Chalcopyrite-dark colored sphalerite (disseminated and small veins) Chalcopyrite-light colored sphalerite (disseminated and small veins) Quartz-K-feldspar-pyrite alteration zone (”quartz-porphyry body” with semi-massive pyrite) Quartz-K-feldspar-pyrite alteration zone (”quartz-porphyry body” with disseminated pyrite) Barren quartz-K-feldspar-pyrite alteration zone (”quartz-porphyry body”) Kaolinite/dickite alteration zone Supergene oxidation zone Low sulfidation state Intermediate sulfidation state 200 0 800 Intermediate sulfidation state High sulfidation state 850 py 900 mol % ZnS rim int 5 er re py te 10 late stage light colored sphalerite with covellite and chalcocite co mol % FeS 150 b early stage dark colored sphaleritechalcopyrite dia py py py? py? me py? 950 1000 Dark colored sphalerite inclusion in pyrite, in semi-massive sulfide body (with chalcopyrite and arsenopyrite) Dark colored sphalerite in semi-massive chalcopyrite-sphalerite lens Dark colored sphalerite in irregular chlacopyrite-sphalerite vein crosscutting disseminated pyrite Light colored sphalerite from irregular vein, associated with covellite and chalcosite (with core to rim profile) Disseminated light colored sphalerite, associated with covellite and chalcocite py Dark colored sphalerite in equilibrium with pyrite py? Uncertain equilibrium of sphalerite with pyrite Fig. 6. a. Whole-rock Au and Ag concentrations of samples with different mineralization and hydrothermal alteration styles. b. Microprobe analyses of sphalerite from early chalcopyrite-sphalerite-pyrite assemblages (with dark-colored sphalerite) and late-stage assemblages, including light-colored sphalerite, covellite, and chalcocite. All the samples were collected in the potassic (quartz-K-feldspar-pyrite) alteration zone of the Gedabek ore deposit (see sample locations in Fig. 3b: GE-11-02, GE-11-04, and GE-1105). The arrow shows a core to rim profile from a single light-colored sphalerite mineral. The limits of sulfidation states of the hydrothermal fluid are based on Einaudi et al. (2003). Both diagrams are based on data by Hemon (2013). the age of ore formation at the Gedabek deposit and to contribute to our understanding of the regional magmatic evolution. Four samples have been dated in this study by LA-ICPMS U-Pb zircon geochronology. The analytical procedures are similar to those described in Moritz et al. (2020). The results are presented in Figure 7a-d and the detailed data set can be found in the electronic Appendix Table A1. Two dikes overprinted by hydrothermal alteration in the central part of the open pit at the Gedabek deposit have been dated (Fig. 3b). One highly silicified gabbroic diorite dike (sample GE11-17; Fig. 5a) crosscutting the Bathonian host rocks of the Gedabek deposit has yielded a weighted mean age of 164.3 ± 0.7 Ma (n = 18, MSWD = 1.5; Fig. 7a). Seven zircons from a granodiorite dike overprinted by potassic alteration (sample GE-11-06; Fig. 5c) have yielded ages between 139.6 ± 1.5 and 148.8 ± 2.6 Ma. Three of the zircons are considered as inherited, therefore a weighted mean age of 140.3 ± 0.9 Ma was calculated for only the remaining four youngest zircon grains (MSWD = 0.84; Fig. 7b). One unaltered granodiorite from Maarif (MA-11-02; Fig. 3a) to the north of Gedabek and one unaltered porphyritic granodiorite dike at Kharkhar (XX-1101; Fig. 3a) have yielded, respectively, weighted mean ages of 133.0 ± 0.7 Ma (n = 37, MSWD = 2.0; Fig. 7c), and of 125.1 ± 0.5 Ma (n = 27, MSWD = 1.8; Fig. 7d). The 40Ar/39Ar incremental-heating experiments yielded ages for one muscovite (sample GE-11-23) and three K-feldspar samples (GE-11-04B, GE-11-16B, and GE-11-27) from the potassic alteration zone within the open pit of the Gedabek deposit (Fig. 3b), where the highest ore grades are located. The analytical procedures are similar to those described in Mederer et al. (2019). The results are presented in Figure 7e-h and the detailed data set can be found in the electronic Appendix Table A2. Muscovite of sample GE-11-23 has yielded a weighted mean plateau age of 139.8 ± 0.9 Ma for 99.3% of the released gas, which overlaps with its inverse isochron age of 140.1 ± 1.0 Ma with an MSWD of 0.2 (Fig. 7e). K-feldspar of sample GE-11-27 has yielded a weighted mean plateau age of 138.5 ± 1.1 Ma for 88.3% of the released gas, which overlaps with its inverse isochron age of 139.2 ± 1.4 Ma with an MSWD of 1.7 (Fig. 7f). For sample GE-11-16B, K-feldspar has yielded a weighted mean plateau age of 136.4 ± 0.9 Ma for 61.1% of the released gas, which overlaps with its inverse isochron age of 136.9 ± 1.0 Ma with an MSWD of 0.9 (Fig. 7g). Finally, K-feldspar from sample GE-11-04B has yielded a weighted mean plateau age of 136.1 ± 0.9 Ma for 81.2% of the released gas, which overlaps with its inverse isochron age of 136.3 ± 0.9 Ma with an MSWD of 0.6 (Fig. 7h). Whole-rock major and trace element geochemistry Nineteen rock samples from the Gedabek district were analyzed in this study for major and trace elements. Altered and mineralized rock samples were not considered in the petrogenetic classification diagrams, in particular those using major elements (Fig. 8a). The analytical procedures are similar to the ones described by Moritz et al. (2020). The results are presented in the electronic Appendix Table A3. Two groups of samples are considered in this study based on their absolute radiometric ages (see above) and their relative ages constrained by field and stratigraphic relationships (Fig. 3; Sosson et al., 2010; Mederer et al., 2013, 2014, 2019; Calder et al., 193 GEDABEK MINING DISTRICT, AZERBAIJAN 166 Pb/ 238 164 206 162 Mean age:164.3 ± 0.7 Ma MSWD = 1.5 (n = 18) 138 136 238 134 Pb/ 132 130 128 Mean age:133.0 ± 0.7 Ma MSWD = 2.0 (n = 37) c 140 Mean age:140.3 ± 0.9 Ma MSWD = 0.84 (n = 4) b XX-11-01 128 126 124 122 120 Mean age:125.1 ± 0.5 Ma MSWD = 1.8 (n = 27) d 0 20 40 Cumulative 60 39 80 Ar released (%) e 125 120 0 GE-11-04B 20 40 Cumulative 39 60 80 Ar released (%) 25 0 g 100 Inverse isochron age: 139.2 ± 1.4 Ma MSWD = 1.7 GE-11-27 0 150 136.1 ± 0.9 Ma (81.2 % of 39Ar) Inverse isochron age: 136.3 ± 0.9 Ma MSWD = 0.6 50 100 135 130 75 39 GE-11-23 Ar/ Ar age (Ma) Inverse isochron age: 140.1 ± 1.0 Ma MSWD = 0.2 138.5 ± 1.1 Ma (88.3 % of 39Ar) 100 20 40 Cumulative 39 60 80 Ar released (%) f 100 125 136.4 ± 0.9 Ma (61.1 % of 39Ar) 100 75 39 120 Ar/ Ar age (Ma) 130 125 50 40 40 142 40 139.8 ± 0.9 Ma (99.3 % of 39Ar) 39 Ar/ Ar age (Ma) 140 39 Ar/ Ar age (Ma) 144 150 140 40 146 118 150 110 148 130 MA-11-02 140 GE-11-06 150 138 a 206 238 U age (Ma) 142 Pb/ U age (Ma) 168 160 206 152 GE-11-17 U age (Ma) 206 Pb/ 238 U age (Ma) 170 25 0 Inverse isochron age: 136.9 ± 1.0 Ma MSWD = 0.9 GE-11-16B 0 20 40 Cumulative 39 60 80 Ar released (%) h 100 Fig. 7. a-b-c-d. 206Pb/238U weighted average plots of LA-ICP-MS U-Pb zircon ages. a. Sample GE-11-17, altered gabbroic diorite dike from Gedabek open pit, see Figure 5a. b. Sample GE-11-06, altered granodiorite dike from Gedabek open pit, see Figure 5c. c. Sample MA-11-02, unaltered granodiorite at Maarif. d. Sample XX-11-01, unaltered porphyritic granodiorite dike at Kharkhar. e-f-g-h. 40Ar/39Ar age spectra for muscovite. e. Sample GE-11-23, see Figure 5g. f-g-h. K-feldspar, samples GE-11-27, see Figure 5d; GE-11-04B, see Figure 5f, and GE-11-16B, respectively, of the “quartz-feldspar porphyry” lithology from the central open pit of the Gedabek ore deposit (Fig. 3b). All reported errors are 2σ. 2019); they include the following: (1) Middle Jurassic (essentially Bajocian and Bathonian) and (2) Late Jurassic-Early Cretaceous rock units. The total alkali (Na2O + K2O) vs. SiO2 wt % (Fig. 8a), and the immobile element classification (Zr/TiO2 vs. Nb/Y, Fig. 8b) diagrams indicate that the Middle Jurassic samples of this study have, respectively, basaltic to basaltic andesitic and andesitic/basaltic to subalkaline basaltic compositions. Late Jurassic-Early Cretaceous samples are rhyodacitic-dacitic to andesitic in composition. This is supported by the Th versus Co discrimination diagram (Fig. 8c), in which the Late Jurassic-Early Cretaceous rock samples have a calc-alkaline dacitic-rhyolitic-trachytic composition, whereas the Middle Jurassic rock samples are basaltic andesite and andesite and sit astride on the calc-alkaline and island-arc tholeiitic fields. The magmatic series distinction is also documented by the Zr versus Y diagram (Fig. 8d), in which the Middle Jurassic rocks range from tholeiitic, through transitional to calc-alkaline 194 MORITZ ET AL. compositions, whereas the Late Jurassic-Early Cretaceous samples plot predominantly in the shoshonite field and marginally in the calc-alkaline and transitional fields. In the primitive mantle-normalized trace element spider diagrams (Fig. 8e-f), both the Middle Jurassic and Late Jurassic-Early Cretaceous magmatic rocks have negative Nb, Ta, and Ti anomalies typical for subduction-related magmas. The Late Jurassic-Early Cretaceous magmatic rocks are typically more enriched in light ion lithophile and high field strength elements (LILE: Cs, Rb, Ba, K; HFSE: Th, U, Nb, Ta; see left-hand parts of Fig. 8e-f). The Middle Jurassic rocks of this study have flatter, less fractionated chondrite-normalized rare earth element (REE) patterns in comparison to the Late Jurassic-Early Cretaceous magmatic rocks (Fig. 8g-h). Among the Late Jurassic-Early Cretaceous rocks, one can distinguish two groups, with Group II having a U-shaped pattern and being more depleted in middle and heavy REE concentrations in comparison to Group I (Fig. 8h). The Jurassic and Cretaceous rocks of this study have normal arc compositions based on the La/Yb versus Yb diagram (Fig. 8i). However, Late Jurassic-Early Cretaceous magmatic rocks have distinctly higher La/Yb ratios with respect to Middle Jurassic samples (Fig. 8i), which is consistent with the more fractionated REE patterns of the Late Jurassic-Early Cretaceous magmatic rocks (Fig. 8h). Similarly, the Late Jurassic-Early Cretaceous magmatic rocks have more elevated Th/Yb and Ta/Yb ratios with respect to Middle Jurassic samples (Fig. 8j), which is consistent with the HFSE-enriched patterns of the Late Jurassic-Early Cretaceous magmatic rocks (Fig. 8f). Due to their high La/Yb and Th/Yb ratios, the Late Jurassic-Early Cretaceous magmatic rocks fall within the field of mature island-arc rocks. In comparison, the Middle Jurassic rocks of this study, which yielded low La/Yb and Th/Yb ratios, fall at the transition between primitive and mature island-arc domains (Fig. 8k). Whole-rock radiogenic isotopes Five samples from Late Jurassic-Early Cretaceous magmatic rocks yielded 143Nd/144Nd and 87Sr/86Sr ratios of, respectively, 0.51270 to 0.51275 and 0.70360 to 0.70383 (Fig. 8l). The analytical procedures are similar to the ones described by Moritz et al. (2020). The results are presented in the electronic Ap- pendix Table A3. All the data fall to the left of the 87Sr/86Sr Uniform Reservoir (URt, Fig. 8l) and above the 143Nd/144Nd Chondritic Uniform Reservoir (CHURt of 0.51246 at 135 Ma and 0.51243 at 165 Ma, not shown in Fig. 8l). This supports a mantle-dominated source reservoir (Faure, 1986). Magmatic Evolution in the Gedabek Area and Timing of Ore Formation Our LA-ICP-MS U-Pb zircon dating is in line with the long magmatic evolution demonstrated in earlier studies (Sadikhov and Shatova, 2016, 2017; Sadikhov et al., 2018; Sadikhov, 2019). The Middle Jurassic Atabek-Slavayanka, Gabahtepe, and Gilambir felsic plutons of the northern Gedabek district belong to the oldest magmatic events in the study area (Figs. 3a, 4; Sadikhov and Shatova, 2016, 2017; Sadikhov, 2019). The highly silicified gabbroic diorite dike (sample GE-11-17; Fig. 5a) crosscutting Middle Jurassic host rocks of the Gedabek deposit (Fig. 7a), dated at 164.3 ± 0.7 Ma, confirms that the Atabek-Slavayanka and Gilambir plagiogranite and Gabahtepe quartz-diorite/diorite (Sadikhov and Shatova, 2016, 2017; Sadikhov, 2019) were roughly coeval with the basaltic/gabbroic and basaltic andesitic/gabbroic dioritic magmatism of the Middle Jurassic (Bajocian-Bathonian) host rocks of the Gedabek area (Figs. 3a, 4). Because of the large compositional gap between the contemporaneous felsic and mafic rocks, it suggests that the Middle Jurassic magmatism had a predominantly bimodal character (Fig. 8a), although the data remain scarce and further studies will be necessary to confirm this interpretation. After bimodal Middle Jurassic magmatism, the Gedabek area has recorded a long Late Jurassic to Early Cretaceous intrusive evolution from 159 ± 1 Ma at Gabahtepe to 138 ± 2 Ma at Dashkesan (Figs. 3, 4; Sadikhov and Shatova, 2017; Sadikhov, 2019). Our new data show that the Late Jurassic-Early Cretaceous magmatic evolution is as young as 125.1 ± 0.5 Ma at Kharkhar (Figs. 3a, 4, 7d). Our data combined with those of previous studies (Sadikhov and Shatova, 2017; Sadikhov et al., 2018) indicate that the younger magmatism has a predominantly dacitic/granodioritic and a subsidiary andesitic/dioritic composition (Fig. 8a). The combined lithogeochemical data of our study and from previous studies (Sadikhov and Shatova, 2016, 2017; Sadikhov et al., 2018) are consistent with each other, and they allow us to Fig. 8. Major and trace element, and Nd and Sr isotope data of Jurassic and Early Cretaceous magmatic rocks from the Gedabek district. Black symbols are from this study and open symbols are from previous studies by Sadikhov and Shatova (2016, 2017), Sadikhov et al. (2018), and Sadikhov (2019). The light and dark gray fields are a compilation of magmatic rock data from previous studies in the Somkheto-Karabagh belt and the Kapan block at Alaverdi, Bolnisi, Qizilbulaq/Mehmana, Kapan, and Shikahogh (see Fig. 2 for locations; Mederer et al., 2013, 2014; Calder et al., 2019; Hässig et al., 2020): MJ and LJ-EC are, respectively, Middle Jurassic and Late Jurassic-Early Cretaceous rocks from all locations, MJ-A and MJ-K are from Middle Jurassic rocks, respectively, at Alaverdi only and Kapan-Qizilbulaq/Mehmana, and LJ-EC-A and LJ-EC-K are from Late Jurassic-Early Cretaceous rocks, respectively, at Alaverdi-Bolnisi and Kapan-Shikahogh. a. TAS volcanic classification (Le Maître, 2002), with equivalent names of coarse-grained intrusive rocks (Middlemost, 1994). b. Classification based on immobile elements (Winchester and Floyd, 1977). c. Th vs. Co classification diagram (Hastie et al., 2007). d. Zr vs. Y discrimination diagram (Barrett and MacLean, 1999); e. and f. Primitive mantle-normalized trace element spider diagrams (normalization with respect to Taylor and McLennan, 1985). g. and h. Rare earth element normalized diagrams (normalization with respect to Sun and McDonough, 1989), sample XX-11-01 is from Kharkhar and sample MA-11-02 from Maarif (see Fig. 3a for locations). Group II consists of samples DJ-11-01/02A/02B from Djaygir, and MA-11-02/03 and GE-11-36 from Maarif; Group I includes the remaining samples from Gedabek, Kharkhar, and Garadagh. i. Th/Yb vs. Ta/Yb discrimination (Hastie et al., 2007), La/Yb vs. Yb discrimination diagram (Castillo et al., 1999). j. Th/Yb vs. Ta/Yb discrimination diagram (Pearce, 1982). k. La/Yb vs. Th/Yb discrimination diagram (Condie, 1989). l. Initial strontium and neodymium isotope compositions (recalculated based on U-Pb zircon ages); the bulk Earth 87Sr/86Sr URt was calculated according to Faure (1986) at 135 Ma (right vertical line) and 165 Ma (left vertical line), and the 143Nd/144Nd CHUR t of 0.51246 at 135 Ma and of 0.51243 at 165 Ma falls below the x-axis, therefore they are not shown here. 195 GEDABEK MINING DISTRICT, AZERBAIJAN a 0.1 Na 2 O + K 2 O (wt%) Granite 55 c 60 SiO2 (wt%) 65 d Sample/Primitive mantle g Tholeiitic MJ 20 40 Y (ppm) 60 LJ-EC 10 1 Sample/Chondrite 100 Sample/Chondrite ional it Trans Cs Rb Ba Th U K Ta Nb La Ce Sr Nd Hf Zr Sm Ti Tb Y MJ h Amphibole fractionation Group II MA-11-02 133.0 ± 0.7 Ma La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu j SH time LJ-EC-A CA Th/Yb 1 time 0 2 4 6 Yb (ppm) 8 Nd / 144Nd ture ma arc nd isla LJ 0.5127 MJ-K 1 e itiv arc primsland i 0.1 0.2 MJ -A 0.5 e tim 1 Th/Yb 2 5 10 0.5126 0.1 0.2 Ta/Yb l nd K tre eto CSE kh elt -E LJ to om h b S g NW ng ba o a al Kar -A LJ-EC -K -EC y TH 0.02 0.5128 k 10 La/Yb 10 143 50 K 0.1 rra ea ntl Ma MJ- Normal arc MJ -K LJ-EC -A MJ 0.5 1 time LJ-E C-A MJ-A MJ-K CHUR t 0.7035 0.51246 (135 Ma) 0.51243 (165 Ma) 2 URt La/Yb LJ-EC 5 Group I 10 10 i XX-11-01 125.1 ± 0.5 Ma LJ-EC 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 15 0 EC LJ- e Cs Rb Ba Th U K Ta Nb La Ce Sr Nd Hf Zr Sm Ti Tb Y 10 e lin ka -al lc Ca tim 100 1 Adakite 1 f previous studies, see captions 20 ic nit ho s ho 0 0 MJ 1 LJ-EC S 0.5 Nb/Y 100 10 25 0.2 200 this study 10 Alkaline basalt Zr/TiO2 alt e 0.1 300 30 100 Sample/Primitive mantle 400 e esit and and 20 Co (ppm) Bas hyte trac 10 Sub-alkaline basalt 0.001 0.05 75 HK-SH site nde ic a te yoli - rh IAT 0.1 0 70 alt Bas CA ite Dac Th (ppm) 50 Andesite - Basalt Subduction component Basalt Gabbro 1 0.01 Late Jurassic-Early Cretaceous this study Middle Jurassic Late Jurassic-Early Cretaceous previous studies, Middle Jurassic see captions 2.5 0.0 45 Dacite Granodiorite Andesite Diorite Zr (ppm) BA GD 100 Rhyodacite-Dacite Andesite 5.0 10 b Trachyandesite 7.5 0.7040 0.7045 Sr / 86 Sr 87 0.7050 0.7055 196 MORITZ ET AL. Sr/Y 60 plag iocla 40 0 45 actio natio n G a 55 2.2 G 60 SiO2 (wt%) 65 75 tion frac net 1.8 Dy/Yb G 1.6 1.2 45 70 Kharkhar Garadagh 2.0 1.4 G G 50 Kharkhar Garadagh n 20 se fr Maarif atio 80 Djaygir am ph Maarif Djaygir b 50 55 ibo le fra 60 SiO2 (wt%) cti gar 100 Late Jur.-Early Cret. this study Middle Jurassic Late Jur.-Early Cret. previous Middle Jurassic studies, see captions G= Gedabek intrusion amph garne ibole and t fracti onatio n 120 G G ati on G 65 70 on 75 Fig. 9. Geochemical diagrams with mineral fractionation trends. a. Sr/Y vs. SiO2 (wt %) diagram with plagioclase and amphibole-garnet fractionation trends. b. Dy/Yb vs. SiO2 (wt %) diagram with amphibole and garnet fractionation trends from Davidson et al. (2007). See Figure 3a for sample locations at Djaygir, Kharkhar, Garadagh, Maarif, and Gedabek. distinguish the Middle Jurassic and Late Jurassic-Early Cretaceous magmatic events based on different discriminatory, and chondrite- and mantle-normalized spider diagrams (Fig. 8dk). Magmatic evolution in the Somkheto-Karabagh segment of the Gedabek area started with Middle Jurassic, dominantly tholeiitic to transitional (Fig. 8d) and primitive island-arc compositions (Fig. 8k) with relatively flat, undifferentiated REE patterns (Fig. 8g). Subsequent Late Jurassic-Early Cretaceous magmatism had dominantly calc-alkaline to shoshonitic (Fig. 8d) and mature island-arc compositions (Fig. 8d) with fractionated REE patterns (Fig. 8g). We conclude that the Somkheto-Karabagh belt of the Gedabek area records progressive arc maturation over a duration of approximately 50 m.y. from 173 ± 2 Ma at Gagahtepe (Sadikhov, 2019) to 125.1 ± 0.5 Ma at Kharkhar (this study; Figs. 3a, 4). The Late Triassic and Early Jurassic intrusion ages reported by Sadikhov and Shatova (2016, 2017) at Bayan, Gilambir, and Gabahtepe may indicate that the onset of magmatism is even older, but such ages remain open to question, since the hostrock ages have been mapped as Middle Jurassic (Fig. 3a). The combined radiogenic isotope data collected in previous studies (Sadilhov et al., 2018; Sadikhov, 2019) and our investigation show that the 87Sr/86Sr and 143Nd/144Nd ratios, respectively, decrease and increase during Middle Jurassic to Late Jurassic-Early Cretaceous evolution of the source magma res- ervoirs (Fig. 8l). This reflects an evolution over time of the magma reservoir with a more dominant mantle component during the Late Jurassic-Early Cretaceous magmatic evolution in the Gedabek area. Thickening of the arc over time is supported by increasing La/Yb ratios from the Middle Jurassic to Late Jurassic-Early Cretaceous magmatic rocks, reaching nearly adakite-like compositions for the latter (Fig. 8i). They are consistent with amphibole and garnet fractionation during thickening and maturation of a magmatic arc (Richards and Kerrich, 2007; Richards, 2011). Indeed, the U-shaped and depleted middle to heavy REE patterns of the Group II Late Jurassic-Early Cretaceous rocks (Fig. 8h) can be attributed to amphibole fractionation (Richards and Kerrich, 2007; Richards, 2011). Positive covariation of the Sr/Y ratios with increasing SiO2 concentrations (Fig. 9a) is consistent with amphibole and garnet fractionation in a deeper crustal environment for Late-Jurassic-Early Cretaceous rocks sampled at Djaygir, Maarif, Kharkhar, and Garadagh (Fig. 3a). By contrast, Late-Jurassic-Early Cretaceous rocks sampled at Gedabek (this study and Sadikhov et al., 2018), and at Barum and Gabahtepe (Fig. 3a; Sadikhov and Shatova, 2017), as well as the Middle Jurassic rock samples display a negative covariation of Sr/Y ratios with increasing SiO2 concentrations, which is consistent with shallower crustal environments and plagioclase-dominant fractionation (Fig. 9a). Both negative and positive covariations of Dy/Yb ratios with increasing SiO2 are consistent, respectively, with amphibole and garnet fractionation during petrogenesis of the Late Jurassic-Early Cretaceous magmatic rocks (Fig. 9b). The garnet fractionation trend corresponds to samples collected at Kharkhar, Garadagh, and Djaygir, which coincide with the location of the main porphyry Cu cluster of the Gedabek district (Fig. 3a; Babazadeh et al., 1990). Our geochronological data indicate that the ore deposits of the Gedabek district were formed at the end of an ~50-m.y.long arc maturation and crustal thickening evolution (Figs. 4, 10). At the Gedabek deposit (Fig. 3b), hydrothermal alteration minerals (muscovite and K-feldspar) from the potassic alteration zone have yielded 40Ar/39Ar ages between 139.8 ± 0.9 and 136.1 ± 0.9 Ma, which overprint the youngest granodiorite dike event dated in this deposit at 140.3 ± 0.9 Ma (GE-11-06, see Figs. 4, 5c, 7b). The later granodiorite dike (GE-11-06) and the dated alteration muscovite (GE-11-23) at Gedabek have overlapping ages (Fig. 7b, e) and can be considered as broadly coeval with Fe-Co skarn ore formation at Dashkesan (Fig. 3a), which is associated with granodiorite and granite emplacement between 143 ± 2 and 138 ± 2 Ma (Fig. 4; Sadikhov, 2019). Molybdenite from Kharkhar dated previously at 133.3 ± 0.5 Ma (Moritz et al., 2016a) yields a slightly younger age than the hydrothermal alteration minerals at Gedabek (Fig. 4). Within analytical error, molybdenite from Kharkhar is coeval with granodioritic magmatism dated in our study at 133.0 ± 0.7 Ma at Maarif (Figs. 3a, 4, 7c). The ~133 Ma granodioritic magmatism at Maarif belongs to the same granodiorite event observed in Djaygir, Kharkhar, and Garadagh, which is characterized by a strong amphibole and garnet fractionation trend (Fig. 9). Thus, porphyry mineralization at ~133 Ma coincides both spatially and temporally with the youngest magmatic and crustal thickening event of the Gedabek district. 197 GEDABEK MINING DISTRICT, AZERBAIJAN (1): ~175 to ~160 Ma: Middle Jurassic Nascent magmatic arc - Flat subduction Tholeiitic to transitional, bimodal magmatism Southern Neotethys ocean SW Somkheto-Karabagh arc (Eurasian margin) Arc construction NE Northern Neotethys ocean South Armenian block Plagiogranite (~175-165 Ma) (2): ~160 to ~125 Ma: Late Jurassic-Early Cretaceous Magmatic arc maturation - Slab steepening Medium to high-K calc-alkaline magmatism Porphyry-epithermal systems of the Gedabek district (~140-133 Ma) Southern Neotethys ocean SW Somkheto-Karabagh arc Magmatic arc migration Arc thickening Northern Neotethys ocean NE South Armenian block Diorite, granite, granodiorite (~160-130 Ma) Slab roll-back Asthenospheric mantle upwelling Fig. 10. Summary of the Middle Jurassic to Early Cretaceous geodynamic, magmatic, and metallogenic evolution of the Gedabek district, Somkheto-Karabagh belt, Lesser Caucasus, Azerbaijan: ~50-m.y.-long magmatic arc construction culminating with Early Cretaceous porphyry-epithermal ore deposit formation. This sequence of arc maturation and final porphyry-epithermal ore formation is also observed at the Alaverdi-Teghout and Kapan-Shikahogh districts (Figs. 2, 4). The late timing of epithermal and porphyry mineralization in the Gedabek district, after an ~50-m.y.-long arc maturation is reminiscent of the evolution in many porphyry-epithermal districts, where ore formation typically took place after significant crustal thickening (Fig. 10), and once sufficient amounts of fertile magmas were generated over time by MASH processes (Richards, 2003, 2015; Cooke et al., 2005; Sillitoe, 2010). Jurassic-Early Cretaceous Arc Maturation of the Southern Eurasian Margin Previous studies in the Somkheto-Karabagh belt have also documented the compositional evolution of the magmatic rocks from the Middle Jurassic to the Late Jurassic-Early Cretaceous in the Kapan-Shikahogh and Alaverdi-Teghout districts (Fig. 2; Mederer et al., 2013, 2019; Calder et al., 2019). Similar to the Gedabek area, Late Jurassic-Early Cretaceous magmatic rocks from the Kapan-Shikahogh and Alaverdi-Teghout districts have dominantly calc-alkaline to shoshonitic and mature island-arc compositions, whereas Middle Jurassic magmatic rocks have dominantly tholeiitic to transitional and primitive island-arc compositions (Fig. 8d, k). Concomitant increases of La/Yb, Th/Yb, and Ta/Yb ratios from Middle Jurassic to Late Jurassic-Early Cretaceous magmatic rocks at the Kapan-Shikahogh and Alaverdi-Teghout districts mimics the same trend as observed in the Gedabek area (Fig. 8i-j). This is also reflected by the chondrite- and mantle-normalized trace element diagrams documenting similar overlapping trends for Middle Jurassic and Late Jurassic-Early Cretaceous magmatic rocks along the entire Somkheto-Karabagh belt and its southern extension in the Kapan block (Fig. 8e-h), from the Alaverdi-Teghout through Gedabek to the Kapan-Shikahogh districts (Fig. 2). In brief, the Somkheto-Karabagh belt and the Kapan block have a preserved record of progressive magmatic arc maturation from a nascent Middle Jurassic arc setting, with a bimodal magma nature, to an evolved Late Jurassic-Early Cretaceous arc environment with a thickened crust (Fig. 10). The nature of the magma reservoirs also changed over time in a consistent pattern in all three districts (Fig. 8l). Middle Jurassic rocks at Alaverdi-Teghout, Gedabek, and Kapan-Shikahogh have systematically higher 87Sr/86Sr ratios and lower 143Nd/144Nd ratios when compared to Late Jurassic-Early Cretaceous rocks in each district (Fig. 8l). This variation of radiogenic isotope composition documents an increasing mantle component during magma petrogenesis from nascent Middle Jurassic to mature Late Jurassic-Early Cretaceous arc evolution along the entire Somkheto-Karabagh belt and Kapan block. We concur with Mederer et al. (2013) and Calder et al. (2019), who suggested slab roll-back and an associated asthenospheric mantle upwelling as an explanation for the shift to a more dominant mantle signature during Late Jurassic-Early Cretaceous magmatism (Fig. 10). Our interpretation is consistent with studies by Rolland et al. (2011), who recognized a 198 MORITZ ET AL. major thermal event in the Somkheto-Karabagh belt at ~166 to 167 Ma, which they have attributed to a major exhumation episode and a slab roll-back geodynamic setting. The broad north to south migration of intrusive activity documented by the spatial distribution of U-Pb zircon ages in the Gedabek district (Fig. 3) is consistent with progressive slab roll-back along the western Eurasian margin during Jurassic to Cretaceous evolution. The Late Jurassic-Early Cretaceous magmatic rocks from the Alaverdi-Teghout district have the highest 87Sr/86Sr ratios and lowest 143Nd/144Nd ratios, whereas those from Kapan-Shikahogh have the lowest 87Sr/86Sr ratios and highest 143Nd/144Nd ratios, and those from Gedabek have intermediate compositions (Fig. 8l). This indicates an along-arc variation of the composition of the magmatic source reservoir, from a higher crustal component in the northwest at Alaverdi-Teghout to a higher mantle component in the southeast at Kapan-Shikahogh (Fig. 2). We attribute the northwest to southeast isotopic trend to differences in metamorphic basement architecture. Indeed, major Proterozoic and Paleozoic basement massifs crop out in the Bolnisi and Alaverdi-Teghout districts, at the northern tip of the Somkheto-Karabagh belt (Fig. 2; Shengelia et al., 2006; Zakariadze et al., 2007). By contrast, no rocks older than the Middle Jurassic have been reported so far in the Kapan-Shikahogh districts (Mederer et al., 2019), despite intensive drilling, mapping, and underground mining. This suggests a more important interaction of mantle-derived magmas with old crust in the northwestern part of the Somkheto-Karabagh belt (at Alaverdi/Teghout, Fig. 2), which is underlain by Proterozoic and Paleozoic basement. In comparison, such crustal interaction was negligible to absent in the southeastern part of the belt (at Kapan/Shikahogh, Fig. 2), where basement rocks were scarce or absent during the Mesozoic along the Eurasian margin. Concomitantly with the northwest to southeast radiogenic isotope trend (Fig. 8l), there is a progressive younging of magmatism from the northwestern extremity of the Somkheto-Karabagh belt to the Kapan block (Fig. 4). Indeed, at Alaverdi-Teghout, the magmatism dated so far has a duration of ~15 m.y. during the Middle Jurassic. At Gedabek, the extensive magmatism lasted for ~50 m.y., from the Middle Jurassic to the Early Cretaceous at ~133 Ma. At Kapan-Shikahogh, magmatism also covers the Middle Jurassic to Early Cretaceous, but with the exception of one sample, it outlasted the Gedabek magmatism, with the youngest age at ~129 Ma (Fig. 4). Dating of magmatism by U-Pb zircon and K-Ar geochronology in the Qizilbulaq-Mehmana area, located in between the Gedabek and the Kapan-Shikahogh districts (Fig. 2), has yielded ages between 154 and 131 Ma (Ismet et al., 2003; Galoyan et al., 2013), and fits within the NW- to SE-younging trend of magmatism. This trend is consistent with Hässig et al. (2020), who have reported the same regional northwest to southeast younging of Jurassic to Early Cretaceous magmatism from the western Greater Caucasus to the southernmost Lesser Caucasus. In each mining district, porphyry-epithermal ore formation systematically took place at the end of the magmatic evolution. It is diachronous at the scale of the belt, since it goes hand in hand with the magmatic evolution, starting at 146 Ma at Teghout in the north (Fig. 2; Re-Os molybdenite age, Mori- tz et al., 2016a), followed by Kharkhar at 133 Ma (Fig. 3a; ReOs molybdenite age, Moritz et al., 2016a), and 140 to 136 Ma at Gedabek (Figs. 2, 3a; 40Ar/39Ar muscovite and K-feldspar ages, this study). No ore formation ages have been obtained so far in the Shikahogh district (Fig. 2), but stockwork-type Cu-Au-Mo orebodies occur at the outer contact of the Early Cretaceous intrusions (Achikgiozyan et al., 1987), which constrains porphyry-type ore formation in the Shikahogh district to less than 139 to 129 Ma. Along the entire Jurassic to Early Cretaceous Somkheto-Karabagh belt and Kapan block, the Gedabek district stands out as the segment with the highest density of latest Late Middle Jurassic and Early Cretaceous porphyry-epithermal ore deposits and prospects. Further studies will need to examine if this high ore deposit and prospect density can be directly correlated with the long duration of magmatic arc construction and crustal thickening over ~50 m.y. in the Gedabek area. Alternatively, the shorter magmatic arc construction of ~15 m.y. recognized at Alaverdi-Teghout and Kapan-Shikahogh may reflect our failure so far to recognize and date isotopically older Jurassic rocks in each district. The Lesser Caucasus and Eastern Pontides Arcs: Evidence for a Continuous Jurassic-Early Cretaceous Metallogenic Belt Along the Eurasian Margin Previous studies in the Eastern Pontides, Turkey, have also recognized Early Cretaceous magmatic and ore-forming events at İspir-Ulutaş (Table 1; Figs. 2, 4; Delibaş et al., 2016, 2019; Karsli et al., 2021). Molybdenite from the porphyry Cu stage at İspir-Ulutaş has been dated by Re-Os at 131.0 ± 0.7 Ma (Delibaş et al., 2019), which is only slightly younger than the Re-Os molybdenite age of 133.3 ± 0.5 Ma at Kharkhar in the Gedabek district (Figs. 3a, 4; Moritz et al., 2016a), and overlaps with Early Cretaceous porphyry Cu-related magmatism in the Shikahogh district in the Kapan block (Fig. 4). Therefore, we conclude that there is a major Late Jurassic to Early Cretaceous porphyry-epithermal belt, which can be traced along the southern Eurasian margin from the Eastern Pontides to the southern Lesser Caucasus (Fig. 2). Our knowledge about Late Jurassic and Early Cretaceous magmatism in the Eastern Pontides is still fragmentary. Data about Late Jurassic and Early Cretaceous magmatism is scarce in the Eastern Pontides (Hässig et al., 2020). Furthermore, there is still debate about the onset of N-verging subduction of the northern Neotethys, whether it was as late as the Early Cretaceous (Karsli et al., 2021) or much earlier during the Triassic (Okay et al., 2020). It also sets time constraints on the oldest possible porphyry-epithermal systems that could have been emplaced in the Eastern Pontides. Other districts should be tested in the Eastern Pontides to identify the presence of Early Cretaceous or Jurassic porphyry-epithermal systems. One target area might be Olur (Table 1; Önal et al., 2017), which is located in the easternmost Eastern Pontides (Fig. 2), where the magmatic setting is dominated by Jurassic rocks, and alteration and ore types are comparable with those of the Alaverdi and Kapan districts (Fig. 2; Mederer et al., 2014, 2019; Calder et al., 2019). Nevertheless, ore formation at Olur has been interpreted as Eocene only on the basis of reported Eocene magmatic intrusions (Önal et al., 2017), despite the lack of isotope dating. An additional target area is GEDABEK MINING DISTRICT, AZERBAIJAN the Dambludka/Dambludi prospect in the southern part of the Bolnisi district in Georgia, which is located directly west to the Armenian Alaverdi-Teghout district, at the transition between the Eastern Pontides and the Somkheto-Karabagh belt (Fig. 2). The Dambludka/Dambludi prospect consists of high-grade polymetallic (Cu-Zn-Pb-Au) quartz-sulfide veins hosted mainly by magmatic, and by subsidiary sedimentary rocks with uncertain Jurassic to Cretaceous ages of the Loki massif (Table 1; Georgian Mining Corporation, 2018, 2019). In addition to the Late Jurassic-Early Cretaceous porphyry-epithermal ore belt that can be outlined from the Eastern Pontides to the Lesser Caucasus, there is potential for the discovery of volcanogenic massive sulfide deposits associated with nascent arc formation and Middle Jurassic (or earlier) magmatic rocks of this belt, characterized by tholeiitic to transitional compositions (this study, see Fig. 8d; Mederer et al., 2013, 2019; Calder et al., 2019). Indeed, in the Kapan district, southern Armenia (Fig. 2), Mederer et al. (2019) have described 162-m.y.-old ore deposit systems, with orebody, hydrothermal and magmatic rock characteristics typical of a submarine setting (e.g., Centralni West, Table 1), i.e., comparable to volcanogenic massive sulfide (VMS)-type deposits. Additionally, farther to the west in the Central Pontides, Günay et al. (2019) have reported an Early Jurassic VMS deposited dated at 178 Ma. The Gedabek district experienced intense uplift (Babazadeh et al., 1990), and the magmatic arc underwent major erosion and unroofing of the plutons during the Early Cretaceous (Sosson et al., 2010). Given such an uplift and exhumation setting, it remains open to question how the Early Cretaceous epithermal and porphyry systems have been preserved in the Gedabek district. Indeed, epithermal ore deposits, which form within the uppermost part of the crust, are particularly vulnerable to rapid erosion, which explains why such preserved deposits are predominantly late Cenozoic in age (Hedenquist et al., 2000; Simmons et al., 2005). Concealment by basin sedimentation or tectonic processes shortly following ore formation are necessary to preserve old epithermal systems (e.g., Kesler et al., 2004; Chambefort and Moritz, 2006; Márton et al., 2010). The same applies to porphyry systems for which burial beneath postmineral rock sequences enhances the preservation potential (Sillitoe et al., 2019). Further studies will be necessary to understand the Early Cretaceous postmineral processes that may explain the preservation of porphyry-epithermal systems in the Gedabek district. Such a knowledge can then be applied to other segments of the metallogenic belt extending from the Eastern Pontides to the Lesser Caucasus and allow us to understand whether the sparse distribution of Jurassic and Early Cretaceous ore deposits is a result of erosion below the levels of preservation of porphyry-epithermal systems, as stated previously (Richards, 2015). Alternatively, a more accurate understanding of postmineral burial and tectonic processes, combined with a more exhaustive geochronological data set for magmatism, and hydrothermal and ore deposit events, might allow us to identify prospective segments within the orogenic belt consisting of concealed fertile Jurassic and Early Cretaceous settings. Our contribution and previous studies provide abundant evidence for the Mesozoic magmatic and metallogenic con- 199 tinuity from the Eastern Pontides to the southernmost Lesser Caucasus (e.g., Moritz and Baker, 2019; Hässig et al., 2020; Moritz et al., 2020). By contrast, the Jurassic and Early Cretaceous geologic and metallogenic evolution of the Somkheto-Karabagh belt and the Kapan block is totally disconnected from the one in the adjacent Alborz in Iran (Moritz et al., 2016a). First of all, the NE-oriented Araks strike-slip fault constitutes a major regional stratigraphic and structural limit between the Alborz and the Lesser Caucasus (see AF, Fig. 2; Sosson et al., 2010; Rolland, 2017). For instance, basaltic arc magmatism in the Alborz only started during the Barremian (mid-Early Cretaceous; Wensink and Varekamp, 1980), and the thick sedimentary basin sequences of the Late Triassic to Early Jurassic Shemshak Formation in Iran (Fürsich et al., 2005) are totally unknown in the Lesser Caucasus (Sosson et al., 2010). Moreover, while the Greater Caucasus, the Alborz and other Iranian terranes were affected by the Triassic-Jurassic Cimmerian orogeny (Adamia et al., 2011; Masoodi et al., 2013), there is no evidence for such an orogenic phase in the Lesser Caucasus and the Eastern Pontides (Sosson et al., 2010; Topuz et al., 2013; Hässig et al., 2015; Rolland, 2017). In brief, the Iranian Alborz and the Lesser Caucasus have major contrasting Mesozoic tectonic, magmatic, and sedimentary records, which also reflect different metallogenic evolutions, and explain the absence of any metallogenic continuity of the Mesozoic belt from the Lesser Caucasus to the Alborz. Similarly, the Jurassic Sanandaj-Sirjan zone in Iran maybe considered as the southern counterpart of the Jurassic Somkheto-Karabagh belt and Kapan zone of the Lesser Caucasus. However, the Sanandaj-Sirjan zone is known as a particularly unmineralized zone, devoid of porphyry Cu deposits (Zarasvandi et al., 2020), and therefore cannot be viewed as an extension of the well-endowed Caucasian Jurassic magmatic belts. By contrast, once the various Gondwana terranes (South Armenian block and the Tauride-Anatolide platform; see SAB and TAP, Figs. 1, 2) were accreted to the Eurasian margin by the Paleocene, the eastern Turkish tectonic zones, the Lesser Caucasus, and the Iranian Urumieh-Dokhtar and Alborz arcs shared a common regional tectonic, magmatic, and metallogenic setting from the Eocene. Thus, the Cenozoic ore deposit array of the South Armenian block in the southernmost Lesser Caucasus can be extended into the Iranian Cenozoic porphyry and epithermal Alborz and Urumieh-Dokhtar belts (Fig. 1; e.g., Aghazadeh et al., 2015; Simmonds and Moazzen, 2015). However, there are distinct differences between the South Armenian block deposits and those from the Iranian tectonic zones. Indeed, the porphyry-epithermal systems of the South Armenian block are predominantly Eocene and Oligocene in age (Rezeau et al., 2016, 2019; Grosjean et al., 2019), and were related to transpressional strike-slip tectonics during a subduction to postcollisional setting evolution (Hovakimyan et al., 2019) By contrast, the Iranian porphyry and epithermal systems are predominantly Miocene in age (Aghazadeh et al., 2015; Hassanpour et al., 2015; Simmonds and Moazzen, 2015; with the exception of two porphyry occurrences, which are late Oligocene), and were linked to postcollisional extension and lithospheric mantle delamination (Shafiei et al., 2009; Aghazadeh et al., 2015). The north to south younging of the porphyry systems, from Eocene-Oligocene in the southernmost Lesser Caucasus to predominantly 200 MORITZ ET AL. Miocene in Iran, coincides with the progressive north to south younging of the Arabia-Eurasia collision (Agard et al., 2011). Conclusions In this study, we have documented the existence of a Middle Jurassic to Early Cretaceous magmatic and porphyry-epithermal belt extending from the Eastern Pontides to the southernmost Lesser Caucasus. The Middle Jurassic to Early Cretaceous metallogenic belt certainly has the potential for future porphyry and epithermal discoveries. The different settings of the Somkheto-Karabagh belt and the Kapan block demonstrate that Jurassic to Early Cretaceous magmatic rocks and ore deposits have been preserved from erosion. Our study of the Gedabek district shows that favorable regional conditions for porphyry-epithermal genesis, including long arc maturation and crustal thickening, were reached during the Jurassic and Early Cretaceous. We have learned from our studies in the Somkheto-Karabagh belt that there is an along-arc migration of events, and that magmatism and ore formation were diachronous. Further studies are required to understand whether the high density of ore deposits and prospects of the Gedabek area is a feature restricted to the Somkheto-Karabagh belt. Indeed, we need to understand if the Gedabek ore deposit district is the result of a perfect juxtaposition of geologic settings and processes, e.g., a long magmatic maturation over ~50 m.y., resulting in significant crustal thickening during slab retreat and asthenospheric mantle upwelling. Alternatively, we must ask ourselves if our current knowledge and interpretations are biased due to an absence of data along the remaining Jurassic-Early Cretaceous belt, in particular along the Eastern Pontides segment. Once the Early Cretaceous postmineral preservation processes are more adequately constrained in the major ore deposit centers along the Eastern Pontides and Lesser Caucasus, we might be able to identify and focus on potential target areas along this belt to explore for concealed ore deposits. Acknowledgments The research was supported by the Swiss National Science Foundation through the research grants 200020-138130, 200020-155928, and 200021-188714, and the SCOPES Joint Research Projects IB7620-118901, and IZ73Z0-128324. P. Hemon thanks the Society of Economic Geologists for a Student Research Grant obtained in 2011. The authors would like to thank the staff of the Azerbaijan International Mining Company for great hospitality, accommodation, logistical support, property access, and sample handling in the Gedabek mining district. We thank F. Caponi, M. Senn, M.-C. Pinget, J.-M. Boccard, A. Martignier, and D. Dominguez for sample preparation, XRF and isotope analyses, thin and polished section preparation, SEM imagery and zircon separation. Yann Rolland and Timothy Baker are thanked for their comments and corrections, which greatly improved the quality of this manuscript. 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Zohrabyan, S.A., and Melkonyan, R.L., 1999, Role of structural factors on the location of mineralization in iron-pyrite deposits of the Alaverdi-Kapan zone: Proceedings of the National Academy of Sciences of the Republic of Armenia, Earth Sciences, v. 52, p. 31–40 (in Russian with English abs.). Zürcher, L., Bookstrom, A.A., Hammarstrom, J.M., Mars, J.C., Ludington, S.D., Zientek, M.L., Dunlap, P., and Wallis, J.C., 2019, Tectono-magmatic evolution of porphyry belts in the central Tethys region of Turkey, the Caucasus, Iran, western Pakistan, and southern Afghanistan: Ore Geology Reviews, v. 111, no. 102849. Robert Moritz is professor at the University of Geneva in Switzerland, and teaches and leads research projects in economic geology and geochemistry. He is currently the SEG Regional Vice-President for Europe. Robert obtained his Ph.D. in geology in 1988 at McMaster University, Ontario, Canada. From 1988 to 1991, he was a research associate at the Institut National de Recherche Scientifique in Quebec City, Canada. His current research activities are focused on the metallogenic, geodynamic, and magmatic evolution of the Tethyan orogenic belt, with projects in the Lesser Caucasus, Turkey, and southeast Europe, and mainly on porphyry and epithermal systems.
