Proceedings Chapter

Structural control of the Cenozoic porphyry Cu-Mo, epithermal and skarn deposits and prospects, Central Tethyan belt, Lesser Caucasus

HOVAKIMYAN, Samvel, et al.

Abstract

The Cenozoic evolution of the central segment of the Tethyan metallogenic belt is dominated by the oblique convergence and final collision of Gondwana-derived terranes and the Arabian plate with Eurasia, which created a favorable setting for the formation of the highly mineralized -Ordubad pluton inthe southernmost Lesser Caucasus, in the Zangezur-Ordubad mining district. Paleostress reconstructions indicate anti-clockwise rotation from NE-oriented compression during the early and middle Eocene to NNW-oriented compression during the Pliocene. During the Eocene the N-S oriented faults are consistent with dextral strike-slip tectonics, correspond to synthetic faults and control the main porphyry Cu-Mo and epithermal deposits and prospects. The sinistral E-W oriented en- échelon faults correspond to antithetic faults. This strike-slip kinematics is consistent with the regional NE-oriented compression in the Zangezur-Ordubad district and concomitant with final subduction of the Neotethys along the Eurasian margin. Sinistral strike-slip kinematics along the E-W oriented faults resulted in clockwise rotation of the [...]

Reference

HOVAKIMYAN, Samvel, et al. Structural control of the Cenozoic porphyry Cu-Mo, epithermal and skarn deposits and prospects, Central Tethyan belt, Lesser Caucasus. In: Proceedings of the 14th SGA Biennial Meeting. 2017.

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1 / 1 Structural control of the Cenozoic porphyry Cu-Mo, epithermal and skarn deposits and prospects, Central Tethyan belt, Lesser Caucasus

Samvel Hovakimyan, Robert Moritz University of Geneva, Geneva, Switzerland

Rodrik Tayan, Rafael Melkonyan, Marianna Harutyunyan Institute of Geological Sciences of the National Academy of Sciences of the Republic of

the control of the porphyry Cu-Mo, epithermal and skarn Abstract. The Cenozoic evolution of the central segment of systems hosted by the Meghri-Ordubad pluton. the Tethyan metallogenic belt is dominated by the oblique The aim of this study is to understand how ore deposit convergence and final collision of Gondwana-derived and prospect location, ore body geometry in the Zangezur- terranes and the Arabian plate with Eurasia, which created Ordubad mining district are linked to the long-lasting a favorable setting for the formation of the highly mineralized Meghri-Ordubad pluton inthe southernmost Eocene to Mio-Pliocene regional strike-slip tectonics, and Lesser Caucasus, in the Zangezur-Ordubad mining district. far-field plate tectonic evolution from Eocene subduction Paleostress reconstructions indicate anti-clockwise rotation to Miocene post-collision. from NE-oriented compression during the early and middle We discuss the paleostress and the kinematic Eocene to NNW-oriented compression during the Pliocene. environment of the major strike-slip and oblique-slip ore- During the Eocene the N-S oriented faults are consistent controlling faults throughout the Cenozoic tectonic with dextral strike-slip tectonics, correspond to synthetic evolution of the Meghri-Ordubad pluton based on detailed faults and control the main porphyry Cu-Mo and epithermal structural field mapping of the ore districts, stereonet deposits and prospects. The sinistral E-W oriented en- compilation of ore-bearing fractures and vein orientations échelon faults correspond to antithetic faults. This strike-slip kinematics is consistent with the regional NE-oriented in the major porphyry and epithermal deposits, and the compression in the Zangezur-Ordubad district and paleostress reconstructions. concomitant with final subduction of the Neotethys along the Eurasian margin. Sinistral strike-slip kinematics along the E-W oriented faults resulted in clockwise rotation of the 2 Major regional district-scale structures individual blocks of the Zangezur-Ordubad district. During the Oligocene and Miocene anti-clockwise rotation of the The Zangezur-Ordubad region consists of the main paleostress compressional orientation resulted in reactivation of existing ore-controlling structures in a Nakhitchevan and Zangezur tectonic blocks (Fig. 1), sinistral strike-slip tectonic regime, which is consistent with which behaved as two separate entities since the middle the re-orientation of the tectonic plate kinematics and re- Eocene (Tayan et al. 1976), when uplifting of the organization of the Arabia-Eurasia collision. Zangezur block started with respect to the Nakhitchevan block. The two tectonic blocks are separated by the NNW- oriented dextral strike-slip -Ordubad fault zone (Fig. 1; Tayan et al. 1976). To the east, the major regional NNW-oriented, dextral strike-slip Khustup-Giratagh fault zone separates the Zangezur block from the block, in other words the Mesozoic Eurasian margin (Fig. 1). 1 Introduction The Zangezur block is crosscut by numerous N-S, E-W, The Zangezur-Ordubad mining district consists of the NE- and NW-oriented faults, which are the main ore- and Meghri-Ordubad pluton in the southernmost Lesser magma-controlling structures of the Zangezur-Ordubad Caucasus, Central Tethyan belt (Moritz et al. 2016a). It district (Fig. 1). The majority of the Cenozoic magmatism, was formed by repeated intrusive activity from the mid- ore deposits and prospects are confined to a central N-S- Eocene subduction to the Miocene post-collisional oriented array, located between the Khustup-Giratagh and evolution of the southernmost Lesser Caucasus, with the Salvard-Ordubad fault zones, and with a distinct pulsed ore formation (Karamyan 1978; Melkonyan et al. discordant orientation with respect to the two regional 2008; Moritz et al. 2016a, b; Rezeau at al. 2016). It is a fault zones (Fig.1). It has been defined as the central very fertile area and contains sixteen porphyry Cu-Mo, magma- and ore-controlling zone by previous authors, and twenty epithermal Au and base metal and three skarn W, it records a long lasting and multi-stage tectonic and Cu-Mo, Fe deposits and prospects. metallogenic evolution, with structurally controlled Regional strike-slip faults played an important role in magmatic intrusions and ore occurrences (Fig. 1; Karamyan 1978; Tayan 1998).

S02 – Ore forming magmatic-hydrothermal processes along active margins 303 Figure 1. Structural map of the Zangezur-Ordubad mining This strike-slip kinematics is consistent with the regional district (after Karamyan et al. 1974; Tayan et al. 1998; NE-oriented compression in the Zangezur-Ordubad Hovakimyan et al. 2016) with locations of the major porphyry mining district revealed by the paleostress indicators and Cu-Mo and epithermal Au-polymetallic and skarn Fe, Cu-Mo corresponding to Eocene SW- to NE-oriented plate and W deposits and prospects. convergence and Neotethys subduction beneath Eurasia along the Lesser Caucasus-Zagros segment of the Tethyan belt (Barrier and Vrielynck 2008). Sinistral strike-slip 3 Eocene tectonic and ore control regime kinematics along the E-W oriented faults resulted in clockwise rotation of the individual blocks of the Paleostress reconstructions reveal a NE-SW-oriented Zangezur-Ordubad district (Figs. 1 and 2). Such block compressional setting during the early and middle Eocene, rotation is typical for strike-slip fault systems, with the which was favorable for dextral displacements along the blocks rotating synthetically with respect to the main two major, regional NNW-oriented Khustup-Giratakh and master faults (Kim et al. 2014). Salvard-Ordubad strike- slip faults (Fig.1). This resulted in During the Eocene, dextral displacement along the the formation of a N-S oriented transrotational basin, major N-S oriented strike-slip faults were favorable for known as the Central magma and ore- controlling zone creating of NE-oriented en-échelon normal faults or (Tayan 1998). extension fractures. These faults can be observed from the Since the Eocene the N-S oriented faults are consistent regional scale down to the ore body scale in the porphyry with subparallel dextral strike-slip tectonics and and epithermal systems. The N-S oriented faults, in correspond to synthetic faults (Fig. 1; Tashtun, Meghriget, particular at their intersection with E-W and NE-oriented Spetry, Tey, Terterasar, and Nshanakar faults) faults, were important ore-controlling structures for the and the sinistral E-W oriented en-échelon faults emplacement of major porphyry Cu-Mo (e.g., Dastakert, correspond to antithetic faults (Fig. 1; Aramazd, Voghji, Hanqasar, Aygedzor and Agarak) and epithermal Au, base Meghrasar, Meghriget-Cav, Bughakyar and Agarak faults).

304 Mineral Resources to Discover - 14th SGA Biennial Meeting 2017, Volume 1 metal (e.g., Tey-Lichkvaz and Terterasar) deposits and W oriented, which is consistent with N-S oriented prospects. compression during the Miocene. The NE- to NNE-oriented structures were important controls of the skarn deposits and prospects. They occur mainly in the northern and southern blocks (Fig.1). The Svaranc Fe skarn deposit related with the regional NNW-oriented Khustup-Giratagh dextral strike- slip fault and the Kefashen Cu-Mo and W prospects occur at the contact of the intrusion and Middle Devonian to Late Permian carbonate rock and shale along a NW- oriented thrust zone (Fig.1; Harutyunyan 1995).

Figure 3. Characteristics of the major N-S oriented ore- controlling faults. a from the early and middle Eocene to early Oligocene. b during the late Miocene with the formation of the Meghri – Tey graben.

Figure 2. Clockwise block rotation in the Zangezur-Ordubad mining district. 5 Miocene to Pliocene tectonic regime: structural control of the Lichk porphyry- epithermal system 4 Oligocene tectonic regime: structural control of the world class Kadjaran Paleostress reconstructions in the Zangezur-Ordubad porphyry deposit region indicate a progressive rotation of the major compression from NNE-oriented during the Oligocene to The paleostress data indicate a progressive anti-clockwise N-S-oriented during the Miocene and finally to NNW- rotation of the main stress axes from regional NE-oriented oriented during the Pliocene, which is consistent with the compression (Fig. 3a) to NNE-oriented compression re-orientation of the tectonic plate kinematics and re- during the Oligocene (Fig. 3b) and to N-S compression organization of the Arabia-Eurasia collision since at least during the Miocene. Therefore, since the Oligocene, the late Miocene (Allen et al. 2004; Austermann and magmatic intrusions and ore deposits were progressively Iaffladano 2013). emplaced under a different regional tectonic regime than The early Miocene E-W oriented extensional setting their Eocene counterparts. was favorable for intruding the early Miocene porphyritic The Oligocene giant Kadjaran porphyry deposit formed granite-granodiorite of the Voghji massif along the in the immediate vicinity of the NNW oriented Tashtun footwall of the Tashtun fault (Fig. 1). This reveals that the and E-W oriented Voghji fault intersection (Fig. 1). The E- Tashtun fault had an essentially oblique, normal fault W-, NE- and N-S oriented ore and dike controls reveal behavior and controlled the western boundary of the that structures inherited from the Eocene dextral strike- Meghri-Tey graben since the early Miocene (Figs. 1 and slip tectonics were reactived during the Oligocene. 3b; Tayan et al. 1998). The eastern boundary of the graben However, the reverse motion along the E-W and NE- was controlled by the N-S oriented Meghriget fault (Figs. oriented faults controlling the 26-27 Ma-old ore-bearing 1 and 3b). The geometry and N-S orientation of the veins at the Kadjaran porphyry deposit is not compatible Meghri-Tey graben is consistent with E-W and NE- with dextral strike-slip tectonics under a NE-oriented orientation of the main extensional stress axes during the compression. These reverse fault geometries indicate that Miocene and Pliocene, respectively (Fig. 1). ore formation at Kadjaran occurred under a different The Miocene Lichk prospect is hosted by a 22.2 Ma- tectonic regime, more consistent with progressive NNE- to old porphyritic granodiorite emplaced within a release N-S oriented compression compatible with the paleostress bend between the western and eastern segments of the rotation from the late Oligocene to Miocene (Fig. 3b). Tashtun fault (Fig. 1). The geometry of the release bend is In the Kadjaran deposit, the early porphyry veinlets are inconsistent with dextral kinematics along the Tasthtun predominantly NE- to NNE-oriented and late chalcedony fault. However, it could have formed during sinistral and carbonate veinlets crosscutting 22 Ma-old kinematics. Dextral kinematics is recorded along the granodiorite porphyry dikes are mainly steeply-dipping E- eastern segment of the Tashtun fault during the Oligocene,

S02 – Ore forming magmatic-hydrothermal processes along active margins 305 with displacement of the early Oligocene diorite porphyry SCOPES projects IB7620-118901 and IZ73Z0-128324 and dike. During the Miocene mineralization event, the the Swiss National Science Foundation projects 200020- Tashtun fault had a sinistral oblique-slip kinematics, 138130, 200020-155928 and 200020-168996. S. which is recorded by sinistral displacement of segments of Hovakimyan would like to thank the Swiss government for the epithermal system controlled by the NE-oriented awarding the Swiss Government Excellence Postdoctoral Lichk fault. Thus, we conclude that the Lichk deposit and Scholarship for the 2014-2015 academic year, Foundation its host granodiorite porphyry were emplaced during Ernst et Lucie Schmidheiny from the University of Geneva Miocene sinistral reactivation of the Tashtun fault, which for a scholarship for the 2015-2016 academic year, was behaving as a dextral tectonic system until the early Foundation Azad and the Swiss Chapter of the Armenian Oligocene. The switch of the Tashtun fault behavior General Benevolent Union (AGBU). resulted in the development of a pull-apart basin and the formation of the Lichk porphyry - epithermal system. It coincides with the progressive rotation of the main References compressional orientation from the early Oligocene to the Miocene, and then the Pliocene (Fig. 3). Allen MB, Jackson J, Walker R (2004) Late Cenozoic reorganization of the Arabia-Eurasia collision and the comparison of short-term and long-term deformation rates: Tectonics, v. 23, TC2008 6 Discussion and conclusions Austermann J, Iaffaldano G (2013) The role of the Zagros orogeny in slowing down Arabia-Eurasia convergence since ~5 Ma: Tectonics, v. 32, p. 351–363 The proposed tectonic model explains the structural Barrier E, Vrielynck B. (eds) (2008) Palaeotectonic Maps of the control of porphyry Cu-Mo, epithermal and skarn deposits Middle East. CGMW and prospects of the Zangezur- Ordubad mining during the Harutyunyan MA (1995) The features of geological structure, early Eocene to Mio-Pliocene tectonic evolution of the mineralization and genesis of skarn of the Zangezur ore district: district in the context of regional strike-slip tectonics. Abstract of unpublished doctoral thesis. Yerevan State University. 20p. (in Russian) The progressive change of the main compressional Hovakimyan S, Moritz R, Tayan R, Melkonyan R, Harutyunyan M, paleostress orientation recorded in the Zangezur-Ordubad (2016) Regional strike-slip tectonics and porphyry Cu-Mo and region, rotating from NE during the early and middle epithermal ore deposit formation during Cenozoic subduction to Eocene to NNE during the early Oligocene to N-S during post-collisional evolution of the southernmost Lesser Caucasus, the Miocene and finally to NNW- during the Pliocene, is Tethyan belt. 14th Swiss Geoscience Meeting, 18- 19 November 2016, Geneva, Switzerland, abstract volume, p.61-62 consistent with the re-orientation of the tectonic plate Karamyan KA (1978) Geology, structure and the conditions of kinematics from Eocene subduction to Mio-Pliocene post- formation of the copper-molybdenum deposits of the Zangezur collision. ore region. Yerevan; Publishing House of the Academy of During the Eocene NE-oriented compression created Sciences Armenian SSR, 179 p. (in Russian) the essentially dextral strike-slip tectonic regime along the Karamyan KA, Tayan RN, Guyumdjyan OP (1974) The main features major N-S oriented strike-slip fault. The structures formed of intrusion magmatism Zangezur region of the Armenian SSR. Izvestia of Academy of Sciences of Arm.SSR, Nauki o Zemle, during Eocene dextral strike-slip faulting, concomitant №1, 54-65 with final subduction of the Neotethys, were repeatedly Kim Y-S, Peacock David CP, Sanderson David J (2004) Fault damage reactivated during the subsequent Neogene tectonic zones: Journal of Structural Geology 26, p. 503–517 evolution of the Zangezur-Ordubad region, as one evolved Moritz R, Melkonyan R, Selby D, Popkhadze N, Gugushvili V, Tayan from a subduction to a post-subduction geodynamic R, Ramazanov V (2016a) Metallogeny of the Lesser Caucasus: setting. From arc construction to post-collision evolution. Spec Pub Soc Econ Geol 19: 157-192 The Oligocene and Miocene deposits and prospects Moritz R, Rezeau H, Ovtcharova M, Tayan R, Melkonyan R, were formed essentially in a sinistral strike-slip tectonic Hovamkimyan S, Ramazanov V, Selby D, Ulianov A, Chiaradia regime, which created the favorable geometry and M, Putlitz B (2016b) Long-lived, stationary magmatism and adequate conditions for the emplacement of vein and pulsed porphyry systems during Tethyan subduction to post- stockwork-type porphyry Cu-Mo deposits, including the collision evolution in the southernmost Lesser Caucasus, Armenia and Nakhitchevan: Gondwana Research, 37, 465-503 giant Oligocene Kadjaran deposit and the Miocene Lichk Rezeau H, Moritz R, Wotzlaw JF, Tayan R, Melkonyan R, Ulianov A, prospect. Selby D, d’Abzaz FX, Stern RA (2016) Temporal and genetic This contribution underscores the importance of link between incremental pluton assembly and pulsed porphyry regional strike-slip tectonics as a fundamental control on Cu-Mo formation in accretionary orogens. Geology, v. 44 no. 8, the formation of Cenozoic porphyry-epithermal systems p. 627-630 and associated magmatism within the Lesser Caucasus, Tayan RN (1998) On central magma-ore controlling zone of the Zangezur ore region. Proceedings of the National Academy of which is comparable to many other metallogenic belts. Sciences of the Republic of Armenia, Earth Sciences, v. 51, №3, p.20-26 (in Russian with English abstract) Acknowledgements Tayan RN, Plotnikov EP, Abdurakhmanov RU (1976) Some features of emplacement of geological structure of the Zangezour- Nakhichevan region of Lesser Caucasus. Proceedings of the This study was financially supported by the National National Academy of Sciences of the Republic of Armenia, Academy of Sciences of Republic of Armenia, the Series of Earth Science, v. 29, № 4, 12–20 (in Russian)

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