Tectonomagmatic Controls on the Çöpler Epithermal Au and Cevizlidere Porphyry Cu-Au-Mo Deposits (Central Eatern Turkey) and the Genesis of the Porphyry-Epithermal Mineralization at the Çöpler Epithermal Au Deposit

  • Author / Creator
    Imer, Ali
  • The Munzur Mountains in central eastern Turkey are an emerging belt of intrusion-related precious and base metal deposits. Two recent discoveries, the Çöpler epithermal Au and Cevizlidere porphyry Cu-Mo-Au deposits, lie 50 km apart and are located along the northern and southern margins of the Munzur Mountain range, respectively. The Çöpler deposit is centered around shallow-level dioritic to granodioritic intrusive rocks of the Çöpler-Kabataş magmatic complex, which have been emplaced into a succession of regionally metamorphosed Late Paleozoic–Mesozoic sedimentary rocks and Mesozoic carbonate rocks. Cevizlidere is also formed in association with porphyritic diorites and granodiorites crosscutting the Paleozoic limestones. 40Ar/39Ar dating of two igneous biotite samples from Çöpler yielded plateau ages of 43.75±0.26 Ma and 44.19±0.23, whereas igneous hornblende from a third sample yielded a plateau age of 44.13±0.38. These ages closely overlap with 40Ar/39Ar ages of hydrothermal sericite (44.44±0.28 Ma) and biotite (43.84±0.26 Ma), and Re–Os ages from two molybdenite samples (44.6±0.2 and 43.9±0.2 Ma). Two biotite separates obtained from syn-mineral diorite porphyry from Cevizlidere yielded 40Ar/39Ar ages of 25.49±0.10 Ma and 25.10±0.14 Ma. 40Ar/39Ar age of hydrothermal biotite (24.73±0.08 Ma) and Re-Os ages of two molybdenite separates (24.90±0.10 Ma and 24.78±0.10 Ma) are slightly younger than the cooling ages of the diorite porphyry. Geochronological data suggests that the duration of magmatic-hydrothermal activity in both districts was short-lived (<1 m.y.) and that porphyry-style mineralization developed shortly after magma emplacement. No suitable minerals were found that could be used to date the epithermal system at Çöpler, but it is inferred to be close in age to the precursor porphyry system. The whole-rock geochemical characteristics of the intrusive rocks from the Çöpler-Kabataş magmatic complex and Cevizlidere are consistent with derivation from subduction-modified mantle sources. Although the area is tectonically complex, regional comparisons suggest that the intrusive system at Çöpler was formed in a back-arc setting behind the Southern Neotethys arc, in response to Paleocene slab roll-back and upper-plate extension. Cevizlidere was formed in a similar tectonic setting in the late Oligocene during a period of regional extension, following a period of contractional deformation and magmatic quiescence. The kinematic switch at this time was possibly related to the break-off of the Southern Neotethys oceanic slab prior to the Arabia–Eurasia continent-continent collision, implying a pre-collisional timing for the Cevizlidere deposit. Çöpler features a centrally-located subeconomic porphyry Cu-Au system characterized by a potassically-altered (biotite-K-feldspar-magnetite) core overprinted by a more extensive phyllic (quartz-sericite) alteration zone. The potassic alteration zone is associated with M-type hairline magnetite and B-type quartz ± magnetite ± sulfide veinlets, whereas the enveloping phyllic-altered assemblages contain abundant D-type quartz-pyrite and lesser polymetallic quartz-sulfide veinlets. Overprinting intermediate-sulfidation epithermal mineralization is divided into two stages. Main-stage epithermal mineralization is characterized by carbonate-sulfide veinlets consisting of arsenical pyrite, arsenopyrite, marcasite, chalcopyrite, tennantite/tetrahedrite, galena, and sphalerite. Late-stage sooty pyrite veinlets contain some realgar and orpiment and are associated with zones of extensive carbonate alteration. Manto-type carbonate-replacement zones sporadically occurring in the distal portions of the porphyry system also constitute a significant gold resource. Polyphase brine inclusions (~47–62 wt.% NaCl equiv.) in early B-type quartz ± magnetite ± sulfide veinlets were trapped with low salinity (~3–5.5 wt.% NaCl equiv.) vapor-rich inclusions at temperatures ~390°C and at a depth of ~1.5 km under lithostatic conditions. Fluids associated with the overprinting phyllic alteration were slightly cooler (~370°C) and less saline (37–42 wt.% NaCl equiv.). Fluid inclusions in carbonate-sulfide veinlets trapped moderate salinity (4–15 wt.% NaCl equiv.) fluids at ~290°C, whereas sooty pyrite veinlets were formed from low temperature (~100°C) and low to moderate salinity (1–14 wt.% NaCl equiv.) fluids. Combined fluid inclusion and stable isotope data indicate that the Au mineralizing system at Çöpler progressed from a high temperature porphyry system towards a relatively low temperature intermediate-sulfidation epithermal system. The early stages of epithermal mineralization developed from cooling and neutralization of predominantly magmatic-sourced hydrothermal fluids, whereas some involvement of meteoric waters was recorded during late stage epithermal mineralization. Overall, the porphyry-epithermal system at Çöpler was structurally and lithologically controlled, and the role of carbonate cover rocks as a pressure seal and also as a neutralizing agent was critical for its formation.

  • Subjects / Keywords
  • Graduation date
    Spring 2015
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.