The Geology of the Kişladağ Porphyry Gold Deposit, Turkey
Published:January 01, 2016
T. Baker, D. Bickford, S. Juras, P. Lewis, Y. Oztas, K. Ross, A. Tukac, F. Rabayrol, A. Miskovic, R. Friedman, R.A. Creaser, R. Spikings, 2016. "The Geology of the Kişladağ Porphyry Gold Deposit, Turkey", Tectonics and Metallogeny of the Tethyan Orogenic Belt, Jeremy P. Richards
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The Kişladağ porphyry gold deposit (16.8 Moz) is located in western Anatolia, Turkey, and is hosted in a nested complex of monzonite porphyries that intruded coeval volcanic rocks of the Beydagi stratovolcano and the Menderes metamorphic basement. The intrusions and volcanic rocks have a high K calc-alkaline to shoshonitic affinity similar to the regional volcanic rocks of western Anatolia. Three main intrusive phases are recognized with average gold grades highest in the early intrusions, Intrusion 1 (~0.8 g/t Au) and Intrusion 2 (~0.7 g/t Au), followed by the weakly mineralized Intrusion 3 (typically <0.2 g/t Au). The highest gold (~0.84 g/t) is also associated with the higher temperature potassic (biotite-K feldspar ± actinolite) core of the deposit in Intrusion 1. Molybdenum is most closely associated with Au, whereas the Cu concentration on average is unusually low (~200 ppm) but increases with depth (500-1,000 ppm). Surrounding and partly overlapping the potassic zone is a distinct tourmaline-white mica (± pyrite ± albite ± quartz) alteration with tourmaline abundant up to 500 m from the center of the deposit. White mica is more widely distributed with compositions varying from proximal muscovite-paragonite to distal phengite. Stockwork veinlets are common within the potassic and tourmaline-white mica zones and evolve from volumetrically minor quartz-rich, to quartz-pyrite, to quartz-pyrite with tourmaline envelopes, to the most abundant pyrite-tourmaline veins and breccias, and finally pyrite-only veins. A poorly mineralized advanced argillic alteration assemblage (quartz-alunite ± dickite ± pyrophyllite ± pyrite) postdates the tourmaline-white mica alteration and is particularly abundant in the eastern flank of the deposit and as a lithocap. The most widespread alteration is argillic comprising kaolinite ± smectite ± pyrite ± quartz, and overprinting all alteration phases, and is particularly widespread in the surrounding volcanic package.
New geochronological results from the Kisladag deposit constrain the timing and duration of the main gold mineralization stage to <0.4 m.y. (14.76 ± 0.01-14.36 ± 0.02 Ma). The system evolved in the following sequence: (1) Intrusion 1 (>14.76 ± 0.01 Ma), (2) Intrusion 2 (14.76 ± 0.01 Ma), (3) potassic alteration coeval with mineralization (14.4 ± 0.1 Ma), and (4) Intrusion 3 (14.36 ± 0.02 Ma). The deposition of gold is constrained by the emplacement of the sulfide mineralization dated at 14.49 ± 0.06 Ma by Re-Os on molybdenite.
The Kişladağ deposit is classified as a gold-only porphyry deposit due to its exceptionally low Cu/Au ratio («0.03). There are few economically significant global analogues—examples include the Maricunga porphyry deposits (9.8 Moz Au) in Chile and La Colosa (33.2 Moz Au) in Columbia. The low Cu/Au ratio may in part be related to the shallow level of emplacement (<1 km?) but also reflects the postcollisional setting. The deposit formed at least 50 m.y. after closure of the northern Neotethys ocean that was related to Cretaceous collision and compression, and 15 m.y. after the commencement slab roll-back of the southern Neotethys ocean and the onset of upper plate extension in the late Eocene to early Oligocene. The Miocene volcanic rocks that host Kisladag are in part related to a slab tear that resulted in upwelling of asthenospheric mantle, which melted previously metasomatized subcontinental lithospheric mantle. Postcollision extension, fertile upper mantle, shallow subduction, and slab tear-induced magmatism, and shallow level of emplacement may have been important factors in the gold-rich nature of Kisladag.
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Tectonics and Metallogeny of the Tethyan Orogenic Belt
The Tethyan orogenic belt stretches from the Alps, through the Carpathians and Balkans, Taurides and Caucasus, Zagros, Makran, and Himalayas, to Indochina and into the southwest Pacific Ocean. It represents a complete Wilson Cycle, from opening and closure of the Paleotethys Ocean in the mid-Paleozoic to the Late Triassic, opening of the Neotethys Ocean in the Permian-Early Triassic, and its progressive closure throughout the late Mesozoic and Cenozoic eras. The current state of the orogen includes all stages of convergence from active subduction beneath the Makran and eastern Mediterranean, through advanced continental collision in the Caucasus/Taurides and Zagros, to syn- to postcollisional readjustment in the Carpathians, Balkans, Himalayas, and Indochina (Richards, 2015).
The region has been the focus of significant recent attention from geologists interested both in its tectonic evolution and metallogeny, made possible by increased accessibility to many of the geographic sections of the orogen. Key breakthroughs in understanding its tectonic history have come through improved geochronological techniques and expansion of the database of samples and events dated, combined with more accurate paleogeographic and tectonic models. In parallel, an improved understanding of the subtle relationships between tectonomagmatic and metallogenic processes have refined interpretations that were once based on simplistic assumptions (e.g., that porphyry deposits only form above active subduction zones). Indeed, economic geologists have been among the key drivers of these advances by demanding more accurate and predictive tectonomagmatic models for ore formation that can reliably inform mineral exploration.
Consequently, the Tethyan orogen is now understood to be the best preserved global example of a collisional orogen, where all stages of convergence can be observed in real or recent geological time, and the detailed relationships to ore formation, commonly reflecting tectonic changes measured on submillion-year timescales, can be accurately documented and modeled.
In this volume, we present a selection of papers that showcase this advancement in knowledge, with examples from Eastern Europe to South Asia.Beginning in the Balkans, Knaak et al. (2016) describe the variety of mineral deposits that occur in the emergent worldclass Timok region of eastern Serbia. The origin of the Late Cretaceous Timok Magmatic Complex remains debated, but the authors propose that arc magmatism was focused by dextral transtensional structures, followed by complex structural rearrangement in the Cenozoic. Porphyry Cu-Au deposits, polymetallic replacement deposits, and sedimentary rockhosted Au deposits occur in close spatial, and possibly genetic, relationship to the Late Cretaceous arc rocks. A key contribution of this study is the detailed reconstruction of later Cenozoic fault movements that led to structural dislocation and oroclinal bending, complicating geologic and metallogenic correlations in the region.
- absolute age
- gold ores
- igneous rocks
- metal ores
- Middle East
- plate tectonics
- plutonic rocks
- stockwork deposits
- structural controls
- volcanic rocks
- Kisladag Deposit
- Menderes Metamorphic Basement