Ore petrology,hydrothermal alteration,fluid inclusions,and sulfur stable isotopes of the Milin Kamak intermediate sulfidation epithermal Au-Ag deposit in Western Srednogorie,Bulgaria |
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| Institution: | 1. Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran;2. United States Geological Survey, Box 25046, MS 973, Denver Federal Center, Denver, CO 80225, USA;3. Mining Department, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran;4. Geological Survey of Norway (NGU), Leiv Eirikssons vei 39, 7491 Trondheim, Norway;1. Beijing Research Institute of Uranium Geology, Beijing 100029, China;2. Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China;3. Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, Tasmania 7001, Australia;4. Zijin Mining Group Co. Ltd, Shanghang 364200, Fujian, China;1. Department of Economic Geology, Tarbiat Modares University, Tehran, Iran;2. Dept. d''Enginyeria Minera, Industrial i TIC, Universitat Politècnica de Catalunya, Barcelona, Spain |
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| Abstract: | The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50 km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Milin Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000 m, widths from several cm to 3–4 m, rarely to 10–15 m, an average of 80–90 m depth (a maximum of 200 m) and dip steeply to the south. The average content of gold is 5.04 g/t and silver – 13.01 g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H2O-rich with homogenization temperature (Th) ranging from 238 to 345 °C as the majority of the measurements are in the range 238–273 °C. Ice-melting temperatures (Tm) range from ?2.2 to ?4.1 °C, salinity – from 3.7 to 6.6 wt.% NaCl equiv. These measurements imply an epithermal environment and low- to moderate salinity of the ore-forming fluids.δ34S values of pyrite range from ?0.49 to +2.44‰. The average calculated δ34S values are 1.35‰. The total range of δ34S values for pyrite are close to zero suggesting a magmatic source for the sulfur. |
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| Keywords: | Milin Kamak Bulgaria Gold Hydrothermal alteration Fluid inclusions Sulfur stable isotopes |
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