Chadormalu Kiruna-type magnetite-apatite deposit,Bafq district,Iran: Insights into hydrothermal alteration and petrogenesis from geochemical,fluid inclusion,and sulfur isotope data |
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| Institution: | 1. Faculty of Earth Sciences, Shahid Beheshti University, Evin, 1983963113 Tehran, Iran;2. Dept. of Earth Sciences, University of New Brunswick, 2 Bailey Drive, Fredericton, NB E3B 5A3, Canada;1. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China;2. Ore Deposit and Exploration Centre (ODEC), Hefei University of Technology, Hefei 230009, China;3. Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Private Bag 79, Hobart, Australia;1. Roy M. Huffington Department of Earth Sciences, Southern Methodist University, P.O. Box 750395, Dallas, TX 75275-0395, United States;2. Department of Earth, Planetary and Space Sciences, University of California, 595 Charles Young Drive E., Los Angeles, CA 90095-1567, United States;3. Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, United States;4. CNRS-INSU, ISTerre, Le Bourget du Lac, France;5. Université Savoie Mont Blanc, ISTerre, Le Bourget du Lac, France;1. Department of Geology, Faculty of Science, University of Sistan and Baluchestan, Zahedan 98167-45639, Iran;2. Department of Geology, Faculty of Science, University of Tehran, Tehran 14155-64155, Iran;3. Department of Geology and Environmental Earth Sciences, Miami University, OH 45056, USA;4. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;5. Department of Earth and Environmental Sciences, Faculty of Science, Yamagata University, Yamagata 990-8560, Japan;1. Geochemistry Department, Faculty of Earth Sciences, Kharazmi University, Tehran 15719, Iran;2. SEE, University of Leeds, Leeds LS2 9JT, UK;3. Isotope Geology Unit, Scottish Universities Research and Reactor Centre, Eaast Kilbride, Glasgow Gs75 0QU, UK;1. Department of Earth and Environmental Sciences, University of Michigan, 1100 North University Ave, Ann Arbor, MI, USA;2. Department of Geology and Andean Geothermal Center of Excellence (CEGA), Universidad de Chile, Plaza Ercilla 803, Santiago, Chile;3. Department of Geology, University of Illinois, 605 E. Springfield Ave., Champaign, IL, USA;4. Department of Geological Sciences, University of Oregon, 1275 E 13[th] Ave., Eugene, OR, USA;5. Compañia Minera del Pacífico, Brasil N 1050, Vallenar Región de Atacama, Chile;1. Faculty of Earth Sciences, Shahid Beheshti University, P.O. Box 19839-69411, Tehran, Iran;2. Nuclear Science and Technology Research Institute, Atomic Energy Organization of Iran, P.O. Box 14155-1339, Tehran, Iran |
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| Abstract: | The Chadormalu is one of the largest known iron deposits in the Bafq metallogenic province in the Kashmar-Kerman belt, Central Iran. The deposit is hosted in Precambrian-Cambrian igneous rocks, represented by rhyolite, rhyodacite, granite, diorite, and diabasic dikes, as well as metamorphic rocks consisting of various schists. The host rocks experienced Na (albite), calcic (actinolite), and potassic (K-feldspar and biotite) hydrothermal alteration associated with the formation of magnetite–(apatite) bodies, which are characteristic of iron oxide copper-gold (IOCG) and iron oxide-apatite (IOA) systems. Iron ores, occurring as massive-type and vein-type bodies, consist of three main generations of magnetite, including primary, secondary, and recrystallized, which are chemically different. Apatite occurs as scattered irregular veinlets in various parts of the main massive ore-body, as well as apatite-magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks. Minor pyrite occurs as a late phase in the iron ores. Chemical composition of magnetite is representative of an IOA or Kiruna-type deposit, which is consistent with other evidence.Whole rock geochemical data from various host rocks confirm the occurrence of Na, Ca, and K alteration consistent with the formation of albite, actinolite, and K-feldspar, respectively. The geochemical investigation also includes the nature of calc-alkaline igneous rocks, and helps elaborating on the spatial and temporal association, and possible contribution of mafic to felsic magmas to the evolution of ore-bearing hydrothermal fluids.Fluid inclusion studies on apatites from massive- and vein-type ores show a range of homogenization temperatures from 266 to 580 °C and 208–406 °C, and salinities from 0.5 to 10.7 wt.% and 0.3–24.4 wt.% NaCl equiv., respectively. The fluid inclusion data suggest the involvement of evolving fluids, from low salinity-high temperature, to high salinity-low temperature, in the formation of the massive- and vein-type ores, respectively. The δ34S values obtained for pyrite from various parts of the deposit range between +8.9 and +14.4‰ for massive ore and +18.7 to +21.5‰ for vein-type ore. A possible source of sulfur for the 34S-enriched pyrite would be originated from late Precambrian-early Cambrian marine sulfate, or fluids equilibrated with evaporitic sulfates.Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical, fluid inclusion, and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the Chadormalu deposit. In the first stages of mineralization, magmatic derived fluids had a dominant role in the formation of the massive-type ores, whereas a later brine with higher δ34S contributed to the formation of the vein-type ores. |
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| Keywords: | Chadormalu Magnetite-Apatite Bafq district Central Iran Hydrothermal alteration Kiruna-type Sulfur isotope |
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