Fluid inclusion evidence for hydrothermal fluid evolution in the Darreh-Zar porphyry copper deposit,Iran |
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| Institution: | 1. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;2. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;4. No. 243 Geological Party of Nuclear Industry, Chifeng 024006, Inner Mongolia, China;1. Department of Earth Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran;2. Department of Earth Science, Shahid Beheshti University, Tehran, Iran;3. Department of Mining, Lahijan Branch, Islamic Azad University, Tehran, Iran;1. Guangzhou College South China University of Technology, Guangzhou 510800, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;4. Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, Crawley, WA 6009, Australia;5. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037, China;6. Henan Academy of Land and Resources Sciences, Zhengzhou 450053, China;7. Department of Earth Sciences, University of New Brunswick, N.B, E3B 5A3, Canada |
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| Abstract: | The Darreh-Zar porphyry copper deposit is associated with a quartz monzonitic–granodioritic–porphyritic stock hosted by an Eocene volcanic sedimentary complex in which magmatic hydrothermal fluids were introduced and formed veins and alteration. Within the deepest quartz-rich and chalcopyrite-poor group A veins, LVHS2 inclusions trapped high salinity, high temperature aqueous fluids exsolved directly from a relatively shallow magma (0.5 kbar). These late fluids were enriched in NaCl and reached halite saturation as a result of the low pressure of magma crystallization and fluid exsolution. These fluids extracted Cu from the crystallizing melt and transported it to the hydrothermal system. As a result of ascent, the temperature and pressure of these fluids decreased from 600 to 415 °C, and approximately 500–315 bars. At these conditions, K-feldspar and biotite were stabilized. Type A veins were formed at a depth of ～1.2 km under conditions of lithostatic pressure and abrupt cooling. Upon cooling and decompressing, the fluid intersected with the liquid–vapor field resulting in separation of immiscible liquid and vapor. This stage was recorded by formation of LVHS1, LVHS3 and VL inclusions. These immiscible fluids formed chalcopyrite–pyrite–quartz veins with sericitic alteration envelopes (B veins) under the lithostatic–hydrostatic pressure regime at temperatures between 415 and 355 °C at 1.3 km below the paleowater table. As the fluids ascended, copper contents decreased and these fluids were diluted by mixing with the low salinity-external fluid. Therefore, pyrite-dominated quartz veins were formed in purely hydrostatic conditions in which pressure decreased from 125 bars to 54 bars and temperature decreased from 355 to 298 °C. During the magmatic-hydrothermal evolution, the composition and P–T regime changed drastically and caused various types of veins and alterations. The abundance of chalcopyrite precipitation in group B veins suggests that boiling and cooling were important factors in copper mineralization in Darreh-Zar. |
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| Keywords: | Porphyry copper deposit Fluid evolution Fluid inclusion Iran |
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