Evolution of the Mineralizing Fluids and Possible Genetic Links between Miduk Porphyry Copper and Latala Vein Type Deposits, Kerman Copper Belt, South Iran

Abstract

The Cenozoic Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran is a major host to porphyry Cu-Mo-Au deposits (PCDs), represented by the world-class Sarcheshmeh deposit and Miduk deposit in the south and the Sungun deposit in the north. Vein type, base and/or precious metal deposits are also common and some are spatially associated with PCDs. Latala and Chahmessi are vein type, base and precious metal deposits in the north and southwest Miduk deposit. The area is covered mainly by Paleocene-Eocene volcanic and pyroclastic rocks of basaltic, basaltic-andesitic and trachy-andesitic compositions, and minor marls and limestones. The volcanic and pyroclastic rocks are intruded by Miocene shallow intrusions of quartz diorite, quartz monzonite and granodiorite compositions.The rocks are host to a set of ore-bearing quartz veins. Mineralization in both the Chahmessi and Latala deposits are controlled by faults and fractures. The role of the ring structures and faults in the distribution of hydrothermal alteration zones and mineralization is important in the Latala deposit. In these veins, euhedral quartz with sulfide mineralization occurs as open space fillings, minor replacement bodies and hydrothermal breccia. The veins consist of quartz, calcite, pyrite, chalcopyrite, galena, sphalerite, bornite and minor sulfosalts, particularly enargite. According to studies based on fluid inclusions in the Miduk porphyry, three types of fluids are responsible for mineralization. Homogenization temperatures and salinity in porphyry-type fluids vary from 566 to 162 °C and 61.3 to 1.2 wt% NaCl equiv. For the Latala vein type base and precious metals deposit, homogenization temperature and salinity vary from 380 to 131 °C and 10.6 to 0.17 wt% NaCl equiv. The gas phase in fluid inclusions of Latala is dominated by CO2 but also shows the presence of CO and H2, characterizing reducing conditions associated with ore deposition. The change from lithostatic to hydrostatic regime, boiling and fluid dilution associated with the introduction of meteoric fluids provides an explanation for the widespread Th and salinity data. Calculated pressure for examples of Miduk fluid inclusions varies from 700 to 200 bars. These pressures correspond to depths of 2500 to 1500 metres for porphyry mineralization. The three-phase fluid inclusions, corresponding to magmatic fluid, show the highest pressure. The Latala base and precious metals deposit has formed at pressures between 200 and 100 bars, corresponding to a depth of less than 1 km. Sphalerite mineralization occurs in shallow parts of the sedimentary-volcanic sequence from magmatic fluids diluted by meteoric fluids and also occurs in more distal parts of the porphyry. The sulphur isotopic composition for sulfide minerals varies between -9.8 and -1.0‰, which correspond to values of magmatic sulfur. This suggests that magmatic water was responsible for transportation of metals in Latala. Epithermal mineral precipitation occurred upon dilution of the low-salinity magmatic fluid with meteoric water, which entered the hydrothermal system as it cooled and successively diluted during continued magmatic fluid ascent.