Economic Geology
Nima Rahimi; Shojaeddin Niroomand; Mohammad Lotfi; Mojtaba Rahimi Shahid
Abstract
The Janja Cu-Mo porphyry deposit is located at 70 km south of the Nehbandan, Sistan suture zone, Eastern Iran. The porphyry mineralization in the Janja deposit is temporally and spatially associated with the diorite to quartz diorite and granodiorite granular to porphyry stocks that intruded in the Cretaceous ...
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The Janja Cu-Mo porphyry deposit is located at 70 km south of the Nehbandan, Sistan suture zone, Eastern Iran. The porphyry mineralization in the Janja deposit is temporally and spatially associated with the diorite to quartz diorite and granodiorite granular to porphyry stocks that intruded in the Cretaceous flysch units. The Janja intrusions are represented by a Calc-alkaline and metaluminous geochemical affinity, and belong to the I-type granitoid series and subduction-related magmas in composition. Hydrothermal alterations in the area have been completely influenced by the Janja intrusion and as a result of the activity of these hydrothermal fluids, various types of potassic, propylitic, argillic and rarely phyllic alteration zones have been formed. In this deposit, three mineralization styles have been recognized including disseminated, vein-veinlet and stockwork which mineralization is mainly associated with potassic alteration. Mineralization zones in porphyry systems, including the supergene, enriched and hypogene zone, have been identified in the Janja deposit, which are the result of changes in the water table, weathering and erosion effects. The main sulfide minerals consist of chalcopyrite, pyrite, covellite, chalcocite, molybdenite, bornite, and oxide minerals including magnetite, hematite, goethite and hydro carbonate minerals including malachite and azurite. Fluid inclusion studies showed a homogenization temperature range from 301 to 540 ˚C and a mean salinity of 19 wt%NaCl for two-phase inclusions and a homogenization temperature range between 254 and >550 ˚C and mean salinities of 54 wt % NaCl for multiphase fluid inclusions. The results of these studies show that mixing processes have taken place in the Janja deposit and have caused the deposition of Cu-Mo-(Au) mineralization. Eventually, according to the various characteristics of the Janja deposit, including tectonic environment, host rock, mineralogy, ore-forming fluid, metal ore assemblage, mineralization and alteration patterns, and comparison of these characteristics with other porphyry deposits, it can be concluded that mineralization in Janja deposit is comparable with continental margin-type porphyry Cu-Mo-(Au) deposits.
