Microthermometric Considerations for the Kanif (SE Birjand) and Basiran (SW Birjand) Manganese Prospects, Birjand, South-Khorasan, Eastern Iran.

Abstract

Two manganese prospects were studied. The Kanif prospect is hosted within an ophiolitic complex located 110 km southeast of Birjand, Southern Khorasan province (eastern Iran). The ophiolitic sequence in this region hosts manganese ore occurring as small discrete patches associated with radiolarian cherts. Ore minerals identified by XRD methods and petrographic studies are pyrolusite, hematite, and goethite showing replacement, colloidal and brecciated textures. Carbonate and silica are the gangue minerals. Based on the ICP-ES-MS methods, the average grade of Kanif is 33.92% Mn. Fluid inclusions hosted by calcite from Kanif demonstrate that the ore-forming solutions had salinities within the range of 0.5-4.5 wt% NaCl eq., homogenization temperatures within the range 100-220˚C and densities of about 0.8-1 g/cm3. Pressure is estimated to be about 50 bars, corresponding to a depth of ~150 meters at the time of formation. The Basiran prospect features veins/veinlets and is located 212 km SW of Birjand, Southern Khorasan province (eastern Iran). These veins/veinlets are hosted by andesitic rocks of Eocene to Oligocene age. Ore minerals identified by XRD methods and petrographic studies are pyrolusite, psilomelane, hematite, goethite and limonite, displaying colloform and open-space filling textures. Gypsum, carbonate and silica are the gangue minerals. Alteration zones, specifically argillic alteration zone, are developed along the veins/veinlets within the andesitic wall rocks. Based on the mineralogical and geochemical data, the primary manganese minerals were Mn oxides and hydroxides, which have gradually been converted to psilomelane and finally pyrolusite. The average Mn grade within the veins/veinlets is 25.95%. Fluid inclusion data show that the ore-forming solutions had salinities within the range of 0.5-5.5 wt% NaCl eq., TH range of 120-220˚C and density about 0.8-1 g/cm3. The pressure was estimated to be less than 50 bars, corresponding to a depth of ~150 meters and a hydrothermal origin. This study focused on investigation of fluid inclusions based on petrography, variety, morphologies, salinity and homogenization temperature for different styles of manganese prospects. Kanif is located in Sistan zone and Basiran is located in lut block. Results and Interpretation of microthermometric data suggest hydrothermal origins for both the Kanif and Basiran Mn prospects.