Geochemistry and origin of Mn deposits in the Bela ophiolite complex, Balochistan, Pakistan

摘要

We have studied geochemical characteristics, mineralogy and origin of the manganese deposits in Bela ophiolitic complex.Geochemical investigation was conducted in order to discuss the elemental correlations and to infer the probable origin ofmanganese deposits in Bela ophiolites. Ore microscopy was conducted to identify diferent manganese minerals and theirparagenesis. Psilomelane and braunite were found to be the major ore minerals. Mineral paragenesis sequence as observedwas braunite forming frst. Psilomelane formed in later stages because it has been found that psilomelane is altering the braunite. Magnetite was observed as a secondary mineral as vein flling and cutting through both the braunite and psilomelane,therefore, younger than the psilomelane and braunite. The gangue minerals observed in the studied samples were quartz,cryptocrystalline silica and calcite. The correlations among diferent major and trace elements showed diversity of relations.MnO showed negative correlation with Fe2O3 (? 0.73), Si2O (? 0.27), positive correlation with Al2O3 (0.54), TiO2 (0.36),MgO (0.22), Pb (0.23), Ni (0.07), Cr (0.12), and no correlation was established with Zn, Cu, Co. Binary diagram of Si versusAl and ternary discrimination diagrams of Fe–(Ni + Co + Cu) × 10–Mn and Ni–Zn–Co showed hydrothermal-diagenetictype deposits. Furthermore, the present study suggests that the enriched manganiferous fuid during its upward movementwithin the Tethys oceanic crust near spreading center started precipitating Mn along with Fe on the sea foor. Later on, thesemanganese minerals were obducted on land between Indian plate and Helmond block of Eurasian plate in existing positionaccompanying pillow basalt and pelagic sediments.