Genesis of Manganese Deposits in the Ali Khanzai Block of the Zhob Ophiolite, Pakistan: Inferences from Geochemistry and Mineralogy.

The Zhob ophiolite comprises the Naweoba, Omzha and Ali Khanzai blocks, which are surrounded by the sediments of the Alozai Group and Loralai Formation. The Ali Khanzai Block contains metamorphic, ultramafic, gabbroic, volcanic and volcaniclastic rocks with associated chert. The Zhob manganese deposits found in the Ali Khanzai Block, occur in banded, lenticular and massive forms within red to brown coloured metachert. Braunite and pyrolusite are the main constituent manganese-bearing minerals with minor hausmannite, hematite and barite while quartz is the major gangue mineral with some carbonate minerals. Geochemical evidence from the major oxides indicates that the manganese mineralization and associated metachert at Zhob were formed by hydrothermal activity with little contribution from contemporaneous volcanic materials and this is confirmed by high Fe/Mn and low Co/Zn ratios and trace element patterns. These deposits formed along with seafloor spreading centres and were later obducted as part of Ali Khanzai Block of Zhob ophiolite. [ABSTRACT FROM AUTHOR]