GENESIS OF MANGANESE ORE DEPOSITS OF LASBELA AREA, BALOCHISTAN PAKISTAN

Manganese mineral and ore occurrences, the associated underlying ophiolitic rocks of tholeiitic composition of Aptian-Maastrichtian and the overlying sediments of Jurassic-Cretaceous age were sampled from lasbela area and their field characteristics were noted. Samples collected from Manganese mineralization zones and the associated rocks from nine localities, namely khrrarri Dhora, Gecheri Dhora, Gadani Ridge, Dadi Dhora, Bhampani Dhora, Draoari Dhora, Porat Dhora, Siro Dhora and Sanjro Dhora, representing to southern part of the Axial Belt were investigated petrologically, minerlogically and geochemically.The above investigations of the underlying the noleitic pillow basalt was considered as the host rock of manganese ores and minerals and the overlying pelagic sediments were carried to determine the degree of correspondence in the ophiolitic rocks, mineralized zones and the overlying sediments having indications of metalliferous ore deposit developments of varying magnitudes.The occurrence of cryptocrystalline to crystalline silica, dolomite, calcite and ferruginous constituents, serpentines etc. were considered to indicate the stages of mineralogical alterations and replacement variable elevated temperatures. The temperature distribution and pH controls in the localities during mineralization and then after have been discussed in the light of mineral assemblages identified through X-ray analyses.The mineralogical associations classified as main, associated and accessory manganese minerals are discussed to elaborate the paragenetic sequence of the minerals available in the mineralized zones. The possible geological conditions which favoured the formation of minerals of high and low temperatures have also been anticipated.Selected major, minor and trace elements (Si, Al, Fe, Ca, Mg, Na, K, Mn, Ti, Cr, Ni, Co, Cu, Zn, Ba, Zr, Li, Sr and Pb) in manganese ores, minerals and host rocks were quantitatively estimated to discuss and elaborate the possible degrees of geochemical correspondence among the element concentrations and the genesis of the minerals. The differential leaching and precipitation of the elements estimated were considered to facilitate the study of possible environments of mineralization together with the effects of tectonics and fumarolic actions at the sea bottom. The Si and Ti concentrations in the samples under study have been discussed to evaluate the possible variations in the geochemical parameters which gave rise to the concentrations of the manganese ores and minerals. The relationship in the characteristics of the photolytic orcks of the localities under study with that of Mid Oxceanic Ridge Basalt (MORB) and the possibilities of hydrothermal origin of the minerals identified have been described. The low concentration of Ni Co, Cu and Zn and low Si/Al ratio also appear to indicate the similarities of manganese deposits of Lasbela with that of MORB and the dominance of hydrothermal environment during mineralization. The wide range in Ti and Si concentrations in the ores and minerals have been discussed in the light of variations in temperature, hydrostatic pressure and differential leaching at the sea bottom due to interactions in pelagic sediments, fumarolic actions and the ophiolites.The higher unexpected concentration of Li in the parent rocks and the formation of lithiophorite were considered due to possible hydrothermal solution action during mineralization