Mineral chemistry of manganese ores associated with Precambrian Eastern Ghats complex of Andhra Pradesh-Orissa, India

A large number of manganese deposits (dominantly low to medium grade with high iron, phosphorous and silica) occur in the Precambrian Eastern Ghats complex of Andhra Pradesh and Orissa. The manganese ore bands are syngenetic and syntectonic with the metasedimentary country rocks which comprised of khondalite, quartzite and calc-silicate granulite. They have been metamorphosed under granulite facies followed by granitisation, retrograde metamorphism and supergene enrichment. Braunite, bixbyite, jacobsite, hausmannite, vredenburgite, magnetite, hollandite, pyrophanite, together with spessartite, rhodonite represent the primary manganese oxide and silicate minerals. Cryptomelane, romanechite, pyrolusite, goethite, lithiophorite, ramsdellite, birnessite are the secondary minerals which form the matrix for the primary minerals, replace them and are also observed as veins, cavity fillings and interstitial fillings. Goethite, graphite, hematite and pyrite, together with quartz, orthoclase, garnet, diopside, kaolinite and minor amounts of apatite, collophane, gorceixite, sillimanite, plagioclase, zircon, biotite and muscovite are the gangue minerals. Mineral chemistry of different primary and secondary minerals have been described. Phosphorous in the manganese ores of Eastern Ghats complex is present in almost all the minerals but with varying proportions. The abundance of apatite, gorceixite and collophane in the Mn ores is very small. Order of phosphorous content established in this study is primary minerals