Fluid inclusion studies in cogenetic hematite, hausmannite, and gangue minerals from high-grade manganese ores in the Kalahari manganese field, South Africa

Fluid inclusions in hematite and hausmannite from high-grade Wessels-type ore from the Kalahari manganese field were studied using infrared microscopy. The data obtained suggest that both minerals were deposited cogenetically, along with gangue minerals such as calcite and datolite, from high-salinity fluids. The minerals constituting the high-grade manganese ore were deposited at temperatures below 200°C, well below the temperature range of 200°to 400°C that was estimated on the basis of the thermodynamic stability of common mineral assemblages. The observed melting behavior suggests that the enclosed fluids are rich in Ca and/or Mg salts. It is concluded that an important part of the salt load of the hydrothermal fluid can be attributed to metasomatic interaction with the Ca-Mn-Mg carbonate-rich sedimentary protore to the Wessels-type ore.