Abstract:
The Gamsberg East orebody is the least studied orebody of the Gamsberg zinc (Zn) deposit. The Gamsberg Zn deposit is a largest undeveloped Broken Hill-type deposit, which is well known for relatively low zinc grade as well as manganese (Mn) being a problem and penalty element. The occurrence of manganese within the sphalerite crystal lattice is one of the reasons for the lack of mining development over the past three decades. The recent metallurgical test works of the Gamsberg East ore showed that alabandite floats faster than sphalerite and this adds to the Mn penalty factor. Alabandite (MnS) was first reported as trace concentrations, but it was most recently found in anomalous concentrations in the Gamsberg East orebody. Up to 16 %wt alabandite occurs within the pelitic schist of the Gams Formation, and concentrations below 2 %wt occur within the top half of meta-pelite ore. The occurrence of alabandite is also associated with thicker or well developed portions of the ore horizon, which is also associated with manganese enrichment. The model of formation for alabandite is similar to that of sphalerite and Fe-sulphides during metal-sulphide formation in the Gamsberg Zn deposit. Alabandite is therefore pre-metamorphic and its formation is controlled by change in redox water conditions from chemogenic to detrital facies, sulphur fugacity, change in pH and hydrothermal fluids with temperature less than 300 °C, rich in manganese and iron but poor in zinc. Manganese is also hosted in silicate and oxide minerals, such as by pyrophanite, jacobsite, franklinite, amphiboles, micas, pyroxenes/pyroxenoids, and garnets.
