Bibliography: pages 143-151. / Sugilite, a purple mineral belonging to the milarite group, occurs in the lower manganese orebody at Wessels Mine, in the Kalahari Manganese Field. This orebody was formed in the lowermost manganiferous horizon of the Hotazel Member of the Voelwater Jasper Formation, part of the volcanogenic sedimentary iron formation of the Griqualand West Sequence. At Wessels Mine, which is located northwest of Kuruman in the northwestern Cape Province, evidence of a widespread and pervasive hydrothermal event which took place around 1300 Ma is found in the form of upgrading of the manganese-ore horizons and the formation of zoned silicate-mineral assemblages. The presence of unusual minerals such as glaucochroite, iron akermanite, xonotlite and hydrogarnets of various types constrains the main phase of metamorphism to between 400 and 450 °C in a low pressure, hydrous environment with XCO2 ≤ 0,02. All the minerals which occur in these assemblages are described and discussed in terms of their chemistry and formation.