A study of high-grade calc-silicate rocks in the Southern Bushmanland Domain, Namaqua Metamorphic province, including the garies wollastonite deposit

Abstract

In the Namaqualand region, Northern Cape, South Africa, calc-silicate rocks are present in the highest-grade metamorphic zone (upper amphibolite to granulite facies) of the southern Bushmanland Domain, Namaqua Province. Minor amounts of calc-silicate rocks occur as small isolated discontinuous layers, pods and lenses in the investigated area just outside of Kliprand, while the Garies area exposes a larger occurrence of calc-silicate rocks which involves relatively pure concentrations of wollastonite that are presently mined. Both these sites are characterised by wollastonite-rich calc-silicate assemblages. The rocks from these areas provide a unique opportunity to study the physical conditions and fluid regime of granulite facies metamorphism in the Bushmanland Domain. Mineral chemistry and petrology of fifty calc-silicate samples from the Garies area were studied in detail, and twenty calc-silicate samples from the Kliprand area were studied for comparison to constrain the P-T conditions of granulite facies metamorphism and understand the characteristics of fluid compositions.