Geological setting of Zambian emerald deposits

Abstract

The Kafubu emerald deposits occur within rocks of the Muva Supergroup which form the youngest part of pre-Katangan basement immediately southwest of the well known Copperbelt of Zambia. Within the Muva Supergroup are persistent bands of talc—chlorite—amphibole (tremolite/actinolite) - magnetite schist, which are intruded by pegmatites. These pegmatites are believed to be related to neighbouring granitoids which originated or were rejuvenated during early stages of Pan-African orogeny. Pegmatites occur as feldspar—quartz—muscovite bodies or as minor quartz—tourmaline veins. Contact aureoles of the pegmatitic veins with the ultramafic schists are usually altered to phlogopite—biotite—tourmaline aggregates and the minor veins are often concordant to the foliation of the country rocks. The emeralds are found in the contact zones, and sometimes within the quartz—tourmaline veins. The emerald fields are considered comparable in quantity and quality of material to the well known Colombian fields, but their lithological setting differs considerably. Striking similarities were found between the Zambian occurrences and those of South Africa and Zimbabwe.