CGS Foreign Development Cooperation - Zambia

Emerald mineralization in the Kafubu area, Zambia

The project conducted by the CGS in 2001 was undertaken on the request of the Zambian Ministry of Mines and Minerals Development, Lusaka. Emerald is by far the most important gemstone mined in the country and the Zambian government is looking for ways to boost the efficiency of its emerald mining sector. In the past two decades, Zambia has become a significant gem-producing country. The Kafubu area, being believed to produce up to 20 per cent of the world emerald production, represents an important economic potential for Zambia.

Documentation of the boreholes drilled by Kamakanga Ltd. within emerald-parent rocks, Kamakanga mine (photo by V. Žáèek).

The major project objectives involved the study of the geological setting, and gathering all key information and data regarding the origin and distribution of emerald mineralization in the Kafubu – Ndola Rural Restricted area. Besides the paragenetic-geochemical features of the mineral assemblages this study provided the first quantitative geochemical, petrological and mineralogical data on the major rock types and minerals in the Kafubu area.

Highly magnesian talc-chlorite ± actinolite ± magnetite metabasites, identified as metamorphosed Cr-rich komatiites, that host the emerald mineralization provided the chromium necessary for the crystallization of emeralds. Emerald-bearing phlogopite schists are confined to the contacts between quartz-tourmaline veins magnesian metabasites. The Li-Cs-Ta quartz-feldspar pegmatites are commonly enriched in beryllium and Ta-Nb minerals.

The fluorine- and boron-rich fluids deposited quartz-tourmaline veins and altered adjacent metabasites into the phlogopite schists. Data on pegmatite occurrences point to the existence of a single major Kafubu pegmatite field with the closure of the system occurring within the interval of 452-447 Ma (40K/40Ar dating of muscovite).

Emerald samples from the Kafubu area range in intensity of colour from light green to dark green, having many inclusions and being moderately fractured. Electron microprobe analyses of Kafubu emeralds show contents of 0.17–0.59 wt. % Cr2O3. For the first time, data on fluid inclusions in beryl/emerald, tourmaline and quartz were obtained for these deposits and the mineralization pT conditions were estimated.

Mine face with beryl mineralization, Fibolele mine, Kafubu area (photo by A. Seifert).

The significant features governing emerald mineralization have been recognized, and recommendations for exploration have been presented. These recommendations involve assistance, information, and advice to the Zambian government in planning future policies for attracting private investment, as the potential for new emerald occurrences in the Kafubu area still remains very high.

Publication

Emerald mineralization in the Kafubu area, Zambia
by Seifert, A. V., Žáèek, V., Vrána, S., Pecina, V., Zachariáš, J. & Zwaan (Hanco), J. C., Bulletin of Geosciences, Vol. 79, No. 1, 1-40, 2004 (pdf, 1.4 MB)