sThe Use SAVN_Kimberlite.htm of Vetiver grass in the Revegetation of Kimberlite Spoils in respect to South African Diamond Mining. --- Dr. M. P. S. Berry,
Introduction

Spoils from diamond mining and processing of Kimberlite may be either a coarse fraction of tailings or a fine fraction known as slimes. Tailings dumps may cover an area of 100 to 200 ha and be as much as 80 meters high with a natural angle of repose of between 30� and 35�. Slirnes dams may cover an area of similar size with walls 20 m high and a slope of 20�.

Kimberlite by nature is dark in color, easily weathered, high in smectite clays and may be high in sodium. These chemical and physical characteristics make slopes of kimberlite spoil dumps highly erodible, hostile for pant: growth and consequently difficult to revegetate. The problem is further exacerbated by the fact that many diamond mines are situated in semi-arid environments that are subject to temperature extremes and low and unpredictable rainfall. Furthermore, some exotic plant species are well adapted to these harsh conditions and establish comparatively easily to the exclusion of preferred indigenous species.

Vegetation trials

Vegetation trials with a suite of different indigenous grass species have been disappointing. Germination tends to be low and seedling mortality extremely high due to high ground temperatures, inadequate moisture availability and constant erosion of substrate surface. Some success was obtained where kimberlite spoils were top dressed with soil to stabilize slope and provide a better growth medium. However, this is extremely costly and in many instances not possible due to the lack of soil and inaccessibility of mid-slopes.

Vetiver Trials

Trials with Vetiver have been conducted on both tailings dumps and slimes dumps at several different sites. In all instances where plants were successfully established, vetiver has been found to grow vigorously on kimberlite spoils and met both the mechanical and vegetative requirements for rehabilitation. More particularly:

• Rows of vetiver planted at appropriate intervals contained runoff and arrested erosion. Consequently costly mechanical contouring of slopes was not necessary.
• Deep rooting Vetiver was able to obtain sufficient moisture from kimberlite spoils and survive extended drought periods.
• Vetiver withstood ground surface temperatures of more than 50� C in summer and over wintered sub-zero temperatures.
• Vetiver was well adapted to growing in alkaline kimberlite soils high in sodium.
• Dense tall tufts of vetiver trapped organic matter and created an ideal micro-habitat (suitable substrate and shade) for the establishment of indigenous grass species.
• Vegetative propagation of vetiver ensures that there is no threat of the species escaping to become an exotic weed.

Conclusion

In conclusion vetiver has been found to have the necessary attributes for self-sustainable growth on kimberlite tailings dumps and slimes dams. The species is likely to play an increasingly important role in the rehabilitation of kimberlite spoils. As such nurseries are being established at several mines to meet expected future demand.


Dr. M. P. S. Berry, Group Ecologist, De Beers Consolidated Mines Ltd., 36 Stockdale Street, PO Box 616,Kimberley 8300, South Africa. Fax (0531) 807 230