Navachab Gold Mine
The first gold-bearing quartz veins in Namibia were discovered
in the Rehoboth district in the Sinclair sequence
volcanogenic host rock as early as 1899. During
the pegging boom of 1933 and 1934, many prospects opened up
and exploited, but all were later closed down, mainly due
to the low and erratic grade of the mineralisation. Most
recently however, Namibia gold production received a new boost.
The Navachab gold deposit was discovered as a result of a
geochemical exploration program in October 1984, during
exploration for carbonate-hosted gold deposits area. It
was discovered on the farm Navachab, 6 km south of the
main Okahandja-Swakopmund tar road. Karibib is in the main
railway line and the power to the mine is drawn from
nearby SWAWEK 260 kV power line.
An appraisal was carried in 1986 and
followed by feasibility study in 1987, after which a
decision was made to proceed with the development of a
mine. Construction work began in 1988 and the first gold
bar was poured only 21 month later in December 1989,
establishing Namibia as one of the gold producing
countries in the world.
The mine was completed at a capital cost of N$ 85 million.
The plant was commissioned in November, with full
production being achieved in January 1990.
The 35 metre-thick ore body is hosted in a thick
marble unit. The ore body dips at 70' to the west and
plunges at 14' to the north and it is mined by open-cast
method to a depth of over 200 metres. The ore body is estimated
to contain 10.4 million tones of ore with average grade of
2.3 grams of gold per ton and a further 6.5 million tones
of marginal ore with an average grade of 0.66 grams per
ton. It was originally anticipated, that the life of mine
would be in the region of 13 years. It envisaged that an
increase in the milling to 840 000 tones per annum may be
possible which will allow a decrease in the planned head
feed grade. The carbon-in-pulp process recovers 85% of
gold. After C.I.P. extraction, elution and smelting the
unrefined bullion is sold to Switzerland, where it is
refined.
Pink nosib formation quartzites and arkose occur on the
eastern edge of the mining area and are overlain by other
formation mixtures. The marble-hosted gold skarn
mineralisation is related to multistage mineralisation,
from 800 metres north-east of the main ore body, greisen
and pegmatite's are localised around a late stage,
fluorite which is interpreted to be possible heat source
for the final concentration of low grade gold deposits.
Two types can be recognized by mineralisation: 1) skarn
related gold mineralisation within marble/calc silicate
zone. This zone hosts the bulk of gold mineralisation, 2)
the hanging wall banded grey marble and melted dolomites.
This zone hosts cross-cutting vein storkwork style ore
body of limited tonnage.
The possibility of upgrading the
marginal ore reserves using dense medium separation (d.m.s.)
was examined in a pilot campaign. Gold discoveries of
60% to 81% were achieved at a concentrate grade of 3 to 4
grams of gold per ton. The alternative of increasing plant
milling capacity is now being investigated. The resultant
plant throughout would lead to scale economics and lower
grade material could then become profitable.
Diamond drilling during the
last years indicate extensive strike extensions to
the ore body and it is still open ended at 600 metres
north of the planned open pit. With 14 plunge to the ore
body it is not possible to mine extensions by open-cast
methods, and the possibility of underground mining is
being evaluated constantly.
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