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Namibia is a country rich in pegmatites, and many of those are concentrated in the Karibib - Usakos area. Tourmaline rich pegmatites are particulary common and sometimes host beautiful and gemmy green, blue and red tourmalines. However, the larger pegmatites are generally rich in lithium, tin and tantalum rather than in boron. Tin mining was carried out in huge pegmatites at Uis and Nai-Nais north of Karibib in the past. Two pegmatites - Helicon and Rubicon in the southwest of the small town of Karibib are known for there huge lithium resources in form of amblygonite, petalite and lepidolite.
Both the Helicon and Rubicon pegmatites were mined for many decades. While the Helicon pegmatite mine was closed some 15 years ago, the Rubicon mine remained a working mine. Unfortunately, the exploitation of lithium from brines in Chile and other countries proved to be much more economic and cost-saving than crushing hard rock lithium ore. So only very few lithium pegmatites are still worked today with the Rubicon closing down in 1999. Today a large open pit and a few unsafe underground workings remain, which are easily acessible, if you take the right gravel pad (road)from Karibib. The offices and mining houses are deserted and a bunch of baboons is inhabiting the open pit. Very african indeed !
Upon entering the open pit, you can clearly see the dip of the pegmatite body into northerly directions. A lot of lepidolite, quartz, feldspar and mica is still lying around...and there are also a LOT of wasp nests scattered at every overhang. Luckily we visited this place in wintertime and the night was pretty cold, so the wasps were still a bit sluggish and stiff. But in summertime this will certainly change...so beware of the wasps !
While searching for lithium minerals, we suddenly saw our first giant petalite crystal. In fact there are quite a few of them, often arranged in a network like pattern of pinkish crystals, which nicely contrasts with the white feldspar - quartz matrix. The observed maximum size of the petalite crystals is about 2 m and though they are very compact, there surface is heavily weathered and quite brittle. The rims of the crystals are often covered by dendrites of black manganese hydroxides or possibly other black minerals. Though the crystals are well exposed, it is unlikely, that the present outcrop exhibit the largest petalite crystals in this pegmatite. Probably larger and fresher crystals of petalite have been discovered in the process of the underground mining of the Rubicon pegmatite.
Lithium minerals have a tendency to form giant crystals and aggregates, as can be seen in the giant Etta and Harding spodumene crystals in the US as well the occurence of giant triphylite crystals of up to 2 m size in pegmatites on the nearby Farm Tsaobismund. Elsewhere large amblygonite aggregates up to 150 kg (Ubini, Western Australia) and 6 x 2 m large crystals of montebrasite (Tip Top pegmatite, Black Hills, South Dakotah, USA) have been reported. Possibly lithium ions play a crucial role in the formation of megacrystals of some pegmatite minerals, but certainly much more research is needed on this matter.
If you travel to Namibia and wants to see giant crystals in situ, Rubicon is certainly a good place to visit. Please have a look around, but please do not damage or vandalize the petalite crystals, as other visitors would like to see them intact as well. And beware of baboons, scorpions, snakes and wasps !
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The Rubicon pegmatite in a nutshell :
Mineralogy : |
A complex lithium bearing pegmatite with additonal rare metals such as tin, tantalum, caesium and bismuth. Apart from petalite this pegmatite may host other megacrystals of lithium silicates, quartz and feldspar. |
Crystal Size : |
The maximum visible size of the petalite crystals is about 1.5 m, but most probably other even larger petalite crystals have been discovered (and crushed) during the mining process. |
Geology & Origin : |
The Rubicon pegmatite is a post-orogenic zoned pegmatite, which intruded into Damara quartz diorites and granites. It is part of a larger pegmatite swarm in the vicinity of Karibib, including the nearby Helicon pegmatite.
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Current status : |
Active mining ceased in 1999 and the mine infrastructure rapidly deteriorates. However the exposures in the open pit are still in fairly good condition, though the petalite crystals are highly weathered and brittle. |
Remarks : |
If you want to visit the place, be aware of wasps, baboons and scorpions !
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Other notable & famous petalite occurences :
- A crystal of 3 x 3 m size was reported from the Luolamäki pegmatite, Turku, Finland.
- Splendid crystals up to 25 cm occur in the Paprok pegmatites, Pakistan.
- The Bikita pegmatite, Zimbabwe hosts the largest single accumulation of petalite known - several 100.000 tons - and certainly also yield large petalite crystals.
- Another pegmatite exceptional rich in petalite is the Tanco pegmatite, Bernic Lake, Manitoba, Canada.
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Giant pinkish petalite crystals in the upper portion of the pegmatite
Photo : Giant Crystal Project
Close up of the heavily weathered petalite crystals
Photo : Giant Crystal Project
The rims of the petalite crystals are enhanced by manganese dendrites (red arrows).
Note the abundance of wasps
along the walls (red circle) and click the image for a closer view !
Photo : Giant Crystal Project
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Resources and relevant weblinks :
Though the Rubicon pegmatite was mined for many decades by german KLÖCKNER and other companies, there seemed to be only limited literature available about its geology and mineralogy. We did not found any essential online information about this pegmatite. However, there is an Namibian Geological Survey open file report, which can be bought at its office in Windhoek :
DIEHL, BJM & SCHNEIDER, GIC (1990) : Geology and mineralisation of the Rubicon Pegmatite, Namibia
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