May 8, 2015

Pandanus candelabrum as an indicator species for diamond rich kimberlite pipes in West African jungles

There is a report this month in the journal Economic Geology on a little known tropical plant species in the Pandanaceae family. In West Africa, it apparently grows in kimberlite rich soils. Since kimberlite is a mineral which is typically rich in diamonds, this is a significant discovery in economic botany. Unfortunately, the article, a single author contribution by Stephen Haggerty, is behind a pay wall, and I have not obtained a copy yet. There is a nice summary in Science by Eric Hand that explains some of the geology behind diamond formation, deep below the surface. I did not know, for instance, that diamonds are formed hundreds of kilometers below the surface and reach the top by being pushed through pipes of kimberlite in explosive events, sometimes at speeds greater than the speed of sound.



Pandanus is a genus of palm-like trees in the monocot clade with a silt-like aerial roots. According to Anthropogen, it is used in cooking and to extract perfumes and aromatic oils in some tropical countries and its many species are widespread across the tropical regions in south American and Asian as well as Africa. Here is a photo from another page on the same site, a nice ethnobotany web resource (exact species unknown).



It is in Africa, though, that Pandanus is about to get a huge amount of attention due to its alleged association with diamond deposits in soil rich in kimberlite. Kimberlite is a mineral highly  enriched in magnesium, potassium, and phosphorous, but from the short excerpt I have read in Science, it is not immediately clear why this particular mixture wouldn't be good for just about all plants. Unless they are present at extremely high concentrations that are toxic for plants without a specific adaptations to this soil type. Haggerty has evidently made the observation that P. candelabrum (a tentative identification made with help from botanists) grows preferentially where kimberlite pipes have been discovered, and so there is obvious interest in using this species to prospect for new diamond mines. I am curious to read the actual article since Haggerty is himself not trained in botany (he is a geologist specializing in diamond formation), and none of the botanists who assisted him in the identification are co-authors on this paper. I am especially curious about how strong the correlation is between P. candelabrum growth and kimberlite rich soils, what statistical method he used to establish this, and how many independent observations went into making this connection. He seems to have decades of field experience, particularly in West Africa, but that doesn't mean he is a competent botanist. If he's right, this could mean a boon for diamond prospecting in Liberia and Cameroon, places which have traditionally seen desperate violence over access to so called 'blood diamonds' as well as the political turmoil in general that has often hit West African nations, making diamonds an unfortunate currency to obtain arms by nearly all sides involved. The movie Blood Diamond starring Leonardo de Caprio confronted the troubling international politics over this issue. I wonder to what extent the local economies would be the primary beneficiaries of this discovery, versus foreign interests who have not traditionally had the local people's interest in mind? That's assuming the correlation is real and that P. candelabrum (or whatever species it really is if this identification is not correct) can be used as an indicator species for locating diamond patches. If it is not correct, then it could just be a massive fishing expedition. The nice thing about science is that we can wait for more data to come in before deciding. Given the potential economic implications involved, I imagine it won't be long before we have plenty of it.

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