My suggestion.

As opposed to industrial diamonds.

The diamond industry consists of segments that mines, processes and markets gem diamonds and industrial diamonds. Gem quality diamonds are mined primarily ...
www.photius.com/diamonds/the_diamond_industry.html

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Note added at 1 hr (2009-07-07 21:29:21 GMT)
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Well, I got that wrong, despite the promising start:

les exportations officielles du DIAMANT DE PRODUCTION ARTISANALE ET INDUSTRIELLE se sont globalement chiffrées ŕ 2 303 462,29 carats ...
www.digitalcongo.net/article/17035

Le prix moyen pour le DIAMANT DE PRODUCTION ARTISANALE se négocie aux alentours de 30 $ US/carat. Tandis que le prix moyen de la vente des shipments de la Miba pour les DIAMANTS INDUSTRIELS est aux alentours de 14 $ US le carat alors que celui de la Sengamines avoisine les 22 $ US le carat.
http://www.congo-actualites.net/spip.php?article380&debut_ar...

However, the above includes the following -
Pour les responsables de la direction technique de la structure d’encadrement du SECTEUR MINIER ARTISANAL, les recettes des exportations du diamant brut au premier semestre devront atteindre les 15 millions l’an –

which seems to suggest that "production artisanale" might refer to the way the diamonds are mined or otherwise gathered ... Not that I can see why the manner in which diamonds are brought out of the earth should affect the price.

However :

Cette équipe, précise l’arrêté a pour mission de vérifier l’authenticité du colis acheté avant son scellage, procéder à l’expertise provisoire, en déterminer la valeur approximative ainsi que le droit dû à la province. Le DIAMANT DE PRODUCTION ARTISANALE A TOUJOURS ECHAPPE AU CONTROLE DE L’ETAT faisant ainsi perdre à la caisse du trésor public un manque à gagner consistant, rappelle-t-on.
http://www.un.int/drcongo/archives/BQ-1331.htm

suggests that "production artisanale" does indeed refer not to the use to which the raw diamonds are put, but to the manner in which they are collected, i.e. many of those obtained on a casual (artisanal) basis are smuggled out of the country.

And the World Bank agrees (though I think not a great deal of either their English or their translation):
The average value of INDUSTRIALLY MINED DIAMONDS was about 350$/carat. of ARTISANALLY MINED DIAMONDS about 75$/carat. 3/ The Bank's International Trade ...
www-wds.worldbank.org/external/default/.../multi0page.txt


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Note added at 1 hr (2009-07-07 21:40:16 GMT)
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If you don't like "artisanally mined diamonds" (I don't), how about "casually mined diamonds":

MOST DIAMONDS ARE FOUND IN DEEP MINE SHAFTS, which require substantial capital to dig and maintain, although some are discovered in widely-spread surface deposits, which tend to be MINED MORE CASUALLY
http://www.epsjournal.org.uk/pdfs/eps_v1n1_gold.pdf

While OP Singh works out a way to legitimise the illegal and CASUAL MINING by villagers, big diamond players like Shirish Shah are looking forward to a ...
www.indiarightsonline.com/.../1b9ae90484567e56e525740b00827...

Use of the Hands &Pans area for CASUAL MINING can be described as light. ...... with the Middle Fork; Diamond Creek from the California-Oregon state ...
https://docs.co.nevada.ca.us/dsweb/.../Document-98317

Native Americans who use the area will be consulted prior to surface disturbing activities which require BLM authorization (excluding CASUAL MINING use).
www.blm.gov/pgdata/etc/medialib/blm/mt/blm.../rod1992.pdf

Of course we have nothing to suggest that this "artisanal" production involves mining, as opposed to simply picking the things up out of the sand (or whatever), except that "Congo-actualités" reference above which refers to the "secteur MINIER artisanal".

I seem to recall there having been found here on ProZ a word for this casual "discovery" of gemstones, possibly in relation to Sierra Leone. Was it as simple as "prospecting"?

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Note added at 1 hr (2009-07-07 21:43:22 GMT)
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Here we go: "panned diamonds" might work.

http://www.proz.com/kudoz/french_to_english/military_defense...