Diamonds across the world : Diamonds (Mines) 
Alrosa, Russian Federation
Anglo American plc, United Kingdom
Blue Nile, USA : Diamond retail e-commerce company in the world
De Beers Group, Belgium
Debswana Diamond Company Ltd., Botswana.
Dominion Diamond Corporation, Canada

Gem Diamonds, United Kingdom

James Allen, USA : privately-held retail diamond company in the world
Lucara, Canada
Petra Diamonds, United Kingdom
Rio Tinto, Australia (Argyle Mines)
Rio-Tinto Diamonds, United Kingdom
Rockwell Diamonds, Canada
Website not working so sharing links to Wikipedia

Diamond mines are only in 12 countries
(Nothing in Europe, South America, Antarctica)
This is from our reserach and we can not gurantee. If there are mistakes, do email it to Datacentre.

Africa continent
Country : Angola (3 diamond mines)
Catoca, Fucauma, Luarica

Country : Botswana (6 diamond mines)
Damtshaa, Jwaneng, Letlhakane, Orapa, Karowe, Lerala

Country : South Africa (7 diamond mines)
Baken, Cullinan (previously "Premier mine"), Finsch,
Kimberley, Northern Cape, Koffiefontein, Venetia

Country : Zimbabwe (3 diamond mines/ fields)
Baba Diamonds Fields, Marange diamond fields, Murowa

Country : Tanzania (1 diamond mine)

Country : Lesotho (1 diamond mine)

Country : Democratic Republic of the Congo (1 diamond mine)

Asia continent
Country : Russia (8 diamond mines)
Mirny GOK, Udachny GOK, Jubilee, Grib, Aikhal, Komsomolskaya,
International, Zarnitsa

Country : India (2 diamond mine)
Kollur, Panna

Country : Indonesia (1 diamond mine)

Australasia continent
Country : Australia (2 diamond mine)
Argyle, Merlin

North America continent
Country : Canada (7 diamond mines)
Diavik (Northwest Territories), Ekati (Northwest Territories)
Jericho ( Nunavut), Snap Lake (Northwest Territories), Victor,
Gahcho Kue (Northwest Territories), Renard (Quebec )