Non-kimberlitic diamondiferous igneous rocks: 25 years on

Four main paradigms exist in diamond geology at this time: (1) Diamonds are related only to kimberlites; (2) Diamondiferous kimberlites can only form within ancient, Archean cratons; (3) Diamondiferous kimberlites can only form within the thickest lithospheric blocks of cratons; and (4) Natural diamonds are formed only in ultra high-pressure environments. The existing data demonstrate that these paradigms are not always correct. Primary, diamondiferous kimberlites can occur not only within Archean cratons, but also within collisional belts of different types and within epicratonic, essentially ensialic orogenic belts. In addition, there are numerous occurrences of igneous, non-kimberlitic, diamondiferous rocks which include representatives of the following groups: (1) Volcanic rocks: lamproites, lamprophyres, picrites, meimechites, and alkali-basalts. (II) Plutonic rocks: peridotites and pyroxemites. There are non-kimberlitic rocks which may contain economic diamond mineralization. Although, the ultramafic rocks are likely to contain a lower-grade of diamond mineralization, than the volcanic rock-types. However, such types of mineralization can produce medium sized and, probably, large alluvial placer deposits. The existing criteria for prospecting and preliminary evaluation of primary diamond deposits, based on 'traditional' experience in cratonic areas, is therefore non-applicable in prospecting for new types of diamond deposit.