Lamproite is a class of alkaline, potassium- and magnesium-rich igneous rocks that, alongside kimberlite, transports diamonds from mantle depths to the surface. Until the discovery of the Argyle pipe in the East Kimberley of Western Australia in 1979, kimberlite was thought to be the only diamond-bearing primary host. The Argyle find re-wrote that part of economic geology: olivine lamproite turned out to be a productive diamond source on a scale that produced more than 90 per cent of the world's pink diamond supply for the four decades the mine operated.

Mineralogy

Lamproite is distinguished from kimberlite by its chemistry rather than by texture alone. It is high in K₂O (typically 4-8 per cent), undersaturated in silica, and rich in titanium, with characteristic phenocryst phases including phlogopite, leucite, sanidine, K-richterite (a potassic amphibole), olivine, and titanian potassic richterite. Diopside, perovskite, and apatite occur as accessory phases. Kimberlite, by contrast, is dominated by olivine in a matrix of phlogopite, monticellite, calcite, and serpentine. The two rocks share a deep mantle source and an explosive emplacement style but represent different parental magmas.

Eruptive form

Lamproite pipes such as Argyle and the West Kimberley Ellendale field tend to be carrot- or champagne-glass-shaped diatremes that flare upward from a narrow root zone, sometimes capped by a shallow tuff ring or maar crater. Argyle's main pipe is an example. The Prairie Creek lamproite at Murfreesboro in Arkansas, now operated as the Crater of Diamonds State Park, is a smaller and economically marginal example but historically important as the first North American diamond pipe identified.

Argyle and Ellendale

Argyle (Western Australia) operated from 1983 to November 2020 as a Rio Tinto-owned open-pit and later block-cave mine, producing brown, champagne, and the rare pink, red, blue, and violet diamonds that defined the modern fancy-coloured market. The pipe was an olivine lamproite with phlogopite and titanian potassic richterite phenocrysts. The Ellendale pipes, also in Western Australia, produced principally yellow diamonds and operated intermittently into the 2010s. Both fields confirmed lamproite as a primary diamond host and sent exploration teams worldwide back to re-evaluate alkaline ultramafic occurrences they had previously dismissed.

Distribution

Diamondiferous lamproite remains rare. Most of the world's primary diamond production still comes from kimberlite, but lamproite occurrences are recorded in Western Australia, Arkansas, Spain (Cancarix), India (Bunder, Wajrakarur field), and parts of southern Africa. The economic threshold for a productive pipe is high: most lamproites worldwide are barren or carry only sub-economic diamond content. Trace-element and isotope chemistry now allows mantle-source modelling that helps explorers distinguish promising bodies from those unlikely to host diamond.