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The Argyle (AK1) pipe in the Kimberley region of Western Australia is the world’s largest source of natural diamonds, and it has produced more than 835 million carats since mining began in 1983. The ~1.2 Ga olivine lamproite pipe lies within the Paleoproterozoic Halls Creek orogen at the southeastern margin of the Kimberley craton, and it was emplaced during a period of extension associated with large-scale, NNE-trending strikeslip faulting of the orogen. AK1 is composed of four coalesced, steep-sided diatremes aligned along an NNE-trending fault and tapering to narrow feeder zones at depth. The body is infilled by volcaniclastic olivine lamproite and cut by late olivine lamproite dikes. Two distinct groups of volcaniclastic rocks are present. The dominant type comprises mainly quartz-rich lapilli tuffs and coarse ash tuffs formed by numerous phreatomagmatic eruptions, when olivine lamproite magma was erupted through water-rich sands and silts of the Carr Boyd Group. In contrast, latestage olivine lamproite lapilli tuffs, devoid of accidental quartz grains, fill the center of the northern diatreme. Following emplacement, the body was tilted 30° to the north and extended north-south by the sinistral northnorthwest–south-southeast Gap fault system and east-northeast–west-southwest by the dextral Razor Ridge fault. The Razor Ridge fault offsets the most southerly diatreme (southern tail) from the main part of AK1. Reversal of structural offsets affecting AK1 reveals a geometry which closely resembles that of other ultramafic diatremes. Variations in diamond grade and quality within AK1 indicate that at least two distinct magmas with unique diamond contents have been emplaced at Argyle.

The richly diamondiferous ~1180 Ma Argyle AK1 lamproite pipe at the margin of the Kimberley craton of Western Australia is underlain by a depleted Archean lithospheric root composed mostly of garnet-poor lherzolite. Peridotite xenoliths (some diamondiferous) define a cratonic paleogeotherm with a ~200-km-thick lithosphere, comparable with estimates from present-day seismic S-wave tomography. The Argyle lamproite is highly enriched in incompatible elements and formed by very small degrees of partial melting under reduced H2O- and HF-rich conditions of depleted lithospheric mantle that had undergone long-term (>2 Ga) geochemical enrichment. Multiple metasomatic and thermal events including episodic formation of diamond have impacted on the lithosphere of the Kimberley craton, both predating and postdating Paleoproterozoic reworking of its margins and amalgamation within the larger North Australian craton. At Argyle, the inventory of older (Archean?) peridotitic diamonds in the craton root was augmented by Proterozoic (1.58 Ga) eclogitic diamonds with distinctive light carbon isotope compositions to generate Argyle’s rich diamond grades. The Argyle lamproite and other brief episodes of kimberlite, lamprophyre, and lamproite magmatism (some diamondiferous) on the Kimberley craton all bear their own geochemical and isotopic signature, reflecting variable relative contributions from asthenospheric and enriched lithospheric mantle sources. Mantle melting and eruption of small volumes of these diverse magmas may have been triggered by small short-lived thermal perturbations from the asthenosphere and/or tectonic events elsewhere on the Australian continent, triggered by global plate reconfiguration.