Abstract The 36-year evaluation history of the AK1 lamproite of the Argyle diamond mine (1980–2016) captures an important chapter in the development of diamond deposit evaluation. The resource potential was recognized early in the evaluation process, despite indications of a fine diamond size-frequency distribution and lower-quality stones. High diamond density and the size-frequency distribution characteristics allowed development of sampling methods. These included large-diameter core sampling and analysis of 20-kg samples of NQ/split HQ core for microdiamonds, which were significantly cheaper than traditional methods and unique to the diamond industry at the time. These methods permitted increasingly deep evaluation programs that augmented resources, underpinned the underground block cave feasibility study and, for the first time, revealed four coalescing vents of the AK1 orebody to –735 m reduced level. The majority of the deposit has high to moderate grades (2–5 ct/t), with extremely high grades in the uppercentral parts (>10 ct/t) and low grades in the north (0–1 ct/t). Despite some anomalous areas, at the scale of mining the AK1 deposit is striking in its size-frequency distribution homogeneity. Diamond size-quality distribution has also remained consistent for many years, being lower in the south and higher in the central-north with respect to the main central part of the deposit. The largest diamond deposit in the world (by contained diamond carats) and the largest producer, AK1 has sustained annual production averaging >25 million carats per annum (more than twice its nearest competitor). Size, homogeneity, and high grades (average 3.5 ct/t over 36 years) have been crucial to its longevity and economic success.