Tectonic and Structural Controls on Diamondiferous Kimberlite and Lamproite and Their Bearing on Area Selection for Diamond Exploration

Abstract

Abstract Tectonic histories and structural settings of the Diavik, Murowa, Argyle, and Bunder deposits—two kimberlitic- and two lamproitic-hosted diamond resources, respectively—are described to bring attention to similarities and differences that may help to better understand their tectonic and structural controls, and to derive some general principles about the evolution of primary diamond deposits that may be applicable to diamond exploration. As the evolution of all four deposits was multistage and took place over billions of years, possible tectonic and structural controls were assessed for the entire history of their host cratons. To facilitate comparison, each craton is discussed in five stages: (1) Mesoarchean lithosphere formation, (2) Neoarchean overprint of Early Archean protocontinental nuclei leading to cratonization, (3) Proterozoic breakup of Archean cratons and postbreakup modifications until kimberlite/lamproite emplacement, (4) tectonic and structural controls of emplacement, and (5) postemplacement preservation and erosion of diamondiferous host rocks. Whether kimberlite or lamproite, the formation and survival of cool Early Archean P-type roots, or remnants thereof, were essential requirements for deposit formation. Beginning with the breakup of the Archean protocratons, the tectonic settings of the kimberlitic and lamproitic deposits diverged significantly. The Murowa and Diavik deposit sites remained well within the Mesoarchean nuclei of their respective cratons while passive rifting occurred at craton margins, whereas the Argyle and Bunder deposits are located above or near the rifted Proterozoic craton margins. Higher P-type diamond grades survived in the roots sampled by the kimberlites than in those sampled by the lamproites. Additions of Proterozoic eclogites with subduction signatures to preexisting, relatively cool craton roots significantly improved the diamond grade of the Diavik kimberlite and raised the grade of the Argyle lamproite from uneconomic to one of the highest-grade deposits (by carats) in the world. As to kimberlite and lamproite emplacement, no definitive correlations with plume events can be made for any of the deposits, though a case can be made for some that plate margin processes were involved in metasomatic enrichment at depth as well as triggering the melting process. Emplacement sites for all four deposits were controlled by local structures.