Distinct Groups of Low- and High-Fe Ferropericlase Inclusions in Super-Deep Diamonds: An Example from the Juina Area, Brazil

Diamonds from the Rio Sorriso placer in Juina area, Mato Grosso State, Brazil, contain mineral inclusions of ferropericlase associated with MgSiO3, CaSiO3, magnesite, merrillite, and other minerals. The diamonds are resolved into two distinct genetic compositional groups: (1) protogenetic, high-Ni low-Fe (Ni = 8270–10,660 ppm; mg# 0.756–0.842) ferropericlases, (2) syngenetic, low-Ni high-Fe 600–3050 0.477–0.718) ferropericlases. Based on crystallographic orientation relationships between natural host diamonds, ferropericlases originate upper part lower mantle, while most likely, lithosphere. Mineral form ultramafic lower-mantle (MgSiO3, which we suggest as bridgmanite, CaSi-perovskite, ferropericlase) lithospheric (CaSiO3, breyite, Ca(Si,Ti)O3, associations. presence magnesite merrillite association confirmed existence a deep-seated carbonatitic association. hosting have different carbon-isotopic compositions (δ13C −5.52 ± 0.75‰ versus −7.07 1.23‰ VPDB, respectively). It implies stratification mantle: composition tends to become isotopically heavier (less depleted 13C) than diamonds. These regularities may characterize not only area Brazil but also parts world.