Sr-bearing perovskite and loparite from lamproite and agpaitic nepheline syenite pegmatites

The paragenesis and compositional variation of strontium-bearing perovskite and loparite occurring in lamproites and agpaitic nepheline syenite pegmat ites are described. Olivine lamproites from West Kimberley (Australia), Kap amba (Zambia) and Prairie Creek-American Mine (Arkansas) typically contain perovskite with complex oscillatory zoning and a low Sr content (<3 wt.% Sr O). Perovskite in olivine-free madupitic lamproite from the Leucite Hills ( Wyoming) is enriched in Sr (3-7 wt.% SrO) and rare-earth elements relative to perovskite occurring in olivine lamproite. The perovskite in the lamproi te from Hills Pond (Kansas) is unusual in containing Si (0.2-2.0 wt.% SiO2) , being relatively-enriched in Sr (3-6 wt.% SrO), and exhibiting complex se ctor-zoning. Perovskite crystals from lamproites show no regularities in zo nation trends, which may be either of increasing or decreasing Sr content f rom core to rim. Agpaitic nepheline syenite pegmatites from Pegmatite Peak and Gordon Butte (Montana) contain strontian calcian loparite (10-19 wt.% S rO), and are significantly enriched in Sr relative to loparite found in agp aitic nepheline syenites from the Khibina and Lovozero (Russia) complexes. Naturally occurring perovskite-group minerals exhibit a continuous solid-so lution between tausonite and loparite-(Ce), but not between tausonite and p erovskite. The,Sr-rich perovskite, strontian loparite, and ceroan tausonite are found only in alkaline silicate rocks that lack primary carbonates; Na -Sr-poor, Nb-rich perovskite belonging to the perovskite-latrappite-lueshit e series form in Sio(2)-poor environments characterized by the presence of primary carbonate. In the magmas that form the latter rocks, Sr is preferen tially partitioned into carbonates rather than titanates.