Chromite, mg-ilmenite and priderite as indicators minerals of diamondiferous cretaceous kimberlites and lamproites from Côte d'Ivoire (West Africa)

Abstract

Seguela kimberlites are characterized by xenocrysts chromites with elevated contents of TiO2 (0.6-5%) due to reaction with the host rock and Magmatic. Chromites associated with diamonds have high levels of Cr 2O3 (usually > 55% wt), MgO (9-12%wt) and Al 2O3 (12% wt). The Cr content in xenocryst chromites is pressure dependent and thus indicative of diamond potential. Two groups characterized Seguela kimberlites chromites analyses. The first group is characterized by high contents of MgO (> 8.7 wt%) and Cr2O 3 (>57.8 wt.%). They contain more than 0.8 wt% TiO2. The Cr-Ti chromites are phenocrysts crystallized from TiO2-rich kimberlitic magmas derived from lithospheric mantle source. The second group present elevated contents of TiO2 (1-5%wt) intermediate Cr 2O3 (30%wt) and relatively low Al2O3 (<3%). The first group kimberlitic chromites are useful in diamond exploration. Chromites are associated with Mg-rich-ilmenite (Fe3+/Fe 2+ < 0.6), in kimberlite which is an important mineral indicator in diamond research. Priderite (TiO2 > 75%wt) with high K/(K+Ba > 0.8) ratio and jeppeyite with elevate BaO content (> 16%wt) and badeleyite (ZrO2> 75% wt) are characteristics minerals of Seguela olivine lamproite. These signatures allow to supose the geotectonic hypothesis of within plate continental Stratiform or Alpin (MORB) complex suggest by chromites Cr-spinels and spinels studies. Kimberlites contain diamonds with a large range in size, varying from microdiamonds (< 1 mm) weighting on average about 1 mg (0.005 carats) up to large diamonds 27 carats.29 page(s