کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4717209 | 1354428 | 2009 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Contrasting compositions and textures of ilmenite in the Catoca kimberlite, Angola, and implications in exploration for diamond Contrasting compositions and textures of ilmenite in the Catoca kimberlite, Angola, and implications in exploration for diamond](/preview/png/4717209.png)
The Catoca group-I kimberlite, the only currently active diamond-producing mine in Angola, was emplaced in the northeastern part of the Lucapa structure. We focus here on compositional and textural variations in ilmenite from drill-core material, in the hope of elucidating events before and during the emplacement of the kimberlitic magma. We have characterized four main variants of ilmenite, with enrichments in Fe3+, Mg, Mn and nearly stoichiometric ilmenite, and in seven textural classes, and have distinguished crystals of variable size, ranging from micro- to megacrysts. Most ilmenite is found to derive, through a complex process, from replacement of Fe3+-rich ilmenite, presumably originating by mantle metasomatism at a relatively high fO2. This Fe3+-rich ilmenite reacted with fluids under reducing conditions, producing Mg-rich ilmenite. The Mn-rich ilmenite is produced by interaction with a late CO2-rich fluid. The Mg-rich ilmenite is here clearly a minor phase and a late product of replacement. The absence of fresh Mg-rich ilmenite and the occurrence of Fe3+-rich ilmenite do not seem to be convincing arguments to exclude the presence of diamond crystals in a kimberlite. Compositional attributes must thus be considered with caution, and only in light of textural studies, in exploration programs.
Journal: Lithos - Volume 112, Supplement 2, November 2009, Pages 966–975