Manganoan ilmenite as kimberlite/diamond indicator mineral

F. V. Kaminsky*, E. A. Belousova

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    27 Citations (Scopus)

    Abstract

    Manganoan ilmenite was identified in Juina, Brazil kimberlitic rocks among other megacrysts. It forms oval, elongated, rimless grains comprising 8-30 wt.% of the heavy fraction. Internally the grains are homogeneous. The chemical composition of Mn-ilmenite is almost stoichiometric for ilmenite except for an unusually high manganese content, with MnO = 0.63-2.49 wt.% (up to 11 wt.% in inclusions in diamond) and an elevated vanadium admixture (V2O3 = 0.21-0.43 wt.%). By the composition, Mn-ilmenite megacrysts and inclusions in diamond are almost identical. The concentrations of trace elements in Mn-ilmenite, compared to picroilmenite, are much greater and their variations are very wide. Chondrite-normalized distribution of trace elements in Mn-ilmenite megacrysts is similar to the distribution in Mn-ilmenites included in diamond. This confirms that Mn-ilmenite in kimberlites is genetically related to diamond. The finds of Mn-ilmenite known before in kimberlitic and related rocks are late- or postmagmatic, metasomatic phases. They either form reaction rims on grains of picroilmenite or other ore minerals, or compose laths in groundmass. In contrast to those finds, Mn-ilmenite megacrysts in Juina kimberlites are a primary mineral phase with a homogeneous internal structure obtained under stable conditions of growth within lower mantle and/or transition zone. In addition to pyrope garnet, chromian spinel, picroilmenite, chrome-diopside, and magnesian olivine, manganoan ilmenite may be considered as another kimberlite/diamond indicator mineral.

    Original languageEnglish
    Pages (from-to)1212-1220
    Number of pages9
    JournalRussian Geology and Geophysics
    Volume50
    Issue number12
    DOIs
    Publication statusPublished - Dec 2009

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