Ruthenium variation in chromite from komatiites and komatiitic basalts-a potential mineralogical indicator for nickel sulfide mineralization

Marek Locmelis*, Marco L. Fiorentini, Stephen J. Barnes, Norman J. Pearson

*Corresponding author for this work

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

More than 390 chromite grains from komatiites and komatiitic basalts from the Yilgarn craton of WesternAustralia and the Finnish part of the Fennoscandian Shield were analyzed using in situ laser ablation inductivelycoupled plasma mass spectrometry (LA-ICP-MS) to identify ruthenium (Ru) signatures in chromiteassociated with nickel sulfide-bearing rocks. Results indicate a potential method to discriminate mineralizedand barren komatiite and komatiitic basalt units based on Ru concentrations in chromite and indicate potentialfor chromite to be used as a resistate indicator mineral in exploration for komatiite-associated nickel sulfidedeposits.Chromites from barren komatiites and komatiitic basalts display Ru concentrations mostly between ∼150and 600 ppb. Chromites from mineralized units have distinctly lower Ru contents (<150 ppb). These resultscan be interpreted in terms of the much higher partition coefficient for Ru into sulfide liquid compared to thatof Ru into chromite, resulting in much lower Ru concentrations in chromite where both chromite and sulfideliquid are present and competing for Ru. As a result, the Ru content of chromite can be used to determine ifa komatiite melt equilibrated with a sulfide liquid during crystallization, and therefore, if a system and/orsequence is prospective for nickel sulfide mineralization.The strength of this method compared to previous whole-rock exploration techniques derives from combining(1) the geochemical properties of a chalcophile element that records an ore-forming process while beingstrongly immobile during postmagmatic processes, with (2) the in situ analysis of a mineral that is generally preservedeven in highly altered and mildly weathered komatiites and that is a common constituent of detritalheavy mineral samples. Chromite Ru content has potential as a prospectivity indicator, applicable to a widerange of media including bedrock, laterites, and detrital resistates heavy mineral samples.

Original languageEnglish
Pages (from-to)355-364
Number of pages10
JournalEconomic Geology
Volume108
Issue number2
DOIs
Publication statusPublished - Mar 2013

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