Probe and SIMS investigation of clinopyroxene inclusions in chromites from the Troodos chromitites (Cyprus): Implications for dunite–chromitite genesis Anna Merlini a, ⁎, Giovanni Grieco a , Luisa Ottolini b , Valeria Diella c a Dipartimento di Scienze della Terra, Università degli Studi di Milano, via S. Botticelli, 23-20133 Milano, Italy b CNR-Istituto di Geoscienze e Georisorse (IGG), Sezione di Pavia, via A. Ferrata, 1-27100 Pavia, Italy c CNR-Istituto per la Dinamica dei Processi Ambientali (IDPA), Sezione di Milano, via S. Botticelli, 23-20133 Milano, Italy abstract article info Article history: Received 16 December 2010 Received in revised form 6 June 2011 Accepted 7 June 2011 Available online 17 June 2011 Keywords: Chromite REE Clinopyroxene Troodos Ophiolite SIMS Chromite ores formation is still a debated topic and, in this study, detailed analyses of major, minor elements by EMPA and Rare Earth Elements (REE) by SIMS, were performed on silicate inclusions detected in chromite grains of chromitite pods, enveloping dunites and on clinopyroxene of lherzolitic host rock of well known Trodoos chromite ores. Results show the complexity of relationships among lithologies that reflects the subtlety of genetic events and of chromite ore occurrence. Analyses of textural and chemical features have led to a better understanding of the chromite ore genetic process, that is related to a supra-subduction geodynamic setting where partial melting processes were overlapped by metasomatic events. Metasomatism, that marks the general genetic context, is characterized by the presence of a hydrated boninitic melt that favors the precipitation of chromite ores. Chromite ores, typical of ophiolite complexes and usually enveloped by dunite are, in this case, characterized by the presence of two different types of dunites whose geochemical differences are reflected by olivine mineral chemistry and by different REE patterns of analyzed clinopyroxenes. Such geochemical marks, related to different magmatic and metasomatic events, could be a main key for location of fertile or barren dunites in terms of chromite ore occurrence in the field. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In the last decade, investigation of ophiolite peridotites has provided new data important for the understanding of genetic processes, such as partial melting, melt–rock interaction and melt fractionation, that affects mantle evolution (e.g. Kelemen et al., 1992; Zhou et al., 2005). Several models have been proposed in order to explain podiform chromitites formation. Irvine (1975, 1977) and Zhou et al. (1996) proposed a mixing process of Si-rich and primitive basaltic melts as the most important genetic mechanism in chromitite formation. Although such models account for a large accumulation of chromium spinel, they do not deal with the low solubility of Cr in basaltic melt, and with the limited dimensions of chromite layers in ophiolites. The presence of randomly scattered chromitites within the ultramafic rocks in several ophiolite complexes has been largely documented (Kubo, 2002; Merlini et al., 2009; Zhou and Robinson, 1997). They show a wide range of textures, from small pods or disseminated layers to larger lenses, which are considered a valuable resource in many countries. The study of textural and petrological relationships between chromite ores and ultramafic host rocks can help to understand the complex and irregular distribution and shape of such ores in this geological context. The well documented presence of an enveloping dunite surround- ing chromite ore is a feature common to almost all ophiolites (Kubo, 2002; Lago et al., 1982; Zhou et al., 2005; Zhou and Robinson, 1997). On the other hand dunite bodies in mantle peridotites often do not host any chromite ore. As a consequence, the characterization of dunite features and their relationship with the occurrence of chromite ore can help the understanding of chromitite genesis and distribution. Three main origins have been proposed for dunite (Zhou et al., 2005) and are summarized below: 1) residual dunite formed after extensive partial melting of peridotite; 2) cumulate dunite formed by fractionation of olivine from a mafic melt; 3) replacing dunite that is the product of reaction between pyroxene- bearing host rock and olivine saturated magma which dissolves orthopyroxene in the host peridotite and sometimes crystallizes olivine. In this paper, a very well exposed mantle section of Cyprus ophiolite, extending from clinopyroxene rich harzburgite country rock through enveloping dunite till chromite ore, was studied. One way to unravel the complexity of ophiolite chromitites occurrence and genesis is to perform detailed small-scale studies of host rock-ore transitions. With this purpose silicate inclusions major Ore Geology Reviews 41 (2011) 22–34 ⁎ Corresponding author. Tel.: +39 0250315620; fax: +39 0250315597. E-mail address: anna.merlini@unimi.it (A. Merlini). 0169-1368/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2011.06.002 Contents lists available at ScienceDirect Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev