Genesis of chromitites from Korydallos, Pindos Ophiolite Complex, Greece, based on spinel chemistry and PGE-mineralogy

Abstract

The Pindos Ophiolite Complex, located in northwestern Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. In Korydallos are encountered both types of chromitites. These are podiform chromitites that have small dimensions and occur sub-concordantly to the hosting peridotites. The Cr-rich chromitites contain magnesiochromite with high Cr# [Cr/(Cr + Al): 0.65-0.68] and low platinum-group element (PGE) contents (294.1 ppb), whereas the Al-rich ones host spinel with low Cr# (0.44-0.48) and elevated total PGE grades (28830 ppb). The former display a nearly flat C1-normalized PGE-pattern, whereas the latter show a positively sloped normalized PGE-pattern. The in situ mineralogical investigation of the Cr-rich chromitites revealed a platinum-group mineral (PGM) assemblage dominated by small (≤ 3 μm) sperrylite, laurite and erlichmanite grains (determined by recalculated qualitative analytical data). Textural relations suggest crystallization under conditions of high fS 2 and fAs and/or low T. The in concentrates mineralogical study of the Al-rich chromitites showed that the PGM assemblage that they host is dominated by Pd-Cu and Pd-Au-Cu alloys. The vast majority of these alloys is associated with abundant secondary BMS (base-metal sulfides) and BMA (base-metal alloys), thus confirming that a sulfide melt scavenged the PGE + Au of the silicate magma from which chromian spinel had already started to crystallize. Both assemblages were affected by an invasion of an oxidizing aqueous fluid in the investigated chromitites. Combined data indicate that the chromitites from the Korydallos area crystallized from a progressively differentiating MORB/IAT melt, produced in a small backarc basin in a supra-subduction zone setting.

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

“…In contrast, the majority of the supra-Moho chromitites are Al-rich and characterized by a variable content of TiO 2 (0.15 wt % to 0.8 wt %). Confirming the previous work by [8,[14][15][16][17]21], the composition of the Alapevsky chromite indicates the coexistence of the Al-rich and Cr-rich chromitites, a common feature of many ophiolitic belts worldwide [22,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50].…”

Chromite Composition and Accessory Minerals in Chromitites from Sulawesi, Indonesia: Their Genetic Significance

“…However, the presence of both Al-rich and Cr-rich chromitites within one single ophiolite complex has been documented worldwide [26,27,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. This coexistence can be explained with the following models as summarized in [52]: (1) intrusions of different melts derived from differently depleted mantle sources (i.e.,: MORB versus boninite), during the geodynamic evolution of the oceanic lithosphere from the MOR towards the SSZ; (2) mixing of several magmas produced by multi-stage melting of a partially re-fertilized and fluid-metasomatized residual source, in the SSZ; (3) the reaction of a single intrusion of a boninitic parental melt with country-rock peridotites characterized by variable residual composition; (4) fractional precipitation during differentiation of a single batch of magma with initial high-Cr boninitic composition, in the SSZ; and (5) bimodal distribution and vertical zoning with the Cr-rich chromitite located in the deep mantle section and the Al-rich chromitite occurring higher in the succession, close or above the Moho transition.…”

Alteration of mélange-hosted chromitites from Korydallos, Pindos ophiolite complex, Greece: evidence for modification by a residual high-T post-magmatic fluid

“…Note that the "Western Hellenic Ophiolites" (WHO) are separated from the "Eastern Hellenic Ophiolites" (EHO) by a black dashed line (P: Pindos; modified after Dilek et al 2007), b -simplified geological map of the Pindos ophiolitic massif, showing the location of the study area (Korydallos district; modified after Kostopoulos 1989; BACKGROUND INFORMATION AND RELEVANT PREVIOUS WORKS Tarkian et al (1996) and Prichard et al (2008) studied the noble metal inventory of the chromitites from the district of Korydallos and the platinum-group mineral (PGM) assemblages that they host. In a similar manner Kapsiotis et al (2010) and Kapsiotis (2013) focused on the geological investigation of the chromitite outcrops and explained their genesis on the basis of spinel compositions and platinum-group element (PGE) mineralogical data. A first, but short, description of the mélange formation in the Korydallos area was given by Kapsiotis (2013).…”

“…In a similar manner Kapsiotis et al (2010) and Kapsiotis (2013) focused on the geological investigation of the chromitite outcrops and explained their genesis on the basis of spinel compositions and platinum-group element (PGE) mineralogical data. A first, but short, description of the mélange formation in the Korydallos area was given by Kapsiotis (2013). According to that study the mélange in the Korydallos locality is a chaotic lithological formation consisting of a rather complex mixture of sedimentary, volcanic and plutonic tectonic blocks set in an intensely strained groundmass.…”

“…It is made up of reddish to dark brown, subhedral to euhedral magnesiochromite grains (Kapsiotis 2013) that are up to 1.5 mm in diameter. All high-Cr chromitite specimens display an irregular net of brittle fractures, which is the most profound characteristic of the impact of deformation on the chromitite (Text- fig.…”