Orthopyroxenite Hosted Chromitite Veins Anomalously Enriched In Platinum-Group Minerals From The Havana-Matanzas Ophiolite, Cuba

The Havana-Matanzas Ophiolite contains one of the few examples of ophiolitic platinum group minerals (PGM)-rich chromitites associated with orthopyroxenites in the mantle section of ophiolitic complexes. The chromidtes occur as veins hosted by orthopymxenite bands within mantle peridotites. The peridotites are mostly harzburgites and their accessory chromite shows high Al compositions (Cr# [Cr/(Cr+Al), atomic ratio] = 0.39-0.50). which are typical of spinels in abyssal peridotites. Conversely, chromite from the chromitite veins and their host orthopyroxenite are high-Cr (Cr# = 0.72-0.73 and 0.62-0.69, respectively). with lower Mg# [Mg/(Mg-Fe2+), atomic ratio]. This suggests that both the chromitite and the orthopyroxenite limmed from melts with boninitic affinity. The abundant PGM inclusions found in the chromitites are mainly Os-rich laurite grains, which is also characteristic of chromitites formed from magmas with boninitic affinity. Therefore, we propose that the chromitite veins and the orthopyroxenite bands probably firmed contemporaneously in the lice-arc setting of an intra-oceanic an during subduction. The chromitite-orthopyroxenite pair of the Havana-Matanzas Ophiolite could could form after the reaction of a Si-rich melt with boninitic affinity and mantle harzburgite. with the orthopyroxenite bands preserving fingerprints of the infiltration of boninitic-affinity melts within the mantle. The small volume of limning chromitite could maximize the efficiency for the mechanical collection of the. PGM, forming in the parental melt of these rocks, resulting in the anomalous enrichment of primary PGM in the chromitites.