Petrogenesis of Fe-Ti-(P) oxide bearing layered gabbroic intrusion in the Northern Eastern Desert of Egypt: insights into parent melt composition and genesis of oxide ores

This study presents comprehensive mineralogical and geochemical investigations of Fe-Ti-(P) oxide-bearing gabbros at Abu Murrat in the Northern Eastern Desert, Egypt, unraveling their petrogenesis, magma evolution, and metallogenic significance within the Arabian-Nubian Shield. The Abu Murrat layered gabbroic intrusion primarily comprises pyroxene gabbros, pyroxene-hornblende gabbros, hornblende gabbros, biotite-hornblende gabbros, and leucogabbros. It hosts layers and lenses of Fe-Ti-(P) oxide ores directed in a characteristic NW-SE direction, consistent with the Najd trend. These ores found as disseminated (25–35 vol%), semi-massive (50–60 vol%), and massive (75–85 vol%) ores, mainly composed of titanomagnetite with subordinate ilmenite ± apatite alongside silicate gangues. The Abu Murrat gabbroic parent melt has undergone extensive fractionation as elucidated from high apatite contents (P₂O₅: up to 5.46 wt%), low bulk Mg# (22–44), Cr (42–110 ppm), and Ni (10–43 ppm) contents, along with An_31-43 content of plagioclase, akin to the highly evolved upper zones of Skaergaard, Bushveld, Sept Iles, and Abu Ghalaga layered intrusions. The occurrence of granodiorite xenoliths within the Abu Murrat gabbros, the dominance of orthopyroxene as a mafic phase, along with a wide range of K/Rb ratios and LREE enrichment, indicates significant crustal contamination. The gabbroic lithologies exhibit low SiO₂, high enrichment in FeO^t and TiO₂, moderate enrichment in trace elements, and relatively fractionated REE patterns with a notable absence of positive Eu anomalies, indicating ferrobasaltic parent melts. Their high-Fe-Ti characteristics and low MgO content likely indicate low mantle potential temperatures due to partial melting of the plume head, which results from adiabatic decompression. The Abu Murrat gabbroic intrusion was formed by mantle plume activity within a continental rift environment under a high oxygen fugacity, at temperatures between 800 and 1150 °C and pressures ranging from 2 to 5 Kbar. These conditions are favorable for the liquid immiscibility hypothesis, which indicates the generation of the Abu Murrat Fe-Ti-(P) oxide ore deposits during the late stage of the evolution of Fe-rich residual melt.