Genesis of magmatic ilmenite ores associated with the Mazua ultramafic intrusion, NE Mozambique

David A.B. Unganai, Akira Imai, Ryohei Takahashi, Daud L. Jamal, Andrea Agangi, Takashi Hoshide, Hinako Sato

研究成果: ジャーナルへの寄稿学術誌査読

抄録

The Mazua ultramafic intrusion is among the most promising intrusions hosting Fe-Ti oxide ores in Mozambique. Fe-Ti oxide ores are mainly composed of ilmenite occurring as lenses, veins and layers, either massive or disseminated in hornblende pyroxenite. This study discusses the nature and origin of the intrusion and related ilmenite ore body on the basis of whole-rock and mineral chemistry. Textural and structural evidences support a cumulate origin for these rocks, including the occurrence of relict cumulate textures, layering of alternating oxides and silicate-rich rocks, and size-grading of silicate-rich layers. Primary magmatic features have, however, largely been overprinted by subsolidus processes. The occurrence of the cumulate assemblage (Fe-Ti oxides and clinopyroxene), without plagioclase and olivine, suggests that the magma underwent differentiation before its emplacement. The evolved magmatic nature of the intrusion is consistent with the calculated Mg-number of approximately 50 for the melt in equilibrium with clinopyroxene crystals. The high TiO2 concentrations (>4 wt%) of the evolved magma, by differentiation, are interpreted as the main factors controlling the crystallization of Fe-Ti oxides. We propose that the ores formed from crystallization and settling of Fe-Ti oxide minerals from an evolved basaltic magma. This model is consistent with (1) the occurrence of Fe-Ti oxides and clinopyroxene as cumulates in relation to the coexisting amphibole, (2) the layering structures of alternating oxides and silicate matrix, (3) the scarcity of apatite supported by the extremely low whole-rock P2O5 concentrations and (4) the restricted occurrence of ore veins, excluding the formation from immiscible oxide melts.

本文言語英語
論文番号104760
ジャーナルOre Geology Reviews
143
DOI
出版ステータス出版済み - 4月 2022

!!!All Science Journal Classification (ASJC) codes

  • 地質学
  • 地球化学および岩石学
  • 経済地質学

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