Mineral chemistry and fluid inclusion composition as petrogenetic tracers of iron oxide-apatite ores from Hormuz Island, Iran

Faramarzi, Narges Sadat; Jamshidibadr, Mahboobeh; Heuss-Assbichler, Soraya und Borg, Gregor (2019): Mineral chemistry and fluid inclusion composition as petrogenetic tracers of iron oxide-apatite ores from Hormuz Island, Iran. In: Journal of African Earth Sciences, Bd. 155: S. 90-108

Abstract

Hormuz Island is a salt diapir in southern Iran, which also comprises transported blocks of rhyolitic and rhyodacitic rocks, which were brought to the surface during the island's diapiric emergence from the Persian Gulf. The rhyolites (558 +/- 7 Ma) and rhyodacites, have both formed from the same peraluminous calc-alkaline I-type magma, in a volcanic arc settings at an active continental margin. The volcanic rocks contain significant quantities of accessory apatite. The majority of the small crystals of apatites (type-I) have crystallized during an early magmatic phase. Additionally, large single crystals of apatite (type-II) occur together with magnetite in veins within the rhyodacite rocks. The geochemical investigation of the two types of apatite revealed they both formed from the same magma source. Based on the microthermometric characteristics of primary fluid inclusions, two different events during the formation of apatite type-II crystals were distinguished. Our study revealed that in addition to the igneous fluids, a second set of fluid inclusions was trapped in the core of the crystals, indicating a post magmatic interaction with external basinal fluids during the growth of apatite type-II. On Hormuz Island, iron oxides occur as well in different styles from massive iron oxide bodies, magnetite-apatite veins, to red magnetic-hematitic soils. Based on the volcanic structures and textures of the massive iron oxide bodies as well as geochemical results from the magnetite, it is proposed that a source potential for both Fe and P could have been an immiscible iron-rich volatile phase which evolved from the parental felsic magma. Results from fieldwork, microscopy, and geochemistry revealed that mega-crystals of hematite and specularite in the magnetite-apatite veins were formed from magmatic-hydrothermal fluids released from the crystallizing magmas. The occurrence of exotic banded iron ores, red soils and alternating bands of hematite with evaporite minerals could be the result of seawater-rhyolite interactions by circulating exhalative hydrothermal fluids.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 1464-343X
• Sprache: Englisch