Mineralogical and geochemical characteristics of the Zaccar Fe-(Ba-Pb-Zn-Cu) deposit in Ain Defla, Algeria (Northwestern Algeria)

摘要

The Zaccar metasomatic-type iron deposit in Northwestern Algeria is hosted in Jurassic carbonate sequences proximal to Neogene volcanic rocks. The deposit consists of iron carbonates and oxides, associated with minor polymetallic sulfide and sulfate minerals. Microscopic observation, X-ray diffractometry (XRD), scanning electron microscopy with energy-dispersive X-ray spectrometry (SEMEDS), fluid inclusion microthermometry, atomic absorption spectrometry (AAS), and inductively coupled plasma mass spectrometry (ICP-MS) were conducted on ores and host rocks to clarify mineralogical and geochemical the Zaccar iron deposit. Analyses indicate that the carbonate rocks show light rare-earth element (LREE)-enriched REE patterns with a Eu negative anomaly and almost no negative Ce anomaly, suggesting a shallow submarine depositional environment less than 100 m deep. Country limestone is partly replaced by the original epigenetic metasomatic ore of ankerite and siderite, associated with minor pyrite, chalcopyrite, galena, and barite. Abundant hematite was formed by supergene enrichment of iron carbonates controlled by groundwater level at low to medium temperature. The iron oxide mineralization indicates the positive Eu anomaly, lack of Ce anomaly, high Nd/Yb ratio, and high Eu/Sm ratio, which suggests a hydrothermal signature of iron carbonates as epigenetic mineralization, confirming replacement phenomena. The genesis of this kind of iron mineralization is likely related to basinal brines; a second type of iron oxide is represented by specularite (=high temperature variety of hematite) hosted in rhyolite of Miocene age. The microthermometry conducted on fluid inclusions trapped in quartz associated with specularite indicates high temperature and salinities (300 to 320 degrees C, 38 to 40 wt% NaCl eq), suggesting that specularite was formed by hydrothermal activity related to Neogene volcanism, evolved from the mixing of magmatic and meteoric waters.