Alteration of the Damiao anorthosite complex in the northern North China Craton: Implications for high-grade iron mineralization

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• 作者：Houmin Li ; Lixing Li ; Zhaochong Zhang ; M. Santosh ; Mingjun Liu ; Yanhe Cui ; Xiuqing Yang ; Jing Chen ; Tong Yao
• 关键词：Damiao type iron deposit ; Hydrothermal mineralization ; Alteration ; Anorthosite ; Fe&ndash ; Ti oxide inclusion
• 刊名：Ore Geology Reviews
• 出版年：March, 2014
• 年：2014
• 卷：57
• 期：Complete
• 页码：574-588
• 全文大小：1809 K

文摘

The Damiao type iron deposit is hosted in a typical Proterozoic anorthosite complex in the northern North China Craton. The types of ores in Damiao mainly comprise massive Fe ores, massive Fe-P ores, and disseminated Fe and Fe-P ores. The disseminated Fe and Fe-P ores formed by fractional crystallization are generally hosted in oxide-apatite gabbronorite and account for 70% of the proven reserve of the Damiao type iron ore. The massive Fe and Fe-P ores account for 30% of the proven reserve of the Damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite, showing typical features of hydrothermal mineralization. The contact between the massive orebodies and wall rocks is sharp and straight. The anorthosite comprises white and dark varieties, with the former resulted by the alteration of the latter that occurs as relicts. Petrographic observation and electron microprobe analyses show abundant Fe-Ti oxide inclusions in plagioclase which impart the dark color to the rock. The similar spider diagram patterns between fresh and altered plagioclase and between dark- and white-colored anorthosite imply a genetic relationship between the dark and white types. During the alteration of anorthosite, CaO and MgO were slightly decreased, the SiO₂, Al₂O₃ and Na₂O were significantly increased, and the TFe₂O₃ and TiO₂ were significantly decreased. The TFe₂O₃ and TiO₂ in the dark-colored anorthosite have a range of 4.86-12.18 wt.% and 0.37-1.65 wt.%, respectively. However, The TFe₂O₃ and TiO₂ in the white-colored anorthosite have a range of 1.67-3.1 wt.% and 0.14-0.31 wt.%, respectively. These features suggest that the alteration of the anorthosite led the Fe element by leaching from the dark-colored anorthosite at highly oxidized condition, and then precipitated within the fractures of the anorthosite, thus forming the massive Fe and Fe-P orebodies. Because the estimated amount of transported Fe is much more abundant than the proven ore reserve, we infer that there should be huge potential for prospecting Damiao type iron ores.