The Sedmentary Characteristics And Genesis Of The Ningxiang-type Iron Ore In The West Of Hubei Province

Ningxiang oolitic hematite in Devonian is one of the most important iron oredeposit, about which metallogenic process and biological genetic research direction ismore active in recent years. Based on sedimentology, geochemistry, ore depositgeology and other disciplines, comparison of Xuanlong-type oolitic hematite inPrecambrian, the ore forming process is stuied comprehensively and we discuss thecontrol factors of ore mineralization process and the biological role.The natural type of Ningxiang iron ore can be divided into oolitic hematite ore,oolitic chlorite siderite ore and the mixed one. The oolitic hematite ore is divided intofour basic components: endogenous particles, terrigenous clastic, fillings and pore.The main mineral composition of hematite is hematite, limonite, chlorite, quartz,calcite, phosphate rock, dolomite and trace mineral. The oolitic particle size mainlydistribute in0.1~0.5mm, which is significantly less than the Xuanlong-type iron ore.The core of different composition, structure and even cause can be the base of the thesedimentary layers, which means that the sedimentary layers are not affected by thebase. More than90%iron oolite has not a core. The light and dark laminae are nottypical. The shape of the oolites is multiple.The Western Hubei Province in late Devonian was mainly shallow-seacontinental shelf facies. Yuntaiguan formation is a typical littoral beach deposition, ofwhich lithology is single, bedding structure is developed, fossil are rare.Huangjiadeng formation lithology is green and purple shale, quartz sandstone,generally with oolitic hematite and horizontal bedding, which is shore-floodplainsedimentary environment. The upper of Xiejingsi formation is sandstone and shalecontaining oolitic chlorite siderite layer (Fe4); Lower segment in the eastern segmentcontaining limestone, oolitic hematite beds (Fe3), which born the melt rich ore; thewest is shale sandstone containing acid rich ores. The formation is shallow shelfenvironment.The Devonian strata of the area can be divided into three third-order sequences.The ore-bearing strata are analyzed in detail. The Ningxiang-type iron ore formed inthe transgression. Iron ore is consists of4layers, where the Fe1and Fe2are born in Huangjiadeng formation and while Fe3and Fe4are born in the Xiejingsi formationupper Devonian upper. Most ore are born in the transition of sandstone to shale orcarbonate. Affecting by sea-level change, the output part of sedimentary iron ore isobviously selective.The typical iron deposits in different regions were sampling. The main elements,trace element and rare earth elements are analysed, based on which the source of ironmaterial, possible redox environment changes and biological in the ore formingprocess is discussed.The geochemical sample analysis from different regions shows that differenttype of ores and minerals corresponds to different redox environment. Withferruginous oolitic mineral composition, the forming process of the ore experiencedcomplex redox environment evolution.Finally, the iron ore formation mechanism is discussed from four aspects: theancient geography, oxidation and reduction environment, sea level change andbiological mineralization. And the formation model is divided into four stages:prepareing stage of the ore materials--iron oolite forming stage--iron ore formingstage.