This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral ...This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral composition,nine types of ooids and three possible scenarios for their formation have been identified.The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment,including fluctuations in theredox regime.The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters.The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.展开更多
Yandi Channel Iron deposit is located in the Hamersley Province,Pilbara region of northwestern Australia and contains one of the world’s largest iron resources.Yandi CID was deposited in pre-existing palaeochannel in...Yandi Channel Iron deposit is located in the Hamersley Province,Pilbara region of northwestern Australia and contains one of the world’s largest iron resources.Yandi CID was deposited in pre-existing palaeochannel incised into Hamersley Group.Hamersley Group contains BIFs and provides source of ore.The deposition began between Late Oligocene and Mid Miocene.During Early-Mid Miocene,the local climate increased continuously and accompanied with heavily rainfall,resulting in weathering and rework processes to the ore body.The ore body is contained in Marillana Formation,which consists of Munjina Member,Barimunya Member(main CID zone)and the uppermost Iowa Eastern Member.Yandi CID is characterised by a simple mineralogy,dominantly goethite and hematite.Hematite granules consist of pelletoids and pisoids.The pelletoids formed upper part of ore body and pisoids formed lower part.Weathering of iron fragments leads to dissolution and precipitation of goethite and formed vitreous goethite surrounding the hematite granules.Some goethite formed matrix that contains large amount of porosities,quartz and hematite granules.Silica mobilization happened multiple times.Some dissolved and precipitated in hematite granules,and some dissolved in groundwater and precipitated in macro voids in matrix.The climate change also leads to the replacement of vegetation.Wood fragments were driven by river flow and deposited in upper CID.Lowering of the water table resulted in developing of extensive alteration zones which reduced the quality of ore.Overall,Yandi CID is unique production of iron-rich materials,erosion,global climates changes,plates drifting,rainforest vegetation and palaeochannel.展开更多
文摘This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral composition,nine types of ooids and three possible scenarios for their formation have been identified.The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment,including fluctuations in theredox regime.The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters.The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.
文摘Yandi Channel Iron deposit is located in the Hamersley Province,Pilbara region of northwestern Australia and contains one of the world’s largest iron resources.Yandi CID was deposited in pre-existing palaeochannel incised into Hamersley Group.Hamersley Group contains BIFs and provides source of ore.The deposition began between Late Oligocene and Mid Miocene.During Early-Mid Miocene,the local climate increased continuously and accompanied with heavily rainfall,resulting in weathering and rework processes to the ore body.The ore body is contained in Marillana Formation,which consists of Munjina Member,Barimunya Member(main CID zone)and the uppermost Iowa Eastern Member.Yandi CID is characterised by a simple mineralogy,dominantly goethite and hematite.Hematite granules consist of pelletoids and pisoids.The pelletoids formed upper part of ore body and pisoids formed lower part.Weathering of iron fragments leads to dissolution and precipitation of goethite and formed vitreous goethite surrounding the hematite granules.Some goethite formed matrix that contains large amount of porosities,quartz and hematite granules.Silica mobilization happened multiple times.Some dissolved and precipitated in hematite granules,and some dissolved in groundwater and precipitated in macro voids in matrix.The climate change also leads to the replacement of vegetation.Wood fragments were driven by river flow and deposited in upper CID.Lowering of the water table resulted in developing of extensive alteration zones which reduced the quality of ore.Overall,Yandi CID is unique production of iron-rich materials,erosion,global climates changes,plates drifting,rainforest vegetation and palaeochannel.
