The Oolitic Iron Deposits and Environmental Analysis of the Devonian Yangmaba Formation in the Shigouli Profile, Beichuan County, Longmenshan Area

Key words: 
• iron oolitic /
• genetic analysis /
• sedimentary model /
• Yangmaba Formation /
• Longmenshan area

Abstract: Iron oolites of the Middle Devonian Yangmaba Formation in the Longmenshan area are an important form of iron deposit in China's Ningxiang-type oolitic hematite deposit. To recover their sedimentary environment and ge-netic mechanism,the sedimentary characteristics of iron oolites were studied in detail by thin section identification and scanning electron microscope analysis and detailed measurement of the Ganxi Shigouli section. The study shows that the eutrophic iron is concentrated in layers and lenses of bioclastic limestone,oolitic bioclastic limestone and bioclastic oolitic limestone. The surrounding rock is silty mudstone and mudstone. Iron oolites are important stores and carriers of iron and occur in four types,depending on the difference in mineral composition:microlites,chlorite oolites,ferritic oolites and iron oolites. Iron oolites are deposited in a lagoon at the edge of the reef. The distribution of oolites enabled the genetic distribution pattern of oolitic iron at the reef edge to be established. In turn,from the outer reef shoal to the inner shoal,to the lagoon,normal or ferritic oolites,chlorite oolites,chlorite thin-skin oolites and iron were developed.