Geochemical Characteristics of Chert of Hongshan Iron Deposit in Gansu Province and Its Petrogenic Significance

The chert from Hongshan iron deposit is closely associated with the iron ore body, and some cherts are iron ores themself. Chemical analysis of the chert shows that it generally has the features of high content of Si and Fe, low content of Al, and higher content of K₂O than Na₂O, and the ratio of Fe/Ti is between 57.14-218.74, (Fe+Mn)/Ti is between 57.54-224.16, Al/(Al+Fe+Mn) is between 0.05-0.14, which are all according with the features of hydrothermal sedimentary chert, but with little terrigenous materials. Trace element analysis of the chert shows that most of the trace elements are lower than the Clarke value and the total REE is lower. Normalized by the North American shale, HREE is richer than LREE, and the geochemical characteristics of the chert indicate that they are hydrothermally sedimentary origin, but with existence of certain continental sources. So it can be concluded that the Hongshan iron deposit is associated with hydrothermal deposite with terrigenous materials and it was formed in the environment of continental margin.