Geological Characteristics And Ore Genesis Of The Hongshan Iron Deposit In The Beishan Mountains, Gansu, China

The Beishan orogen is an ideal area of studying the metal mineralization under the background of orogen because of the complex tectonic environment.The Hongshan iron deposit located in central southern margin of continental fault-uplift zone in Beishan Xingxingxia-Mazong Shan, Gansu province, which is found in an earlier batch of medium and large iron deposits in Beishan. In recent years, although we have made great progress in prospecting, but for lacking in theoretical research, the origin of deposit is still controversial. Based on the Hongshan iron deposit as the object of study, after detailed field investigations on the basis of research on ore mineralogy, petrography and geochemistry, it is believed that the Hongshan iron deposit in the hot brine exhalogene metamorphic iron deposit. On the basis of previous studies, the following main conclusions are made. 1、Ore-bearing strata of the Hongshan iron deposit in Jixian System Pingtoushan Fm of a metamorphosed detrital rock-carbonate rock formation, deposit is consistent with the attitude of rock, with conspicuous strata-bound. Iron ore series is quartzite type fringe magnetite, ores generally has banded(fringe) structure, disseminated structure, ores minerals with single composition. 2、The geochemistry of syndepositional marine volcanic rocks of ore district found that mafic volcanic rocks and felsic volcanic rocks have characteristics of bimodal volcanic rocks and the Hongshan iron deposits were formed in continental rift environments, which are consistent with the event of the tectonic evolution by analysising the trace element of volcanic rocks. 3、Hongshan iron deposit contains a large number of grey-purple jasper clumps and silica bands. Through studying on geochemical characteristics of siliceous rocks, that siliceous rocks of ore district are submarine hydrothermal sediment had been found, representing gel deposition on the SiO2 facies and iron facies of submarine hydrothermal eruption. 4、REE of ore-bearing strata of marble have obvious positive Eu anomaly, not obvious Ce anomaly, and averaged 31.5 of Y/Ho, consistent with the characteristics of submarine exhalative sedimentary products.5、A large marble in depositing in ore district indicates that ore formed in the condition of alkaline, that the paleo-environment was marine oxidation environment had been indicated through Th/U, V/Cr, Ni/Co and V/(V+Ni). 6、Through this work in the paper, combined with previous research results and compared to typical Sedex type iron deposits, it is thought that the Hongshan iron deposit is a hot brine exhalogene-metamorphic iron deposit, it mainly formed by precipitation of the eruption hot iron-containing brine, and extensive alteration and metasomatism were accompanied when a large number of iron ore formed.