BIF Geochemical Characteristics And Geological Significancein Songshan Area

Songshan area is located in the southern margin of the north China craton. It is one of the most typical regional which recorded the Precambrian geology of China. The discovery of BIF is one of the most important progress of Songshan geological research in recent years. Banded Iron Formation(referred to as BIF) have great significance for the study of Precambrian geology and ore prospecting.This article selects Songshan area`s iron ore and surrounding rocks as the research object. Through field profile measuring, petrological and geochemical characteristics of this iron ore deposit, discussed the metallogenic material source and the tectonic environmen, achieve the following results:(1)BIF occurs in the neoarchaean Dengfeng group, The main lithology is magnetite quartzite, plagioclase amphibolite, etc. Magnetite quartzite has Fine grained granite blastic texture and banded structure, minerals are mainly quartz(55%~75%), magnetite(25%~35%), hornblende(5%±), etc.(2)Major elements of the ore is mainly composed of SiO2, Fe2O3 and FeO. Trace elements and rare earth elements content is very low, relative concentration of large ion lithophile elements as K, Rb, Ba, Th etc, and loss of high field strength elements such as Nb, Zr and Hf etc. After standardization of PAAS it has loss of light rare earth elements, enrichment of heavy rare earth elements, Eu positive anomaly(Eu/Eu * average being 1.31), Ce slightly negative anomaly(Ce/Ce * average being 0.90) etc.(3)Iron ore deposit formed in the stability exhalative sedimentary stage of volcanic activity, Si and Fe sedimentary in anoxic sea water environment formed the banded structure. Si and Fe in BIF were mainly from volcanic activity. While few fragmentary material joined.(4)The original rock of BIF is mainly of basic volcanic rock, mud stone and some intermediate-acidic volcanic rocks, Amphibolite geochemical characteristics shows of island arc tholeiite and mid-ocean ridge basalt, suggests that this area might be the early back-arc basin environment at that time, The sedimentary environment of the ore deposit was near continental margin area, and in the sedimentary process influenced by ocean volcanic activities within.(5)The geodynamic background of BIF in Songshan area was on the edge of convergent plate subduction environment.(6)The found of BIF in Songshan area could point out the direction of iron ore prospecting, in the future to strengthen in Guojiayao and Wananshan BIF belt of north and south extension direction of prospecting work, and expected to find a certain scale of Anshan-type iron ore deposit.