Geochemistry Of Ore-bearing Rocks And Ore Genesis Of Yangbishan Iron Deposit In Heilongjiang Province

Yangbishan deposit in Jiamusi area is a large-scale iron-tungsten deposit,which has been discovered and developed earlier,but has been little research.It is located within the central of Jiamusi Massif,the east of Mudanjiang fault.The iron formations mainly occur in metamorphic rock series of Dapandao Formation of Xingdong Group.The formation is mainly composed of sillimanite-garnet-biotite-quartz schist and sericite-garnet-quartz schist.In iron formation,magnetite usually shows a directional distribution and close relationship with garnet and biotite.The major elements compositions of iron formation and its wall rocks show the protolith of both siliceous ferruginous sedimentary rock and aluminous magnesian siliceous ferruginous rock,belong to colloidal chemical sedimentary rock.Also,their high degree of Al₂O₃ and TiO₂ implies the addition of terrigenous clastic when they deposited.On one hand,the enrichment of light rare earth,the Eu negative abnormality and the stability of heavy rare earth contents?the same as distribution patterns of Archaean sediments?illustrated by chondrite-normalized REE patterns of iron formations,prove that the iron formations deposited in passive continental margin setting,and according to the Th-Co-Zr/10 diagram,the source of sediment from iron formation is featured by both continental island arc and passive continental margin.On the other hand,garnet and biotite are close to magnetite and the iron formations were influenced by high amphibolite facies metamorphism?T=632?⁷69??and enriched owing to it in the light of the garnet-biotite geothermometer.The zircon U-Pb dating of banded and massive ore samples shows that the age of detrital zircon is dispersed,from 1006Ma to 2711Ma.The minimal age of magmatic zircon?1006Ma?limits its lower age of sedimentation,suggesting that iron formations had finished deposition in early Proterozoic while the maximum age of magmatic zircon?2711Ma?suggests that Xingdong Group is the oldest crystalline basement in Jiamusi Massif.The metamorphic episode of iron formations implied by metamorphic zircon occurred in early Ordovician,suggesting that iron formations were influenced by Late-Pan Africa tectonic metamorphism event which developed extensively in the region.To sum up,Yangbishan iron deposit belongs to the Superior-type BIF,depositing in early Proterozoic,enriched by the influence of Late-Pan Africa tectonic metamorphism event in later period and the high amphibolite facies metamorphism,and the metamorphic temperature reached about 632?⁷69?.