The Study On Metallogenic Environment And High-grade Iron Deposits Formation Mechanism Of Gongchangling,Liaoning Province

The Gongchangling iron deposit is located in the Anshan-Benxi area,northeastern margin of theNorth china plate,being famous for its Anshan-type iron deposits,which are around by archean granite,and specially for its high-grade iron ore. Intricate and chronic geologic processes blurred original ore appearance and added new ore likeness, so as not to correctly and perfectly recognize metallogenic environment and high-grade iron ore formation mechanism nowadays.The paper has a comprehensive study on Gongchangling’s iron deposit material sources and metallogenic environment by means of detailed field geological survey, indoor microscopic observation, petrology, geochemistry and combining the stable isotopes results and geological age results. the paper has a in-depth study on the high-grade iron formation mechanism by comparing the petrology character between high-grade iron ore and magnetite-quartzite,"artered rock". the main conclusions are as follows:(1) Folds in this district can be divided into four levels in scale:the first-level folds control the overall distribution of Gongchangling iron ore belt(the reverse S-shaped fold);the second-level folds refer to ones that involve multiple strata in scale, which is the most important folds in No.1,No.2 and Du-Bapanling mines.the type folds provided the room for the high-grade iron body; the third-level folds refer to ones that occur in second-level folds with the same axis, generally involving only two or three layers of rocks,which is prevalent and small.so they have little impact on the orebody. the forth-level folds refer to interlayer folds, which can indicate the terrane sliding direction.(2) Fault are prevalent, the EW and NE trending normal faults are bigger and others are generally less and small in No.1 and No.2 mines; the NE reverses faults are the most important ones in Dumu-Bapanling mine,which destroyed the orebody continuity; Faults in No.2 mine have diverse properties, including both strike reverse faults, only which can control high-grade deposits, and transverse faults which is harmful to high-grade orebody continuity. The former ones is older than the later ones.(3) The iron-bearing strat of the No.1 and that of the No.3 mine are same as K layer to the upper iron-bearing belt of the No.2 mine; the Fel and Fe2 in the No.l and the No.3 mine are equal to the Fe4 and Fe6 in the No.2 mine. Material sources of iron ore is closely related to submarine hydrothermal activities, and there is no or less containing-aluminum clastic matter joining;the iron ore is formed by marine chemical sedimentary in a reducing environment. The iron ore is close to amphibolites, the original rocks of which is classified to mid oceanic ridges(floor) tholeiite,and biotite leptynite, the original rocks of which is greywacke formed from continental island arc.Combining the mine material resource and archean metallogenic background,the metallogenic environment for Gongchangling iron deposits is back-arc basin.(4) The high-grade ore comed from magnetite quartzite,the best sits for which are fault and fold core. the high-grade magnetite orebodies show positive relation to the development of the "altered rocks", which are composed of chlorite,garnet and biotite. the original rock of "altered rock" is muddy-silty, the muddy-silty can absorbed the SiO2 and formed garnet, chlorite, biotite, etc.The formation mechanisms of high-grade iron ore includes Fe-concentrating enrichment mechanism and Si-removal and Fe-concentrating mechanism.(5) The regional metamorphism can provided metamorphic hydrothermal, ore storage space, migration dynamics of metamorphic hydrothermal and the desired temperature and pressure conditions for mineral transformation. The metamorphic hydrothermal can leaching FeO in the magnetite quartzite. So regional metamorphism is important conditions for the formation of high-grade ore. there are multilayer magnetic quartzite in Gongchangling and there are muddy-silty between two layers of magnetite quartzite, both are benifical to deformation and SiO2 absorption, so the high-grade ores in No.2 mine are more and larger.