Metallogenic Tectonic Environment And Tectonic Geochemistry Characteristics Of The Fault In Banshigou Iron Deposit, Baishan City, Jilin Province

Banshigou iron deposit in Baishan City,Jilin Province is a typical sedimentary metamorphic iron deposit with complex tectonic deformation and metamorphism.Sedimentary metamorphic iron deposit could be divided into two types according to metallogenic tectonic environment:original metallogenic tectonic environment and secondary metallogenic tectonic environment.As for Banshigou iron deposit,there are many researches about secondary metallogenic tectonic environment while there are few researches about original metallogenic tectonic environment.The researches about the faults are mainly from the aspects of tectonic geology,lacking understandings of tectonic geochemistry characteristics.In this paper,we recognize original rocks by collecting new and old samples of representive ore and surrounding rock in Banshigou iron deposit and analyzing geochemistry characteristics of major elements,trace elements and REE.Also,we conclude original metallogenic tectonic environment by basic rock and intermediate-basic rock's geochemistry characteristics of trace elements and rare earth elements?REE?in ore-bearing formation of Banshigou iron deposit.Besides,this paper summarizes the secondary metallogenic tectonic environment of Banshigou iron deposit.by the tectonic deformation characteristics of ore bodies and surrounding rocks.Rock samples in compression faults and surrounding rock were collected during surveying typical compression fault section in Banshigou iron deposit.Based on the analysis result of major element and trace element,this paper uses element tectonic section,isocon and the ratio of characteristic element to study the tectonic geochemistry of faults.The Banshigou iron deposit is located in the eastern part of the northern margin of the North China block.The ore body is mainly located at the core of the fold in the mining area.The rock in the mining area can be divided into two major categories:the supracrustal rock of Yangjiadian Formation in the Anshan Group of the Antarctic and the TTG intrusive rock.Because the ore-bearing formation is formed in the supracrustal rock of the basement metamorphic rock series,the supracrustal rock is the surrounding rock of the ore body,and the iron ore body and the supracrustal rock are folded together.According to the rock combination,the supracrustal rock in the mining area is divided into five layers.They are dark gneiss,amphibolite,magnetite quartzite,hornblende schist and light gneiss from the bottom to the topAccording to petrographic and geochemical analysis,the original rocks of magnetite quartzite is mainly sedimentary rock,while the original rock of surrounding rock is volcanic rock,which has the metallogenic conditions for the deposition after volcanic eruption.The magnetite quartzite has higher Eu anomaly,slightly higher Y anomaly and Y/Ho ratio,indicating that the metallogenic process is influenced by both hydrothermal and seawater,and its trace element characteristics are consistent with the features of the island arc graywacke.In the surrounding rocks,the protoliths of the biotite hornblende plagioclase gneiss,amphibolite,and hornblende schist are all basalts,while the biotite plagioclase gneiss's original rocks are rhyolite.This paper selects the biotite hornblende plagioclase gneiss,amphibolite and hornblende schist to reflect the metallogenic tectonic environment.According to the identification diagram of tectonic setting,the amphibolite and hornblende schist belong to island arc environment.The biotite hornblende plagioclase gneiss belongs to continental marginal arc environment,but the trace elements and rare earth elements of the amphibolite,hornblende schist and biotite hornblende plagioclase gneiss are all consistent with the characteristics of the island arc basalt.Therefore,it is speculated that the original metallogenic tectonic environment should belong to island arc environment.Secondary tectonic deformation is an important reason for the formation of iron ore bodies and iron-rich ore deposits,and the iron ore body is enriched in the fold core.The Banshigou area has undergone three stages of deformation.The first stage of tectonic deformation is stretching plastic fold,making the original ore-bearing layer form the zigzag in the layer and hook-like folds.The second stage of deformation forms a multiple syncline with a nearly eastwest-trend axis and north metallogenic belt and south metallogenic belt.The third stage of deformation is a wide anticline with a northeast-trend axis superposed to further enrich the ore body.Therefore,it is speculated that the secondary tectonic environment of the Banshigou iron deposit should be a three-stages regional fold deformation.In the NO.17 mine group and Zhaojiagou mine group of the Banshigou iron deposit,this paper selects sections with the compression faults and tectonic rocks for tectonic geochemistry.According to the geochemical sections measured named by P8 and P10,Al,Ti,V,U and Th enrich in faults,while Fe,Si,Ca,Na,Co,Ni,Cr and Mn deplete in faults.As per mass balance calculation and isocon analysis,the elements that migrate to the fault are K,P,Ti,V,Rb,Sr,U and Th.The elements that escape from the fault are Si,Fe,Ca,Na,Mn,Ni,Co and Cr.Since K,Rb,and Sr are elements with a large ionic radius,Ti,V,U and Th are elements with a larger ionic radius in transition elements,and Fe,Si,Co,Ni,Cr and Mn are elements with a smaller ionic radius in transition elements.It is inferred that elements with larger ionic radius before?B group generally tend to migrate and concentrate in compression faults,and elements with smaller ionic radius after?B group tend to migrate and disperse in compression faults,indicating the element with a large ionic radius before the?B group has different tectonic geochemistry characteristics compared with the element with a small ionic radius after the?B group.Since the different elements before the?B group and aftr the?B group have different or even opposite migration and variation regularity in compression faults,the ratio of characteristic elements,such as SiO₂/Al₂O₃,?Fe₂O₃+CaO+MgO?/Al₂O₃,K₂O/Na₂O,V/Cr and Rb/?Ni+Co?can be used to predict the presence of a compression fault.