Study On The Geological Characteristics And Enrichment Regularities Of Mineralization Of Guandi Fe Deposit In Helong,Jilin Province

Guandi Fe deposit,in Helong,Jilin province,is located in the north eastern edge of the North China craton and in the northwest margin of Longgang massif which located in the north of the Jiao-liao-Ji Belt.Guandi Fe deposit is one of the important deposits belong to Helong archean iron-rich mineralization Belt.The primary surface formation are the middle and upper segment of Archeozoic Sandaogou group.Falut and fold structure are widely distributed in mining area.NW-trending structure are mainly fold and interlayer fracture zone.Fengmigou Fault is the largest-scale,NE-trending fault,which controlled the hydrothermal activity and the emplacement of diorite dyke and made a big damage to the ore body.Magmatic rocks distributed in mining area are simple,mainly shown as intrusive diorite dykes.Guandi deposit is distributed in the lower strata of upper segment of Archeozoic Sandaogou group,which is a series of deep metamorphic basic-intermediate acid-acidic volcanic rocks-sedimentary formation.15 Iron bodes groups are discontinuously distributed in mining area influenced by tectonism.Number ? ? ? ? ? ? ? X? group are relatively large-scale,consisting of industrial ore bodies.Morpphology of ore bodis are statiform,stratoid and lenticulate type.Ore rock is magnetite-quartzite,consisted of banded iron and quartz.Ore structure types are mainly banded structure and disseminated structure.Amphibolite and felsic gneiss are the most important ore-bearing rock.There protolith respectively are tholeiite and acid volcanic rock after ptotolith reconstruction which are formed in island arc environment.Amphibolite are chosen to testing Zircon U-Pb dating,the testing result can be separated into three groups:The age of first group is 2724±22Ma,which are explained to the age of capture zircons,means.that there were-2.7Ga magmatic event in the study area.The second group is entirely magmatic zircon with clearly zone texture,yield an age of 2556±17Ma which represents the forming age of amphibolite,Zircons from the third group are characterized with core-mantle texture,yield an age of 2452±23Ma,which represents the age of metamorphism.The method of study on the age of BIF is usually test the age of the wall-rock of ore body.Therefore,Guandi iron deposit was formed in 2556±17Ma and experienced metamorphous reforming in 2452±23Ma.By study on the geochemistry of the ore rock,magnetite quartzite were formed in anoxic marine environment without contamination of terrigenous detrital.Fe was mainly from hydrothermal exhalative process related to eruption of submarine colcano and Si wasalso from thermal water system.The transportation of Fe was by solube F2+ and the precipitation mechanism of Fe was probably related to microbial activities existed in Archean oxygen-deficient environment.The original Fe-and Si-sedimentary was transformed into banded iron formation during later metamorphism,resulting in the activation and migration of ore-forming materials and recrystallization of magnetite and quartz.According to the study,Guandi Fe deposit was considered that formed in an arc-environment at the end of Neoarchean.Arc-continent collision and arc-acr collision occurred in?2.45Ga resulted in subsequent metamorphism.By comparison with domestic and international typical BIF deposit,we consider that Guandi Fe deposit is typical Algoma-type BIF deposit.Mineralization enrichment studies found that Guandi BIF deposit are closely related to Archaean supracrustal rock and consist of the wall rock of Guandi deposit.Ore body and ancient supracrustal rock were formed at the same time.Later fault structure damage the continuity of ore body.The fracture structure also provides a channel for the migration of the hydrothermal fluid,but hydrothermal action on the transformation of Guandi iron deposit was not obcious.Fold structure are favorable for thickening of ore bodies which is often occurred at the hinge zone of the fold.