Study On The Geological Characteristics And Metallogenic Potentiality Evaluation Of Jiangjiagou Au Deposit In Jiutai,jilin Province

Jiangjiagou Au deposit?the original Santai Au deposit?is situated in Shanghewai town of Jiutai area in Changchun,Jilin Province.The deposit is located in the middle of Daheishan horst???which belong to Jilin eugeosyncline fold belt???of Jilin-Heilongjiang fold system???.It is also located in the eastern segment of Songnen Massive's southern margin,which is a part of the Xing'an-Mongolia Orogenic Belt lying between the Siberian Craton and the North China Craton with superior metallogenic geological conditions.The major outcropping layer of ore district is metamorphic unit of Jifanggou Group,a unit that previsously consisted of intermediate-felsic volcanic rocks,volcaniclastic rocks and clastic sedimentary rocks.The Jifanggou Group metarhyolites formed in the Late Devonian?Zircon U-Pb ages of 365±2Ma?,which was derived from partial melting of juvenile lower crustal and formed in the late of post-collision relative extensional enviroment.The main structures of ore district are NW ductile shear zone and brittle fractures of NW and NE from late superposition.The magmatic rocks include the Silengshan alkaline granite and diorite veins,felsic veins etc.The ore-hosting rocks is sericite quartz schist and sericite chlorite quartz schist from Jifanggou Group.And the Carboniferous magmatic activity provides a heat source for the initial enrichment of the ore-forming minerals in the strata.The ore-controlling structures are the NW later brittle fractures,then the ore bodies filled into the interlaminar fracture of Jifanggou ductile shear zone eventually.Jiangjiagou MCC is comprised of metamorphic core,middle ductile deformation belt and sedimentary cover.There is a detached fault zones which are equipped with the properties of normal fault between middle ductile deformation belt and sedimentary cover.The core includes Silengshan alkaline granite and basic-ultrabasic rock?serpentine?,and the alkaline granite belongs to the typical A type granite forming in the Early Carboniferous?338±2Ma?,which was derived from the migmatization of crust-mantle material and formed in the post orogenic extensional environment.The middle ductile deformation belt is composed of Jifanggou Formation which undergone low greenschist facies metamorphism,developing layer-paralled ductile shear zone,mylonite fabric which include boudinage structrue,rotated porphyroblast etc.and widely developing stretching lines.The sedimentary cover is the early Permian Zhesi Formation.The tectonic was formed in the Early Carboniferous strongly stretching background,resulted from the strongly emplacement of alkaline granite.The extensional function had sustained to the Permian and controlled the sedimentation of Zhesi Formation to some extent.However,there is no obvious genetic relationship between with the tectonic system and Jiangjiagou gold deposit.Besides,the result of geochemical anomaly show that alkali granite is closely related to rare and REE metal anomaly?Zr,Nb,Yb,Be,etc.?,equiping with well metallogenic potential.There are seven gold ore bodies and five mineralized bodies in Jiangjiagou ore district.The ore bodies are mainly in the shape of nervation,lentoid and irregular,overall trending nearly to NW,leaning to NE and distributing diagonally with the characteristics of“On Steep Under Slow”.Ore types are albite dominated felsic vein type and altered type with mylonitization.The ore minerals are pyrite,hematite,magnetite and chalcopyrite,sphalerite,galena etc.secondly.The gangue minerals are quartz,feldspar,sericite,calcite,etc.Majortexturesoforesare automorphism-hypidiomorphism granular texture,cataclastic texture,metasomatic texture,emulsion texture,etc.The major structures are sparse impregnation structure and impregnation structure.The country rock alterations are mainly silicification,sericitization,chloritization and slight kaolinization,carbonatation,potash feldspathization,albitization.Then the silicification,sericitization and albitization are closely related to the Au mineralization.The main metallogenic stage's fluids belong to NaCl-H₂O system with middle temperature?133?²52??,middle-low salinity?0.87¹9.0wt%?and low density?0.82¹.03g/cm³?.The metallogenic pressure approximately ranges from 50 to 100 MPa and the depth concentrated in 5.00⁸.25km.The hydrogen and oxygen isotopes analyses show that the metallogenic fluids are mainly from mantle-derived fluids and may be mixed with the meteoric water later.The carbon and oxygen isotopes analyses indicate that the CO₂ in the metallogenic fluids is from mantle.The?³⁴S values of sulfur isotopes show that the metallogenic material is mainly originated from deep material,and partly from the strata sulfur.Taking all this into account,we conclude that the genetic type of Jiangjiagou Au deposit formed in the early Cretaceous,which belongs to the type of mesothermal hydrothermal vein deposit with mantle fluids.It is formed in the strongly extensional enviroment that is related to the lithosphere thinning after the dismantling being caused by subduction of the Paleo-Pacific plate under the Eurasian continent.According to the extraction of peripheral ore proctection information such as geological characteristics,geochemical anomaly etc.of Jiangjiagou Au Deposit,we speculate that the periphery possesses the metallogenic potential of gold and rare and REE metals.