Geological And Geochemical Characteristics And Genesis Of Baligou Gold Deposit In Linjiang City,Jilin Province

The study area locates in Laoling uplift belt,and the east section of the north margin of the North China platform.Laoling uplift belt,which belongs to Liao-Ji palaeoproterozoic rift zone,experienced several collision tectonics,extensional cracking and metamorphic processes;as a result,tectonic-magmatic activity and metallogenic condition is excellent in this area,making the Laoling uplift belt a polymetallic metallogenic belt.Large gold deposit as Huanggoushan and middle-small gold deposit as Banmiaozi and as Baligou,Nancha,Dasongshu,Goujingou and etc.are discovered in the belt.Baligou gold deposit is discovered recently,and is currently in the exploration stage with a low level of research.Ore-hosting rock of Baligou gold deposit are slate and schist of greenschist faces Huashan formation,early Proterozoic.The orebody is controlled by thrust-brittle-brittle fracture structure,with the ductile fracture locating on the side of the Huashan Formation in the contact zone between the Huashan Formation and the Zhenzhumen Formation in the gold mining area.The brittle fracture develops on the basis of ductile fracture,constituting a tough-brittle fracture structure.The ore body is a sulfide-containing quartz vein,and the main ore minerals are pyrite,pyrrhotite and arsenopyrite.Wall rock alterations mainly includes silicification,yellow iron mica and carbonation.The gold orebody is located at the outer contact zone of the Balitougou biotite intrusive body,and the biotite monzogranite is the parent metallurgical body of the gold deposit.The weighted average age of zircon LA-ICP-MS 206Pb/238 U is 159.6 ±2.2 Ma,a diagenetic age of the rock mass,which is in early late jurassic.The main elements result show that the Baliligou granite is a high-K calc-alkaline series and a weak peraluminous monzonitic granite.The total amount of rare earth elements(?REE)is relatively low,and the fractionation of light and heavy rare earths is obvious.The distribution curve shows a steep right-dip type: Yb N(2.74)>Ho N,weak positive anomaly in Eu/Eu*(1.07~1.14)and weak negative anomaly in Ce /Ce*(0.85~0.88).The trace elements Rb,Ba,K,P,and Ti are enriched,and Nb,Ta,and Ce are depleted.The basic compatible components are Co(2.94~4.05×10-6),Ni(1.87~3.14×10-6),and low content of Cr(3.88~4.84×10-6).Sr content is(428~458×10-6)higer than 400×10-6,and Yb content is(0.63-0.77×10-6 lower than 2×10-6,indicating the High "Sr" low "Yb" granite.The plagioclase in the magma source area is in the melting phase,the pyroxene and hornblende are partially melted,and the garnet is the residual phase.The rock sample data points are in the R1-R2 structural environmental discrimination map,located in the same-collision granite area.In the Rb-Y+Nb tectonic environment discrimination map,the rock sample points are located in the volcanic arc granite area and are close to the Boundaries of same-collisional granite.The zircon ?Hf(t)is-20.98~-16.00,indicating the model age is TDM2=2.2~2.5Ga.In the ?Hf(t)-t diagram,the sample data points are located between the Hf isotopic evolution lines of the 1.8~2.5Ga,indicating that the magma source material is the Paleoproterozoic-New Archaeozoic base material and its chemical composition is equivalent to Metamorphic sandstone and amphibolite immiscibility in the melt experiment(case rock).In the discriminative plot of biotite and hornblende magma source regions,sample data points are located in the crust and radon mixed source area.Rocks have the chemical composition of adakites.In the(La/Yb)N-Yb N and Sr/Y-Y discriminate diagrams,the rock sample points are all located in the Adakite area,and the basaltic magma from the lithospheric mantle invaded into the thickened cratonic continental crust in the bottom,which lead the melting of ancient crusts to become "C-type" adakites.The diagenesis temperature,pressure(depth)and oxygen fugacity of Baligou long granite were estimated using the chemical compositions of biotite and hornblende.The biotite was estimated to have a crystallization temperature of 750-780° C,a pressure of 131.77 Mpa to 143.89 Mpa(5.0 km to 5.5 km),and an oxygen fugacity f(O2)value of 10-13 to 10-14.Amphibolite estimates that the crystallization temperature is 736 ~ 817 °C,the pressure is 1.54 ~ 3.27kbar(5.81 ~ 12.35km),the sample point is located in the high oxygen fugacity zone.This high oxygen fugacity rock is favorable for fluid enrichment of ore after the element Au enters the magmatic stage.Quartz fluid inclusions are mainly liquid H2 O,homogenization temperature is 194~207.5°C,salinity is 5.4~6.3% Na Cleqv,fluid density is 0.90~0.92g/cm3,indicates low salinity and low density mineralization fluid.The estimated metallogenic depth is 5.6~6.2 km.The symbiotic mineral pairs of sphalerite and pyrrhotite are estimated to have an ore-forming temperature of 347.5°C and fs2?10-6 bar,which are high-temperature,high-sulfur fugatile ore-forming fluids.In summary,the Ba Ligou gold deposit was formed under the dynamics of the crushing and orogenic geodynamics caused by the subduction of the Paleo-Asian oceanic plate to the Eurasian plate during Late Jurassic.The deposit geology and the geochemistry of the deposits all have typical features of orogenic gold deposits,indicating the "shallow to build mountain" gold deposit.