Study On The Mineralization Of Skarn-vein Type Lead-zinc Deposits In The Northern Of De'rbugan Metallogenic Belt,the Great Xing'an Range

De'rbugan metallogenic belt is located on the Erguna block in the northern part of the Great Xing'an Range,which is one of the important lead-zinc(silver)polymetallic metallogenic belts in northeast China.The study region is located in the northern part of the De'rbugan metallogenic belt,and there are many typical lead-zinc deposits,such as Qiyimuchang,Dongjun,Xiahulin,Erdaohezi,Derbur and Biliyagu deposits.The Pb-Zn deposits in the northern section of The De'rbugan metallogenic belt can be divided into two types according to the geological characteristics and mineralization types:hydrothermal vein type(Qiyimuchang,Dongjun,Erdaohezi,Derbur and Biliyagu)and skarn type(Xiahulin).This study selected the Xiahulin skarn type deposit,the Erdaohezi,Derbur and Biliyagu hydrothermal vein type Pb-Zn deposit as the main research objects to carry out the geological characteristics of ore deposit,the genesis,metallogenic epoch and metallogenic tectonic environment systematacially,and combined with the regional tectonic evolution to establish two mineralization models of Pb-Zn deposits in study area.The ore-body of the Xiahulin skarn type Pb-Zn deposit mainly occurs in the intrusive contact zone between Jurassic quartz porphyry and Neoproterozoic Sinian Erguna formation marble,and the ore-body shape is obviously controlled by the contact zone.According to the relation of vein cutting and mineral symbiosis,it can be divided into five stages:(?)skarn stage,(?)oxide stage,(?)early sulfide stage,(?)late sulfide stage and(?)quarts-calcite stage.Fluid inclusions show that the deposit mainly develops three types of primary fluid inclusions:liquid-rich two phase inclusions(VL),gas-rich two phase inclusions(LV)and halite-bearing there phase inclusions(SL).The homogenization temperature from?to?stages is as follows:352??488?,288??395?,255??360?,201??302?and 135??195?,the salinity is respectively:8.4%?53.9wt.%,5.3%?15.6wt.%,4.6%?13.7wt.%,5.1%?10.6wt.%and 0.9%?5.3wt.%.The?³⁴S_V-CDTranges of sulfur isotopes is-5.9‰?4.8‰,and the lead isotope ranges are:²⁰⁸Pb/²⁰⁴Pb:38.352?38.415,²⁰⁷Pb/²⁰⁴Pb:15.575?15.598,²⁰⁶Pb/²⁰⁴Pb:18.41?18.518.Therefore,the ore-forming fluid has undergone an evolution process from high temperature and high salinity in the early stage to low temperature and low salinity in the late stage of the Na Cl-H₂O system hydrothermal solution.Hydrogen and oxygen isotopes show that the early ore-forming hydrothermal fluid mainly comes from magmatic water,and mixed with meteoric water in the late stage.Boiling is the important mechanism of metal precipitation.During the mineralization process,the change of oxygen fugacity and p H value of the hydrothermal fluid decreased slightly,indicating that the hydrothermal environment changed from weakly alkaline to weakly acidic.The ore-forming materials are mainly from intermediate-acid magma and the lead is derived from crust-mantle mixed source.The orebodies of Erdaohezi,Derbur and Biliyagu hydrothermal vein type Pb-Zn deposits occur in the strata of Tamulangou Formation and Manketouebo Formation.The rhyolitic clastic tuff is the main host rock,and the orebodies are veins and veinlets.According to the relationship of vein cutting and mineral association,the Erdaohezi deposit can be divided into four metallogenic stages:(?)pyrite±Dolomite-quartz stage,(?)pyrite±chalcopyrite-quartz stage,(?)quartz-polymetallic sulfide stage,(?)quartz-calcite-poor sulfide stage.According to the fluid inclusion studies,Erdaohezi deposit mainly developed two types of primary inclusions:liquid-rich two phase inclusions(VL)and gas-rich two phase inclusions(LV).The homogenization temperatures of stage?-?are 195??265?,155??243?,165??212?and 135??189?,respectively,and the salinity are:9.5%?12.0wt.%,5.9%?9.9wt.%,4.2%?8.0wt.%and0.9%?4.6wt.%.Derbur deposit can be divided into four metallogenic stages:(?)pyrite-Dolomite stage,(?)pyrite±chalcopyrite-quartz stage,(?)quartz-polymetallic sulfide stage,(?)calcite-fluorite-poor sulfide stage.It mainly developed iquid-rich two phase inclusions(VL),the homogenization temperatures of stage?-?are 201??275?,185??263?,163??242?and 125??201?,respectively,and the salinity are:9.1%?12.7wt.%,7.2%?11.5wt.%,3.5%?8.1wt.%and 0.9%?5.3wt.%.Biliyagu deposit also can be divided into four metallogenic stages:(?)pyrite±Dolomite-quartz stage,(?)pyrite±chalcopyrite-quartz stage,(?)quartz-polymetallic sulfide stage,(?)calcite-quartz stage.It only developed iquid-rich two phase inclusions(VL),and the homogenization temperature of stage?-?are 215??292?,192??271?,163??233?and 125??168?,respectively,and the salinity are:8.1%?11.5wt.%,6.1%?8.5wt.%,3.5?6.6wt.%and 1.1%?5.7wt.%.The?³⁴S_V-CDT ranges of sulfur isotopes of these three deposits are 1.4‰?5.5‰,-1.4‰?7.2‰and 5.5‰?7.2‰,respectively.The lead isotope ranges are:²⁰⁸Pb/²⁰⁴Pb:38.078?38.45,38.085?38.49 and 38.239?38.603,²⁰⁷Pb/²⁰⁴Pb:15.528?15.625,15.529?15.975 and 15.567?15.675,²⁰⁶Pb/²⁰⁴Pb:18.13?18.487,18.28?18.518 and 18.431?18.513.Therefore,the ore-forming fluid of the typical hydrothermal vein type Pb-Zn deposit in the study area belongs to the medium-low temperature and low salinity Na Cl-H₂O system hydrothermal solution.Hydrogen and oxygen isotopes show that the fluid is the mixed source of meteoric water and magmatic water,and the meteoric water is the main source.During the mineralization process,the oxygen fugacity of the hydrothermal fluid basically does not change,and the decrease of p H value proves that the hydrothermal environment changes from weakly alkaline to weakly acidic.The ore-forming materials are mainly from deep magma and have the characteristics of crust-mantle mixed source.The study of metallogenic chronology shows that the Xiahulin Pb-Zn deposit is in Early Jurassic(199.7±1.5Ma),and the ore-forming rock is relatively enriched in IREE and large ion lithphilic elements,and depleted in HREE and high field strength elements,the tectonic setting was the active continental margin after the Mongolia-Okhotsk ocean subduction.The Erdaohezi,Derbur and Biliyagu Pb-Zn deposits were formed in the Early Cretaceous(137.7±1.8Ma,141.74±0.32Ma and 131.3±2.4Ma),which formed in a closed tectonic extensional environment after the Mongolia-Okhotsk ocean.The results show that the skarn and hydrothermal vein-type Pb-Zn deposits in the northern part of the De'rbugan metallogenic belt are the products of mineralization in different periods,but they were all formed under the background of the Mongolia-Okhotsk ocean tectonic domain.Based on the comprehensive analysis of regional tectonic evolution history,magmatic activity and deposit mineralization,the following metallogenic models of the study area are established:1)In the early Jurassic,the Mongolia-Okhotsk plate subducted to the active continental margin formed under the Erguna block,and the crustal material melted to form the parent magma of the quartz porphyry of the Xiahulin.The metal minerals were enriched and ore-forming at the marble contact zone,and finally the Xiahulin Pb-Zn skarn deposit was formed.2)In the early Cretaceous,the Mongolia-Okhotsk Ocean had closed,and the study area was under extensional environment.Stretching environment makes the lithospheric mantle delamination,upwelling of the asthenosphere material,the partial melting of crust,crust-mantle material mixing,swelling magma along the fracture,formed the Erdaohezi,Derbur and Biliyagu porphyry magma,the differentiated hydrothermal precipitation mixed with meteoric precipitation in the shallow part of the crust to form hydrothermal vein type Pb-Zn deposits.