Metallogenesis Of Endogenetic Metal Deposits In The Great Xing’an Range,NE China

The Great Xing’an Range,located in Northeast China,is one of the main endogenetic metallogenic belts in China.The Great Xing’an Range has charactericists of superior metallogenic conditions,multiple metallogenic periods,high metallogenic intensity and diversity of ore deposit types.A large number of Cu,Mo,Au,Pb,Zn,Ag,W,and Sn deposits have been formed during its geological history.As one of the significant metallogenic belts in China,Many experts have conducted lot of research on geochronology,geochemistry and mineralization of endogenetic metal deposits in the Great Xing’an Range.However,many focused on one or several metal deposits or on local mineralization in the region.Moreover,there is lack of unified understanding of various types of deposits formed in the whole region during Phanerozoic.In recent years,the publications of research results on accurate geochronology of deposits,the detailed study of mineralization of polymetallic deposits,and the continuous discovery of many new deposits have led to further understanding of mineralization in this region.Based on the above,we performed systematic sampling on the five typical deposits（Bianjiadayuan Ag-Pb-Zn deposit,Hongling Cu-Zn deposit,Yongxin Au deposit,Duobaoshan Cu deposit and Xiaokelehe Cu-Mo deposit）for geological investigation and comprehensive indoor research.Combing the works of typical deposits with previous research on representative endogenetic metal deposits and related magmatism in the Great Xing’an Range,this thesis studies the mineralization of endogenetic metal deposits in the whole region and the evolution process of three micro-continental blocks and two intracontinental oceans that related to regional mineralization.Based on the above studies,this thesis summarizes the metallogenic regularity of endogenetic metal deposits in the Great Xing’an Range,obtaining the following understanding:In terms of tectonic position,the Great Xing’an Range is located at the eastern part of the Central Asian Orogenic Belt,roughly in NNE syncline across the Erguna,Xing’an and Songnen blocks;In terms of tectonic attributes,the“Xing’an block”may be a micro-continent within the Paleo-Asian Ocean,which experienced the accretion of island arcs and back-arc basins during Paleozoic.It was involved in an intracontinental evolution process during the Mesozoic.The“Xing’an block”belongs to a relatively new terrane compared to Erguan and Songnen blocks.The Xinlin-Xiguitu Ocean（which between the Erguna block and Xing’an micro-continent）was closed after an evolutionary history of intra-oceanic subduction,back-arc extension,and oceanic subduction during Neoproterozoic to Cambrian.The two blocks collided and were welded to form Erguna-Xing’an united continent at ca.～495 Ma.The subduction boundary between Xinlin-Xiguitu Ocean and Erguna block has an affinity with Andean-type active continental margin.During Early Ordovician,the Nenjiang Ocean between the Erguna-Xing’an united continent and the Songnen block began to subduct beneath the former.The identification of the Early Paleozoic Duobaoshan-Nenjiang-Zalantun island arc and the continuous development of the Xinglong-Arshan back-arc basin,proved the existence of the Paleozoic trench-arc-basin system in the eastern margin of Erguna-Xing’an united continent.The Nenjiang Ocean was closed at ca.320 Ma,and all the continents in the study area were welded into a joint continent.Since the Mesozoic,the Great Xing’an Range was under an extensional setting after the final closure of the Paleo-Asian Ocean and during that period it was affected by the tectonic evolution of the Mongolia-Okhotsk Ocean and Paleo-Pacific Ocean.This tectonic regime controls the Yanshanian magmatic and metallogenic events in the Great Xing’an Range.Typical ore deposits:（1）The Bianjiadayuan Ag-Pb-Zn deposit in Linxi County,Inner Mongolia is a newly discovered deposit in recent years,which is located in the southern section of Huanggang-Ganzhuermiao metallogenic belt.There are three main types of ore bodies,i.e.Ag-Pb-Zn vein type,breccia Pb-Zn type and porphyritic Cu-Mo-Sn type.The hydrothermal vein type Pb-Zn-Ag ore body is controlled by NW trending faults.The metal sulfideδ³⁴S ranged from-2.1‰to 3.9‰,mostly between 0 and 3‰,with an average of1.8‰.The ore-forming fluid mainly sourced from magmatic water,which was mixed with meteoric water in the later mineralization stage.The ore-forming fluid in the main metallogenic period has the characteristics of medium to low temperature,medium to low salinity and medium to low density.The results indicate that it is a typical mesothermal hydrothermal vein type deposit.The three types of ore bodies developed in the mining area are relatively independent in space and closely related in genesis,composing a Cu-Mo-Sn-Ag-Pb-Zn hydrothermal metallogenic system.The intrusive rocks in the mining area dated at 136.2～133.1 Ma.The acid intrusive body has the characteristics of A2-type granitoid,and the diorite has the geochemical characteristics similar to high Ti sanukitoid,which constitute bimodal magmatism in this area.The deposit was formed in the intense extensional tectonic setting controlled by the post-orogenic extension of the Mongolia-Okhotsk Suture and the oblique subduction of the Paleo-Pacific Ocean in the early Cretaceous.（2）Hongling skarn type Cu-Zn deposit in Ganzhuermiao,Inner Mongolia is located north of Huanggang-Ganzhuermiao metallogenic belt.The magmatic and wall rocks that are most closely related to mineralization are granodiorite（porphyrite）and marble of the Lower Permian Dashizhai Formation.The ore body occurs at the contact zone between the granodiorite and marble and is controlled by NE trending faults.Theδ³⁴S range is relatively larger（-4.5～-0.5‰）and the ore-forming fluid is dominated by magmatic water in the early stage,fluid mixing occurs in the main ore-forming stage,and meteoric water dominates in the final stage.The carbon source may be igneous carbonate rock,and its evolution is mainly affected by meteoric water.The Early Cretaceous（～145-133 Ma）A2 type granitoids are also developed in this area.The deposit was formed under the environment of lithospheric extension and lower crustal delamination jointly controlled by Mongolia Okhotsk post-collisional extension and Paleo Pacific oblique subduction.（3）Yongxin low sulfide epithermal gold deposit in Nenjiang County,Heilongjiang Province is a gold deposit strictly controlled by faults,and the NE trending faults are the main ore controlling and hosting structures.The ore bodies are located in and near the hydrothermal breccia bodies at the contact zone between Late Carboniferous granitic mylonite and syenogranite.Theδ³⁴S value of the gold bearing pyrite is 1.2～5.4‰,concentrated in 4.5～5‰.The ore-forming fluid is mainly sourced from magmatic water and formation water,and there is obvious contamination of meteoric water.The youngest granite U-Pb age（115 Ma）and pyrite Rb-Sr age（114.6±1.2 Ma）in the mining area indicate that the mineralization is later than ca.115 Ma.The deposit was formed in a transitional tectonic regime of large-scale extension to compression transformation caused by Paleo-Pacific Oceanic subduction in the late Early Cretaceous.（4）Duobaoshan Cu deposit in Nenjiang County,Heilongjiang Province is a typical porphyry deposit.The magmatic rock associated with mineralization is Early Ordovician granodiorite.The ore body mainly occurs in the granodiorite in the granodiorite porphyry,and a few occur in the andesite of Duobaoshan Formation.The wall rock alteration has the characteristics of typical porphyry alteration zoning.The physicochemical characteristics of the deposit indicate that sulfur in ore-forming materials(δ³⁴S value is-3.2～-1.8)has deep source characteristics and may originated from the mantle.The hydrogen and oxygen isotopes suggest that the ore-forming fluid is characterized by the mixing of magmatic and atmospheric water.The ore-forming fluid in the early stage of mineralization has the characteristics of magmatic water,and it may be a kind of hydrothermal solution of Na Cl-H₂O-CO₂ system with high temperature and medium to low salinity.The ore-forming fluid in the late stage is the mixture of rock slurry and meteoric water.The immiscibility of fluid caused by fluid decompression and cooling is the main mechanism of ore-forming precipitation.The deposit was formed in an island arc setting in the Early Ordovician.（5）the Xiaokelehe porphyry Cu（Mo）deposit in Xinlin County,Heilongjiang Province has close relationship with the Early Cretaceous granodiorite porphyry.Its metallogenic material(δ³⁴S value is-1.2～2.4)also has the characteristics of a mantle source.The ore-forming fluid shows the evolution trending from a high temperature and high salinity H₂O-Na Cl system in the early period to a medium to high-temperature and medium to high salinity H₂O-Na Cl system in the main metallogenic period,and then to a medium low-temperature,low salinity and H₂O-Na Cl system.The deposit was formed in the Early Cretaceous extensional setting.The mineralization periods of endogenetic metal deposits in The Great Xing’an Range include 483-471 Ma,320-310 Ma,250-210 Ma,180-160 Ma,150-130 Ma and125-110 Ma,which correspond to the stages of Caledonian,Hercynian,Indosinian,and Yanshanian（The Yanshanian stage can be subdivided into three sub stages:Early to Middle Jurassic,Late Jurassic to Early Cretaceous and late Early Cretaceous）.The Caledonian mineralization is related to the island arc magmatism under the background of the active continental margin triggered by the subduction of the ocean beneath the Erguna block between the Erguna Xing’an block and the Songnen block in the Early to Middle Ordovician.The deposit type in this period is the porphyritic Cu deposit.Hercynian mineralization is closely related to the evolution of island arc and back-arc basin under the background of the Carboniferous active continental margin.The deposit types are mainly VMS type Cu and SEDEX type Fe-Zn.In addition,orogenic Au deposit and pyroxenite-related Ti-Fe deposit also formed.The ore-forming materials of these deposits are mainly sourced from the mantle or lower crust,which may be related to the upwelling of the asthenosphere caused by the separation of subducted Nenjiang Oceanic plate.The ore-forming fluid shows the mixing characteristics of magmatic water and meteoric water.The ore-forming materials of some SEDEX type deposit were sourced from seawater,which is closely related to the evolution of Paleozoic back-arc basins.The Indosinian mineralization took place under the regional extensional setting after the final closure of the Paleo-Asian Ocean.The Indosinian deposit types in the northern part of the Great Xing’an Range are mainly epithermal Au deposit,porphyry Cu-Mo deposit and skarn Fe-Cu-（Mo）deposit.In contrast,the middle and southern parts mainly contain hydrothermal vein type Pb-Zn-Ag polymetallic and porphyritic Cu-Mo deposit.The ore-forming materials were sourced from mantle and deep crust,and the ore-forming fluid was generally mixed with magmatic and meteoric water.The Yanshanian mineralization is the most intensive and widespread mineralization in the Great Xing’an Range.The ore-forming materials mainly sourced from magma in lower crust,and exhibit evident crust-mantle mixing.The ore-forming materials of the deposits located in the northern and southern margin of the Great Xing’an Range may be mixed with the crustal materials in the adjacent blocks（or Cratons）.It can be divided into three metallogenic sub periods:（i）porphyry skarn Mo-Cu,high-temperature hydrothermal W-Mo and medium to high-temperature hydrothermal vein type Pb-Zn-Ag mineralization related to the subduction and closure of Mongolia Okhotsk Ocean during the early and middle Jurassic,（ii）polymetallic mineralization controlled by the post-collisional extension of Mongolia Okhotsk suture zone and the oblique subduction of Paleo-Pacific Ocean in the Late Jurassic to Early Cretaceous.Mineralization reached its peak in this subperiod,and（iii）epithermal and mesothermal vein type Au-（Ag）mineralization controlled by faults in the late Early Cretaceous under the environment of extension to compression transition caused by westward subduction of the Paleo-Pacific Ocean.The mineralization of endogenetic ore deposits in the Great Xing’an Range has obvious zoning and superposition.The endogenetic metal deposits in the northern part of the Great Xing’an Range are mainly distributed in Huma-Heihe-Nenjiang,the northeast part of Derbugan Fault and Hulunbuir-Yakeshi areas.The metal types are mainly Cu,Mo,and Au,then Pb,Zn,and Ag.The genetic characteristics are mainly porphyry Cu-Mo,epithermal Au,medium-low temperature hydrothermal vein type Te-Au-Ag,medium to low temperature hydrothermal vein type Pb-Zn-Ag deposits,and SEDEX Fe-Zn,medium to high temperature hydrothermal vein type W and skarn Fe-Cu-（Mo）deposits.The ore deposits in the southern part of the Great Xing’an Range are densely distributed in the main ridge of the Great Xing’an Mountains and its east and west sides,Xilamulun Fault area,and Arshan-Tuquan area.The metal types are mainly Sn,Pb,Zn,Ag,Cu,and Mo.The genetic types are mainly medium to low temperature hydrothermal vein type Pb-Zn-Ag polymetallic,Sn polymetallic,porphyry type Cu-Mo,and skarn type Sn polymetallic and Cu-Pb-Zn deposits.The superposition of mineralization is not only reflected by multi-stage mineralization in the single metallogenic belt,but also in a single deposit that has experienced the superposition of the same or another metallogenic type in later stages.It is an important factor in the great metallogenic potential in this area.Based on the distribution,metallogenic periods,and mineralization element combination of endogenetic metal deposits in the Great Xing’an Range,it can be divided into six regional metallogenic series.The mineralization of endogenetic ore deposits in the Great Xing’an Range is closely related to the regional tectonic evolution.The establishment of the regional metallogenic model can provide a better theory for the evaluation of regional metallogenic potential and future prospecting.