Study On Metallogenesis Of Cuihongshan Fe-Cu Polymetallic Deposit In Lesser Xing'an Range

Cuihongshan Fe-Cu polymetallic deposit,located in the Lesser Xing'an Range-Zhangguangcai Range metallogenic belt,is a large skarn deposit related to Mesozoic magmatic emplacement discovered and explored in the Lesser Xing'an Range,Northeast China in the 1960s.Geologists pay more attentions to its metallogenesis,ore genesis since it was discovered.On the basis of pevious studies,this paper has carried out a systematic studies of geological,fluid geology,chronology,element and isotope geochemistry.The results show that:The exposed geological bodies in the mining area mainly include Early Paleozoic intrusions composed of biotie grantie and syenite granite,Late Paleozoic to Mesozoic intrusions composed of monzogranite and porphyry granite,Mesozoic intrusions represented by granite diorite and quartz diorite.The whole mining area is located in the nearly NNW trending structural belt on the two groups of conjugate faults in NNE-NWW direction.The deposit is composed of 110 ore bodies which are divided into four sections:Cuibei,Cuinan,Cuigang and Cuizhong sections.The ore minerals are mainly composed of magnetite,molybdenite,pyrite,chalcopyrite,sphalerite and galena,etc.The wall-rock alterations includes skarnization,K-feldsparization,biotitization,propylitization,sericitization,silicification,etc.Skarnization is the most closely related wall-rock alteration to mineralization.The geological process of mineralization can be divided into five stages:prograde skarn stage(?),retrograde skarn stage(?),oxide stage(?),Fe-Cu sulfide stage(?),Pb-Zn sulfide stage(?)and quartz-carbonate stage(?).The fluid inclusions in Cuihongshan deposit can be divided into four types:W-type,S-type,C-type and PW-type inclusions.And W-type inclusions are divided into W₁-type inclusions and W₂-type inclusions.The homogeneous temperature of the fluid inclusions from skarn stage(I)to carbonate stage(V)of Cuihongshan Fe-Cu polymetallic deposit are 342.9?507.6?,297.8?417.6?,195.3?366.1?,192.6?298.3?,and 147.8?222.4?,respectively.And the salinities of fluid inclusions are14.83%?60.80%NaCleqv.,3.85%?42.2%NaCl_eqv.,1.8%?10.2%NaCl_eqv.,2.73%?8.27%NaCl_eqv.,and 1.05%?5.99%NaCl_eqv.,respectively.The results of laser Raman analysis show that the gas composition of inclusions from the garnet,diopside and epidote in prograde skarn stage is H₂O.The gas composition of inclusions from the quartz in retrograde skarn stage and oxide stage is H₂O.The gas composition of inclusions from the quartz in Fe-Cu sulfide stage is H₂O,little CO₂and CO₂+CH₄.The gas composition of inclusions from the fluorite in Pb-Zn sulfide stage is mainly H₂O.The gas composition of inclusions from the calcite in quartz-carbonate stage is mainly H₂O.The result of Raman component analysis of the fluid inclusions and H-O isotope of quartz reveals that the initial ore-forming fluid of Cuihongshan Fe-Cu polymetallic deposit derived from exsolved fluid of magma,which is high temperature,high salinity and high oxygen fugacity NaCl-H₂O-CO₂±CH₄fluid system.During the evolution of ore-forming fluid,there was continuous addition of meteoric water,and the main ore-forming fluid is medium-high temperature,medium-high salinity and reductive property NaCl-H₂O-CO₂±CH₄fluid system.In the late stage of mineralization,the ore-forming fluid is mainly meteoric water,and the ore-forming fluid is H₂O-NaCl fluid system.S-Pb isotope reveals that the ore-forming materials are mainly derived from magma and mixed with crust derived materials.The geochronology reveals that the crystallization age of monzogranite is 192.4±9 Ma,which is basically consistent with the previous geochronology(192-199ma),Zircon U-Pb ages of Cassiterite from the calcic skarn and the magnesian skarn(195.4±1.9Ma and 191.2±7.5Ma)and Re-Os metallogenic dating(198.9±3.7Ma).The study of geochemical reveals that the monzogranite belong to metaluminous high-K calc-alkaline series.The REE characteristics show that monzogranite is characterized by enrichment of light rare earth elements and relatively depletion of heavy rare earth elements.The REE characteristics also show that the monzogranite has the characteristics of negative Eu anomaly.The trace element characteristics show that the monzogranite is rich in Rb,Th,U,K and depleted in Ba,Sr and high field strength elements such as Nb,Ta,P,Ti,etc.The Sr-Nd-Pb-Hf isotopic studies of the ore-forming rocks show the magma of monzogranite was derived from partial melting of Neoproterozoic-Mesoproterozoic crust and mixed with a small amount of Mesoproterozoic crustal substances.Combined with above research results and the background of regional tectonic evolution,it is revealed that Cuihongshan Fe-Cu polymetallic deposit was in the extensional environment after the closure of the paleo Asian Ocean in Late Triassic to Early Jurassic.The regional lithospheric extension caused the large-scale asthenosphere upwelling.The continuous underplating of mantle derived magma resulted in partial melting of the early formed lower crust,leading to the formation of the initial magma chamber,in which a small amount of mantle material was mixed.Since then,magma has been continuously emplaced.The separation of magma melt flow makes the ore-forming fluid enrich Fe,Cu,Mo,W and other metal elements.The ore bearing fluid finally interacts with carbonate strata,forming Cuihongshan Fe-Cu polymetallic deposit.