Metallogenesis Of Lead-zinc-gold-silver In The Qingchengzi Orefield,Liaoning Province

The Liaodong Peninsula is located in the eastern part of the North China Craton(NCC)and the northeastern part of the Paleoproterozoic Jiao-Liao-Ji Belt(JLJB).The area has a complete record of the complex geological evolution from the Archean to the Cenozoic.A large number of geological events were imprinted on the magmatic rocks,metamorphic rock series and mineral resources.This provides favorable conditions for the study of the Archean multi-stage crustal accretion and reconstruction events of the NCC,the restoration of the micro-continental collage in the Paleoproterozoic period(which participated in the formation of the Columbia supercontinent),the decratonization/ lithospheric thinning in the east,and the study of the genesis of large-scale mineral resources has provided superior conditions and made this area a hot spot for geological research in recent years.There are many Paleoproterozoic magmatic rocks(e.g.,Liaoji granite)in the Liaodong Peninsula.The information of genesis and tectonic environment recorded by these rocks can be used as an important evidence for us to explore and inversion the tectonic evolution model of the Paleoproterozoic JLJB.In addition,a large amount of ~20,000 km2 Mesozoic granites are distributed in the Liaodong Peninsula,which provides favorable conditions for studying the Mesozoic decratonization mechanism and the genetic connection with large-scale mineralization.Therefore,the study of typical magmatic-mineralization in Liaodong Peninsula is helpful for us to understand the tectonic evolution pattern of the JLJB,the genetic relationship with the large-scale metal-nonmetallic mineralization in Paleoproterozoic,the mechanism of lithospheric thinning and the relationship with the large-scale polymetallic mineralization in the Mesozoic.Based on the full collection of regional data,this paper conducted a detailed field geological survey and systematic sample collection of Qingchengzi orefield,which is located in the northeast of Liaodong Peninsula.The typical Zhenzigou,Diannan and Xiquegou lead-zinc deposits and Baiyun,Huangdianzi,Xiaotongjiapuzi gold deposits and Gaojiapuzi silver deposit are selected for the study of geological characteristics,fluid inclusions,hydrogen-oxygen-sulfur-lead isotopic geochemistry and diagenesis geochronology.The geochemical natures of ore-forming fluids,source of materials and genesis of Pb-Zn-Au-Ag deposits are identified.It defines the emplacement age of magmatic rocks,the genesis of rocks and the relationship with mineralization,and then discusses the metallogenic tectonic setting,and on this basis,establishes the metallogenic model of Qingchengzi orefield.Detailed field geological surveys and existing geochronological data indicate that there are two phases of mineralization in the lead-zinc deposit: Paleoproterozoic stratiform mineralization(~1.8Ga)and Mesozoic vein-type mineralization(~221Ma).The genesis of the Paleoproterozoic stratiform mineralization is a sedimentary exhalative deposit(SEDEX).The fluid inclusions and hydrogen and oxygen isotopic compositions show that the SEDEX mineralized ore-forming fluid is a medium temperature-low salinity Na Cl-H2 O system,which originates from the primary magmatic water;the rare earth elements(REEs)and sulfur-lead isotopes of sulfide indicate that SEDEX mineralized ore-forming materials are mainly from wall-rocks and Paleoproterozoic magma.The Mesozoic vein-type mineralization is a medium temperature hydrothermal vein type deposit controlled by fractures.The ore-forming fluid is the medium temperature-low salinity Na Cl-CO2-H2 O system,which is the mixed source of magmatic water and meteoric water.The ore-forming materials have three sources: granitic magma(Late Triassic)(mainly),wall-rocks and Paleoproterozoic stratiformed ore body,indicating that the Mesozoic vein-type mineralization has the "reforming effect" on the Paleoproterozoic stratiformed ore body.The geological characteristics of the gold-silver deposits in the orefield are relatively similar.The fluid inclusions,ore REEs,and hydrogen-oxygensulfur-lead isotopes show that the composition of the ore-forming fluids and ore-forming materials is similar to the vein-type lead-zinc mineralization in the orefield,and all formed in the Late Triassic(~221Ma),which indicates that the vein-type lead-zinc-gold-silver mineralization in the orefield is a product of the same stage of magmatism.The vein-type lead-zinc-gold-silver deposits are distributed in clusters,which may be the products of different evolution stages of the same hydrothermal fluid.In addition,the host rock and the lead-zinc-gold-silver deposits have important genetic links.The isotope geochemistry shows that the Dashiqiao Formation and Langzishan Formation of the Liaohe Group are important lead-zinc source beds,while the Gaixian formation is the main source of gold-silver.This understanding has important guiding significance for regional lead-zinc-gold-silver polymetallic deposit exploration.LA-ICP-MS zircon U-Pb geochronology results show that there are at least four phases of magmatism in the orefield:(1)Early Paleoproterozoic(~2206Ma,represented by striped granite porphyry),(2)Late Paleoproterozoic(~1904Ma,represented by Dadingzi pluton),(3)Triassic(243-220 Ma,represented by Shuangdinggou and Xinling plutons),and(4)Middle Jurassic(~164Ma,represented by Yaojiagou pluton).Based on the study of the Paleoproterozoic magmatic rocks in the area and the previous studies on the Liaohe Group,this paper believes that the JLJB experienced the whole process of ocean basin formation(Liaoji Ocean)-expansion-subduction(include slab roll-back)-extinction in the Paleoproterozoic period,and finally closed between Longgang and Nangrim Blocks,forming the Jiao-Liao-Ji orogenic belt.The formation of stratiformed lead-zinc mineralization in this study is closely related to the post-orogenic extension of the JLJB.During the Mesozoic,the eastern part of the NCC experienced a large-scale lithospheric thinning.The Mesozoic magmatic rocks exposed in the Qingchengzi orefield are related to decratonization,and the Triassic magmatism can be used as a sign of initial craton destruction.The dynamic mechanism is the subduction-collision of the Yangtze Craton and the NCC.The formation of Late Triassic vein-type lead-zinc-gold-silver mineralization in this area is related to this tectonic setting.