Paleozoic-mesozoic Granites Characteristics And Their Relationship With Gold Mineralization In The Northern Margin Of North China Craton

The northern margin of the North China Craton(NNCC)has undergone numerous tectonic and magmatic phases associated with various gold mineralization events between the Devonian and Cretaceous periods.The origin of gold mineralization is a debated subject in the NNCC;however,two main hypotheses are popular:the fluids either have a metamorphic-hydrothermal origin or a magmatic-hydrothermal origin.This study concentrated on four gold districts:from west to east(Daqingshan,Zhangjiakou,West Liaoning,and Changbaishan).The ore bodies of NNCC gold deposits studied are mainly gold-bearing quartz veins,disseminated ores,and altered rocks.Dahuabei pluton is located in the west region of the Hadamengou gold deposit in Daqingshan district.Also,it intruded the Wulashan group in the form of the batholith and was formed in the Hercynian period.The Dongping mining area in the Zhangjiakou district consists of the Shuiquangou(Dongping)syenite-monzonite complex.It is surrounded by Late Archean amphibolite,volcanic sedimentary mixed rock gneiss,and amphibolite of the Sanggan Group.The Xitaizi rock mass is a batholith,and it occurred in the southwest of the Jinchanggouliang-Erdaogou mining area within the West Liaoning district.It intrudes into the upper Archean Jianping Group and is covered by Upper Jurassic volcanic rocks.There is likewise massive granodiorite in the marginal facies of Duimiangou,which is gray and granular in texture.Haigou mining area in the Changbaishan district experienced an intense magmatic activity,which led to Haigou rock mass and associated dikes,Dahaigou quartz diorite,etc.The Haigou rock mass with ages ranging from327 to 329 Ma is the main host rock of the Haigou gold deposit.These deposits have geological characteristics similar to the geological features of fluid exsolution,such as pegmatite dykes,unidirectional solidification texture(UST),quartz eyes,fine and coarse grain domains.We specifically study the link between the gold deposits(Hadamengou,Dongping,Jinchanggouliang,Erdaogou and Haigou)and associated magmatic activity.The Dahuabei and Haigou granites and the Dongping syenite have an alkaline affinity.In contrast,the Xitaizi-Jinchanggouliang and Xiaoxigou granites,as well as the Duimiangou quartz monzonites,are calc-alkaline to alkaline rocks.They are predominantly metaluminous and highly fractionated I-type granites,except for the Xiaoxigou granite which is an A-type granite with peraluminous characteristics.This indicates variable mixing between depleted mantle-derived mafic magmas and ancient crust derived magmas.These rocks range from ilmenite to magnetite series.The studied rocks also show plagioclase accumulation and fractional crystallization that happened during magma differentiation.They present medium-high oxidation states and a low evolution degree,except the Xiaoxigou granites that most evolved.They are High potassium(calc-alkaline and alkaline)and their K-metasomatism is controlled by K-feldspar alteration.K is a typical alkaline element with strong activity,especially in hydrothermal solutions as well as the Au~+likewise has strong hydrothermal activity,all these properties promote a close relationship between Au and K.Therefore,the close relationship between gold mineralization and alkaline rocks in the NNCC is due to K-enrichment of these rocks.The majority of biotite samples of the Duimiangou granodiorite and those from Dahuabei granite plot between the NNO(Nickel-Nickel-Oxide buffer)and MH(magnetite hematite buffer).All the biotite test points in Xitaizi monzogranite and some Duimiangou granodiorite samples plot above MH buffer.The biotite's halogen chemical properties in Dahuabei granite in the Hadamengou deposit are consistent with porphyry Mo.Whereas the granitoids in the Jinchanggouliang-Erdaogou gold field are consistent with porphyry Cu-Au deposits.Based on the relationship between magmatic crystallization temperature and oxidation state,the Dahuabei granite,Xitaizi monzogranite and Duimiangou granodiorite display the features of the rocks associated with porphyry Cu-Au deposits,which may be beneficial to mineralization and Au migration.However,Haigou granite presents a feature close to porphyry Cu-Au and Mo deposits.The magmatic-hydrothermal fluid system in the Hadamengou,Jinchanggouliang Erdaogou and Haigou gold fields,especially related to the Dahuabei batholith,Duimingou granodiorite complex body and Haigou pluton,respectively.The magmatic events overlap the gold mineralizing episodes in the NNCC.We have identified four magmatic episodes between the Middle Paleozoic and Mesozoic,at 400-320 Ma,240-220 Ma,200-160 Ma,and 143-125 Ma.On the other hand,gold mineralization occurred from the Carboniferous to Cretaceous periods(390-110 Ma),peaking in the Middle Jurassic(170-160Ma).The hydrogen-oxygen isotopes studied NNCC gold deposits show that the fluid was trapped in the quartz or K-feldspar from contemporaneous granite.The available sulfur,oxygen,and carbon isotopic data from the studied NNCC gold deposits indicate that the ore-forming fluids were derived from a mixture of magmatic fluids and meteoric waters that interacted with the wall rocks,save for the Hadamengou and Jinchanggouliang gold deposits where the data indicate that the sulfur is of multi-source,with the involvement of organic matter and other regional crustal rocks.The intrusive rocks and sulfides in the NNCC present similar lead isotope compositions,implying that the lead had a common origin.The gold-forming materials coming from the mixing of these fluids are the product of several alkaline magmatic episodes in this region.Therefore,this research has established that gold mineralization is spatially and temporally associated with alkaline magmatism in the NNCC.The NNCC is characterized by both alkalic post-collisional or anorogenic magmatism and by calc-alkalic Andean-type arc subduction-related magmatism.Both tectonic settings were controlled by:(1)collision between the North China craton and the Bainaimiao arc,(2)subduction of the Paleo-Asian-ocean plate beneath the NCC,(3)collision between the Siberian Craton and the North China craton,and(4)subduction of the western Paleo-Pacific plate beneath the North China craton.These events were associated with magmatic episodes,with suites characterized by alkaline and calc-alkaline features that correspond to post-collisional or anorogenic environments and Andean-type arc-related subduction environments,respectively.The NNCC is marked by several alkaline magmatism activities closely related to different mineralization events.The NNCC gold deposits display several similarities with porphyry Cu-Au-Mo deposits and alkaline related to gold deposits,belonging to the intrusion-related gold deposits(IRGD)system.