Study On The Genesis And Mineralization Of Hongshan Complex In Han-xing Area,Southern Hebei Province

Han-Xing area is located in Handan and Xingtai in the south of Hebei Province,in the middle of North China Craton and in the south of Taihang Mountain.Large-scale Mesozoic high-magnesium diorite intrusions developed in the area,which were studied in detail by predecessors.There is a unique Hongshan alkaline complex in the east of Han-Xing area,which is rare in the North China Craton.Geological prospectors found some copper-gold mineralization(spots)around Hongshan alkaline complex.It is generally believed that the formation of copper-gold mineralization is closely related to alkaline rocks,which has proved a new direction for prospecting in Han-Xing area.Therefore,it is of great research value to study the genesis of Hongshan alkaline complex and its relationship with copper-gold mineralization.The predecessors have carried out extensive geochronological and geochemical studies here,but there is no systematic analysis of the genesis of rock mass from the perspective of genetic mineralogy.In order to describe the whole process of rock mass formation in detail and accurately,on the basis of petrographic observation,the major elements of plagioclase and hornblende minerals are analyzed by using electron probe technology,the U-Pb age of zircon is measured by laser ablation plasma mass spectrometer,and the major trace elements of the whole rock are analyzed by using X-ray fluorescence spectrometer and inductively coupled plasma mass spectrometer.The genetic mineralogy of amphibole,plagioclase and zircon is systematically studied from the perspective of genetic mineralogy,and the physical and chemical parameters of magma such as temperature,pressure,oxygen fugacity and water content during mineral crystallization are calculated.The diagenetic age is limited in combination with zircon U-Pb age,and the diagenetic substances are traced according to whole rock geochemistry.The results show that there are many kinds of amphiboles in Hongshan complex,including edenite,magnesite,actinolite,magnesite,magnesite,tremolite and actinolite.The calculation results of amphibole thermometer show that there are two stages of amphibole crystallization,one is in the temperature range of 850 ? 950? and the other is in the temperature range of 600 ? 750?.The amphibole has the characteristics of mixed source of crust and mantle,and the amphibole oxygen fugacity meter shows that magma has the characteristics of high oxygen fugacity.The water content of the whole complex is low,with the highest value of 6.27%,and the alkaline rock mass is poorer than the calc-alkaline rock mass,generally below 2%.The plagioclase is mainly composed of felspar and mesofeldspar,and has a zonal structure.The An composition curve shows that the zonal is rhythmic zonal.The genetic mineralogical study of zircon indicates that zircon originated from magmatic zircon,and its material source belongs to continental zircon.In addition,the rock mass contains a large number of inherited zircons.The weighted average age of zircons in calc-alkaline rocks is 129.3±2.5 Ma ?134.8±5.7 Ma Ma,and that in alkaline rocks is 128.5±2.0Ma ?130.8±2.5 Ma Ma.The major elements in the rock are rich in silicon and aluminum,but poor in iron and magnesium.The REE model partition curve is characterized by enrichment of light REE and loss of heavy REE,which has a tendency to tilt to the right.The above evidences show that Hongshan complex is characterized by magma mixing,and there is a two-stage magmatic evolution process,namely,the deep magma chamber process and the shallow crystallization differentiation process,during which it has experienced many magma mixing processes,which is characterized by high oxygen fugacity,and the oxygen fugacity has obviously increased in the process.High oxygen fugacity is beneficial to the migration of copper and gold elements in magma,but the lack of water in magma may be one of the factors inhibiting the scale development of copper and gold deposits in this area.According to zircon geochronology,the calc-alkaline rock mass in Hongshan complex is older than alkaline rock mass.