Geochemical Characteristics And Prospecting Significance Of Rock Mass In Liaoning Baiyun

Baiyun area is located in the east of Liaoning Province,and the geotectonics is located in the northeast margin of the North China landmass.It is a part of Liaoji rift valley.The study area has experienced a long geological process,with frequent tectonic and magmatic activities.The main minerals in the area are gold,silver,lead-zinc and other minerals.The development of Mesozoic granitic magmatism in this area is an ideal place to study the genesis,the nature of magma source area and the structural attribute of granitic rocks.In this paper,the Mesozoic granitic rocks and dykes in Baiyun area have been studied systematically in petrography,isotopic chronology and petrochemistry.The chronological framework of Mesozoic magmatism in Baiyun area has been established,and the genesis of rocks in different periods,the nature of magmatic source areas and the tectonic background of their formation have been discussed,which is helpful to further improve the dynamic background of diagenesis and mineralization and to find ore in the area Exploration is of great practical significance.The analysis results and conclusions are as follows:?1?The shuangdinggou rock body in Baiyun area can be divided into central facies?granite?,main facies?granodiorite diorite?and marginal facies diorite,and central facies LA-ICPMS zircon U-Pb The dating results show that the emplacement time of the shuangdinggou rock body is 219±1 Ma,which is consistent with the emplacement time of the granite porphyry vein body?221±4 Ma?in this area.The age of the formation of the regional diorite vein and lamprophyre vein is later than 216±5 Ma and 208±2 Ma,which represents the magmatic activity of the Triassic.?2?The granitoids in the central phase of the shuangdinggou rock body have similar geochemical characteristics with the granitic porphyry vein in the region,which are characterized by high silicon,rich alkali,potassium sodium ratio close to 1,significant fractionation of light and heavy rare earth elements,weak EU Negative anomaly,there are a lot of dark inclusions in the rock mass and their geochemical characteristics indicate that it is a high potash calc alkaline quasi aluminous weak peraluminous I-type granite,originated from the partial melting of the thickened lower crust,plus a small amount of mantle material.?3?The lamprophyre vein in danyin gold mine area has very low Si O₂?36.23-44.97%?,high K₂O,relatively rich LREE and large ion lithophile elements?Rb,Th and K?,while it lacks high field strength elements TA,Nb and Ti.Its primary magma comes from mantle source area.The rocks are rich in large ionic lithophile elements and have very low Nb/U ratio?0.61-2.7?.Combined with the Hf isotopic characteristics of previous studies,it is shown that lamprophyre is derived from partial melting of enriched lithospheric mantle.?4?The lead-zinc deposit from zhenzigou lead-zinc deposit has very low Si O₂content of 53.32%-65.82%in diorite,and enriched in high-strength elements?Nb,Ta depletion?and large ion lithophile elements?Rb,Ba,K?.The characteristics of rare earth trace elements are basically the same as those of granite porphyry and lamprophyre.Combined with previous studies,it is considered that the lead-zinc deposit is a granitic magma.?5?According to the field observation evidence and previous data,the granitic porphyry,lamprophyre and diorite of Indosinian are closely related to the mineralization of the mining area.It is found that the diagenesis mineralization age is Triassic,and the source of ore-forming materials is closely related to magmatic rocks in the study area.These characteristics indicate that the magmatism of Triassic provided heat source and material for mineralization.Lead zinc,gold and silver deposits may be the products of the evolution of the magmatic system in the Indosinian period.Therefore,a systematic study of the spatial distribution of various dikes is of great practical significance for the exploration of deep and peripheral ore deposits in the study area.