Geological Characteristics And Genesis Of Xingyuan Fluorite Deposit In Fengning,Hebei Province

The Xingyuan fluorite deposit is located in the Fengning area of Hebei Province,which is one of the important fluorite ore concentration areas in China.It is one of the many large-scale fluorite deposits in the metallogenic belt.The metallogenic conditions in this area are superior,but because of its low average grade,it has not been developed.Therefore,the predecessors have less research and attention to the mine,and also restrict the deep prospecting work of the fluorite deposit in this area,affecting the development of the regional fluorite industry.Therefore,based on the detailed investigation of the field metallogenic geological characteristics of the Fengning Xingyuan fluorite deposit,combined with the characteristics of indoor rare earth elements and fluid inclusions,this paper discusses the ore-controlling factors,prospecting indicators and genesis of the fluorite deposit in this area.The understanding is as follows:（1）The Xingyuan fluorite deposit in Fengning,Hebei Province is mainly hosted in the igneous rocks of the Zhangjiakou Formation,and the deposit is mainly controlled by the NNW and NW-trending sinistral shear fault zone;the ore body extends well and the occurrence is stable.The ore structure is mainly self-shaped,semi-self-shaped-other-shaped granular structure;the ore structure is mainly brecciated,veined,fine vein network veined,grape-like,and cave structure;the alteration of surrounding rock is simple,mainly fluoritization and silicification,followed by sericitization,pyritization and kaolinization.（2）According to the field interpenetration relationship of veins,the mineralization in this area is divided into one mineralization period and hydrothermal period,three mineralization stages:（1）deep purple fluorite-quartz vein stage;（2）green,khaki fluorite-quartz vein stage;（3）White,light purple grape-like fluorite vein stage.（3）Through the study of field granite porphyry vein and fluorite ore-controlling structure,it is shown that the granite porphyry vein and fluorite vein in the mining area of the fluorite deposit are controlled by the same compression-shear fault structure.The width of the vein is5-10 m and the extension is 500-800 m.The ore body is mainly produced in the fault fracture zone or the contact zone of the surrounding rock of the rock mass,and the space is closely related.The standardized distribution model of porphyry veins and ore rare earth elements chondrite is consistent,combined with the field spatial relationship,indicating that the ore-forming geological body is granite porphyry vein.The zircon LA-ICP-MS U-Pb age of the granite porphyry is 137.9±3.4Ma,indicating that it was formed in the Early Cretaceous.（4）The study on the characteristics of fluid inclusions in fluorite veins at different metallogenic stages of Xingyuan fluorite deposit shows that the inclusion types of the fluorite deposit are mainly gas-liquid two-phase inclusions(L_H2O+V_H2O).The results of fluid temperature measurement show that the temperature of the first stage is 300-320℃,the temperature of the second stage is 200-300℃,and the temperature of the third stage is160-200℃（low temperature）,which is mainly medium and low temperature fluid.The salinity is 0.35-5.09%Na Cl,which is a low salinity fluid.The calculation shows that the metallogenic pressure range is 273-889×10⁵Pa,and the metallogenic depth is 0.91-2.96 km,indicating that the metallogenic depth is shallow and belongs to the epithermal deposit with low salinity.（5）Based on the output characteristics of the ore body,the spatial relationship between the ore body and the rock mass,and the structural characteristics of the ore,it is considered that the ore-forming element F mainly comes from the early Cretaceous granite porphyry of the Yanshan period,and the ore-forming element Ca comes from the leaching and extraction of the deep volcanic rock strata,and migrates to the shallow fracture zone through the fracture structure fluid.Filling mineralization,pressure and temperature reduction are the main precipitation and enrichment mechanisms of fluorite deposits.The deposit type is a medium-low temperature magmatic hydrothermal fluorite deposit related to volcanism.（6）The prospecting direction of the region is:（1）strata,the volcanic rocks of the Zhangjiakou Formation are the direct surrounding rocks of the fluorite ore body,and the regional fluorite deposits are mainly produced in the volcanic rock strata of the formation.（2）Structure,the northwest shear fault near the granite porphyry is the main fluorite ore-controlling structure in the region.（3）Alteration.Fluoritization is the main and direct prospecting location.In addition,silicification,sericitization,pyritization and kaolinization are hydrothermal alteration marks.（4）Geochemical anomaly,F anomaly area is the main prospecting range.（5）Magmatic rock,Early Cretaceous granite is fluorite ore-forming geological body。（7）Deep prospecting potential:Through research,it is found that the nature of the ore-controlling structure is a compressive and torsional structure,and it is inferred that the deep part has great prospecting potential.The ore-controlling fault has the characteristics of left-lateral movement.It is inferred that the ore body is mainly pitched to the northwest,and the pitch angle is about 70°.The northwest pitch direction of No.1 ore body is the most important prospecting target area in this area.