Features Of Cryptoexplosion Breccia And Implications On Mineralization In Wuan,Hebei

Wu'an area is located in the northern part of the North China plate and southern tip of the Taihang Mountains.Frequent and intense magmatic activities in the area forms many Complexes.In the contact zone between the Complexes and the surrounding rock or near the limestone catch in the rock mass,not only developed wide skarnization,but also distributed wide diorite and limestone breccias,and these breaks of rocks are usually in the form of the breccia belt.Near the complexes,the breccia was the diorite rock breaks and changed to limestone breaks with gradually approaching to the surrounding rock.It is generally believed that this type of breccia is the breccia of synsedimentary origin.In this paper,through the study of rock,mineralogy and mineral major and minor elements of breccia samples collected in the field,the following conclusions are obtained:1.The studied area's breccia has the following characteristics: 1)Most of the breccia is limestone fragments,a small part of the breccia is diorite fragments,this is the significant "local materials" features of studied area's breccia;2)The shape of breccia is angular,these breccias can be piece up well.3)Breccia gravel diameter varied widely,and arranged in disorder.2.Cement composition was similar to breccia and consist of calcium carbonateand a small amount of silicon composition,and contains hematite and other metal minerals.The matrix composition is complex,it consist of surrounding rocks chips and a small a mount of quartz and metal minerals.3.Cryptoexplosive breccia is widely developed "fumarolic structure",and usually have directionality.Most of the edge of breccia growed calcite and the calcite crystals was bigger than calcite in breccias.Part of the breccia was wrapped in siliceous shell and formed siliceous shell cryptoexplosive breccia,which indicates that the formation of breccia in the study area is related to the rich volatiles and rich silicon fluid.By comparing the characteristics of different types of breccia identification,it can be found that the breccia in the study area has significant characteristics of cryptoexplosive breccia,so it is considered that the breccia is a cryptogenic breccia.4.The overlapping area of of "rock mass + skarn + cryptogenic breccia" in the study area should have good mineralization potential,especially in the vicinity ofthe hidden blasting breccia along the weak structure,Can refer to as a prospecting sign.5.It is inferred that the mechanism of the cryptoexplosive breccia in Wu'an is that:the fault structure in this area provided conduits for the upward migration of magma-hydrothermal fluids.In the process of moving upwards and approaching the earth surface,the pressures of magma-hydrothermal fluids was declined and varieties of fluid was boiling and gasifying.The process produced a large number of gases.The original structure conduit was enclosed by silication,it leaded to these gases have no place to escape,so these gases quickly gathered to produce great pressure.Ultimately,when the pressure exceed the compressive strength of covered surrounding rocks,the cryptoexplosion happened at the shallow crust.Late hydrothermal continue to invade,it cemented fragments and breccias to form cryptoexplosion breccias in situ.