Study On Characteristics And Its Metallogenic Implication Of Cryptoexplosive Breccias From The Chating Cu(Au) Ore District In Xuancheng,Anhui Province

Chating copper-gold deposit in Xuancheng,Anhui Province,is a large deposit discovered in Nanling-Xuancheng Mesozoic-Cenozoic volcanic-sedimentary basin in the shallow covered area of the middle and lower reaches of the Yangtze River in recent years.Previous studies on Chating copper-gold deposit and magmatic rocks have been carried out,and some significant achievements have been obtained.The master's thesis takes the cryptoexplosive breccia?tube?, which is closely related to Chating copper-gold deposit in space is taken as the research object.Through systematic geological research,the characteristics of cryptoexplosive breccia?tube?are revealed,and the possible diagenetic mechanism is discussed.At the same time,the ore-forming hydrothermal fluid inclusions in cryptoexplosive breccia?tube?are studied to explore the relationship between cryptoexplosive breccia and mineralization and the genetic types of the mineral deposit,then establish the genetic metallogenic model.The following results have been achieved:1?The main boby of rock pipes locates in the ore-bearing quartz diorite porphyry intrusion of Chating copper-gold deposit,in which develops a tube-shaped cryptoexplosive breccia in space.,and part of the boundary reaches the Triassic limestone?marble?.The caprock at the top of the rock pipe is the Volcanic rock and Quaternary system of the Cretaceous Formation in the Cretaceous,and the surface bedrock is not exposed.According to the characteristics of the breccia in cryptoexplosive breccia,it can be divided into three rock types:cryptoexplosive magmatic clastic breccia,cryptoexplosive hydrothermal breccia and blasting clastic rock.The rock?cylinder?shows obvious zoning in bth borizontal and vertical directions.Form the center of the rock tube to the surrounding rock,the diorite is divided horizontally into the central zone,transitional zone and marginal zone,etc.While the vertical zoning is characterized by three facies zones,the upper lasting phase,the middle-deep seismic phase,and the deep facies,respectively.It is revealed that the magmatic hydrothermal fluids migrate moves upward with the magma and precipitates hydrothermal fluids continuously,accumulating on the top of magma,due to the shielding effect of the overlying rock mass?str atum?,magma?hydrothermal?explosion took place under the underground concealed condition,and the multi-stage concealed explosion superimposed to form the cylindrical structure concealed explosion breccia.2?Copper-gold ore bodies and cryptoexplosive breccia?barrels?have good spatial coincidence.Fine-vein disseminated pyrite and chalcopyrite ores often occur in rock breccia,quartz veins and anhydrite veins,as well as ore-forming hydrothermal fluid filling along the fissures due to the influence of ro ck fissures,which can form large veins or massive ores.In addition,breccia ores are also developed.There are alteration types and zoning characteristics similar to porphyry deposits in cryptoexplosive breccia?barrel?,such as deep silicification,potassium?sodium?feldspar,etc.In the middle,pyritization,sericitization,chloritization and anhydrite are the main types of hydrothermal alteration,while in the shallow part,kaolinization and other low-temperature alteration types are mainly developed.3?It is discover during the petrographic observation about the fluid inclusions of ore-bearing quartz veins in cryptoexplosive breccia?barrel?that fluid inclusions are mainly composed of pure liquid phase,gas-liquid two-phase and multi-phase inclusions with sbu-crystals,where the gas-liquid two-phase inclusions are the dominant.The in-situ composition test of single fluid inclusion shows that H₂O is the main component in the gas and liquid phase of the fluid inclusion;the homogenization method shows that the metallogenic temperature ranges from 144.2?to 485.6?,the median temperature is210.6?,the fluid salinity is 0-56.30 wt%NaCl,and the median salinity is1.05wt%NaCl,indicating that the metallogenic fluid in the main metallogenic stage is the fluid system with a medium-low temperature and low salinity.It is suggested that the fluids in the early stage of mineralization may be characterized by high temperature and high salinity.The cryptoexplosion during the diagenesis of cryptoexplosive breccia results the reductions of the temperature and pressure of the ore-forming thermal fluid,and the changes in the physochemical conditions such as pH?f_O2?f_S2,which ultimately leads to the unloading of minerals in the fluid.4?Compared with typical porphyry deposits,the occurrence location,occurrence,alteration type and zoning of Chating copper-gold deposit are similar to those of porphyry deposits.However,the mineralization enrichment position of the deposit is consistent with cryptoexplosive breccia tube?body?,and the characteristics of vein-like,massive mineralization with strong development of anhydrite and relatively low homogeneous temperat ure in the main metallogenic stage of copper-gold deposit are also obviously different.Therefore,according to the characteristics of the deposit,Chating copper-gold deposit is considered to be a cryptoexplosive breccia deposit closely related to intermediate-acid epithermal porphyry intrusive rocks.