A Study On The Geological And Geochemical Characteristics And Genesis Of The Chating Cu-Au Ore Deposit In Xuancheng City,Anhui Province

The Chating Cu-Au deposit is a large-sized deposit discovered currently in Nanling-Xuancheng Basin of Anhui Pronvince and fewer attention has been paid to it.In this study,the general knowledge of regional geology is widely collected,the cross-sections of the ore deposit are detailedly in detail and drill-core samples are systematically observed.The geological characteristics of the Chating Cu-Au deposit are understood combined with the researches on the mineral component and structure of the ores.Furthermore,the geochemical characteristics of the ore-forming fluid inclusions and stable isotopes of the Chating Cu-Au deposit were also systematically investigated.The main achievements and new understandings are as follows:The Nanling-Xuancheng Basin in which the Chating Cu-Au deposit located has special geological characteristics.It develops both volcanic rocks and intrusive rocks,and the quartz diorite porphyry in which the Chating Cu-Au deposit hosted.The petrography characters and isotopic geological age of that volcanic rocks and intrusive rocks indicate the Mesozoic magmatism in the Nanling-Xuancheng Basin has double characteristics,depression area(volcanic basin)and upwelling area in the structure-magma-ore deposit zone of the Middle and Lower Reaches of Yangtze River.It hints that the mineralization in the Nanling-Xuancheng Basin has dual natures,that is,it may develop either porphyry-skarn-vein type magmatic hytrothermal Cu-Au polymetallic deposits or volcanic-subvolcanic hydrothermal Fe(S)deposits.The Chating Cu-Au depodit hosted in hidden intrusive stock of quartz diorite porphyry.The scope of mineralized body or ore body is probably same as that of the crytoexplosion breccia pipe occurres in the intrusive rock body.The hydrothermal alteration types such as silicification,potassic alteration,beresitization,choritization develop in the mineralized intrusive,and has obvious zonal distribution.The ores have thread vein,network vein,veinlet-disseminated,fine grained-disseminated structures.All these characteristics show that the Chating Cu-Au deposit is a typical porphyry deposit.Otherwise,small lens-shaped bodies of skarn develop in the instrusive rock body in which the ore body hosted and hydrothermal anhydritization is well-developed.The anhydrite cement rublles of the cryptoexplosive breccia,even anhydrite rocks formed locally.These characteristics are different from those of the porphyry deposits.The Re-Os isotopic age of the pyrite from the Chating deposit is about 139 Ma,which is the same as the age of LA-ICP MS zircon U-Pb of the quartz diorite porphyry.The geochemical characteristics of H-O,C-O,S,Pb isotopes show that the ore-forming fluid and ore-forming elements mainly come from magma,a few from atmosphericprecipitation and stratum.The studies of fluid inclusions show that ore-forming fluid has the characteristics of medium temperature,low salinity and low density.The ore deposit formed in lower pressure and small degree of depth.It is hold that the Chating Cu-Au deposit is a porphyry deposit related to the late Yanshanian magmatic intrusion.