The Geological Characteristics And Genesis Of The Fudiyingzi Cu Deposit In Heihe City,Heilongjiang Province

The Fudiyingzi Copper Deposit is tectonically located at the northern part of the Hegenshan-Heihe fault zone,the collision junction of Xing'an massif and Songnen massif,which lies to northeast of Yiershi-Huma Caledonian-Hercynian-Yanshanian-Quaternary Cu-Mo-Au-Pb-Zn-W-Fe-Ti metallogenic belt.The study area is located at the junction of the plateboundries,has complex geological background with closure of ancient Asian Ocean,orogeny of Central Asian,subduction and collision of the Pacific plate,etc.These tectonic movements triggered magmatic activities to provide power and material source for the mineralization of this area,where copper and copper polymetallic deposits are developed and have great potential for prospecting.Based on the previous research work,combined with the methods of field geological survey and indoor comprehensive research,some main conclusions were obtained as follows:The ore body of the diyingzi copper deposit is stratified and lensed in a set of primitive-medium-acidic volcanic eruption-sedimentary formation in the mining area.The main host rock arepyroxene amphibolite,plagioclase amphibolite,and felsic hornstone.The major minerals of ore include chalcopyrite,sphalerite,pyrite,pyrrhotite and trace amounts of native gold and silver.The gangue minerals are quartz and feldspar.The mineralization process can be divided into three stages:early stage silicification and disseminated pyrite mineralization,mid stage polymetallic sulfide quartz vein,and late stage pyrite vein.The main type of rock alteration include silicification,chloritization,sericitization,pyritization,and carbonation.Laboratory study indicated the protolith of arepyroxene amphibolite is ultrabasic volcanic rock whose petrochemically poor silicon?SiO₂,41.1%⁴1.3%?,poor alkali?Na₂O+K₂O,0.35%⁰.50%?,rich iron,rich magnesium?FeO+Fe₂O₃+MgO,46.4%⁴7.4%?.The m/f ratio between 4.1⁴.4,which belongs to the ferruginous sub-alkaline ultrabasic rock.Determination of arepyroxene amphibolite showed that the rare earth elements have characteristics of extremely low?REE(?REE=20.8310^-630.56310^-6),rich in LREE,lack of HREE,and have obviously positive anomalies of Ce and Eu??Ce=5.01⁵.68,?Eu=1.54¹.89?.The characteristics of trace elements are rich in Rb,K,lack of Nb,indicated that there is the addition of ocean crust material in magma.The results of metallogenic fluid study showed that the type of fluid inclusions is Two-phase liquid-vapour inclusion,the homogenization temperature range is 189³92?,and the salinity range is 2.23¹7.4%NaCleq.It can be clearly divided into two endpoints of high temperature?>320?high salinity?>14NaCleq?fluid and medium temperature?²50??low salinity?⁶NaCleq?fluid,representing magmatic water and heated ancient sea water respectively.The result of LA-ICP-MS zircon U-Pb Chronology indicated that the eruption age of the protolith of arepyroxene amphibolite,the host rock,is about 310.5±9.3Ma.After that the protolith suffered from the thermal contact metamorphism and formed hornfelsed rock in about 255±22Ma.Combined with previous studies,it revealed that the Fudiyingzi Copper Deposit was formed under the tectonical background of subduction of ancient Asian oceanic crust to Xing'an block in Late Carboniferous epoch,caused by volcanic eruptions,and the metallogenic age of the deposit was a little bit later than 310.5Ma.According to previous isotope studies,the sulfur of metal minerals in the Fudiyingzi copper deposit is mainly magmatic.Based on the above studies,it was determined that the genetic type of the Fudiyingzi copper deposit is the volcanogenic massive sulfide deposit of Noranada type.