Porphyry Copper(Gold) System In Duolong District And Its Metallogenetic Regularities

As an important discovery of Bangong co–Nujiang metallogenic belt(BNMB)in recent years,the Duolong super– large copper(gold)district discovered the indicated copper metal resource exceeds 20 million tons by drilling,associated gold metal resource of more than 420 tons in total,and with 1 super– large deposit,4 large deposits and 3 small deposits.There were also numerous prospective areas and small placer gold deposits.It was believed that this district formed under the geodynamic settings of the Bangong co– Nujiang Neo–Tethys ocean crust subduction northward beneath the South Qiantang terrane,which was a set of typical porphyry Cu(Au)deposits in magmatic arc setting.Therefore,this district is an excellent example for studying deposits in porphyry copper system related to oceanic crust subduction.However,the metallogenetic regularities of Duolong district have not been well understood,and the linkage between various types of deposits is not sufficient,these restricting the mineral exploration and the resource evaluation in this district.Depending on “the Minerogenetic Series for Mineral Deposits” theory and the academic ideas of “All– Position Mineralization,Absence Prospecting”,this paper define the deposit types of the Duobuza porphyry type,the Nardon breccia pipe type and the Tiegelongnan epithermal type in Duolong district.By the detail comparative study,this paper found that these three types of deposit constitute an integrated porphyry copper system,which the Duobuza deposit type was located in the low–level domain of the system,Nardon deposit type was located on the top of low–level domain of the system,and the Tiegelongnan deposit type was located in the high–level domain of the system,and the relative ubiety of these types of deposit can be used as an important basis for mineral exploration and evaluation.On this basis,this paper founded “the Minerogenetic Sub– Series related to the combination of the intermediate– acid volcanic rocks– hypabyssal intrusive mass in Duolong district”,and then summarized its characters.Using the re–interpretation of the datas such as the geophysics and the high–resolution remote sensing images of Duolong district,this paper identified the precursor pluton,which ahead of formed where have been emplaced below the bottom of porphyry copper system by the deep magma,and closely related to the formation of the deposit in this district.Base on this point,a new view that the Tiegeshan uplift located in the middle of the Duolong district belongs to a typical magmatic intrusion dome structure was put forward,and reconstructed the framework of ore field structure in this area.The deposits in the Duolong district located around the Tiegeshan dome,and linked with the fossil volcanic edifice closely were proposed in this paper,and believe that somewhere in Duolong district around this precursor pluton also have the potential to find porphyry copper system.The metallogenic geological conditions of the Duolong district were summarized from the tectonic position and the geodynamic settings,magmatic rock conditions,structural conditions and sedimentology conditions.Based on the analysis,a regional metallogenic model has been established,and several problems that have long plagued the prospecting and exploration of the Duolong district were explained.Finally,this paper summarized the favorable geological exploration guides for this porphyry copper system in Duolong district.The inheritance and evolution of ore deposits and the preservation and transformation of ore bodies are put forward in this paper.The key preservation condition is the cover of post– mineralization volcanic rocks after the porphyry copper system formed.The structure after mineralization leading to the missing ore body in the Duobuza and the Tiegelongnan deposits,and shows the huge potentials in the depths of these deposits.In regional prospecting and exploration,the precursor pluton should be pay attention to identified,therefore,the satellite gravity exploration technique,seismic exploration technique and district scale the ground high–precision magnetic survey are all effective exploration techniques for the future mineral exploration.