Porphyry Copper Deposit Model And Exploration Technique In Zhongdian, Yunnan

Zhongdian (27°41′~28°32′N,99°40′~100°15′E) is one of the most important copper polymetallic metallogenic belt in China, which is located in the south Yidun island arc of middle part of Three Rivers area. It has won great attention for the discovery of Pulang porphyry copper deposit. In the area, attitude is high (2500-5000m);The period of snow coverage is long; Percentage of forest coverage is large; Steep terrain leads a very inconvenient traffic condition. So it is a great challenge to explore the porphyry copper deposit here. This study takes the Pulang porphyry copper deposit as the typic deposit, and establishes the porphry copper ore deposit model of Zhongdian, with the anylasis of geologic setting. To explore the concealed ore-bearing porphyry and identify the concealed structure framework, multiscale analysis and multidirectional and multiscale edge detection of potential field have been realized. Furthermore, correlation of multi-disciplinary was accomplished; multi-disciplinary location prediction model of porphyry copper deposit of Zhongdian was established; ore targets were delineated, and the result was verified by field work. As a statisfied result, four new mineralization area were found.Zhongdian arc forms at the splitted continental margin. During Carnian time, the continental crust in Zhongdian arc is thin, and arc magma was less contaminated; the porphyry is much femic; tectonic setting is similar to that of island arc; Pulang porphyry copper deposit corresponds to diorite-type porphyry copper model rather than classic type. During Norian time, the continental crust is compressed to thicken by low angle subduction of Ganzi-Litang ocean plate, and arc magma was more contaminated, and the porphyry is much felsic; tectonic setting is similar to that of continental arc; Xuejiping porphyry copper deposit corresponds to monzonite-type porphyry copper model.Different from established alteration zoning model of Pulang porphyry copper deposit, it is discovered that the typic phyllic zone (phyllite zone) is not obvious. The characteristic of alteration zoning is similar to diorite-type porphyry copper model, and the ore deposit is in rich of gold. By contrasting the alteration and mineralization characteristics of Pulang porphyry copper deposit with those of Xuejiping porphyry copper deposit, obvious differences are found that the characteristic of alteration zoning of Xuejiping porphyry copper deposit is similar to monzonite-type porphyry copper model, and the metallogenic environment of Pulang porphyry copper deposit is more basic.Plenty of mafic magmatic enclaves were found in the porphyry in Pulang porphyry copper deposit. Some enclaves are gradual to the host rocks, and there is quartz-mafic mineral ocellar texture in the enclaves, which show the evidence to the magma mixing. It has been proved that the injection of basic magma was the major control factor to porphyry copper deposit, and the occurrence of mafic magmatic enclaves can be an indicator for prospecting porphyry copper deposits in Zhongdian.The Bengge plutons was suggested not to be Cenozoic, and its syenite was determined to be shoshonite with some alkaline mafic minerals. The rock has the similar trace elements characters to arc magma with a deep source and emplaced around 201 Ma, a little later than the Zhongdian arc porphyry, suggesting it formed in the back-arc spreading setting.With the application of analytical signal, Euler deconvolution and multiscale edge detection to potential fields processing, it is found that the methods are unsensitive to the directional information. Multidirectional and multiscale edge detection method are suggested and realized. It is realism to get the precise edges of the anomaly sources at different depth, which takes effect to the 3D structure frame in regional prognosis of mineral resources.Using shift invariance discrete wavelet transform to multiscale analysis of potential fields, it is possible to more precise separation of the overlying anomaly at multiscale, and set up relationship between different scale aeromagnetic anomaly and porphyry copper deposits in Zhongdian.The accuracy of SRTM data is analyzed, and the catchment basin and stream system are automaticly extracted with SRTM data. Otherwise based on catchment basin, heavy placer anomaly is intergrated with fuzzy logic model in GIS.Ensure the fuction of each subject in mineral resources Prognosis. With the correlation analysis among subjects, multi-disciplinary location prediction model of porphyry copper deposite of Zhongdian is established. ore targets were delineated and and verified by field work. 4 new mineralization areas were foud.