| The gold metallogenic belt of Dadu river is located in the north of south to northern tectonic belt of Xikang Yunnan axis, where Xianshui river, the longmen mountain and river panxi rift valley form the pecial tectonic position that the trigeminal rift intersects, which is an important gold metallogenic belt in southwest China. This area is suffered from the subduction, collision and intracontinental convergence of the northern part of north China plate, the eastern part of the Yangtze plate and the west of Indian plate forms an inverted triangle, where the structure is complex and folds, faults are very common, extruded the north-south and east-west two-way. This area develops a large number of ductile shear zone during the subduction and collision of plate, these ductile zones distribute a lot of felsic veins and quartz vein. And these large ductile nappe structures lead to the intrusive activity of granite. The study about this area finds that granite magma is not from deep, but the result of partial melting in ductile shear zone during the division and collision of tectonic plate, which forms a large number of layer and interlayer slip inside ore storage space, intense metamoiphism and deformation, which create the extremely advantageous geological background and ore-forming conditions for the regional gold mineralization. In this area, the length is 60 km from north to south and the width is thousands of meters to 30 km from east to west, where rock gold deposits(points) have been found more than 60, which forms the famous the “jingu” of Dadu river in Kangding. Through the further work in the region, we expect to achieve the goal of new, large and superlarge deposits, and gain ore-search breakthrough.Baijintaizi deposit is a typical ore deposit in this religion, which is located in Kangding county and belongs to Sanhe countryside, ore bodies is located in the internal nappe of Kangding complex and the core of north-south arch of Jixinliangzi, which is close to east wing parts, controlled by the north-south thrust belt, and belongs to the western margin gold metallogenic belt of Yangtze platform in the northern section. However, since the deposit was exploited, the topic has not yet been discussed, which exists mines. I select the deposit as the research object in this paper and emphasize on the vertical zoning of elements in the ore deposit, trying to reveal a deposit formation by seeking the vertical zoning of elements, so as to provide the reference on the prospecting for deep predictive.In this research, the author personally went to field geological investigation in the mining area, collected samples of ore body and wall rock, and microscopically authenticate polished section and thin indoors, analysizing the trace elements of the samples by ICP-MS, making major element test by selecting a typical sample.The main research content of this article including: regional geological background, characteristics of regional magmatic rock, geologic characteristics of the ore deposit, geochemical features of mining area, vertical zonal regularities of elements. We get many results through the above research, as follow:1.The surrounding rock of ore deposits is mainly Zali group mixed granite. Its feature: light rare earth is heavier than heavy rare earth, the fractionation of rare earth is obvious, weak negative europium anomaly, this feature is under the condition of crustal thickening, the distribution characteristics of REE of granite of different type of magma intrusion, which remelts sial form this granite.2. Types of wall rock alteration are mainly silicification, pyritization, sericitization, chloritization, carbonatization, curtain petrochemical, etc. The wall rock alteration has obvious vertical zoning phenomenon. In the upper of deposit, it is mainly silicification, pyritization; at the bottom, there is mainly silicification, pyrite, chalcopyrite, galena, mineralization and carbonatization.3. The attitude of ore bodie is upper gentle, lower steep, geniculate. The host rock of deposit is main granite, and gold is mainly hosted in pyrite and quartz.4. Element on the vertical space in the deposit has obvious regular: REE of quartz at the bottom of ore deposit is heavier than the top, namely higher quartz is purer. The content of Cu、Pb、Bi and the ratio of Pb/Sb in pyrite goes up from the upper to the the bottom, and the content of Li、Co、Ni、Sr、Mo、Ba and the ratio of Co/Ni lowers obviously; the content of Zn、Pb、Ni、Ba、Sb、Sr and the ratio of Pb/Sb in quartz rises from the upper to the the bottom, and the content of Cu、Li、Sr、Mo and the ratio of Co/Ni, Mo/Bi reduces obviously, the content of Be、Cd、W、Bi is a little change.5. Pyrite sulfur isotope analysis results in the quartz veins show that δ34S value is 0.7‰~1.1‰, δ34S mean value is 0.97‰, the homogenization degree is higher, concentrated, and it is close to the meteorite sulfur, showing obvious magmatic sulfur or mantle source sulfur isotope composition characteristics. these characteristics prove sulfur in ore body comes from deep magma, and herald the gold mineralization has close relation with magmatic hydrothermal. Uniform temperature of the fluid inclusion in quartz shows that ore-forming temperature is higher at the bottom.6. In the mining area, basic diabasic dike is closely associated with containing gold quartz. The zircon U-Pb age of diabase is 425.3±3.1Ma, and the age of containing gold quartz formation is 32.4~37.7Ma, the average age is 43 Ma, the age of both is obvious, the metallogenic epoch is greatly later than the mafic dike. But these basic dikes(body) indicate that its location have occurred the tension of the lower crust or the upper mantle, which indicates that Dadu river fracture is the deep fracture of the lower crust or the upper mantle. Under the regional extensional environment, it is not only conducive to the rising emplacement of basic magma in the deep crust or upper mantle, and but is advantageous to the migration of the deep hydrothermal fluid. |
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