Study Of Regional Tectonics, Metallogenesis And Ore Exploration In Gansu Province

Three collision-type orogenic belts (Beishan, Qilian Mountain and West Qinling) in Palaeozoic age are present in Gansu Province, which is thus the most complicated tectonic zone in China. Studies show that Qilian Mountain is the predominant Palaeozoic massive sulfide metallogenic belt of copper polymetallic deposit associated with marine volcanics, whereas Longshoushan in the north Qilian Mountain is believed to be the most significant magmatic copper nickel sulfide (PGE) metallogenic zone. And West Qinlin is suggested to be the key area of altered gold-bearing ore.The palaeo-tectonic pattern in Gansu Province had been formed in Palaozoic. From the Early to Late Paleozoic, Gansu Province once belonged to Siberian plate, Kazakhstan plate, Tarim plate, Northern China plate, Chaidamu-Qilian plate and Yangzi plate, sedately. Actually its Palaozoic history represents the process of plate convergence, which is believed to be a dynamic movement of plate destruction, rather than a simple motion of getting together. In Cambrian, oceanic crust in Paleo-Qinling, Paleo-Qilian and Paleo-Beishan were fractured due to the compression caused by plate movement and then subducted beneath the rigid plate; or fractured along the active continental margins and subducted in different phases. In the later case, the subduction line moved gradually towards the ocean and oceanic basin. Therefore, the ocean shrinked and finally destructed, and sedimentary-volcanic accumulations and accretions were consequently formed in active continental margins. Each subduction could result in the formation of small piece of continental crust, leading to continental plates expanding and colliding to others eventually, and thus the development of Beishan, Qilian Mountain and West Qinling collision-type orogenic belts in Palaeozoic age. In conclusion, Gansu Province was largely in the process of plate convergence after Proterozoic Era into a mono-plate in the Late Palaeozoic. Tectonic activities in later phases had not changed, but altered the primary pattern into more complicated stages. For example, Gansu plot was compressed by the collision between Hindu and Eurasia plate in Middle Cenozoic, and regional uplifting and subsidence occurred along the original fractures, which contributed to the complex of the present geologic pattern.This project aims to analyze the natures of geophysical field and crustal structure of the orogenic belts in Gansu Province, and then interpret the links between geophysical field and metallization. Based on the investigated results of hydrographic deposits(scale:1:200000), we analyzed the distributions of 39 elements (SiO₂. Al₂O₃, Fe₂O₃, CaO, MgO, K₂O, Na₂O, P, Ti, Ba, Mn, Cu, Zn, Pb, Sr, Zr, Cr, Ni, La, V, Th, Co, Nb, Y, Ag, Cd, Li, As, Sb, Hg, W, Mo, B, Be, Bi, Sn, F, Au and U, the first 7 elements were measured as oxides) in strata of different ages. Thus, we divided the geochemical field of Gansu Province into 7 geochemical provinces, 21 geochemical regions and 14 geochemical zones; Then we also discussed their characteristics and the relations with the already found ore deposits.We also proposed an original idea that Gansu Province can be divided into 5 metallogenic regions (type I), 8 metallogenic provinces (type II), 12 metallogenic belts (type III) and 22 sub-belts of metallizaion (type IV). We investigated the metallogenic background and the anomalies of each sub-belt (type IV) and further partitioned metallogenic fields (type V). According to the study of the mineralogenetic epoch, environments, geological metallogenesis and naturally grouping of ore deposits, the minerogenic series, types and sub-series in Gansu Province have been generally determined. We finally drew the conclusion that Gansu Province has 11 types of metallogenic series and 39 metallogenetic series.In addition, we also focused on the the main metallic ores, such as gold, copper, lead, zinc and tungsten ore deposits, in the aspect of the sources, the spatial distribution and enrichment of main metallic ores, suggested the possible controlling factors on metallic ore deposits, provide evidence in exploring prospects.