The Relationship Of Tectonics-Magmatism And Mineralization In NingMa Area

The middle-lower reaches of Yangtze River is a famous Mesozoic Cu-Fe-Au ore belt in China. Ningma area which is one of the most suitable regions for mineralization of Cu-Fe polymetallic ore lies Yangtze Plate, east of the lower Yangtze tectonic-magmatic belt. Lots of geologic research、mineral exploration、scientific research have been done in this area. Mineralization and lithology are controlled by complex fault system, magmatism are common and magmatic rocks are widespread in this area. This thesis focus on the magmatic rocks, structure and typical ore deposits in Ningma district and the achievements are as follows: accomplished LA-ICP-MS zircon U-Pb dating for lava of four main volcanic cycles(Longwangshan cycle, Dawangshan cycle, Gushan cycle and Niangniangshan cycle) and some ore-bearing rocks in Ningma area, analyzed the regional character of tectonic and magmatite, systematically summarized the features of some typical ore depositsMesozoic lava, a trachyandensite-andisite-quatz andisite-dacite-quatz trachyte volcanic succession, is the main formation stratum in research area and basement rocks occur sporadically. The faults, which mainly directed to NNE, NW and EW and controlled the space distribution of Fe-Cu metallogenic belt in Ningwu basin, are formed in early Yanshan epoch. Majority of the magmatic activity occurred in Yanshanian, magmatic rocks are progeny of Longwangshan, Dawangshan, Gushan and Niangniangshan volcanic spurting, and the prophyrite geneticed from Dawangshan cycle is most correlative to metallogenesis.This thesis analyzed the main element, trace element, REE and Pb isotope system of the lava in this area. The lava are mainly shoshonitic series. The fractional crystallization of the four volcanic cycles became more intensive from early to late stage, but slightly weaker than adjacent Lujiang-Zongyang basin. The parental magma derived from mantle, with no obvious upper crust material contamination. The erupt time of the lava from four volcanic cycle are132.3±1.0Ma,130.4±1.6Ma,128.1±1.9Ma and127.2±1.1Ma, respectively, all belong to early Cretaceous. It suggest that there was a sudden and intensive volcanic eruption event in late Mesozoic, from132Ma to127Ma, lasted only3-5Ma. The intrusive time of the pyroxene-bearing diorite porphyrite from Washan iron deposite is127.6±4.4Ma, considering the error range, the main formation time is129.8Ma, belongs to Dawangshan cycle magma production.The thesis mainly makes a research and summary on the ore-controlling structure, the composition and the ore fabrics of the porphyrite iron deposits and vein hydrothermal Cu-Au deposits in the basin。The author selects Meishan iron ore deposit、Jishan iron ore deposit and Fenghuangshan iron ore deposit as the tipical ore deposit, and then summarize the metallogenic factors including reserves, geologic environment and deposit characteristics。The thesis makes a point that the "sudden" delamination should be the main mechanism of the reduction of the lithosphere in Late Mesozoic of the Middle and lower Yangtze River, although delamination and thermal erosion are reciprocal for Nanjing-Wuhu Basin. The porphyrite iron deposits and vein hydrothermal Cu deposits form in this basin keep a contemporaneity with the enormous reduction of the lithosphere in the compressional orogenic environment at Yanshanian in Eastern China. So the author considers the former have a relationship with the melting of upper mantle, and mantle metallogenic material getting into magma system caused by the continued upwelling of the asthenosphere induced by the reduction。The thesis summarize the space-time structure of the mineralization in Ningma area at Yanshanian:(1) intermediate and acid magmas emplaced the uplift area around Nanjin-Wuhu Basin at135Ma, then produced porphyry-skarn Cu deposits; porphyrite iron deposits formed at about129-127Ma, and vein hydrothermal Cu deposits probably formed at about129Ma and128Ma in two-stage in this area。(2)The magmatism-mineralization in Late Jurassic-Early Cretaceous in Ningma area is influence remarkable by tectonic movement. The magmatism-mineralization results from the geodynamics environment geodynamic environment changing from compression to extension, and the metallogenic belt makes an accordance with the fault zone. The ore field distribute in the intersection region of faults.