Research On Yanshanian Metallogenic Geodynamic Setting And Metallogenic Model In Lu-Zong Basin, Anhui Province

There is an inherited-type volcanic basin developed during Yanshan period in Luzong volcanic basin on the Lower Yangtze region, and an important role for the sub-ore-forming unit of large scale mineralization collection, which is holded between Tan-Lu fault and Yangtze fault. On the basis of the collection and secondary development on the number of previous studies data, throngh field geological investigation, sample collection and microscope oberservation, emphasising on space-time evolution of tectonic-magmatism-mineralization, from the view of three-dimensional and ore field scale, the strcture feature of different time and order are analysised systematically,and ore-controlling structure,magmatism and their space and time relationship are investigated in order to ascertain the deep geodynamic processes of deep faulting-magmatic activity under global tectonics system and the surfacial response of tectonic-mineralization.Using the method of "diamond-shaped strain analysis",through identifying the strcture orders of rock-and ore-controlling,analysising the structure system,the mineralization space texture in Luzong basin is established.By geochronologically studyting on magatic rocks related mineralization, restrict the times of mineralization,the time texture of mineralization in Luzong bansin is established.Further, Mineralization dynamic setting and dynamic process in Luzong basin during Yanshanian period are probed and metallogenic geodynamic model are established.We get some improvements and understandings as following:1.Petrological and geochemical results of magmatic rocks related to mineralization showed that the igneous rocks belong to adakitic calc-alkaline intrusion series and shoshonitic volcanic-intrusion series.The former mianly distributes in Shaxi region and the latter in the interior of basin.They are derived from the different magama sources by the same deep magmatiam process. The results of trace element and isotope indicate that the volcanics is mainly derived from EMI mantle.Its eruption environment is back-arc rift,not typical of intracontinental rift.2.Combined the information including ore microcope observation,EPMA of pyrites,REE and trace elements of magmatic rocks and ore,it indicates that the metal mineralization including porphyry-type iron, sedimentary hydrothermal-transformation-type iron, hydrothermal vein-type Cu-Au deposits are all related to Yanshanian magmatism.Adakitic calc-alkaline intrusive magmatiam resulted in the formation of porphyry copper deposit,and shoshonite magmatism controlled the porphyry-type, sedimentary hydrothermal-transformation-type, hydrothermal vein-type mineralization. 3. Integrated the results of research geochemical, petrographic and metallogenic chronology, presented Luo River iron ore rock is subvolcanic coarse pyroxene porphyry between the period of volcanic activity,which belongs to Zhuanqiao group,not the volcanic lava of previous view. We contrast and analysis the characteristics of trace element and rare earth of single mineral magnetite from Longqiao Iron deposit and Luohe-Nihe Iron deposit,and it show that there is a link between the sedimentary hydrothermal-transformation-type and the porphyry-type in genesis.The magma of hydrothermal mineralization for the Longqiao Iron deposit is similar with subvolcano rock in Nihe-Luohe; The genesis of Bamaoshan Iron deposit may belong to reworked sedimentary, and its horizon could compare to the Longqiao Iron deposit; The hydrothermal vein-type Copper deposit of Jingbian is different with Zhujiaao,Yutan,Wolong deposit in genesis from the research of mineralization characteristic,it Should be a further comparative study with Shaxi porphyry copper deposit.4. By using high-precision LA-ICP-MS zircon U-Pb isotopic dating technique, The ages of main ore-forming rock are obtained,134.0±1.5Ma of Shaxi,129.6±0.8Ma of Ba Maoshan, and 129.7±1.4Ma of Yutan, and 132.8±2.6Ma of Nihe,133.3±0.6Ma and 133.2±1.1Ma of Luohe respectively.The time texture of rock-and ore-forming in Luzong basin are established. Combined magmatism evolution in Luzong basin and neihbouring area,it can concluded that the large scale mineralization in area of the middle and lower of Changjiang Rive occurred at 200～160 Ma,140 Ma or so and 130-110Ma,and the mineralization in Luzong occurred in the latter two periods,corresponding to impression(thickening)-extension(thinning) and large scale lithosphere delamination resultede from extension respectively.5.The results of analyzing of the structural controlled mineralization and dynamic mechanism by "diamond-shaped strain analysis"show that the rock-and ore-forming in Luzong bain are controlled by double factor including deep subduction of Pacific plate and crust-mantle interaction. The discordogenic fault and the foundational fault in the area belong to first sequence of structural surface which come from the dynamic field of Pacific plate and the Eurasian plate: S4(NE40°),S2(NE280°),S3(NE310°);These structural surfaces control large-scale eruption-intrusive activities in Yanshan period,and they also restrict the distribution of metallogenic belt region. First sequence of structural surface and its rupture(NE40°and NNW350°) form the boundary which shape into smaller scale transtensional or face-shear structures and regional of second sequence of structural surface,and they have some controlling effect on the spatial distribution of mineralization of hydrothermal vein-type Cu-Au deposit in late eruption.6.The space texture of mineralization in Luzong basin is eatablished,which is as followings:(1)three metallogenic belts:Sahxi-Dong Gushan Cu-Au,Longqian-luohe Fe-Cu (Au)and Huang tun-Zongyang Metallogenic belts;(2)three metallogenic rings:inner ring of high temperature Fe,S mineralization,middle ring of middle-low temperature Fe,Cu mineralization and outer ring of middle-low temperature Cu,Pb,Zn mineralization. (3) We divide two ore blocks in the view of three dimensions:one is calc-alkaline intrusion ore block found in Shaxi region and deep basin which is related toporphyry-type mineralization,the other is shoshonitic volcanic-intrusion ore block found in basin which is related to porphyry-type, sedimentary hydrothermal-transformation-type, hydrothermal vein-type mineralization. 7. A comprehensive understanding of deep magma geochemical the information,structural framework of ancient geography, plate setting discrimination, laws and activity of regional magmatic, "Analysis of strain Diamond",we get the kownledge that the basic framework of NE directional deep fault was formed during North China and Yangtze plate docking; Early structure of Yanshan period was a great space to diagenetic mineralization,which belong to Pacific and Eurasian tectonic plate system, the formation of new China. After the Indian plate into the Cretaceous in this area had a certain impact, accommodation, use of the new Chinese system of structural features form the main structure of tensile. However,large scale of oceanic crust fragments(Ancient oceanic crust)joined into lithosphere mantle and mantle basaltic magma raised during lithosphere thicked in deep。8. Then large-scale delamination of lithospheric thinning occurred in the weak region of plate suture zone. On this basis, Yanshanian magma-metallogenic dynamics model of Lu-zong was constructed.