| The western Qinling orogenic belt is the assembled orogenic belt between Yangtze plate and North China plate and the Songpan-Ganzi micro plate, this region unders the complicated tectonic process from Paleozoic to Mesozoic, During this period, magmatic activity and large-scale gold mineralization occurred. The Xiqing mountain metallogenic belt is located in the most southern margin of the West Qinling district. near the Mianlue paleo-suture zone,which belongs to the convergent margin of the plates, there are intrusive rocks of the Indosinian. The spatial distribution of this rock bodies are closely related to the plate tectonics. At present, the Dashui gold deposit, the Xinqu gold deposit, the Zhongqu gold deposit and other gold deposits have been found in the Xiqing mountain metallogenic belt where has become the important gold metallogenic belt in the western Qinling district. The Xinqu gold deposit be occurred in the Daguanshan formation carbonate rocks of Lower Permian, the tectonic position of the part of the orebody is the same as the vein rocks, mineralized alteration added up to the veined granodiorite porphyry. This paper mainly not only includes the study of Micropetrography and geological survey of Xinqu gold deposit,and but also analyses the characteristic of petrochemistry, geochemistry and isotope chronology of the intrusive rocks and the veined rocks related to gold mineralization.In addition, The paper also includes the electron microprobe chemical analysis of the gold particles and the similar contrast with the adjacent gold deposit. The main achievements and results obtained are as follows:(1)In the Xinqu gold deposit, zircon U-Pb isotopic age of the veined granodiorite porphyry related to gold mineralization is 200.66±0.79Ma(MSWD=0.46), its age, which occurred afer the formation of rock mass, is Late Indosinian, the age of the veined granodiorite porphyry limit the age of mineralization.(2)Zhonggezhala rocks, in the northern margin of Xinqu gold deposit, are quartz monzonite and hornblende monzonite. the lithology of Zhong Qu rocks are granodiorite porphyry. the lithology of rock veins are biotite granodiorite porphyry. Theirs geochemical analysis results show: the percentage content of SiO2 is 53.59~64.56%, K2O% is 3.83~6.49%,Na2O% is 1.81~3.06%,CaO% is 2.7~6.56%,Al2O3% is 14.83~18.48%,MgO% is 1.51~4.44%.They belong to high potassium Ca-alkaline series to shoshonite series,having Peraluminous characteristics and Metaluminous characteristics.The granodiorite porphyry of Xinqu gold deposit is Mg andesite(MA). The trace element Enrich Cs, K, Sr, Pb and other large ion Pro stone elements, and loss Nb, Sb, P, Zr, Ti, there is not the negative anomaly of Eu.(3)The igneous petrotectonic assemblages of the Xin Qu gold deposit indicate that the magmatic processe was related to oceanic subduction,during the magmatic evolution process, Mantle and crustal materials had mixed to the initial magma.The area of the Xinqu gold deposit is a accretionary magmatic arc. At the end of Triassic, Old Tethys, between Yangtze plate and North China plate, was not completely closed. The phase belongs to Mediterranean type remnant ocean. Subduction and collision were simultaneous.(4)In the Xinqu gold deposit, The main mineral of gold ore is the independent natural gold, the particle size is from the microscopic level to submicroscopic level. The Modes of occurrence of Au mainly are intergranular gold, fissure gold and inclusion gold. According to the analysis of electron microprobe chemical, the percentage of Au is 98.09% ~ 100.59%. Correspondingly, the fineness of gold is 981~ 999, which belongs to the series of natural gold.(5)Xinqu gold deposit has the same characteristics as the orogenic gold deposits: it occured the active continental margin and located the compressional/transpressional environment, its tectonic background is accretionary magmatic arc,.The spatial distribution of the regional gold deposits,containing Xinqu gold deposit,is closely related to plate-tectonics.The shape of the ore bodies discovered is vein. which formed in the overlapping regions between the high angle thrust faults and sub-strike slip fault. Fineness of gold is higher than 900, which changes in a smaller range. |
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