| The West Qinling area is one of the major gold producing areas in China, its abundant gold deposits, unique geotectonic position and contained in the complicated geological information, have made it an ideal selection of geological scholars to study the tectonic, magmatic activity, metamorphism and mineralization.The Lizi gold deposit is located in the south of the Shangdan suture belt, is the transfer of eastern and western Qinling conversion parts and transfer of the Qinling and Qilian conversion parts, and exactly in Tianshui Lizi area of reverse "S" structure of the Lizi turn end of anticline, is a typical gold deposit in the metallogenic belt of the West Qinling. This paper regard the Lizi goldfield as the target area to study, to outcrop structural analysis as the foundation, combine with the regional structure and micro structure analysis, focus on studying the deformation characteristics of the main ore controlling structure in detail, to determine deformation sequence of the structure of mining area, and discuss the relationship between structure and metallogenesis. Obtained the following understanding of the main:1) With intense tectonic deformation, Lizi goldfield has the characteristics of multi stage activities, there are at least four periods deformation, from early to late as follows: NW-trending ductile dextral strike-slip shear faults ?D1? and NE-trending ductile brittle tenso-shear faults ?D2?, NE-trending ductile brittle overthrust faults ?D1? and NE-trending brittle faults ?D4?, they overlapped each other to set limits, reformed and destroyed. Those together constitute the overall structural framework of the Lizi goldfield. D1 period deformation is accompanied by the early Indosinian subduction regional large-scale dextral strike slip shear movement of Qinling Mountains orogenic belt. In the study area, it mainly developed in Jiancaowan and Kuangou exploration goldfield of early Paleozoic strata, the overall trend to NW extension, the partial twist nearly SN and NNE trend, showing intense dextral compresso-shear structure; D2 period deformation developped in the whole region,mainly to NE-trending, and inferred that it is the product of progressive deformation of D1; D3 period deformation mainly developed in Suishizi and Yingfang exploration goldfield of early Paleozoic strata and Indosinian granite, to widely developed with axial surface cleavage of asymmetric fold and shaft and face north dipping thrusting nappe fault is the main deformation style, to NE, NNW, NNE-trending extention, cutting early mineralized quartz veins, and in relation to Indosinian collision background of Qinling orogenic belt; D4 period deformation, developped in whole region, mainly to NE-trending, the shallow level brittle faults and the wide and gentle fold structure as the main features, reformed and destroyed the early stucture, geological body and ore body.2) Orebody of Lizi goldfield is mainly controlled by NW trending ductile shear zone, NE-trending tenso-shear tectonic belt and NE-trending overthrust faults, and in different mining areas exhibited different characteristics respectively. Jiancaowan and Kuangou exploration goldfield is typical ductile shear zone controlled orebody, orebody mainly distribute along the mylonite foliation, veins and ductile shear zone with the same trend, the overall form is NNW,NW extension, Partial twist nearly SN,NNE trend; NE, NEE ductile-brittle tenso-shear tectonic belt is main ore-controlling structure of Suishizi exploration goldfield, overall orebody extension is NE trending, partially EW-trending, with the same structural trace, on trend with branch composite phenomenon, with NE lateral trending; Yingfang and Liushagou exploration goldfield are similar to Suishizi exploration goldfield, mainly controlled by NE-trending ductile-brittle fault fracture zone, roof and floor structure with strong mineralization, mostly invasion, fine vein, grid partially, with NW en echelon arrangement and more obvious isometric structure.3) Developed ductile shear zone and overthrust faults in the western Qinling orogenic belt are particularly important ore controlling factors in different periods for gold mineralization, provide motive support, migration channel and storage space for gold activation, migration, deposition and mineralization. The two periods ore-controlling structure in the West Qinling area exhibited significant features, structural factors of gold mineralization not only is single overthrust fault, early ductile shearing is even more important. The distribution of goldfield today with Wenxian-Maqu arc structure exists anastomosis, probably because of mineralization of the early ductile shear zone after,under the action of late overthrust structure, the convergence of arcuate structure position changed. |
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