湘东雁林寺金矿田及邻区构造变形事件与控矿构造属性

Deformation events and the attributes of ore-controlling structures in the Yanlinsi gold orefield and its adjacent areas in eastern Hunan

雁林寺金矿田位于湘东北金矿区南部,发育大量中小型金矿床(点)。前人对区内包括控矿构造在内的各类变形的运动学特征及形成时代和机制尚缺乏探讨和解析,从而影响到对矿床形成和保存规律的全面认识。鉴此,笔者等基于区域构造特征和大量露头构造的详细解析,厘定了雁林寺金矿田及邻区的构造变形序列及其时代背景,并结合矿床地质和同位素测年等其他资料,探讨了成矿时代和控矿构造属性。主要认识如下:(1)研究区自早至晚经历了新元古代中期NW—SE向挤压、志留纪早期NW—SE向挤压、志留纪末花岗岩体主动侵位挤压、中三叠世晚期NW—SE向挤压、晚三叠世NNW—SSE向—S—N向挤压、中侏罗世晚期NWW—SEE向—近E—W向挤压、白垩纪NW—SE向伸展、古近纪中晚期NE—SW向—NNE—SSW向挤压、古近纪晚期—新近纪初NW—SE向挤压等9期构造事件,形成了不同走向和规模的褶皱、逆断裂、顺层剪切带、正断裂、右行和左行走滑断裂与剪切破裂、断陷盆地、劈理、膝折等构造类型,以及部分构造走向的后期偏转。(2)区内存在志留纪末和晚三叠世两期金成矿作用,均与同期花岗质岩浆活动有关。(3)雁林寺金矿田容矿构造主要有前中生代顺层脆韧性剪切带和层间断裂、中—晚三叠世的NW向—NWW向右行走滑断裂和剪切裂隙、花岗岩枝的内外接触带等3类。志留纪末金矿床的导矿构造为先期NE向深部逆断裂,晚三叠世金矿床的导矿构造为中三叠世晚期的NE向逆断裂、晚三叠世早期的NEE向和EW向逆断裂。对两期金矿床而言,成矿后各期变形事件中形成的不同类型断裂均可能成为破矿构造。

The Yanlinsi gold field is located in the south of the northeastern Hunan gold mining area,where a large number of small and medium-sized gold deposits are developed.Predecessors have not explored and analyzed the kinematic characteristics,formation ages and mechanisms of various types of deformations including orecontrolling structures in the area,affecting a comprehensive understanding of the formation and preservation laws of ore deposits.In view of this,based on the regional structural characteristics and detailed analysis of a large number of surface outcrop structures,the authors determined the deformation sequences and their ages of the Yanlinsi gold field and its adjacent areas,and then combined with deposit geology and isotope dating,discussed the mineralization ages and attributes of ore-controlling structures.The main achievements are as follows:①The study area has experienced 9 tectonic events from early to late such as regional NW—SE compression in the middle Neoproterozoic,NW—SE compression in the early Silurian,active emplacement and compression of granite bodies in the late Silurian,NW—SE compression in the late Middle Triassic,NNW—SSE to S—N compression in the Late Triassic,NWW—SEE to E—W compression in the late Middle Jurassic,NW—SE extension in the Cretaceous,NE—SW to NNE—SSW compression in the middle—late Paleogene and NW—SE compression during the late Paleogene to early Neogene,resulted in different trends and scales of structures such as folds,thrust faults,bedding shear zones,normal faults,dextral and sinistral strike-slip faults and shear fractures,faulted basins,cleavages and kinks,as well as late deflections of some structural trends.②There were two stages of gold mineralization in the area during the late Silurian and late Triassic,both of which are related to contemporaneous granitic magmatic activity.③The main ore-bearing structures in the Yanlinsi gold field include three types:pre Mesozoic bedding brittle—ductile shear zones and interlayer faults,NW-to NWW-trending dextral strike-slip faults and shear fractures formed during Middle to Late Triassic,and internal and external contact zones of granite branches.The ore-passing structures of the late Silurian gold deposits were pre NE-trending deep thrust faults,while those of the late Triassic gold deposits were NE-trending thrust faults in the late Middle Triassic,NEE-and EW-trending thrust faults in the early Late Triassic.For the two stages of gold deposits,different types of faults formed during each deformation events after mineralization may become ore-breaking structures.