湘东北万古金矿区变形序列及其对控矿构造属性的约束

Deformation sequence and its constraints on the attributes of ore-controlling structures of Wangu gold deposit in northeast Hunan

湘东北万古-黄金洞地区是湖南重要的金矿产区之一。前人关于区内控矿断裂形成时代的研究相对薄弱,对区内不同时代构造类型的总结也不全面。鉴于此,通过地表露头构造观测、解析,结合已有区域构造研究成果,厘定了万古金矿区的构造变形序列及其时代背景,探讨了成矿时代,确定了矿区控矿构造的类型和形成时代。主要认识:(1)研究区从早至晚经历了7期主要变形事件:①新元古代中期受NNE向挤压,形成NWW向板劈理、顺层剪切逆断裂和褶皱;②志留纪晚期受SN向挤压,形成EW向板劈理和逆断裂;③中三叠世晚期受NW向挤压,形成NWW向右行走滑断裂、NE向逆冲剪切破裂和断裂;④晚三叠世受SN向挤压,形成NW-NNW向右行剪切破裂、NE向左行走滑断裂、NEE向左行逆冲剪切破裂等;⑤中侏罗世晚期受NWW向挤压,形成NNE向逆断裂、EW向右行走滑断裂;⑥白垩纪区域NW-SE向伸展,形成NE向正断裂和断陷盆地;⑦古近纪中晚期受NE向挤压,形成EW向左行走滑断裂。(2)志留纪晚期构造活化导致矿质初步富集,燕山期花岗质岩浆活动导致金矿床形成。(3)区内容矿构造主要为新元古代中期形成的NWW向北倾顺层剪切逆断裂;导矿构造为中三叠世晚期形成的NE向逆断裂;古近纪EW向左行走滑断裂为破矿构造,志留纪、中三叠世晚期和晚三叠世形成的逆断裂和走滑断裂也可能切错或限制NWW向矿脉发育。

Wangu-Huangjindong area is one of the most important gold producing areas in Hunan province.Previous studies on the formation age of ore-controlling faults in the area are meager,and the summary of structural types in different times is not comprehensive.Through observation and analysis of surface outcrop structures,combined with the existing research results of regional tectonic events,this paper determined the tectonic deformation sequence and their age background of Wangu gold deposit,discussed the metallogenic age,and determined the types and formation ages of ore-controlling structures.The main achievements are as follows:(1)The study area has experienced seven main deformation events from early to late:①Regional NNE compression in the Middle Neoproterozoic formed NWW-trending slaty cleavages,bedding thrust shear faults and fold;②Regional SN compression in the Late Silurian formed EW-trending slaty cleavages and thrust faults;③Regional NW compression in the Late Middle Triassic formed NWW-trending dextral strike-slip faults,NE-trending thrust shear fractures and faults;④Regional SN compression in the Late Triassic formed NW-NNW-trending dextral shear fractures,NEtrending sinistral strike-slip faults,NEE-trending sinistral strike-slip-thrust shear fractures;⑤Regional NWW compression in the Late Middle Jurassic formed NNE-trending thrust faults and EW-trending dextral strike-slip faults;⑥Regional NW-SE extension in the Cretaceous formed NE-trending normal faults and faulted basin;⑦Regional NE compression in the Middle Late Paleogene formed EW-trending sinistral strike-slip faults.(2)The preliminary enrichment of minerals is caused by the tectonic activation in Late Silurian,and the formation of gold deposit is caused by the granitic magmatism of Yanshanian.(3)The host structure is mainly the NWW-trending and northward-dipping thrust interlayer shear faults formed in the middle of Neoproterozoic;NE-trending thrust faults of Late Middle Triassic are the passages of ore fluid;the Paleogene EW-trending sinistral strike-slip faults can become ore-breaking structures;the thrust faults and strike-slip faults formed in Silurian,the Late Middle Triassic and Late Triassic may also cut or limit the development of NWW-trending veins.