湖南铲子坪-大坪金矿区变形序列及控矿构造

Deformation sequences and ore-controlling structures of the Chanziping–Daping gold mining area in Hunan Province,China

湖南铲子坪-大坪金矿区位于雪峰弧形构造带西南段,金矿脉主要呈北西西向—北北西向,其次为北北东向。尽管现有研究表明北东向断裂为导矿和容矿构造、北西向断裂为容矿构造,但对控矿断裂的性质和形成时代缺乏明确可靠的认识。文章根据对地表露头构造和矿化蚀变的观测、解析,结合区域构造特征、构造演化和测年资料等,厘定了铲子坪-大坪金矿区构造变形序列及其时代背景,确定了控矿构造类型及其属性。研究认为,研究区自早至晚经历了6期主要变形事件:志留纪晚期受到北西西向挤压,形成北北东走向的褶皱、板劈理和脆韧性剪切带;中三叠世晚期受到北北西向挤压,形成北西西向—北西向右行走滑断裂和剪切破裂、南北向左行剪切破裂、北西向和北北东向共轭剪切破裂、北东东向的逆断裂和叠加褶皱;晚三叠世早期受到南北向挤压,形成北西向—北北西向右行走滑断裂和剪切破裂、北北东向—北东向左行剪切破裂和断裂、北东东向左行膝折构造;中侏罗世晚期受到北西西—近东西向挤压,形成南北向—北北东向逆断裂、北西向—北西西向左行剪切破裂、北东向右行逆冲剪切破裂、北北东向—近南北向的破劈理、面理褶皱和石香肠;古近纪中晚期受到北东向挤压,形成北北东向—南北向右行剪切破裂和断裂、北东东向左行剪切破裂、北西向的逆断裂和破劈理;古近纪晚期—新近纪初期受到北西向挤压,形成北东向逆冲剪切破裂、北西西向右行剪切破裂。研究区北北东向矿脉形成于志留纪晚期和晚三叠世,北西西向—北北西向矿脉形成于晚三叠世晚期。志留纪晚期成矿与断裂运动导致的构造活化作用有关,晚三叠世晚期成矿与同期大规模花岗质岩浆活动有关。导矿构造主要为志留纪晚期北西西向挤压形成的北北东向大断裂即脆韧性剪切带。主要容矿构造为中三叠世晚期北北西向挤压形成的北西西向—北西向右行走滑断裂、晚三叠世早期南北向挤压形成的北西向—北北西向右行走滑断裂,其次为志留纪晚期北西西向挤压形成的北北东向脆韧性剪切带。

The Chanziping–Daping gold deposit area is located in the southwest section of the Xuefeng arc-shaped structural belt,with mainly NWW-NNW-trending and secondary NNE-trending Au veins.Existing studies proposed the NE-trending faults as the ore-passing and ore-bearing structures and the NW-trending faults as the ore-bearing structures.However,there is no clear and reliable understanding of the nature and age of ore-controlling faults.Given this,the authors carried out detailed field observation and analysis of surface outcrop structures and mineralization alteration,and then combined with regional structural characteristics,tectonic evolutions,and dating data,determined the deformation sequences and their ages in the Chanziping–Daping gold deposit area,and determined the types and attributes of ore-controlling structures.The study suggests that the study area experienced six main deformation events from early to late:Regional NWW compression during the late Silurian which resulted in the NNE-trending folds,slaty cleavages and brittle-ductile shear zones;Regional NNW compression in the late Middle Triassic which caused the formation of NWW-to-NW-trending dextral strike-slip faults and shear fractures,NS-trending sinistral shear fractures,NW-and NNE-trending conjugate shear fractures,NEE-trending thrust faults and superimposed folds;Regional NS compression in the early Late Triassic which led to the development of NW-to-NNW-trending dextral strike-slip faults and shear fractures,NNE-to-NE-trending sinistral shear fractures and faults,and NEE-trending sinistral kinks;Regional NWW-to-near EW-compression in the late Middle Jurassic which resulted in the NS-to-NNE-trending thrust faults,NW-to-NWW-trending sinistral shear fractures,NE-trending dextral thrust shear fracture,NNE-to-near NS-trending fracture cleavages,foliation folds and boudins;Regional NE compression in the middle-late Paleogene which led to the development of NNE-to-NS-trending dextral shear fractures and faults,NEE-trending sinistral shear fractures,NW-trending thrust faults and fracture cleavages;Regional NW compression during the late Paleogene to early Neogene which led to the formation of NE-trending thrust shear fractures and NWW-trending dextral shear fractures.The NNE-trending mineral veins in the study area formed in the late Silurian and the late Late Triassic,and the NWW-to-NNW-trending mineral veins formed in the late Late Triassic.The mineralization in the late Silurian was associated with the tectonic activation caused by the fault movement,and the mineralization in the late Late Triassic was related to large-scale granitic magmatism in the same period.The ore-passing structures are mainly the large NNE-trending faults,namely the brittle-ductile shear zones formed by NWW-compression in the late Silurian.The main ore-bearing structures are the NWW-to-NW-trending dextral strike-slip faults formed by NNW compression in the late Middle Triassic,NW-to-NNW-trending dextral strike-slip faults formed by NS compression in the early Late Triassic,with next NNE-trending brittle-ductile shear zones formed by NWW compression in the late Silurian.