柴北缘锡铁山铅锌矿床构造变形特征及其地质意义

Structural Characteristics and Ore-Controlling Law of Xitieshan Lead-Zinc Mine in North Qaidam Basin

锡铁山铅锌矿床位于柴达木盆地北缘,是我国西北地区重要的有色金属矿床之一。系统的地表调查和坑道编录表明,矿区不同岩石单元构造变形及力学特征不同,既有赋存于滩间山群绿片岩内部的早期深层次韧性-韧脆性变形构造,也有赋存于滩间山群原c岩组紫红色砂岩中的晚期浅层次脆性变形构造。结合区域上柴北缘造山带构造演化事件时间序列以及矿区构造特征的分析表明,韧性-韧脆性变形构造与陆-陆深俯冲碰撞造山作用及俯冲板片的折返有关,矿区浅层次脆性变形应形成于滩间山群原c岩组紫红色含砾砂页岩沉积之后。应力场恢复显示早期韧性-韧脆性变形构造形迹的主应力σ1方向主要为NE/NEE-SW/SWW方向,倾角为5°~60°,表明矿区早期变形阶段具有NE/NEE-SW/SWW向近水平挤压、左行走滑、斜向逆冲的性质;而晚期脆性变形恢复的主应力方向有2个,锡铁山沟地区表现为EW方向,无名沟-中间沟地区为NW-SE方向。对不同中段控矿断裂构造形成时的主应力状态恢复结果显示NW向断裂构造主应力σ1状态为NE-SW向,显示压扭性逆冲-走滑断层性质,而NE向断裂构造主应力σ1状态为NW-SE向,显示张扭性正-滑断层性质,分别为上述早期和晚期变形应力场的产物。锡铁山矿体分布受控于左行逆冲和左行滑覆构造运动,矿区北西部成矿较为有利,成矿后的NEE-EW向断层左行运动对矿体产生破坏作用,导致西侧矿体南移,东侧矿体北移。

The Xitieshan lead-zinc ore deposit,located in the north of Qaidam Basin,is one of the most important nonferrous metals deposits in Northwest China.Based on systematic field investigations and mine compiling,this research finds that the structural deformation and mechanical characteristics of different rock units in the mining area are different.The early deep ductile-ductile brittle deformation tectonic domain is represented in the greenschist of the Tanjianshan Group.The late shallow brittle deformation tectonic domain is represented in the purple red sandstone of the original C formation of Tanjianshan Group.Combining with the time series of tectonic evolution events and tectonic features of the orogenic belt in the northern margin of Qaidam orogenic belt,this research suggests that the deep-seated ductile-ductile brittle deformation is related to the compressional continental subduction and the roll-back of subducted plate and the shallow brittle deformation should form later than the pebbly-red shale of Tanjianshan Group.Stress field analysis and recovery suggests that the principal stress orientation of the early ductile-brittle ductile deformation structural track should be NE/NEE-SW/SWW and the angle of dip should between 5°-60°.The research reveals that the early deformation stage should have undergone NE/NEE-SW/SWW trend compression,left slip and oblique thrust.The principal stress orientations of the later brittle deformation of Xitieshan valley and the Wuming to Middle valley are different,trending EW and NW-SE,respectively.The principal stress recovery result of the ore-control fault from different depths shows that the principal stress orientation of NW-trend fault should be NE-SW,suggesting these faults should be shear thrust-strike slip fault.The principal stress orientation of NE-trend fault should be NW-SE,indicating these faults are transtensional normal-slip fault.They should be the products of the early to late deformation stress field.The orebody distributions of Xitieshan deposit are controlled by the sinistral thrust and slip tectonic movement.The favorable ore-forming area is the northwest.The sinistral movement of the post-mineralization NEE-EW trend fault destroyed the ore body,leading to the southward movement of western orebody and the northward movement of eastern orebody.