赣东北金山金矿床构造变形特征及其区域构造意义

金山金矿产于赣东北断裂带的次级剪切带中,其成矿作用与韧性剪切带的动力变质作用密切相关。本文通过对矿区金矿体的地质特征和运动学特征的分析,认为金山金矿成矿期经历了两期韧性剪切作用,即早期由NNW向SSE的韧性推覆剪切,晚期沿NE方向的左行韧性走滑剪切,分别形成NW向超糜棱岩型矿体和NE方向石英脉型矿体,两期韧剪变形均发生在新元古代,对应于江南造山带在碰撞造山阶段和后造山伸展阶段的动力变质事件。成矿后,矿区先受到NW向的挤压应力场作用,形成NE走向的逆断层、NW走向的张性断层以及SN走向的左行压扭断层,之后转为NW向的拉张应力场,形成NE走向的正断层。金山金矿床的构造变形特征指示了赣东北断裂带活动的阶段性,赣东北地区在晋宁期经历了两期构造-岩浆-变质事件;加里东-印支期构造活动比较弱;燕山期本区构造-岩浆活动强烈,引起赣东北断裂带的再次活动。

Structural Deformation in the Jinshan Gold Deposit and its Implications to the Tectonic Evolution of the Northeastern Jiangxi Province

The Jinshan gold deposit is developed in the secondary shear zones of the Northeastern Jiangxi Province Fault Zone.Its ore formation is related to the dynamic metamorphism of these ductile shear belts.Based on field investigation and thin-section observation,two periods of ductile shearing deformation are recognized in the area:the early ductile thrust shearing resulted in the NW-trending ultramylonite-type gold ore-bodies which mainly occurred in the Wujiawu-Dawu section;while the late sinistral strike-slip ductile shearing produced the NE-trending quartz veins-type gold ore-bodies which mainly occurred in the Yangshan section.By analysis of the gold deposit formation age and the shear zone development age,it is suggested that both deformational events occurred during the Neoproterozoic,corresponding to two tectonic-magmatic-metamorphic events during the syn-and post-orogenic stages in the Jiangnan Orogen,respectively.After the ore formation,the Jinshan deposit underwent a NW-SE compression,producing NE-trending thrust faults,NW-trending normal faults and NS-trending sinistral transpressional faults,followed by a NW-SE extension,which resulted in NE-trending normal faults.These structural features in the Jinshan gold deposit probably corresponded to the episodic activities of the Northeastern Jiangxi Province Fault Zone,which experienced two tectonic-magmatic-metamorphic events in the Jinningian,a weak structural activity in the Caledonian and a strong re-activation in the Yanshanian.