黑龙江铜山断裂的变形特征及铜山铜矿床蚀变带-矿体重建

Deformation characteristics of the Tongshan fault within Tongshan porphyry copper deposit,Heilongjiang Province,and restoration of alteration zones and orebodies

黑龙江铜山铜矿床系多宝山铜矿田的重要组成部分,它和多宝山矿床同是中亚造山带东段最古老的斑岩铜矿床(奥陶纪)。铜山断裂为铜山斑岩铜矿床内最为重要的一条成矿后断裂,它截切矿体和蚀变带,因而导致矿化中心、深部找矿方向不明。现阶段的研究对其运动学特征还存有较大争议,缺乏对该带变形特征与性质的细致观察与鉴别。据此,本文开展详细地野外及室内研究工作,取得如下新认识:1)铜山断裂为近东西走向的压扭性断裂,最典型的构造几何学特征为发育北东-北东东走向劈理、构造透镜体、以及岩脉及热液脉扭曲现象。2)断裂带内石英、黄铜矿、黄铁矿、闪锌矿的镜下变形特征和石英C轴组构特征显示低温变形条件,依据矿物和岩石变形特点判断铜山断裂主体为脆性断裂。3)构造解析表明铜山断裂运动学特征为:上盘由南东向北西方向斜向逆冲。综合断裂上、下盘地质体界线、蚀变和脉系分布特征等,判断上盘相对下盘大致沿NW320°方向水平移动距离700~800m,垂向抬升550~700m,错开蚀变外带(青磐岩化带、石英-绢云母-伊利石-绿泥石化带)和矿化带。4)铜山断裂的次级断裂截切了中晚三叠世白云母花岗岩,推测铜山断裂活动时限晚于中晚三叠世。5)复原铜山断裂上盘和下盘的空间位置至铜山断层活动前,重建铜山铜矿床蚀变带-矿化体,初步判断铜山断裂活动前铜山矿床为纺锤形态。根据重建后矿化和蚀变的分布规律推断下盘Ⅲ号矿体的南侧位置应有尚未发现的成矿斑岩和矿体,为深部找矿提供了依据。

The Tongshan copper deposit is situated in the Duobaoshan copper ore field,Heilongjiang Province. It and Duobaoshan porphyry copper deposit are the oldest（ Ordovician） porphyry copper deposits within the eastern part of the Central Asian Orogenic Belt. The Tongshan fault,the most important post-mineralization fault in the Tongshan copper deposit,cuts orebodies and alteration zones,which leads to mineralized center unknown and direction for further prospecting unclear. Its current kinematic characteristics is still under controversial,moreover,detailed reporting involving deformation feature descriptions is lacking. This paper carried out both detailed indoor and outdoor studies,and several understandings were accomplished： 1） The Tongshan fault,with a nearly EW strike,belongs to a compression-shear fault. Its most typical geometric feature is the development of NEE-strike cleavages,structural lenses and twisted dykes and hydrothermal veins. 2） Microscopic deformation features of quartz,pyrite,chalcopyrite and sphalerite,together with quartz fabric features analyzed by EBSD,indicate low temperature deformation condition. The Tongshan fault is considered to be brittle fault as a whole by the deformation characteristics of minerals and rocks. 3） Structural analysis indicates that relative to the footwall,the hanging wall slipped through SE to NW. The fault displacement is estimated by matching geological boundaries within the hanging wall and footwall and studying the distribution regularity of alteration zones and hydrothermal veins of the Tongshan area. The hanging wall was horizontally offset with a distance of 700 ~ 800 m along direction of around NW320°,and was lifted 550 ~ 700 m vertically. As a result,outer alteration zones and mineralized zones were cut off. 4） A secondary fault of the Tongshan fault cuts through the Late-Middle Triassic muscovite granite,so the activity time of the Tongshan fault was later than the Late-Middle Triassic.5） The distribution of alteration zones and orebodies of the Tongshan porphyry deposit is restorated by displacement recovery of the Tongshan fault,which shows that the Tongshan deposit was in spindle morphology before the Tongshan fault activated. It can be inferred from the distribution regularity of mineralization and alteration,that the porphyry,related to mineralization,and undiscovered orebodies may exist in the south of orebody Ⅲ in the footwall of the Tongshan fault.