韧性剪切带型金矿三阶段构造成矿模式——以广东河台金矿床为例

Three-stage Structural Mineralization Model for Ductile Shear Zone Related Gold Deposits: A Case Study of the Hetai Gold Deposit,Guangdong,South China

基于对粤西河台韧性剪切带型金矿的构造解析,本文提出了韧性剪切带型金矿成矿的一种新构造模式,即:在大型韧性剪切带运动指向的前锋,当扩展弱化而出现分支糜棱岩带时,就会在韧性剪切带中出现由强变形带包绕的构造透镜体弱变形域。由于透镜体域中央岩石处于脆性环境,在变形分解过程中,强变形带中含金流体会通过岩石中的微破裂渗透到相对低压的弱变形构造透镜体域中央,并通过构造泵吸机制在其中产生周期性的液压致裂与裂开‒愈合,这为在韧性剪切阶段活动的金提供了一个理想的沉淀场所。上述构造机制很好地解释了河台金矿床中透镜状特富矿体的成因。河台含金韧性剪切带在韧性、韧‒脆性及脆性阶段在同位空间并列与叠加了不同类型金矿体,从早到晚分别形成细脉‒浸染型、石英脉型与破碎带蚀变岩型金矿体。河台韧性剪切带群为粤西深层次逆冲推覆构造前缘陡坡带的分支糜棱岩带,其韧性剪切阶段为左旋平‒逆剪切,韧‒脆性与脆性阶段转变为右旋平‒逆剪切,并依此讨论了金矿体的侧伏规律及隐伏矿体的预测方向。

Based on structural analysis of the ductile shear zone related gold deposits in Hetai,western Guangdong,South China,a new structural mineralization model for ductile-shear zone related gold deposits is proposed.When the expansion abates and a branch mylonite zone appears at the progression front of a large ductile shear zone,a weak deformation domain of tectonic lens surrounded by strong deformation will appear in the ductile shear zone.Since the rock in the center of the tectonic lens is in brittle environment,during the process of deformation partitioning,the auriferous fluid in the strong deformed belts will penetrate through the micro-fracture in the rock and reach the center of the tectonic lens which is characterized by relatively low pressure.Furthermore,the weak deformation domain is an ideal precipitating site for auriferous fluid in the ductile-shear stage,where tectonic pumping triggered the periodic hydrofracturing and crack-healing.This structural mechanism can explain the genesis of the lenticular extra-rich ore-bodies in the Hetai gold deposit.In the ductile,ductile-brittle and brittle stages,different types of gold ore bodies are juxtaposed and superposed in the same space,forming veinlet-disseminated type,quartz-vein type,and altered-rock type orebodies from the early to the late stages in the Hetai gold-bearing ductile shear zone,respectively.It is believed that a series of ductile shear zones in Hetai belong to the branch mylonite belts of the steep slope zone in the western Guangdong deep level thrust nappe structure,which is characterized by left-lateral slip-thrust shearing during the ductile shear stage,and converted to the right-lateral slip-thrust shearing during the ductile-brittle and brittle shear stages.In this paper,the lateral trending of the orebodies and the prediction of concealed orebodies are further discussed.