斑岩铜矿蚀变分带与成矿机制:玉龙矿床水-岩反应热力学平衡模拟例析  

Alteration zonation and metallogenic mechanism of porphyry copper deposits:A case study of thermodynamic equilibrium simulation of fluid-rock interactions in Yulong deposit

作　　者：张少颖 和文言[2] 高雪[2] 田成华 肖仪武 ZHANG ShaoYing;HE WenYan;GAO Xue;TIAN ChengHua;XIAO YiWu(BGRIMM Technology Group,Beijing 100160,China;Frontiers Science Center for Deep-time Digital Earth,State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]矿冶科技集团有限公司,北京100160 [2]中国地质大学(北京)地质过程与矿产资源国家重点实验室,深时数字地球前沿科学中心,北京100083

出　　处：《岩石学报》2024年第6期1837-1852,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42302082、42372098);国家重点研发计划项目(2022YFF0800902);高等学校学科创新引智计划(BP0719021);中国地质大学地质过程与矿产资源国家重点实验室专项基金(MSFGPMR201804);深时数字地球前沿科学中心“深时数字地球”中央高校科技领军人才团队项目(2652023001)联合资助.

摘　　要：蚀变分带和成矿机制的准确厘定是建立斑岩成矿模型与找矿预测的关键。本文以新生代金沙江-哀牢山成矿带的玉龙斑岩铜矿为例,通过质量作用定律(LMA)和吉布斯自由能最小化模型(GEM),构建含矿热液与斑岩侵入体的pH-f O 2相图和动态传输模型,以揭示蚀变分带成因和金属成矿机制。LMA与GEM结果显示初始成矿流体pH值为4.7,logf_(O2)=-23.0(ΔFMQ=+2.7),且溶解Cu含量为1138×10^(-6),Mo为1.2×10^(-6)。研究表明,当该酸性及强氧化性流体流入二长花岗斑岩体时,在温度为450~360℃范围内,代表钾硅酸盐化蚀变的钾长石、黑云母、硬石膏、赤铁矿和磁铁矿的矿物逐渐沉淀,且与钾硅酸盐化蚀变相关流体具有较高pH值(5.0~7.0)和氧逸度(ΔFMQ=+2.9~+3.6)特征;当温度在360~320℃范围时,代表青磐岩化蚀变阶段的典型矿物如绿帘石、铁绿泥石和斜绿泥石等逐渐形成,流体pH值(5.0~6.4)和氧逸度(ΔFMQ=+1.1)均有所下降;当温度进一步从320℃下降到200℃时,流体pH值(5.0~5.7)进一步小幅下降,而氧逸度则(ΔFMQ=+1.7)略有回升,在此期间,绢云母和方解石等开始沉淀并形成典型的绢英岩化蚀变。此外,以HMoO_(4)^(-)和MoO_(4)^(2-)为载体的Mo在狭窄高温区间(450~370℃)内沉淀,而以CuCl(CuCl_(4)^(3-)、CuCl_(2)^(-)、CuCl)为主要载体的Cu则在在中、高温(450~300℃)范围中沉淀。通过利用LMA反演及GEM正演相结合定量化地刻画了玉龙斑岩铜矿水岩反应过程,由此揭示了斑岩矿床蚀变分带是逐渐冷却的单一岩浆热液与斑岩体不断反应的结果,且不同温度窗口对应着钾硅酸盐化(450~360℃)、青磐岩化(360~320℃)和绢英岩化(320~200℃)蚀变矿物的形成,故含矿流体温度的快速下降可能是玉龙铜矿蚀变叠加的重要因素。此外,Cu、Mo络合离子溶解度对温度变化的差异响应,导致了Mo矿化主要发育于靠近斑岩体的高温区域,而Cu则以网脉状-浸染状叠加到Mo矿化�Accurate delineation of alteration zones and ore-forming mechanisms is crucial for establishing porphyry metallogenic models and ore prospecting prediction.Taking the Yulong porphyry copper deposit in the Cenozoic Jinshajiang-Ailaoshan metallogenic belt as a study case,this paper employs the law of mass action(LMA)and the Gibbs free energy minimization(GEM)model to construct the pH-f O 2 phase diagram and dynamic transport model for ore-bearing hydrothermal fluid and porphyry intrusion to reveal the genesis of alteration zoning and metal mineralization of the deposit.The modeled results indicate an initial ore-forming fluid pH of 4.7,logf_(O2)=-23.0(ΔFMQ=+2.7),with dissolved Cu and Mo contents of 1138×10^(-6) and 1.2×10^(-6).When the acidic and oxidized fluid infiltrates the monzonite granite porphyry within the temperature range of 450℃to 360℃,minerals associated with such potassic alterations as K-feldspar,biotite,anhydrite,hematite and magnetite gradually precipitate;and the fluids related to potassic alteration exhibit higher pH values(5.0~7.0)and oxygen fugacity(ΔFMQ=+2.9~+3.6)during this process.While at temperatures ranging from 360℃to 320℃,typical minerals representing the propylitic alteration stage,such as actinolite,chlorite and epidote,gradually form;and both of the fluid pH values(5.0 to 6.4)and oxygen fugacity(ΔFMQ=+1.1)decrease during this stage.As the temperature further decreases from 320℃ to 200℃,the fluid pH values(5.0~5.7)experience a slight additional decline,while the oxygen fugacity shows a slight increase(ΔFMQ=+1.7).During this period,minerals such as sericite and calcite begin to precipitate,marking the onset of typical phyllic alteration.Additionally,molybdenum(Mo),carried by HMoO-4 and MoO 2-4,precipitates in a narrow high-temperature range(450~370℃);while copper(Cu),primarily carried by CuCl(CuCl_(4)^(3-),CuCl_(2)^(-),CuCl),precipitates in the mid to high-temperature range(450~300℃).By employing the LMA inverse modeling and GEM forward modeling,this study quantita

关 键 词：水岩反应 热力学平衡模拟 玉龙斑岩铜矿 pH-f O 2相图 动态传输模型 

分 类 号：P611[天文地球—矿床学] P618.41[天文地球—地质学]