镁铁质岩浆周期性补给对云南普朗斑岩Cu-Au矿床的制约:能量约束下热力学模拟  

Constraints from Periodic Replenishment of Mafic Magma on Porphyry Mineralization in the Pulang Porphyry Cu-Au Deposit,Yunnan Province:Energy-constrained Thermodynamic Modeling

作　　者：张少颖 和文言[2,3] 肖仪武 ZHANG Shaoying;HE Wenyan;XIAO Yiwu(BGRIMM Technology Group,Beijing100160,China;Frontiers Science Center for Deep-time Digital Earth,China University of Geosciences,Beijing100083,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing100083,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,北京100083 [3]中国地质大学(北京)深时数字地球前沿科学中心,北京100083

出　　处：《现代地质》2024年第4期922-933,共12页Geoscience

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)

摘　　要：镁铁质岩浆周期性补给于硅酸质岩浆房是形成大型斑岩矿床的关键因素。本文以普朗超大型斑岩Cu-Au矿床为例,通过能量约束体系下的热力学方法模拟浅部硅酸质岩浆房中镁铁质岩浆周期性补给过程,定量评估该过程对形成大型斑岩矿床的控制作用。普朗矿床成矿前粗粒石英闪长玢岩(CQD)和成矿期石英二长斑岩(QMP)复式岩体中均普遍发育镁铁质暗色微粒包体(MMEs),岩相学特征显示斑岩体中角闪石和黑云母发育韵律环带结构或港湾状溶蚀结构以及针柱状磷灰石的存在均指示发生了镁铁质岩浆混合作用。与单一的分离结晶模型(FC)相比,多阶段岩浆补给-分离结晶模型(R3FC)显示,镁铁质岩浆的补给一方面会抑制长石的结晶,另一方面会促进钙铁镁和铁镁等多类型角闪石的形成,并大幅提前黑云母的结晶次序。以硅酸质岩浆物质摩尔分数变化与挥发分之间相关性为参照,获得的熔体H_(2) O、SCSS(硫化物饱和时硅酸盐熔体中的S含量)和Cl溶解度显示,镁铁质岩浆补给将在岩浆演化早期提高而在晚期降低残余熔体H_(2)O含量(0.16%、0.04%、-0.30%),持续提高熔体SCSS(78.74×10^(-6)、94.44×10^(-6)和137.88×10^(-6))和Cl溶解度(0.04%、0.10%和0.20%),但对Cu含量影响有限。结果表明,能量约束体系下的R3FC和FC热力学模型不仅能够合理解释普朗复式斑岩体矿物结构特征,也定量验证了镁铁质岩浆的补给对成矿岩体异常高H_(2) O、S和Cl含量的贡献。Periodic replenishment of mafic magma into silicic magma chambers is a critical factor in the forma-tion of large-scale porphyry deposits.Using the Pulang giant porphyry copper-gold deposit as an example,this study aims to quantitatively assess the significance of the formation of process porphyry deposits by constructing an energy-constrained thermodynamic model.Mafic microgranular enclaves(MMEs)are widely developed in both the pre-ore coarse-grained quartz diorite porphyry(CQD)and the syn-ore quartz monzonite porphyry(QMP)in the Pulang deposit.Petrological characteristics with rhythmic zoning and resorption textures of amphi-bole and biotite,and the presence of elongated apatife,both indicate the replenishment of mafic magma.Com-pared to the fractional crystallization model(FC),the multi-stage replenishment-fractional model(R3FC)indi-cates that the replenishment of mafic magma would suppress the crystallization of feldspar,and promote the for-mation of multiple types of amphiboles and significantly advance the crystallization time of magmatic biotite.Using the correlation between the molar fraction variations of siliceous magma materials and volatiles as a refer-ence,the results indicate that the replenishment of mafic magma would increase the H_(2)O content of the residual melt in the early stages and decrease it in the late stage of magma evolution(0.16%,0.04%,and-0.30%).It will continuously increase the SCSS(sulfur concentration at sulfide saturation in silicate melt;78.74×10^(-6),94.44×10^(-6) and 137.88×10^(-6)),and Cl solubility(0.04%,0.10%and 0.20%),but the effect on Cu solubility is limited.The results indicated that the R3FC and FC models under the energy-con-strained system can not only explain the petrological characteristics of the Pulang porphyry intrusions but also quantitatively verify the contribution of mafic magma replenishment to the abnormally high H_(2)O,S,and Cl con-tents in the ore-forming rocks.

关 键 词：岩浆混合 热力学模拟 挥发分 普朗斑岩Cu-Au矿床 

分 类 号：P611.5[天文地球—矿床学] P611.11[天文地球—地质学] P588.11