广西大厂矿田高峰锡多金属矿床花岗斑岩白云母化学特征及其地质意义  

Chemical variation and significance of white mica in granite porphyry from Gaofeng tin-polymetallic deposit in Dachang ore field,Guangxi

作　　者：王葆华[1,2] 胡荣国[1,2] 司建涛[3] 赵义来[1,2] 刘希军[1,2] 李赛赛[1,2] 沙培哲 WANG Bao-hua;HU Rong-guo;SI Jian-tao;ZHAO Yi-lai;LIU Xi-jun;LI Sai-sai;SHA Pei-zhe(College of Earth Sciences,Guilin University of Technology,Guilin 541006,China;Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541006,China;No.2 Institute of Geological&Mineral Resource Survey of Henan,Zhengzhou 450001,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541006 [2]桂林理工大学广西隐伏金属矿产勘查重点实验室,广西桂林541006 [3]河南省地矿局第二地质矿产调查院,郑州450001

出　　处：《桂林理工大学学报》2021年第3期471-483,共13页Journal of Guilin University of Technology

基　　金：国家自然科学基金项目(42073049,41703054);广西自然科学基金项目(2020GXNSFAA297049,2020GXNSFAA297091,2017GXNSFBA198164,2016GXNSFCA380022)。

摘　　要：广西高峰矿床位于大厂矿田的南端,区内出露的岩浆岩主要为呈南北走向,并对早期形成的矿体产生了叠加改造作用的花岗斑岩岩墙。为探讨花岗斑岩在岩浆冷却结晶时及岩浆期后热液流体之来源和相关交代作用,对花岗斑岩中以未矿化斑晶(WM-1)、包体(WM-2)、矿化斑晶(WM-3)以及基质(WM-4)4种形式产出的白云母进行了详细的电子探针分析。结果显示:花岗斑岩中的WM-1和WM-2类型云母属于铁锂云母和富锂多硅白云母,WM-1白云母可能是熔体冷却结晶过程中,在流体的作用下钾长石和铝硅酸盐发生反应所形成的产物,而WM-2白云母则为WM-1白云母其后发生脱水熔融作用过程中的残留物,两者都属于广义上的原生白云母;WM-3和WM-4则属于普通白云母和多硅白云母,为后期热液成因的次生白云母。与原生白云母相比,次生白云母具有相对富硅、镁,贫铁、钠、钛、铝、锂和氟的特点,暗示在花岗斑岩上侵结晶的过程中,不同阶段形成的原生白云母和次生白云母其共存的流体在来源和成分上有显著的差异性,热液流体存在不连续演化的现象。早期流体相对富Fe、Ti、Li和F,其来源很可能是矿物分离结晶过程中由于熔体中水含量增加而压力的降低,导致岩浆中的水达到饱和而出溶流体;而晚期热液流体相对富含CO_(2)、MgO和SiO_(2),来源于浅部地壳或地表大气降水,携带了大量的CO_(2),并溶解和萃取了围岩中的部分Mg和Si之后,沿早期形成的控矿构造进入深部与后期填充的花岗斑岩脉发生岩水反应,导致白云母发生绿鳞石和契尔马克替代:R^(3+)+Al^(Ⅳ)=Si+R^(2+)(R^(3+)=Al,Fe;R^(2+)=Mg,Mn),使其转化为普通白云母+绿鳞石的混溶体。Gaofeng ore deposit is located in the southern part of Dachang tin-polymetallic ore field,adjacent to the axis of the Dachang anticline,Guangxi.The granite porphyry dikes is one of the main intrusive rocks in Gaofeng region,which are controlled by nearly SN extensional tectonic.Previous studies show that the granite porphyry dikes are spatially and temporally associating with mineralization.To further evaluate the fluid origin of granite porphyry during magmatic cooling and crystallization,as well as later accociated metasomatism of postmagmatic hydrothermal events,detailed electron microprobe analyses are performed on four types of white mica on the basis of textural criteria and compositions:occurring as unmineralized phenocrysts(WM-1),inclusions enclosed in quartz(WM-2),mineralized phenocrysts(WM-3)and matrix(WM-4)as one of rock-forming minerals.According to the textural evidence and chemical compositions,types WM-1 and WM-2 belong to primary white mica that formed during the cooling and crystallization process of granite melt,which are classified as zinnwaldite and Li-phengite.More concretely,type WM-1 may be the production of the reaction between Kfeldspar,aluminosilicate and liquid fluid during melt cooling and crystallization.Type WM-2 is the subsequent dehydration and melt residue of WM-1.In contrast,mineralized phenocrysts and matrix white micas are classified as muscovite and phengite,which belong to secondary white mica formed during postmagmatic hydrothermal fluids rock interaction or hydrothermal alteration processes.Secondary white micas contain higher MgO and SiO_(2) but lower FeO_(t),Na_(2)O,TiO_(2),Al_(2)O_(3) Li_(2)O and F than primary white micas,indicating that the coexisting magmatic origin or hydrothermal origin fluids might be accociated with inclusion,unmineralized phenocrysty,mineralized phenocrysty and matrix white micas formation are not continuous episode,but differences in composition.The early fluids are relatively rich in Fe,Ti,Li and F.Their origin are probably the exsolution fluid

关 键 词：高峰矿床 花岗斑岩 白云母 热液流体 锡多金属矿床 

分 类 号：P597.4[天文地球—地球化学]