闪锌矿中单个流体包裹体成分LA-ICP-MS分析及其指示意义:以南岭新田岭钨矿床为例

LA-ICP-MS analysis of single fluid inclusions in sphalerite and its implications:A case study from Xintianling tungsten deposit in Nanling region,South China

单个流体包裹体成分LA-ICP-MS分析在精准示踪成矿物质来源和精细刻画成矿过程方面具有独特优势,但已有研究主要聚焦于透明的脉石矿物中的流体包裹体,对用于矿石矿物较少,二者之间有何异同特别是谁更能代表成矿流体组成目前研究薄弱。闪锌矿是岩浆热液矿床和MVT型矿床中常见的矿石矿物,其通常发育流体包裹体并在透射光下具有透明-半透明特征,是研究流体包裹体较为理想的矿石矿物。文章选择南岭新田岭钨矿硫化物阶段的闪锌矿及共生石英为研究对象,开展流体包裹体成分LA-ICP-MS对比分析。分析结果显示,闪锌矿和石英中的流体包裹体组成存在较大差异,前者异常富Cu、Ag和Sn等金属元素,后者富Li、B、Na、K、Rb、Sr、Cs和Pb等元素。结合闪锌矿本身微量元素特征,文章认为元素Cu、Ag和Sn的超常富集与其从寄主矿物扩散进入流体包裹体有关。在基于大离子亲石元素的流体成因类型判别图中,闪锌矿和石英中的流体包裹体组成均能有效示踪成矿流体来源,但后者示踪效果更好。总体而言,共生石英中流体包裹体组成可能更能代表成矿流体组成,闪锌矿因其莫氏硬度较低、金属元素含量高等原因,元素易发生后期扩散/改变,流体包裹体组成可能不能代表真实流体信息。在研究矿石矿物流体包裹体时,需谨慎对待某些元素的超常富集。综合研究脉石矿物流体包裹体和矿石矿物本身元素组成是成矿流体研究更准确的手段。

LA-ICP-MS(Laser ablation-inductively coupled plasma-mass spectrometry)analysis of single fluid inclu-sion has remarkable advantages in revealing the origin of ore-forming fluids and tracing the specific ore-forming processes,which,however,has been mainly conducted on transparent gangue minerals.The difference in fluid in-clusion compositions between gangue and ore minerals and which one can more effectively represent the oreforming fluids are poorly understood.Sphalerite is one of the most common ore minerals in magmatic-hydrother-mal and MVT deposits,which can host abundant fluid inclusions and be transparent or translucent under transparent light,becoming favorable for studying fluid inclusions.In this contribution,sphalerite and paragenetic quartz from the sulfide-stage veins in the Xintianling skarn W deposit,Nanling region were selected for studying the compositions of fluid inclusions by LA-ICP-MS.The results show that sphalerite and quartz have contrasted fluid inclusion compositions,of which the former is more enriched in Cu,Ag and Sn while the latter is enriched in Li,B,Na,K,Rb,Sr,Cs and Pb.Combined with the elemental compositions of host sphalerite,it is considered that the super-enrichment of Cu,Ag and Sn were related to elemental diffusion from the sphalerite into the fluid inclu-sions rather than indicating the real compositions of the fluids.In the genetic discrimination diagrams for differently-sourced fluids,the fluid inclusions of sphalerite and quartz both plot into the area of skarn-type deposits,well reflecting the origin of the studied fluids,but the latter has better indicative effects.In summary,the composi-tions of fluid inclusions in quartz can accurately reflect the information of the fluids,while some elements in sphalerite are artificial due to the elemental diffusion.Therefore,it should be cautious when studying the fluid in-clusion compositions in ore minerals.Integrated studies on fluid inclusions in gangue minerals and elemental compositions of ore minerals can be more effective to trace the ore-forming fluids and processes.