| Sulfides are not only the primary mineral type in nature but also the significant carriers for many critical metals.S-Fe-Cu are the common elements in sulfides and the change of their isotopic compositions can provide effective evidence for determining the source of ore-forming materials,elucidating the enrichment mechanism of critical metals,discussing the ore-forming processes and predicting the prospecting potential for sulfide deposits.Laser ablation(multi-collector)inductively coupled plasma mass spectrometry(LA(MC)-ICP-MS)can achieve qualitative analysis in micron scale and become an important technique in analytical geochemistry.However,matrix effect is a great challenge in LA-(MC)-ICP-MS technique for high-precision analysis.Although matrix matching reference materials with homogenous chemical composition are the best choice to overcome this problem.But the complex origins and the large quantity of natural minerals make it impossible to meet the actual analysis needs just by looking for natural samples with homogenous composition as reference materials.Therefore,it is very urgently to seek a universal and artificial method to prepare reference materials and develop non-matrix matching analyses methods.In this research,we compared different technologies to solidify ultra-fine powder,proposed a propagable method for in situ reference material preparation and prepared the matrix-matched sulfides reference materials for in situ S-Fe-Cu isotopic analysis.At the same time,we established the(non-)matrix matching method for high precision FeCu isotopic analysis and developed a new model for laser ablation analysis with high frequency and short time period strategy.Finally,the isotopic compositions of the Longqiao skarn iron deposit,the La’erma gold deposit and the Chang’e-5 lunar samples were studied based on the reference materials and analyses methods in this research,which provides effective in-situ information for revealing the evolution of related geological processes.1.Development of high-quality sulfides S-Fe-Cu isotope reference materials for laser ablation analysis(artificial and natural).In this thesis,it is the first time that combine ultra-fine powder with plasma-activated sintering(PAS)technique for the preparation of sulfides S-Fe-Cu isotope reference materials.Initial pyrite and chalcopyrite minerals with extremely inhomogeneity composition were ground to ultra-fine powder(d90<4μm)and realized isotopic homogenization.Then we investigated the feasibility of synthesizing pyrite and chalcopyrite powder by the pressed powder pellets,high-temperature melting(HTM)and PAS technology.We studied the solidified effect by comparing surface morphology,laser ablation behavior and S-Fe isotopic composition in different samples.After discussed the optimal range of solidify parameters of PAS technology we prepared the sulfides S-Fe-Cu isotopic reference materials successfully(the series of PAS-Py600 and PAS-Cpy).It should be note that the PAS technology can not only remove impurities and gases adsorbed on the surface of particles by discharge and activation under the action of unique pulse current,but also avoid the phase change and "nugget effect" of sulfide in the process of consolidation.The results show that the combination of ultrafine powder with PAS technology is an ideal solution for the synthesis of in situ reference materials,and this method can be extended to the preparation of trace elements or isotope reference materials of other matrix components.In addition,we obtained a batch of natural chalcopyrite and pyrrhotite samples with relatively homogenous S-Fe-Cu isotopic composition(the composition of S and Fe-Cu isotope are better than 0.36%o(2SD)and 0.19%o(2SD),respectively)after a lot of trial work and long-term homogenization and stability verification experiments.These samples are abundant(>8 kg)and can be provided to the field of analytical geochemistry.2.Research on in situ(non-)matrix matching method for high-precision Fe-Cu isotopic analysis.The fractionation in laser ablation and mass discrimination effect in mass spectrometer are important factors that affecting the accurate determination of LA(MC)-ICP-MS.Here,we compared the difference of laser system and the plasma mode and discussed their influences on Fe-Cu(non-)matrix matching analysis.The stronger thermal effect in the nanosecond laser caused the worser fractionation,which makes the stricter instrument condition during Fe-Cu isotope analysis with high precision requirement(the deviation up to～0.26‰ at the condition of～3.5)cm-2).The femtosecond laser exhibits a larger energy density tolerance range than nanosecond laser,which may also be related to the small thermal effect of femtosecond laser.At the same time,we use fs-LA-MC-ICP-MS performed under the wet"plasma mode,the accurate results can be achieved during non-matrix matching analysis in pure iron international standard sample IRMM-014(or IRMM-524A)calibrate against pyrite,chalcopyrite,pyrrhotite and pentlandite for Fe isotope analysis and the pure copper GBW02141 calibrate chalcopyrite samples for Cu isotope,respectively.We believe that the non-matrix matching analysis may benefit from the"stoichiometric mode" of femtosecond,which effectively inhibits isotope fractionation during laser ablation.Meanwhile,the "wet" plasma mode can improve the tolerance of ICP to different matrix samples,thus providing the possibility of non-matrix matching correction.The results show that femtosecond laser combined with "wet" plasma has an indispensable advantage in high-precision non-matrix matching analysis of isotopes.3.A new analytical mode and application of the LA-(MC)-ICP-MS in the earth sciences.Higher spatial resolution and more efficient and accurate analysis are always the development direction and challenge of micro analytical technology.Usually,the EPMA or SIMS are used to analyze the element content or isotopic composition at high spatial resolution(<10 μm).Considering the potential down-hole fractionation and the insufficient detection of weak signals during the LA-(MC)-ICP-MS high spatial resolution analysis.Here,we propose a new laser analysis strategy of high frequency and short time laser ablation combined with linear regression calibration for data reduction.Using the new analysis model,the rapid and efficient analysis of multielement content(10 μm),U-Pb dating(analysis time of single point about 15 seconds)and Sr or Hf isotope analysis(more than 120 points per hour)were achieved.At the same time,a breakthrough in S isotopic composition analysis with high resolution(～8μm)was achieved by using the new analysis model(the spatial resolution of LA-MCICP-MS for S isotope analysis are usually larger than 20μm).These results show that the new laser analysis model has a good application prospect in the field of earth science. |
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