Research On Preparation Methods Of Sulfide Reference Materials For In Situ PGEs And S-Pb Isotope Analyses

The platinum group elements?PGEs?and sulfur?S?-lead?Pb?isotopes in sulfide minerals are important geochemical tracers in the earth sciences.However,in situ analyses of PGEs and S-Pb isotope compositions in natural sulfides using laser-ablation?multi-collector?inductively coupled plasma mass spectrometry?LA-?MC?-ICP-MS?are limited by a lack of suitable sulfide reference materials for a long time.A new synthetic method to produce sulfide reference materials was reported in this study.The hydrothermal synthesis technique was used to prepare the initial nano-FeS₂particles.Trace elements were added to the reaction medium and then entered into the lattice of the nano-FeS₂ particles during the crystal growth process,therefore avoid the elements volatilization and the nugget effect during melting process.The powder-pressed pellets prepared by the nano-FeS₂ particles?500-600 nm?exhibited excellent cohesion and were suitable for laser ablation microanalysis.Using this method,we synthesized four sulfide reference materials with different mass fractions of trace elements?10th-01,11th-01,11th-02 and 11th-03?.The homogeneity of trace elements and S-Pb isotope were verified by LA-?MC?-ICP-MS,while the composition of S-Pb isotope were determined by Stable Isotope Ratio Mass Spectrometry?IR-MS?and SN-MC-ICP-MS,respectively.Repeated measurements using LA-ICP-MS demonstrated good homogeneity for most of the trace elements?RSD<3%for PGEs,Au and Pb?,except Os?4.43%?,Ir?3.21%?and Re?5.87%?in 10th-01 and Ru?5.5%?,Pd?3.76%?in 11th-03.The results also indicate that these samples are homogeneous in S isotope ratios?0.11-0.23‰,2SD?.In addition,in situ analytical results of?³⁴S_V-CDT in four synthetic sulfide reference materials are consistent with the values obtained by IR-MS.In the Pb isotope analysis,the external reproducibilities?RSD,k=2%?of Pb are were 0.06%,0.05%and 0.05%for ²⁰⁸Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and²⁰⁶Pb/²⁰⁴Pb,while the external reproducibilities of 11th-01 are ²⁰⁸Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb were 0.17%,0.16%and 0.15%,respectively.Compared with 10th-01,the poor reproducibility of ^20xPb/²⁰⁴Pb in 11th-01 was attributed to the lower mass fraction of Pb(72.2 mg g^-1),which resulted in a lower ²⁰⁴Pb signal intensity.Four sulfide reference materials were used as external standards to certify two commercial sulfide standards,MASS-1 and STDGL3#35.Accurate results from the analysis for trace elements were obtained,indicating that the synthesized sulfide reference materials are appropriate matrix-matched materials available for calibration in sulfides using LA-ICP-MS.The results also indicated that the hydrothermal synthesis of the nanoparticles can serve as a potentially effective approach for the preparation of microanalysis reference materials.It is noteworthy that when undertaking the hydrothermal synthesis of multielement reference materials,one should carefully understand the partition coefficients of the elements in different materials.The sulfide reference materials prepared by this research were used as external standard combine with LA-ICP-MS to quantitative analysis PGEs in geological samples from Jinchuan Ni-Cu-?PGE?sulfide deposit.Compared with the previous literatures which were conducted on SN-ICP-MS by fire assay and tellurium coprecipitation,in situ micro-analysis not only simplified experimental process,but also can reveal the exist form of PGEs in pyrrhotite and pentlandite from the micro-scale.The analysis results indicate the sulfide reference materials and analysis method in this research can meet the needs of practical geological research.