Change of surface oxide layer of pyrite samples prepared by resin embedding polishing method after long-term placement and its effect on TOF-SIMS analysis

In the micro-in-situ analysis of geochemical trace elements in gold-bearing pyrite resin target by TOF-SIMS, it is found that the signal of 56Fe32S−in negative ion mode is obviously weaker than that of 56Fe16O2−, and this phenomenon occurs in several pyrite particles on the same resin target. In this study, the surface of natural pyrite was characterized by TOF-SIMS, and the effect of resin embedding grinding and polishing on the surface of ore deposit and TOF-SIMS test was investigated. The results show that the FexSy− characteristic ion peaks of the surface mass spectra are disturbed by oxidation peaks such as FexOz− and FexSmOn, especially the intensity of FeS− is much lower than that of FeO2−. In addition, the surface oxidation rate of pyrite under different sample preparation methods was also studied. The cracks and grooves on the surface of cleavage pyrite can accelerate the surface oxidation. The resin target preparation method used for individual pyrite crystals can obtain a perfect surface that meets the surface roughness of TOF-SIMS. At the same time, the existence of oxide layer can slow down the oxidation rate of the surface to some extent. For in-situ pyrite wrapped in rock, the resin target sample preparation method is difficult to flatten the surface, and the uneven surface will lead to faster oxidation rate and thicker oxidation layer, thus interfering with data calibration. This shows that in the TOF-SIMS analysis of geological samples, attention should be paid to the removal of the surface oxide layer, especially the oxidizable mineral resin target samples, and the sample preparation methods which can reduce the surface fluctuation of mineral samples should be explored.