Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) elemental mapping and its applications in ore geology

With the development of two-dimensional trace element mapping by laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS), it is now possible to reveal in much greater detail any compositional interior textures of the pyrites, thus permitting the investigation of the history of pyrite crystals and providing new insight into the genesis and evolution of mineralisation. Exploiting the advantages of high spatial resolution, low detection limits, and capability of full quantification, LA-ICP-MS elemental mapping is being widely applied to imaging sulphides from various types of deposits. In this study, we applied the LA-ICP-MS elemental mapping technique on pyrites from different types of deposits from China and Canada, for the purpose of monitoring the changes of physio-chemical condition, defining ore genesis, and revealing the distribution patterns of precious metals. The interior compositional textures of pyrites show that the mineralization system of the Bayinwula roll-front U deposit in Inner Mongolia was open and continuously affected by the re-charge of oxidized groundwater, along with a periodic change of pH and Eh that affected the activities of sulphate bacteria and the associated U mineralization. The trace element maps of pyrites from the Zhenzigou Pb-Zn deposit in Liaoning Province indicate that several episodes of fluids were involved and responsible for the mineralisation, namely, an early stage of syn-sedimentary origin and a late hydrothermal mineralisation related to the Yanshanian magmatic activity. The trace element distribution patterns of pyrites from the Palaeoproterozoic placer Au deposit in Canada showed that the subeuhedral-euhedral pyrite, which is a dominant type of pyrite in the conglomerates, is detrital origin and later modified by hydrothermal (or metamorphic) fluids, and Au is mostly associated with the detrital pyrite grains/cores, and disseminated in the porosity on the surface.