Determination of Composition of Pyrite in the Baishantang Copper Deposit by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry and Electron Microprobe

Determination of trace elements in analyzed mineral phase by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is a new in situ technique for mineral phase analyses. As an important mineral in porphyry copper deposits, the major and trace elements of pyrite can provide important information for the ore-forming process. A method for determination of the trace elements in pyrite by LA-ICP-MS and major elements by Electron Microprobe was developed and has been applied to the Baishantang porphyry copper ore district. For the LA-ICP-MS experiment, the laser beam is 60 μm, the carrier gas is helium, the repetition frequency is 5 Hz, the laser energy is 6 J/cm², and the analysis time of single point is 60 s. Iron was used as an internal standard and MASS-1 was used to calibrate the data. Analysis precision of most elements is better than 10%. For the similar optical properties of pyrite and arsenopyrite, the differences of physical properties can be used to distinguish them. Pyrite in the Baishantang porphyry copper deposit is depleted in sulfur but rich in iron, indicating a hydrothermal origin. The trace element composition of pyrite indicates that pyrite was formed at a medium depth and belongs to the medium-low temperature hydrothermal type related to volcanism. This conclusion has provided important evidence for the ore genesis and the source of ore-forming fluids of the Baishantang porphyry copper deposit, which can also guide the next-step exploration.