Porphyry-type molybdenum (copper) deposits have long been a focus of geological studies.770 Molybdenum(Copper) Deposit,a newly discovered porphyry-type deposit in the Northern Greater Khingan Mountains,has seen limited reporting.This study examines pyrite and chalcopyrite within 770 Molybdenum (Copper) Deposit using electron microscopy and EPMA(Electron Probe Micro-analysis) to investigate the crystal morphology and the major and trace element compositions of these sulfides,providing a comprehensive understanding of their chemical characteristics and geological significance.The 770 Molybdenum (Copper) Deposit,a large porphyry-type molybdenum (copper) deposit,has its ore bodies hosted in Late Jurassic granite porphyry.Alteration zones are pided into a central potassic zone and a peripheral pyrite-sericite zone.EPMA results show pyrite with sulfur content generally below 53.45 %,iron content below 46.55 %,and a w(S)/w(Fe) ratio≥1.148,indicating that the deposit-s pyrite is low-iron,low-sulfur pyrite,formed under conditions of high sulfur fugacity.The trace-to-major element correlations suggest elements like Zn,Mo,Ni,Co,and As exist in pyrite as mineral inclusions.The w(Co)/w(Ni) ratio(2.25-4.50) in pyrite indicates a magmatic-hydrothermal origin,while the [n(Cu)＋n(Fe)]/n(S) ratio in chalcopyrite(average 0.91) suggests formation in a mid to low-temperature(around 200 ℃) hydrothermal environment.