Abstract: 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 divided 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 or in isomorphic forms. 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.