Abstract: Abstract: The Bolong copper deposit is another large-size porphyry deposit discovered after the Duobuza porphyry copper deposit in the Duolong ore district. In this paper, the authors systematically investigated the alterations and vein systems in the Bolong copper deposit based on field geological records and indoor microscopic identifications. The results show that the Bolong copper deposit is characterized by obvious alteration zonation of potassic zone→pyrite phyllic zone→argillation superimposed pyrite phyllic zone→hornfels zone (or propylitization zone on the outer side) from the deep part (core) to the shallow part (or the outer side). Four types of veins (M, A, B, D) can be recognized in the deposit, with A B veins being most developed. the potassic zone, pyrite phyllic zone and A, B veins are related to the mineralization. A comparison with the typical alteration features of porphyry deposits both in China and abroad shows that the alteration features of the Bolong copper deposit are similar to features of the “monzonite” model, and the characteristics of the mineral assemblages are similar to those of the Bajo de la Alumbrera porphyry Cu deposit in Argentina and the Qulong copper deposit and Duobuza copper deposit in Tibet. However, the Bolong deposit has its unique feature that it possesses a large number of sparsely ? densely disseminated and veined magnetites from the potassic zone to the pyrite phyllic zone.