This paper is the result of mineral exploration engineering.

Objective The late Yanshannian epoch was the most important period of multi-metal mineralization of porphyry Mo at the Geza island arc in Zhongdian area, Yunnan province. In this paper, we chose the No.Ⅳ granitic diorite porphyry body of Tongchanggou large-scale porphyry molybdenum-copper deposit in this area as the research object, attempting to reveal the elemental migration rule of porphyry body in the process of mineralized alteration and the relationship between the peripheral rock alteration and mineralization.

Methods In this paper, the major elements, trace elements and rare earth elements in the original rock and the rocks in different alteration zones of No.Ⅳ granodiorite porphyry are analyzed respectively. The mass balance and migration amount of these major elements, trace elements and rare earth elements are calculated and analyzed by using the normalized Isocon method.

Results The results show that K-silicate alteration, sericite-quartz alteration, and propylitization were involved in the process of the mineralization and alteration of the porphyry body, and SiO₂, K₂O and volatile matters are major elements migrating in the alteration zones while a large amount of Na₂O migrated out; while major elements such as Al₂O₃, TiO₂ and P₂O₅, and high field strength elements such as Zr, Nb, Hf, Th and Ta, and rare earth elements all present poor migration activity, belonging to inert components; mineralizing elements such as Cu, Pb, Zn and Ag, and indicator elements such as Sb and As show a trend to migrate out, reflecting the potential to find relevant types of ore around the rock body; the sericite-quartz zone is the most closely related to Mo mineralization, followed by K-silicate alteration; the deposition and mineralization mechanism of Mo is different from that of Cu, the former is mainly under the control of "converted barrier of pH", and the latter is under the control of "silicon-calcium surface" and "epigenetic structure interface"; this porphyry is small in scale, with a low background value of Mo but high migration amount of over 3000%, and around 30% of the rock body is molybdenum deposit, which implies the deep-seated magma chamber contributed tremendously to the mineralization.

Conclusions This work provides a geological reference for the source of oreforming materials, the study of mineralization and the prospecting and exploration of the Tongchanggou deposit.